Oxidative stress (OS)‐induced mitochondrial damage and the subsequent osteoblast dysfunction contributes to the initiation and progression of osteoporosis. Notoginsenoside R1 (NGR1), isolated from Panax notoginseng, has potent antioxidant effects and has been widely used in traditional Chinese medicine. This study aimed to investigate the protective property and mechanism of NGR1 on oxidative‐damaged osteoblast. Osteoblastic MC3T3‐E1 cells were pretreated with NGR1 24 h before hydrogen peroxide administration simulating OS attack. Cell viability, apoptosis rate, osteogenic activity and markers of mitochondrial function were examined. The role of C‐Jun N‐terminal kinase (JNK) signalling pathway on oxidative injured osteoblast and mitochondrial function was also detected. Our data indicate that NGR1 (25 μM) could reduce apoptosis as well as restore osteoblast viability and osteogenic differentiation. NGR1 also reduced OS‐induced mitochondrial ROS and restored mitochondrial membrane potential, adenosine triphosphate production and mitochondrial DNA copy number. NGR1 could block JNK pathway and antagonize the destructive effects of OS. JNK inhibitor (SP600125) mimicked the protective effects of NGR1while JNK agonist (Anisomycin) abolished it. These data indicated that NGR1 could significantly attenuate OS‐induced mitochondrial damage and restore osteogenic differentiation of osteoblast via suppressing JNK signalling pathway activation, thus becoming a promising agent in treating osteoporosis.
Pathological stimuli, such as bacterial activity, dental bleaching, and nonpolymerized resin monomers, can cause death of dental pulp cells (DPCs) through oxidative stress- (OS-) induced mitochondrial dysfunction. However, the crucial molecular mechanisms that mediate such a phenomenon remain largely unknown. OS is characterized by the overproduction of reactive oxygen species (ROS), e.g., H2O2, O2−, and ⋅OH. Mitochondria are a major source of ROS and the principal attack target of ROS. Cyclophilin D (CypD), as the only crucial protein for mitochondrial permeability transition pore (mPTP) induction, facilitates the opening of mPTP and causes mitochondrial dysfunction, leading to cell death. In the present study, we hypothesized that CypD-mediated mitochondrial molecular pathways were closely involved in the process of OS-induced death of human DPCs (HDPCs). We tested the phenotypic and molecular changes of HDPCs in a well-established OS model—H2O2 treatment. We showed that H2O2 dramatically reduced the viability and increased the death of HDPCs in a time- and dose-dependent manner by performing MTT, flow cytometry, and TUNEL assays and quantifying the expression changes of Bax and Bcl-2 proteins. H2O2 also induced mitochondrial dysfunction, as reflected by the increased mitochondrial ROS, reduced ATP production, and activation of mPTP (decreased mitochondrial membrane potential and enhanced intracellular Ca2+ level). An antioxidant (N-acetyl-L-cysteine) effectively preserved mitochondrial function and significantly attenuated H2O2-induced cytotoxicity and death. Moreover, H2O2 treatment markedly upregulated the CypD protein level in HDPCs. Notably, genetic or pharmacological blockade of CypD significantly attenuated H2O2-induced mitochondrial dysfunction and cell death. These findings provided novel insights into the role of a CypD-dependent mitochondrial pathway in the H2O2-induced death in HDPCs, indicating that CypD may be a potential therapeutic target to prevent OS-mediated injury in dental pulp.
Background: Resin monomer induced dental pulp injury presents a mitochondrial dysfunction related pathology. Melatonin has been regarded as a strong mitochondrial protective bioactive compound from pineal gland. However, it remains unknown whether melatonin can prevent dental pulp from resin monomer induced injury. The aim of the study is to investigate the effects of melatonin on TEGDMA, a major component in dental resin, induced mouse pre-odontoblast cell lines (mDPC6T) mitochondrial apoptosis and to verify whether JNK/MAPK signaling pathway mediate the protective effect of melatonin. Methods: We adopted a well-established TEGDMA-induced mDPC6T apoptosis model to investigate the preventive effect of melatonin by detecting cell viability, apoptosis rate, expression of apoptosis related protein, mitochondrial ROS (mtROS) production, mitochondrial membrane potential (MMP) and adenosine triphosphate (ATP) level. Inhibitors of MAPKs signaling were used to explore which pathway was participated in TEGDMA induced apoptosis. Finally, we verified the role of JNK/MAPK pathway during the protective effects of melatonin above by the agonist and antagonists of JNK.Results: Melatonin attenuated TEGDMA induced mDPC6T apoptosis via reducing mtROS production, rescuing MMP and ATP level. Meanwhile, the mitochondrial dysfunction and apoptosis was alleviated by the JNK/MAPK inhibitor SP600125 but not the other MAPKs signaling inhibitors. Furthermore, melatonin down-regulated the expression of phosphorylated-JNK, and eliminated the active effects of Anisomycin on JNK/MAPK pathway, which mimicked the effects of the SP600125.Conclusion: Our findings demonstrated that melatonin protected mDPC6T against TEGDMA induced apoptosis via JNK/MAPK signaling and maintenance of mitochondrial function, which presented a novel therapeutic strategy for prevention against resin monomer-induced dental pulp injury.
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