Characterization of Lipid Droplet and Its Regulation by Caveolin-1 in Endothelial Cells

Lipid Droplet (LD) is a unique organelle involved in many biological processes such as cellular energy homeostasis and lipid metabolism. One of the LD‐associated proteins reported is Caveolin‐1 (Cav‐1). Cav‐1 is a 21‐kDa integral membrane protein with a putative hairpin structure and localized in caveolae microdomains on the plasma membrane. Recent studies have shown that Cav‐1 can be redirected to the surface of LD, implying a novel function of Cav‐1. Endothelial cells (EC), as a key cell type segregating plasma lipids from tissue, are highly enriched in Cav‐1, suggesting the potential role of Cav‐1 in regulating LD homeostasis in EC. In this study, we first show that LDs are formed in EC at atheroma, indicating the potential physiological function of LD in EC. We next find that LD formation is significantly reduced in EC isolated from Cav‐1 null mice. Fatty acid uptake is not altered in Cav‐1 deficient EC, suggesting an intracellular regulation of LD by Cav‐1. We therefore measure LD formation and degradation separately in Cav‐1 deficient EC. Interestingly, activity of diacylglycerol acyltransferases is increased in Cav‐1 null EC while breakdown of triglyceride (TG) is not significantly changed. Taken together, our findings showed that LD can be observed in EC in vivo and its formation is regulated by Cav‐1 independently of fatty acid uptake and TG biosynthesis.