title: Effect of M3 muscarinic acetylcholine receptor deficiency on collagen antibody-induced arthritis.
abstract: BACKGROUND
  There is increasing evidence that the non-neuronal cholinergic system might be of importance for the pathology of rheumatoid arthritis. The role of M3 muscarinic acetylcholine receptor (M3R) in this regard has, however, not been investigated to date. Thus, in the present study we analyzed if M3R deficiency might have a protective effect on experimentally induced arthritis.
  
  
  METHODS
  Collagen antibody-induced arthritis (CAIA) was evoked in M3R-deficient (M3R(-/-)) mice and wild-type (WT) littermates. Severity of arthritis was assessed by scoring of paw swelling. The joints of arthritic and nonarthritic animals were analyzed for histopathological changes regarding synovial tissue, cartilage degradation and bone destruction. Further, gene expression analysis of respective markers was performed. Systemic and local inflammatory response was determined by flow cytometry and immunohistochemistry for leukocytes as well as mRNA and protein measurements for pro-inflammatory cytokines and chemokines.
  
  
  RESULTS
  In arthritic M3R(-/-) mice the number of leukocytes, specifically neutrophils, was enhanced even though clinical arthritis score was not significantly different between WT and M3R(-/-) mice with CAIA. In M3R(-/-) mice, levels of neutrophil chemoattractant chemokine C-X-C-motif ligand 2 (CXCL2) as well as the pro-inflammatory cytokine interleukin-6 were already strongly increased in mice with low arthritis score, whereas WT mice only showed prominent expression of these markers when reaching high arthritis scores. Furthermore, arthritic M3R(-/-) mice displayed a stronger degradation of collagen II in the articular cartilage and, most strikingly, histopathological evaluation revealed more severe bone destruction in arthritic mice with M3R deficiency compared to WT littermates. Moreover, in M3R(-/-) mice, gene expression of markers for bone degradation (matrix metalloproteinase 13, cathepsin K and receptor activator of nuclear factor-κB ligand) was already increased in mice with low arthritis score.
  
  
  CONCLUSIONS
  Taken together, the present study shows that while M3R(-/-) mice were not protected from CAIA, they had a tendency toward a higher inflammatory response after arthritis induction than WT mice. Further, arthritis-induced joint destruction was significantly stronger in mice with M3R deficiency, indicating that stimulation of M3R might have protective effects on arthritis.
authors.affiliation: Laboratory of Experimental Trauma Surgery, Justus-Liebig University Giessen, Kerkraderstrasse 9, 35394, Giessen, Germany. janet.beckmann@chiru.med.uni-giessen.de.
authors.forename: Janet
authors.initials: J
authors.lastname: Beckmann
authors.affiliation: Laboratory of Experimental Trauma Surgery, Justus-Liebig University Giessen, Kerkraderstrasse 9, 35394, Giessen, Germany. nicole.dittmann@med.uni-giessen.de.
authors.forename: Nicole
authors.initials: N
authors.lastname: Dittmann
authors.affiliation: Laboratory of Experimental Trauma Surgery, Justus-Liebig University Giessen, Kerkraderstrasse 9, 35394, Giessen, Germany. iris.schuetz@chiru.med.uni-giessen.de.
authors.forename: Iris
authors.initials: I
authors.lastname: Schütz
authors.affiliation: Department of Pharmacology, School of Pharmacy, Goethe-University Frankfurt, Max-von-Laue Strasse 9, 60438, Frankfurt am Main, Germany. klein@em.uni-frankfurt.de.
authors.forename: Jochen
authors.initials: J
authors.lastname: Klein
authors.affiliation: Laboratory of Experimental Trauma Surgery, Justus-Liebig University Giessen, Kerkraderstrasse 9, 35394, Giessen, Germany. katrin.s.lips@chiru.med.uni-giessen.de.
authors.forename: Katrin Susanne
authors.initials: KS
authors.lastname: Lips
mesh_terms: D000818:Animals; D001169:Arthritis, Experimental / Q000378:metabolism* / Q000473:pathology*; D005260:Female; D018836:Inflammation Mediators / Q000378:metabolism; D008297:Male; D051379:Mice; D008810:Mice, Inbred C57BL; D018345:Mice, Knockout; D043587:Receptor, Muscarinic M3 / Q000172:deficiency*
chemical_list: D018836:Inflammation Mediators; D043587:Receptor, Muscarinic M3