Effects of preconception exposure to rotenone on progeny depend on the degree of maternal toxicity

Parental exposure to toxicants can affect progeny health, including when those exposures occur prior to conception. However, most published preconception studies have involved exposures that result in loading of pollutants to gametes, or toxic effects to parents which could indirectly affect germ cell or gamete health. Here, we took advantage of the biology of Caenorhabditis elegans to carry out a preconception study in which we minimized the potential for maternal loading of toxicants, and used an exposure paradigm that either did (high concentration) or did not (low concentration) significantly impact the health of the P0 generation. We hypothesized that preconception exposure to mitochondrial toxicants (rotenone, and in some cases antimycin A or pyraclostrobin) during germ cell and gamete development, at levels not causing P0 toxicity, would impact mitochondrial processes in germ cells or gametes prior to conception, and that changes would be observed in offspring. The high rotenone concentration altered P0 growth, mitochondrial respiration, gene expression, induction of the mitochondrial unfolded protein response, and susceptibility to secondary challenge-induced dopaminergic neurodegeneration. However, we observed minor or no P0 effects at the low concentration. The F1 progeny of both low and high concentrations showed few effects, with most occurring in the high-exposure offspring. The only effects observed in the F1 offspring of the low exposure were a 1.7% decrease in egg size (but size later in development was not different from offspring of controls), and a slightly increased sensitivity to dopaminergic neurodegeneration caused by a secondary rotenone exposure. This study is a follow-up of Mello et. al. 2022 (PMID: 35273616; GEO: GSE195584) Overall design: Worms were exposed to Rotenone .03 or .5 uM or 0.25% DMSO (control) in liquid culture. P0 samples were subsampled from liquid culture at the L4 stage. For F1 samples, P0's were treated with a 48 hr washout period in liquid culture. They were then bleached to synchronize F1 generation, which were cultured in the same conditions as P0 except for no DMSO or rotenone were added. Detailed description of experimental methods can be found in Mello et. al. 2022 (doi: 10.3389/fimmu.2022.840272). Libraries were made with 500ng total RNA/sample and 9 PCR cycles.