Purpose: To examine the potential role of transient receptor potential canonical 6 (TRPC6) in the survival of retinal ganglion cells (RGCs) in the rat retinal ischemia/reperfusion (IR) model.
Methods: TRPC6 expression in normal rat retina was analyzed by RT-PCR, Western blot analysis, in situ hybridization, and immunohistochemistry. The rat retinal IR model was established, and then the time course of TRPC6 expression was evaluated. Pharmacologic experiments were conducted. The expression of brain-derived neurotrophic factor (BDNF) was measured in the retinal IR model. Densities of surviving RGCs were estimated by counting fluorogold-labeled cells in 12 standard retinal areas.
Results: TRPC6 mRNA and protein are selectively enriched in the RGC layer of the retina. A 60-minute interval of retinal ischemia could induce the elevation of TRPC6 mRNA and protein, both of which peaked 24 hours after reperfusion. TRPC6 protein expression decreased dramatically 1 week later, accompanied by substantial RGC loss. The TRPC channel's agonist significantly increased RGC survival, and the antagonist reduced cell density. The transcription level of the bdnf gene was enhanced at 24 hours; this paralleled the increase of TRPC6. When TRPC6 was blocked, the BDNF precursor (proBDNF), rather than its mature form (mBDNF), increased at 24 hours.
Conclusions: This study documents the pattern of TRPC6 expression in the retinal IR model and provides evidence that activating TRPC channels before ischemia has early neuroprotective effects on RGCs in vivo. The protection of TRPC6 is BDNF mediated, and proBDNF-p75(NTR) signaling may contribute to the death of RGCs in retinal ischemia injury.