Oxidative Stress–Mediated Thrombospondin-2 Upregulation Impairs Bone Marrow–Derived Angiogenic Cell Function in Diabetes Mellitus

Abstract

Objective— Circulating angiogenic cells play an essential role in angiogenesis but are dysfunctional in diabetes mellitus characterized by excessive oxidative stress. We hypothesize that oxidative stress–mediated upregulation of thrombospondin-2 (TSP-2), a potent antiangiogenic protein, contributes to diabetic bone marrow–derived angiogenic cell (BMAC) dysfunction. Approach and Results— BMACs were isolated from adult male type 2 diabetic db/db mice and control db/+ (C57BLKS/J) mice. In Matrigel tube formation assay, angiogenic function was impaired in diabetic BMACs, accompanied by increased oxidative stress and nicotinamide adenine dinucleotide phosphate oxidase activity. BMAC angiogenic function was restored by overexpression of dominant negative Rac1 or by overexpression of manganese superoxide dismutase. TSP-2 mRNA and protein were both significantly upregulated in diabetic BMACs, mediated by increased oxidative stress as shown by a decrease in TSP-2 level after overexpression of dominant negative Rac1 or manganese superoxide dismutase. Silencing TSP-2 by its small interfering RNA in diabetic BMACs improved BMAC function in tube formation, adhesion, and migration assays. Notably, the upregulation of TSP-2 was also found in BMACs from streptozotocin-induced type 1 diabetic mice, and normal BMACs with high glucose treatment. let-7f, a microRNA which has been related to endothelial angiogenic function, is found to play key role in TSP-2 increase, but let-7f did not directly interact with TSP-2 mRNA. Conclusions— The upregulation of TSP-2 mediated by increased oxidative stress contributes to angiogenesis dysfunction in diabetic BMACs.