Cyclic Tensile Strain Upregulates Pro-Inflammatory Cytokine Expression Via FAK-MAPK Signaling in Chondrocytes

Abstract

Excessive mechanical stimulation is considered an important factor in the destruction of chondrocytes. Focal adhesion kinase (FAK) is non-receptor tyrosine kinase related to a number of different signaling proteins. Little is known about the function of FAK in chondrocytes under mechanical stimulation. In the present study, we investigated the function of FAK in mechanical signal transduction and the mechanism through which cyclic tensile strain (CTS) induces expression of inflammation-related factors. Mouse ATDC5 chondrogenic cells were subjected to CTS of 0.5 Hz to 10% cell elongation with an FAK inhibitor. The expression of genes encoding COX-2, IL-1β, and TNF-α was examined using real-time RT-PCR after CTS application with FAK inhibitor. Phosphorylation of p-38, ERK, and JNK was analyzed by Western blotting. Differences in COX-2 expression following pretreatment with FAK, p-38, ERK, and JNK inhibitors were compared by Western blotting. We found that CTS increased the expression of genes encoding COX-2, IL-1β, and TNF-α and activated the phosphorylation of FAK, p-38, ERK, and JNK. Pretreatment with an FAK inhibitor for 2 h reduced the expression of genes encoding COX-2, IL-1β, and TNF-α induced by CTS-associated inflammation and decreased phosphorylation of FAK, p-38, ERK, and JNK. Pretreatment with FAK, p-38, ERK, and JNK inhibitors markedly suppressed COX-2 and IL-1β protein expression. In conclusion, FAK appears to regulate inflammation in chondrocytes under CTS via MAPK pathways.

Protective effects of cilengitide on inflammation in chondrocytes under excessive mechanical stress

“…Scale bars = 50 µm. (Su et al, 2014;Sumi et al, 2018;Yanoshita et al, 2018). In this study, high-magnitude cyclic tensile stress was applied on ATDC5 chondrocytes in a condition of 10% cell elongation for 24 h, which caused the upregulated expression of inflammatory cytokines and matrixdegrading enzymes (Figure 2).…”

“…We have been investigating the relationship between excessive mechanical stress and chondrogenic destruction. The cyclic tensile stress is associated with expression of many kinds of inflammatory cytokines and proteinase in chondrocytes (Su et al, ; Sumi et al, ; Yanoshita et al, ). In this study, high‐magnitude cyclic tensile stress was applied on ATDC5 chondrocytes in a condition of 10% cell elongation for 24 h, which caused the upregulated expression of inflammatory cytokines and matrix‐degrading enzymes (Figure ).…”

“…In addition, a previous study reported that the expression of inflammatory response genes is controlled by MAPKs and transcriptional regulator NF‐κB in even chondrocytes (Saklatvala, ). Moreover, we previously demonstrated that FAK is a crucial signaling molecule and is initially stimulated by integrin activation, which can result in tyrosine (Tyr397) phosphorylation of FAK (depending on the integrin‐ECM interaction) and potentially the activation of MAPKs under mechanical stress (Yanoshita et al, ). The present study showed that the inhibition of activated integrin αVβ3 and αVβ5 caused a significant decrease in the phosphorylation of FAK, ERK, JNK, p‐38, and NF‐κB, which are also enhanced under excessive mechanical stress (Figure ).…”

“…It has previously been reported that the application of a 3% strain (0.17 Hz and 2 h) on chondrocytes resulted in weak or no biological response, whereas loading between 3 and 10% strain (0.17–0.5 Hz and 2–12 h) led to anabolic responses (Bleuel et al, ). We have conducted in vitro study applying the mechanical strain on this condition (10% elongation, 0.5 Hz, and 3 h), which is considered as excessive stress for chondrocytes (Sumi et al, ; Yanoshita et al, ). The cells were harvested 1, 3, 6, 12, and 24 h after the application of excessive mechanical stress and were frozen at −80°C until used for real‐time reverse‐transcription polymerase chain reaction (RT‐PCR) and western blot analysis.…”

Cells under stress: The mechanical environment shapes inflammasome responses to danger signals

“…Ventilator‐induced cyclic stretch of alveolar macrophages activates the macrophage NLRP3 inflammasome, and also in lung endothelial cells, to produce IL‐1β. Mechanotransduction modulates the macrophage inflammatory response in other systems as well . For instance, macrophages cultured on softer substrates down‐regulated inflammatory cytokine expression .…”