HDL endocytosis and resecretion.

Area of Science:

• Biochemistry
• Cell Biology
• Metabolic Diseases

Background:

• High-density lipoprotein (HDL) plays a key role in reverse cholesterol transport, moving cholesterol from peripheral tissues to the liver.
• The mechanism of HDL holo-particle endocytosis and its physiological significance, particularly its connection to selective lipid uptake, have been debated for decades.
• Understanding HDL endocytosis is crucial for comprehending cholesterol homeostasis in atherosclerosis-related tissues.

Purpose of the Study:

• To review and critically summarize current knowledge on HDL endocytosis and resecretion.
• To elucidate the relationship between HDL endocytosis, selective lipid uptake, and cholesterol transfer.
• To discuss the role of HDL endocytosis in maintaining cholesterol homeostasis in the liver, macrophages, and endothelium.

Main Methods:

• Literature review focusing on HDL endocytosis, resecretion (retro-endocytosis), and transcytosis.
• Critical summary of current research on receptors mediating HDL endocytosis (SR-BI, F1-ATPase, CD36).
• Analysis of intracellular HDL transport routes and the fate of endocytosed HDL (resecretion or degradation).

Main Results:

• HDL endocytosis and resecretion appear to be a redundant pathway under normal physiological conditions.
• Specific receptors like SR-BI, F1-ATPase, and CD36 mediate HDL endocytosis.
• HDL can be resecreted (retro-endocytosis) or degraded after cellular uptake, depending on the tissue type.

Conclusions:

• HDL endocytosis and resecretion are generally redundant but become vital for maintaining cellular cholesterol homeostasis when lipid metabolism is disturbed.
• HDL retro-endocytosis offers an alternative pathway for tissues to manage cholesterol levels during metabolic dysfunction.
• Further research is needed to fully delineate the physiological relevance and mechanisms of HDL uptake and transport.