title: Thrombin receptor deficiency leads to a high bone mass phenotype by decreasing the RANKL/OPG ratio.
abstract: Thrombin and its receptor (TR) are, respectively, expressed in osteoclasts and osteoblasts. However, their physiological roles on bone metabolism have not been fully elucidated. Here we investigated the bone microarchitecture by micro-computed tomography (μCT) and demonstrated increased trabecular and cortical bone mass in femurs of TR KO mice compared to WT littermates. Trabecular thickness and connectivity were significantly enhanced. The physiological role of TR on both inorganic and organic phases of bone is illustrated by a significant increase in BMD and a decrease in urinary deoxypyridinoline (DPD) crosslink concentration in TR KO mice. Moreover, TR KO cortical bone expanded and had a higher polar moment of inertia (J), implying stronger bone. Bone histomorphometry illustrated unaltered osteoblast and osteoclast number and surface in femoral metaphyses, indicating that thrombin/TR regulates osteoblasts and osteoclasts at functional levels. Serum analysis showed a decrease in RANKL and an increase in osteoprotegerin (OPG) levels and reflected a reduced RANKL/OPG ratio in the TR KO group. In vitro experiments using MC3T3 pre-osteoblasts demonstrated a TR-dependent stimulatory effect of thrombin on the RANKL/OPG ratio. This effect was blocked by TR antagonist and p42/p44-ERK inhibitor. In addition, thrombin also intensified p42/p44-ERK expression and phosphorylation. In conclusion, the thrombin/TR system maintains normal bone remodeling by activating RANKL and limiting OPG synthesis by osteoblasts through the p42/44-ERK signaling pathway. Consequently, TR deficiency inhibits osteoclastogenesis, resulting in a high bone mass phenotype.
authors.affiliation: Department of Physiology, Radboud Institute for Molecular Life Sciences, Radboud University Medical Center, The Netherlands.
authors.forename: Kukiat
authors.initials: K
authors.lastname: Tudpor
authors.affiliation: Department of Internal Medicine, Erasmus Medical Center, Rotterdam, The Netherlands.
authors.forename: Bram C J
authors.initials: BC
authors.lastname: van der Eerden
authors.affiliation: Department of Physiology, Radboud Institute for Molecular Life Sciences, Radboud University Medical Center, The Netherlands.
authors.forename: Prapaporn
authors.initials: P
authors.lastname: Jongwattanapisan
authors.affiliation: Department of Pathology, Academic Medical Center, University of Amsterdam, Amsterdam, The Netherlands.
authors.forename: Joris J T H
authors.initials: JJ
authors.lastname: Roelofs
authors.affiliation: Department of Internal Medicine, Erasmus Medical Center, Rotterdam, The Netherlands.
authors.forename: Johannes P T M
authors.initials: JP
authors.lastname: van Leeuwen
authors.affiliation: Department of Physiology, Radboud Institute for Molecular Life Sciences, Radboud University Medical Center, The Netherlands.
authors.forename: René J M
authors.initials: RJ
authors.lastname: Bindels
authors.affiliation: Department of Physiology, Radboud Institute for Molecular Life Sciences, Radboud University Medical Center, The Netherlands. Electronic address: Joost.Hoenderop@radboudumc.nl.
authors.forename: Joost G J
authors.initials: JG
authors.lastname: Hoenderop
mesh_terms: D016475:3T3 Cells; D000818:Animals; D001862:Bone Resorption; D001842:Bone and Bones / Q000473:pathology / Q000502:physiology*; D018938:Caco-2 Cells; D002118:Calcium / Q000737:chemistry; D005269:Femur / Q000473:pathology; D006801:Humans; D008297:Male; D051379:Mice; D008810:Mice, Inbred C57BL; D018345:Mice, Knockout; D016328:NF-kappa B / Q000378:metabolism; D010006:Osteoblasts / Q000378:metabolism; D053244:Osteoprotegerin / Q000378:metabolism*; D010641:Phenotype; D016133:Polymerase Chain Reaction; D053245:RANK Ligand / Q000378:metabolism*; D018179:Receptors, Thrombin / Q000172:deficiency / Q000235:genetics*; D015398:Signal Transduction; D013917:Thrombin / Q000378:metabolism; D055114:X-Ray Microtomography
chemical_list: D016328:NF-kappa B; D053244:Osteoprotegerin; D053245:RANK Ligand; D018179:Receptors, Thrombin; C506030:TNFRSF11B protein, human; C505688:TNFSF11 protein, human; C506031:Tnfrsf11b protein, mouse; C505689:Tnfsf11 protein, mouse; D013917:Thrombin; D002118:Calcium
keywords: Osteoblast; Osteopetrosis; Osteoprotegerin; Receptor activator of nuclear factor-κB ligand; Thrombin receptor