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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]

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]

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 1.88 nM PEDF-34 was 71% RGC neuroprotective at 21 days after optic nerve crush compared to intact controls, whilst daily eye drops containing 1.88 nM PEDF-34 promoted 87% RGC survival. After topical eye drop delivery, PEDF-34 was detected in the vitreous body within 30 min and attained physiologically relevant concentrations in the retina by 4 h peaking at 1.4 ± 0.05 nM by 14 days. In eye drop- compared to intravitreal-treated PEDF-34 animals, 55% more RGC axons regenerated 250 μm 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. [ABSTRACT FROM AUTHOR]