Fig. 1

The decline of melatonin (MT) was accompanied by the enhanced osteoclastogenic potential and oxidative stress in the aging process. A–D The plasma concentration of MT, oxidative stress markers including AOPPs, MDA and SOD-1 in young(3-month-old) mice and old (18-month-old) mice. Data represent mean ± S.D. of at least three independent experiments (n = 3 per group). E–G Western blot analysis of the TRAP and CTSK expression in the femoral metaphysis. H–I Representative images of TRAP staining for assessment of the number of TRAP-positive cells in the femoral metaphysis. Scale bar = 200 μm. J–K Flow cytometry analyses of the number and proportion of monocytes in the bone marrow cavity. Data represent mean ± S.D. of at least three independent experiments (n = 6 per group). L DCFH fluorescence analyses of intracellular ROS level in bone marrow monocytes (BMMs) from young and old mice. Data represent mean ± S.D. of at least three independent experiments (n = 3 per group). (M) Representative TRAP staining images of osteoclast differentiation of BMMs from young and old mice. Scale bar = 100 μm. N Quantification of TRAP + multinucleated cells (> 3 nuclei/cell) per field. O Representative rhodamine's Phalloidin staining for F-actin ring formation in BMMs from young and old mice. Scale bar = 50 μm. *p < 0.05, **p < 0.01, ***p < 0.001, ****p < 0.0001