The role of vascular smooth muscle cell dysfunction in abdominal aortic aneurysm pathogenesis: Insights into disease mechanisms

Abdominal aortic aneurysms (AAA) are pathological dilations of the abdominal aorta. Progressive weakening of the aortic wall can lead to life-threatening rupture. Many AAA patients are asymptomatic, making diagnosis challenging. No biomarkers are available to predict disease progression or rupture risk. The only treatment option is invasive surgery, which carries risks and may require follow-up procedures. The lack of medication is caused by the insufficient understanding of the underlying disease mechanisms. More insight into the cells and proteins involved in aortic wall weakening could contribute to improved diagnostics and non-invasive treatments. The aortic wall consists of three layers: the tunica intima (endothelial cells), the tunica adventitia (elastic fibers), and the tunica media (primarily vascular smooth muscle cells, vSMC). vSMC provide structural support and regulate blood pressure and flow through contraction. In AAA tissue, vSMC numbers and structural matrix production are reduced, but the precise mechanisms remain unclear. This thesis investigates the role of vSMC dysfunction in AAA development and progression. In vitro experiments were conducted using vSMC from AAA patients and healthy controls to identify involved proteins and pathways. Additionally, a 3D model was developed to mimic the complex environment of the aorta. In Chapter 2, available literature on vSMC dysfunction in AAA was summarized, identifying five main mechanisms: cell death, phenotypic switch, reduced matrix production, impaired cell division, and disrupted contraction. These insights highlight the importance of vSMC in AAA but have not yet resulted in non-invasive treatments or biomarkers. In Chapter 3, a proteomics screening was performed on vSMC from AAA patients, revealing new proteins not previously identified in prior studies using whole AAA tissue. This underscores the value of cell-specific vSMC research. Chapter 4 describes the development of a protocol to isolate primary vSMC from AAA tissue and measure their contractile capacity in vitro. In Chapter 5, it was found that vSMC contraction in AAA patients varies widely, with contraction levels correlated to the protein NUAK1. Experimental reduction of NUAK1 decreased contraction and disrupted the connection between the cytoskeleton and matrix components, confirming NUAK1’s role in AAA. In Chapter 6, a novel patient-specific Vessel-on-Chip model was developed, in which vSMC and endothelial cells were cultured together. This model demonstrated that vSMC from AAA patients form larger, leakier vessels, potentially due to reduced levels of the protein GJA1, which regulates communication between vSMC and endothelial cells. This thesis provides new insights into vSMC-related mechanisms in AAA. Further validation in advanced models is necessary to translate these findings into biomarkers and therapeutic targets, with the ultimate goal of improving the quality of life for AAA patients.