Thiazolidinediones inhibit proliferation of microvascular and macrovascular cells by a PPARγ-independent mechanism

Aims/hypothesis: This study evaluated the hypothesis that peroxisome proliferator-activated receptor-gamma (PPAR gamma) agonists, including thiazolidinediones (TZDs) and the rexinoid LG100268 (LG), directly affect human vascular cell function (proliferation, cell cycle, protein expression, lactate release) independently of (1) their PPAR gamma-activating potential and (2) the cells' vascular origin. Methods: Human umbilical vein endothelial cells (HUVECs), human adult vein endothelial cells (HAVECs), human retinal endothelial cells (HRECs) and human retinal pericytes (HRPYCs) were incubated (48 h) with 2-50 mu mol/l rosiglitazone (RSG), RWJ241947 (RWJ), pioglitazone (PIO), troglitazone (TRO), 15-deoxy-Delta(12,14)-prostaglandin J(2) (PGJ(2)) and LG. Proliferation, cell cycle distribution, protein expression, peroxisome proliferator-activated receptor responsive element (PPRE) transcriptional activity and mitochondrial effects were determined by [H-3]thymidine incorporation, FACS analyses, western blots, reporter assays and lactate release respectively. Results: In HUVECs, RSG, RWJ, PIO, TRO, PGJ(2) and LG reduced (p < 0.01) proliferation (due to a G(0)/G(1) cell cycle arrest) by up to 23%, 36%, 38%, 86%, 99% and 93% respectively. The antiproliferative response was similar in HRPYCs and HAVECs, but was attenuated in HRECs. Whereas p21(WAF-1/Cip1) and p27(Kip) were differently affected in HUVECs, all agents reduced (p < 0.05) expression of cyclins (D3, A, E, B), cyclin-dependent kinase-2 and hyperphosphorylated retinoblastoma protein. The rank order of the antiproliferative effects of TZDs in HUVECs (RSG approximate to PIO approximate to RWJ < TRO) contrasted their PPRE transcriptional activities (TRO < PIO < RSG < RWJ), but correlated with cellular lactate release. Proliferation inhibition and lactate release were mimicked by rotenone (mitochondrial complex I inhibitor). Conclusions/interpretation: In conclusion, this study suggests that the antiproliferative action of the TZDs in vascular cells is independent of their PPAR gamma-activating and associated insulin-sensitising potential, but could relate to mitochondrial mechanisms.