Episodic ozone exposure in Long-Evans rats has limited effects on cauda sperm motility and non-coding RNA populations.
Epidemiological evidence suggests the potential for air pollutants to induce male reproductive toxicity. Of these studies, exposure to the oxidant air pollutant, ozone, during sensitive windows in the sperm lifecycle has been associated with impaired sperm motility. Based on these findings, herein, we designed a study to investigate the effects of episodic exposure to ozone during the stage of sperm maturation in the rat. Long-Evans rats were exposed to either filtered air or ozone (0.4 or 0.8 ppm) for five non-consecutive days over two weeks. Ozone exposure failed to impact male reproductive organ weights nor sperm motility as measured by computer-assisted sperm analysis ~24 hours following the final exposure. Furthermore, circulating sex hormones remained unchanged despite increased T3 and T4 in the 0.8 ppm group. While there were some shifts in the gene expression of the testis indicative of altered adrenergic signaling in the rats exposed to 0.8 ppm ozone, there were minimal impacts on small non-coding RNAs detected in cauda sperm. Only two piwi-interacting RNAs (piRNAs) were altered in the mature sperm of ozone-exposed rats (piR-rno-346434 and piR-rno-227431). We further analyzed our data to determine if any non-coding RNAs that were associated with poorer motility could be identified. Within this analysis, we found a total of n = 7 microRNAs (miRNAs), n = 8 RNA fragments, and n = 1,682 piRNAs that were well correlated with sperm motility. Interestingly, the entire group of piRNAs associated with sperm motility was elevated in the samples with the lowest motile sperm. Utilizing our exposure paradigm, we were unable to substantiate the relationship between ozone exposure and reduced sperm motility during maturation. However, our approaches allowed us to identify a suite of non-coding RNAs (miRNAs, RNA fragments, and piRNAs) that were associated with sperm motility in rats. With additional investigation, these RNAs may prove to have functional roles in the acquisition of motility or be unique biomarkers for male reproductive toxicity.