Shear stress modulates macrophage-induced urokinase plasminogen activator expression in human chondrocytes

Abstract

IntroductionSynovial macrophages, which can release proinflammatory factors, are responsible for the upregulation of cartilage-breakdown proteases and play critical roles in cartilage degradation during the progression of osteoarthritis (OA). In addition, shear stress exerts multifunctional effects on chondrocytes by inducing the synthesis of catabolic or anabolic genes. However, the interplay of macrophages, chondrocytes, and shear stress during the regulation of cartilage function remains poorly understood. We investigated the mechanisms underlying the modulation of human chondrocyte urokinase plasminogen activator (uPA) expression by macrophages and shear stress.MethodsHuman chondrocytes were stimulated by peripheral blood-macrophage- conditioned medium (PB-MCM), or exposure of chondrocytes cultured in PB-MCM to different levels of shear stress (2 to 20 dyn/cm2). Real-time polymerase chain reaction was used to analyze uPA gene expression. Inhibitors and small interfering RNA were used to investigate the mechanism for the effects of PB-MCM and shear stress in chondrocytes.ResultsStimulation of human chondrocytes with PB-MCM was found to induce uPA expression. We demonstrated that activation of the JNK and Akt pathways and NF-κB are critical for PB-MCM-induced uPA expression. Blocking assays by using IL-1ra further demonstrated that IL-1β in PB-MCM is the major mediator of uPA expression in chondrocytes. PB-MCM-treated chondrocytes subjected to a lower level of shear stress showed inhibition of MCM-induced JNK and Akt phosphorylation, NF-κB activation, and uPA expression. The PB-MCM-induced uPA expression was suppressed by AMP-activated protein kinase (AMPK) agonist. The inhibitor or siRNA for AMPK abolished the shear-mediated inhibition of uPA expression.ConclusionsThese data support the hypothesis that uPA upregulation stimulated by macrophages may play an active role in the onset of OA and in the shear-stress protection against this induction.

Low Shear Stress Attenuates COX‐2 Expression Induced by Resistin in Human Osteoarthritic Chondrocytes

“…Previous in vivo studies have demonstrated that mechanical loading facilitates the strengthening of the bone and that flow‐induced shear force in the cartilage initiates a repair mechanism (Suh et al, ; Robling et al, ). Moreover, previous in vitro studies, both ours and others’, have indicated that low fluid shear stress (∼2–10 dyn/cm 2 ) may contribute to a chondroprotective effect on cartilage and that high shear stress (∼10–20 dyn/cm 2 ) may induce inflammation, cell death, and cartilage degradation (Yokota et al, ; Yeh et al, ; Wang et al, ; Zhu et al, ; Yeh et al, ; Guan et al, ). These studies have elucidated that the different intensities of shear forces may have a differential potential in regulating cellular signaling and function in chondrocytes and therefore control the cartilage homeostasis.…”

“…Previous studies have demonstrated that fluid shear stress‐regulated cellular signaling and the function of chondrocytes are time‐, mode‐ and magnitude‐dependent. It has been indicated that high shear force promotes the catabolic destruction of cartilage, whereas the low shear stress effect on cartilage is chondroprotective (Yokota et al, ; Yeh et al, , ; Wang et al, ; Zhu et al, ; Guan et al, ). Our present results showed that the pre‐shear effect on cells with 2 dyn/cm 2 of shear stress attenuates the resistin effect on catabolic COX‐2 expression in human OA chondrocytes.…”

“…It has been demonstrated that obesity increases the mechanical overloading on the cartilage and results in the secretion of inflammatory adipokines from the adipocytes. These two effects could then affect chondrocyte and cartilage homeostasis and then initiate the formation of the OA phenotype: both result in the increased expressions of catabolic cytokines, cyclooxygenase (COX)‐2, and matrix metalloproteinases, but result in the decreased expressions of anabolic collagen II and aggrecan (Considine et al, ; Roos and Dahlberg, ; Sharma and Chang, ; Gabay et al, ; Griffin et al, ; Vuolteenaho et al, ; Yeh et al, ). However, the specifics of the synergistic or antagonistic interaction between mechanical force and adipokines on cartilage homeostasis are still unclear and need further clarification.…”

“…Excessive stress loading on the cartilage disrupts the homeostasis within the cartilage and hence leads to irreversible cartilage erosion and OA formation. However, accumulating evidence has also indicated that mechanical stimuli at an appropriate intensity may be essential and beneficial for cartilage constitution (Roos and Dahlberg, ; Sharma and Chang, ; Gabay et al, ; Griffin et al, ; Yeh et al, ). Previous in vivo studies have demonstrated that mechanical loading facilitates the strengthening of the bone and that flow‐induced shear force in the cartilage initiates a repair mechanism (Suh et al, ; Robling et al, ).…”

2 dyn/cm2 shear force upregulates kruppel‐like factor 4 expression in human chondrocytes to inhibit the interleukin‐1β‐activated nuclear factor‐κB

“…ined. ERK5 downregulation by siERK5 or XMD8-92 significantly inhibited 2 dyn/cm 2 shear force-increased KLF4 mRNA expression and p1901-Luc luciferase activity (Figure 5d) compared with siCL-or DMSO/shear force-treated cells.3.6 | PPARγ and KLF4 inhibit IL-1β-activated NF-κB in human primary and SW1353 chondrocytes under 2 dyn/cm 2 shear force stimulation Our previous studies have demonstrated the positive role of 2 dyn/cm 2 shear force in human primary chondrocytes(Su et al, 2017;Yeh et al, 2009Yeh et al, , 2013. Thus, we determined whether PPARγ-KLF4 play a downstream positive regulator of 2 dyn/cm 2 shear force in human chondrocytes.…”