Molecular mechanisms responsible for the reduced expression of cholesterol transporters from macrophages by low-dose...

Area of Science:

• Cardiovascular Biology
• Immunology
• Molecular Medicine

Background:

• Atherosclerosis involves chronic inflammation and cholesterol deposition in arteries.
• Macrophage cholesterol efflux is critical, mediated by scavenger receptor B1 (SR-B1) and ATP-binding cassette transporters ABCA1/ABCG1.
• Low-grade inflammation's role in regulating these efflux pathways is not fully understood.

Purpose of the Study:

• To elucidate the mechanisms by which low-grade inflammation affects macrophage cholesterol efflux.
• To identify key molecular players linking inflammation to impaired cholesterol transport.

Main Methods:

• Primary bone-marrow-derived macrophages were treated with low-dose lipopolysaccharide (LPS).
• Expression levels of SR-B1, ABCA1, and ABCG1 were measured.
• Nuclear receptor levels and promoter binding were assessed.
• Key signaling pathways including IRAK1, Tollip, and GSK3β were investigated.

Main Results:

• Low-dose LPS significantly reduced SR-B1, ABCA1, and ABCG1 expression and cholesterol efflux.
• LPS decreased nuclear retinoic acid receptor-α (RARα) levels and its binding to target gene promoters.
• Glycogen synthase kinase 3β (GSK3β) activation, mediated by IRAK1 and Tollip, was responsible for reduced RARα and subsequent downregulation of efflux transporters.
• Interleukin-1 receptor-associated kinase M (IRAK-M) was found to counteract IRAK1 activity.

Conclusions:

• A novel intracellular signaling network regulated by low-dose endotoxemia disrupts macrophage cholesterol efflux.
• This disruption, involving IRAK1, Tollip, GSK3β, and RARα, contributes to the pathogenesis of atherosclerosis.