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.