Chen Xuesong, Macica Carolyn M, Ng Kong Wah, Broadus Arthur E
Section of Endocrinology, Department of Internal Medicine, Yale University School of Medicine, New Haven, Connecticut 06520-2080, USA.
J Bone Miner Res. 2005 Aug;20(8):1454-61. doi: 10.1359/jbmr.2005.20.8.1454. Epub 2005 Mar 28.
Mechanical forces play a critical role in regulating skeletal mass and structure. We report that mechanical loading induces PTHrP in osteoblast-like cells and that TREK-2 stretch-activated potassium channels seem to be involved in this induction. Our data suggest PTHrP as a candidate endogenous mediator of the anabolic effects of mechanical force on bone.
Mechanical force has anabolic effects on bone. The PTH-related protein (PTHrP) gene is known to be mechanically inducible in smooth muscle cells throughout the organism, and N-terminal PTH and PTHrP products have been reported to have anabolic effects in bone. We explored the idea that PTHrP might be a candidate mediator of the effects of mechanical force on bone.
Mechanical loading was applied by swelling osteoblast-like cells in hypotonic solution and/or by application of cyclical stretch through a FlexerCell apparatus. RNase protection assay and real-time quantitative PCR analysis were used to assay PTHrP gene expression.
Stretching UMR201-10B osteoblast-like cells by swelling in hypotonic solutions rapidly increased PTHrP mRNA. This induction was insensitive to gadolinium and nifedipine, to the removal of extracellular calcium, and to depletion of endoplasmic reticulum calcium, indicating that neither stretch-activated cation channels, L-type calcium channels, nor ER calcium is involved in the induction of PTHrP. The TREK family potassium channels are activated by both stretch and intracellular acidosis, and we identified these channels in osteoblast-like cells by PCR. Intracellular acidification increased PTHrP mRNA expression in UMR-201-10B cells, and siRNA targeted against the TREK-2 gene reduced endogenous TREK-2 expression and dampened PTHrP mRNA induction. Cyclical stretch also induced PTHrP in UMR-201-10B osteoblast-like cells and in MLO-A5 post-osteoblast-pre-osteocyte cells, the latter a stage in the osteoblastic differentiation program that is likely to be a key target of force in vivo. Our evidence suggests PTHrP as a candidate mediator of the anabolic effects of mechanical force on bone.
机械力在调节骨骼质量和结构中起关键作用。我们报告称，机械负荷可在成骨样细胞中诱导甲状旁腺激素相关蛋白（PTHrP），且TREK - 2牵张激活钾通道似乎参与了这一诱导过程。我们的数据表明，PTHrP是机械力对骨骼合成代谢作用的候选内源性介质。
机械力对骨骼具有合成代谢作用。已知甲状旁腺激素相关蛋白（PTHrP）基因在整个生物体的平滑肌细胞中可被机械诱导，并且据报道，N端甲状旁腺激素和PTHrP产物在骨骼中具有合成代谢作用。我们探讨了PTHrP可能是机械力对骨骼作用的候选介质这一观点。
通过在低渗溶液中使成骨样细胞肿胀和/或通过FlexerCell装置施加周期性牵张来施加机械负荷。采用核糖核酸酶保护测定法和实时定量PCR分析来检测PTHrP基因表达。
通过在低渗溶液中肿胀来拉伸UMR201 - 10B成骨样细胞可迅速增加PTHrP mRNA。这种诱导对钆、硝苯地平、去除细胞外钙以及内质网钙耗竭均不敏感，表明牵张激活阳离子通道、L型钙通道或内质网钙均不参与PTHrP的诱导。TREK家族钾通道可被牵张和细胞内酸中毒激活，我们通过PCR在成骨样细胞中鉴定出了这些通道。细胞内酸化增加了UMR - 201 - 10B细胞中PTHrP mRNA的表达，而针对TREK - 2基因的小干扰RNA（siRNA）降低了内源性TREK - 2表达并减弱了PTHrP mRNA的诱导。周期性牵张也在UMR - 201 - 10B成骨样细胞和MLO - A5成骨细胞前体 - 骨细胞中诱导了PTHrP，后者是成骨细胞分化程序中的一个阶段，可能是体内机械力的关键作用靶点。我们的证据表明，PTHrP是机械力对骨骼合成代谢作用的候选介质。
