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Background Peripheral polyneuropathies are clinically difficult situations and can be caused by exposure to occupational hazardous materials, such as N-hexane, which is still being used in developing countries. Autologous transplantation with bone marrow-mesenchymal stem cells (BMSCs) could be a promising therapeutical approach but its effect on toxic chemical-induced neuropathy remains undetermined. The present study sought to understand whether BMSCs could improve axon regeneration in Hexane-caused polyneuropathies and attempted to understand the associated molecular mechanisms. Methods A rat model of 2,5-hexanedine (HD)-induced polyneuropathy was established by intraperitoneally injection of 400 mg/kg/day HD, 5 times/week for 5 weeks. After the development of characteristic phenotypes, rats were given a single bolus tail-vein injection of BMSCs (5×107 cells/kg) and followed-up for 5 weeks. Sciatic nerves of HD/HD + BMSCs treated rats, as a representative tissue for peripheral nerve, were analyzed using electron microscopy, immunohistochemistry, western blotting and RNA sequencing. To further dissect the underlying mechanism, cultured DRG neurons +/- Schwann cells were challenged with HD/BMSC-derived conditional medium (BMSC-CM), in the presence or absence of NGF/Akt/mTOR inhibitors, recombinant NGF, miRNA mimics or miRNA inhibitors and further tested for changes in cellular and molecular levels. Results BMSCs engrafting significantly improved motor function recovery. Accelerated axon regeneration in sciatic nerves was evidenced by transmission electron microscopy, GAP43 western blotting and MBP/SMI312 immunostaining. Increased NGF expression and signaling activation was evidenced in response to BMSC/BMSC-CM treatment. In cultured cells, BMSC-CM’s effect was abolished by anti-NGF antibody or TrkA inhibitor K252a but reinforced by recombinant NGF. The activation of PI3K-Akt-mTOR-CREB signaling was observed and Akt and mTOR inhibitors were shown to attenuate BMSCS-promoted axon regeneration. While NGF was shown to be secreted by BMSCs in culture medium, miRNA array suggested certain miRNAs might also participate to regulate NGF expression. Three let-7 family miRNAs, including let-7a-5p, let-7d-5p and let-7e-5p, and 69 other miRNAs were found to be differentially expressed in HD and HD/BMSC groups. The regulatory effect of let-7e-5p on NGF expression was examined using miRNA mimics and inhibitors. Conclusions Together, our study demonstrated that BMSC transplantation significantly improve axon regeneration in hexane-induced polyneuropathy by activating NGF-PI3K-Akt-mTOR-CREB signaling via two independent mechanisms.

Background N-hexane, with its metabolite 2,5-hexanedine (HD), is an industrial hazardous material. Chronic hexane exposure causes segmental demyelination in the peripheral nerves, and high-dose intoxication may also affect central nervous system. Demyelinating conditions are difficult to treat and stem cell therapy using bone marrow mesenchymal stem cells (BMSCs) is a promising novel strategy. Our previous study found that BMSCs promoted motor function recovery in rats modeling hexane neurotoxicity. This work aimed to explore the underlying mechanisms and focused on the changes in spinal cord. Methods Sprague Dawley rats were intoxicated with HD (400 mg/kg/day, i.p, for 5 weeks). A bolus of BMSCs (5 × 107 cells/kg) was injected via tail vein. Demyelination and remyelination of the spinal cord before and after BMSC treatment were examined microscopically. Cultured oligodendrocyte progenitor cells (OPCs) were incubated with HD ± BMSC-derived conditional medium (BMSC-CM). OPC differentiation was studied by immunostaining and morphometric analysis. The expressional changes of Hes1, a transcription factor negatively regulating OPC-differentiation, were studied. The upstream Notch1 and TNFα/RelB pathways were studied, and some key signaling molecules were measured. The correlation between neurotrophin NGF and TNFα was also investigated. Statistical significance was evaluated using one-way ANOVA and performed using SPSS 13.0. Results The demyelinating damage by HD and remyelination by BMSCs were evidenced by electron microscopy, LFB staining and NG2/MBP immunohistochemistry. In vitro cultured OPCs showed more differentiation after incubation with BMSC-CM. Hes1 expression was found to be significantly increased by HD and decreased by BMSC or BMSC-CM. The change of Hes1 was found, however, independent of Notch1 activation, but dependent on TNFα/RelB signaling. HD was found to increase TNFα, RelB and Hes1 expression, and BMSCs were found to have the opposite effect. Addition of recombinant TNFα to OPCs or RelB overexpression similarly caused upregulation of Hes1 expression. The secretion of NGF by BMSC and activation of NGF receptor was found important for suppression of TNFα production in OPCs. Conclusions Our findings demonstrated that BMSCs promote remyelination in the spinal cord of HD-exposed rats via TNFα/RelB-Hes1 pathway, providing novel insights for evaluating and further exploring the therapeutical effect of BMSCs on demyelinating neurodegenerative disease.

Oral squamous cell carcinoma (OSCC) is aggressive accompanied with poor prognosis. We previously isolated the most invasive cells resembling the invasive tumour front by microfluidic technology and explored their differentially expressed microRNAs (miRNAs) in our previous work. Here, we verified the miR‐29b‐3p as a guarder that suppressed migration and invasion of OSCC cells and was down‐regulated in the most invasive cells. Besides that, the invasion suppression role of miR‐29b‐3p was achieved through the IL32/AKT pathway. Thus, miR‐29b‐3p and IL32 might serve as therapeutic targets for blocking the progression and improving the outcome of OSCC.

2,5-hexanedione (HD) is the ultimate neurotoxic metabolite of hexane, causing the progression of nerve diseases in human. It was reported that HD induced apoptosis and oxidative stress. Taurine has been shown to be a potent antioxidant. In the present study, we investigated the protection of taurine against HD-induced apoptosis in PC12 cells and the underlying mechanism. Our results showed the decreased viability and increased apoptosis in HD-exposed PC12 cells. HD also induced the disturbance of Bax and Bcl-2 expression, the loss of MMP, the release of mitochondrial cytochrome c and caspase-3 activation in PC12 cells. Moreover, HD resulted in an increase in reactive oxygen species (ROS) level and a decline in the activities of superoxidedismutase and catalase in PC12 cells. However, taurine pretreatment ameliorated the increased apoptosis and the alterations in key regulators of mitochondria-dependent pathway in PC12 exposed to HD. The increased ROS level and the decreased activities of the antioxidant enzymes in HD group were attenuated by taurine. These results indicate that pretreatment of taurine may, at least partly, prevent HD-induced apoptosis via inhibiting mitochondria-dependent pathway. It is also suggested that the potential of taurine against HD-induced apoptosis may benefit from its anti-oxidative property.

Chronic exposure to n-hexane, a widely used organic solvent in industry, induces central-peripheral neuropathy, which is mediated by its active metabolite, 2,5-hexanedione (HD). We recently reported that transplantation of bone marrow-mesenchymal stem cells (BMSC) significantly ameliorated HD-induced neuronal damage and motor deficits in rats. However, the mechanisms remain unclear. Here, we reported that inhibition of HD-induced autophagy contributed to BMSC-afforded protection. BMSC transplantation significantly reduced the levels of microtubule-associated protein 1 light chain 3-II (LC3-II) and the degradation of sequestosome-1 (p62) in the spinal cord and sciatic nerve of HD-intoxicated rats. Downregulation of autophagy by BMSC was also confirmed in VSC4.1 cells exposed to HD. Moreover, inhibition of autophagy by PIK III mitigated the neurotoxic effects of HD and, meanwhile, abolished BMSC-afforded neuroprotection. Furthermore, we found that BMSC failed to interfere with Beclin 1, but promoted activation of mammalian target of rapamycin (mTOR). Unc-like kinse 1 (ULK1) was further recognized as the downstream target of mTOR responsible for BMSC-mediated inhibition of autophagy. Altogether, BMSC transplantation potently ameliorated HD-induced autophagy through beclin 1-independent activation of mTOR pathway, providing a novel insight for the therapeutic effects of BMSC against n-hexane and other environmental toxicants-induced neurotoxicity.

Studies suggested that the conditioned medium of mesenchymal stem cells (MSC-CM) inhibited the increased apoptosis in various cells. However, there are no reports underlying the protection of MSC-CM against 2,5-hexanedione (HD)-induced apoptosis in neural cells. In the present study, the viability was observed in PC12 cells that received HD alone or with MSC-CM by 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide assay. Apoptosis was estimated by Hoechst 33342 staining and flow cytometry. Mitochondrial transmembrane potential was examined by rhodamine 123. Moreover, we investigated the expression of Bax and Bcl-2, cytochrome c translocation, and caspase 3 activity by real-time polymerase chain reaction, Western blot, and immunochemistry. Nerve growth factor (NGF) was examined in MSCs and MSC-CM. Our results showed that MSC-CM promoted cell survival and reduced apoptosis in HD-exposed PC12 cells. Moreover, MSC-CM significantly reversed disturbance of Bax and Bcl-2, ameliorated disruption of mitochondrial transmembrane potential, and reduced release of cytochrome c and activity of caspase 3 in HD-exposed PC12 cells. In the meantime, NGF was detected in MSCs and MSC-CM. These findings demonstrate that MSC-CM protects against HD-induced apoptosis in PC12 cells via inhibiting mitochondrial pathway. Our results indicate that NGF in MSC-CM may be involved in the protection of MSC-CM against HD-induced apoptosis. Our study clarifies the protection of MSC-CM on HD neurotoxicity and its underlying mechanism.

Purpose This study investigated the color stability of composite resins for a facing crown cured with a high output photo-curing unit (Hyper LII, YAMAHACHI DENTAL MFG., CO.). Methods Four brands of composite resins for a facing crown after polymerization with Hyper LII were immersed in coffee. Color measurement was carried out before and 1, 2, and 4 weeks after immersion, and the results were compared. Results 1. After immersion in coffee, the L* values decreased gradually, the a* values showed little change, and the b* values increased gradually in all resins. 2. The difference in the color difference values (deltaE*ab) between each material became greater with time; the deltaE*ab after 4 weeks immersion were from 3.0 [Dentacolor (DEC), dentin specimen] to 6.3 [Solidex (SOL), enamel specimen] on polished surfaces, and from 0.9 [Gradia (GRA), dentin specimen] to 5.2 (SOL, enamel specimen) on non-polished surfaces. However, the deltaE*ab were 1/3 to 1/5 better than those of our previous studies. 3. The enamel specimens showed larger color differences than the dentin specimens. 4. When polished surfaces were compared with non-polished surfaces, Cesead II (CEII), DEC and SOL showed almost equal color differences while GRA showed larger color differences. Conclusions This study suggests that composite resins for a facing crown cured with a high output photo-curing unit result in a decrease of color changes with time and an improvement of color stability.