The effect of E2 or NAC on osteocyte senescence in ovariectomized mice. A. Representative micrographs of paraffin sections of tibias from 16-week-old mice of each group stained immunohistochemically for p16INK4a. B. The percentages of p16INK4a-positive cells were determined by image analysis. C. Representative micrographs of paraffin sections of tibias from 16-week-old mice of each group stained immunohistochemically for β-gal. D. The percentages of β-gal-positive cells were determined by image analysis. E. Representative western blots of bone tissue extracts showing expression of p16INK4a; β-tubulin was used as loading control for the western blots in the sham, OVX, OVX+E2 and OVX+NAC groups. F. p16INK4a protein levels relative to β-tubulin protein levels were assessed by densitometric analysis and expressed relative to levels in sham-operated mice. Data are presented as the mean ± SEM of determinations, each data-point was the mean of five specimens. **P<0.01 versus sham mice. #P<0.05, ##P<0.01 versus OVX mice. A, C. Magnification, 400×.