ABSTRACT Pathologic fibrosis of the heart or lung results in fatal organ failure with no current cure, short of transplantation. In order to successfully ameliorate cardiac and pulmonary fibrotic disorders, a better understanding of the pathogenesis of organ fibrosis is vital. Fibrogenesis among organs exhibit both common and unique features. Among these, myofibroblasts are key common, fibrosis-effector cells. It has long been known that the response to changes in the mechanical properties of the surrounding tissue/matrix, along with active TGF-?, are critical drivers of myofibroblast differentiation. Although integrins and other receptors participate in cell-matrix interactions, the specific mechanosensor driving myofibroblast has remained elusive. We have recently identified TRPV4 as the critical mechanosensor for driving both myofibroblast differentiation and fibrosis in the lung. TRPV4 is a stretch-activatable, plasma membrane cation channel in the transient receptor potential, vanilloid family (TRPV4). Moreover, TRPV4 drives myofibroblast differentiation and fibrosis at levels of matrix stiffness that are directly biologically and clinically relevant to cardiac and pulmonary disease. We have confirmed recent observations demonstrating TRPV4's importance to cardiac myofibroblast differentiation, and our novel preliminary data further suggests that both the heart and lung pro-fibrotic signals depends on TRPV4's signal pathway interactions with the ?-isoform of PI3K. Based on this data, we have formulated the novel hypothesis that the TRPV4-PI3K? signaling axis mediates mechanotransduction that drives myofibroblast differentiation and fibrosis in both the heart and lung. Intriguingly, the details of how TRPV4-PI3K? interact to drive fibrosis appear to quite different and organ-specific. Two coordinated specific aims will determine the mechanism whereby TRPV4-PI3K? mechanosignal transduction pathways mediate myofibroblast differentiation and fibrosis in the heart and lungs, respectively. These aims will use gain and loss function experimental designs with both genetic and pharmacologic approaches to determine the key TRPV4-PI3K? pathway interactions that drive myofibroblast differentiation and fibrosis. TRPV4-PI3K? axis will be interrogated using hierarchical experimental systems at the cellular level, at the level of established experimental murine models, and at the level of human disease. When complete, we will have a detailed and comprehensive understanding of the precise mechanism by which the TRPV4-PI3K? axis mediates cardiac and pulmonary fibrosis. As several small molecule, selective inhibitors of both PI3K? and TRPV4 are in various phases of development, the knowledge gained from this ?proof of concept? study could rapidly translate into novel therapeutic approaches for both cardiac and pulmonary fibrotic disorders.