Insulin-Like Growth Factor-II Is Increased in Systemic Sclerosis-Associated Pulmonary Fibrosis and Contributes to the Fibrotic Process via Jun N-Terminal Kinase- and Phosphatidylinositol-3 Kinase-Dependent Pathways

Systemic sclerosis (SSc)-related pulmonary fibrosis, for which there are few effective therapies, is the most common cause of SSc-related mortality. We examined insulin-like growth factor (IGF)-II expression in explanted lung tissues from control and SSc patients to determine its role in the pathogenesis of fibrosis. IGF-II levels in vivo were detected using immunohistochemistry. Primary lung fibroblasts were cultured from lung tissues, and IGF-II mRNA was measured using reverse transcriptase-polymerase chain reaction. Western blot analysis measured extracellular matrix (ECM) production and phosphorylated signaling molecules. Immunostaining revealed increased IGF-II expression in fibroblastic foci of SSc lungs. Furthermore, primary SSc lung fibroblasts had a fourfold increase in IGF-II mRNA and a twofold increase in IGF-II protein compared with normal lung fibroblasts. IGF-II mRNA in SSc lung fibroblasts was expressed primarily from the P3 promoter of the IGF-II gene, and IGF-II induced both a dose- and time-dependent increase in collagen type I and fibronectin production. IGF-II triggered the activation of both phosphatidylinositol-3 kinase and Jun N-terminal kinase signaling cascades, the inhibition of which diminished IGF-II-induced ECM production. Our study demonstrates increased local IGF-II expression in SSc-associated pulmonary fibrosis both in vitro and in vivo as well as IGF-II-induced ECM production through both phosphatidylinositol-3 kinase- and Jun N-terminal kinase-dependent pathways. Our results provide novel insights into the role of IGF-II in the pathogenesis of SSc-associated pulmonary fibrosis.