Abstract 149: Endothelial-specific Overexpression of Metallothionein Prevents Diabetes Mellitus-induced Impairment in Ischemia Angiogenesis via Preservation of Hif-1á/sdf-1 in Endothelial Progenitor Cells

Diabetes mellitus associated dysfunction of endothelial progenitor cells (EPCs) may contribute to dysregulation of endothelial regeneration. Whether oxidative protection of EPCs by an antioxidant, such as the protein metallothionein (MT) can have positive angiogenic effects and by what mechanisms remain unclear. Endothelial-specific MT overexpression (JTMT) mice were made diabetic by high fat diet followed by streptozocin administration (HFD/STZ). Diabetic hind limb ischemia (HLI) was established by femoral artery ligation. Bone marrow mononuclear cells (MNCs) collected from JTMT mice were transplanted into db/db mice with HLI. Blood reperfusion was monitored. High glucose and hypoxia conditions in culture were adopted to mimic diabetic ischemia. Compared with wild-type (WT) littermates, JTMT mice were resistant to diabetes-induced impairment in ischemia angiogenesis and blood reperfusion in HFD/STZ diabetes. Similarly, transplantation of MT overexpressing MNCs showed better therapeutic effect on db/db mice with HLI than transplantation of WT MNCs. These changes were accompanied by increased mobilization and infiltration of EPCs in JTMT mice, and enhanced incorporation of EPCs into capillaries in JTMT MNCs transplanted db/db mice. Furthermore, EPCs from JTMT mice exhibited augmented cell survival, tube formation, and migration capacities under diabetic ischemia-like conditions. Mechanistically, the expression of hypoxia-inducible factor 1α (HIF-1α) and the secretion of stromal cell-derived factor (SDF-1) in blood and expression in ischemic tissues were upregulated in JTMT and JTMT-MNC transplanted db/db mice, and in cultured JTMT EPCs, which were accompanied by marked amelioration of oxidative stress. However, MT-mediated elevation of SDF-1 and improvements of function in EPCs were all abrogated by siRNA knockdown of HIF-1α expression without effect on the anti-oxidative capacity of MT. Endothelial-specific MT elevation is sufficient to protect against diabetes mellitus-induced impairment of ischemia angiogenesis by promoting EPC function. The benefits of MT are predominantly mediated by upregulation of the HIF-1α/SDF-1 pathway.