Nrf2 dynamically regulates RANKL-induced osteoclastogenesis and cathepsin K function.

Osteoclasts mediate bone resorption primarily through the protease Cathepsin K. RANKL, the master cytokine driving osteoclastogenesis, elevates reactive oxygen species (ROS) levels that promote osteoclast differentiation; however, excessive ROS can lead to oxidative stress and cellular damage. To counteract the detrimental effects of ROS, osteoclasts activate antioxidant defense mechanisms, including the NRF2 pathway. Here, we identify that antioxidant responses are dynamically regulated during osteoclastogenesis and osteoclast activation. Through a combined bioinformatic and genetic approach using engineered mouse models, we demonstrate a dual role of RANKL in regulating antioxidant responses in osteoclasts: while it suppresses glutathione-mediated antioxidant defenses, RANKL activates Nrf2-dependent mechanisms during osteoclast differentiation. Genetic deletion of Nrf2 (Nfe2l2) in vitro enhances osteoclast formation, whereas impairs osteoclast resorptive function, reducing cathepsin K activity. Nrf2-deficient osteoclasts exhibit increased lipid peroxidation, mitochondrial dysfunction, and lysosomal instability without alterations in cell viability. Together, these findings identify NRF2 as a critical regulator of osteoclast function, essential for maintaining redox balance and lysosomal integrity during bone resorption. This study reveals an intricate interplay between RANKL-induced oxidative signaling and antioxidant regulation, highlighting NRF2 as a critical determinant of osteoclast-mediated bone resorption.