EZH2 and osteoporosis: In the osteoblastic niche, SIRT1 promotes the secretion of crucial chemokines, such as C-C motif chemokine ligand 3 (CCL3), C-C motif chemokine ligand 5 (CCL5), and C-X-C motif chemokine ligand 10 (CXCL10), by upregulating dishevelled-associated activator of morphogenesis 2 (DAAM2) through the acetylation of enhancer of zeste homolog 2 (EZH2), activating and recruiting CD4<sup>+</sup> CTLs that eliminate senescent osteoblasts in a major histocompatibility complex class II (MHC-II)-dependent manner, slowing the bone ageing process and ameliorating osteoporosis.