Objective: The liver is one of the critical organs for lipoprotein metabolism and a major source for phospholipid transfer protein (PLTP) expression. The effect of liver-specific PLTP deficiency on plasma lipoprotein production and metabolism in mice was investigated.
Approach and results: We created a liver-specific PLTP-deficient mouse model. We measured plasma high-density lipoprotein (HDL) and apolipoprotein B (apoB)-containing lipoprotein (or non-HDL) levels and their production rates. We found that hepatic ablation of PLTP leads to a significant decrease in plasma PLTP activity, HDL lipids, non-HDL lipids, apoAI, and apoB levels. In addition, nuclear magnetic resonance examination of lipoproteins showed that the deficiency decreases HDL and apoB-containing lipoprotein particle numbers, as well as very low-density lipoprotein particle size, which was confirmed by electron microscopy. Moreover, HDL particles from the deficient mice are lipid-poor ones. To unravel the mechanism, we evaluated the apoB and triglyceride production rates. We found that hepatic PLTP deficiency significantly decreases apoB and triglyceride secretion rates. To investigate the role of liver PLTP on HDL production, we set up primary hepatocyte culture studies and found that the PLTP-deficient hepatocytes produce less nascent HDL. Furthermore, we found that exogenous PLTP promotes nascent HDL production through an ATP-binding cassette A 1-mediated pathway.
Conclusions: Liver-specific PLTP deficiency significantly reduces plasma HDL and apoB-containing lipoprotein levels. Reduction of production rates of both particles is one of the mechanisms.
Keywords: atherosclerosis; high-density lipoproteins; liver; phospholipid transfer protein; very low-density lipoproteins.