PI3K p110γ overexpression in idiopathic pulmonary fibrosis lung tissue and fibroblast cells: in vitro effects of its inhibition

Idiopathic pulmonary fibrosis (IPF) is a progressive fibroproliferative disease whose molecular pathogenesis remains unclear. In a recent paper, we demonstrated a key role for the PI3K pathway in both proliferation and differentiation into myofibroblasts of normal human lung fibroblasts treated with TGF-beta. In this research, we assessed the expression of class I PI3K p110 isoforms in IPF lung tissue as well as in tissue-derived fibroblast cell lines. Moreover, we investigated the in vitro effects of the selective inhibition of p110 isoforms on IPF fibroblast proliferation and fibrogenic activity. IHC was performed on normal and IPF lung tissue. Expression levels of PI3K p110 isoforms were evaluated by western blot and flow cytometry analysis. Fibroblast cell lines were established from both normal and IPF tissue and the effects of selective pharmacological inhibition as well as specific gene silencing by small interfering RNAs were studied in vitro. No significant differences between normal and IPF tissue/tissue-derived fibroblasts were observed for the expression of PI3K p110 alpha, beta and,5 isoforms whereas p110 gamma was more greatly expressed in both IPF lung homogenates and ex vivo fibroblast cell lines. Myofibroblasts and bronchiolar basal cells in IPF lungs exhibited strong immunoreactivity for p110 gamma. Positive staining for the markers of proliferation proliferating cell nuclear antigen and cyclin D1 was also shown in cells of fibrolastic foci. Furthermore, both p110 gamma pharmacological inhibition and gene silencing were able to significantly inhibit proliferation rate as well as alpha-SMA expression in IPF fibroblasts. Our data suggest that PI3K p110 gamma isoform may have an important role in the etio-pathology of IPF and can be a specific pharmacological target. Laboratory Investigation (2013) 93, 566-576; doi:10.1038/labinvest.2013.6; published online 25 February 2013