Loss of NAMPT in Aging Retinal Pigment Epithelium Reduces NAD Availability and Promotes Cellular Senescence

Retinal pigment epithelium (RPE) performs numerous functions critical to retinal health and visual function. RPE senescence is a hallmark of aging and degenerative retinal disease development. Here, we evaluated the temporal expression of key nicotinamide adenine dinucleotide (NAD)-biosynthetic genes and associated levels of NAD, a principal regulator of energy metabolism and cellular fate, in mouse RPE. NAD levels declined with age and correlated directly with decreased nicotinamide phosphoribosyltransferase (NAMPT) expression, increased expression of senescence markers (p16, p21, ApoJ, CTGF and β-galactosidase) and significant reductions in SIRT1 expression and activity. We simulated the age-dependent decline in NAD and the related increase in RPE senescence in human (ARPE-19) and mouse primary RPE using the NAMPT inhibitor FK866 and demonstrated the positive impact of NAD-enhancing therapies on RPE cell viability. This, we confirmed in the RPE of mice injected sub-retinally with FK866 in the presence or absence of nicotinamide mononucleotide Our data confirm the importance of NAD to RPE cell biology normally and in aging and demonstrate the potential utility of therapies targeting NAMPT and NAD biosynthesis to prevent or alleviate consequences of RPE senescence in aging and/or degenerative retinal diseases in which RPE dysfunction is a crucial element.