Phloretin inhibits osteoclast differentiation and alleviates disuse osteoporosis through the PI3K/AKT/NF-κB pathway

Mechanical unloading that results from aging, prolonged bed rest, or spaceflight leads to disuse osteoporosis (DOP), a significant public health concern. However, the mechanisms underlying this condition, as well as effective therapeutic strategies, remain incompletely defined. In this study, significant bone deterioration, increased osteoclast activation, and upregulation of the PI3K/Akt/NF-κB signaling cascade were observed in femoral specimens from hindlimb suspension (HLS) mice, a well-established DOP model. Phloretin, a naturally occurring flavonoid with notable antioxidant and anti-inflammatory activities, has shown anti-osteoclastogenic effects in chemically induced models. Nevertheless, its therapeutic efficacy and direct molecular targets in mechanical unloading-induced bone loss, a condition characterized by a distinct pathophysiology, remain largely undefined. Herein, we demonstrated that phloretin markedly suppressed osteoclastogenesis, attenuated excessive bone resorption and effectively counteracted bone loss in the hindlimb-unloading murine model. Complementing these in vivo findings, primary osteoclast cultures revealed that phloretin reduced osteoclast formation and activity by inhibiting the PI3K/Akt/NF-κB signaling axis. Importantly, pharmacological activation of the PI3K pathway with 740 Y-P significantly reduced Phloretin's inhibitory effects on osteoclast differentiation and bone protection, confirming that this pathway is the primary regulatory target. Unlike general anti-resorptive agents, phloretin specifically addresses the PI3K-mediated signaling activation triggered by mechanical unloading. Our findings provide robust evidence for the application of phloretin as a targeted therapy for disuse-related skeletal disorders.