Shengyang Jiang

Arsenic trioxide mediates HAPI microglia inflammatory response and subsequent neuron apoptosis through p38/JNK MAPK/STAT3 pathway.

Arsenic is a widely distributed toxic metalloid all over the world. Inorganic arsenic species are supposed to affect astrocytic functions and to cause neuron apoptosis in CNS. Microglias are the key cell type involved in innate immune responses in CNS, and microglia activation has been linked to inflammation and neurotoxicity. In this study, using ELISA, we showed that Arsenic trioxide up-regulated the expression and secretion of IL-1β in a dose-dependent manner and a time-dependent manner in cultured HAPI microglia cells. The secretion of IL-1β caused the apoptosis of SH-SY5Y. These pro-inflammatory responses were inhibited by the STAT3 blocker, AG490 and P38/JNK MAPK blockers SB202190, SP600125. Further, Arsenic trioxide exposure could induce phosphorylation and activation of STAT3, and the translocation of STAT3 from the cytosol to the nucleus in this HAPI microglia cell line. Thus, the STAT3 signaling pathway can be activated after Arsenic trioxide treatment. However, P38/JNK MAPK blockers SB202190, SP600125 also obviously attenuated STAT3 activation and transnuclear transport induced by Arsenic trioxide. In concert with these results, we highlighted that the secretion of IL-1β and STAT3 activation induced by Arsenic trioxide can be mediated by elevation of P38/JNK MAPK in HAPI microglia cells and then induced the toxicity of neurons.

Involvement of CLEC16A in activation of astrocytes after LPS treated.

CLEC16A, C-type lectin domain family 16, member A was recently found to be associated with inflation process in the autoimmune diseases. In this study, we elucidated the dynamic expression changes and localization of CLEC16A in lipopolysaccharide (LPS)-induced neuroinflammatory processes in adult rats. CLEC16A expression was strongly induced in active astrocytes in inflamed cerebral cortex. In vitro studies indicated that the up-regulation of CLEC16A may be involved in the subsequent astrocyte activation following LPS challenge. And Knock-down of CLEC16A in cultured primary astrocytes by siRNA showed that CLEC16A was required for the activation of astrocytes induced by LPS. Collectively, these results suggested CLEC16A may be important in host defense in astrocyte-mediated immune response. Understanding the cell signal pathway may provide a novel strategy against inflammatory and immune reaction in neuroinflammtion in CNS.

2, 3, 7, 8-Tetrachlorodibenzo-p-dioxin induces premature senescence of astrocytes via WNT/β-catenin signaling and ROS production

2, 3, 7, 8‐tetrachlorodibenzo‐p‐dioxin (TCDD) is a ubiquitous environmental contaminant that could exert significant neurotoxicity in the human nervous system. Nevertheless, the molecular mechanism underlying TCDD‐mediated neurotoxicity has not been clarified clearly. Herein, we investigated the potential role of TCDD in facilitating premature senescence in astrocytes and the underlying molecular mechanisms. Using the senescence‐associated β‐galactosidase (SA‐β‐Gal) assay, we demonstrated that TCDD exposure triggered significant premature senescence of astrocyte cells, which was accompanied by a marked activation of the Wingless and int (WNT)/β‐catenin signaling pathway. In addition, TCDD altered the expression of senescence marker proteins, such as p16, p21 and GFAP, which together have been reported to be upregulated in aging astrocytes, in both dose‐ and time‐dependent manners. Further, TCDD led to cell‐cycle arrest, F‐actin reorganization and the accumulation of cellular reactive oxygen species (ROS). Moreover, the ROS scavenger N‐acetylcysteine (NAC) markedly attenuated TCDD‐induced ROS production, cellular oxidative damage and astrocyte senescence. Notably, the application of XAV939, an inhibitor of WNT/β‐catenin signaling pathway, ameliorated the effect of TCDD on cellular β‐catenin level, ROS production, cellular oxidative damage and premature senescence in astrocytes. In summary, our findings indicated that TCDD might induce astrocyte senescence via WNT/β‐catenin and ROS‐dependent mechanisms. Copyright

Arsenic trioxide mediates HAPI microglia inflammatory response and the secretion of inflammatory cytokine IL-6 via Akt/NF-κB signaling pathway

Arsenic is a widely distributed toxic metalloid in around the world. Inorganic arsenic species are deemed to affect astrocytes functions and to cause neuron apoptosis. Microglia are the key cell type involved in innate immune responses in CNS, and microglia activation has been linked to inflammation and neurotoxicity. In this study, using ELISA and reverse transcriptase PCR (RT-PCR), we showed that Arsenic trioxide up-regulated the expression and secretion of IL-6 in a dose-dependent manner and a time-dependent manner in cultured HAPI microglia cells. These pro-inflammatory responses were inhibited by the Akt blocker, LY294002. Further, Arsenic trioxide exposure could induce phospho rylationand degradation of IкBα, and the translocation of NF-κB p65 from the cytosol to the nucleus in this HAPI microglia cell line. Thus, the NF-кB signaling pathway can be activated after Arsenic trioxide treatment. Besides, Akt blocker LY294002 also obviously attenuated NF-кB activation and transnuclear induced by Arsenic trioxide. In concert with these results, we highlighted that the secretion of pro-inflammatory cytokine and NF-кB activation induced by Arsenic trioxide can be mediated by elevation of p-Akt in HAPI microglia cells.

Autophagy potentially protects against 2,3,7,8‐tetrachlorodibenzo‐p‐Dioxin induced apoptosis in SH‐SY5Y cells

The environmental toxicant TCDD may elicit cytotoxic effects by inducing reactive oxygen species (ROS) generation. Autophagy is one of the first lines of defense against oxidative stress damage. Herein, we investigated whether autophagy played a regulatory role in TCDD‐induced neurotoxicity. Here, we showed that TCDD exposure caused marked autophagy in SH‐SY5Y cells, whose dose range was close to that inducing apoptosis. Electron microscopic and Western blot analyses revealed that TCDD induced autophagy at a starting dose of approximate 100 nM. Interestingly, 100–200 nM TCDD exposure resulted in obviously decreased cell viability and evident apoptotic phenotype. Furthermore, the levels of pro‐apoptotic molecules, Bax and cleaved‐PARP, increased significantly, whereas Bcl2 declined after exposed to 100 nM TCDD. In addition, the apoptosis was verified using flow cytometrical analysis. These data strongly suggested that TCDD induced both autophagy and apoptosis at a similar dose range in SH‐SY5Y cells. Interestingly, pretreatment with ROS scavenger, N‐acetyl‐cysteine (NAC), could effectively block both TCDD‐induced apoptosis and autophagy. More surprisingly, inhibition of autophagy with 3‐methyladenine (3MA), remarkably augmented TCDD‐induced apoptosis. The findings implicated that the onset of autophagy might serve as a protective mechanism to ameliorate ROS‐triggered cytotoxic effects in human SH‐SY5Y neuronal cells under TCDD exposure.

ROS-mediated apoptosis of HAPI microglia through p53 signaling following PFOS exposure

Perfluorooctane sulfonate (PFOS), the most extensively studied member of perfluoroalkyl and polyfluoroalkyl substances (PFASs), has been thought to be toxic to the central nervous system (CNS) of mammals. However, the neurotoxic effects of PFOS remain largely unknown. In this study, the effect of PFOS on microglial apoptosis was examined. The results showed that PFOS could significantly reduce the cell viability and mediate cell apoptosis in HAPI microglia, which was closely accompanied with ROS production and p53 overexpression. Moreover, p53 interference significantly ameliorated PFOS-triggered cytotoxic effects in HAPI microglia, including the downregulation of cleaved PARP and cleaved caspase 3. Interestingly, NAC, a ROS inhibitor, inhibited p53 expression, and decreased the apoptosis of HAPI microglia. Taken together, these findings suggest that upregulated production of ROS plays a vital role in PFOS-mediated apoptosis in HAPI microglia via the modulation of p53 signaling.

Perfluorooctane sulfonate (PFOS) impairs the proliferation of C17.2 neural stem cells via the downregulation of GSK‐3β/β‐catenin signaling

The neurotoxic effects of perfluorooctane sulfonate (PFOS) have attracted significant research attention in recent years. In the present study, we investigated the impact of PFOS exposure on the physiology of neural stem cells (NSCs) in vitro. We showed that PFOS exposure markedly attenuated the proliferation of C17.2 neural stem cells in both dose‐ and time‐dependent manners. Additionally, we found that PFOS decreased Ser9 phosphorylation of glycogen synthase kinase‐3β (pSer9‐GSK‐3β), leading to the activation of GSK‐3β and resultant downregulation of cellular β‐catenin. Furthermore, blockage of GSK‐3β with lithium chloride significantly attenuated both the PFOS‐induced downregulation of GSK‐3β/β‐catenin and the proliferative impairment of C17.2 cells. Notably, the expression of various downstream targets was altered accordingly, such as c‐myc, cyclin D1 and survivin. In conclusion, the present study demonstrated that PFOS decreased the proliferation of C17.2 cells via the negative modulation of the GSK‐3β/β‐catenin pathway. We present the potential mechanisms underlying the PFOS‐induced toxic effects on NSCs to provide novel insights into the neurotoxic mechanism of PFOS. Copyright

GART expression in rat spinal cord after injury and its role in inflammation.

The glycinamide ribonucleotide transformylase (GART) gene, a trifunctional polypeptide, has phosphoribosylglycinamide formyltransferase, phosphoribosylglycinamide synthetase, and phosphoribosylaminoimidazole synthetase activity, and is required for de novo purine biosynthesis. GART is highly conserved in vertebrates. Alternative splicing of GART results in two transcript variants encoding different isoforms. However, the expression and function of GART in the central nervous system lesion are still unclear. In this study, we used a traumatic spinal cord injury (SCI) model in adult Sprague-Dawley rats and investigated the dynamic changes of GART protein expression in the spinal cord. Western blot analysis revealed that GART was present in sham-operated spinal cord. It gradually increased, reached a peak at day 3 after SCI, and then declined during the following days. Double immunofluorescence staining revealed a widespread of GART, and the majority of GARTs are detected in astrocytes. After injury, GART expression was increased predominantly in astrocytes, positively correlated with the highly expressed proliferating cell nuclear antigen (PCNA). Knockdown of GART expression in cultured primary astrocytes by siRNA revealed that expression of GART in astrocytes plays a role in the LPS-induced release of pro-inflammatory factors, such as TNF-α and IL-6. These results showed that GART may participate in the pathophysiology of SCI, and more research is needed to have a good understanding of its function and mechanism.

Zinc deficiency impairs the renewal of hippocampal neural stem cells in adult rats: involvement of FoxO3a activation and downstream p27kip1 expression

Zinc plays an important role in the development and maintenance of central neural system. Zinc deficiency has been known to alter normal brain function, whose molecular mechanism remains largely elusive. In the present study, we established a zinc deficiency‐exposed rat model, and, using western blot and immunohistochemical analyses, found that the expression of FoxO3a and p27kip1 was remarkably up‐regulated in the rat brain hippocampus. Immunofluorescence assay showed that FOXO3a and p27kip1 were significantly co‐localized with nestin, the marker of neural stem cells (NSCs). Furthermore, we identified that the proportion of proliferating NSCs was markedly decreased in zinc‐deficient rat hippocampaus. Using C17.2 neural stem cells, it was revealed that exposure to zinc chelator N,N,N’,N’‐tetrakis‐(2‐pyridylmethy) ethylenediamine induced the expression of FoxO3a and p27kip1, which coincided with reduced NSC proliferation. Furthermore, depletion of FoxO3a inhibited p27kip1 expression and restored the growth of NSCs. On the basis of these data, we concluded that FoxO3a/p27kip1 signaling might play a significant role in zinc deficiency‐induced growth impairment of NSCs and consequent neurological disorders.

Downregulation of Mfn2 participates in manganese-induced neuronal apoptosis in rat striatum and PC12 cells

&NA; Manganese (Mn) is a widely distributed trace element that is essential for normal brain function and development. However, chronic exposure to excessive Mn has been known to lead to neuronal loss and manganism, a disease with debilitating motor and cognitive deficits, whose clinical syndrome resembling idiopathic Parkinsons disease (IPD). However, the precise molecular mechanism underlying Mn neurotoxicity remains largely unclear. Accumulating evidence indicates that abnormal mitochondrial functionality is an early and causal event in Mn‐induced neurodegeneration and apoptosis. Here, we investigated whether Mitofusin 2 (Mfn2), a highly conserved dynamin‐related protein (DRP), played a role in the regulation of Mn‐induced neuronal apoptosis. We revealed that Mfn2 was significantly dysregulated in rat striatum and PC12 neuronal‐like cells following Mn exposure. Western blot analysis revealed that the expression of Mfn2 was remarkably decreased following different concentrations of Mn exposure. Immunohistochemistry analysis confirmed a remarkable downregulation of Mfn2 in rat striatum after Mn exposure. Immunofluorescent staining showed that Mfn2 was expressed predominantly in neurons, and neuronal loss of Mfn2 was associated with the expression of active caspase‐3 following Mn exposure. Importantly, overexpression of Mfn2 apparently attenuated Mn‐induced neuronal apoptosis. Notably, treatment with caspase‐3 inhibitor Ac‐DEVD‐CH could not rescue Mn‐induced downregulation of Mfn2, suggesting that Mn‐induced mfn2 occurs prior to neuronal apoptosis. Taken together, these results indicated that down‐regulated expression of Mfn2 might contribute to the pathological processes underlying Mn neurotoxicity.