30 results on '"Ahmed, Zubair"'
Search Results
2. Overexpression of Reticulon 3 Enhances CNS Axon Regeneration and Functional Recovery after Traumatic Injury.
- Author
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Alhajlah S, Thompson AM, and Ahmed Z
- Subjects
- Animals, Axons pathology, Behavior, Animal, Carrier Proteins genetics, Cells, Cultured, Disease Models, Animal, Female, Ganglia, Spinal pathology, Motor Activity, Optic Nerve Injuries genetics, Optic Nerve Injuries pathology, Optic Nerve Injuries physiopathology, Rats, Sprague-Dawley, Retinal Ganglion Cells pathology, Signal Transduction, Spinal Cord Injuries genetics, Spinal Cord Injuries pathology, Spinal Cord Injuries physiopathology, Up-Regulation, Vesicular Transport Proteins genetics, Vesicular Transport Proteins metabolism, Rats, Axons metabolism, Carrier Proteins metabolism, Ganglia, Spinal metabolism, Nerve Regeneration, Neuronal Outgrowth, Optic Nerve Injuries metabolism, Retinal Ganglion Cells metabolism, Spinal Cord Injuries metabolism
- Abstract
CNS neurons are generally incapable of regenerating their axons after injury due to several intrinsic and extrinsic factors, including the presence of axon growth inhibitory molecules. One such potent inhibitor of CNS axon regeneration is Reticulon (RTN) 4 or Nogo-A. Here, we focused on RTN3 as its contribution to CNS axon regeneration is currently unknown. We found that RTN3 expression correlated with an axon regenerative phenotype in dorsal root ganglion neurons (DRGN) after injury to the dorsal columns, a well-characterised model of spinal cord injury. Overexpression of RTN3 promoted disinhibited DRGN neurite outgrowth in vitro and dorsal column axon regeneration/sprouting and electrophysiological, sensory and locomotor functional recovery after injury in vivo. Knockdown of protrudin, however, ablated RTN3-enhanced neurite outgrowth/axon regeneration in vitro and in vivo. Moreover, overexpression of RTN3 in a second model of CNS injury, the optic nerve crush injury model, enhanced retinal ganglion cell (RGC) survival, disinhibited neurite outgrowth in vitro and survival and axon regeneration in vivo, an effect that was also dependent on protrudin. These results demonstrate that RTN3 enhances neurite outgrowth/axon regeneration in a protrudin-dependent manner after both spinal cord and optic nerve injury.
- Published
- 2021
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3. Retinal Ganglion Cell Survival and Axon Regeneration after Optic Nerve Transection is Driven by Cellular Intravitreal Sciatic Nerve Grafts.
- Author
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Ahmed Z, Suggate EL, Logan A, and Berry M
- Subjects
- Animals, Astrocytes pathology, Cell Survival, Ependymoglial Cells pathology, Intravitreal Injections, Ligands, Macrophage Activation, Macrophages pathology, Male, Rats, Inbred F344, Receptors, Nerve Growth Factor metabolism, rho GTP-Binding Proteins metabolism, Axons pathology, Nerve Regeneration, Optic Nerve Injuries pathology, Retinal Ganglion Cells pathology, Sciatic Nerve transplantation
- Abstract
Neurotrophic factors (NTF) secreted by Schwann cells in a sciatic nerve (SN) graft promote retinal ganglion cell (RGC) axon regeneration after either transplantation into the vitreous body of the eye or anastomosis to the distal stump of a transected optic nerve. In this study, we investigated the neuroprotective and growth stimulatory properties of SN grafts in which Schwann cells had been killed (acellular SN grafts, ASN) or remained intact (cellular SN grafts, CSN). We report that both intravitreal ( ivit ) implanted and optic nerve anastomosed CSN promote RGC survival and when simultaneously placed in both sites, they exert additive RGC neuroprotection. CSN and ASN were rich in myelin-associated glycoprotein (MAG) and axon growth-inhibitory ligand common to both the central nervous system (CNS) and peripheral nervous system (PNS) myelin. The penetration of the few RGC axons regenerating into an ASN at an optic nerve transection (ONT) site is limited into the proximal perilesion area, but is increased >2-fold after ivit CSN implantation and increased 5-fold into a CSN optic nerve graft after ivit CSN implantation, potentiated by growth disinhibition through the regulated intramembranous proteolysis (RIP) of p75
NTR (the signalling trans-membrane moiety of the nogo-66 trimeric receptor that binds MAG and associated suppression of RhoGTP). Mϋller cells/astrocytes become reactive after all treatments and maximally after simultaneous ivit and optic nerve CSN/ASN grafting. We conclude that simultaneous ivit CSN plus optic nerve CSN support promotes significant RGC survival and axon regeneration into CSN optic nerve grafts, despite being rich in axon growth inhibitory molecules. RGC axon regeneration is probably facilitated through RIP of p75NTR , which blinds axons to myelin-derived axon growth-inhibitory ligands present in optic nerve grafts., Competing Interests: The authors declare no conflict of interest. The funders had no role in the design of the study; in the collection, analyses, or interpretation of data; in the writing of the manuscript, or in the decision to publish the results.- Published
- 2020
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4. Pigment Epithelium-Derived Factor Promotes Axon Regeneration and Functional Recovery After Spinal Cord Injury.
- Author
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Stevens AR, Ahmed U, Vigneswara V, and Ahmed Z
- Subjects
- Animals, Axons drug effects, Cell Survival drug effects, Disease Models, Animal, Female, Ganglia, Spinal drug effects, Ganglia, Spinal metabolism, Nerve Growth Factors metabolism, Neurites drug effects, Neurites metabolism, Neuroprotection drug effects, RNA, Messenger genetics, RNA, Messenger metabolism, Rats, Sprague-Dawley, Receptors, Nerve Growth Factor metabolism, Sciatic Nerve drug effects, Sciatic Nerve physiopathology, Signal Transduction drug effects, Spinal Cord Injuries pathology, Up-Regulation drug effects, Axons physiology, Eye Proteins pharmacology, Nerve Growth Factors pharmacology, Nerve Regeneration drug effects, Recovery of Function drug effects, Serpins pharmacology, Spinal Cord Injuries physiopathology
- Abstract
Although neurons in the adult mammalian CNS are inherently incapable of regeneration after injury, we previously showed that exogenous delivery of pigment epithelium-derived factor (PEDF), a 50-kDa neurotrophic factor (NTF), promoted adult retinal ganglion cell neuroprotection and axon regeneration. Here, we show that PEDF and other elements of the PEDF pathway are highly upregulated in dorsal root ganglion neurons (DRGN) from regenerating dorsal column (DC) injury paradigms when compared with non-regenerating DC injury models. Exogenous PEDF was neuroprotective to adult DRGN and disinhibited neurite outgrowth, whilst overexpression of PEDF after DC injury in vivo promoted significant DC axon regeneration with enhanced electrophysiological, sensory, and locomotor function. Our findings reveal that PEDF is a novel NTF for adult DRGN and may represent a therapeutically useful factor to promote functional recovery after spinal cord injury.
- Published
- 2019
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5. BMP4/Smad1 Signalling Promotes Spinal Dorsal Column Axon Regeneration and Functional Recovery After Injury.
- Author
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Farrukh F, Davies E, Berry M, Logan A, and Ahmed Z
- Subjects
- Animals, Carrier Proteins metabolism, Dependovirus metabolism, Female, Ganglia, Spinal metabolism, Neuronal Outgrowth, Rats, Sprague-Dawley, TOR Serine-Threonine Kinases metabolism, Axons physiology, Bone Morphogenetic Protein 4 metabolism, Nerve Regeneration physiology, Recovery of Function, Signal Transduction, Smad1 Protein metabolism, Spinal Cord Injuries metabolism, Spinal Cord Injuries physiopathology
- Abstract
Signalling through the BMP4/Smad1 pathway promotes corticospinal tract axon regeneration and functional recovery in mice. However, unlike humans and rats, mice do not cavitate. Here, we investigated if activation of the BMP4/Smad1 pathway promotes axon regeneration and functional recovery in a rat model that cavitates. We show that dorsal root ganglion neurons (DRGN) in injury models, including the non-regenerating dorsal column (DC) and the regenerating sciatic nerve (SN) crush and preconditioning (p) SN + DC (pSN + DC) paradigms, regulate the BMP4/Smad1 signalling pathway. For example, mRNA expression of positive regulators of the BMP4/Smad1 pathway was highly up-regulated whilst negative regulators were significantly down-regulated in DRGN in the regenerating SN and pSN + DC models compared to non-regenerating DC models, matched by concomitant changes in protein expression detected in DRGN by immunohistochemistry. BMP4 peptide promoted significant DRGN survival and disinhibited neurite outgrowth in vitro, whilst AAV-BMP4 delivery in vivo stimulated DC axon regeneration and functional recovery in a model that cavitates. Our results show that activation of the BMP4/Smad1 pathway is a potential therapeutic target in the search for axon regenerative signalling pathways in the CNS.
- Published
- 2019
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6. Effects of siRNA-Mediated Knockdown of GSK3β on Retinal Ganglion Cell Survival and Neurite/Axon Growth.
- Author
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Ahmed Z, Morgan-Warren PJ, Berry M, Scott RAH, and Logan A
- Subjects
- Animals, Male, Rats, Rats, Sprague-Dawley, Axons metabolism, Glycogen Synthase Kinase 3 beta deficiency, Glycogen Synthase Kinase 3 beta genetics, Neurites metabolism, RNA, Small Interfering genetics, Retinal Ganglion Cells cytology
- Abstract
There are contradictory reports on the role of the serine/threonine kinase isoform glycogen synthase kinase-3β (GSK3β) after injury to the central nervous system (CNS). Some report that GSK3 activity promotes axonal growth or myelin disinhibition, whilst others report that GSK3 activity prevents axon regeneration. In this study, we sought to clarify if suppression of GSK3β alone and in combination with the cellular-stress-induced factor RTP801 (also known as REDD1: regulated in development and DNA damage response protein), using translationally relevant siRNAs, promotes retinal ganglion cell (RGC) survival and neurite outgrowth/axon regeneration. Adult mixed retinal cell cultures, prepared from rats at five days after optic nerve crush (ONC) to activate retinal glia, were treated with siRNA to GSK3β (siGSK3β) alone or in combination with siRTP801 and RGC survival and neurite outgrowth were quantified in the presence and absence of Rapamycin or inhibitory Nogo-A peptides. In in vivo experiments, either siGSK3β alone or in combination with siRTP801 were intravitreally injected every eight days after ONC and RGC survival and axon regeneration was assessed at 24 days. Optimal doses of siGSK3β alone promoted significant RGC survival, increasing the number of RGC with neurites without affecting neurite length, an effect that was sensitive to Rapamycin. In addition, knockdown of GSK3β overcame Nogo-A-mediated neurite growth inhibition. Knockdown of GSK3β after ONC in vivo enhanced RGC survival but not axon number or length, without potentiating glial activation. Knockdown of RTP801 increased both RGC survival and axon regeneration, whilst the combined knockdown of GSK3β and RTP801 significantly increased RGC survival, neurite outgrowth, and axon regeneration over and above that observed for siGSK3β or siRTP801 alone. These results suggest that GSK3β suppression promotes RGC survival and axon initiation whilst, when in combination with RTP801, it also enhanced disinhibited axon elongation., Competing Interests: The authors declare no conflict of interest. The funders had no role in the design of the study; in the collection, analyses, or interpretation of data; in the writing of the manuscript, or in the decision to publish the results.
- Published
- 2019
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7. Return of function after CNS axon regeneration: Lessons from injury-responsive intrinsically photosensitive and alpha retinal ganglion cells.
- Author
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Berry M, Ahmed Z, and Logan A
- Subjects
- Animals, Crush Injuries, Disease Models, Animal, Myelin Sheath, Optic Nerve Injuries metabolism, Recovery of Function physiology, Axons physiology, Nerve Regeneration physiology, Optic Nerve Injuries physiopathology, Retinal Ganglion Cells physiology
- Abstract
This review addresses issues relating to the survival and axon regeneration of both intrinsically photosensitive retinal ganglion cells (ipRGC) and αRGC, and possible ensuing patterns of functional recovery after optic nerve crush, all of which are broadly relevant to recovery from injury in the central nervous system (CNS) as whole. Although much needs to be clarified about the connectivity, function and patterns of myelination of regenerated CNS axons, the results of recent research on activity-induced αRGC axon regeneration associated with functional restitution have highlighted key focal obstacles to recovery including neurotrophic support, axon misguidance, target recognition failure and dysmyelination. Pan RGC survival/axon regeneration requires receptor binding and downstream signalling by a cocktail of growth factors, more generally defined in the CNS by the individual trophic requirements of neuronal subsets within a given disconnected centre. Resolution of the problem of failed axon guidance and target recognition is complicated by a confounding paradox that axon growth inhibitory ligand disinhibition required for axon regeneration may mask axon guidance cues that are essential for accurate re-innervation. The study of the temporal parameters of remyelination of regenerated αRGC axons may become feasible if they establish permanent homologous connections, allowing time for new myelin sheaths to fully form. Unless near complete re-innervation of denervated targets is re-instated in the CNS, debilitating dysfunctional neurological sequelae may ensue from the resulting imbalance in connectivity., (Copyright © 2018. Published by Elsevier Ltd.)
- Published
- 2019
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8. Activation of the BMP4/Smad1 Pathway Promotes Retinal Ganglion Cell Survival and Axon Regeneration.
- Author
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Thompson A, Berry M, Logan A, and Ahmed Z
- Subjects
- Animals, Bone Morphogenetic Protein 4 pharmacology, Cell Survival physiology, Cells, Cultured, Female, Immunohistochemistry, Nerve Crush, Optic Nerve Injuries physiopathology, RNA, Messenger genetics, RNA, Small Interfering, Rats, Rats, Inbred F344, Rats, Sprague-Dawley, Real-Time Polymerase Chain Reaction, TOR Serine-Threonine Kinases metabolism, Axons physiology, Bone Morphogenetic Protein 4 metabolism, Nerve Regeneration physiology, Retinal Ganglion Cells physiology, Signal Transduction physiology, Smad1 Protein metabolism
- Abstract
Purpose: We investigate if the BMP4/Smad1 intracellular signaling pathway is neuroprotective and axogenic in adult rodent retinal ganglion cells (RGC) in vivo and in vitro., Methods: Adult retinal cultures were prepared from intact and after optic nerve crush (ONC) injured rats that have been stimulated to survive and regenerate using an intravitreal peripheral nerve (PN) graft. Laser capture microdissection (LCM) then was used to isolate RGC with and without neurites. Quantitative RT-PCR determined changes in BMP4/Smad1 signaling pathway mRNA. Immunohistochemistry confirmed localization of BMP4 and activation of Smad1 in ONC+PN-stimulated RGC in vivo. BMP4 peptide was used to stimulate RGC survival and neurite/axon regeneration in vitro and in vivo. Finally, the rapamycin sensitivity of the effects was determined in BMP4-stimulated RGC in vitro and in vivo., Results: In retinal cultures prepared from intact and ONC+PN-stimulated rats, RGC with neurites had upregulated regeneration-related and BMP4/Smad1 signaling pathway mRNA levels, while low levels of these mRNAs were present in RGC isolated without neurites. An optimal dose of 200 ng/mL BMP4 peptide in vitro promoted approximately 30% RGC survival and disinhibited RGC neurite outgrowth, despite the presence of inhibitory CNS myelin extracts. BMP4 also promoted approximately 30% RGC survival in vivo and stimulated significant RGC axon regeneration at 100, 200, and 400 μm beyond the lesion site. Finally, the response of RGC to BMP4 treatment in vitro and in vivo was rapamycin-insensitive., Conclusions: Activation of the BMP4/Smad1 pathway promotes survival and axon regeneration independent of mTOR and, therefore, may be of therapeutic interest.
- Published
- 2019
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9. siRNA-Mediated Knockdown of the mTOR Inhibitor RTP801 Promotes Retinal Ganglion Cell Survival and Axon Elongation by Direct and Indirect Mechanisms.
- Author
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Morgan-Warren PJ, O'Neill J, de Cogan F, Spivak I, Ashush H, Kalinski H, Ahmed Z, Berry M, Feinstein E, Scott RA, and Logan A
- Subjects
- Animals, Cell Survival physiology, Disease Models, Animal, Enzyme-Linked Immunosorbent Assay, Gene Knockdown Techniques, Immunohistochemistry, Immunosuppressive Agents pharmacology, Intravitreal Injections, Male, Nerve Crush, Nerve Growth Factors metabolism, Optic Nerve Injuries etiology, Optic Nerve Injuries prevention & control, Rats, Rats, Wistar, Retinal Ganglion Cells metabolism, Sirolimus pharmacology, TOR Serine-Threonine Kinases metabolism, Transcription Factors, Transfection, Axons physiology, Gene Expression Regulation physiology, Nerve Regeneration physiology, RNA, Small Interfering pharmacology, Repressor Proteins genetics, Retinal Ganglion Cells cytology, TOR Serine-Threonine Kinases antagonists & inhibitors
- Abstract
Purpose: To investigate, using in vivo and in vitro models, retinal ganglion cell (RGC) neuroprotective and axon regenerative effects and underlying mechanisms of siRTP801, a translatable small-interfering RNA (siRNA) targeting the mTOR negative regulator RTP801., Methods: Adult rats underwent optic nerve (ON) crush (ONC) followed by intravitreal siRTP801 or control siRNA (siEGFP) every 8 days, with Brn3a+ RGC survival, GFAP+ reactive gliosis, and GAP43+ regenerating axons analyzed immunohistochemically 24 days after injury. Retinal cultures, prepared from uninjured animals or 5 days after ONC to activate retinal glia, were treated with siRTP801/controls in the presence/absence of rapamycin and subsequently assessed for RGC survival and neurite outgrowth, RTP801 expression, glial responses, and mTOR activity. Conditioned medium was analyzed for neurotrophin titers by ELISA., Results: Intravitreal siRTP801 enabled 82% RGC survival compared to 45% with siEGFP 24 days after ONC, correlated with greater GAP43+ axon regeneration at 400 to 1200 μm beyond the ONC site, and potentiated the reactive GFAP+ Müller glial response. In culture, siRTP801 had a direct RGC neuroprotective effect, but required GFAP+ activated glia to stimulate neurite elongation. The siRTP801-induced neuroprotection was significantly reduced, but not abolished, by rapamycin. The siRTP801 potentiated the production and release of neurotrophins NGF, NT-3, and BDNF, and prevented downregulation of RGC mTOR activity., Conclusions: The RTP801 knockdown promoted RGC survival and axon elongation after ONC, without increasing de novo regenerative sprouting. The neuroprotection was predominantly direct, with mTORC1-dependent and -independent components. Enhanced neurite/axon elongation by siRTP801 required the presence of activated retinal glia and was mediated by potentiated secretion of neurotrophic factors.
- Published
- 2016
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10. Eye drop delivery of pigment epithelium-derived factor-34 promotes retinal ganglion cell neuroprotection and axon regeneration.
- Author
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Vigneswara V, Esmaeili M, Deer L, Berry M, Logan A, and Ahmed Z
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- Analysis of Variance, Animals, Axons physiology, Disease Models, Animal, Dose-Response Relationship, Drug, Eye Proteins metabolism, Female, GAP-43 Protein metabolism, In Vitro Techniques, Intravitreal Injections, Nerve Growth Factors metabolism, Ophthalmic Solutions therapeutic use, Optic Nerve Injuries drug therapy, Rats, Rats, Sprague-Dawley, Retina cytology, Serpins metabolism, Tubulin metabolism, Axons drug effects, Eye Proteins pharmacology, Nerve Growth Factors pharmacology, Nerve Regeneration drug effects, Neuroprotective Agents pharmacology, Retinal Ganglion Cells drug effects, Serpins pharmacology
- Abstract
Axotomised retinal ganglion cells (RGCs) die rapidly by apoptosis and fail to regenerate because of the limited availability of neurotrophic factors and a lack of axogenic stimuli. However, we have recently showed that pigment epithelium-derived factor (PEDF) promotes RGC survival and axon regeneration after optic nerve crush injury. PEDF has multiple fragments of the native peptide that are neuroprotective, anti-angiogenic and anti-inflammatory. Here we investigated the neuroprotective and axogenic properties of a fragment of PEDF, PEDF-34, in retinal neurons in vitro and when delivered by intravitreal injection and eye drops in vivo. We found that PEDF-34 was 43% more neuroprotective and 52% more neuritogenic than PEDF-44 in vitro. Moreover, in vivo, intravitreal delivery of 1.88nM PEDF-34 was 71% RGC neuroprotective at 21days after optic nerve crush compared to intact controls, whilst daily eye drops containing 1.88nM PEDF-34 promoted 87% RGC survival. After topical eye drop delivery, PEDF-34 was detected in the vitreous body within 30min and attained physiologically relevant concentrations in the retina by 4h peaking at 1.4±0.05nM by 14days. In eye drop- compared to intravitreal-treated PEDF-34 animals, 55% more RGC axons regenerated 250μm beyond the optic nerve lesion. We conclude that daily topical eye drop application of PEDF-34 is superior to weekly intravitreal injections in promoting RGC survival and axon regeneration through both direct effects on retinal neurons and indirect effects on other retinal cells., (Copyright © 2015. Published by Elsevier Inc.)
- Published
- 2015
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11. Combined suppression of CASP2 and CASP6 protects retinal ganglion cells from apoptosis and promotes axon regeneration through CNTF-mediated JAK/STAT signalling.
- Author
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Vigneswara V, Akpan N, Berry M, Logan A, Troy CM, and Ahmed Z
- Subjects
- Animals, Apoptosis genetics, Disease Models, Animal, Female, Nerve Regeneration drug effects, Nerve Regeneration genetics, Nerve Regeneration physiology, Optic Nerve metabolism, Optic Nerve Injuries metabolism, Rats, Rats, Sprague-Dawley, Retinal Ganglion Cells cytology, STAT3 Transcription Factor metabolism, Apoptosis drug effects, Axons metabolism, Caspase 2 metabolism, Caspase 6 metabolism, Ciliary Neurotrophic Factor metabolism, Cysteine Endopeptidases metabolism, Retinal Ganglion Cells metabolism, Signal Transduction drug effects, Signal Transduction genetics, Signal Transduction physiology
- Abstract
We have previously shown that crushing the optic nerve induces death of retinal ganglion cells by apoptosis, but suppression of CASP2, which is predominantly activated in retinal ganglion cells, using a stably modified short interfering RNA CASP2, inhibits retinal ganglion cell apoptosis. Here, we report that combined delivery of short interfering CASP2 and inhibition of CASP6 using a dominant negative CASP6 mutant activates astrocytes and Müller cells, increases CNTF levels in the retina and leads to enhanced retinal ganglion cell axon regeneration. In dissociated adult rat mixed retinal cultures, dominant negative CASP6 mutant + short interfering CASP2 treatment also significantly increases GFAP+ glial activation, increases the expression of CNTF in culture, and subsequently increases the number of retinal ganglion cells with neurites and the mean retinal ganglion cell neurite length. These effects are abrogated by the addition of MAB228 (a monoclonal antibody targeted to the gp130 component of the CNTF receptor) and AG490 (an inhibitor of the JAK/STAT pathway downstream of CNTF signalling). Similarly, in the optic nerve crush injury model, MAB228 and AG490 neutralizes dominant negative CASP6 mutant + short interfering CASP2-mediated retinal ganglion cell axon regeneration, Müller cell activation and CNTF production in the retina without affecting retinal ganglion cell survival. We therefore conclude that axon regeneration promoted by suppression of CASP2 and CASP6 is CNTF-dependent and mediated through the JAK/STAT signalling pathway. This study offers insights for the development of effective therapeutics for promoting retinal ganglion cell survival and axon regeneration., (© The Author (2014). Published by Oxford University Press on behalf of the Guarantors of Brain. All rights reserved. For Permissions, please email: journals.permissions@oup.com.)
- Published
- 2014
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12. AMIGO3 is an NgR1/p75 co-receptor signalling axon growth inhibition in the acute phase of adult central nervous system injury.
- Author
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Ahmed Z, Douglas MR, John G, Berry M, and Logan A
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- Animals, COS Cells, Central Nervous System injuries, Chlorocebus aethiops, Female, Ganglia, Spinal metabolism, Membrane Proteins genetics, Rats, Rats, Wistar, Receptor, Nerve Growth Factor genetics, Trauma, Nervous System genetics, Axons metabolism, Central Nervous System metabolism, Membrane Proteins metabolism, Receptor, Nerve Growth Factor metabolism, Trauma, Nervous System metabolism
- Abstract
Axon regeneration in the injured adult CNS is reportedly inhibited by myelin-derived inhibitory molecules, after binding to a receptor complex comprised of the Nogo-66 receptor (NgR1) and two transmembrane co-receptors p75/TROY and LINGO-1. However, the post-injury expression pattern for LINGO-1 is inconsistent with its proposed function. We demonstrated that AMIGO3 levels were significantly higher acutely than those of LINGO-1 in dorsal column lesions and reduced in models of dorsal root ganglion neuron (DRGN) axon regeneration. Similarly, AMIGO3 levels were raised in the retina immediately after optic nerve crush, whilst levels were suppressed in regenerating optic nerves, induced by intravitreal peripheral nerve implantation. AMIGO3 interacted functionally with NgR1-p75/TROY in non-neuronal cells and in brain lysates, mediating RhoA activation in response to CNS myelin. Knockdown of AMIGO3 in myelin-inhibited adult primary DRG and retinal cultures promoted disinhibited neurite growth when cells were stimulated with appropriate neurotrophic factors. These findings demonstrate that AMIGO3 substitutes for LINGO-1 in the NgR1-p75/TROY inhibitory signalling complex and suggests that the NgR1-p75/TROY-AMIGO3 receptor complex mediates myelin-induced inhibition of axon growth acutely in the CNS. Thus, antagonizing AMIGO3 rather than LINGO-1 immediately after CNS injury is likely to be a more effective therapeutic strategy for promoting CNS axon regeneration when combined with neurotrophic factor administration.
- Published
- 2013
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13. Pigment epithelium-derived factor is retinal ganglion cell neuroprotective and axogenic after optic nerve crush injury.
- Author
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Vigneswara V, Berry M, Logan A, and Ahmed Z
- Subjects
- Animals, Axons pathology, Cell Survival drug effects, Disease Models, Animal, Female, Nerve Crush, Optic Nerve pathology, Optic Nerve Injuries pathology, Protease Inhibitors pharmacology, Rats, Rats, Sprague-Dawley, Retinal Ganglion Cells pathology, Axons drug effects, Eye Proteins pharmacology, Nerve Growth Factors pharmacology, Nerve Regeneration drug effects, Optic Nerve drug effects, Optic Nerve Injuries drug therapy, Retinal Ganglion Cells drug effects, Serpins pharmacology
- Abstract
Purpose: To investigate neuroprotective and axogenic properties of pigment epithelium-derived factor (PEDF) in retinal ganglion cells (RGC) in vitro and in vivo., Methods: Adult rat retinal cultures were treated with combinations of PBS and PEDF with or without a cell permeable analogue of cAMP, and RGC survival and neurite lengths quantified. The optic nerves of anesthetised rats were also crushed intraorbitally to transect all RGC axons followed by intravitreal injections of either PBS, PEDF, or cAMP+PEDF every 7 days. RGC were back filled with FluoroGold to quantify RGC survival and longitudinal optic nerve sections were stained with GAP43 antibodies to detect regenerating RGC axons., Results: An optimal dose of 2.5 × 10(-5) μg/μL, promoted 65% more RGC survival than controls in vitro, increasing by 4.4- and 5-fold the number of RGC with neurites and the mean neurite length, respectively. Addition of cAMP with or without PEDF did not potentiate RGC survival or the mean number of RGC with neurites, but enhanced RGC neurite length by 1.4-fold, compared with PEDF alone. After optic nerve crush (ONC), PEDF protected RGC from apoptosis and increased the numbers of regenerating RGC axons in the optic nerve by 4.6- and 3.4-fold, respectively when compared with controls. cAMP did not enhance PEDF-induced RGC neuroprotection, but potentiated its neuroregenerative effects by 2- to 3-fold, increasing the number of RGC axons regenerating at 500 and 1000 μm from the lesions site., Conclusions: This study is the first to demonstrate that PEDF enhances both RGC survival and axon regeneration in vitro and in vivo.
- Published
- 2013
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14. Epidermal growth factor receptor antagonists and CNS axon regeneration: mechanisms and controversies.
- Author
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Berry M, Ahmed Z, Douglas MR, and Logan A
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- Animals, Axons pathology, Brain Injuries drug therapy, Brain Injuries pathology, Central Nervous System anatomy & histology, Central Nervous System pathology, Drug Discovery, Humans, Myelin Sheath metabolism, Neuroglia metabolism, Signal Transduction physiology, Spinal Cord Injuries drug therapy, Spinal Cord Injuries pathology, Axons physiology, Central Nervous System physiology, ErbB Receptors antagonists & inhibitors, Nerve Regeneration physiology
- Abstract
The reasons for the failure of central nervous system (CNS) axons to regenerate include the presence of myelin- and non-myelin derived inhibitory molecules, neuronal apoptosis and the absence of a potent neurotrophic stimulus. Transactivation of the epidermal growth factor receptor (EGFR) has been implicated in signalling inhibition of axon growth in the CNS. Small molecule EGFR inhibitors such as AG1478 and PD168393 promote CNS axon growth after optic nerve transection despite the presence of inhibitory molecules in the environment of the regenerating axon. However, our results demonstrate that phosphorylated EGFR (pEGFR) is not present on regenerating axons and that the majority of pEGFR is present in glia, suggesting that EGFR cannot play a direct intra-axonal role in signalling inhibition and thus disinhibited CNS axon growth must be indirectly mediated by glia. We argue that EGFR may not have a role in signalling axon growth inhibition since AG1478 and PD168393 promotes neuronal neurite outgrowth in CNS myelin-inhibited cultures after EGFR knockdown. This review discusses the current evidences for and against the involvement of EGFR in signalling myelin inhibition., (Copyright © 2010 Elsevier Inc. All rights reserved.)
- Published
- 2011
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15. Citron kinase regulates axon growth through a pathway that converges on cofilin downstream of RhoA.
- Author
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Ahmed Z, Douglas MR, Read ML, Berry M, and Logan A
- Subjects
- Actins metabolism, Animals, Axons physiology, Cells, Cultured, Disease Models, Animal, Down-Regulation genetics, Down-Regulation physiology, Intracellular Signaling Peptides and Proteins genetics, Lim Kinases physiology, Male, Nerve Regeneration genetics, Polymerization, Protein Serine-Threonine Kinases genetics, Rats, Rats, Sprague-Dawley, Signal Transduction genetics, rho-Associated Kinases physiology, Axons enzymology, Cofilin 1 metabolism, Growth Cones enzymology, Intracellular Signaling Peptides and Proteins physiology, Nerve Regeneration physiology, Protein Serine-Threonine Kinases physiology, Signal Transduction physiology, rhoA GTP-Binding Protein metabolism
- Abstract
Axon regeneration in the adult central nervous system (CNS) is prevented by inhibitory molecules present in myelin, which bind to a receptor complex that leads to downstream RhoGTP activation and axon growth cone collapse. Here, we compared expression of Citron kinase (Citron-K), a target molecule of RhoGTP in non-regenerating dorsal root ganglion neurons (DRGN) after dorsal column (DC) injury, and in regenerating DRGN after either sciatic nerve (SN) injury or preconditioning SN+DC lesion models. We show by microarray that Citron-K mRNA levels in DRGN of a non-regenerating DC injury model were elevated 2-fold compared to those of intact control DRGN. Conversely, Citron-K levels were reduced by 2 and 2.4-fold at 10 days post lesion in the regenerating SN and preconditioning SN+DC lesion models, respectively, compared to levels in control intact DRGN. Western blotting and immunohistochemistry confirmed these observations and localised Citron-K immunostaining to both DRGN and satellite glia. In dissociated, adult rat DRG cell cultures, 80% knockdown of Citron-K, in the presence of inhibitory concentrations of CNS myelin extract (CME), promoted significant disinhibited DRGN neurite outgrowth, only when cells were stimulated with neurotrophic factors. The levels of RhoGTP remained unchanged after Citron-K knockdown in the presence of CME while enhanced cofilin levels correlated with disinhibited DRGN neurite outgrowth. This observation suggests that Citron-K plays a role in axon growth downstream of Rho activation. We conclude that Citron-K regulates actin polymerisation downstream of RhoA and may offer a potentially novel therapeutic approach for promoting CNS axon regeneration., (Copyright © 2010 Elsevier Inc. All rights reserved.)
- Published
- 2011
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16. Satellite glia not DRG neurons constitutively activate EGFR but EGFR inactivation is not correlated with axon regeneration.
- Author
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Ahmed Z, Read ML, Berry M, and Logan A
- Subjects
- Activating Transcription Factor 3 metabolism, Analysis of Variance, Animals, Blotting, Western, Cells, Cultured, GAP-43 Protein metabolism, Galanin metabolism, Immunohistochemistry, Male, Nerve Crush, Neurons cytology, Neuropeptide Y metabolism, Oligonucleotide Array Sequence Analysis, Phosphorylation, Rats, Rats, Sprague-Dawley, Reverse Transcriptase Polymerase Chain Reaction, Axons metabolism, ErbB Receptors metabolism, Ganglia, Spinal metabolism, Nerve Regeneration physiology, Neuroglia metabolism, Neurons metabolism, Sciatic Nerve physiology
- Abstract
To test the possibility that phosphorylated epidermal growth factor receptor (pEGFR) mediates axon growth inhibition, we determined if pEGFR levels were raised in dorsal root ganglia (DRG) after non-regenerating dorsal column (DC) lesions and suppressed in regenerating sciatic nerve (SN) and preconditioning (P) SN+DC lesioned DRG. Levels of EGFR mRNA and protein in DRG were unchanged between control and all injury models. Satellite glia and not DRG neurons (DRGN) constitutively contained pEGFR and, only in PSN+DC rats, were levels significantly reduced in these cells. In vitro, siRNA mediated knockdown of EGFR (siEGFR) mRNA and protein was associated with suppressed RhoA activation, but fibroblast growth factor-2 (FGF2) was a mandatory requirement for DRGN neuritogenesis after addition of inhibitory concentrations of CNS myelin. Thus, EGFR activation in satellite glia was not consistently correlated with DRGN axogenesis and siEGFR reduction of pEGFR with attenuated Rho-GTP signalling did not promote DRGN disinhibited neurite outgrowth without exogenous FGF2 stimulation. Together, these data argue against a direct intra-axonal involvement of pEGFR in axon regeneration.
- Published
- 2010
- Full Text
- View/download PDF
17. Off-target effects of epidermal growth factor receptor antagonists mediate retinal ganglion cell disinhibited axon growth.
- Author
-
Douglas MR, Morrison KC, Jacques SJ, Leadbeater WE, Gonzalez AM, Berry M, Logan A, and Ahmed Z
- Subjects
- ADAM Proteins metabolism, ADAM17 Protein, Animals, Cell Proliferation, Cells, Cultured, Culture Media, Conditioned chemistry, Cyclic AMP metabolism, ErbB Receptors genetics, ErbB Receptors metabolism, Female, Humans, Mice, Nerve Growth Factors metabolism, Nerve Regeneration drug effects, Nerve Regeneration physiology, Neuroglia cytology, Neuroglia physiology, Optic Nerve cytology, Optic Nerve metabolism, Optic Nerve pathology, RNA, Small Interfering genetics, RNA, Small Interfering metabolism, Rats, Rats, Inbred F344, Rats, Sprague-Dawley, Rats, Wistar, Receptor, trkA genetics, Receptor, trkA metabolism, Receptor, trkB genetics, Receptor, trkB metabolism, Receptor, trkC genetics, Receptor, trkC metabolism, Recombinant Fusion Proteins genetics, Recombinant Fusion Proteins metabolism, Axons drug effects, Axons physiology, Axons ultrastructure, ErbB Receptors antagonists & inhibitors, Quinazolines pharmacology, Retinal Ganglion Cells cytology, Retinal Ganglion Cells drug effects, Retinal Ganglion Cells physiology, Tyrphostins pharmacology
- Abstract
Inhibition of central nervous system axon growth is reportedly mediated in part by calcium-dependent phosphorylation of axonal epidermal growth factor receptor, with local administration of the epidermal growth factor receptor kinase inhibitors AG1478 and PD168393 to an optic nerve lesion site promoting adult retinal ganglion cell axon regeneration. Here, we show that epidermal growth factor receptor was neither constitutively expressed, nor activated in optic nerve axons in our non-regenerating and regenerating optic nerve injury models, a finding that is inconsistent with phosphorylated epidermal growth factor receptor-dependent intra-axonal signalling of central nervous system myelin-related axon growth inhibitory ligands. However, epidermal growth factor receptor was localized and activated within most glia in the retina and optic nerve post-injury, and thus an indirect glial-dependent mechanism for stimulated retinal ganglion cell axon growth by epidermal growth factor receptor inhibitors seemed plausible. Using primary retinal cultures with added central nervous system myelin extracts, we confirmed previous reports that AG1478/PD168393 blocks epidermal growth factor receptor activation and promotes disinhibited neurite outgrowth. Paradoxically, neurites did not grow in central nervous system myelin extract-containing cultures after short interfering ribonucleic acid-mediated knockdown of epidermal growth factor receptor. However, addition of AG1478 restored neurite outgrowth to short interfering ribonucleic acid-treated cultures, implying that epidermal growth factor receptor does not mediate AG1478-dependent effects. TrkA-/B-/C-Fc fusion proteins and the kinase blocker K252a abrogated the neuritogenic activity in these cultures, correlating with the presence of the neurotrophins brain derived neurotrophic factor, nerve growth factor and neurotrophin-3 in the supernatant and increased intracellular cyclic adenosine monophosphate activity. Neurotrophins released by AG1478 stimulated disinhibited retinal ganglion cell axon growth in central nervous system myelin-treated cultures by the induction of regulated intramembraneous proteolysis of p75(NTR) and Rho inactivation. Retinal astrocytes/Müller cells and retinal ganglion cells were the source of neurotrophins, with neurite outgrowth halved in the presence of glial inhibitors. We attribute AG1478-stimulated neuritogenesis to the induced release of neurotrophins together with raised cyclic adenosine monophosphate levels in treated cultures, leading to axon growth and disinhibition by neurotrophin-induced regulated intramembraneous proteolysis of p75(NTR). These off-target effects of epidermal growth factor receptor kinase inhibition suggest a novel therapeutic approach for designing treatments to promote central nervous system axon regeneration.
- Published
- 2009
- Full Text
- View/download PDF
18. Epidermal growth factor receptor inhibitors promote CNS axon growth through off-target effects on glia.
- Author
-
Ahmed Z, Jacques SJ, Berry M, and Logan A
- Subjects
- Analysis of Variance, Animals, Axons physiology, Carbazoles pharmacology, Cell Proliferation drug effects, Cells, Cultured, Central Nervous System cytology, Central Nervous System metabolism, Culture Media, Conditioned pharmacology, Cyclic AMP metabolism, Enzyme Inhibitors pharmacology, Enzyme-Linked Immunosorbent Assay methods, ErbB Receptors genetics, Ganglia, Spinal cytology, Glial Fibrillary Acidic Protein metabolism, Indole Alkaloids pharmacology, Myelin Sheath metabolism, Nerve Crush methods, Nerve Growth Factors metabolism, Neuroglia chemistry, Quinazolines pharmacology, RNA, Small Interfering metabolism, RNA, Small Interfering pharmacology, Rats, S100 Proteins metabolism, Transfection methods, Axons drug effects, ErbB Receptors antagonists & inhibitors, Neuroglia physiology, Neurons cytology, Neurons drug effects, Tyrphostins pharmacology
- Abstract
Administration of epidermal growth factor receptor (EGFR) inhibitors (e.g. AG1478/PD168393) promotes central nervous system (CNS) axon regeneration in vivo by an unknown mechanism. Here, we show that EGFR activation is not required for AG1478-/PD168393-induced neurite outgrowth in cultures of dorsal root ganglion neurons (DRGN) with added inhibitory CNS myelin extract (CME), but is mediated by the paracrine and autocrine actions of the glia-/neuron-derived neurotrophins (NT) NGF, BDNF and NT-3 through Trk signalling in DRGN potentiated by elevated cAMP levels. The DRGN neurite growth seen in CME-inhibited cultures treated with AG1478 is eradicated by blocking Trk signalling but undiminished after siRNA knockdown of >90% EGFR. Moreover, addition of the combined triplet of NT restores neurite outgrowth in CME-inhibited cultures, when cAMP levels are raised. Accordingly, we suggest that chemical EGFR inhibitors act independently of EGFR, inducing glia and neurons to secrete NT and raising cAMP levels in DRG cultures, leading to Trk-dependent disinhibited DRGN neurite outgrowth.
- Published
- 2009
- Full Text
- View/download PDF
19. Schwann cell-derived factor-induced modulation of the NgR/p75NTR/EGFR axis disinhibits axon growth through CNS myelin in vivo and in vitro.
- Author
-
Ahmed Z, Suggate EL, Brown ER, Dent RG, Armstrong SJ, Barrett LB, Berry M, and Logan A
- Subjects
- ADAM Proteins metabolism, ADAM Proteins pharmacology, ADAM17 Protein, Animals, Apoptosis Regulatory Proteins genetics, Apoptosis Regulatory Proteins physiology, Cells, Cultured, ErbB Receptors physiology, Female, GAP-43 Protein physiology, GPI-Linked Proteins, Myelin Proteins, Nerve Growth Factors pharmacology, Nogo Receptor 1, Optic Nerve physiology, Phosphorylation, RNA, Small Interfering genetics, Rats, Rats, Inbred F344, Receptors, Cell Surface, Receptors, Peptide physiology, Retinal Ganglion Cells physiology, Up-Regulation, Axons physiology, Myelin Sheath physiology, Nerve Regeneration physiology, Schwann Cells physiology
- Abstract
When associated with the Nogo receptor (NgR), the transmembrane receptor p75NTR signals growth cone collapse. Arrest of CNS axon growth in vivo is mediated by CNS myelin-derived inhibitory ligands through either an unknown pathway after NgR- and Ca2+-dependent activation of the epidermal growth factor receptor (EGFR), and/or sequential Rho-A/ROCK/LIM-kinase/cofilin phosphorylation leading to actin depolymerization. Paradoxically, rat retinal ganglion cell (RGC) axons regenerate through the CNS myelin-rich transected optic nerve after intravitreal sciatic nerve grafting without inhibitory ligand neutralization. Here, we show that optic nerve regeneration in vivo correlates with Schwann cell-derived factor-induced cleavage of NgR and Nogo-A, and inactivation of p75NTR signalling by the induction of regulated intramembranous proteolysis (RIP) and the release of both extracellular (p75ECD) and intracellular (p75ICD) domains. Hence, Schwann cell-derived factors compromise inhibitory signalling by (i) antagonizing ligand/NgR binding with metalloproteinase-cleaved Nogo-A peptides; (ii) RIP of p75NTR; (iii) competitively blocking NgR/p75NTR clustering with soluble p75ECD; and (iv) consequent reduced downstream EGFR phosphorylation and suppression of Rho-A activation. Moreover, in RGC cultures, exogenous tumour necrosis- converting enzyme (TACE) initiates RIP of p75NTR, reduces EGFR phosphorylation, suppresses activation of Rho-A, cleaves the ECD from both NgR and TROY, and disinhibits neurotrophic factor (NTF) stimulated RGC neurite outgrowth in the presence of CNS myelin. Soluble NgRECD binds all CNS myelin-derived ligands and thus has the potential to act as an inhibitory signalling antagonist, but the role of TROY and its shed ectodomain in growth cone mobility is unknown. siRNA knockdown of p75NTR also inactivates Rho-A and disinhibits NTF-stimulated RGC neurite outgrowth in cultures with added CNS myelin. In all the above experimental paradigms, Schwann cell-derived factor/NTF-induced attenuation of NgR/p75NTR signalling suppresses EGFR activation, thereby potentiating axon growth disinhibition.
- Published
- 2006
- Full Text
- View/download PDF
20. Prospects for mTOR-mediated functional repair after central nervous system trauma.
- Author
-
Berry, Martin, Ahmed, Zubair, Morgan-Warren, Peter, Fulton, Daniel, and Logan, Ann
- Subjects
- *
MTOR protein , *DEVELOPMENTAL neurobiology , *CELLULAR signal transduction , *PROTEIN kinase B , *AXONS , *NERVOUS system regeneration , *SPINAL cord injuries - Abstract
Recent research has suggested that the growth of central nervous system (CNS) axons during development is mediated through the PI3K/Akt/mammalian target of rapamycin (mTOR) intracellular signalling axis and that suppression of activity in this pathway occurs during maturity as levels of the phosphatase and tensin homologue (PTEN) rise and inhibit PI3K activation of mTOR, accounting for the failure of axon regeneration in the injured adult CNS. This hypothesis is supported by findings confirming that suppression of PTEN in experimental adult animals promotes impressive axon regeneration in the injured visual and corticospinal motor systems. This review focuses on these recent developments, discussing the therapeutic potential of a mTOR-based treatment aimed at promoting functional recovery in CNS trauma patients, recognising that to fulfil this ambition, the new therapy should aim to promote not only axon regeneration but also remyelination of regenerated axons, neuronal survival and re-innervation of denervated targets through accurate axonal guidance and synaptogenesis, all with minimal adverse effects. The translational challenges presented by the implementation of this new axogenic therapy are also discussed. [ABSTRACT FROM AUTHOR]
- Published
- 2016
- Full Text
- View/download PDF
21. Combined suppression of CASP2 and CASP6 protects retinal ganglion cells from apoptosis and promotes axon regeneration through CNTF-mediated JAK/STAT signalling.
- Author
-
Vigneswara, Vasanthy, Akpan, Nsikan, Berry, Martin, Logan, Ann, Troy, Carol M., and Ahmed, Zubair
- Subjects
CASPASE inhibitors ,RETINAL ganglion cells ,APOPTOSIS ,AXONS ,NERVOUS system regeneration ,CILIARY neurotrophic factor ,STAT proteins - Abstract
Optic nerve injuries cause death of retinal ganglion cells and degeneration of their axons. Vigneswara et al. show that combined delivery of caspase-2 and caspase-6 inhibitors into the eye promotes retinal ganglion cell survival and axon regeneration in a rodent model, an effect that is mediated through the JAK/STAT pathway.We have previously shown that crushing the optic nerve induces death of retinal ganglion cells by apoptosis, but suppression of CASP2, which is predominantly activated in retinal ganglion cells, using a stably modified short interfering RNA CASP2, inhibits retinal ganglion cell apoptosis. Here, we report that combined delivery of short interfering CASP2 and inhibition of CASP6 using a dominant negative CASP6 mutant activates astrocytes and Müller cells, increases CNTF levels in the retina and leads to enhanced retinal ganglion cell axon regeneration. In dissociated adult rat mixed retinal cultures, dominant negative CASP6 mutant + short interfering CASP2 treatment also significantly increases GFAP+ glial activation, increases the expression of CNTF in culture, and subsequently increases the number of retinal ganglion cells with neurites and the mean retinal ganglion cell neurite length. These effects are abrogated by the addition of MAB228 (a monoclonal antibody targeted to the gp130 component of the CNTF receptor) and AG490 (an inhibitor of the JAK/STAT pathway downstream of CNTF signalling). Similarly, in the optic nerve crush injury model, MAB228 and AG490 neutralizes dominant negative CASP6 mutant + short interfering CASP2-mediated retinal ganglion cell axon regeneration, Müller cell activation and CNTF production in the retina without affecting retinal ganglion cell survival. We therefore conclude that axon regeneration promoted by suppression of CASP2 and CASP6 is CNTF-dependent and mediated through the JAK/STAT signalling pathway. This study offers insights for the development of effective therapeutics for promoting retinal ganglion cell survival and axon regeneration. [ABSTRACT FROM PUBLISHER]
- Published
- 2014
- Full Text
- View/download PDF
22. Caspase-2 Is Upregulated after Sciatic Nerve Transection and Its Inhibition Protects Dorsal Root Ganglion Neurons from Apoptosis after Serum Withdrawal.
- Author
-
Vigneswara, Vasanthy, Berry, Martin, Logan, Ann, and Ahmed, Zubair
- Subjects
CASPASES ,SCIATIC nerve ,APOPTOSIS ,SERUM ,AFFERENT pathways ,NEURON development ,AXONS - Abstract
Sciatic nerve (SN) transection-induced apoptosis of dorsal root ganglion neurons (DRGN) is one factor determining the efficacy of peripheral axonal regeneration and the return of sensation. Here, we tested the hypothesis that caspase-2 (CASP2) orchestrates apoptosis of axotomised DRGN both in vivo and in vitro by disrupting the local neurotrophic supply to DRGN. We observed significantly elevated levels of cleaved CASP2 (C-CASP2), compared to cleaved caspase-3 (C-CASP3), within TUNEL+DRGN and DRG glia (satellite and Schwann cells) after SN transection. A serum withdrawal cell culture model, which induced 40% apoptotic death in DRGN and 60% in glia, was used to model DRGN loss after neurotrophic factor withdrawal. Elevated C-CASP2 and TUNEL were observed in both DRGN and DRG glia, with C-CASP2 localisation shifting from the cytosol to the nucleus, a required step for induction of direct CASP2-mediated apoptosis. Furthermore, siRNA-mediated downregulation of CASP2 protected 50% of DRGN from apoptosis after serum withdrawal, while downregulation of CASP3 had no effect on DRGN or DRG glia survival. We conclude that CASP2 orchestrates the death of SN-axotomised DRGN directly and also indirectly through loss of DRG glia and their local neurotrophic factor support. Accordingly, inhibiting CASP2 expression is a potential therapy for improving both the SN regeneration response and peripheral sensory recovery. [ABSTRACT FROM AUTHOR]
- Published
- 2013
- Full Text
- View/download PDF
23. Off-target effects of epidermal growth factor receptor antagonists mediate retinal ganglion cell disinhibited axon growth.
- Author
-
Douglas, Michael R., Morrison, Kevin C., Jacques, Steven J., Leadbeater, Wendy E., Gonzalez, Ana Maria, Berry, Martin, Logan, Ann, and Ahmed, Zubair
- Subjects
EPIDERMAL growth factor ,CENTRAL nervous system ,AXONS ,RETINAL ganglion cells ,PROTEOLYSIS ,CHEMICAL inhibitors - Abstract
Inhibition of central nervous system axon growth is reportedly mediated in part by calcium-dependent phosphorylation of axonal epidermal growth factor receptor, with local administration of the epidermal growth factor receptor kinase inhibitors AG1478 and PD168393 to an optic nerve lesion site promoting adult retinal ganglion cell axon regeneration. Here, we show that epidermal growth factor receptor was neither constitutively expressed, nor activated in optic nerve axons in our non-regenerating and regenerating optic nerve injury models, a finding that is inconsistent with phosphorylated epidermal growth factor receptor-dependent intra-axonal signalling of central nervous system myelin-related axon growth inhibitory ligands. However, epidermal growth factor receptor was localized and activated within most glia in the retina and optic nerve post-injury, and thus an indirect glial-dependent mechanism for stimulated retinal ganglion cell axon growth by epidermal growth factor receptor inhibitors seemed plausible. Using primary retinal cultures with added central nervous system myelin extracts, we confirmed previous reports that AG1478/PD168393 blocks epidermal growth factor receptor activation and promotes disinhibited neurite outgrowth. Paradoxically, neurites did not grow in central nervous system myelin extract-containing cultures after short interfering ribonucleic acid-mediated knockdown of epidermal growth factor receptor. However, addition of AG1478 restored neurite outgrowth to short interfering ribonucleic acid-treated cultures, implying that epidermal growth factor receptor does not mediate AG1478-dependent effects. TrkA-/B-/C-Fc fusion proteins and the kinase blocker K252a abrogated the neuritogenic activity in these cultures, correlating with the presence of the neurotrophins brain derived neurotrophic factor, nerve growth factor and neurotrophin-3 in the supernatant and increased intracellular cyclic adenosine monophosphate activity. Neurotrophins released by AG1478 stimulated disinhibited retinal ganglion cell axon growth in central nervous system myelin-treated cultures by the induction of regulated intramembraneous proteolysis of p75NTR and Rho inactivation. Retinal astrocytes/Müller cells and retinal ganglion cells were the source of neurotrophins, with neurite outgrowth halved in the presence of glial inhibitors. We attribute AG1478-stimulated neuritogenesis to the induced release of neurotrophins together with raised cyclic adenosine monophosphate levels in treated cultures, leading to axon growth and disinhibition by neurotrophin-induced regulated intramembraneous proteolysis of p75NTR. These off-target effects of epidermal growth factor receptor kinase inhibition suggest a novel therapeutic approach for designing treatments to promote central nervous system axon regeneration. [ABSTRACT FROM PUBLISHER]
- Published
- 2009
- Full Text
- View/download PDF
24. ROCK inhibition promotes adult retinal ganglion cell neurite outgrowth only in the presence of growth promoting factors
- Author
-
Ahmed, Zubair, Berry, Martin, and Logan, Ann
- Subjects
- *
RETINAL ganglion cells , *CENTRAL nervous system , *NERVOUS system regeneration , *AXONS , *NEURON development , *GROWTH factors , *CELLULAR signal transduction , *LABORATORY rats , *ENZYME inhibitors - Abstract
Abstract: Lesioned central nervous system (CNS) axons fail to regenerate because of limited availability of neurotrophic factors (NTF) to promote neuron survival and drive axon regeneration through an environment rich in multiple myelin- and non myelin-derived axon growth inhibitory ligands that initiate growth cone collapse through the Rho/Rho kinase (ROCK) signalling pathway. However, pharmacological inhibition of Rho and ROCK promotes neurite outgrowth in PC12, Ntera-2 cells and embryonic/early postnatal neurons in culture. We have used our well-characterised CNS myelin-inhibited adult rat retinal culture model to show that Y27632 only promotes disinhibited neurite outgrowth if RGC are co-stimulated with ciliary neurotrophic factor (CNTF). Y27632 in CNTF-stimulated retinal cultures promotes optimal RGC neurite outgrowth at 10 μM concentrations, while higher concentrations negatively correlate with RGC neurite outgrowth and survival. Raising the levels of cAMP in Y27632-treated retinal cultures also promotes significant RGC neurite outgrowth, an effect that is potentiated by the further inclusion of CNTF. Our results suggest that Y27632-induced ROCK inhibition promotes robust disinhibited axon regeneration of adult neurons only when growth promoting factors are added and/or cAMP levels are raised. [Copyright &y& Elsevier]
- Published
- 2009
- Full Text
- View/download PDF
25. Optimisation of siRNA-mediated RhoA silencing in neuronal cultures
- Author
-
Suggate, Ellen L., Ahmed, Zubair, Read, Martin L., Eaton-Charnock, Kimberley, Douglas, Michael R., Gonzalez, Ana-Maria, Berry, Martin, and Logan, Ann
- Subjects
- *
SMALL interfering RNA , *GENE silencing , *CELLULAR signal transduction , *AXONS , *NEURON development , *RETINAL ganglion cells , *LABORATORY rats - Abstract
Abstract: In investigating the consequences of gene silencing in axon growth disinhibition strategies in cultured retinal ganglion cells (RGC), we conducted experiments designed to silence RhoA signalling in PC12 and primary adult rat retinal cell cultures (containing RGC) by siRNA-mediated RhoA mRNA knockdown. We demonstrate wide differences in the levels of RhoA mRNA knockdown, dose-dependent cell toxicity, and induction of endogenous inflammatory cytokine and interferon responses to siRNA therapy. Toxicity effects observed with RhoA-siRNA was significantly reduced with “Stealth” chemical modification of the sequence, promoting ∼50% and 70% knockdown of RhoA mRNA and protein in retinal cells, respectively, while promoting significant disinhibited RGC neurite outgrowth in the presence of inhibitory CNS myelin. Our results highlight differential responsiveness of cell lines compared to primary cultured cells, and demonstrate the efficacy of the “Stealth” modification to reduce siRNA-induced interferon responses, thereby increasing target cell viability and reducing off-target effects of the delivered nucleic acids. [Copyright &y& Elsevier]
- Published
- 2009
- Full Text
- View/download PDF
26. Regeneration of axons in the visual system.
- Author
-
Berry, Martin, Ahmed, Zubair, Lorber, Barbara, Douglas, Michael, and Logan, Ann
- Subjects
- *
NERVOUS system regeneration , *AXONS , *RETINAL ganglion cells , *VISUAL pathways , *METALLOPROTEINASES , *APOPTOSIS - Abstract
This review will describe the unique advantages that are offered by the visual system of mammals and other vertebrates for studying the regenerative responses of the central nervous system (CNS) to injury, and recent insights provided by such studies. In the mouse and rat visual system a variety of experimental paradigms promote survival of retinal ganglion cells (RGC) and optic nerve regeneration, probably through stimulation by neurotrophic factors (NTF) either directly, or indirectly through retinal astrocyte/Müller cell intermediary activation. NTF induce disinhibition of axon growth through regulated intramembranous proteolysis of p75^{NTR}, and the inactivation of RhoA and EGFR signalling. The concomitant release of metalloproteinases (MMP) and plasminogen activators from RGC axons, and tissue inhibitors of metalloproteinases from optic nerve glia repress scarring and thereby reduce titres of scar-derived inhibitory ligands expressed in the wound. MMP also degrade myelin-derived inhibitory ligands along regenerating axon trajectories after regulated release from glia at the growing front of regenerating RGC axons. Optic nerve transection induces apoptosis of RGC which is blocked by anti-apoptotic regimes and thus, in combination with blockers of axon-growth inhibitory signalling and promoters of axon growth may be a therapeutic formula for promoting sustained axon regeneration. All these findings in the visual system are translatable to the CNS as a whole and thus strategies that successfully promote visual axon regeneration will be equally effective elsewhere in the CNS. Future developments likely to advance the field of regenerative research include a greater understanding of phylogenetic differences in the response of the CNS to injury, the role of NTF, cAMP, EGFR, glia/neuron interactions in disinhibiting and promoting axon growth, the control of neuron death, and effective drug delivery. [ABSTRACT FROM AUTHOR]
- Published
- 2008
27. Matrix metalloproteases: degradation of the inhibitory environment of the transected optic nerve and the scar by regenerating axons
- Author
-
Ahmed, Zubair, Dent, Russell G., Leadbeater, Wendy E., Smith, Conrad, Berry, Martin, and Logan, Ann
- Subjects
- *
METALLOPROTEINASES , *AXONS , *OPTIC nerve , *EXTRACELLULAR matrix proteins - Abstract
Abstract: After injury to the central nervous system, a glial/collagen scar forms at the lesion site, which is thought to act as a physicochemical barrier to regenerating axons. We have shown that scar formation in the transected optic nerve (ON) is attenuated when robust growth of axons is stimulated. Matrix metalloproteases (MMP), modulated by tissue inhibitors of MMP (TIMP), degrade a wide variety of extracellular matrix components (ECM) and may be activated by growing axons to remodel the ECM to allow regeneration through the inhibitory environment of the glial or collagen scar. Here, we investigate whether MMP levels are modulated in a nonregenerating (scarring) versus a regenerating (nonscarring) model of ON injury in vivo. Western blotting and immunohistochemistry revealed that MMP-1, -2, and -9 levels were higher and TIMP-1 and TIMP-2 levels were lower in regenerating compared to nonregenerating ON and retinae. In situ zymography demonstrated significantly greater MMP-related gelatinase activity in the regenerating model, mainly colocalized to astrocytes in the proximal ON stump and around the lesion site. These results suggest that activation of MMP and coincident down-regulation of TIMP may act to attenuate the inhibitory scarring in the regenerating ON, thus transforming the ON into a noninhibitory pathway for axon regrowth. [Copyright &y& Elsevier]
- Published
- 2005
- Full Text
- View/download PDF
28. Inhibition of Chk2 promotes neuroprotection, axon regeneration, and functional recovery after CNS injury.
- Author
-
Taylor, Matthew J., Thompson, Adam M., Alhajlah, Sharif, Tuxworth, Richard I., and Ahmed, Zubair
- Subjects
- *
AXONS , *RETINAL ganglion cells , *CHECKPOINT kinase 2 , *CENTRAL nervous system injuries , *PIGMENT epithelium-derived factor , *CHECKPOINT kinase 1 , *MEDICAL sciences - Abstract
The article discusses a study which showed that targeting of the central ataxia telangiectasia-mutated-checkpoint kinase-2 (ATM-Chk2) pathway regulating the response to double-strand breaks slows neural decline in Drosophila models of chronic neurodegeneration. Results show that Chk2 inhibitor, prexasertib, represents a treatment option to promote functional recovery after spinal cord or optic nerve injury. Also cited are the neuroprotective effects of prexasertib and the experimental design.
- Published
- 2022
- Full Text
- View/download PDF
29. Receptor Tyrosine Kinases: Molecular Switches Regulating CNS Axon Regeneration.
- Author
-
Vigneswara, Vasanthy, Kundi, Sarina, and Ahmed, Zubair
- Subjects
- *
CENTRAL nervous system regeneration , *PROTEIN-tyrosine kinases , *MOLECULAR switches , *AXONS , *CELLULAR signal transduction , *GENETIC regulation - Abstract
The poor or lack of injured adult central nervous system (CNS) axon regeneration results in devastating consequences and poor functional recovery. The interplay between the intrinsic and extrinsic factors contributes to robust inhibition of axon regeneration of injured CNS neurons. The insufficient or lack of trophic support for injured neurons is considered as one of the major obstacles contributing to their failure to survive and regrow their axons after injury. In the CNS, many of the signalling pathways associated with neuronal survival and axon regeneration are regulated by several classes of receptor tyrosine kinases (RTK) that respond to a variety of ligands. This paper highlights and summarises the most relevant recent findings pertinent to different classes of the RTK family of molecules, with a particular focus on elucidating their role in CNS axon regeneration. [ABSTRACT FROM AUTHOR]
- Published
- 2012
- Full Text
- View/download PDF
30. An Ugo1-like protein is associated with optic atrophy ‘plus’ disorders.
- Author
-
Abrams, Alexander J., Hufnagel, Robert B., Rebelo, Adriana, Zanna, Claudia, Patel, Neville, Gonzalez, Michael A., Campeanu, Ion J., Griffin, Laurie B., Groenewald, Saskia, Strickland, Alleene V., Tao, Feifei, Speziani, Fiorella, Caporali, Leonardo, La Morgia, Chiara, Liguori, Rocco, Lodi, Raffaele, Ahmed, Zubair M., Sund, Kristen L., Wang, Xinjian, and Krueger, Laura A.
- Subjects
- *
ATROPHY , *AXONS , *GENETIC mutation , *NEUROPATHY , *MITOCHONDRIAL membranes , *NUCLEOTIDE sequence - Published
- 2015
- Full Text
- View/download PDF
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