Mitochondrial aconitase suppresses immunity by modulating oxaloacetate and the mitochondrial unfolded protein response

Accumulating evidence indicates that mitochondria play crucial roles in immunity. However, the role of the mitochondrial Krebs cycle in immunity remains largely unknown, in particular at the organism level. Here we show that mitochondrial aconitase, ACO-2, a Krebs cycle enzyme that catalyzes the conversion of citrate to isocitrate, inhibits immunity against pathogenic bacteria in C. elegans. We find that the genetic inhibition of aco-2 decreases the level of oxaloacetate. This increases the mitochondrial unfolded protein response, subsequently upregulating the transcription factor ATFS-1, which contributes to enhanced immunity against pathogenic bacteria. We show that the genetic inhibition of mammalian ACO2 increases immunity against pathogenic bacteria by modulating the mitochondrial unfolded protein response and oxaloacetate levels in cultured cells. Because mitochondrial aconitase is highly conserved across phyla, a therapeutic strategy targeting ACO2 may eventually help properly control immunity in humans.

Systematic transcriptome analysis associated with physiological and chronological aging in Caenorhabditis elegans

Aging is associated with changes in a variety of biological processes at the transcriptomic level, including gene expression. Two types of aging occur during a lifetime: chronological and physiological aging. However, dissecting the difference between chronological and physiological ages at the transcriptomic level has been a challenge because of its complexity. We analyzed the transcriptomic features associated with physiological and chronological aging using Caenorhabditis elegans as a model. Many structural and functional transcript elements, such as noncoding RNAs and intron-derived transcripts, were up-regulated with chronological aging. In contrast, mRNAs with many biological functions, including RNA processing, were down-regulated with physiological aging. We also identified an age-dependent increase in the usage of distal 3' splice sites in mRNA transcripts as a biomarker of physiological aging. Our study provides crucial information for dissecting chronological and physiological aging at the transcriptomic level.

Age-dependent upregulation of Y RNAs in Caenorhabditis elegans

Y RNA is a conserved small non-coding RNA whose functions in aging remain unknown. Here, we sought to determine the role of C. elegans Y RNA homologs, CeY RNA (CeY) and stem-bulge RNAs (sbRNAs), in aging. We found that the levels of CeY and sbRNAs generally increased during aging. We showed that CeY was downregulated by oxidative and thermal stresses, whereas several sbRNAs were upregulated by oxidative stress. We did not observe lifespan phenotypes by mutations in CeY-coding yrn-1. Future research under various genetic and environmental conditions is required to further evaluate the role of Y RNA in C. elegans aging.

A PTEN variant uncouples longevity from impaired fitness in Caenorhabditis elegans with reduced insulin/IGF-1 signaling

Insulin/IGF-1 signaling (IIS) regulates various physiological aspects in numerous species. In Caenorhabditis elegans, mutations in the daf-2/insulin/IGF-1 receptor dramatically increase lifespan and immunity, but generally impair motility, growth, and reproduction. Whether these pleiotropic effects can be dissociated at a specific step in insulin/IGF-1 signaling pathway remains unknown. Through performing a mutagenesis screen, we identified a missense mutation daf-18(yh1) that alters a cysteine to tyrosine in DAF-18/PTEN phosphatase, which maintained the long lifespan and enhanced immunity, while improving the reduced motility in adult daf-2 mutants. We showed that the daf-18(yh1) mutation decreased the lipid phosphatase activity of DAF-18/PTEN, while retaining a partial protein tyrosine phosphatase activity. We found that daf-18(yh1) maintained the partial activity of DAF-16/FOXO but restricted the detrimental upregulation of SKN-1/NRF2, contributing to beneficial physiological traits in daf-2 mutants. Our work provides important insights into how one evolutionarily conserved component, PTEN, can coordinate animal health and longevity.

Reduced insulin/IGF1 signaling prevents immune aging via ZIP-10/bZIP-mediated feedforward loop

A hallmark of aging is immunosenescence, a decline in immune functions, which appeared to be inevitable in living organisms, including Caenorhabditis elegans. Here, we show that genetic inhibition of the DAF-2/insulin/IGF-1 receptor drastically enhances immunocompetence in old age in C. elegans. We demonstrate that longevity-promoting DAF-16/FOXO and heat-shock transcription factor 1 (HSF-1) increase immunocompetence in old daf-2(−) animals. In contrast, p38 mitogen-activated protein kinase 1 (PMK-1), a key determinant of immunity, is only partially required for this rejuvenated immunity. The up-regulation of DAF-16/FOXO and HSF-1 decreases the expression of the zip-10/bZIP transcription factor, which in turn down-regulates INS-7, an agonistic insulin-like peptide, resulting in further reduction of insulin/IGF-1 signaling (IIS). Thus, reduced IIS prevents immune aging via the up-regulation of anti-aging transcription factors that modulate an endocrine insulin-like peptide through a feedforward mechanism. Because many functions of IIS are conserved across phyla, our study may lead to the development of strategies against immune aging in humans.

VRK-1 extends life span by activation of AMPK via phosphorylation

Vaccinia virus-related kinase (VRK) is an evolutionarily conserved nuclear protein kinase. VRK-1, the single Caenorhabditis elegans VRK ortholog, functions in cell division and germline proliferation. However, the role of VRK-1 in postmitotic cells and adult life span remains unknown. Here, we show that VRK-1 increases organismal longevity by activating the cellular energy sensor, AMP-activated protein kinase (AMPK), via direct phosphorylation. We found that overexpression of vrk-1 in the soma of adult C. elegans increased life span and, conversely, inhibition of vrk-1 decreased life span. In addition, vrk-1 was required for longevity conferred by mutations that inhibit C. elegans mitochondrial respiration, which requires AMPK. VRK-1 directly phosphorylated and up-regulated AMPK in both C. elegans and cultured human cells. Thus, our data show that the somatic nuclear kinase, VRK-1, promotes longevity through AMPK activation, and this function appears to be conserved between C. elegans and humans.

Inhibition of the oligosaccharyl transferase in Caenorhabditis elegans that compromises ER proteostasis suppresses p38-dependent protection against pathogenic bacteria

The oligosaccharyl transferase (OST) protein complex mediates the N-linked glycosylation of substrate proteins in the endoplasmic reticulum (ER), which regulates stability, activity, and localization of its substrates. Although many OST substrate proteins have been identified, the physiological role of the OST complex remains incompletely understood. Here we show that the OST complex in C. elegans is crucial for ER protein homeostasis and defense against infection with pathogenic bacteria Pseudomonas aeruginosa (PA14), via immune-regulatory PMK-1/p38 MAP kinase. We found that genetic inhibition of the OST complex impaired protein processing in the ER, which in turn up-regulated ER unfolded protein response (UPR^ER). We identified vitellogenin VIT-6 as an OST-dependent glycosylated protein, critical for maintaining survival on PA14. We also showed that the OST complex was required for up-regulation of PMK-1 signaling upon infection with PA14. Our study demonstrates that an evolutionarily conserved OST complex, crucial for ER homeostasis, regulates host defense mechanisms against pathogenic bacteria.

N-linked glycosylation is essential for the function of various proteins, but its effects on physiology at an organism level remain poorly understood. Using the roundworm Caenorhabditis elegans, we show that the oligosaccharyl transferase (OST) complex, which mediates the N-glycosylation of substrate proteins in the ER, reduces susceptibility to pathogenic bacteria, Pseudomonas aeruginosa. We find that OST enhances defense against P. aeruginosa via maintenance of ER unfolded protein response (UPR^ER) and up-regulation of cytosolic p38 MAP kinase signaling. Our findings propose an intriguing model for the organellar crosstalk between the ER and the cytosol in host defense mechanisms. Because the OST complex components are highly conserved among eukaryotes, our study on the regulation of cellular signaling and C. elegans physiology by the OST complex will provide an insight into the function of its mammalian counterpart.

RNAi targeting Caenorhabditis elegans α-arrestins has little effect on lifespan

Background: α-arrestins are a family of proteins that are implicated in multiple biological processes, including metabolism and receptor desensitization.

Methods: Here, we sought to examine the roles of α-arrestins in the longevity of Caenorhabditis elegans through an RNA interference screen.

Results: We found that feeding worms with bacteria expressing double-stranded RNA against each of 24 out of total 29 C. elegans α-arrestins had little effect on lifespan. Thus, individual C. elegans α-arrestins may have minor effects on longevity.

Conclusions: This study will provide useful information for future research on the functional role of α-arrestins in aging and longevity.

Survival assays using Caenorhabditis elegans

Caenorhabditis elegans is an important model organism with many useful features, including rapid development and aging, easy cultivation, and genetic tractability. Survival assays using C. elegans are powerful methods for studying physiological processes. In this review, we describe diverse types of C. elegans survival assays and discuss the aims, uses, and advantages of specific assays. C. elegans survival assays have played key roles in identifying novel genetic factors that regulate many aspects of animal physiology, such as aging and lifespan, stress response, and immunity against pathogens. Because many genetic factors discovered using C. elegans are evolutionarily conserved, survival assays can provide insights into mechanisms underlying physiological processes in mammals, including humans.