Angiogenic growth factor expression in rat skeletal muscle in response to exercise training

Abstract

Angiogenesis occurs in skeletal muscle in response to exercise training. To gain insight into the regulation of this process, we evaluated the mRNA expression of factors implicated in angiogenesis over the course of a training program. We studied sedentary control (n = 17) rats and both sedentary (n = 18) and exercise-trained (n = 48) rats with bilateral femoral artery ligation. Training consisted of treadmill exercise (4 times/day, 1-24 days). Basal mRNA expression in sedentary control muscle was inversely related to muscle vascularity. Angiogenesis was histologically evident in trained white gastrocnemius muscle by day 12. Training produced initial three- to sixfold increases in VEGF, VEGF receptors (KDR and Flt), the angiopoietin receptor (Tie-2), and endothelial nitric oxide synthase mRNA, which dissipated before the increase in capillarity, and a substantial (30- to 50-fold) but transient upregulation of monocyte chemoattractant protein 1 mRNA. These results emphasize the importance of early events in regulating angiogenesis. However, we observed a sustained elevation of the angiopoietin 2-to-angiopoietin 1 ratio, suggesting continued vascular destabilization. The response to exercise was (in general) tempered in high-oxidative muscles. These findings place importance on cellular events coupled to the onset of angiogenesis.

Multi-scale Computational Models of Pro-angiogenic Treatments in Peripheral Arterial Disease

“…Although the exact relationship has not been experimentally measured, we used experimental data on the dependence of VEGF release on HIF1a and O 2 26,29,48,59 to formulate an empirical relationship between oxygen tension (averaged across the myocyte cross section) and local VEGF release. 32 Non-exercise trained rats do not increase VEGF secretion in response to hypoxia 29,40,47 but exercise-trained rats do, 29,59 and based on experimental data, 26,59 we assume that the maximum hypoxia-induced secretion increase is six times the level of VEGF secretion in normoxia. 24,32 VEGF Transport and VEGF-receptor Binding VEGF released by the myocyte into the interstitial space diffuses and (in the case of VEGF 164 ) can be (2) and NRP1 (N).…”

“…24,31,32 The receptor densities change for exercise-trained rats and mice following ligation. 29,53 The VEGF secretion rate is set so that the non-diseased muscle reaches the measured steady state concentration of VEGF, approximately 1 pM. 24,31,32,36 The above equations are general, and can be used to include additional molecular families that are involved in angiogenesis, for example: PlGF, Neuropilin-2, angiopoietins and Tie receptors, semaphorins and plexins, ephrins and Eph receptors.…”

“…We have previously shown that the model predicts VEGF signaling to be at its strongest during the first week following femoral ligation. 24 We simulate here a time point 7 days after ligation; blood oxygenation has begun to return to normal due to collateralization, and VEGF receptors are upregulated 3.5, 7.2, and 2.1 times control levels 29,53 (VEGFR1, VEGFR2, and Neuropilin, respectively). Although the rat is exercise-trained, the muscle is at rest in this simulation.…”

“…The oxygen-VEGF secretion relationship 24,32 is based on experimental data on the regulation by oxygen of the expression of VEGF via its transcription factor, hypoxia-inducible factor 1a (HIF1a). 26,29,48,59 The complexity of this system-including the interactions of VEGF ligands with their receptors and co-receptors, as well as the development of spatial gradients in an anatomically representative geometry-makes it impossible to achieve a quantitative understanding using experimental methods alone. We build here on our previously constructed models: studying VEGF interactions with VEGF receptors in healthy and ligated rat extensor digitorum longus (EDL) 24,31,32 and in human vastus lateralis muscle, 36 and interactions with Neuropilin-1 (NRP1) and placental growth factor (PlGF) in vitro.…”

“…33,34 The most common animal model of PAD is surgical ligation of the femoral or iliac arteries. 3,29,44,47,51,53 Although this does not completely reproduce the symptoms of PAD, it has become a valuable tool and a useful correlation. Thus, the simulations we present here are for rat EDL muscle following femoral ligation.…”