HMGB2 promotes chondrocyte proliferation under negative pressure through the phosphorylation of AKT

Cells in articular cartilage are zonal arranged. Cells in superficial zone cartilage are generally small and proliferative. Appropriate negative pressure stimulation is beneficial to cell survival and tissue repair. Whether negative pressure has promotive impact on the proliferation activity of the superficial zone chondrocytes is of interest. In this study, we isolated superficial chondrocytes from the mandibular condylar cartilage of rats. After negative pressure treatment, the cells were collected for RNA-sequencing, quantitative real-time PCR and western blotting assays, aiming to detect the proliferative responses of chondrocytes to negative pressure and explore the potential molecular mechanisms. Data from RNA-sequencing analysis indicated that the superficial chondrocytes responded to the 4 h -10 kPa treatment by a significant increase in proliferation. In addition, the expression of high-mobility group box 2 (HMGB2) and the phosphorylation of AKT were obviously promoted. Knockdown of HMGB2 decreased AKT phosphorylation and diminished the negative pressure-induced proliferation of chondrocytes, as shown by decreased expression of Ki67 and cyclin-dependent kinase 6 (CDK6). In contrast, overexpression of HMGB2 enhanced AKT phosphorylation and further promoted proliferative activity. Moreover, LY294002, an AKT inhibitor, suppressed the proliferative activity of chondrocytes under negative pressure, while SC79, an activator of AKT phosphorylation, enhanced the proliferation of chondrocytes. Our data demonstrated that HMGB2 exhibits a promotion impact on chondrocyte proliferation under negative pressure via the phosphorylation of AKT. These results provide a new perspective for superficial zone chondrocytes proliferation under negative pressure, which should be benefit for cartilage regeneration.