The Role of The Thrombospondins In Intimal Hyperplasia

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Restenosis secondary to intimal hyperplasia (IH) after balloon angioplasty to treat arterial blockages in peripheral arteries is a significant cause of disability and death. The thrombospondins (TSPs) are multifunctional matricellular proteins central to the development of intimal hyperplasia. They are not part of the arterial wall structure, but exert their physiologic effects on arterial structure by binding cytokines, cell-surface receptors, proteases and other proteins. This proposal focuses on three TSPs integral to the development of intimal hyperplasia – TSP-1, TSP-2 and TSP-5. We have studied the effects of TSP-1 on vascular smooth muscle cell (VSMC) proliferation and migration and its importance in the development of intimal hyperplasia; however, increasing evidence exists that TSP-2 and TSP-5 have separate and contributory roles in this pathology. All three TSPs are substrates of ADAMTS (A Disintegrin And Metalloproteinase with Thrombospondin Motifs) proteins. ADAMTSs digest TSPs, enhancing or inhibiting TSP function, since the fragments left after digestion have distinct effects themselves on intimal hyperplasia. Therefore, ADAMTS-1,-4, and-7 will also be studied as they are involved in PAD and were also identified to be regulated by TSPs in our prior VSMC gene study. Our long-term goal is to understand how TSPs can be manipulated therapeutically to prevent intimal hyperplasia in vivo. The objective of this proposal is to determine how TSP-1, TSP-2 and TSP-5 specifically contribute to the development of intimal hyperplasia. Our central hypothesis is that the expression, bioavailability, signaling pathways and changes in gene expression induced by TSP-1, TSP-2 and TSP-5 and their interactions with ADAMTSs have distinct effects on regulating the development of IH. This hypothesis was formulated on the basis of our strong preliminary data, our publications and the literature. The rationale for the proposed project is that understanding the roles of TSPs on intimal hyperplasia will result in identification of therapeutic targets to inhibit intimal hyperplasia and restenosis after balloon angioplasty. Our hypothesis will be tested by pursuing the following Specific Aims: 1) determine the role that TSP-1, TSP-2 and TSP-5 each have on intimal hyperplasia; 2) determine the differential effects of TSP-1, TSP-2 and TSP-5 on protein and microRNA expression (i.e., miR-17~92 cluster), and their downstream effects on VSMC function; and 3) establish the role of ADAMTSs in TSP-1, TSP-2 and TSP-5 activity and in the development of intimal hyperplasia. The methodologies utilized to investigate these Specific Aims include: 1) modified Boyden chamber to assess chemotaxis and colorimetric assay to assess for proliferation in VSMCs; 2) western blot, ELISA and immunoPCR for cell signaling and protein expression; 3) quantitative real time polymerase chain reaction for gene expression; 4) two animal models of intimal hyperplasia – common carotid artery balloon injury in rats and ligation in mice; 5) use of knockout mice and siRNA for knockdown of TSP and ADAMTS genes in vitro and in vivo to see effects on VSMCs and intimal hyperplasia, respectively; and 6) morphometric analysis, western blot and immunohistochemical staining for analysis of arterial specimens. The siRNA work will also involve testing our novel siRNAs directed at TSP/ADAMTS combinations that may prove to be a highly effective method of blocking intimal hyperplasia at the time of angioplasty. The significance of the proposed research is that the findings will provide a major advance toward identifying new strategies for preventing restenosis due to intimal hyperplasia. The proposed research in this application is innovative, in our opinion, because the findings will define the interactions of multiple TSPs and peptidases with TSP motifs (ADAMTSs) in vascular disease and mechanisms through which these systems can be manipulated with novel siRNAs to improve clinical outcomes. The findings from this application will advance efforts to improve quality of life and longevity by providing safer and more effective therapeutic options for patients with peripheral arterial disease.