Effects of PPAR-γ ligands on vascular smooth muscle marker expression in hypertensive and normal arteries

Abstract

Having previously demonstrated that glucose transporter-4 (GLUT4) expression was reduced in aortas and carotid arteries of deoxycorticosterone acetate (DOCA) salt-hypertensive rats, we hypothesized that troglitazone (TG), through activation of peroxisome proliferator-activated receptor-γ (PPAR-γ), would stabilize GLUT4 expression and possibly preserve the differentiated phenotype in vascular smooth muscle cells. In DOCA salt-hypertensive rats treated with TG (100 mg/day), there was a significant ( P < 0.001) decrease in systolic blood pressure (BP; 149.9 ± 4.4 mmHg) compared with the untreated DOCA salt-hypertensive rats (202.2 ± 10.34 mmHg). Separate trials with rosiglitazone (RS; 3 mg/day) demonstrated a significant ( P < 0.001) decrease in BP (DOCA salt, 164.2 ± 9.8 vs. DOCA-RS, 124.9 ± 3.7 mmHg) comparable to that with TG. Expression of GLUT4, h-caldesmon, and smooth muscle myosin heavy chain SM2 was significantly decreased in aortas of DOCA salt-hypertensive rats and was reversed by TG to levels similar to those in aortas of sham-treated rats. TG (50 μM) induced GLUT4 and h-caldesmon expression in 24-h culture of explanted carotid arteries of DOCA salt-hypertensive rats, and the endogenous PPAR-γ ligand 15-deoxy-Δ12–14-prostaglandin J2 (PGJ2; 20 μM) and TG (50 μM) similarly increased GLUT4, h-caldesmon, and SM2 protein expression in explanted aortas. The expression of activated, phosphorylated Akt was increased by PGJ2 and TG with no significant effect on total Akt levels. Inhibition of phosphorylated Akt expression using the phosphatidylinositol 3-kinase inhibitor LY-294002 (16 μM) abrogated the increased expression of h-caldesmon and SM2. These data demonstrate that PPAR-γ agonists maintain or induce expression of markers of the contractile phenotype independently of their effects on hypertension, and that this effect may be mediated through activation of phosphatidylinositol 3-kinase/Akt.