Mechanisms of Aortic Fibrosis

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The activation, migration, proliferation and abundant matrix synthesis by the normally quiescent medial vascular smooth muscle cell (VSMC) are central events in the development of atherosclerotic lesions. Our recent findings have revealed that lysyl oxidase (LO), the extracellular enzyme which oxidizes peptidyl lysine to initiate the covalent crosslinking and insolubilization of soluble forms of elastin and collagen, plays previously unexpected roles strongly influencing the behavior of VSMC. We have found that LO is strongly chemotactic for VSMC and that it binds to a surface receptor of these cells indicated by our preliminary results to contain a beta1 integrin subunit. Following binding to the VSMC surface, LO enters the cell and then concentrates within the cell nucleus. We have also found that histone H1 is oxidized within VSMC nuclei by endogenous LO. These events are accompanied by increased production of collagen and phosphorylation of intracellular signaling proteins. Our guiding hypothesis is that LO may serve as an important activator of VSMC functions, acting both as an extracellular and intracellular signal stimulating phenotypic changes in the VSMC as in arterial disease. Specific Aims of this project are: (1) Elucidate the mechanism and significance of LO binding to plasma membrane receptors. We will identity the VSMC membrane proteins acting as holoreceptor(s) of LO and assess their roles in the responses of VSMC to LO binding, uptake, and activation of signal transduction pathways. (2) Elucidate the nature of the nuclear modifications catalyzed by LO and the potential consequences on gene expression. We will identify nuclear proteins which can be oxidized by nuclear LO and assess for the effect of LO on the transcription of specific collagen genes of VSMC. (3) Characterize the expression, intraeellular and extracellular localization and abundance of LO in VSMC in response to vascular injury. Immunocytochemistry and in situ transcription assays will be used to probe for the expression and intra- and extracellular localization of LO within normal vascular tissue and in vascular lesions induced in a rat femoral artery injury model. Taken together, these studies will explore mechanisms by which LO may influence activities of the VSMC that occur in atherosclerosis.