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

Division of Pulmonary and Critical Care Medicine and Department of Pathology, University of Michigan Medical School, Ann Arbor, Michigan; University Health Network, Ontario Cancer Institute, University of Toronto, Toronto, Ontario, Canada; and Division of Cardiology, Duke University Medical Center, Durham, North Carolina

Correspondence and requests for reprints should be addressed to Eric S. White, M.D., Division of Pulmonary and Critical Care Medicine, University of Michigan Medical School, 6301 MSRB III/0642, 1150 West Medical Center Drive, Ann Arbor, MI 48109-0642. E-mail: docew{at}umich.edu

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 –smooth muscle actin (-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 -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, -SMA, proliferation, and collagen production was upregulated. Addition of transforming growth factor- to wild-type cells, but not pten^–/– cells, resulted in increased -SMA expression in a time-dependent fashion. In pten^–/– cells, reconstitution of PTEN decreased -SMA expression, proliferation, and collagen production, whereas overexpression of PTEN in wild-type cells inhibited transforming growth factor-–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.

Key Words: fibrosis • myofibroblast • phosphatase • PTEN • smooth muscle actin

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