ATP binding cassette G1-dependent cholesterol efflux during inflammation

Area of Science:

• Biochemistry
• Molecular Biology
• Cardiovascular Research

Background:

• ATP binding cassette transporter G1 (ABCG1) is crucial for cellular cholesterol efflux to high-density lipoprotein (HDL), maintaining macrophage cholesterol homeostasis.
• HDL undergoes significant remodeling during acute inflammation, characterized by lipid changes and incorporation of serum amyloid A (SAA).

Purpose of the Study:

• To investigate the impact of inflammation-induced HDL remodeling on ABCG1-dependent cholesterol efflux.
• To determine the roles of SAA and phospholipid enrichment in altered HDL function during inflammation.

Main Methods:

• Comparison of ABCG1-mediated cholesterol efflux using normal and acute phase (AP) mouse HDL.
• Analysis of HDL from SAA knockout (SAAKO) mice.
• Enzymatic hydrolysis of AP HDL with Group IIA secretory phospholipase A(2) (sPLA(2)-IIA).

Main Results:

• Lipid-free SAA mimics apolipoprotein A-I in mediating cholesterol efflux from ABCA1 and ABCG1.
• AP HDL with SAA showed a modest increase in ABCG1-dependent efflux compared to normal HDL.
• AP HDL from SAAKO mice enhanced ABCG1 efflux more than AP HDL with SAA.
• sPLA(2)-IIA hydrolysis reduced AP HDL's ability to facilitate ABCG1-mediated cholesterol transfer, indicating phospholipid enrichment is key.
• AP human HDL, lacking PL enrichment, was less effective in ABCG1 efflux than normal human HDL.

Conclusions:

• Inflammatory HDL remodeling affects ABCG1-dependent cholesterol efflux independently of SAA presence.
• Phospholipid enrichment of HDL during inflammation is the primary driver of altered ABCG1-mediated cholesterol efflux.