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Deng J, Sun C, Zheng Y, Gao J, Cui X, Wang Y, Zhang L, Tang P. In vivo imaging of the neuronal response to spinal cord injury: a narrative review. Neural Regen Res 2024; 19:811-817. [PMID: 37843216 PMCID: PMC10664102 DOI: 10.4103/1673-5374.382225] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/07/2023] [Revised: 05/15/2023] [Accepted: 07/07/2023] [Indexed: 10/17/2023] Open
Abstract
Deciphering the neuronal response to injury in the spinal cord is essential for exploring treatment strategies for spinal cord injury (SCI). However, this subject has been neglected in part because appropriate tools are lacking. Emerging in vivo imaging and labeling methods offer great potential for observing dynamic neural processes in the central nervous system in conditions of health and disease. This review first discusses in vivo imaging of the mouse spinal cord with a focus on the latest imaging techniques, and then analyzes the dynamic biological response of spinal cord sensory and motor neurons to SCI. We then summarize and compare the techniques behind these studies and clarify the advantages of in vivo imaging compared with traditional neuroscience examinations. Finally, we identify the challenges and possible solutions for spinal cord neuron imaging.
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Affiliation(s)
- Junhao Deng
- Department of Orthopedics, The Fourth Medical Center of Chinese PLA General Hospital, Beijing, China
- National Clinical Research Center for Orthopedics, Sports Medicine and Rehabilitation, Beijing, China
- School of Life Sciences, Tsinghua University, Beijing, China
| | - Chang Sun
- Department of Orthopedics, The Fourth Medical Center of Chinese PLA General Hospital, Beijing, China
- National Clinical Research Center for Orthopedics, Sports Medicine and Rehabilitation, Beijing, China
- Department of Orthopedics, Air Force Medical Center, PLA, Beijing, China
| | - Ying Zheng
- Medical School of Chinese PLA, Beijing, China
| | - Jianpeng Gao
- Department of Orthopedics, The Fourth Medical Center of Chinese PLA General Hospital, Beijing, China
- National Clinical Research Center for Orthopedics, Sports Medicine and Rehabilitation, Beijing, China
| | - Xiang Cui
- Department of Orthopedics, The Fourth Medical Center of Chinese PLA General Hospital, Beijing, China
- National Clinical Research Center for Orthopedics, Sports Medicine and Rehabilitation, Beijing, China
| | - Yu Wang
- Institute of Orthopedics, The First Medical Center, Chinese PLA General Hospital, Beijing, China
- Key Lab of Regenerative Medicine in Orthopedics, Key Laboratory of Musculoskeletal Trauma and War Injuries PLA, Beijing, China
| | - Licheng Zhang
- Department of Orthopedics, The Fourth Medical Center of Chinese PLA General Hospital, Beijing, China
- National Clinical Research Center for Orthopedics, Sports Medicine and Rehabilitation, Beijing, China
| | - Peifu Tang
- Department of Orthopedics, The Fourth Medical Center of Chinese PLA General Hospital, Beijing, China
- National Clinical Research Center for Orthopedics, Sports Medicine and Rehabilitation, Beijing, China
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2
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Zhao Q, Jiang C, Zhao L, Dai X, Yi S. Unleashing Axonal Regeneration Capacities: Neuronal and Non-neuronal Changes After Injuries to Dorsal Root Ganglion Neuron Central and Peripheral Axonal Branches. Mol Neurobiol 2024; 61:423-433. [PMID: 37620687 DOI: 10.1007/s12035-023-03590-7] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/23/2023] [Accepted: 08/16/2023] [Indexed: 08/26/2023]
Abstract
Peripheral nerves obtain remarkable regenerative capacity while central nerves can hardly regenerate following nerve injury. Sensory neurons in the dorsal root ganglion (DRG) are widely used to decipher the dissimilarity between central and peripheral axonal regeneration as axons of DRG neurons bifurcate into the regeneration-incompetent central projections and the regeneration-competent peripheral projections. A conditioning peripheral branch injury facilitates central axonal regeneration and enables the growth and elongation of central axons. Peripheral axonal injury stimulates neuronal calcium influx, alters the start-point chromatin states, increases chromatin accessibility, upregulates the expressions of regeneration-promoting genes and the synthesis of proteins, and supports axonal regeneration. Following central axonal injury, the responses of DRG neurons are modest, resulting in poor intrinsic growth ability. Some non-neuronal cells in DRGs, for instance satellite glial cells, also exhibit diminished injury responses to central axon injury as compared with peripheral axon injury. Moreover, DRG central and peripheral axonal branches are respectively surrounded by inhibitory glial scars generated by central glial cells and a permissive microenvironment generated by Schwann cells and macrophages. The aim of this review is to look at changes of DRG neurons and non-neuronal cells after peripheral and central axon injuries and summarize the contributing roles of both neuronal intrinsic regenerative capacities and surrounding microenvironments in axonal regeneration.
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Affiliation(s)
- Qian Zhao
- Key Laboratory of Neuroregeneration of Jiangsu and Ministry of Education, Co-Innovation Center of Neuroregeneration, NMPA Key Laboratory for Research and Evaluation of Tissue Engineering Technology Products, Nantong University, Nantong, Jiangsu, China
| | - Chunyi Jiang
- Key Laboratory of Neuroregeneration of Jiangsu and Ministry of Education, Co-Innovation Center of Neuroregeneration, NMPA Key Laboratory for Research and Evaluation of Tissue Engineering Technology Products, Nantong University, Nantong, Jiangsu, China
- Department of Pathology, Nantong University Affiliated Hospital, Nantong, Jiangsu, China
| | - Li Zhao
- Key Laboratory of Neuroregeneration of Jiangsu and Ministry of Education, Co-Innovation Center of Neuroregeneration, NMPA Key Laboratory for Research and Evaluation of Tissue Engineering Technology Products, Nantong University, Nantong, Jiangsu, China
| | - Xiu Dai
- Key Laboratory of Neuroregeneration of Jiangsu and Ministry of Education, Co-Innovation Center of Neuroregeneration, NMPA Key Laboratory for Research and Evaluation of Tissue Engineering Technology Products, Nantong University, Nantong, Jiangsu, China.
| | - Sheng Yi
- Key Laboratory of Neuroregeneration of Jiangsu and Ministry of Education, Co-Innovation Center of Neuroregeneration, NMPA Key Laboratory for Research and Evaluation of Tissue Engineering Technology Products, Nantong University, Nantong, Jiangsu, China.
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3
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Warfield R, Robinson JA, Podgorski RM, Miller AD, Burdo TH. Neuroinflammation in the Dorsal Root Ganglia and Dorsal Horn Contributes to Persistence of Nociceptor Sensitization in SIV-Infected Antiretroviral Therapy-Treated Macaques. THE AMERICAN JOURNAL OF PATHOLOGY 2023; 193:2017-2030. [PMID: 37734588 PMCID: PMC10699130 DOI: 10.1016/j.ajpath.2023.08.014] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 05/10/2023] [Revised: 07/17/2023] [Accepted: 08/16/2023] [Indexed: 09/23/2023]
Abstract
Despite the development of antiretroviral therapy (ART), HIV-associated distal sensory polyneuropathy remains prevalent. Using SIV-infected rhesus macaques, this study examined molecular mechanisms of peripheral and central sensitization to infer chronic pain from HIV infection. Previous studies identified atrophy in nociceptive neurons during SIV infection, which was associated with monocyte infiltration into the dorsal root ganglia (DRG). However, the sensory signaling mechanism connecting this pathology to symptoms remains unclear, especially because pain persists after resolution of high viremia and inflammation with ART. We hypothesized that residual DRG and dorsal horn neuroinflammation contributes to nociceptive sensitization. Using three cohorts of macaques [uninfected (SIV-), SIV-infected (SIV+), and SIV infected with ART (SIV+/ART)], this study showed an increase in the cellular and cytokine inflammatory profiles in the DRG of SIV+/ART macaques compared with uninfected animals. It found significant increase in the expression of nociceptive ion channels, TRPV1, and TRPA1 among DRG neurons in SIV+/ART compared with uninfected animals. SIV-infected and SIV+/ART animals showed reduced innervation of the nonpeptidergic nociceptors into the dorsal horn compared with uninfected animals. Finally, there were a significantly higher number of CD68+ cells in the dorsal horn of SIV+/ART macaques compared with uninfected animals. In summary, these data demonstrate that neuroinflammation, characteristics of nociceptor sensitization, and central terminal atrophy persists in SIV+/ART animals.
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Affiliation(s)
- Rebecca Warfield
- Department of Microbiology, Immunology, and Inflammation, Center for NeuroVirology and Gene Editing, Lewis Katz School of Medicine, Temple University, Philadelphia, Pennsylvania
| | - Jake A Robinson
- Department of Microbiology, Immunology, and Inflammation, Center for NeuroVirology and Gene Editing, Lewis Katz School of Medicine, Temple University, Philadelphia, Pennsylvania
| | - Rachel M Podgorski
- Department of Microbiology, Immunology, and Inflammation, Center for NeuroVirology and Gene Editing, Lewis Katz School of Medicine, Temple University, Philadelphia, Pennsylvania
| | - Andrew D Miller
- Section of Anatomic Pathology, Department of Biomedical Sciences, Cornell University College of Veterinary Medicine, Ithaca, New York
| | - Tricia H Burdo
- Department of Microbiology, Immunology, and Inflammation, Center for NeuroVirology and Gene Editing, Lewis Katz School of Medicine, Temple University, Philadelphia, Pennsylvania.
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4
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Kim H, Skuba A, Xia J, Han SB, Zhai J, Hu H, Kang SH, Son YJ. Oligodendrocyte precursor cells stop sensory axons regenerating into the spinal cord. Cell Rep 2023; 42:113068. [PMID: 37656624 DOI: 10.1016/j.celrep.2023.113068] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/01/2022] [Revised: 07/17/2023] [Accepted: 08/18/2023] [Indexed: 09/03/2023] Open
Abstract
Primary somatosensory axons stop regenerating as they re-enter the spinal cord, resulting in incurable sensory loss. What arrests them has remained unclear. We previously showed that axons stop by forming synaptic contacts with unknown non-neuronal cells. Here, we identified these cells in adult mice as oligodendrocyte precursor cells (OPCs). We also found that only a few axons stop regenerating by forming dystrophic endings, exclusively at the CNS:peripheral nervous system (PNS) borderline where OPCs are absent. Most axons stop in contact with a dense network of OPC processes. Live imaging, immuno-electron microscopy (immuno-EM), and OPC-dorsal root ganglia (DRG) co-culture additionally suggest that axons are rapidly immobilized by forming synapses with OPCs. Genetic OPC ablation enables many axons to continue regenerating deep into the spinal cord. We propose that sensory axons stop regenerating by encountering OPCs that induce presynaptic differentiation. Our findings identify OPCs as a major regenerative barrier that prevents intraspinal restoration of sensory circuits following spinal root injury.
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Affiliation(s)
- Hyukmin Kim
- Department of Neural Sciences, Shriners Hospitals Pediatric Research Center, Lewis Katz School of Medicine, Temple University, Philadelphia, PA, USA
| | - Andy Skuba
- Department of Neural Sciences, Shriners Hospitals Pediatric Research Center, Lewis Katz School of Medicine, Temple University, Philadelphia, PA, USA
| | - Jingsheng Xia
- Department of Medicine, New Jersey Medical School, Rutgers University, Newark, NJ, USA
| | - Sung Baek Han
- Department of Neural Sciences, Shriners Hospitals Pediatric Research Center, Lewis Katz School of Medicine, Temple University, Philadelphia, PA, USA
| | - Jinbin Zhai
- Department of Neural Sciences, Shriners Hospitals Pediatric Research Center, Lewis Katz School of Medicine, Temple University, Philadelphia, PA, USA
| | - Huijuan Hu
- Department of Medicine, New Jersey Medical School, Rutgers University, Newark, NJ, USA
| | - Shin H Kang
- Department of Neural Sciences, Shriners Hospitals Pediatric Research Center, Lewis Katz School of Medicine, Temple University, Philadelphia, PA, USA
| | - Young-Jin Son
- Department of Neural Sciences, Shriners Hospitals Pediatric Research Center, Lewis Katz School of Medicine, Temple University, Philadelphia, PA, USA.
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5
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Perez-Gianmarco L, Kukley M. Understanding the Role of the Glial Scar through the Depletion of Glial Cells after Spinal Cord Injury. Cells 2023; 12:1842. [PMID: 37508505 PMCID: PMC10377788 DOI: 10.3390/cells12141842] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/22/2023] [Revised: 06/30/2023] [Accepted: 07/11/2023] [Indexed: 07/30/2023] Open
Abstract
Spinal cord injury (SCI) is a condition that affects between 8.8 and 246 people in a million and, unlike many other neurological disorders, it affects mostly young people, causing deficits in sensory, motor, and autonomic functions. Promoting the regrowth of axons is one of the most important goals for the neurological recovery of patients after SCI, but it is also one of the most challenging goals. A key event after SCI is the formation of a glial scar around the lesion core, mainly comprised of astrocytes, NG2+-glia, and microglia. Traditionally, the glial scar has been regarded as detrimental to recovery because it may act as a physical barrier to axon regrowth and release various inhibitory factors. However, more and more evidence now suggests that the glial scar is beneficial for the surrounding spared tissue after SCI. Here, we review experimental studies that used genetic and pharmacological approaches to ablate specific populations of glial cells in rodent models of SCI in order to understand their functional role. The studies showed that ablation of either astrocytes, NG2+-glia, or microglia might result in disorganization of the glial scar, increased inflammation, extended tissue degeneration, and impaired recovery after SCI. Hence, glial cells and glial scars appear as important beneficial players after SCI.
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Affiliation(s)
- Lucila Perez-Gianmarco
- Achucarro Basque Center for Neuroscience, 48940 Leioa, PC, Spain
- Department of Neurosciences, University of the Basque Country, 48940 Leioa, PC, Spain
| | - Maria Kukley
- Achucarro Basque Center for Neuroscience, 48940 Leioa, PC, Spain
- IKERBASQUE Basque Foundation for Science, 48009 Bilbao, PC, Spain
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Bennet BM, Pardo ID, Assaf BT, Buza E, Cramer SD, Crawford LK, Engelhardt JA, Galbreath EJ, Grubor B, Morrison JP, Osborne TS, Sharma AK, Bolon B. Scientific and Regulatory Policy Committee Technical Review: Biology and Pathology of Ganglia in Animal Species Used for Nonclinical Safety Testing. Toxicol Pathol 2023; 51:278-305. [PMID: 38047294 DOI: 10.1177/01926233231213851] [Citation(s) in RCA: 1] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/05/2023]
Abstract
Dorsal root ganglia (DRG), trigeminal ganglia (TG), other sensory ganglia, and autonomic ganglia may be injured by some test article classes, including anti-neoplastic chemotherapeutics, adeno-associated virus-based gene therapies, antisense oligonucleotides, nerve growth factor inhibitors, and aminoglycoside antibiotics. This article reviews ganglion anatomy, cytology, and pathology (emphasizing sensory ganglia) among common nonclinical species used in assessing product safety for such test articles (TAs). Principal histopathologic findings associated with sensory ganglion injury include neuron degeneration, necrosis, and/or loss; increased satellite glial cell and/or Schwann cell numbers; and leukocyte infiltration and/or inflammation. Secondary nerve fiber degeneration and/or glial reactions may occur in nerves, dorsal spinal nerve roots, spinal cord (dorsal and occasionally lateral funiculi), and sometimes the brainstem. Ganglion findings related to TA administration may result from TA exposure and/or trauma related to direct TA delivery into the central nervous system or ganglia. In some cases, TA-related effects may need to be differentiated from a spectrum of artifactual and/or spontaneous background changes.
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Affiliation(s)
| | | | | | - Elizabeth Buza
- University of Pennsylvania, Philadelphia, Pennsylvania, USA
| | | | | | | | | | | | - James P Morrison
- Charles River Laboratories, Inc., Shrewsbury, Massachusetts, USA
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Shafqat A, Albalkhi I, Magableh HM, Saleh T, Alkattan K, Yaqinuddin A. Tackling the glial scar in spinal cord regeneration: new discoveries and future directions. Front Cell Neurosci 2023; 17:1180825. [PMID: 37293626 PMCID: PMC10244598 DOI: 10.3389/fncel.2023.1180825] [Citation(s) in RCA: 5] [Impact Index Per Article: 5.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/06/2023] [Accepted: 05/08/2023] [Indexed: 06/10/2023] Open
Abstract
Axonal regeneration and functional recovery are poor after spinal cord injury (SCI), typified by the formation of an injury scar. While this scar was traditionally believed to be primarily responsible for axonal regeneration failure, current knowledge takes a more holistic approach that considers the intrinsic growth capacity of axons. Targeting the SCI scar has also not reproducibly yielded nearly the same efficacy in animal models compared to these neuron-directed approaches. These results suggest that the major reason behind central nervous system (CNS) regeneration failure is not the injury scar but a failure to stimulate axon growth adequately. These findings raise questions about whether targeting neuroinflammation and glial scarring still constitute viable translational avenues. We provide a comprehensive review of the dual role of neuroinflammation and scarring after SCI and how future research can produce therapeutic strategies targeting the hurdles to axonal regeneration posed by these processes without compromising neuroprotection.
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8
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Zheng B, Tuszynski MH. Regulation of axonal regeneration after mammalian spinal cord injury. Nat Rev Mol Cell Biol 2023; 24:396-413. [PMID: 36604586 DOI: 10.1038/s41580-022-00562-y] [Citation(s) in RCA: 57] [Impact Index Per Article: 57.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Accepted: 11/04/2022] [Indexed: 01/06/2023]
Abstract
One hundred years ago, Ramón y Cajal, considered by many as the founder of modern neuroscience, stated that neurons of the adult central nervous system (CNS) are incapable of regenerating. Yet, recent years have seen a tremendous expansion of knowledge in the molecular control of axon regeneration after CNS injury. We now understand that regeneration in the adult CNS is limited by (1) a failure to form cellular or molecular substrates for axon attachment and elongation through the lesion site; (2) environmental factors, including inhibitors of axon growth associated with myelin and the extracellular matrix; (3) astrocyte responses, which can both limit and support axon growth; and (4) intraneuronal mechanisms controlling the establishment of an active cellular growth programme. We discuss these topics together with newly emerging hypotheses, including the surprising finding from transcriptomic analyses of the corticospinal system in mice that neurons revert to an embryonic state after spinal cord injury, which can be sustained to promote regeneration with neural stem cell transplantation. These gains in knowledge are steadily advancing efforts to develop effective treatment strategies for spinal cord injury in humans.
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Affiliation(s)
- Binhai Zheng
- Department of Neurosciences, School of Medicine, University of California San Diego, La Jolla, CA, USA. .,VA San Diego Research Service, San Diego, CA, USA.
| | - Mark H Tuszynski
- Department of Neurosciences, School of Medicine, University of California San Diego, La Jolla, CA, USA. .,VA San Diego Research Service, San Diego, CA, USA.
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Noristani HN. Intrinsic regulation of axon regeneration after spinal cord injury: Recent advances and remaining challenges. Exp Neurol 2022; 357:114198. [DOI: 10.1016/j.expneurol.2022.114198] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/17/2022] [Revised: 07/20/2022] [Accepted: 08/02/2022] [Indexed: 11/16/2022]
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Noristani HN, Kim H, Pang S, Zhong J, Son YJ. Co-targeting B-RAF and PTEN Enables Sensory Axons to Regenerate Across and Beyond the Spinal Cord Injury. Front Mol Neurosci 2022; 15:891463. [PMID: 35557554 PMCID: PMC9087900 DOI: 10.3389/fnmol.2022.891463] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/07/2022] [Accepted: 03/30/2022] [Indexed: 11/25/2022] Open
Abstract
Primary sensory axons in adult mammals fail to regenerate after spinal cord injury (SCI), in part due to insufficient intrinsic growth potential. Robustly boosting their growth potential continues to be a challenge. Previously, we showed that constitutive activation of B-RAF (rapidly accelerated fibrosarcoma kinase) markedly promotes axon regeneration after dorsal root and optic nerve injuries. The regrowth is further augmented by supplemental deletion of PTEN (phosphatase and tensin homolog). Here, we examined whether concurrent B-RAF activation and PTEN deletion promotes dorsal column axon regeneration after SCI. Remarkably, genetically targeting B-RAF and PTEN selectively in DRG neurons of adult mice enables many DC axons to enter, cross, and grow beyond the lesion site after SCI; some axons reach ∼2 mm rostral to the lesion by 3 weeks post-injury. Co-targeting B-RAF and PTEN promotes more robust DC regeneration than a pre-conditioning lesion, which additively enhances the regeneration triggered by B-RAF/PTEN. We also found that post-injury targeting of B-RAF and PTEN enhances DC axon regeneration. These results demonstrate that co-targeting B-RAF and PTEN effectively enhances the intrinsic growth potential of DC axons after SCI and therefore may help to develop a novel strategy to promote robust long-distance regeneration of primary sensory axons.
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Affiliation(s)
- Harun N. Noristani
- Shriners Hospitals Pediatric Research Center and Center for Neural Repair, Lewis Katz School of Medicine, Temple University, Philadelphia, PA, United States
- *Correspondence: Harun N. Noristani,
| | - Hyukmin Kim
- Shriners Hospitals Pediatric Research Center and Center for Neural Repair, Lewis Katz School of Medicine, Temple University, Philadelphia, PA, United States
| | - Shuhuan Pang
- Shriners Hospitals Pediatric Research Center and Center for Neural Repair, Lewis Katz School of Medicine, Temple University, Philadelphia, PA, United States
| | - Jian Zhong
- Burke Medical Research Institute, Weill Cornell Medical College of Cornell University, White Plains, NY, United States
| | - Young-Jin Son
- Shriners Hospitals Pediatric Research Center and Center for Neural Repair, Lewis Katz School of Medicine, Temple University, Philadelphia, PA, United States
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Long-term in vivo imaging of mouse spinal cord through an optically cleared intervertebral window. Nat Commun 2022; 13:1959. [PMID: 35414131 PMCID: PMC9005710 DOI: 10.1038/s41467-022-29496-x] [Citation(s) in RCA: 15] [Impact Index Per Article: 7.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/28/2021] [Accepted: 03/17/2022] [Indexed: 11/08/2022] Open
Abstract
The spinal cord accounts for the main communication pathway between the brain and the peripheral nervous system. Spinal cord injury is a devastating and largely irreversible neurological trauma, and can result in lifelong disability and paralysis with no available cure. In vivo spinal cord imaging in mouse models without introducing immunological artifacts is critical to understand spinal cord pathology and discover effective treatments. We developed a minimally invasive intervertebral window by retaining the ligamentum flavum to protect the underlying spinal cord. By introducing an optical clearing method, we achieve repeated two-photon fluorescence and stimulated Raman scattering imaging at subcellular resolution with up to 15 imaging sessions over 6-167 days and observe no inflammatory response. Using this optically cleared intervertebral window, we study neuron-glia dynamics following laser axotomy and observe strengthened contact of microglia with the nodes of Ranvier during axonal degeneration. By enabling long-term, repetitive, stable, high-resolution and inflammation-free imaging of mouse spinal cord, our method provides a reliable platform in the research aiming at interpretation of spinal cord physiology and pathology.
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12
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Winter CC, He Z, Jacobi A. Axon Regeneration: A Subcellular Extension in Multiple Dimensions. Cold Spring Harb Perspect Biol 2022; 14:a040923. [PMID: 34518340 PMCID: PMC8886981 DOI: 10.1101/cshperspect.a040923] [Citation(s) in RCA: 4] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/24/2022]
Abstract
Axons are a unique cellular structure that allows for the communication between neurons. Axon damage compromises neuronal communications and often leads to functional deficits. Thus, developing strategies that promote effective axon regeneration for functional restoration is highly desirable. One fruitful approach is to dissect the regenerative mechanisms used by some types of neurons in both mammalian and nonmammalian systems that exhibit spontaneous regenerative capacity. Additionally, numerous efforts have been devoted to deciphering the barriers that prevent successful axon regeneration in the most regeneration-refractory system-the adult mammalian central nervous system. As a result, several regeneration-promoting strategies have been developed, but significant limitations remain. This review is aimed to summarize historic progression and current understanding of this exciting yet incomplete endeavor.
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Affiliation(s)
- Carla C Winter
- F.M. Kirby Neurobiology Center, Boston Children's Hospital, Boston, Massachusetts 02115, USA
- Department of Neurology and Ophthalmology, Harvard Medical School, Boston, Massachusetts 02115, USA
- PhD Program in Biological and Biomedical Sciences, Harvard Medical School, Boston, Massachusetts 02115, USA
| | - Zhigang He
- F.M. Kirby Neurobiology Center, Boston Children's Hospital, Boston, Massachusetts 02115, USA
- Department of Neurology and Ophthalmology, Harvard Medical School, Boston, Massachusetts 02115, USA
| | - Anne Jacobi
- F.M. Kirby Neurobiology Center, Boston Children's Hospital, Boston, Massachusetts 02115, USA
- Department of Neurology and Ophthalmology, Harvard Medical School, Boston, Massachusetts 02115, USA
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13
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Hilton BJ, Husch A, Schaffran B, Lin TC, Burnside ER, Dupraz S, Schelski M, Kim J, Müller JA, Schoch S, Imig C, Brose N, Bradke F. An active vesicle priming machinery suppresses axon regeneration upon adult CNS injury. Neuron 2022; 110:51-69.e7. [PMID: 34706221 PMCID: PMC8730507 DOI: 10.1016/j.neuron.2021.10.007] [Citation(s) in RCA: 34] [Impact Index Per Article: 17.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/30/2021] [Revised: 09/03/2021] [Accepted: 10/01/2021] [Indexed: 12/16/2022]
Abstract
Axons in the adult mammalian central nervous system fail to regenerate after spinal cord injury. Neurons lose their capacity to regenerate during development, but the intracellular processes underlying this loss are unclear. We found that critical components of the presynaptic active zone prevent axon regeneration in adult mice. Transcriptomic analysis combined with live-cell imaging revealed that adult primary sensory neurons downregulate molecular constituents of the synapse as they acquire the ability to rapidly grow their axons. Pharmacogenetic reduction of neuronal excitability stimulated axon regeneration after adult spinal cord injury. Genetic gain- and loss-of-function experiments uncovered that essential synaptic vesicle priming proteins of the presynaptic active zone, but not clostridial-toxin-sensitive VAMP-family SNARE proteins, inhibit axon regeneration. Systemic administration of Baclofen reduced voltage-dependent Ca2+ influx in primary sensory neurons and promoted their regeneration after spinal cord injury. These findings indicate that functional presynaptic active zones constitute a major barrier to axon regeneration.
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Affiliation(s)
- Brett J Hilton
- Laboratory of Axonal Growth and Regeneration, German Center for Neurodegenerative Diseases (DZNE), Venusberg Campus 1/99, 53127 Bonn, Germany
| | - Andreas Husch
- Laboratory of Axonal Growth and Regeneration, German Center for Neurodegenerative Diseases (DZNE), Venusberg Campus 1/99, 53127 Bonn, Germany
| | - Barbara Schaffran
- Laboratory of Axonal Growth and Regeneration, German Center for Neurodegenerative Diseases (DZNE), Venusberg Campus 1/99, 53127 Bonn, Germany
| | - Tien-Chen Lin
- Laboratory of Axonal Growth and Regeneration, German Center for Neurodegenerative Diseases (DZNE), Venusberg Campus 1/99, 53127 Bonn, Germany
| | - Emily R Burnside
- Laboratory of Axonal Growth and Regeneration, German Center for Neurodegenerative Diseases (DZNE), Venusberg Campus 1/99, 53127 Bonn, Germany
| | - Sebastian Dupraz
- Laboratory of Axonal Growth and Regeneration, German Center for Neurodegenerative Diseases (DZNE), Venusberg Campus 1/99, 53127 Bonn, Germany
| | - Max Schelski
- Laboratory of Axonal Growth and Regeneration, German Center for Neurodegenerative Diseases (DZNE), Venusberg Campus 1/99, 53127 Bonn, Germany
| | - Jisoo Kim
- Laboratory of Axonal Growth and Regeneration, German Center for Neurodegenerative Diseases (DZNE), Venusberg Campus 1/99, 53127 Bonn, Germany; Department of Stem Cell and Regenerative Biology, Center for Brain Science, and Harvard Stem Cell Institute, Harvard University, Cambridge, MA 02138, USA
| | | | - Susanne Schoch
- Institute of Neuropathology, Medical Faculty, University of Bonn, 53105 Bonn, Germany
| | - Cordelia Imig
- Department of Molecular Neurobiology, Max Planck Institute of Experimental Medicine, 37075 Göttingen, Germany
| | - Nils Brose
- Department of Molecular Neurobiology, Max Planck Institute of Experimental Medicine, 37075 Göttingen, Germany
| | - Frank Bradke
- Laboratory of Axonal Growth and Regeneration, German Center for Neurodegenerative Diseases (DZNE), Venusberg Campus 1/99, 53127 Bonn, Germany.
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14
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Two Novel Hydroxymethylbilane Synthase Splicing Mutations Predispose to Acute Intermittent Porphyria. Int J Mol Sci 2021; 22:ijms222011008. [PMID: 34681668 PMCID: PMC8541332 DOI: 10.3390/ijms222011008] [Citation(s) in RCA: 4] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/16/2021] [Revised: 10/04/2021] [Accepted: 10/08/2021] [Indexed: 11/16/2022] Open
Abstract
Acute intermittent porphyria (AIP) is an autosomal dominant genetic disease caused by a lack or decrease in hydroxymethylbilane synthase (HMBS) activity. It is characterized by acute nerve and visceral attacks caused by factors in the process of heme synthesis. The penetrance rate of this disease is low, and the heterogeneity is strong. Here, we reported two novel HMBS mutations from two unrelated Chinese AIP patients and confirmed the pathogenicity of these two mutations. We found the HMBS c.760–771+2delCTGAGGCACCTGGTinsGCTGCATCGCTGAA and HMBS c.88-1G>C mutations by second-generation sequencing and Sanger sequencing. The in vitro expression analysis showed that these mutations caused abnormal HMBS mRNA splicing and premature termination or partial missing of HMBS protein. Homologous modeling analysis showed that the HMBS mutants lacked the amino acids which are crucial for the enzyme activity or the protein stability. Consistently, enzyme activity analysis confirmed that the HMBS mutants’ overexpression cells exhibited the reduced enzyme activity compared with the HMBS wildtype overexpression cells. Our study identified and confirmed two novel pathogenic HMBS mutations which will expand the molecular heterogeneity of AIP and provide further scientific basis for the clinical diagnosis of AIP.
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15
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Aldskogius H, Kozlova EN. Dorsal Root Injury-A Model for Exploring Pathophysiology and Therapeutic Strategies in Spinal Cord Injury. Cells 2021; 10:2185. [PMID: 34571835 PMCID: PMC8470715 DOI: 10.3390/cells10092185] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/28/2021] [Revised: 08/19/2021] [Accepted: 08/20/2021] [Indexed: 12/12/2022] Open
Abstract
Unraveling the cellular and molecular mechanisms of spinal cord injury is fundamental for our possibility to develop successful therapeutic approaches. These approaches need to address the issues of the emergence of a non-permissive environment for axonal growth in the spinal cord, in combination with a failure of injured neurons to mount an effective regeneration program. Experimental in vivo models are of critical importance for exploring the potential clinical relevance of mechanistic findings and therapeutic innovations. However, the highly complex organization of the spinal cord, comprising multiple types of neurons, which form local neural networks, as well as short and long-ranging ascending or descending pathways, complicates detailed dissection of mechanistic processes, as well as identification/verification of therapeutic targets. Inducing different types of dorsal root injury at specific proximo-distal locations provide opportunities to distinguish key components underlying spinal cord regeneration failure. Crushing or cutting the dorsal root allows detailed analysis of the regeneration program of the sensory neurons, as well as of the glial response at the dorsal root-spinal cord interface without direct trauma to the spinal cord. At the same time, a lesion at this interface creates a localized injury of the spinal cord itself, but with an initial neuronal injury affecting only the axons of dorsal root ganglion neurons, and still a glial cell response closely resembling the one seen after direct spinal cord injury. In this review, we provide examples of previous research on dorsal root injury models and how these models can help future exploration of mechanisms and potential therapies for spinal cord injury repair.
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Affiliation(s)
- Håkan Aldskogius
- Laboratory of Regenertive Neurobiology, Biomedical Center, Department of Neuroscience, Uppsala University, 75124 Uppsala, Sweden;
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16
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Zhai J, Kim H, Han SB, Manire M, Yoo R, Pang S, Smith GM, Son YJ. Co-targeting myelin inhibitors and CSPGs markedly enhances regeneration of GDNF-stimulated, but not conditioning-lesioned, sensory axons into the spinal cord. eLife 2021; 10:63050. [PMID: 33942723 PMCID: PMC8139830 DOI: 10.7554/elife.63050] [Citation(s) in RCA: 6] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/11/2020] [Accepted: 05/03/2021] [Indexed: 12/20/2022] Open
Abstract
A major barrier to intraspinal regeneration after dorsal root (DR) injury is the DR entry zone (DREZ), the CNS/PNS interface. DR axons stop regenerating at the DREZ, even if regenerative capacity is increased by a nerve conditioning lesion. This potent blockade has long been attributed to myelin-associated inhibitors and (CSPGs), but incomplete lesions and conflicting reports have prevented conclusive agreement. Here, we evaluated DR regeneration in mice using novel strategies to facilitate complete lesions and analyses, selective tracing of proprioceptive and mechanoreceptive axons, and the first simultaneous targeting of Nogo/Reticulon-4, MAG, OMgp, CSPGs, and GDNF. Co-eliminating myelin inhibitors and CSPGs elicited regeneration of only a few conditioning-lesioned DR axons across the DREZ. Their absence, however, markedly and synergistically enhanced regeneration of GDNF-stimulated axons, highlighting the importance of sufficiently elevating intrinsic growth capacity. We also conclude that myelin inhibitors and CSPGs are not the primary mechanism stopping axons at the DREZ.
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Affiliation(s)
- Jinbin Zhai
- Shriners Hospitals Pediatric Research Center and Center for Neural Repair and Rehabilitation, Lewis Katz School of Medicine, Temple University, Philadelphia, United States.,Center for Neural Repair and Rehabilitation, Lewis Katz School of Medicine, Temple University, Philadelphia, United States
| | - Hyukmin Kim
- Shriners Hospitals Pediatric Research Center and Center for Neural Repair and Rehabilitation, Lewis Katz School of Medicine, Temple University, Philadelphia, United States.,Center for Neural Repair and Rehabilitation, Lewis Katz School of Medicine, Temple University, Philadelphia, United States
| | - Seung Baek Han
- Shriners Hospitals Pediatric Research Center and Center for Neural Repair and Rehabilitation, Lewis Katz School of Medicine, Temple University, Philadelphia, United States.,Center for Neural Repair and Rehabilitation, Lewis Katz School of Medicine, Temple University, Philadelphia, United States
| | - Meredith Manire
- Shriners Hospitals Pediatric Research Center and Center for Neural Repair and Rehabilitation, Lewis Katz School of Medicine, Temple University, Philadelphia, United States.,Center for Neural Repair and Rehabilitation, Lewis Katz School of Medicine, Temple University, Philadelphia, United States
| | - Rachel Yoo
- Shriners Hospitals Pediatric Research Center and Center for Neural Repair and Rehabilitation, Lewis Katz School of Medicine, Temple University, Philadelphia, United States.,Center for Neural Repair and Rehabilitation, Lewis Katz School of Medicine, Temple University, Philadelphia, United States
| | - Shuhuan Pang
- Shriners Hospitals Pediatric Research Center and Center for Neural Repair and Rehabilitation, Lewis Katz School of Medicine, Temple University, Philadelphia, United States.,Center for Neural Repair and Rehabilitation, Lewis Katz School of Medicine, Temple University, Philadelphia, United States
| | - George M Smith
- Shriners Hospitals Pediatric Research Center and Center for Neural Repair and Rehabilitation, Lewis Katz School of Medicine, Temple University, Philadelphia, United States.,Center for Neural Repair and Rehabilitation, Lewis Katz School of Medicine, Temple University, Philadelphia, United States
| | - Young-Jin Son
- Shriners Hospitals Pediatric Research Center and Center for Neural Repair and Rehabilitation, Lewis Katz School of Medicine, Temple University, Philadelphia, United States.,Center for Neural Repair and Rehabilitation, Lewis Katz School of Medicine, Temple University, Philadelphia, United States
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17
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Yeh HY, Lee JC, Chi HH, Chen CC, Liu Q, Yen CT. Longitudinal intravital imaging nerve degeneration and sprouting in the toes of spared nerve injured mice. J Comp Neurol 2021; 529:3247-3264. [PMID: 33880774 DOI: 10.1002/cne.25162] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/16/2020] [Revised: 02/26/2021] [Accepted: 04/14/2021] [Indexed: 12/19/2022]
Abstract
Neuropathic pain is pain caused by damage to the somatosensory nervous system. Both degenerating injured nerves and neighboring sprouting nerves can contribute to neuropathic pain. However, the mesoscale changes in cutaneous nerve fibers over time after the loss of the parent nerve has not been investigated in detail. In this study, we followed the changes in nerve fibers longitudinally in the toe tips of mice that had undergone spared nerve injury (SNI). Nav1.8-tdTomato, Thy1-GFP and MrgD-GFP mice were used to observe the small and large cutaneous nerve fibers. We found that peripheral nerve plexuses degenerated within 3 days of nerve injury, and free nerve endings in the epidermis degenerated within 2 days. The timing of degeneration paralleled the initiation of mechanical hypersensitivity. We also found that some of the Nav1.8-positive nerve plexuses and free nerve endings in the fifth toe survived, and sprouting occurred mostly from 7 to 28 days. The timing of the sprouting of nerve fibers in the fifth toe paralleled the maintenance phase of mechanical hypersensitivity. Our results support the hypotheses that both injured and intact nerve fibers participate in neuropathic pain, and that, specifically, nerve degeneration is related to the initiation of evoked pain and nerve sprouting is related to the maintenance of evoked pain.
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Affiliation(s)
- Han-Yuan Yeh
- Department of Life Science, National Taiwan University, Taipei, Taiwan
| | - Jye-Chang Lee
- Graduate Institute of Pharmacology, National Taiwan University College of Medicine, Taipei, Taiwan
| | - Han-Hsiung Chi
- Department of Life Science, National Taiwan University, Taipei, Taiwan
| | - Chih-Cheng Chen
- Institute of Biomedical Science, Academia Sinica, Taipei, Taiwan
| | - Qin Liu
- Department of Anesthesiology and the Center for the Study of Itch, Washington University School of Medicine, St. Louis, Missouri, USA
| | - Chen-Tung Yen
- Department of Life Science, National Taiwan University, Taipei, Taiwan
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18
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Ewan EE, Avraham O, Carlin D, Gonçalves TM, Zhao G, Cavalli V. Ascending dorsal column sensory neurons respond to spinal cord injury and downregulate genes related to lipid metabolism. Sci Rep 2021; 11:374. [PMID: 33431991 PMCID: PMC7801468 DOI: 10.1038/s41598-020-79624-0] [Citation(s) in RCA: 8] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/29/2020] [Accepted: 12/07/2020] [Indexed: 02/08/2023] Open
Abstract
Regeneration failure after spinal cord injury (SCI) results in part from the lack of a pro-regenerative response in injured neurons, but the response to SCI has not been examined specifically in injured sensory neurons. Using RNA sequencing of dorsal root ganglion, we determined that thoracic SCI elicits a transcriptional response distinct from sciatic nerve injury (SNI). Both SNI and SCI induced upregulation of ATF3 and Jun, yet this response failed to promote growth in sensory neurons after SCI. RNA sequencing of purified sensory neurons one and three days after injury revealed that unlike SNI, the SCI response is not sustained. Both SCI and SNI elicited the expression of ATF3 target genes, with very little overlap between conditions. Pathway analysis of differentially expressed ATF3 target genes revealed that fatty acid biosynthesis and terpenoid backbone synthesis were downregulated after SCI but not SNI. Pharmacologic inhibition of fatty acid synthase, the enzyme generating palmitic acid, decreased axon growth and regeneration in vitro. These results support the notion that decreased expression of lipid metabolism-related genes after SCI, including fatty acid synthase, may restrict axon regenerative capacity after SCI.
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Affiliation(s)
- Eric E Ewan
- Department of Neuroscience, Washington University School of Medicine, 660 S. Euclid Ave, Campus Box 8108, St. Louis, MO, 63110-1093, USA
| | - Oshri Avraham
- Department of Neuroscience, Washington University School of Medicine, 660 S. Euclid Ave, Campus Box 8108, St. Louis, MO, 63110-1093, USA
| | - Dan Carlin
- Department of Neuroscience, Washington University School of Medicine, 660 S. Euclid Ave, Campus Box 8108, St. Louis, MO, 63110-1093, USA
| | - Tassia Mangetti Gonçalves
- Department of Neuroscience, Washington University School of Medicine, 660 S. Euclid Ave, Campus Box 8108, St. Louis, MO, 63110-1093, USA
| | - Guoyan Zhao
- Department of Neuroscience, Washington University School of Medicine, 660 S. Euclid Ave, Campus Box 8108, St. Louis, MO, 63110-1093, USA
| | - Valeria Cavalli
- Department of Neuroscience, Washington University School of Medicine, 660 S. Euclid Ave, Campus Box 8108, St. Louis, MO, 63110-1093, USA. .,Hope Center for Neurological Disorders, Washington University School of Medicine, St. Louis, MO, 63110, USA. .,Center of Regenerative Medicine, Washington University School of Medicine, St. Louis, MO, 63110, USA.
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19
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Nichols EL, Smith CJ. Functional Regeneration of the Sensory Root via Axonal Invasion. Cell Rep 2021; 30:9-17.e3. [PMID: 31914401 PMCID: PMC6996490 DOI: 10.1016/j.celrep.2019.12.008] [Citation(s) in RCA: 7] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/13/2019] [Revised: 10/15/2019] [Accepted: 12/03/2019] [Indexed: 12/11/2022] Open
Abstract
Regeneration following spinal root avulsion is broadly unsuccessful
despite the regenerative capacity of other PNS-located nerves. By combining
focal laser lesioning to model root avulsion in zebrafish, time-lapse imaging,
and transgenesis, we identify that regenerating DRG neurons fail to recapitulate
developmental paradigms of actin-based invasion after injury. We demonstrate
that inducing actin reorganization into invasive components via pharmacological
and genetic approaches in the regenerating axon can rescue sensory axon spinal
cord entry. Cell-autonomous induction of invasion components using
constitutively active Src induces DRG axon regeneration, suggesting an intrinsic
mechanism can be activated to drive regeneration. Furthermore, analyses of
neuronal activity and animal behavior show restoration of sensory circuit
activity and behavior upon stimulating axons to re-enter the spinal cord via
invasion. Altogether, our data identify induction of invasive components as
sufficient for functional sensory root regeneration after injury. Dorsal root ganglion (DRG) sensory axons are unable to regenerate into
the spinal cord after injury. Nichols and Smith demonstrate in zebrafish that
injured DRG axons do not initiate actin-based invasion components during
re-entry into the spinal cord. Pharmacological and cell-autonomous genetic
manipulations that promote actin-mediated cell invasion to restore sensory
behavior.
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Affiliation(s)
- Evan L Nichols
- Department of Biological Sciences, University of Notre Dame, Notre Dame, IN, USA; Center for Stem Cells and Regenerative Medicine, University of Notre Dame, Notre Dame, IN, USA
| | - Cody J Smith
- Department of Biological Sciences, University of Notre Dame, Notre Dame, IN, USA; Center for Stem Cells and Regenerative Medicine, University of Notre Dame, Notre Dame, IN, USA.
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20
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Wu D, Jin Y, Shapiro TM, Hinduja A, Baas PW, Tom VJ. Chronic neuronal activation increases dynamic microtubules to enhance functional axon regeneration after dorsal root crush injury. Nat Commun 2020; 11:6131. [PMID: 33257677 PMCID: PMC7705672 DOI: 10.1038/s41467-020-19914-3] [Citation(s) in RCA: 22] [Impact Index Per Article: 5.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/14/2020] [Accepted: 11/05/2020] [Indexed: 12/26/2022] Open
Abstract
After a dorsal root crush injury, centrally-projecting sensory axons fail to regenerate across the dorsal root entry zone (DREZ) to extend into the spinal cord. We find that chemogenetic activation of adult dorsal root ganglion (DRG) neurons improves axon growth on an in vitro model of the inhibitory environment after injury. Moreover, repeated bouts of daily chemogenetic activation of adult DRG neurons for 12 weeks post-crush in vivo enhances axon regeneration across a chondroitinase-digested DREZ into spinal gray matter, where the regenerating axons form functional synapses and mediate behavioral recovery in a sensorimotor task. Neuronal activation-mediated axon extension is dependent upon changes in the status of tubulin post-translational modifications indicative of highly dynamic microtubules (as opposed to stable microtubules) within the distal axon, illuminating a novel mechanism underlying stimulation-mediated axon growth. We have identified an effective combinatory strategy to promote functionally-relevant axon regeneration of adult neurons into the CNS after injury.
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Affiliation(s)
- Di Wu
- Department of Neurobiology and Anatomy, Marion Murray Spinal Cord Research Center, Drexel University College of Medicine, Philadelphia, PA, USA
| | - Ying Jin
- Department of Neurobiology and Anatomy, Marion Murray Spinal Cord Research Center, Drexel University College of Medicine, Philadelphia, PA, USA
| | - Tatiana M Shapiro
- Department of Neurobiology and Anatomy, Marion Murray Spinal Cord Research Center, Drexel University College of Medicine, Philadelphia, PA, USA
| | - Abhishek Hinduja
- Department of Neurobiology and Anatomy, Marion Murray Spinal Cord Research Center, Drexel University College of Medicine, Philadelphia, PA, USA
| | - Peter W Baas
- Department of Neurobiology and Anatomy, Marion Murray Spinal Cord Research Center, Drexel University College of Medicine, Philadelphia, PA, USA
| | - Veronica J Tom
- Department of Neurobiology and Anatomy, Marion Murray Spinal Cord Research Center, Drexel University College of Medicine, Philadelphia, PA, USA.
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21
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Canty AJ, Jackson JS, Huang L, Trabalza A, Bass C, Little G, Tortora M, Khan S, De Paola V. In vivo imaging of injured cortical axons reveals a rapid onset form of Wallerian degeneration. BMC Biol 2020; 18:170. [PMID: 33208154 PMCID: PMC7677840 DOI: 10.1186/s12915-020-00869-2] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/14/2019] [Accepted: 09/16/2020] [Indexed: 12/22/2022] Open
Abstract
Background Despite the widespread occurrence of axon and synaptic loss in the injured and diseased nervous system, the cellular and molecular mechanisms of these key degenerative processes remain incompletely understood. Wallerian degeneration (WD) is a tightly regulated form of axon loss after injury, which has been intensively studied in large myelinated fibre tracts of the spinal cord, optic nerve and peripheral nervous system (PNS). Fewer studies, however, have focused on WD in the complex neuronal circuits of the mammalian brain, and these were mainly based on conventional endpoint histological methods. Post-mortem analysis, however, cannot capture the exact sequence of events nor can it evaluate the influence of elaborated arborisation and synaptic architecture on the degeneration process, due to the non-synchronous and variable nature of WD across individual axons. Results To gain a comprehensive picture of the spatiotemporal dynamics and synaptic mechanisms of WD in the nervous system, we identify the factors that regulate WD within the mouse cerebral cortex. We combined single-axon-resolution multiphoton imaging with laser microsurgery through a cranial window and a fluorescent membrane reporter. Longitudinal imaging of > 150 individually injured excitatory cortical axons revealed a threshold length below which injured axons consistently underwent a rapid-onset form of WD (roWD). roWD started on average 20 times earlier and was executed 3 times slower than WD described in other regions of the nervous system. Cortical axon WD and roWD were dependent on synaptic density, but independent of axon complexity. Finally, pharmacological and genetic manipulations showed that a nicotinamide adenine dinucleotide (NAD+)-dependent pathway could delay cortical roWD independent of transcription in the damaged neurons, demonstrating further conservation of the molecular mechanisms controlling WD in different areas of the mammalian nervous system. Conclusions Our data illustrate how in vivo time-lapse imaging can provide new insights into the spatiotemporal dynamics and synaptic mechanisms of axon loss and assess therapeutic interventions in the injured mammalian brain.
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Affiliation(s)
- Alison Jane Canty
- Wicking Dementia Research and Education Centre, University of Tasmania, Hobart, Australia.
| | - Johanna Sara Jackson
- Dementia Research Institute at Imperial College, Department of Brain Sciences, Imperial College London, London, W12 0NN, UK
| | - Lieven Huang
- Institute of Clinical Sciences, Faculty of Medicine, Imperial College London, London, W12 0NN, UK
| | - Antonio Trabalza
- Institute of Clinical Sciences, Faculty of Medicine, Imperial College London, London, W12 0NN, UK
| | - Cher Bass
- Institute of Clinical Sciences, Faculty of Medicine, Imperial College London, London, W12 0NN, UK
| | - Graham Little
- Institute of Clinical Sciences, Faculty of Medicine, Imperial College London, London, W12 0NN, UK
| | - Maria Tortora
- Institute of Clinical Sciences, Faculty of Medicine, Imperial College London, London, W12 0NN, UK
| | - Shabana Khan
- Institute of Clinical Sciences, Faculty of Medicine, Imperial College London, London, W12 0NN, UK
| | - Vincenzo De Paola
- Institute of Clinical Sciences, Faculty of Medicine, Imperial College London, London, W12 0NN, UK. .,Medical Research Council London Institute of Medical Sciences, London, W12 0NN, UK.
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22
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Kiyoshi C, Tedeschi A. Axon growth and synaptic function: A balancing act for axonal regeneration and neuronal circuit formation in CNS trauma and disease. Dev Neurobiol 2020; 80:277-301. [PMID: 32902152 PMCID: PMC7754183 DOI: 10.1002/dneu.22780] [Citation(s) in RCA: 14] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/06/2020] [Revised: 08/29/2020] [Accepted: 08/31/2020] [Indexed: 12/13/2022]
Abstract
Axons in the adult mammalian central nervous system (CNS) fail to regenerate inside out due to intrinsic and extrinsic neuronal determinants. During CNS development, axon growth, synapse formation, and function are tightly regulated processes allowing immature neurons to effectively grow an axon, navigate toward target areas, form synaptic contacts and become part of information processing networks that control behavior in adulthood. Not only immature neurons are able to precisely control the expression of a plethora of genes necessary for axon extension and pathfinding, synapse formation and function, but also non-neuronal cells such as astrocytes and microglia actively participate in sculpting the nervous system through refinement, consolidation, and elimination of synaptic contacts. Recent evidence indicates that a balancing act between axon regeneration and synaptic function may be crucial for rebuilding functional neuronal circuits after CNS trauma and disease in adulthood. Here, we review the role of classical and new intrinsic and extrinsic neuronal determinants in the context of CNS development, injury, and disease. Moreover, we discuss strategies targeting neuronal and non-neuronal cell behaviors, either alone or in combination, to promote axon regeneration and neuronal circuit formation in adulthood.
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Affiliation(s)
- Conrad Kiyoshi
- Department of Neuroscience, Wexner Medical Center, The Ohio State University, Columbus, OH 43210, USA
| | - Andrea Tedeschi
- Department of Neuroscience, Wexner Medical Center, The Ohio State University, Columbus, OH 43210, USA
- Discovery Theme on Chronic Brain Injury, The Ohio State University, Columbus, OH 43210, USA
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23
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Duncan GJ, Manesh SB, Hilton BJ, Assinck P, Plemel JR, Tetzlaff W. The fate and function of oligodendrocyte progenitor cells after traumatic spinal cord injury. Glia 2019; 68:227-245. [PMID: 31433109 DOI: 10.1002/glia.23706] [Citation(s) in RCA: 57] [Impact Index Per Article: 11.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/31/2019] [Revised: 07/24/2019] [Accepted: 08/01/2019] [Indexed: 12/27/2022]
Abstract
Oligodendrocyte progenitor cells (OPCs) are the most proliferative and dispersed population of progenitor cells in the adult central nervous system, which allows these cells to rapidly respond to damage. Oligodendrocytes and myelin are lost after traumatic spinal cord injury (SCI), compromising efficient conduction and, potentially, the long-term health of axons. In response, OPCs proliferate and then differentiate into new oligodendrocytes and Schwann cells to remyelinate axons. This culminates in highly efficient remyelination following experimental SCI in which nearly all intact demyelinated axons are remyelinated in rodent models. However, myelin regeneration comprises only one role of OPCs following SCI. OPCs contribute to scar formation after SCI and restrict the regeneration of injured axons. Moreover, OPCs alter their gene expression following demyelination, express cytokines and perpetuate the immune response. Here, we review the functional contribution of myelin regeneration and other recently uncovered roles of OPCs and their progeny to repair following SCI.
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Affiliation(s)
- Greg J Duncan
- Department of Neurology, Jungers Center for Neurosciences Research, Oregon Health and Science University, Portland, Oregon
| | - Sohrab B Manesh
- Graduate Program in Neuroscience, International Collaboration on Repair Discoveries (ICORD), University of British Columbia (UBC), Vancouver, British Columbia, Canada
| | - Brett J Hilton
- Deutsches Zentrum für Neurodegenerative Erkrankungen (DZNE), Bonn, Germany
| | - Peggy Assinck
- MRC Centre for Regenerative Medicine, University of Edinburgh, Edinburgh, UK
| | - Jason R Plemel
- Department of Medicine, Division of Neurology, Neuroscience and Mental Health Institute, University of Alberta, Calgary, Alberta, Canada
| | - Wolfram Tetzlaff
- Graduate Program in Neuroscience, International Collaboration on Repair Discoveries (ICORD), University of British Columbia (UBC), Vancouver, British Columbia, Canada.,Departments of Zoology and Surgery, University of British Columbia, Vancouver, British Columbia, Canada
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24
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Combining molecular intervention with in vivo imaging to untangle mechanisms of axon pathology and outgrowth following spinal cord injury. Exp Neurol 2019; 318:1-11. [DOI: 10.1016/j.expneurol.2019.04.003] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/18/2018] [Revised: 03/20/2019] [Accepted: 04/07/2019] [Indexed: 12/17/2022]
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25
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Weng YL, Wang X, An R, Cassin J, Vissers C, Liu Y, Liu Y, Xu T, Wang X, Wong SZH, Joseph J, Dore LC, Dong Q, Zheng W, Jin P, Wu H, Shen B, Zhuang X, He C, Liu K, Song H, Ming GL. Epitranscriptomic m 6A Regulation of Axon Regeneration in the Adult Mammalian Nervous System. Neuron 2019; 97:313-325.e6. [PMID: 29346752 DOI: 10.1016/j.neuron.2017.12.036] [Citation(s) in RCA: 264] [Impact Index Per Article: 52.8] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/23/2017] [Revised: 11/05/2017] [Accepted: 12/22/2017] [Indexed: 02/07/2023]
Abstract
N6-methyladenosine (m6A) affects multiple aspects of mRNA metabolism and regulates developmental transitions by promoting mRNA decay. Little is known about the role of m6A in the adult mammalian nervous system. Here we report that sciatic nerve lesion elevates levels of m6A-tagged transcripts encoding many regeneration-associated genes and protein translation machinery components in the adult mouse dorsal root ganglion (DRG). Single-base resolution m6A-CLIP mapping further reveals a dynamic m6A landscape in the adult DRG upon injury. Loss of either m6A methyltransferase complex component Mettl14 or m6A-binding protein Ythdf1 globally attenuates injury-induced protein translation in adult DRGs and reduces functional axon regeneration in the peripheral nervous system in vivo. Furthermore, Pten deletion-induced axon regeneration of retinal ganglion neurons in the adult central nervous system is attenuated upon Mettl14 knockdown. Our study reveals a critical epitranscriptomic mechanism in promoting injury-induced protein synthesis and axon regeneration in the adult mammalian nervous system.
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Affiliation(s)
- Yi-Lan Weng
- Department of Neuroscience, Mahoney Institute for Neurosciences, Perelman School of Medicine, University of Pennsylvania, Philadelphia, PA 19104, USA; Institute for Cell Engineering, Johns Hopkins University School of Medicine, Baltimore, MD 21205, USA
| | - Xu Wang
- Division of Life Science, State Key Laboratory of Molecular Neuroscience, Hong Kong University of Science and Technology, Hong Kong, China
| | - Ran An
- Department of Neuroscience, Mahoney Institute for Neurosciences, Perelman School of Medicine, University of Pennsylvania, Philadelphia, PA 19104, USA; Institute for Cell Engineering, Johns Hopkins University School of Medicine, Baltimore, MD 21205, USA; Department of Neurology, State Key Laboratory of Medical Neurobiology, Huashan Hospital, Fudan University, Shanghai 200040, China
| | - Jessica Cassin
- Human Genetic Pre-graduate Program, Johns Hopkins University School of Medicine, Baltimore, MD 21205, USA
| | - Caroline Vissers
- Biochemistry, Cellular, and Molecular Biology Graduate Program, Johns Hopkins University School of Medicine, Baltimore, MD 21205, USA
| | - Yuanyuan Liu
- State Key Laboratory of Reproductive Medicine, Department of Histology and Embryology, Nanjing Medical University, Nanjing 211166, China
| | - Yajing Liu
- School of Life Science and Technology, ShanghaiTech University, Shanghai 201210, China
| | - Tianlei Xu
- Department of Biostatistics and Bioinformatics, Rollins School of Public Health, Emory University, Atlanta, GA 30322, USA
| | - Xinyuan Wang
- Department of Neuroscience, Mahoney Institute for Neurosciences, Perelman School of Medicine, University of Pennsylvania, Philadelphia, PA 19104, USA; School of Basic Medical Sciences, Fudan University, Shanghai 200040, China
| | - Samuel Zheng Hao Wong
- Department of Neuroscience, Mahoney Institute for Neurosciences, Perelman School of Medicine, University of Pennsylvania, Philadelphia, PA 19104, USA; Cellular and Molecular Medicine Graduate Program, Johns Hopkins University School of Medicine, Baltimore, MD 21205, USA
| | - Jessica Joseph
- Cellular and Molecular Medicine Graduate Program, Johns Hopkins University School of Medicine, Baltimore, MD 21205, USA
| | - Louis C Dore
- Department of Chemistry, University of Chicago, Chicago, IL 60637, USA; Institute for Biophysical Dynamics, University of Chicago, Chicago, IL 60637, USA; Howard Hughes Medical Institute, University of Chicago, Chicago, IL 60637, USA
| | - Qiang Dong
- Department of Neurology, State Key Laboratory of Medical Neurobiology, Huashan Hospital, Fudan University, Shanghai 200040, China
| | - Wei Zheng
- National Center for Advancing Translational Sciences, NIH, Bethesda, MD 20892, USA
| | - Peng Jin
- Department of Human Genetics, School of Medicine, Emory University, Atlanta, GA 30322, USA
| | - Hao Wu
- Department of Biostatistics and Bioinformatics, Rollins School of Public Health, Emory University, Atlanta, GA 30322, USA
| | - Bin Shen
- State Key Laboratory of Reproductive Medicine, Department of Histology and Embryology, Nanjing Medical University, Nanjing 211166, China
| | - Xiaoxi Zhuang
- Department of Neurobiology, University of Chicago, Chicago, IL 60637, USA
| | - Chuan He
- Department of Chemistry, University of Chicago, Chicago, IL 60637, USA; Institute for Biophysical Dynamics, University of Chicago, Chicago, IL 60637, USA; Howard Hughes Medical Institute, University of Chicago, Chicago, IL 60637, USA
| | - Kai Liu
- Division of Life Science, State Key Laboratory of Molecular Neuroscience, Hong Kong University of Science and Technology, Hong Kong, China
| | - Hongjun Song
- Department of Neuroscience, Mahoney Institute for Neurosciences, Perelman School of Medicine, University of Pennsylvania, Philadelphia, PA 19104, USA; Human Genetic Pre-graduate Program, Johns Hopkins University School of Medicine, Baltimore, MD 21205, USA; Biochemistry, Cellular, and Molecular Biology Graduate Program, Johns Hopkins University School of Medicine, Baltimore, MD 21205, USA; Cellular and Molecular Medicine Graduate Program, Johns Hopkins University School of Medicine, Baltimore, MD 21205, USA; Department of Cell and Developmental Biology, Perelman School of Medicine, University of Pennsylvania, Philadelphia, PA 19104, USA; The Epigenetics Institute, Perelman School of Medicine, University of Pennsylvania, Philadelphia, PA 19104, USA; Institute for Regenerative Medicine, Perelman School of Medicine, University of Pennsylvania, Philadelphia, PA 19104, USA
| | - Guo-Li Ming
- Department of Neuroscience, Mahoney Institute for Neurosciences, Perelman School of Medicine, University of Pennsylvania, Philadelphia, PA 19104, USA; Biochemistry, Cellular, and Molecular Biology Graduate Program, Johns Hopkins University School of Medicine, Baltimore, MD 21205, USA; Cellular and Molecular Medicine Graduate Program, Johns Hopkins University School of Medicine, Baltimore, MD 21205, USA; Department of Cell and Developmental Biology, Perelman School of Medicine, University of Pennsylvania, Philadelphia, PA 19104, USA; Institute for Regenerative Medicine, Perelman School of Medicine, University of Pennsylvania, Philadelphia, PA 19104, USA.
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26
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Cheng YT, Lett KM, Schaffer CB. Surgical preparations, labeling strategies, and optical techniques for cell-resolved, in vivo imaging in the mouse spinal cord. Exp Neurol 2019; 318:192-204. [PMID: 31095935 DOI: 10.1016/j.expneurol.2019.05.010] [Citation(s) in RCA: 17] [Impact Index Per Article: 3.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/13/2019] [Revised: 04/25/2019] [Accepted: 05/10/2019] [Indexed: 11/16/2022]
Abstract
In vivo optical imaging has enabled detailed studies of cellular dynamics in the brain of rodents in both healthy and diseased states. Such studies were made possible by three advances: surgical preparations that give optical access to the brain; strategies for in vivo labeling of cells with structural and functional fluorescent indicators; and optical imaging techniques that are relatively insensitive to light scattering by tissue. In vivo imaging in the rodent spinal cord has lagged behind than that in the brain, largely due to the anatomy around the spinal cord that complicates the surgical preparation, and to the strong optical scattering of the dorsal white matter that limits the ability to image deep into the spinal cord. Here, we review recent advances in surgical methods, labeling strategies, and optical tools that have enabled in vivo, high-resolution imaging of the dynamic behaviors of cells in the spinal cord in mice. Surgical preparations that enable long-term optical access and robust stabilization of the spinal cord are now available. Labeling strategies that have been used in the spinal cord tend to follow those that have been used in the brain, and some recent advances in genetically-encoded labeling strategies remain to be capitalized on. The optical imaging methods used to date, including two photon excited fluorescence microscopy, are largely limited to imaging the superficial layers of the spinal cord by the optical scattering of the white matter. Finally, we show preliminary data that points to the use of higher-order nonlinear optical processes, such as three photon excited fluorescence, as a means to image deeper into the mouse spinal cord.
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Affiliation(s)
- Yu-Ting Cheng
- Nancy E. and Peter C. Meinig School of Biomedical Engineering, Cornell University, Ithaca, NY, USA; Department of Neurobiology and Behavior, Cornell University, Ithaca, NY, USA
| | - Kawasi M Lett
- Nancy E. and Peter C. Meinig School of Biomedical Engineering, Cornell University, Ithaca, NY, USA
| | - Chris B Schaffer
- Nancy E. and Peter C. Meinig School of Biomedical Engineering, Cornell University, Ithaca, NY, USA.
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27
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Perrin FE, Noristani HN. Serotonergic mechanisms in spinal cord injury. Exp Neurol 2019; 318:174-191. [PMID: 31085200 DOI: 10.1016/j.expneurol.2019.05.007] [Citation(s) in RCA: 47] [Impact Index Per Article: 9.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/05/2019] [Revised: 05/07/2019] [Accepted: 05/08/2019] [Indexed: 12/12/2022]
Abstract
Spinal cord injury (SCI) is a tragic event causing irreversible losses of sensory, motor, and autonomic functions, that may also be associated with chronic neuropathic pain. Serotonin (5-HT) neurotransmission in the spinal cord is critical for modulating sensory, motor, and autonomic functions. Following SCI, 5-HT axons caudal to the lesion site degenerate, and the degree of axonal degeneration positively correlates with lesion severity. Rostral to the lesion, 5-HT axons sprout, irrespective of the severity of the injury. Unlike callosal fibers and cholinergic projections, 5-HT axons are more resistant to an inhibitory milieu and undergo active sprouting and regeneration after central nervous system (CNS) traumatism. Numerous studies suggest that a chronic increase in serotonergic neurotransmission promotes 5-HT axon sprouting in the intact CNS. Moreover, recent studies in invertebrates suggest that 5-HT has a pro-regenerative role in injured axons. Here we present a brief description of 5-HT discovery, 5-HT innervation of the CNS, and physiological functions of 5-HT in the spinal cord, including its role in controlling bladder function. We then present a comprehensive overview of changes in serotonergic axons after CNS damage, and discuss their plasticity upon altered 5-HT neurotransmitter levels. Subsequently, we provide an in-depth review of therapeutic approaches targeting 5-HT neurotransmission, as well as other pre-clinical strategies to promote an increase in re-growth of 5-HT axons, and their functional consequences in SCI animal models. Finally, we highlight recent findings signifying the direct role of 5-HT in axon regeneration and suggest strategies to further promote robust long-distance re-growth of 5-HT axons across the lesion site and eventually achieve functional recovery following SCI.
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Affiliation(s)
- Florence Evelyne Perrin
- University of Montpellier, Montpellier, F-34095 France; INSERM, U1198, Montpellier, F-34095 France; EPHE, Paris, F-75014 France
| | - Harun Najib Noristani
- Shriners Hospitals Pediatric Research Center, Center for Neural Repair, Lewis Katz School of Medicine, Temple University, Philadelphia, PA 19140, USA; Department of Anatomy and Cell Biology, Lewis Katz School of Medicine, Temple University, Philadelphia, PA 19140, USA.
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28
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Zheng B, Lorenzana AO, Ma L. Understanding the axonal response to injury by in vivo imaging in the mouse spinal cord: A tale of two branches. Exp Neurol 2019; 318:277-285. [PMID: 30986398 PMCID: PMC6588497 DOI: 10.1016/j.expneurol.2019.04.008] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/31/2019] [Revised: 04/05/2019] [Accepted: 04/11/2019] [Indexed: 01/01/2023]
Abstract
Understanding the basic properties of how axons respond to injury in the mammalian central nervous system (CNS) is of fundamental value for developing strategies to promote neural repair. Axons possess complex morphologies with stereotypical branching patterns. However, current knowledge of the axonal response to injury gives little consideration to axonal branches, nor do strategies to promote axon regeneration. This article reviews evidence from in vivo spinal cord imaging that axonal branches markedly impact the degenerative and regenerative responses to injury. At a major bifurcation point, depending on whether one or both axonal branches are injured, neurons may choose either a more self-preservative response or a more dynamic response. The stabilizing effect of the spared branch may underlie a well-known divergence in neuronal responses to injury, and illustrates an example where in vivo spinal cord imaging reveals insights that are difficult to elucidate with conventional histological methods.
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Affiliation(s)
- Binhai Zheng
- Department of Neurosciences, School of Medicine, University of California San Diego, La Jolla, CA, USA; VA San Diego Healthcare System, San Diego, CA, USA.
| | - Ariana O Lorenzana
- Department of Neurosciences, School of Medicine, University of California San Diego, La Jolla, CA, USA
| | - Le Ma
- Department of Neuroscience, Jefferson Synaptic Biology Center, Vickie and Jack Farber Institute for Neuroscience, Sydney Kimmel Medical College, Thomas Jefferson University, Philadelphia, PA, USA
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29
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Schaffran B, Hilton BJ, Bradke F. Imaging in vivo dynamics of sensory axon responses to CNS injury. Exp Neurol 2019; 317:110-118. [PMID: 30794766 DOI: 10.1016/j.expneurol.2019.02.010] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/29/2018] [Revised: 02/13/2019] [Accepted: 02/17/2019] [Indexed: 01/25/2023]
Abstract
Axons in the adult mammalian brain and spinal cord fail to regenerate upon lesion. In vivo imaging serves as a tool to investigate the immediate response of axons to injury and how the same injured axons behave over time. Here, we describe the dynamic changes that injured sensory axons undergo and methods of imaging them in vivo. First, we explain how sensory axons in the dorsal column of the adult mouse spinal cord respond to axotomy. Then, we highlight practical considerations for implementing two-photon based in vivo imaging of these axons. Finally, we describe future directions for this technique, including the possibility of in vivo imaging of subcellular dynamics within the axon.
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Affiliation(s)
| | - Brett J Hilton
- German Center for Neurodegenerative Diseases, Bonn, Germany
| | - Frank Bradke
- German Center for Neurodegenerative Diseases, Bonn, Germany.
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30
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Knockdown of Fidgetin Improves Regeneration of Injured Axons by a Microtubule-Based Mechanism. J Neurosci 2019; 39:2011-2024. [PMID: 30647150 DOI: 10.1523/jneurosci.1888-18.2018] [Citation(s) in RCA: 19] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/24/2018] [Revised: 11/21/2018] [Accepted: 12/24/2018] [Indexed: 12/16/2022] Open
Abstract
Fidgetin is a microtubule-severing protein that pares back the labile domains of microtubules in the axon. Experimental depletion of fidgetin results in elongation of the labile domains of microtubules and faster axonal growth. To test whether fidgetin knockdown assists axonal regeneration, we plated dissociated adult rat DRGs transduced using AAV5-shRNA-fidgetin on a laminin substrate with spots of aggrecan, a growth-inhibitory chondroitin sulfate proteoglycan. This cell culture assay mimics the glial scar formed after CNS injury. Aggrecan is more concentrated at the edge of the spot, such that axons growing from within the spot toward the edge encounter a concentration gradient that causes growth cones to become dystrophic and axons to retract or curve back on themselves. Fidgetin knockdown resulted in faster-growing axons on both laminin and aggrecan and enhanced crossing of axons from laminin onto aggrecan. Strikingly, axons from within the spot grew more avidly against the inhibitory aggrecan concentration gradient to cross onto laminin, without retracting or curving back. We also tested whether depleting fidgetin improves axonal regeneration in vivo after a dorsal root crush in adult female rats. Whereas control DRG neurons failed to extend axons across the dorsal root entry zone after injury, DRG neurons in which fidgetin was knocked down displayed enhanced regeneration of axons across the dorsal root entry zone into the spinal cord. Collectively, these results establish fidgetin as a novel therapeutic target to augment nerve regeneration and provide a workflow template by which microtubule-related targets can be compared in the future.SIGNIFICANCE STATEMENT Here we establish a workflow template from cell culture to animals in which microtubule-based treatments can be tested and compared with one another for their effectiveness in augmenting regeneration of injured axons relevant to spinal cord injury. The present work uses a viral transduction approach to knock down fidgetin from rat neurons, which coaxes nerve regeneration by elevating microtubule mass in their axons. Unlike previous strategies using microtubule-stabilizing drugs, fidgetin knockdown adds microtubule mass that is labile (rather than stable), thereby better recapitulating the growth status of a developing axon.
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Yao M, Sun H, Yuan Q, Li N, Li H, Tang Y, Leung GK, Wu W. Targeting proteoglycan receptor PTPσ restores sensory function after spinal cord dorsal root injury by activation of Erks/CREB signaling pathway. Neuropharmacology 2019; 144:208-218. [PMID: 30393073 DOI: 10.1016/j.neuropharm.2018.10.035] [Citation(s) in RCA: 11] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/23/2018] [Revised: 10/22/2018] [Accepted: 10/23/2018] [Indexed: 12/26/2022]
Abstract
Dorsal root injury commonly results in irreversible loss of sensory functions because of the limited intrinsic regenerative capacity of adult sensory axons and the growth-inhibitory environment at the dorsal root entry zone (DREZ) between the dorsal root and the spinal cord. Chondroitin sulfate proteoglycans (CSPGs) are the dominant suppressors of axonal regeneration, acting via neuronal receptors including protein tyrosine phosphatase-σ (PTPσ). ISP (Intracellular Sigma Peptide) is a small peptide mimetic of the PTPσ wedge region that has been developed to target PTPσ and relieve CSPG inhibition. Extracellular regulated kinases (Erks) and cAMP response element binding protein (CREB) are signaling molecules downstream of CSPGs and PTPσ; they are expressed in neurons and essential for axon growth. In this study, we observed that ISP administration could promote sensory function restoration in adult rats after dorsal spinal root crush injury. Our results show that systemic ISP administration would not only significantly increase sensory axon regeneration and functional recovery, but also activate Erk and CREB signaling pathway. Furthermore, ISP has also been verified to increase dorsal root ganglion axonal remyelination in vitro. These results suggest that modulation of PTPσ by ISP represents a promising therapeutic strategy for sensory neuronal injuries.
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Affiliation(s)
- Min Yao
- School of Biomedical Sciences, The University of Hong Kong, Hong Kong SAR, 999077, China; Department of Surgery, The University of Hong Kong, Hong Kong SAR, 999077, China
| | - Haitao Sun
- School of Biomedical Sciences, The University of Hong Kong, Hong Kong SAR, 999077, China; The National Key Clinical Specialty, The Engineering Technology Research Center of Education Ministry of China, Guangdong Provincial Key Laboratory on Brain Function Repair and Regeneration, Department of Neurosurgery, Zhujiang Hospital, Southern Medical University, Guangzhou, 510282, China
| | - Qiuju Yuan
- School of Chinese Medicine, Faculty of Medicine, The Chinese University of Hong Kong, Hong Kong, 999077, China
| | - Ning Li
- Department of Surgery, The University of Hong Kong, Hong Kong SAR, 999077, China
| | - Heng Li
- School of Biomedical Sciences, The University of Hong Kong, Hong Kong SAR, 999077, China
| | - Yinjuan Tang
- Department of Basic Medicine Sciences, Xiangnan University, Chenzhou, 423000, Hunan Province, China
| | - Gilberto Kk Leung
- Department of Surgery, The University of Hong Kong, Hong Kong SAR, 999077, China; Guangdong-Hongkong-Macau Institute of CNS Regeneration (GHMICR), Jinan University, Guangzhou, 510632, China.
| | - Wutian Wu
- School of Biomedical Sciences, The University of Hong Kong, Hong Kong SAR, 999077, China; Guangdong-Hongkong-Macau Institute of CNS Regeneration (GHMICR), Jinan University, Guangzhou, 510632, China; Re-Stem Biotechnology Co., Ltd, Suzhou, 215300, China.
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Neumann B, Linton C, Giordano-Santini R, Hilliard MA. Axonal fusion: An alternative and efficient mechanism of nerve repair. Prog Neurobiol 2018; 173:88-101. [PMID: 30500382 DOI: 10.1016/j.pneurobio.2018.11.004] [Citation(s) in RCA: 23] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/09/2018] [Revised: 11/22/2018] [Accepted: 11/26/2018] [Indexed: 02/07/2023]
Abstract
Injuries to the nervous system can cause lifelong morbidity due to the disconnect that occurs between nerve cells and their cellular targets. Re-establishing these lost connections is the ultimate goal of endogenous regenerative mechanisms, as well as those induced by exogenous manipulations in a laboratory or clinical setting. Reconnection between severed neuronal fibers occurs spontaneously in some invertebrate species and can be induced in mammalian systems. This process, known as axonal fusion, represents a highly efficient means of repair after injury. Recent progress has greatly enhanced our understanding of the molecular control of axonal fusion, demonstrating that the machinery required for the engulfment of apoptotic cells is repurposed to mediate the reconnection between severed axon fragments, which are subsequently merged by fusogen proteins. Here, we review our current understanding of naturally occurring axonal fusion events, as well as those being ectopically produced with the aim of achieving better clinical outcomes.
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Affiliation(s)
- Brent Neumann
- Neuroscience Program, Monash Biomedicine Discovery Institute and Department of Anatomy and Developmental Biology, Monash University, Melbourne VIC 3800, Australia.
| | - Casey Linton
- Clem Jones Centre for Ageing Dementia Research, Queensland Brain Institute, The University of Queensland, Brisbane, QLD 4072, Australia
| | - Rosina Giordano-Santini
- Clem Jones Centre for Ageing Dementia Research, Queensland Brain Institute, The University of Queensland, Brisbane, QLD 4072, Australia
| | - Massimo A Hilliard
- Clem Jones Centre for Ageing Dementia Research, Queensland Brain Institute, The University of Queensland, Brisbane, QLD 4072, Australia.
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33
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Nascimento AI, Mar FM, Sousa MM. The intriguing nature of dorsal root ganglion neurons: Linking structure with polarity and function. Prog Neurobiol 2018; 168:86-103. [PMID: 29729299 DOI: 10.1016/j.pneurobio.2018.05.002] [Citation(s) in RCA: 75] [Impact Index Per Article: 12.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/06/2017] [Revised: 04/26/2018] [Accepted: 05/01/2018] [Indexed: 11/26/2022]
Abstract
Dorsal root ganglion (DRG) neurons are the first neurons of the sensory pathway. They are activated by a variety of sensory stimuli that are then transmitted to the central nervous system. An important feature of DRG neurons is their unique morphology where a single process -the stem axon- bifurcates into a peripheral and a central axonal branch, with different functions and cellular properties. Distinctive structural aspects of the two DRG neuron branches may have important implications for their function in health and disease. However, the link between DRG axonal branch structure, polarity and function has been largely neglected in the field, and relevant information is rather scattered across the literature. In particular, ultrastructural differences between the two axonal branches are likely to account for the higher transport and regenerative ability of the peripheral DRG neuron axon when compared to the central one. Nevertheless, the cell intrinsic factors contributing to this central-peripheral asymmetry are still unknown. Here we critically review the factors that may underlie the functional asymmetry between the peripheral and central DRG axonal branches. Also, we discuss the hypothesis that DRG neurons may assemble a structure resembling the axon initial segment that may be responsible, at least in part, for their polarity and electrophysiological features. Ultimately, we suggest that the clarification of the axonal ultrastructure of DRG neurons using state-of-the-art techniques will be crucial to understand the physiology of this peculiar cell type.
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Affiliation(s)
- Ana Isabel Nascimento
- Nerve Regeneration Group, Instituto de Biologia Molecular e Celular-IBMC and Instituto de Inovação e Investigação em Saúde, University of Porto, Rua Alfredo Allen, 208, 4200-135 Porto, Portugal; Instituto de Ciências Biomédicas Abel Salazar-ICBAS, Rua Jorge Viterbo Ferreira 228, 4050-313 Porto, Portugal
| | - Fernando Milhazes Mar
- Nerve Regeneration Group, Instituto de Biologia Molecular e Celular-IBMC and Instituto de Inovação e Investigação em Saúde, University of Porto, Rua Alfredo Allen, 208, 4200-135 Porto, Portugal
| | - Mónica Mendes Sousa
- Nerve Regeneration Group, Instituto de Biologia Molecular e Celular-IBMC and Instituto de Inovação e Investigação em Saúde, University of Porto, Rua Alfredo Allen, 208, 4200-135 Porto, Portugal.
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34
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González-Fernández E, Jeong HK, Fukaya M, Kim H, Khawaja RR, Srivastava IN, Waisman A, Son YJ, Kang SH. PTEN negatively regulates the cell lineage progression from NG2 + glial progenitor to oligodendrocyte via mTOR-independent signaling. eLife 2018; 7:32021. [PMID: 29461205 PMCID: PMC5839742 DOI: 10.7554/elife.32021] [Citation(s) in RCA: 16] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/14/2017] [Accepted: 02/19/2018] [Indexed: 12/11/2022] Open
Abstract
Oligodendrocytes (OLs), the myelin-forming CNS glia, are highly vulnerable to cellular stresses, and a severe myelin loss underlies numerous CNS disorders. Expedited OL regeneration may prevent further axonal damage and facilitate functional CNS repair. Although adult OL progenitors (OPCs) are the primary players for OL regeneration, targetable OPC-specific intracellular signaling mechanisms for facilitated OL regeneration remain elusive. Here, we report that OPC-targeted PTEN inactivation in the mouse, in contrast to OL-specific manipulations, markedly promotes OL differentiation and regeneration in the mature CNS. Unexpectedly, an additional deletion of mTOR did not reverse the enhanced OL development from PTEN-deficient OPCs. Instead, ablation of GSK3β, another downstream signaling molecule that is negatively regulated by PTEN-Akt, enhanced OL development. Our results suggest that PTEN persistently suppresses OL development in an mTOR-independent manner, and at least in part, via controlling GSK3β activity. OPC-targeted PTEN-GSK3β inactivation may benefit facilitated OL regeneration and myelin repair.
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Affiliation(s)
- Estibaliz González-Fernández
- Shriners Hospitals Pediatric Research Center, Temple University Lewis Katz School of Medicine, Philadelphia, Unites States
| | - Hey-Kyeong Jeong
- Shriners Hospitals Pediatric Research Center, Temple University Lewis Katz School of Medicine, Philadelphia, Unites States
| | - Masahiro Fukaya
- Department of Anatomy, Kitasato University School of Medicine, Sagamihara, Japan
| | - Hyukmin Kim
- Shriners Hospitals Pediatric Research Center, Temple University Lewis Katz School of Medicine, Philadelphia, Unites States
| | - Rabia R Khawaja
- Shriners Hospitals Pediatric Research Center, Temple University Lewis Katz School of Medicine, Philadelphia, Unites States
| | - Isha N Srivastava
- Shriners Hospitals Pediatric Research Center, Temple University Lewis Katz School of Medicine, Philadelphia, Unites States
| | - Ari Waisman
- Institute for Molecular Medicine, University Medical Center of the Johannes Gutenberg University of Mainz, Mainz, Germany
| | - Young-Jin Son
- Shriners Hospitals Pediatric Research Center, Temple University Lewis Katz School of Medicine, Philadelphia, Unites States.,Department of Anatomy and Cell Biology, Temple University Lewis Katz School of Medicine, Philadelphia, United States
| | - Shin H Kang
- Shriners Hospitals Pediatric Research Center, Temple University Lewis Katz School of Medicine, Philadelphia, Unites States.,Department of Anatomy and Cell Biology, Temple University Lewis Katz School of Medicine, Philadelphia, United States
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35
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In Vivo Imaging of CNS Injury and Disease. J Neurosci 2017; 37:10808-10816. [PMID: 29118209 DOI: 10.1523/jneurosci.1826-17.2017] [Citation(s) in RCA: 23] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/22/2017] [Revised: 10/02/2017] [Accepted: 10/03/2017] [Indexed: 02/06/2023] Open
Abstract
In vivo optical imaging has emerged as a powerful tool with which to study cellular responses to injury and disease in the mammalian CNS. Important new insights have emerged regarding axonal degeneration and regeneration, glial responses and neuroinflammation, changes in the neurovascular unit, and, more recently, neural transplantations. Accompanying a 2017 SfN Mini-Symposium, here, we discuss selected recent advances in understanding the neuronal, glial, and other cellular responses to CNS injury and disease with in vivo imaging of the rodent brain or spinal cord. We anticipate that in vivo optical imaging will continue to be at the forefront of breakthrough discoveries of fundamental mechanisms and therapies for CNS injury and disease.
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36
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Abstract
In this issue of Neuron, Tedeschi et al. (2016) describe the voltage-gated calcium channel subunit alpha2delta2 as a developmental switch from axon elongation to synapse formation and transmission that doubles as a suppressor of axon regeneration, providing a molecular clue for the synaptic stabilization hypothesis of CNS regeneration failure.
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Affiliation(s)
- Jessica M Meves
- Neurosciences Graduate Program and Department of Neurosciences, University of California San Diego, School of Medicine, 9500 Gilman Drive, MC 0691, La Jolla, CA 92093, USA
| | - Binhai Zheng
- Neurosciences Graduate Program and Department of Neurosciences, University of California San Diego, School of Medicine, 9500 Gilman Drive, MC 0691, La Jolla, CA 92093, USA.
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37
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Filous AR, Schwab JM. Determinants of Axon Growth, Plasticity, and Regeneration in the Context of Spinal Cord Injury. THE AMERICAN JOURNAL OF PATHOLOGY 2017; 188:53-62. [PMID: 29030051 DOI: 10.1016/j.ajpath.2017.09.005] [Citation(s) in RCA: 35] [Impact Index Per Article: 5.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 06/20/2017] [Revised: 09/15/2017] [Accepted: 09/21/2017] [Indexed: 12/30/2022]
Abstract
The mechanisms that underlie recovery after injury of the central nervous system have rarely been definitively established. Axon regrowth remains the major prerequisite for plasticity, regeneration, circuit formation, and eventually functional recovery. The attributed functional relevance of axon regrowth, however, will depend on several subsequent conditional neurobiological modifications, including myelination and synapse formation, but also pruning of aberrant connectivity. Despite the ability to revamp axon outgrowth by altering an increasing number of extracellular and intracellular targets, disentangling which axons are responsible for the recovery of function from those that are functionally silent, or even contributing to aberrant functions, represents a pertinent void in our understanding, challenging the intuitive translational link between anatomical and functional regeneration. Anatomic hallmarks of regeneration are not static and are largely activity dependent. Herein, we survey mechanisms leading to the formation of dystrophic growth cone at the injured axonal tip, the subsequent axonal dieback, and the molecular determinants of axon growth, plasticity, and regeneration in the context of spinal cord injury.
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Affiliation(s)
- Angela R Filous
- Spinal Cord Injury Division, Department of Neurology, The Ohio State University, Wexner Medical Center, Columbus, Ohio.
| | - Jan M Schwab
- Spinal Cord Injury Division, Department of Neurology, The Ohio State University, Wexner Medical Center, Columbus, Ohio; Department of Neuroscience, The Ohio State University, Wexner Medical Center, Columbus, Ohio; Department of Physical Medicine and Rehabilitation, The Ohio State University, Wexner Medical Center, Columbus, Ohio; Center for Brain and Spinal Cord Repair, Spinal Cord Injury Medicine, The Ohio State University, Wexner Medical Center, Columbus, Ohio.
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38
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Postinjury Induction of Activated ErbB2 Selectively Hyperactivates Denervated Schwann Cells and Promotes Robust Dorsal Root Axon Regeneration. J Neurosci 2017; 37:10955-10970. [PMID: 28982707 DOI: 10.1523/jneurosci.0903-17.2017] [Citation(s) in RCA: 13] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/29/2017] [Revised: 09/20/2017] [Accepted: 09/27/2017] [Indexed: 11/21/2022] Open
Abstract
Following nerve injury, denervated Schwann cells (SCs) convert to repair SCs, which enable regeneration of peripheral axons. However, the repair capacity of SCs and the regenerative capacity of peripheral axons are limited. In the present studies we examined a potential therapeutic strategy to enhance the repair capacity of SCs, and tested its efficacy in enhancing regeneration of dorsal root (DR) axons, whose regenerative capacity is particularly weak. We used male and female mice of a doxycycline-inducible transgenic line to induce expression of constitutively active ErbB2 (caErbB2) selectively in SCs after DR crush or transection. Two weeks after injury, injured DRs of induced animals contained far more SCs and SC processes. These SCs had not redifferentiated and continued to proliferate. Injured DRs of induced animals also contained far more axons that regrew along SC processes past the transection or crush site. Remarkably, SCs and axons in uninjured DRs remained quiescent, indicating that caErbB2 enhanced regeneration of injured DRs, without aberrantly activating SCs and axons in intact nerves. We also found that intraspinally expressed glial cell line-derived neurotrophic factor (GDNF), but not the removal of chondroitin sulfate proteoglycans, greatly enhanced the intraspinal migration of caErbB2-expressing SCs, enabling robust penetration of DR axons into the spinal cord. These findings indicate that SC-selective, post-injury activation of ErbB2 provides a novel strategy to powerfully enhance the repair capacity of SCs and axon regeneration, without substantial off-target damage. They also highlight that promoting directed migration of caErbB2-expressing SCs by GDNF might be useful to enable axon regrowth in a non-permissive environment.SIGNIFICANCE STATEMENT Repair of injured peripheral nerves remains a critical clinical problem. We currently lack a therapy that potently enhances axon regeneration in patients with traumatic nerve injury. It is extremely challenging to substantially increase the regenerative capacity of damaged nerves without deleterious off-target effects. It was therefore of great interest to discover that caErbB2 markedly enhances regeneration of damaged dorsal roots, while evoking little change in intact roots. To our knowledge, these findings are the first demonstration that repair capacity of denervated SCs can be efficaciously enhanced without altering innervated SCs. Our study also demonstrates that oncogenic ErbB2 signaling can be activated in SCs but not impede transdifferentiation of denervated SCs to regeneration-promoting repair SCs.
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Nadrigny F, Le Meur K, Schomburg ED, Safavi-Abbasi S, Dibaj P. Two-photon laser-scanning microscopy for single and repetitive imaging of dorsal and lateral spinal white matter in vivo. Physiol Res 2017; 66:531-537. [PMID: 28248542 DOI: 10.33549/physiolres.933461] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/25/2022] Open
Abstract
We developed appropriate surgical procedures for single and repetitive multi-photon imaging of spinal cord in vivo. By intravenous anesthesia, artificial ventilation and laminectomy, acute experiments were performed in the dorsal and lateral white matter. By volatile anesthesia and minimal-invasive surgery, chronic repetitive imaging up to 8 months were performed in the dorsal column through the window between two adjacent spines. Transgenic mouse technology enabled simultaneous imaging of labeled axons, astrocytes and microglia. Repetitive imaging showed positional shifts of microglia over time. These techniques serve for investigations of cellular dynamics and cell-cell interactions in intact and pathologically changed spinal tissue.
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Affiliation(s)
- F Nadrigny
- Max-Planck-Institute for Experimental Medicine, Göttingen, Germany.
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Hoeber J, König N, Trolle C, Lekholm E, Zhou C, Pankratova S, Åkesson E, Fredriksson R, Aldskogius H, Kozlova EN. A Combinatorial Approach to Induce Sensory Axon Regeneration into the Dorsal Root Avulsed Spinal Cord. Stem Cells Dev 2017; 26:1065-1077. [PMID: 28562227 DOI: 10.1089/scd.2017.0019] [Citation(s) in RCA: 8] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/12/2022] Open
Abstract
Spinal root injuries result in newly formed glial scar formation, which prevents regeneration of sensory axons causing permanent sensory loss. Previous studies showed that delivery of trophic factors or implantation of human neural progenitor cells supports sensory axon regeneration and partly restores sensory functions. In this study, we elucidate mechanisms underlying stem cell-mediated ingrowth of sensory axons after dorsal root avulsion (DRA). We show that human spinal cord neural stem/progenitor cells (hscNSPC), and also, mesoporous silica particles loaded with growth factor mimetics (MesoMIM), supported sensory axon regeneration. However, when hscNSPC and MesoMIM were combined, sensory axon regeneration failed. Morphological and tracing analysis showed that sensory axons grow through the newly established glial scar along "bridges" formed by migrating stem cells. Coimplantation of MesoMIM prevented stem cell migration, "bridges" were not formed, and sensory axons failed to enter the spinal cord. MesoMIM applied alone supported sensory axons ingrowth, but without affecting glial scar formation. In vitro, the presence of MesoMIM significantly impaired migration of hscNSPC without affecting their level of differentiation. Our data show that (1) the ability of stem cells to migrate into the spinal cord and organize cellular "bridges" in the newly formed interface is crucial for successful sensory axon regeneration, (2) trophic factor mimetics delivered by mesoporous silica may be a convenient alternative way to induce sensory axon regeneration, and (3) a combinatorial approach of individually beneficial components is not necessarily additive, but can be counterproductive for axonal growth.
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Affiliation(s)
- Jan Hoeber
- 1 Department of Neuroscience, Uppsala University , Uppsala, Sweden
| | - Niclas König
- 1 Department of Neuroscience, Uppsala University , Uppsala, Sweden
| | - Carl Trolle
- 1 Department of Neuroscience, Uppsala University , Uppsala, Sweden
| | - Emilia Lekholm
- 1 Department of Neuroscience, Uppsala University , Uppsala, Sweden .,2 Department of Pharmaceutical Biosciences, Uppsala University , Uppsala, Sweden
| | | | - Stanislava Pankratova
- 4 Institute of Neuroscience and Pharmacology, University of Copenhagen , Copenhagen, Denmark
| | - Elisabet Åkesson
- 5 Department of Neurobiology, Care Sciences and Society, Karolinska Institutet , Stockholm, Sweden
| | - Robert Fredriksson
- 2 Department of Pharmaceutical Biosciences, Uppsala University , Uppsala, Sweden
| | - Håkan Aldskogius
- 1 Department of Neuroscience, Uppsala University , Uppsala, Sweden
| | - Elena N Kozlova
- 1 Department of Neuroscience, Uppsala University , Uppsala, Sweden
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41
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Weng YL, An R, Cassin J, Joseph J, Mi R, Wang C, Zhong C, Jin SG, Pfeifer GP, Bellacosa A, Dong X, Hoke A, He Z, Song H, Ming GL. An Intrinsic Epigenetic Barrier for Functional Axon Regeneration. Neuron 2017; 94:337-346.e6. [PMID: 28426967 PMCID: PMC6007997 DOI: 10.1016/j.neuron.2017.03.034] [Citation(s) in RCA: 105] [Impact Index Per Article: 15.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/24/2016] [Revised: 02/05/2017] [Accepted: 03/23/2017] [Indexed: 12/15/2022]
Abstract
Mature neurons in the adult peripheral nervous system can effectively switch from a dormant state with little axonal growth to robust axon regeneration upon injury. The mechanisms by which injury unlocks mature neurons' intrinsic axonal growth competence are not well understood. Here, we show that peripheral sciatic nerve lesion in adult mice leads to elevated levels of Tet3 and 5-hydroxylmethylcytosine in dorsal root ganglion (DRG) neurons. Functionally, Tet3 is required for robust axon regeneration of DRG neurons and behavioral recovery. Mechanistically, peripheral nerve injury induces DNA demethylation and upregulation of multiple regeneration-associated genes in a Tet3- and thymine DNA glycosylase-dependent fashion in DRG neurons. In addition, Pten deletion-induced axon regeneration of retinal ganglion neurons in the adult CNS is attenuated upon Tet1 knockdown. Together, our study suggests an epigenetic barrier that can be removed by active DNA demethylation to permit axon regeneration in the adult mammalian nervous system.
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Affiliation(s)
- Yi-Lan Weng
- Institute for Cell Engineering, Johns Hopkins University School of Medicine, Baltimore, MD 21205, USA
- Department of Neurology, Johns Hopkins University School of Medicine, Baltimore, MD 21205, USA
| | - Ran An
- Institute for Cell Engineering, Johns Hopkins University School of Medicine, Baltimore, MD 21205, USA
- Department of Neurology, Johns Hopkins University School of Medicine, Baltimore, MD 21205, USA
- Department of Neurology, Huashan Hospital, State Key Laboratory of Medical Neurobiology, Fudan University, Shanghai 200040, China
| | - Jessica Cassin
- Institute for Cell Engineering, Johns Hopkins University School of Medicine, Baltimore, MD 21205, USA
- Pre-doctoral Human Genetics Training Program, Johns Hopkins University School of Medicine, Baltimore, MD 21205, USA
| | - Jessica Joseph
- Institute for Cell Engineering, Johns Hopkins University School of Medicine, Baltimore, MD 21205, USA
- Graduate Program in Cellular and Molecular Medicine, Johns Hopkins University School of Medicine, Baltimore, MD 21205, USA
| | - Ruifa Mi
- Department of Neurology, Johns Hopkins University School of Medicine, Baltimore, MD 21205, USA
| | - Chen Wang
- F.M. Kirby Neurobiology Center, Boston Children's Hospital, and Department of Neurology, 300 Longwood Avenue, Boston, MA 02115, USA
| | - Chun Zhong
- Institute for Cell Engineering, Johns Hopkins University School of Medicine, Baltimore, MD 21205, USA
- Department of Neurology, Johns Hopkins University School of Medicine, Baltimore, MD 21205, USA
| | - Seung-Gi Jin
- Center for Epigenetics, Van Andel Research Institute, Grand Rapids, MI 49503, USA
| | - Gerd P. Pfeifer
- Center for Epigenetics, Van Andel Research Institute, Grand Rapids, MI 49503, USA
| | - Alfonso Bellacosa
- Cancer Epigenetics and Cancer Biology Programs, Fox Chase Cancer Center, Philadelphia, PA 19111, USA
| | - Xinzhong Dong
- The Solomon H. Snyder Department of Neuroscience, Johns Hopkins University School of Medicine, Baltimore, MD 21205, USA
| | - Ahmet Hoke
- Department of Neurology, Johns Hopkins University School of Medicine, Baltimore, MD 21205, USA
| | - Zhigang He
- F.M. Kirby Neurobiology Center, Boston Children's Hospital, and Department of Neurology, 300 Longwood Avenue, Boston, MA 02115, USA
| | - Hongjun Song
- Institute for Cell Engineering, Johns Hopkins University School of Medicine, Baltimore, MD 21205, USA
- Department of Neurology, Johns Hopkins University School of Medicine, Baltimore, MD 21205, USA
- Pre-doctoral Human Genetics Training Program, Johns Hopkins University School of Medicine, Baltimore, MD 21205, USA
- Graduate Program in Cellular and Molecular Medicine, Johns Hopkins University School of Medicine, Baltimore, MD 21205, USA
- The Solomon H. Snyder Department of Neuroscience, Johns Hopkins University School of Medicine, Baltimore, MD 21205, USA
- Department of Neuroscience, Mahoney Institute for Neurosciences, Perelman School for Medicine, University of Pennsylvania, Philadelphia, PA 19104, USA
| | - Guo-li Ming
- Institute for Cell Engineering, Johns Hopkins University School of Medicine, Baltimore, MD 21205, USA
- Department of Neurology, Johns Hopkins University School of Medicine, Baltimore, MD 21205, USA
- Graduate Program in Cellular and Molecular Medicine, Johns Hopkins University School of Medicine, Baltimore, MD 21205, USA
- The Solomon H. Snyder Department of Neuroscience, Johns Hopkins University School of Medicine, Baltimore, MD 21205, USA
- Department of Neuroscience, Mahoney Institute for Neurosciences, Perelman School for Medicine, University of Pennsylvania, Philadelphia, PA 19104, USA
- Department of Psychiatry and Behavioral Sciences, Johns Hopkins University School of Medicine, Baltimore, MD 21205, USA
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Tedeschi A, Bradke F. Spatial and temporal arrangement of neuronal intrinsic and extrinsic mechanisms controlling axon regeneration. Curr Opin Neurobiol 2016; 42:118-127. [PMID: 28039763 DOI: 10.1016/j.conb.2016.12.005] [Citation(s) in RCA: 92] [Impact Index Per Article: 11.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/26/2016] [Revised: 12/07/2016] [Accepted: 12/08/2016] [Indexed: 01/30/2023]
Abstract
Axon regeneration and neuronal tissue repair varies across animal lineages as well as in the mammalian central and peripheral nervous systems. While the peripheral nervous system retains the ability to self-repair, the majority of axons in the adult mammalian central nervous system (CNS) fail to reactivate intrinsic growth programs after injury. Recent findings, however, suggest that long-distance axon regeneration, neuronal circuit assembly and recovery of functions in the adult mammalian CNS are possible. Here, we discuss our current knowledge of the cell signaling pathways and networks controlling axon regeneration. In addition, we outline a number of combinatorial strategies that include among others microtubule-based treatments to foster regeneration and functional connectivity after CNS trauma.
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Affiliation(s)
- Andrea Tedeschi
- German Center for Neurodegenerative Diseases (DZNE), Ludwig-Erhard-Allee 2, 53175 Bonn, Germany.
| | - Frank Bradke
- German Center for Neurodegenerative Diseases (DZNE), Ludwig-Erhard-Allee 2, 53175 Bonn, Germany.
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Hackett AR, Lee JK. Understanding the NG2 Glial Scar after Spinal Cord Injury. Front Neurol 2016; 7:199. [PMID: 27895617 PMCID: PMC5108923 DOI: 10.3389/fneur.2016.00199] [Citation(s) in RCA: 64] [Impact Index Per Article: 8.0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/12/2016] [Accepted: 10/31/2016] [Indexed: 01/05/2023] Open
Abstract
NG2 cells, also known as oligodendrocyte progenitor cells, are located throughout the central nervous system and serve as a pool of progenitors to differentiate into oligodendrocytes. In response to spinal cord injury (SCI), NG2 cells increase their proliferation and differentiation into remyelinating oligodendrocytes. While astrocytes are typically associated with being the major cell type in the glial scar, many NG2 cells also accumulate within the glial scar but their function remains poorly understood. Similar to astrocytes, these cells hypertrophy, upregulate expression of chondroitin sulfate proteoglycans, inhibit axon regeneration, contribute to the glial-fibrotic scar border, and some even differentiate into astrocytes. Whether NG2 cells also have a role in other astrocyte functions, such as preventing the spread of infiltrating leukocytes and expression of inflammatory cytokines, is not yet known. Thus, NG2 cells are not only important for remyelination after SCI but are also a major component of the glial scar with functions that overlap with astrocytes in this region. In this review, we describe the signaling pathways important for the proliferation and differentiation of NG2 cells, as well as the role of NG2 cells in scar formation and tissue repair.
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Affiliation(s)
- Amber R. Hackett
- Miami Project to Cure Paralysis, The Neuroscience Graduate Program, Department of Neurological Surgery, University of Miami Miller School of Medicine, Miami, FL, USA
| | - Jae K. Lee
- Miami Project to Cure Paralysis, The Neuroscience Graduate Program, Department of Neurological Surgery, University of Miami Miller School of Medicine, Miami, FL, USA
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44
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Tedeschi A, Dupraz S, Laskowski CJ, Xue J, Ulas T, Beyer M, Schultze JL, Bradke F. The Calcium Channel Subunit Alpha2delta2 Suppresses Axon Regeneration in the Adult CNS. Neuron 2016; 92:419-434. [PMID: 27720483 DOI: 10.1016/j.neuron.2016.09.026] [Citation(s) in RCA: 164] [Impact Index Per Article: 20.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/11/2016] [Revised: 07/21/2016] [Accepted: 09/01/2016] [Indexed: 12/22/2022]
Abstract
Injuries to the adult CNS often result in permanent disabilities because neurons lose the ability to regenerate their axon during development. Here, whole transcriptome sequencing and bioinformatics analysis followed by gain- and loss-of-function experiments identified Cacna2d2, the gene encoding the Alpha2delta2 subunit of voltage-gated calcium channels (VGCCs), as a developmental switch that limits axon growth and regeneration. Cacna2d2 gene deletion or silencing promoted axon growth in vitro. In vivo, Alpha2delta2 pharmacological blockade through Pregabalin (PGB) administration enhanced axon regeneration in adult mice after spinal cord injury (SCI). As PGB is already an established treatment for a wide range of neurological disorders, our findings suggest that targeting Alpha2delta2 may be a novel treatment strategy to promote structural plasticity and regeneration following CNS trauma.
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Affiliation(s)
- Andrea Tedeschi
- Axonal Growth and Regeneration, German Center for Neurodegenerative Diseases, 53175 Bonn, Germany
| | - Sebastian Dupraz
- Axonal Growth and Regeneration, German Center for Neurodegenerative Diseases, 53175 Bonn, Germany
| | - Claudia J Laskowski
- Axonal Growth and Regeneration, German Center for Neurodegenerative Diseases, 53175 Bonn, Germany
| | - Jia Xue
- Genomics and Immunoregulation, LIMES-Institute, University of Bonn, 53115 Bonn, Germany
| | - Thomas Ulas
- Genomics and Immunoregulation, LIMES-Institute, University of Bonn, 53115 Bonn, Germany
| | - Marc Beyer
- Genomics and Immunoregulation, LIMES-Institute, University of Bonn, 53115 Bonn, Germany
| | - Joachim L Schultze
- Genomics and Immunoregulation, LIMES-Institute, University of Bonn, 53115 Bonn, Germany; Platform for Single Cell Genomics and Epigenomics, German Center for Neurodegenerative Diseases, 53175 Bonn, Germany
| | - Frank Bradke
- Axonal Growth and Regeneration, German Center for Neurodegenerative Diseases, 53175 Bonn, Germany.
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45
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Kim MS, El-Fiqi A, Kim JW, Ahn HS, Kim H, Son YJ, Kim HW, Hyun JK. Nanotherapeutics of PTEN Inhibitor with Mesoporous Silica Nanocarrier Effective for Axonal Outgrowth of Adult Neurons. ACS APPLIED MATERIALS & INTERFACES 2016; 8:18741-18753. [PMID: 27386893 DOI: 10.1021/acsami.6b06889] [Citation(s) in RCA: 10] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/06/2023]
Abstract
Development of therapeutic strategies such as effective drug delivery is an urgent and yet unmet need for repair of damaged nervous systems. Phosphatase and tensin homolog deleted on chromosome 10 (PTEN) regulates axonal regrowth of central and peripheral nervous systems; its inhibition, meanwhile, facilitates axonal outgrowth of injured neurons. Here we show that nanotherapeutics based on mesoporous silica nanoparticles loading PTEN-inhibitor bisperoxovanadium (BpV) are effective for delivery of drug molecules and consequent improvement of axonal outgrowth. Mesoporous nanocarriers loaded BpV drug at large amount (27 μg per 1 mg of carrier), and released sustainably over 10 d. Nanocarrier-BpV treatment of primary neurons from the dorsal root ganglions (DRGs) of rats and mice at various concentrations induced them to actively take up the nanocomplexes with an uptake efficiency as high as 85%. The nanocomplex-administered neurons exhibited significantly enhanced axonal outgrowth compared with those treated with free-BpV drug. The expression of a series of proteins involved in PTEN inhibition and downstream signaling was substantially up-/down-regulated by the nanocarrier-BpV system. Injection of the nanocarriers into neural tissues (DRG, brain cortex, and spinal cord), moreover, demonstrated successful integration into neurons, glial cells, oligodendrocytes, and macrophages, suggesting the possible nanotherapeutics applications in vivo. Together, PTEN-inhibitor delivery via mesoporous nanocarriers can be considered a promising strategy for stimulating axonal regeneration in central and peripheral nervous systems.
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Affiliation(s)
| | | | | | | | - Hyukmin Kim
- Shriners Hospital's Pediatric Research Center and Department of Anatomy and Cell Biology, Temple University School of Medicine , Philadelphia, Pennsylvania 19140, United States
| | - Young-Jin Son
- Shriners Hospital's Pediatric Research Center and Department of Anatomy and Cell Biology, Temple University School of Medicine , Philadelphia, Pennsylvania 19140, United States
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46
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Wu D, Klaw MC, Kholodilov N, Burke RE, Detloff MR, Côté MP, Tom VJ. Expressing Constitutively Active Rheb in Adult Dorsal Root Ganglion Neurons Enhances the Integration of Sensory Axons that Regenerate Across a Chondroitinase-Treated Dorsal Root Entry Zone Following Dorsal Root Crush. Front Mol Neurosci 2016; 9:49. [PMID: 27458339 PMCID: PMC4932115 DOI: 10.3389/fnmol.2016.00049] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/28/2016] [Accepted: 06/07/2016] [Indexed: 11/13/2022] Open
Abstract
While the peripheral branch of dorsal root ganglion neurons (DRG) can successfully regenerate after injury, lesioned central branch axons fail to regrow across the dorsal root entry zone (DREZ), the interface between the dorsal root and the spinal cord. This lack of regeneration is due to the limited regenerative capacity of adult sensory axons and the growth-inhibitory environment at the DREZ, which is similar to that found in the glial scar after a central nervous system (CNS) injury. We hypothesized that transduction of adult DRG neurons using adeno-associated virus (AAV) to express a constitutively-active form of the GTPase Rheb (caRheb) will increase their intrinsic growth potential after a dorsal root crush. Additionally, we posited that if we combined that approach with digestion of upregulated chondroitin sulfate proteoglycans (CSPG) at the DREZ with chondroitinase ABC (ChABC), we would promote regeneration of sensory axons across the DREZ into the spinal cord. We first assessed if this strategy promotes neuritic growth in an in vitro model of the glial scar containing CSPG. ChABC allowed for some regeneration across the once potently inhibitory substrate. Combining ChABC treatment with expression of caRheb in DRG significantly improved this growth. We then determined if this combination strategy also enhanced regeneration through the DREZ after dorsal root crush in adult rats in vivo. After unilaterally crushing C4-T1 dorsal roots, we injected AAV5-caRheb or AAV5-GFP into the ipsilateral C5-C8 DRGs. ChABC or PBS was injected into the ipsilateral dorsal horn at C5-C8 to digest CSPG, for a total of four animal groups (caRheb + ChABC, caRheb + PBS, GFP + ChABC, GFP + PBS). Regeneration was rarely observed in PBS-treated animals, whereas short-distance regrowth across the DREZ was observed in ChABC-treated animals. No difference in axon number or length between the ChABC groups was observed, which may be related to intraganglionic inflammation induced by the injection. ChABC-mediated regeneration is functional, as stimulation of ipsilateral median and ulnar nerves induced neuronal c-Fos expression in deafferented dorsal horn in both ChABC groups. Interestingly, caRheb + ChABC animals had significantly more c-Fos+ nuclei indicating that caRheb expression in DRGs promoted functional synaptogenesis of their axons that regenerated beyond a ChABC-treated DREZ.
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Affiliation(s)
- Di Wu
- Department of Neurobiology and Anatomy, Drexel University College of Medicine Philadelphia, PA, USA
| | - Michelle C Klaw
- Department of Neurobiology and Anatomy, Drexel University College of Medicine Philadelphia, PA, USA
| | - Nikolai Kholodilov
- Department of Neurology, Columbia University in the City of New York New York, NY, USA
| | - Robert E Burke
- Department of Neurology, Columbia University in the City of New YorkNew York, NY, USA; Department of Pathology and Cell Biology, Columbia University in the City of New YorkNew York, NY, USA
| | - Megan R Detloff
- Department of Neurobiology and Anatomy, Drexel University College of Medicine Philadelphia, PA, USA
| | - Marie-Pascale Côté
- Department of Neurobiology and Anatomy, Drexel University College of Medicine Philadelphia, PA, USA
| | - Veronica J Tom
- Department of Neurobiology and Anatomy, Drexel University College of Medicine Philadelphia, PA, USA
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47
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Silver J. The glial scar is more than just astrocytes. Exp Neurol 2016; 286:147-149. [PMID: 27328838 DOI: 10.1016/j.expneurol.2016.06.018] [Citation(s) in RCA: 69] [Impact Index Per Article: 8.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/24/2016] [Revised: 06/14/2016] [Accepted: 06/17/2016] [Indexed: 01/06/2023]
Affiliation(s)
- Jerry Silver
- Case Western Reserve University, School of Medicine, Department of Neurosciences, Cleveland, OH 44106, USA.
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48
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Liu Y, Kelamangalath L, Kim H, Han SB, Tang X, Zhai J, Hong JW, Lin S, Son YJ, Smith GM. NT-3 promotes proprioceptive axon regeneration when combined with activation of the mTor intrinsic growth pathway but not with reduction of myelin extrinsic inhibitors. Exp Neurol 2016; 283:73-84. [PMID: 27264357 DOI: 10.1016/j.expneurol.2016.05.021] [Citation(s) in RCA: 31] [Impact Index Per Article: 3.9] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/28/2015] [Revised: 05/13/2016] [Accepted: 05/17/2016] [Indexed: 11/25/2022]
Abstract
Although previous studies have identified several strategies to stimulate regeneration of CNS axons, extensive regeneration and functional recovery have remained a major challenge, particularly for large diameter myelinated axons. Within the CNS, myelin is thought to inhibit axon regeneration, while modulating activity of the mTOR pathway promotes regeneration of injured axons. In this study, we examined NT-3 mediated regeneration of sensory axons through the dorsal root entry zone in a triple knockout of myelin inhibitory proteins or after activation of mTOR using a constitutively active (ca) Rheb in DRG neurons to determine the influence of environmental inhibitory or activation of intrinsic growth pathways could enhance NT-3-mediate regeneration. Loss of myelin inhibitory proteins showed modest enhancement of sensory axon regeneration. In mTOR studies, we found a dramatic age related decrease in the mTOR activation as determined by phosphorylation of the downstream marker S6 ribosomal subunit. Expression of caRheb within adult DRG neurons in vitro increased S6 phosphorylation and doubled the overall length of neurite outgrowth, which was reversed in the presence of rapamycin. In adult female rats, combined expression of caRheb in DRG neurons and NT-3 within the spinal cord increased regeneration of sensory axons almost 3 fold when compared to NT-3 alone. Proprioceptive assessment using a grid runway indicates functionally significant regeneration of large-diameter myelinated sensory afferents. Our results indicate that caRheb-induced increase in mTOR activation enhances neurotrophin-3 induced regeneration of large-diameter myelinated axons.
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Affiliation(s)
- Yingpeng Liu
- Shriners Hospitals Pediatric Research Center, Temple University School of Medicine, Philadelphia, PA 19140, USA
| | - Lakshmi Kelamangalath
- Shriners Hospitals Pediatric Research Center, Temple University School of Medicine, Philadelphia, PA 19140, USA
| | - Hyukmin Kim
- Shriners Hospitals Pediatric Research Center, Temple University School of Medicine, Philadelphia, PA 19140, USA
| | - Seung Baek Han
- Shriners Hospitals Pediatric Research Center, Temple University School of Medicine, Philadelphia, PA 19140, USA
| | - Xiaoqing Tang
- Shriners Hospitals Pediatric Research Center, Temple University School of Medicine, Philadelphia, PA 19140, USA
| | - Jinbin Zhai
- Shriners Hospitals Pediatric Research Center, Temple University School of Medicine, Philadelphia, PA 19140, USA
| | - Jee W Hong
- Shriners Hospitals Pediatric Research Center, Temple University School of Medicine, Philadelphia, PA 19140, USA
| | - Shen Lin
- Shriners Hospitals Pediatric Research Center, Temple University School of Medicine, Philadelphia, PA 19140, USA
| | - Young-Jin Son
- Shriners Hospitals Pediatric Research Center, Temple University School of Medicine, Philadelphia, PA 19140, USA
| | - George M Smith
- Shriners Hospitals Pediatric Research Center, Temple University School of Medicine, Philadelphia, PA 19140, USA.
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49
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Inhibitory Injury Signaling Represses Axon Regeneration After Dorsal Root Injury. Mol Neurobiol 2015; 53:4596-605. [PMID: 26298667 DOI: 10.1007/s12035-015-9397-6] [Citation(s) in RCA: 16] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/20/2015] [Accepted: 08/14/2015] [Indexed: 01/05/2023]
Abstract
Following injury to peripheral axons, besides increased cyclic adenosine monophosphate (cAMP), the positive injury signals extracellular-signal-regulated kinase (ERK), c-Jun N-terminal kinase (JNK), and signal transducer and activator of transcription 3 (STAT-3) are locally activated and retrogradely transported to the cell body, where they induce a pro-regenerative program. Here, to further understand the importance of injury signaling for successful axon regeneration, we used dorsal root ganglia (DRG) neurons that have a central branch without regenerative capacity and a peripheral branch that regrows after lesion. Although injury to the DRG central branch (dorsal root injury (DRI)) activated ERK, JNK, and STAT-3 and increased cAMP levels, it did not elicit gain of intrinsic growth capacity nor the ability to overcome myelin inhibition, as occurred after peripheral branch injury (sciatic nerve injury (SNI)). Besides, gain of growth capacity after SNI was independent of ERK and cAMP. Antibody microarrays of dynein-immunoprecipitated axoplasm from rats with either DRI or SNI revealed a broad differential activation and transport of signals after each injury type and further supported that ERK, JNK, STAT-3, and cAMP signaling pathways are minor contributors to the differential intrinsic axon growth capacity of both injury models. Increased levels of inhibitory injury signals including GSK3β and ROCKII were identified after DRI, not only in axons but also in DRG cell bodies. In summary, our work shows that activation and transport of positive injury signals are not sufficient to promote increased axon growth capacity and that differential modulation of inhibitory molecules may contribute to limited regenerative response.
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50
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Wong LE, Gibson ME, Arnold HM, Pepinsky B, Frank E. Artemin promotes functional long-distance axonal regeneration to the brainstem after dorsal root crush. Proc Natl Acad Sci U S A 2015; 112:6170-5. [PMID: 25918373 PMCID: PMC4434726 DOI: 10.1073/pnas.1502057112] [Citation(s) in RCA: 20] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
Recovery after a spinal cord injury often requires that axons restore synaptic connectivity with denervated targets several centimeters from the site of injury. Here we report that systemic artemin (ARTN) treatment promotes the regeneration of sensory axons to the brainstem after brachial dorsal root crush in adult rats. ARTN not only stimulates robust regeneration of large, myelinated sensory axons to the brainstem, but also promotes functional reinnervation of the appropriate target region, the cuneate nucleus. ARTN signals primarily through the RET tyrosine kinase, an interaction that requires the nonsignaling coreceptor GDNF family receptor (GFRα3). Previous studies reported limited GFRα3 expression on large sensory neurons, but our findings demonstrate that ARTN promotes robust regeneration of large, myelinated sensory afferents. Using a cell sorting technique, we demonstrate that GFRα3 expression is similar in myelinated and unmyelinated adult sensory neurons, suggesting that ARTN likely induces long-distance regeneration by binding GFRα3 and RET. Although ARTN is delivered for just 2 wk, regeneration to the brainstem requires more than 3 mo, suggesting that brief trophic support may initiate intrinsic growth programs that remain active until targets are reached. Given its ability to promote targeted functional regeneration to the brainstem, ARTN may represent a promising therapy for restoring sensory function after spinal cord injury.
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Affiliation(s)
- Laura Elisabeth Wong
- Department of Integrated Physiology and Pathobiology, Tufts University School of Medicine, Boston, MA 02111; and
| | - Molly E Gibson
- Department of Integrated Physiology and Pathobiology, Tufts University School of Medicine, Boston, MA 02111; and
| | | | - Blake Pepinsky
- Chemical and Molecular Therapeutics, Biogen Idec, Inc., Cambridge, MA 02142
| | - Eric Frank
- Department of Integrated Physiology and Pathobiology, Tufts University School of Medicine, Boston, MA 02111; and
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