Biphasic effect of pioglitazone on isolated human endothelial progenitor cells: involvement of peroxisome proliferator-activated receptor-gamma and transforming growth factor-beta1.

Endothelial progenitor cells (EPCs) have been implicated in vascular repair and found to be functionally impaired in patients with diabetes. We evaluated the effects of the anti-diabetic drug pioglitazone on human EPC function and the involvement of PPAR-gamma and TGF-beta1. EPCs in culture were characterized at day 7 by the development of colony-forming units (CFUs) and flow cytometry assessment of differentiation marker (DiI-ac-LDL/lectin, KDR and CD31). Adhesion on fibronectin and fibrinogen in flow was analyzed as functional parameter. Treatment with pioglitazone for 72 hours increased the number of EPC-CFUs, DiI-ac-LDL(+)/lectin(+), CD31(+) and KDR(+) EPCs at 1 microM but not at 10 microM. Since pioglitazone did not significantly alter proliferation and apoptosis in cultured EPCs, the increase in EPC number was most likely attributable to augmented adhesion and differentiation. Indeed, pioglitazone increased EPC adhesion in flow at 1 microM, an effect prevented by PPAR-gamma and beta2-integrin blockade. In contrast, pioglitazone did not promote EPC adhesion at 10 microM; however, increased adhesion became evident by co-incubation with a blocking TGF-beta1 antibody. As determined by ELISA, pioglitazone induced a persistent increase in TGF-beta1 secretion only at 10 microM when a significantly elevated expression of endoglin, the accessory receptor for TGF-beta1, was also observed. Taken together, pioglitazone exerts biphasic effects on the function of isolated EPCs, causing a PPAR-gamma-dependent stimulation at 1 microM and a TGF-beta1-mediated suppression at 10 microM. These results may help to define optimal therapeutic doses of pioglitazone for improving endothelial dysfunction.