Negative Regulation of Myofibroblast Differentiation by PTEN (Phosphatase and Tensin Homolog Deleted on Chromosome 10)

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Abstract
Rationale: Myofibroblasts are primary effector cells in idiopathic pulmonary fibrosis (IPF). Defining mechanisms of myofibroblast differentiation may be critical to the development of novel therapeutic agents. Objective: To show that myofibroblast differentiation is regulated by phosphatase and tensin homolog deleted on chromosome 10 (PTEN) activity in vivo, and to identify a potential mechanism by which this occurs. Methods: We used tissue sections of surgical lung biopsies from patients with IPF to localize expression of PTEN and α–smooth muscle actin (α-SMA). We used cell culture of pten−/− and wild-type fibroblasts, as well as adenoviral strategies and pharmacologic inhibitors, to determine the mechanism by which PTEN inhibits α-SMA, fibroblast proliferation, and collagen production. Results: In human lung specimens of IPF, myofibroblasts within fibroblastic foci demonstrated diminished PTEN expression. Furthermore, inhibition of PTEN in mice worsened bleomycin-induced fibrosis. In pten−/− fibroblasts, and in normal fibroblasts in which PTEN was inhibited, α-SMA, proliferation, and collagen production was upregulated. Addition of transforming growth factor-β to wild-type cells, but not pten−/− cells, resulted in increased α-SMA expression in a time-dependent fashion. In pten−/− cells, reconstitution of PTEN decreased α-SMA expression, proliferation, and collagen production, whereas overexpression of PTEN in wild-type cells inhibited transforming growth factor-β–induced myofibroblast differentiation. It was observed that both the protein and lipid phosphatase actions of PTEN were capable of modulating the myofibroblast phenotype. Conclusions: The results indicate that in IPF, myofibroblasts have diminished PTEN expression. Inhibition of PTEN in vivo promotes fibrosis, and PTEN inhibits myofibroblast differentiation in vitro.