Deletion of h2-calponin in Macrophages Facilitates Cell Motility and Lipid Clearance: A Novel Mechanism to Attenuate Arterial Atherosclerosis

Abstract

Arterial atherosclerosis, a major cardiovascular risk condition, is a chronic inflammatory disease. The atherosclerotic plaques are built up by excessive lipid deposition and accumulation of apoptotic immune cells. Macrophages migrate into atherosclerotic lesions and function in scavenging extracellular lipid and mediating the inflammatory process. Lipid-laden macrophages transform into foam cells and loss their migration ability. The retention of foam cells at arterial intima promotes the growth of atherosclerotic plaques. Calponin is an actin filament-associated protein and its h2 isoform regulates cell proliferation, migration and other cell motility-based functions. We previously demonstrated that removal of h2-calponin in macrophages enhances cell migration and phagocytosis. Deletion of h2-calponin in macrophages significantly attenuated the development of inflammatory arthritis in mouse models (our unpublished results). In the present study, we investigated the function of h2-calponin-null mouse macrophages and foam cells in lipid clearance as well as their migration and transendothelial migration abilities. Foam cells are produced in culture by loading mouse peritoneal macrophages with acetylated low density lipoprotein. Lipid phagocytosis was quantified using Oil Red O staining of intracellular lipid droplets. Migration and transendothelial migration were examined using Transwell assay system. Foam cell apoptosis was studied using terminal deoxynucleotidyl transferase dUTP nick end labeling (TUNEL) assay. The results showed that h2-calponin-null macrophages exhibit significantly higher lipid engulfment and faster migration and transendothelial migration than wild type controls. The h2-calponin-null foam cells retained higher migration capacity than that of wild type cells, which potentially facilitates migrating out of the arterial intima, reducing accumulation of apoptotic cells, and attenuating atherosclerotic lesions. The data demonstrate that h2-calponin is a novel molecular target for modulating macrophage functions and the development of new therapeutic approaches to the prevention and treatment of atherosclerosis.