Muscle-specific Asah1 knockout mice develop whole-body insulin resistance
Authors: Choi Ran Hee , Sharma Ankit , Turapov Tursun , Tsosura Thais , Summers Scott , Holland William 
Published: May 2024

Skeletal muscle is a major tissue for glucose and lipid metabolism. Increasing ectopic deposition of lipid species is often found in obese populations, and this has been associated with the development of insulin resistance. Sphingolipids, particularly ceramides (Cer), are bioactive lipid species, and their accumulation in metabolically active tissues has been shown to desensitize insulin action. For example, using palmitate or Cer analogues in C2C12 or L6 myotubes increases long chain Cer accumulation in the myotubes and inhibits insulin-stimulated Akt phosphorylation. Moreover, inhibiting Cer synthesis improves insulin stimulated glucose uptake in obese rats and mice. However, genetic approaches to evaluating ceramide's effects have been limited to in vitro system and the effects of Cer in skeletal muscle on energy metabolism remain unprobed. Here, we developed and utilized a genetically modified mouse model to induce endogenous Cer accumulation in selectively in skeletal muscle to determine the effects of Cer accrual in skeletal muscle metabolism. Mice were fed high-fat diet (HFD) for 30-day or 60-day. Thirty-day diet intervention significantly increased muscle Cer, which returned to the baseline after 60-days of HFD. We found the expression of acid ceramidase ( Asah1) gene, which is responsible for degrading Cer, was highly elevated only in skeletal muscle from mice fed 30- and 60-day HFD, indicating Asah1 may be an important regulator of muscle ceramides. In order to probe the effect of Asah1 expression on muscle metabolism, we generated tamoxifen-inducible muscle-specific Asah1 knockout mice (Asah1MKO) and provided HFD for 20 weeks. There was no difference in bodyweight between control littermates (Asah1fl/fl) and Asah1MKO during the intervention. We confirmed that Asah1MKO mice significantly increased muscle Cer contents compared to Asah1fl/fl controls. At 18-week of HFD feeding, mice from both groups were tested for insulin and glucose tolerance, but there was no change between the groups. Finally, the mice were tested by hyperinsulinemic-euglycemic clamp to determine whether increased muscle Cer affects whole-body insulin sensitivity. Interestingly, we found that HFD-fed Asah1MKO mice dramatically reduced glucose infusion rate required to maintain euglycemia and blunt 2-deoxyglucose uptake into skeletal muscle compared to controls. These data suggest that Cer accrual in skeletal muscle can be a major contributor to whole-body insulin resistance. In summary, we found that Asah1 is increased only in skeletal muscle in response to HFD, and knocking out Asah1 in mouse skeletal muscle impairs whole-body insulin sensitivity, suggesting that the levels of muscle Cer are potentially critical in the development of insulin resistance. This research work was supported by the National Institute of Health grant (R01DK115824). This is the full abstract presented at the American Physiology Summit 2024 meeting and is only available in HTML format. There are no additional versions or additional content available for this abstract. Physiology was not involved in the peer review process.