Non-coding RNA alterations in mature sperm following episodic ozone exposure in Long-Evans rats.
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Ozone exposure has been associated with male infertility in epidemiological studies. However, causal evidence remains limited and mixed. Coinciding with the length of sperm maturation, post-pubescent rats were exposed to air or ozone (0.4 ppm or 0.8 ppm) for a total of 5 days (4 hours/day) distributed across 2 weeks (n=8/group). On the morning after the final exposure, mature sperm were collected from the cauda epididymis for motility assessment and (non-coding) ncRNA-seq. There were no effects of ozone exposure on any metric of sperm motility assessed in the freshly collected sample. Utilizing a statistical threshold of p<0.05 and ±2.5-fold change, we failed to detect any differentially expressed tRNA-derived fragments at either ozone concentration. At 0.8 ppm, microRNAs miR-24-1-5p and miR-141-5p were upregulated in the sperm, whereas miR-341 was downregulated. Due to the number of piRNAs described in the piRBase annotation for rat (>31,000), a more stringent threshold of p<0.001 and ±2.5-fold change was used to identify differentially expressed targets. 0.4 ppm ozone exposure resulted in 23 upregulated and 14 downregulated piRNAs in mature rat sperm. Eleven upregulated and 10 downregulated piRNAs were found with 0.8 ppm exposure. Of these, only 4 were shared in both statistical significance and directionality between the two concentrations. Additional analyses are underway to determine if observed ncRNA changes may correlate with poor indices of sperm health. Identification of such associations may provide unique insights on the role of ncRNAs in male reproductive toxicity and the potential influence of ozone exposure. Does not reflect EPA Policy.