Regulation of blood vessel stiffness by focal adhesions of vascular smooth muscle
Saphirstein, Robert Jason
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The operation of the cardiovascular system is inherently mechanical. Changes in the stiffness of the vascular tree have been implicated in various pathophysiologic states, and increased aortic stiffening with age is an acknowledged biomarker and cause of cardiovascular disease. However, the sources and mechanisms of vascular stiffness are not well understood. While the extracellular matrix is generally regarded as the major component, little is known regarding how contractile, differentiated vascular smooth muscle cells (VSMCs) contribute to blood vessel stiffness. In this dissertation, I employed a multi-scale approach to test the hypothesis that VSM focal adhesions (FAs), subcellular structures linking the cortical cytoskeleton to the surrounding matrix, dynamically regulate the stiffness of veins and arteries. First, I measured cortical stiffness in VSMCs, which along with FA size, increased in response to contractile activation in a Src-dependent manner. To directly test the applicability of these results to tension and stiffness development at a higher length scale, I examined vascular mechanics by applying small sinusoidal stretches to vascular tissue. Agonistinduced contraction increased tissue stress and stiffness in a Src- and FAK-dependent manner. Subsequent phosphotyrosine screening and follow-up with phosphosite-specific antibodies confirmed the involvement of FA proteins, including FAK, Src, CAS, and paxillin. Taken together, these results identify the FA of the VSMC, in particular the F AK-Src signaling complex, as a significant regulator of vascular stiffness and stress, although the details of this regulation were found to differ between arteries and veins. To examine the role of focal adhesions in cardiovascular disease, I performed additional experiments in an aging model that suggest aberrant FA signaling may be an important component of aging induced cardiovascular disease. With the ultimate goal of reducing vascular stiffness by disrupting FA protein-protein interactions, I screened several candidate decoy peptides using a high-throughput cell-based assay. Overall, this work documents the FA as a regulator of vascular stiffness and a potential novel therapeutic target for stiffness in cardiovascular disease.
Thesis (Ph.D.)--Boston University