Exposure to eucalyptus smoke during sperm maturation alters motility and non-coding RNAs in caudal sperm.
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Concern about infertility in firefighters has been raised since the early 1990s, in part due to variable occupational exposures that span from heat stress to the thousands of chemicals in smoke. While hyperthermia is a well-recognized male reproductive hazard, little information exists on the effects of inhaled biomass smoke on fertility. Hence, the purpose of this study was to determine if exposure to smoke from eucalyptus combustion induces adverse effects on sperm. Long-Evans rats were exposed for 1 hour to either a low or high concentration of smoke generated by a tube furnace system set to 500°C for 4 consecutive days on the first week and 3 days on the second week. Daily mean particulate matter and CO concentrations were 11.0 mg/m3 and 11.4 ppm, or 23.7 mg/m3 and 20.9 ppm for the low and high exposures, respectively. Caudal sperm samples were collected for functional and transcriptomic alterations the day after the final exposure. Sperm collected from the low exposure group had a 5% reduction in progressive tracking compared to rats exposed to filtered air, indicating an impairment for linear movement. Notably, this decrease was accompanied by alterations in the non-coding RNA populations found in mature sperm thru Illumina RNAseq. A total of 14 microRNAs, including those already associated with reproductive disorders, were increased in the low exposure group (e.g., miR-10b, -146, and -92). An additional 79 tRNA-derived fragments and 5 piwi-interacting RNAs were different between the low exposure and filtered air groups. Importantly, these changes in sperm progressive movement and non-coding RNAs were not found in the rats exposed to high smoke concentrations. We have recently replicated the effects of smoke on sperm motility at a lower concentration of ~4 mg/m3, which persisted despite filtration. Collectively, our work in rats provides novel evidence that exposure to biomass smoke can have potential adverse effects on sperm motility and necessitates the continued study of this exposure on male fertility and the developmental outcomes in their offspring. This study was approved by the U.S. EPA IACUC and does not reflect U.S. EPA policy.