Stress hormone potentiates Zn 2+ -induced neurotoxicity via TRPM7 channel in dopaminergic neuron

High Magnesium Promotes the Recovery of Binocular Vision from Amblyopia via TRPM7

Abnormal visual experience during the critical period can cause deficits in visual function, such as amblyopia. High magnesium (Mg2+) supplementary can restore ocular dominance (OD) plasticity, which promotes the recovery of amblyopic eye acuity in adults. However, it remains unsolved whether Mg2+ could recover binocular vision in amblyopic adults and what the molecular mechanism is for the recovery. We found that in addition to the recovery of OD plasticity, binocular integration can be restored under the treatment of high Mg2+ in amblyopic mice. Behaviorally, Mg2+-treated amblyopic mice showed better depth perception. Moreover, the effect of high Mg2+ can be suppressed with transient receptor potential melastatin-like 7 (TRPM7) knockdown. Collectively, our results demonstrate that high Mg2+ could restore binocular visual functions from amblyopia. TRPM7 is required for the restoration of plasticity in the visual cortex after high Mg2+ treatment, which can provide possible clinical applications for future research and treatment of amblyopia.

The effects of neuronal cell differentiation on TRPM7, TRPM8 and TRPV1 channels in the model of Parkinson's disease

Transient Receptor Potential Melastatin-like 7 (TRPM7), Transient Receptor Potential Melastatin-like 8 (TRPM8) and Transient Receptor Potential Vanilloid-like 1 (TRPV1) channels are expressed in neurological tissues such as brain cortex, dorsal root ganglion and hippocampal neurons and involved in several neurological diseases. The SH-SY5Y neuronal cell line is frequently used as a cellular model of neurodegenerative diseases including Parkinson's disease. The differentiated SH-SY5Y cells have much neuronal structure, function and exaggerated neuronal marker expression. However, we have less data about how differentiation induces TRP channel expression and how TRP channels have a role in cellular functions in Parkinson's disease model in SH-SY5Y cells. Hence, we aimed to investigate the effects of differentiation phenomena on TRPM7, TRPM8 and TRPV1 cation channel expression and related Ca²⁺ signaling. We also made some other analysis to elucidate TRP channels' function in MPP induced apoptosis, mitochondrial membrane potential levels, intracellular reactive oxygen species production, caspase 3 and caspase 9 enzyme activities in differentiated or undifferentiated SH-SY5Y neuronal cells. Herein we concluded that TRPM7, TRPM8 and TRPV1 cation channels have pivotal effects on differentiation and MPP induced Parkinson's disease model in SH-SY5Y cells.

New insight into Parkinson's disease pathogenesis from reactive oxygen species-mediated extracellular Zn2+ influx

BACKGROUND

Parkinson's disease (PD) is the common neurodegenerative disorder in the elderly characterized by motor symptoms such as tremors, which is caused by selective loss of nigral dopaminergic neurons. Oxidative stress induced by the auto-oxidation of dopamine has been implicated as a key cause of the selective loss of dopaminergic neurons.

METHODS

To understand the selective loss of nigral dopaminergic neurons, the PD pathogenesis is reviewed focused on paraquat (PQ) and 6-hydroxydopamine (6-OHDA)-induced PD in rats.

RESULTS

Reactive oxygen species (ROS), which are produced by PQ and 6-OHDA, are retrogradely transported to presynaptic glutamatergic neuron terminals. ROS activate presynaptic transient receptor potential melastatin 2 (TRPM2) cation channels and induce extracellular glutamate accumulation in the substantia nigra pars compacta (SNpc), followed by age-related intracellular Zn2+ dysregulation. Loss of nigral dopaminergic neurons is accelerated by age-related intracellular Zn2+ dysregulation in the SNpc of rat PD models. The intracellular Zn2+ dysregulation in nigral dopaminergic neurons is linked with the rapid influx of extracellular Zn2+ via postsynaptic AMPA receptor activation, suggesting that PQ- and 6-OHDA-induced pathogenesis is linked with age-related intracellular Zn2+ dysregulation in the SNpc. Postsynaptic TRPM2 channels may be also involved in intracellular Zn2+ dysregulation in the SNpc.

CONCLUSION

A novel mechanism of nigral dopaminergic degeneration, in which ROS induce rapid intracellular Zn2+ dysregulation, figures out the PD pathogenesis induced by PQ and 6-OHDA in rats. This review deals with new insight into PD pathogenesis from ROS-mediated extracellular Zn2+ influx and its proposed defense strategy.

Screening a specific Zn(ii)-binding peptide for improving the cognitive decline of Alzheimer's disease in APP/PS1 transgenic mice by inhibiting Zn2+-mediated amyloid protein aggregation and neurotoxicity

Zn2+ has been implicated in the progression of Alzheimer's disease (AD), as amyloid-β protein (Aβ) aggregation and neurotoxicity are mediated by zinc ions. Therefore, development of metal chelators for inhibiting and regulating metal-triggered Aβ aggregation has received attention as a strategy for treating AD. Here, we used an approach based on phage display to screen for a Zn(ii)-binding peptide that specifically blocks Zn-triggered Aβ aggregation. A fixed Zn(ii) resin was prepared using Ni-IDA affinity resin, and the target Zn(ii) was screened by interaction with a heptapeptide phage library. After negative biopanning against IDA and four rounds of positive biopanning against Zn(ii), high specificity Zn(ii)-binding phages were obtained. Through DNA sequencing and ELISA, 15 sets of Zn(ii)-binding peptides with high histidine contents were identified. We chose a highly specific peptide against Zn(ii) with the sequence of H-M-Q-T-N-H-H, and its abilities to chelate Zn2+ and inhibit Zn2+-mediated Aβ aggregation were assessed in vitro. We loaded the Zn(ii)-binding peptide onto PEG-modified chitosan nanoparticles (NPs) to improve the stability and the bioavailability of the Zn(ii) binding peptide. PEG-modified chitosan NPs loaded with Zn(ii)-binding peptide (PEG/PZn-CS NPs) reduced Zn2+ concentrations and Aβ secretion in mouse neuroblastoma (N)2a cells stably over-expressing the APP Swedish mutation (N2aswe). Zn2+-Induced neurotoxicity, oxidative stress, and apoptosis were attenuated by PEG/PZn-CS NPs. Intranasal administration of PEG/PZn-CS NPs improved the cognitive ability of APPswe/PS1d9 (APP/PS1) double-transgenic mice and reduced Aβ plaques in the mouse brain. This study indicated that a Zn(ii)-binding peptide and its NPs have promise as a potential anti-AD agent.

Role of the chanzyme TRPM7 in the nervous system in health and disease

The channel kinase (chanzyme) transient receptor potential melastatin-like 7 (TRPM7) has a unique dual protein structure composed of an ion channel with an α-kinase domain on its C-terminus. In the nervous system, under physiological conditions, TRPM7 contributes to critical neurobiological processes ranging from synaptic transmission to cognitive functions. Following certain pathological triggers, TRPM7 mediates neurotoxicity, neuro-injuries, and neuronal death. Here, we summarize the current knowledge of TRPM7 functions in neuronal systems in health and disease. The molecular mechanisms by which this chanzyme might regulate synaptic and cognitive functions are discussed. We also discuss the lack of knowledge regarding the molecular mechanisms responsible for turning TRPM7 into "a vicious tool" that mediates neuronal death following certain pathological triggers. Some synthetic and natural pharmacological modulators of the TRPM7 channel and its α-kinase are reviewed. We suggest that based on current knowledge, we should reshape our thinking regarding the implications of TRPM7 in neurological and neurodegenerative disorders. Moreover, we propose a paradigm shift concerning the targeting of TRPM7 as a therapeutic approach for treating certain neurological diseases. We agree that TRPM7 overexpression or overactivation may mediate neurodegenerative processes following certain triggers. However, TRPM7 dysfunction and/or downregulation might also be among the pathological changes leading to neurodegeneration. Consequently, further investigations are required before we decide whether blocking or activating the chanzyme is the correct therapeutic approach to treat certain neurological and/or neurodegenerative diseases.

Extracellular Zn2+ Influx into Nigral Dopaminergic Neurons Plays a Key Role for Pathogenesis of 6-Hydroxydopamine-Induced Parkinson's Disease in Rats

Parkinson's disease (PD) is a progressive neurological disease characterized by a selective loss of nigrostriatal dopaminergic neurons. The exact cause of the neuronal loss remains unclear. Here, we report a unique mechanism of nigrostriatal dopaminergic neurodegeneration, in which extracellular Zn²⁺ influx plays a key role for PD pathogenesis induced with 6-hydroxydopamine (6-OHDA) in rats. 6-OHDA rapidly increased intracellular Zn²⁺ only in the substantia nigra pars compacta (SNpc) of brain slices and this increase was blocked in the presence of CaEDTA, an extracellular Zn²⁺ chelator, and 6-cyano-7-nitroquinoxaline-2,3-dione (CNQX), an α-amino-3-hydroxy-5-methyl-4-isoxazolepropionate (AMPA) receptor antagonist, indicating that 6-OHDA rapidly increases extracellular Zn²⁺ influx via AMPA receptor activation in the SNpc. Extracellular Zn²⁺ concentration was decreased under in vivo SNpc perfusion with 6-OHDA and this decrease was blocked by co-perfusion with CNQX, supporting 6-OHDA-induced Zn²⁺ influx via AMPA receptor activation in the SNpc. Interestingly, both 6-OHDA-induced loss of nigrostriatal dopaminergic neurons and turning behavior to apomorphine were ameliorated by co-injection of intracellular Zn²⁺ chelators, i.e., ZnAF-2DA and N,N,N',N'-Tetrakis(2-pyridylmethyl)ethylenediamine (TPEN). Co-injection of TPEN into the SNpc blocked 6-OHDA-induced increase in intracellular Zn²⁺ but not in intracellular Ca²⁺. These results suggest that the rapid influx of extracellular Zn²⁺ into dopaminergic neurons via AMPA receptor activation in the SNpc induces nigrostriatal dopaminergic neurodegeneration, resulting in 6-OHDA-induced PD in rats.

Neurotoxicity of Zinc

Zinc-induced neurotoxicity has been shown to play a role in neuronal damage and death associated with traumatic brain injury, stroke, seizures, and neurodegenerative diseases. During normal firing of "zinc-ergic" neurons, vesicular free zinc is released into the synaptic cleft where it modulates a number of postsynaptic neuronal receptors. However, excess zinc, released after injury or disease, leads to excitotoxic neuronal death. The mechanisms of zinc-mediated neurotoxicity appear to include not only neuronal signaling but also regulation of mitochondrial function and energy production, as well as other mechanisms such as aggregation of amyloid beta peptides in Alzheimer's disease. However, recent data have raised questions about some of our long-standing assumptions about the mechanisms of zinc in neurotoxicity. Thus, this review explores the most recent published findings and highlights the current mechanistic controversies.

SLC41A1 and TRPM7 in magnesium homeostasis and genetic risk for Parkinson's disease

Parkinson's disease (PD) is a neurodegenerative disorder of the central nervous system with a clinically heterogeneous presentation that includes progressive loss of dopaminergic (DA) neurons in the substantia nigra. A minority of PD cases are familial and are caused by mutations in single genes. Most cases, however, are idiopathic PD, a complex multifactorial disorder with environmental and genetic contributors to etiology. Here, we first briefly summarize published evidence that among environmental contributors is dietary deficiency of magnesium. We then review genetic data suggesting that mutations in genes encoding two proteins contributing to cellular magnesium homeostasis confer risk for PD or other Parkinsonian conditions. First, the gene encoding magnesium transporter SLC41A1 is, among others, a candidate for the causative gene in the PARK16 locus where variation is associated with risk for idiopathic Parkinsonian disease. Studies of the function of SLC41A1 in animal models are needed to test whether this protein has a role in maintenance of dopaminergic neurons. Second, in a small study, a hypomorphic variant of TRPM7, a magnesium-permeable channel, was over-represented in cases of amyotrophic lateral sclerosis/ Parkinson dementia complex versus controls from the same ethnic group. Although this association was not detected in a second study, in zebrafish Trpm7 is necessary for terminal differentiation and reduction of toxin-sensitivity in dopaminergic neurons. Overall, epidemiological results support the possibility that mutations in genes relevant to magnesium homeostasis would alter PD risk, but deeper genetic analyses of PD patients are necessary to confirm whether SLC41A1 and TRPM7 are among such genes.

Effect of crowding, temperature and age on glia activation and dopaminergic neurotoxicity induced by MDMA in the mouse brain

3,4-methylenedyoxymethamphetamine (MDMA or "ecstasy"), a recreational drug of abuse, can induce glia activation and dopaminergic neurotoxicity. Since MDMA is often consumed in crowded environments featuring high temperatures, we studied how these factors influenced glia activation and dopaminergic neurotoxicity induced by MDMA. C57BL/6J adolescent (4 weeks old) and adult (12 weeks old) mice received MDMA (4×20mg/kg) in different conditions: 1) while kept 1, 5, or 10×cage at room temperature (21°C); 2) while kept 5×cage at either room (21°C) or high (27°C) temperature. After the last MDMA administration, immunohistochemistry was performed in the caudate-putamen for CD11b and GFAP, to mark microglia and astroglia, and in the substantia nigra pars compacta for tyrosine hydroxylase, to mark dopaminergic neurons. MDMA induced glia activation and dopaminergic neurotoxicity, compared with vehicle administration. Crowding (5 or 10 mice×cage) amplified MDMA-induced glia activation (in adult and adolescent mice) and dopaminergic neurotoxicity (in adolescent mice). Conversely, exposure to a high environmental temperature (27°C) potentiated MDMA-induced glia activation in adult and adolescent mice kept 5×cage, but not dopaminergic neurotoxicity. Crowding and exposure to a high environmental temperature amplified MDMA-induced hyperthermia, and a positive correlation between body temperature and activation of either microglia or astroglia was found in adult and adolescent mice. These results provide further evidence that the administration setting influences the noxious effects of MDMA in the mouse brain. However, while crowding amplifies both glia activation and dopaminergic neurotoxicity, a high environmental temperature exacerbates glia activation only.