Non-hypoxic stabilization of HIF-Iα during coordinated interaction between Akt and angiopoietin-1 enhances endothelial commitment of bone marrow stem cells

We previously reported that mesenchymal stem cells (MSC) co-expressing Akt and angiopoietin-1 (Ang-1) preserved infarcted heart function via angiomyogenesis. The present study determined the mechanism of co-overexpression of Akt and Ang-1 in promoting endothelial commitment of MSC. The cells were transduced with vectors encoding for Akt ( ^AktMSC), Ang-1 ( ^Ang-1MSC), and both Akt and Ang-1 ( ^AAMSC) using Empty vector transduced MSC ( ^EmpMSC) as control. Molecular studies indicated a coordinated interaction between Akt and Ang-1 in ^AAMSC and led to non-hypoxic stabilization of hypoxia inducible factor-1α (HIF-Iα) which accentuated under 4-h anoxia. We also observed HIF-Iα dependent induction of hemeoxygenase-1, endothelial specific markers and VEGF in ^AAMSC. Vascular commitment of ^AAMSC was confirmed by immunostaining, Western blotting and flow cytometry for endothelial specific early and late markers including Flt1, Flk1, Tie2, VCAM-1, and von Willebrand Factor-VIII (vWF-VIII) in HIF-Iα dependent fashion besides exhibiting higher emigrational activity and angiogenesis in vitro. ^AAMSC transplanted into rat model of myocardial infarction showed higher Flk1 and Flt1 positivity and also promoted intrinsic Flk1 ⁺ and Flt1 ⁺ cell mobilization into the infarcted heart. Given the ease of availability of MSC and simplicity of approach to co-overexpress Ang-1 and Akt to enhance their endothelial commitment, the strategy will be significant for cellular angiogenesis to treat ischemic heart.