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Franco ML, García-Carpio I, Comaposada-Baró R, Escribano-Saiz JJ, Chávez-Gutiérrez L, Vilar M. TrkA-mediated endocytosis of p75-CTF prevents cholinergic neuron death upon γ-secretase inhibition. Life Sci Alliance 2021; 4:4/4/e202000844. [PMID: 33536237 PMCID: PMC7898468 DOI: 10.26508/lsa.202000844] [Citation(s) in RCA: 7] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/08/2020] [Revised: 01/11/2021] [Accepted: 01/11/2021] [Indexed: 12/13/2022] Open
Abstract
The findings shed light into the adverse effects of GSIs observed in the Alzheimer’s field and explain, at least in part, the unexpected worsening in cognition observed in the semagacestat Phase 3 trial. γ-secretase inhibitors (GSI) were developed to reduce the generation of Aβ peptide to find new Alzheimer’s disease treatments. Clinical trials on Alzheimer’s disease patients, however, showed several side effects that worsened the cognitive symptoms of the treated patients. The observed side effects were partially attributed to Notch signaling. However, the effect on other γ-secretase substrates, such as the p75 neurotrophin receptor (p75NTR) has not been studied in detail. p75NTR is highly expressed in the basal forebrain cholinergic neurons (BFCNs) during all life. Here, we show that GSI treatment induces the oligomerization of p75CTF leading to the cell death of BFCNs, and that this event is dependent on TrkA activity. The oligomerization of p75CTF requires an intact cholesterol recognition sequence (CRAC) and the constitutive binding of TRAF6, which activates the JNK and p38 pathways. Remarkably, TrkA rescues from cell death by a mechanism involving the endocytosis of p75CTF. These results suggest that the inhibition of γ-secretase activity in aged patients, where the expression of TrkA in the BFCNs is already reduced, could accelerate cholinergic dysfunction and promote neurodegeneration.
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Affiliation(s)
- María Luisa Franco
- Molecular Basis of Neurodegeneration Unit, Institute of Biomedicine of València (IBV-CSIC), València, Spain
| | - Irmina García-Carpio
- Molecular Basis of Neurodegeneration Unit, Institute of Biomedicine of València (IBV-CSIC), València, Spain
| | - Raquel Comaposada-Baró
- Molecular Basis of Neurodegeneration Unit, Institute of Biomedicine of València (IBV-CSIC), València, Spain
| | - Juan J Escribano-Saiz
- Molecular Basis of Neurodegeneration Unit, Institute of Biomedicine of València (IBV-CSIC), València, Spain
| | - Lucía Chávez-Gutiérrez
- Vlaams Instituut voor Biotechnologie Katholieke Universiteit (VIB-KU) Leuven Center for Brain and Disease, Leuven, Belgium
| | - Marçal Vilar
- Molecular Basis of Neurodegeneration Unit, Institute of Biomedicine of València (IBV-CSIC), València, Spain
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2
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Xie Y, Seawell J, Boesch E, Allen L, Suchy A, Longo FM, Meeker RB. Small molecule modulation of the p75 neurotrophin receptor suppresses age- and genotype-associated neurodegeneration in HIV gp120 transgenic mice. Exp Neurol 2020; 335:113489. [PMID: 33007293 DOI: 10.1016/j.expneurol.2020.113489] [Citation(s) in RCA: 10] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/09/2020] [Revised: 09/07/2020] [Accepted: 09/28/2020] [Indexed: 12/21/2022]
Abstract
The persistence of HIV in the central nervous system leads to cognitive deficits in up to 50% of people living with HIV even with systemic suppression by antiretroviral treatment. The interaction of chronic inflammation with age-associated degeneration places these individuals at increased risk of accelerated aging and other neurodegenerative diseases and no treatments are available that effectively halt these processes. The adverse effects of aging and inflammation may be mediated, in part, by an increase in the expression of the p75 neurotrophin receptor (p75NTR) which shifts the balance of neurotrophin signaling toward less protective pathways. To determine if modulation of p75NTR could modify the disease process, we treated HIV gp120 transgenic mice with a small molecule ligand designed to engage p75NTR and downregulate degenerative signaling. Daily treatment with 50 mg/kg LM11A-31 for 4 months suppressed age- and genotype-dependent activation of microglia, increased microtubule associated protein-2 (MAP-2), reduced dendritic varicosities and slowed the loss of parvalbumin immunoreactive neurons in the hippocampus. An age related accumulation of microtubule associated protein Tau was identified in the hippocampus in extracellular clusters that co-expressed p75NTR suggesting a link between Tau and p75NTR. Although the significance of the relationship between p75NTR and Tau is unclear, a decrease in Tau-1 immunoreactivity as gp120 mice entered old age (>16 months) suggests that the Tau may transition to more pathological modifications; a process blocked by LM11A-31. Overall, the effects of LM11A-31 are consistent with strong neuroprotective and anti-inflammatory actions that have significant therapeutic potential.
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Affiliation(s)
- Youmie Xie
- Department of Neurology, University of North Carolina, Chapel Hill, NC 27599, United States of America
| | - Jaimie Seawell
- Department of Neurology, University of North Carolina, Chapel Hill, NC 27599, United States of America; The Edward Via College of Osteopathic Medicine, Spartanburg, SC 29303, United States of America
| | - Emily Boesch
- School of Pharmacy, University of North Carolina, Chapel Hill, NC 27599, United States of America
| | - Lauren Allen
- Department of Neurology, University of North Carolina, Chapel Hill, NC 27599, United States of America
| | - Ashley Suchy
- Department of Neurology, University of North Carolina, Chapel Hill, NC 27599, United States of America
| | - Frank M Longo
- Department of Neurology and Neurological Sciences, Stanford University School of Medicine, Stanford, CA 94305, United States of America
| | - Rick B Meeker
- Department of Neurology, University of North Carolina, Chapel Hill, NC 27599, United States of America; Neurobiology Curriculum, University of North Carolina, Chapel Hill, NC 27599, United States of America.
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Mohamed R, Shanab AY, El Remessy AB. Deletion of the Neurotrophin Receptor p75 NTR Prevents Diabetes-Induced Retinal Acellular Capillaries in Streptozotocin-Induced Mouse Diabetic Model. ACTA ACUST UNITED AC 2017; 4. [PMID: 29658956 DOI: 10.15406/jdmdc.2017.04.00129] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/19/2023]
Abstract
Diabetic retinopathy is characterized by early stage of retinal neuro-inflammation that triggers development of acellular capillaries and a late stage of pathological neovascularization. Due to limited treatment options, there is a pressing need to develop new therapeutics. Our group discovered that diabetes-impaired processing of the nerve growth factor precursor (proNGF) resulting in its accumulation and its receptor p75NTR. Here, we examine the protective effects of modulating p75NTR in experimental model of diabetic retinopathy. Diabetes was induced using streptozotocin in both wild type (WT) and p75NTR knockout (p75KO) mice. Retinal inflammation and microvascular dysfunction were assessed. Western blot analysis was performed to assess expression of apoptotic and inflammatory markers and levels of the neurotrophin, p75NTR and ephrin-B2. Deletion of p75NTR did not alter body weight or diabetes status compared to WT mice. In WT-mice, diabetes triggered retinal inflammation, significant decrease in pericyte count and marked increase in development of occluded (acellular) capillary formation after 24-weeks. Deletion of p75NTR prevented acellular capillary, restored pericyte count, and inhibited the retinal Ephrin-B2, activation of the stress-kinase JNK and apoptotic marker cleaved caspase-3 in the diabetic retina. Deletion of p75NTR reduced retinal inflammation, and proNGF expression. These effects coincided with increased NGF level and TrkA activation in the diabetic retina. Targeting p75NTR using genetic approach protected the retina from the impact of long-term diabetes in mediating microvascular degeneration and maintains the balance of NGF/proNGF level. Together, these results provide rationale that targeting p75NTR may offer novel and effective therapeutic strategy to combat diabetic retinopathy.
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Affiliation(s)
- Riyaz Mohamed
- Charlie Norwood Veterans Affairs Medical Center, USA
| | | | - Azza B El Remessy
- Charlie Norwood Veterans Affairs Medical Center, USA.,Augusta Biomedical Research Foundation, USA
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Richner M, Ulrichsen M, Elmegaard SL, Dieu R, Pallesen LT, Vaegter CB. Peripheral nerve injury modulates neurotrophin signaling in the peripheral and central nervous system. Mol Neurobiol 2014; 50:945-70. [PMID: 24752592 DOI: 10.1007/s12035-014-8706-9] [Citation(s) in RCA: 108] [Impact Index Per Article: 10.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/23/2013] [Accepted: 04/01/2014] [Indexed: 12/21/2022]
Abstract
Peripheral nerve injury disrupts the normal functions of sensory and motor neurons by damaging the integrity of axons and Schwann cells. In contrast to the central nervous system, the peripheral nervous system possesses a considerable capacity for regrowth, but regeneration is far from complete and functional recovery rarely returns to pre-injury levels. During development, the peripheral nervous system strongly depends upon trophic stimulation for neuronal differentiation, growth and maturation. The perhaps most important group of trophic substances in this context is the neurotrophins (NGF, BDNF, NT-3 and NT-4/5), which signal in a complex spatial and timely manner via the two structurally unrelated p75(NTR) and tropomyosin receptor kinase (TrkA, Trk-B and Trk-C) receptors. Damage to the adult peripheral nerves induces cellular mechanisms resembling those active during development, resulting in a rapid and robust increase in the synthesis of neurotrophins in neurons and Schwann cells, guiding and supporting regeneration. Furthermore, the injury induces neurotrophin-mediated changes in the dorsal root ganglia and in the spinal cord, which affect the modulation of afferent sensory signaling and eventually may contribute to the development of neuropathic pain. The focus of this review is on the expression patterns of neurotrophins and their receptors in neurons and glial cells of the peripheral nervous system and the spinal cord. Furthermore, injury-induced changes of expression patterns and the functional consequences in relation to axonal growth and remyelination as well as to neuropathic pain development will be reviewed.
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Affiliation(s)
- Mette Richner
- Danish Research Institute of Translational Neuroscience DANDRITE, Nordic EMBL Partnership, and Lundbeck Foundation Research Center MIND, Department of Biomedicine, Aarhus University, Ole Worms Allé 3, 8000, Aarhus C, Denmark
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Differential effects of riluzole on subpopulations of adult rat dorsal root ganglion neurons in vitro. Neuroscience 2010; 166:942-51. [DOI: 10.1016/j.neuroscience.2009.12.058] [Citation(s) in RCA: 12] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/14/2009] [Revised: 12/23/2009] [Accepted: 12/23/2009] [Indexed: 12/29/2022]
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Dicer is required for survival of differentiating neural crest cells. Dev Biol 2010; 340:459-67. [PMID: 20144605 DOI: 10.1016/j.ydbio.2010.01.039] [Citation(s) in RCA: 108] [Impact Index Per Article: 7.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/07/2009] [Revised: 01/28/2010] [Accepted: 01/29/2010] [Indexed: 11/20/2022]
Abstract
The neural crest (NC) lineage gives rise to a wide array of cell types ranging from neurons and glia of the peripheral nervous system to skeletal elements of the head. The mechanisms regulating NC differentiation into such a large number of cell types remain largely unknown. MicroRNAs (miRNAs) play key roles in regulating developmental events suggesting they may also play a role during NC differentiation. To determine what roles miRNAs play in differentiation of NC-derived tissues, we deleted the miRNA processing gene Dicer in NC cells using the Wnt1-Cre deleter line. We show that deletion of Dicer soon after NC cells have formed does not affect their migration and colonization of their targets in the embryo. However, the post-migratory NC is dependent on Dicer for survival. In the head, loss of Dicer leads to a loss of NC-derived craniofacial bones while in the trunk, cells of the enteric, sensory and sympathetic nervous systems are lost during development. We found that loss of Dicer does not prevent the initial differentiation of NC but as development progresses, NC derivatives are lost due to apoptotic cell death. When Dicer is deleted, both Caspase-dependent and -independent apoptotic pathways are activated in the sensory ganglia but only the Caspase-dependent apoptotic program was activated in the sympathetic nervous system showing that the specific endogenous apoptotic programs are turned on by loss of Dicer. Our results show that Dicer and miRNAs, are required for survival of NC-derived tissues by preventing apoptosis during differentiation.
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Zherebitskaya E, Akude E, Smith DR, Fernyhough P. Development of selective axonopathy in adult sensory neurons isolated from diabetic rats: role of glucose-induced oxidative stress. Diabetes 2009; 58:1356-64. [PMID: 19252136 PMCID: PMC2682687 DOI: 10.2337/db09-0034] [Citation(s) in RCA: 116] [Impact Index Per Article: 7.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 12/15/2022]
Abstract
OBJECTIVE Reactive oxygen species (ROS) are pro-oxidant factors in distal neurodegeneration in diabetes. We tested the hypothesis that sensory neurons exposed to type 1 diabetes would exhibit enhanced ROS and oxidative stress and determined whether this stress was associated with abnormal axon outgrowth. RESEARCH DESIGN AND METHODS Lumbar dorsal root ganglia sensory neurons from normal or 3- to 5-month streptozotocin (STZ)-diabetic rats were cultured with 10 or 25-50 mmol/l glucose. Cell survival and axon outgrowth were assessed. ROS were analyzed using confocal microscopy. Immunofluorescent staining detected expression of manganese superoxide dismutase (MnSOD) and adducts of 4-hydroxy-2-nonenal (4-HNE), and MitoFluor Green dye detected mitochondria. RESULTS Dorsal root ganglion neurons from normal rats exposed to 25-50 mmol/l glucose did not exhibit oxidative stress or cell death. Cultures from diabetic rats exhibited a twofold (P < 0.001) elevation of ROS in axons after 24 h in 25 mmol/l glucose compared with 10 mmol/l glucose or mannitol. Perikarya exhibited no change in ROS levels. Axonal outgrowth was reduced by approximately twofold (P < 0.001) in diabetic cultures compared with control, as was expression of MnSOD. The antioxidant N-acetyl-cysteine (1 mmol/l) lowered axonal ROS levels, normalized aberrant axonal structure, and prevented deficits in axonal outgrowth in diabetic neurons (P < 0.05). CONCLUSIONS Dorsal root ganglia neurons with a history of diabetes expressed low MnSOD and high ROS in axons. Oxidative stress was initiated by high glucose concentration in neurons with an STZ-induced diabetic phenotype. Induction of ROS was associated with impaired axonal outgrowth and aberrant dystrophic structures that may precede or predispose the axon to degeneration and dissolution in human diabetic neuropathy.
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Affiliation(s)
- Elena Zherebitskaya
- Division of Neurodegenerative Disorders, St Boniface Hospital Research Centre, Winnipeg, Manitoba, Canada
| | - Eli Akude
- Division of Neurodegenerative Disorders, St Boniface Hospital Research Centre, Winnipeg, Manitoba, Canada
- Department of Pharmacology & Therapeutics, University of Manitoba, Winnipeg, Manitoba, Canada
| | - Darrell R. Smith
- Division of Neurodegenerative Disorders, St Boniface Hospital Research Centre, Winnipeg, Manitoba, Canada
- Department of Pharmacology & Therapeutics, University of Manitoba, Winnipeg, Manitoba, Canada
| | - Paul Fernyhough
- Division of Neurodegenerative Disorders, St Boniface Hospital Research Centre, Winnipeg, Manitoba, Canada
- Department of Pharmacology & Therapeutics, University of Manitoba, Winnipeg, Manitoba, Canada
- Corresponding author: Paul Fernyhough,
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Jankowski MP, McIlwrath SL, Jing X, Cornuet PK, Salerno KM, Koerber HR, Albers KM. Sox11 transcription factor modulates peripheral nerve regeneration in adult mice. Brain Res 2009; 1256:43-54. [PMID: 19133245 PMCID: PMC2666926 DOI: 10.1016/j.brainres.2008.12.032] [Citation(s) in RCA: 112] [Impact Index Per Article: 7.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/14/2008] [Revised: 11/20/2008] [Accepted: 12/07/2008] [Indexed: 12/17/2022]
Abstract
The ability of adult peripheral sensory neurons to undergo functional and anatomical recovery following nerve injury is due in part to successful activation of transcriptional regulatory pathways. Previous in vitro evidence had suggested that the transcription factor Sox11, a HMG-domain containing protein that is highly expressed in developing sensory neurons, is an important component of this regenerative transcriptional control program. To further test the role of Sox11 in an in vivo system, we developed a new approach to specifically target small interfering RNAs (siRNAs) conjugated to the membrane permeable molecule Penetratin to injured sensory afferents. Injection of Sox11 siRNAs into the mouse saphenous nerve caused a transient knockdown of Sox11 mRNA that transiently inhibited in vivo regeneration. Electron microscopic level analysis of Sox11 RNAi-injected nerves showed that regeneration of myelinated and unmyelinated axons was inhibited. Nearly all neurons in ganglia of crushed nerves that were Sox11 immunopositive showed colabeling for the stress and injury-associated activating transcription factor 3 (ATF3). In addition, treatment with Sox11 siRNAs in vitro and in vivo caused a transcriptional and translational level reduction in ATF3 expression. These anatomical and expression data support an intrinsic role for Sox11 in events that underlie successful regeneration following peripheral nerve injury.
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Affiliation(s)
- Michael P. Jankowski
- Department of Neurobiology, University of Pittsburgh School of Medicine, 200 Lothrop Street, Pittsburgh, PA 15261, USA
| | - Sabrina L. McIlwrath
- Department of Neurobiology, University of Pittsburgh School of Medicine, 200 Lothrop Street, Pittsburgh, PA 15261, USA
| | - Xiaotang Jing
- Department of Medicine, University of Pittsburgh School of Medicine, 200 Lothrop Street, Pittsburgh, PA 15261, USA
| | - Pamela K. Cornuet
- Department of Medicine, University of Pittsburgh School of Medicine, 200 Lothrop Street, Pittsburgh, PA 15261, USA
| | - Kathleen M. Salerno
- Department of Medicine, University of Pittsburgh School of Medicine, 200 Lothrop Street, Pittsburgh, PA 15261, USA
| | - H. Richard Koerber
- Department of Neurobiology, University of Pittsburgh School of Medicine, 200 Lothrop Street, Pittsburgh, PA 15261, USA
| | - Kathryn M. Albers
- Department of Neurobiology, University of Pittsburgh School of Medicine, 200 Lothrop Street, Pittsburgh, PA 15261, USA
- Department of Medicine, University of Pittsburgh School of Medicine, 200 Lothrop Street, Pittsburgh, PA 15261, USA
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Wallace VC, Blackbeard J, Pheby T, Segerdahl AR, Davies M, Hasnie F, Hall S, McMahon SB, Rice AS. Pharmacological, behavioural and mechanistic analysis of HIV-1 gp120 induced painful neuropathy. Pain 2007; 133:47-63. [PMID: 17433546 PMCID: PMC2706950 DOI: 10.1016/j.pain.2007.02.015] [Citation(s) in RCA: 127] [Impact Index Per Article: 7.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/07/2006] [Revised: 01/30/2007] [Accepted: 02/20/2007] [Indexed: 01/11/2023]
Abstract
A painful neuropathy is frequently observed in people living with human immunodeficiency virus type 1 (HIV-1). The HIV coat protein, glycoprotein 120 (gp120), implicated in the pathogenesis of neurological disorders associated with HIV, is capable of initiating neurotoxic cascades via an interaction with the CXCR4 and/or CCR5 chemokine receptors, which may underlie the pathogenesis of HIV-associated peripheral neuropathic pain. In order to elucidate the mechanisms underlying HIV-induced painful peripheral neuropathy, we have characterised pathological events in the peripheral and central nervous system following application of HIV-1 gp120 to the rat sciatic nerve. Perineural HIV-1 gp120 treatment induced a persistent mechanical hypersensitivity (44% decrease from baseline), but no alterations in sensitivity to thermal or cold stimuli, and thigmotactic (anxiety-like) behaviour in the open field. The mechanical hypersensitivity was sensitive to systemic treatment with gabapentin, morphine and the cannabinoid WIN 55,212-2, but not with amitriptyline. Immunohistochemical studies reveal: decreased intraepidermal nerve fibre density, macrophage infiltration into the peripheral nerve at the site of perineural HIV-1 gp120; changes in sensory neuron phenotype including expression of activating transcription factor 3 (ATF3) in 27% of cells, caspase-3 in 25% of cells, neuropeptide Y (NPY) in 12% of cells and galanin in 13% of cells and a spinal gliosis. These novel findings suggest that this model is not only useful for the elucidation of mechanisms underlying HIV-1-related peripheral neuropathy but may prove useful for preclinical assessment of drugs for the treatment of HIV-1 related peripheral neuropathic pain.
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Affiliation(s)
- Victoria C.J. Wallace
- Pain Research Group, Department of Anaesthetics, Pain Medicine and Intensive Care, Faculty of Medicine, Imperial College London, Chelsea and Westminster Hospital Campus, 369 Fulham Road, London SW10 9NH, UK
| | - Julie Blackbeard
- Pain Research Group, Department of Anaesthetics, Pain Medicine and Intensive Care, Faculty of Medicine, Imperial College London, Chelsea and Westminster Hospital Campus, 369 Fulham Road, London SW10 9NH, UK
| | - Timothy Pheby
- Pain Research Group, Department of Anaesthetics, Pain Medicine and Intensive Care, Faculty of Medicine, Imperial College London, Chelsea and Westminster Hospital Campus, 369 Fulham Road, London SW10 9NH, UK
| | - Andrew R. Segerdahl
- Pain Research Group, Department of Anaesthetics, Pain Medicine and Intensive Care, Faculty of Medicine, Imperial College London, Chelsea and Westminster Hospital Campus, 369 Fulham Road, London SW10 9NH, UK
| | - Meirion Davies
- Neurorestoration Group, Wolfson CARD, Kings College London, Guy’s Hospital Campus, London SE1 1UL, UK
| | - Fauzia Hasnie
- Pain Research Group, Department of Anaesthetics, Pain Medicine and Intensive Care, Faculty of Medicine, Imperial College London, Chelsea and Westminster Hospital Campus, 369 Fulham Road, London SW10 9NH, UK
| | - Susan Hall
- Department of Anatomy and Human Sciences, Kings College London, Guy’s Hospital Campus, London SE1 1UL, UK
| | - Stephen B. McMahon
- Neurorestoration Group, Wolfson CARD, Kings College London, Guy’s Hospital Campus, London SE1 1UL, UK
| | - Andrew S.C. Rice
- Pain Research Group, Department of Anaesthetics, Pain Medicine and Intensive Care, Faculty of Medicine, Imperial College London, Chelsea and Westminster Hospital Campus, 369 Fulham Road, London SW10 9NH, UK
- Corresponding author. Tel.: +44 020 8746 8156; fax: +44 020 8237 5109.
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Tan J, Shepherd RK. Aminoglycoside-induced degeneration of adult spiral ganglion neurons involves differential modulation of tyrosine kinase B and p75 neurotrophin receptor signaling. THE AMERICAN JOURNAL OF PATHOLOGY 2006; 169:528-43. [PMID: 16877354 PMCID: PMC1780161 DOI: 10.2353/ajpath.2006.060122] [Citation(s) in RCA: 50] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Accepted: 04/13/2006] [Indexed: 01/19/2023]
Abstract
Aminoglycoside antibiotics induce sensorineural hearing loss by destroying hair cells of the organ of Corti, causing progressive secondary degeneration of primary auditory or spiral ganglion neurons (SGNs). Recent studies show that the p75 neurotrophin receptor (NTR) is aberrantly up-regulated under pathological conditions when the neurotrophin receptor tyrosine kinases (Trks) are presumptively down-regulated. We provide in vivo evidence demonstrating that degenerating SGNs induced an augmented p75NTR expression and a coincident reduction of TrkB expression in their peripheral processes. Nuclear transcription factors c-Jun and cyclic AMP response element-binding protein phosphorylated by p75NTR- and TrkB-activated signal pathways, respectively, also showed a corresponding differential modulation, suggesting an activation of apoptotic pathways, coupled to a loss of pro-survival neurotrophic support. Our findings identified brain-derived neurotrophic factor (BDNF) expression in hair and supporting cells of the adult cochlea, and its loss, specifically the mature form, would impair TrkB-induced signaling. The precursor of BDNF (pro-BDNF) is differentially cleaved in aminoglycoside-deafened cochleae, resulting in a predominant up-regulation of a truncated form of pro-BDNF, which colocalized with p75NTR-expressing SGN fibers. Together, these data suggest that an antagonistic interplay of p75NTR and TrkB receptor signaling, possibly modulated by selective BDNF processing, mediates SGN death in vivo.
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Affiliation(s)
- Justin Tan
- Department of Otolaryngology, 32 Gisborne St., East Melbourne, Victoria 3002, Australia.
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