Arthritis & Rheumatism, Volume 63,
November 2011 Abstract Supplement

Abstracts of the American College of
Rheumatology/Association of Rheumatology Health Professionals
Annual Scientific Meeting
Chicago, Illinois November 4-9, 2011.


JAK2 Mediates the Stimulatory Effects of Transforming Growth Factor beta on Fibroblast Activation and Tissue Fibrosis.

Dees1,  Clara, Tomcik2,  Michal, Palumbo1,  Katrin, Akhmetshina3,  Alfiya, Horn1,  Angelika, Zerr1,  Pawel, Distler4,  Oliver

Department of Internal Medicine 3 and Institute for Clinical Immunology, University of Erlangen-Nuremberg, Erlangen, Germany
Institute of Rheumatology, Department of Clinical and Experimental Rheumatology, 1st Faculty of Medicine, Charles University, Prague, Czech Republic
Department of Internal Medicine III and Institute for Clinical Immunology, University of Erlangen-Nuremberg, Erlangen, Germany
University Hospital Zurich, Zurich, Switzerland

Background/Purpose:

Systemic sclerosis (SSc) is characterized by an uncontrolled activation of fibroblasts resulting in the release of excessive amounts of extracellular matrix components. Janus kinase 2 (JAK2) is a key-regulator of cytokine signaling and mutations in the JAK2 gene have been identified as key-event in the molecular pathogenesis of myeloproliferative diseases. In the present study, we evaluated the role of JAK2 in the pathogenesis of SSc and analyzed the potential of JAK2 inhibition as a novel anti-fibrotic approach.

Methods:

Activation of JAK2 was determined by immunohistochemistry for pJAK2. Dermal fibroblasts were stimulated with TGFb and incubated with the specific JAK2 inhibitor TG 101209 in different concentrations. Fibroblast activation was determined by staining for a-smooth muscle actin (aSMA) and stress fibers. Bleomycin-induced dermal fibrosis and tight-skin 1 (Tsk-1) mice were used to evaluate the anti-fibrotic potential of a specific JAK2 inhibition in vivo.

Results:

Increased activation of JAK2 with prominent accumulation of pJAK2 particularly in fibroblasts was observed in skin of SSc patients. Of note, the activation of JAK2 persisted in cultured SSc fibroblasts. Inhibition of JAK2 by the selective JAK2 inhibitor TG 101209 or by siRNA abrogated the activated phenotype of SSc fibroblasts by decreasing the formation of stress fibers by 41 ± 5 %, the expression of aSMA by 41 ± 6 % and the basal mRNA levels of col 1a1 and col 1a2 by 59 ± 4 % and 51 ± 3 % (p < 0.05 each). These inhibitory effects in the absence of exogenous stimulation were only observed in SSc fibroblasts, but not in resting healthy dermal fibroblasts. However, stimulation of healthy fibroblasts with TGFb increased time-dependently the levels of pJAK2. Pre-incubation with TG 101209 abrogated the stimulatory effects of TGFb on fibroblast activation with decreases in stress fiber formation by 74 ± 12 %, aSMA expression by 84 ± 11 % (p < 0.05) and reduced col 1a1 and col 1a2 mRNA levels by 90 ± 21 % and 92 ± 14 % (p < 0.05). In addition, the expression of the TGFb target genes CTGF and PAI-1 was potently reduced. Consistently, inhibition of JAK2 exerted potent anti-fibrotic effects in experimental fibrosis. In the model of bleomycin-induced fibrosis, treatment with TG 101209 decreased dermal thickening by 95 ± 5 % (p = 0.007), hydroxyproline content by 76 ± 7 % (p < 0.001) and myofibroblast counts completely back to baseline levels (p = 0.001). Potent anti-fibrotic effects were also observed in the Tsk-1 model. Application of TG 101209 reduced hypodermal thickening, hydroxyproline content and myofibroblast counts by 82 ± 10 % (p = 0.002), 75 ± 25 % (p = 0.03) and 99 ± 13 % (p = 0.01).

Conclusion:

We demonstrate that JAK2 is activated in SSc in a TGFb-dependent manner and mediates the stimulatory effects of TGFb on fibroblasts. Inhibition of JAK2 reduced collagen synthesis specifically in SSc fibroblasts, prevented fibroblast activation and exerted potent anti-fibrotic effects in experimental fibrosis. As inhibitors of JAK2 are currently evaluated in clinical trials for myeloproliferative disorders and are well tolerated, our findings might have direct translational implications and stimulate clinical trials with JAK2 inhibitors in SSc patients.

To cite this abstract, please use the following information:
Dees, Clara, Tomcik, Michal, Palumbo, Katrin, Akhmetshina, Alfiya, Horn, Angelika, Zerr, Pawel, et al; JAK2 Mediates the Stimulatory Effects of Transforming Growth Factor beta on Fibroblast Activation and Tissue Fibrosis. [abstract]. Arthritis Rheum 2011;63 Suppl 10 :2427
DOI:

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