Journal
BIOCHEMICAL AND BIOPHYSICAL RESEARCH COMMUNICATIONS
Volume 417, Issue 2, Pages 824-829Publisher
ACADEMIC PRESS INC ELSEVIER SCIENCE
DOI: 10.1016/j.bbrc.2011.12.045
Keywords
MT1-MMP; Mechanosensitivity; Osteocytes; Pulsating fluid flow; Mechanical loading
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Funding
- University of Amsterdam
- Research Institute MOVE of the VU University Amsterdam
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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. (C) 2011 Elsevier Inc. All rights reserved.
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