The iNOS expression itself. Contrary results were reported by Gassner and colleagues (1999), who found a suppression of IL-1-induced NO production after 12?6 h of CTS with even higher (20 ) strains. The reason for this is unclear. Madhaven and colleagues (2006) explored different durations of low CTS (3 , 0.25 Hz) and found out that the effects of the mechanical loading are persistent. Even after the removal of CTS, the IL-1 induced pro-inflammatory gene PXD101 web transcription were diminished for hours [29]. Furthermore, TNF- and IL-1 suppress actions that can counteract cartilage destruction, such as the expression of tissue inhibitor of metalloproteinase 2 (TIMP-2) and the expression or synthesis of proteoglycans [27,79,80]. CTS at 6 and 0.05 Hz was able to neutralize this suppression [27,53]. They further reported that TIMP-2 levels, although not suppressed by Il-1,PLOS ONE | DOI:10.1371/journal.pone.0119816 March 30,16 /Cyclic Tensile Strain and Chondrocyte MetabolismTable 7. Effects of CTS on pro-inflammatory factors. Frequency 0.05 Hz Loading duration 10 min – 48 h 24 h 2?6 h 0.17 Hz 6h 12 h 24 h 0.5 Hz 01 h 03 h 06 h 12 h 12 h 12 h 18 h 24 h 24 h 24 h 24 h 36 h 48 h 48 h Strain magnitude 3? 12?8 20 7 7 7 10 10 10 7 10 16 7 7 7 10 16 7 7 16 ” ” ” ” ” ” ” ” ” ” ” ” ” ” ” ” iNOS ” NO ” a b “a b ” #a bCOX-PGEReference [20,27,48,53,76] [76] [52,77] [47] [47] [47]” ” ” “[37] [37] [37] [36] [37] [26] [36] [28] [36] [37] [26] [36] [28] [26]Effects of CTS on pro-inflammatory factors relative to unloaded controls, sorted by loading frequency # Grazoprevir custom synthesis levels of loaded cells were decreased relative to unloaded cells Levels of loaded cells were unchanged relative to unloaded cellsa b” Levels of loaded cells were increased relative to unloaded cells Cells were seeded on fibronectin Cells were seeded on collagen Idoi:10.1371/journal.pone.0119816.twere hyper-induced by a combination of IL-1?and CTS [27]. TIMP-1 levels, however, were neither altered by TNF- nor by IL-1?or CTS [27,53]. In summary, low magnitude CTS (2?0 ) was beneficial to already inflamed joints. These effects were persistent even after the removal of CTS. Interestingly, in a non-inflammatory environment CTS between 12 and 18 mimics the effects of the inflammatory mediator IL-1 and induces similar reactions to those found in osteoarthritis, whereas lower strains were not sufficient to induce anti-inflammatory actions.DiscussionThe systematic investigation of cellular responses to mechanical signals requires well characterized and reproducible methods. In vitro cell stretching instruments encompass the possibility to strain cells in monolayer cyclically in a controlled and defined manner by deforming the substrate where the cells were attached. The system is well investigated and established [15,19,81] but nonetheless requires some considerations. It has been reported that not the complete membrane strain is transferred to the cells attached on it. Measured in direction of the strain, in uniaxial experiments 79 ?34 of the strain were transferred to fibroblasts [82] and 63 ?11 were transferred to tenocytes [83]. In other experiments, 37 ?8 and 45?0 of biaxial strains were transferred to tenocytes and bone marrow-derived stromal cells [15,83].PLOS ONE | DOI:10.1371/journal.pone.0119816 March 30,17 /Cyclic Tensile Strain and Chondrocyte MetabolismGilchrist et al. (2007) pointed out that some cells exhibit extremely different strain behavior to the applied loa.The iNOS expression itself. Contrary results were reported by Gassner and colleagues (1999), who found a suppression of IL-1-induced NO production after 12?6 h of CTS with even higher (20 ) strains. The reason for this is unclear. Madhaven and colleagues (2006) explored different durations of low CTS (3 , 0.25 Hz) and found out that the effects of the mechanical loading are persistent. Even after the removal of CTS, the IL-1 induced pro-inflammatory gene transcription were diminished for hours [29]. Furthermore, TNF- and IL-1 suppress actions that can counteract cartilage destruction, such as the expression of tissue inhibitor of metalloproteinase 2 (TIMP-2) and the expression or synthesis of proteoglycans [27,79,80]. CTS at 6 and 0.05 Hz was able to neutralize this suppression [27,53]. They further reported that TIMP-2 levels, although not suppressed by Il-1,PLOS ONE | DOI:10.1371/journal.pone.0119816 March 30,16 /Cyclic Tensile Strain and Chondrocyte MetabolismTable 7. Effects of CTS on pro-inflammatory factors. Frequency 0.05 Hz Loading duration 10 min – 48 h 24 h 2?6 h 0.17 Hz 6h 12 h 24 h 0.5 Hz 01 h 03 h 06 h 12 h 12 h 12 h 18 h 24 h 24 h 24 h 24 h 36 h 48 h 48 h Strain magnitude 3? 12?8 20 7 7 7 10 10 10 7 10 16 7 7 7 10 16 7 7 16 ” ” ” ” ” ” ” ” ” ” ” ” ” ” ” ” iNOS ” NO ” a b “a b ” #a bCOX-PGEReference [20,27,48,53,76] [76] [52,77] [47] [47] [47]” ” ” “[37] [37] [37] [36] [37] [26] [36] [28] [36] [37] [26] [36] [28] [26]Effects of CTS on pro-inflammatory factors relative to unloaded controls, sorted by loading frequency # Levels of loaded cells were decreased relative to unloaded cells Levels of loaded cells were unchanged relative to unloaded cellsa b” Levels of loaded cells were increased relative to unloaded cells Cells were seeded on fibronectin Cells were seeded on collagen Idoi:10.1371/journal.pone.0119816.twere hyper-induced by a combination of IL-1?and CTS [27]. TIMP-1 levels, however, were neither altered by TNF- nor by IL-1?or CTS [27,53]. In summary, low magnitude CTS (2?0 ) was beneficial to already inflamed joints. These effects were persistent even after the removal of CTS. Interestingly, in a non-inflammatory environment CTS between 12 and 18 mimics the effects of the inflammatory mediator IL-1 and induces similar reactions to those found in osteoarthritis, whereas lower strains were not sufficient to induce anti-inflammatory actions.DiscussionThe systematic investigation of cellular responses to mechanical signals requires well characterized and reproducible methods. In vitro cell stretching instruments encompass the possibility to strain cells in monolayer cyclically in a controlled and defined manner by deforming the substrate where the cells were attached. The system is well investigated and established [15,19,81] but nonetheless requires some considerations. It has been reported that not the complete membrane strain is transferred to the cells attached on it. Measured in direction of the strain, in uniaxial experiments 79 ?34 of the strain were transferred to fibroblasts [82] and 63 ?11 were transferred to tenocytes [83]. In other experiments, 37 ?8 and 45?0 of biaxial strains were transferred to tenocytes and bone marrow-derived stromal cells [15,83].PLOS ONE | DOI:10.1371/journal.pone.0119816 March 30,17 /Cyclic Tensile Strain and Chondrocyte MetabolismGilchrist et al. (2007) pointed out that some cells exhibit extremely different strain behavior to the applied loa.
