Arthritis & Rheumatism, Volume 62,
November 2010 Abstract Supplement

Abstracts of the American College of
Rheumatology/Association of Rheumatology Health Professionals
Annual Scientific Meeting
Atlanta, Georgia November 6-11, 2010.


Nr4a1 Ameliorates the Pro-Fibrotic Effects of TGF in Systemic Sclerosis (SSc) and Might Be an Interesting Target for Anti-Fibrotic Therapies.

Palumbo1,  Katrin, Akhmetshina1,  Alfiya, Zerr1,  Pawel, Tomcik1,  Michal, Horn1,  Angelika, Dees1,  Clara, Distler3,  Oliver

Department of Internal Medicine III and Institute for Clinical Immunology, University of Erlangen-Nuremberg, Erlangen, Germany
Friedrich Alexander Univ, Erlangen, Germany
University Hospital Zurich, Zurich, Switzerland
University of Erlangen, Erlangen, Germany

Background:

Nuclear receptor 4 a 1 (Nr4a1) is a unique transcription factor which belongs to the superfamily of orphan nuclear receptors. Unlike most nuclear receptors, members of Nr4a receptors do not seem to require ligand binding for activation. Nr4a1 is known to be a regulator of macrophage gene expression in inflammation, cell death and cell growth. The aim of the present study was to investigate the role of Nr4a1 in TGFb signaling and in the pathogenesis of SSc.

Methods:

The expression of Nr4a1 in cells and tissue was analyzed by real-time PCR, Western Blot and immunofluorescence. Collagen synthesis was quantified by real-time PCR, SirCol- and hydroxyproline assay. The role of Nr4a1 in fibrosis and potential therapeutic implication were evaluated in three different mouse models: bleomycin-induced dermal fibrosis, tight-skin-1 (tsk-1) mice and mice infected with adenovirus overexpressing constitutively active TGFb receptor I.

Results:

The expression of Nr4a1 was significantly elevated in the skin of SSc patients compared to healthy controls. Moreover, mRNA levels of Nr4a1 were increased in cultured SSc fibroblasts. Stimulation with TGFb strongly increased the mRNA and protein levels of Nr4a1 in cultured fibroblasts, indicating that TGFb might drive the overexpression in SSc. siRNA-mediated knock-down of Nr4a1 in human fibroblasts potently induced the expression of collagen mRNA and protein. An increased release of collagen was also observed in murine fibroblasts isolated from Nr4a1 deficient mice. On the other hand, stimulation of Nr4a1 signaling, either by overexpression of Nr4a1 or by incubation with the Nr4a1 agonist Cytosporone B, strongly reduced the collagen synthesis in cultured fibroblasts. These data suggest that Nr4a1 is in the centre of a negative feedback loop, which restricts the pro-fibrotic effects of TGFb in SSc. Consistently, mice lacking Nr4a1 were more sensitive to bleomycin induced fibrosis with 2 fold more pronounced dermal thickening, myofibroblast counts and hydroxyproline content upon challenge with bleomycin compared to wildtype mice. Moreover, AAV-TGFRI virus infected Nr4a1 deficient mice and tsk-1 mice lacking Nr4a1 showed also significantly increased fibrosis compared to control mice expressing Nr4a1. Next, we investigated, whether therapeutic activation of Nr4a1 by Cytosporone B prevents experimental fibrosis. Treatment with Cytosporone B completely prevented fibrosis in all mouse models and reduced dermal thickness, myofibroblast counts and hydroxyproline content to levels similar to control mice.

Conclusion:

We demonstrate that Nr4a1 is upregulated in SSc in a TGFb dependent manner. Nr4a1 negatively regulates the extracellular matrix (ECM) production by limiting the pro-fibrotic effects of TGFb in vitro as well as in vivo. Thus, we first describe a negative feedback loop, in which the concomitant upregulation of Nr4a1 limits the pro-fibrotic effects of TGFb in SSc. In addition, activation of Nr4a1 signaling by Cytosporone B might be a novel therapeutic approach for fibrotic diseases.

To cite this abstract, please use the following information:
Palumbo, Katrin, Akhmetshina, Alfiya, Zerr, Pawel, Tomcik, Michal, Horn, Angelika, Dees, Clara, et al; Nr4a1 Ameliorates the Pro-Fibrotic Effects of TGF in Systemic Sclerosis (SSc) and Might Be an Interesting Target for Anti-Fibrotic Therapies. [abstract]. Arthritis Rheum 2010;62 Suppl 10 :611
DOI: 10.1002/art.28379

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