Trichloroethylene exposure alters dimethylated histone three lysine four in protein kinase A signaling pathway chromatin of rat sperm†.

Histone three lysine four dimethylation (H3k4me2) in sperm is conserved across species and is linked to transgenerational epigenetic inheritance. To test whether H3K4me2 is a target for transgenerational inheritance of toxicity, a daily gavage bolus exposure of trichloroethylene (TCE) (1000 mg/kg/day) was given to rats for 14 weeks, then epididymal sperm were isolated and native chromatin immunoprecipitation followed by next generation sequencing (ChIP-seq) of H3K4me2 was performed. Differential region analysis determined there were 2608 significantly differential H3K4me2 regions after TCE exposure, 477 were significantly increased and 2131 were significantly decreased. Z-score enrichment of differential regions determined there were significantly decreased H3k4me2 in the coding and regulatory regions of genes in the PKA signaling pathway. These changes account for TCE induced spermatozoal toxicity and show H3K4me2 is a target for paternal inheritance of toxicity.

Differential toxicity of water versus gavage exposure to trichloroethylene in rats.

Trichloroethylene (TCE) is a persistent environmental contaminant that causes male reproductive toxicity. We investigated whether transient increases in TCE exposure modulated male reproductive toxicity by exposing rats via daily oral to repeated gavage exposures (1000 mg/kg/day) and through drinking water (0.6% TCE) for 14 weeks. The gavage route resulted in reversible reduction of epididymis weight, and reduced body weight that persisted for up to 12-weeks after cessation of exposure. Physiologically-based pharmacokinetic modeling predicted that the gavage route results in higher Cmax and AUC exposure of TCE compared to drinking water exposure, explaining the observed differences in toxicity between dosing regimens.

From the Cover: Sperm Molecular Biomarkers Are Sensitive Indicators of Testicular Injury following Subchronic Model Toxicant Exposure.

Traditional testis histopathology endpoints remain the gold standard for evaluating testicular insult and injury in a non-clinical setting, but are invasive and unfeasible for monitoring these effects clinically in humans. Assessing testicular injury in humans relies on semen and serum hormone analyses, both of which are insensitive and poor indicators of effect. Therefore, we hypothesized that sperm messenger RNA (mRNA) transcripts and DNA methylation marks can be used as translatable and sensitive indicators or testicular injury. Dose-response studies using adult male Fischer 344 rats subchronically exposed to model Sertoli cell toxicants (0.14, 0.21, and 0.33% 2,5-hexanedione, and 30, 50, and 70 mg/kg/day carbendazim), and a model germ cell toxicant (1.4, 3.4, and 5.1 mg/kg/day cyclophosphamide) for 3 months were evaluated for testicular injury by traditional histopathological endpoints, changes in sperm mRNA transcript levels using custom PCR arrays, and alterations in sperm DNA methylation via reduced representation bisulfite sequencing. Testis histopathological evaluation and PCR array analysis of the sperm transcriptome identified dose-dependent changes elicited by toxicant exposure (P < 0.05). Global sperm DNA methylation analysis of subchronic 0.33% 2,5-hexandione and 5.1 mg/kg/day cyclophosphamide exposure using a Monte Carlo approach did not identify differentially methylated regions (methylation difference > 10% and q < 0.05) with robust signatures. Overall, these results suggest that sperm mRNA transcripts are sensitive indicators of low dose toxicant-induced testicular injury in the rat, while sperm DNA methylation changes are not. Additionally, the Monte Carlo analysis is a powerful approach that can be used to assess the robustness of signals resulting from -omic studies.