Profibrotic Mechanisms of the TRPV4-PI3K-gamma Protein Complex

摘要

ABSTRACT Idiopathic pulmonary fibrosis (IPF) is a fatal disorder with urgent need for a medical cure. In order to successfully ameliorate pulmonary fibrosis, a better understanding of fibrotic pathogenesis is vital. Myofibroblasts are key 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-β, are critical drivers of myofibroblast differentiation. Although integrins and other receptors participate in cell-matrix interactions, the specific mechanosensor driving myofibroblast differentiation has remained elusive. We have 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 pulmonary disease. We have demonstrated TRPV4’s importance to myofibroblast differentiation and experimental pulmonary fibrosis and human IPF. Our novel published and preliminary data further suggests that TRPV4’s pro-fibrotic actions depend on its biochemical association with cytosolic PI3Kγ via PI3kγ’s unique aminoterminal, non-catalytic domain, followed by the translocation of the protein complex to the plasma membrane. Based on this data, we have formulated the novel hypothesis that the TGFβ drives myofibroblast differentiation and pulmonary fibrosis by inducing the TRPV4-PI3Kγ protein complex to translocate to the plasma membrane. Three coordinated specific aims with gain and loss function experimental designs will determine the key TRPV4-PI3Kγ pathway interactions that drive myofibroblast differentiation and fibrosis. They will utilize gain and loss of function design in in silico, in vitro and in vivo systems at the structural level, cellular level, and at the levels of established experimental murine models, and in human disease. AIM 1 will precisely define the amino acid(s) interacting sites between TRPV4 and PI3Kγ, AIM 2 will determine the mechanism whereby TGFβ induces the translocation of TRPV4-PI3Kγ complexes to the PM where they act to drive myofibroblast differentiation and AIM 3 will test the concept that the aminoterminal domain of PI3Kγ is necessary and sufficient to drive pulmonary fibrosis in vivo. All key findings will be validated in normal and IPF patient-derived cells and tissue. When complete, we will have a detailed and comprehensive understanding of the precise mechanism by which the TRPV4-PI3Kγ axis mediates pulmonary fibrosis. As several small molecule, selective inhibitors of both PI3Kγ 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 pulmonary fibrotic disorders.