ABCA1 and HDL₃ are required to modulate smooth muscle cells phenotypic switch after cholesterol loading

Cholesterol-loaded smooth muscle cells (SMCs) modify their phenotypic behavior becoming foam cells. To characterize the role of ABCA1 and HDL₃ in this process, we evaluated HDL₃ effects on cholesterol-induced phenotypic changes in SMCs expressing or not ABCA1.

SMCs, isolated from the aortae of wild-type (WT) and Abca1 knock-out (KO) mice, were cholesterol-loaded using a "water-soluble cholesterol''.

Cholesterol loading downregulates the expression of Acta2 and calponin (SMC markers), and increases the expression of Mac-2, CD11b and MHCII (inflammation-related genes and surface antigens) and Abca1, Abcg1. HDL₃ normalizes SMC marker expression and reduces the expression of inflammation-related genes/proteins in WT cells, an effect not observed with free apoA-I. The effect of HDL₃ is almost lost in Abca1 KO cells, as well as when Abca1 is silenced in WT SMC. HDL₃ does not differently affect cholesterol downloading in WT or KO cells and stimulates phospholipids removal in WT cells. Similarly, the expression of myocardin and its modulators, such as miR-143/145, is reduced by cholesterol loading in WT and Abca1 KO SMCs; HDL₃ normalizes their levels in WT cells but not in KO cells. On the contrary, cholesterol loading induces Klf4 expression while HDL₃ restores Klf4 to basal levels in WT cells, but again this effect is not observed in KO cells.

Our results indicate that HDL₃, by interacting with ABCA1, modulates the miR143/145-myocardin axis and prevents the cholesterol-induced gene expression modification in SMCs regardless of its cholesterol unloading capacity.