Lectin-like oxidized low-density lipoprotein receptor-1 (LOX-1) and cardiac fibroblast growth

Lectin-like oxidized low-density lipoprotein receptor-1 (LOX-1) regulates growth of a variety of cells and is important in inflammation, oxidative stress, and tissue remodeling. Recent studies show that LOX-1 deletion limits cardiac remodeling after sustained hypertension. We posited that LOX-1 may affect cardiac fibroblast growth and collagen secretion. To examine this postulate, we studied growth pattern of cardiac fibroblasts from hearts of wild-type and LOX-1 knockout (KO) mice. LOX-1 KO fibroblasts exhibited dramatically reduced growth when compared with wild-type mice fibroblasts and became much larger than wild-type mice fibroblasts in serial cultures, suggesting arrest of cell division. Western blotting and immunofluorescence showed that cell division control protein 42, a key regulator for cell division, was markedly downregulated in LOX-1 KO fibroblasts. The cytoskeletal organization in these fibroblasts was significantly altered in strand orientation, and some fibroblasts were completely devoid of F-actin. Furthermore, NADPH oxidase expression and generation of reactive oxygen species, as well as cell proliferation signals serine/threonine-specific protein kinase and murine double minute 2, were significantly reduced in LOX-1 KO fibroblasts. To confirm the essential role of LOX-1 in fibroblast growth, LOX-1 KO fibroblasts were transfected with h-LOX-1 cDNA. After transfection, the altered pattern of cytoskeletal organization, as well as expression of cell division control protein 42, serine/threonine-specific protein kinase, and murine double minute 2, was normalized. In congruent with these in vitro data, we found that the cardiac fibroblast number and expression of fibronectin and procoallagen-1/collagen were significantly lower in hypertensive LOX-1 KO mice hearts than in hypertensive wild-type mice hearts subjected to sustained hypertension (angiotensin II infusion). These findings implicate LOX-1 in cytoskeletal organization and growth of cardiac fibroblasts.