Angiotensin II Induction of Osteopontin Expression and DNA Replication in Rat Arteries

Abstract

We recently identified the adhesive protein osteopontin as a novel smooth muscle cell product overexpressed in rat developing neointima and human atheroma. Although osteopontin is a candidate stimulant for intimal lesion progression because of its chemotactic and calcium binding functions, factors controlling osteopontin expression in arteries remain poorly defined. In vitro, smooth muscle cell expression of osteopontin is associated with cell cycle transit or alterations in cell phenotype, and it is increased by angiotensin II (Ang II) stimulation. In the present studies, we investigated both osteopontin expression and DNA replication in the arterial wall in response to chronic Ang II infusion in vivo. Rat carotid arteries with or without intimal thickening (induced by balloon catheterization) were examined. Ang II (250 ng/kg per minute) or vehicle was coinfused with bromodeoxyuridine (to label replicating DNA in vivo) for 2 weeks beginning 4 weeks after injury. With Ang II, smooth muscle cells overexpressed osteopontin as shown by protein immunohistochemistry, in situ hybridization, and Northern blot analyses. Osteopontin mRNA levels were increased markedly (approximately fivefold) in the normal artery media and injured artery neointima, but levels remained low in the injured artery media, in positive correlation (R2 = 0.88, P < .001) with DNA replication in the smooth muscle layers, further suggesting that osteopontin may be a growth-associated, phenotype-dependent gene for smooth muscle cells. However, osteopontin expression in neointima was not restricted to areas showing DNA replication, suggesting a nonobligatory association. Ang II induced severe hypertension. Arterial osteopontin expression was increased also by chronic catecholamine infusion, a model of vascular growth stimulation showing labile pressure elevations. Osteopontin induction in smooth muscle cells may contribute to Ang II-dependent intimal lesion progression and vascular remodeling events associated with renovascular diseases or hyperadrenergic disorders.

Angiotensin II–accelerated atherosclerosis and aneurysm formation is attenuated in osteopontin-deficient mice

“…OPN expression is low in the normal arterial wall, and chronic Ang II infusion has been shown to induce arterial OPN expression in rat carotid arteries (21). Real-time RT-PCR from RNA samples obtained from the thoracic aorta 2 weeks after Ang II infusion confirmed that littermate wild-type control mice had low basal OPN levels.…”

“…Ang II functions as a potent proinflammatory stimulus and upregulates the expression of many redox-sensitive cytokines, chemokines, and growth factors involved in the pathogenesis of atherosclerosis, including OPN (21). The expression of OPN is also induced by high glucose, and OPN is highly expressed in atherosclerotic lesions of diabetic patients, suggesting that OPN may be involved in the pathogenesis of diabetic vascular complications and the accelerated atherosclerosis seen in diabetes (7,8).…”

“…Ang II profoundly induces OPN expression in the arterial wall (21). Activation of the renin-angiotensin system (RAS) is a common feature in patients with the metabolic syndrome and type 2 diabetes, who have a fourfold higher risk for the development of atherosclerosis (22)(23)(24).…”

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

“…, Hidekatsu NAKASHIMA 3) , Mari ISHIDA 2) , Narimasa MIHO 1) , Mariko SAWANO 2) , Nwe Nwe SOE 2) , Masahiko KURABAYASHI 4) , Kazuaki CHAYAMA 1) , Masao YOSHIZUMI 2) , and Takafumi ISHIDA 1) Introduction Osteopontin (OPN) is an acidic, secreted glycoprotein that binds to αvβ3 and other integrins via its arginine-glycineaspartate (RGD) motif (1). It is produced by osteoblasts, macrophages, vascular smooth muscle cells (VSMC) and T cells in response to biological stimuli (e.g., growth factors, glucose, and mechanical stimuli) and plays various roles in bone morphogenesis, cell transformation, immune cell activation, and bacterial resistance (1)(2)(3).…”

“…It is produced by osteoblasts, macrophages, vascular smooth muscle cells (VSMC) and T cells in response to biological stimuli (e.g., growth factors, glucose, and mechanical stimuli) and plays various roles in bone morphogenesis, cell transformation, immune cell activation, and bacterial resistance (1)(2)(3). OPN is not typically present in normal blood vessels, but its expression is increased in human atherosclerotic plaques, neointima after experimental angioplasty, and transplant arteriosclerosis (4)(5)(6).…”