Endothelial overexpression of metallothionein prevents diabetes mellitus-induced impairment in ischemia angiogenesis via preservation of HIF-1α/SDF-1/VEGF signaling in endothelial progenitor cells

Diabetes-induced oxidative stress is one of the major contributors to dysfunction of endothelial progenitor cells (EPCs) and impaired endothelial regeneration. Thus, we tested whether increasing antioxidant protein metallothionein (MT) in EPCs promotes angiogenesis in a hind limb ischemia (HLI) model in endothelial MT transgenic (JTMT) mice with high fat diet and streptozocin-induced diabetes. Compared with littermate wild-type (WT) diabetic mice, JTMT diabetic mice had improved blood flow recovery and angiogenesis after HLI. Similarly, transplantation of JTMT bone marrow-derived mononuclear cells (BM-MNCs) stimulated greater blood flow recovery in db/db mice with HLI than did WT BM-MNCs. The improved recovery was associated with augmented EPC mobilization and angiogenic function. Further, cultured EPCs from diabetic patients exhibited decreased MT expression, increased cell apoptosis and impaired tube formation; while cultured JTMT-EPCs had enhanced cell survival, migration, and tube formation in hypoxia/hyperglycemic conditions compared with WT-EPCs. Mechanistically, MT overexpression enhanced hypoxia-inducible factor 1α (HIF-1α), stromal cell-derived factor (SDF-1) and vascular endothelial growth factor (VEGF) expression, and reduced oxidative stress in ischemic tissues. MT’s pro-EPC effects were abrogated by siRNA knockdown of HIF-1α without affecting MT’s anti-oxidant action. These results indicate that endothelial MT overexpression is sufficient to protect against diabetes-induced impairment of angiogenesis by promoting EPC functions most likely through upregulation of HIF-1α/SDF-1/VEGF signaling and reducing oxidative stress.