Apolipoprotein E recycling: implications for dyslipidemia and atherosclerosis

Area of Science:

• Lipid Metabolism
• Cell Biology
• Molecular Medicine

Background:

• Triglyceride-rich lipoproteins (TRLs) follow a complex intracellular pathway after endocytosis, distinct from low-density lipoproteins.
• Apolipoprotein E (apoE) derived from TRLs is differentially sorted, with a significant portion remaining in peripheral recycling endosomes.

Purpose of the Study:

• To review the current understanding of apolipoprotein E (apoE) recycling from TRLs.
• To explore the role of apoE recycling in regulating plasma apoE levels postprandially.
• To elucidate the link between TRL-derived apoE, cellular cholesterol transport, and HDL metabolism.

Main Methods:

• Review of current literature on TRL and HDL metabolism.
• Analysis of intracellular trafficking of TRL and HDL components.
• Integration of findings on apoE isoforms (apoE3 vs. apoE4) and their impact on cholesterol homeostasis.

Main Results:

• TRL-derived apoE is mobilized from endosomes by high-density lipoproteins (HDLs) or apoA-I for resecretion, forming new apoE-containing HDL.
• HDL-mediated apoE recycling involves cholesterol efflux and the targeting of HDL-derived apoA-I to endosomes containing apoE and cholesterol.
• Impaired recycling of TRL-derived apoE4, unlike apoE3, is associated with intracellular cholesterol accumulation.

Conclusions:

• A novel intracellular pathway for apoE recycling exists, linking TRL metabolism, cellular cholesterol transport, and HDL metabolism.
• Defective apoE recycling, particularly apoE4, may underlie its known effects on HDL metabolism and cholesterol accumulation.
• Understanding apoE recycling is crucial for comprehending postprandial lipid regulation and associated metabolic disorders.