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D.J. Calkins, J.Y. Koh, R.M. Sappington; TRPV1 Channels Modulate Pressure–Induced Death of Retinal Ganglion Cells . Invest. Ophthalmol. Vis. Sci. 2006;47(13):1557.
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© ARVO (1962-2015); The Authors (2016-present)
Vision loss in glaucoma is associated with sensitivity to intraocular pressure and the death of retinal ganglion cells (RGCs). The robust apoptotic response of RGCs in glaucoma suggests they could express an intrinsic mechanism for mediating sensitivity to pressure. We asked whether members of the transient receptor potential (TRP) family of cation–specific ion channels could mediate this sensitivity, because of their role in mechanosensation and in mediating Ca2+–dependent apoptotic death in other neurons.
We used PCR and in situ hybridization to examine expression of genes encoding TRP subunits across six sub–families in whole rat and primate retina and in RGCs isolated from rat retina using immuno–magnetic separation. We also compared expression in primary cultures of rat RGCs exposed to elevated pressure. Based on the pattern of expression, we tested how exposure to agonists and antagonists specific to the capsaicin–sensitive, vanilloid TRP subunit TRPV1 modulate of the survival of RGCs at ambient or elevated pressure.
Rat and primate retina express eight TRP subunits across the TRPC, TRPM and TRPV subfamilies, with some differences between the species. Expression in rat RGCs is the same as whole rat retina, including TRPV1. While the pattern of expression was similar in the RGC cultures, exposure to elevated pressure for 24 hours induced a 16–fold increase in expression of TRPV1 that preceded a 35% apoptotic loss of RGCs. Treatment with the broad spectrum calcium channel antagonists ruthenium red and 2–APB reduced pressure–induced RGC apoptosis, while specific antagonism of TRPV1 with iodo–resiniferatoxin (IDX) returned RGC survival to ambient levels. Chelation of extracellular Ca2+ also reduced pressure–induced RGC death. In contrast, specific activation of TRPV1 with capsaicin at ambient pressure mimicked the apoptotic effects of elevated pressure.
RGCs express a number of TRP channels across the TRPC, TRPM and TRPV families that may underlie the Ca2+–dependence of pressure–induced RGC death in culture. In particular, TRPV1 is a strong candidate for mediating the intrinsic sensitivity of RGCs to pressure and could contribute to their loss in glaucoma.
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