ARTHRITIS & RHEUMATISM Vol. 64, No. 8, August 2012, pp 2724–2733 DOI 10.1002/art.34444 © 2012, American College of Rheumatology Hedgehog Signaling Controls Fibroblast Activation and Tissue Fibrosis in Systemic Sclerosis Angelika Horn, 1 Katrin Palumbo, 1 Cinzia Cordazzo, 2 Clara Dees, 1 Alfiya Akhmetshina, 1 Michal Tomcik, 3 Pawel Zerr, 1 Jerome Avouac, 4 Johannes Gusinde, 1 Jochen Zwerina, 1 Hermine Roudaut, 5 Elisabeth Traiffort, 5 Martial Ruat, 5 Oliver Distler, 6 Georg Schett, 1 and Jo ¨rg H. W. Distler 1 Objective. Hedgehog signaling not only plays cru- cial roles during human development but also has been implicated in the pathogenesis of several diseases in adults. The aim of the present study was to investigate the role of the hedgehog pathway in fibroblast activation in systemic sclerosis (SSc). Methods. Activation of the hedgehog pathway was analyzed by immunohistochemistry and real-time polymerase chain reaction (PCR). The effects of sonic hedgehog (SHH) on collagen synthesis were analyzed by reporter assays, real-time PCR, and Sircol assays. Myo- fibroblast differentiation was assessed by quantification of -smooth muscle actin and stress fiber staining. The role of hedgehog signaling in vivo was analyzed by adenoviral overexpression of SHH and using mice lack- ing 1 allele of the gene for inhibitory receptor Patched homolog 1 (Ptch / mice). Results. SHH was overexpressed and resulted in activation of hedgehog signaling in patients with SSc, with accumulation of the transcription factors Gli-1 and Gli-2 and increased transcription of hedgehog target genes. Activation of hedgehog signaling induced an activated phenotype in cultured fibroblasts, with differ- entiation of resting fibroblasts into myofibroblasts and increased release of collagen. Adenoviral overexpression of SHH in the skin of mice was sufficient to induce skin fibrosis. Moreover, Ptch / mice with increased hedge- hog signaling were more sensitive to bleomycin-induced dermal fibrosis. Conclusion. We demonstrated that the hedgehog pathway is activated in patients with SSc. Hedgehog signaling potently stimulates the release of collagen and myofibroblast differentiation in vitro and is sufficient to induce fibrosis in vivo. These findings identify the hedgehog cascade as a profibrotic pathway in SSc. Systemic sclerosis (SSc) is a fibrosing connective tissue disease that primarily affects the skin but also affects the lungs, heart, and gastrointestinal tract (1). Tissue fibrosis often results in failure of the affected organs and can cause high morbidity and increased mortality. Tissue fibrosis in SSc is caused by an excessive release of extracellular matrix (ECM) by aberrantly activated fibroblasts (2). However, the molecular mech- anisms underlying this pathologic and persistent activa- tion of SSc fibroblasts are incompletely understood. Supported by the Deutsche Forschungsgesellschaft (grants DI 1537/2-1, DI 1537/4-1, AK 144/1-1, and SCHE 1583/7-1), the Inter- disciplinary Center of Clinical Research, Erlangen (IZKF grant A20), CMH Research Project 00000023728, and the DFG (Immunobone program). 1 Angelika Horn, Katrin Palumbo, MSc, Clara Dees, Dipl Biol, Alfiya Akhmetshina, PhD, Pawel Zerr, MSc, Johannes Gusinde, PhD, Jochen Zwerina, MD, Georg Schett, MD, Jo ¨rg H. W. Distler, MD: University of Erlangen–Nuremberg, Erlangen, Germany; 2 Cinzia Cordazzo: University of Erlangen–Nuremberg, Erlangen, Germany, and University of Pisa, Pisa, Italy; 3 Michal Tomcik, MD: University of Erlangen–Nuremberg, Erlangen, Germany, and Charles University Prague, Prague, Czech Republic; 4 Jerome Avouac, MD, PhD: Univer- sity of Erlangen–Nuremberg, Erlangen, Germany, and Paris Descartes University, Cochin Hospital, AP-HP, Paris, France; 5 Hermine Rou- daut, PhD, Elisabeth Traiffort, PhD, Martial Ruat, PhD: CNRS, UPR3294, Institut de Neurobiologie Alfred Fessard IFR2118, Gif-sur- Yvette, France; 6 Oliver Distler, MD: Zurich Center of Integrative Human Physiology and University Hospital Zurich, Zurich, Switzer- land. Dr. O. Distler has received consulting fees from Actelion, Pfizer, Ergonex, Bristol-Myers Squibb, Sanofi-Aventis, United Bio- Source, Medac, Swedish Orphan Biovitrum, Novartis, 4D Sciences, and Active Biotec (less than $10,000 each). Dr. J. H. W. Distler has received consulting fees, speaking fees, and/or honoraria from Acte- lion, Pfizer, Ergonex, Bristol-Myers Squibb, Celgene, Bayer Pharma, JB Therapeutics, Anaphore, Sanofi-Aventis, Novartis, Array Bio- pharma, and Active Biotec, and he owns stock in 4D Sciences. Address correspondence to Jo ¨rg H. W. Distler, MD, Depart- ment of Internal Medicine 3 and Institute for Clinical Immunology, University of Erlangen–Nuremberg, Germany. E-mail: joerg.distler@ uk-erlangen.de. Submitted for publication June 2, 2011; accepted in revised form February 14, 2012. 2724