Tongjian Cai

Manganese induces dopaminergic neurodegeneration via microglial activation in a rat model of manganism

Manganese is an essential trace element required for normal development and bodily functions. However, exposure of the brain to excessive amounts of manganese results in neurotoxicity. Although previous studies examining manganese neurotoxicity have focused on neuronal injury, especially direct injury to dopaminergic neurons, the effects of manganese-induced neurotoxicity on glial cells have not been reported. The current study was designed to examine the effect of manganese on microglial activation, and the underlying mechanism of manganese-induced dopaminergic neuronal injury in vivo. We established an animal model of manganism by intrastriatal injection of MnCl(2).4H(2)O into male Sprague-Dawley rats. One day after administration of manganese, a few microglial cells in the substantia nigra (SN) were activated, although the number of tyrosine hydroxylase (TH)-immunoreactive neurons in the SN was unaffected. Seven days after administration of manganese, a marked reduction in the number of TH-immunoreactive neurons was observed in the SN, and the majority of microglial cells were activated. We found that manganese upregulated inducible nitric oxide synthase (iNOS) and tumor necrosis factor alpha (TNF-alpha) gene expression, as well as iNOS, TNF-alpha, and interleukin-1beta (IL-1beta) protein levels in the SN. Furthermore, treatment with minocycline, an inhibitor of microglial activation, attenuated microglial activation and mitigated IL-1beta, TNF-alpha, and iNOS production as well as dopaminergic neurotoxicity induced by manganese. These results suggested that dopaminergic neurons could be damaged by manganese neurotoxicity, and that the activated microglial cells and their associated activation products played an important role in this neurodegenerative process.

The Role of α-synuclein and Tau Hyperphosphorylation-Mediated Autophagy and Apoptosis in Lead-induced Learning and Memory Injury

Lead (Pb) is a well-known heavy metal in nature. Pb can cause pathophysiological changes in several organ systems including central nervous system. Especially, Pb can affect intelligence development and the ability of learning and memory of children. However, the toxic effects and mechanisms of Pb on learning and memory are still unclear. To clarify the mechanisms of Pb-induced neurotoxicity in hippocampus, and its effect on learning and memory, we chose Sprague-Dawley rats (SD-rats) as experimental subjects. We used Morris water maze to verify the ability of learning and memory after Pb treatment. We used immunohistofluorescence and Western blotting to detect the level of tau phosphorylation, accumulation of α-synuclein, autophagy and related signaling molecules in hippocampus. We demonstrated that Pb can cause abnormally hyperphosphorylation of tau and accumulation of α-synuclein, and these can induce hippocampal injury and the ability of learning and memory damage. To provide the new insight into the underlying mechanisms, we showed that Grp78, ATF4, caspase-3, autophagy-related proteins were induced and highly expressed following Pb-exposure. But mTOR signaling pathway was suppressed in Pb-exposed groups. Our results showed that Pb could cause hyperphosphorylation of tau and accumulation of α-synuclein, which could induce ER stress and suppress mTOR signal pathway. These can enhance type II program death (autophgy) and type I program death (apoptosis) in hippocampus, and impair the ability of learning and memory of rats. This is the first evidence showing the novel role of autophagy in the neurotoxicity of Pb.

Lead poisoning in China: a nightmare from industrialisation

Recently, new cases of lead poisoning have been reported in China. In early January, 2011, 228 children in Huaining County, Anhui Province, had blood lead concentrations higher than 100 μg/L, the acceptable level in China and many other countries. 23 of the children with blood lead higher than 250 μg/L had to be sent to a hospital for treatment. The local authority then shut down a factory making batteries that was the source of pollution. From 2009 until now, lead poisoning in several provinces of China has aff ected more than 4000 children (fi gure). In Jiyuan City, Henan Province, blood samples from 1008 of 3108 children (32%) living near lead smelters showed lead concentrations higher than 250 μg/L. In August, 2009, the waste discharges from a local smelter caused lead poisoning in 851 of 1016 children in Fengxiang County, Shaanxi Province. More than 170 children had to be admitted to hospital. In the same month, 1354 of 1958 children living near the Wugang Manganese Smelting Plant in Hunan Province had blood lead concentrations higher than 100 μg/L. Both cases sparked riots by local residents. Similar lead poisoning cases also took place in Jiangsu, Fujian, Sichuan, Yunnan, and Guangdong Provinces. Children are especially susceptible to chronic lead exposure, with eff ects including physical, cognitive, and neurobehavioural impairment. There is no safe concentration of blood lead below which children are not aff ected. Cases in children are particularly sensitive in China because of the country’s one child per family policy. The number of riots and protests sparked by environmental problems has been escalating at a rate of about 30% per year, according to Shengxian Zhou, the Environmental Protection Minister in China. by providing fi nishing touches—ie, opportunities to optimise one’s repertoire of skills—therefore producing more rounded and marketable young professionals by better equipping students with crosscutting skill sets. Our ongoing experiences with case competitions suggest that longstanding traditions of academic globalhealth programmes that are located exclusively in public health schools might need to give way to more integrated instruction that incorporates competencies and training from several disciplines. Development of synergies within and across professional, vocational, and technical schools will be important to tackle future multidimensional challenges in global health. With the substantial and increased interest in global health among students worldwide, the model of case competitions complements traditional, structured, and specialised higher education. Student teams optimise their combined inventories of diverse, but synergistic, skills and experiences, thus making the whole greater than the sum of its parts. Refl ections from past participants suggest that the competition is a more memorable university experience than are obligatory prerequisites for career qualifi cations.

Effect of Microglia Activation on Dopaminergic Neuronal Injury Induced by Manganese, and Its Possible Mechanism

Manganese (Mn) is an essential trace element. It is known to have various functions, such as participating in enzymatic synthesis, and promoting hematopoiesis. On the other hand, it can cause toxic injury upon excess intake. However, toxic effects and its mechanism on glial cells are unclear. In the present study, we demonstrated that MnCl2 can activate microglia, and that this can cause dopaminergic neuronal injury. Investigation of the underlying mechanisms showed that inducible nitric oxide synthase (iNOS), tumor necrosis factor-α (TNF-α), interleukin-1β (IL-1β) was induced and highly expressed following Mn treatment. Moreover, pretreatment with S-methylisothiourea (SMT. iNOS inhibitor), Mn-induced iNOS expression and dopaminergic neuronal injury were partly reverse. Pretreatment with minocycline (microglia activation inhibitor), Mn-induced activation of microglia and dopaminergic neuronal injury was partly reverse. Taken together, our results showed that Mn can cause microglia activation, which can up-regulate the level of IL-1β, TNF-α and iNOS, and these inflammatory factors can cause dopaminergic neuronal injury. SMT and minocycline prevent Mn-induced dopaminergic neuronal injury.

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.

n-3 polyunsaturated fatty acids inhibit lipopolysaccharide-induced microglial activation and dopaminergic injury in rats.

Increasing evidence indicates that neuroinflammation plays an important role in neurotoxins-induced neurodegenerations. Microglia are a type of glial cells in the brain and play as the first and main form of active immune defense in the central nervous system. Accumulated data suggest that the activation of microglia plays a critical role in neurotoxicities induced by environmental toxicants. So the inhibition of microglia has been proven to be an effective strategy against neurotoxic effects. In the present study, we found that n-3 polyunsaturated fatty acids can inhibit both microglial activation and dopaminergic injury in the substantia nigra of Sprague-Dawley rats induced by lipopolysaccharide, one of the major constituents of the outer membrane of Gram-negative bacteria. Moreover, n-3 polyunsaturated fatty acids inhibited lipopolysaccharide-induced activation of nuclear factor-κB, an important transcription factor involved in microglial activation. Taken together, our results provided the first in vivo evidence that n-3 polyunsaturated fatty acids can inhibit the damage of dopaminergic neurons induced by lipopolysaccharide through their inhibitory effects on nuclear factor-κB-dependent microglial activation.

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.

Acute cold exposure and rewarming enhanced spatial memory and activated the MAPK cascades in the rat brain

Cold is a common stressor that is likely to occur in everyday occupational or leisure time activities. Although there is substantial literature on the effects of stress on memory from behavioral and pharmacologic perspectives, the effects of cold stress on learning and memory were little addressed. The aims of the present work were to investigate the effects of acute cold exposure on Y-maze learning and the activation of cerebral MAPK cascades of rats. We found that the 2-hour cold exposure (-15 degrees C) and a subsequent 30-min rewarming significantly increased the performance of the rats in the Y-maze test. Serum corticosterone (CORT) level was increased after the cold exposure. After a transient reduction following the cold exposure, the P-ERK levels in the hippocampus and PFC drastically increased 30 min later. The levels of P-JNK increased gradually after the cold exposure in all the three brain regions we investigated, but the level of P-p38 only increased in the PFC. The levels of GABAA receptor alpha1 subunit remained unchanged after the cold exposure. Furthermore, the performance of rats treated with cold plus muscimol or bicuculline in the Y-maze test was similar to that of the rats treated with those GABAergic agents alone. These results demonstrated that acute cold exposure and the subsequent rewarming could result in enhanced performance of spatial learning and memory, and the activation of MAPKs in the brain. However, GABAA receptor may not be involved in the acute cold exposure-induced enhancement of memory.

Manganese Induces Tau Hyperphosphorylation through the Activation of ERK MAPK Pathway in PC12 Cells

Manganese has long been known to induce neurological degenerative disorders. Emerging evidence indicates that hyperphosphorylated tau is associated with neurodegenerative diseases, but whether such hyperphosphorylation plays a role in manganese-induced neurotoxicity remains unclear. To fill this gap, we investigated the effects of manganese on tau phosphorylation in PC12 cells. In our present research, treatment of cells with manganese increased the phosphorylation of tau at Ser199, Ser202, Ser396, and Ser404 as detected by Western blot. Moreover, this manganese-induced tau phosphorylation paralleled the activation of extracellular signal-regulated kinase (ERK) mitogen-activated protein kinase (MAPK). The mitogen-activated protein kinase kinase-1 (MEK1) inhibitor PD98059, which inhibits the activation of ERK MAPK, partially attenuated manganese-induced tau hyperphosphorylation and cytotoxicity. Moreover, the activation of ERK MAPK was involved in the activation of glycogen synthase kinase-3β (GSK-3β) kinase, which also contributed to the hyperphosphorylation of tau and the cytotoxicity in PC12 cells induced by manganese. Taken together, we found for the first time that the exposure to manganese can cause the hyperphosphorylation of tau, which may be connected with the activation of ERK MAPK.

Proteasome inhibition is associated with manganese-induced oxidative injury in PC12 cells

Manganese has been known to induce neurological disorders similar to Parkinsons disease. The dysfunction of ubiquitin-proteasome system, a pathway involved in detoxification and targeting of damaged proteins, is connected with Parkinsons disease pathogenesis. Oxidative stress may be involved in Parkinsons disease, and may also be associated with manganese-induced neurotoxicity. In the present study, we determined the effects of manganese chloride on proteasome activity in PC12 cells. Furthermore, we investigated the relationship between oxidative stress and the change of proteasome activity. The proteasome activity of PC12 cells was measured by an ELISA method. Selective oxidative stress parameters, including malondialdehyde and protein carbonyl, were measured in PC12 cells treated with manganese chloride. Cell survival and apoptosis were measured by methyl thiazolyl tetrazolium and terminal transferase-mediated dUTP nick end-labeling. In our research, manganese chloride exposure inhibited the activity of proteasome and induced oxidative stress. Both can be reversed by antioxidant agent N-acetylcysteine. N-acetylcysteine also inhibited the cytotoxicity induced by manganese chloride. In conclusion, our results imply that proteasome inhibition may be associated with manganese-induced cytotoxicity in dopaminergic neurons, which may be connected with oxidative damage.