The Role of SOX9 in IGF-II-Mediated Pulmonary Fibrosis.

Pulmonary fibrosis (PF) associated with systemic sclerosis (SSc) results in significant morbidity and mortality. We previously reported that insulin-like growth factor-II (IGF-II) is overexpressed in lung tissues and fibroblasts from SSc patients, and IGF-II fosters fibrosis by upregulating collagen type I, fibronectin, and TGFβ. We now show that IGF-II augments mRNA levels of profibrotic signaling molecules TGFβ2 ( p ≤ 0.01) and TGFβ3 ( p ≤ 0.05), collagen type III ( p ≤ 0.01), and the collagen posttranslational modification enzymes P4HA2 ( p ≤ 0.05), P3H2 ( p ≤ 0.05), LOX ( p = 0.065), LOXL2 ( p ≤ 0.05), LOXL4 ( p ≤ 0.05) in primary human lung fibroblasts. IGF-II increases protein levels of TGFβ2 ( p ≤ 0.01), as well as COL3A1, P4HA2, P4Hβ, and LOXL4 ( p ≤ 0.05). In contrast, IGF-II decreases mRNA levels of the collagen degradation enzymes cathepsin (CTS) K, CTSB , and CTSL and protein levels of CTSK ( p ≤ 0.05). The SRY-box transcription factor 9 (SOX9) is overexpressed in SSc lung tissues at the mRNA ( p ≤ 0.05) and protein ( p ≤ 0.01) levels compared to healthy controls. IGF-II induces SOX9 in lung fibroblasts ( p ≤ 0.05) via the IGF1R/IR hybrid receptor, and SOX9 regulates TGFβ2 ( p ≤ 0.05), TGFβ3 ( p ≤ 0.05), COL3A1 ( p ≤ 0.01), and P4HA2 ( p ≤ 0.001) downstream of IGF-II. Our results identify a novel IGF-II signaling axis and downstream targets that are regulated in a SOX9-dependent and -independent manner. Our findings provide novel insights on the role of IGF-II in promoting pulmonary fibrosis.