The role of semaphorin 3A on chondrogenic differentiation.

Osteoblast-derived semaphorin3A (Sema3A) has been reported to be involved in bone protection, and Sema3A knockout mice have been reported to exhibit chondrodysplasia. From these reports, Sema3A is considered to be involved in chondrogenic differentiation and skeletal formation, but there are many unclear points about its function and mechanism in chondrogenic differentiation. This study investigated the pharmacological effects of Sema3A in chondrogenic differentiation. The amount of Sema3A secreted into the culture supernatant was measured using an enzyme-linked immunosorbent assay. The expression of chondrogenic differentiation-related factors, such as Type II collagen (COL2A1), Aggrecan (ACAN), hyaluronan synthase 2 (HAS2), SRY-box transcription factor 9 (Sox9), Runt-related transcription factor 2 (Runx2), and Type X collagen (COL10A1) in ATDC5 cells treated with Sema3A (1,10 and 100 ng/mL) was examined using real-time reverse transcription polymerase chain reaction. Further, to assess the deposition of total glycosaminoglycans during chondrogenic differentiation, ATDC5 cells were stained with Alcian Blue. Moreover, the amount of hyaluronan in the culture supernatant was measured by enzyme-linked immunosorbent assay. The addition of Sema3A to cultured ATDC5 cells increased the expression of Sox9, Runx2, COL2A1, ACAN, HAS2, and COL10A1 during chondrogenic differentiation. Moreover, it enhanced total proteoglycan and hyaluronan synthesis. Further, Sema3A was upregulated in the early stages of chondrogenic differentiation, and its secretion decreased later. Sema3A increases extracellular matrix production and promotes chondrogenic differentiation. To the best of our knowledge, this is the first study to demonstrate the role of Sema3A on chondrogenic differentiation.

ANGPTL2 Promotes Inflammation via Integrin α5ß1 in Chondrocytes.

BACKGROUND: Angiopoietin-like protein 2 (ANGPTL2) is a secreted molecule with numerous physiologic and pathologic functions, for example, in angiogenesis, hematopoiesis, and tumorigenesis. Although recent studies implicated ANGPTL2 in chronic inflammation in mouse peritoneal macrophages, human ligamentum flavum fibroblasts, and human retinal microvascular endothelial cells, the mechanism underlying ANGPTL2-associated inflammation in chondrocytes remains unclear. Therefore, it was investigated whether ANGPTL2 is expressed in or functions in chondrocytes. METHODS: Expression of ANGPTL2 and its receptor, integrin α5ß1 were examined over time in ATDC5 cells using real-time RT-PCR (reverse transcription-polymerase chain reaction) analysis. ATDC5 cells were then incubated with or without ANGPTL2 for 3 hours, and expression of the IL-1ß, TNF-α, COX-2, aggrecanase (ADAMTS)-5, matrix metalloproteinase (MMP)-3, and MMP-13 genes were examined using real-time RT-PCR. Additionally, phosphorylation of ERK, JNK, p38, Akt, and NF-κB was examined by western blotting. Furthermore, it was also investigated for the effect of anti-integrin α5ß1 antibody on the expression of inflammatory markers and intracellular signaling pathways. RESULTS: ANGPTL2 induced the phosphorylation of all 3 MAPKs, Akt, and NF-κB and dramatically upregulated the expression of inflammation-related factor genes. Inhibiting the activation of integrin α5ß1 suppressed these reactions. CONCLUSION: ANGPTL2 may induce inflammatory factors by stimulating the integrin α5ß1/MAPKs, Akt, and NF-κB signaling pathway.

FAK inhibition protects condylar cartilage under excessive mechanical stress.

OBJECTIVES: Excessive mechanical stress is assumed to be a major cause of temporomandibular joint (TMJ) osteoarthritis (OA). +Focal adhesion kinase (FAK) is a cytoplasmic non-receptor tyrosine kinase involved in a variety of signaling pathways. Little has been reported on the function of FAK in TMJ-OA. In the present study, we investigated the effect of FAK inhibition on TMJ cartilage under excessive mechanical loading stress. MATERIALS AND METHODS: Articular cartilage explants were harvested from the TMJ of rats and subjected to mechanical loading in the presence of an FAK inhibitor in organ culture. The gene expression of inflammatory cytokines was examined after the application of mechanical loading with or without FAK inhibitor. Paraffin-embedded sections of articular cartilage were stained with hematoxylin and eosin, safranin O and fast Green, toluidine blue, TUNEL staining, and immunohistochemical staining and was performed to investigate the protein expression of IL-1ß and MMP-13. RESULTS: Treatment with FAK inhibitor reduced the gene expression of inflammatory cytokines and inhibited the degradation of articular cartilage, as determined histologically. FAK inhibitor treatment also suppressed the protein expression of IL-1ß and MMP-13 in the hypertrophic zone, as determined immunohistologically. CONCLUSION: Treatment with FAK inhibitor suppresses inflammation and protects condylar cartilage under excessive mechanical loading.

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

Chondrocytes constantly receive external stimuli, which regulates remodeling. An optimal level of mechanical stress is essential for maintaining chondrocyte homeostasis, however, excessive mechanical stress induces inflammatory cytokines and protease, such as matrix metalloproteinases (MMPs). Therefore, excessive mechanical stress is considered to be one of the main causes to cartilage destruction leading to osteoarthritis (OA). Integrins are well-known as cell adhesion molecules and act as receptors for extracellular matrix (ECM), and are believed to control intracellular signaling pathways both physically and chemically as a mechanoreceptor. However, few studies have focused on the roles and functions of integrins in inflammation caused by excessive mechanical stress. In this study, we examined the relationship between integrins (αVß3 and αVß5) and the expression of inflammatory factors under mechanical loading in chondrocytes by using an integrin receptor antagonist (cilengitide). Cilengitide suppressed the gene expression of interleukin-1ß (IL-1ß), tumor necrosis factor-α (TNF-α), matrix metalloproteinase-3 (MMP-3), and MMP-13 induced by excessive mechanical stress. In addition, the protein expression of IL1-ß and MMP-13 was also inhibited by the addition of cilengitide. Next, we investigated the involvement of intracellular signaling pathways in stress-induced integrin signaling in chondrocytes by using western blotting. The levels of p-FAK, p-ERK, p-JNK, and p-p38 were enhanced by excessive mechanical stress and the enhancement was suppressed by treatment with cilengitide. In conclusion, this study revealed that excessive mechanical stress may activate integrins αVß3 and αVß5 on the surface of chondrocytes and thereby induce an inflammatory reaction by upregulating the expression of IL-1ß, TNF-α, MMP-3, and MMP-13 through phosphorylation of FAK and MAPKs.

Semaphorin 3A Inhibits Inflammation in Chondrocytes under Excessive Mechanical Stress.

BACKGROUND: Excessive mechanical stress causes inflammation and destruction of cartilage and is considered one of the cause of osteoarthritis (OA). Expression of semaphorin 3A (Sema3A), which is an axon guidance molecule, has been confirmed in chondrocytes. However, there are few reports about Sema3A in chondrocytes, and the effects of Sema3A on inflammation in the cartilage are poorly understood. The aim of this study was to examine the role of Sema3A in inflammation caused by high magnitude cyclic tensile strain (CTS). METHODS: Expression of Sema3A and its receptors neuropilin-1 (NRP-1) and plexin-A1 (PLXA1) in ATDC5 cells was examined by Western blot analysis. ATDC5 cells were subjected to CTS of 0.5 Hz, 10% elongation with added Sema3A for 3 h. Gene expression of IL-1ß, TNF-ɑ, COX-2, MMP-3, and MMP-13 was examined by qPCR analysis. Furthermore, the phosphorylation of AKT, ERK, and NF-κB was detected by Western blot analysis. RESULTS: Added Sema3A inhibited the gene expression of inflammatory cytokines upregulated by CTS in a dose-dependent manner. Addition of Sema3A suppressed the activation of AKT, ERK, and NF-κB in a dose-dependent manner. CONCLUSIONS: Sema3A reduces the gene expression of inflammatory cytokines by downregulating the activation of AKT, ERK, and NF-κB pathways in ATDC5 cells under CTS.

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

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-1ß, 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-1ß, 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-1ß, 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-1ß protein expression. In conclusion, FAK appears to regulate inflammation in chondrocytes under CTS via MAPK pathways.