Ciliary neurotrophic factor protects retinal ganglion cells from axotomy‐induced apoptosis via modulation of retinal glia in vivo

Adenoviral-mediated transfer of ciliary neurotrophic factor (CNTF) to the retina rescued retinal ganglion cells (RGCs) from axotomy-induced apoptosis, presumably via activation of the high affinity CNTF receptor alpha (CNTFRalpha) expressed on RGCs. CNTF can also activate astrocytes, via its low affinity leukemia inhibitory receptor beta expressed on mature astrocytes, suggesting that CNTF may also protect injured neurons indirectly by modulating glia. Adenoviral-mediated overexpression of CNTF in normal and axotomized rat retinas was examined to determine if it could increase the expression of several glial markers previously demonstrated to have a neuroprotective function in the injured brain and retina. Using Western blotting, the expression of glial fibrillary acid protein (GFAP), glutamate/aspartate transporter-1 (GLAST-1), glutamine synthetase (GS), and connexin 43 (Cx43) was examined 7 days after intravitreal injections of Ad.CNTF or control Ad.LacZ. Compared to controls, intravitreal injection of Ad.CNTF led to significant changes in the expression of CNTFRalpha, pSTAT(3), GFAP, GLAST, GS, and Cx43 in normal and axotomized retinas. Taken together, these results suggest that the neuroprotective effects of CNTF may result from a shift of retinal glia cells to a more neuroprotective phenotype. Moreover, the modulation of astrocytes may buffer high concentrations of glutamate that have been shown to contribute to the death of RGCs after optic nerve transection.