PMK-1 p38 MAPK promotes cadmium stress resistance, the expression of SKN-1/Nrf and DAF-16 target genes, and protein biosynthesis in Caenorhabditis elegans

Modulation of Pseudomonas aeruginosa-induced avoidance behavior by Shen Qi pills via mitogen-activated protein kinase PMK-1 and forkhead box protein O DAF-16 in Caenorhabditis elegans

BACKGROUND

Avoidance behavior is one of the core features of anxiety and related in-depth study can help to reveal the biological basis of these disorders. In recent years, traditional Chinese medicine has incorporated Shen Qi pills to treat neuropsychiatric disorders, such as depression and post-traumatic stress, and has achieved significant therapeutic effects. However, its specific mechanism of action is still unclear.

PURPOSE

The aim of this study was to link the avoidance phenotype to psychiatric disorders by utilizing the Caenorhabditis elegans as a biological model, revealing the potential common mechanisms underlying the treatment of these disorders with Shen Qi pills.

METHODS

Avoidance behavior and immunity of C. elegans as a phenotypic entry point to explore the molecular mechanisms by which Shen Qi pills affects avoidance behavior with the help of pmk-1 and daf-16 mutants and RNA interference techniques.

RESULTS

We found that the intervention of Shen Qi pills can delay the avoidance behavior of C. elegans to P. aeruginosa, improve the immunity level, and reduce the up-regulation of pmk-1 and daf-16 genes induced by P. aeruginosa. Shen Qi pills did not improve the immunity of pmk-1 mutant but could still enhance the immunity of daf-16 mutant. After daf-16 knockout, Shen Qi pills could not delay its avoidance behavior, which was consistent with the results shown in the neuron-specific silencing of daf-16 C. elegans.

CONCLUSION

These findings reveal the conclusion that Shen Qi pills regulate the avoidance behavior of C. elegans induced by P. aeruginosa via PMK-1 and DAF-16, with the latter acting directly on neurons independent of immune pathways.

Biofilm proficient Bacillus subtilis prevents neurodegeneration in Caenorhabditis elegans Parkinson's disease models via PMK-1/p38 MAPK and SKN-1/Nrf2 signaling

Parkinson's disease (PD) is a no-curable neurodegenerative disease of pandemic distribution for which only palliative treatments are available. A hallmark of PD is injury to dopaminergic neurons in the substantia nigra pars compacta. Here, we report that Caenorhabditis elegans colonized by biofilm-forming Bacillus subtilis is resistant to injury of dopaminergic neurons caused by treatment with the PD-related neurotoxin 6-hydroxydopamine (6-OHDA). Biofilm-forming B. subtilis-colonized C. elegans display dopamine-dependent behaviors indistinguishable from those of 6-OHDA-untreated worms colonized by gut commensal E. coli OP50. In C. elegans PD model strains with early dopaminergic neuron decay or overexpressing human alpha-synuclein, biofilm-forming B. subtilis colonization had neuroprotective effects and prevents alpha-synulcein aggregation, respectively. The B. subtilis-controlled insulin/IGF-1 signaling (ILS), whose downregulation prevents aging-related PD, is not involved in protecting against 6-OHDA-related injury. We demonstrate that biofilm-forming B. subtilis activates PMK-1 (p38 MAPK)/SKN-1 (Nrf2) signaling, which protects C. elegans from 6-OHDA-induced dopaminergic neuron injury.

Bacillus amyloliquefaciens WF2020 isolated from fermented pickles promotes longevity and health in Caenorhabditis elegans via JNK and p38 MAPK pathways

Bacillus amyloliquefaciens, a potential probiotic for use in food and feed production, can exert anti-aging effects in a strain-specific manner. However, the molecular mechanisms underlying its anti-aging effects remain poorly understood. This study explored the effects of B. amyloliquefaciens WF2020 (WF2020), isolated from Chinese fermented pickles, on longevity and health and investigated the underlying mechanisms in Caenorhabditis elegans. Interestingly, WF2020 was found to increase mean lifespan, worm length, body bends, and resistance to heat, oxidative stress, and Staphylococcus aureus infection. It also improved mitochondrial transmembrane potential and antioxidative status, reduced lipid accumulation and oxidative damage, and altered the expression of several genes involved in cell apoptosis, fat metabolism, host tolerance to heat and oxidative stress, and immune responses, compared to Escherichia coli OP50 (OP50), a standard food source for C. elegans. Moreover, WF2020-fed loss-of-function mutants for nsy-1, sek-1, pmk-1, jkk-1, jnk-1, daf-16, and hsf-1 did not exhibit lifespan extension. Additionally, WF2020-fed pmk-1 and jnk-1 mutants showed similar worm length, body bends, lipid accumulation, mitochondrial transmembrane potential, and antioxidative properties to the OP50 group. Correspondingly, WF2020 significantly upregulated the expression of nsy-1, sek-1, pmk-1, jkk-1, and jnk-1 and increased the proportion of DAF-16::GFP in the nucleus, along with the expression of HSP-16.2::GFP. In conclusion, WF2020 activated the p38 MAPK and JNK pathways to regulate the functions of HSF-1 and DAF-16, thereby promoting longevity and health in C. elegans. These findings suggest that WF2020 could be a potential probiotic or a starter for use in food and feed production to delay aging and promote health.

Cadmium exposure induces multigenerational inheritance of germ cell apoptosis and fertility suppression in Caenorhabditis elegans

Cadmium is a significant environmental pollutant that poses a substantial health hazard to humans due to its propensity to accumulate in the body and resist excretion. We have a comprehensive understanding of the damage caused by Cd exposure and the mechanisms of tolerance, however, the intricate mechanisms underlying multigenerational effects resulting from Cd exposure remain poorly understood. In this study, Caenorhabditis elegans were used as a model organism to investigate Cd-induced multigenerational effects and its association with epigenetic modifications. The results showed that Cd exposure leads to an increase in germ cell apoptosis and a decrease in fertility, which can be passed down to subsequent generations. Further analysis revealed that transcription factors DAF-16/FOXO and SKN-1/Nrf2 play essential roles in responding to Cd exposure and in the transgenerational induction of germ cell apoptosis. Additionally, histone H3K4 trimethylation (H3K4me3) marks stress-responsive genes and enhances their transcription, ultimately triggering multigenerational germ cell apoptosis. This study provides compelling evidence that the detrimental effects of Cd on the reproductive system can be inherited across generations. These findings enhance our understanding of the multigenerational effects of environmental pollutants and may inform strategies for the prevention and control of such pollutants.

Sulforaphane Exposure Prevents Cadmium-Induced Toxicity and Mitochondrial Dysfunction in the Nematode Caenorhabditis elegans by Regulating the Insulin/Insulin-like Growth Factor Signaling (IIS) Pathway

Cadmium (Cd) is a heavy metal that is highly toxic to humans and animals. Its adverse effects have been widely associated with mitochondrial alterations. However, there are not many treatments that target mitochondria. This study aimed to evaluate the impact of sulforaphane (SFN) pre-exposure against cadmium chloride (CdCl2)-induced toxicity and mitochondrial alterations in the nematode Caenorhabditis elegans (C. elegans), by exploring the role of the insulin/insulin-like growth factor signaling pathway (IIS). The results revealed that prior exposure to SFN protected against CdCl2-induced mortality and increased lifespan, body length, and mobility while reducing lipofuscin levels. Furthermore, SFN prevented mitochondrial alterations by increasing mitochondrial membrane potential (Δψm) and restoring mitochondrial oxygen consumption rate, thereby decreasing mitochondrial reactive oxygen species (ROS) production. The improvement in mitochondrial function was associated with increased mitochondrial mass and the involvement of the daf-16 and skn-1c genes of the IIS signaling pathway. In conclusion, exposure to SFN before exposure to CdCl2 mitigates toxic effects and mitochondrial alterations, possibly by increasing mitochondrial mass, which may be related to the regulation of the IIS pathway. These discoveries open new possibilities for developing therapies to reduce the damage caused by Cd toxicity and oxidative stress in biological systems, highlighting antioxidants with mitochondrial action as promising tools.

Stage-specific exposure of Caenorhabditis elegans to cadmium identifies unique transcriptomic response cascades and an uncharacterized cadmium responsive transcript

Age/stage sensitivity is considered a significant factor in toxicity assessments. Previous studies investigated cadmium (Cd) toxicosis in Caenorhabditis elegans, and a plethora of metal-responsive genes/proteins have been identified and characterized in fine detail; however, most of these studies neglected age sensitivity and stage-specific response to toxicants at the molecular level. This present study compared the transcriptome response between C. elegans L3 vs L4 larvae exposed to 20 µM Cd to explore the transcriptional hallmarks of stage sensitivity. The results showed that the transcriptome of the L3 stage, despite being exposed to Cd for a shorter period, was more affected than the L4 stage, as demonstrated by differences in transcriptional changes and magnitude of induction. Additionally, T08G5.1, a hitherto uncharacterized gene located upstream of metallothionein (mtl-2), was transcriptionally hyperresponsive to Cd exposure. Deletion of one or both metallothioneins (mtl-1 and/or mtl-2) increased T08G5.1 expression, suggesting that its expression is linked to the loss of metallothionein. The generation of an extrachromosomal transgene (PT08G5.1:: GFP) revealed that T08G5.1 is constitutively expressed in the head neurons and induced in gut cells upon Cd exposure, not unlike mtl-1 and mtl-2. The low abundance of cysteine residues in T08G5.1 suggests, however, that it may not be involved directly in Cd sequestration to limit its toxicity like metallothionein, but might be associated with a parallel pathway, possibly an oxidative stress response.

Mitochondrial p38 Mitogen-Activated Protein Kinase: Insights into Its Regulation of and Role in LONP1-Deficient Nematodes

p38 Mitogen-Activated Protein Kinase (MAPK) cascades are central regulators of numerous physiological cellular processes, including stress response signaling. In C. elegans, mitochondrial dysfunction activates a PMK-3/p38 MAPK signaling pathway (MAPKmt), but its functional role still remains elusive. Here, we demonstrate the induction of MAPKmt in worms deficient in the lonp-1 gene, which encodes the worm ortholog of mammalian mitochondrial LonP1. This induction is subjected to negative regulation by the ATFS-1 transcription factor through the CREB-binding protein (CBP) ortholog CBP-3, indicating an interplay between both activated MAPKmt and mitochondrial Unfolded Protein Response (UPRmt) surveillance pathways. Our results also reveal a genetic interaction in lonp-1 mutants between PMK-3 kinase and the ZIP-2 transcription factor. ZIP-2 has an established role in innate immunity but can also modulate the lifespan by maintaining mitochondrial homeostasis during ageing. We show that in lonp-1 animals, ZIP-2 is activated in a PMK-3-dependent manner but does not confer increased survival to pathogenic bacteria. However, deletion of zip-2 or pmk-3 shortens the lifespan of lonp-1 mutants, suggesting a possible crosstalk under conditions of mitochondrial perturbation that influences the ageing process. Furthermore, loss of pmk-3 specifically diminished the extreme heat tolerance of lonp-1 worms, highlighting the crucial role of PMK-3 in the heat shock response upon mitochondrial LONP-1 inactivation.

Symbiont-mediated immune priming in animals through an evolutionary lens

Protective symbionts can defend hosts from parasites through several mechanisms, from direct interference to modulating host immunity, with subsequent effects on host and parasite fitness. While research on symbiont-mediated immune priming (SMIP) has focused on ecological impacts and agriculturally important organisms, the evolutionary implications of SMIP are less clear. Here, we review recent advances made in elucidating the ecological and molecular mechanisms by which SMIP occurs. We draw on current works to discuss the potential for this phenomenon to drive host, parasite, and symbiont evolution. We also suggest approaches that can be used to address questions regarding the impact of immune priming on host-microbe dynamics and population structures. Finally, due to the transient nature of some symbionts involved in SMIP, we discuss what it means to be a protective symbiont from ecological and evolutionary perspectives and how such interactions can affect long-term persistence of the symbiosis.

Integrated transcriptomics and metabolomics unravel the metabolic pathway variations for barley β-glucan before and after fermentation with L. plantarum DY-1

The results of our previous study showed that the structure and function of β-glucan in barley were changed after fermentation by L. plantarum DY-1. In this study, the antioxidant activities of RBG (regular barley β-glucan, unfermented) and FBG (barley β-glucan, fermented with L. plantarum DY-1) were evaluated by adopting an in vivo animal model, Caenorhabditis elegans (C. elegans). We also carried out an integrated transcriptomic and metabolomic profiling for RBG and FBG to delineate their signature pathways. RBG treatment has better effects on SOD enzyme activity and ROS levels than FBG, while FBG treatment has better effects on the CAT enzyme activity and MDA content than RBG in C. elegans. Transcription group analysis showed that FBG mainly decreases the expression of the Cyp-D gene to inhibit the calcium signaling pathway, promotes the Wnt signaling pathway by up-regulating the GSK-3β gene and improving the oxidative damage of C. elegans; RBG mainly inhibits calcium signal pathways by reducing the expression of ANT-solute carrier family 25 genes, promoting life adjustment pathways by reducing the expression of the HSP-12.6 gene to improve the oxidative stress of C. elegans. Joint analysis showed that the difference between FBG and RBG in the regulation of oxidative stress is mainly reflected in the metabolism pathway of arachidonic acid. Under the regulation of FBG, the expression of the C03H5.4 gene was decreased, the expression of leukotriene A4, prostaglandin G2, arachidonic acid and phosphatidylcholine was decreased, and the expression of 14,15-DiHETrE was increased. Under the regulation of RBG, the expression of gene C03H5.4 was up-regulated, the expression of metabolites such as leukotriene B4 was up-regulated, and the expression of arachidonic acid and phosphatidylcholine was down-regulated.

Lactobacillus Regulates Caenorhabditis elegans Cell Signaling to Combat Salmonella Infection

Salmonella typhimurium DT104 infection causes the death of Caenorhabditis elegans, which can be prevented by certain Lactobacillus isolates. However, the molecular mechanisms of both the host response to the infection and the protection by Lactobacillus are largely unclear. The present study has investigated the life-span and gene expression of both wild-type (WT) and mutants in some key components of cell signaling in response to S. typhimurium infection and protection from Lactobacillus zeae. The results indicated that the gene expression of daf-16 in the DAF/ insulin-like growth factor (DAF/IGF) pathway, ced-3 and ced-9 in the programmed cell death (PCD) pathway, lys-7, spp-1, and abf-3 for antimicrobial peptide production, and bar-1 involved in the production of other defense molecules was all significantly upregulated when the wild-type (WT) was subjected to DT104 infection. On the contrary, the gene expression of tir-1, sek-1, and pmk-1 in the p38 mitogen-activated protein kinase (MAPK) pathway and clec-60, sod-3, and skn-1 for the production of other defense molecules was significantly suppressed by DT104. Pretreatment of the worms with L. zeae LB1 significantly upregulated the expression of almost all the tested genes except for ced-3, ced-9, abf-2, age-1, and dbl-1 compared with the nematode infected with DT104 only. Mutants defective in the cell signaling or other defense molecules of C. elegans were either more susceptible (defective in nsy-1, sek-1, pmk-1, ced-3, ced-9, skn-1, or daf-16) or more resistant (defective in age-1 or dbl-1) to DT104 infection than the WT except for the mutant defective in sod-3. Mutants defective in antimicrobial peptides (lys-7 or abf-3) were also more susceptible than the WT. In contrast, the mutant defective in spp-1 became more resistant. When all the mutants were pretreated with L. zeae LB1, five mutants that are defective in nsy-1, sek-1, pmk-1, abf-3, or lys-7 showed no response to the protection from LB1. These results suggest that L. zeae LB1 can regulate C. elegans cell signaling including the p38 MAPK pathway and downstream production of antimicrobial peptides and defense molecules to combat Salmonella infection.

Structural characterization of ginseng oligopeptides and anti-aging potency evaluation in Caenorhabditis elegans

The functions of ginseng polysaccharide have been widely explored, yet, the antiaging activity of ginseng oligopeptides (GOPs) has not been well explored. In the current study, seven novel GOPs were isolated, and their antiaging activity was explored in a Caenorhabditis elegans (C. elegans) model. Of interest, all the GOPs showed lifespan extending effects in C. elegans models. Out of the GOPs treatments, 0.75 mM GOP-1 (EHGEYE) prolonged the N2 nematodes lifespan by 42.5%. Additionally, GOP-1 had a strong free radical-scavenging activity, and up-regulated the survival of the N2 C. elegans under oxidative and thermal stresses. Further study revealed that GOP-1 up-regulated the transcription factor daf-16 and jnk-1 expressions, thus we inferred that GOP-1 promotes the lifespan and stress resistances through a JNK-1-DAF-16 pathway. The current study revealed that the ginseng oligopeptides are potential antiaging agents.

Heat shock pretreatment induced cadmium resistance in the nematode Caenorhabditis elegans is depend on transcription factors DAF-16 and HSF-1

Cadmium (Cd) exposure poses a serious environmental problem due to the metal's bioaccumulation and difficult to eliminate from body. Understanding the mechanisms of Cd detoxification and resistance can provide insights into methods to protect against the damaging effects of the heavy metal. In the present study, we found that heat shock (HS) pretreatment increased Cd resistance of the nematode Caenorhabditis elegans by reducing the bagging phenotype and protecting the integrity of the intestinal barrier. HS pretreatment increased the expression of heat shock protein-16.2 (HSP-16.2) prior to Cd exposure, and HS-induced Cd resistance was absent in worms with hsp-16.2 loss-of-function mutation. Worm strain with daf-2(e1370) mutation presented enhanced HS-induced Cd resistance, which was eliminated in worm strains of daf-16(mu86) and hsf-1(sy441). HS pretreatment increased DAF-16 nuclear localization and HSF-1 granule formation prior to Cd exposure. DAF-16 and HSF-1 was essential in reducing bagging formation and protecting the integrity of intestinal barrier after HS pretreatment. In conclusion, the present study demonstrated that HS-induced Cd resistance in C. elegans is regulated by the DAF-16/FOXO and HSF-1 pathways through regulation of HSP-16.2 expression.

Cholesterol Regulates Innate Immunity via Nuclear Hormone Receptor NHR-8

Cholesterol is an essential nutrient for the function of diverse biological processes and for steroid biosynthesis across metazoans. However, the role of cholesterol in immune function remains understudied. Using the nematode Caenorhabditis elegans, which depends on the external environment for cholesterol, we studied the relationship between cholesterol and innate immunity. We found that the transporter CHUP-1 is required for the effect of cholesterol in the development of innate immunity and that the cholesterol-mediated immune response requires the nuclear hormone receptor NHR-8. Cholesterol acts through NHR-8 to transcriptionally regulate immune genes that are controlled by conserved immune pathways, including a p38/PMK-1 MAPK pathway, a DAF-2/DAF-16 insulin pathway, and an Nrf/SKN-1 pathway. Our results indicate that cholesterol plays a key role in the activation of conserved microbicidal pathways that are essential for survival against bacterial infections.

Effect of soil microbial feeding on gut microbiome and cadmium toxicity in Caenorhabditis elegans

Microbial community of an organism plays an important role on its fitness, including stress responses. In this study, we investigated the effect of the culturable subset of soil microbial community (SMB) on the stress response of the soil nematode Caenorhabditis elegans, upon exposure to one of the major soil contaminants, cadmium (Cd). Life history traits and the stress responses to Cd exposure were compared between SMB- and Escherichia coli strain OP50-fed worms. SMB-fed worms showed higher reproduction rates and longer lifespans. Also, the SMB-fed worms showed more tolerant response to Cd exposure. Gene expression profiling suggested that the chemical stress and immune response of worms were boosted upon SMB feeding. Finally, we investigated C. elegans gut microbial communities in the presence and absence of Cd in OP50- and SMB-fed C. elegans. In the OP50-fed worms, changes in microbial community by Cd exposure was severe, whereas in the SMB-fed worms, it was comparatively weak. Our results suggest that the SMB affects the response of C. elegans to Cd exposure and highlight the importance of the gut microbiome in host stress response.

Bacteria affect Caenorhabditis elegans responses to MeHg toxicity

The organic form of mercurial complex, methylmercury (MeHg), is a neurotoxin that bioaccumulates in the food web. Studies in model organisms, such as Caenorhabditis elegans (C. elegans), provide powerful insights on the role of genetic factors in MeHg-induced toxicity. C. elegans is a free living worm that is commonly cultured in nematode growth medium (NGM) agar plates seeded with bacteria. The bacteria have broad impact on C. elegans biology, including development, reproduction and lifespan, as well as metabolism of experimental chemicals. We hypothesized that MeHg toxicity in C. elegans could be modified by the bacterial food. Using a C. elegans wild-type (WT) strain and transgenic reporter strains, we found that bacterial food reduced the chronic toxicity of MeHg in C. elegans in a dose- and live-status-dependent manner. The MeHg-induced death rate in C. elegans was highest in fasted worms, followed by dehydrated dead bacteria, dead bacteria and live bacteria fed worms. Among the different bacterial foods, dehydrated dead bacteria fed worms were most sensitive to the toxicity of MeHg. The distinct bacteria food (dehydrated dead bacteria food) attenuated oxidative stress and development delay in C. elegans exposed to MeHg. The FOXO transcriptional factor DAF16 was not changed by MeHg but modified by the distinct bacteria food. Independent of MeHg treatment, daf-16 expression in fed worms migrated from the intestine to muscle. We conclude that, in chronic exposure studies in C. elegans, the effects of bacteria on toxicological outcomes should be considered.

Steroids originating from bacterial bile acid degradation affect Caenorhabditis elegans and indicate potential risks for the fauna of manured soils

Bile acids are steroid compounds from the digestive tracts of vertebrates that enter agricultural environments in unusual high amounts with manure. Bacteria degrading bile acids can readily be isolated from soils and waters including agricultural areas. Under laboratory conditions, these bacteria transiently release steroid compounds as degradation intermediates into the environment. These compounds include androstadienediones (ADDs), which are C₁₉-steroids with potential hormonal effects. Experiments with Caenorhabditis elegans showed that ADDs derived from bacterial bile acid degradation had effects on its tactile response, reproduction rate, and developmental speed. Additional experiments with a deletion mutant as well as transcriptomic analyses indicated that these effects might be conveyed by the putative testosterone receptor NHR-69. Soil microcosms showed that the natural microflora of agricultural soil is readily induced for bile acid degradation accompanied by the transient release of steroid intermediates. Establishment of a model system with a Pseudomonas strain and C. elegans in sand microcosms indicated transient release of ADDs during the course of bile acid degradation and negative effects on the reproduction rate of the nematode. This proof-of-principle study points at bacterial degradation of manure-derived bile acids as a potential and so-far overlooked risk for invertebrates in agricultural soils.

Bacterial diet and weak cadmium stress affect the survivability of Caenorhabditis elegans and its resistance to severe stress

Stress may have negative or positive effects in dependence of its intensity (hormesis). We studied this phenomenon in Caenorhabditis elegans by applying weak or severe abiotic (cadmium, CdCl₂) and/or biotic stress (different bacterial diets) during cultivation/breeding of the worms and determining their developmental speed or survival and performing transcriptome profiling and RT-qPCR analyses to explore the genetic basis of the detected phenotypic differences. To specify weak or severe stress, developmental speed was measured at different cadmium concentrations, and survival assays were carried out on different bacterial species as feed for the worms. These studies showed that 0.1 μmol/L or 10 mmol/L of CdCl₂ were weak or severe abiotic stressors, and that E. coli HT115 or Chitinophaga arvensicola feeding can be considered as weak or severe biotic stress. Extensive phenotypic studies on wild type (WT) and different signaling mutants (e.g., kgb-1Δ and pmk-1Δ) and genetic studies on WT revealed, inter alia, the following results. WT worms bred on E. coli OP50, which is a known cause of high lipid levels in the worms, showed high resistance to severe abiotic stress and elevated gene expression for protein biosynthesis. WT worms bred under weak biotic stress (E. coli HT115 feeding which causes lower lipid levels) showed an elevated resistance to severe biotic stress, elevated gene expression for the innate immune response and signaling but reduced gene expression for protein biosynthesis. WT worms bred under weak biotic and abiotic stress (E. coli HT115 feeding plus 0.1 μmol/L of CdCl₂) showed high resistance to severe biotic stress, elevated expression of DAF-16 target genes (e.g., genes for small heat shock proteins) but further reduced gene expression for protein biosynthesis. WT worms bred under weak biotic but higher abiotic stress (E. coli HT115 feeding plus 10 μmol/L of CdCl₂) showed re-intensified gene expression for the innate immune response, signaling, and protein biosynthesis, which, however, did not caused a higher resistance to severe biotic stress. E. coli OP50 feeding as well as weak abiotic and biotic stress during incubations also improved the age-specific survival probability of adult WT worms. Thus, this study showed that a bacterial diet resulting in higher levels of energy resources in the worms (E. coli OP50 feeding) or weak abiotic and biotic stress promote the resistance to severe abiotic or biotic stress and the age-specific survival probability of WT.

Cadmium-induced serotonergic neuron and reproduction damages conferred lethality in the nematode Caenorhabditis elegans

Cadmium is a ubiquitous environmental toxicant. The use of Caenorhabditis elegans as a model for monitoring cadmium exposure has revealed several conserved signaling pathways. However, little is known about the killing process during lethality assay. In the present study, we investigated the effects serotonergic neuronal and reproductive damages on cadmium exposure in C. elegans. We found that sterile hermaphrodites, males and worms that passed reproduction span presented high cadmium resistance compared to those of young adults. The results demonstrated that reproduction process other than reproduction capacity conferred cadmium sensitivity. Cadmium exposure resulted in high ratio bagging phenotype, which was a severe reproductive deficit with embryos hatched internally that could cause worms to die early. The mechanism of bagging formation was ascribed to cadmium-induced egg laying deficiency that led embryos to retain and hatch in uterus. The addition of serotonin and imipramine promoted egg laying and thereby increased cadmium resistance. The results demonstrated that vulval muscles responsible for egg laying were still functional, while the serotonergic hermaphrodite specific neurons might be dysfunctional under cadmium exposure. Cadmium exposure resulted in shrinkage of serotonergic neuronal body and reduced expressions of tryptophan hydroxylase, the key enzyme for serotonin synthesis. The protection of serotonergic neuron through transient thermal preconditioning improved survival rate. In conclusion, our study demonstrated that damages of serotonergic neurons and reproduction conferred to cadmium-induced lethality.

Cell Signaling of Caenorhabditis elegans in Response to Enterotoxigenic Escherichia coli Infection and Lactobacillus zeae Protection

Enterotoxigenic Escherichia coli (ETEC) infection causes the death of Caenorhabditis elegans, which can be prevented by certain Lactobacillus isolates. The host response of C. elegans to ETEC infection and its regulation by the isolates are, however, largely unclear. This study has revealed that, in agreement with the results of life-span assays, the expression of the genes encoding p38 mitogen-activated protein kinase (MAPK) pathway (nsy-1, sek-1, and pmk-1), insulin/insulin-like growth factor (DAF/IGF) pathway (daf-16), or antimicrobial peptides (lys-7, spp-1, and abf-3) and other defensing molecules (abf-2, clec-85) was upregulated significantly when the wild-type nematode (N2) was subjected to ETEC infection. This upregulation was further enhanced by the pretreatment with Lactobacillus zeae LB1, but not with L. casei CL11. Mutants defective in the cell signaling of C. elegans were either more susceptible (defective in NSY-1, SEK-1, PMK-1, or DAF16) or more resistant (defective in AGE-1, DBL-1, SKN-1, or SOD-3) to ETEC infection compared with the wild-type. Mutants defective in antimicrobial peptides (LYS-7, SPP1, or ABF-3) were also more susceptible. In addition, mutants that are defective in NSY-1, SEK-1, PMK-1, DAF16, ABF-3, LYS-7, or SPP1 showed no response to the protection from L. zeae LB1. The expression of the genes encoding antimicrobial peptides (lys-7, spp-1, and abf-3) and other defensing molecules (abf-2, clec-60, and clec-85) were almost all upregulated in AGE-1- or DBL-1-defective mutant compared with the wild-type, which was further enhanced by the pretreatment of L. zeae LB1. The expression of these genes was, however, mostly downregulated in NSY-1- or DAF-16-defective mutant. These results suggest that L. zeae LB1 regulates C. elegans signaling through the p38 MAPK and DAF/IGF pathways to control the production of antimicrobial peptides and defensing molecules to combat ETEC infection.

Nickel toxicity in P. lividus embryos: Dose dependent effects and gene expression analysis

Many industrial activities release Nickel (Ni) in the environment with harmful effects for terrestrial and marine organisms. Despite many studies on the mechanisms of Ni toxicity are available, the understanding about its toxic effects on marine organisms is more limited. We used Paracentrotus lividus as a model to analyze the effects on the stress pathways in embryos continuously exposed to different Ni doses, ranging from 0.03 to 0.5 mM. We deeply examined the altered embryonic morphologies at 24 and 48 h after Ni exposure. Some different phenotypes have been classified, showing alterations at the expenses of the dorso-ventral axis as well as the skeleton and/or the pigment cells. At the lowest dose used, Ni mainly induced a multi-spicule phenotype observed at 24 h after treatment. On the contrary, at the highest dose of Ni (0.5 mM), 90% of embryos showed no skeleton and no pigment cells. Therefore, we focused on this dose to study protein and gene expression patterns at 24 and 48 h after exposure. Among the proteins analyzed, i.e. p38MAPK, Grp78 and Mn-SOD, only p38MAPK was induced by Ni treatment. Moreover, we analyzed the mRNA profiles of a pool of genes that are involved in stress response and in development mechanisms, i.e. the transcription factors Pl-NFkB and Pl-FOXO; a marker of DNA repair, Pl-XPB/ERCC3; a mitogen-activated protein kinase (MAPK), Pl-p38; an ER stress gene, Pl-grp78; an adapter protein, Pl-14-3-3ε; two markers of pigment cells, Pl-PKS1 and Pl-gcm. The spatial expression of mesenchymal marker genes has been evaluated in Ni-treated embryos at both 24 and 48 h after exposure. Our results indicated that Ni acts at several levels in P. lividus sea urchin, by affecting embryo development, influencing the embryonic immune response and activating stress response pathways to counteract the suffered injury and to promote embryos surviving.