Translocation Of Trpv4-Pi3kg Complexes To The Plasma Membrane Drives Myofibroblast Differentiation

Myofibroblasts are key contributors to pathological fibrotic conditions of several major organs. The transdifferentiation of fibroblasts into myofibroblasts requires both a mechanical signal and transforming growth factor-beta (TGF-beta) signaling. The cation channel transient receptor potential vanilloid 4 (TRPV4) is a critical mediator of myofibroblast transdifferentiation and in vivo fibrosis through its mechanosensitivity to extracellular matrix stiffness. Here, we showed that TRPV4 promoted the transdifferentiation of human and mouse lung fibroblasts through its interaction with phosphoinositide 3-kinase gamma (PI3K gamma), forming nanomolar-affinity, intracellular TRPV4-PI3K gamma complexes. TGF-beta induced the recruitment of TRPV4-PI3K gamma complexes to the plasma membrane and increased the activities of both TRPV4 and PI3K gamma. Using gain- and loss-of-function approaches, we showed that both TRPV4 and PI3K gamma were required for myofibroblast transdifferentiation as assessed by the increased production of alpha-smooth muscle actin and its incorporation into stress fibers, cytoskeletal changes, collagen-1 production, and contractile force. Expression of various mutant forms of the PI3K gamma catalytic subunit (p110 gamma) in cells lacking PI3K gamma revealed that only the noncatalytic, amino-terminal domain of p110 gamma was necessary and sufficient for TGF-beta-induced TRPV4 plasma membrane recruitment and myofibroblast transdifferentiation. These data suggest that TGF-beta stimulates a noncanonical scaffolding action of PI3K gamma, which recruits TRPV4-PI3K gamma complexes to the plasma membrane, thereby increasing myofibroblast transdifferentiation. Given that both TRPV4 and PI3K gamma have pleiotropic actions, targeting the interaction between them could provide a specific therapeutic approach for inhibiting myofibroblast transdifferentiation.