Vascular smooth muscle cell (VSMC) proliferation and migration are responses to arterial injury that are highly important to the processes of restenosis and atherosclerosis. In the arterial balloon injury model in the rat, platelet-derived growth factor (PDGF) and basic fibroblast growth factor (bFGF) are induced in the vessel wall and regulate these VSMC activities. Novel insulin sensitizing agents, thiazolidinediones, have been demonstrated to inhibit insulin and epidermal growth factor-induced growth of VSMCs. We hypothesized that these agents might also inhibit the effect of PDGF and bFGF on cultured

Angiotensin II (A II ) is a critical factor in cardiac remodeling which involves hypertrophy, fibroblast proliferation, and extracellular matrix production. However, little is known about the mechanism by which A II accelerates these responses. Osteopontin is an acidic phosphoprotein with RGD (arginine-glycine-aspartate) sequences that are involved in the vascular smooth muscle cell remodeling process. We identified the presence of osteopontin mRNA and protein in cultured rat cardiac fibroblasts and its prominent regulation by A II (10 Ϫ 11 M). Osteopontin message levels were increased fourfold ( P Ͻ 0.01) and protein fivefold ( P Ͻ 0.05) at 24 h after addition of A II (10 Ϫ 7 M). This response was inhibited by the AT 1 receptor blocker, losartan. Osteopontin mRNA levels were increased in hypertrophied ventricles from animals with renovascular hypertension (1.6-fold, P Ͻ 0.05) and aortic banding (2.9-fold, P Ͻ 0.05). To examine the function of osteopontin, we determined its effects on ( a ) the ability of cardiac fibroblasts to contract three-dimensional collagen gels and ( b ) cardiac fibroblast growth. A monoclonal antibody against osteopontin partially blocked A II -induced three-dimensional collagen gel contraction by cardiac fibroblasts (64 Ϯ 4 vs. 86 Ϯ 5% in the presence of antibody, P Ͻ 0.05), while osteopontin itself promoted contraction of the gels by fibroblasts (71 Ϯ 5%, P Ͻ 0.05 compared with control). Either a monoclonal antibody against ␤ 3 integrin which is a ligand for osteopontin or the RGD peptide blocked both A II and osteopontin-induced collagen gel contraction. Thus, the osteopontin RGD sequence binds to ␤ 3 integrins on the fibroblast to promote fibroblast binding to collagen. A II induced a threefold increase in DNA synthesis of cardiac fibroblasts, which was completely blocked by antibodies against osteopontin and ␤ 3 integrin, or by RGD peptide, but not by controls. Thus, A II -induced growth of cardiac fibroblasts also requires osteopontin engagement of the ␤ 3 integrin. Taken together, these results provide the first evidence that osteopontin is a potentially important mediator of A II regulation of cardiac fibroblast behavior in the cardiac remodeling process. ( J. Clin. Invest. 1996. 98:2218-2227.)

mice expressed less CD68, C-C-chemokine receptor 2, and VCAM-1. In response to intraperitoneal thioglycollate, recruitment of leukocytes in OPN -/-mice was impaired, and OPN -/-leukocytes exhibited decreased basal and MCP-1-directed migration. Furthermore, macrophage viability in atherosclerotic lesions from Ang II-infused ApoE -/-OPN -/-mice was decreased. Finally, Ang II-induced abdominal aortic aneurysm formation in ApoE -/-OPN -/-mice was reduced and associated with decreased MMP-2 and MMP-9 activity. These data suggest an important role for leukocytederived OPN in mediating Ang II-accelerated atherosclerosis and aneurysm formation.

Background-This study is the first to examine the effect of direct angiotensin II type 2 (AT 2 ) receptor stimulation on postinfarct cardiac function with the use of the novel nonpeptide AT 2 receptor agonist compound 21 (C21). Methods and Results-Myocardial infarction (MI) was induced in Wistar rats by permanent ligation of the left coronary artery. Treatment with C21 (0.01, 0.03, 0.3 mg/kg per day IP) was started 24 hours after MI and was continued until euthanasia (7 days after MI). Infarct size was assessed by magnetic resonance imaging, and hemodynamic measurements were performed via transthoracic Doppler echocardiography and intracardiac Millar catheter. Cardiac tissues were analyzed for inflammation and apoptosis markers with immunoblotting and real-time reverse transcription polymerase chain reaction. C21 significantly improved systolic and diastolic ventricular function. Scar size was smallest in the C21-treated rats. In regard to underlying mechanisms, C21 diminished MI-induced Fas-ligand and caspase-3 expression in the peri-infarct zone, indicating an antiapoptotic effect. Phosphorylation of the p44/42 and p38 mitogen-activated protein kinases, both involved in the regulation of cell survival, was strongly reduced after MI but almost completely rescued by C21 treatment. Furthermore, C21 decreased MI-induced serum monocyte chemoattractant protein-1 and myeloperoxidase as well as cardiac interleukin-6, interleukin-1␤, and interleukin-2 expression, suggesting an antiinflammatory effect. Conclusions-Direct

The present study provides the first evidence that cardiomyocytes are a prominent source of OP in vivo and suggests that induction of OP expression is strongly associated with ventricular hypertrophy.