Electronic Thesis and Dissertation Repository


Doctor of Philosophy


Medical Biophysics


Dr. J. Geoffrey Pickering


Vascular smooth muscle cells (SMCs) impart stability to blood vessels, regulate vascular tone, and elaborate extracellular matrix (ECM). In healthy arteries, SMCs physically associate with one another in layered, circumferential arrangements and perform their functions in this context. However, there are circumstances in which SMCs lose their organization and their functionality. The purpose of this thesis was to identify new determinants of SMC-based vascular integrity.

Using a novel model of human SMC collectivization, I found that SMC-SMC adhesion entails the formation of adherens junction complexes consisting of cadherin-11 and N-cadherin hybrid nanotracks. These complexes formed rapidly and depended on withdrawal of TGFß signaling. Furthermore, SMC-SMC adhesion through cadherin- 11/N-cadherin complexes was necessary for calcium signaling propagation among cells. I also identified cadherin-11/N-cadherin adherens junctions complexes in human aorta. These findings revealed a novel mechanism by which SMCs collectivize, with relevance to vascular stability and function.

I next evaluated a SMC dysfunction cascade in the dilated ascending aorta of patients with bicuspid aortic valves (BAV). I discovered the existence of senescent SMCs in the ascending aorta of these patients. I also identified a BAV SMC senescence- associated secretome that favours ECM degradation. Importantly, this involved increased expression of MMP1. In vivo, senescent SMCs were associated with MMP1 expression and with surrounding areas of collagen fibril degradation. This suggests a novel vascular pathology of senescence-induced MMP1 expression and concomitant ECM degradation. I identified that inhibiting p38 MAPK activity abrogated BAV SMC senescence in vitro and decreased MMP1 expression. Together, these findings reveal a premature SMC senescence cascade in BAV aortopathy that may be controlled by p38 MAPK activity.

Finally, I examined the molecular underpinnings of SMC dysfunction in patients with loss-of-function SMAD3 mutations. Loss-of-function SMAD3 mutations lead to a

! ""!syndrome of skeletal and cardiovascular abnormalities called Loeys-Dietz Syndrome Type III (LDS3). Like in BAV disease, the ascending aorta is particularly vulnerable in LDS3. Through next generation RNA sequencing of SMCs isolated from LDS3 aortas, I uncovered novel transcriptome and signaling programs that may be perturbed in LDS3. Furthermore, by studying the response to TGFß1, I found evidence to strongly suggest that TGFß signaling is re-wired in LDS3 SMCs, including pro-inflammatory features and emergence of a Wnt signature.

In summary, this thesis provides several new insight into the molecular determinants of SMC behavior in health and disease, with relevance to human aortic stability.

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