In a search for factors up-regulated by mechanical strain in osteocytes, we discovered that chemokine (C-C motif) ligand 7 (CCL7), a chemotactic myokine, was highly expressed in MLO-Y4 osteocyte-like cells. Although MLO-Y4 cells secrete potent chemotactic factors for osteoclast precursors, CCL7 was not responsible for this activity. CCL7 was increased in osteocytes in response to tooth movement in vivo. Since mechanical loading plays a crucial role in maintaining osteocyte viability, CCL7 was tested for protective activity and found to be protective against cell death induced by dexamethasone and etoposide. CCL7 specific antibody partially, but in combination with indomethacin, completely abrogated the protective effects of fluid flow shear stress against dexamethasone-induced cell death. CCL7 activated the β-catenin pathway through phosphorylation of glycogen synthase kinase 3 (GSK-3), suggesting that this pathway is responsible for the observed protective effects. A related cytokine, CCL2, also produced by MLO-Y4 cells but not regulated by mechanical loading, proved to be more potent and protected against cell death induced by not only dexamethasone, but also by Tumor Necrosis Factor α (TNFα). Whereas osteocytes may produce CCL2 in constitutively low levels, a major function of mechanically induced CCL7 may be to selectively protect osteocytes in an autocrine manner against glucocorticoid-induced cell death.
AguirreJI1PlotkinLIStewartSAWeinsteinRSParfittAMManolagasSC. (2006). Osteocyte apoptosis is induced by weightlessness in mice and precedes osteoclast recruitment and bone loss. J Bone Miner Res21:605-615.
2.
AhujaSSZhaoSBellidoTPlotkinLIJimenezFBonewaldLF (2003). CD40 ligand blocks apoptosis induced by tumor necrosis factor alpha, glucocorticoids, and etoposide in osteoblasts and the osteocyte-like cell line murine long bone osteocyte-Y4. Endocrinology144:1761-1769.
3.
BakkerAKlein-NulendJBurgerE (2004). Shear stress inhibits while disuse promotes osteocyte apoptosis. Biochem Biophys Res Commun320:1163-1168.
4.
BeerakaSSNatarajanKPatilRManneRKPrathiVSKolaparthiVS (2013). Clinical and radiological assessment of effects of long-term corticosteroid therapy on oral health. Dent Res J (Isfahan)10:666-673.
5.
BoehmeSALioFMMaciejewski-LenoirDBaconKBConlonPJ (2000). The chemokine fractalkine inhibits Fas-mediated cell death of brain microglia. J Immunol165:397-403.
6.
ChenDJiXHarrisMAFengJQKarsentyGCelesteAJ. (1998). Differential roles for bone morphogenetic protein (BMP) receptor type IB and IA in differentiation and specification of mesenchymal precursor cells to osteoblast and adipocyte lineages. J Cell Biol142:295-305.
7.
ChenWQingHHeYWangJZhuZWangH (2010). Gene expression patterns of osteocyte-like MLO-Y4 cells in response to cyclic compressive force stimulation. Cell Biol Int34:425-432.
8.
FengJQWardLMLiuSLuYXieYYuanB. (2006). Loss of DMP1 causes rickets and osteomalacia and identifies a role for osteocytes in mineral metabolism. Nat Genet38:1310-1315.
9.
FrostHM (1960). Measurement of osteocytes per unit volume and volume components of osteocytes and canaliculae in man. Henry Ford Hosp Med Bull8:208-211.
10.
GoveyPMJacobsJMTiltonSCLoiselleAEZhangYFreemanWM. (2014). Integrative transcriptomic and proteomic analysis of osteocytic cells exposed to fluid flow reveals novel mechano-sensitive signaling pathways. J Biomech47:1838-1845.
11.
GuGHentunenTANarsMHärkönenPLVäänänenHK (2005). Estrogen protects primary osteocytes against glucocorticoid-induced apoptosis. Apoptosis10:583-595.
12.
HoshinoAUehaSHanadaSImaiTItoMYamamotoK. (2013). Roles of chemokine receptor CX3CR1 in maintaining murine bone homeostasis through the regulation of both osteoblasts and osteoclasts. J Cell Sci126(Pt 4):1032-1045.
13.
JähnKLara-CastilloNBrottoLMoCLJohnsonMLBrottoM. (2012). Skeletal muscle sectreted factors prevent glucocorticoid-induced osteocyte apoptosis through activation of β-catenin. Eur Cell Mater24:197-209.
14.
JilkaRLWeinsteinRSBellidoTRobersonPParfittAMManolagasSC (1999). Increased bone formation by prevention of osteoblast apoptosis with parathyroid hormone. J Clin Invest104:439-446.
15.
KitaseYBarraganLQingHKondohSJiangJXJohnsonML. (2010). Mechanical induction of PGE2 in osteocytes blocks glucocorticoid-induced apoptosis through both the beta-catenin and PKA pathways. J Bone Miner Res25:2657-2668.
16.
KuriharaTBravoR (1996). Cloning and functional expression of mCCR2, a murine receptor for the C-C chemokines JE and FIC. J Biol Chem271:11603-11607.
17.
LeuchtPTemiyasathitSRussellAArguelloJFJacobsCRHelmsJA. (2013). CXCR4 antagonism attenuates load-induced periosteal bone formation in mice. J Orthop Res31:1828-1838.
18.
LiADubeySVarneyMLDaveBJSinghRK (2003). IL-8 directly enhanced endothelial cell survival, proliferation, and matrix metalloproteinases production and regulated angiogenesis. J Immunol170:3369-3376.
19.
LiXOminskyMSNiuQTSunNDaughertyBD’AgostinD. (2008). Targeted deletion of the sclerostin gene in mice results in increased bone formation and bone strength. J Bone Miner Res23:860-869.
20.
LiuSZhouJTangWJiangXRoweDWQuarlesLD (2006). Pathogenic role of Fgf23 in Hyp mice. Am J Physiol Endocrinol Metab291:E38-E49.
21.
MannVHuberCKogianniGJonesDNobleB (2006). The influence of mechanical stimulation on osteocyte apoptosis and bone viability in human trabecular bone. J Musculoskelet Neuronal Interact6:408-417.
22.
ManolagasSC (2000). Birth and death of bone cells: basic regulatory mechanisms and implications for the pathogenesis and treatment of osteoporosis. Endocr Rev21:115-137.
23.
NakashimaTHayashiMFukunagaTKurataKOh-HoraMFengJQ. (2011). Evidence for osteocyte regulation of bone homeostasis through RANKL expression. Nat Med17:1231-1234.
24.
NobleBSPeetNStevensHYBrabbsAMosleyJRReillyGC. (2003). Mechanical loading: biphasic osteocyte survival and targeting of osteoclasts for bone destruction in rat cortical bone. Am J Physiol Cell Physiol284:C934-C943.
25.
O’BrienCAJiaDPlotkinLIBellidoTPowersCCStewartSA. (2004). Glucocorticoids act directly on osteoblasts and osteocytes to induce their apoptosis and reduce bone formation and strength. Endocrinology145:1835-1841.
OtaKQuintPWeivodaMMRuanMPedersonLWestendorfJJ. (2013). Transforming growth factor beta 1 induces CXCL16 and leukemia inhibitory factor expression in osteoclasts to modulate migration of osteoblast progenitors. Bone57:68-75.
28.
PaicFIgweJCNoriRKronenbergMSFranceschettiTHarringtonP. (2009). Identification of differentially expressed genes between osteoblasts and osteocytes. Bone45:682-692.
29.
ParfittAM (1977). The cellular basis of bone turnover and bone loss: a rebuttal of the osteocytic resorption–bone flow theory. Clin Orthop Relat Res127:236-247.
30.
PavlinDGoldmanESGluhak-HeinrichJMagnessMZadroR (2000). Orthodontically stressed periodontium of transgenic mouse as a model for studying mechanical response in bone: the effect on the number of osteoblasts. Clin Orthod Res3:55-66.
31.
PlotkinLIWeinsteinRSParfittAMRobersonPKManolagasSCBellidoT (1999). Prevention of osteocyte and osteoblast apoptosis by bisphosphonates and calcitonin. J Clin Invest104:1363-1374.
32.
RollinsBJ (1997). Chemokines. Blood90:909-928.
33.
SchmidtSRainerJPlonerCPresulERimlSKoflerR (2004). Glucocorticoid-induced apoptosis and glucocorticoid resistance: molecular mechanisms and clinical relevance. Cell Death Differ11(Suppl 1):S45-S55.
34.
ShahnazariMChuVWronskiTJNissensonRAHalloranBP (2013). CXCL12/CXCR4 signaling in the osteoblast regulates the mesenchymal stem cell and osteoclast lineage populations. FASEB J27:3505-3513.
35.
TarzamiSTCalderonTMDeguzmanALopezLKitsisRNBermanJW (2005). MCP-1/CCL2 protects cardiac myocytes from hypoxia-induced apoptosis by a G(alphai)-independent pathway. Biochem Biophys Res Commun335:1008-1016.
36.
TeitelbaumSL (2004). Postmenopausal osteoporosis, T cells, and immune dysfunction. Proc Natl Acad Sci USA101:16711-16712.
37.
ThorburnA (2004). Death receptor-induced cell killing. Cell Signal16:139-144.
38.
TomkinsonAReeveJShawRWNobleBS (1997). The death of osteocytes via apoptosis accompanies estrogen withdrawal in human bone. J Clin Endocrinol Metab82:3128-3135.
39.
VerborgtOGibsonGJSchafflerMB (2000). Loss of osteocyte integrity in association with microdamage and bone remodeling after fatigue in vivo. J Bone Miner Res15:60-67.
40.
WangZGuoJ (2013). Mechanical induction of BMP-7 in osteocyte blocks glucocorticoid-induced apoptosis through PI3K/AKT/GSK3β pathway. Cell Biochem Biophys67:567-574.
41.
WeinsteinRSJilkaRLParfittAMManolagasSC (1998). Inhibition of osteoblastogenesis and promotion of apoptosis of osteoblasts and osteocytes by glucocorticoids. Potential mechanisms of their deleterious effects on bone. J Clin Invest102:274-282.
42.
WeinsteinRSNicholasRWManolagasSC (2000). Apoptosis of osteocytes in glucocorticoid-induced osteonecrosis of the hip. J Clin Endocrinol Metab85:2907-2912.
43.
WintgesK1BeilFTAlbersJJeschkeASchweizerMClaassB. (2013). Impaired bone formation and increased osteoclastogenesis in mice lacking chemokine (C-C motif) ligand 5 (Ccl5). J Bone Miner Res28:2070-2080.
44.
WrightLMMaloneyWYuXKindleLCollin-OsdobyPOsdobyP (2005). Stromal cell-derived factor-1 binding to its chemokine receptor CXCR4 on precursor cells promotes the chemotactic recruitment, development and survival of human osteoclasts. Bone36:840-853.
45.
YanoSMentaverriRKanuparthiDBandyopadhyaySRiveraABrownEM. (2005). Functional expression of beta-chemokine receptors in osteoblasts: role of regulated upon activation, normal T cell expressed and secreted (RANTES) in osteoblasts and regulation of its secretion by osteoblasts and osteoclasts. Endocrinology146:2324-2335.
46.
YoshinoTKishiHNagataTTsukadaKSaitoSMuraguchiA (2001). Differential involvement of p38 MAP kinase pathway and Bax translocation in the mitochondria-mediated cell death in TCR- and dexamethasone-stimulated thymocytes. Eur J Immunol31:2702-2708.
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