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

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-Δ^12-14-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.