Circadian CLOCK-PPARδ Axis Regulates Phosphatidylcholine Homeostasis in Diabetic Kidney Disease

Background: Abnormal lipid metabolism in podocytes is a significant pathogenic mechanism in diabetic kidney disease (DKD). Peroxisome proliferator-activated receptors (PPARs) are key links between circadian clock genes and lipid metabolism. Previous studies have shown that PPARδ is highly expressed in podocytes but is decreased in DKD. However, the mechanism by which decreased PPARδ expression leads to podocyte damage remains to be fully elucidated. Methods: Adult C57BL/6J mice and podocyte-specific Ppard knockout mice (podocyte-Ppard -/-) were used to construct a type II diabetes model in vivo. Primary podocytes were cultured in 30 mM high glucose. RNA sequencing and lipidomics analysis were employed to investigate the association between the circadian clock and metabolism. Chromatin immunoprecipitation (ChIP) qPCR analysis and dual-luciferase reporter gene assays were conducted to explore the relationship between CLOCK and Ppard. Results: Rhythmic oscillations of PPARδ were diminished in podocytes from DKD mice. Podocyte-Ppard-/- diabetic mice exhibited increased urinary protein excretion and glomerular injury compared to Ppardfl/fl diabetic mice. Overexpression of PPARδ attenuated proteinuria and podocyte injury. ChIP-qPCR analysis confirmed the binding of CLOCK to PPARδ. Treatment with an agonist at the peak of PPARδ expression was more effective in reducing urinary protein and alleviating podocyte injury. Knockdown of podocyte Ppard or exposure to a high glucose environment both disrupted phosphatidylcholine (PC) metabolism in podocytes. ChIP-qPCR analysis demonstrated that PPARδ regulates PC metabolism by modulating Chpt1 expression. Conclusion: CLOCK transcriptionally regulates the rhythmic expression of PPARδ, leading to rhythmic patterns of PC metabolism in podocytes. Disruption of the CLOCK-PPARδ axis results in podocyte damage and proteinuria. Funding: Government Support – Non-U.S.