Hui-Li Wang

Epigenetic histone modification regulates developmental lead exposure induced hyperactivity in rats

Lead (Pb) exposure was commonly considered as a high environmental risk factor for the development of attention-deficit/hyperactivity disorder (ADHD). However, the molecular basis of this pathological process still remains elusive. In light of the role of epigenetics in modulating the neurological disease and the causative environment, the alterations of histone modifications in the hippocampus of rats exposed by various doses of lead, along with concomitant behavioral deficits, were investigated in this study. According to the free and forced open field test, there showed that in a dosage-dependent manner, lead exposure could result in the increased locomotor activity of rats, that is, hyperactivity: a subtype of ADHD. Western blotting assays revealed that the levels of histone acetylation increased significantly in the hippocampus by chronic lead exposure, while no dramatic changes were detected in terms of expression yields of ADHD-related dopaminergic proteins, indicating that histone acetylation plays essential roles in this toxicant-involved pathogenesis. In addition, the increased level of histone acetylation might be attributed to the enzymatic activity of p300, a typical histone acetyltransferase, as the transcriptional level of p300 was significantly increased upon higher-dose Pb exposure. In summary, this study first discovered the epigenetic mechanism bridging the environmental influence (Pb) and the disease itself (ADHD) in the histone modification level, paving the way for the comprehensive understanding of ADHDs etiology and in further steps, establishing the therapy strategy of this widespread neurological disorder.

Multiple epigenetic factors predict the attention deficit/hyperactivity disorder among the Chinese Han children

Attention deficit/hyperactivity disorder (ADHD) is one of the most common psychiatric disorders of childhood. Despite its prevalence, the critical factors involved in its development remain to be identified. It was recently suggested that epigenetic mechanisms probably contribute to the etiology of ADHD. The present study was designed to examine the associations of epigenetic markers with ADHD among Chinese Han children, aiming to establish the prediction model for this syndrome from the epigenetic perspective. We conducted a pair-matching case-control study, and the ADHD children were systematically evaluated via structured diagnostic interviews, including caregiver interviews, based on the Diagnostic and Statistical Manual of Mental Disorders, 4th edition, revised criteria (DSM-IV-R). The expression levels of risk genes DAT1, DRD4, DRD5, as well as their promoter methylation, were determined respectively, followed by the expression profiles of histone-modifying genes p300, MYST4, HDAC1, MeCP2. The multivariate logistic regressions were performed to establish ADHD prediction models. All of the seven genes tested were identified as risk factors for ADHD. The methylation of one critical CpG site located upstream of DRD4 was shown to affect its transcription, suggesting a role in ADHDs development. Aberrant DNA methylation and histone acetylation were indicated in ADHD patients. In addition, a prediction model was established using the combination of p300, MYST4 and HDAC1, with the accuracy of 0.9338. This is, to our knowledge, the first study to clearly demonstrate the associations between epigenetic markers and ADHD, shedding light on the preliminary diagnosis and etiological studies of this widespread disorder.

Developmental Lead Exposure Alters Synaptogenesis through Inhibiting Canonical Wnt Pathway In Vivo and In Vitro

Lead (Pb) exposure has been implicated in the impairment of synaptic plasticity in the developing hippocampus, but the mechanism remains unclear. Here, we investigated whether developmental lead exposure affects the dendritic spine formation through Wnt signaling pathway in vivo and in vitro. Sprague–Dawley rats were exposed to lead throughout the lactation period and Golgi-Cox staining method was used to examine the spine density of pyramidal neurons in the hippocampal CA1 area of rats. We found that lead exposure significantly decreased the spine density in both 14 and 21 days-old pups, accompanied by a significant age-dependent decline of the Wnt7a expression and stability of its downstream protein (β-catenin). Furthermore, in cultured hippocampal neurons, lead (0.1 and 1 µM lead acetate) significantly decreased the spine density in a dose-dependent manner. Exogenous Wnt7a application attenuated the decrease of spine density and increased the stability of the downstream molecules in Wnt signaling pathway. Together, our results suggest that lead has a negative impact on spine outgrowth in the developing hippocampus through altering the canonical Wnt pathway.

Kiwifruit Alleviates Learning and Memory Deficits Induced by Pb through Antioxidation and Inhibition of Microglia Activation In Vitro and In Vivo

Lead (Pb) exposure, in particular during early postnatal life, increases susceptibility to cognitive dysfunction and neurodegenerative outcomes. The detrimental effect of Pb exposure is basically due to an increasing ROS production which overcomes the antioxidant systems and finally leads to cognitive dysfunction. Kiwifruit is rich in the antioxidants like vitamin C and polyphenols. This study aims to investigate the effects and mechanism of kiwifruit to alleviate learning and memory deficits induced by Pb exposure. Sprague-Dawley (SD) rat pups acquired Pb indirectly through their mothers during lactation period and after postnatal day 21 (PND21) directly acquired Pb by themselves. Five kinds of kiwifruits were collected in this study and the amounts of vitamin C and polyphenols in them were measured and the antioxidation effects were determined. Among them, Qinmei kiwifruit (Qm) showed the strongest antioxidation effects in vitro. In vivo, Qm significantly repaired Pb-induced learning and memory deficits and dendritic spine loss. In addition, Pb compromised the enzymatic activity and transcriptional levels of SOD and GSH-Px and decreased the microglial activation, which, to some extent, could be reversed by Qm kiwifruit administration. The results suggest that kiwifruit could alleviate Pb-induced cognitive deficits possibly through antioxidative stress and microglia inactivation. Consequently, kiwifruit could be potentially regarded as the functional food favorable in the prevention and treatment of Pb intoxication.

Early developmental bisphenol-A exposure sex-independently impairs spatial memory by remodeling hippocampal dendritic architecture and synaptic transmission in rats.

Bisphenol-A (BPA, 4, 4′-isopropylidene-2-diphenol), a synthetic xenoestrogen that widely used in the production of polycarbonate plastics, has been reported to impair hippocampal development and function. Our previous study has shown that BPA exposure impairs Sprague-Dawley (SD) male hippocampal dendritic spine outgrowth. In this study, the sex-effect of chronic BPA exposure on spatial memory in SD male and female rats and the related synaptic mechanism were further investigated. We found that chronic BPA exposure impaired spatial memory in both SD male and female rats, suggesting a dysfunction of hippocampus without gender-specific effect. Further investigation indicated that BPA exposure causes significant impairment of dendrite and spine structure, manifested as decreased dendritic complexity, dendritic spine density and percentage of mushroom shaped spines in hippocampal CA1 and dentate gyrus (DG) neurons. Furthermore, a significant reduction in Arc expression was detected upon BPA exposure. Strikingly, BPA exposure significantly increased the mIPSC amplitude without altering the mEPSC amplitude or frequency, accompanied by increased GABAARβ2/3 on postsynaptic membrane in cultured CA1 neurons. In summary, our study indicated that Arc, together with the increased surface GABAARβ2/3, contributed to BPA induced spatial memory deficits, providing a novel molecular basis for BPA achieved brain impairment.

Bisphenol-A exposure alters memory consolidation and hippocampal CA1 spine formation through Wnt signaling in vivo and in vitro

Bisphenol-A (BPA) has been implicated in the impairment of brain function, but the mechanism remains elusive. Our previous work has found that developmental BPA exposure impairs dendritic spine formation in the DG area of the hippocampus in rats. In the present study, we were to investigate the effects of BPA exposure on memory consolidation and its underlying mechanism, especially focusing on the canonical Wnt signaling pathway. BPA was administered to early developmental male Sprague-Dawley (SD) rat pups by intraperitoneal injection with BPA at the dosages of 50, 250 and 500 μg kg−1 per day for seven days (from postnatal day (PND) 7 to PND 14), as well as chronically exposed to male rats with dosages of 0.15 mg kg−1 per day and 7.50 mg kg−1 per day through drinking water containing BPA from the prenatal period to 12 weeks old. Further studies were conducted in cultured hippocampal neurons to observe the BPA-induced spine density changes and mechanism in vitro. The results showed that BPA exposure significantly impaired spatial memory in adult rats, accompanied by decreased hippocampal CA1 dendritic spine density. Besides, we observed dramatic changes of Wnt related proteins in BPA exposed little pups and cultured hippocampal neurons. In brief, β-catenin phosphorylation level was significantly increased and Wnt7a, one of its upstream ligands, was significantly decreased following BPA exposure. Additionally, in cultured hippocampal neurons, exogenous Wnt7a application reversed the BPA-induced dendritic spine impairment and the decreased β-catenin phosphorylation level. In summary, this study reported that BPA exposure may produce long-lasting effects and provide a novel mechanism for memory deficits induced by BPA.

Role of Wnt/β-catenin signaling in the protective effect of epigallocatechin-3-gallate on lead-induced impairments of spine formation in the hippocampus of rats

The Wnt/β-catenin signaling pathway has been implicated in the development of dendritic spines, which are the structural basis for the induction of long-term potentiation. We have previously shown that exposure to Pb during development causes damage to the spines on hippocampal pyramidal neurons by decreasing the activity of the Wnt/β-catenin signaling pathway. Epigallocatechin-3-gallate (EGCG), the most abundant catechin in green tea, has been shown to recover impaired hippocampal-dependent long-term potentiation in rats exposed to Pb. We report here an investigation of whether this protective function of EGCG works by regulating the Wnt/β-catenin signaling pathway to refine the formation of spines in rats exposed to Pb during development. Sprague-Dawley rat pups were exposed to Pb from parturition to weaning and EGCG (10, 25 and 50 mg kg−1) was given intraperitoneally from postnatal day 14 to postnatal day 21. We found that exposure to Pb significantly decreased the density of dendritic spines and spine head size of pyramidal neurons in the hippocampal CA1 areas; EGCG (10 and 25 mg kg−1) reversed this Pb-induced spine damage. EGCG (10 and 25 mg kg−1) also recovered the expression of Wnt7a and β-catenin phosphorylation after exposure to Pb. However, 50 mg kg−1 of EGCG did not restore the spine morphology and the activity of the Wnt/β-catenin pathway on rats exposed to Pb. EGCG did not exert any protective effect on Pb2+-induced damage in cultured hippocampal neurons when Wnt7a shRNA applied. Our results show that EGCG (within a certain dose range) has a significant protective effect on spine formation and maturation through Wnt/β-catenin signaling in young rats exposed to Pb. This effect involves the up-regulation of Wnt7a expression and the attenuation of phospho-β-catenin expression. EGCG may be a potential complementary agent in the treatment of Pb poisoning.

Chronic Lead Exposure and Mixed Factors of Gender×Age×Brain Regions Interactions on Dendrite Growth, Spine Maturity and NDR Kinase

NDR1/2 kinase is essential in dendrite morphology and spine formation, which is regulated by cellular Ca2+. Lead (Pb) is a potent blocker of L-type calcium channel and our recent work showed Pb exposure impairs dendritic spine outgrowth in hippocampal neurons in rats. But the sensitivity of Pb-induced spine maturity with mixed factors (gender×age×brain regions) remains unknown. This study aimed to systematically investigate the effect of Pb exposure on spine maturity in rat brain with three factors (gender×age×brain regions), as well as the NDR1/2 kinase expression. Sprague–Dawley rats were exposed to Pb from parturition to postnatal day 30, 60, 90, respectively. Golgi-Cox staining was used to examine spine maturity. Western blot assay was applied to measure protein expression and real-time fluorescence quantitative PCR assay was used to examine mRNA levels. The results showed chronic Pb exposure significantly decreased dendritic length and impaired spine maturity in both rat hippocampus and medial prefrontal cortex. The impairment of dendritic length induced by Pb exposure tended to adolescence > adulthood, hippocampus > medial prefrontal cortex and female > male. Pb exposure induced significant damage in spine maturity during adolescence and early adult while little damage during adult in male rat brain and female medial prefrontal cortex. Besides, there was sustained impairment from adolescence to adulthood in female hippocampus. Interestingly, impairment of spine maturity followed by Pb exposure was correlated with NDR1/2 kinase. The reduction of NDR1/2 kinase protein expression after Pb exposure was similar to the result of spine maturity. In addition, NDR2 and their substrate Rabin3 mRNA levels were significantly decreased by Pb exposure in developmental rat brain. Taken together, Pb exposure impaired dendrite growth and maturity which was subject to gender×age×brain regions effects and related to NDR1/2 signal expression.

β-Asarone Rescues Pb-Induced Impairments of Spatial Memory and Synaptogenesis in Rats.

Chronic lead (Pb) exposure causes cognitive deficits. This study aimed to explore the neuroprotective effect and mechanism of β-asarone, an active component from Chinese Herbs Acorus tatarinowii Schott, to alleviate impairments of spatial memory and synaptogenesis in Pb-exposed rats. Both Sprague-Dawley developmental rat pups and adult rats were used in the study. Developmental rat pups were exposed to Pb throughout the lactation period and β-asarone (10, 40mg kg-1, respectively) was given intraperitoneally from postnatal day 14 to 21. Also, the adult rats were exposed to Pb from embryo stage to 11 weeks old and β-asarone (2.5, 10, 40mg kg-1, respectively) was given from 9 to 11 weeks old. The level of β-asarone in brain tissue was measured by High Performance Liquid Chromatography. The Morris water maze test and Golgi-Cox staining method were used to assess spatial memory ability and synaptogenesis. The protein expression of NR2B subunit of NMDA receptor, Activity-regulated cytoskeleton-associated protein (Arc/Arg3.1) and Wnt family member 7A (Wnt7a) in hippocampus, as well as mRNA expression of Arc/Arg3.1 and Wnt7a, was also explored. We found that β-asarone could pass through the blood brain barrier quickly. And β-asarone effectively attenuated Pb-induced reduction of spine density in hippocampal CA1 and dentate gyrus areas in a dose-dependent manner both in developmental and adult rats, meanwhile the Pb-induced impairments of learning and memory were partially rescued. In addition, β-asarone effectively up-regulated the protein expression of NR2B, Arc and Wnt7a, as well as the mRNA levels of Arc/Arg3.1 and Wnt7a, which had been suppressed by Pb exposure. The results suggest the neuroprotective properties of β-asarone against Pb-induced memory impairments, and the effect is possibly through the regulation of synaptogenesis, which is mediated via Arc/Arg3.1 and Wnt pathway.

Multiple regulatory aspects of histone methyltransferase EZH2 in Pb-induced neurotoxicity

Pb is a pervasive environmental threat to human health. Although remarkable progress has been made in its neurotoxicity, the precise molecular mechanisms underlying this widespread toxicant still remain elusive. In this study, the detailed roles of EZH2, a transcriptional repressor, in the regulation of Pb-led neurotoxicity were investigated, highlighting its sub-functionalization, compartmentalization, functional chaperones and downstream partners. Based on the findings, EZH2’s protein levels were significantly reduced in response to Pb treatment; EZH2’s gain-of-function trials recovered the dampened neurite outgrowth; EZH2’ recruitment to ploycomb complex, as well as its interaction with cytosolic Vav1, was altered in a distinct manner, suggesting that EZH2’s multiple roles were markedly redistributed in this context; EZH2’s cytosolic and nuclear presence differed in their respective response towards Pb treatment; EZH2 directly occupied the promoters of EGR2, NGFR and CaMKK2, genes responsible for various nerve functions and repair mechanisms, and essentially contributed to their aberrant expression. It indicated that EZH2 mediated the dynamic changes of a cascade of key molecules and consequently the related neurological impairments. In summary, EZH2 emerges as a central player to regulate Pb-led neurotoxicity in a transcriptionally dependent and independent manner, and thereby provided a promising molecular target for medical intervention.