Paracrine Osteogenic Signals via Bone Morphogenetic Protein-2 Accelerate the Atherosclerotic Intimal Calcification In Vivo

Abstract

Objective-Vascular calcification is an important risk factor for cardiovascular diseases. Here, we investigated a role of dedifferentiated vascular smooth muscle cells (VSMCs) in the atherosclerotic intimal calcification. Methods and Results-We prepared human cultured VSMCs in either redifferentiatiated or dedifferentiated state and analyzed the gene expressions of bone-calcification regulatory factors. Expression of bone morphogenetic protein-2 (BMP-2), a potent initiator for osteoblast differentiation, was significantly enhanced in dedifferentiated VSMCs. Furthermore, endogenous BMP-2 antagonists, such as noggin, chordin, and matrix gamma-carboxyglutamic acid protein, were all downregulated in the dedifferentiated VSMCs. Conditioned medium from dedifferentiated VSMCs, but not from redifferentiated VSMCs, stimulated the osteoblastic differentiation of the mesenchymal progenitor C2C12 cells, which was abolished by BMP-2 knockdown. In atherosclerotic intima from apolipoprotein (apo)E-deficient mice, ␣SM-actin-positive cells, presumably dedifferentiated VSMCs, expressed BMP-2. We generated BMP-2-transgenic mice using ␣SM-actin promoter and crossed them with apoE-deficient mice (BMP-2-transgenic/apoE-knockout).Significantly accelerated atherosclerotic intimal calcification was detected in BMP-2-transgenic/apoE-knockout mice, although serum lipid concentration and atherosclerotic plaque size were not different from those in apoE-knockout mice. Enhanced calcification appeared to be associated with the frequent emergence of osteoblast-like cells in atherosclerotic intima in BMP-2-transgenic/apoE-knockout mice. V ascular calcification has been an important risk factor for cardiovascular diseases as well as all-causal mortality. 1,2 There are several types of vascular calcification, such as calcification in intima associated with atherosclerosis and calcification in tunica media (medial calcification), which is often observed in elderly people and patients with diabetes mellitus and/or chronic kidney disease. 3 Recently, we have reported an important role of senescent vascular smooth muscle cells (VSMCs) in the formation of medial calcification associated with aging. 4 However, the molecular mechanism(s) governing atherosclerotic intimal calcification remains to be elucidated. Atherosclerotic calcification of coronary artery is a significant risk for the unsuccessful coronary intervention and balloon-induced coronary artery dissection. 5 Calcification score of coronary arteries assessed by electron beam computer tomography has been reported to correlate well with the incidence of cardiovascular diseases. 6 Furthermore, calcification was found to be a reliable marker of plaque instability, defined as plaques that have undergone rupture using autopsy specimens. 7 However, there is a controversy around this with arguments describing calcification as a marker of plaque stability as well. Negative correlation between extensive calcification and plaque instability was shown, and the pattern of calcification rather than the vo...

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