Thymosin β4 Activates Integrin-Linked Kinase and Decreases Endothelial Progenitor Cells Apoptosis Under Serum Deprivation

Thymosin beta 4 (T beta 4) has been suggested to regulate multiple cell signal pathways and a variety of cellular functions such as cell migration, proliferation, survival, and angiogenesis. Here, we investigated the effect of Tb4 on endothelial progenitor cells (EPCs) apoptosis induced by serum deprivation and the corresponding signal transduction pathways involved in this process. Circulating EPCs, isolated from healthy volunteers, were cultured in the absence or presence of Tb4 and various signal cascade inhibitors. Apoptosis was evaluated with Annexin V immunostaining and cytosolic cytochrome c expression. Incubation of EPCs with Tb4 caused a concentration dependent increase in cell viability and proliferation activity. It also caused an inhibitory effect on EPCs apoptosis, which was abolished by PI3K inhibitors (either LY294002 or Wortmannin) or JNK MAPK inhibitor SP600125. In addition, the expression and activity of caspase-3 and -9 were decreased by Tb4, which markedly increased the Bcl-2/Bax ratio within EPCs. Furthermore, Tb4 was immunoprecipitated with integrin-linked kinase (ILK), accompanied by augmentation of ILK activity. Transfection of EPCs with ILK-siRNA resulted in abolishment of the activation of ILK-Akt and the ameliorative effect on apoptosis by Tb4. Together, Tb4 mediated inhibitory effect on EPCs apoptosis under serum deprivation can be attributed, at least in part, to ILK-Akt activation. The activation of JNK MAP Kmight also be involved in this process. J. Cell. Physiol. 226: 2798-2806, 2011. (C) 2010 Wiley-Liss, Inc.