PGC-1α repression dysregulates lipid metabolism and induces lipid droplet accumulation in retinal pigment epithelium.

Drusen, the yellow deposits under the retina, are composed of lipids and proteins, and represent a hallmark of age-related macular degeneration (AMD). Lipid droplets are also reported in the retinal pigment epithelium (RPE) from AMD donor eyes. However, the mechanisms underlying these disease phenotypes remain elusive. Previously, we showed that Pgc-1α repression, combined with a high-fat diet (HFD), induce drastic AMD-like phenotypes in mice. We also reported increased PGC-1α acetylation and subsequent deactivation in the RPE derived from AMD donor eyes. Here, through a series of in vivo and in vitro experiments, we sought to investigate the molecular mechanisms by which PGC-1α repression could influence RPE and retinal function. We show that PGC-1α plays an important role in RPE and retinal lipid metabolism and function. In mice, repression of Pgc-1α alone induced RPE and retinal degeneration and drusen-like deposits. In vitro inhibition of PGC1A by CRISPR-Cas9 gene editing in human RPE (ARPE19- PGC1A KO) affected the expression of genes responsible for lipid metabolism, fatty acid ß-oxidation (FAO), fatty acid transport, low-density lipoprotein (LDL) uptake, cholesterol esterification, cholesterol biosynthesis, and cholesterol efflux. Moreover, inhibition of PGC1A in RPE cells caused lipid droplet accumulation and lipid peroxidation. ARPE19-PGC1A KO cells also showed reduced mitochondrial biosynthesis, impaired mitochondrial dynamics and activity, reduced antioxidant enzymes, decreased mitochondrial membrane potential, loss of cardiolipin, and increased susceptibility to oxidative stress. Our data demonstrate the crucial role of PGC-1α in regulating lipid metabolism. They provide new insights into the mechanisms involved in lipid and drusen accumulation in the RPE and retina during aging and AMD, which may pave the way for developing novel therapeutic strategies targeting PGC-1α.

The Anti-Aging Hormone Klotho Promotes Retinal Pigment Epithelium Cell Viability and Metabolism by Activating the AMPK/PGC-1α Pathway.

Initially discovered by Makuto Kuro-o in 1997, Klotho is a putative aging-suppressor gene when overexpressed and accelerates aging when deleted in mice. Previously, we showed that α-Klotho regulates retinal pigment epithelium (RPE) functions and protects against oxidative stress. However, the mechanisms by which Klotho influences RPE and retinal homeostasis remain elusive. Here, by performing a series of in vitro and in vivo experiments, we demonstrate that Klotho regulates cell viability under oxidative stress, mitochondrial gene expression and activity by inducing the phosphorylation of AMPK and p38MAPK, which in turn phosphorylate and activate CREB and ATF2, respectively, triggering PGC-1α transcription. The inhibition of Klotho in human RPE cells using CRISPR-Cas9 gene editing confirmed that a lack of Klotho negatively affects RPE functions, including mitochondrial activity and cell viability. Proteomic analyses showed that myelin sheath and mitochondrial-related proteins are downregulated in the RPE/retina of Kl-/- compared to WT mice, further supporting our biochemical observations. We conclude that Klotho acts upstream of the AMPK/PGC-1α pathway and regulates RPE/retinal resistance to oxidative stress, mitochondrial function, and gene and protein expressions. Thus, KL decline during aging could negatively impact retinal health, inducing age-related retinal degeneration.