Cellular Conditions Responsible for Methylmercury-Mediated Neurotoxicity.

Methylmercury (MeHg) is a widely known environmental pollutant that causes severe neurotoxicity. MeHg-induced neurotoxicity depends on various cellular conditions, including differences in the characteristics of tissues and cells, exposure age (fetal, childhood, or adulthood), and exposure levels. Research has highlighted the importance of oxidative stress in the pathogenesis of MeHg-induced toxicity and the site- and cell-specific nature of MeHg-induced neurotoxicity. The cerebellar granule cells and deeper layer cerebrocortical neurons are vulnerable to MeHg. In contrast, the hippocampal neurons are resistant to MeHg, even at high mercury accumulation levels. This review summarizes the mechanisms underlying MeHg-mediated intracellular events that lead to site-specific neurotoxicity. Specifically, we discuss the mechanisms associated with the redox ability, neural outgrowth and synapse formation, cellular signaling pathways, epigenetics, and the inflammatory conditions of microglia.

Methylmercury induces hyperalgesia/allodynia through spinal cord dorsal horn neuronal activation and subsequent somatosensory cortical circuit formation in rats.

Methylmercury (MeHg) is known to cause serious neurological deficits in humans. In this study, we investigated the occurrence of MeHg-mediated neuropathic pain and identified the underlying pathophysiological mechanism in a rat model of MeHg exposure. Rats were exposed to MeHg (20 ppm in drinking water) for 3 weeks. Neurological damage was observed in the primary afferent neuronal system, including the dorsal root nerve and the dorsal column of the spinal cord. The MeHg-exposed rats showed hyperalgesia/allodynia, compared to controls, as evidenced by a significant decrease in the threshold of mechanical pain evaluated using an algometer with calibrated forceps. Immunohistochemistry revealed the accumulation of activated microglia in the dorsal root nerve, dorsal column, and dorsal horn of the spinal cord. Western blot analyses of the dorsal part of the spinal cord demonstrated an increase in inflammotoxic and inflammatory cytokines and a neuronal activation related protein, phospho-CRE bunding protein (CREB). The results suggest that dorsal horn neuronal activation was mediated by inflammatory factors excreted by accumulated microglia. Furthermore, analyses of the cerebral cortex demonstrated increased expression of phospho-CREB and thrombospondin-1, which is known to be an important factor for excitatory synapse formation, specifically in the somatosensory cortical area. In addition, the expression of pre- and post-synaptic markers was increased in this cortex area. These results suggested that the new cortical circuit was wired specifically in the somatosensory cortex. In conclusion, MeHg-mediated dorsal horn neuronal activation with inflammatory microglia might induce somatosensory cortical rewiring, leading to hyperalgesia/allodynia.

Methylmercury-Mediated Oxidative Stress and Activation of the Cellular Protective System.

Methylmercury (MeHg) is a well-known neurotoxicant that causes severe intoxication in humans. In Japan, it is referred to as Minamata disease, which involves two characteristic clinical forms: fetal type and adult type depending on the exposed age. In addition to MeHg burden level, individual susceptibility to MeHg plays a role in the manifestation of MeHg toxicity. Research progress has pointed out the importance of oxidative stress in the pathogenesis of MeHg toxicity. MeHg has a high affinity for selenohydryl groups, sulfhydryl groups, and selenides. It has been clarified that such affinity characteristics cause the impairment of antioxidant enzymes and proteins, resulting in the disruption of antioxidant systems. Furthermore, MeHg-induced intracellular selenium deficiency due to the greater affinity of MeHg for selenohydryl groups and selenides leads to failure in the recoding of a UGA codon for selenocysteine and results in the degradation of antioxidant selenoenzyme mRNA by nonsense-mediated mRNA decay. The defect of antioxidant selenoenzyme replenishment exacerbates MeHg-mediated oxidative stress. On the other hand, it has also been revealed that MeHg can directly activate the antioxidant Keap1/Nrf2 signaling pathway. This review summarizes the incidence of MeHg-mediated oxidative stress from the viewpoint of the individual intracellular redox system interactions and the MeHg-mediated aforementioned intracellular events. In addition, the mechanisms of cellular stress pathways and neuronal cell death triggered by MeHg-mediated oxidative stress and direct interactions of MeHg with reactive residues of proteins are mentioned.

Decreased plasma thiol antioxidant capacity precedes neurological signs in a rat methylmercury intoxication model.

The main target organ for MeHg is the nervous system, and its neurological dysfunction remains irreversible. Therefore, predictive biomarkers associated with individual susceptibility to MeHg and future clinical severity are needed to protect against the progression of MeHg toxicity. In this study, we demonstrated that plasma thiol antioxidant capacity (-SHp) is a useful predictive biomarker associated with future clinical severity using MeHg-intoxicated rats administered 1 mg/kg/day for 4 weeks. Blood samples were collected from the subclavian vein of each rat once a week to examine total blood mercury concentrations and the levels of plasma oxidative stress markers. Time course analyses of the correlation between these weekly blood examination values and hind limb crossing signs score after 4 weeks of MeHg exposure were performed, and plasma -SHp levels after 2 weeks of MeHg exposure showed strong correlations with future hind limb crossing sign scores. Neuropathological changes also developed in parallel with hind limb crossing sign scores. Quantitative analysis of vacuolar areas in the spinal cord showed a strong correlation with hind limb crossing sign scores. In conclusion, evaluation of plasma -SHp levels allowed us to detect individuals at risk for health damage and could protect the sensitive population against MeHg toxicity.

Pregnant rats exposed to low-level methylmercury exhibit cerebellar synaptic and neuritic remodeling during the perinatal period.

Methylmercury (MeHg) is a potent neurotoxic chemical, and gestational exposure to MeHg is known to cause developmental impairments in fetuses. Although it is well established that fetuses are extremely susceptible to MeHg toxicity, limited studies have investigated the effect of low-level MeHg exposure on mothers. In this study, we demonstrated that exposure of pregnant rats to low-level MeHg (1 ppm in drinking water) induced cerebellar synaptic and neuritic remodeling during the perinatal period between gestational day 20 and postnatal day (PND) 1. MeHg-induced neurodegeneration, for example, cerebellar granule cell death, was not detected and fetuses were delivered normally and exhibited normal development. The maternal cerebellar synaptic and neuritic changes were restored by PND 21. To elucidate the mechanisms underlying these perinatal changes in MeHg-exposed pregnant rats, we investigated proteins related to synapse formation and neurite outgrowth. We identified suppression of the tropomyosin receptor kinase (Trk) A pathway and reduced activity-regulated cytoskeleton-associated protein (Arc) expression in MeHg-exposed pregnant rats during the perinatal period, mirroring the decreased expression of synaptic and neuritic proteins. MeHg-exposed pregnant rats also exhibited increased perinatal plasma corticosterone levels and decreased estradiol levels compared to vehicle-exposed pregnant rats. Similar to the synaptic and neuritic changes, TrkA pathway activity, Arc expression, and plasma hormone levels were subsequently normalized. These results suggest that exposure of pregnant rats to low-level MeHg affected perinatal cerebellar synaptic and neuritic remodeling through modulation of the TrkA pathway and Arc expression which may be caused by MeHg-induced hormonal changes.

Local Vibration Stimuli Induce Mechanical Stress-Induced Factors and Facilitate Recovery From Immobilization-Induced Oxidative Myofiber Atrophy in Rats.

Muscle atrophy can be caused by unloading stress such as microgravity environments or cast immobilization. Therapies for such disuse muscle atrophy and their underlying mechanisms are incompletely understood. Here, we investigated the therapeutic effects of local vibration stimulation on immobilization-induced skeletal muscle atrophy. A rat model was made by placing the left hindlimb in a cast for 1 week, leading to oxidative myofiber atrophy without myopathic changes in soleus skeletal muscle. Vibration stimulus (90 Hz, 15 min) to the plantar fascia of the atrophic hindlimb was performed once a day using a hand-held vibration massager after removal of a cast at the end of the immobilization period. After 2 weeks, rats were dissected, and quantitative analysis of the cross-sectional areas of soleus myofibers was performed. The results revealed that vibration induced significant recovery from disuse muscle atrophy, compared with untreated immobilized samples. Furthermore, vibration treatment suppressed the fiber transition from slow to fast fiber types compared with vibration-untreated immobilized samples. Western blotting analyses of mechanical stress-induced factors revealed that the expression of mechano-growth factor (MGF), systemic insulin-like growth factor I, and the mechanotransduction protein, Yes-associated protein 1 (YAP1), was decreased in untreated immobilized soleus muscle, whereas vibration stimulation restored their expression. No change in the level of phosphorylation of YAP1Ser127 was observed, leading to no change in p-YAP1/YAP1 ratio in vibration-treated immobilized soleus muscle. The results indicate that vibration stimulus is effective to restore immobilization-induced inactivation of YAP1 pathway. Phosphorylation of ERK 1/2, but not AKT, was enhanced in vibration-treated immobilized soleus muscle. Furthermore, vibration stimuli restored immobilization-induced downregulation of the paired box transcription factor, PAX7, a critical factor for regenerative myogenesis in muscle satellite cells. Our results indicate that cyclic vibration stimuli are effective in activating satellite cells and facilitate recovery from immobilization-induced oxidative myofiber atrophy through upregulation of MGF and YAP1.

Environmental stresses suppress nonsense-mediated mRNA decay (NMD) and affect cells by stabilizing NMD-targeted gene expression.

Nonsense-mediated mRNA decay (NMD) is a cellular mechanism that eliminates mRNAs that harbor premature translation termination codons (PTCs). Here, we investigated the effects of environmental stresses (oxidative stress and endoplasmic reticulum (ER) stress) on NMD activity. Methylmercury (MeHg) was used to cause oxidative stress and thapsigargin to stress the ER. NMD suppression, evidenced by upregulation of NMD-sensitive mRNAs and a decrease in UPF1 phosphorylation, was observed in MeHg-treated myogenic cells, cerebral cortical neuronal cells, and astroglial cells. Mild ER stress amplified NMD suppression caused by MeHg. To elucidate the cause of stress-induced NMD suppression, the role of the phospho-eIF2α/ATF4 pathway was investigated. Knockdown and non-phosphorylatable eIF2α-transfection studies demonstrated the critical role of phospho-eIF2α-mediated repression of translation in mild ER stress-induced NMD suppression. However, NMD suppression was also observed in phospho-eIF2α-deficient cells under mild ER stress. Mechanistic target of rapamycin suppression-induced inhibition of cap-dependent translation, and downregulation of the NMD components UPF1, SMG7, and eIF4A3, were probably involved in stress-induced NMD suppression. Our results indicate that stress-induced NMD suppression has the potential to affect the condition of cells and phenotypes of PTC-related diseases under environmental stresses by stabilizing NMD-targeted gene expression.

Fasudil, a Rho-Associated Coiled Coil-Forming Protein Kinase Inhibitor, Recovers Methylmercury-Induced Axonal Degeneration by Changing Microglial Phenotype in Rats.

Methylmercury (MeHg) is an environmental neurotoxicant that induces neuropathological changes. In this study, we established chronic MeHg-intoxicated rats. These rats survived, and sustained MeHg-induced axonal degeneration, including the dorsal root nerve and the dorsal column of the spinal cord; these changes persisted 12 weeks after MeHg withdrawal. We demonstrated for the first time the restorative effect of Fasudil, a specific inhibitor of Rho-associated coiled coil-forming protein kinase, on axonal degeneration and corresponding neural dysfunction in the established chronic MeHg-intoxicated rats. To investigate the mechanism of this restorative effect, we focused on the expression of Rho protein families. This was supported by our previous study, which demonstrated that cotreatment with Fasudil prevented axonal degeneration by mitigating neurite extension/retraction incoordination caused by MeHg-induced suppression of Rac1 in vitro and in subacute MeHg-intoxicated rats. However, the mechanism of the restorative effect of Fasudil on axonal degeneration in chronic MeHg-intoxicated rats differed from MeHg-mediated neuritic extension/retraction incoordination. We found that the restorative effect of Fasudil was caused by the Fasudil-induced change of microglial phenotype, from proinflammatory to anti-inflammatory; moreover, Fasudil suppressed Rho-associated coiled coil-forming protein kinase activity. Treatment with Fasudil decreased the expression of proinflammatory factors, including tumor necrosis factor-α, inducible nitric oxide synthase, interleukin-1ß, and interleukin-6; furthermore, it inactivated the nuclear factor kappa-light-chain-enhancer of activated B cells pathway. Additionally, Fasudil treatment was associated with increased levels of anti-inflammatory factors arginase-1 and interleukin-10. These results suggest that Rho-associated coiled coil-forming protein kinase inhibition may recover MeHg-mediated axonal degeneration and neural dysfunction in chronic MeHg intoxication.

Methylmercury induces oxidative stress and subsequent neural hyperactivity leading to cell death through the p38 MAPK-CREB pathway in differentiated SH-SY5Y cells.

Methylmercury (MeHg) induces site-specific cerebrocortical neuronal cell death. In our previous study using an in vivo mouse model, we reported that MeHg-induced cerebrocortical neuronal cell death may be due to neural hyperactivity triggered by activation of kinase pathways. However, the detailed molecular mechanism remained to be completely understood. In this study, we analyzed detailed signaling pathways for MeHg-induced neuronal cell death using all-trans-retinoic acid (RA) differentiated SH-SY5Y cells, which show neuron-like morphological changes and express neuron/synapse markers for cerebrocortical neurons. Time course studies revealed that MeHg-induced upregulation of c-fos, a marker of neural activation, preceded neuronal cell death. These results were similar to those observed in a MeHg-intoxicated mouse model. We observed early expression of the oxidative stress marker thymidine glycol followed by activation of p44/42 mitogen-activated protein kinase (MAPK) and p38 MAPK, and an increase in cAMP response element binding protein (CREB). Investigation of the effects of specific kinase inhibitors revealed that SB203580, a specific inhibitor for p38 MAPK, significantly blocked the upregulation of c-fos and the subsequent neuronal cell death. In contrast, PD98059 and U0126, specific inhibitors for p44/p42 MAPK, showed no effects on MeHg-induced neurotoxicity. Furthermore, the antioxidants Trolox and edaravone significantly suppressed MeHg-induced thymidine glycol expression, p38 MAPK-CREB pathway activation, and neurotoxicity. Altogether, these results suggest that MeHg-induced oxidative stress and subsequent activation of the p38 MAPK-CREB pathway contribute to cerebrocortical neuronal hyperactivity and subsequent neuronal cell death.

In situ different antioxidative systems contribute to the site-specific methylmercury neurotoxicity in mice.

Methylmercury (MeHg), an environmental toxicant, induces site-specific neurotoxicity in adult human and animal models. In this study, we demonstrated that MeHg-induced neuropathological changes of the brain in mice were remarkable in the cerebrocortical neurons of deeper layers (dl-CCNs), but not in the CCNs of shallow layers (sl-CCNs) and the hippocampal neurons of cornu ammonis 1 (CA1-HNs). Total mercury concentration was not corresponded to the pathological changes. Here, we investigated the cause of such site-specific MeHg neurotoxicity with a focus on in situ antioxidative systems due to its critical role in MeHg intoxication. We performed in situ analyses of antioxidative enzymes expression using RT-qPCR analyses from laser microdissected sl-CCNs, dl-CCNs, and CA1-HNs samples, and immunohistochemistry. The results of antioxidative enzymes expression analyses demonstrated the lowest basal expression levels of mRNA and proteins, especially manganese superoxide dismutase (Mn-SOD) and glutathione peroxidase 1 (GPx1) in dl-CCNs. In addition, the Mn-SOD expression showed a lowest response to MeHg in dl-CCNs. We also performed enzymatic activity analyses for antioxidative enzymes using separated cerebral cortex and hippocampus. The results of enzymatic activity analyses indicate that the expression levels of antioxidative enzymes reflect their enzymatic activities. Immunostaining of thymidine glycerol, a sensitive oxidative stress marker, showed selectively increased expression in dl-CCNs after the exposure to MeHg but not in sl-CCNs and CA1-HNs, suggesting the occurrence of MeHg-induced oxidative stress in dl-CCNs. The differences in MeHg-induced occurrence of oxidative stress and pathological changes in sl-CCNs, dl-CCNs, and CA1-HNs corresponded to the basal level of Mn-SOD and GPx1 expression and the different protective response of Mn-SOD expression to MeHg. These findings suggest that the in situ different antioxidative systems play a role in the site-specific neurotoxicity of MeHg.

Endoplasmic reticulum stress preconditioning modifies intracellular mercury content by upregulating membrane transporters.

Endoplasmic reticulum (ER) stress preconditioning protects cells against methylmercury (MeHg) cytotoxicity by inducing integrated stress responses such as eIF2α phosphorylation, ATF4 accumulation, and nonsense-mediated mRNA decay (NMD) suppression. Here we demonstrated that ER stress preconditioning results in the upregulation of membrane transporters, leading to a decrease in intracellular mercury content. Our analyses showed that ER stress preconditioning upregulated the expression of methionine transporters that affect the cellular influx of MeHg, LAT1, LAT3, and SNAT2; and a membrane transporter that affects the efflux of MeHg, ABCC4, in MeHg-susceptible myogenic cells. Among these, ABCC4 transporter expression exhibited the greatest elevation. The functional significance of ABCC4 transporter in the efflux of MeHg was shown by the ABCC4 inhibition study. Additionally, we identified the role of phospho-eIF2α/ATF4 pathway in the upregulation of LAT1, SNAT2, and ABCC4 and the role of NMD suppression in LAT3 upregulation. Further, we detected that ER stress preconditioning amplified membrane transporter expression most likely through the translation of the upregulated mRNAs caused by ATF4-dependent transcription and NMD suppression. Taken together, these results suggested that the phospho-eIF2α/ATF4 pathway activation and NMD suppression may represent therapeutic targets for the alleviation of MeHg cytotoxicity by enhancing mercury efflux besides inducing protective stress responses.

Site-specific neural hyperactivity via the activation of MAPK and PKA/CREB pathways triggers neuronal degeneration in methylmercury-intoxicated mice.

Methylmercury (MeHg) induces site-specific neurotoxicity in the adult brain. In this study, we investigated the site-specific expression of the signaling cascade related to neural activity in a mouse model of MeHg intoxication showing neurodegeneration only in the deep layer of the cerebral cortex, especially layer IV. We performed time course studies of c-fos and brain-derived neurotrophic factor (BDNF) expression levels which are proper markers of neural activity. We showed that upregulation of both markers preceded the neuronal degeneration in the cerebral cortex. Immunohistochemical analysis revealed the site-specific upregulation of c-fos in the deep layer of the cerebral cortex. Western blot analysis showed that c-fos and BDNF expression was associated with CREB phosphorylation, which was triggered by the activation of the p44/42 MAPK, p38 MAPK and PKA pathways. However, we did not detect any changes in the expression levels of c-fos and BDNF proteins and no signs of neuronal degeneration in the hippocampus and cerebellum, despite the fact that we could detect accumulation of MeHg in these two brain regions. These results suggested an intriguing possibility that MeHg-induced neuronal degeneration was caused by site-specific neural hyperactivity triggered by the activation of MAPK and PKA/CREB pathways followed by c-fos and BDNF upregulation.

Methylmercury Causes Blood-Brain Barrier Damage in Rats via Upregulation of Vascular Endothelial Growth Factor Expression.

Clinical manifestations of methylmercury (MeHg) intoxication include cerebellar ataxia, concentric constriction of visual fields, and sensory and auditory disturbances. The symptoms depend on the site of MeHg damage, such as the cerebellum and occipital lobes. However, the underlying mechanism of MeHg-induced tissue vulnerability remains to be elucidated. In the present study, we used a rat model of subacute MeHg intoxication to investigate possible MeHg-induced blood-brain barrier (BBB) damage. The model was established by exposing the rats to 20-ppm MeHg for up to 4 weeks; the rats exhibited severe cerebellar pathological changes, although there were no significant differences in mercury content among the different brain regions. BBB damage in the cerebellum after MeHg exposure was confirmed based on extravasation of endogenous immunoglobulin G (IgG) and decreased expression of rat endothelial cell antigen-1. Furthermore, expression of vascular endothelial growth factor (VEGF), a potent angiogenic growth factor, increased markedly in the cerebellum and mildly in the occipital lobe following MeHg exposure. VEGF expression was detected mainly in astrocytes of the BBB. Intravenous administration of anti-VEGF neutralizing antibody mildly reduced the rate of hind-limb crossing signs observed in MeHg-exposed rats. In conclusion, we demonstrated for the first time that MeHg induces BBB damage via upregulation of VEGF expression at the BBB in vivo. Further studies are required in order to determine whether treatment targeted at VEGF can ameliorate MeHg-induced toxicity.

Three Case Reports of Successful Vibration Therapy of the Plantar Fascia for Spasticity Due to Cerebral Palsy-Like Syndrome, Fetal-Type Minamata Disease.

Fetal-type Minamata disease is caused by the exposure to high concentrations of methylmercury in the fetal period and shows cerebral palsy-like clinical features. Relief of spasticity is a major task of rehabilitation to improve their activities of daily living. Here we report the effect of long-term vibration therapy on bilateral lower-limb spasticity in 3 patients with fetal-type Minamata disease. We used a simple, inexpensive, and noninvasive approach with hand-held vibration massagers, which were applied to the plantar fascia at 90 Hz for 15 minutes. The effect was observed soon after the first treatment and resulted in better performance of the repetitive facilitation. Vibration therapy for 1 year improved Modified Ashworth Scale for the ankle flexors in 2 cases. The labored gait improved and gait speed increased in another case. Continued vibration therapy for another 1 year further improved Modified Ashworth Scale score and range of motion of ankle dorsiflexion in 1 case. This case showed the decreased amplitude of soleus H-reflex after the 15-minute vibration therapy, suggesting that α-motor neuron excitability was suppressed. Vibration therapy using a hand-held vibration massager may offer safe and effective treatment for lower-limb spasticity in patients with chronic neurological disorders.

Prenatal low-dose methylmercury exposure impairs neurite outgrowth and synaptic protein expression and suppresses TrkA pathway activity and eEF1A1 expression in the rat cerebellum.

Methylmercury (MeHg) is a highly neurotoxic environmental chemical that can cause developmental impairments. Human fetuses and neonates are particularly susceptible to MeHg toxicity; however, the mechanisms governing its effects in the developing brain are unclear. In the present study, we investigated the effects of prenatal and lactational MeHg exposure on the developing cerebellum in rats. We demonstrated that exposure to 5ppm MeHg decreased postnatal expression of pre- and postsynaptic proteins, suggesting an impairment in synaptic development. MeHg exposure also reduced neurite outgrowth, as shown by a decrease in the expression of the neurite marker neurofilament H. These changes were not observed in rats exposed to 1ppm MeHg. In order to define the underlying mechanism, we investigated the effects of MeHg exposure on the tropomyosin receptor kinase (Trk) A pathway, which plays important roles in neuronal differentiation and synapse formation. We demonstrated suppression of the TrkA pathway on gestation day 20 in rats exposed to 5ppm MeHg. In addition, down-regulation of eukaryotic elongation factor 1A1 (eEF1A1) was observed on postnatal day 1. eEF1A1 knockdown in differentiating PC12 cells impaired neurite outgrowth and synaptic protein expression, similar to the results of MeHg exposure in the cerebellum. These results suggest that suppression of the TrkA pathway and subsequent decreases in eEF1A1 expression induced by prenatal exposure to MeHg may lead to reduced neurite outgrowth and synaptic protein expression in the developing cerebellum.

Decreased plasma thiol antioxidant barrier and selenoproteins as potential biomarkers for ongoing methylmercury intoxication and an individual protective capacity.

Manifestation of methylmercury (MeHg) toxicity depends on individual susceptibility to MeHg, as well as MeHg burden level. Therefore, biomarkers that reflect the protective capacity against MeHg are needed. The critical role of oxidative stress in the pathogenesis of MeHg cytotoxicity has been demonstrated. Because MeHg has high affinity for selenohydryl groups, sulfhydryl groups, and selenides, and causes posttranscriptional defects in selenoenzymes, proteins with selenohydryl and sulfhydryl groups should play a critical role in mediating MeHg-induced oxidative stress. Here, plasma oxidative stress markers and selenoproteins were investigated in MeHg-intoxicated rats showing neuropathological changes after 4 weeks of MeHg exposure. The thiol antioxidant barrier (-SHp) level significantly decreased 2 weeks after MeHg exposure, which is an early stage at which no systemic oxidative stress, histopathological changes, or clinical signs were detected. Diacron reactive oxidant metabolite (d-ROM) levels significantly increased 3 weeks after MeHg exposure, indicating the occurrence of systemic oxidative stress. Rats treated with lead acetate or cadmium chloride showed no changes in levels of -SHp and d-ROM. Selenoprotein P1 abundance significantly decreased in MeHg-treated rats, whereas it significantly increased in rats treated with Pb or Cd. Plasma selenium-dependent glutathione peroxidase (GPx3) activity also significantly decreased after MeHg exposure, whereas plasma non-selenoenzyme glutathione reductase activity significantly increased in MeHg-treated rats. The results suggest that decreased capacity of -SHp and selenoproteins (GPx3 and selenoprotein P) can be useful biomarkers of ongoing MeHg cytotoxicity and the individual protective capacity against the MeHg body burden.

Low concentrations of methylmercury inhibit neural progenitor cell proliferation associated with up-regulation of glycogen synthase kinase 3ß and subsequent degradation of cyclin E in rats.

Methylmercury (MeHg) is an environmental neurotoxicant. The developing nervous system is susceptible to low concentrations of MeHg; however, the effect of MeHg on neural progenitor cell (NPC) proliferation, a key stage of neurogenesis during development, remains to be clarified. In this study, we investigated the effect of low concentrations of MeHg on NPCs by using a primary culture system developed using the embryonic rat cerebral cortex. NPC proliferation was suppressed 48h after exposure to 10nM MeHg, but cell death was not observed. Western blot analyses for cyclins A, B, D1, and E demonstrated that MeHg down-regulated cyclin E, a promoter of the G1/S cell cycle transition. Cyclin E has been shown to be degraded following the phosphorylation by glycogen synthase kinase 3ß (GSK-3ß). The time course study showed that GSK-3ß was up-regulated 3h after exposure to 10nM MeHg, and cyclin E degradation 48h after MeHg exposure. We further demonstrated that GSK-3ß inhibitors, lithium and SB-415286, suppressed MeHg-induced inhibition of NPC proliferation by preventing cyclin E degradation. These results suggest that the inhibition of NPC proliferation induced by low concentration of MeHg was associated with up-regulation of GSK-3ß at the early stage and subsequent degeneration of cyclin E.

Occupational therapy intervention to inspire self-efficacy in a patient with spinal ataxia and visual disturbance.

We report a case of a patient with severe ataxia and visual disturbance due to vitamin E deficiency, whose self-efficacy was inspired by intervention with an appropriate occupational therapy activity. Before the handloom intervention, her severe neurological deficits decreased her activities of daily living (ADL) ability, which made her feel pessimistic and depressed. The use of a handloom, however, inspired her sense of accomplishment because she could perform the weft movement by using her residual physical function, thereby relieving her pessimistic attitude. This perception of capability motivated her to participate in further rehabilitation. Finally, her eager practice enhanced her ADL ability and quality of life (QOL). The result suggests that it is important to provide an appropriate occupational therapy activity that can inspire self-efficacy in patients with chronic refractory neurological disorders because the perception of capability can enhance the motivation to improve performance in general activities, ADL ability and QOL.

Methylmercury causes neuronal cell death through the suppression of the TrkA pathway: in vitro and in vivo effects of TrkA pathway activators.

Methylmercury (MeHg) is an environmental toxin which induces cell death specific for the nervous systems. Here we show that MeHg causes neuronal cell death through the suppression of the tropomyosin receptor kinase A (TrkA) pathway, and that compounds activating the TrkA pathway prevent MeHg-induced nerve damage in vitro and in vivo. We first investigated the mechanism of MeHg-induced neurotoxicity in differentiating neurons using PC12 cells. Exposure to 100nM MeHg for 1day induced apoptosis in differentiating PC12 cells. Further, MeHg-induced apoptosis was preceded by inhibition of neurite extension, as determined by ELISA analyses of the neurite-specific protein neurofilament triplet H protein (NF-H). To determine the mechanism of MeHg-induced apoptosis, we evaluated the effects of MeHg on the TrkA pathway, which is known to regulate neuronal differentiation and viability. Western blot analysis demonstrated that, like the TrkA phosphorylation inhibitor K252a, MeHg inhibited phosphorylation of TrkA and its downstream effectors. Furthermore, GM1 ganglioside and its analog MCC-257, which enhance TrkA phosphorylation, overcame the effect of MeHg in neurons, supporting the involvement of the TrkA pathway in MeHg-induced nerve damage. Finally, we demonstrated that MCC-257 rescued the clinical sign and pathological changes in MeHg-exposed rats. These findings indicate that MeHg-induced apoptosis in neuron is triggered by inhibition of the TrkA pathway, and that GM1 ganglioside and MCC-257 effectively prevent MeHg-induced nerve damage.

Methylmercury exposure and neurological outcomes in Taiji residents accustomed to consuming whale meat.

Methylmercury (MeHg) is a major environmental neurotoxicant that causes damage to the central nervous system. In Japan, industrial emission of MeHg has resulted in MeHg intoxication in Minamata and Niigata, the so-called Minamata disease. Humans are exposed to MeHg derived from natural sources, primarily fish and fish predators. Therefore, MeHg continues to be an environmental risk to human health, particularly in susceptible populations that frequently consume substantial amounts of fish or fish predators such as whale. This study aimed to investigate the health effects of MeHg exposure in adults. The subjects were 194 residents (117 males, 77 females; age 20-85 years) who resided in the coastal town of Taiji, the birthplace of traditional whaling in Japan. We analyzed hair for mercury content and performed detailed neurological examinations and dietary surveys. Audiometry, magnetic resonance imaging, and electromyography were performed to diagnose neurological defects. Whole blood mercury and selenium (Se) levels were measured in 23 subjects. The geometric mean of the hair mercury levels was 14.9 µg/g. Twelve subjects revealed hair mercury levels >50 µg/g (NOAEL) set by WHO. Hair mercury levels significantly correlated with daily whale meat intake. These results suggested that residents in Taiji were highly exposed to MeHg by ingesting MeHg-contaminated whale meat. Multivariate regression analysis demonstrated no significant correlations between hair mercury levels and neurological outcomes, whereas some of the findings significantly correlated with age. A significantly positive correlation between whole blood mercury and Se levels was observed and the whole blood mercury/Se molar ratios of all subjects were <1. These findings suggested that sufficient Se intake might be one of causes of the absence of adverse effects of MeHg exposure in this study.