Lead is widely distributed in the environment and has become a global public health issue. It is well known that lead exposure induces not only neurodevelopmental toxicity but also neurodegenerative diseases, with learning and memory impairment in the later stage. However, the molecular mechanisms remain elusive. The present study investigated the effects of early life and lifetime lead exposure on cognition and identified the molecular mechanisms involved in aged rats. The results herein demonstrated that the lead concentration in peripheral blood and brain tissues in aged rats was significantly increased in a lead dose-dependent manner. High-dose lead exposure caused cognitive functional impairment in aged rats, concomitant with a longer escape latency and a lower frequency of crossing the platform via Morris water maze testing compared to those in the control and low-dose lead exposure groups. Importantly, neuron functional defects were still observed even in early life lead exposure during the prenatal and weaning periods in aged rats. The neurotoxicity induced by lead exposure was morphologically evidenced by a recessed nuclear membrane, a swollen endoplasmic reticulum, and mitochondria in the neurons. Mechanistically, the exposure of aged rats to lead resulted in increasing free calcium concentration, reactive oxygen species, and apoptosis in the hippocampal neurons. Lead exposure increased RyR3 expression and decreased the levels of p-CaMKIIα/CaMKIIα and p-CREB/CREB in the hippocampus of aged rats. These findings indicated that early life lead exposure-induced cognition disorder was irreversible in aged rats. Lead-induced neurotoxicity might be related to the upregulation of RyR3 expression and high levels of intracellular free calcium with increasing lead concentration in injured neurons.

Heavy metal lead (Pb) is widely distributed in the environment and can induce neurodegeneration. Accumulating evidence has shown that ryanodine receptors (RyRs) play vital roles in neurodegenerative brain. However, whether aberrant RyRs levels contribute to Pb-induced neurodegeneration has largely remained unknown. In the present study, we report the important role of elevated levels of RyRs in Pb-induced neurodegeneration. Pb was found to upregulate the levels of RyRs in the rat hippocampal tissues and rat pheochromocytoma (PC12) cells. Furthermore, exposure to Pb induced neurodegenerative cognitive impairment in rats, depressed the long-term potentiation (LTP) in the rat brain slices, increased the neuronal intracellular free calcium concentration ([Ca2+]i), inhibited the phosphorylation of Ca2+/calmodulin-dependent protein kinase II (CaMKII) and cyclic adenosine 30,50-monophosphate (cAMP) response element binding protein (CREB) as well as the expression of anti-apoptotic protein B-cell lymphoma 2 (Bcl2), and activated the phosphorylation of extracellular regulated protein kinases (Erk) protein both in vitro and in vivo. In addition, the knockdown of RyR3 in PC12 cells significantly decreased the [Ca2+]i levels, increased the CaMKII alpha and CREB phosphorylation, decrease the phosphorylation of Erk, and elongated the cognitive function-related neurite outgrowth after exposure to Pb. Moreover, treatment with a RyRs agonist showed the involvement of RyRs in Pb-induced depression in LTP in the rat brain slices. In summary, we determined that Pb-mediated upregulation of RyRs led to neurodegeneration via high levels of free calcium, depression of the calcium-dependent CaMKII alpha/CREB mnemonic signaling pathway, and activation of the calcium-dependent Erk/Bcl2 apoptotic signaling pathway. These findings on the impact of Pb on the levels of RyRs could further improve our understanding of Pb-induced neurotoxicity and provide a promising molecular target to antagonize Pb-induced neurodegenerative diseases. (C) 2019 Elsevier B.V. All rights reserved.

目的 了解铅冶炼企业对周边儿童血铅水平的影响.方法 于2011年9～11月对居住于某铅冶炼企业周边6个自然村的0～15周岁常住儿童进行调查,将自然村分为3个地区,即位于企业主导风的下风向(A区)、侧风向(B区)、上风向(C区),共252人.用MP-2溶出分析仪和血液荧光测定仪进行血铅值和血锌原卟啉含量测定.结果 该企业周边儿童血铅值中位数为95.29μg/L,P2.5～P75为66.41～165.43 μg/L,血铅超标率为46.83％.其中A区血铅水平(136.15 μg/L)高于B区(90.02 ug/L)及C区(82.62 μg/L),差异有统计学意义(P＜0.01);不同性别儿童血铅水平无明显差异(P＞0.05);0～7岁儿童血铅水平(122.45 μg/L)高于8～15岁儿童(85.33 μg/L),差异有统计学意义(Z=-5.506,P＜0.01).血锌原卟啉与血铅值水平呈正相关(rs=0.404,P＜0.O1).居住地位于企业主导风的下风向、年龄相对较低(0～7岁)是儿童血铅超标的危险因素,OR值分别为2.230(95％CI:1.164～4.272)和0.831 (95％CI:0.777～0.890).结论 铅冶炼企业可能对周边儿童体内血铅水平有一定影响.

Although the neurotoxic mechanism of lead (Pb2+) has been extensively studied, it is not well understood. The effects of Pb2+ on free cytosolic calcium (Ca2+) concentration and calcium-regulated events have been suggested to be major mechanisms in Pb2+ toxicity. Based on our previous findings that Pb2+ changes calcium release through ryanodine receptors (RyRs), the modulation of endoplasmic reticulum (ER) vesicular RyRs by Pb2+ was investigated further in the present study. The results of [3H]ryanodine binding assays showed that in the presence of a free Ca2+ concentration ([Ca2+]f) of 100μM, Pb2+ modulated the equilibrium of [3H]ryanodine binding to brain RyRs, with a U-type dose-response curve, where minimal binding was observed at a free Pb2+ concentration ([Pb2+]f) of 0.39μM. This modulation was also observed over a time course. Scatchard analysis indicated that both an increase in Kd and a possible decrease in Bmax were responsible for the decrease in binding induced by low [Pb2+]f. Moreover, the effects of Pb2+ on the function of ER RyRs in neurons might also be controlled by other RyR modulators. Whole-cell patch-clamp experiments revealed that dynamic calcium oscillations evoked by specific RyR agonists were depressed rapidly and reversibly by exposure to 10μM Pb2+. Our study indicates that RyRs are molecular targets of Pb2+, and this interaction disturbs Ca2+ signals and leads to neurotoxicity.

Introduction Lead, cadmium, arsenic, and mercury are widely used in industry and among the leading toxic agents detected in the environment. The deleterious effects encountered after exposure to these individual metals in low doses are well documented. However, human exposure to environmental chemicals is most correctly characterised as an exposure to mixtures, and little is known about the combined impact of these metals. Methods In our study, the combined impacts of these four metal mixtures (MM) in low doses on synaptic homeostasis as well as the related mechanisms were investigated in cultured hippocampal neurons and NGF-differentiated PC12 cells. F-actin staining was used to emerge the structure of dendrites and spines for synaptic morphology analysis. Immunofluorescence and RT-PCR were applied to examine the expressions of serum-inducible kinase (Snk) and spine-associated Rap guanosinetriphosphatase activating protein (SPAR). The plasmids of shRNA-Snk, SPAR-Wt and SPAR-Mut (S1328) were constructed for transfection Assays. Results MM exposure declined the density and length of dendritic spines, and dendrite branches in dose-effect relationship in hippocampal neurons. And the mushroom and thin spines were decreased. Simultaneously, the Snk expression were up-regulated accompanying with the down-regulation of SPAR expression. Similar to what observed in the hippocampal neurons, the synaptic morphology analysis of NGF-differentiated PC12 cells showed their neurite length and tip end numbers were declined in dose-effect relationship after MM exposure, which accompanied with the up-regulation of Snk and the down-regulation of SPAR. Snk agonist aggravated these impairment, whereas, Snk knockdown and SPAR overexpression attenuated the changes of neurite outgrowth. In addition, SPAR-Mut (S1328) overexpression performed a better reversion than SPAR-Wt overexpression in the changes of neurite outgrowth induced by MM-exposure. Conclusion These results indicated that combined exposure to low doses MM disturbed the synaptic homeostasis, and Snk-SPAR pathway might be a novel target to prevent MM induced neurotoxicity.

Background: Autism spectrum disorders (ASD) are hereditary, heterogeneous and biologically complex neurodevelopmental disorders. Individual studies on gene expression in ASD cannot provide clear consensus conclusions. Therefore, a systematic review to synthesize the current findings from brain tissues and a search tool to share the meta-analysis results are urgently needed. Methods: Here, we conducted a meta-analysis of brain gene expression profiles in the current reported human ASD expression datasets (with 84 frozen male cortex samples, 17 female cortex samples, 32 cerebellum samples and 4 formalin fixed samples) and knock-out mouse ASD model expression datasets (with 80 collective brain samples). Then, we applied R language software and developed an interactive shared and updated database (dbMDEGA) displaying the results of meta-analysis of data from ASD studies regarding differentially expressed genes (DEGs) in the brain. Results: This database, dbMDEGA (https://dbmdega.shinyapps.io/dbMDEGA/), is a publicly available web-portal for manual annotation and visualization of DEGs in the brain from data from ASD studies. This database uniquely presents meta-analysis values and homologous forest plots of DEGs in brain tissues. Gene entries are annotated with meta-values, statistical values and forest plots of DEGs in brain samples. This database aims to provide searchable meta-analysis results based on the current reported brain gene expression datasets of ASD to help detect candidate genes underlying this disorder. Conclusion: This new analytical tool may provide valuable assistance in the discovery of DEGs and the elucidation of the molecular pathogenicity of ASD. This database model may be replicated to study other disorders.

Based on how the silent information regulator 2 homolog 1 (SIRT1) regulates the cyclic AMP response element binding protein (CREB), which is the molecular switch of long-term memory that maintains cognitive function, it is postulated that the impact of lead (Pb) on SIRT1 is one of the mechanisms leading to Pb-induced cognitive and learning deficits. Hence, the purpose of this study was to investigate the effect of Pb exposure on the expression of SIRT1, and the reversion effect of resveratrol, which is an activator of SIRT1. We examined the effects of maternal rat ingestion of Pb in drinking water during gestation and lactation on the expression of SIRT1 and CREB in the hippocampus of their offspring at postnatal week 3 (PNW3) and 52 (PNW52), and then reexamined these effects in offspring after intragastric administration of resveratrol for 4 weeks. Pb exposure decreased SIRT1 and CREB phosphorylation in a dose-dependent manner in the rat hippocampus at both PNW3 and 52, and resveratrol reversed those losses. These results indicated that SIRT1 might be a novel target to prevent Pb neurotoxicity.