Fenofibrate Attenuates Kidney Injury by Enhancing Use of Fatty Acids from Lipid Droplets in Proximal Tubules

Background: Previous studies demonstrate decreased PPARα- and KLF15-mediated fatty acid beta-oxidation (FAO) and increased lipid droplet formation in proximal tubules (PTs) in AKI. However, it remains unclear whether this increase in lipid droplets is a consequence or a driver of PT injury. The aim of the study is to test the hypothesis that fenofibrate, a PPARα agonist, attenuates PT injury, AKI and eventual interstitial fibrosis by enhancing the utilization of fatty acids from lipid droplets. Methods: 9-week-old FVB/N mice were fed a 0.2% fenofibrate or regular chow diet for 12 days, followed by vehicle or aristolochic acid I (AAI) (2 mg/kg, IP, every 72 hours for 9days). Acute phase is 3 days after last dose of AAI and remodeling phase is 3 weeks after the last dose of AAI. Kidney function was assessed by blood urea nitrogen (BUN), serum creatinine, and FITC sinistrin-based GFR. Histological analyses (PAS, H&E) and immunostaining with RT-PCR were conducted for markers of FAO, lipid droplet formation, PT and fibrotic markers. SnRNA-seq was conducted in WT and PT-specific Klf15 knockout (Klf15PTKO) mice post-AAI. Results: Fenofibrate restored kidney function (BUN, creatinine, and GFR) and lotus lectin expression, and reduced fibrotic markers (vimentin, a-sma, sirus red) as compared to control mice, during the acute and remodeling phase post-AAI treatment. The number of lipid droplets in PT cells, per cross-sectional area, were reduced in fenofibrate- as compared to vehicle-treated-AAI mice (Oil-Red-O, Perilipin 2 (PLIN2) staining). Fenofibrate also increased the expression of FAO and lipid droplet genes (Ppara, Klf15, Pgc1a, Cpt1a, Acaa2, Acox1, Lpin2) and reduced the expression of fibrotic genes (Tgfb, Col1a1) as compared to vehicle-treated mice. Klf15PTKO attenuated these salutary effects of fenofibrate post-AAI treatment. SnRNA-seq also showed a reduction in transcripts involved in utilization of lipid droplets (Lpin2, Gpat4, Gpam, and Dgat1) in PT cells in Klf15PTKO as compared to Klf15fl/fl mice post-AAI. Conclusion: PPARα-KLF15 agonism attenuates AKI to CKD transition by enhancing fatty acid oxidation metabolism through increased utilization of lipid droplets in PT cells post-AAI treatment. Funding: NIDDK Support, Veterans Affairs Support