Inhibition of the Arp2/3 complex represses human lung myofibroblast differentiation and attenuates bleomycin-induced pulmonary fibrosis.

BACKGROUND AND PURPOSE The Arp2/3 multiprotein complex regulates branched polymerisation of the actin cytoskeleton, and may contribute to collagen synthesis and fibrogenesis in the lung. EXPERIMENTAL APPROACH Expression of Arp2/3 components was assessed in human lung fibroblasts and in the bleomycin-induced pulmonary fibrosis model in mice. The Arp2/3 complex was repressed with the allosteric inhibitor CK666 and with interfering RNAs targeting the ARP2, ARP3 and ARPC2 subunits (siARP2, siARP3, siARPC2) in CCD16-Lu human lung fibroblasts in vitro. Mice received daily intraperitoneal injections of CK666 from the 7th to the 14th day after tracheal bleomycin instillation. KEY RESULTS Expression of Arp2/3 complex subunits mRNAs was increased in fibroblasts treated with TGF-β1 and in the lungs of bleomycin-treated mice compared to controls. In vitro, CK666 and siARPC2 inhibited cell growth and TGFβ1-induced α-smooth muscle actin (ACTA2) and collagen-1 (COL1) expression. CK666 also decreased ACTA2 and COL1 expression in unstimulated cells. CK666 reduced AKT phosphorylation and repressed phospho-GSK3β, β-catenin and MRTF-A levels in unstimulated fibroblasts. In vivo, CK666 reduced levels of both procollagen-1 and insoluble collagen in bleomycin-treated mice. CONCLUSION AND IMPLICATIONS Expression of the Arp2/3 complex was increased in profibrotic environments in vitro and in vivo. Inhibition of the Arp2/3 complex repressed ACTA2 and COL1 expression and repressed an AKT/phospho-GSK3β/β-catenin/MRTF-A pathway in lung fibroblasts. CK666 exerted antifibrotic properties in the lung in vivo. Inhibition of the Arp2/3 complex could represent an interesting new therapy for IPF and other fibrotic interstitial lung diseases.