Lactational exposure to environmentally relevant benzo(a)pyrene causes astrocytic activation and anxiety-like behavior in male mice

The role of periaqueductal gray astrocytes in anxiety-like behavior induced by acute stress

Astrocytes in the central nervous system play a vital role in modulating synaptic transmission and neuronal activation by releasing gliotransmitters. The 5-HTergic neurons in the ventrolateral periaqueductal gray (vlPAG) are important in anxiety processing. However, it remains uncertain whether the regulation of astrocytic activity on vlPAG 5-HTergic neurons is involved in anxiety processing. Here, through chemogenetic manipulation, we explored the impact of astrocytic activity in the PAG on the regulation of anxiety. To determine the role of astrocytes in the control of anxiety, we induced anxiety-like behaviors in mice through foot shock and investigated their effects on synaptic transmission and neuronal excitability in vlPAG 5-HTergic neurons. Foot shock caused anxiety-like behaviors, which were accompanied with the increase of the amplitude and frequency of miniature excitatory postsynaptic currents (mEPSCs), the area of slow inward currents (SICs), and the spike frequency of action potentials (AP) in vlPAG 5-HTergic neurons. The chemogenetic inhibition of vlPAG astrocytes was found to attenuate stress-induced anxiety-like behaviors and decrease the heightened synaptic transmission and neuronal excitability of vlPAG 5-HTergic neurons. Conversely, chemogenetic activation of vlPAG astrocytes triggered anxiety-like behaviors, enhanced synaptic transmission, and increased the excitability of vlPAG 5-HTergic neurons in unstressed mice. In summary, this study has provided initial insights into the pathway by which astrocytes influence behavior through the rapid regulation of associated neurons. This offers a new perspective for the investigation of the biological mechanisms underlying anxiety.

PAHs as environmental pollutants and their neurotoxic effects

Polycyclic aromatic hydrocarbons (PAHs), which are widely present in incompletely combusted air particulate matter <2.5 μm (PM2.5), tobacco and other organic materials, can enter the human body through various routes and are a class of environmental pollutants with neurotoxic effects. PAHs exposure can lead to abnormal development of the nervous system and neurobehavioral abnormalities in animals, including adverse effects on the nervous system of children and adults, such as a reduced learning ability, intellectual decline, and neural tube defects. After PAHs enter cells of the nervous system, they eventually lead to nervous system damage through mechanisms such as oxidative stress, DNA methylation and demethylation, and mitochondrial autophagy, potentially leading to a series of nervous system diseases, such as Alzheimer's disease. Therefore, preventing and treating neurological diseases caused by PAHs exposure are particularly important. From the perspective of the in vitro and in vivo effects of PAHs exposure, as well as its effects on human neurodevelopment, this paper reviews the toxic mechanisms of action of PAHs and the corresponding prevention and treatment methods to provide a relevant theoretical basis for preventing the neurotoxicity caused by PAHs, thereby reducing the incidence of diseases related to the nervous system and protecting human health.

Developmental exposure to polycyclic aromatic hydrocarbons (PAHs): Focus on benzo[a]pyrene neurotoxicity

Polycyclic Aromatic Hydrocarbons (PAHs) are a class of ubiquitous organic compounds produced during the incomplete combustion or pyrolysis of organic material. Dietary source is the main route for PAH human exposure by environmental contamination, food industrial processing or domestic cooking methods. The most studied PAH is benzo[a]pyrene (B[a]P), due to its harmful and multiple effects on human health: in addition to its well-known carcinogenic effects, emerging evidence indicates that B[a]P also induces neurotoxicity earlier and at lower doses than B[a]P-induced carcinogenicity making B[a]P neurotoxicity relevant to human health risk assessment. Developmental neurotoxicity of B[a]P has indeed received increasing attention: both human and experimental studies provide evidence of detrimental effects of prenatal or early postnatal B[a]P exposure, even at low doses. Indeed, in some of the multi-dose animal studies, maximal adverse effects were observed at lower B[a]P doses, according to a non-monotonic dose-response curve typical of endocrine-disrupting compounds. In substantial agreement with epidemiological studies, both rodents and zebrafish developmentally exposed to B[a]P exhibit long-term changes in multiple behavioural domains, in the absence of overt toxicological effects at birth (e.g. body weight and morphologic abnormalities). Notably, most targeted behavioural responses converge on locomotor activity and emotional profile, often, but not always, leading to a disinhibitory/hyperactive profile.

Gestational 1-nitropyrene exposure causes anxiety-like behavior partially by altering hippocampal epigenetic reprogramming of synaptic plasticity in male adult offspring

1-Nitropyrene (1-NP), a typical nitro-polycyclic aromatic hydrocarbon, is a developmental toxicant. This study was to evaluate gestational 1-NP-induced anxiety-like behavior in male adult offspring. Pregnant mice were orally administered to 1-NP daily throughout pregnancy. Anxiety-like behaviors, as determined by Elevated Plus-Maze (EPM) and Open-Field Test (OFT), were showed in male adult offspring whose mothers were exposed to 1-NP. Gestational 1-NP exposure reduced dendritic arborization, dendritic length and dendritic spine density in ventral hippocampus of male adult offspring. Additional experiments showed that gephyrin, an inhibitory synaptic marker, was reduced in fetal forebrain and hippocampus in male adult offspring. Nrg1 and Erbb4, two gephyrin-related genes, were reduced in 1-NP-exposed fetuses. Accordingly, 5hmC contents in two CpG sites (32008909 and 32009239) of Nrg1 gene and three CpG sites (69107743, 69107866 and 69107899) of Erbb4 gene were decreased in 1-NP-exposed fetuses. Mechanistically, ten-eleven translocation (TET) activity and alpha-ketoglutarate (α-KG) content were decreased in 1-NP-exposed fetal forebrain. Supplementation with α-KG alleviated 1-NP-induced downregulation of gephyrin-related genes, prevented hippocampal synaptic damage, and improved anxiety-like behavior in male adult offspring. These results indicate that early-life 1-NP exposure causes anxiety-like behavior in male adulthood partially by altering hippocampal epigenetic reprogramming of synaptic plasticity.

Aspirin ameliorates the neurotoxicity of benzo[a]pyrene in mice and HT22 cells: Possible role of miRNA-mRNA network

Benzo[a]pyrene (B[a]P) is neurotoxic, however, the mechanism and potential prevention are yet not clear. This study explored the miRNA-mRNA network in the B[a]P-induced neurotoxicity in mice and HT22 cells and the intervention of aspirin (ASP). HT22 cells were treated for 48 h with DMSO, B[a]P (20 μM), or both B[a]P (20 μM) and ASP (4 μM). Following B[a]P treatment, compared to the DMSO controls, HT22 cells showed injured cell morphology, reduced cell viability and neurotrophic factor concentrations, and increased LDH leakage, Aβ_1-42, and inflammatory factor concentrations, which were improved by ASP. RNA sequencing and qPCR verified the significant differences of miRNA and mRNA profiles following B[a]P treatment, which were rescued by ASP. Bioinformatics analysis suggested the miRNA-mRNA network could be involved in the neurotoxicity of B[a]P and the intervention of ASP. The neurotoxicity and neuroinflammation were induced in mice's brains by B[a]P, and the target miRNA and mRNA were proved to be consistent with in vitro, which were ameliorated by ASP. The findings demonstrate a possible role of miRNA-mRNA network in the B[a]P-induced neurotoxicity. If this is confirmed by additional experiments, it will provide a promising pathway of intervention against B[a]P, using ASP or other agents with fewer toxic effects.

Aspirin ameliorates the cognition impairment in mice following benzo[a]pyrene treatment via down-regulating BDNF IV methylation

Benzo[a]pyrene (B[a]P) is neurotoxic, however, the mechanisms remain unclear and there is no effective prevention. Available evidence suggests a role of DNA methylation in B[a]P-induced neurotoxicity. This study investigated the brain-derived neurotrophic factor (BDNF) IV methylation in the development of and aspirin intervention against B[a]P's neurotoxicity in mice and HT22 cells. Mice were intraperitoneally treated with solvent or B[a]P (0.5, 2, and 10 mg/kg b.w.) for 60 days. An intervention group was treated simultaneously with B[a]P (10 mg/kg, i.p.) and aspirin (10 mg/kg, daily water-drinking). The treated mice showed a dose-dependent cognitive and behavioral impairment, and cerebral cell apoptosis, which were alleviated by aspirin co-treatment. Following B[a]P treatment, DNA methyltransferase (DNMTs) and BDNF IV hypermethylation were increased in the cerebral cortex of mice compared to controls, while significant decreases were found in BDNF IV and BDNF mRNA, and BDNF protein levels. Aspirin co-treatment rescued DNMTs activation and BDNF IV hypermethylation, and mitigated the recession in BDNF mRNA and protein induced by B[a]P treatment. Similar results were shown in HT22 cells. These findings reveal a critical role of BDNF IV methylation in the neurotoxicity of B[a]P, and demonstrate a promising prevention of aspirin against B[a]P-induced cognitive impairment via inhibiting BDNF IV hypermethylation.

Transcriptome aberration associated with altered locomotor behavior of zebrafish (Danio rerio) caused by Waterborne Benzo[a]pyrene

Waterborne Benzo[a]pyrene (B[a]P) pollution is a global threat to aquatic organisms. The exposure to waterborne B[a]P can disrupt the normal locomotor behavior of zebrafish (Danio rerio), however, how it affect the locomotor behavior of adult zebrafish remains unclear. Herein, B[a]P at two concentrations (0.8 μg/L and 2.0 μg/L) were selected to investigate the molecular mechanisms of the affected locomotor behavior of zebrafish by B[a]P based on transcriptome profiling. Adverse effects of B[a]P exposure affecting locomotor behavior in zebrafish were studied by RNA sequencing, and the locomotion phenotype was acquired. The gene enrichment results showed that the differentially highly expressed genes (atp2a1, cdh2, aurka, fxyd1, clstn1, apoc1, mt-co1, tnnt3b, and fads2) of zebrafish are mainly enriched in adrenergic signaling in cardiomyocytes (dre04261) and locomotory behavior (GO:0007626). The movement trajectory plots showed an increase in the locomotor distance and velocity of zebrafish in the 0.8 μg/L group and the opposite in the 2.0 μg/L group. The results showed that B[a]P affects the variety of genes in zebrafish, including motor nerves, muscles, and energy supply, and ultimately leads to altered locomotor behavior.

Benzo(a)pyrene exposure induced neuronal loss, plaque deposition, and cognitive decline in APP/PS1 mice

Background

Exposure to benzo(a)pyrene (BaP) was associated with cognitive impairments and some Alzheimer’s disease (AD)-like pathological changes. However, it is largely unknown whether BaP exposure participates in the disease progression of AD.

Objectives

To investigate the effect of BaP exposure on AD progression and its underlying mechanisms.

Methods

BaP or vehicle was administered to 4-month-old APPswe/PS1dE9 transgenic (APP/PS1) mice and wildtype (WT) mice for 2 months. Learning and memory ability and exploratory behaviors were evaluated 1 month after the initiation/termination of BaP exposure. AD-like pathological and biochemical alterations were examined 1 month after 2-month BaP exposure. Levels of soluble beta-amyloid (Aβ) oligomers and the number of Aβ plaques in the cortex and the hippocampus were quantified. Gene expression profiling was used to evaluate alternation of genes/pathways associated with AD onset and progression. Immunohistochemistry and Western blot were used to demonstrate neuronal loss and neuroinflammation in the cortex and the hippocampus. Treatment of primary neuron-glia cultures with aged Aβ (a mixture of monomers, oligomers, and fibrils) and/or BaP was used to investigate mechanisms by which BaP enhanced Aβ-induced neurodegeneration.

Results

BaP exposure induced progressive decline in spatial learning/memory and exploratory behaviors in APP/PS1 mice and WT mice, and APP/PS1 mice showed severer behavioral deficits than WT mice. Moreover, BaP exposure promoted neuronal loss, Aβ burden and Aβ plaque formation in APP/PS1 mice, but not in WT mice. Gene expression profiling showed most robust alteration in genes and pathways related to inflammation and immunoregulatory process, Aβ secretion and degradation, and synaptic formation in WT and APP/PS1 mice after BaP exposure. Consistently, the cortex and the hippocampus of WT and APP/PS1 mice displayed activation of microglia and astroglia and upregulation of inducible nitric oxide synthase (iNOS), glial fibrillary acidic protein (GFAP), and NADPH oxidase (three widely used neuroinflammatory markers) after BaP exposure. Furthermore, BaP exposure aggravated neurodegeneration induced by aged Aβ peptide in primary neuron-glia cultures through enhancing NADPH oxidase-derived oxidative stress.

Conclusion

Our study showed that chronic exposure to environmental pollutant BaP induced, accelerated, and exacerbated the progression of AD, in which elevated neuroinflammation and NADPH oxidase-derived oxidative insults were key pathogenic events.

Resveratrol prevents benzo(a)pyrene-induced disruption of mitochondrial homeostasis via the AMPK signaling pathway in primary cultured neurons

Exposure to benzo(a)pyrene (BaP) has been shown to cause mitochondrial dysfunction and injury to neural cells. Resveratrol (RSV) has been studied as an antioxidant, anti-inflammatory, anti-apoptotic, and anticancer agent and can modulate mitochondrial function in vitro and in vivo. However, the molecular mechanisms underlying RSV's protection against mitochondrial dysfunction have not been fully elucidated. To investigate whether RSV can effectively prevent BaP-induced mitochondrial dysfunction, we tested the effects of RSV in primary neuronal models. Our results confirmed that neurons exhibited mitochondrial dysfunction and apoptosis in the mitochondrial pathway after BaP-treatment, and that pretreatment with RSV could reduce that dysfunction. Further, our results indicated that RSV pretreatment enhanced mitochondrial biogenesis via the AMPK/PGC-1α pathway and activated mitophagy via the PINK1-Parkin and AMPK/ULK1 pathways, thereby coordinating mitochondrial homeostasis. We also found that RSV could alleviate mitochondrial network fragmentation caused by BaP. This work provided insights into the role of RSV in preventing BaP-induced primary neuronal apoptosis in the mitochondrial pathway, mainly via regulation of mitochondrial biogenesis and mitophagy through AMPK pathway, thus maintaining the integrity of the mitochondrial network.

Bacopa monnieri inhibits apoptosis and senescence through mitophagy in human astrocytes

Benzo[a]pyrene (B[a]P), a polycyclic aromatic hydrocarbon, is a potent neurotoxic agent that is responsible for impaired neuronal development and is associated with aging. Here, it was demonstrated that extracts of Bacopa monnieri (BM), a traditional Ayurvedic medicine, diminished the B[a]P-induced apoptosis and senescence in human astrocytes. BM was demonstrated to protect the immortalized primary fetal astrocytes (IMPHFA) from B[a]P-induced apoptosis and senescence by reducing the damaged mitochondria that produced reactive oxygen species (ROS). Furthermore, it was shown that B[a]P-triggered G2 arrest could be altered by BM, thus indicating that BM could reverse the cell cycle arrest and mediate a normal cell cycle in IMPHFA cells. In addition, the lifespan of Caenorhabditis elegans was assessed, which confirmed these effects in the presence of BM, compared to the B[a]P-treated group. Furthermore, the anti-senescence and anti-apoptotic activities of BM were observed to be mediated through the protective effect of mitophagy, and inhibition of mitophagy could not protect the astrocytes from mitochondrial ROS-induced apoptosis and senescence in BM-treated cells. Moreover, it was revealed that BM induced Parkin-dependent mitophagy to exert its cytoprotective activity in IMPHFA cells. In conclusion, the anti-senescence and anti-apoptotic effects of BM in astrocytes could combat pollution and aging-related neurological disorders.