The objective of this application is to identify whether mobilization and activation of cardiac primitive cells by the local administration of growth factors, HGF and IGF-1, results in homing of these cells to damaged regions of the heart induced by aging alone or aging and myocardial infarction together. The translocated cells are expected to promote myocardial regeneration and to reinstitute function. The intervention with growth factors will be compared with the local injection of cardiac clonogenic cells expanded in vitro to determine the form of cellular therapy that has superior beneficial effects on the heart. The hypothesis is raised that the HGF-c-Met and the IGF-1-IGF-1R system are upregulated in the migrated cells by the local delivery of HGF and IGF-1. This response may lead to cell invasion of the dead myocardium and, ultimately, to cardiac repair. The direct implantation of a large number of clonogenic cells, in the absence of growth factors, is assumed to trigger a similar phenomenon through the activation of HGF-c-Met and IGF-1-IGF-1R via autocrine mechanisms present in these high quantities of engrafted undifferentiated cells. Paracrine and autocrine pathways may both be operative following growth factor treatment. It is postulated that faced with acute damage, the c-Met-positive mobilized and implanted cells express alpha-v-beta-3 and alpha-6-beta-4 integrin receptors, which interact with c-Met and the extracellular compartment, facilitating cell locomotion throughout the areas of injury in the aged and aged infarcted heart. This process is regulated by the release of plasmatic fibrinogen/fibrin and plasmatic fibronectin within the early dying tissue. Integrin clustering phosphorylate focal adhesion kinase which, in turn, phosphorylates paxillin and p130(CAS) enhancing cell migration by modifying the polymerization of the actin cytoskeleton. Myocardial regeneration is then initiated and newly formed myocytes may function as 'non-professional phagocytes, removing dead cells and debris. This cleaning operation attenuates inflammation, macrophage infiltration and fibroblast accumulation. In chronic scarred myocardial damage, alpha-4-beta-1, alpha-2-beta-1and alpha-6-beta-4 integrin receptors are upregulated in primitive cells and this molecular change favors their interaction with collagen and cellular fibronectin. The HGF-c-Met system promotes the synthesis of collagenases and, thereby, the translocation of primitive cells. Collagen is degraded and cardiac repair occurs. To validate the primary role of c-Met, integrin receptors and the molecular components required for myocytes to operate as """"""""non-professional"""""""" phagocytes, adenoviral-associated vectors carrying dominant negative mutated proteins will be employed. If the approach discussed here will be successful, the molecular control of myocardial regeneration in the aged and aged-infarcted heart will be, at least in part, identified. The results to be obtained could have important clinical implications for a novel treatment of the old failing heart.
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