Aesculetin Inhibits Bone Resorption Through Down-Regulating Differentiation and Lysosomal Formation in Osteoclasts

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Abstract Objectives For the optimal resorption of mineralized bone extracellular matrix, osteoclasts require the generation of a resorption lacuna characterized by the presence of specific proteases and a low pH. Thus, bone resorption by osteoclasts highly rely on lysosomes, the organelles specialized in intra- and extracellular material degradation. Aesculetin, a derivative of coumarin, possesses anti-inflammatory and anti-bacterial effects. The purpose of this study was to identify that aesculetin inhibited osteoclast differentiation and bone resorption through down-regulating lysosomal formation. Methods Raw 264.7 cells were cultured for 5 days on α-MEM with 10% FBS in the absence or presence of 50 ng/ml RANKL and 1–10 μM aesculetin. Tartrate-resistance acid phosphatase (TRAP) staining and bone resorption assay were performed by using assay kits. Western blotting was conducted with antibodies of target proteins involved in activation and lysosome biogenesis of osteoclasts. Immunocytochemical analysis employed LysoTracker for lysosome staining and α-tubulin antibody conjugated with FITC. Results Aesculetin inhibited RANKL-treated formation of multinucleated osteoclasts with a reduction of TRAP activity. When 1–10 μM aesculetin was treated to RANKL-exposed osteoclasts, the bone resorption was highly suppressed in osteoclasts. In addition, aesculetin reduced cellular expression of carbonic anhydrase II, vacuolar-type H (+)-ATPase D2 and cathepsin K elevated by RANKL, all involved in the bone resorption. Furthermore, aesculetin curtailed cellular induction of autophagy-related (Atg)5, Atg7 and small GTPase Rab7 elevated by RANKL for lysosome transportation/secretion and bone resorption in osteoclasts. Conclusions Aesculetin was effective in retarding osteoclast differentiation and secretory lysosome formation for osteoclast resorption, indicating that this compound may be a potential agent for the treatment of osteoporosis. Funding Sources No funding sources to report.