Article

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.

1 Follower
 · 
310 Views
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: In this article, bone cells and their intercellular communications have been reviewed. Gap junctions and hemichannels are the main routes of interactions in bone tissue. They play a substantial role in survival and cell death, since pro-apoptotic signals can propagate through them. Different adhesion molecules are required for apoptosis, particularly caspase family as well as noncaspase proteases. The disruption outcome of apoptosis could result in bone-related diseases such as osteonecrosis. Anti-apoptotic strategies include inhibition of caspase, poly [ADP-ribose] polymerase (PARP), and Bcl-2 proteins as well as induction of the PKB/Akt pathway and inhibitors of apoptosis (IAP) family of proteins. Thus, understanding the mechanism of apoptosis gives detailed insights of anti-apoptotic molecular targets. Based on these targets, different treatments were designed and produced such as estrogen replacement therapy, administration of different bisphosphonates, raloxifene, calcitonin, sodium fluoride, calcium, and vitamin D. As a result, new applicable drugs for treatment of related bone problems can be proposed for clinical approach especially in the early stage of diseases.
    Journal of Orthopaedic Surgery and Research 01/2015; 10(1):15. DOI:10.1186/s13018-015-0152-5 · 1.58 Impact Factor
  • [Show abstract] [Hide abstract]
    ABSTRACT: Osteocyte apoptosis due to microdamage and/or oxidative stress is related to increased local bone turnover and resorption observed in various bone diseases. Previous data on osteoblasts and osteoclasts have linked reactive oxygen species and antioxidants to bone remodelling. This study performs a comprehensive analysis on the effect of antioxidants such as glutathione (GSH), N-acetylcysteine and lipoic acid (LA) on starvation-induced osteocyte apoptosis and on cytokines involved in bone remodelling such as the receptor activator kB ligand (RANKL), osteoprotegerin (OPG) and sclerostin. For this study, apoptosis was induced by serum starvation in a murine osteocyte-like cell line MLO-Y4; this condition mimics in part osteocyte apoptosis due to microdamage. The results show that starvation-induced apoptosis and expression of RANKL, OPG and sclerostin are redox regulated processes. All antioxidants are able to inhibit the apoptosis due to starvation. They down-regulate the expression and the release of RANKL, the expression of sclerostin and RANKL/OPG ratio, whereas they only in part up-regulate OPG expression. Antioxidants mediate their effect on starvation-induced apoptosis by JNK signalling and on cytokine expression by both JNK and ERK1/2 activities. This study shows the possible involvement of biological antioxidants such as GSH and LA on redox regulated mechanisms related to apoptosis and expression of cytokines involved in bone remodelling. Moreover, it suggests that both JNK and ERK1/2 may be useful biological targets for drugs affecting bone diseases associated with increased oxidative stress.
    Calcified Tissue International 02/2015; 96(4). DOI:10.1007/s00223-015-9961-0 · 2.75 Impact Factor
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: Introduction: In view of the relationship between physical activity and nutrition onbody composition, we assessed lean and fat mass and BMC (total and regional) in professional Indian sportswomen and compared it with apparently healthy age and sex matched females. Methods: This cross-sectional study included 104 sportswomen and an equal number of age matched normal healthy females (controls). They were evaluated for anthropometry and body composition (fat, lean mass, and bone mineral content (BMC) by DXA. Results: Mean age (19.1±1.3 vs. 19.4± 1.5 years) and body mass index(21.34± 3.02 vs. 21.26± 4.05kg/m2) were comparable in both groups. Sportswomen had higher intake of energy, macronutrients, calcium, phosphorus and magnesium. Total lean mass (33.67± 3.49 vs. 31.14± 3.52 kg, p<0.0001), appendicular skeletal muscle index (5.84±0.57 vs. 5.46±0.63kg/m2; p <0.0001) and BMC (2.27±0.32 vs. 2.13±0.34 kg, p<0.002) was significantly higher and percentage fat mass was significantly lower (33.1±7.5 vs. 37.0±8.3; p <0.0001) among sportswomen when compared to controls. Conclusions: Indian sportswomen have a higher total and regional lean mass, BMC, and lower percentage fat mass when compared with healthy females. Physical activity, energy, protein and calcium intake were positively associated with lean mass and BMC.
    03/2015; 19(2):288-91. DOI:10.4103/2230-8210.149323

Full-text

Download
218 Downloads
Available from
May 27, 2014

Gaël Y Rochefort