Receptor-independent LDL macropinocytosis by macrophages contributes to the pathogenesis of atherosclerosis

Gabor Csanyi,Hui-Ping Lin, Bhupesh Singla Pushpankur Ghoshal,Mary Cherian-Shaw and David Fulton

Augusta University, USA

Vascular Biology Center, USA

Posters & Accepted Abstracts: J Cardiovasc Dis Diagn

Abstract :

Aims: Hypercholesterolemic mice lacking CD36 and SRA, two major scavenger receptors (SRs), are only partially protected from atherosclerosis. These results support the existence of an alternative, receptor-independent pathway of lipid internalization that contributes to the pathogenesis of atherosclerosis. This study was designed to examine the role of macrophage macropinocytosis in the development of atherosclerosis.

Methods: Macropinocytosis was stimulated in wild type (WT), CD36- /-, SRA-/- and CD36-/-/SRA-/- bone marrow-derived macrophages using pharmacological approaches (M CSF) and overexpression of constitutively active Ras (H RasG12V). Atherosclerosis was induced by a single PCSK9- AAV injection (ip), partial left carotid artery ligation and Western diet (three weeks). Macropinocytosis was inhibited by the amiloride derivative EIPA and deletion of NHE1 in myeloid cells (LysmCre+ NHE1f/f mice).

Results: MCSF and overexpression of H RasG12V stimulated nLDL (50 μg/ml) internalization in WT, CD36-/-, SRA /- and CD36-/-/SRA- /- macrophages approximately 3-fold compared to respective controls. Stimulation of macropinocytosis significantly increased uptake of oxand ac-LDL (50 μg/ml) in WT and CD36-/-/SRA-/- macrophages. The macropinocytosis inhibitor EIPA abolished lipid internalization in MCSFtreated and H RasG12V-overexpressing macrophages, confirming the uptake mechanism as macropinocytosis. Both wild type (WT) and CD36-/-/SRA- /- mice treated with EIPA using an osmotic pump developed significantly less atherosclerosis compared to controls. Loss of NHE1 in myeloid cells decreased lesion size by ~80% compared to Cre- mice. Body weight, blood pressure and plasma cholesterol levels were not different between groups.

Conclusions: To our knowledge, the findings of the present study demonstrate for the first time that macrophage macropinocytosis contributes to the pathogenesis of atherosclerosis.