Behavioral deficits can emerge after the removal of manganese (Mn) exposures in humans and other mammals. Although epidemiological studies provide substantial evidence supporting latency, challenges reproducing such effects in alternative models have slowed mechanistic understanding. Here, we report in 2 systems, human-induced pluripotent stem cell (hiPSC)-derived and Caenorhabditis elegans, that prior chronic exposure elicits clear latent neurotoxic effects in gene expression and functional outcomes. To identify these effects and investigate underlying mechanisms, single-cell RNA sequencing was employed in hiPSC-derived cortical culture to provide comparisons of transcriptomic changes immediately following versus after cessation of chronic Mn exposures. Transcriptomic alterations revealed latent effects after cessation of elevated Mn that were not detected immediately following 40-day exposures. To confirm the reproducibility of the observed latent magnification of chronic Mn-induced neurotoxicity, behavioral endpoints were evaluated in C. elegans. We detected a significant amplification of 2 motor phenotypes after a period of exposure cessation. These data demonstrate, in 2 genetic and mechanistically tractable systems, the detection of novel latent neurotoxic effects not detected until the cessation of a chronic exposure at a magnitude well beyond the effects of the chronic Mn exposure itself. Identified alterations support a linkage between the latent effects following chronic Mn exposure and a broad range of neurodegenerative etiologies and provide insight into the cellular pathways involved. Using both in vitro and in vivo experimental models provides complementary evidence that substantially strengthens the robustness and translational relevance of these novel findings.

INTRODUCTION:Alzheimer's disease (AD) involves complex regulatory disruptions across multiple brain cell types, yet the comprehensive intracellular causal mechanisms remain poorly understood. METHODS:We present an integrative analysis framework using single-nucleus transcriptomics with matched subject-level genotype data from 272 AD patients in the Religious Orders Study and Rush Memory and Aging Project (ROSMAP) and construct causality-based, cell-type-specific gene regulatory networks (GRNs). RESULTS:Our method identifies regulatory genes among transcription factors (TFs) and non-TFs, generating a complete and accurate causal regulatory map across brain cell types. Our analyses reveal both established and novel regulations, pathways, and cell-type-specific hub genes in AD. Beyond constructing transcriptome-wide GRNs, we quantitatively evaluate hub genes and distinguish those with regulatory versus responsive roles. DISCUSSION:Our study provides a comprehensive map of cell-type-specific causal GRNs in AD, with a methodology applicable to other complex diseases such as cancer, enabling dynamic pathway exploration, hypothesis generation, and functional interpretation. HIGHLIGHTS:Comprehensive causal regulatory maps across six brain cell types revealed cell-type-specific regulatory mechanisms that move beyond traditional correlation-based and TF-centric model limitations. Novel and established hub genes and functional modules were compared across cell types, providing insights into cellular functions related to AD. Hub gene roles as regulators or targets were quantitatively evaluated within cell-type GRNs. The constructed GRNs show upstream non-TF genes regulating TFs and interconnected TF regulatory modules, highlighting the complexity of AD regulatory mechanisms beyond TF-centric assumptions.

Understanding manganese (Mn) neurotoxicity requires experimental models that realistically reflect human exposure scenarios. A key limitation of current in vitro paradigms is the reliance on acute, high-concentration exposures, which may not accurately capture the molecular consequences of long-term Mn accumulation. To address this, this study compared transcriptomic responses to acute (6-hour) and chronic (40-day) Mn exposures in SH-SY5Y cells, using Mn concentrations spanning near-physiological to sub-cytotoxic ranges. The 6-hour exposure design replicates a widely applied acute duration in the literature, while the 40-day duration was selected to mimic prolonged, low-level Mn burden reported in epidemiological and occupational studies. Bulk RNA sequencing revealed that chronic Mn exposure induced distinct and more extensive transcriptional alterations compared to acute exposure, independent of concentration. Pathway enrichment analyses indicated that cellular functions selectively perturbed under chronic conditions are highly relevant to neurodegenerative risks and aligns with independent Parkinson’s disease transcriptomic datasets. These pathways include axonal guidance signaling, amyloid fiber formation, extracellular matrix organization, and synaptic functioning. In contrast, acute exposures primarily disturbed intracellular ion homeostasis maintenance mechanisms. Protein kinase A signaling and metallothionein-mediated metal-binding pathway were the only two pathways that were shared between both applied durations exposed at Mn concentrations with reported adverse outcomes. Transcriptomic alterations in this study highlighted the contribution of mechanisms related to normal Mn-dependent cellular functions in the development of its neurotoxicity. Furthermore, these results emphasized that exposure duration is a critical determinant to be considered when evaluating long-term Mn overload-induced neurodegeneration via in vitro platforms.

Obesity is a multifactorial metabolic disorder influenced by genetic, lifestyle, and environmental factors. Increasing evidence suggests that early-life environmental exposures can induce persistent alterations in adipose tissue, contributing to long-term metabolic dysfunction. Manganese (Mn) is an essential trace element involved in mitochondrial function, redox homeostasis, and energy metabolism; however, both Mn deficiency and overexposure have been associated with adverse metabolic outcomes. Despite epidemiological studies linking Mn exposure to obesity-related disorders, the cellular mechanisms underlying Mn-mediated metabolic disruption remain poorly understood. Here, we investigated whether transient Mn exposure during the early adipogenesis induces persistent molecular and metabolic alterations in mature adipocytes. Using the 3T3-L1 cell line, pre-adipocytes were exposed to increasing Mn concentrations (0, 5, 10, 50, 100, or 500 µM) during the first 48 hours of differentiation (confluence phase). Mn was subsequently removed, and cells were either maintained as non-differentiated controls or differentiated using a defined 3T3-L1 protocol designed to generate adipocytes with white morphology and beige-like features. Upon maturation, adipogenic markers, lipid accumulation, β-adrenergic-induced lipolysis, glucose transporter gene expression, and antioxidant defense-related protein and gene expression were assessed. Early Mn exposure elicited persistent concentration-dependent alterations in adipogenic programming, characterized by reduced lipid accumulation and sustained suppression of the adipogenic regulators PPARγ and C/EBPα. Fully differentiated adipocytes also exhibited persistently impaired expression of glucose transporter genes and reduced hormone-sensitive lipase activation, leading to diminished lipid mobilization under β-adrenergic stimulation. Combined, these findings demonstrate that transient Mn exposure during the initial stages of adipocyte differentiation is sufficient to cause long-term alteration of adipogenic programming and provides evidence for a mechanism of persistent metabolic disruption. Importantly, lower Mn concentrations were associated with selected persistent alterations in adipocyte maturation, whereas the strongest effects observed at 500 µM Mn likely included cellular stress or toxicity-associated responses.

Studying neurotoxicological responses in a physiologically relevant and translatable manner remains a major challenge in biomedical research. Consequently, there has been a major push toward establishing human tissue-native approaches in research and diagnostic pipelines. Here, we present a transparent microfluidic lab-on-a-chip platform integrating an embedded array of enzymatic electrochemical glutamate sensors for real-time monitoring of extracellular neurotransmitter dynamics in human induced pluripotent stem cell-derived (hiPSC) neuronal cell cultures. The system enables continuous, multimodal-compatible interrogation of cellular responses under controlled microenvironmental conditions. We validated the platform by measuring glutamate dynamics in under baseline conditions and following exposure to the environmental neurotoxins methylmercury (MeHg) and manganese (Mn); both known to alter glutamate dynamics. The sensors exhibited stable operation over more than one week in culture and reliably detected glutamate transients with concentrations up to 120 μM glutamate. MeHg exposure resulted in significant alterations in extracellular glutamate relative to control conditions, indicating disrupted glutamate homeostasis. Similarly, neuronal cultures exposed to 500 μM Mn for 24 h demonstrated significantly altered glutamate uptake dynamics. These results validate the proposed platform as a robust tool for investigating neurotoxin-induced perturbations in glutamatergic signaling and demonstrate the feasibility of integrating electrochemical enzymatic sensing into microfluidic systems for neurotoxicity research and discovery.

Manganese (Mn) is an essential metal required for many physiological functions, and deficiency or overexposure is associated with neurological dysfunction and neuropathology. Tight homeostatic control of Mn in the body is required to maintain optimal physiological levels and protect against toxicity. Mn homeostasis has been studied for decades, but there has been limited knowledge of the molecular mechanisms until recently, when the first human genetic disorders of Mn metabolism were described. These discoveries led to the identification of the Mn transporters SLC30A10, SLC39A14, and SLC39A8, which spurred a transformation of research into Mn homeostatic mechanisms. This review provides an overview of Mn physiology and homeostasis and the role of the critical Mn transporters and discusses the progress made within recent years toward understanding how these transporters work together to regulate brain Mn biology under both physiological and pathophysiological Mn conditions.

Methylmercury (MeHg) exposure poses a significant neurotoxic health risk, especially in early development. While acute MeHg exposure is associated with persistent neurotoxicity, it remains unclear whether and how low-level developmental MeHg exposures during juvenile stages contribute to long-term declines in brain function, particularly later in life during aging. To address this question, we utilized the genetically tractable nematode model C. elegans, exposing worms at the early larval stage to 10 nM or 50 nM MeHg for 24 h. Motor function was then assessed across various adult stages to evaluate long-term effects of early-life exposure. We hypothesized that the motor function of aged worms would be impaired following developmental MeHg exposure. In a human stem-cell neuronal model of MeHg neurotoxicity, we found changes in the expression of the human homolog of STI-1. We further hypothesized that the protein STI-1, a protein co-cochaperone in the protein quality control pathway, modifies the age-dependent neurobehavioral effects of early MeHg exposure. In the two motor functions, namely crawling on a solid surface and swimming in liquid, aged worms' moving speed was significantly reduced by prior MeHg exposure at larval stages. In the sti-1 KO animals, the moving speed across all adult stages was significantly decreased; however, the moving speed during swimming was increased by MeHg exposure in the sti-1 KO young adults. MeHg exposure also increased exploratory behavior wild-type animals, while the sti-1 KO animals showed a severe defect in this behavior. The deletion of sti-1 also caused an abnormal response of mitochondria to the uncoupler carbonyl cyanide p-trifluoro-methoxyphenyl hydrazone (FCCP) and elevated reactive oxygen species (ROS) production upon MeHg exposure. In the stem-cell neuronal model, we also found alterations in mitochondrial energetic gene pathways consistent with the worm findings. Together, these novel findings establish that developmental MeHg exposure leads to a decline in motor function in aged worms. Moreover, mitochondrial dysfunction associated with sti-1 KO accelerates the onset of motor impairment, suggesting a synergistic effect between genetic susceptibility and early-life toxicant exposure.

Manganese (Mn) and iron (Fe) are essential trace metals. Both are essential for multiple physiological processes, including brain function, metabolism, and cellular respiration. However, excessive exposure to these metals can have detrimental health effects, particularly in occupational exposures, such as mining, welding, battery production, and iron and steel manufacturing. Mn and Fe accumulate in astrocytes, especially in brain regions involved in motor control and cognition, such as the substantia nigra and globus pallidus in the basal ganglia. Excessive exposure to Mn and Fe induces oxidative stress, neuronal damage and neurodegeneration, and has been implicated in various neurodegenerative diseases, including Alzheimer's disease (AD) and Parkinson's disease (PD). Here, we investigated the effects of combined Mn and Fe exposure on C8-D1A astrocytic cells and explored the associated oxidative stress pathways. Our results demonstrated that Mn exposure decreased Superoxide dismutase 2 (Sod2) mRNA expression and one of its upstream regulators, Signal Transducer and Activator of Transcription 3 (STAT3) protein and gene levels, associated with an increase in oxidative stress, whereas Fe exposure had no effect on this pathway. Interestingly, combined Mn and Fe exposure decreased reactive oxygen species (ROS) levels and upregulated the expression of the antioxidant gene NAD(P)H quinone dehydrogenase 1 (NQO1) compared to Mn and Fe exposure alone. Our findings suggest that combined Mn and Fe exposure activate the Nuclear factor erythroid 2-related factor 2 (NRF2)/NQO1 antioxidant signaling pathway in C8-D1A astrocytic cells, mitigating oxidative stress and protecting cells from damage. By understanding these mechanisms, novel therapeutic targets for neurodegenerative diseases associated with occupational metal exposures may be identified.

A critical component of evaluating whether a chemical can cause human neurotoxicity is hazard identification, which typically involves a comprehensive literature search to identify and synthesize epidemiological, animal, and mechanistic data for the chemical of interest. The key characteristics (KCs) concept has proven to be a useful tool for searching, organizing, and evaluating mechanistic data for hazard identification. KCs are the established chemical and biological properties of known human neurotoxic agents based on understanding of their mechanisms of neurotoxicity. KCs were originally developed for carcinogens but have now also been published for endocrine- and metabolism-disruptors and various organ-selective toxic chemicals. To identify KCs associated with neurotoxic chemicals, an expert committee was convened to consider current mechanistic understanding of chemicals known to be neurotoxic in humans with the goal of identifying established molecular and cellular actions of neurotoxic chemicals. After extensive discussion, the committee reached consensus on 10 KCs. Here, we describe the 10 proposed KCs and provide chemical-related examples to support their inclusion. Several important considerations emerged from the committee’s deliberations including: (1) a mechanistic action need not be unique to neurotoxicity to be considered a KC of neurotoxic chemicals; (2) many, if not most, neurotoxic chemicals exhibit multiple KCs, and the relative importance of any specific KC and/or its causal relationship to other KCs may vary depending on life stage at the time of exposure and/or the exposure paradigm; and (3) data indicating a chemical exhibits one or more KCs of neurotoxic chemicals suggests that the chemical poses a neurotoxic hazard but does not necessarily identify the risk that the chemical presents to humans. These considerations, as well as potential applications of KCs in neurotoxicology, are discussed. The committee also strongly recommended that the list of proposed KCs of neurotoxic chemicals be viewed as a “living document” that is reviewed and revised in response to emerging insights on mechanisms of neurotoxicity, as well as lessons learned from the application of these proposed KCs, including but not limited to their use as a tool for the systemic identification and review of mechanistic data for assessment of neurotoxic hazards.

Understanding how distinct neuronal subtypes contribute to Alzheimer's disease (AD) pathology remains a major challenge. Patient-derived induced pluripotent stem cell (iPSC) studies have shown neuronal subtype-specific molecular and pathological signatures, yet the underlying metabolic shifts driving this selective vulnerability are not completely understood. Here we present iNeuron-GEM, the first manually curated, genome-scale metabolic network of human neurons that integrates transcriptomic and metabolic knowledge to resolve subtype-specific metabolic states. By coupling iNeuron-GEM with single nucleus RNA sequencing data from post-mortem human cohort studies, ROSMAP and SEA-AD, we capture neuronal subtype-specific metabolic features and fluxes and identify perturbations in lipid and energy metabolism across excitatory and inhibitory neurons. Integrative analysis with NPS-AD data shows overlapping metabolic disruptions in AD and schizophrenia (SCZ), suggesting shared molecular vulnerabilities between neurodegenerative and neuropsychiatric disorders. We also developed a computational pipeline to infer transcriptional regulation of metabolic pathways and identify NR6A1 and NR3C1 as important regulators of lipid dysregulation in AD neurons. Our study establishes iNeuron-GEM as a framework to identify neuronal subtype-specific metabolic vulnerabilities in complex brain disorders.

Methylmercury (MeHg), an environmental pollutant, reaches the human body predominantly through contaminated fish consumption, potentially leading to severe neurological disorders. Upon ingestion MeHg reaches the brain and selectively accumulates in astrocytes. The activation of nuclear factor erythroid 2-related factor 2 (Nrf2) has been identified as a key early response to MeHg-induced oxidative injury, positioning it as a potential therapeutic target. However, recent studies suggest that Nrf2 activation alone may not be sufficient to mitigate MeHg toxicity, indicating the existence of other protective mechanisms. The signal transducer and activator of transcription 3 (STAT3) signaling pathway, known for its role in cell growth and survival, has emerged as a potential player in redox homeostasis. In this study, we investigated the role of STAT3 in acute (≤ 24 h) MeHg-induced neurotoxicity. MeHg exposure induced STAT3 expression in C8-D1A astrocytic cells. Our data demonstrated that pharmacological inhibition of STAT3 using AG490 or C188-9 exacerbated MeHg-induced cell death and compromised antioxidant responses. Furthermore, to fully characterize the role of STAT3 in oxidative stress, we used two different antioxidants, N-acetylcysteine (NAC) and Trolox. Conversely, reactive oxygen species (ROS)-scavenging antioxidants partially ameliorated STAT3 activation, suggesting that MeHg-induced STAT3 activation is mediated, at least in part, by mechanisms independent of ROS. Our findings suggest that STAT3 contributes to neuroprotection against MeHg exposure in astrocytes and is, at least in part, regulated by the increase in ROS levels within these cells.

Metabolic dysfunctions have been increasingly studied in neurodegenerative diseases like Alzheimer's Disease (AD), where neurons must meet high energy demands for neurotransmission and synaptic activity through oxidative phosphorylation and glycolysis-driven ATP production. Metabolic disturbances in these functions were reported for pathophysiological changes in AD. Detailed mechanisms underlying metabolic alterations in specific neuronal subtypes remain insufficiently explored. We generated a neuronal subtype-specific genome-scale metabolic network – i Neuron-GEM , using single-nucleus RNA-sequencing (snRNA-seq) data from two AD cohort studies: the Religious Orders Study and Memory and Aging Project (ROSMAP) and Seattle Alzheimer's Disease Brain Cell Atlas (SEA-AD). We tested the accuracy of i Neuron-GEM reconstruction using neuron-specific metabolic tasks and refined the reconstruction with metabolomics data from human induced pluripotent stem cell (iPSC)-derived neurons and cerebrospinal fluid. Using i Neuron-GEM , we performed in silico metabolic analysis on snRNA-seq data from the Mount Sinai Neuropsychiatric Symptoms in AD (NPS-AD) Study to identify key metabolic changes in neuronal subtypes. We also improved our metabolic predictions using supervised machine learning approaches to identify disrupted metabolic reactions and pathways in inhibitory and excitatory neurons associated with AD pathology. We report the first in silico metabolic reconstruction of neurons, i Neuron-GEM , containing 1339 metabolites, 3900 metabolic reactions, and 1703 genes. This metabolic reconstruction can achieve essential neuronal metabolic functions. Results from integrated metabolic analysis combined with a supervised machine learning approach identified that excitatory neurons exhibited more significant metabolic alterations between healthy and AD individuals compared to inhibitory neurons. These alterations included metabolic reactions linked to genes (i.e. ACSL1, ELOVL2 , and ACSBG2 ) and metabolites (i.e. homoserine, ornithine, and choline), concordant with those implicated in AD progression. Our analysis revealed key mechanistic changes in fatty acid synthesis, glycerophospholipid metabolism and branched-chain amino acid catabolism in excitatory neurons during AD progression. We present the first manually curated metabolic reconstruction of human neurons, named i Neuron-GEM . This metabolic reconstruction is useful for integrating multi-omics data and predicting metabolic changes in neuronal subtypes in AD. The findings from integrated i Neuron-GEM analyses enable the identification of metabolic signatures and druggable targets in AD.

Exposure to environmental chemicals such as lead (Pb) during vulnerable developmental periods and even in adult stage can result in adverse health outcomes later in life. Human cohort studies have demonstrated associations between Pb exposure and Alzheimer’s Disease (AD) onset in later life which were further corroborated by findings from animal studies. The molecular pathway linking Pb exposure and increased AD risk, however, remains elusive. In this work, we used human iPSC-derived cortical neurons as a model system to study the effects of Pb exposure on AD-like pathogenesis in human cortical neurons. We exposed neural progenitor cells and differentiated neurons derived from human iPSC to Pb concentrations of 0, 15, and 50 ppb for 48 hours, simulating developmental and adult Pb exposure, respectively. Various techniques, including immunofluorescence, Western blotting, RNA-sequencing, enzyme-linked immunosorbent assay (ELISA), microelectrode array (MEA), and Förster resonance energy transfer (FRET) reporter cell lines, were employed to assess changes in AD-like pathogenesis in differentiated cortical neurons. The susceptibility of Pb-exposed neurons to cellular stressors such as PHF-Tau and MPP+ was evaluated through secondary stress assays. Exposing neural progenitor cells to low dose Pb, mimicking a developmental exposure can result in altered neurite morphology. Differentiated neurons exhibit altered calcium homeostasis, synaptic plasticity, epigenetic landscape along with elevated AD-like pathogenesis markers, including phosphorylated Tau, Tau aggregates and Aβ42/40. Furthermore, Pb-exposed cortical neurons exhibited significantly increased calcium dynamics and overall neuronal activity. Adult neurons exposed to Pb demonstrated heightened vulnerability to PHF-Tau and MPP+-induced cytotoxicity, with these changes persisting even after Pb withdrawal. Collectively, our findings propose a plausible molecular mechanism to account for the increased risk of AD in populations with a history of Pb exposure.

Manganese (Mn) is an essential trace element crucial for various physiological processes, but excessive exposure can lead to significant health concerns, particularly neurotoxicity. This review synthesizes current knowledge on Mn-induced oxidative stress and its role in cellular dysfunction and disease. We discuss how Mn promotes toxicity through multiple mechanisms, primarily through reactive oxygen species (ROS) generation, which leads to oxidative stress and disruption of cellular processes. The review examines key pathways affected by Mn toxicity, including mitochondrial dysfunction, endoplasmic reticulum stress, inflammasome activation, and epigenetic modifications. Recent studies have identified promising therapeutic compounds, including both synthetic and natural substances such as probucol, metformin, curcumin, resveratrol, and daidzein, which demonstrate protective effects through various mechanisms, including antioxidant enhancement, mitochondrial function preservation, and epigenetic pathway modulation. Understanding these mechanisms provides new insights into potential therapeutic strategies for Mn-induced disorders. This review also highlights future research directions, emphasizing the need for developing targeted therapies and investigating combination approaches to address multiple aspects of Mn toxicity simultaneously.

The objective of the present review is to discuss the involvement of altered mitochondrial quality control in Mn-induced neurotoxicity. Existing data demonstrate that mitochondrial autophagy (mitophagy) and brain mitochondrial unfolded protein response (mtUPR) are activated in response to Mn exposure to counteract the Mn-induced mitochondrial dysfunction. Both mitophagy and mtUPR have significant overlap and mechanistic intersections with the integrated stress response (ISR). Increased Mn exposures impair mitochondrial dynamics, further aggravating Mn-induced mitochondrial dysfunction. Specifically, Mn suppresses PTEN-induced kinase 1 (PINK1)-Parkin-dependent mitophagy through a variety of mechanisms, including nitric oxide synthase 2 (NOS2)-dependent PINK1 S-nitrosylation, inhibition of transcription factor EB (TFEB) signaling, and mammalian target of rapamycin complex 1 (mTORC1) activation. In addition, Mn promotes mitochondrial fission by up-regulating dynamin-1-like protein (Drp1) expression and phosphorylation via the activation of c-Jun N-terminal kinase (JNK) and inhibition of sirtuin 1 (SIRT1)/peroxisome proliferator-activated receptor gamma coactivator 1-alpha (PGC-1α) pathways. Concomitantly, Mn impairs mitochondrial fusion by inhibiting mitofusin (Mfn) 1/2 and dynamin-like 120 kDa protein (Opa1) expression, leading to a reduction in mitochondrial size and disruption of the mitochondrial network. High-dose Mn exposure results in inhibition of peroxisome proliferator-activated receptor gamma coactivator 1α (PGC-1α)/nuclear factor erythroid 2-related factor 2 (NRF2)-dependent mitochondrial biogenesis. The latter may be mediated by inhibition of SIRT1/SIRT3 activity, as well as modulation of PINK1/ zinc finger protein 746 (ZNF746)/PGC-1α axis. Alterations in the mitochondrial quality control system may contribute to Mn-induced neuronal damage and neuroinflammation, indicating that dysregulation of the brain mitochondrial dynamics is an important mechanism by which Mn induces its neurotoxicity.

The objective of this review is to examine the direct evidence implicating epigenetic mechanisms in manganese (Mn)-induced neurotoxicity, with particular emphasis on the modulation of non-coding RNA (ncRNA) expression and histone modifications. Existing data demonstrate that Mn exposure modulates expression of various types of ncRNAs, especially micro RNAs (miRNAs or miRs), long non-coding RNAs (lncRNAs), and circular RNAs (circRNAs). Through regulation of target gene expression, these differentially expressed ncRNAs likely mediate Mn-induced neuronal oxidative stress, ferroptosis, apoptosis, autophagy, inflammation, as well as α-synuclein expression. Additionally, Mn exposure affects histone acetylation in neurons by modulating enzymes such as histone deacetylases (HDACs) and histone acetyltransferases (HATs). These Mn-induced changes in histone acetylation enhance neuronal oxidative stress by down-regulating antioxidant gene expression and promoting neuroinflammation. Alterations in HDACs activity and the ensuing histone acetylation modifications play a role in Mn-induced down-regulation of glutamate transporter 1 (GLT-1) and glutamate-aspartate transporter (GLAST) expression which results in reduced glutamate uptake and ensuing excitotoxicity. Additionally, Mn exposure impacts the methylation of genes involved in neuroinflammation, neurogenesis, neuronal migration, signal transduction, mitochondrial functioning, cell cycle, and DNA damage response, as well as apoptosis. Detailed analysis reveals that Mn-induced DNA methylation leads to the down-regulation of brain-derived neurotrophic factor (BDNF) expression and the up-regulation of p53. Collectively, current evidence indicates that epigenetic mechanisms are key mediators of manganese (Mn)-induced neurotoxicity in both in vivo and in vitro models. However, the specific target genes and downstream signaling pathways involved in Mn-associated epigenetic regulation have yet to be fully characterized.

Acrolein, an α,β-unsaturated aldehyde and reactive oxygen species (ROS), originates from both endogenous mechanisms, such as lipid peroxidation, and exogenous sources, including the decomposition of organic matter. Elevated levels of acrolein are detected in the brains of individuals with Alzheimer's and Parkinson's diseases, as well as those with traumatic brain or spinal cord injuries. Environmental exposure, including smoking and industrial emissions, further contribute to acrolein accumulation. Despite their recognized immediate neurotoxic effects, the chronic implications on neurodegeneration remain elusive. To elucidate these effects, human induced pluripotent stem cell (hiPSC)-derived human cortical neurons (∼Day 60 postdifferentiation) were subjected to 0, 1, and 10 μM concentrations of acrolein for 2 days following a nonexposure relaxation period (7 days) to assess the persistence of the resulting phenotypes. Immunofluorescence and calcium imaging demonstrated sustained alterations in the synaptic density and neuronal activity in acrolein-exposed differentiated neurons. Moreover, a persistent and dose-dependent neuronal hyperactivity was identified through microelectrode array analysis. Acrolein exposure also precipitated sustained elevations in Alzheimer's Disease-related phosphorylated Tau (p-tau) pathology and mitochondrial stress, along with diminished cellular resilience to subsequent stressors. Collectively, these findings support a persistent neurotoxic effect of acrolein, highlighting its potential implications for neurodegenerative disorders.

INTRODUCTION:Underlying glutamate dysregulation in Alzheimer's disease can be worsened by environmental factors like manganese (Mn) exposure. This study examined how excess Mn affects glutamatergic signaling and neurotransmission in a beta-amyloid mouse model. METHODS:APP/PSEN1 and control mice were exposed to systemic Mn subcutaneously. Gene expression, glutamate clearance dynamics, electroencephalography (EEG) activity, and sleep architecture were analyzed using quantitative polymerase chain reaction (qPCR), Western blot, ex vivo hippocampal slices, and EEG recordings. RESULTS:Mn exposure elevated brain Mn levels and altered glutamate dynamics in both WT and APP/PSEN1 mice. Wild-type (WT) mice showed faster glutamate clearance, increased spiking, disrupted sleep, and brain wave changes. APP/PSEN1 mice exhibited slower glutamate clearance, altered gene expression, increased glial fibrillary acidic protein (GFAP), and changes in non-rapid eye movement (NREM) delta and rapid eye movement (REM) alpha power. DISCUSSION:Mn exposure altered glutamate clearance and brain activity, particularly in WT mice. APP/PSEN1 mice showed impaired clearance, limited gene expression changes, and altered EEG patterns, suggesting distinct or pre-existing compensatory mechanisms. HIGHLIGHTS:Manganese exposure significantly alters glutamate clearance dynamics differentially in wild-type and APP/PSEN1 mouse models of Alzheimer's disease. Acute manganese treatment disrupts sleep architecture, evidenced by changes in electroencephalography (EEG) patterns and vigilance states. APP/PSEN1 mice exhibit slower glutamate clearance and altered gene expression compared to wild-type mice following manganese exposure. Distinct brain wave frequency shifts were observed in response to manganese treatment, particularly affecting delta, theta, and alpha rhythms. Findings suggest a potential exacerbation of excitatory/inhibitory imbalances due to environmental manganese exposure in Alzheimer's pathology.

Abnormal levels of potassium are linked to several health conditions, including high blood pressure, cardiac dysfunction, kidney damage, and osteoporosis. Given the limited availability of in vivo measurement techniques, there is a need for novel methods to measure potassium to enhance the diagnosis and management of potassium metabolism related diseases. This study aimed to evaluate the feasibility of compact neutron generator based in vivo measurement system for quantification of potassium using rat carcasses. A cohort of thirty-nine rats (n = 20 males and 19 females, average weight 255 ± 15 and 163 ± 7 g) were sacrificed, and their carcasses were placed in polyethylene bottles. The rats were then positioned and irradiated in a carefully designed irradiation cave built alongside the neutron generator with an optimized thermal neutron flux and radiation dose ratio. The irradiation time was 10 min, followed by a 5-min decay and 2-h measurement using a high efficiency high purity germanium detector(HPGe). RESULTS: The average potassium concentration in male and female rats was found to be comparable (male 2874 ± 161 and female 2866 ± 144 μg/g). A marginally positive correlation between potassium concentration and weight was found in female rats only (male(20) = 0.07, P = 0.76 and female r(19) = 0.34, P = 0.15). We assessed the influence of manganese toxicity on potassium levels and observed no significant impact. These results were consistent with our previous study in mice. CONCLUSION: This study suggests that in vivo neutron activation analysis could serve as a promising method to quantify potassium and to investigate the storage and metabolism of potassium in human and in animals.

The objective of the present narrative review was to synthesize existing clinical and epidemiological findings linking manganese (Mn) exposure biomarkers to autism spectrum disorder (ASD) and attention deficit hyperactivity disorder (ADHD), and to discuss key pathophysiological mechanisms of neurodevelopmental disorders that may be affected by this metal. Existing epidemiological data demonstrated both direct and inverse association between Mn body burden and ASD, or lack of any relationship. In contrast, the majority of studies revealed significantly higher Mn levels in subjects with ADHD, as well as direct relationship between Mn body burden with hyperactivity and inattention scores in children, although several studies reported contradictory results. Existing laboratory studies demonstrated that impaired attention and hyperactivity in animals following Mn exposure was associated with dopaminergic dysfunction and neuroinflammation. Despite lack of direct evidence on Mn-induced neurobiological alterations in patients with ASD and ADHD, a plethora of studies demonstrated that neurotoxic effects of Mn overexposure may interfere with key mechanisms of pathogenesis inherent to these neurodevelopmental disorders. Specifically, Mn overload was shown to impair not only dopaminergic neurotransmission, but also affect metabolism of glutamine/glutamate, GABA, serotonin, noradrenaline, thus affecting neuronal signaling. In turn, neurotoxic effects of Mn may be associated with its ability to induce oxidative stress, apoptosis, and neuroinflammation, and/or impair neurogenesis. Nonetheless, additional detailed studies are required to evaluate the association between environmental Mn exposure and/or Mn body burden and neurodevelopmental disorders at a wide range of concentrations to estimate the potential dose-dependent effects, as well as environmental and genetic factors affecting this association.