Summary: Aging drives the accumulation of senescent cells (SnCs) including stem/progenitor cells in bone marrow, which contributes to aging‐related bone degenerative pathologies. Local elimination of SnCs has been shown as potential treatment for degenerative diseases. As LepR⁺ mesenchymal stem/progenitor cells (MSPCs) in bone marrow are the major population for forming bone/cartilage and maintaining HSCs niche, whether local elimination of senescent LepR⁺ MSPCs delays aging‐related pathologies and improves local microenvironment need to be well defined. In this study, we performed local delivery of tetramethylpyrazine (TMP) in bone marrow of aging mice, which previously showed to be used for the prevention and treatment of glucocorticoid‐induced osteoporosis (GIOP). We found the increased accumulation of senescent LepR⁺ MSPCs in bone marrow of aging mice, and TMP significantly inhibited the cell senescent phenotype via modulating Ezh2‐H3k27me3. Most importantly, local delivery of TMP improved bone marrow microenvironment and maintained bone homeostasis in aging mice by increasing metabolic and anti‐inflammatory responses, inducing H‐type vessel formation, and maintaining HSCs niche. These findings provide evidence on the mechanisms, characteristics and functions of local elimination of SnCs in bone marrow, as well as the use of TMP as a potential treatment to ameliorate human age‐related skeletal diseases and to promote healthy lifespan.

A fracture is the most dangerous complication of osteoporosis in patients because the associated disability and mortality rates are high. Osteoporosis impairs fracture healing and prognosis, but how intramembranous ossification (IO) or endochondral ossification (EO) during fracture healing are affected and whether these two kinds of ossification are different between glucocorticoid-induced osteoporosis (GIOP) and estrogen deficiency-induced osteoporosis (EDOP) are poorly understood. In this study, we established two bone repair models that exhibited repair via IO or EO and compared the pathological progress of each under GIOP and EDOP. In the cortical drill-hole model, which is repaired through IO, osteogenic differentiation was more seriously impaired in EDOP at the early stage than in GIOP. In the periosteum scratch model, in which EO is replicated, chondrocyte hypertrophy progression was delayed in both GIOP and EDOP. The in vitro results were consistent with the in vivo results. Our study is the first to establish bone repair models in which IO and EO occur separately, and the results strongly describe the differences in bone repair between GIOP and EDOP.

Free fatty acids display diverse effects as signalling molecules through GPCRs in addition to their involvement in cellular metabolism. GPR120, a G protein-coupled receptor for long-chain unsaturated fatty acids, has been reported to mediate adipogenesis in lipid metabolism. However, whether GPR120 also mediates osteogenesis and regulates BMMSCs remain unclear. In this study, we showed that GPR120 targeted the bi-potential differentiation of BMMSCs in a ligand dose-dependent manner. High concentrations of TUG-891 (a highly selective agonist of GPR120) promoted osteogenesis via the Ras-ERK1/2 cascade, while low concentrations elevated P38 and increased adipogenesis. The fine molecular regulation of GPR120 was implemented by up-regulating different integrin subunits (α1, α2 and β1; α5 and β3). The administration of high doses of TUG-891 rescued oestrogen-deficient bone loss in vivo, further supporting an essential role of GPR120 in bone metabolism. Our findings, for the first time, showed that GPR120-mediated cellular signalling determines the bi-potential differentiation of BMMSCs in a dose-dependent manner. Additionally, the induction of different integrin subunits was involved in the cytoplasmic regulation of a seesaw-like balance between ERK and p38 phosphorylation. These findings provide new hope for developing novel remedies to treat osteoporosis by adjusting the GPR120-mediated differentiation balance of BMMSCs.

Long-term use of glucocorticoids is a widespread clinical problem, which currently has no effective solution other than discontinuing the use. Eicosapentaenoic acid (EPA), an omega-3 long chain polyunsaturated fatty acid (n-3 PUFA), which is largely contained in fish or fish oil, has been reported to promote cell viability and improve bone metabolism. However, little is known about the effects of EPA on dexamethasome (Dex)-induced cell apoptosis. In this study, we showed that EPA-induced autophagy of murine bone marrow-derived mesenchymal stem cells (mBMMSCs). Meanwhile, EPA, but not arachidonic acid (AA), markedly inhibited Dex-induced apoptosis and promoted the viability of mBMMSCs. We also observed that EPA-induced autophagy was modulated by GPR120, but not GPR40. Further experiments showed that the mechanism of EPA-induced autophagy associated with GPR120 modulation involved an increase in the active form of AMP-activated protein kinase and a decrease in the activity of mammalian target of RAPA. The protective effect of EPA on Dex-induced apoptosis via GPR120-meditated induction of adaptive autophagy was supported by in vivo experiments. In summary, our findings may have important implications in developing future strategies to use EPA in the prevention and therapy of the side effects induced by long-term Dex-abuse.

Postmenopausal osteoporosis is one of the most prominent worldwide public health problems and the morbidity is increasing with the aging population. It has been demonstrated that early diagnosis and intervention delay the disease progression and improve the outcome. Therefore, searching for biomarkers that are able to identify postmenopausal women at high risk for developing osteoporosis is an effective way to improve the quality of life of patients, and alleviate social and economic burdens. In the present study, a protein array was used to identify potential biomarkers. The bone mineral densities of 10 rats were dynamically measured in an ovariectomized model by micro‑computed tomography assessment, and the early stage of osteoporosis was defined. Through the protein array‑based screening, the expression levels of six serum protein biomarkers in ovariectomized rats were observed to alter at the initiation stage of the postmenopausal osteoporosis. Fractalkine, tissue inhibitor of metalloproteinases‑1 and monocyte chemotactic protein‑1 were finally demonstrated to be increased in the serum of eight enrolled postmenopausal osteoporosis patients using ELISA assay and were correlated with the severity of progressive bone loss. These biomarkers may be explored as potential early biomarkers to readily evaluate and diagnose postmenopausal osteoporosis in the clinic.