Osteopontin Deficiency Attenuates Atherosclerosis in Female Apolipoprotein E–Deficient Mice

Abstract

Objective-Osteopontin (OPN), a noncollagenous adhesive protein, is implicated in atherosclerosis, in which macrophages within atherosclerotic plaques express OPN. However, it is not known whether the elevated OPN expression is a cause or result of atherosclerosis. Methods and Results-We generated mice that lacked OPN and crossed them with apolipoprotein (apo) E-deficient mice and analyzed these mice with a mixed C57BL/6ϫ129 background after 36 weeks on a normal chow diet. In female mice, OP ϩ/Ϫ E Ϫ/Ϫ and OP Ϫ/Ϫ E Ϫ/Ϫ mice had significantly smaller atherosclerotic and inflammatory lesions compared with OP ϩ/ϩ E Ϫ/Ϫ mice, and that was reflected by smaller area of MOMA-2-positive staining. In male mice, however, there was no significant difference in the atherosclerosis lesion areas among 3 genotypes. In both OP Ϫ/Ϫ E Ϫ/Ϫ and OP ϩ/ϩ E Ϫ/Ϫ mice, typical atherosclerotic lesions were detected, which include necrotic core, foamy cell collections, and cholesterol clefts. However, we found that vascular mineral-deposited areas in 60-week-old male OP Ϫ/Ϫ E Ϫ/Ϫ mice were significantly increased compared with those in OP ϩ/ϩ E Ϫ/Ϫ male mice. Key Words: osteopontin Ⅲ atherosclerosis Ⅲ macrophage Ⅲ calcification Ⅲ lipid metabolism A therosclerosis is characterized as a chronic inflammatory process of the vessel wall. Atherosclerosis is initiated by the infiltration of monocytes and T-lymphocytes into activated endothelium, followed by their migration into the intima and subsequent lipid accumulation within macrophages. In late stages of atherosclerosis, calcification is a common advanced complication. Osteopontin (OPN), a noncollagenous adhesive protein, was first found at sites of dystrophic calcification and is synthesized at high levels by macrophages in calcified aortic valves and atherosclerotic plaques. 1 The expression of OPN protein was detected in not only macrophages but also vascular smooth muscle cells within atherosclerotic lesion. [1][2][3][4][5] In addition, it was shown that vascular smooth muscle cells during the proliferative and migratory phase, but not the quiescent and contractile phase, expressed OPN in a model of balloon catheter injury of rat carotid artery. 2 More importantly, Liaw et al 6 reported that neutralizing antibodies directed against OPN inhibited rat carotid neointimal thickening after endothelial denudation. Taken together, these results suggested that OPN can play a pivotal role in the early stage of atherosclerosis, including proliferation and migration of smooth muscle cells as well as at the late stage of atherosclerosis, characterized by calcified atheromatous plaque formation. Conclusions-TheseTo more directly address the question of whether OPN initiates the development of atherosclerotic lesion and plays a role in calcification, we took advantage of OPN-deficient mice we had recently generated. 7 We crossed them with apolipoprotein (apo) E-deficient mice and made OPN and apoE double-deficient mice. In mice deficient for OPN gene expression, OPN mRNA was not detected in any organs. ...

Aldosterone-induced osteopontin gene transcription in vascular smooth muscle cells involves glucocorticoid response element

“…27 In addition, it was reported that in OPN-defective mice, fibrosis and arteriosclerotic changes were attenuated. 28,29 In this study, OPN gene transcription activity was enhanced dose-dependently and timedependently in Aldo-stimulated rVSMCs, which is consistent with reports in other various cell species, such as renal mesangium cells, 19 renal fibroblasts 21 and vascular endothelial cells. 30 As the basal levels of Aldo in the plasma of humans are around 3Â10 À10 M, a significant increase in OPN transcription starting at a concentration of 10 À9 M, as was observed in this in vitro analysis, seems to be within the clinical plasma Aldo fluctuation range.…”

Loss of Matrix Metalloproteinase-9 or Matrix Metalloproteinase-12 Protects Apolipoprotein E–Deficient Mice Against Atherosclerotic Media Destruction but Differentially Affects Plaque Growth

“…In turn, the lower amounts of osteopontin may have adversely affected collagen deposition or reduced plaque growth by decreasing macrophage infiltration. 22 Paradoxically, collagen content was increased in the absence of MMP-9 after mouse carotid ligation. 23 We speculate that these apparently discrepant results may be related to model differences, more specifically to the absence (the former study) or presence (our study) of macrophages, which have been documented to induce SMCs to switch to a synthetic phenotype in an MMP-dependent manner.…”

Angiotensin II-Induced Osteopontin Expression in Vascular Smooth Muscle Cells Involves Gq/11, Ras, ERK, Src and Ets-1

“…In the present study, valsartan attenuated OPN expression and neointimal formation in the balloon-injured rat carotid artery. Accumulating evidence suggest that OPN plays an important role in the development of atherosclerosis (9,11). Importantly, OPN disruption has been shown to attenuate Ang II-accelerated atherosclerosis and aneurysm formation (10).…”

“…Studies have demonstrated that OPN promotes migration, extracellular matrix invasion, and proliferation of VSMC (5,7). Furthermore, OPN transgenic mice show exaggerated atherosclerosis and neointimal formation (8,9), while OPN deficiency attenuates atherosclerosis (10,11). These findings indicate that OPN plays an important role in the development of atherosclerosis and restenosis after coronary intervention.…”