Caenorhabditis elegans is an exceptionally valuable model for aging research because of many advantages, including its genetic tractability, short lifespan, and clear age‐dependent physiological changes. Aged C. elegans display a decline in their anatomical and functional features, including tissue integrity, motility, learning and memory, and immunity. Caenorhabditis elegans also exhibit many age‐associated changes in the expression of microRNAs and stress‐responsive genes and in RNA and protein quality control systems. Many of these age‐associated changes provide information on the health of the animals and serve as valuable biomarkers for aging research. Here, we review the age‐dependent changes in C. elegans and their utility as aging biomarkers indicative of the physiological status of aging.

Excessive glucose causes various diseases and decreases lifespan by altering metabolic processes, but underlying mechanisms remain incompletely understood. Here, we show that Lipin 1/LPIN‐1, a phosphatidic acid phosphatase and a putative transcriptional coregulator, prevents life‐shortening effects of dietary glucose on Caenorhabditis elegans. We found that depletion of lpin‐1 decreased overall lipid levels, despite increasing the expression of genes that promote fat synthesis and desaturation, and downregulation of lipolysis. We then showed that knockdown of lpin‐1 altered the composition of various fatty acids in the opposite direction of dietary glucose. In particular, the levels of two ω‐6 polyunsaturated fatty acids (PUFAs), linoleic acid and arachidonic acid, were increased by knockdown of lpin‐1 but decreased by glucose feeding. Importantly, these ω‐6 PUFAs attenuated the short lifespan of glucose‐fed lpin‐1‐inhibited animals. Thus, the production of ω‐6 PUFAs is crucial for protecting animals from living very short under glucose‐rich conditions.

Mitochondria are crucial organelles that generate cellular energy and metabolites. Recent studies indicate that mitochondria also regulate immunity. In this review, we discuss key roles of mitochondria in immunity against pathogen infection and underlying mechanisms, focusing on discoveries using Caenorhabditis elegans. Various mitochondrial processes, including mitochondrial surveillance mechanisms, mitochondrial unfolded protein response (UPRmt), mitophagy, and reactive oxygen species (ROS) production, contribute to immune responses and resistance of C. elegans against pathogens. Biological processes of C. elegans are usually conserved across phyla. Thus, understanding the mechanisms of mitochondria-mediated defense responses in C. elegans may provide insights into similar mechanisms in complex organisms, including mammals.

MON-2, which mediates Golgi-endosome trafficking, mediates mitochondrial inhibition–induced longevity by enhancing autophagy.

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Nonsense-mediated mRNA decay (NMD) is a biological surveillance mechanism that eliminates mRNA transcripts with premature termination codons. In Caenorhabditis elegans, NMD contributes to longevity by enhancing RNA quality. Here, we aimed at identifying NMD-modulating factors that are crucial for longevity in C. elegans by performing genetic screens. We showed that knocking down each of algn-2/asparagine-linked glycosylation protein, zip-1/bZIP transcription factor, and C44B11.1/FAS apoptotic inhibitory molecule increased the transcript levels of NMD targets. Among these, algn-2 exhibited an age-dependent decrease in its expression and was required for maintaining normal lifespan and for longevity caused by various genetic interventions. We further demonstrated that upregulation of ALGN-2 by inhibition of daf-2/insulin/IGF-1 receptor contributed to longevity in an NMD-dependent manner. Thus, algn-2, a positive regulator of NMD, plays a crucial role in longevity in C. elegans, likely by enhancing RNA surveillance. Our study will help understand how NMD-mediated mRNA quality control extends animal lifespan. INTRODUCTIONEukaryotic cells are equipped with mechanisms that maintain proper gene expression and prevent the production of deleterious proteins. Nonsense-mediated mRNA decay (NMD) is an mRNA quality control mechanism that monitors and degrades abnormal transcripts with premature termination codons (PTCs) (He and Jacobson, 2015;Kim and Maquat, 2019;Kurosaki et al., 2019). NMD targets also include mRNAs with long (>1 kb) 3 0 untranslated regions, upstream open reading frames, or selenocysteine-encoding UGA codons (He and Jacobson, 2015;Kim and Maquat, 2019;Kurosaki et al., 2019). Thus, NMD is crucial for RNA quality surveillance and the maintenance of the correct transcriptome in organisms. Key evolutionarily conserved components of NMD have been identified by using model organisms, including the budding yeast Saccharomyces cerevisiae and the nematode Caenorhabditis elegans. A genetic screen using C. elegans has identified the main NMD components, smg (suppressor with morphological effect on genitalia)-1 through smg-7 (Hodgkin et al., 1989;Mango, 2001). SMG-1 is a phosphatidylinositol 3-kinase-related kinase that phosphorylates SMG-2/UPF1 RNA helicase (Hodgkin et al., 1989;Mango, 2001). This event activates the NMD machinery and leads to the cleavage of target mRNAs via the endonuclease SMG-6 (

PDZ domain‐containing proteins (PDZ proteins) act as scaffolds for protein–protein interactions and are crucial for a variety of signal transduction processes. However, the role of PDZ proteins in organismal lifespan and aging remains poorly understood. Here, we demonstrate that KIN‐4, a PDZ domain‐containing microtubule‐associated serine‐threonine (MAST) protein kinase, is a key longevity factor acting through binding PTEN phosphatase in Caenorhabditis elegans. Through a targeted genetic screen for PDZ proteins, we find that kin‐4 is required for the long lifespan of daf‐2/insulin/IGF‐1 receptor mutants. We then show that neurons are crucial tissues for the longevity‐promoting role of kin‐4. We find that the PDZ domain of KIN‐4 binds PTEN, a key factor for the longevity of daf‐2 mutants. Moreover, the interaction between KIN‐4 and PTEN is essential for the extended lifespan of daf‐2 mutants. As many aspects of lifespan regulation in C. elegans are evolutionarily conserved, MAST family kinases may regulate aging and/or age‐related diseases in mammals through their interaction with PTEN.

Aging is associated with changes in a variety of biological processes at the transcriptomic level, including gene expression. Two types of aging occur during life time: 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 usingCaenorhabditis elegansas 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.