MT1-MMP modulates the mechanosensitivity of osteocytes
ABSTRACT 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.
Full-textDOI: · Available from: Astrid Diana Bakker, Dec 17, 2013
- SourceAvailable from: Kimbal Cooper
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- "It is plausible that MMP14 is activated downstream of stretchactivated Ca þ2 channels which are known to be active in these cells (Lee et al., 1999). This conjecture is supported by the fact that there is a greater intensity of MMP14 immunostaining in stretched cells which are in the process of detaching from the cell sheet and is consistent with recent data describing a role for MMP14 in mechanosensitivity of osteocytes (Kulkarni et al., 2012). At this point, without a commercially available small molecule inhibitor specific for MMP14, we are unable to make a more definitive conclusion as to the precise role of MMP14. "
ABSTRACT: Zebrafish keratocytes collectively migrate rapidly when established in explant cultures but little is known about the signals that initiate motility or the signal transduction pathways that result in an epithelial to mesenchymal transition. Matrix metalloproteinases (MMPs) are strong candidates for playing a role in this regulation and have previously not been analysed in this wound healing model system. Results presented here document a rapid and dramatic rise in MMP14a, MMP2, MMP9 and MMP13a mRNA levels over time. In a motility assay, a broad-spectrum MMP inhibitor and an inhibitor specific for MMP2 and MMP9 significantly decrease cell migration in a dose dependent manner but treatment with an MMP13 specific inhibitor significantly increases cell sheet area. Immunofluorescence staining with an antibody specific for the catalytic domain of MMP14 indicates that activated MMP14 protein is highly expressed on cells at the leading edge of a sheet compared with follower cells in the centre of the sheet, and is augmented further in leader cells that are stretched, thus likely in the process of detaching from the cell sheet. These data are consistent with a model in which active MMP14 at the leading edge of cell sheets in explant cultures triggers activation of MMP2 and/or MMP9, thus creating promigratory signal(s) that outweigh the inhibitory role of targets cleaved by MMP13. Taken together, these data suggest that MMPs play an important but complex role in regulating the collective cell migration of zebrafish keratocytes and provide support for the relevance of using zebrafish as a model for human disease.12/2013; 20(2). DOI:10.1002/cbi3.10006
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- "It was found that mechanical stimulation by means of a pulsatile fluid flow induced stabilization of β-catenin in osteocytes in a FAK-dependent mechanism . Interestingly, knockdown of membrane-type matrix metalloproteinase-1 (MT1-MMP) increased the number and size of focal adhesions in cultured MLO-Y4 osteocytes concomitantly with an enhanced NO production and c-jun and c-fos mRNA expression in response to mechanical stimulation . This indicates that MT1-MMP knockdown osteocytes have an increased sensitivity to mechanical loading and demonstrates a novel and unexpected potential role for MT1-MMP in mechanosensing. "
ABSTRACT: The human skeleton is a miracle of engineering, combining both toughness and light weight. It does so because bones possess cellular mechanisms wherein external mechanical loads are sensed. These mechanical loads are transformed into biological signals, which ultimately direct bone formation and/or bone resorption. Osteocytes, since they are ubiquitous in the mineralized matrix, are the cells that sense mechanical loads and transduce the mechanical signals into a chemical response. The osteocytes then release signaling molecules, which orchestrate the recruitment and activity of osteoblasts or osteoclasts, resulting in the adaptation of bone mass and structure. In this review, we highlight current insights in bone adaptation to external mechanical loading, with an emphasis on how a mechanical load placed on whole bones is translated and amplified into a mechanical signal that is subsequently sensed by the osteocytes. This article is part of a Special Issue entitled Osteocyte.Bone 10/2012; 54(2). DOI:10.1016/j.bone.2012.10.013 · 3.97 Impact Factor
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- "Of the three types of cells comprising bone, osteocytes are the most abundant, making up 95% of all cells in bone ( and references therein), yet little is known of osteocyte biology and function. Recent studies have begun to elucidate the role of osteocytes in bone formation, bone function, bone maintenance and bone pathology         , but many questions regarding the fundamental biology of these cells remain. Issues that are still poorly understood include: 1) the potential variation in the morphology of osteocytes in bones with different origins (intramembranous vs endochondral) and their different roles in vertebrate body plans, (e.g., do osteocytes function differently in long bones vs bony flat plates); 2) what temporal limits exist on osteocyte preservation in the bony matrix, and whether preservation is dependent on taxon, bone type, geologic time, depositional environment or other factors; and 3) if these cells persist and can be shown to be endogenous to the organisms, can chemical/molecular analyses of these remnants shed light on the physiology, phylogeny, and/or ecology of extinct organisms across geological time. "
ABSTRACT: Here we describe variations in osteocytes derived from each of the three bone layers that comprise the turtle shell. We examine osteocytes in bone from four extant turtle species to form a morphological 'baseline', and then compare these with morphologies of osteocytes preserved in Cenozoic and Mesozoic fossils. Two different morphotypes of osteocytes are recognized: flattened-oblate osteocytes (FO osteocytes), which are particularly abundant in the internal cortex and lamellae of secondary osteons in cancellous bone, and stellate osteocytes (SO osteocytes), principally present in the interstitial lamellae between secondary osteons and external cortex. We show that the morphology of osteocytes in each of the three bone layers is conserved through ontogeny. We also demonstrate that these morphological variations are phylogenetically independent, as well as independent of the bone origin (intramembranous or endochondral). Preservation of microstructures consistent with osteocytes in the morphology in Cenozoic and Mesozoic fossil turtle bones appears to be common, and occurs in diverse diagenetic environments including marine, freshwater, and terrestrial deposits. These data have potential to illuminate aspects of turtle biology and evolution previously unapproachable, such as estimates of genome size of extinct species, differences in metabolic rates among different bones from a single individual, and potential function of osteocytes as capsules for preservation of ancient biomolecules.Bone 05/2012; 51(3):614-20. DOI:10.1016/j.bone.2012.05.002 · 3.97 Impact Factor