High-density lipoprotein transport through aortic endothelial cells involves scavenger receptor BI and ATP-binding...

Area of Science:

• Cardiovascular Biology
• Endothelial Cell Biology
• Lipid Metabolism

Background:

• Cholesterol efflux from macrophage foam cells is a critical step in reverse cholesterol transport, influencing atherosclerosis development.
• High-density lipoproteins (HDL) and apolipoprotein A-I (apoA-I) act as cholesterol acceptors, requiring passage across the endothelium to reach intimal cells.
• Previous research demonstrated apoA-I transcytosis across endothelial cells, modulated by ATP-binding cassette transporter A1 (ABCA1).

Purpose of the Study:

• To investigate the interaction of mature HDL with endothelial cells (ECs).
• To elucidate the mechanisms and transporters involved in HDL binding, internalization, and transcytosis across ECs.
• To determine the specific roles of scavenger receptor class B type I (SR-BI), ABCA1, and ATP-binding cassette transporter G1 (ABCG1) in HDL transport.

Main Methods:

• Utilized cell surface biotinylation and immunofluorescence microscopy to track HDL association with ECs.
• Employed endothelial cells cultured on inserts to assess HDL binding, internalization, and translocation in a transwell system.
• Applied RNA interference (RNAi) to silence SR-BI, ABCA1, and ABCG1 expression and evaluate their impact on HDL transport and inulin permeability.

Main Results:

• Endothelial cells exhibit specific and saturable binding of HDL, with approximately 30% internalized.
• HDL is translocated from the apical to the basolateral side of ECs in a temperature-dependent manner, with reduced particle size but intact protein.
• Silencing SR-BI or ABCG1 significantly reduced HDL binding and transcytosis, while ABCA1 silencing had no effect; combined silencing did not further impair HDL transport.

Conclusions:

• Endothelial cells actively bind, internalize, and transcytose HDL particles.
• HDL transcytosis across ECs is mediated by either SR-BI or ABCG1, highlighting their distinct roles in reverse cholesterol transport.
• ABCA1 does not appear to play a significant role in the transcytosis of intact HDL particles by endothelial cells.