Z Gastroenterol 2012; 50 - P1_04
DOI: 10.1055/s-0031-1295734

Neutralization of Bone Morphogenetic Protein (BMP)–9 in mouse liver reduces CCl–4 mediated fibrogenesis

K Breitkopf-Heinlein 1, Q Li 2, MJ Goumans 3, E Wiercinska 3, P ten Dijke 3, S Dooley 4
  • 1Molecular Hepatology – Alcohol Associated Diseases, II. Medical Clinic, Faculty of Medicine at Mannheim, University of Heidelberg, Mannheim
  • 2II. Medizinische Klinik Universtitätsklinikum Mannheim, Universitäts Heidelberg, Mannheim, Germany
  • 3Molecular Cell Biology; Leiden University Medical Center, Leiden, The Netherlands
  • 4II. Med. Klinik; Medizinische Fakultät Mannheim der Universität Heidelberg, Mannheim

BMP9, a member of the TGFβ family of cytokines, is mainly expressed in liver. We therefore investigated responses to BMP9 in vitro in hepatic stellate cells (HSC) and hepatocytes (HC) and in vivo. In vascular endothelial cells and most likely in other cell types as well, BMP9 exerts its effects by binding to, and signaling via ALK1.HSC/HC were isolated from mice livers by collagenase digestion and were analyzed during primary culture. Target genes of BMP9 were identified by micro array analyses (Affymetrix). Neutralization of BMP9/ALK1 signaling in vivo was achieved using an adenovirus expressing the extracellular ligand binding domain of ALK1 fused to Fc (AdALK1-Fc). Fibrosis was provoked by repeated i.p. injections of CCl4.During in vitro transdifferentiation of mouse HSC to myofibroblasts, expression of BMP9 increased. Further, BMP9 induced proliferation in LX–2, a human HSC line. Target genes of BMP9 in HC include Id-proteins and hepcidin as well as several detoxifying enzymes. In combination with TGFβ, BMP9 or over expression of Id–1 strongly enhanced HC apoptosis. BMP9 (but not BMP2, –6 or TGFβ) induced Smad1 signaling was specifically inhibited by AdALK1-Fc, implying that ALK1-Fc is a specific inhibitor of BMP9 signaling. CCl4 provoked fibrogenesis in mice was significantly attenuated by co-injecting AdALK1-Fc. By Immunohistochemistry, we found that proliferation and apoptosis are reduced by AdALK1-Fc. Conclusion: BMP9 expression increases during fibrogenesis, induces proliferation of HSC, which secrete increasing amounts of BMP9 during transdifferentiation. In the presence of TGFβ (which increases after damage) this BMP9 mediates apoptosis of HC via induction of Id proteins. Proliferating HSC fill the space where HC died and bridging fibrosis forms. When BMP9 is neutralized, HSC proliferation and HC apoptosis are reduced resulting in less collagen deposition and reduced bridging. Thereby BMP9 plays an important pro-fibrogenic role in the liver.