A25 THE “UPSIDE-DOWN OR OUTSIDE-IN”: UNDERSTANDING HOW FOXL1+ TELOCYTES GOVERN THE EPITHELIAL-MESENCHYMAL CROSSTALK IMPACTING CELL BEHAVIOR BY USING PROTEOMICS STRATEGIES

Abstract

Abstract Background The mechanical information contained in the basement membrane (BM) is translated into intracellular signals via a process called mechanotransduction. The integrin-mediated cellular adhesions are found at the center of this outside-in mechanism connecting specific extracellular matrix (ECM) proteins with intracellular adaptors proteins that relay the signal via F-actin cytoskeleton turnover, Rho GTPase activity and eventually down to the nucleus. Dysregulation in any step of this tightly controlled process is a major contributor of disease development. Mesenchymal Foxl1+-telocytes (TCs) are known as a communication hub between stromal and epithelial cells from their proximity to the BM and from their potential roles in epithelial mechanical support and cell signaling. We have shown that BMPR1A signaling deletion in TCs (TCΔBmpr1a) induces stem cell niche defects, stromagenesis and colonic dysplasia in mouse model of GI diseases. Thus far, no study explored TCs relevance in microenvironment biomechanics and its subsequent impact in epithelial mechanotransduction. Aims Understand how TCΔBmpr1a can modulate mechanotransduction to induce early dysplastic changes in mouse colon. Methods Matrisomics was performed to determine the inventory of ECM proteins expressed solely in the GI stromal compartment following tissue deconstruction of control and TCΔBmpr1a mice colons. Collagen fibers analysis, histological and biochemical methods were used to further characterize the matrix biodynamics. Proteomics of the associated epithelial compartment was also done to expose mechanosensors and signaling cascades affecting cell behaviour. Results Matrisomics indicate modulations in fiber assembly proteins (collagens (CL), Decorin, Biglycan), ECM remodelling enzymes (LOXL1, TGM2), growth factors (LTBP1, WNT2B) and cell adhesion mediators (Periostin). This is associated with a reorganization in CL fiber alignment, cellular delocalization of TGM2 and increased unfolded CL content. TCΔBmpr1a leads to shortcomings in matrix assembly, hence variations in the ECM architecture and a novel epithelial mechanotransduction potential. Deregulations in matrix-to-cell communication were shown by proteomic analysis of the epithelial-enriched compartment of colonic dysplastic areas, with modulations of mechanosensors such as focal adhesion components (integrins, paxillin), F-actin cytoskeleton (gelsolin, RhoA) and nuclear lamina (Prelamin A/C, nesprin). Conclusions Taken together, these results suggest that TCΔBmpr1a can reprogram epithelial cells by impacting on matrix biodynamics and epithelial mechanotransduction. Modulation in this fine regulated sequence of communication from TCs to the epithelial nucleus via ECM could lead to the etiology of GI pathologies. Funding Agencies CIHR