ChE PhD Dissertation Defense: Mohammad Hamrangsekachaee

PhD Dissertation Defense: Endothelial Glycocalyx: Response to Fluid and Solid Mechanics in its Environment

Mohammad Hamrangsekachaee

Location: Snell Library 033 and Zoom

Abstract: Atherosclerosis, a precursor to cardiovascular diseases (CVDs), accounts for 37% of deaths in individuals under 70 years old, primarily due to endothelial cell (EC) dysfunction. The glycocalyx (GCX), a carbohydrate-rich structure on ECs lining the vessel luminal surface, is crucial for EC function and vascular health by regulating vascular tone, hemostasis, permeability, and mechanotransduction. Therefore, cellular models emulating the vascular mechanical environment are vital for understanding GCX’s role and its interaction with mechanical surroundings. This dissertation introduces an innovative in vitro model to investigate the combined effects of tissue stiffness and shear stress on endothelial cell function.

Tunable non-swelling gelatin-methacrylate (GelMA) hydrogels were fabricated with stiffnesses of 2.5 and 5 kPa, representing healthy vessel tissues, and 10 kPa, corresponding to diseased vessel tissues. Immunocytochemistry analysis showed that on hydrogels with different levels of stiffness, the GCX’s major polysaccharide components exhibited dysregulation in distinct patterns. For example, there was a significant decrease in heparan sulfate expression on pathological substrates (10 kPa), while sialic acid expression increased with increased matrix stiffness.

GelMA hydrogels were then integrated into a flow chamber designed to generate physiological flow conditions. The combined effects of fluid shear stress and substrate stiffness were analyzed for heparan sulfate, sialic acid, hyaluronic acid, syndecan-1, CD44, and YAP. Under shear stress, heparan sulfate’s coverage was reduced at 10 kPa, while sialic acid and CD44 expression increased at 10 kPa. YAP activation
showed increased nuclear translocation and decreased phosphorylation at 10 kPa. Our findings revealed that substrate stiffness and mechanical forces significantly influence GCX expression and endothelial cell function.

This research highlights the critical role of the mechanical environment on GCX in vascular health, particularly in the context of atherosclerosis. By developing an innovative in vitro model that integrates tissue rigidity and shear stress, we have provided a more precise simulation of the vascular environment. This model offers a valuable tool for further understanding EC mechanotransduction and developing targeted treatments for cardiovascular diseases.