Proteomic Analysis Reveals a New Benefit of Periodic Mechanical Stress on Chondrocytes

In recent years, a variety of studies have been performed to investigate the cellular responses of periodic mechanical stress. In our previous studies, we found that periodic mechanical stress can promote proliferation and matrix synthesis through the integrin beta 1-mediated ERK1/2 pathway, and we used proteomic analysis to detect quantitative changes in chondrocytes under periodic mechanical stress. Despite these results, the effects and mechanisms of periodic mechanical stress are still not fully understood, so in this study we extended our study using phosphoproteomic techniques.

We used phosphoproteomic techniques to detect phosphorylation changes in chondrocytes under periodic mechanical stress and combined the results with the quantitative proteomic data to further explore the underlying mechanisms. Data were obtained by phosphorylation inhibition, quantitative real-time PCR (qPCR) analysis, western blot analysis and immunofluorescence assay.

From phosphoproteomic analysis, a total of 1073 phosphorylated proteins and 2054 phosphopeptides were identified. The number of significant differentially expressed proteins and phosphopeptides was 97 and 108, respectively (ratio >1.20 or <0.83 at p<0.05). Periodic mechanical stress increased glycogen synthase kinase 3-beta (GSK3-beta) phosphorylation at Y216, promoted the phosphorylation of beta-catenin, decreased beta-catenin levels and suppressed the expression of type I collagen. In contrast, inhibition of GSK3-beta by TWS119, which specifically inhibits the phosphorylation of Y216, suppressed the phosphorylation of beta-catenin, which resulted in the accumulation of beta-catenin and an increase in the expression of type I collagen.

We successfully constructed differentially expressed phosphoproteomic profiles of rat chondrocytes under periodic mechanical stress, and discovered a potential new therapeutic benefit in which periodic mechanical stress suppressed the formation of type I collagen in the matrix of chondrocytes via phosphorylation of GSK3-beta and beta-catenin.