Taurine alleviates endoplasmic reticulum stress in the chondrocytes from patients with osteoarthritis

Abstract

Osteoarthritis (OA), characterized by pain and stiffness, swelling, deformity and dysfunction of joints, affects large numbers of population. The purpose of this study was to discover the effects of taurine in human OA chondrocytes and explore the underlying mechanisms. 46 patients with different grades of OA were recruited. Of these patients, 24 underwent total knee replacement and cartilages were harvested. The mRNA expressions of type II collagen (Collagen II) and endoplasmic reticulum (ER) stress markers (GRP78, GADD153 and Caspase-12) in cartilages were quantified by qRT-PCR. Cell viability and apoptosis of patient-derived chondrocytes were assessed by the CCK-8 assay and flow cytometry assay, respectively. Meanwhile, protein levels of Collagen II and ER stress markers both in cartilages and chondrocytes were evaluated by Western blot. The mRNA and protein levels of Collagen II decreased as OA progressed, while the expressions of ER stress markers increased dramatically. H₂O₂ induced ER stress in chondrocytes, as shown by the significant increase in the expression of ER stress markers, inhibited chondrocyte viability and Collagen II synthesis, promoted apoptosis. However, taurine treatment inhibited these above phenomena. These results indicated that taurine exhibited anti-OA effect by alleviating H₂O₂ induced ER stress and subsequently inhibiting chondrocyte apoptosis.

Keywords: ER stress; H2O2; Taurine; anti-apoptosis; osteoarthritis.

Figure 1.

Representative radiographs of patients with different OA grades. Radiographs II (n = 22) and III (n = 15) demonstrated the degenerative changes of OA while radiographs I (n = 9) illustrated a preserved joint space.

Figure 2.

The expression of Collagen II, GRP78, GADD153 and Caspase-12 in cartilages from patients with different OA grades. (a) mRNA and (b) protein expressions of Collagen II and ER stress markers were determined via qRT-PCR analysis and Western blot analysis, respectively. (c) was the statistical analysis of (b). Data were presented as mean ± SEM. Experiments were repeated in triplicate. *p < 0.05, **p < 0.01 and ***p < 0.001 compared to grade I. #p < 0.05 and ##p < 0.01compared to grade II.

Figure 3.

Concentration dependent toxicity of taurine and H₂O₂. Effects of (a) H₂O₂ (0.1, 0.2, 0.3, 0.4, 0.5, 1 and 2 mM) and (b) taurine (5, 10, 15, 20, 25, 30, 35 mM) on the cell viability of OA patient-derived chondrocytes were measured via CCK-8 assay. Data were presented as mean ± SEM. *p < 0.05, **p < 0.01 and ***p < 0.001 compared to control.

Figure 4.

Taurine treatment affected the viability and apoptosis of H₂O₂-stimulated chondrocytes. (a) chondrocyte viability was measured by the CCK-8 assay. (b), statistical bar graph showing the apoptosis ratio. (c), chondrocytes were stained with Annexin V/propidium iodide and analyzed by flow cytometry. Data were presented as mean ± SEM. Experiments were repeated in triplicate. *p < 0.05, **p < 0.01 and ***p < 0.001 compared to control. #p < 0.05 and ##p < 0.01compared to the H₂O₂ group.

Figure 5.

Taurine treatment affected the expressions of Collagen II, GRP78, GADD153 and Caspase-12 in H₂O₂-treated chondrocytes. (a)Western blot were used to assay the protein expressions and β-actin was used as a loading control. (b) was the statistical analysis of (a). Data were presented as mean ± SEM. Experiments were repeated in triplicate. *p < 0.05, **p < 0.01 and ***p < 0.001 compared to control. #p < 0.05 and ##p < 0.01 compared to the H₂O₂ group.