Transcriptomics Reveal Altered Metabolic and Signaling Pathways in Podocytes Exposed to C16 Ceramide-Enriched Lipoproteins

Abstract

Sphingolipids are bioactive lipids associated with cellular membranes and plasma lipoproteins, and their synthesis and degradation are tightly regulated. We have previously determined that low plasma concentrations of certain ceramide species predict the development of nephropathy in diabetes patients with normal albumin excretion rates at baseline. Herein, we tested the hypothesis that altering the sphingolipid content of circulating lipoproteins can alter the metabolic and signaling pathways in podocytes, whose dysfunction leads to an impairment of glomerular filtration. Cultured human podocytes were treated with lipoproteins from healthy subjects enriched in vitro with C16 ceramide, or D-erythro 2-hydroxy C16 ceramide, a ceramide naturally found in skin. The RNA-Seq data demonstrated differential expression of genes regulating sphingolipid metabolism, sphingolipid signaling, and mTOR signaling pathways. A multiplex analysis of mTOR signaling pathway intermediates showed that the majority (eight) of the pathway phosphorylated proteins measured (eleven) were significantly downregulated in response to C16 ceramide-enriched HDL2 compared to HDL2 alone and hydroxy ceramide-enriched HDL2. In contrast, C16 ceramide-enriched HDL3 upregulated the phosphorylation of four intermediates in the mTOR pathway. These findings highlight a possible role for lipoprotein-associated sphingolipids in regulating metabolic and signaling pathways in podocytes and could lead to novel therapeutic targets in glomerular kidney diseases.

Immunolocalization of Sphingolipid Catabolism Enzymes along the Nephron: Novel Early Urinary Biomarkers of Renal Damage

“…In addition, it has been reported that dysregulation of sphingolipid metabolism in podocytes can compromise the proper functioning of the glomerular basement membrane, leading to proteinuria, glomerular fibrosis, and glomerulosclerosis [51]. Sphingosine-1phosphate induces tubule interstitial renal inflammation and fibrosis in diabetic nephropathy [52].…”

Ammonium Persulfate-Loaded Carboxylic Gelatin–Methacrylate Nanoparticles Promote Cardiac Repair by Activating Epicardial Epithelial–Mesenchymal Transition via Autophagy and the mTOR Pathway

“…Consistent with the RNA-Seq data, the expression levels of lysosome-related genes (Lamp1, 38,39 Lamp2, 38,39 Ctsz, 38 Ctsc, 40 and Ctsl 39 ) were increased from day 1 to day 3 in the NPs/ APS group compared to that in the ctrl group. The expression levels of mTOR-related genes (mTOR, Pik3ca, 41 Clip1, 42 Igf1, 41 and Slc38a9 43 ), cell motility-related genes (Chd2, 44 Kif 26b, 45 Gsn, 46 Myolf, 47 and Wipf1 48 ), and endothelial cellrelated genes (VWF, 25 Smad6, 49 and Eng 50 ) were also upregulated at day 3 in the NPs/APS group compared to that in the ctrl group. The expressions of autophagy-related genes (Atg14, 36 Atg4c, 51 Atg12, 36 LC3b 36,37 ) were elevated at day 1 in the NPs/APS group compared to those in the ctrl group, but gradually decreased from day 2 to day 3 compared to those at day 1.…”

Circulating Sphingolipids in Insulin Resistance, Diabetes and Associated Complications

“…The relative proportion of sphingolipids carried by each lipoprotein may differentially impact metabolic and signaling pathways at the cell/tissue level, and therefore provide crucial information and a better understanding of the role of sphingolipids in diabetic complications. Supporting this concept, our group has shown that, in podocytes exposed to LDL enriched with specific sphingolipids, the impact on metabolic and signaling pathways is quite distinct from that of HDL enriched with the same sphingolipids [ 215 ]. In conclusion, our data in type 2 diabetes and in type 1 diabetes demonstrated that plasma and lipoprotein sphingolipids are associated with diabetic kidney disease.…”