Figure 5.

Changes in bone cells caused by aging. Cell membranes were essential components of living organisms. With aging, cell membrane components of bone cells changed, PC increased, PE decreased, and the lamin A/C component of the nuclear membrane decreased and mutated; in the cytoplasm, the increase of Sirt3 expression promoted adipogenesis and osteogenesis, and SA-b-Gal, a cellular senescence marker, was increased. The decrease of OPG was conducive to osteoclast formation. The decrease of Alkbh1 inhibited the osteogenic differentiation of BMSCs, but promoted their adipogenic differentiation. Moreover, nuclear morphology was shrunk, and telomere length was shortened. Also, mitochondrial morphological and functional defects were increased, including reduced biogenesis, mitochondrial dysfunction, and bioenergetic exhaustion, and the number of lysosomes and the activity of enzymes within lysosomes were increased, such as TRAP. Senescent osteoblast exosomes regulate endothelial cell function, promote cell senescence and apoptosis, and reduce cell proliferation.