Delineating the role of ceramides in kidney disease and fibrosis

Background: Ceramides are bioactive lipid species that contribute to lipotoxicity and cell death. The rate limiting, first step in the ceramide biosynthesis pathway is catalyzed by serine palmitoyl transferase (SPT) comprising of 3 different subunits (SPTLC1, SPTLC2, SPTLC3). In this study, we examined whether kidney tubule specific SPT overexpression was sufficient to induce tubular injury in C57BL/6 mice. Methods: We generated a transgenic mouse with overexpression of a fused construct encoding a functional SPT heterodimer fSPT(SPTLC1, SPTLC2 and ssSPTa) selectively in the kidney tubules by crossing floxed fSPT mice with mice carrying the Pax8-rtTA/LC1 transgenes. Male and female floxed fSPT mice and fSPTOE mice were treated with doxycycline chow (600mg/kg) for 14 days at 8 weeks of age. Metabolic balance studies were performed at 10 and 20 weeks of age for urine collection. Kidneys were isolated to evaluate kidney injury and histology. Overexpression of kidney ceramides was confirmed with lipidomic analyses. Statistical analyses were performed using unpaired Student’s t-test. Results: Compared to floxed controls, fSPTOE mice had a 5.3-fold increase in Sptlc1 and Sptlc2 expression in the kidneys (p< 0.01, n=8-10 mice/group for males, n=2-4 mice for females). Lipidomic analyses of kidneys demonstrated that fSPTOE mice had 1.68 fold higher ceramides (Cer 18:1;O2/22:0: 53,664 ± 15319 vs floxed: 30,779 ± 8763 pmol/g, p< 0.001), 6.54 fold higher dihydroceramides (Cer 18:0;O2/22:0: 9122 ± 3510 vs floxed: 1395 ± 1188 pmol/g, p=0.001), 5.5 fold higher sphinganine (656 ± 578 vs floxed: 119 ± 44.2 pmol/g, p=0.01) and 1.77 fold higher sphingosine (6134 ±2817 vs floxed: 3464 ± 589 pmol/g, p< 0.01) relative to floxed controls. Despite similar food intake and body weight between the two groups, fSPTOE mice had increased water intake (8.0 ± 0.7 vs floxed 3.6 ± 1.6 ml/day, p=0.01) and urine volume (3.6 ± 0.6 vs floxed 1.2 ± 0.4 ml/day, p=0.04) at 20 weeks of age. Serum electrolytes were comparable between the two groups although blood urea nitrogen (floxed 29.2 ± 11.6 vs fSPTOE 79.2 ± 35.2 mg/dl, p=0.02) and creatinine (floxed 0.2 ± 0.01 vs fSPTOE 0.34 ± 0.1 mg/dl, p=0.02) were elevated. Compared to floxed controls, fSPTOEmice had 30.2 ± 22.2 fold increase in kidney Havcr1 expression (p< 0.01) without significant differences in kidney col1a1 and Fn1 expression. Kidney histology demonstrated moderate tubular injury with varying degrees of fibrosis by Trichrome staining in the fSPTOE mice. Male and female floxed and fSPTOE showed similar trends without any sex differences. Conclusion: Overexpression of SPT results in significant increase in kidney sphingolipids with evidence of tubular injury. Studies are currently ongoing to investigate whether overexpression of SPT exacerbates acute or chronic kidney disease. This abstract was presented at the American Physiology Summit 2026 and is only available in HTML format. There is no downloadable file or PDF version. The Physiology editorial board was not involved in the peer review process.