[Show abstract][Hide abstract] ABSTRACT: The etiological role of dysregulated autophagy in neurodegenerative diseases has been a subject of intense investigation. While manganese (Mn) is known to cause dopaminergic (DAergic) neurodegeneration, it has yet to be determined whether the dysregulation of autophagy plays a role in Mn-induced neuronal injury. In this study, we investigated the effect of Mn on autophagy in a rat model of manganism, a neurodegenerative disease associated with excessive exposure to Mn. After a single intrastriatal injection of Mn, the short- (4-12 h) and long-term (1-28 days) effect of Mn on DAergic neurons and autophagy were examined. Marked reduction in the number of TH-immunoreactive neurons in the substantia nigra pars compacta (SNpc) as well as TH protein expression, and a significant increase of apomorphine-induced rotations were observed in rats after Mn injection. Manganese also induced the down-regulation of dopamine levels and D1 dopamine receptor expression. In addition, autophagy was dysregulated and inhibited, as evidenced by increased number of abnormal lysosomes, decreased protein expression of Beclin1, and decreased ratio of microtubule-associated protein 1 light chain 3 (LC3) II over LC3 I, concomitant with activated mammalian target of rapamycin (mTOR)/p70 ribosomal protein S6 kinase (p70s6k) signaling. In contrast, in the early phase of Mn exposure, the level of autophagy was not be suppressed but compensatorily activated. Although the morphology of the DAergic neuron was intact in the early phase, Mn caused a significant decrease in TH-immunoreactivity and a significant increase in apomorphine-induced rotations in the presence of wortmannin, an inhibitor of autophagy. Taken together, these results demonstrate, for the first time, that autophagy may play a protective role against Mn-induced neuronal damage, whilst dysregulation of autophagy at later phases may mediate DAergic neurodegeneration.
Full-text · Article · Apr 2013 · Neurotoxicity Research
[Show abstract][Hide abstract] ABSTRACT: 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.
Full-text · Article · Jul 2012 · International journal of biological sciences
[Show abstract][Hide abstract] ABSTRACT: 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.
[Show abstract][Hide abstract] ABSTRACT: 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.
Preview · Article · Oct 2010 · Toxicological Sciences
[Show abstract][Hide abstract] ABSTRACT: Mitochondrial impairment is hypothesized to contribute to cell injury during cold stress. Mitochondria fission and fusion are closely related in the function of the mitochondria, but the precise mechanisms whereby these processes regulate cell injury during cold stress remain to be determined. HEK293 cells were cultured in a cold environment (4.0+/-0.1 degrees C) for 2, 4, 8, or 12h. Western blot analyses showed that these cells expressed decreased fission-related protein Drp1 and increased fusion-related protein Mfn2 at 4h; meanwhile, electron microscopy analysis revealed large and long mitochondrial morphology within these cells, indicating increased mitochondrial fusion. With silencing of Mfn2 but not of Mfn1 by siRNA promoted cold-stress-induced cell death with decreased ATP production in HEK293 cells. Our results show that increased expression of Mfn2 and mitochondrial fusion are important for mitochondrial function as well as cell survival during cold stress. These findings have important implications for understanding the mechanisms of mitochondrial fusion and fission in cold-stress-induced cell injury.
No preview · Article · Jun 2010 · Biochemical and Biophysical Research Communications
[Show abstract][Hide abstract] ABSTRACT: EB1089 exhibits a high level of antiproliferative activity against various tumors. However, it is not known whether the mechanism of EB1089 induced the growth inhibition in human hepatic-carcinoma. Here we found that EB1089 significantly reduced cell growth in human hepatoma cells (Hep-G2) and blocked Hep-G2 cell-associated tumor formation in nude mice. The growth inhibition was linked to cell cycle G1 phase arrest by the accumulation of p27 and a reduction of Skp2. Knockdown of Skp2 reversed the p27 induction and G1 arrest. Taken together, our data indicate that EB1089 inhibitory activity is associated with alteration of cell cycle checkpoints through Skp2-dependent p27 induction in Hep-G2 cells.
No preview · Article · Feb 2009 · Cancer Investigation
[Show abstract][Hide abstract] ABSTRACT: Experimental and occupational exposure to methyl tert-butyl ether (MTBE) has been reported to induce neurotoxicological and neurobehavioral effects, such as headache, nausea, dizziness, and disorientation, etc. However, the molecular mechanisms involved in MTBE-induced neurotoxicity are still not well understood. In the present study, we investigated the effects of MTBE on spatial memory and the expression and function of GABA(A) receptor in the hippocampus. Our results demonstrated that intraventricular injection of MTBE impaired the performance of the rats in a Morris water maze task, and significantly increased the expression of GABA(A) receptor alpha1 subunit in the hippocampus. The phosphorylation of ERK1/2 decreased after the MTBE injection. Furthermore, the decreased ability of learning and the reduction of phosphorylated ERK1/2 level of the MTBE-treated rats was partly reversed by bicuculline injected 30 min before the training. These results suggested that MTBE exposure could result in impaired spatial memory. GABA(A) receptor may play an important role in the MTBE-induced impairment of learning and memory by regulating the phosphorylation of ERK in the hippocampus.
No preview · Article · Feb 2009 · Toxicology and Applied Pharmacology
[Show abstract][Hide abstract] ABSTRACT: Manganese has been known to induce neurological disorders similar to Parkinson's disease. The dysfunction of ubiquitin-proteasome system, a pathway involved in detoxification and targeting of damaged proteins, is connected with Parkinson's disease pathogenesis. Oxidative stress may be involved in Parkinson's 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.