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Chandrika D Mahalingam, Tanuka Datta, Rashmi V Patil, Jaclynn Kreider, R Daniel Bonfil, Keith L Kirkwood, Steven A Goldstein, Abdul B Abou-Samra and Nabanita S Datta

) or catabolic showing decreased bone mass and hypercalcemia ( Dobnig & Turner 1997 , Schiller et al . 1999 , Marx 2000 ). The control of bone mass involves osteoblasts, the bone-forming cells, osteoclasts, the bone-resorbing cells, and osteocytes

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E Mrak, I Villa, R Lanzi, M Losa, F Guidobono and A Rubinacci

osteoblasts and osteoclasts in modulating bone turnover ( Ezzat et al. 1993 ). Maor et al. (1989) showed that GH is able to directly induce bone formation in vitro . The effects of GH on bone cells are mediated through the functional GH

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A Tumber, MC Meikle and PA Hill

We have studied the survival requirements of osteoblasts to test the hypothesis that osteoblasts undergo programmed cell death (PCD) or apoptosis unless they are continuously signalled by other cells not to do so. Osteoblasts survived for 6 days in culture at high cell density in the absence of other cell types, serum or exogenous proteins, but they died with the morphological features of apoptosis in these conditions at low cell density. Osteoblast survival was enhanced during the first 2 days of culture by the addition of the sulphydryl compound, cysteine to the culture medium which was converted intracellularly to the antioxidant glutathione. Catalase, an enzyme decomposing hydrogen peroxide, also protected the cells, whereas superoxide dismutase had no effect. Therefore, osteoblasts in culture are sensitive to toxic compounds derived from molecular oxygen, i.e. hydroxyl radicals or hydrogen peroxide spontaneously generated in CMRL medium containing ascorbate and ferrous ions. Conditioned medium from high density cultures prevented osteoblast apoptosis in low density cultures, as long as antioxidants were also present. The enhancing effect of conditioned medium on osteoblast survival was prevented by neutralizing antibodies to insulin-like growth factor-I (IGF-I) and IGF-II but not by antibodies to either platelet-derived growth factor (PDGF) or basic fibroblast growth factor (bFGF). These results suggest that in addition to regulating cell growth and differentiation, IGF-I and IGF-II also function as survival factors for osteoblasts. Our data also indicate that antioxidants are required for osteoblast survival and that they enhance growth factor mediated osteoblast survival.

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Nabanita S Datta, Tareq A Samra, Chandrika D Mahalingam, Tanuka Datta and Abdul B Abou-Samra

D1 in differentiated mature osteoblasts ( Chen et al . 2004 , Datta et al . 2005 , 2010 ). The physiological role of PTH1R phosphorylation, internalization, and desensitization in bone cells and skeletal development remains largely unknown. In

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Ryoko Yamamoto, Tomoko Minamizaki, Yuji Yoshiko, Hirotaka Yoshioka, Kazuo Tanne, Jane E Aubin and Norihiko Maeda

). FGF23 is expressed primarily in bones, most notably in osteoblasts and osteocytes ( Riminucci et al . 2003 , Kolek et al . 2005 , Yoshiko et al . 2007 b ). Indeed, analyses of Fgf23 -null ( Fgf23 −/− ) mice on a Hyp (a mouse model of X

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Anyonya R Guntur and Clifford J Rosen

skeleton. Osteoblasts, the bone forming cells of the skeleton, are essential in both these pathways ( Kronenberg 2003 ). Osteoblasts originate from mesenchymal stem cells (MSC) that are multipotent and can differentiate into a number of lineages including

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S Takai, Y Hanai, R Matsushima-Nishiwaki, C Minamitani, T Otsuka, H Tokuda and O Kozawa

functional cells, osteoblasts and osteoclasts, responsible for bone formation and bone resorption respectively ( Nijweide et al . 1986 ). Bone resorption may be enhanced by the increased local production of inflammatory cytokines such as tumor necrosis

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Karla J Suchacki, Fiona Roberts, Andrea Lovdel, Colin Farquharson, Nik M Morton, Vicky E MacRae and William P Cawthorn

. Central to this adjustment is the highly regulated interplay of two distinct bone cell types, the osteoblast and the osteoclast, which have opposing functions ( Crockett et al . 2011 ). Osteoblasts comprise 5% of all bone cells and facilitate the

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P J D Delhanty, B C J van der Eerden, M van der Velde, C Gauna, H A P Pols, H Jahr, H Chiba, A J van der Lely and J P T M van Leeuwen

of UAG in osteoblasts. In vivo , ghrelin may have an indirect effect on bone through its stimulation of GH release. However, the GHS-R1a agonist hexarelin inhibits markers of bone resorption in the rat, an effect not observed with GH treatment

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Misuzu Yamashita, Fumio Otsuka, Tomoyuki Mukai, Hiroyuki Otani, Kenichi Inagaki, Tomoko Miyoshi, Junko Goto, Masahiro Yamamura and Hirofumi Makino

( Reddi 1997 ). BMPs also play a pivotal regulatory role in mesoderm induction and dorsoventral patterning of developing limb buds and are known to promote differentiation of mesenchymal stem cells into chondrocytes and osteoblasts as well as the