Promoting Axon Regeneration in Adult CNS by Targeting Liver Kinase B1

Asporin and CD109, expressed in the injured neonatal spinal cord, attenuate axonal re-growth in vitro

Axonal regeneration is restricted in adults and causes irreversible motor dysfunction following spinal cord injury (SCI). In contrast, neonates have prominent regenerative potential and can restore their neural function. Although the distinct cellular responses in neonates have been studied, how they contribute to neural recovery remains unclear. To assess whether the secreted molecules in neonatal SCI can enhance neural regeneration, we re-analyzed the previously performed single-nucleus RNA-seq (snRNA-seq) and focused on Asporin and Cd109, the highly expressed genes in the injured neonatal spinal cord. In the present study, we showed that both these molecules were expressed in the injured spinal cords of adults and neonates. We treated the cortical neurons with recombinant Asporin or CD109 to observe their direct effects on neurons in vitro. We demonstrated that these molecules enhance neurite outgrowth in neurons. However, these molecules did not enhance re-growth of severed axons. Our results suggest that Asporin and CD109 influence neurites at the lesion site, rather than promoting axon regeneration, to restore neural function in neonates after SCI.

Recent progress and challenges in the treatment of spinal cord injury

Spinal cord injury (SCI) disrupts the structural and functional connectivity between the higher center and the spinal cord, resulting in severe motor, sensory, and autonomic dysfunction with a variety of complications. The pathophysiology of SCI is complicated and multifaceted, and thus individual treatments acting on a specific aspect or process are inadequate to elicit neuronal regeneration and functional recovery after SCI. Combinatory strategies targeting multiple aspects of SCI pathology have achieved greater beneficial effects than individual therapy alone. Although many problems and challenges remain, the encouraging outcomes that have been achieved in preclinical models offer a promising foothold for the development of novel clinical strategies to treat SCI. In this review, we characterize the mechanisms underlying axon regeneration of adult neurons and summarize recent advances in facilitating functional recovery following SCI at both the acute and chronic stages. In addition, we analyze the current status, remaining problems, and realistic challenges towards clinical translation. Finally, we consider the future of SCI treatment and provide insights into how to narrow the translational gap that currently exists between preclinical studies and clinical practice. Going forward, clinical trials should emphasize multidisciplinary conversation and cooperation to identify optimal combinatorial approaches to maximize therapeutic benefit in humans with SCI.

Advances in molecular therapies for targeting pathophysiology in spinal cord injury

INTRODUCTION

Spinal cord injury (SCI) affects 25,000-50,000 people around the world each year and there is no cure for SCI patients currently. The primary injury damages spinal cord tissues and secondary injury mechanisms, including ischemia, apoptosis, inflammation, and astrogliosis, further exacerbate the lesions to the spinal cord. Recently, researchers have designed various therapeutic approaches for SCI by targeting its major cellular or molecular pathophysiology.

AREAS COVERED

Some strategies have shown promise in repairing injured spinal cord for functional recoveries, such as administering neuroprotective reagents, targeting specific genes to promote robust axon regeneration of disconnected spinal fiber tracts, targeting epigenetic factors to enhance cell survival and neural repair, and facilitating neuronal relay pathways and neuroplasticity for restoration of function after SCI. This review focuses on the major advances in preclinical molecular therapies for SCI reported in recent years.

EXPERT OPINION

Recent progress in developing novel and effective repairing strategies for SCI is encouraging, but many challenges remain for future design of effective treatments, including developing highly effective neuroprotectants for early interventions, stimulating robust neuronal regeneration with functional synaptic reconnections among disconnected neurons, maximizing the recovery of lost neural functions with combination strategies, and translating the most promising therapies into human use.

Growth arrest and DNA damage-inducible alpha regulates muscle repair and fat infiltration through ATP synthase F1 subunit alpha

BACKGROUND

Skeletal muscle fat infiltration is a common feature during ageing, obesity and several myopathies associated with muscular dysfunction and sarcopenia. However, the regulatory mechanisms of intramuscular adipogenesis and strategies to reduce fat infiltration in muscle remain unclear. Here, we identified the growth arrest and DNA damage-inducible alpha (GADD45A), a stress-inducible histone folding protein, as a critical regulator of intramuscular fat (IMAT) infiltration.

METHODS

To explore the role of GADD45A on IMAT infiltration and muscle regeneration, the gain or loss function of GADD45A in intramuscular preadipocytes was performed. The adipocyte-specific GADD45A knock-in (KI) mice and high IMAT-infiltrated muscle model by glycerol injection (50 μL of 50% v/v GLY) were generated. RNA-sequencing, histological changes, gene expression, lipid metabolism, mitochondrial function and the effect of dietary factor epigallocatechin-3-gallate (EGCG) treatment (100 mg/kg) on IMAT infiltration were studied.

RESULTS

The unbiased transcriptomics data analysis indicated that GADD45A expression positively correlates with IMAT infiltration and muscle metabolic disorders in humans (correlation: young vs. aged people, Gadd45a and Cebpa, r²  = 0.20, P < 0.05) and animals (correlation: wild-type [WT] vs. mdx mice, Gadd45a and Cebpa, r²  = 0.38, P < 0.05; NaCl vs. GLY mice, Gadd45a and Adipoq/Fabp4, r²  = 0.80/0.71, both P < 0.0001). In vitro, GADD45A overexpression promotes intramuscular preadipocyte adipogenesis, upregulating the expression of adipogenic genes (Ppara: +47%, Adipoq: +28%, P < 0.001; Cebpa: +135%, Fabp4: +16%, P < 0.01; Pparg: +66%, Leptin: +77%, P < 0.05). GADD45A knockdown robustly decreased lipid accumulation (Pparg: -57%, Adipoq: -35%, P < 0.001; Fabp4: -37%, P < 0.01; Leptin: -28%, P < 0.05). GADD45A KI mice exhibit inhibited skeletal muscle regeneration (myofibres: -40%, P < 0.01) and enhanced IMAT infiltration (adipocytes: +20%, P < 0.05). These KI mice have impaired exercise endurance and mitochondrial function. Mechanistically, GADD45A affects ATP synthase F1 subunit alpha (ATP5A1) ubiquitination degradation (ubiquitinated ATP5A1, P < 0.001) by recruiting the E3 ubiquitin ligase TRIM25, which decreases ATP synthesis (ATP production: -23%, P < 0.01) and inactivates the cAMP/PKA/LKB1 signalling pathway (cAMP: -36%, P < 0.01; decreased phospho-PKA and phospho-LKB1 protein content, P < 0.01). The dietary factor EGCG can protect against muscle fat infiltration (triglyceride: -64%, P < 0.05) via downregulating GADD45A (decreased GADD45A protein content, P < 0.001).

CONCLUSIONS

Our findings reveal a crucial role of GADD45A in regulating muscle repair and fat infiltration and suggest that inhibition of GADD45A by EGCG might be a potential strategy to combat fat infiltration and its associated muscle dysfunction.

Research hotspots and trends for axon regeneration (2000-2021): a bibliometric study and systematic review

BACKGROUND

Axons play an essential role in the connection of the nervous system with the rest of the body. Axon lesions often lead to permanent impairment of motor and cognitive functions and the interaction with the outside world. Studies focusing on axon regeneration have become a research field with considerable interest. The purpose of this study is to obtain an overall perspective of the research field of axonal regeneration and to assist the researchers and the funding agencies to better know the areas of greatest research opportunities.

METHODS

We conducted a bibliometric analysis and Latent Dirichlet Allocation (LDA) analysis of the global literature on axon regeneration based on the Web of Science (WoS) over the recent 22 years, to address the research hotspots, publication trends, and understudied areas.

RESULTS

A total of 21,018 articles were included, which in the recent two decades has increased by 125%. Among the top 12 hotspots, the annual productions rapidly increased in some topics, including axonal regeneration signaling pathway, axon guidance cues, neural circuits and functional recovery, nerve conduits, and cells transplant. Comparatively, the number of studies on axon regeneration inhibitors decreased. As for the topics focusing on nerve graft and transplantation, the annual number of papers tended to be relatively stable. Nevertheless, the underlying mechanisms of axon regrowth have not been completely uncovered. A lack of notable research on the epigenetic programs and noncoding RNAs regulation was observed. The significance of cell-type-specific data has been highlighted but with limited research working on that. Functional recovery from neuropathies also needs further studies.

CONCLUSION

The last two decades witnessed tremendous progress in the field of axon regeneration. There are still a lot of challenges to be tackled in translating these technologies into clinical practice.

Liver Kinase B1 Functions as a Regulator for Neural Development and a Therapeutic Target for Neural Repair

The liver kinase B1 (LKB1), also known as serine/threonine kinase 11 (STK11) and Par-4 in C. elegans, has been identified as a master kinase of AMPKs and AMPK-related kinases. LKB1 plays a crucial role in cell growth, metabolism, polarity, and tumor suppression. By interacting with the downstream signals of SAD, NUAK, MARK, and other kinases, LKB1 is critical to regulating neuronal polarization and axon branching during development. It also regulates Schwann cell function and the myelination of peripheral axons. Regulating LKB1 activity has become an attractive strategy for repairing an injured nervous system. LKB1 upregulation enhances the regenerative capacity of adult CNS neurons and the recovery of locomotor function in adult rodents with CNS axon injury. Here, we update the major cellular and molecular mechanisms of LKB1 in regulating neuronal polarization and neural development, and the implications thereof for promoting neural repair, axon regeneration, and functional recovery in adult mammals.

Reprogramming neurons for regeneration: The fountain of youth

Neurons in the central nervous system (CNS) are terminally differentiated cells that gradually lose their ability to support regeneration during maturation due to changes in transcriptomic and chromatin landscape. Similar transcriptomic changes also occur during development when stem cells differentiate into different types of somatic cells. Importantly, differentiated cells can be reprogrammed back to induced pluripotent stems cells (iPSCs) via global epigenetic remodeling by combined overexpression of pluripotent reprogramming factors, including Oct4, Sox2, Klf4, c-Myc, Nanog, and/or Lin28. Moreover, recent findings showed that many proneural transcription factors were able to convert non-neural somatic cells into neurons bypassing the pluripotent stage via direct reprogramming. Interestingly, many of these factors have recently been identified as key regulators of CNS neural regeneration. Recent studies indicated that these factors could rejuvenate mature CNS neurons back to a younger state through cellular state reprogramming, thus favoring regeneration. Here we will review some recent findings regarding the roles of genetic cellular state reprogramming in regulation of neural regeneration and explore the potential underlying molecular mechanisms. Moreover, by using newly emerging techniques, such as multiomics sequencing with big data analysis and Crispr-based gene editing, we will discuss future research directions focusing on better revealing cellular state reprogramming-induced remodeling of chromatin landscape and potential translational application.

Single-nucleus RNA sequencing identified cells with ependymal cell-like features enriched in neonatal mice after spinal cord injury

The adult mammalian central nervous system has limited regenerative ability, and spinal cord injury (SCI) often causes lifelong motor disability. While regeneration is limited in adults, injured spinal cord tissue can be regenerated and neural function can be almost completely restored in neonates. However, difference of cellular composition in lesion has not been well characterized. To gain insight into the age-dependent cellular reaction after SCI, we performed single-nucleus RNA sequencing, analyzing 4,076 nuclei from sham and injured spinal cords from adult and neonatal mice. Clustering analysis identified 18 cell populations. We identified previously undescribed cells with ependymal cell-like gene expression profile, the number of which was increased in neonates after SCI. Histological analysis revealed that these cells line the central canal under physiological conditions in both adults and neonates. We confirmed that they were enriched in the lesion only in neonates. We further showed that these cells were positive for the cellular markers of ependymal cells, astrocytes and radial glial cells. This study provides a deeper understanding of neonate-specific cellular responses after SCI, which may determine regenerative capacity.

Identification of the Fosl1/AMPK/autophagy axis involved in apoptotic and inflammatory effects following spinal cord injury

Strategies for reducing spinal cord injury (SCI) have become a research focus because an effective treatment of SCI is unavailable. The objective of this study was to explore the underlying mechanisms of Fosl1 following SCI. Based on the analysis of the Gene Expression Omnibus (GEO) database, Fosl1 was found to be highly enhanced in SCI. This result was confirmed in our animal model, and Fosl1 was found to be obviously expressed in neurons. Next, we treated PC-12 cells with H₂O₂ to mimic injured neurons and further verified that Fosl1 silencing upregulated AMPK expression, promoted autophagy and inhibited inflammation and apoptosis. Subsequently, a special inhibitor of AMPK was used to examine the role of AMPK, and we learned that the inhibition of AMPK suppressed autophagy and promoted inflammation and apoptosis following Fosl1 silencing. These changes completely reversed the beneficial effects of Fosl1 silencing on injured PC-12 cells. Moreover, treatment with an AMPK activator resulted in effects that were opposite those of the inhibitor. Finally, rats were injected intrathecally with si-Fosl1 to detect its role in vivo. The results showed that si-Fosl1 improved neurological function and decreased apoptosis and inflammation at 14 d postoperation, and the activator further benefited the rats of si-Fosl1 treatment. In conclusion, Fosl1 inhibits autophagy and promotes inflammation and apoptosis through the AMPK signaling pathway following SCI in vivo and in vitro.

Harnessing rAAV-retro for gene manipulations in multiple pathways that are interrupted after spinal cord injury

This paper explores the potential of rAAV2-retro to deliver gene modifying cargoes to the cells of origin of multiple pathways that are interrupted by spinal cord injury (SCI), summarizing data from previous studies and new data from additional experiments. rAAV-retro exhibits uniquely robust and reliable long-distance retrograde transport from pre-terminal axons and synapses back to neuronal bodies. Previous studies have documented that various AAV-based genetic modifications can enable axon regeneration after SCI, but these have targeted the cells of origin of one pathway at a time. In contrast, rAAV-retro can simultaneously transduce large numbers of neurons of origin of multiple spinal pathways with single injections into the spinal cord. Our initial studies use Rosa^tdTomato and double transgenic PTEN^f/f; Rosa^tdTomato mice in which transfection with rAAV-retro/Cre deletes PTEN and activates tdT expression in the same neurons. Injections of rAAV-retro/Cre into the cervical, thoracic and lumbar spinal cord led to topographically specific retrograde transduction in cortical motoneurons and neurons in subcortical regions that give rise to different spinal pathways. Our results confirm and extend previous studies indicating selective transduction of neurons that terminate at the level of the injection with minimal retrograde transduction of axons in transit to lower levels. We document feasibility of using rAAV-retro expressing shRNA against PTEN along with a GFP reporter (rAAV-retro-shPTEN/GFP) to effectively knock down PTEN in multiple populations of neurons, which can be used in any species. Some limitations and caveats of currently available rAAV-retros are discussed. Together, our results support the potential applications of rAAV-retro for AAV-based gene-modifications for SCI.

The Role of Lipids, Lipid Metabolism and Ectopic Lipid Accumulation in Axon Growth, Regeneration and Repair after CNS Injury and Disease

Axons in the adult mammalian nervous system can extend over formidable distances, up to one meter or more in humans. During development, axonal and dendritic growth requires continuous addition of new membrane. Of the three major kinds of membrane lipids, phospholipids are the most abundant in all cell membranes, including neurons. Not only immature axons, but also severed axons in the adult require large amounts of lipids for axon regeneration to occur. Lipids also serve as energy storage, signaling molecules and they contribute to tissue physiology, as demonstrated by a variety of metabolic disorders in which harmful amounts of lipids accumulate in various tissues through the body. Detrimental changes in lipid metabolism and excess accumulation of lipids contribute to a lack of axon regeneration, poor neurological outcome and complications after a variety of central nervous system (CNS) trauma including brain and spinal cord injury. Recent evidence indicates that rewiring lipid metabolism can be manipulated for therapeutic gain, as it favors conditions for axon regeneration and CNS repair. Here, we review the role of lipids, lipid metabolism and ectopic lipid accumulation in axon growth, regeneration and CNS repair. In addition, we outline molecular and pharmacological strategies to fine-tune lipid composition and energy metabolism in neurons and non-neuronal cells that can be exploited to improve neurological recovery after CNS trauma and disease.

Inhibition of Brd4 by JQ1 Promotes Functional Recovery From Spinal Cord Injury by Activating Autophagy

Spinal cord injury (SCI) is a destructive neurological disorder that is characterized by impaired sensory and motor function. Inhibition of bromodomain protein 4 (Brd4) has been shown to promote the maintenance of cell homeostasis by activating autophagy. However, the role of Brd4 inhibition in SCI and the underlying mechanisms are poorly understood. Thus, the goal of the present study was to evaluate the effects of sustained Brd4 inhibition using the bromodomain and extraterminal domain (BET) inhibitor JQ1 on the regulation of apoptosis, oxidative stress and autophagy in a mouse model of SCI. First, we observed that Brd4 expression at the lesion sites of mouse spinal cords increased after SCI. Treatment with JQ1 significantly decreased the expression of Brd4 and improved functional recovery for up to 28 day after SCI. In addition, JQ1-mediated inhibition of Brd4 reduced oxidative stress and inhibited the expression of apoptotic proteins to promote neural survival. Our results also revealed that JQ1 treatment activated autophagy and restored autophagic flux, while the positive effects of JQ1 were abrogated by autophagy inhibitor 3-MA intervention, indicating that autophagy plays a crucial role in therapeutic effects Brd4 induced by inhibition of the functional recovery SCI. In the mechanistic analysis, we observed that modulation of the AMPK-mTOR-ULK1 pathway is involved in the activation of autophagy mediated by Brd4 inhibition. Taken together, the results of our investigation provides compelling evidence that Brd4 inhibition by JQ1 promotes functional recovery after SCI and that Brd4 may serve as a potential target for SCI treatment.

AMPK controls the axonal regenerative ability of dorsal root ganglia sensory neurons after spinal cord injury

Regeneration after injury occurs in axons that lie in the peripheral nervous system but fails in the central nervous system, thereby limiting functional recovery. Differences in axonal signalling in response to injury that might underpin this differential regenerative ability are poorly characterized. Combining axoplasmic proteomics from peripheral sciatic or central projecting dorsal root ganglion (DRG) axons with cell body RNA-seq, we uncover injury-dependent signalling pathways that are uniquely represented in peripheral versus central projecting sciatic DRG axons. We identify AMPK as a crucial regulator of axonal regenerative signalling that is specifically downregulated in injured peripheral, but not central, axons. We find that AMPK in DRG interacts with the 26S proteasome and its CaMKIIα-dependent regulatory subunit PSMC5 to promote AMPKα proteasomal degradation following sciatic axotomy. Conditional deletion of AMPKα1 promotes multiple regenerative signalling pathways after central axonal injury and stimulates robust axonal growth across the spinal cord injury site, suggesting inhibition of AMPK as a therapeutic strategy to enhance regeneration following spinal cord injury.

Silk fibroin nanoscaffolds for neural tissue engineering

The nervous system is a crucial component of the body and damages to this system, either by injury or disease, can result in serious or potentially lethal consequences. An important problem in neural engineering is how we can stimulate the regeneration of damaged nervous tissue given its complex physiology and limited regenerative capacity. To regenerate damaged nervous tissue, this study electrospun three-dimensional nanoscaffolds (3DNSs) from a biomaterial blend of silk fibroin (SF), polyethylene glycol (PEG), and polyvinyl alcohol (PVA). The 3DNSs were characterised to ascertain their potential suitability for direct implant into the CNS. The biological activity of 3DNSs was investigated in vitro using PC12 cells and their effects on reactive astrogliosis were assessed in vivo using a photothrombotic model of ischaemic stroke in mice. Results showed that the concentration of SF directly affected the mechanical characteristics and internal structure of the 3DNSs, with formulations presenting as either a gel-like structure (SF ≥ 50%) or a nanofibrous structure (SF ≤ 40%). In vitro assessment revealed increased cell viability in the presence of the 3DNSs and in vivo assessment resulted in a significant decrease in glial fibrillary acidic protein (GFAP) expression in the peri-infarct region (p < 0.001 for F2 and p < 0.05 for F4) after stroke, suggesting that 3DNSs could be suppressing reactive astrogliosis. The findings enhanced our understanding of physiochemical interactions between SF, PEG, and PVA, and elucidated the potential of 3DNSs as a potential therapeutic approach to stroke recovery, especially if these are used in conjunction with drug or cell treatment.

ANXA1 directs Schwann cells proliferation and migration to accelerate nerve regeneration through the FPR2/AMPK pathway

Many factors are involved in the process of nerve regeneration. Understanding the mechanisms regarding how these factors promote an efficient remyelination is crucial to deciphering the molecular and cellular processes required to promote nerve repair. Schwann cells (SCs) play a central role in the process of peripheral nerve repair/regeneration. Using a model of facial nerve crush injury and repair, we identified Annexin A1 (ANXA1) as the extracellular trigger of SC proliferation and migration. ANXA1 activated formyl peptide receptor 2 (FPR2) receptors and the downstream adenosine 5'-monophosphate (AMP)-activated protein kinase (AMPK) signaling cascade, leading to SC proliferation and migration in vitro. SCs lacking FPR2 or AMPK displayed a defect in proliferation and migration. After facial nerve injury (FNI), ANXA1 promoted the proliferation of SCs and nerve regeneration in vivo. Collectively, these data identified the ANXA1/FPR2/AMPK axis as an important pathway in SC proliferation and migration. ANXA1-induced remyelination and SC proliferation promotes FNI regeneration.

Elevating sestrin2 attenuates endoplasmic reticulum stress and improves functional recovery through autophagy activation after spinal cord injury

Spinal cord injury (SCI) is a devastating neurological trauma that causes losses of motor and sensory function. Sestrin2, also known as hypoxia inducible gene 95, is emerging as a critical determinant of cell homeostasis in response to cellular stress. However, the role of sestrin2 in the neuronal response to endoplasmic reticulum (ER) stress and the potential mechanism remain undefined. In this study, we investigated the effects of sestrin2 on ER stress and delineated an underlying molecular mechanism after SCI. Here, we found that elevated sestrin2 is a protective process in neurons against chemical ER stress induced by tunicamycin (TM) or traumatic invasion, while treatment with PERK inhibitor or knockdown of ATF4 reduces sestrin2 expression upon ER stress. In addition, we demonstrated that overexpression of sestrin2 limits ER stress, promoting neuronal survival and improving functional recovery after SCI, which is associated with activation of autophagy and restoration of autophagic flux mediated by sestrin2. Moreover, we also found that sestrin2 activates autophagy dependent on the AMPK-mTOR signaling pathway. Consistently, inhibition of AMPK abrogates the effect of sestrin2 on the activation of autophagy, and blockage of autophagic flux abolishes the effect of sestrin2 on limiting ER stress and neural death. Together, our data reveal that upregulation of sestrin2 is an important resistance mechanism of neurons to ER stress and the potential role of sestrin2 as a therapeutic target for SCI. Graphical abstract.

Advances in the Signaling Pathways Downstream of Glial-Scar Axon Growth Inhibitors

Axon growth inhibitors generated by reactive glial scars play an important role in failure of axon regeneration after CNS injury in mature mammals. Among the inhibitory factors, chondroitin sulfate proteoglycans (CSPGs) are potent suppressors of axon regeneration and are important molecular targets for designing effective therapies for traumatic brain injury or spinal cord injury (SCI). CSPGs bind with high affinity to several transmembrane receptors, including two members of the leukocyte common antigen related (LAR) subfamily of receptor protein tyrosine phosphatases (RPTPs). Recent studies demonstrate that multiple intracellular signaling pathways downstream of these two RPTPs mediate the growth-inhibitory actions of CSPGs. A better understanding of these signaling pathways may facilitate development of new and effective therapies for CNS disorders characterized by axonal disconnections. This review will focus on recent advances in the downstream signaling pathways of scar-mediated inhibition and their potential as the molecular targets for CNS repair.

Upregulating Lin28a Promotes Axon Regeneration in Adult Mice with Optic Nerve and Spinal Cord Injury

Severed CNS axons fail to regenerate in adult mammals and there are no effective regenerative strategies to treat patients with CNS injuries. Several genes, including phosphatase and tensin homolog (PTEN) and Krüppel-like factors, regulate intrinsic growth capacity of mature neurons. The Lin28 gene is essential for cell development and pluripotency in worms and mammals. In this study, we evaluated the role of Lin28a in regulating regenerative capacity of diverse populations of CNS neurons in adult mammals. Using a neuron-specific Thy1 promoter, we generated transgenic mice that overexpress Lin28a protein in multiple populations of projection neurons, including corticospinal tracts and retinal ganglion cells. We demonstrate that upregulation of Lin28a in transgenic mice induces significant long distance regeneration of both corticospinal axons and the optic nerve in adult mice. Importantly, overexpression of Lin28a by post-injury treatment with adeno-associated virus type 2 (AAV2) vector stimulates dramatic regeneration of descending spinal tracts and optic nerve axons after lesions. Upregulation of Lin28a also enhances activity of the Akt signaling pathway in mature CNS neurons. Therefore, Lin28a is critical for regulating growth capacity of multiple CNS neurons and may become an important molecular target for treating CNS injuries.

Liver kinase B1 depletion from astrocytes worsens disease in a mouse model of multiple sclerosis

Liver kinase B1 (LKB1) is a ubiquitously expressed kinase involved in the regulation of cell metabolism, growth, and inflammatory activation. We previously reported that a single nucleotide polymorphism in the gene encoding LKB1 is a risk factor for multiple sclerosis (MS). Since astrocyte activation and metabolic function have important roles in regulating neuroinflammation and neuropathology, we examined the serine/threonine kinase LKB1 in astrocytes in a chronic experimental autoimmune encephalomyelitis mouse model of MS. To reduce LKB1, a heterozygous astrocyte-selective conditional knockout (het-cKO) model was used. While disease incidence was similar, disease severity was worsened in het-cKO mice. RNAseq analysis identified Kyoto Encyclopedia of Genes and Genomes (KEGG) pathways enriched in het-cKO mice relating to mitochondrial function, confirmed by alterations in mitochondrial complex proteins and reductions in mRNAs related to astrocyte metabolism. Enriched pathways included major histocompatibility class II genes, confirmed by increases in MHCII protein in spinal cord and cerebellum of het-cKO mice. We observed increased numbers of CD4+ Th17 cells and increased neuronal damage in spinal cords of het-cKO mice, associated with reduced expression of choline acetyltransferase, accumulation of immunoglobulin-γ, and reduced expression of factors involved in motor neuron survival. In vitro, LKB1-deficient astrocytes showed reduced metabolic function and increased inflammatory activation. These data suggest that metabolic dysfunction in astrocytes, in this case due to LKB1 deficiency, can exacerbate demyelinating disease by loss of metabolic support and increase in the inflammatory environment.

Emerging molecular therapeutic targets for spinal cord injury

Introduction: Spinal cord injury (SCI) is a complicated and devastating neurological disorder. Patients with SCI usually have dramatically reduced quality of life. In recent years, numerous studies have reported advances in understanding the pathophysiology of SCI and developing preclinical therapeutic strategies for SCI, including various molecular therapies, and yet there is still no cure. Areas covered: After SCI, tissue damage, responses and repair involve interactions among many cellular components, including neurons, axons, glia, leukocytes, and other cells. Accordingly, numerous cellular genes and molecules have become therapeutic targets for neural tissue repair, circuit reconstruction, and behavioral restoration. Here, we review the major recent advances in biological and molecular strategies to enhance neuroprotection, axon regeneration, remyelination, neuroplasticity and functional recovery in preclinical studies of SCI. Expert opinion: Researchers have made tremendous progress in identifying individual and combined molecular therapies in animal studies. It is very important to identify additional highly effective treatments for early neuroprotective intervention and for functionally meaningful axon regeneration and neuronal reconnections. Because multiple mechanisms contribute to the functional loss after SCI, combining the most promising approaches that target different pathophysiological and molecular mechanisms should exhibit synergistic actions for maximal functional restoration. [Databases searched: PubMed; inclusive dates: 6/27/2019].

The Application of Omics Technologies to Study Axon Regeneration and CNS Repair

Traumatic brain and spinal cord injuries cause permanent disability. Although progress has been made in understanding the cellular and molecular mechanisms underlying the pathophysiological changes that affect both structure and function after injury to the brain or spinal cord, there are currently no cures for either condition. This may change with the development and application of multi-layer omics, new sophisticated bioinformatics tools, and cutting-edge imaging techniques. Already, these technical advances, when combined, are revealing an unprecedented number of novel cellular and molecular targets that could be manipulated alone or in combination to repair the injured central nervous system with precision. In this review, we highlight recent advances in applying these new technologies to the study of axon regeneration and rebuilding of injured neural circuitry. We then discuss the challenges ahead to translate results produced by these technologies into clinical application to help improve the lives of individuals who have a brain or spinal cord injury.