Date of Award

Summer 2002

Document Type

Dissertation

Degree Name

Doctor of Philosophy (PhD)

Committee Director

Russell L. Prewitt

Committee Member

Gerald Pepe

Committee Member

Paul H. Ratz

Committee Member

Patricia Williams

Abstract

Elevated blood pressure is associated with varying degrees of arterial remodeling. The mechanisms by which extracellular mechanical stress is converted into intracellular alterations in signal transduction and gene expression have yet to be fully elucidated. Our goal was to investigate the early events in the vascular smooth muscle response to acute hypertension and to identify mediators involved in long-term hypertensive remodeling.

In the acute phase of hypertension we targeted cell surface integrin and growth factor receptors thought to be mechanically sensitive. The signaling molecules FAK, Src and ERK-MAPK are known to be triggered by integrin engagement and growth factor receptor tyrosine kinase (RTK) activation. Pairs of rat mesenteric arteries were pressurized to 90 mmHg (control), and then one was raised to 140 mmHg for 1, 3, 5 or 10 minutes. Western blotting using phosphorylation-specific antibodies revealed that Src-pY418 (autophosphorylation site) was elevated 3-fold over control values at 1 minute, whereas significant FAK-Y 397(autophosphorylation site) activation was observed only following 3 minutes of pressure stimulus, and was blocked entirely by PP1, a selective Src inhibitor. Src-pY215 activity, which is associated with prior activation of the PDGF receptor, was not apparent at any of the time points tested. In addition, peak ERK-MAPK activation was identified at 5 minutes and was not affected by the presence of AG 1296, a PDGF receptor inhibitor. These data demonstrate that autophosphorylation of Src-Y418 is an early event in pressure mechanotransduction and is required for downstream FAK-Y397 activation, and PDGF receptor activation does not appear to be involved in the initial response.

With regard to chronic arterial remodeling, previous studies in our laboratory showed that PDGF-A mRNA expression is increased in 1K1C hypertensive rats. We evaluated the ability of PDGF-AA to stimulate growth of carotid vascular smooth muscle in normotensive rats. Results identified an outward hypertrophic growth response in a manner similar to that seen in hypertensive remodeling. Next we evaluated the effect of PDGF receptor inhibition on vascular hypertrophy and ECM modification in 1K1C hypertensive rats treated with CGP-53716, a PDGF receptor inhibitor. Our results indicated that PDGF receptor inhibition does not block the hypertensive hypertrophic response, although we found significant changes in extracellular matrix composition. Overall, it appears that PDGF is not an absolute requirement for hypertrophic remodeling in 1K1C hypertension, but may play a pivotal role in ECM modification.

Comments

A Dissertation Submitted to the Faculty of Old Dominion University and Eastern Virginia Medical School in Partial Fulfillment of the Requirements for the Degree of Philosophy in Biomedical Sciences.

DOI

10.25777/zjsr-7w61

ISBN

9780493882949

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