MicroRNA-181a (miR-181a) is upregulated in osteosarcoma, and its overexpression promotes the proliferation and inhibits the apoptosis of osteosarcoma cells. However, the mechanism of miR‑181a as an oncogene remains to be fully elucidated in osteosarcoma. Cleavage factor (CF) Im25 links alternative polyadenylation to glioblastoma tumor suppression, however, its role in osteosarcoma has not been reported. In the present study, it was confirmed that the expression of miR‑181a was upregulated in osteosarcoma, and that silencing miR‑181a inhibited the proliferation and promoted the apoptosis of osteosarcoma cells. miRNAs are short non‑coding RNAs, which regulate target mRNAs by binding predominantly to the 3'untranslated region (3'UTR), inducing either translational repression or degradation of the target. In the present study, target genes of miR‑181a were screened using miRanda, which is a commonly used prediction algorithm. It was found that miR‑181a targeted the 3'UTR of CFIm25 mRNA. Subsequent experiments confirmed that miR‑181a downregulated the expression of CFIm25 in osteosarcoma cells. Finally, it was demonstrated that the CFIm25 protein was also downregulated in osteosarcoma tissues, and inhibited the proliferation and promoted the apoptosis of the cells. Elucidating the roles of miR‑181a and CFIm25 in osteosarcoma not only assists in further understanding the pathogenesis and progression of this disease, but also offers novel targets for effective therapies.

Background Aging‐associated osteoporosis is frequently seen in the elderly in clinic, but efficient managements are limited because of unclear nosogenesis. The current study aims to investigate the role of melatonin on senescent bone marrow stromal cells (BMSCs) and the underlying regulating mechanism. Methods Melatonin levels were tested by ELISA. Gene expression profiles were performed by RNA‐sequencing, enrichment of H3K36me2 on gene promoters was analyzed by Chromatin Immunoprecipitation Sequencing (ChIP‐seq), and chromatin accessibility was determined by Assay for Transposase‐Accessible Chromatin with high‐throughput sequencing (ATAC‐seq). Osteogenesis of BMSCs in vitro was measured by Alizarin Red and Alkaline Phosphatase staining, and in vivo effects of melatonin was assessed by histological staining and micro computed tomography (micro‐CT) scan. Correlation of NSD2 expression and severity of senile osteoporosis patients were analyzed by Pearson correlation. Results Melatonin levels were decreased during aging in human bone marrow, accompanied by downregulation of the histone methyltransferase nuclear receptor binding SET domain protein 2 (NSD2) expression in the senescent BMSCs. Melatonin stimulated the expression of NSD2 through MT1/2‐mediated signaling pathways, resulting in the rebalancing of H3K36me2 and H3K27me3 modifications to increase chromatin accessibility of the osteogenic genes, runt‐related transcription factor 2 (RUNX2) and bone gamma‐carboxyglutamate protein (BGLAP). Melatonin promoted osteogenesis of BMSCs in vitro, and alleviates osteoporosis progression in the aging mice. In clinic, severity of senile osteoporosis (SOP) was negatively correlated with melatonin level in bone marrow, as well as NSD2 expression in BMSCs. Similarly, melatonin remarkably enhanced osteogenic differentiation of BMSCs derived from SOP patients in vitro. Conclusions Collectively, our study dissects previously unreported mechanistic insights into the epigenetic regulating machinery of melatonin in meliorating osteogenic differentiation of senescent BMSC, and provides evidence for application of melatonin in preventing aging‐associated bone loss.

Large numbers of elderly people have aging-associated osteoporosis, but efficient approaches to ameliorate bone loss are limited due to our poor understanding of the underlying mechanisms. In this study, we found that melatonin levels in bone marrow decreased with age, and melatonin primarily enhanced the osteogenic potential of mesenchymal stem cells (MSCs) derived from elderly donors compared with fetal- or young adult-derived MSCs. Mechanistic studies indicated melatonin treatment alleviated the senescence-related hypermethylation of the MMSET promoter, leading to elevated expression of the histone methyltransferase NSD2, and promoted the histone H3 dimethylation modification at lysine 36 of the osteogenic genes RUNX2 and SP7/OSTERIX as a consequence. MMSET depletion partially abolished the effects of melatonin on osteogenesis in senescent MSCs in vitro. Moreover, melatonin treatment promoted bone formation and alleviated the progression of osteoporosis in a mouse model of aging. Clinically, severity of senile osteoporosis (SOP) in patients was associated with melatonin levels in bone marrow plasma and the MMSET expression in MSCs, and melatonin treatment enhanced osteoblastogenesis from MSCs derived from SOP patients. Our study discovered a previously unreported epigenetic regulatory role for melatonin in alleviating MSC senescence and suggests that melatonin may be a potent agent for preventing aging-associated osteoporosis.