Insight into cognitive decline from Zn 2+ dynamics through extracellular signaling of glutamate and glucocorticoids

Intracellular Zn2+ promotes extracellular matrix remodeling in dexamethasone-treated trabecular meshwork

Given the widespread application of glucocorticoids in ophthalmology, the associated elevation of intraocular pressure (IOP) has long been a vexing concern for clinicians, yet the underlying mechanisms remain inconclusive. Much of the discussion focuses on the extracellular matrix (ECM) of trabecular meshwork (TM). It is widely agreed that glucocorticoids impact the expression of matrix metalloproteinases (MMPs), leading to ECM deposition. Since Zn2+ is vital for MMPs, we explored its role in ECM alterations induced by dexamethasone (DEX). Our study revealed that in human TM cells treated with DEX, the level of intracellular Zn2+ significantly decreased, accompanied by impaired extracellular Zn2+ uptake. This correlated with changes in several Zrt-, Irt-related proteins (ZIPs) and metallothionein. ZIP8 knockdown impaired extracellular Zn2+ uptake, but Zn2+ chelation did not affect ZIP8 expression. Resembling DEX's effects, chelation of Zn2+ decreased MMP2 expression, increased the deposition of ECM proteins, and induced structural disarray of ECM. Conversely, supplementation of exogenous Zn2+ in DEX-treated cells ameliorated these outcomes. Notably, dietary zinc supplementation in mice significantly reduced DEX-induced IOP elevation and collagen content in TM, thereby rescuing the visual function of the mice. These findings underscore zinc's pivotal role in ECM regulation, providing a novel perspective on the pathogenesis of glaucoma.NEW & NOTEWORTHY Our study explores zinc's pivotal role in mitigating extracellular matrix dysregulation in the trabecular meshwork and glucocorticoid-induced ocular hypertension. We found that in human trabecular meshwork cells treated with dexamethasone, intracellular Zn2+ significantly decreased, accompanied by impaired extracellular Zn2+ uptake. Zinc supplementation rescues visual function by modulating extracellular matrix proteins and lowering intraocular pressure, offering a direction for further exploration in glaucoma management.

Deconstruction of Neurotrypsin Reveals a Multi-factorially Regulated Activity Affecting Myotube Formation and Neuronal Excitability

Neurotrypsin (NT) is a highly specific nervous system multi-domain serine protease best known for its selective processing of the potent synaptic organizer agrin. Its enzymatic activity is thought to influence processes of synaptic plasticity, with its deregulation causing accelerated neuromuscular junction (NMJ) degeneration or contributing to forms of mental retardation. These biological effects are likely to stem from NT-based regulation of agrin signaling. However, dissecting the exact biological implications of NT-agrin interplay is difficult, due to the scarce molecular detail regarding NT activity and NT-agrin interactions. We developed a strategy to reliably produce and purify a catalytically competent engineered variant of NT called "NT-mini" and a library of C-terminal agrin fragments, with which we performed a thorough biochemical and biophysical characterization of NT enzyme functionality. We studied the regulatory effects of calcium ions and heparin, identified NT's heparin-binding domain, and discovered how zinc ions induce modulation of enzymatic activity. Additionally, we investigated myotube differentiation and hippocampal neuron excitability, evidencing a dose-dependent increase in neuronal activity alongside a negative impact on myoblast fusion when using the active NT enzyme. Collectively, our results provide in vitro and cellular foundations to unravel the molecular underpinnings and biological significance of NT-agrin interactions.

Behavioural multigenerational effects induced by the administration of very low doses of zinc during pregnancy, lactation, and prepuberal period in the rat

In studies from this laboratory, the chronic administration of ZnTe during pregnancy, lactation, and prepuberal stages of litter (F₁ generation) modified the behavioral patterns of motivated exploration, lateralized exploration, social activity, and survival responses of maturing rats. To determine whether these affected behaviors would extend to the next generation, F₁ litter rats previously exposed to tellurium (Te) up to 30-day-old were left at rest with no further treatment up to 90-day-old. Then, F₁ female rats were mated with normal untreated male rats, and in the next generation (F₂), the litter rats at 30-day-old preserved the modified behaviors previously observed in their parents. The study revealed that Te effects were intergenerational. Here, considering that ZnTe was used in the previous study and that Zn ion has many physiological functions in the cell, experiments were conducted to elucidate if Zn would have an intergenerational effect similar to Te. Working with the same experimental setup as in the previous study but using ZnCl₂ instead of ZnTe, results revealed that none of the behavioral responses studied were affected by the F₁ generation. However, in the F₂ generation, lateralized exploration and survival behavior were inhibited, suggesting that Zn also has an intergenerational effect.

Disruption of zinc transporter ZnT3 transcriptional activity and synaptic vesicular zinc in the brain of Huntington's disease transgenic mouse

Background

Huntington’s disease (HD) is a neurodegenerative disease that involves a complex combination of psychiatric, cognitive and motor impairments. Synaptic dysfunction has been implicated in HD pathogenesis. However, the mechanisms have not been clearly delineated. Synaptic vesicular zinc is closely linked to modulating synaptic transmission and maintaining cognitive ability. It is significant to assess zinc homeostasis for further revealing the pathogenesis of synaptic dysfunction and cognitive impairment in HD.

Results

Histochemical staining by autometallography indicated that synaptic vesicular zinc was decreased in the hippocampus, cortex and striatum of N171-82Q HD transgenic mice. Analyses by immunohistochemistry, Western blot and RT-PCR found that the expression of zinc transporter 3 (ZnT3) required for transport of zinc into synaptic vesicles was obviously reduced in these three brain regions of the HD mice aged from 14 to 20 weeks  and  BHK  cells  expressing  mutant  huntingtin. Significantly, dual-luciferase reporter gene and chromatin immunoprecipitation assays demonstrated that transcription factor Sp1 could activate ZnT3 transcription via its binding to the GC boxes in ZnT3 promoter. Moreover, mutant huntingtin was found to inhibit the binding of Sp1 to the promoter of ZnT3 and down-regulate ZnT3 expression, and the decline in ZnT3 expression could be ameliorated through overexpression of Sp1.

Conclusions

This is first study to reveal a significant loss of synaptic vesicular zinc and a decline in ZnT3 transcriptional activity in the HD transgenic mice. Our work sheds a novel mechanistic insight into pathogenesis of HD that mutant huntingtin down-regulates expression of ZnT3 through inhibiting binding of Sp1 to the promoter of ZnT3 gene, causing disruption of synaptic vesicular zinc homeostasis. Disrupted vesicular zinc ultimately leads to early synaptic dysfunction and cognitive deficits in HD. It is also suggested that maintaining normal synaptic vesicular zinc concentration is a potential therapeutic strategy for HD.

The S100B Alarmin Is a Dual-Function Chaperone Suppressing Amyloid-β Oligomerization through Combined Zinc Chelation and Inhibition of Protein Aggregation

Amyloid beta (Aβ) aggregation and imbalance of metal ions are major hallmarks of Alzheimer's disease (AD). Indeed, amyloid plaques of AD patients are enriched in zinc and Aβ42, and AD related-cognitive decline is dependent on extracellular zinc concentration. In vitro, zinc induces the formation of polymorphic Aβ42 oligomers that delay the formation of amyloid fibers at the expense of increased cellular toxicity. S100B is an inflammatory alarmin and one of the most abundant proteins in the brain and is upregulated in AD and associated with amyloid plaques, where it exerts extracellular functions. Recent findings have uncovered novel neuroprotective functions for S100B as a suppressor of Aβ aggregation and toxicity and in the regulation of zinc homeostasis in neurons. Here we combine biophysical and kinetic approaches to demonstrate that such S100B protective functions converge, making the protein a dual-function chaperone capable of suppressing the formation of toxic Aβ oligomers through both chelation of zinc and inhibition of protein aggregation. From detailed kinetic analysis of Aβ42 aggregation monitoring ThT fluorescence, we show that substoichiometric S100B prevents the formation of toxic off-pathway oligomers that are formed by monomeric Aβ42 in the presence of zinc. Indeed, S100B is effective when added during the lag and transition phases of Aβ42 aggregation, and its action under these circumstances results from its ability to buffer zinc, as it perfectly mimics the effect obtained with the chelating agent EDTA. Further, bioimaging analysis combining transmission electron microscopy and atomic force microscopy confirms that catalytic amounts of S100B partly revert the formation of toxic oligomers. Taken together these results indicate a new role for S100B as a dual chaperone whose distinct functions are interrelated and depend on the relative levels of zinc, S100B, and Aβ, which dynamically evolve during AD.

Two similar Schiff-base receptor based quinoline derivate: Highly selective fluorescent probe for Zn(II)

As is known, Zn²⁺ plays a vital role in a variety of biological processes but excessive exposure of Zn²⁺ to human beings can cause toxicity, inducing a series of overt poisoning symptoms and neurodegenerative disorders. Thus, we designed and synthesized two quinoline-derived Schiff-bases HL₁ and HL₂, and investigated the fluorescence emission responses of these two Schiff-bases to various metal ions. A significant enhancement in fluorescence emission band centered at 450 nm was observed in the ethanolic solution of HL₁ with addition of Zn²⁺, while remarkably lower fluorescence emission enhancement was obtained in the case of HL₂ in which one methyl group was introduced to the azomethine carbon. In addition, HL₁ showed good selectivity and high sensitivity towards Zn²⁺ in the existence of other various interfering metal ions, and the reversibility and regeneration of HL₁ were also perfect for extending its applications in environmental and biological systems. Therefore, HL₁ could be identified as a fluorescent probe for sensing Zn²⁺ environmentally and biologically.

Morphine-element interactions - The influence of selected chemical elements on neural pathways associated with addiction

Addiction is a pressing social problem worldwide and opioid dependence can be considered the strongest and most difficult addiction to treat. Mesolimbic and mesocortical dopaminergic pathways play an important role in modulation of cognitive processes and decision making and, therefore, changes in dopamine metabolism are considered the central basis for the development of dependence. Disturbances caused by excesses or deficiency of certain elements have a significant impact on the functioning of the central nervous system (CNS) both in physiological conditions and in pathology and can affect the cerebral reward system and therefore, may modulate processes associated with the development of addiction. In this paper we review the mechanisms of interactions between morphine and zinc, manganese, chromium, cadmium, lead, fluoride, their impact on neural pathways associated with addiction, and on antinociception and morphine tolerance and dependence.

S100A6 and Its Brain Ligands in Neurodegenerative Disorders

The S100A6 protein is present in different mammalian cells and tissues including the brain. It binds Ca²⁺ and Zn²⁺ and interacts with many target proteins/ligands. The best characterized ligands of S100A6, expressed at high level in the brain, include CacyBP/SIP and Sgt1. Research concerning the functional role of S100A6 and these two ligands indicates that they are involved in various signaling pathways that regulate cell proliferation, differentiation, cytoskeletal organization, and others. In this review, we focused on the expression/localization of these proteins in the brain and on their possible role in neurodegenerative diseases. Published results demonstrate that S100A6, CacyBP/SIP, and Sgt1 are expressed in various brain structures and in the spinal cord and can be found in different cell types including neurons and astrocytes. When it comes to their possible involvement in nervous system pathology, it is evident that their expression/level and/or subcellular localization is changed when compared to normal conditions. Among diseases in which such changes have been observed are Alzheimer’s disease (AD), amyotrophic lateral sclerosis (ALS), epileptogenesis, Parkinson’s disease (PD), Huntington’s disease (HD), and others.

A novel dual-function probe for recognition of Zn2+ and Al3+ and its application in real samples

A dual-function probe NAHH based on naphthalene was synthesized and characterized. Based on the combination effects derived from the inhabitation of photo-induced electron transfer (PET) and CN isomerization, probe NAHH achieved in the recognition of Zn2+ and Al3+ both through obvious fluorescence enhancement and color changes detected by naked eye, respectively. Probe NAHH showed high sensitivity with the limit of detection as low as 3.02 × 10-7 M for Zn2+ and 7.55 × 10-8 M for Al3+, indicated the capability of probe NAHH in trace detection for Zn2+ and Al3+. The binding ratio of NAHH with Zn2+ and Al3+ were all 1:1 determined by Job plot, and the corresponding association constant was calculated as 8.48 × 104 M-1 and 4.45 × 105 M-1, respectively. The mechanism was further confirmed by FT-IR, 1H NMR titration and ESI-MS analysis. Furthermore, probe NAHH was successfully applied in logic gate construction and the detection of Zn2+ and Al3+ in Songhua River and test stripe. Fluorescence imaging experiments confirmed that NAHH could be used to monitor Zn2+ in plant root.

S100 family proteins in inflammation and beyond

The S100 family proteins possess a variety of intracellular and extracellular functions. They interact with multiple receptors and signal transducers to regulate pathways that govern inflammation, cell differentiation, proliferation, energy metabolism, apoptosis, calcium homeostasis, cell cytoskeleton and microbial resistance. S100 proteins are also emerging as novel diagnostic markers for identifying and monitoring various diseases. Strategies aimed at targeting S100-mediated signaling pathways hold a great potential in developing novel therapeutics for multiple diseases. In this chapter, we aim to summarize the current knowledge about the role of S100 family proteins in health and disease with a major focus on their role in inflammatory conditions.

S100 Proteins in Alzheimer's Disease

S100 proteins are calcium-binding proteins that regulate several processes associated with Alzheimer's disease (AD) but whose contribution and direct involvement in disease pathophysiology remains to be fully established. Due to neuroinflammation in AD patients, the levels of several S100 proteins are increased in the brain and some S100s play roles related to the processing of the amyloid precursor protein, regulation of amyloid beta peptide (Aβ) levels and Tau phosphorylation. S100 proteins are found associated with protein inclusions, either within plaques or as isolated S100-positive puncta, which suggests an active role in the formation of amyloid aggregates. Indeed, interactions between S100 proteins and aggregating Aβ indicate regulatory roles over the aggregation process, which may either delay or aggravate aggregation, depending on disease stage and relative S100 and Aβ levels. Additionally, S100s are also known to influence AD-related signaling pathways and levels of other cytokines. Recent evidence also suggests that metal-ligation by S100 proteins influences trace metal homeostasis in the brain, particularly of zinc, which is also a major deregulated process in AD. Altogether, this evidence strongly suggests a role of S100 proteins as key players in several AD-linked physiopathological processes, which we discuss in this review.

The redox biology of redox-inert zinc ions

Zinc(II) ions are redox-inert in biology. Yet, their interaction with sulfur of cysteine in cellular proteins can confer ligand-centered redox activity on zinc coordination sites, control protein functions, and generate signalling zinc ions as potent effectors of many cellular processes. The specificity and relative high affinity of binding sites for zinc allow regulation in redox biology, free radical biology, and the biology of reactive species. Understanding the role of zinc in these areas of biology requires an understanding of how cellular Zn²⁺ is homeostatically controlled and can serve as a regulatory ion in addition to Ca²⁺, albeit at much lower concentrations. A rather complex system of dozens of transporters and metallothioneins buffer the relatively high (hundreds of micromolar) total cellular zinc concentrations in such a way that the available zinc ion concentrations are only picomolar but can fluctuate in signalling. The proteins targeted by Zn²⁺ transients include enzymes controlling phosphorylation and redox signalling pathways. Networks of regulatory functions of zinc integrate gene expression and metabolic and signalling pathways at several hierarchical levels. They affect enzymatic catalysis, protein structure and protein-protein/biomolecular interactions and add to the already impressive number of catalytic and structural functions of zinc in an estimated three thousand human zinc proteins. The effects of zinc on redox biology have adduced evidence that zinc is an antioxidant. Without further qualifications, this notion is misleading and prevents a true understanding of the roles of zinc in biology. Its antioxidant-like effects are indirect and expressed only in certain conditions because a lack of zinc and too much zinc have pro-oxidant effects. Teasing apart these functions based on quantitative considerations of homeostatic control of cellular zinc is critical because opposite consequences are observed depending on the concentrations of zinc: pro- or anti-apoptotic, pro- or anti-inflammatory and cytoprotective or cytotoxic. The article provides a biochemical basis for the links between redox and zinc biology and discusses why zinc has pleiotropic functions. Perturbation of zinc metabolism is a consequence of conditions of redox stress. Zinc deficiency, either nutritional or conditioned, and cellular zinc overload cause oxidative stress. Thus, there is causation in the relationship between zinc metabolism and the many diseases associated with oxidative stress.

Is Vulnerability of the Dentate Gyrus to Aging and Amyloid-β1-42 Neurotoxicity Linked with Modified Extracellular Zn2+ Dynamics?

The basal levels of extracellular Zn²⁺ are in the range of low nanomolar concentrations in the hippocampus and perhaps increase age-dependently. Extracellular Zn²⁺ dynamics is critical for cognitive activity and excess influx of extracellular Zn²⁺ into hippocampal neurons is a known cause of cognitive decline. The dentate gyrus is vulnerable to aging in the hippocampus and affected in the early stage of Alzheimer's disease (AD). The reasons remain unclear. Neurogenesis-related apoptosis may induce non-specific neuronal depolarization by efflux of intracellular K⁺ in the dentate gyrus and be markedly increased along with aging. Extracellular Zn²⁺ influx into dentate granule cells via high K⁺-induced perforant pathway excitation leads to cognitive decline. Modified extracellular Zn²⁺ dynamics in the dentate gyrus of aged rats is linked with vulnerability to cognitive decline. Amyloid-β_1-42 (Aβ_1-42) is a causative candidate for AD pathogenesis. When Aβ_1-42 concentration reaches picomolar in the extracellular compartment in the dentate gyrus, Zn-Aβ_1-42 is formed in the extracellular compartment and rapidly taken up into dentate granule cells, followed by Aβ_1-42-induced cognitive decline that is due to Zn²⁺ released from Aβ_1-42, suggesting that dentate granule cells are sensitive to extracellular Zn²⁺-dependent Aβ_1-42 toxicity. This paper deals with proposed vulnerability of the dentate gyrus to aging and Aβ_1-42 neurotoxicity.

Blockade of Rapid Influx of Extracellular Zn2+ into Nigral Dopaminergic Neurons Overcomes Paraquat-Induced Parkinson's Disease in Rats

The herbicide paraquat (PQ) has been reported to enhance the risk of developing Parkinson's disease (PD) from epidemiological studies. PQ-induced reactive oxygen species (ROS) are linked with a selective loss of nigrostriatal dopaminergic neurons. Here, we first report a unique mechanism of nigrostriatal dopaminergic degeneration, in which rapid intracellular Zn²⁺ dysregulation via PQ-induced ROS production causes PD in rats. When the substantia nigra pars compacta (SNpc) of rats was perfused with PQ, extracellular concentrations of glutamate and Zn²⁺ were increased and decreased, respectively, in the SNpc. These changes were ameliorated by co-perfusion with Trolox, an antioxidative agent. In in vitro slice experiments, PQ rapidly increased extracellular Zn²⁺ influx via AMPA receptor activation. Both loss of nigrostriatal dopaminergic neurons and increase in turning behavior in response to apomorphine were markedly reduced by coinjection of PQ and intracellular Zn²⁺ chelator, i.e., ZnAF-2DA into the SNpc. Furthermore, loss of nigrostriatal dopaminergic neurons induced with a low dose of PQ, which did not induce any behavioral abnormality, was completely blocked by coinjection of ZnAF-2DA. The present study indicates that rapid influx of extracellular Zn²⁺ into dopaminergic neurons via AMPA receptor activation, which is initially induced by PQ-mediated ROS production in the SNpc, induces nigrostriatal dopaminergic degeneration, resulting in PQ-induced PD in rats. Intracellular Zn²⁺ dysregulation in dopaminergic neurons is the cause of PQ-induced pathogenesis in the SNpc, and the block of intracellular Zn²⁺ toxicity leads to defending PQ-induced pathogenesis.

AMPA-induced extracellular Zn2+ influx into nigral dopaminergic neurons causes movement disorder in rats

On the basis of the findings that the rapid influx of extracellular Zn²⁺ into nigral dopaminergic neurons causes dopaminergic neurodegeneration, here we report that AMPA causes movement disorder in rats. AMPA markedly increased turning behavior in response to apomorphine 1 and 2 weeks after AMPA injection into the substantia nigra pars compacta (SNpc), while AMPA-induced movement disorder was suppressed by co-injection of intracellular Zn²⁺ chelators, i.e., ZnAF-2DA and TPEN, suggesting that AMPA-induced movement disorder is due to intracellular Zn²⁺ dysregulation. Furthermore, AMPA markedly induced loss of nigrostriatal dopaminergic neurons 2 weeks after AMPA injection into the SNpc, while AMPA-induced neurodegeneration was also suppressed in the SNpc and the striatum by co-injection of ZnAF-2DA and TPEN. AMPA rapidly increased nigral intracellular Zn²⁺ after AMPA injection into the SNpc and this increase was blocked by co-injection of TPEN. These results indicate that AMPA receptor activation rapidly increases influx of extracellular Zn²⁺ into nigral dopaminergic neurons and causes nigrostriatal dopaminergic neurodegeneration, resulting in movement disorder in rats. The evidence that AMPA-induced intracellular Zn²⁺ dysregulation causes movement disorder via nigrostriatal dopaminergic neurodegeneration suggests that AMPA receptors, probably Ca²⁺- and Zn²⁺-permeable GluR2-lacking AMPA receptors are potential targets for overcoming Parkinson's syndrome.

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.

Novel Defense by Metallothionein Induction Against Cognitive Decline: From Amyloid β1-42-Induced Excess Zn2+ to Functional Zn2+ Deficiency

The role of metallothioneins (MTs) in cognitive decline associated with intracellular Zn²⁺ dysregulation remains unclear. Here, we report that hippocampal MT induction defends cognitive decline, which was induced by amyloid β_1-42 (Aβ_1-42)-mediated excess Zn²⁺ and functional Zn²⁺ deficiency. Excess increase in intracellular Zn²⁺, which was induced by local injection of Aβ_1-42 into the dentate granule cell layer, attenuated in vivo perforant pathway LTP, while the attenuation was rescued by preinjection of MT inducers into the same region. Intraperitoneal injection of dexamethasone, which increased hippocampal MT proteins and blocked Aβ_1-42-mediated Zn²⁺ uptake, but not Aβ_1-42 uptake, into dentate granule cells, also rescued Aβ_1-42-induced impairment of memory via attenuated LTP. The present study indicates that hippocampal MT induction blocks rapid excess increase in intracellular Zn²⁺ in dentate granule cells, which originates in Zn²⁺ released from Aβ_1-42, followed by rescuing Aβ_1-42-induced cognitive decline. Furthermore, LTP was vulnerable to Aβ_1-42 in the aged dentate gyrus, consistent with enhanced Aβ_1-42-mediated Zn²⁺ uptake into aged dentate granule cells, suggesting that Aβ_1-42-induced cognitive decline, which is caused by excess intracellular Zn²⁺, can more frequently occur along with aging. On the other hand, attenuated LTP under functional Zn²⁺ deficiency in dentate granule cells was also rescued by MT induction. Hippocampal MT induction may rescue cognitive decline under lack of cellular transient changes in functional Zn²⁺ concentration, while its induction is an attractive defense strategy against Aβ_1-42-induced cognitive decline.

Extracellular Zn2+ Is Essential for Amyloid β1-42-Induced Cognitive Decline in the Normal Brain and Its Rescue

Brain Aβ_1-42 accumulation is considered an upstream event in pathogenesis of Alzheimer's disease. However, accumulating evidence indicates that other neurochemical changes potentiate the toxicity of this constitutively generated peptide. Here we report that the interaction of Aβ_1-42 with extracellular Zn²⁺ is essential for in vivo rapid uptake of Aβ_1-42 and Zn²⁺ into dentate granule cells in the normal rat hippocampus. The uptake of both Aβ_1-42 and Zn²⁺ was blocked by CaEDTA, an extracellular Zn²⁺ chelator, and by Cd²⁺, a metal that displaces Zn²⁺ for Aβ_1-42 binding. In vivo perforant pathway LTP was unaffected by perfusion with 1000 nm Aβ_1-42 in ACSF without Zn²⁺ However, LTP was attenuated under preperfusion with 5 nm Aβ_1-42 in ACSF containing 10 nm Zn²⁺, recapitulating the concentration of extracellular Zn²⁺, but not with 5 nm Aβ_1-40 in ACSF containing 10 nm Zn²⁺ Aβ_1-40 and Zn²⁺ were not taken up into dentate granule cells under these conditions, consistent with lower affinity of Aβ_1-40 for Zn²⁺ than Aβ_1-42 Aβ_1-42-induced attenuation of LTP was rescued by both CaEDTA and CdCl₂, and was observed even with 500 pm Aβ_1-42 Aβ_1-42 injected into the dentate granule cell layer of rats induced a rapid memory disturbance that was also rescued by coinjection of CdCl₂ The present study supports blocking the formation of Zn-Aβ_1-42 in the extracellular compartment as an effective preventive strategy for Alzheimer's disease.SIGNIFICANCE STATEMENT Short-term memory loss occurs in normal elderly and increases in the predementia stage of Alzheimer's disease (AD). Amyloid-β_1-42 (Aβ_1-42), a possible causing peptide in AD, is bound to Zn²⁺ in the extracellular compartment in the hippocampus induced short-term memory loss in the normal rat brain, suggesting that extracellular Zn²⁺ is essential for Aβ_1-42-induced short-term memory loss. The evidence is important to find an effective preventive strategy for AD, which is blocking the formation of Zn-Aβ_1-42 in the extracellular compartment.