Xuefeng Shen

Ergosta-4,6,8(14),22-tetraen-3-one induces G2/M cell cycle arrest and apoptosis in human hepatocellular carcinoma HepG2 cells.

BACKGROUND Mushrooms have been used in Asia as traditional foods and medicines for a long time. Ergosta-4,6,8(14),22-tetraen-3-one (ergone) is one of the well-known bioactive steroids, which exists widely in various medicinal fungi such as Polyporus umbellatus, Russula cyanoxantha, and Cordyceps sinensis. Ergone has been demonstrated to possess cytotoxic activity. However, the molecular mechanisms by which ergone exerts its cytotoxic activity are currently unknown. METHODS In the present study, ergone possessed a remarkable anti-proliferative activity toward human hepatocellular carcinoma HepG2 cells. We assayed the cell cycle by flow cytometry using PI staining; investigated the exposure of phosphatidylserine at the outer layer of the cytoplasmic membrane by the FITC-annexin V/PI staining; observed the nuclear fragmentation by Hoechst 33258 staining and studied the protein expression of Bax, Bcl-2, p-53, procaspase-3, -8, -9, PARP and cleaved PARP by Western blotting analysis. RESULTS Cells treated with ergone showed typical markers of apoptosis: G2/M cell cycle arrest, chromatin condensation, nuclear fragmentation, and phosphatidylserine exposure. Furthermore, PARP-cleavage; activation of caspase-3, -8, -9; up-regulation of Bax and down-regulation of Bcl-2 were observed in HepG2 cells treated with ergone, which show that both the intrinsic and extrinsic apoptotic pathways are involved in ergone-induced apoptosis in HepG2 cells. Ergosta-4,6,8(14),22-tetraen-3-one induces G2/M cell cycle arrest and apoptosis in HepG2 cells in a caspase-dependent manner. GENERAL SIGNIFICANCE In this study, we reported for the first time that ergone-induced apoptosis through activating the caspase. These results would be useful for the further utilization of many medicinal fungi in cancer treatment.

Involvement of microglia activation in the lead induced long-term potentiation impairment.

Exposure of Lead (Pb), a known neurotoxicant, can impair spatial learning and memory probably via impairing the hippocampal long-term potentiation (LTP) as well as hippocampal neuronal injury. Activation of hippocampal microglia also impairs spatial learning and memory. Thus, we raised the hypothesis that activation of microglia is involved in the Pb exposure induced hippocampal LTP impairment and neuronal injury. To test this hypothesis and clarify its underlying mechanisms, we investigated the Pb-exposure on the microglia activation, cytokine release, hippocampal LTP level as well as neuronal injury in in vivo or in vitro model. The changes of these parameters were also observed after pretreatment with minocycline, a microglia activation inhibitor. Long-term low dose Pb exposure (100 ppm for 8 weeks) caused significant reduction of LTP in acute slice preparations, meanwhile, such treatment also significantly increased hippocampal microglia activation as well as neuronal injury. In vitro Pb-exposure also induced significantly increase of microglia activation, up-regulate the release of cytokines including tumor necrosis factor-alpha (TNF-α), interleukin-1β (IL-1β) and inducible nitric oxide synthase (iNOS) in microglia culture alone as well as neuronal injury in the co-culture with hippocampal neurons. Inhibiting the microglia activation with minocycline significantly reversed the above-mentioned Pb-exposure induced changes. Our results showed that Pb can cause microglia activation, which can up-regulate the level of IL-1β, TNF-α and iNOS, these proinflammatory factors may cause hippocampal neuronal injury as well as LTP deficits.

Changes in the synaptic structure of hippocampal neurons and impairment of spatial memory in a rat model caused by chronic arsenite exposure

Many epidemiological studies and in vitro experiments have found that chronic arsenic exposure may influence memory formation. The goal of this study was to create an animal model of memory impairment induced by chronic arsenite exposure and to study the underlying mechanisms. Sixty male Sprague-Dawley (SD) male rats were randomly divided into a control group, a low-dose sodium arsenite exposure group and a high-dose sodium arsenite exposure group. Sodium arsenite was administered by adding it to drinking water for 3 months. Then, the spatial memory of the rats was examined with Morris water maze and Y maze. The concentration of arsenic in the blood and the brain was determined by an atomic fluorescence absorption spectrometer. The ultra-structure of hippocampal neurons was observed by an electron microscope. Timm staining was used for observing mossy fibers. We found that the concentration of arsenic in the blood and the brain increased in a dose-response manner (P<0.05). The performance of rats in the arsenite exposed group (15 mg/kg) was significantly impaired in the Morris water maze and Y maze tasks than those in the control group (P<0.05). Sodium arsenite exposure resulted in abnormal structural changes in the myelin sheaths of nerve fibers and decreases in the terminals of mossy fibers. Together, chronic sodium arsenite exposure through drinking water results in detrimental changes in the neuronal synapses, which may contribute to the arsenite-induced impairment of spatial memory.

The changes of miRNA expression in rat hippocampus following chronic lead exposure.

miRNAs have been found to contribute to normal brain functions, nervous system diseases, as well as neurotoxicities induced by external agents. However, whether they are involved in lead-induced neurotoxicities is still not clear. To identify that, a lead-induced chronic neurotoxicity model of rats was built. Both miRNA microarray analysis and qRT-PCR were performed to determine the change of miRNA expression in hippocampus. Then 3 bioinformatics databases were used to analyze the relative target genes of these miRNA, which were further confirmed by qRT-PCR and Western blot. In the present study, lead exposure resulted in the changed expression of 7 miRNAs: miR-204, miR-211, miR-448, miR-449a, miR-34b, and miR-34c were greatly up-regulated while miR-494 was greatly down-regulated. Bioinformatics analysis results showed that the target genes of 6 up-regulated miRNAs were related to neural injury and neurodegeration, axon and synapse function, neural development and regeneration. Correspondingly, the expression levels of mature mRNAs and proteins of three target genes (Bcl-2, Itpr1, and Map2k1) were greatly repressed, verifying the results of bioinformatics analysis. Taken together, our results showed that the expression of several miRNAs reported to be associated with neurophysiological pathways and neurodegenerative diseases changed in rat hippocampus following chronic lead exposure. These miRNAs may play important roles in lead-induced neurotoxicity.

Manganese induces the overexpression of α-synuclein in PC12 cells via ERK activation

Manganese has been known to induce neurological disorders. In the present study, we determined the effect of manganese on the expression of α-synuclein in PC12 cells and its role in manganese-induced cytotoxicity. We also investigated the relationship between α-synuclein expression and the change of ERK1/2 MAPK activity. In our research, manganese exposure induced the overexpression of α-synuclein, while siRNA knockdown of α-synuclein reversed manganese-induced cytotoxicity. Furthermore, manganese induced the activation of ERK1/2 MAPK. The MEK1 inhibitor PD98059, which inhibits the activation of ERK MAPK, attenuated the overexpression of α-synuclein and the cytotoxicity induced by manganese. In conclusion, our studies show that manganese may induce the overexpression of α-synuclein via ERK1/2 activation, which may play a role in manganese-induced cytotoxicity.

Pb exposure attenuates hypersensitivity in vivo by increasing regulatory T cells

Pb is a common environmental pollutant affecting various organs. Exposure of the immune system to Pb leads to immunosuppression or immunodysregulation. Although previous studies showed that Pb exposure can modulate the function of helper T cells, Pb immunotoxicity remains incompletely understood. In this study, we investigated the effect of Pb exposure on T cell development, and the underlying mechanism of Pb-induced suppression of the delayed-type hypersensitivity (DTH) response in vivo. Sprague-Dawley rats were exposed to 300 ppm Pb-acetate solution via the drinking water for six weeks, and we found that Pb exposure significantly increased Pb concentrations in the blood by 4.2-fold (p<0.05) as compared to those in the control rats. In Pb-exposed rats, the amount of thymic CD4(+)CD8(-) and peripheral CD4(+) T cells was significantly reduced, whereas, CD8(+) population was not affected. In contrast to conventional CD4(+) T cells, Foxp3(+) regulatory T cells (Tregs) were increased in both the thymus and peripheral lymphoid organs of Pb-exposed rats. In line with the increase of Tregs, the DTH response of Pb-exposed rats was markedly suppressed. Depletion of Tregs reversed the suppression of DTH response by Pb-exposed CD4(+) T cells in an adoptive transfer model, suggesting a critical role of the increased Tregs in suppressing the DTH response. Collectively, this study revealed that Pb-exposure may upregulate Tregs, thereby leading to immunosuppression.

Reduction of Brain Barrier Tight Junctional Proteins by Lead Exposure: Role of Activation of Nonreceptor Tyrosine Kinase Src via Chaperon GRP78

Lead (Pb) has long been recognized as a neurodevelopmental toxin. Developing blood-brain barrier (BBB) is known to be a target of Pb neurotoxicity; however, the underlying mechanisms are still unclear. Recent evidence suggests that intracellular nonreceptor protein tyrosine kinase Src regulates tight junctional proteins (TJPs). This study was designed to investigate whether Pb acted on the Src-mediated cascade event leading to an altered TJP expression at BBB. Rats aged 20-22 days were exposed to Pb in drinking water (0, 100, 200, and 300 ppm Pb) for eight weeks. Electron microscopic and Western blot analyses revealed a severe leakage of BBB and significantly decreased expressions of TJP occludin and ZO-1. When cultured brain endothelial RBE4 cells were exposed to 10μM Pb for 24 h, expressions of phosphor-Src and an upstream regulator GRP78 were significantly increased by 6.42-fold and 8.29-fold (p < 0.01), respectively. Inactivation of Src pathway by a Src-specific inhibitor reversed Pb-induced downregulation of occludin, but not ZO-1; small interfering RNA knockdown of GRP78 attenuated Pb-induced Src phosphorylation and occludin reduction. Furthermore, Pb exposure caused redistribution of GRP78 from endoplasmic reticulum to cytosol and toward cell member. However, the data from immunoneutralization studies did not show the involvement of cell-surface GRP78 in regulating Src phosphorylation upon Pb exposure, suggesting that the cytosolic GRP78, rather than cell-surface GRP78, was responsible to Pb-induced Src activation and ensuing occludin reduction. Taken together, this study provides the evidence of a novel linkage of GRP78, Src activation to downregulation of occludin, and BBB disruption during Pb exposure.

Effect of acetazolamide and gingko biloba on the human pulmonary vascular response to an acute altitude ascent

Acetazolamide and gingko biloba are the two most investigated drugs for the prevention of acute mountain sickness (AMS). Evidence suggests that they may also reduce pulmonary artery systolic pressure (PASP). To investigate whether these two drugs for AMS prevention also reduce PASP with rapid airlift ascent to high altitude, a randomized controlled trial was conducted on 28 healthy young men with acetazolamide (125 mg bid), gingko biloba (120 mg bid), or placebo for 3 days prior to airlift ascent (397 m) and for the first 3 days at high altitude (3658 m). PASP, AMS, arterial oxygen saturation (Sao2), mean arterial pressure (MAP), heart rate (HR), forced vital capacity (FVC), forced expiratory volume in the first second (FEV1), and peak expiratory flow (PEF) were assessed both at 397 m and 3658 m. HR, PEF, and PASP increased with altitude exposure (p<0.05), and SaO2 decreased (p<0.05). PASP with acetazolamide (mean at 3658 m, 26.2 mm Hg; incremental change, 4.7 mm Hg, 95% CI., 2.6-6.9 mm Hg) was lower than that with ginkgo biloba (mean at 3658 m, 33.7 mm Hg, p=0.001; incremental change, 13.1 mm Hg, 95%CI., 9.6-16.5 mm Hg, p=0.002), and with placebo (mean at 3658 m, 34.7 mm Hg, p<0.001; 14.4 mm Hg, 95% CI., 8.8-20.0 mm Hg, p=0.001). The data show that a low prophylactic dosage of acetazolamide, but not gingko biloba, mitigates the early increase of PASP in a quick ascent profile.

Involvement of CTR1 and ATP7A in lead (Pb)-induced copper (Cu) accumulation in choroidal epithelial cells

The blood-cerebrospinal fluid barrier (BCB) plays a key role in maintaining copper (Cu) homeostasis in the brain. Cumulative evidences indicate that lead (Pb) exposure alters cerebral Cu homeostasis, which may underlie the development of neurodegenerative diseases. This study investigated the roles of Cu transporter 1 (CTR1) and ATP7A, two Cu transporters, in Pb-induced Cu accumulation in the choroidal epithelial cells. Pb exposure resulted in increased intracellular (64)Cu retention, accompanying with up-regulated CTR1 level. Knockdown of CTR1 using siRNA before Pb exposure diminished the Pb-induced increase of (64)Cu uptake. The expression level of ATP7A was down-regulated following the Pb exposure. ATP7A siRNA knockdown, or PCMB treatment, inhibited the (64)Cu efflux from the cells, while the following additional incubation with Pb failed to further increase the intracellular (64)Cu retention. Cu exposure, or intracellular Cu accumulation following the tetracycline (Tet)-induced overexpression of CTR1, did not result in significant change in ATP7A expression. Taken together, these data indicate that CTR1 and ATP7A play important roles in Cu transport in choroidal epithelial cells, and the Pb-induced intracellular Cu accumulation appears to be mediated, at least in part, via the alteration of CTR1 and ATP7A expression levels following Pb exposure.

Adult lead exposure increases blood-retinal permeability: A risk factor for retinal vascular disease

Low-to-moderate level developmental and adult lead exposure produces retinal dysfunction and/or degeneration in humans and experimental animals. Although high level in vivo or in vitro lead disrupts blood-brain-barrier tight junctions and increases its permeability, the blood-retinal-barrier (BRB) has not been examined. There were four overall goals. First, generate environmentally relevant dose-response models of short-term lead exposure in adult rats. Second, assess retinal histology and functional integrity of the BRB. Third, investigate the transmembrane proteins occludin and claudin-5 as targets mediating the increased BRB permeability. Fourth, examine the contribution of the PI3K-Akt signaling pathway as a mechanism underlying increased BRB permeability. Young adult rats were given water, 0.01% or 0.02% lead drinking solutions for six weeks. In control, 0.01% and 0.02% groups the six week mean blood [Pb] were 1, 12.5 and 19μg/dl, respectively. We employed histology, stereology, quantitative image analysis, immunoblots and densitometry, and pharmacology techniques. Major findings were that adult lead exposure produced dose-dependent 1) decreases in outer and inner nuclear layer thickness, 2) increases in BRB permeability, 3) decreases in occludin and claudin-5 expression, 4) increases in pAkt (Ser473), but not pAkt (Thr308), expression, and 5) wortmannin partially or completely blocked the increased BRB permeability and changes in protein expression. These results indicate that lead-induced increases in PI3K-Akt signaling partially underlie the increased BRB permeability and advance our knowledge about lead-induced retinotoxicity. Furthermore, they suggest that environmental and occupational lead exposures are risk factors for increased BRB permeability in diseases such as age-related macular degeneration, diabetes and stroke.