Leptin protects rat articular chondrocytes from cytotoxicity induced by TNF-α in the presence of cyclohexamide

Abstract

Objective: Although leptin appears to be an important local and systemic factor influencing cartilage homeostasis, the role of leptin in chondrocyte death is largely unknown. Tumor necrosis factor α (TNF-α) is a pro-inflammatory cytokine that plays a central role in the pathogenesis of articular diseases. This study examines whether leptin modulates TNF-α-induced articular chondrocyte death.

Methods: Primary rat articular chondrocytes were isolated from knee joint cartilage slices. To induce cell death, the chondrocytes were treated with TNF-α. To examine whether leptin modulates the extent of TNF-α-mediated chondrocyte death, the cells were pretreated with leptin for 3 h before TNF-α treatment followed by viability analysis. To examine the mechanism by which leptin modulates the extent of TNF-α-mediated chondrocyte death, we utilized mitochondrial membrane potential (MMP) measurements, flow cytometry, nuclear morphology observation, co-immunoprecipitation, western blot analysis and confocal microscopy.

Results: We demonstrated that leptin suppresses TNF-α induced chondrocyte death. We further found that apoptosis partially contributes to TNF-α induced chondrocyte death while necroptosis primarily contributes to TNF-α induced chondrocyte death. In addition, we observed that leptin exerts anti-TNF-α toxicity via c-jun N-terminal kinase (JNK) in rat articular chondrocytes.

Conclusion: Based on our findings, we suggest that the leptin present in the articular joint fluid protects articular chondrocytes against cumulative mechanical load and detrimental stresses throughout a lifetime, delaying the onset of degenerative changes in chondrocytes. We can further hypothesize that leptin protects articular chondrocytes against destructive stimuli even in the joints of osteoarthritis (OA) patients.

Keywords: Apoptosis; JNK; Leptin; Necroptosis; TNF-α.