Non-canonical NLRP3 Inflammasome Activation in Geographic Atrophy

Geographic atrophy (GA) is an advanced form of age-related macular degeneration (AMD) characterized by central loss of vision due to retinal pigmented epithelium (RPE) degeneration. Currently there is no therapy available for GA because of its unclear etiology. We recently discovered that DICER1 deficit causes a pathologic accumulation of Alu RNA transcripts in the RPE of human GA eyes and that the accumulated Alu RNAs activate the NLRP3 inflammasome, which in turn leads to IL-18/MyD88-dependent RPE cell death (Kaneko et al., Nature 2011; Tarallo et al., Cell 2012). In exciting, new preliminary studies we have discovered that Alu RNA-induced NLRP3 inflammasome activation occurs in a non-canonical fashion- a newly described pathway in which caspase 4 (aka caspase 11 in mouse) is required for the NLRP3 inflammasome activation (in contrast the canonical inflammasome activation is independent of caspase 4). Our studies in both cell culture and mouse models have demonstrated that caspase 4 is required for the NLRP3 inflammasome activation and for Alu RNA-induced RPE degeneration. On this basis, now I propose to define role of caspase 4-mediated non-canonical NLRP3 inflammasome activation in the context of GA and identify critical signaling pathways regulating caspase 4 activation via these following aims. Aim 1: Define the signaling pathways that regulate caspase 4 activation by Alu RNA. This aim will systematically analyze the signaling pathways regulating caspase 4 activation in the context of Alu RNA-induced NLRP3 inflammasome activation in GA. Aim 2 will elucidate the mechanisms of caspase 4 activation of the NLRP3 inflammasome. Finally (Aim 3), we will measure caspase 4 activity in human tissues representing the full spectrum of AMD disease grade and seek to more fully define the dependency of caspase 4 on a variety of models of DICER1/Alu RNA-induced RPE degeneration. These studies will illuminate the molecular foundation of GA, unravel novel regulatory checkpoints of NLRP3 inflammasome activation, and provide a strong molecular foundation for exploiting new therapeutic targets in AMD.