Metformin promotes apoptosis of senescent chondrocytes by disrupting the Bcl-xL/Mcl-1–Bak interaction

Introduction The accumulation of senescent chondrocytes (SEC) beyond the body’s tolerance capacity is a key contributor to osteoarthritis (OA) pathogenesis. Metformin (Met), a first-line oral medication for type 2 diabetes, has shown therapeutic potential in various diseases. This study aims to explore the therapeutic effects and underlying mechanisms of Met in OA. Methods Cellular senescence was induced in immortalized human chondrocytes using doxorubicin (Dox), confirmed by β-galactosidase staining and western blotting. The effects of Met on SEC viability, mitochondrial membrane potential, and apoptosis were assessed. Protein expression and interactions were analyzed by western blot and live-cell fluorescence resonance energy transfer (FRET) analysis. Results Met promoted death of SEC and reduced mitochondrial membrane potential, inducing caspase- and reactive oxygen species (ROS)-dependent apoptosis. Met upregulated Bak and Bim expression, downregulated Mcl-1, and activated Caspase-3, Caspase-8, and Caspase-9, leading to PARP cleavage. FRET analysis revealed that Met disrupted Mcl-1/Bak and Bcl-xL/Bak binding while facilitating Bim-Bak interaction, promoting Bak dimerization. Discussion This study provides the first evidence that Met induces apoptosis of SEC by reducing Mcl-1-Bak and Bcl-xL-Bak interactions while enhancing Bim-Bak binding, suggesting a novel therapeutic strategy for OA by targeting senescent chondrocytes through mitochondrial apoptosis pathways.