(721a) Invited Talk: Modeling Endothelin-Driven Stress Fiber Formation in Valve Interstitial Cells

Calcific aortic valve disease (CAVD) is a slow, but active, disease that progresses from mild valve thickening to impaired leaflet motion and biomineralization. Since no pharmacological therapies have shown efficacy in halting/reversing progression of CAVD, therapy options are limited to interventional replacement or repair. A hallmark of CAVD is activation of the aortic valve interstitial cells (AVICs) into myofibroblasts, where the AVICs secrete extracellular matrix and matrix remodeling enzymes while also producing robust actin stress fibers (SFs). We have developed a computational signaling model of SF dynamics in response to endothelin-1 stimulation with the goal of predicting SF formation. Importantly, the signaling model allows for AVIC contraction to be separated into effects due to SF concentration versus unit contractility. Based on a preliminary reaction diagram, small molecule inhibitors targeting ROCK1/2 and GEFH1/LARG were selected to manipulate MLC2 phosphorylation (i.e., unit contractility) and/or actin polymerization (i.e., SF mass fraction) over wide ranges. Immunocytochemistry and Western blot time course experiments, along with literature values of kinetic parameters, were used to parameterize a mechanistic model of endothelin-1-induced contractility. results indicate that MLC2 phosphorylation and actin polymerization follow disparate time-dependent responses. This signaling model allows for a deeper understanding of AVIC contractile processes by separating effects of changes in unit contractility from those of actin polymerization. Future work will add uncertainty quantification to the cell signaling model, facilitating the design of new experiments.