We previously showed that Pla2g12bhlb218/hlb218 (Pla2g12bmt/mt) mice injected with viruses expressing mutant PCSK9, fed a western diet had significantly lower plasma lipids and fewer atherosclerotic plaques. Here, we aimed to explain mechanisms for resistance to hyperlipidemia and atherosclerosis in these mice. We performed studies in 3-month-old male and female chow fed Pla2g12bmt/mt and control mice. Dual x-ray absorptiometry did not reveal any significant differences in body weight, fat weight and fat percentage in Pla2g12bmt/mt mice compared to controls. Moreover, there were no significant differences in energy expenditure and food intake between mutant and control mice. However, these mice had significantly lower levels of plasma glucose, insulin, triglyceride, cholesterol, HDL-c, LDL-c, apoB48, and apoB100. In oral fat tolerance test Pla2g12bmt/mt mice showed significant defects in triglyceride absorption. Furthermore, these mice excreted more fecal triglyceride, but not cholesterol. Oil Red O, H & E staining, transmission electron microscopy, and quantifications of lipids in the duodenum indicated accumulation of large lipid droplets and dilated endoplasmic reticulum. These studies suggest that Pla2g12bmt/mt mice have significant defect in intestinal fat absorption. These defects were not due to reductions in apoB and MTP expression. RNA-Seq analysis of duodenal samples revealed upregulation of glycerolipid metabolism, arachidonic acid metabolism, oxidative phosphorylation, and thermogenesis. These pathways were likely upregulated to increase cellular catabolism and oxidation of accumulated lipids. Down upregulated pathways were related to pancreatic secretion, protein digestion and absorption. Despite severe defects in fat absorption, these mice maintain normal growth and physiology. These mice may serve as model to understand metabolism in hypolipidemia disorders associated with significant defects in lipid absorption such as abetalipoproteinemia and hypobetalipoproteinemia.
Read full abstract