Checkpoint Function of PTPalpha in Pathological Fibrogenesis in the Lung

项目总结/文摘

PROJECT SUMMARY/ABSTRACT Fibrogenesis, the formation of fibrous connective tissue, is essential in development and wound healing. When unrestrained, however, pathologic fibrogenesis contributes to progressive fibrosis of the lungs and other organs leading to organ failure. Diffuse, progressive fibrosis of the lungs is a hallmark of idiopathic pulmonary fibrosis (IPF), a condition that is relentlessly progressive and ultimately fatal. While recent trials have shown that pirfenidone and nintedanib can slow the rate of decline in lung function, novel mechanism-based therapies that not only slow the progression of fibrosis but resolve established fibrosis are urgently needed. We have discovered that protein tyrosine phosphatase-α (PTPα) promotes TGFβ-dependent fibrogenic responses in lung fibroblasts, representing a key checkpoint in the fibrogenic pathway. This project will address the hypothesis that PTPα promotes fibrosis in the lung by indirectly controlling the phosphorylation state of tyrosine residues in the cytoplasmic tail of TGFβ receptor (TβR)II thus enhancing Smad-dependent fibrogenic signals in fibroblasts. Our experimental construct is that PTPα amplifies and prolongs fibrogenic signals from TβRs and the ECM in the context of integrin-based focal adhesions thus enhancing production of collagen and fibronectin leading to tissue fibrosis. Using a combination of pharmacological, biochemical (mass spec, immunoprecipitation, in vitro analysis of recombinant proteins, and phospho-proteomic analysis), and molecular (siRNA gene silencing, RNA Seq) approaches in cultured human and murine fibroblasts, we will determine how PTPα is recruited to the TGFβ receptor complex and regulates tyrosine phosphorylation of TβRs and associated molecules in the receptor complex indirectly through Src tyrosine kinases. We will then ascertain the effects of PTPα on downstream Smad-dependent expression of profibrotic genes including collagen, fibronectin, α-SMA, and miR-29. We will assess the importance of PTPα in myofibroblast differentiation, proliferation, and apoptosis. We will then determine how PTPα is recruited to focal adhesions and integrates signals from a mechanically stiff `fibrotic' ECM with signals transduced through Src, TβRs, and FAK culminating in fibrogenic responses. These studies will employ molecular and imaging-based approaches with expression of fluorescent fusion proteins in fibroblasts grown on ECM-coated polyacrylamide hydrogels of varying stiffness. We will then test our hypothesis in preclinical animal models of pulmonary fibrosis. We will determine the effect of fibroblast-specific genetic deletion of PTPα in our Ptpraf/f mice using Cre driven by fibroblast-specific promoters (DERMO1, Col1a1, and Col1a2) in three models of pulmonary fibrosis: (i) adenoviral expression of recombinant TGF-β; (ii) single dose and (iii) multiple dose intratracheal bleomycin. The role of Src kinases will be assessed in these models using gene-targeted mice and pharmacological inhibitors. Ultimately, this knowledge will be used to develop small molecule or biological approaches selectively targeting these profibrotic pathways to treat pulmonary fibrosis in humans.