Severely altered cholesterol homeostasis in macrophages lacking apoE and SR-BI

Area of Science:

• Cardiovascular Biology
• Lipid Metabolism
• Atherosclerosis Research

Background:

• Scavenger receptor class B type I (SR-BI) and apolipoprotein E (apoE) play critical roles in lipid transport.
• Mice deficient in both SR-BI and apoE (DKO mice) exhibit severe dyslipidemia and premature death due to accelerated atherosclerosis.

Purpose of the Study:

• To investigate the impact of combined SR-BI and apoE deficiency on macrophage cholesterol homeostasis.
• To elucidate the mechanisms underlying altered cholesterol metabolism in DKO macrophages.

Main Methods:

• Analysis of total cholesterol (TC) and free cholesterol (FC) in macrophages from DKO mice and controls.
• Bone marrow transplantation experiments to differentiate between systemic and cell-intrinsic effects.
• Incubation of macrophages with high-density lipoprotein (HDL) and apoA-I to assess cholesterol efflux and uptake.

Main Results:

• DKO macrophages accumulated significantly more TC and FC compared to apoE-/- macrophages, with evidence of lysosomal lipid engorgement.
• Macrophage-specific SR-BI deficiency exacerbated cholesterol accumulation in the presence of HDL.
• Altered cholesterol trafficking, including the formation of peri-nuclear FC pools, was observed in DKO macrophages.

Conclusions:

• The dyslipidemia in DKO mice and intrinsic alterations in macrophage cholesterol trafficking both contribute to abnormal cholesterol homeostasis.
• These cellular defects in macrophage cholesterol metabolism are likely key drivers of accelerated atherosclerosis in DKO mice.