title: Positive regulation of osteoclastic differentiation by growth differentiation factor 15 upregulated in osteocytic cells under hypoxia.
abstract: Osteocytes are thought to play a role as a mechanical sensor through their communication network in bone. Although osteocytes are the most abundant cells in bone, little attention has been paid to their physiological and pathological functions in skeletogenesis. Here, we have attempted to delineate the pivotal functional role of osteocytes in regulation of bone remodeling under pathological conditions. We first found markedly increased osteoclastic differentiation by conditioned media (CM) from osteocytic MLO-Y4 cells previously exposed to hypoxia in vitro. Using microarray and real-time PCR analyses, we identified growth differentiation factor 15 (GDF15) as a key candidate factor secreted from osteocytes under hypoxia. Recombinant GDF15 significantly promoted osteoclastic differentiation in a concentration-dependent manner, with concomitant facilitation of phosphorylation of both p65 and inhibitory-κB in the presence of receptor activator of nuclear factor-κB ligand. To examine the possible functional significance of GDF15 in vivo, mice were subjected to ligation of the right femoral artery as a hypoxic model. A significant increase in GDF15 expression was specifically observed in tibias of the ligated limb but not in tibias of the normally perfused limb. Under these experimental conditions, in cancellous bone of proximal tibias in the ligated limb, a significant reduction was observed in bone volume, whereas a significant increase was seen in the extent of osteoclast surface/bone surface when determined by bone histomorphometric analysis. Finally, the anti-GDF15 antibody prevented bone loss through inhibiting osteoclastic activation in tibias from mice with femoral artery ligation in vivo, in addition to suppressing osteoclastic activity enhanced by CM from osteocytes exposed to hypoxia in vitro. These findings suggest that GDF15 could play a pivotal role in the pathogenesis of bone loss relevant to hypoxia through promotion of osteoclastogenesis after secretion from adjacent osteocytes during disuse and/or ischemia in bone.
authors.affiliation: Laboratory of Molecular Pharmacology, Division of Pharmaceutical Sciences, Kanazawa University Graduate School of Natural Science and Technology, Kakuma-machi, Kanazawa, Ishikawa, Japan.
authors.forename: Eiichi
authors.initials: E
authors.lastname: Hinoi
authors.forename: Hiroki
authors.initials: H
authors.lastname: Ochi
authors.forename: Takeshi
authors.initials: T
authors.lastname: Takarada
authors.forename: Eri
authors.initials: E
authors.lastname: Nakatani
authors.forename: Takashi
authors.initials: T
authors.lastname: Iezaki
authors.forename: Hiroko
authors.initials: H
authors.lastname: Nakajima
authors.forename: Hiroyuki
authors.initials: H
authors.lastname: Fujita
authors.forename: Yoshifumi
authors.initials: Y
authors.lastname: Takahata
authors.forename: Shinya
authors.initials: S
authors.lastname: Hidano
authors.forename: Takashi
authors.initials: T
authors.lastname: Kobayashi
authors.forename: Shu
authors.initials: S
authors.lastname: Takeda
authors.forename: Yukio
authors.initials: Y
authors.lastname: Yoneda
mesh_terms: D000818:Animals; D000906:Antibodies / Q000008:administration & dosage / Q000494:pharmacology; D001862:Bone Resorption / Q000473:pathology; D002454:Cell Differentiation / Q000187:drug effects; D015687:Cell Hypoxia / Q000187:drug effects; D003035:Cobalt / Q000494:pharmacology; D005263:Femoral Artery / Q000187:drug effects / Q000473:pathology; D055436:Growth Differentiation Factor 15 / Q000037:antagonists & inhibitors / Q000378:metabolism*; D008026:Ligation; D051379:Mice; D008810:Mice, Inbred C57BL; D016328:NF-kappa B / Q000378:metabolism; D010010:Osteoclasts / Q000166:cytology* / Q000187:drug effects / Q000378:metabolism; D010011:Osteocytes / Q000166:cytology* / Q000187:drug effects / Q000378:metabolism*; D053245:RANK Ligand / Q000494:pharmacology; D015398:Signal Transduction / Q000187:drug effects; D012995:Solubility / Q000187:drug effects; D015854:Up-Regulation / Q000187:drug effects
chemical_list: D000906:Antibodies; D055436:Growth Differentiation Factor 15; D016328:NF-kappa B; D053245:RANK Ligand; D003035:Cobalt; C018021:cobaltous chloride