Background Exercise stimulates the vascular response in pathological conditions, including ischemia; however, the molecular mechanisms by which exercise improves the impaired hypoxia-induced factor (HIF)-1α–mediated response to hypoxia associated with aging are poorly understood. Here, we report that swimming training (ST) modulates the vascular response to ischemia in aged (24-month-old) mice. Methods and Results Aged wild-type mice (MMP-2+/+) that maintained ST (swimming 1 h/d) from day 1 after surgery were randomly assigned to 4 groups that were treated with either vehicle, LY294002, or deferoxamine for 14 days. Mice that were maintained in a sedentary condition served as controls. ST increased blood flow, capillary density, and levels of p-Akt, HIF-1α, vascular endothelial growth factor, Fit-1, and matrix metalloproteinase-2 (MMP-2) in MMP-2+/+ mice. ST also increased the numbers of circulating endothelial progenitor cells and their function associated with activation of HIF-1α. All of these effects were diminished by LY294002, an inhibitor of phosphatidylinositol 3-kinase; enhanced by deferoxamine, an HIF-1α stabilizer; and impaired by knockout of MMP-2. Finally, bone marrow transplantation confirmed that ST enhanced endothelial progenitor cell homing to ischemic sites in aged mice. Conclusions ST can improve neovascularization in response to hypoxia via a phosphatidylinositol 3-kinase–dependent mechanism that is mediated by the HIF-1α/vascular endothelial growth factor/MMP-2 pathway in advanced age.

Smooth muscle cell (SMC) migration from the tunica media to the intima, a key event in neointimal formation, requires proteolytic degradation of elastin-rich extracellular matrix barriers. Although cathepsin S (Cat S) is overexpressed in atherosclerotic and neointimal lesions, its exact role in SMC behavior remains primarily unresolved. We examined the involvement of Cat S on SMC migration through an extracellular matrix barrier and its localization in SMCs. A selective Cat S inhibitor and the endogenous inhibitor cystatin C significantly attenuated SMC invasion across elastin gel. Western blotting and cell surface biotinylation analysis demonstrated localization of the 28-kd active form of Cat S on the SMC surface, consistent with its role in the proteolysis of subcellular matrices. Treatment with interferon-gamma or interleukin-beta1 significantly augmented the ability of SMC membranes to degrade elastin along with a significant increase in the level of active Cat S compared with controls. Immunofluorescence and confocal microscopy showed a punctuated pattern of Cat S clusters at the periphery of SMCs; further studies demonstrated partial co-localization of Cat S and integrin alphanubeta3 at the cell surfaces. These findings demonstrate that active Cat S co-localizes with integrin alphanubeta3 as a receptor on the SMC surface, playing an important role in the invasive behavior of SMCs.

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Objective-Although we recently showed that the administration of catechins reduced the neointimal formation in a rat balloon-injury model, the precise molecular mechanisms are largely unknown. In the present study, we tried to determine these mechanisms using an in vitro SMC invasion system. Methods and Results-Boyden chamber assay was used to examine the effect of catechins on the invasive behavior of SMCs. The invasive activity of SMCs through collagen gel was restrained by EGCG in a concentration-dependent manner. The data from gelatin and collagen zymography and Western blot revealed that EGCG blocks the activation of pro-matrix metalloproteinase (MMP)-2 during an invasion assay and in the conditioned medium of cultured SMCs as well as the activities of MMP-2 and membrane type 1-MMP (MT1-MMP) even at 0.1 to 0.3 mol/L of EGCG. EGCG was found to restrain MT1-MMP cat -dependent pro-MMP-2 activation. EGCG upregulated the expression of tissue inhibitor of MMP-2 (TIMP-2) protein. Reverse zymography showed that the increased TIMP-2 to expression was validated by an increased activity. The data from decreased TIMP-2 activity using its siRNA suggested that upregulation of TIMP-2 expression may be one of the major mechanisms for inhibition of SMC invasion by EGCG. Conclusions-These results indicate that EGCG targets multiple MMP-mediated SMC cellular events and provides a new major mechanism for the SMC invasion through upregulation of TIMP-2 expression to modulate MMP activity.

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