Academic Centre for Dentistry Amsterdam, University of Amsterdam and VU University Amsterdam, Department of Oral Cell Biology, Research Institute MOVE, Amsterdam, The Netherlands.
Biochem Biophys Res Commun. 2012 Jan 13;417(2):824-9. doi: 10.1016/j.bbrc.2011.12.045. Epub 2011 Dec 19.
Membrane-type matrix metalloproteinase-1 (MT1-MMP) is expressed by mechanosensitive osteocytes and affects bone mass. The extracellular domain of MT1-MMP is connected to extracellular matrix, while its intracellular domain is a strong modulator of cell signaling. In theory MT1-MMP could thus transduce mechanical stimuli into a chemical response. We hypothesized that MT1-MMP plays a role in the osteocyte response to mechanical stimuli. MT1-MMP-positive and knockdown (siRNA) MLO-Y4 osteocytes were mechanically stimulated with a pulsating fluid flow (PFF). Focal adhesions were visualized by paxillin immunostaining. Osteocyte number, number of empty lacunae, and osteocyte morphology were measured in long bones of MT1-MMP(+/+) and MT1-MMP(-/-) mice. PFF decreased MT1-MMP mRNA and protein expression in MLO-Y4 osteocytes, suggesting that mechanical loading may affect pericellular matrix remodeling by osteocytes. MT1-MMP knockdown enhanced NO production and c-jun and c-fos mRNA expression in response to PFF, concomitantly with an increased number and size of focal adhesions, indicating that MT1-MMP knockdown osteocytes have an increased sensitivity to mechanical loading. Osteocytes in MT1-MMP(-/-) bone were more elongated and followed the principle loading direction, suggesting that they might sense mechanical loading. This was supported by a lower number of empty lacunae in MT1-MMP(-/-) bone, as osteocytes lacking mechanical stimuli tend to undergo apoptosis. In conclusion, mechanical stimulation decreased MT1-MMP expression by MLO-Y4 osteocytes, and MT1-MMP knockdown increased the osteocyte response to mechanical stimulation, demonstrating a novel and unexpected role for MT1-MMP in mechanosensing.
膜型基质金属蛋白酶-1（MT1-MMP）由机械敏感的成骨细胞表达，影响骨量。MT1-MMP 的细胞外结构域与细胞外基质相连，而其细胞内结构域是细胞信号的强调节剂。理论上，MT1-MMP 可以将机械刺激转化为化学反应。我们假设 MT1-MMP 在成骨细胞对机械刺激的反应中起作用。用脉动液流（PFF）机械刺激 MT1-MMP 阳性和敲低（siRNA）的 MLO-Y4 成骨细胞。用整联蛋白免疫染色观察粘着斑。在 MT1-MMP(+/+)和 MT1-MMP(-/-)小鼠的长骨中测量成骨细胞数量、空陷窝数量和成骨细胞形态。PFF 降低了 MLO-Y4 成骨细胞中 MT1-MMP 的 mRNA 和蛋白表达，表明机械加载可能通过成骨细胞影响细胞外基质重塑。MT1-MMP 敲低增强了对 PFF 的 NO 产生和 c-jun 和 c-fos mRNA 表达，同时粘着斑的数量和大小增加，表明 MT1-MMP 敲低的成骨细胞对机械加载的敏感性增加。MT1-MMP(-/-)骨中的成骨细胞更细长且遵循主要的加载方向，表明它们可能感知机械加载。这一点得到了 MT1-MMP(-/-)骨中较少的空陷窝的支持，因为缺乏机械刺激的成骨细胞往往会发生凋亡。总之，机械刺激降低了 MLO-Y4 成骨细胞中 MT1-MMP 的表达，而 MT1-MMP 敲低增加了成骨细胞对机械刺激的反应，证明了 MT1-MMP 在机械感觉中的新的和意外的作用。
