Dietary and environmental factors have opposite AhR-dependent effects on C. elegans healthspan

Results

C. elegans AHR-1 is differentially involved in stress response

Loss of AHR-1 extends C. elegans’ health- and lifespan [8]. Since lifespan extension often correlates with increased resistance to different types of stressors [29], we assessed AhR role in stress resistance by exposing wild-type and ahr-1 mutants to either heat shock, metabolic stressors (i.e. high concentrations of glucose or the hypoxia mimetic iron chelator 2,2’Bipyridyl, BP) or UVB light. As expected, the development and fertility of wild-type animals were affected by all insults in a dose-dependent manner (Figure 1) [30, 31]. Consistent with our previous data [8] loss of ahr-1 increased heat-stress resistance (Figure 1A, 1B), but it did not confer resistance to any of the newly tested insults (Figure 1C–1H). Actually, UVB-induced developmental delay and embryonic lethality were significantly more affected in the ahr-1(ju145) mutants than in wild-type worms (Figure 1G, 1H). To further characterize animals’ stress response, we quantified the expression of C. elegans transgenic reporters for different phase-I and phase-II genes typically regulated by AhR in mammals: cyps (e.g., CYP1A1 or CYP1B1), ugts (e.g.,UGT1A1 or UGT1A6), and gsts (e.g.,GSTA1 or GSTA2) [11, 32, 33]. Out of nine tested reporters, we found five genes (cyp-35A2, cyp-35B1,gst-4, cyp-37A1, and ugt-29) differentially expressed by at least ten percent upon ahr-1 RNAi (Supplementary Figure 1; Supplementary Table 1). Unexpectedly, when crossed into the ahr-1(ju145) mutant background, we observed an opposite effect on cyp-35B1 while the gst-4 and the ugt-29 expression remained increased and reduced respectively in the ahr-1 mutant (Supplementary Figure 1C, 1D, 1E). We previously showed that the ahr-1 mutant lives longer than wild-type [8] and in line with the differential effect between ahr-1 RNAi and the mutant, we now found that ahr-1 RNAi does not extend the lifespan of the wild-type animals (Table 1; Supplementary Figure 1F). These data suggest either different modes of action of ahr-1 silencing and mutation or tissue-specific effects disclosed by the RNAi treatment. Of note, while in most cases tissue-specific ahr-1 RNAi had no effects, health- and lifespan were significantly shortened when RNAi was enhanced in the nervous system (Table 1; Supplementary Figure 1G). Taken together results described so far reveal a complex AHR-1 role in C. elegans’ lifespan and response to stress in a tissue- and insult-dependent manner.

Figure 1. Loss of ahr-1 differentially regulates resistance to stressors. (A) Survival in response to heat shock. Curves show the pooled data of 60 worms in 3 independent replicates. Statistical test: Log-Rank test, * significance vs. wild-type. (B) Fertility after heat stress. Shown are the number (left panel) and viability (right panel) of eggs laid from gravid adults treated with heat shock for the indicated time. Mean + SEM of pooled data from 18 worms/condition in 3 independent experiments are shown. (C, D) Development and fertility in response to the indicated concentration of glucose. Means (+SEM) of 3 independent replicates are shown. N = number of individuals in panel (C), 9 individuals were used in panel (D). (E, F) Development and fertility in response to the indicated concentration of iron chelator (BP). Means (+SEM) of 3 and 4 independent replicates are shown. N = number of individuals in panel (E), 9 individuals were used in panel (F). (G, H) Development and fertility in response to indicated doses of UVB. Fertility was assessed at a dose of 600 J/m². Means (+SEM) of 3 independent replicates are shown. N = number of individuals in panel (G), 9 individuals were used in panel (H). (B–H) Statistical test: 2-way ANOVA with Tukey’s multiple comparisons test, * significance vs. wild-type, # significance vs. control (untreated), p-value < 0.05.

Table 1. Survival analysis upon tissue-specific ahr-1 RNAi.

Condition	Genotype	Description	Lifespan and healthspan (days)	N	n	P-value
N2 con			19.88 ± 0.29 16.00 ± 0.25	280	5
N2 ahr-1	wild-type	wild-type	19.46 ± 0.29 15.33 ± 0.25	264	5	0.14 0.04
NR222 con	rde-1(ne219); kzIs9 [lin-26p::nls::GFP + lin-26p::rde-1) + rol-6(su1006)]	hypodermis-specific RNAi [88]	19.07 ± 0.34 15.12 ± 0.26	120	2
NR222 ahr-1			18.78 ± 0.30 15.21 ± 0.29	120	2	0.23 0.65
NL2098 con	rrf-1(pk1417)	germline-specific RNAi [89, 90]	18.26 ± 0.45 14.16 ± 0.34	120	2
NL2098 ahr-1			18.24 ± 0.43 13.98 ± 0.34	120	2	0.83 0.89
NL2550 con	ppw-1(pk2505)	RNAi only in somatic tissues [91]	19.51 ± 0.59 15.92 ± 0.53	120	2
NL2550 ahr-1			18.78 ± 0.46 15.25 ± 0.40	120	2	0.11 0.19
WM118 con	rde-1(ne300); neIs9 [myo-3::HA::RDE-1+ pRF4(rol-6(su1006)]	muscle-specific RNAi [92]	15.49 ± 0.45 11.91 ± 0.29	120	2	0.92 0.27
WM118 ahr-1			15.40 ± 0.45 11.44 ± 0.29	120	2
VP303 con	rde-1(ne219); kbIs7 [nhx-2p::rde-1 + rol-6(su1006)]	intestine-specific RNAi [93]	18.68 ± 0.41 16.52 ± 0.33	120	2	0.47 0.72
VP303 ahr-1			18.50 ± 0.37 16.78 ± 0.32	120	2
TU3401 con	sid-1(pk3321); uls69[myo-2p::mCherry + unc-119p::sid-1]	nervous system specific RNAi [94]	16.48 ± 0.31 12.47 ± 0.23	180 3
TU3401 ahr-1			17.23 ± 0.32 13.03 ± 0.24	180	3	0.09 0.11
TU3311 con	uIs60[Punc119::YFP; Punc119::sid-1]	RNAi enhanced in the nervous system [94]	19.99 ± 0.44 15.87 ± 0.37	180	3
TU3311 ahr-1			17.50 ± 0.43 14.11 ± 0.37	180	3	0.001 0.003
Mean life- and healthspans +/- SEM of pooled data are shown. The L4440 plasmid was used as a negative control. Statistical analysis was performed between ahr-1 and control RNAi using the Log-rank test. The number of worms is specified as N, while the number of replicates is specified as n.

AHR-1 differentially regulates lifespan in response to potential modulators of its activity

In mammals, AhR exerts its functions primarily in response to ligands or modulators of its activity, such as exogenous substances (e.g. xenobiotics) or endogenous products of metabolism (e.g. microbiota-associated factors) [24]. The xenobiotic BaP exerts toxic effects in mammals through AhR-dependent cyps expression [25], and it can induce cyps expression also in C. elegans [34]. We observed that similar to mammals BaP significantly increased the expression of cyp-35B1 and exerted toxic effects by affecting animals’ development in a dose-dependent manner. However, these effects were largely ahr-1-independent (Supplementary Figure 2A, 2B). Interestingly, we found that BaP treatment from adulthood, consistent with its toxic effects, significantly shortened animals’ health- and lifespan, with a more pronounced effect on ahr-1 mutants, indicating a protective role of AHR-1 against BaP-curtailed longevity (Figure 2A, 2B). In mammals, UVB radiations activate AHR-1 through the formation of 6-formylindolo[3,2-b]carbazole (FICZ) [20, 21]. In C. elegans UVB radiation shortens lifespan, induces embryonic lethality and germline cells apoptosis in a dose-dependent manner [35, 36]. We showed that ahr-1(ju145) is more sensitive to UVB-induced embryonic lethality (Figure 1H). Accordingly, and in line with the notion that loss of AhR sensitizes mammalian cells to UVB-induced apoptosis loss [37], we found that UVB-induced germ cell apoptosis is significantly more increased in the ahr-1 mutant’s germline compared to wild-type animals (Supplementary Figure 2C). UVB irradiation increases Cyp1A1 expression in human keratinocytes in an AHR-dependent manner [20]. Interestingly, similar to the above results with BaP, although UVB tent to increase cyp-35B1 expression in an ahr-1-independent manner (Supplementary Figure 2D), it decreased animals’ lifespan and motility with a significantly stronger effect on the ahr-1(ju145) compared to wild-type animals (Figure 2C, 2D). Our results indicate an evolutionarily conserved protective role of AhR in response to environmental AhR activators identified in vertebrates (BaP and UVB). Finally, as diet- and microbiota-associated factors modulate AhR activity in mammals, we took advantage of two common Escherichia coli strains used as a food source for C. elegans, HT115(DE3) and OP50(xu363). Strikingly, we found that the reduced expression of the cyp-35B1::GFP reporter (Supplementary Figure 3B), as well as the beneficial effects on lifespan, motility (Figure 2E, 2F), heat resistance and pharyngeal pumping (Supplementary Figure 3A, 3C, 3D), elicited in the ahr-1 mutants fed HT115 are abolished when animals are fed OP50. Instead, the different bacteria neither affected the fertility in basal condition (Supplementary Figure 3E) nor the increased sensitivity to UVB (Supplementary Figure 3F, 3G) of the ahr-1 mutant. This is consistent with our previous findings showing germline sensitivity to UVB-induced apoptosis does not correlate with lifespan outcomes [36]. The lipid droplet content, which did not change between wild-type and ahr-1 mutants, was however similarly affected by the different bacteria (not shown). Results described so far indicate that known AhR modulators differentially affect C. elegans lifespan in an ahr-1-dependent manner but that classical detoxification related genes (cyps) are possibly not the major targets of C. elegans AHR-1. To gain further insight into CeAhR plasticity of potential relevance for stress response and aging we turned to the results of a transcriptomic analysis recently carried out in the lab (Brinkmann et al. in preparation). A thorough analysis of the most differentially expressed genes between wild-type and ahr-1(ju145) revealed that many of them are known to be affected not only during C. elegans aging but also by dietary compounds (e.g. quercetin, resveratrol, bacteria), which modulate AhR activity in mammals (Tables 2 and 3). Interestingly, quantitative PCR analysis of some of these genes (atf-2, K04H4.2, egl-46, T20F5.4, ptr-4, dyf-7, clec-209, C01B4.6, C01B4.7, F56A4.3) confirmed their ahr-1 dependency in basal conditions and supported a specific AhR-bacteria regulatory effect: their expression was generally not affected by UVB or BaP but their reduced expression in the ahr-1(ju145) mutants fed H115 bacteria, similar to cyp-35B1, was abolished in animal fed an OP50 diet (Supplementary Figure 4). Altogether, results shown so far indicate an evolutionarily conserved, protective role for AhR against BaP and UVB, and identify a new role for AhR in environmentally regulated aging with dietary bacteria as an important component in ahr-1-signaling-mediated longevity.

Figure 2. AHR-1 displays evolutionarily conserved functions and affects aging in a diet-dependent manner. (A, B) ahr-1 is more sensitive to xenobiotic stress. Pooled lifespan/healthspan curves of 120 worms/condition in 2 independent replicates treated with either DMSO or 5 μM BaP from adulthood are shown. (C, D) ahr-1 is more sensitive to UVB stress. Pooled lifespan/healthspan curves of 300 (wt control, ahr-1 control), 180 (wt UVB) and 178 (ahr-1 UVB) worms/condition in 3 independent replicates either left untreated or treated with 1200 J/m² UVB from adulthood are shown. (E, F) AHR-1 affects aging in a diet-dependent manner. Pooled lifespan/healthspan curves of 170 (wt OP50) and 180 (all other conditions) worms/condition in 3 independent replicates grown either on HT115 or OP50 are shown. (A–F) Statistical test: Log-Rank test, # significance vs. control/HT115, * significance vs. wt, p-value < 0.05.

Table 2. List of the most robust over-expressed genes in ahr-1vs. wild-type.

Gene Name	human ortholog	Molecular function	Modulators	logFC	adj. p-value
irld-35		unknown	bacterial infection; temperature	1.968	0.0019
clec-209		carbohydrate binding	bacterial infection; aging; quercetin; heat shock	1.882	0.0182
F56A4.2		unknown	aging; bacterial infection; temperature	1.882	0.0182
C01B4.6	GALM	catalytic activity, isomerase activity, carbohydrate binding		1.671	9.3 * 10-9
Y19D10A.16	GALM	catalytic activity, isomerase activity, carbohydrate binding		1.671	9.3 * 10-9
F56A4.3	GSTP1	unknown	bacterial infection	1.660	0.0013
srd-61		unknown		1.614	0.0001
srd-75		unknown	bacterial infection	1.614	0.0001
C01B4.7		unknown	bacterial infection	1.605	0.0028
Y19D10A.4		transmembrane transporter activity	heat shock; bacterial infection	1.605	0.0028
Human orthologs were extracted using the BioMart tool (https://parasite.wormbase.org/biomart). Modulators of these genes with potential relevance for AHR-1 activity were selected from WormBase. For log fold change values (logFC) a base of 2 is used.

Table 3. List of the most robust under-expressed genes in ahr-1 vs. wild-type.

Gene Name	human ortholog	Molecular function	Modulators	logFC	adj. p-value
R02F11.1		unknown	bacterial infection; bacterial diet	-2.308	0.0312
hbl-1	ZNF513
ZNF462	RNA polymerase II regulatory region sequence-specific DNA binding, RNA polymerase II transcription factor activity, sequence-specific DNA binding, transcription factor activity, metal ion binding	bacterial infection; quercetin; aging	-2.013	0.0171
atf-2		RNA polymerase II regulatory region DNA binding, transcriptional repressor activity, RNA polymerase II core promoter proximal region sequence-specific binding, transcription factor activity, protein binding	ahr-1; bacterial infection; quercetin; aging	-1.958	0.0227
lpr-4		unknown	bacterial infection; quercetin; bacterial diet; indole	-1.834	0.0227
K04H4.2		chitin binding	ahr-1; bacterial infection; bacterial diet	-1.831	0.0248
egl-46	INSM1 INSM2	RNA polymerase II transcription factor activity, sequence-specific DNA binding, RNA polymerase II transcription factor binding	bacterial infection; quercetin; aging	-1.823	0.0406
T20F5.4		unknown	bacterial infection; quercetin	-1.803	0.0400
ptr-4	PTCHD3	unknown	resveratrol; bacterial infection; quercetin; bacterial diet; aging	-1.766	0.0162
lpr-5		unknown	bacterial infection; bacterial diet; aging; quercetin; indole	-1.752	0.0227
dyf-7		protein self-association	quercetin; bacterial infection; temperature	-1.743	0.0227
Human orthologs were extracted using the BioMart tool (https://parasite.wormbase.org/biomart). Modulators of these genes with potential relevance for AHR-1 activity were selected from WormBase. For log fold change values (logFC) a base of 2 is used.

Loss of ahr-1 affects age-associated pathologies in a diet-dependent manner

The critical role of AHR-1 in C. elegans neurons [14, 15, 17] and motility [8, 9] prompted us to investigate whether diet-dependent effects also influence age-related neuromuscular pathologies. A growing body of evidence indeed indicates microbiota can affect various aspects of C. elegans’ health-span [38–42]. Notably, loss of ahr-1 extended life- and health-span of two age-associated disease models, namely animals with muscle expression of aggregation-prone proteins polyglutamine (polyQ₄₀) and α-synuclein (Figure 3), and these beneficial effects were significantly suppressed when animals were fed an OP50 diet instead of HT115 (Figure 3A, 3B, 3E, 3F). Despite being longer-lived, ahr-1 mutants fed HT115 displayed a greater number and size of polyQ₄₀ and α-synuclein aggregates, which is nonetheless in line with studies revealing no direct correlation between aggregates and toxic effects [43]. Moreover, the increase in aggregation was mainly regulated in a diet-independent manner (Figure 3C, 3D, 3G, 3H), indicating that the ahr-1-diet interaction effect on health-span is independent of its effect on protein aggregation. Somewhat surprisingly, when we investigated the effect of ahr-1 deficiency in another pro-aggregation model - a C. elegans strain expressing a pan-neuronal human amyloid-beta (Aβ) peptide [44] - we found that contrary to the other models, it reduced animals’ life- and health-span, yet interestingly in a diet-dependent manner (Supplementary Figure 5A–5D).

Figure 3. ahr-1 mutants increase aggregation but extend lifespan in a diet-dependent manner. (A, B) Kaplan Meier curves of polyQ;wt and polyQ;ahr-1 of 180 worms/condition in 3 independent experiments are shown. * p-value < 0.05 vs. polyQ;wt, # p-value < 0.05 vs. HT115, statistical test: Log-rank test. (C) Representative fluorescence images of 10-days old polyQ;wt and polyQ;ahr-1 on HT115 and OP50. (D) Quantification of aggregates in 10-days old polyQ;wt and polyQ;ahr-1. Mean + 95 % CI of pooled data from 34 (wt HT115), 29 (wt OP50), 26 (ahr-1 HT115), and 35 (ahr-1 OP50) worms in 3 independent replicates is shown. Statistical test: One-way ANOVA with Tukey’s multiple comparisons test, * p-value < 0.05 vs. polyQ;wt, ^# p-value < 0.05 vs. HT115. (E, F) Kaplan Meier curves of a-syn;wt and a-syn;ahr-1 of 120 worms/condition in 2 independent experiments are shown. * p-value < 0.05 vs. a-syn;wt, # p-value < 0.05 vs. HT115, statistical test: Log-rank test. (G) Representative fluorescence images of the head muscles of 7-days old a-syn;wt and a-syn;ahr-1 on HT115 and OP50. (H) Quantification of aggregates in 7- days old a-syn;wt and a-syn;ahr-1. Mean + 95 % CI of pooled data from 77 (wt HT115), 82 (wt OP50), 88 (ahr-1 HT115), and 92 (ahr-1 OP50) worms in 3 independent replicates is shown. Statistical test: One-way ANOVA with Tukey’s multiple comparisons test, * p-value < 0.05 vs. a-syn;wt, ^# p-value < 0.05 vs. HT115.

Given that temperature may affect aging and associated pathologies depending on the bacterial diet and genetic background [38, 45] we next tested whether the healthy aging phenotype of ahr-1 is also temperature-dependent. Despite the increased resistance to heat shock of ahr-1(ju145) mutants, and opposite to the lifespan at 20° C, ahr-1-depleted animals were short-lived on an HT115 diet at 25° C. Yet, again, this difference in the lifespan of wild-type and ahr-1 was abolished on the OP50 diet, which per se already shortened the lifespan at 25° C of wild-type animals (Figure 4A, 4B). The higher temperature also prevented the beneficial diet-dependent effects of loss of ahr-1 on life- and health-span in the polyQ strain (Figure 4C, 4D), while the number of polyQ aggregates increased according to the rise in temperature but still in a diet-independent manner (Figure 4E, 4F). Overall our data uncovered a new diet- and temperature-dependent effect of AhR in modulating aging and associated neuromuscular pathologies, which is nonetheless uncoupled from the age-dependent increase in protein aggregation.

Figure 4. At 25° C, ahr-1(ju145) is short-lived and loses its protection against the toxicity of polyQ₄₀ aggregates. (A, B) Kaplan Meier curves of wild-type and ahr-1(ju145) at 25° C. Pooled data of 180 worms/condition in 3 independent replicates are shown. * p-value < 0.05 vs. wt, # p-value < 0.05 vs. HT115, statistical test: Log-rank test. (C, D) Kaplan Meier curves of polyQ;wt and polyQ;ahr-1. Worms were grown at 25° C from day 3 (indicated by arrowhead). Pooled data of 150 worms/condition in 3 independent replicates are shown. * p-value < 0.05 vs. wt, # p-value < 0.05 vs. HT115, statistical test: Log-rank test. (E) Representative fluorescence images of 10-days old polyQ;wt and polyQ;ahr-1 grown at 25° C from day 3. (F) Quantification of aggregates in 10-days old polyQ;wt and polyQ;ahr-1 grown at 25° C from day 3. Mean + 95 % CI of pooled data from 21 (wt HT115), 19 (wt OP50), 20 (ahr-1 HT115) and 19 (ahr-1 OP50) worms/condition in 2 independent replicates are shown. * p-value < 0.05 vs. wt, statistical test: One-way ANOVA with Tukey’s multiple comparisons test.

Bacterial tryptophan metabolism mediates the beneficial effect of the ahr-1 mutant

In search of the potential factor responsible for the diet-dependent differences, we first ruled out an effect of the different bacteria on the ahr-1 expression (Figure 5A) and an effect of the different bacteria growing media (not shown). These results point to a specific role of bacteria components on the modulation of AHR-1-regulated processes. We thus asked whether metabolically active bacteria are required for the observed differences. To this end, we compared the heat-stress resistance of animals fed alive bacteria with that of animals fed bacteria either killed before seeding on plates or killed on the plates two days after seeding (thus allowing metabolites secretion). Very interestingly, killing bacteria before seeding completely abolished the differences between wild-type and ahr-1 fed HT115 (Figure 5B, 5C), indicating that a factor produced by metabolically active HT115 bacteria may influence the AHR-1-mediated effects. In support of this possibility, the increased resistance to stress of ahr-1 mutants observed on alive HT115 bacteria persisted when bacteria were killed after growing for two days on the feeding plates (Figure 5D). In line with the heat shock experiments, killing the bacteria before seeding also completely suppressed the increased lifespan of the ahr-1 mutants on HT115 with no major effects on animals fed OP50 (Figure 5E). These data point towards HT115 secreted metabolites playing a role in ahr-1-mediated life- and health-span, likely via gut ingestion or neuronal sensing [38].

Figure 5. Metabolically active bacteria are required for the differences in lifespan between wild-type and ahr-1 on HT115. (A) ahr-1 mRNA expression in wild-type worms feeding on HT115 or OP50. Pooled data of 3 independent replicates are shown. No statistical significance was observed with the t-test. (B–D) Survival upon heat stress in 7-days old wild-type and ahr-1(ju145) feeding on either HT115 or OP50. Pooled data of 60 worms/condition in 3 independent experiments are shown. * p-value < 0.05 vs. wt, # p-value < 0.05 vs. HT115, statistical test: Log-rank test. (B) Alive bacteria were used as a food source. (C) Bacteria were killed by UVB irradiation before seeding to the NGM. (D) Bacteria had grown on the NGM for 2 days before being killed by UVB irradiation. (E) Kaplan Meier curves of wild-type and ahr-1(ju145) on UVB-killed bacteria. Pooled data of 120 (wt HT115, ahr-1 HT115, ahr-1 OP50) and 110 (wt OP50) worms in 2 independent experiments are shown. * p-value < 0.05 vs. wt, # p-value < 0.05 vs. HT115, statistical test: Log-rank test.

A mass spectrometric analysis of the two bacteria supernatants revealed on the one hand that the subtracted spectrum between HT115 and OP50 showed three prominent peaks (Figure 6A) with m/z 361 likely being an arginine-tryptophan (Arg-Trp) dipeptide. On the other hand, the medium of OP50 was enriched in an alanine-glutamate (Ala-Glu) dipeptide (Figure 6B). In mammals, Trp and its metabolites (such as indole) modulate AhR activity [23, 46, 47] and in C. elegans Trp was shown to abolish some of the different phenotypes observed between alive HT115 and OP50 [48]. We found that supplementation of L-tryptophan completely abolished the heat-stress resistance of ahr-1(ju145) on HT115 - and partially suppressed the difference also between wild-type and ahr-1(ju145) on OP50 (Figure 6C, 6D). Overall, these data point towards a potential role of Trp metabolism in ahr-1-bacteria-regulated age-associated phenotypes.

Figure 6. Tryptophan supplementation abolishes the differences between wild-type and ahr-1. (A) Positive ESI MS analysis. The HT115 BPC after the subtraction of the OP50 BPC is shown. Masses in peak 2 are shown as an inset. (B) Positive ESI-mass spectrum of OP50(L4440) medium after subtraction of the HT115(L4440) spectrum. Masses peak 22 are shown as an inset. m/z 219 is likely an Ala-Glu dipeptide. (C, D) Heat stress survival after tryptophan supplementation with indicated concentrations of tryptophan. Survival curves of 7-days old worms feeding on HT115 supplemented with tryptophan are shown. The curves show pooled data from or 40 worms/condition in 2 independent replicates (1.25 mg trp) or 60 worms/condition in 3 independent experiments (2.5 mg trp). * p-value < 0.05 vs. wt, # p-value < 0.05 vs. HT115, statistical test: Log-rank test.

Abbreviations

Aβ: amyloid-beta; AhR: aryl hydrocarbon receptor; AIP: AhR interacting protein (also XAP2); Arnt: AhR nuclear translocator; BaP: benzo(a)pyrene; bHLH/PAS: basic helix–loop–helix/PER–ARNT–SIM; BP: 2,2’Bipyridyl; CYP: cytochrome P450; FICZ: 6-formylindolo[3,2-b]carbazole; GABA: gamma-Aminobutyric acid; Glu: glutamate; GST: glutathione-S-transferase; HSP90: heat shock protein 90; PolyQ: polyglutamine; ROS: reactive oxygen species; TCDD: 2,3,7,8-tetrachlorodibenzodioxin; Trp: tryptophan; UGT: uridine diphosphate glucuronosyl transferase; XRE: xenobiotic responsive element.

Author Contributions

Conceptualization: N.V. Formal analysis: V.B., A.Sc., N.V. Funding acquisition: V.B., N.V. Investigation: V.B., D.P., A.Sh. Supervision: N.V. Resources: N.V. Visualization: V.B. Writing -original draft-: V.B., N.V. Writing -review and editing-: A.Sc.

Acknowledgments

Most nematode strains utilized in this work were provided by the Caenorhabditis Genetics Center, funded by the NIH Office of Research Infrastructure Programs (P40 OD010440). Other nematodes or bacteria strains were kindly provided by David Depomerai (University of Nottingham), Sheila Nathan (University of Malaysia), and Shawn Xu (University of Michigan). We thank Sabine Metzger (University of Cologne) for the performance of mass spectrometry. We further thank Wormbase and the GENiE network funded by the European Cooperation in Science and Technology (COST Action BM1408).

Conflicts of Interest

The authors declare no conflicts of interest.

Funding

This work was financially supported by funding to N.V. from the German Research Foundation (DFG VE366/8-1). V.B. was supported by a Ph.D. scholarship by the Jürgen Manchot Foundation.

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