REGULATION OF CELLULAR CONTRACTILITY BY TGFΒ AND DYNAMIC STRETCH IN FIBROBLASTS
Namrata Gundiah1, Ankur Kulkarni1, Siddhartha Jaddivada1, Reena Sayani1, Paturu Kondaiah1, Paul Watton2
1Indian Institute of Science, India;
2University of Sheffield, UK
Cellular homeostasis is maintained by dynamic feedback with the local microenvironment and involves a complex interplay of biochemical and mechanical factors. Loss of homeostatic conditions is hypothesized to alter the cellular mechanobiology and lead to the progression of fibrosis through secretion and deposition of extracellular matrix proteins which alter the tissue mechanics. Fibroblasts in the connective tissue mediate these changes and are guided by chemical and mechanical signals such as profibrotic biochemical factors (TGFb) and the cyclic stretch. Earlier studies have investigated the effects of TGFβ on fibrosis; the mechanobiological response of cells to bio-mechanical stimuli is yet to be elucidated. We treated mouse fibroblasts with TGFβ in the presence or absence of cyclic stretch using a custom built biaxial stretcher. Changes in cell contractility were quantified using traction force microscopy. These results show that treatment with TGFβ increased stress fiber formation and yielded clear polarization in the cellular morphology. In addition, we cultured cells on polyacrylamide gels of varying stiffness and show, using a regularized Fourier Transform Traction Cytometry inverse approach, that TGFβ treatment affects cell contractility.
Lastly, we used a systems biology approach implemented via reaction-diffusion equations with results from the traction experiments to simulate the formation and de-adhesion of bonds between the cytoskeleton and the substrate in response to dynamic stretching. The model predicts changes in the dynamics of focal adhesion recruitment and actomyosin contractility which are concomitant with an increase in stress fiber activation due to TGFβ. Ongoing investigations are aimed at measuring changes in cell contractility due to the combined effects of cyclicstretching and TGFβ. Our studies provide further insight into the intricate interplay of chemo-mechanical factors which govern cell contractility and ultimately the fibrotic response; a better understanding of these will aid in the design of novel therapeutic regimes.