Transcriptional and Post-Transcriptional Regulation in Testicular Toxicity

The control of gene expression occurs at multiple levels one of which is controlled by epigenetic regulation. In this work, it was hypothesised that changes in DNA methylation (transcriptional level) and miRNA expression (post-transcriptional level) might be involved in the mechanism of compound-induced testicular toxicity. mRNA and miRNA analysis of mouse testis was performed following exposure to dibutyl phthalate, 17β-estradiol and doxorubicin. Pathway analysis of transcriptional changes revealed all three chemicals interfered with the steroidogenic pathway, with further modulation of oxidative stress pathways in doxorubicin models. Doxorubicin exhibited a profound effect on the testis by decreasing the expression of germ cell-specific transcripts and increasing the expression of Leydig cell transcripts, apoptotic genes and pro-apoptotic miRNAs (miR-145, miR-26a, miR29 family). The post-transcriptional regulatory activity of these proapoptotic miRNAs was demonstrated by decreased transcript expression of their target DNA-methyl transferases (Dnmt) transcripts. An extensive deregulation of DNA methylation was observed that could be a consequence of altered Dnmts levels. Hypomethylation of genes, such as Cdkn2a and Pcna2, led to activation of p53 signaling. The same experiment was repeated in in vitro models of the testis. Pathway analysis revealed miRNA-mRNAs regulation of signaling pathways between germ cell-Sertoli cell and Sertoli cell-Sertoli cell junctions. A systematic review was conducted to establish the role of epigenetic-mediated mechanisms in toxicant-induced male reproductive toxicity. The study identified that decrease in Dnmt levels following chemical exposure could play a role in germ cell apoptosis. Also, the aberrant methylation of H19 could serve as a useful biomarker in the transgenerational effects of chemicals. The findings from this project provide further insight into the mechanisms of compound-induced testicular toxicity, through the utilization of genomics and a systematic review approach to published work. It identified epigenetic mechanisms both at the transcriptional and post-transcriptional levels are involved in the mechanism of toxicity.