Title: “Effects of Substrate Stiffness, Cadherin Junction and Shear Flow on Tensional Homeostasis in Cells and Cell Clusters”
Dimitrije Stamenovic, PhD – BU BME (Co-Advisor)
Michael Smith, PhD – BU BME (Co-Advisor)
Joe Tien, PhD – BU BME (Chair)
Michael Albro, PhD – BU ME
Joana Figueiredo, PhD – Instituto de Investigacao e Inovacao em Saude do Porto Universidade
It is believed that for normal biological functions the cell(s) must maintain its cytoskeletal tension stable, at a preferred set-point level, under external perturbations. This is known as tensional homeostasis. Breakdown of tensional homeostasis is closely associated with disease progression, including cancer, atherosclerosis, and thrombosis. The exact mechanism and the relevant environmental conditions for the maintenance of tensional homeostasis are not yet fully understood. This thesis investigates the impacts of substrate stiffness, availability of functional cadherin junctions and steady shear stress on tensional homeostasis of cells and cell clusters.
Using micropattern traction microscopy we measure cellular traction forces and their temporal fluctutaions. The lower the temporal fluctuations, the more homeostasis the cell tension is considered to be. Results demonstrated that substrate stiffness, cadherin cell-cell junctions and shear stress all impact tensional homeostasis. In particular, we found that stiffer substrates promoted tensional homeostasis in endothelial cells, but were detrimental to tensional homeostasis in vascular smooth muscle cells. We also found that E-cadherins were essential for tensional homeostasis of gastric cancer cells and that mutations of E-cadherin had domain-specific effects. Finally, laminar flow-induced shear stress led to increased traction field fluctuations in endothelial cell monolayers, contrary to reports of physiological shear promoting vascular homeostasis. A possible reason for this discrepancy might be the limitation of our approach which could not account for mechanical balance of traction forces in the monolayers.
Through the exploration of these environmental factors, we have shown that tensional homeostasis was a length scale-dependent and cell type-dependent phenomenon. These insights suggest that future studies need to take a more comprehensive approach and aim to make observations of different cell types on multiple length scales, in order decipher the mechanism of tensional homeostasis and its role in (patho)physiology.