Macropinocytosis Regulates Metabolic Reprogramming To Potentiate Osteoclast Differentiation

Osteoclast differentiation and bone resorption are processes with high energy demands, and macropinocytosis serves as an efficient mechanism to mitigate nutrient shortages in cells with high metabolic demands by scavenging nutrients. However, the interrelationship between metabolic state, osteoclast differentiation, and macropinocytosis in bone-related diseases remains inadequately understood. We conducted in vitro osteoclast induction using murine bone marrow-derived macrophages (BMMs) and RAW 264.7 cells to investigate the role of macropinocytosis in metabolic changes and osteoclast differentiation. Additionally, we employed lipopolysaccharide (LPS) treatment to simulate inflammatory conditions in vitro, and analyzed the function of macropinocytosis in the metabolic profile and inflammatory osteoclastogenesis. Furthermore, we utilized ligature-induced murine periodontitis (C57BL/6 mice, male, 4-6 weeks old) and ovariectomy (OVX)-induced bone loss murine models (C57BL/6 mice, female, 10 weeks old) to assess the impact of macropinocytosis on bone resorption in vivo. All experiments using mice were approved by the Research Ethics Committee [permit number: No.2023(122)]. Enhanced macropinocytosis was observed to facilitate osteoclast formation, with LPS stimulation further augmenting osteoclast differentiation and upregulating macropinocytosis. This process met the energy requirements of osteoclastogenesis through oxidative phosphorylation and glycolysis. Furthermore, macropinocytosis was significantly elevated in models of periodontitis and OVX mice, and its inhibition led to the restoration of bone mass in a dose-dependent manner. Macropinocytosis serves as a critical metabolic regulator during osteoclast differentiation, and targeting this pathway presents a promising therapeutic strategy for bone-related diseases.