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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.)

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]

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]

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]