Meisel, J.D. et al. (2019) International Worm Meeting "Suppression of distinct mitochondrial mutants by hypoxia."

Ruvkun, G., Mootha, V.K., Meisel, J.D., Ast, T.

[International Worm Meeting, 2019]

Molecular oxygen (O2) is central to mitochondrial physiology and disease - it is the driving force for oxidative phosphorylation and required for many biochemical reactions within the mitochondria, but can also combine with electrons leaked from the respiratory chain to form damaging species, or directly inhibit oxygen-sensitive processes. Recent work has shown that hypoxia (11% oxygen) is an effective treatment for a mouse model of Leigh Syndrome that carries a deletion in Ndufs4 encoding a subunit of Complex I. However the precise molecular mechanism underlying the rescue by hypoxia remains elusive, and it is unknown whether hypoxia rescue will extend to other mitochondrial mutants and disease models. Here, we establish that hypoxia can rescue a Complex I mutant in C. elegans, as nduf-7(et19) animals benefit from 1% oxygen, displaying increased growth rate and reduced expression the mitochondrial stress reporter hsp-6::gfp. We also extend this finding to frataxin/FRH-1, a mitochondrial protein thought to be required for iron sulfur (Fe-S) cluster biosynthesis and classified as an essential gene. Loss of frataxin in humans underlies Friedreich's ataxia, for which there are no proven therapies. We show that C. elegans carrying a deletion in frh-1 are viable when propagated at 1% oxygen. Remarkably, when grown in hypoxia, frh-1(tm5913) mutants are competent for Fe-S cluster biosynthesis, while animals lacking other Fe-S cluster biosynthesis components, namely NFS-1 and ISCU-1, are not viable in any oxygen tension. These results extend to human cell culture and yeast, and we show that hypoxia is able to increase bioavailable iron in cells as well as directly promote frataxin-independent Fe-S synthesis in vitro. Both frh-1 and nduf-7 mutants are exquisitely sensitive to hyperoxia (50% oxygen), and in ongoing work we have identified genetic suppressors which may shed light on the mechanisms underlying hypoxia's beneficial effects, as well as provide new candidates for therapeutic pathways.

Way, A. et al. (2017) International Worm Meeting "A network of transcription factors regulates lysosomal lipolysis in C. elegans."

Mony, V.K., Way, A., O'Rourke, E.J.

[International Worm Meeting, 2017]

Adaptation to nutritional changes is a prominent example of plasticity in living organisms. Evolutionary conserved pathways like Insulin signaling, mechanistic Target of Rapamycin (mTOR), TGF- beta , caloric restriction (CR) and Notch receptor pathways have been characterized for their effects in growth and reproduction along with changes in fat metabolism in response to nutritional stress. Within each of these pathways "canonical" transcription factors (TFs) control the expression of distinctive downstream effectors. On the other hand, many TFs have shared regulators and targets. Given the plasticity in nutrient responses, it is an open question whether different upstream nutrient sensors would canalize nutritional information through their canonical TFs to activate adaptive responses, or whether the adaptive downstream effectors would be controlled by a small subset of specialized TFs common to all nutrient sensing pathways modulating a given adaptive molecular response. We have performed transcriptional analyses to dissect the regulation of genes encoding the C. elegans lysosomal lipases lipl-1, lipl-3 and lipl-4. Although known to have at least partially redundant roles, here we show that the genes encoding these lysosomal lipases are differentially controlled by a network of transcriptional activators and repressors that yield distinct expression patterns in animals with altered nutrient sensing or nutritional status. Surprisingly, HLH-30 (mammalian TFEB), a transcription factor we established to be required for activation of the lipl genes in fasting conditions, is found to be required for induction of lysosomal lipase upon mTOR inhibition but not in CR, insulin deficient, TGF-beta deficient, sterile worms, or other tested models of metabolic dysregulation. By contrast, DAF-16 (mammalian FOXO) is found to control lysosomal lipases downstream of multiple nutrient sensing pathways. Similarly surprising, PHA-4, a gene activating gene expression in CR animals, and NHR-49 a master activator of beta-oxidation upon fasting, act as repressors of the lipl genes, suggesting a dual role for PHA-4 and NHR-49 in adaptation to food scarcity. Additionally, DAF-3 (co-SMAD), NHR-80 (HNF4), SKN-1 (Nfr2), and HSF-1 contribute to regulation of the expression of the lysosomal lipases. All in all, we found that although the specificity of lipase expression depended on the same TFs downstream of multiple nutrient regulatory pathways, they are also under the promiscuous regulation of disparate TFs. *Way A. and Mony V.K. contributed equally to the work presented in the abstract.