Placenta growth factor is not required for exercise-induced angiogenesis

Angiogenesis is a tightly regulated process, both during development and adult life. Animal models with mutations in the genes coding for placental growth factor (PlGF), a member of vascular endothelial growth factor (VEGF) family, or the tyrosine kinase domain of the PlGF receptor (Flt-1) have revealed differences between normal physiological angiogenesis and pathological angiogenesis associated with conditions such as tumor growth, arthritis and atherosclerosis. In the present paper, we investigated the potential role of PlGF in regulating physiological angiogenesis by analyzing vascular changes in heart and skeletal muscles of wild-type and Plgf-/- mice following prolonged and sustained physical training. Sedentary Plgf-/- mice showed a reduced capillary density in both heart and skeletal muscles as compared to wild-type mice (P < 0.05). However, after a 6-week training period, heart/body weight ratio, citrate synthase activity, vessel density and capillary/myocyte ratio were significantly increased in both wild-type and Plgf-/- mice (all P < 0.05). At the same time intercapillary distance was significantly reduced. Finally, acute exercise was not associated with any change in PlGF protein level in the skeletal muscle. Our results demonstrate that PlGF is not necessary for exercise-training-induced angiogenesis. We thus suggest that the role of PlGF is confined to the selective regulation of angiogenesis only under pathological conditions.