STAT3 as a Multi‐organ Target for Tissue Fibrosis

Abstract

Despite recent therapeutic developments, pulmonary fibrosis remains a debilitating disease with poor prognosis. In order to create effective treatments, promising molecular targets need to be identified and validated. Across multiple organs, mesenchymal derived myofibroblasts play an essential role in matrix deposition and tissue contraction. We previously carried out a high‐content, RNAi screen to characterize myofibroblast cytoskeletal phenotypes (α‐SMA and organized F‐actin) in cultured fibroblasts. Hits from this screen, including STAT3 (Signal transducer and activator of transcription 3), were validated in primary lung fibroblasts from patients with IPF (idiopathic pulmonary fibrosis) on compliant hydrogels. To further evaluate STAT3 as a therapeutic target, we have focused on LLL12, a small molecule inhibitor of STAT3. LLL12 dose‐dependently (0.3, 1.0μM) reduced RNA expression of profibrotic genes (ACTA2, CTGF, COL1A1, and FN1) as well as protein deposition of collagen III and fibronectin, in TGFβ stimulated cultured fibroblasts. LLL12 also reduced contractile force, as measured by traction force microscopy, to levels comparable to that seen with inhibition of Rho kinase (Y27632, 20μM). In an effort to support the role of STAT3 as a multi‐organ regulator of tissue fibrosis we confirmed similar effects of LLL12 in primary human hepatic stellate cells and cardiac fibroblasts. Using the bleomycin model of pulmonary fibrosis we assessed the in vivo efficacy of STAT3 inhibition. The lungs of the mice treated therapeutically (day 14–28) with LLL12 (5 mg/kg i.p. daily) showed reduced collagen and fibrotic matrix content measured by hydroxyproline and trichrome histology. RNA expression of COL1A1, FN1, CTGF, and ACTA2 also decreased (~50%) in the mice treated with LLL12. Importantly, in the mice which did not receive bleomycin, LLL12 had no effect on RNA expression of these genes. These data not only validate the RNAi screening approach, but also point towards STAT3 as an important molecular target for regulation of myofibroblast activation in pulmonary fibrosis and other fibrotic diseases.Support or Funding InformationSupported by NIH RO1 HL092961 and HL113796, and Boehringer Ingelheim.