Integrin-collagen signaling and control of fibroblast proliferation

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. 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 ¿1 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 as a tumor suppressor by negatively regulating proliferation by repressing the integrin-phosphoinositol 3-kinase (PI3K)/Akt signaling pathway. When normal lung fibroblasts are cultured on polymerized collagen, we have found that 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 and removing one of the major physiological negative feedback signals regulating proliferation. This enables IPF fibroblasts to circumvent the negative regulatory effects of polymerized collagen. We hypothesize that: ¿1 integrin-type I collagen interaction results in aberrant regulation of PTEN. This leads to unrestrained PI3K/Akt/S6K1 activity and underlies the pathologic proliferation of IPF fibroblasts on polymerized collagen. 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 ¿1 integrin-type I collagen interaction. Aim 3. Validation of in vitro studies implicating abnormal function of the ¿1 integrin PI3K/Akt/S6K1-PTEN signaling axis in IPF fibrogenesis by in vivo methodology.