Role of Transient Receptor Potential Vanilloid 4 (TRPV4) Calcium-permeable Channels in Fibro-inflammatory Diseases

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Tissue fibrosis and foreign body response (FBR) have emerged as two major public health problems globally over the last few decades. While fibrosis is an outcome of a dysregulated wound healing process, FBR, a chronic inflammatory disease, develops when the body responds and reacts to the implantation of biological materials. Interestingly, recent studies have associated these non-specific inflammatory diseases with altering stiffness although the exact underlying mechanisms by which mechanical cues can regulate the diseases remain poorly understood. The objective of this thesis work is to determine how the changing of tissue stiffness and implant rigidity mediates disease progression of fibrosis and FBR respectively. Here we identify a novel role of a polymodal mechanosensitive calcium channel, Transient Receptor Potential Vanilloid 4 (TRPV4), as a potential cell membrane receptor/channel in the pathophysiology of FBR and skin fibrosis associated with Scleroderma, a multisystem idiopathic fibro-inflammatory connective tissue disorder. Our results showed that TRPV4 is over expressed in fibrotic skin tissue and colocalize with alpha-smooth muscle actin (a-SMA), a common myofibroblast marker. Using mouse model, we demonstrated that TRPV4 knockout mice are protected from bleomycin-induced skin fibrosis development. Additionally, in a separate mouse model, we showed that genetic ablation of the TRPV4 channel protects mice from implantation-induced macrophage foreign body giant cell (FBGC) formation, macrophage accumulation, and FBR development to biomaterials. The results of our studies also determined an essential role of TRPV4 for macrophage fusion and the mechanism by which TRPV4 and matrix stiffness leads to cytoskeletal remodeling through a feed-forward functional interaction generating cellular force to modulate FBGC formation. We also identified a mechanosensing domain of TRPV4 which is crucial for FBGC generation. Altogether, the results presented in this thesis suggest TRPV4 as a potential regulator of stiffness-dependent fibrosis and inflammation development, and multinucleated FBGC formation. The results of this thesis work proposes that interaction between TRPV4 and substrate stiffness leads to cytoskeletal remodeling and cellular force generation to modulate FBGC formation under FBR. Overall, the work presented in this thesis provides a better understanding about the role of mechanosensitive calcium channel TRPV4 in the regulation of fibro-inflammatory diseases and highlights the possibilities of therapeutically targeting of this channel for disease management.