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Inactivation of fatty acid amide hydrolase exacerbates experimental fibrosis by enhanced endocannabinoid-mediated activation of CB1
  1. Katrin Palumbo-Zerr1,
  2. Angelika Horn1,
  3. Alfiya Distler1,
  4. Pawel Zerr1,
  5. Clara Dees1,
  6. Christian Beyer1,
  7. Enrico Selvi2,
  8. Benjamin F Cravatt3,
  9. Oliver Distler4,
  10. Georg Schett1,
  11. Jörg H W Distler1
  1. 1Department of Internal Medicine III and Institute for Clinical Immunology, University of Erlangen-Nuremberg, Erlangen, Germany
  2. 2Department of Clinical Medicine and Immunological Sciences, University of Siena, Siena, Italy
  3. 3The Department of Chemical Physiology and The Skaggs Institute for Chemical Biology, The Scripps Research Institute, La Jolla, California, USA
  4. 4Center of Experimental Rheumatology and Zurich Center of Integrative Human Physiology, University Hospital Zurich, Zurich, Switzerland
  1. Correspondence to Dr Jörg H W Distler, Department of Internal Medicine III and Institute for Clinical Immunology, University of Erlangen-Nuremberg, Ulmenweg 18, Erlangen D-91054, Germany; joerg.distler{at}uk-erlangen.de

Abstract

Background Selective targeting of the cannabinoid receptors CB1 and CB2 by synthetic compounds has revealed opposing roles of both receptors in fibrosis.

Objectives To characterise the role of endogenous cannabinoids (endocannabinoids) and their predominant receptor in fibrosis.

Methods The levels of endocannabinoids in mice were modulated by pharmacological or genetic inactivation of the enzyme fatty acid amide hydrolase (FAAH). The predominant receptor for endocannabinoids was determined by selective inhibition of either CB1 or CB2. The extent of fibrosis upon challenge with bleomycin was determined by quantification of dermal thickness, hydroxyproline content and myofibroblast counts.

Results The expression of FAAH is decreased in systemic sclerosis fibroblasts. FAAH-deficient mice with strongly increased levels of endocannabinoids were more sensitive to bleomycin. Consistently, pharmacological inhibition of FAAH significantly exacerbated bleomycin-induced fibrosis. Inhibition of CB1 completely abrogated the profibrotic effects of FAAH inactivation. In contrast, inhibition of CB2 only modestly enhanced fibrosis, indicating that CB1 is the predominant receptor for endocannabinoids in experimental fibrosis.

Conclusions Increased levels of endocannabinoids induced by inactivation of FAAH worsen experimental fibrosis via activation of CB1. These findings highlight the profibrotic effects of endocannabinoids and suggest that CB1 maybe a more promising candidate for targeted treatments in fibrotic diseases than CB2.

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