Palmitate Diet-induced Loss of Cardiac Caveolin-3: A Novel Mechanism for Lipid-induced Contractile Dysfunction

Abstract

Obesity is associated with an increased risk of cardiomyopathy, and mechanisms linking the underlying risk and dietary factors are not well understood. We tested the hypothesis that dietary intake of saturated fat increases the levels of sphingolipids, namely ceramide and sphingomyelin in cardiac cell membranes that disrupt caveolae, specialized membrane micro-domains and important for cellular signaling. C57BL/6 mice were fed two high-fat diets: palmitate diet (21% total fat, 47% is palmitate), and MCT diet (21% medium-chain triglycerides, no palmitate). We established that high-palmitate feeding for 12 weeks leads to 40% and 50% increases in ceramide and sphingomyelin, respectively, in cellular membranes. Concomitant with sphingolipid accumulation, we observed a 40% reduction in systolic contractile performance. To explore the relationship of increased sphingolipids with caveolins, we analyzed caveolin protein levels and intracellular localization in isolated cardiomyocytes. In normal cardiomyocytes, caveolin-1 and caveolin-3 co-localize at the plasma membrane and the T-tubule system. However, mice maintained on palmitate lost 80% of caveolin-3, mainly from the T-tubule system. Mice maintained on MCT diet had a 90% reduction in caveolin-1. These data show that caveolin isoforms are sensitive to the lipid environment. These data are further supported by similar findings in human cardiac tissue samples from non-obese, obese, non-obese cardiomyopathic, and obese cardiomyopathic patients. To further elucidate the contractile dysfunction associated with the loss of caveolin-3, we determined the localization of the ryanodine receptor and found lower expression and loss of the striated appearance of this protein. We suggest that palmitate-induced loss of caveolin-3 results in cardiac contractile dysfunction via a defect in calcium-induced calcium release.

Heterozygous caveolin-3 mice show increased susceptibility to palmitate-induced insulin resistance

“…2013). To investigate if PALM diet feeding has any effect on the heart in vivo, we performed echocardiography on mice starting from 6 weeks of age every 2 weeks in all diet‐fed mice.…”

“…2013). Therefore, to address the role of CAV3 in insulin signal transduction pathway, we determined the effects of palmitate‐induced loss of CAV3 on the activity of IR downstream targets, IRS‐1 and Akt.…”

“…6A) strongly suggests that the effect of palmitate is mediated through the accumulation of sphingolipids in the membrane, as we have previously shown (Knowles et al. 2013). The IR, IRS‐1, Akt, and GLUT4 data further suggest that loss of CAV3 dissociates signaling through the insulin receptor cascade, because enhanced IRS‐1 activation does not lead to increased Akt activation.…”

“…2013) and repeated for these studies. Briefly, high‐lipid diets were custom‐made by Harlan Laboratories and all high‐fat diets contained 200 g/kg fat (20%).…”

Molecular mechanism of lipid-induced cardiac insulin resistance and contractile dysfunction

“…A possible novel mechanism for lipid-induced cardiac contractile dysfunction includes the loss of caveolin-3 during cardiac lipid oversupply [101]. Caveolins are the defining protein constituents of caveolae, which are responsible for the invagination of the plasma membrane.…”