Abstract
Purpose :
Peroxisome proliferator-activated receptor alpha (PPARα) is a nuclear receptor regulating lipid metabolism. The function of PPARα in the RPE remains unclear. This study aimed to test the hypothesis that PPARα is a therapeutic target for age-related macular degeneration (AMD).
Methods :
RPE morphology was studied by anti-ZO-1 staining or scanning electron microscopy imaging from PPARα-deficient (Pparα-/-) mice and age and genetic background-matched wild-type (WT) mice. Subretinal activated microglia was counted after anti-Iba1 staining. Retinal function and thickness were measured by ERG and OCT, respectively. Mitochondrial function was analyzed by an XFe96 analyzer. Gene expression was determined by Realtime PCR. Proteins expression was studied by Western blotting or immunostaining.
Results :
Decreased PPARα expression was observed in the RPE and retina of human donors with dry AMD, compared to those in non-AMD donors. Abca4/Rdh8 double knock-out (DKO) mice showed significantly declined PPARα levels in the retina and RPE, which were reversed by fenofibrate (PPARα agonist). Fenofibrate restored the retinal function and thickness in DKO mice. Pparα KO resulted in dramatically enlarged areas of RPE cells and disorganized microvilli morphology. ERG c wave amplitudes were significantly decreased, and AMD-related RPE phenotypes, such as tight junction fragmentation, were observed in Pparα-/-mice, suggesting an impaired RPE barrier. Microglia were dramatically accumulated in the subretinal space, and elevated levels of RPE-derived TNFα and CTGF were detected in Pparα-/-mice, suggesting Pparα KO contributed to the subretinal inflammation. In Pparα-/-RPE, PPARα target genes, PDK1 and FABP3, were significantly downregulated. Lipid droplets were dramatically accumulated either in BODIPY-stained Pparα-/-RPE flatmounts or the Bruch’s membrane in Oil red-stained cryosection. Pparα-/-RPE cells showed mitochondrial dysfunction. Fenofibric acid activated, while Pparα siRNA decreased FAO in primary RPE cells. Increased mitochondrial Fis1 and decreased Mfn2, PGC-1α, and Sirt1 levels were observed in primary Pparα-/-RPE cells. Mitochondrial DNA copy number significantly declined in isolated Pparα-/-RPE. These results indicated that PPARα deficiency alters mitochondrial dynamics and biogenesis.
Conclusions :
PPARα is a new drug target for dry AMD with the mechanisms of inhibiting inflammation and regulating mitochondrial functions.
This abstract was presented at the 2023 ARVO Annual Meeting, held in New Orleans, LA, April 23-27, 2023.