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The efficacy of longevity interventions in Caenorhabditis elegans is determined by the early life activity of RNA splicing factors

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Abstract

Geroscience aims to target the aging process to extend healthspan. However, even isogenic individuals show heterogeneity in natural aging rate and responsiveness to pro-longevity interventions, limiting translational potential. Using RNAseq analysis of young, isogenic, subpopulations of Caenorhabditis elegans selected solely on the basis of the splicing pattern of an in vivo minigene reporter that is predictive of future life expectancy, we find a strong correlation in young animals between predicted life span and alternative splicing of mRNAs related to lipid metabolism. The activity of two RNA splicing factors, Reversed Polarity-1 (REPO-1) and Splicing Factor 1 (SFA-1), early in life is necessary for C. elegans response to specific longevity interventions and leads to context-specific changes to fat content that is mirrored by knockdown of their direct target POD-2/ACC1. Moreover, POD-2/ACC1 is required for the same longevity interventions as REPO-1/SFA-1. In addition, early inhibition of REPO-1 renders animals refractory to late onset suppression of the TORC1 pathway. Together, we propose that splicing factor activity establishes a cellular landscape early in life that enables responsiveness to specific longevity interventions and may explain variance in efficacy between individuals.

Author summary

Efficacy of pro-longevity interventions in Caenorhabditis elegans is determined by the activity of splicing factors early in life.

Citation: Dutta S, Perez Matos MC, Heintz C, Mutlu AS, Piper M, Mistry M, et al. (2025) The efficacy of longevity interventions in Caenorhabditis elegans is determined by the early life activity of RNA splicing factors. PLoS Biol 23(11): e3003504. https://doi.org/10.1371/journal.pbio.3003504

Academic Editor: Alex P. Gould, The Francis Crick Institute, UNITED KINGDOM OF GREAT BRITAIN AND NORTHERN IRELAND

Received: October 25, 2024; Accepted: October 30, 2025; Published: November 21, 2025

Copyright: © 2025 Dutta et al. This is an open access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.

Data Availability: All raw and processed data are all contained in the S1 Data through S7 Data files. Western Blot and other gel images raw data are in S1 Raw Images file. All seq files are available from the GEO repository: GSE292723, GSM8864219, GSM8864220, GSM8864221, GSM8864222, GSM8864223, GSM8864224, GSM8864225, GSM8864226, GSM8864227, GSM8864228, GSM8864229, GSM8864230. Links to data found in S1 Text file.

Funding: WBM was funded for this work by the National Institutes of Health, NIA/NIH R01AG044346 and R01AG051954. This work was also supported by the American Federation for Aging Research/ Glenn Foundation for Medical Research Breakthroughs in Gerontology Award to MCW. MCW was also funded by HHMI. The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript.

Competing interests: The authors have declared that no competing interests exist.

Abbreviations: ACC1, Acetyl CoA Carboxylase 1; DR, dietary restriction; eCLIP, enhanced cross-linking immunoprecipitation; IIS, insulin-like growth factor signalling; LL, long life; MEF, mouse embryonic fibroblast; REPO-1, Reversed Polarity-1; SFA-1, Splicing Factor 1; SL, short life; SRS, stimulated Raman scattering; WT, wild-type

Introduction

Aging is the key risk factor for most noncommunicable chronic diseases. In the last 20 years, the field of geroscience has discovered genetic, metabolic, and pharmacological pro-longevity interventions that delay aging in multiple species and might be used to promote healthspan in the elderly. These interventions include dietary restriction (DR), intermittent fasting, and genetic or pharmacological modulation of key metabolic and stress response pathways [1]. However, the effectiveness of these interventions is highly variable between individuals, sexes, and genotypes [2]. Given the greater heterogeneity in humans compared to laboratory model organisms, such variance currently limits effective translation of geroscience discoveries to usable therapeutics for the elderly. Understanding the biological mechanisms that underpin heterogeneity of treatment response is therefore needed if we are to leverage the discovery of anti-aging regimens to alleviate diseases of aging in people.

Results

Deregulation of pre-mRNA splicing has been implicated in multiple age-related chronic diseases [3], and changes in expression of key splicing regulators and splicing of their targets are associated with longevity in mice and humans [4,5]. Moreover, specific RNA splicing factors have been shown to be causally linked to the effects of pro-longevity interventions in Caenorhabditis elegans [68]. We therefore hypothesized that changes in alternative splicing of specific pre-mRNAs might be coupled to both the rate of biological aging and response to longevity interventions. To test this, we first sought to define early RNA processing events that correlate with subsequent life expectancy. Fluorescent mini gene reporters of a single exon 5 skipping event in ret-1 [9] in C. elegans can be used to sort isogenic animals at day 6 of adulthood into subpopulations with short or long life (LL) expectancies, identifying animals that are naturally aging poorly or well [6]. Animals with prevalent ret-1 exon 5 inclusion (GFP) at day 6 show life span extension compared to isogenic animals with exon 5 skipping (mCherry), defined therefore as having LL expectancy versus short life (SL) expectancy, respectively (Fig 1A1C). We isolated LL or SL subpopulations at day 6 day in sextuplicate (Figs 1C and S1A) and performed 75-bp paired-end RNA-Seq followed by analysis of gene expression and differential isoform usage (S1S3 Tables). This allowed us to define genes in which either expression level or isoform usage differed between LL versus SL animals.

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Fig 1. Early life alternative splicing of mRNAs related to lipid metabolism and known longevity pathway correlate with subsequent life expectancy.

A. Schematic illustrating the fluorescence expression pattern of ret-1 splicing reporter worm. Inclusion/exclusion of exon 5 results in GFP/mCherry expression, respectively. B. Representative images of ad-libitum fed ret-1 reporter worms segregated at Day 6 based on their splicing pattern. C. Survivorship of the worm sub-populations separated at Day 6 (P < 0.0001, 1 of 6 replicates). Worms that age slowly are marked “LL” (Long Life-expectancy) and worms that age rapidly as “SL” (Short Life-expectancy). D. WormCat visualization of categories enriched in down and upregulated genes in LL vs. SL worms. Padj < 0.01 and fold change >1.5 was used as cutoff to mark differentially expressed genes. E. WormCat visualization of categories enriched in genes that exhibit differential isoform usage in LL vs. SL worms. Data underlying the graphs in this figure can be found in S1 Data.

https://doi.org/10.1371/journal.pbio.3003504.g001

First, we used WormCat [10] to identify functional signatures in genes significantly up- or downregulated in the LL expectancy animals (Fig 1D; S3 Table). LL animals have decreased expression of multiple functional categories including genes regulating signaling and the proteosome, while genes required for stress response/detoxification and proteolysis, processes known to be longevity-related, are increased. LL animals also show widespread changes in genes required for lipid metabolism, with subsets of lipid metabolic genes showing increased expression, suggesting differences in their lipid metabolism or composition (S1BS1E Fig). Differential isoform usage between LL and SL animals is enriched for pathways implicated in aging such as signaling, proteolysis, and lipid metabolism further suggesting that splicing of pre-mRNAs specifically linked to these pathways is coupled to life expectancy (Figs 1E and S1F; S4 Table). Notably, differential transcript usage in SL versus LL groups includes genes specific to lipid metabolism, such as cpt-5, cpt-6, acox-3, and lpb-1. Instead of a generalized loss of splicing fidelity in animals that are aging poorly, these data suggest that heterogeneity in expression and splicing of genes in specific functional categories, including lipid metabolism and proteolysis, early in the life of an individual is coupled to life expectancy.

If heterogeneity in RNA splicing of specific functional classes of pre-mRNAs is linked to life expectancy, we reasoned that specific RNA splicing-mediated processes may also underlie variation in response to longevity interventions. Previously, we identified causal roles for the RNA splicing factors SFA-1 and REPO-1 in life span extension by DR and suppression of the target of rapamycin complex 1 (TORC1) in C. elegans [6]. REPO-1 is a component of the SF3A subunit in the U2snRNP of the spliceosome whereas SFA-1/SFA-1 is a branch-point binding protein that interacts with the UAF proteins and recruits U2 snRNP in the 3′ splice site recognition during early spliceosome assembly [11]. The link between DR and RNA splicing appears conserved, as upregulation of spliceosome components including SF3A in the liver is a signature of DR in rhesus monkeys [12]. We sought to define how these RNA splicing factors causally modulate aging, and whether splicing status in an individual might impact its responsiveness to various pro-longevity interventions.

To define whether REPO-1 and SFA-1 activity modulates the efficacy of all longevity interventions or shows specificity, we designed RNAi clones that inhibit REPO-1 or SFA-1 in C. elegans without impacting neighboring gene expression (S2 Fig). Using these specific RNAi clones, we examined the role of REPO-1 and SFA-1 in a series of long-lived C. elegans mutants, targeting distinct longevity pathways. RNAi of REPO-1 and SFA-1 fully suppresses life span extension via the DR mimic eat-2(ad1116) (Fig 2A and 2B), and mutations to multiple components of the TORC1 pathway (raga-1(ok386), rsks-1(ok1255)) (Figs 2C, 2D, and S3A) [6] and electron transport machinery (clk-1(qm30), isp-1(qm150), nuo-6(qm200)) (Figs 2E, 2F and S3BS3D). However, knockdown of REPO-1 or SFA-1 had no effect on life span extension via mutations to multiple components of the insulin/insulin-like growth factor signaling (IIS) pathway (age-1(hx546)/PI3K, daf-2(e1370)/InR) (Figs 2G, 2H, and S3E) [6], despite blocking life span extension by overexpression of the IIS mediator DAF-16/FOXO (S3F and S3G Fig). We confirmed repo-1 RNAi inhibited repo-1 expression equally in both longevity-responsive and nonresponsive mutations (S3H Fig). REPO-1 and SFA-1 activity thus determines responsiveness to specific longevity interventions, rather than modulating global changes that render animals refractory to life span extension by any means.

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Fig 2. REPO-1 and SFA-1 are required for life span extension in DR, TORC1, and ETC mutant longevity but dispensable for IIS longevity.

A, B. Survivorship of wild-type (WT) and eat-2(ad1116) worms −/+ repo-1 RNAi (P = 0.8753) and sfa-1 RNAi (P = 0.5658) (p-values comparing wild-type N2 on RNAi vs. eat-2(ad1116) on RNAi, ≥ 3 replicates). C, D. Survivorship of WT and raga-1(ok386) worms −/+ repo-1 RNAi (P = 0.5407) and sfa-1 RNAi (P = 0.002) (p-values comparing wild-type N2 on RNAi vs. raga-1(ok386) on RNAi, ≥3 replicates). repo-1 and sfa-1 RNAi were administered from hatch. E, F. Survivorship of wild-type (WT) and clk-1(qm30) worms −/+ repo-1 RNAi (P = 0.1838 and sfa-1 RNAi (P = 0.86) (p-values comparing wild-type N2 on RNAi vs. clk-1(qm30) on RNAi, ≥3 replicates). repo-1 and sfa-1 RNAi were administered from hatch. G, H. Survivorship curve of wild-type (WT) and age-1(hx546) worms −/+ repo-1 RNAi (P < 0.0001) and sfa-1 RNAi (P < 0.0001) (p-values comparing wild-type N2 on RNAi vs. age-1(hx546) on RNAi, ≥3 replicates). repo-1 and sfa-1 RNAi were administered from hatch. I. UpSet plot (UpSetR R package) quantifying genes in different longevity mutants that respond differently on repo-1 knockdown compared to wild-type N2 worms. Category of genes shared by SF-dependent mutants are highlighted in yellow. J. WormCat visualization of categories enriched in 620 shared genes that are differentially affected on loss of REPO-1 in splicing factor-dependent pathways compared to wild-type N2 worms. Data underlying the graphs in this figure can be found in S2 Data.

https://doi.org/10.1371/journal.pbio.3003504.g002

We leveraged this longevity intervention specificity to define the mechanisms underpinning the effects of REPO-1 on life span extension. We examined the transcriptional effects of repo-1 RNAi on wild-type (WT) animals and a panel of long-lived mutants that either require REPO-1 and SFA-1 for their effects (splicing factor “SF”-dependent) or are refractory to them (SF-independent). We performed four replicates of 75-bp paired-end RNA-Seq on WT (N2), three SF-dependent mutants, eat-2(ad1116), raga-1(ok386), clk-1(qm30), and one SF-independent mutant, age-1(hx546), with and without repo-1 RNAi (S5 Table). Principal component analysis showed that the transcriptomes of WT, age-1(hx546) and raga-1(ok386) cluster most tightly, suggesting they share more similarity to each other than to eat-2(ad1116) and clk-1(qm30) (S3I Fig). Interestingly, repo-1 RNAi drove significant changes specifically in eat-2(ad1116), raga-1(ok386), and clk-1(qm30) mutants yet had a less pronounced effect on WT and age-1(hx546) worms, closely mirroring the specific longevity effects of repo-1 knockdown (S3I Fig). To identify those changes in gene expression resulting from loss of repo-1 that are specific to each long-lived mutant, we compared the transcriptional effects of repo-1 knockdown on each long-lived mutant to the effects of repo-1 knockdown on WT worms. We identified genes whose expression responded differently to repo-1 RNAi in the long-lived mutants compared to WT (S6 Table). These genes were further categorized and grouped based on the mutant in which they were found (Fig 2I). Interestingly, in contrast to the widespread differences induced by repo-1 RNAi in each of the SF-dependent mutants, only 6 genes responded differently on repo-1 knockdown in the SF-independent mutant age-1(hx546) compared to WT worms (Fig 2Iand S6 Table). Together, these data suggest that REPO-1 has unique functional roles in the physiology of SF-dependent mutants not seen in WT or IIS mutants, further supporting the idea that REPO-1 activity mediates responsiveness to specific longevity interventions.

We sought to identify the unique role of REPO-1 in SF-dependent longevity interventions (Fig 2I yellow). We reasoned that processes by which REPO-1 mediates longevity might be reflected in the 620 genes that are differentially regulated by repo-1 RNAi across all SF-dependent long-lived mutants (S6 Table). We used the WormCat platform [10] to identify signatures in these shared 620 differentially regulated genes. REPO-1 dependent gene categories enriched across all splicing sensitive pathways included RNA processing, suggesting indirect or compensatory changes in the posttranscriptional machinery on loss of REPO-1 specifically in these longevity pathways. Strikingly, metabolism was one of the most significantly enriched REPO-1 dependent terms, with lipid metabolism being one of the most enriched sub-categories (Figs 2J and S4AS4D; S7 Table). These data mirror processes coupled to heterogeneity in life expectancy (Fig 1). In addition, we showed previously that loss of SFA-1 specifically reverses expression of lipid metabolism genes induced by DR [6]. Altogether, these data suggest altered lipid metabolism is associated with the effect of REPO-1 and SFA-1 on the aging process and response to treatment.

Next, we examined directly how lipid levels are impacted by repo-1 and sfa-1 RNAi in WT and long-lived mutants. Stimulated Raman scattering (SRS) microscopy in live animals showed that neither sfa-1 and repo-1 RNAi had any effect on lipid content in the intestine of WT C. elegans, yet significantly increased lipid levels in the SF-dependent mutants eat-2(ad1116) and raga-1(ok386) mutants (Fig 3A and 3B). Lipid levels were not affected by loss of REPO-1 or SFA-1 in the splicing-resistant mutant age-1(hx546). Interestingly, sfa-1 and repo-1 RNAi also had no effect on the lipid content of the splicing-sensitive clk-1(qm30) mutant, which have impaired mitochondrial function (Fig 3B), suggesting the mechanism by which these splicing factors impact lipid levels might be linked to mitochondrial function. To further characterize the effect of repo-1 knockdown on lipid metabolism, we performed lipidomics by LC/MS in the long-lived mutants with and without repo-1 RNAi. (S8 Table). We did not observe major differences in the lipidome between strains or with repo-1 RNAi (S5A Fig) Interestingly, neither WT nor age-1(hx546) had any lipid species that significantly changed upon repo-1 knockdown, while all SF-dependent lines, eat-2(ad1116), raga-1(ok386), and clk-1(qm30) did, suggesting that the repo-1 effect on lipid metabolism may be specific to SF-dependent pathways in which REPO-1 is required for longevity (S5C Fig). We examined total triacylglycerol concentration and, analogous to our SRS microscopy, eat-2(ad1116) and raga-1(ok386) trended toward increased triacylglycerides upon loss of REPO-1, although only raga-1(ok386) changes were significant (p-value 0.02) (S5B Fig). Together, these data suggest that the activity of these splicing factors not only specifically regulates expression and splicing of lipid metabolic genes in SF-dependent interventions but also lipid content itself. However, we did not identify a consensus group of lipid species that changed in all SF-dependent mutants. Thus, we looked for shared regulators of lipid metabolism that might represent a causal link between SFA-1/REPO-1 and longevity.

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Fig 3. Loss of REPO-1 specifically affects lipid metabolism in splicing factor-sensitive longevity pathways.

A. Representative images of SRS microscopy showing fat levels in wild-type N2, eat-2(ad1116), raga-1(ok386), clk-1(qm30), and age-1(hx546) on control, repo-1 and sfa-1 RNAi. Worms were fed on RNAi from hatch and imaged 24 hours post-L4 stage. B. Quantification of SRS signal using ImageJ (pooled data quantifying anterior intestine of n = 20−30 worms, N = 3; ### P£0.001 long-lived mutant vs. wildtype on control EV RNAi; *** P£0.001 control EV vs. repo-1/sfa-1 RNAi; n.s. P > 0.05). C. Schematic of enhanced crosslinking immunoprecipitation (eCLIP) in Mouse Embryonic Fibroblasts (MEFs). Created in BioRender. SHARMA, A. (2025) https://BioRender.com/0v2egpn. D. Venn diagram showing targets of SF1 (mammalian SFA-1 ortholog) and SF3A2 (mammalian REPO-1 ortholog) and their overlap in MEFs. True gene targets identified as peaks in IP over input sample that had a log2 fold enrichment > 2 and −log10(p-value) > 2, N = 2. Plot generated using GeneVenn. E. Quantification of SRS signal using Image J. Animals were fed with pod-2 RNAi at day 1 and imaged at day 4 of adulthood (pooled data quantifying anterior intestine of n = 10−30 Caenorhabditis elegans, N = 3, ***P£0.001 control/empty vector vs. pod-2 RNAi; *P = 0.0256; n.s P > 0.05). F–I. Survivorship curves −/+ pod-2 RNAi of wildtype (WT) and F. eat-2(ad1116) (P = 0.057, 2 replicates); G. raga-1(ok386) (P = 0.1923, 4 replicates); H. clk-1(qm30) (P < 0.0001, 2 replicates), and I. age-1(hx546) (P < 0.0001, 3 replicates). RNAi initiated at Day 1 of adulthood. p-values reflect comparison of wild-type N2 fed with pod-2 RNAi vs. long-lived mutant with pod-2 RNAi. Data underlying the graphs in this figure can be found in S3 Data.

https://doi.org/10.1371/journal.pbio.3003504.g003

To understand the mechanism by which SFA-1 and REPO-1 modulate lipid remodeling and longevity, we identified their direct pre-mRNA targets by enhanced cross-linking immunoprecipitation (eCLIP) [13]. We performed eCLIP in both C. elegans and mouse embryonic fibroblast (MEF) cell lines, speculating that true targets that impact life span would be shared between the two splicing factors and conserved across organisms. MEFs were cross-linked followed by IP with SF1 (mammalian SFA-1) and SF3A2 (mammalian REPO-1) antibodies (Fig 3C). True peaks were defined as those showing enrichment of log2 fold change ≥ 2 and −log10(p-value) ≥ 2 over input (S9 Table). Sequencing identified ~964 and ~841 genes targeted by SF1 and SF3A2 in MEFs, respectively. Four hundred twenty-four genes, representing ~50% of total targets, are shared, suggesting that SF1 and SF3A2 act together to regulate splicing (Fig 3D; S9 Table). eCLIP in C. elegans shows that many targets of REPO-1 and SFA-1 are also shared in worms, including tos-1 (Target of Splicing 1), a known and direct target of SFA-1 [14,15] (S4ES4G Fig; S10 Table). Interestingly, in both MEFs and in C. elegans, we find an enrichment of shared target genes involved in RNA processing and in lipid metabolism. One such target involved in lipid metabolism is Acetyl CoA Carboxylase 1 (ACC1), the rate-limiting enzyme of the fatty acid biosynthetic pathway. ACC1 is a target of both SF1 and SF3A2 in MEFs (S8 Table), and the pre-mRNA for POD-2, the C. elegans orthologue of ACC1, was identified as a shared target of SFA-1 and REPO-1 in C. elegans (S10 Table).

POD-2/ACC1 converts acetyl-CoA to malonyl-CoA, thus catalyzing the first step in the formation of de novo lipids. We therefore reasoned that dysfunctional POD-2/ACC1 might alter lipid stores in SFA-1 and REPO-1-depleted animals, and that this might modulate the aging effects in SF-sensitive pro-longevity mutants. To test this, first, we measured lipid content changes through SRS microscopy on the different longevity mutants upon pod-2 RNAi. pod-2 is the ortholog of human ACACA (acetyl-CoA carboxylase alpha), which catalyzes the rate-limiting step in fatty acid synthesis. We therefore hypothesized that upon POD-2 knockdown, lipid content would be suppressed. However, in contrast, POD-2 knockdown phenocopies REPO-1 knockdown (Fig 3E); with eat-2(ad1116) and raga-1(ok386) animals showing increased lipid content upon POD-2 knockdown, and no effect in WT or age-1(hx546) animals, or in clk-1(qm30), a background that is splicing factor sensitive for its effects on longevity, but shows no changes to lipid content by SRS with knockdown of sfa-1 and repo-1. Next, we inhibited life span extension of SF-dependent and SF-independent mutants with and without RNAi of ACC/POD-2. Again, inhibition of POD-2 mirrors completely the longevity intervention specificity of SFA-1 and REPO-1. pod-2 RNAi from day 1 of adulthood fully suppresses life span extension of SF-sensitive eat-2(ad1116), raga-1(ok386), and clk-1(qm30) (Fig 3F3H) mutants but does not suppress life span in the SF-resistant age-1(hx546) (Fig 3I) mutants. Together, these data reveal a striking similarity in the specificity of both the lipid accumulation phenotypes and the responses to specific longevity interventions resulting from knockdown of SFA-1/REPO-1 and by knockdown of their direct target ACC/POD-2. However, our finding that not all SF-sensitive interventions show parallel changes to lipid content or profile after knockdown of repo-1 or sfa-1 (or pod-2) suggests that the underlying mechanism by which splicing factor activity confers longevity may be more complex than through gross changes to lipid abundance.

Disruption of mitochondrial ETC function and DR/TORC1 inhibition operate in temporally distinct time windows to slow aging in C. elegans. Knockdown of ETC complexes only during the L3–L4 stages of larval development increases longevity, while DR and TORC1 inhibition confer longevity benefits in adulthood [16,17]. To understand how REPO-1 and SFA-1 modulate longevity and lipid metabolism across seemingly mechanistically unrelated longevity interventions, we asked when in life these splicing factors act to modulate life span. We fluorescently tagged endogenous REPO-1 and SFA-1 by CRISPR knock-in of wrmScarlet and GFP, respectively. Both splicing factors are expressed in nuclei of all cells (S6A Fig), throughout all life stages (S6B Fig), and ages of C. elegans (S6CS6E Fig). Neither repo-1 mRNA nor REPO-1 total protein diminish with age during adulthood (S6C and S6D Fig). However, REPO-1 levels peak during early development, hinting that splicing factors such as REPO-1 play an important role in early life stages of C. elegans (Figs 4A and S6F).

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Fig 4. REPO-1 and SFA-1 create a permissive landscape during the early stages of development to mediate longevity benefits later in life.

A. Quantification of bands from western blot of CRISPR-tagged endogenous 3XFLAG::REPO-1 worms at early (L1-L2) and late (L3-L4) larval stages and at Day 1 and Day 15 of adulthood. Blots probed with 3XFLAG and actin antibodies. Quantification done using ImageJ, normalized to intensity of actin band and plotted as percent of expression at Day 1 of adulthood (**** P ≤ 0.0001, *** P ≤ 0.001, ** P ≤ 0.01, * P ≤ 0.05; ns P > 0.05; n = 3). B–G. Survivorship of wild-type (WT) and long-lived mutants B. eat-2(ad1116); D. raga-1(ok386), and F. clk-1(qm30) −/+ repo-1 from hatch (- - -) or Day 1 of adulthood (D1-onset) (…). P = 0.5315, 0.0285, 0.2672 for WT repo-1 RNAi hatch vs. eat-2(da1116), raga-1(ok386) and clk-1(qm30) mutants on repo-1 RNAi hatch respectively). P = <0.0001, <0.0001, <0.0001 for WT repo-1 RNAi D1-onset vs. eat-2(da1116), raga-1(ok386), and clk-1(qm30) mutants on repo-1 RNAi D1-onset, respectively). Survivorship of wild-type (WT) and long-lived mutants C. eat-2(ad1116); E. raga-1(ok386), and G. clk-1(qm30) −/+ sfa-1 from hatch (- - -) or Day 1 of adulthood (D1-onset) (…). P = 0.5658, 0.002, <0.0001 for WT sfa-1 RNAi hatch vs. eat-2(da1116), raga-1(ok386), and clk-1(qm30) mutants on sfa-1 RNAi hatch, respectively). P = <0.0001, <0.0001, <0.0001 for WT sfa-1 RNAi D1-onset vs. eat-2(da1116), raga-1(ok386), and clk-1(qm30) mutants on sfa-1 RNAi D1-onset, respectively). H. Quantification of SRS signal using ImageJ (pooled data quantifying anterior intestine of n = 20−30 worms, N = 3; n.s. P > 0.05 control EV vs. repo-1RNAi). repo-1 RNAi was started on day 1 of adulthood and images were taken on day 4. I. Survivorship curve of wild-type N2 worms −/+ repo-1 RNAi in the larval stages −/+ raga-1 RNAi from Day 1 of adulthood (P = 0.0244 wild-type N2 on repo-1 RNAi (larval) vs. wild-type N2 on repo-1 RNAi (larval)+ raga-1 RNAi (D1-onset), 3 replicates). J. Survivorship curve of wild-type N2 worms −/+ sfa-1 RNAi in the larval stages −/+ raga-1 RNAi from Day 1 of adulthood (P = 0.2480 wild-type N2 on sfa-1 RNAi (larval) vs. wild-type N2 on sfa-1 RNAi (larval)+ raga-1 RNAi (D1-onset), 2 replicates). Data underlying the graphs in this figure can be found in S4 Data.

https://doi.org/10.1371/journal.pbio.3003504.g004

To define the temporal window in which REPO-1 and SFA-1 mediate DR, TORC1, and ETC longevity, we subjected eat-2(ad1116), raga-1(ok386), and clk-1(qm30) animals to repo-1 and sfa-1 RNAi from hatch or Day 1 of adulthood (D1-onset). Despite western analysis confirming equal knockdown efficiency by day 3 of adulthood in both conditions (S6GS6J Fig), their effect on longevity was strikingly different; knockdown of both repo-1 and sfa-1 in development fully suppresses longevity in all SF-sensitive mutants. However, adult-onset inhibition had no impact on aging regardless of the timing requirement of the SF-dependent intervention itself (Fig 4B4G). Adult-onset knockdown of REPO-1 also has no effect on the accumulation of lipids as measured by SRS microscopy (Fig 4H). Together, these data suggest REPO-1 and SFA-1 modulate the cellular landscape early in life and that this permissive landscape may contribute to the efficacy of subsequent longevity interventions. Supporting this concept, adult-onset RNAi of raga-1 is sufficient to prolong life span yet has no effect on animals with prior inhibition of either repo-1 or sfa-1 during development (Fig 4I and 4J).

Discussion

Geroscience approaches over the last 20 years have shown that environmental conditions and genetic manipulation can strongly influence the rate of physiological aging. In particular, DR has a strong beneficial effect in a wide variety of organisms tested to date, not only increasing longevity but also protecting against many chronic diseases. Harnessing the molecular and cellular processes mediating the plasticity of aging in response to DR has the potential to yield novel therapeutics that broadly reduce disease incidence in the elderly. However, while there has been much research into the molecular mechanisms mediating longevity interventions using model organisms, little emphasis has been placed on predicting and understanding variance in their efficacy [2]. This is critical, since the same therapeutic treatment can be beneficial or harmful, depending on the sex, genotype, and physiological state of the individual to which it is applied. For example, dosage levels of pharmacological treatments or DR have very different longevity effects in different genotypes [18,19]. Such genotype by diet interaction may well explain the opposing results of two longitudinal life span studies of DR on rhesus monkeys [20].

Beyond inter-genotype variation to longevity interventions, substantial variation also exists in inter-individual responses. Even within isogenic populations of C. elegans, or inbred Drosophila and mouse strains, high variance exists both for life span itself and response to DR/DR mimetics. Indeed, for interventions such as methionine restriction, though median life span of mice and rats is increased, a sub-population dies earlier than non-restricted controls [21]. A “one size fits all” approach to DR or DR mimetics is therefore unlikely to be useful therapeutically. Successfully translating geroscience to human application requires accurately predicting a given individual’s response to a given treatment, depending on the genotype and physiology of the individual. Such an approach will allow treatments to be assigned to each individual in a personalized way, maximizing health benefits. The first step toward this end is to identify biological variables that predict individual-specific optimal aging interventions in model organisms, to provide the foundation for a personalized medicine approach to healthy aging therapeutics in humans.

Here, we show that in C. elegans, a single RNA exon skipping event can predict the life expectancy of isogenic animals. We leveraged this finding to define functional categories of genes that are differentially expressed or spliced in isogenic animals that long- or short-lived. Animals that naturally age well show gene expression and RNA splicing changes enriched in specific ontology classes, including signaling, proteolysis, and lipid metabolism. We utilized splicing factor-dependent and independent longevity pathways to define RNA splicing-mediated processes coupled to variation in response to anti-aging interventions in C. elegans. Regulation of genes tied to lipid metabolism was a shared process correlated to both WT life expectancy and response to treatment. REPO-1 and SFA-1 activity modulate lipid levels in SF-dependent mutants and bind to POD-2/ACC pod-2 transcripts directly. REPO-1, SFA-1, and POD-2 specifically modulate efficacy of the same pro-longevity mutations and show similar effects on lipid content. Lastly, we show that modulating the activity of REPO-1 and SFA-1 early in life determines whether subsequent application of a pro-longevity intervention, in this case inhibition of RAGA-1, successfully slows aging.

Our data reveal a link between the early life activity of splicing factors and the efficacy of certain longevity interventions, as well as to context-dependent changes in lipid accumulation. Yet, we were not able to identify any common lipid signature or change in lipid abundance that links a specific lipid alteration to longevity. More work is needed to determine if a common change in SF-sensitive mutants can explain the role of pod-2 in life span. Interestingly, POD-2 has also been linked to longevity seen in germlineless glp-1 mutants, which also have lipid phenotypes [22]. This will likely require further work to dissect the tissues and cell types in which splicing factors and POD-2 act to modulate aging, and more nuanced examination of lipid composition changes at defined locations in those cell types.

This work demonstrates that the efficacy of a pro-longevity intervention can be strongly influenced by prior events, in this case the activity of a splicing factor earlier in the life of the individual. If this phenomenon is conserved in mammals, it raises important questions about how we design and implement anti-aging therapeutics. Ultimately, it might be possible to predict response to treatment and optimize the intervention via analysis of a subset of RNA splicing events. Such an approach is key if we are to move beyond biomarkers of physiological age towards biomarkers that facilitate precision medicine approaches to interventional geroscience.

Supporting information

S1 Fig. Early life alternative splicing of RNAs related to lipid metabolism and known longevity pathway correlates with subsequent life expectancy.

A. Survivorship curves and imaging of five of six different biological replicates of LL vs. SL worms that were used for RNA-Seq analysis (Replicate 2 shown in Fig 1). B–E. Validation of gene expression changes in LL vs. SL worms in RNA-Seq. qRT-PCR of metabolic genes B. fat-7; C. acdh-1; D. acdh-2; and E. gst-10 in the SL and LL worm sub-populations at Day 6 (****P ≤ 0.0001, ***P ≤ 0.001, **P ≤ 0.01, *P ≤ 0.05; ns P > 0.05). P-values calculated with unpaired, two-tailed Welch’s t test. qRT-PCR data are mean + s.e.m. of 3 biological replicates. F. WormCat visualization of categories enriched in genes that exhibit differential local splicing events in LL vs. SL worms. Data underlying the graphs in this figure can be found in S5 Data.

https://doi.org/10.1371/journal.pbio.3003504.s001

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S2 Fig. Specificity of RNAi to REPO-1.

A. Schematic representing the position of genes repo-1 and rbm-34 in the Caenorhabditis elegans genome operon CEOP4488 and the target sequences of the old repo-1 RNAi from the Ahringer library (repo-1Ahringer RNAi) and the newly constructed repo-1FL, repo-1short RNAi, and rbm-34FL RNAi. Approximate positions of the qRT-PCR probes are marked. B. repo-1Ahringer RNAi knocks down both repo-1 and rbm-34. qRT-PCR of repo-1 and rbm-34 expression in Day 1 wild-type worms on control and repo-1Ahringer RNAi from hatch. C. qRT-PCR of repo-1 and rbm-34 expression in Day 1 wild-type worms fed with control, repo-1FL, repo-1short and rbm-34FL RNAi from hatch (****P ≤ 0.0001, ***P ≤ 0.001, **P ≤ 0.01, *P ≤ 0.05; ns P > 0.05). P-values calculated with unpaired, two-tailed Welch’s t test. qRT-PCR data are mean + s.e.m. of 3 biological replicates. Increased signal of repo-1 and rbm-34 on treatment with repo-1FL and rbm-34FL RNAi, respectively, is likely due to non-specific signals from the siRNAs produced by bacteria that are ingested by the worms. Note that repo-1short RNAi is able to knockdown repo-1 with equal efficiency as repo-1Ahringer RNAi but has no effect on rbm-34 expression. D–G. Knockdown of repo-1 and not rbm-34 blocks life span extension in a C. elegans model of longevity. Survivorship of wild-type (WT) and isp-1(qm150) worms with or without D. repo-1Ahringer (P = 0.5434), E. repo-1FL (P = 0.1228), F. repo-1short RNAi (P = 0.0006, shorter-lived), and G. rbm-34FL RNAi (P ≤ 0.0001) (P-values are comparing wild-type RNAi vs. isp-1(qm150) RNAi in each case). Data underlying the graphs in this figure can be found in S6 Data.

https://doi.org/10.1371/journal.pbio.3003504.s002

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S3 Fig. The effect of loss of REPO-1 and SFA-1 is conserved across other mutants in the different longevity pathways.

A. Effect of loss of REPO-1 is conserved across other mutants of the TORC1 pathway. Survivorship of wild-type (WT) and rsks-1(ok1255) −/+ repo-1 RNAi (P = 0.0803, wild-type N2 repo-1 RNAi vs. rsks-1(ok1255) repo-1 RNAi, 2 replicates). RNAi was administered from hatch. B–D. Effect of loss of REPO-1 is conserved across other mutants of the ETC pathway. B. Survivorship of wild-type (WT) and isp-1(qm50) on repo-1 RNAi (P < 0.0001, wild-type N2 repo-1 RNAi vs. isp-1(qm50) repo-1 RNAi, 2 replicates). RNAi was administered from hatch. C. Survivorship of WT and nuo-6(qm200) on repo-1 RNAi (P = 0.9116, wild-type N2 repo-1 RNAi vs. nuo-6(qm200) repo-1 RNAi, 2 replicates). RNAi was administered from hatch. D. Survivorship of WT and nuo-6(qm200) on sfa-1 RNAi (P < 0.0001, wild-type N2 sfa-1 RNAi vs. nuo-6(qm200) sfa-1 RNAi, 2 replicates). RNAi was administered from hatch. E. Effect of loss of REPO-1 is conserved across other mutants of the rIIS pathway. Survivorship of wild-type (WT) and daf-2(e1370) −/+ repo-1 RNAi (P < 0.0001, wild-type N2 repo-1 RNAi vs. daf-2(e1370) repo-1 RNAi, 2 replicates). RNAi was administered from hatch. F, G. Survivorship of wild-type (WT) and DAF-16a/b over-expressor worms (daf-16p::DAF16a/b::GFP) −/+ repo-1 RNAi (P = 0.8994) and sfa-1 RNAi (P = 0.8718) (P-values are comparing WT on RNAi vs. mutant on RNAi, 2 replicates). RNAi was administered from hatch. H. REPO-1 is knocked down in different mutants with equal efficiency. qPCR showing ~50% knockdown of repo-1 in different longevity mutants fed with empty vector and repo-1 RNAi from hatch and collected at Day 1 of adulthood (****P ≤ 0.0001, ***P ≤ 0.001, **P ≤ 0.01, *P ≤ 0.05; ns P > 0.05). P-values calculated with unpaired, two-tailed Welch’s t test. qRT–PCR data are mean + s.e.m. of 3 biological replicates. I. Principal Component Analysis of RNA Seq Samples in different longevity mutants −/+ repo-1 RNAi. Data underlying the graphs in this figure can be found in S6 Data.

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S4 Fig. Loss of REPO-1 specifically affects lipid metabolism in splicing factor-sensitive longevity pathways.

A. Expression of fat-3 by qRT-PCR in wild-type and different mutants −/+ repo-1 and sfa-1 RNAi at Day 1. B. Normalized counts of fat-3 transcript in RNA-Seq of wild-type and different mutants −/+ repo-1 RNAi at Day 1. C. Expression of cpt-5 by qRT-PCR in wild-type and different mutants −/+  repo-1 and sfa-1 RNAi at Day 1. D. Normalized counts of cpt-5 transcript in RNA-Seq of wild-type and different mutants −/+ repo-1 RNAi at Day 1. (****P ≤ 0.0001, ***P ≤ 0.001, **P ≤ 0.01, *P ≤ 0.05; ns P > 0.05). P-values calculated with unpaired, two-tailed Welch’s t test. RNA-seq data are mean + s.e.m. of normalized read counts of 4 biological replicates. qRT-PCR data are mean + s.e.m. of 3 biological replicates. E. Schematic representing eCLIP in worms. F. Venn diagram displaying the overlap of RNA targets with enrichment >2-fold (log2 fold change >1, IP vs. Input) in SFA-1 and REPO-1. G. Validation of tos-1 as a target of SFA-1 and REPO-1. Semi-quantitative PCR showing differential isoforms of tos-1 in Day 1 worms on loss of repo-1 and sfa-1 using RNAi. Red arrow marks the appearance of a different isoform of tos-1 on loss of repo-1 and sfa-1. Data underlying the graphs in this figure can be found in S7 Data. The data plotted in panels B and D were taken from values in S5 Table.

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S5 Fig. Loss of REPO-1 specifically changes the lipidome of splicing factor-sensitive pathways.

A. Principal component analysis (PCA) of Median Quantitation of Lipid Species across strains and conditions. Each point represents a biological sample, colored according to experimental condition. The ellipses represent 95% confidence intervals for each group. B. Boxplot of total triacylglycerol (TG) abundance (nmol/mg of protein) in each experimental condition. We performed Wilcoxon test between Control and repo-1 RNAi in each strain. Only raga-1 control vs. raga-1 repo-1 RNAi was significant (fold change = 0.59, p-value = 0.02). C. Volcano plots for each strain comparing control vs. repo-1 RNAi. Groups were compared with t test, followed by Benjamini–Horchberg correction for multiple comparisons. Significant changes were defined as log fold change >1 or < 1 and p-value <0.05. Significant changes are highlighted in red and listed in the table. Data underlying the graphs in this figure can be found in S7 Data.

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S6 Fig. REPO-1 is expressed at elevated levels in early larval stages of worm development and might be crucial for its function in this time window.

A. Fluorescent microscope images of worms with CRISPR tagged REPO-1::GFP and CRISPR tagged SFA-1::wrmScarlet at Day 1. Worms imaged at 20× magnification. White arrows mark the presence of REPO-1 and absence of SFA-1 in early embryos. B. Fluorescent microscope images of CRISPR tagged REPO-1 fused to GFP and CRISPR tagged SFA-1 fused to wrmScarlet from the egg stage to Day 1 of adulthood. C. REPO-1 and SFA-1 mRNA levels do not change with age. Normalized counts of repo-1 and sfa-1 transcripts at Day 3 and Day 15 in WT and eat-2(ad1116) worms. Transcript counts obtained from previously published RNA-Seq data (Heintz and colleagues. Nature 2017 [6]). D, E. REPO-1 protein levels do not change with age. D. Western blotting of CRISPR tagged endogenous 3XFLAG::REPO-1 worms at Day1, Day 5, Day 10, and Day 15 of adulthood. Blots probed with 3XFLAG and actin antibodies. Ponceau staining of the blot shows equal loading. E. Western blotting of CRISPR-tagged endogenous 3XFLAG::REPO-1 worms at L1–L2, L3–L4, Day 1, and Day 15 of adulthood. Blots probed with 3XFLAG and actin antibodies. Ponceau staining of the blot shows equal loading. F. Quantification of 3XFLAG:REPO-1 normalized to actin. Blots quantified using ImageJ and represented as percent of expression at Day 1 of adulthood. G, H. Adult-onset RNAi efficiently knocks down REPO-1 and SFA-1 comparable to RNAi from hatch. Western blotting of CRISPR tagged endogenous G. 3XFLAG::REPO-1 worms −/+ repo-1 RNAi; I. 3XFLAG::SFA-1 worms −/+ sfa-1 RNAi from hatch or Day 1 of adulthood (D1-onset). Samples collected on Day 1, Day 2, and Day 3 to measure efficiency of knockdown. Lysates probed for 3XFLAG as a readout of REPO-1/SFA-1 and actin as loading control. Quantification of knockdown of H. REPO-1 and J. SFA-1 normalized to actin. Blots quantified using ImageJ and represented as percent of RNAi untreated control. (****P ≤ 0.0001, ***P ≤ 0.001, **P ≤ 0.01, *P ≤ 0.05; ns P > 0.05). P-values calculated with unpaired, two-tailed Welch’s t test. Data underlying the graphs in this figure can be found in S7 Data.

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S2 Table. This table contains differentially expressed genes from RNA-Seq of worms with long life expectancy (LL) vs. short life expectancy (SL) and the WormCat functional categories of the genes.

A. all genes from differential expression analysis; B. significant genes only (log fold change > 1.5 and padj < 0.01); C. significant downregulated genes; D. significant upregulated genes; E. WormCat categories of significantly downregulated in LL vs. SL; F. WormCat categories of significantly upregulated in LL vs. SL.

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S6 Table. This table contains analysis of the repo-1 knockdown effect in the eat-2(ad1116), raga-1(ok386), clk-1(qm30), and age-(hx546) mutants.

It contains the full list of genes from the analysis in each mutant and genes that respond significantly differently to repo-1 RNAi using an adjusted p-value cut-off of 0.05. The table also contains a list of the shared 620 genes that respond differentially on loss of repo-1 in eat-2(ad1116), raga-1(ok386), and clk-1(qm30) compared to wild-type N2 worms.

https://doi.org/10.1371/journal.pbio.3003504.s012

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S9 Table. This table contains the eCLIP targets of SF1 and SF3A2 in MEFs.

For both S1 and SF3A2, there are lists for—A. all peaks from Replicate 1; B. significant peaks from Replicate 1 [log2 fold change > 2, −log10(P-value) > 2]; C. all peaks from Replicate 2; D. significant peaks from Replicate 2 [log2 fold change > 2, −log10(P-value) > 2]. This table also contains the reproducible SF1 and SF3A2 gene targets from both the runs and the shared targets.

https://doi.org/10.1371/journal.pbio.3003504.s015

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S10 Table. This table contains the eCLIP targets of SFA-1 and REPO-1 in Caenorhabditis elegans.

A. Significant peaks of SFA-1 [log2 fold change > 1, −log10(P-value) > 1]; B. significant peaks of REPO-1 [log2 fold change > 1, −log10(P-value) > 1]; C. unique and shared targets of SFA-1 and REPO-1.

https://doi.org/10.1371/journal.pbio.3003504.s016

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Acknowledgments

We are thankful to H. Kuroyanagi for sharing the ret-1 splicing reporter strain. We thank Caenorhabditis Genetics Center for providing worm strains. We are also grateful to members of the Mair laboratory for helpful discussions on the project and the manuscript.

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