Jeong J et al. (2019) Nanotoxicology "Developing adverse outcome pathways on silver nanoparticle-induced reproductive toxicity via oxidative stress in the nematode Caenorhabditis elegans using a Bayesian network model."

Choi I, Song T, Choi J, Chatterjee N, Jeong J, Cha YK

[Nanotoxicology, 2019]

An adverse outcome pathway (AOP) is a framework that organizes the mechanistic or predictive relationships between molecular initiating events (MIEs), key events (KEs), and adverse outcomes (AOs). Previously, we intensively investigated the molecular mechanism that underlies toxicity caused by AgNPs in the nematode Caenorhabditis elegans. Using transcriptomics, functional genetics, and various molecular/biochemical tools, we identified oxidative stress as the major mechanism underlying toxicity and reproduction failure as the outcome. With this information, here we conducted a case study of building an AOP to link oxidative stress with reproductive toxicity. To validate this AOP, we filled the gaps by conducting further experiments on its elements, such as NADPH oxidase, ROS formation, PMK-1 P38 MAPK activation, HIF-1 activation, mitochondrial damage, DNA damage, and apoptosis. The establishment of a causal link between the MIE and AO is critical for the construction of an AOP. Therefore, causal relationships between each KE and AO were verified by using functional genetic mutants of each KE. By combining these experimental data with our previously published results, we established causal relationships between the MIE, KEs, and AO using a Bayesian network (BN) model, culminating in an AOP entitled 'NADPH oxidase and P38 MAPK activation leading to reproductive failure in C. elegans ( https://aopwiki.org/aops/207)' . Overall, our approach shows that an AOP can be developed using existing data and further experiments can be conducted to fill the gaps between the MIE, KEs, and the AO. This study also shows that BN modeling has the potential to identify causal relationships in an AOP.

Hipkiss AR (2007) Mech Ageing Dev "On why decreasing protein synthesis can increase lifespan."

Hipkiss AR

[Mech Ageing Dev, 2007]

An explanation is offered for the increased lifespan of Caenorhabditis elegans when mRNA translation is inhibited due to loss of the initiation factor IFE-2 [Hansen, M., Taubert, T., Crawford, D., Libina, N., Lee, S.-J., Kenyon, C., 2007. Lifespan extension by conditions that inhibit translation in Caenorhabditis elegans. Ageing Cell 6, 95-110; Pan, K.Z., Palter, J.E., Rogers, A.N., Olsen, A., Chen, D., Lithgow, G.J., Kapahi, P., 2007. Inhibition of mRNA translation extends lifespan in Caenorhabditis elegans. Ageing Cell 6, 111-119; Syntichaki, P., Troulinaki, K., Tavernarakis, N., 2007. eIF4E function in somatic cells modulates ageing in Caenorhabditis elegans. Nature 445, 922-926]. It is suggested that the general reduction of protein synthesis, due to the decreased frequency of mRNA translation, also lowers the cellular load of erroneously synthesized polypeptides which the constitutive protein homeostatic apparatus (proteases and chaperones proteins) normally eliminates. This situation results in "spare" proteolytic and chaperone function which can then deal with those proteins modified post-synthetically, e.g. by oxidation and/or glycation, which are thought to contribute to the senescent phenotype. This increased availability of proteolytic and chaperone functions may thereby contribute to the observed increase in organism stress resistance and lifespan.

Preston S et al. (2017) FASEB J "Deguelin exerts potent nematocidal activity via the mitochondrial respiratory chain."

Sternberg PW, Ansell BRE, Andrews KT, Nowell C, Chang BCH, Hofmann A, Crawford S, Korhonen PK, Baell J, Gijs MAM, Fisher GM, Young ND, Preston S, Mouchiroud L, Gasser RB, Jabbar A, Auwerx J, Davis RA, McGee SL, Cornaglia M

[FASEB J, 2017]

As a result of limited classes of anthelmintics and an over-reliance on chemical control, there is a great need to discover new compounds to combat drug resistance in parasitic nematodes. Here, we show that deguelin, a plant-derived rotenoid, selectively and potently inhibits the motility and development of nematodes, which supports its potential as a lead candidate for drug development. Furthermore, we demonstrate that deguelin treatment significantly increases gene transcription that is associated with energy metabolism, particularly oxidative phosphorylation and mito-ribosomal protein production before inhibiting motility. Mitochondrial tracking confirmed enhanced oxidative phosphorylation. In accordance, real-time measurements of oxidative phosphorylation in response to deguelin treatment demonstrated an immediate decrease in oxygen consumption in both parasitic (Haemonchus contortus) and free-living (Caenorhabditis elegans) nematodes. Consequently, we hypothesize that deguelin is exerting its toxic effect on nematodes as a modulator of oxidative phosphorylation. This study highlights the dynamic biologic response of multicellular organisms to deguelin perturbation.-Preston, S., Korhonen, P. K., Mouchiroud, L., Cornaglia, M., McGee, S. L., Young, N. D., Davis, R. A., Crawford, S., Nowell, C., Ansell, B. R. E., Fisher, G. M., Andrews, K. T., Chang, B. C. H., Gijs, M. A. M., Sternberg, P. W., Auwerx, J., Baell, J., Hofmann, A., Jabbar, A., Gasser, R. B. Deguelin exerts potent nematocidal activity via the mitochondrial respiratory chain.

Cheng X et al. (2022) Autophagy "Proteotoxic stress disrupts epithelial integrity by inducing MTOR sequestration and autophagy overactivation."

Zhang H, Zheng H, Zhang P, Cheng X, Zheng K, Zhao H

[Autophagy, 2022]

Macroautophagy/autophagy, an evolutionarily conserved degradation system, serves to clear intracellular components through the lysosomal pathway. Mounting evidence has revealed cytoprotective roles of autophagy; however, the intracellular causes of overactivated autophagy, which has cytotoxic effects, remain elusive. Here we show that sustained proteotoxic stress induced by loss of the <u>RI</u>NG and <u>Ke</u>lch repeat-containing protein C53A5.6/RIKE-1 induces sequestration of LET-363/MTOR complex and overactivation of autophagy, and consequently impairs epithelial integrity in <i>C. elegans</i>. In C53A5.6/RIKE-1-deficient animals, blocking autophagosome formation effectively prevents excessive endosomal degradation, mitigates mislocalization of intestinal membrane components and restores intestinal lumen morphology. However, autophagy inhibition does not affect LET-363/MTOR aggregation in animals with compromised C53A5.6/RIKE-1 function. Improving proteostasis capacity by reducing DAF-2 insulin/IGF1 signaling markedly relieves the aggregation of LET-363/MTOR and alleviates autophagy overactivation, which in turn reverses derailed endosomal trafficking and rescues epithelial morphogenesis defects in C53A5.6/RIKE-1-deficient animals. Hence, our studies reveal that C53A5.6/RIKE-1-mediated proteostasis is critical for maintaining the basal level of autophagy and epithelial integrity.<b>Abbreviations:</b> ACT-5: actin 5; ACTB: actin beta; ALs: autolysosomes; APs: autophagosomes; AJM-1: apical junction molecule; ATG: autophagy related; C. elegans: Caenorhabditis elegans; CPL-1: cathepsin L family; DAF: abnormal dauer formation; DLG-1: Drosophila discs large homolog; ERM-1: ezrin/radixin/moesin; EPG: ectopic P granule; GFP: freen fluorescent protein; HLH-30: helix loop helix; HSP: heat shock protein; LAAT-1: lysosome associated amino acid transporter; LET: lethal; LGG-1: LC3, GABARAP and GATE-16 family; LMP-1: LAMP (lysosome-associated membrane protein) homolog; MTOR: mechanistic target of rapamycin kinase; NUC-1: abnormal nuclease; PEPT-1/OPT-2: Peptide transporter family; PGP-1: P-glycoprotein related; RAB: RAB family; RIKE-1: RING and Kelch repeat-containing protein; SLCF-1: solute carrier family; SQST-1: sequestosome related; SPTL-1: serine palmitoyl transferase family.