Millimeter wave treatment promotes chondrocyte proliferation by upregulating the expression of cyclin-dependent kinase 2 and cyclin A

We investigated the effects of millimeter wave treatment on the expression of the cell cycle regulating proteins cyclin-dependent kinase 2 (CDK2) and cyclin A in chondrocytes. Knee articular cartilage from SD rats was used to establish cultured primary chondrocytes. After identification using toluidine blue staining, passage 2 chondrocytes were randomly divided into different groups and treated with nocodazole or millimeter wave. The RNA expression of CDK2 and cyclin A was measured using RT-PCR, and their protein levels were detected by Western blotting. Cell cycle analysis showed that nocodazole treatment significantly increased the number of G0/G1 and G2/M stage chondrocytes and decreased the amount of S phase cells. In contrast, millimeter wave treatment significantly decreased the number of G0/G1 and G2/M chondrocytes and increased the number of S phase cells. The mRNA and protein levels of CDK2 and cyclin A consistently demonstrated a reverse trend, with the lowest levels in the chondrocytes treated with nocodazole. The expression of CDK2 and cyclin A was higher in chondrocytes receiving millimeter wave treatment than in untreated cells. In conclusion, millimeter wave treatment induces CDK2 and cyclin A expression, accelerates S-phase entry and G2/M transition and promotes chondrocyte cell cycle progression.