Ferroptosis is recently identified, an iron- and reactive oxygen species- (ROS-) dependent form of regulated cell death. This study was designed to determine the existence of ferroptosis in the pathogenesis of type 2 diabetic osteoporosis and confirm that melatonin can inhibit the ferroptosis of osteoblasts through activating Nrf2/HO-1 signaling pathway to improve bone microstructure in vivo and in vitro. We treated MC3T3-E1 cells with different concentrations of melatonin (1, 10, or 100 μM) and exposed them to high glucose (25.5 mM) for 48 h in vitro. Our data showed that high glucose can induce osteoblast cytotoxicity and the accumulation of lipid peroxide, the mitochondria of osteoblast show the same morphology changes as the erastin treatment group, and the expression of ferroptosis-related proteins glutathione peroxidase 4 (GPX4) and cystine-glutamate antiporter (SLC7A11) is downregulated, but these effects were reversed by ferroptosis inhibitor ferrastatin-1 and iron chelator deferoxamine (DFO). Furthermore, western blot and real-time polymerase chain reaction were used to detect the expression levels of nuclear factor erythroid 2-related factor 2 (Nrf2) and heme oxygenase-1 (HO-1); osteogenic capacity was evaluated by alizarin red S staining and the expression of osteoprotegerin, osteocalcin, and alkaline phosphatase; the results showed that the expression levels of these proteins in osteoblasts with 1, 10, or 100 μM melatonins were significantly higher than the high glucose group, but after using Nrf2-SiRNA interference, the therapeutic effect of melatonin was significantly inhibited. We also performed in vivo experiments in a diabetic rat model treated with two concentrations of melatonin (10, 50 mg/kg). Dynamic bone histomorphometry and micro-CT were used to observe the rat bone microstructure, and the expression of GPX4 and Nrf2 was determined by immunohistochemistry. Here, we first report that high glucose induces ferroptosis via increased ROS/lipid peroxidation/glutathione depletion in type 2 diabetic osteoporosis. More importantly, melatonin significantly reduced the level of ferroptosis and improved the osteogenic capacity of MC3T3-E1 through activating the Nrf2/HO-1 pathway in vivo and in vitro.

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The highly selective magnesium transporter non-imprinted in Prader-Willi/Angelman syndrome region protein 2 (NIPA2) has recently been associated with the development and progression of type 2 diabetes osteoporosis, but the mechanisms involved are still poorly understood. Because mitophagy is involved in the pathology of type 2 diabetes osteoporosis, the present study aimed to explore the relationship among NIPA2, mitophagy and osteoblast osteogenic capacity. NIPA2 expression was reduced in C57BKS background db/db mice and in vitro models of type 2 diabetes osteoporosis, and the activation of mitophagy in primary culture osteoblast-derived from db/db mice and in high glucose-treated human fetal osteoblastic cells (hFOB1.19) was observed. Knockdown, overexpression of NIPA2 and pharmacological inhibition of peroxisome proliferator-activated receptor γ coactivator 1-α (PGC-1α) showed that NIPA2 increased osteoblast function, which was likely regulated by PTEN induced kinase 1 (PINK1)/E3 ubiquitin ligase PARK2 (Parkin)-mediated mitophagy via the PGC-1α/ forkhead box O3a(FoxO3a)/mitochondrial membrane potential (MMP) pathway. Furthermore, the negative effect of mitophagy on osteoblast function was confirmed by pharmacological regulation of mitophagy and knockdown of Parkin. Taken together, these results suggest that NIPA2 positively regulates the osteogenic capacity of osteoblasts via the mitophagy pathway in type 2 diabetes. Plasma measurements. Blood samples were collected from the animals' tail veins. The samples were used for measuring the fasting blood glucose (FBG) levels (Roche blood glucose instrument, Roche, Basel, Switzerland). Radioimmunoassay (3v-diagnostic Bioengineer, Shandong, China) was used for the fasting plasma insulin (FINS) analysis, while ELISA (Rat Estrogen/E ELISA Kit, 3v-diagnostic Bioengineer) was used for the plasma estrogen analysis. The insulin sensitivity index (ISI) was calculated as the -ln(FINS•FPG) 42 . Scientific RepoRtS |(2020) 10:3078 | https://doi.

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Objective To investigate the effect of melatonin on the apoptosis of hFOB1.19 cells induced by excess iron. Methods The hFOB1.19 cells were treated with ferric ammonium citrate (300 μmol/L) and melatonin (100 μmol/L) for 24 h. The apoptosis rate and the level of reactive oxygen species (ROS) were analyzed using flow cytometry. Expression of proteins associated with apoptosis, such as Bax and caspase-3, and those associated with the Nrf-2 signaling pathway such as Nrf2 and HO-1 were analyzed using western blotting. Results The level of ROS and the apoptosis rate increased after intervention with excess iron. The levels of Bax in the mitochondria and cleaved caspase-3 in the cytosol increased. However, after pretreatment with melatonin, the level of ROS, apoptosis rate, and expression of apoptosis-associated proteins decreased, and the expression of Nrf2 and HO-1 increased. Conclusion Melatonin inhibits the level of oxidation in osteoblasts via the Nrf2/HO-1 signal pathway, resulting in the reduction of apoptosis induced by excess iron.

In recent years, type 2 diabetic osteoporosis has become a research hotspot for the complications of diabetes, but the specific mechanism of its occurrence and development remain unknown. Ferroptosis caused by iron overload is considered to be one of the important cause of type 2 diabetic osteoporosis. Polycytosine RNA-binding protein 1 (PCBP1), an iron ion chaperone, was considered as a protector of ferroptosis. The present study aimed to investigate the existence of ferroptosis and specific role of PCBP1 in the development of type 2 diabetes. Firstly, a Cell Counting Kit-8 assay was used to detect the changes of osteoblast viability under the influence of high glucose (HG) and/or ferroptosis inhibitor given at different concentrations and at different times. In addition, the morphological changes of mitochondria in osteoblasts under high glucose were examined via transmission electron microscopy, and the expression levels of PCBP1, ferritin and the ferroptosis-related protein glutathione peroxidase 4 (GPX4) under the action of high glucose were detected via western blotting. Furthermore, a lentivirus was used to silence and overexpress PCBP1. Western blotting was used to detect the expression of levels of the osteoblast functional proteins osteoprotegerin (OPG) and osteocalcin (OCN), while flow cytometry was used to detect the changes of reactive oxygen species (ROS) levels in each group. Under the action of high glucose, the viability of osteoblasts was significantly decreased and the number of mitochondria undergoing atrophy was significantly increased, PCBP1 and ferritin expression levels were increased and GPX4 expression was decreased. Western blotting results demonstrated that infection of the lentivirus overexpressing PCBP1, increased the expression levels of ferritin, GPX4, OPG and OCN, compared with the high glucose group. The flow cytometry results identified a reduction in ROS, and an opposite result was obtained after silencing PCBP1. In conclusion, it was suggested that PCBP1 may protect osteoblasts and reduce the harm caused by ferroptosis by promoting ferritin expression under a high glucose environment. Moreover, it was indicated that PCBP1 may be a potential therapeutic target for treating type 2 diabetic osteoporosis.