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5-HT release from platelets and activation of 5-HT2B play a crucial role for development of fibrosis in systemic sclerosis
  1. Clara Dees1,
  2. Alfiya Akhmetshina1,
  3. Nicole Busch1,
  4. Jochen Zwerina1,
  5. Michael Bader3,
  6. Georg Schett1,
  7. Oliver Distler2,
  8. Jörg H W Distler1
  1. 1Department of Internal Medicine, University of Erlangen, Erlangen, Germany
  2. 2Max Delbrück Center for Molecular Medicine, Berlin, Germany
  3. 3Ctr Exp Rheum and Zurich Ctr Integr Hum Physiol, Univ Hosp Zurich, Switzerland

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Purpose

Systemic sclerosis (SSc) is characterised by progressive vascular disease and organ fibrosis. Tryptophanhydroxylase-1 (tph-1) is the rate-limiting enzyme for the synthesis of 5-hydroxytryptamine (5-HT). After synthesis, 5-HT is stored in large amounts within platelets and can be released upon activation. The aim of the present study was to investigate the role of 5-HT release upon platelet activation and whether 5-HT signalling is involved in the pathogenesis of SSc.

Methods

Dermal fibroblasts from SSc patients and healthy individuals were stimulated with 5-HT and incubated with selective inhibitors of different 5-HT receptors. Expression of 5-hydroxytryptamine (serotonin) receptor 2B (5-HT2B) in human sections was analysed by immunohistochemistry. The role of platelet-derived 5-HT and of the 5-HT2B receptor was evaluated in the mouse model of bleomycin-induced dermal fibrosis and in tight-skin-1 (tsk-1) mice.

Results

Stimulation of SSc and healthy dermal fibroblasts with 5-HT significantly increased dose-dependently mRNA and protein levels of collagen by up to 3.1±0.14-fold (p<0.05 for each), which was significantly reduced upon incubation with the selective 5-HT2B inhibitor SB 204741. The expression of 5-HT2B protein was strongly increased in the skin of SSc patients compared to healthy volunteers. In the mouse models of bleomycin-induced fibrosis and tsk-1, the concentration of 5-HT in lesional skin significantly increased from 3.2±0.2 to 5.8±0.5 ng/mg and from 3.5±0.4 to 4.8±0.2 ng/mg, respectively, as analysed by ELISA. Treatment with clopidogrel significantly reduced the 5-HT content of the skin in both models. Along with reduced levels of 5-HT, treatment with clopidogrel decreased dermal thickening upon bleomycin-challenge and prevented also hypodermal thickening in tsk-1 mice. Also selective depletion of 5-HT from platelets by knockdown of tph-1 significantly ameliorated dermal fibrosis in mice lacking tph-1 with a mean reduction in dermal thickening of 61±6% (p<0.05). Mice lacking 5-HT2B were completely protected from bleomycin-induced skin fibrosis with normal skin thickness. Potent anti-fibrotic effects of 5-HT2B inhibitors with normalisation of histological changes and prevention of myofibroblast differentiation were also detected in the tsk-1 model.

Conclusion

We demonstrate increased levels of 5-HT in different animal models of SSc and an activation of 5-HT/5-HT2B signalling in SSc patients. Platelet activation in affected vessels, the subsequent release of the profibrotic mediator 5-HT and the activation of 5-HT2B might provide a novel link between vascular manifestations and tissue fibrosis in SSc.

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