The growth of cells in the blood vessel wall is closely regulated. These cells proliferate during normal development and tissue repair, but in adults vascular smooth muscle (SMC) and endothelial cells (EC) usually turn over slowly. Inappropriate growth of SMC contributes to the pathogenesis of arteriosclerosis and other diseases, hence the importance of understanding the control of this process. This continuation project will test the following specific hypotheses regarding the regulation of the expression of genes that encode modulators of SMC growth in human vascular wall cells themselves: Hypothesis 1. Expression of """"""""growth factor"""""""" genes (e.g. PDGF A, IL-1, ECGF, FGF) in human vascular SMC is regulated by mediators likely to be involved in blood vessel pathology such as IL-1, TNF, thrombin, or growth factors themselves. We will measure steady state levels and transcription rates of specific mRNA species as well as elaboration of growth factor molecules using radioreceptor or immunoassays and bioassays that employ selective antisera to define mitogenic activities. Hypothesis 2. PDGF production by adult human vascular endothelial cells is regulated by both secretion from a preformed pool and de novo gene transcription and translation. We will use thrombin as a model agonist to study the pathway of PDGF release by EC. A novel ELISA has documented a preformed intracellular pool of PDGF in EC that probably contributes to thrombin-induced PDGF release from these cells. Thrombin also increases levels of PDGF A and B mRNA in adult human EC. Nuclear run-on and metabolic labeling experiments will define the contribution of gene transcription and de novo protein synthesis, versus release from the preformed pool, to PDGF secretion by EC in response to thrombin and other mediators (e.g. tumor necrosis factor (TNF), interleukin-1 (IL-1), or tumor promotors). Hypothesis 3. Mitogens or other cytokines induce vascular wall cells to produce factors which inhibit SMC proliferation and may limit excessive propagation and amplification of the vascular response to injury. Alterations in the balance between activities that stimulates and inhibit SMC growth must contribute to deranged SMC growth in vascular pathology. In view of potential positive feedback loops in vascular growth control and constitutive expression of a growth factor gene by cultured human SMC, it is important to define factors that may limit uncontrolled SMC growth. We will test whether interferons (IFN-alpha, beta, or gamma), likely products of leukocytes or other cells found in human atheromata, can inhibit SMC proliferation. Cells in these lesions may also secret IL-1 and TNF, mediators which can induce some cells to produce the growth-inhibitory IFN-beta 2 (also known as BSF-2, HSF, or IL-6). We will test whether various cytokines can induce IFN-beta 2 gene expression in vascular cells and whether this or other """"""""autocrine IFN(s)"""""""" can inhibit SMC growth. Pilot studies of oligoadenylate synthetase mRNA levels and enzyme activity point to inducible IFN expression in SMC. Delineation of such pathways will help to understand the mechanisms that modulate undesirable amplification of local inflammatory related to SMC growth.
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