Multi-Omics and Genome-Scale Modeling Reveal a Metabolic Shift During C. elegans Aging.

In this contribution, we describe a multi-omics systems biology study of the metabolic changes that occur during aging in Caenorhabditis elegans. Sampling several time points from young adulthood until early old age, our study covers the full duration of aging and include transcriptomics, and targeted MS-based metabolomics. In order to focus on the metabolic changes due to age we used two strains that are metabolically close to wild-type, yet are conditionally non-reproductive. Using these data in combination with a whole-genome model of the metabolism of C. elegans and mathematical modeling, we predicted metabolic fluxes during early aging. We find that standard Flux Balance Analysis does not accurately predict in vivo measured fluxes nor age-related changes associated with the Citric Acid cycle. We present a novel Flux Balance Analysis method where we combined biomass production and targeted metabolomics information to generate an objective function that is more suitable for aging studies. We validated this approach with a detailed case study of the age-associated changes in the Citric Acid cycle. Our approach provides a comprehensive time-resolved multi-omics and modeling resource for studying the metabolic changes during normal aging in C. elegans.

Folate Acts in E. coli to Accelerate C. elegans Aging Independently of Bacterial Biosynthesis.

Folates are cofactors for biosynthetic enzymes in all eukaryotic and prokaryotic cells. Animals cannot synthesize folate and must acquire it from their diet or microbiota. Previously, we showed that inhibiting E. coli folate synthesis increases C. elegans lifespan. Here, we show that restriction or supplementation of C. elegans folate does not influence lifespan. Thus, folate is required in E. coli to shorten worm lifespan. Bacterial proliferation in the intestine has been proposed as a mechanism for the life-shortening influence of E. coli. However, we found no correlation between C. elegans survival and bacterial growth in a screen of 1,000+ E. coli deletion mutants. Nine mutants increased worm lifespan robustly, suggesting specific gene regulation is required for the life-shortening activity of E. coli. Disrupting the biosynthetic folate cycle did not increase lifespan. Thus, folate acts through a growth-independent route in E. coli to accelerate animal aging.

Excessive folate synthesis limits lifespan in the C. elegans: E. coli aging model.

BACKGROUND: Gut microbes influence animal health and thus, are potential targets for interventions that slow aging. Live E. coli provides the nematode worm Caenorhabditis elegans with vital micronutrients, such as folates that cannot be synthesized by animals. However, the microbe also limits C. elegans lifespan. Understanding these interactions may shed light on how intestinal microbes influence mammalian aging. RESULTS: Serendipitously, we isolated an E. coli mutant that slows C. elegans aging. We identified the disrupted gene to be aroD, which is required to synthesize aromatic compounds in the microbe. Adding back aromatic compounds to the media revealed that the increased C. elegans lifespan was caused by decreased availability of para-aminobenzoic acid, a precursor to folate. Consistent with this result, inhibition of folate synthesis by sulfamethoxazole, a sulfonamide, led to a dose-dependent increase in C. elegans lifespan. As expected, these treatments caused a decrease in bacterial and worm folate levels, as measured by mass spectrometry of intact folates. The folate cycle is essential for cellular biosynthesis. However, bacterial proliferation and C. elegans growth and reproduction were unaffected under the conditions that increased lifespan. CONCLUSIONS: In this animal:microbe system, folates are in excess of that required for biosynthesis. This study suggests that microbial folate synthesis is a pharmacologically accessible target to slow animal aging without detrimental effects.

Frequent hemodialysis schedules are associated with reduced levels of dialysis-induced cardiac injury (myocardial stunning).

BACKGROUND AND OBJECTIVES: Recurrent hemodialysis (HD)-induced ischemic cardiac injury (myocardial stunning) is common and associated with high ultrafiltration (UF) requirements, intradialytic hypotension, long-term loss of systolic function, increased likelihood of cardiovascular events, and death. More frequent HD regimens are associated with lower UF requirements and improved hemodynamic tolerability, improved cardiovascular outcomes, and reduced mortality compared with conventional thrice-weekly HD. This study investigated the hypothesis that modification of UF volume and rate with more frequent HD therapies would abrogate dialysis-induced myocardial stunning. DESIGN, SETTINGS, PARTICIPANTS, & MEASUREMENTS: A cross-sectional study of 46 patients established on hemodialysis >3 months compared four groups receiving the current range of quotidian therapies: conventional thrice-weekly HD (CHD3); more-frequent HD five to six times/week in a center (CSD) and at home (HSD); and home nocturnal HD (HN). Serial echocardiography quantitatively assessed regional systolic function to identify intradialytic left ventricular regional wall motion abnormalities (RWMAs). Cardiac troponin T (cTnT), N-terminal prohormone brain natriuretic peptide (NT-proBNP), and inflammatory markers were quantified. RESULTS: More frequent HD regimens were associated with lower UF volumes and rates compared with CHD3. Intradialytic fall in systolic BP was reduced in CSD and HSD groups and abolished in HN group. Mean RWMAs per patient reduced with increasing dialysis intensity (CHD3 > CSD > HSD > HN). Home-based groups demonstrated lower high-sensitivity C-reative protein levels, with trends to lower cTnT and NT-proBNP levels in the more frequent groups. CONCLUSIONS: Frequent HD regimes are associated with less dialysis-induced myocardial stunning compared with conventional HD. This may contribute to improved outcomes associated with frequent HD therapies.