Role of Fox03a in Regulating the IPF Fibroblast Phenotype

DESCRIPTION (provided by applicant): Idiopathic Pulmonary Fibrosis (IPF) is a progressive, fatal fibrotic lung disease for which there is no effective therapy. The sentinel morphological lesion is the fibroblastic focus, which is composed of myofibroblasts in a type I collagen rich matrix. Prima facie evidence supports the critical role for myofibroblasts in the relentless progression of IPF given that this is the cell that proliferates and deposits collagen in the alveolar wall. Although studies strongly support the notion that IPF fibroblasts display a distinct pathological phenotype, large gaps in knowledge remain regarding differences between the pathological nature of IPF fibroblasts responsible for progressive fibrosis and the physiologic function of myofibroblasts essential for normal lung repair. The objective of this proposal is to characterize the molecular processes underlying the pathological nature of IPF fibroblasts. We have discovered that polymerized type I collagen suppresses normal fibroblast proliferation via high PTEN activity which inhibits the major PI3K/Akt signaling pathway. In contrast, in IPF fibroblasts, the PI3K/Akt signal is aberrantly activated due to inappropriately low PTEN activity and this permits these cells to elude the proliferation suppressive properties of polymerized collagen. We have generated data indicating that in IPF fibroblasts, the activated PI3K/Akt signal inhibits the function of the FoxO3a transcriptional activator. FoxO3a regulates the cell cycle inhibitor protein p27 and apoptosis inducing protein Bim, two critical proteins involved in the control of cell proliferation and survival, respectively. Our mechanistic studies point to integrin-mediated phosphorylation and/or degradation of FoxO3a as the underlying cause of suppression of FoxO3a function in IPF fibroblasts. We suggest that this pathological defect disrupts the function of the FoxO3a transcriptional activator leading to suppression of p27 and Bim. This may confer IPF fibroblasts with a hyper-proliferative and apoptotic-resistant phenotype. To test our hypothesis we will: Aim 1.Examine the hypothesis that the abnormally activated PI3K/Akt pathway suppresses the function of the FoxO3a transcriptional activator in IPF fibroblasts. Aim 2. Examine the functional role and mechanism of FoxO3a regulation of IPF fibroblast proliferation and survival on polymerized collagen. Aim 3. Examine the molecular mechanism by which the activated integrin/PI3K/Akt signaling pathway suppresses FoxO3a function in IPF fibroblasts. PUBLIC HEALTH RLEVANCE: Idiopathic pulmonary fibrosis (IPF) is a chronic, lethal interstitial lung disease. The sentinel morphological lesion is the fibroblastic focus, which is composed of fibroblasts embedded in a type I collagen rich matrix. Polymerized type I collagen suppresses normal fibroblast proliferation by a mechanism involving maintenance of high PTEN activity which inhibits the PI3K/Akt signal pathway. However, in IPF fibroblasts the PI3K/Akt signal is aberrantly activated due to low PTEN activity, permitting these cells to elude the proliferation suppressive properties of polymerized collagen. We have generated data indicating that in IPF fibroblasts, activated Akt inhibits the function of the FoxO3a transcriptional activator. FoxO3a regulates the expression of critical proteins involved in the control of cell proliferation and survival. We suggest that disruption of the function of FoxO3a may confer IPF fibroblasts with a hyper-proliferative and apoptotic-resistant phenotype. Identifying key regulatory nodes controlling the pathologic behavior of IPF fibroblasts may provide molecular therapeutic targets to limit the progressive fibrosis that characterizes IPF. Identifying key regulatory nodes controlling the pathologic behavior of IPF fibroblasts may provide molecular therapeutic targets to limit the progressive fibrosis that characterizes IPF.