Glucosamine promotes chondrocyte proliferation via the Wnt/ß­catenin signaling pathway.

The present study investigated the mechanism underlying the effects of glucosamine (GlcN) on the proliferation of chondrocytes isolated from the knee cartilage of Sprague­Dawley rats. Chondrocytes were treated with various concentrations of GlcN or without GlcN. The effects of GlcN on chondrocyte proliferation were determined using reverse transcription­polymerase chain reaction, western blot analysis and immunohistochemistry. The results indicated that GlcN significantly improved chondrocyte viability, accelerated G1/S transition during progression of the cell cycle and promoted the expression of cell cycle regulatory proteins, including cyclin D1, cyclin­dependent kinase (CDK)4 and CDK6, thus indicating that GlcN may promote chondrocyte proliferation. Furthermore, GlcN upregulated the expression levels of Wnt­4, Frizzled­2 and ß­catenin, and downregulated the expression of glycogen synthase kinase­3. GlcN also promoted ß­catenin translocation; ß­catenin is able to activate numerous downstream target genes, including cyclin D1. To determine the role of the Wnt/ß­catenin signaling pathway in chondrocyte proliferation, the Wnt/ß­catenin signaling pathway was inhibited using Dickkopf­1 (DKK­1), after which chondrocytes were treated with GlcN. The results demonstrated that the expression levels of ß­catenin and cyclin D1 were decreased in chondrocytes treated with DKK­1 and GlcN. These results suggested that GlcN may promote chondrocyte proliferation via the Wnt/ß­catenin signaling pathway.

Psoralen promotes the expression of cyclin D1 in chondrocytes via the Wnt/ß-catenin signaling pathway.

Psoralen (PSO), the active ingredient of Fructus Psoraleae (FP) the dried ripe fruit of Psoralea corylifolia L., has been commonly used in traditional Chinese medicine (TCM) for the treatment of osteoarthritis (OA). We found that PSO activates cartilaginous cellular functions of rat chondrocytes in vitro. However, the effect of PSO on chondrocyte proliferation and the precise mechanisms involved remain to be elucidated. We investigated the effects of PSO on chondrocytes isolated from Sprague­Dawley (SD) rats and evaluated involvement of the Wnt/ß-catenin signaling pathway. The viability of chondrocytes treated with PSO was increased in a dose- and time-dependent manner, as assessed by MTT assay. We found that the gene expression and protein levels of Wnt-4, Frizzled-2, ß-catenin and cyclin D1 in the PSO-treated chondrocytes were significantly upregulated, while the gene expression and protein level of glycogen synthase kinase-3ß (GSK-3ß) were downregulated, compared with the untreated chondrocytes. By immunofluorescence, we also found that PSO induced ß-catenin nuclear translocation. Importantly, the expression of ß-catenin and cyclin D1 was partly inhibited by Dickkopf-1 (DKK-1), an inhibitor of the Wnt/ß-catenin signaling pathway. Additionally, Col-II expression in chondrocytes was increased after treatment with PSO. Taken together, these results indicate that PSO promotes chondrocyte proliferation by activating the Wnt/ß-catenin signaling pathway, and it may play an important role in the treatment of OA.

Electroacupuncture serum inhibits TNF­α­mediated chondrocyte inflammation via the Ras­Raf­MEK1/2­ERK1/2 signaling pathway.

The Ras­Raf­mitogen­activated protein kinase kinase (MEK)1/2­extracellular signal­regulated kinase (ERK)1/2 signaling pathway contributes to the release of chondral matrix­degrading enzymes and accelerates the degradation of articular cartilage. Electroacupuncture (EA) treatment has been widely used for the treatment of osteoarthritis (OA); however, the mechanism underlying the effects of EA on OA remains unclear. Therefore, the present study evaluated the anti­inflammatory effects and potential underlying mechanisms of EA serum (EAS) on tumor necrosis factor (TNF)­α­mediated chondrocyte inflammation. A total of 30 Sprague Dawley rats were randomly divided into three groups: The blank group; experimental group I, which received 15 min of EA treatment; and experimental group II, which received 30 min of EA treatment. Subsequently, serum samples were obtained. Chondrocytes were isolated from the knee cartilage of Sprague Dawley rats, and were identified using collagen type II immunohistochemistry. TNF­α­treated chondrocytes were used as a cell model, and subsequently the cells were treated with EAS from each group for various durations. The results demonstrated that EAS treatment significantly promoted the viability and inhibited the apoptosis of TNF­α­treated chondrocytes. In addition, interleukin (IL)­1ß concentration was significantly increased in the model group compared with in the control group, whereas EAS significantly reduced IL­1ß concentration in TNF­α­treated chondrocytes. Furthermore, the protein expression levels of Ras, Raf and MEK1/2 were reduced in the EAS groups compared with in the model group. EAS also significantly inhibited the phosphorylation of ERK1/2, and the expression of downstream regulators matrix metalloproteinase (MMP)­3 and MMP­13. In conclusion, these results indicated that EAS may inhibit TNF­α­mediated chondrocyte inflammation via the Ras­Raf­MEK1/2­ERK1/2 signaling pathway in vitro, thus suggesting that EAS may be considered a potential therapeutic strategy for the treatment of OA.

Expressing human SHOX in Shox2SHOX KI/KI mice leads to congenital osteoarthritis­like disease of the temporomandibular joint in postnatal mice.

The temporomandibular joint (TMJ), a unique synovial joint whose development differs from that of other synovial joints, develops from two distinct mesenchymal condensations that grow toward each other and ossify through different mechanisms. The short stature homeobox 2 (Shox2) gene serves an important role in TMJ development and previous studies have demonstrated that Shox2SHOX KI/KI mice display a TMJ defective phenotype, congenital dysplasia and premature eroding of the articular disc, which is clinically defined as a TMJ disorder. In the present study, Shox2SHOX KI/KI mouse models were used to investigate the mechanisms of congenital osteoarthritis (OA)­like disease during postnatal TMJ growth. Shox2SHOX KI/KI mice were observed to develop a severe muscle wasting syndrome from day 7 postnatal. Histological examination indicated that the condyle and glenoid fossa of Shox2SHOX KI/KI mice was reduced in size in the second week after birth. The condyles of Shox2SHOX KI/KI mice exhibited reduced expression levels of collagen type II and Indian hedgehog, and increased expression of collagen type I. A marked increase in matrix metalloproteinase 9 (MMP9) and MMP13 in the condyles was also observed. These cellular and molecular defects may contribute to the observed (OA)­like phenotype of Shox2SHOX KI/KI mouse TMJs.

Bushen Zhuangjin decoction inhibits TM-induced chondrocyte apoptosis mediated by endoplasmic reticulum stress.

Chondrocyte apoptosis triggered by endoplasmic reticulum (ER) stress plays a vital role in the pathogenesis of osteoarthritis (OA). Bushen Zhuangjin decoction (BZD) has been widely used in the treatment of OA. However, the cellular and molecular mechanisms responsible for the inhibitory effects of BZD on chondrocyte apoptosis remain to be elucidated. In the present study, we investigated the effects of BZD on ER stress-induced chondrocyte apoptosis using a chondrocyte in vitro model of OA. Chondrocytes obtained from the articular cartilage of the knee joints of Sprague Dawley (SD) rats were detected by immunohistochemical staining for type Ⅱ collagen. The ER stress-mediated apoptosis of tunicamycin (TM)­stimulated chondrocytes was detected using 4-phenylbutyric acid (4­PBA). We found that 4­PBA inhibited TM-induced chondrocyte apoptosis, which confirmed the successful induction of chondrocyte apoptosis. BZD enhanced the viability of the TM-stimulated chondrocytes in a dose- and time-dependent manner, as shown by MTT assay. The apoptotic rate and the loss of mitochondrial membrane potential (ΔΨm) of the TM-stimulated chondrocytes treated with BZD was markedly decreased compared with those of chondrocytes not treated with BZD, as shown by 4',6-diamidino-2-phenylindole (DAPI) staining, Annexin V-FITC binding assay and JC-1 assay. To further elucidate the mechanisms responsible for the inhibitory effects of BZD on TM­induced chondrocyte apoptosis mediated by ER stress, the mRNA and protein expression levels of binding immunoglobulin protein (Bip), X­box binding protein 1 (Xbp1), activating transcription factor 4 (Atf4), C/EBP­homologous protein (Chop), caspase­9, caspase-3, B-cell lymphoma 2 (Bcl-2) and Bcl-2-associated X protein (Bax) were measured by reverse transcription-polymerase chain reaction (RT-PCR) and western blot analysis. In the TM-stimulated chondrocytes treated with BZD, the mRNA and protein expression levels of Bip, Atf4, Chop, caspase-9, caspase-3 and Bax were significantly decreased, whereas the mRNA and protein expression levels of Xbp1 and Bcl-2 were significantly increased compared with the TM­stimulated chondrocytes not treated with BZD. Additionally, all our findings demonstrated that there was no significant difference between the TM­stimulated chondrocytes treated with BZD and those treated with 4­PBA. Taken together, our results indicate that BZD inhibits TM­induced chondrocyte apoptosis mediated by ER stress. Thus, BZD may be a potential therapeutic agent for use in the treatment of OA.