Ghrelin attenuates methylmercury-induced oxidative stress in neuronal cells

Transcriptomic analysis identifies muscle-specific mitochondrial and vesicular transport genes as methylmercury toxicity targets in a Drosophila model of congenital Minamata disease

Prenatal methylmercury (MeHg) exposure presents a heightened concern in early human development, as has been exemplified in historic cases of congenital minimata disease (CMD). Children who experience CMD characteristically present with various degrees of cognitive and motor symptoms and signs, much like cerebral palsy. MeHg has thus been characterized as a neurotoxicant, where motor deficits are ascribed to central nervous system targets. Skeletal muscle as a post-synaptic MeHg target and contributor to the etiology of CMD has garnered far less attention. Prior studies using Drosophila to model CMD revealed that developmental exposure of MeHg in the larval/pupal stages can elicit graded and latent dose responses affecting adult flight behavior at lower doses (0.4-2.5 ppm in food) and eclosion (emergence from the pupa case) at higher doses (>2.5 ppm in food). The latter phenotype is accompanied by dysmorphogenesis of skeletal muscles. Here, we investigate respective roles for muscle and neural targets in MeHg toxicity. Using RNA-seq analysis, we find that developmental MeHg exposure produces 10 times as many differentially expressed transcripts in indirect flight muscle compared to the ventral nerve cord. Among known MeHg response genes, Nrf2 antioxidant response pathway genes showed muscle-specific MeHg-induced expression changes. Within the muscle transcriptome, the most enriched and significant Gene Ontology terms identified genes required for mitochondrial ribosomal translation at the pupa stage and mitochondrial function (respiratory chain complex I) and vesicle trafficking (ESCRT III) pathways in adults, all showing decreased expression with MeHg exposure. By using an intact, whole-animal developmental model, we identify preferential candidates to evaluate a novel role for muscle-specific mitochondria and intercellular vesicular communication mechanisms as targets in MeHg toxicity and the etiology of CMD.

N-acetylcysteine protects against neurodevelopmental injuries induced by methylmercury exposure during pregnancy and lactation

As an extremely dangerous environmental contaminant, methylmercury (MeHg) results in detrimental health effects in human brain nervous system, one of its main targets. However, as a developmental toxicant, the brain of offspring is vulnerable to MeHg during pregnancy and lactation exposure. Unfortunately, mechanisms of neurodevelopmental injuries induced by MeHg have not been fully elucidated. N-acetylcysteine (NAC) has been used for several decades as an antioxidant to antagonize oxidative stress. However, the molecular mechanisms of NAC alleviating MeHg-induced neurodevelopmental toxicity are not clear. Here, for evaluation of the dose-dependent effects of MeHg exposure on neurodevelopmental injuries of offspring, and the possible protective effects of NAC, the pregnant female mice were exposed to MeHg (4, 8, 12 mg/L, respectively) and NAC (50, 100, 150 mg/kg, respectively) from gestational day 1 (GD1) to postnatal day 21 (PND21). Our results indicated that administering MeHg caused behavioral impairment and neuronal injuries in the cerebral cortex of newborn mice. MeHg dose-dependently caused reactive oxygen species (ROS) overproduction and oxidative stress aggravation, together with expression of Nrf2, HO-1, Notch1, and p21 up-regulation, and CDK2 inhibition. NAC treatment dose-dependently antagonized MeHg-induced oxidative stress that may contribute to alleviating neurobehavioral and neurodevelopmental impairments. These results give insight into that NAC can protect against MeHg-induced neurodevelopmental toxicity by its antioxidation capacity.