Fibrotic extracellular matrix preferentially induces a partial Epithelial–Mesenchymal Transition phenotype in a 3-D agent based model of fibrosis

Abstract

One of the main drivers of fibrotic diseases is epithelial–mesenchymal transition (EMT): a transdifferentiation process in which cells undergo a phenotypic change from an epithelial state to a pro-migratory state. The cytokine transforming growth factor-$\beta$1 (TGF-$\beta$1) has been previously shown to regulate EMT. TGF-$\beta$1 binds to fibronectin (FN) fibrils, which are the primary extracellular matrix (ECM) component in renal fibrosis. We have previously demonstrated experimentally that inhibition of FN fibrillogenesis and/or TGF-$\beta$1 tethering to FN inhibits EMT. However, these studies have only been conducted on 2-D cell monolayers, and the role of TGF-$\beta$1-FN tethering in 3-D cellular environments is not clear. As such, we sought to develop a 3-D computational model of epithelial spheroids that captured both EMT signaling dynamics and TGF-$\beta$1-FN tethering dynamics. We have incorporated the bi-stable EMT switch model developed by Tian et al. (2013) into a 3-D multicellular model to capture both temporal and spatial TGF-$\beta$1 signaling dynamics. We showed that the addition of increasing concentrations of exogeneous TGF-$\beta$1 led to faster EMT progression, indicated by increased expression of mesenchymal markers, decreased cell proliferation and increased migration. We then incorporated TGF-$\beta$1-FN fibril tethering by locally reducing the TGF-$\beta$1 diffusion coefficient as a function of EMT to simulate the reduced movement of TGF-$\beta$1 when tethered to FN fibrils during fibrosis. We showed that incorporation of TGF-$\beta$1 tethering to FN fibrils promoted a partial EMT state, independent of exogenous TGF-$\beta$1 concentration, indicating a mechanism by which fibrotic ECM can promote a partial EMT state.