To Be, or Not to Be: Cellular Homeostasis to Mechanical Perturbations

Abstract

Mechanical homeostasis is an emerging mechanobiology concept that describes the critical biological process to maintain whole-cell/tissue physiology against forces and deformation arising both intra- and extracellularly. Dysregulation of mechanical homeostasis has important implications in pathophysiological conditions such as developmental defect, cardiovascular and pulmonary diseases, and cancer. Mechanical homeostasis has been commonly investigated at molecular, cellular, tissue levels and beyond. However, in mechanical homeostasis collective dynamics at smaller scales and its functional relationship with emergent system-level properties at larger scales remains elusive.

The major contribution of this dissertation is to provide a detailed picture of the functional link between molecular and subcellular events and apparent cellular behaviors under mechanical perturbations. A novel suite of technologies, involving microfabrication, live-cell imaging, high-throughput and multidimensional image processing, and mechanical characterization, have been developed and implemented in this research for the live-cell study of both subcellular and cellular aspects of mechanical homeostasis. By utilizing these techniques, we performed cell stretch experiments and quantitative measurements of biomechanical and biochemical responses with a spatiotemporal resolution to examine cell behaviors upon mechanical perturbation. Our data have revealed that cellular mechanical homeostasis is an emergent phenomenon driven by collective and graduated, yet non-homeostatic, subcellular behaviors (“subcellular rheostasis”) that follow distinct mechanosensitive compensatory paths. We have for the first time shown that subcellular dynamics would observe patterns different from that at the single-cell level. Further investigations have revealed that impairment to the extracellular matrix (ECM) – focal adhesion (FA) – cytoskeleton (CSK) mechanical linkage can lead to an effective exit from cellular mechanical homeostasis by skewing the subcellular rheostasis pattern of FAs, which might be a sensitive gating mechanism of cellular homeostasis. Lastly, a mechano-biophysical model has been constructed in this work to quantitatively recapitulate experimental observations of subcellular rheostasis and its perturbation by different drug treatments. Cross-examination of experimental and theoretical modeling results has unveiled the regulatory roles of different mechanosensitive machineries including catch-slip bonds and myosin motor activity in governing the emergence of cellular mechanical homeostasis.