The effects of early life lead exposure on the expression of insulin-like growth factor 1 and 2 (IGF1, IGF2) in the hippocampus of mouse pups

Effects of food-borne cholesterol supplementation on lead-induced neurodevelopmental impairments of rats based on BDNF signaling pathway and cholesterol metabolism

Despite the ubiquity and prevalence of lead (Pb) in the environment and industry, the mechanism of lead-induced neurotoxicity in the brain remains unclear, let alone its prevention and treatment. In this study, we hypothesized that exogenous cholesterol supplementation acts as an effective remedy for lead-induced neurodevelopmental impairments caused by lead. Forty 21-day-old male rats were randomly divided into four groups and administered 0.1 % lead water and/or 2 % cholesterol-containing feed for 30 d. Ultimately, rats in the lead group lost weight, accompanied by spatial learning and memory impairments as verified by the Morris water maze test, in which the escape latency of rats was prolonged, and the number of crossings in the target platform and the residence time in the target quadrant were significantly diminished compared to the control group. Hematoxylin-Eosin (H&E) staining and Nissl staining illustrated that typical pathological morphology occurred in the brain tissue of the lead group, where the tissue structure was loose, the number of hippocampal neurons and granulosa cells decreased significantly and were arranged loosely, along with enlarged intercellular space, light matrix staining, and decline in Nissl bodies. In addition, inflammatory response and oxidative stress were significantly induced by lead. Immunofluorescence experiments showed apparent activation of astrocytes and microglia, followed by the enhancement of TNF-α and IL-β levels. Moreover, the MDA content in the lead group was elevated dramatically, whereas the activities of SOD and GSH were significantly inhibited. As for the mechanism, western blot and qRT-PCR experiments were performed, where lead could significantly inhibit the BDNF-TrkB signaling pathway, lowering the protein expression of BDNF and TrkB. Cholesterol metabolism was also affected by lead exposure, in which cholesterol metabolism-related protein expression and gene transcription, including SREBP2, HMGCR, and LDLR, were downregulated. However, cholesterol supplementation efficiently detoxified the negative effects of lead-induced neurotoxicity, reversing the inflammatory response, oxidative stress, inactivation of the BDNF signaling pathway, and imbalance of cholesterol metabolism, thus improving the learning and memory ability of rats. In brief, our study demonstrated that cholesterol supplementation could ameliorate the deficiency of learning and memory induced by lead, which is closely associated with the initiation of the BDNF/TrkB signaling pathway and regulation of cholesterol metabolism.

Mechanism of autophagy mediated by IGF-1 signaling pathway in the neurotoxicity of lead in pubertal rats

Lead can damage neuron synapses in the hippocampus and cause synaptic plasticity losses, and learning, memory, and intelligence impairments. Previous studies have focused on the functional and structural plasticity of hippocampal synapses; however, the specific molecular mechanisms behind such impairments are not fully understood. This study aimed to elucidate the molecular mechanisms of cognitive impairment in rats following chronic lead exposure and mitigate or prevent lead toxicity in the central nervous system. We found that lead exposure caused significant damage to rat nervous systems, that is, compared with the control group, the lead treatment group had more autophagosomes in their hippocampal neurons; lower serum and hippocampal IGF-1 levels; lower hippocampal IGF-1, IGF-1R, PI3K, Akt, and mTOR gene expression; and upregulated hippocampal autophagy-associated proteins levels. Brain stereotactic technology was used to conduct autophagy inhibitor in vivo intervention experiments, and the results of these experiments suggest that the autophagy inhibitor DC661 inhibited lead-exposure-induced autophagy and autophagy-related gene expression in the rat hippocampus, possibly through activation of the IGF-1 pathway. Overall, our findings suggest that lead might activate hippocampal autophagy through the IGF-1/PI3K/Akt/mTOR signaling pathway. Therefore, this study provides a novel molecular mechanism underlying developmental toxicity in pubertal rats induced by lead exposure and provides a new target for anticipation and reversal of such neurotoxicity.

Sex-dependent effects of lead and prenatal stress on post-translational histone modifications in frontal cortex and hippocampus in the early postnatal brain

Environmental lead (Pb) exposure and prenatal stress (PS) are co-occurring risk factors for impaired cognition and other disorders/diseases in adulthood and target common biological substrates in the brain. Sex-dependent differences characterize the neurochemical and behavioral responses of the brain to Pb and PS and sexually dimorphic histone modifications have been reported to occur in at-risk brain regions (cortex and hippocampus) during development. The present study sought to examine levels and developmental timing of sexually dimorphic histone modifications (i.e., H3K9/14Ac and H3K9Me3) and the extent to which they may be altered by Pb±PS. Female C57/Bl6 mice were randomly assigned to receive distilled deionized drinking water containing 0 or 100ppm Pb acetate for 2 months prior to breeding and throughout lactation. Half of the dams in each group were exposed to restraint stress (PS, three restraint sessions in plastic cylindrical devices 3×/day at for 30min/day (1000, 1300, and 1600h)) from gestational day 11-19 or no stress (NS). At delivery (PND0) and postnatal day 6 (PND6), pups were euthanized and frontal cortex and hippocampus were removed, homogenized, and assayed for levels of H3K9/14Ac and H3K9Me3. Sex-dependent differences in both levels of histone modifications as well as the developmental trajectory of changes in these levels were observed in both structures and these parameters were differentially affected by Pb±PS in a sex and brain-region-dependent manner. Disruptions of these epigenetic processes by developmental Pb±PS may underlie some of the sex-dependent neurobehavioral differences previously observed in these animals.

The effects of early life lead exposure on the expression of P2X7 receptor and synaptophysin in the hippocampus of mouse pups

The present study was undertaken to investigate the effects of maternal lead exposure on expression of P2X7 receptor and synaptophysin in the hippocampus of mice offspring. Lead exposure initiated from beginning of gestation to weaning. Lead acetate administered in drinking solutions was dissolved in distilled deionized water at the concentrations of 0.1%, 0.5% and 1% groups, respectively. On the 21st postnatal day, the Pb levels were also determined by graphite furnace atomic absorption spectrometry. The expression of P2X7 receptor and synaptophysin in hippocampus was examined by immunohistochemistry and Western blotting. The lead levels in blood and hippocampus of all lead exposure groups were significantly higher than that of the control group (P<0.05). Compared with the control group, the expression of P2X7 receptor was increased in lead exposed groups (P<0.05), but the expression of synaptophysin was decreased (P<0.05). The high expression of P2X7 receptor and low expression of synaptophysin in the hippocampus of pups may contribute to the neurotoxicity associated with maternal Pb exposure.