Integrin-ECM regulation of fibroblast proliferation

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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 IPFfibroblasts 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. Seminal studies have demonstrated that polymerized type I collagen acts as a negative regulator of fibroblast proliferation. Consistent with this, we have found that normal lung fibroblast proliferation is inhibited by polymerized collagen. In contrast, we have found that IPF fibroblasts have escaped this restraint. Our mechanistic studies of this phenomenon point to abnormalities in 01 integrin signaling in response to ligation with type I collagen. We have discovered that integrin-ECM interaction regulates PTEN expression and activity. PTEN is a phosphatase whose baseline activity is constitutively high. It functions by negatively regulating proliferation by repressing the integrin- PI3K/Akt signaling pathway. When normal lung fibroblasts are cultured on polymerized collagen, PTEN activity remains high. In contrast, when IPF fibroblasts are cultured on polymerized collagen PTEN activity is inappropriately low leaving the PI3K/Akt signaling pathway unrestrained. We hypothesize that in IPFfibroblasts 01 integrin-type I collagen interaction results in aberrant regulation of PTEN. To test our hypothesis we will: Aim 1. Determine the role of the PI3K/Akt/S6K1-PTEN signaling axis in enabling IPF fibroblasts to elude the negative proliferative effects of polymerized type I collagen. Aim 2. Define the molecular basis for regulation of PTEN and the PI3K/Akt signal pathway in control and IPF lung fibroblasts by 01 integrin-type I collagen interaction. Aim 3. Validation of in vitro studies implicating abnormal function of the 01 integrin PI3K/Akt/S6K1-PTEN signaling axis in IPF fibrogenesis by in vivo methodology. RELEVANCE (See instructions): The myofibroblast is the effector cell of the relentless IPF fibrotic response. We have discovered that IPF fibroblasts have exaggerated proliferation on polymerized collagen. The mechanism involves low PTEN activity that facilitates aberrant activation of the PI3K/Akt signal. These studies will delineate the molecular processes underlying the pathologically low PTEN activity in IPF fibroblasts and suggest new therapies.