Wound healing is impaired in aging with consequent delay in closure and increased risk for dehiscence and infection. This age-associated impairment in wound repair is due, in part, to delayed neovascularization. The successful growth of new blood vessels requires coordinated cellular functions including migration, proliferation, and biosynthesis/breakdown of matrix proteins. Although each of these processes may be impaired in aging, our preliminary data show that decreased migration of microvascular endothelial cells contributes to delayed angiogenesis. The long-term objective of this proposal is to define the mechanism(s) of impaired migration in aged endothelial cells, and thus, identify potential sites for interventions to improve wound healing in aging. In vitro, migration of aged human microvascular endothelial cells (hmEC) is slowed on collagen I, the major extracellular matrix (ECM) protein present during the angiogenic phase of wound repair. Optimal migration of cells requires the dynamic breaking and forming of cell-matrix contacts. Thus, movement is regulated by matrix degrading proteases (such as interstitial collagenase- matrix metalloprotease I, MMP1), integrins (such as alpha2beta1, which induces MMP1 upon binding to collagen I), and their interaction with the ECM. Aged hmEC express less MMP1 and secrete increased amounts of tissue inhibitor of metalloprotease 1 (TIMP1) relative to young hmEC. Moreover, in vivo, delayed neovascularization of polyvinyl alcohol sponges in aged mice is associated with decreased MMP1 and increased TIMP1 expression. Stimulation of aged hmEC with vascular endothelial growth factor (VEGF) increases their movement, an effect which may result from induction of MMP1. The hypothesis of this application is that aged hmEC have impaired migration due to decreased synthesis of MMP1. We propose that alpha2beta1-collagen I binding does not properly function to induce MMP1 synthesis which is necessary for selective detachment during migration. Moreover, as MMP1 is required to generate ligation sites for alpha2beta1, selective attachment cannot occur in a coordinated fashion. Using young hmEC and young mice as controls, the following Specific Aims are proposed: 1. Elucidate the role of MMP1/TIMP1 in the impaired migration of aged hmEC on collagen I. 2. Define the expression and function of alpha2beta1, and its interaction with MMP1, in impaired attachment and migration of aged hmEC. 3. Identify the mechanism by which VEGF enhances the migration of aged hmEC. 4. Determine the effects of age and VEGF on: expression and function of MMP1/TIMP1 and alpha2beta1, and the migration of microvascular EC during angiogenesis in vivo.
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