title: Inhibitory effect of saliva on osteoclastogenesis in vitro requires toll-like receptor 4 signaling.
abstract: OBJECTIVE
  Saliva can suppress osteoclastogenesis, but the underlying mechanism has not been discovered yet. Considering that endotoxins suppress osteoclastogenesis in bone marrow cultures and that saliva contains endotoxins, it was reasonable to hypothesize that the impact of saliva on osteoclastogenesis requires toll-like receptor 4 signaling.
  
  
  METHODS
  To test this hypothesis, we blocked toll-like receptor 4 signaling with TAK-242 in the presence of saliva in murine bone marrow cultures. Osteoclastogenesis was evaluated based on gene expression analysis and histochemical staining for tartrate-resistant acid phosphatase. Resorption was performed on dentine.
  
  
  RESULTS
  We report that TAK-242 reversed the inhibitory effect of fresh sterile saliva on the formation of multinucleated cells that stained positive for tartrate-resistant acid phosphatase. In line with this finding, TAK-242 increased the expression of the osteoclast functional genes cathepsin K, calcitonin receptor, and tartrate-resistant acid phosphatase in the presence of saliva. TAK-242 also supported the expression of NFATc1, the master regulator of osteoclastogenesis, as well as DC-STAMP and Atp6v0d2, both being cell fusion genes. In support of the hypothesis, depletion of saliva from endotoxin partially reversed the inhibitory effect on osteoclastogenesis. Moreover, salivary pellicle on plastic and titanium did not affect osteoclastogenesis.
  
  
  CONCLUSIONS
  Inhibition of toll-like receptor 4 signaling revealed that saliva can contribute to innate immunity by preventing hematopoietic progenitors to become osteoclasts.
  
  
  CONCLUSIONS
  Saliva can activate pattern recognition receptor signaling through endotoxins and other stress factors, indicating the demand for macrophages rather than for osteoclasts.
authors.affiliation: Department of Preventive, Restorative and Pediatric Dentistry, School of Dental Medicine, University of Bern, Freiburgstrasse 7, 3010, Bern, Switzerland.
authors.forename: Heinz-Dieter
authors.initials: HD
authors.lastname: Müller
authors.affiliation: Department of Oral Surgery and Stomatology, School of Dental Medicine|, University of Bern, Bern, Switzerland.|Department of Oral and Maxillofacial Surgery, School of Dental Medicine, Universitat Internacional de Catalunya, Barcelona, Spain.
authors.forename: Jordi
authors.initials: J
authors.lastname: Caballé-Serrano
authors.affiliation: Department of Preventive, Restorative and Pediatric Dentistry, School of Dental Medicine, University of Bern, Freiburgstrasse 7, 3010, Bern, Switzerland.
authors.forename: Adrian
authors.initials: A
authors.lastname: Lussi
authors.affiliation: Department of Preventive, Restorative and Pediatric Dentistry, School of Dental Medicine, University of Bern, Freiburgstrasse 7, 3010, Bern, Switzerland. reinhard.gruber@zmk.unibe.ch.|Department of Oral Biology, Medical University of Vienna, Sensengasse 2a, 1090, Vienna, Austria. reinhard.gruber@zmk.unibe.ch.
authors.forename: Reinhard
authors.initials: R
authors.lastname: Gruber
mesh_terms: D000818:Animals; D015415:Biomarkers / Q000032:analysis; D001854:Bone Marrow Cells / Q000502:physiology*; D018929:Cell Culture Techniques; D005260:Female; D006801:Humans; D066298:In Vitro Techniques; D051379:Mice; D008807:Mice, Inbred BALB C; D010010:Osteoclasts / Q000502:physiology*; D010012:Osteogenesis / Q000502:physiology*; D012463:Saliva / Q000502:physiology*; D015398:Signal Transduction; D013449:Sulfonamides / Q000494:pharmacology*; D000071681:Tartrate-Resistant Acid Phosphatase; D014025:Titanium / Q000494:pharmacology; D051197:Toll-Like Receptor 4 / Q000502:physiology*
chemical_list: D015415:Biomarkers; D013449:Sulfonamides; D051197:Toll-Like Receptor 4; C507035:ethyl 6-(N-(2-chloro-4-fluorophenyl)sulfamoyl)cyclohex-1-ene-1-carboxylate; D014025:Titanium; D000071681:Tartrate-Resistant Acid Phosphatase
keywords: Dentistry; Endotoxin; Murine bone marrow; Osteoclast; Saliva; Toll-like receptor