Osteocyte: The unrecognized side of bone tissue

INSERM Research Unit 658, Centre Hospitalier Régional, 1 rue Porte Madeleine, 45 032 Orleans, France.
Osteoporosis International (Impact Factor: 4.17). 03/2010; 21(9):1457-69. DOI: 10.1007/s00198-010-1194-5
Source: PubMed

ABSTRACT INTRODUCTION: Osteocytes represent 95% of all bone cells. These cells are old osteoblasts that occupy the lacunar space and are surrounded by the bone matrix. They possess cytoplasmic dendrites that form a canalicular network for communication between osteocytes and the bone surface. They express some biomarkers (osteopontin, beta3 integrin, CD44, dentin matrix protein 1, sclerostin, phosphate-regulating gene with homologies to endopeptidases on the X chromosome, matrix extracellular phosphoglycoprotein, or E11/gp38) and have a mechano-sensing role that is dependent upon the frequency, intensity, and duration of strain. DISCUSSION: The mechanical information transmitted into the cytoplasm also triggers a biological cascade, starting with NO and PGE(2) and followed by Wnt/beta catenin signaling. This information is transmitted to the bone surface through the canalicular network, particularly to the lining cells, and is able to trigger bone remodeling by directing the osteoblast activity and the osteoclastic resorption. Furthermore, the osteocyte death seems to play also an important role. The outcome of micro-cracks in the vicinity of osteocytes may interrupt the canalicular network and trigger cell apoptosis in the immediate surrounding environment. This apoptosis appears to transmit a message to the bone surface and activate remodeling. The osteocyte network also plays a recognized endocrine role, particularly concerning phosphate regulation and vitamin D metabolism. Both the suppression of estrogen following menopause and chronic use of systemic glucocorticoids induce osteocyte apoptosis. On the other hand, physical activity has a positive impact in the reduction of apoptosis. In addition, some osteocyte molecular elements like sclerostin, connexin 43, E11/gp38, and DKK1 are emerging as promising targets for the treatment of various osteo-articular pathologies.

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Available from: Gaël Y Rochefort, Aug 24, 2015
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    • "L. Spiegelberg et al. / Journal of Cranio-Maxillo-Facial Surgery 43 (2015) 214e219 217 Osteocytes derive from osteoblasts that have become 'trapped' in the matrix that they have produced themselves. They maintain contact with each other and with the osteoblasts and osteoclasts that reside at the bone surface by cytoplasmic extensions called dendrites, that extend into channels in the matrix (Rochefort et al., 2010). In this way, osteocytes send signals for bone resorption and formation to osteoclasts and osteoblasts, respectively, and therefore play an essential role in bone maintenance and remodelling (Bonewald, 2007). "
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    ABSTRACT: Radiation therapy (RT) as part head and neck cancer treatment often leads to irradiation of surrounding normal tissue, such as mandibular bone. A reduced reparative capacity of the bone can lead to osteoradionecrosis (ORN). Hyperbaric oxygen therapy (HBOT) is used to treat ORN, based on its potential to raise the oxygen tension in tissues. However, prevention of radiation-induced damage is of great interest. Our purpose was to investigate whether HBOT could prevent radiation-induced damage to murine mandibles.Methods Twenty-eight mice were irradiated in the head and neck region with a single dose (15 Gy) and half of them were subsequently subjected to HBOT. Another 14 mice did not receive any treatment and served as controls. Ten and 24 weeks after RT, mandibles were harvested and analysed histologically and by microcomputed tomography (micro-CT).ResultsMicro-CT analysis showed a reduction in relative bone volume by RT, which was partly recovered by HBOT. Trabecular thickness and separation were also positively influenced by HBOT. Morphologically, HBOT suppressed the osteoclast number, indicating decreased resorption, and decreased the amount of lacunae devoid of osteocytes, indicating increased bone viability.ConclusionsHBOT was able to partly reduce radiation-induced effects on microarchitectural parameters, resorption, and bone viability in mouse mandibles. HBOT could therefore potentially play a role in the prevention of radiation-induced damage to human mandibular bone.
    Journal of Cranio-Maxillofacial Surgery 11/2014; 43(2). DOI:10.1016/j.jcms.2014.11.008 · 2.60 Impact Factor
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    • "Osteocytes, the most abundant cells in bone, represent 90–95% of all cells in the adult skeleton [Rochefort et al. 2010]. They are able to live for several decades within the bone matrix, whereas osteoblasts and osteoclasts have a lifespan of only a few days or weeks [Bonewald, 2011]. "
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    ABSTRACT: Osteoporosis is characterized by a low bone-mineral density associated with skeletal fractures. The decrease in bone-mineral density is the consequence of an unbalanced bone-remodeling process, with higher bone resorption than bone formation. The orchestration of the bone-remodeling process is under the control of the most abundant cell in bone, the osteocyte. Functioning as an endocrine cell, osteocytes are also a source of soluble factors that not only target cells on the bone surface, but also target distant organs. Therefore, any drugs targeting the osteocyte functions and signaling pathways will have a major impact on the bone-remodeling process. This review discusses potential advances in drug therapy for osteoporosis, including novel osteocyte-related antiresorptive and anabolic agents that may become available in the coming years.
    Therapeutic advances in musculoskeletal disease 06/2014; 6(3):79-91. DOI:10.1177/1759720X14523500
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    • "Les ostéocytes jouent un rôle dans la mécanotransduction [12]. Ils perç oivent les changements dans le liquide interstitiel à travers le réseau lacuno-canaliculaire et adaptent la masse osseuse aux charges subies, en régulant l'activité des ostéoblastes et des ostéoclastes [13]. De ce fait, l'activité physique pourrait prévenir la perte osseuse induite par l'alcool. "
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    ABSTRACT: Introduction La consommation excessive d’alcool est connue pour être à l’origine d’une ostéoporose secondaire alors que l’activité physique est recommandée pour prévenir l’ostéoporose. Cette étude a été conçue pour analyser les effets de l’exercice physique sur les paramètres osseux chez des rats ayant une consommation chronique d’alcool. Méthodes Quarante-huit rats Wistar ont été subdivisés en quatre groupes : témoins (C), alcool (A), exercice (E) et alcool + exercice (AE). Les groupes A et AE avaient consommé une solution composée d’éthanol et d’eau (35 % d’éthanol pendant 17 semaines). Les groupes E et AE étaient soumis à un entraînement sur le tapis roulant pendant 14 semaines (60 min/j, cinq fois par semaine). La densité minérale osseuse (DMO) a été évaluée par DXA, les paramètres microarchitecturaux trabéculaires et corticaux ont été évalués par micro-CT et des mesures des concentrations sériques de l’ostéocalcine, des NTx et de la leptine par des tests Elisa. Les paramètres mécaniques osseux ont été évalués par des tests mécaniques. L’apoptose ostéocytaire a été analysée par immunomarquage à la caspase-3 clivée. Résultats Les rats ayant consommé de l’alcool avaient un poids significativement plus faible (−28 %), moins de masse grasse (−46 %) et moins de masse maigre (−25 %) comparativement aux témoins. La DMO (−8 %), l’épaisseur trabéculaire (−12 %) et corticale (−27 %) ont été significativement plus basses dans le groupe alcool alors que la porosité (+38 %) et le nombre de pores (+42 %) étaient plus élevés. L’exercice combiné à la prise d’alcool avait préservé la Tb.Th (+20 %), Ct-Th (+30 %), la contrainte maximale (+26 %) avec une plus grande ct.Po (−24 %) et une moindre apoptose ostéocytaire (−91 %) comparées au groupe A. Cependant, la DMO WB (−4 %) et au niveau du fémur étaient encore plus basses dans le groupe AE par rapport au groupe C. Conclusion L’activité physique régulière a des effets bénéfiques sur certains paramètres microarchitecturaux chez les rats consommant de l’alcool. Cependant, des exercices réguliers sur tapis roulant ne compensent pas les effets néfastes de la consommation chronique d’alcool en termes de densité osseuse.
    Revue du Rhumatisme 10/2013; 80(5):495–502. DOI:10.1016/j.rhum.2013.03.009
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