Integration of Stress Signaling in Caenorhabditis elegans Through Cell-Nonautonomous Contributions of the JNK Homolog KGB-1

JNK Signaling Positively Regulates Acute Ethanol Tolerance in C. elegans

Alcohol use disorder (AUD) is a chronic neurobehavioral condition characterized by a cycle of tolerance development, increased consumption, and reinstated craving and seeking behaviors during withdrawal. Understanding the intricate mechanisms of AUD necessitates reliable animal models reflecting its key features. Caenorhabditis elegans (C. elegans), with its conserved nervous system and genetic tractability, has emerged as a valuable model organism to study AUD. Here, we employ an ethanol vapor exposure model in Caenorhabditis elegans, recapitulating AUD features while maintaining high-throughput scalability. We demonstrate that ethanol vapor exposure induces intoxication-like behaviors, acute tolerance, and ethanol preference, akin to mammalian AUD traits. Leveraging this model, we elucidate the conserved role of c-jun N-terminal kinase (JNK) signaling in mediating acute ethanol tolerance. Mutants lacking JNK signaling components exhibit impaired tolerance development, highlighting JNK's positive regulation. Furthermore, we detect ethanol-induced JNK activation in C. elegans. Our findings underscore the utility of C. elegans with ethanol vapor exposure for studying AUD and offer novel insights into the molecular mechanisms underlying acute ethanol tolerance through JNK signaling.

Triphenyl phosphate induced reproductive toxicity through the JNK signaling pathway in Caenorhabditis elegans

Triphenyl phosphate (TPHP) is a widely used aryl organophosphate flame retardant (OPFR) that has attracted attention due to its frequent detection in the environment and living organisms. To date, the reproductive toxicity of TPHP has been investigated in organisms, but its molecular mechanisms are not fully understood. Caenorhabditis elegans (C. elegans) is the ideal animal for the study of reproductive toxicity following environmental pollutants, with short generation times, intact reproductive structures, and hermaphroditic fertilization. This study aimed to explore the reproductive dysfunction and molecular mechanisms induced by TPHP exposure in C. elegans. Specifically, exposure to TPHP resulted in a reduction in the number of eggs laid and developing embryos in utero, an increase in the number of apoptotic gonadal cells, and germ cell cycle arrest. The JNK signaling pathway is a potential pathway inducing reproductive toxicity following TPHP exposure based on transcriptome sequencing (RNA-seq). Moreover, TPHP exposure induced down-regulation of vhp-1 and kgb-2 gene transcription levels, and the knockout of vhp-1 and kgb-2 in the mutant strains exhibited more severe toxicity in apoptotic gonad cells, embryos, and eggs developing in utero, suggesting that vhp-1 and kgb-2 genes play a crucial role in TPHP-induced reproductive toxicity. Our data provide convergent evidence showing that TPHP exposure results in reproductive dysfunction through the JNK signaling pathway and improve our understanding of the ecotoxicity and toxicological mechanisms of aryl-OPFRs.

Neuronal KGB-1 JNK MAPK signaling regulates the dauer developmental decision in response to environmental stress in Caenorhabditis elegans

In response to stressful growth conditions of high population density, food scarcity, and elevated temperature, young larvae of nematode Caenorhabditis elegans can enter a developmentally arrested stage called dauer that is characterized by dramatic anatomic and metabolic remodeling. Genetic analysis of dauer formation of C. elegans has served as an experimental paradigm for the identification and characterization of conserved neuroendocrine signaling pathways. Here, we report the identification and characterization of a conserved c-Jun N-terminal Kinase-like mitogen-activated protein kinase (MAPK) pathway that is required for dauer formation in response to environmental stressors. We observed that loss-of-function mutations in the MLK-1-MEK-1-KGB-1 MAPK pathway suppress dauer entry. A loss-of-function mutation in the VHP-1 MAPK phosphatase, a negative regulator of KGB-1 signaling, results in constitutive dauer formation, which is dependent on the presence of dauer pheromone but independent of diminished food levels or elevated temperatures. Our data suggest that the KGB-1 pathway acts in the sensory neurons, in parallel to established insulin and TGF-β signaling pathways, to transduce the dauer-inducing environmental cues of diminished food levels and elevated temperature.

miR-71 mediates age-dependent opposing contributions of the stress-activated kinase KGB-1 in Caenorhabditis elegans

Studying the evolutionary processes that shaped aging offers a path for understanding the causes of aging. The antagonistic pleiotropy theory for the evolution of aging proposes that the inverse correlation between age and natural selection strength allows positive selection of gene variants with early-life beneficial contributions to fitness despite detrimental late-life consequences. However, mechanistic understanding of how this principle manifests in aging is still lacking. We previously identified antagonistic pleiotropy in the function of the Caenorhabditis elegans JNK homolog KGB-1, which provided stress protection in developing larvae, but sensitized adults to stress and shortened their lifespan. To a large extent, KGB-1's contributions depended on age-dependent and opposing regulation of the stress-protective transcription factor DAF-16, but the underlying mechanisms remained unknown. Here, we describe a role for the microRNA miR-71 in mediating effects of KGB-1 on DAF-16 and downstream phenotypes. Fluorescent imaging along with genetic and survival analyses revealed age-dependent regulation of mir-71 expression by KGB-1-upregulation in larvae, but downregulation in adults-and showed that mir-71 was required both for late-life effects of KGB-1 (infection sensitivity and shortened lifespan), as well as for early life resistance to cadmium. While mir-71 disruption did not compromise development under protein-folding stress (known to depend on KGB-1), disruption of the argonaute gene alg-1, a central component of the microRNA machinery, did. These results suggest that microRNAs play a role in mediating age-dependent antagonistic contributions of KGB-1 to survival, with mir-71 playing a central role and additional microRNAs potentially contributing redundantly.

Stress resets ancestral heritable small RNA responses

Transgenerational inheritance of small RNAs challenges basic concepts of heredity. In Caenorhabditis elegans nematodes, small RNAs are transmitted across generations to establish a transgenerational memory trace of ancestral environments and distinguish self-genes from non-self-elements. Carryover of aberrant heritable small RNA responses was shown to be maladaptive and to lead to sterility. Here, we show that various types of stress (starvation, high temperatures, and high osmolarity) induce resetting of ancestral small RNA responses and a genome-wide reduction in heritable small RNA levels. We found that mutants that are defective in various stress pathways exhibit irregular RNAi inheritance dynamics even in the absence of stress. Moreover, we discovered that resetting of ancestral RNAi responses is specifically orchestrated by factors that function in the p38 MAPK pathway and the transcription factor SKN-1/Nrf2. Stress-dependent termination of small RNA inheritance could protect from run-on of environment-irrelevant heritable gene regulation.