Genetic deletion of endothelial Caveolin-1 is protective against metabolic disease.

In metabolic disease, the endothelium is exposed to a substantial increase in fatty acid concentrations creating a pathological role for endothelial cells (ECs) as lipid metabolizing cells. One mechanism whereby lipids may enter ECs is by caveolin-1 (Cav1)-mediated endocytosis. Because both ECs and adipocytes both have abundant Cav1 and both can readily take up lipids, we wanted to differentiate the role of Cav1 between the two cell types. For these reasons, we used an inducible EC-specific Cav1 knockout mouse (Cav1 /Cdh5-CreER ). Using these mice, we induced Cav1 genetic deletion from endothelium at 6 weeks, and began a high fat diet (HFD; 60% fat) to induce metabolic disease at 8 weeks. Normal chow fed littermates were used as controls. All mice were examined at 20 weeks (i.e., 12 weeks of HFD). Thus, we had four cohorts: Cre+ HFD, Cre- HFD, Cre+ normal chow, and Cre- normal chow all injected with tamoxifen. All mice regardless of genotype had comparable weight gain within diet groups, and gonadal fat pad mass. Food consumption was similar between groups, and electron microscopy was used to confirm presence of caveola in adipocytes, but not endothelium. Initial experiments examining plasma lipids found HFD Cre+ mice had both increased serum cholesterol (175mg/dL) and LDL (75mg/dL) compared to HFD Cre- controls (cholesterol, 125mg/dL; LDL, 60mg/dL). When these mice were challenged with a bolus of insulin, the blood glucose of Cre+ HFD mice dropped significantly resembling an insulin tolerance curve from normal chow fed controls. Similarly, Cre+ HFD mice were protected from hyperglycemia after bolus glucose injections, resulting in a glucose tolerance phenotype similar to that of a normal chow fed mouse (HFD Cre+ AUC 3000 vs. HFD Cre- AUC 60000). There was no difference in Cre+ or Cre- mice on normal chow diets with serum lipids or after challenge with insulin or glucose. It isn't clear why the insulin and glucose protection correspond with significantly increased lipids in the Cre+ HFD mice. For these reasons, we began investigating the possible mechanisms with primary cultures of Human Adipose Microvascular Endothelial Cells (HAMECs) and knocked down Cav1 with siRNA. In monolayers of HAMEC without any other cell type present, we did not observe altered lipid uptake after addition of 50µM of exogenous fatty acids with a 70% knockdown of Cav1 protein. Additionally, HAMECs seahorse assays were used to determine if there were changes in metabolic function when Cav1 was knocked down. This work provides initial evidence for the unique metabolic roles of endothelial Cav1 during periods of high lipid circulation.