The extracellular matrix is important in embryogenesis and in tissue repair. From in vitro studies using purified components, a better understanding of how cells adhere, migrate, proliferate, and differentiate in response to tissue and cell- specific matrix molecules has been established. We have found that the basement membrane, the extracellular matrix which underlies all epithelial cells and endothelial cells and surrounds nerve cells, promotes cell differentiation in vitro. When cultured on basement membrane, endothelial cells form capillary-like structures with a lumen, chondrocytes form cartilage, salivary cells form glands, etc. Our goal is to define the molecular and cellular events involved in this process. Our approach has been (1) to identify the biologically active matrix components, with respect to cell adhesion, migration, proliferation, and differentiation, (2) localize active sites on the matrix component with synthetic peptides, (3) identify and characterize cellular receptors, (4) gain an understanding of the intracellular events involved in the biological response, and (5) identify genes induced by the extracellular matrix. We work in several in vitro model systems including primary and established breast and melanoma tumor cells, endothelial cells, and salivary glands and cells. We have used the endothelial cell tube assays in vitro and in vivo angiogenesis assays to define molecules which regulate vessel formation in development, repair, and disease. Our goal is to discover new angiogenic regulators that have physiological and clinical relevance. We have worked with the basement membrane protein laminin and identified active sites and cellular receptors for cell adhesion and angiogenesis. Some of these active peptides are being developed into slow release scaffolds for further in vivo testing for wound healing in the skin and in the oral cavity. We have also focused on a gene, thymosin beta 4, that is induced by endothelial cells as they differentiate into capillary-like structures on a basement membrane substratum. We find that thymosin beta 4 promotes dermal wound repair via increased angiogenesis and keratinocyte cell migration. It promotes wound repair in normal animals as well as in animals with delayed wound healing, including diabetic and aged animals. Thymosin beta 4 also promotes hair growth in aged animals and in animals treated with cyclophosphamide, which is a model for chemotherapy-induced hair loss. Hair growth is also stimulated in athymic nude mice which lack abundant hair shafts. We have identified the active site on this protein to a seven amino acid actin binding domain. The cellular receptor may be surface actin. We now have created a transgenic mouse which over-expresses this protein in its skin. The mouse appears to have accelerated wound healing and hair regrowth after shaving. Unexpectedly, the transgenic mouse also has abnormal tooth development which we are currently investigating. This protein is currently in phase 2 human clinical trials for wound healing for diabetic and aged patients. Our goal is to understand how the extracellular matrix regulates tissue formation, repair, and certain pathological processes. We also hope to develop novel therapeutics for dermal and oral wound healing.
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