Quantitative analysis of the mRNA expression levels of BCL2 and BAX genes in human osteoarthritis and normal articular cartilage: An investigation into their differential expression

Osteoarthritis (OA) is primarily characterized by articular cartilage degeneration and chondrocyte loss. Although the role of apoptosis in cartilage pathobiology remains to be elucidated, the apoptotic B-cell CLL/lymphoma 2 (BCL2) gene family is considered to be involved in OA. The purpose of the present study was to quantitatively analyze the mRNA expression profiles of the BCL2-associated X protein (BAX) and BCL2 genes in human OA and in normal cartilage. Cartilage tissue samples were obtained from 78 patients undergoing total knee arthroplasty for OA (OA group) and orthopedic interventions for causes other than OA (control group). Total RNA was isolated from the cartilage tissue specimens and reverse transcribed into cDNA. A highly sensitive and specific reverse transcription quantitative polymerase chain reaction assay was developed for quantification of the mRNA levels of BAX and BCL2, using beta-2 microglobulin as an endogenous control for normalization purposes. Gene expression analysis was performed using the comparative Ct (2(-Delta Delta Ct)) method. The mRNA expression of BAX presented an increasing trend in the OA group compared with the control group, although without statistically significace (P=0.099). By contrast, the expression ratio of BCL2/BAX was found to be significantly decreased (2.76-fold) in the OA group compared with the normal cartilage control group (P=0.022). A notable 4.6-fold overexpression of median mRNA levels of BAX was also observed in patients with stage III OA compared with the control (P=0.034), while the BCL2/BAX ratio was markedly (2.5-fold) decreased (P=0.024). A marked positive correlation was observed between the mRNA levels of BAX and BCL2 in the control group (r(s)=0.728; P<0.001), which was also present in the OA group, although to a lesser degree (r(s)=0.532; P<0.001). These results further implicate apoptosis in the pathogenesis of OA, through molecular mechanisms, which include the aberrant expression of the BCL2 gene family. Further investigation may reveal novel prognostic biomarkers and potential targets for therapeutic interventions in the early stages of OA.