Abnormalities of glycosphingolipid, sulfatide, and ceramide in the polycystic (cpk/cpk) mouse

Polycystic kidney disease is a disorder marked by aberrant renal tubular epithelial cell proliferation and transport abnormalities. Sphingolipids are ubiquitous membrane components implicated in several cellular functions including cell membrane sorting, signaling, growth, ion transport, and adhesion. To investigate a potential pathogenic role for sphingolipids in cystic kidney disease, we studied the sphingolipid content and associated enzymatic activities of the kidneys from cpk/cpk mice and their phenotypically normal litter mates. The neutral glycolipids, including glucosylceramide and lactosylceramide, displayed a striking increase in 3-week-old cpk/cpk mice as did the acidic lipid, ganglioside GM3. However, a correspondingly significant decrease in sulfoglycolipid and ceramide concentration was observed in the cpk/cpk kidneys. Glucosylceramide synthase activity was higher in the kidneys of the cpk/cpk mice than in those of the controls. Kinetic analysis of the glucosylceramide synthase revealed the presence of an endogenous activator in the cystic kidney. A marked decrease in sulfotransferase activity was observed in both whole kidney homogenates and in microsomal preparations that was consistent with the decrement in sulfolipid content. The increase in GM3, glucosyl- and lactosylceramide may therefore be the result of impaired sulfolipid synthesis at the 3-week time point. While sulfolipid and glucosylceramide concentrations are not different at 1 and 2 weeks of age, ceramide concentrations in cystic kidneys are significantly reduced compared to kidneys from phenotypically normal mice. These results suggest that sphingolipids may play a potential role in the proliferative and transport abnormalities associated with cystic renal disease and the development of azotemia.