Inhibition of S1PR4 and supplementation of APOM in Alport Podocytes

Background: Renal lipid dysmetabolism contributes to glomerular disease progression, including Alport Syndrome. We recently identified alterations in the apolipoprotein M/sphingosine-1-phosphate/sphingosine-1-phosphate receptor 4 signaling axis in glomeruli from patients with glomerular disease. Methods: We utilized Col4a3 knockout mice and immortalized podocytes derived from these mice as a mouse model of Alport Syndrome. Mice and podocytes were treated with recombinant apolipoprotein M or the sphingosine-1-phosphate receptor 4 antagonist, CYM50358. Results: Col4a3-/- glomeruli and podocytes exhibited reduced apolipoprotein M and increased sphingosine-1-phosphate receptor 4 expression and increased sphignsoine-1-phosphate levels, mirroring findings in patients with glomerular disease. Treatment with apolipoprotein M or CYM50358 reduced albuminuria, BUN, and plasma creatinine, and ameliorated glomerulosclerosis, tubulointerstitial fibrosis, podocyte loss and foot process effacement. Both treatments reduced triglyceride and cholesterol accumulation in glomeruli and podocytes. RNA-seq analysis of Col4a3-/- revealed that sphingosine-1-phosphate receptor 4 antagonism upregulated lysosomal and autophagy-related genes. Western blot analysis confirmed increased LC3-II/LC3-I ratios and decreased p62, indicating enhanced autophagic flux. Treated podocytes showed increased lysosome numbers and co-localization with lipid droplets. In contrast, apolipoprotein M had no effect on autophagy but promoted cholesterol efflux. Conclusions: The apolipoprotein M/sphingosine-1-phosphate axis is dysregulated in Col4a3-/- podocytes. Targeting this pathway through apolipoprotein M supplementation or sphingosine-1-phosphate receptor 4 antagonism improves renal function and reduces lipid accumulation by enhancing either cholesterol efflux or autophagy, respectively. These findings suggest that restoring lipid homeostasis via targeting the APOM/S1P/S1PR4 axis may be a promising therapeutic strategy for Alport Syndrome and other glomerular diseases.