Adenovirus-mediated expression of caveolin-1 in mouse liver increases plasma high-density lipoprotein levels

Caveolae are 50-100 nm plasma membrane invaginations, which function in cell signaling and transcytosis, as well as in regulating cellular cholesterol homeostasis. These subcompartments of the plasma membrane are characterized by the presence of caveolin proteins. Recent studies have indicated that caveolae may be involved in the regulation of cellular cholesterol efflux to HDL, as well as selective uptake mediated by SR-BI. In the present study, we have determined the effect of caveolin-1 overexpression in mouse liver on plasma lipoprotein metabolism. We evaluated this effect using an adenovirus-mediated gene delivery system. C57BL/6J mice were injected with adenoviruses encoding either caveolin-1 (Adcav-1) or green fluorescent protein (AdGFP) together with a transactivator adenovirus (AdtTA). We found that, after adenovirus injection, caveolin-1 was overexpressed in hepatocytes. Moreover, the recombinant protein was localized to the plasma membrane. We also found that caveolin-1 overexpression induced a marked change in the lipoprotein profile of injected animals. In caveolin-1 overexpressing animals, plasma HDL-cholesterol levels were found to be approximately 2-fold elevated, as compared with control animals. To determine the effect of caveolin-1 on SR-BI-mediated selective uptake, we infected murine hepatocytes in culture with an adenoviral vector carrying the caveolin-1 cDNA or GFP as a control protein. We show that, in primary cultures of hepatocytes, caveolin-1 inhibits DiI-HDL uptake mediated by SR-BI. This result would mechanistically explain the increased plasma HDL-cholesterol levels we observed in caveolin-1 adenovirus-injected animals. In addition, caveolin-1 expression increased the secretion of apolipoprotein A-I in cultured hepatocytes and increased apolipoprotein A-I plasma levels in mice. Our study therefore demonstrates an important role for caveolin-1 in regulating HDL metabolism.