Myocyte vascular endothelial growth factor is required for exercise-induced skeletal muscle angiogenesis

Abstract

We have previously shown, using a Cre-LoxP strategy, that vascular endothelial growth factor (VEGF) is required for the development and maintenance of skeletal muscle capillarity in sedentary adult mice. To determine whether VEGF expression is required for skeletal muscle capillary adaptation to exercise training, gastrocnemius muscle capillarity was measured in myocyte-specific VEGF gene-deleted (mVEGF(-/-)) and wild-type (WT) littermate mice following 6 wk of treadmill running (1 h/day, 5 days/wk) at the same running speed. The effect of training on metabolic enzyme activity levels and whole body running performance was also evaluated in mVEGF(-/-) and WT mice. Posttraining capillary density was significantly increased by 59% (P < 0.05) in the deep muscle region of the gastrocnemius in WT mice but did not change in mVEGF(-/-) mice. Maximal running speed and time to exhaustion during submaximal running increased by 20 and 13% (P < 0.05), respectively, in WT mice after training but were unchanged in mVEGF(-/-) mice. Training led to increases in skeletal muscle citrate synthase (CS) and phosphofructokinase (PFK) activities in both WT and mVEGF(-/-) mice (P < 0.05), whereas β-hydroxyacyl-CoA dehydrogenase (β-HAD) activity was increased only in WT mice. These data demonstrate that skeletal muscle capillary adaptation to physical training does not occur in the absence of myocyte-expressed VEGF. However, skeletal muscle metabolic adaptation to exercise training takes place independent of myocyte VEGF expression.

Figures

Fig. 1.

Basal vascular endothelial growth factor (VEGF) protein and receptor expression in gastrocnemius muscle of exercise-trained VEGF-deficient (mVEGF−/−) and wild-type (WT) mice. VEGF-R1, VEGF receptor 1; VEGF-R2, VEGF receptor 2. Values are means ± SE. *Significantly different compared with WT, P < 0.05.

Fig. 2.

A: representative images showing alkaline phosphatase-stained skeletal muscle sections from the deep gastrocnemius muscle regions of WT and mVEGF−/− mice. Images shown are transverse sections magnified at ×40. B: comparison of capillary-to-fiber ratio, capillary density (no. of capillaries/mm2), and fiber cross-sectional area (FCSA, μm2) in deep and superficial regions of gastrocnemius muscle in sedentary and 6-wk exercise-trained mice. Shaded bars, data from mVEGF−/− mice. Open bars, data from control (WT) mice. Data are means ± SE; n = 5–6 mice/group. P < 0.05, significant difference compared with sedentary mice within same genotype (*) and significantly different compared with WT (†). Data for sedentary mice come from previously published work (48).

Fig. 3.

Comparison of maximal running speed (A) and submaximal endurance exercise capacity (B) in trained mVEGF−/− (n = 8) and WT (n = 7) mice before and after 6 wk aerobic exercise training. Values are means ± SE. *P < 0.05, significantly different compared with before training within the same genotype (*) and significantly different compared with WT, repeated-measures ANOVA (†).

Fig. 4.

Enzyme activities (reported as mmol·kg−1·min−1) for citrate synthase (CS), β-hydroxyacyl-CoA dehydrogenase (HAD), and phosphofructokinase (PFK) in the gastrocnemius muscle of sedentary (untrained) and trained mVEGF−/− and WT littermate mice (n = 4–6/group). Values are means ± SE. Post hoc testing revealing significant difference between mVEGF−/− and WT (*) and significant difference between sedentary and trained within same genotype (†), P <0.05 for all. Data for sedentary mice come from previously published work (48).