Acidosis Is a Key Regulator of Osteoblast Ecto-Nucleotidase Pyrophosphatase/Phosphodiesterase 1 (NPP1) Expression and Activity

Orriss Isabel R.; Key Michelle L.; Hajjawi Mark O. R.Millan Jose L.Arnett Timothy R.

摘要

Previous work has shown that acidosis prevents bone nodule formation by osteoblasts in vitro by inhibiting mineralisation of the collagenous matrix. The ratio of phosphate (P-i) to pyrophosphate (PPi) in the bone microenvironment is a fundamental regulator of bone mineralisation. Both P-i and PPi, a potent inhibitor of mineralisation, are generated from extracellular nucleotides by the actions of ecto-nucleotidases. This study investigated the expression and activity of ecto-nucleotidases by osteoblasts under normal and acid conditions. We found that osteoblasts express mRNA for a number of ecto-nucleotidases including NTPdase 1-6 (ecto-nucleoside triphosphate diphosphohydrolase) and NPP1-3 (ecto-nucleotide pyrophosphatase/phosphodiesterase). The rank order of mRNA expression in differentiating rat osteoblasts (day 7) was Enpp1> NTPdase 4 > NTPdase 6 > NTPdase 5 > alkaline phosphatase > ecto-5-nucleotidase > Enpp3 > NTPdase 1 > NTPdase 3 > Enpp2 > NTPdase 2. Acidosis (pH 6.9) upregulated NPP1 mRNA (2.8-fold) and protein expression at all stages of osteoblast differentiation compared to physiological pH (pH 7.4); expression of other ecto-nucleotidases was unaffected. Furthermore, total NPP activity was increased up to 53% in osteoblasts cultured in acid conditions (P < 0.001). Release of ATP, one of the key substrates for NPP1, from osteoblasts, was unaffected by acidosis. Further studies showed that mineralised bone formation by osteoblasts cultured from NPP1 knockout mice was increased compared with wildtypes (2.5-fold, P < 0.001) and was partially resistant to the inhibitory effect of acidosis. These results indicate that increased NPP1 expression and activity might contribute to the decreased mineralisation observed when osteoblasts are exposed to (C) 2015 The Authors. Journal of Cellular Physiology Published by Wiley Periodicals, Inc.

机译：先前的工作表明,酸中毒阻止由成骨细胞体外骨结节形成抑制胶原的矿化作用矩阵。焦磷酸(PPi)骨微环境是骨的基本监管机构矿化作用。矿化作用的抑制剂,生成细胞外核苷酸的行为ecto-nucleotidases。ecto-nucleotidases的表达和活动成骨细胞在正常和酸性条件。发现成骨细胞信使rna表达为一个数字ecto-nucleotidases包括NTPdase 1 - 6(三磷酸ecto-nucleoside diphosphohydrolase)和NPP1-3 (ecto-nucleotide焦磷酸酶/磷酸二酯酶)。信使rna表达的顺序区分老鼠成骨细胞(第七天)Enpp1 > NTPdase 4 >NTPdase 6 > NTPdase 5 > alkaline phosphatase >ecto-5-nucleotidase > Enpp3 > > 1 NTPdase NTPdase3 > Enpp2 > NTPdase 2。调节NPP1信使rna和蛋白质(2.8倍)表达式在成骨细胞的所有阶段分化与生理pH值(酸碱度7.4);不受影响。成骨细胞培养中增加了53%酸条件(P < 0.001)。的关键基质NPP1,从造骨细胞,是影响酸中毒。表明,矿化骨形成成骨细胞培养从NPP1基因敲除小鼠与野生型相比增加2.5倍,P <0.001)和部分耐药酸中毒的抑制作用。表明NPP1表达和增加活动可能有助于减少矿化观察当成骨细胞作者接触(C) 2015。细胞生理由威利出版期刊、公司。

Acidosis Is a Key Regulator of Osteoblast Ecto-Nucleotidase Pyrophosphatase/Phosphodiesterase 1 (NPP1) Expression and Activity

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