Murine double minute-2 expression is required for capillary maintenance and exercise-induced angiogenesis in skeletal muscle.

Exercise-induced angiogenesis is a key determinant of skeletal muscle function. Here, we investigated whether the E3 ubiquitin ligase murine double minute-2 (Mdm2) exerts a proangiogenic function in exercised skeletal muscle. Mdm2 hypomorphic (Mdm2(Puro/Δ7-9)) mice have a 60% reduction in Mdm2 expression compared with that in wild-type animals. Capillary staining on muscle sections from Mdm2(Puro/Δ7-9) sedentary mice with a wild-type or knockout background for p53 revealed that deficiency in Mdm2 resulted in 20% capillary regression independently of p53 status. In response to one bout of exercise, protein expression of the proangiogenic vascular endothelial growth factor-A (VEGF-A) was increased by 64% in muscle from wild-type animals, and endothelial cell outgrowth from exercised muscle biopsy samples cultured in a 3-dimensional collagen gel was enhanced by 37%. These proangiogenic responses to exercise were impaired in exercised Mdm2(Puro/Δ7-9) mice. Prolonged exercise training resulted in increased Mdm2 protein expression (+49%) and capillarization (+24%) in wild-type muscles. However, exercise training-induced angiogenesis was abolished in Mdm2(Puro/Δ7-9) mice. Finally, exercise training restored Mdm2, VEGF-A, and capillarization levels in skeletal muscles from obese Zucker diabetic fatty rats compared with those in healthy animals. Our results define Mdm2 as a crucial regulator of capillary maintenance and exercise-induced angiogenesis in skeletal muscle.