Knockdown MiR-302b Alleviates LPS-Induced Injury by Targeting Smad3 in C28/I2 Chondrocytic Cells.

Background/aims: Osteoarthritis (OA) is one of the most common chronic degenerative diseases. Many studies have demonstrated the role of microRNAs (miRNAs) in OA; however, the role of miR-302b in OA remains elusive. The aim of this study was to identify the role of miR-302b in LPS-induced injury in chondrocytes.

Methods: Human OA chondrocytes (C28/12 cell line) were transfected with miR-302b inhibitor and miR-302b mimic to investigate the effects of miR-302b expression on chondrocyte apoptosis and inflammation, and to identify the miR-302b target proteins.

Results: LPS treatment of chondrocytes significantly reduced cell viability and increased apoptotic rate. LPS treatment also increased the expression of inflammatory cytokines compared to control. miR-302b was up-regulated in LPS-induced chondrocytes. miR-302b was either suppressed or overexpressed in LPS-induced chondrocytes by transient transfection. miR-302b mimic transfection accelerated the effects of LPS on cell viability, apoptosis and inflammation. Of contrast, miR-302b inhibition represented a reverse effect. Dual luciferase activity demonstrated that Smad3 is a direct target for miR-302b and its expression was negatively regulated by miR-302b. In addition, miR-302b inhibition suppressed inflammation in LPS treated chondrocytes by up-regulating Smad3 expression. Moreover, LPS induced down-regulation of Notch and mTOR signaling pathway-related protein expressions, and miR-302b inhibition increased the expressions of Notch and mTOR signaling pathway-related proteins. We further found that miR-302b negatively regulated Notch2 levels through direct targeting its 3'UTR.

Conclusions: These results suggest that miR-302b suppression may function as a protector in suppressing the inflammation during the development and progression of OA by up-regulating the target Smad3 expression.