Abstract 993: AAV8-mediated Overexpression of Lecithin-cholesterol Acyltransferase Fails to Promote Macrophage Reverse Cholesterol Transport in Vivo
Background Lecithin cholesterol acyltransferase (LCAT) is responsible for esterification of plasma cholesterol and overexpression of LCAT in mice raises HDL cholesterol levels. While LCAT is believed to create a gradient of free cholesterol promoting cellular cholesterol efflux, the role that LCAT plays in promoting reverse cholesterol transport (RCT) in vivo remains unclear. We tested the hypothesis that AAV8-mediated overexpression of LCAT in mice would promote macrophage RCT in vivo.
Methods and Results Recombinant adeno-associated virus serotype 8 (AAV8)-based vectors were used to overexpress human LCAT (h-LCAT) alone or together with human cholesteryl ester transfer protein (h-CETP) in human apoA-I transgenic mice. Cholesterol-loaded and 3H-cholesterol-labeled J774 macrophages were injected intra-peritoneally, plasma sampled at several time points, liver and bile were harvested at 48 hours, and feces were collected continuously over 48 hr. Overexpression of h-LCAT resulted in a 2.9 -fold increase of plasma HDL cholesterol levels. Although there was a significant 77% increase in 3H-cholesterol in plasma, no increase in fecal 3H-sterol excretion was observed in comparison with Lac-z control. When CETP was co-expressed with LCAT the increase in plasma HDL cholesterol levels was 2 fold. No significant difference was observed in plasma tracer or in fecal 3H-sterol excretion in comparison to CETP-expressing controls without LCAT overexpression. In cell culture studies, serum from LCAT overexpressing mice was not more effective in promoting cholesterol efflux from murine bone marrow macrophages than serum from control mice.
Conclusion These results demonstrate that while overexpression of LCAT in mice raises HDL-C levels, it does not promote macrophage RCT. These studies illustrate another example in mice in which an intervention that affects plasma HDL-C levels does not have the expected effect on macrophage RCT.