Abstract 1624: Exercise Training Stimulates Neovascularization in Response to Ischemia via HIF-1α -VEGF-mediated Activation of MMP-2 in Advanced Age
Background: Exercise training (ET) represents a valid toll to stimulate vascular response in physiological and pathological conditions. However, the molecular mechanisms by which ET improves impairment of hypoxia-induced factor (HIF)-1α -mediated hypoxia response associated with ageing are poorly understood. Here, we investigated whether ET modulates the vascular response to ischemia in advanced age by employing a murine hindlimb ischemia model.
Methods and Results: Aged wild-type mice (2 years) that maintained ET (swimming 1 hour/d) from day 1 after surgery were randomly assigned to four groups that were treated with either vehicle (ET), LY294002 (an inhibitor of PI3 kinase; ET-LY), or deferoxamine (an inhibitor of HIF-1α destabilization; ET-DPO) for 15 days. Mice maintained sedentary served as controls (ET (−)). Laser Doppler blood flow and capillary density analyses revealed that revascularization of the ischemic hindlimb relative to the contralateral limb was accelerated in ET compared with ET (−) mice, and these effects were diminished in ET-LY mice. At day 7, the levels of MMP-2, VEGF, Fit-1 mRNAs, insulin-like growth factor-1 (IGF-1), and p-Akt as well as HIF-1α proteins were greater, whereas the levels of prolyl-4-hydroxylase domain-2 and factors inhibiting HIF-1α proteins were smaller in ET mice than in ET (−) mice, and these diminished levels were also seen in ET-LY mice. ET promoted collateral arteriogenesis and reduced hemangioma and microaneurysms; LY treatment attenuated these effects. Furthermore, ET improved circulating EPC numbers, the expression of MMP-2 and HIF-1α, and EPC cellular functions, and these effects were attenuated by LY treatment. Interestingly, these effects of ET were enhanced in ET-DPO mice and impaired in aged MMP-2-deficiency mice. Finally, bone-marrow transplantation confirmed ET enhanced EPCs homing to the sites of ischemia in advanced age. siHIF-1α as well as siVEGF reduced MMP expression and impaired human umbilical vein endothelial cell migration.
Conclusions: Our observations indicate that ET can improve the age-dependent impairment of neovascularization in response to tissue ischemia via an IGF1-PI3K-Akt-dependent mechanism that is mediated by the HIF-1α -VEGF-MMP-2 pathway.