Correlation of lipids enriched in urinary extracellular vesicles released from cathepsin B knockout mice treated with streptozotocin and the development of diabetic kidney disease and hypertension

Cathepsin B (CtsB) is a multifunctional protein that plays an important role in physiology and pathophysiology. Urinary extracellular vesicles (uEVs) represent a mixed population of extracellular vesicles that are released from different cell types including those from the kidney and urinary tract. EVs are enriched in various signaling and bioactive lipids that can serve as important biomarkers of disease. Streptozotocin (STZ) is an antibiotic that causes pancreatic islet beta-cell destruction, diabetic nephropathy, and hypertension. We hypothesized that streptozotocin causes diabetic kidney disease and hypertension in a mechanism involving the release of bioactive lipids from kidney cells and causes renal cell death associated with an increase in oxidative stress. Lipidomics was performed on uEVs isolated from CtsB knockout mice treated with or without STZ and the kidneys from the two groups of mice were used to investigate changes in various proteins associated with cell death. Phosphatidylglycerols (PGs) represented the largest class of lipids that were altered after STZ treatment and LPE(18:1) and LPE(20:3) were among the bioactive lipids enriched in uEVs from CtsB knockout mice treated with STZ compared to untreated CtsB mice. The oxidative stress mediator 4-hydroxy-2-nonenal (4-HNE), glutathione peroxidase 4 (GPX4), and cystine/glutamate antiporter SLC7A11 (XCT) were augmented in the kidneys of CtsB knockout mice compared to untreated CtsB knockout mice. There was activation of caspase-3 in the STZ treated CtsB knockout mice. There were no appreciable difference in the lipid peroxidation enzyme acyl-CoA synthetase long-chain family member 4 (ACSL4) or the inflammatory marker CD93 in the kidneys from the two groups. Taken together, these data suggest STZ may induce oxidative stress and cause renal cell injury and apoptosis but not ferroptosis during the development of diabetic kidney disease and hypertension.