Cypermethrin Stimulates GSK3β-Dependent Aβ and p-tau Proteins and Cognitive Loss in Young Rats: Reduced HB-EGF Signaling and Downstream Neuroinflammation as Critical Regulators

Folate prevents the autism-related phenotype caused by developmental pyrethroid exposure in prairie voles

Neurodevelopmental disorders (NDDs) have dramatically increased in prevalence to an alarming one in six children, and yet both causes and preventions remain elusive. Recent human epidemiology and animal studies have implicated developmental exposure to pyrethroid pesticides, one of the most common classes of pesticides in the US, as an environmental risk factor for autism and neurodevelopmental disorders. Our previous research has shown that low-dose chronic developmental pyrethroid exposure (DPE) changes folate metabolites in the adult mouse brain. We hypothesize that DPE acts directly on molecular targets in the folate metabolism pathway, and that high-dose maternal folate supplementation can prevent or reduce the biobehavioral effects of DPE. We exposed pregnant prairie vole dams chronically to vehicle or low-dose deltamethrin (3 mg/kg/3 days) with or without high-dose folate supplementation (methylfolate, 5 mg/kg/3 days). The resulting DPE offspring showed broad deficits in five behavioral domains relevant to neurodevelopmental disorders (including the social domain); increased plasma folate concentrations; and increased neural expression of SHMT1, a folate cycle enzyme. Maternal folate supplementation prevented most of the behavioral phenotypes (except for repetitive behaviors) and caused potentially compensatory changes in neural expression of FOLR1 and MTHFR, two folate-related proteins. We conclude that DPE causes neurodevelopmental disorder-relevant behavioral deficits; DPE directly alters aspects of folate metabolism; and preventative interventions targeting folate metabolism are effective in reducing, but not eliminating, the behavioral effects of DPE.

GSK3: A potential target and pending issues for treatment of Alzheimer's disease

Glycogen synthase kinase-3 (GSK3), consisting of GSK3α and GSK3β subtypes, is a complex protein kinase that regulates numerous substrates. Research has observed increased GSK3 expression in the brains of Alzheimer's disease (AD) patients and models. AD is a neurodegenerative disorder with diverse pathogenesis and notable cognitive impairments, characterized by Aβ aggregation and excessive tau phosphorylation. This article provides an overview of GSK3's structure and regulation, extensively analyzing its relationship with AD factors. GSK3 overactivation disrupts neural growth, development, and function. It directly promotes tau phosphorylation, regulates amyloid precursor protein (APP) cleavage, leading to Aβ formation, and directly or indirectly triggers neuroinflammation and oxidative damage. We also summarize preclinical research highlighting the inhibition of GSK3 activity as a primary therapeutic approach for AD. Finally, pending issues like the lack of highly specific and affinity-driven GSK3 inhibitors, are raised and expected to be addressed in future research. In conclusion, GSK3 represents a target in AD treatment, filled with hope, challenges, opportunities, and obstacles.

Intracerebroventricular Cutibacterium acnes Generates Manifestations of Alzheimer's Disease-like Pathology in the Rat Hippocampus

The infection hypothesis is a new causative explanation for Alzheimer's disease (AD). In recent decades, various species of bacterial pathogens have been distinguished in the autopsy of Alzheimer's patients; however, the mechanism of bacterial contribution to AD pathology is still unknown. To explore the hypothesis, Cutibacterium acnes (C. acnes) was selected, and effects of its intracerebroventricular (ICV) inoculation in rats was evaluated. The results revealed that C. acnes causes memory impairment, which might be a consequence of upregulated Amyloid β (Aβ) deposits in the hippocampus; Aβ aggregates are co-localized with C. acnes colonies. The key point of our hypothesis is that the activation of the innate immune system by C. acnes through the TLR2/NF-κB/NLRP3 signaling pathway, eventually leads to increased neuroinflammation, which might be resulted from microgliosis and astrogliosis. Neuroinflammation increases oxidative stress and cell apoptosis. Overall, the obtained results of this study support our hypothesis that brain exposure to C. acnes prompted neuroinflammation with similar AD-like pathology.

Neurotoxicity of Pyrethroids in neurodegenerative diseases: From animals' models to humans' studies

Neurodegenerative diseases are associated with diverse symptoms, both motor and mental. Genetic and environmental factors can trigger neurodegenerative diseases. Chemicals as pesticides are constantly used in agriculture and also domestically. In this regard, pyrethroids (PY), are a class of insecticides in which its main mechanism of action is through disruption of voltage-dependent sodium channels function in insects. However, in mammals, they can also induce oxidative stress and enzyme dysfunction. This review investigates the association between PY and neurodegenerative diseases as Alzheimer's, Huntington's, Parkinson's, Amyotrophic Lateral Sclerosis, and Autism in animal models and humans. Published works using specific and non-specific models for these diseases were selected. We showed a tendency toward the development and/or aggravating of these neurodegenerative diseases following exposure to PYs. In animal models, the biochemical mechanisms of the diseases and their interaction with the insecticides are more deeply investigated. Nonetheless, only a few studies considered the specific model for each type of disease to analyze the impacts of the exposure. The choice of a specific model during the research is an important step and our review highlights the knowledge gaps of PYs effects using these models reinforcing the importance of them during the design of the experiments.

Role of an interdependent Wnt, GSK3-β/β-catenin and HB-EGF/EGFR mechanism in arsenic-induced hippocampal neurotoxicity in adult mice

We previously reported the neurotoxic effects of arsenic in the hippocampus. Here, we explored the involvement of Wnt pathway, which contributes to neuronal functions. Administering environmentally relevant arsenic concentrations to postnatal day-60 (PND60) mice demonstrated a dose-dependent increase in hippocampal Wnt3a and its components, Frizzled, phospho-LRP6, Dishevelled and Axin1 at PND90 and PND120. However, p-GSK3-β(Ser9) and β-catenin levels although elevated at PND90, decreased at PND120. Additionally, treatment with Wnt-inhibitor, rDkk1, reduced p-GSK3-β(Ser9) and β-catenin at PND90, but failed to affect their levels at PND120, indicating a time-dependent link with Wnt. To explore other underlying factors, we assessed epidermal growth factor receptor (EGFR) pathway, which interacts with GSK3-β and appears relevant to neuronal functions. We primarily found that arsenic reduced hippocampal phosphorylated-EGFR and its ligand, Heparin-binding EGF-like growth factor (HB-EGF), at both PND90 and PND120. Moreover, treatment with HB-EGF rescued p-GSK3-β(Ser9) and β-catenin levels at PND120, suggesting their HB-EGF/EGFR-dependent regulation at this time point. Additionally, rDkk1, LiCl (GSK3-β-activity inhibitor), or β-catenin protein treatments induced a time-dependent recovery in HB-EGF, indicating potential inter-dependent mechanism between hippocampal Wnt/β-catenin and HB-EGF/EGFR following arsenic exposure. Fluorescence immunolabeling then validated these findings in hippocampal neurons. Further exploration of hippocampal neuronal survival and apoptosis demonstrated that treatment with rDkk1, LiCl, β-catenin and HB-EGF improved Nissl staining and NeuN levels, and reduced cleaved-caspase-3 levels in arsenic-treated mice. Supportively, we detected improved Y-Maze and Passive Avoidance performances for learning-memory functions in these mice. Overall, our study provides novel insights into Wnt/β-catenin and HB-EGF/EGFR pathway interaction in arsenic-induced hippocampal neurotoxicity.

Association of Prenatal Exposure to Organophosphate, Pyrethroid, and Neonicotinoid Insecticides with Child Neurodevelopment at 2 Years of Age: A Prospective Cohort Study

BACKGROUND

Widespread insecticide exposure might be a risk factor for neurodevelopment of our children, but few studies examined the mixture effect of maternal coexposure to organophosphate insecticides (OPPs), pyrethroids (PYRs), and neonicotinoid insecticides (NNIs) during pregnancy on child neurodevelopment, and critical windows of exposure are unknown.

OBJECTIVES

We aimed to evaluate the association of prenatal exposure to multiple insecticides with children's neurodevelopment and to identify critical windows of the exposure.

METHODS

Pregnant women were recruited into a prospective birth cohort study in Wuhan, China, from 2014-2017. Eight metabolites of OPPs (mOPPs), three metabolites of PYRs (mPYRs), and nine metabolites of NNIs (mNNIs) were measured in 3,123 urine samples collected at their first, second, and third trimesters. Children's neurodevelopment [mental development index (MDI) and psychomotor development index (PDI)] was assessed using the Bayley Scales of Infant Development at 2 years of age (N = 1,041 ). Multivariate linear regression models, generalized estimating equation models, and weighted quantile sum (WQS) regression were used to estimate the association between the insecticide metabolites and Bayley scores. Potential sex-specific associations were also examined.

RESULTS

Single chemical analysis suggested higher urinary concentrations of some insecticide metabolites at the first trimester were significantly associated with lower MDI and PDI scores, and the associations were more prominent among boys. Each 1-unit increase in ln-transformed urinary concentrations of two mOPPs, 3,5,6-trichloro-2-pyridinol and 4-nitrophenol, was associated with a decrease of 3.16 points [95% confidence interval (CI): - 5.59 , - 0.74 ] and 3.06 points (95% CI: - 5.45 , - 0.68 ) respectively in boys' MDI scores. Each 1-unit increase in that of trans-3-(2,2-dichloroethenyl)-2,2-dimethylcyclopropanecarboxylic acid (trans-DCCA; an mPYR) was significantly associated with a decrease of 2.24 points (95% CI: - 3.89 , - 0.58 ) in boys' MDI scores and 1.90 points (95% CI: - 3.16 , - 0.64 ) in boys' PDI scores, respectively. Significantly positive associations of maternal urinary biomarker concentrations [e.g., dimethyl phosphate (a nonspecific mOPP) and desmethyl-clothianidin (a relatively specific mNNI)] with child neurodevelopment were also observed. Using repeated holdout validation, a 1-quartile increase in the WQS index of the insecticide mixture (in the negative direction) at the first trimester was significantly associated with a decrease of 3.02 points (95% CI: - 5.47 , - 0.57 ) in MDI scores among the boys, and trans-DCCA contributed the most to the association (18%).

CONCLUSIONS

Prenatal exposure to higher levels of certain insecticides and their mixture were associated with lower Bayley scores in children, particularly in boys. Early pregnancy may be a sensitive window for such an effect. Future studies are needed to confirm our findings. https://doi.org/10.1289/EHP12097.

The Secretome of Human Dental Pulp Stem Cells and Its Components GDF15 and HB-EGF Protect Amyotrophic Lateral Sclerosis Motoneurons against Death

Amyotrophic lateral sclerosis (ALS) is a fatal and incurable paralytic disorder caused by the progressive death of upper and lower motoneurons. Although numerous strategies have been developed to slow disease progression and improve life quality, to date only a few therapeutic treatments are available with still unsatisfactory therapeutic benefits. The secretome of dental pulp stem cells (DPSCs) contains numerous neurotrophic factors that could promote motoneuron survival. Accordingly, DPSCs confer neuroprotective benefits to the SOD1G93A mouse model of ALS. However, the mode of action of DPSC secretome on motoneurons remains largely unknown. Here, we used conditioned medium of human DPSCs (DPSCs-CM) and assessed its effect on survival, axonal length, and electrical activity of cultured wildtype and SOD1G93A motoneurons. To further understand the role of individual factors secreted by DPSCs and to circumvent the secretome variability bias, we focused on GDF15 and HB-EGF whose neuroprotective properties remain elusive in the ALS pathogenic context. DPSCs-CM rescues motoneurons from trophic factor deprivation-induced death, promotes axon outgrowth of wildtype but not SOD1G93A mutant motoneurons, and has no impact on the spontaneous electrical activity of wildtype or mutant motoneurons. Both GDF15 and HB-EGF protect SOD1G93A motoneurons against nitric oxide-induced death, but not against death induced by trophic factor deprivation. GDF15 and HB-EGF receptors were found to be expressed in the spinal cord, with a two-fold increase in expression for the GDF15 low-affinity receptor in SOD1G93A mice. Therefore, the secretome of DPSCs appears as a new potential therapeutic candidate for ALS.

Pesticides at brain borders: Impact on the blood-brain barrier, neuroinflammation, and neurological risk trajectories

Pesticides are omnipresent, and they pose significant environmental and health risks. Translational studies indicate that acute exposure to high pesticide levels is detrimental, and prolonged contact with low concentrations of pesticides, as single and cocktail, could represent a risk factor for multi-organ pathophysiology, including the brain. Within this research template, we focus on pesticides' impact on the blood-brain barrier (BBB) and neuroinflammation, physical and immunological borders for the homeostatic control of the central nervous system (CNS) neuronal networks. We examine the evidence supporting a link between pre- and postnatal pesticide exposure, neuroinflammatory responses, and time-depend vulnerability footprints in the brain. Because of the pathological influence of BBB damage and inflammation on neuronal transmission from early development, varying exposures to pesticides could represent a danger, perhaps accelerating adverse neurological trajectories during aging. Refining our understanding of how pesticides influence brain barriers and borders could enable the implementation of pesticide-specific regulatory measures directly relevant to environmental neuroethics, the exposome, and one-health frameworks.

Partial Least Squares Regression Analysis of Alzheimer's Disease Biomarkers, Modifiable Health Variables, and Cognitive Change in Older Adults with Mild Cognitive Impairment

BACKGROUND

Prior work has shown that certain modifiable health, Alzheimer's disease (AD) biomarker, and demographic variables are associated with cognitive performance. However, less is known about the relative importance of these different domains of variables in predicting longitudinal change in cognition.

OBJECTIVE

Identify novel relationships between modifiable physical and health variables, AD biomarkers, and slope of cognitive change over two years in a cohort of older adults with mild cognitive impairment (MCI).

METHODS

Metrics of cardiometabolic risk, stress, inflammation, neurotrophic/growth factors, and AD pathology were assessed in 123 older adults with MCI at baseline from the Alzheimer's Disease Neuroimaging Initiative (mean age = 73.9; SD = 7.6; mean education = 16.0; SD = 3.0). Partial least squares regression (PLSR)-a multivariate method which creates components that best predict an outcome-was used to identify whether these physiological variables were important in predicting slope of change in episodic memory or executive function over two years.

RESULTS

At two-year follow-up, the two PLSR models predicted, respectively, 20.0% and 19.6% of the variance in change in episodic memory and executive function. Baseline levels of AD biomarkers were important in predicting change in both episodic memory and executive function. Baseline education and neurotrophic/growth factors were important in predicting change in episodic memory, whereas cardiometabolic variables such as blood pressure and cholesterol were important in predicting change in executive function.

CONCLUSION

These data-driven analyses highlight the impact of AD biomarkers on cognitive change and further clarify potential domain specific relationships with predictors of cognitive change.

Neuroinflammation represents a common theme amongst genetic and environmental risk factors for Alzheimer and Parkinson diseases

Multifactorial diseases are characterized by inter-individual variation in etiology, age of onset, and penetrance. These diseases tend to be relatively common and arise from the combined action of genetic and environmental factors; however, parsing the convoluted mechanisms underlying these gene-by-environment interactions presents a significant challenge to their study and management. For neurodegenerative disorders, resolving this challenge is imperative, given the enormous health and societal burdens they impose. The mechanisms by which genetic and environmental effects may act in concert to destabilize homeostasis and elevate risk has become a major research focus in the study of common disease. Emphasis is further being placed on determining the extent to which a unifying biological principle may account for the progressively diminishing capacity of a system to buffer disease phenotypes, as risk for disease increases. Data emerging from studies of common, neurodegenerative diseases are providing insights to pragmatically connect mechanisms of genetic and environmental risk that previously seemed disparate. In this review, we discuss evidence positing inflammation as a unifying biological principle of homeostatic destabilization affecting the risk, onset, and progression of neurodegenerative diseases. Specifically, we discuss how genetic variation associated with Alzheimer disease and Parkinson disease may contribute to pro-inflammatory responses, how such underlying predisposition may be exacerbated by environmental insults, and how this common theme is being leveraged in the ongoing search for effective therapeutic interventions.

Partial Least Squares Analysis of Alzheimer's Disease Biomarkers, Modifiable Health Variables, and Cognition in Older Adults with Mild Cognitive Impairment

OBJECTIVES

To identify novel associations between modifiable physical and health variables, Alzheimer's disease (AD) biomarkers, and cognitive function in a cohort of older adults with Mild Cognitive Impairment (MCI).

METHODS

Metrics of cardiometabolic risk, stress, inflammation, neurotrophic/growth factors, AD, and cognition were assessed in 154 MCI participants (Mean age = 74.1 years) from the Alzheimer's Disease Neuroimaging Initiative. Partial Least Squares analysis was employed to examine associations among these physiological variables and cognition.

RESULTS

Latent variable 1 revealed a unique combination of AD biomarkers, neurotrophic/growth factors, education, and stress that were significantly associated with specific domains of cognitive function, including episodic memory, executive function, processing speed, and language, representing 45.2% of the cross-block covariance in the data. Age, body mass index, and metrics tapping basic attention or premorbid IQ were not significant.

CONCLUSIONS

Our data-driven analysis highlights the significant relationships between metrics associated with AD pathology, neuroprotection, and neuroplasticity, primarily with tasks tapping episodic memory, executive function, processing speed, and verbal fluency rather than more basic tasks that do not require mental manipulation (basic attention and vocabulary). These data also indicate that biological metrics are more strongly associated with episodic memory, executive function, and processing speed than chronological age in older adults with MCI.

Proteomic profiling reveals neuronal ion channel dysregulation and cellular responses to DNA damage-induced cell cycle arrest and senescence in human neuroblastoma SH-SY5Y cells exposed to cypermethrin

Cypermethrin (CYP), a synthetic pyrethroid of class II, is widely used as a pesticide worldwide. The primary target of cypermethrin is a voltage-gated sodium channel. The neurotoxicity of CYP has been extensively studied in terms of affecting neuronal development, increasing cellular oxidative stress, and apoptosis. However, little is known about how it affects the expression of channel proteins involved in synaptic transmission, as well as the effects of cypermethrin on DNA damage and cell cycle processes. We found that the ligand and voltage-gated calcium channels and proteins involved in synaptic transmission including NMDA 1 receptor subunit, alpha 1A-voltage-dependent calcium channel, synaptotagmin-17, and synaptojanin-2 were downregulated in CYP-treated cells. After 48h of CYP exposure, cell viability was reduced with flattened and enlarged morphology. The levels of 23 proteins regulating cell cycle processes were altered in CYP-treated cells, according to a proteomic study. The cell cycle analysis showed elevated G₀/G₁ cell cycle arrest and DNA fragmentation at the sub-G₀ stage after CYP exposure. CYP treatment also increased senescence-associated β-galactosidase positive cells, DNA damage, and apoptotic markers. Taken together, the current study showed that cypermethrin exposure caused DNA damage and hastened cellular senescence and apoptosis via disrupting cell cycle regulation. In addition, despite its primary target sodium channel, CYP might cause synaptic dysfunction via the downregulation of synaptic proteins and dysregulation of synapse-associated ion channels.

Arsenic Induces GSK3β-dependent p-tau, neuronal apoptosis and cognitive impairment via an interdependent hippocampal ERα and IL-1/IL-1R1 mechanism in female rats

Arsenic is an environmental contaminant with potential neurotoxicity. We previously reported that arsenic promoted hippocampal neuronal apoptosis, inducing cognitive loss. Here, we correlated it with tau pathology. We observed that environmentally relevant arsenic exposure increased tau phosphorylation and the principal tau kinase, glycogen synthase kinase-3 beta (GSK3β), in the female rat hippocampal neurons. We detected the same in primary hippocampal neurons. Since a regulated estrogen receptor (ER) level and inflammation contributed to normal hippocampal functions, we examined their levels following arsenic exposure. Our ER screening data revealed that arsenic down-regulated hippocampal neuronal ERα. We also detected an up-regulated hippocampal interleukin-1 (IL-1) and its receptor, IL-1R1. Further, co-treating arsenic with the ERα agonist, 4,4',4''-(4-Propyl-[1H]-pyrazole-1,3,5-triyl)trisphenol (PPT), or IL-1R antagonist (IL-1Ra) resulted in reduced GSK3β and p-tau, indicating involvement of decreased ERα and increased IL-1/IL-1R1 in tau hyperphosphorylation. We then checked whether ERα and IL-1/IL-1R1 had linkage, and detected that while PPT reduced IL-1 and IL-1R1, the IL-1Ra restored ERα, suggesting their arsenic-induced interdependence. We finally correlated this pathway with apoptosis and cognition. We observed that PPT, IL-1Ra and the GSK3β inhibitor, LiCl, reduced hippocampal neuronal cleaved caspase-3 and TUNEL+ve apoptotic count, and decreased the number of errors during learning and increased the saving-memory for Y-Maze Test and retention performance for Passive avoidance test in arsenic-treated rats. Thus, our study reveals a novel mechanism of arsenic-induced GSK3β-dependent tau pathology via interdependent ERα and IL-1/IL-1R1 signaling. It also envisages the protective role of ERα agonist and IL-1 inhibitor against arsenic-induced neurotoxicity.

DMTHB ameliorates memory impairment in Alzheimer's disease mice through regulation of neuroinflammation

BACKGROUND

Alzheimer's disease (AD) is one of the most prevalent neurodegenerative diseases. Growing evidence suggested that AD is associated with neuroinflammation, characterized with the chronic activation of microglial cells and astrocytes along with the subsequent excessive generation of the proinflammatory molecules. This study aimed to investigate the effect and molecular mechanism of Demethylenetetrahydroberberine (DMTHB) on Alzheimer's disease (AD).

METHODS

AD mice model were made by intracranial injection of Aβ_25-35. DMTHB (50 mg/kg or 150 mg/kg) was intragastrically administered every day for three weeks. Morris water maze (MWM) was applied to evaluate the capacity of learning and memory of mice. Pathological change and neuronal death were detected by HE staining Moreover, the expressions of NLRP3, ASC, Caspase 1, IL-6, IL-1β, TNF-α and Tau in the brain tissue were measured by qRT-PCR and western blot.

RESULTS

Our results showed that the cognition of AD mice was significantly improved by DMTHB administration. DMTHB inhibited the activation of the microglia and significantly reduced the expression of Iba-1 in the brains of AD mice. In addition, DMTHB effectively suppressed the activation of NLRP3 inflammasome induced by Aβ_25-35. The results showed that the content of inflammatory cytokine (TNF-α, IL-1β and IL-6) in the brains of AD mice were down-regulated by DMTHB treatment. More importantly, DMTHB treatment significantly alleviated hippocampus neuron deformation and apoptosis.

CONCLUSION

These results indicated that DMTHB could be a potential medicine against AD through regulation of neuroinflammation.

Ginsenoside Rd Attenuates Tau Phosphorylation in Olfactory Bulb, Spinal Cord, and Telencephalon by Regulating Glycogen Synthase Kinase 3β and Cyclin-Dependent Kinase 5

OBJECTIVE

Ginseng is a plant of the family Acanthopanaceae. It has been used for thousands of years in China. It is known as the king of hundred herbs. It was recorded first in Shennong Baicao Jing. It has been found that ginsenoside Rd is a neuroprotective agent. This article aims to explore the protective roles of ginsenoside Rd in Alzheimer's disease. Rd, a Chinese herb, may be a promising treatment drug for Alzheimer's disease (AD) and is also reported to be related to several pathological changes, including the deposition of Aβ and tau hyperphosphorylation in AD as it decreases the deposition of tau hyperphosphorylation in APP transgenic mice.

METHODS

In this study, APP transgenic mice were pretreated with 10 mg/kg Rd for six months, and the effect of Rd on neuropathological deficits in the olfactory bulb, spinal cord, and telencephalon of APP transgenic mice was investigated. The phosphorylation levels of tau (S199/202, S396, S404, and Tau5) and the activities of the proteins glycogen synthase kinase 3β (Tyr216) and cyclin-dependent kinase 5 (P25/P35) were measured.

RESULTS

The pretreatment of Rd effectively decreased the production and deposition of hyperphosphorylated tau (S199/202, S396, and S404) protein by depressing the expression of glycogen synthase kinase 3β (GSK-3β/Tyr216) and cyclin-dependent kinase 5 (CDK5/P25).

CONCLUSION

These findings suggest that ginsenoside Rd could improve the pathological changes of AD in the olfactory bulb, spinal cord, and telencephalon, which further demonstrated the potential therapeutic effect of Rd in early AD.

Reduced TREM2 activation in microglia of patients with Alzheimer's disease

Loss-of-function variants of triggering receptor expressed on myeloid cells 2 (TREM2) increase the risk of developing Alzheimer's disease (AD). The mechanism through which TREM2 contributes to the disease (TREM2 activation vs inactivation) is largely unknown. Here, we analyzed changes in a gene set downstream of TREM2 to determine whether TREM2 signaling is modified by AD progression. We generated an anti-human TREM2 agonistic antibody and defined TREM2 activation in terms of the downstream expression changes induced by this antibody in microglia developed from human induced pluripotent stem cells (iPSC). Differentially expressed genes (DEGs) following TREM2 activation were compared with the gene set extracted from microglial single nuclear RNA sequencing data of patients with AD, using gene set enrichment analysis. We isolated an anti-TREM2-specific agonistic antibody, Hyb87, from anti-human TREM2 antibodies generated using binding and agonism assays, which helped us identify 300 upregulated and 251 downregulated DEGs. Pathway enrichment analysis suggested that TREM2 activation may be associated with Th2-related pathways. TREM2 activation was lower in AD microglia than in microglia from healthy subjects or patients with mild cognitive impairment. TREM2 activation also showed a significant negative correlation with disease progression. Pathway enrichment analysis of DEGs controlled by TREM2 activity indicated that TREM2 activation in AD may lead to anti-apoptotic signaling, immune response, and cytoskeletal changes in the microglia. We showed that TREM2 activation decreases with AD progression, in support of a protective role of TREM2 activation in AD. In addition, the agonistic anti-TREM2 antibody can be used to identify TREM2 activation state in AD microglia.

The effect and mechanism of cypermethrin-induced hippocampal neurotoxicity as determined by network pharmacology analysis and experimental validation

Cypermethrin (CMN) is a widely used artificial synthetic pesticide that causes neurotoxicity in the hippocampus. However, the underlying toxicological targets and mechanisms remain unclear. In this study, network pharmacology analysis and in vitro models were integrated to investigate the effect and mechanism of CMN-induced hippocampal neurotoxicity. A total of 88 targets of CMN-induced hippocampal neurotoxicity were predicted. Gene Ontology (GO) and Kyoto Encyclopedia of Genes and Genomes enrichment (KEGG) analyses suggested that these targets were related to multiple GO terms and signaling pathways. To further investigate underlying mechanism, the top 10 hub targets (Akt1, Tnf, Ptgs2, Casp3, Igf1, Sirt1, Jun, Cat, Il10, and Bcl2l1) were screened. Furthermore, cell viability and lactate dehydrogenase (LDH) assays demonstrated that CMN was toxic to HT22 cells in a time- and dose-dependent manner. Terminal deoxynucleotidyl transferase dUTP nick end labeling (TUNEL) staining revealed that treatment with CMN increased the proportion of apoptotic cells. In addition, the real-time quantitative polymerase chain reaction (RT-qPCR) results indicated that CMN altered the mRNA expression levels of most of the hub targets, with the exceptions of Igf1 and Jun. The results demonstrated that multiple targets and signaling pathways were involved in CMN-induced hippocampal neurotoxicity. These findings provided reference values for subsequent studies of the toxicological mechanism of CMN.

Role of Neuron and Glia in Alzheimer's Disease and Associated Vascular Dysfunction

Amyloidogenicity and vascular dysfunction are the key players in the pathogenesis of Alzheimer’s disease (AD), involving dysregulated cellular interactions. An intricate balance between neurons, astrocytes, microglia, oligodendrocytes and vascular cells sustains the normal neuronal circuits. Conversely, cerebrovascular diseases overlap neuropathologically with AD, and glial dyshomeostasis promotes AD-associated neurodegenerative cascade. While pathological hallmarks of AD primarily include amyloid-β (Aβ) plaques and neurofibrillary tangles, microvascular disorders, altered cerebral blood flow (CBF), and blood-brain barrier (BBB) permeability induce neuronal loss and synaptic atrophy. Accordingly, microglia-mediated inflammation and astrogliosis disrupt the homeostasis of the neuro-vascular unit and stimulate infiltration of circulating leukocytes into the brain. Large-scale genetic and epidemiological studies demonstrate a critical role of cellular crosstalk for altered immune response, metabolism, and vasculature in AD. The glia associated genetic risk factors include APOE, TREM2, CD33, PGRN, CR1, and NLRP3, which correlate with the deposition and altered phagocytosis of Aβ. Moreover, aging-dependent downregulation of astrocyte and microglial Aβ-degrading enzymes limits the neurotrophic and neurogenic role of glial cells and inhibits lysosomal degradation and clearance of Aβ. Microglial cells secrete IGF-1, and neurons show a reduced responsiveness to the neurotrophic IGF-1R/IRS-2/PI3K signaling pathway, generating amyloidogenic and vascular dyshomeostasis in AD. Glial signals connect to neural stem cells, and a shift in glial phenotype over the AD trajectory even affects adult neurogenesis and the neurovascular niche. Overall, the current review informs about the interaction of neuronal and glial cell types in AD pathogenesis and its critical association with cerebrovascular dysfunction.

Hypothyroidism Induces Interleukin-1-Dependent Autophagy Mechanism as a Key Mediator of Hippocampal Neuronal Apoptosis and Cognitive Decline in Postnatal Rats

Thyroid hormone (TH) is essential for brain development, and hypothyroidism induces cognitive deficits in children and young adults. However, the participating mechanisms remain less explored. Here, we examined the molecular mechanism, hypothesizing the involvement of a deregulated autophagy and apoptosis pathway in hippocampal neurons that regulate cognitive functions. Therefore, we used a rat model of developmental hypothyroidism, generated through methimazole treatment from gestation until young adulthood. We detected that methimazole stimulated the autophagy mechanism, characterized by increased LC3B-II, Beclin-1, ATG7, and ATG5-12 conjugate and decreased p-mTOR/mTOR and p-ULK1/ULK1 autophagy regulators in the hippocampus of developing and young adult rats. This methimazole-induced hippocampal autophagy could be inhibited by thyroxine treatment. Subsequently, probing the upstream mediators of autophagy revealed an increased hippocampal neuroinflammation, marked by upregulated interleukin (IL)-1alpha and beta and activated microglial marker, Iba1, promoting neuronal IL-1 receptor-1 expression. Hence, IL-1R-antagonist (IL-1Ra), which reduced hippocampal neuronal IL-1R1, also inhibited the enhanced autophagy in hypothyroid rats. We then linked these events with hypothyroidism-induced apoptosis and loss of hippocampal neurons, where we observed that like thyroxine, IL-1Ra and autophagy inhibitor, 3-methyladenine, reduced the cleaved caspase-3 and TUNEL-stained apoptotic neurons and enhanced Nissl-stained neuronal count in methimazole-treated rats. We further related these molecular results with cognition through Y-maze and passive avoidance tests, demonstrating an IL-1Ra and 3-methyladenine-mediated improvement in learning-memory performances of the hypothyroid rats. Taken together, our study enlightens the critical role of neuroinflammation-dependent autophagy mechanism in TH-regulated hippocampal functions, disrupted in developmental hypothyroidism.

APP Binds to the EGFR Ligands HB-EGF and EGF, Acting Synergistically with EGF to Promote ERK Signaling and Neuritogenesis

The amyloid precursor protein (APP) is a transmembrane glycoprotein central to Alzheimer's disease (AD) with functions in brain development and plasticity, including in neurogenesis and neurite outgrowth. Epidermal growth factor (EGF) and heparin-binding EGF-like growth factor (HB-EGF) are well-described neurotrophic and neuromodulator EGFR ligands, both implicated in neurological disorders, including AD. Pro-HB-EGF arose as a putative novel APP interactor in a human brain cDNA library yeast two-hybrid screen. Based on their structural and functional similarities, we first aimed to verify if APP could bind to (HB-)EGF proforms. Here, we show that APP interacts with these two EGFR ligands, and further characterized the effects of APP-EGF interaction in ERK activation and neuritogenesis. Yeast co-transformation and co-immunoprecipitation assays confirmed APP interaction with HB-EGF. Co-immunoprecipitation also revealed that APP binds to cellular pro-EGF. Overexpression of HB-EGF in HeLa cells, or exposure of SH-SY5Y cells to EGF, both resulted in increased APP protein levels. EGF and APP were observed to synergistically activate the ERK pathway, crucial for neuronal differentiation. Immunofluorescence analysis of cellular neuritogenesis in APP overexpression and EGF exposure conditions confirmed a synergistic effect in promoting the number and the mean length of neurite-like processes. Synergistic ERK activation and neuritogenic effects were completely blocked by the EGFR inhibitor PD 168393, implying APP/EGF-induced activation of EGFR as part of the mechanism. This work shows novel APP protein interactors and provides a major insight into the APP/EGF-driven mechanisms underlying neurite outgrowth and neuronal differentiation, with potential relevance for AD and for adult neuroregeneration.

An epigenome-wide association study of ambient pyrethroid pesticide exposures in California's central valley

BACKGROUND

Pyrethroid pesticide use is increasing worldwide, although the full extent of associated health effects is unknown. An epigenome-wide association study (EWAS) with exploratory pathway analysis may help identify potential pyrethroid-related health effects.

METHODS

We performed an exploratory EWAS of chronic ambient pyrethroid exposure using control participants' blood in the Parkinson's Environment and Genes Study in the Central Valley of California (N = 237). We estimated associations of living and working near agricultural pyrethroid pesticide applications in the past 5 years (binary) with site-specific differential methylation, and used a false discovery rate (FDR) cut off of 0.05 for significance. We controlled for age, sex, education, cell count, and an ancestral marker for Hispanic ethnicity. We normalized methylation values for Type I/II probe bias using Beta-Mixture Quantile (BMIQ) normalization, filtered out cross-reactive probes, and evaluated for remaining bias with Surrogate Variable Analysis (SVA). We also evaluated the effects of controlling for cell count and normalizing for Type I/II probe bias by comparing changes in effect estimates and p-values for the top hits across BMIQ and GenomeStudio normalization methods, and controlling for cell count. To facilitate broader interpretation, we annotated genes to the CpG sites and performed gene set overrepresentation analysis, using genes annotated to CpG sites that were associated with pyrethroids at a raw p < 0.05, and controlling for background representation of CpG sites on the chip. We did this for both a biological process context (Gene Ontology terms) using missMethyl, and a disease set context using WebGestalt. For these gene set overrepresentation analyses we also used an FDR cut off of 0.05 for significance of gene sets.

RESULTS

After controlling for cell count and applying BMIQ normalization, 4 CpG sites were differentially methylated in relation to pyrethroid exposures. When using GenomeStudio's Illumina normalization, 415 CpG sites were differentially methylated, including all four identified with the BMIQ method. In the gene set overrepresentation analyses, we identified 6 GO terms using BMIQ normalization, and 76 using Illumina normalization, including the 6 identified by BMIQ. For disease sets, we identified signals for Alzheimer's disease, leukemia and several other cancers, diabetes, birth defects, and other diseases, for both normalization methods. We identified minimal changes in effect estimates after controlling for cell count, and controlling for cell count generally weakened p-values. BMIQ normalization, however, resulted in different beta coefficients and weakened p-values.

CONCLUSIONS

Chronic ambient pyrethroid exposure is associated with differential methylation at CpG sites that annotate to a wide variety of disease states and biological mechanisms that align with prior research. However, this EWAS also implicates several novel diseases for future investigation, and highlights the relative importance of different background normalization methods in identifying associations.

Neuropathological Mechanisms Associated with Pesticides in Alzheimer's Disease

Environmental toxicants have been implicated in neurodegenerative diseases, and pesticide exposure is a suspected environmental risk factor for Alzheimer’s disease (AD). Several epidemiological analyses have affirmed a link between pesticides and incidence of sporadic AD. Meanwhile, in vitro and animal models of AD have shed light on potential neuropathological mechanisms. In this paper, a perspective on neuropathological mechanisms underlying pesticides’ induction of AD is provided. Proposed mechanisms range from generic oxidative stress induction in neurons to more AD-specific processes involving amyloid-beta (Aβ) and hyperphosphorylated tau (p-tau). Mechanisms that are more speculative or indirect in nature, including somatic mutation, epigenetic modulation, impairment of adult neurogenesis, and microbiota dysbiosis, are also discussed. Chronic toxicity mechanisms of environmental pesticide exposure crosstalks in complex ways and could potentially be mutually enhancing, thus making the deciphering of simplistic causal relationships difficult.

Garcinol pacifies acrylamide induced cognitive impairments, neuroinflammation and neuronal apoptosis by modulating GSK signaling and activation of pCREB by regulating cathepsin B in the brain of zebrafish larvae

The presence of acrylamide (ACR) in food results in evident cognitive decline, accumulation of misfolded proteins, neurotoxicity, neuroinflammation, and neuronal apoptosis leading to progressive neurodegeneration. Here, we used 4 dpf zebrafish larvae exposed to ACR (1mM/3days) as our model, and neuronal proteins were analyzed. Next, we tested the effect of garcinol (GAR), a natural histone-acetylation inhibitor, whose neuroprotection mechanism of action remains to be fully elucidated. Our result revealed that ACR exposure significantly impaired cognitive behavior, downregulated oxidative repair machinery, and enhanced microglia-induced neuronal apoptosis. Moreover, ACR mediated cathepsin-B (CAT-B) translocation acted as the intracellular secretase for the processing of amyloid precursor protein (APP) and served as an additional risk factor for tau hyper-phosphorylation. Here, GAR suppresses ACR mediated CATB translocation as similar with standard inhibitor CA-074. And, this pharmacological repression helped in inhibiting amyloidogenic APP processing and downstream tau hyper-phosphorylation. GAR neuroprotection was accompanied by CREB, ATF1, and BDNF activation promoting neuronal survival. At the same time, GAR subdued cdk5 and GSK3β, the link between APP processing and tau hyper-phosphorylation. Taken together, our findings indicate that GAR rescued from ACR mediated behavioral defects, oxidative injury, neuroinflammation, undesirable APP processing, tau hyper-phosphorylation which in turn found to be CATB dependent.

Neuroprotective effects of a Rhodiola crenulata extract on amyloid-β peptides (Aβ1-42) -induced cognitive deficits in rat models of Alzheimer's disease

BACKGROUND

Rhodiola crenulata has been wildly used as a healthy food, antidepressant and antifatigue for many years in China. Recent studies suggested that Rhodiola crenulata extract (RCE) has cognitive protective effects in the treatment of Alzheimer's disease (AD).

PURPOSE

To assess the protective effects of RCE on cognitive deficits and clarify its therapeutic mechanisms in Aβ_1-42 -induced rat models of AD.

STUDY DESIGN

RCE was prepared by freeze-drying technology. Their protective effects on Aβ_1-42-induced rat models of AD and the preliminary therapeutic mechanisms were studied.

METHODS

The Y maze test and Morris water maze (MWM) test were conducted to evaluate the learning and memory abilities of the rats. Subsequently, biochemical assays, hematoxylin-eosin staining, immunohistochemistry and Western blotting were performed to elucidate the mechanisms.

RESULTS

RCE significantly increased the spontaneous alternation (F (6, 111) = 8.165, p < 0.001), prolonged the swimming time (F (6, 111) = 20.143, p < 0.001) and decreased the escape latency in rat models of AD. In addition, RCE significantly increased the acetylcholine (Ach) level and the choline acetyl transferase (ChAT) activity (F (6, 34) = 6.033, p < 0.001; F (6, 34) = 6.958, p < 0.001, respectively), repaired the damage of hippocampus neurons and prevented Aβ formation in the hippocampus in Aβ_1-42 injected rats. Moreover, RCE increased the superoxide dismutase (SOD) activity and decreased the malondialdehyde (MDA) level in cortex of Aβ_1-42 injected rats (F (6, 34) = 5.097, p < 0.01; F (6, 34) = 2.907, p < 0.05, respectively), significantly reduced the expressions of p-tau (ser396) and induced the expressions of p-GSK3β (ser9) in hippocampus (F (6, 34) = 15.297, p < 0.001; F (6, 34) = 9.652, p < 0.001, respectively).

CONCLUSION

Our findings demonstrated that RCE significantly alleviated the learning and memory deficits in the Aβ_1-42-induced rat models of AD. The mechanisms involved its protection effects against cholinergic system deficiency, oxidative stress damage and GSK3β activation. RCE may be a potential therapeutic medicine with multi-targets to prevent the progression of cognitive deterioration in AD.

Endosulfan and Cypermethrin Pesticide Mixture Induces Synergistic or Antagonistic Effects on Developmental Exposed Rats Depending on the Analyzed Behavioral or Neurochemical End Points

Exposure to pesticides has been associated with neurodevelopmental toxicity. Usually people are exposed to mixtures of pesticides. However, most studies analyze the effects of individual pesticides. Developmental exposure to mixtures of pesticides may result in additive effects or in antagonistic or synergistic effects. The aim of this work was to compare the effects of developmental exposure of rats to cypermethrin or endosulfan with the effects of its mixture on cognitive and motor function and on some underlying mechanisms. Exposure to individual pesticides or the mixture was from gestational day 7 to postnatal day 21. We analyzed the effects, in males and females, on spatial learning and memory, associative learning, anxiety, motor coordination, and spontaneous motor activity. We also analyzed neuroinflammation and NMDA receptor subunits in hippocampus and extracellular GABA in cerebellum. Exposure to the mixture, but not to individual pesticides, impaired spatial memory in males, associative learning in females, and increased motor activity in males and females. This indicates a synergistic effect of cypermethrin and endolsufan exposure on these end points. In contrast, motor coordination was impaired by individual exposure to endosulfan or cypermethrin, associated with increased extracellular GABA in cerebellum, but these effects were prevented in rats exposed to the mixture, indicating an antagonistic effect of cypermethrin and endolsufan exposure on these end points. The results show different interaction modes (synergism or antagonism) of the pesticides, depending on the end point analyzed and the sex of the rats.

Transethnic genome-wide scan identifies novel Alzheimer's disease loci

INTRODUCTION

Genetic loci for Alzheimer's disease (AD) have been identified in whites of European ancestry, but the genetic architecture of AD among other populations is less understood.

METHODS

We conducted a transethnic genome-wide association study (GWAS) for late-onset AD in Stage 1 sample including whites of European Ancestry, African-Americans, Japanese, and Israeli-Arabs assembled by the Alzheimer's Disease Genetics Consortium. Suggestive results from Stage 1 from novel loci were followed up using summarized results in the International Genomics Alzheimer's Project GWAS dataset.

RESULTS

Genome-wide significant (GWS) associations in single-nucleotide polymorphism (SNP)-based tests (P < 5 × 10-8) were identified for SNPs in PFDN1/HBEGF, USP6NL/ECHDC3, and BZRAP1-AS1 and for the interaction of the (apolipoprotein E) APOE ε4 allele with NFIC SNP. We also obtained GWS evidence (P < 2.7 × 10-6) for gene-based association in the total sample with a novel locus, TPBG (P = 1.8 × 10-6).

DISCUSSION

Our findings highlight the value of transethnic studies for identifying novel AD susceptibility loci.

From the Cover: Vulnerability of C6 Astrocytoma Cells After Single-Compound and Joint Exposure to Type I and Type II Pyrethroid Insecticides

A primary mode-of-action of all pyrethroid insecticides (PYRs) is the disruption of the voltage-gated sodium channel electrophysiology in neurons of target pests and nontarget species. The neurological actions of PYRs on non-neuronal cells of the nervous system remain poorly investigated. In the present work, we used C6 astrocytoma cells to study PYR actions (0.1-50 μM) under the hypothesis that glial cells may be targeted by and vulnerable to PYRs. To this end, we characterized the effects of bifenthrin (BF), tefluthrin (TF), α-cypermethrin (α-CYP), and deltamethrin (DM) on the integrity of nuclear, mitochondrial, and lysosomal compartments. In general, 24- to 48-h exposures produced concentration-related impairment of cell viability. In single-compound, 24-h exposure experiments, effective concentration (EC)₁₅s 3-(4,5-dimethyl-thiazol-2-yl)-2,5-diphenyl-tetrazolium bromide (MTT assay) were computed as follows (in μM): BF, 16.1; TF, 37.3; α-CYP, 7.8; DM, 5.0. We found concentration-related damage in several C6-cell subcellular compartments (mitochondria, nuclei, and lysosomes) at ≥ 10^-1 μM levels. Last, we examined a mixture of all PYRs (ie, Σ individual EC₁₅) using MTT assays and subcellular analyses. Our findings indicate that C6 cells are responsive to nM levels of PYRs, suggesting that astroglial susceptibility may contribute to the low-dose neurological effects caused by these insecticides. This research further suggests that C6 cells may provide relevant information as a screening platform for pesticide mixtures targeting nervous system cells by expected and unexpected toxicogenic pathways potentially contributing to clinical neurotoxicity.

Selenomethionine Ameliorates Neuropathology in the Olfactory Bulb of a Triple Transgenic Mouse Model of Alzheimer's Disease

Olfactory dysfunction is an early and common symptom in Alzheimer's disease (AD) and is reported to be related to several pathologic changes, including the deposition of Aβ and hyperphosphorylated tau protein as well as synaptic impairment. Selenomethionine (Se-Met), the major form of selenium in animals and humans, may be a promising therapeutic option for AD as it decreases the deposition of Aβ and tau hyperphosphorylation in a triple transgenic mouse model of AD (3× Tg-AD). In this study, 4-month-old AD mice were treated with 6 µg/mL Se-Met in drinking water for 12 weeks and the effect of Se-Met on neuropathological deficits in olfactory bulb (OB) of 3× Tg-AD mice was investigated. The administration of Se-Met effectively decreased the production and deposition of Aβ by inhibiting β-site amyloid precursor protein cleaving enzyme 1 (BACE1)-regulated amyloid precursor protein (APP) processing and reduced the level of total tau and phosphorylated tau, which depended on depressing the activity and expression of glycogen synthase kinase-3β (GSK-3β) and cyclin-dependent kinase 5 (CDK5). Meanwhile, Se-Met reduced glial activation, relieved neuroinflammation and attenuated neuronal cell death in the OB of AD mice. So Se-Met could improve pathologic changes of AD in the OB, which further demonstrated the potential therapeutic effect of Se-Met in AD.

Developmental perfluorooctane sulfonate exposure results in tau hyperphosphorylation and β-amyloid aggregation in adults rats: Incidence for link to Alzheimer's disease

With regard to the defects of the cognitive function observed after developmental exposure to perfluorooctane sulfonate (PFOS), and earlier studies on the developmental neurotoxicology, the aim of this study was to investigate the role of developmental PFOS exposure in neurodegenerative disorders in later life. Two pathological hallmarks of Alzheimer's disease (AD), Tau hyperphosphorylation and β-amyloid (Aβ) aggregation, were examined. SD rats were exposed to PFOS during only prenatal and/or postnatal period. Tau mRNA and protein levels were elevated by PFOS exposure. The phosphorylation of Tau at S199, T231 and S396 sites were also increased. Besides, PFOS exposure increased the Aβ1-42 levels, as well as the amyloid precursor protein (APP) regulation. The prenatal PFOS exposure caused alterations in the involved proteins at comparable levels with the postnatal and both prenatal and postnatal exposure. Thus, it has raised some evidence that early PFOS exposure can affect processes linked to neurodegeneration, enhancing the AD pathological risk. And PFOS exposures in early life may be of particular etiologic importance of neurodegenerative diseases.