Mitochondria are central players in host immunometabolism as they function not only as metabolic hubs but also as signaling platforms regulating innate immunity. Environmental exposures to mitochondrial toxicants occur widely and are increasingly frequent. Many pesticides target mitochondrial function, including the well-characterized complex I inhibitor, rotenone (Rot). Exposures to these mitotoxicants can pose a serious threat to organismal health and the onset of diseases by disrupting immunometabolic pathways. Our hypothesis is that Rot can disrupt C. elegans immunometabolism and consequently alter pathogen survival. C. elegans eggs were exposed to Rot (0.5 microM) or vehicle (Ctrl - 0.125 uM DMSO) in liquid and harvested once they reached the L4 larval stage (which was ~24h later for the Rot treatment, as it caused growth delay). Inhibition of mitochondrial respiration by Rot was confirmed by measuring the worm oxygen consumption rate. To explore pathways that were modulated by Rot, we performed a transcriptomic analysis and found 179 differentially expressed genes. WormCat analysis revealed that the two major broad enriched categories were stress response -which was mostly represented by pathogen response and detoxification genes- and metabolism -which was mostly represented by lipid and mitochondrial metabolism genes. Next, Ctrl and Rot-exposed worms were depurated for 48h, and further exposed to Pseudomonas aeruginosa (PA14), and Salmonella enterica (SL1344). Rot-exposed worms were more resistant to SL1344 but more susceptible to PA14. The mitochondrial unfolded protein response (mitoUPR) is a well-known immunometabolic pathway in C. elegans which links mitochondria and immunity and provides resistance to pathogen infection. Rot activated the mitoUPR pathway, which was evidenced by increased
hsp-6:GFP expression. Activation was also observed after 24h of exposure to PA14 and SL1344, however, Ctrl PA14-infected worms displayed lower
hsp-6:GFP expression, and Rot rescued its expression only to the level of Ctrl OP50-raised worms. Thus, mitoUPR activation could be involved in the increased resistance to SL1344 but the level of activation in PA14 worms might not have been sufficient to promote resistance. By further exploring our transcriptomic dataset using WormExp and "module-weighted annotations" analysis tools, we identified genes that are known to confer resistance to PA14 that were downregulated by the Rot exposure, including HIF-dependent genes, which may underlie the increased susceptibility to PA14. Together, these results demonstrate that the mitotoxicant rotenone can modulate important pathways associated to the C. elegans immunometabolism and alter pathogen resistance.