Glucosamine suppresses oxidative stress and induces protective autophagy in osteoblasts by blocking the ROS/Akt/mTOR signaling pathway.

Oxidative stress is the crucial pathogenic factor in osteoporosis. Cell autophagy, a major form of self-digestion, plays critical functions in different forms of stress by devouring harmful cytosolic proteins or organelles for the renewal of organelles and to maintain cellular homeostasis. Glucosamine (GlcN) has been widely utilized in treatments for patients with osteoarthritis-related joint pain. It has potential antioxidant effects and its pharmacological effect in osteoblasts remains unclear. The present study aimed to investigate whether autophagy participates in the protective effects of GlcN in osteoblasts under oxidative stress and the possible mechanism. First of all, MC3T3-E1 cells were treated with hydrogen peroxide (H2 O2 ) to induce oxidative stress, as assessed by viability assays, apoptosis, the intracellular reactive oxygen species production. GlcN was capable of inducing autophagy and protected osteoblasts from those cytotoxic effects. Moreover, it significantly attenuated H2 O2 -induced oxidative stress as measured by malondialdehyde, glutathione, nitrite, and superoxide dismutase levels. Importantly, the autophagy level increased in osteoblasts treated with GlcN as represented by an increase in both Beclin1 expression and the LC3 II/I ratio. Immunofluorescence analysis of autophagosomes also confirmed the above results. In addition, GlcN decreased the mammalian target of rapamycin (mTOR) and protein kinase B (Akt). However, the Akt activator (SC79) suppressed the autophagy level induced by GlcN in osteoblasts. Consequently, the antioxidant effects of GlcN were mediated, at least in part, by enhancing autophagy through the Akt/mTOR pathway. These results suggested that GlcN might be a promising candidate for osteoporosis treatment.

Knockdown of microRNA-203 reduces cisplatin chemo-sensitivity to osteosarcoma cell lines MG63 and U2OS in vitro by targeting RUNX2.

Clinical studies have reported that miRNAs abnormal expression are associated with the generation of cisplatin-resistant to osteosarcoma. Our previous research found that miR-203 is downregulated in osteosarcoma cells and overexpressed miR-203 exerts antitumor properties on osteosarcoma cells. However, the role and mechanism of miR-203 in regulating the sensitivity of cisplatin in osteosarcoma cells remains unclear. This study aimed to investigate the effects of miR-203 in cisplatin therapy for osteosarcoma cells in vitro and determined the underlying mechanism. In this study, we found that miR-203 was significantly upregulated in osteosarcoma cells after exposure to cisplatin. miR-203 knockdown reduced the sensitivity of osteosarcoma cells to cisplatin by suppressing cell apoptosis, cell cycle arrest, and inducing invasion. Meanwhile, we found that miR-203 knockdown reduces the therapeutic sensitivity of osteosarcoma cells by upregulating RUNX2. Moreover, we found that RUNX2 silencing sensitizes osteosarcoma cells to chemotherapy treatment of cisplatin. In summary, our findings demonstrated that miR-203 knockdown reduces cisplatin chemo-sensitivity to osteosarcoma cells in vitro by targeting RUNX2, and speculated that miR-203 may be a target for drug resistance of osteosarcoma to cisplatin.

Salidroside suppresses the growth and invasion of human osteosarcoma cell lines MG63 and U2OS in vitro by inhibiting the JAK2/STAT3 signaling pathway.

Previous research has reported that salidroside exerts antitumor properties on numerous types of tumor cells; however, its effect on osteosarcoma cells remains unknown. The present study aimed to investigate the effects of salidroside on the viability, apoptosis and invasion of osteosarcoma cells in vitro, and determine the underlying mechanism of action. The results of an MTT revealed that salidroside suppressed the viability of osteosarcoma cells (MG63 and U2OS cells) in a time­ and concentration­dependent manner. The results of cell morphological analysis (profile observations and Hoechst 33258 staining) and the detection of apoptosis by flow cytometry further indicated that the decrease in osteosarcoma cell viability induced by salidroside was associated with cell apoptosis. Western blot analysis not only confirmed these results but also suggested that salidroside induced the apoptosis of osteosarcoma cells by activating the caspase­9­dependent apoptotic pathway. In addition, we reported that salidroside induced G0/G1 phase arrest and suppressed the invasion of osteosarcoma cells, as measured by flow cytometric cell cycle analysis and a Transwell invasion assay, respectively. Western blot analysis confirmed the aforementioned results. Furthermore, our findings demonstrated that salidroside induced the apoptosis, G0/G1 phase arrest and suppressed the invasion of osteosarcoma cells by inhibiting the janus kinase 2 (JAK2)/signal transducer and activator of transcription 3 (STAT3) signaling pathway, as determined by western blot analysis. In summary, the findings of the present study suggested that salidroside may inhibit the progression of osteosarcoma by suppressing the growth and invasion of osteosarcoma cells. Furthermore, the investigations into the underlying mechanism demonstrated that salidroside exerted notable antitumor activity in osteosarcoma cells by inhibiting the JAK2/STAT3 signaling pathway.

Glucosamine promotes osteoblast proliferation by modulating autophagy via the mammalian target of rapamycin pathway.

Glucosamine is effective in the treatment of osteoarthritis; however, its effect on osteoporosis remains unclear. Decreased activity of osteoblasts is the main cause of osteoporosis. Here, we examined the effects of glucosamine on osteoblasts. The potential underlying mechanisms were explored. The results showed that glucosamine had a biphasic effect on the viability of hFOB1.19 osteoblasts. At low concentrations (<0.6 mM), glucosamine induced hFOB1.19 cell proliferation, whereas at high concentrations (>0.8 mM) it induced apoptosis. The autophagy inhibitor 3-methyladenine (3-MA) was used to verify that glucosamine modulated hFOB1.19 cell viability via autophagy. The induction of apoptosis by high concentrations of glucosamine was significantly exacerbated by 3-MA, whereas the promotion of cell proliferation by low concentrations of glucosamine was significantly suppressed by 3-MA. Autophagy was examined by western blot detection of autophagy-related proteins including LC3, Beclin-1, and SQSTM1/p62 and by immunofluorescence analysis of autophagosomes. Glucosamine activated autophagy in a time- and concentration-dependent manner. Investigation of the underlying mechanism showed that glucosamine inhibited the phosphorylation of m-TOR in a concentration-dependent manner within 48 h, and rapamycin significantly inhibited the phosphorylation of m-TOR. These results demonstrated that glucosamine promoted hFOB1.19 cell proliferation and increased autophagy by inhibiting the m-TOR pathway, suggesting its potential as a therapeutic agent for osteoporosis.

MicroRNA-203 inhibits proliferation and invasion, and promotes apoptosis of osteosarcoma cells by targeting Runt-related transcription factor 2.

Accumulating evidence indicates that microRNA-203 (miR-203) is abnormally expressed in many human tumor tissues and significantly associated with the occurrence, development and clinical outcomes of human tumors. The aim of this study was to determine the target genes and functional significance of miR-203 in osteosarcoma cells. We found reduced expression of miR-203 in osteosarcoma tissues and cells (MG63 and U2-OS) compared with the adjacent normal tissues and normal osteoblastic cells (hFOB1.19), respectively. In vitro studies further demonstrated that exogenous miR-203 overexpression inhibited osteosarcoma cell proliferation and invasion, and promoted apoptosis. At the molecular level, our results confirmed that apoptosis, cell cycle and invasion-related proteins were regulated by miR-203. Our findings also revealed that Runt-related transcription factor 2 (RUNX2) was directly negatively regulated by miR-203. These results suggested that miR-203 may function as a tumor suppressor and may therefore have therapeutic potential in the treatment of human osteosarcoma.