Targeting K(V) channels rescues retinal ganglion cells in vivo directly and by reducing inflammation.

Retinal ganglion cell (RGC) degeneration is an important cause of visual impairment, and results in part from microglia-mediated inflammation. Numerous experimental studies have focused on identifying drug targets to rescue these neurons. We recently showed that K(V)1.1 and K(V)1.3 channels are expressed in adult rat RGCs and that siRNA-mediated knockdown of either channel reduces RGC death after optic nerve transection. Earlier we found that K(V)1.3 channels also contribute to microglial activation and neurotoxicity; raising the possibility that these channels contribute to neurodegeneration through direct roles in RGCs and through inflammatory mechanisms. Here, RGC survival was increased by combined siRNA-mediated knockdown of K(V)1.1 and K(V)1.3 in RGCs, but survival was much greater when knockdown of either channel was combined with intraocular injection of a K(V)1.3 channel blocker (agitoxin-2 or margatoxin). After axotomy, increased expression of several inflammation-related molecules preceded RGC loss and, consistent with a dual mechanism, their expression was differentially affected when channel knockdown in RGCs was combined with K(V)1.3 blocker injection. K(V)1.3 blockers reduced activation of retinal microglia and their tight apposition along RGC axon fascicles after axotomy, but did not prevent their migration from the inner plexiform to the damaged ganglion cell layer. Expression of several growth factors increased after axotomy; and again, there were differences following blocker injection compared with RGC-selective channel knockdown. These results provide evidence that K(V)1.3 channels play important roles in apoptotic degeneration of adult RGCs through cell-autonomous mechanisms mediated by channels in the neurons, and nonautonomous mechanisms mediated by microglia and inflammation.