Regulation of RNA Polymerase I Transcription in Development, Disease, and Aging.

Ribosome biogenesis is a complex and highly energy-demanding process that requires the concerted action of all three nuclear RNA polymerases (Pol I-III) in eukaryotes. The three largest ribosomal RNAs (rRNAs) originate from a precursor transcript (pre-rRNA) that is encoded by multicopy genes located in the nucleolus. Transcription of these rRNA genes (rDNA) by Pol I is the key regulation step in ribosome production and is tightly controlled by an intricate network of signaling pathways and epigenetic mechanisms. In this article, we give an overview of the composition of the basal Pol I machinery and rDNA chromatin. We discuss rRNA gene regulation in response to environmental signals and developmental cues and focus on perturbations occurring in diseases linked to either excessive or limited rRNA levels. Finally, we discuss the emerging view that rDNA integrity and activity may be involved in the aging process.

Reducing the metabolic burden of rRNA synthesis promotes healthy longevity in Caenorhabditis elegans.

Ribosome biogenesis is initiated by RNA polymerase I (Pol I)-mediated synthesis of pre-ribosomal RNA (pre-rRNA). Pol I activity was previously linked to longevity, but the underlying mechanisms were not studied beyond effects on nucleolar structure and protein translation. Here we use multi-omics and functional tests to show that curtailment of Pol I activity remodels the lipidome and preserves mitochondrial function to promote longevity in Caenorhabditis elegans. Reduced pre-rRNA synthesis improves energy homeostasis and metabolic plasticity also in human primary cells. Conversely, the enhancement of pre-rRNA synthesis boosts growth and neuromuscular performance of young nematodes at the cost of accelerated metabolic decline, mitochondrial stress and premature aging. Moreover, restriction of Pol I activity extends lifespan more potently than direct repression of protein synthesis, and confers geroprotection even when initiated late in life, showcasing this intervention as an effective longevity and metabolic health treatment not limited by aging.

Mitigating age-related somatic mutation burden.

Genomes are inherently unstable and require constant DNA repair to maintain their genetic information. However, selective pressure has optimized repair mechanisms in somatic cells only to allow transmitting genetic information to the next generation, not to maximize sequence integrity long beyond the reproductive age. Recent studies have confirmed that somatic mutations, due to errors during genome repair and replication, accumulate in tissues and organs of humans and model organisms. Here, we describe recent advances in the quantitative analysis of somatic mutations in vivo. We also review evidence for or against a possible causal role of somatic mutations in aging. Finally, we discuss options to prevent, delay or eliminate de novo, random somatic mutations as a cause of aging.

The circuitry between ribosome biogenesis and translation in stem cell function and ageing.

Ribosome biogenesis takes place mainly in the nucleolus, a nuclear, non-membrane bound organelle forming around the gene arrays encoding ribosomal RNA (rRNA). Nucleolar activity comprises synthesis, processing and maturation of rRNAs, followed by their assembly with ribosomal proteins into pre-ribosomal particles. The final formation of translation-competent ribosomes in the cytoplasm is the prerequisite for protein synthesis, which is the most energy-consuming cellular process. In adult stem cells, ribosome biogenesis and protein synthesis determine the switch between the quiescent and the activated state, but also decide whether activated stem cells self-renew or differentiate. Given this major impact on cellular function, it seems likely that perturbations of the circuitry between nucleolar activity and translation lead to ageing-related stem cell deterioration. This review provides an overview of how ribosome biogenesis and translation govern stem cell function and discusses the resultant implication in stem cell ageing.

The DrugAge database of aging-related drugs.

Aging is a major worldwide medical challenge. Not surprisingly, identifying drugs and compounds that extend lifespan in model organisms is a growing research area. Here, we present DrugAge (http://genomics.senescence.info/drugs/), a curated database of lifespan-extending drugs and compounds. At the time of writing, DrugAge contains 1316 entries featuring 418 different compounds from studies across 27 model organisms, including worms, flies, yeast and mice. Data were manually curated from 324 publications. Using drug-gene interaction data, we also performed a functional enrichment analysis of targets of lifespan-extending drugs. Enriched terms include various functional categories related to glutathione and antioxidant activity, ion transport and metabolic processes. In addition, we found a modest but significant overlap between targets of lifespan-extending drugs and known aging-related genes, suggesting that some but not most aging-related pathways have been targeted pharmacologically in longevity studies. DrugAge is freely available online for the scientific community and will be an important resource for biogerontologists.

A network pharmacology approach reveals new candidate caloric restriction mimetics in C. elegans.

Caloric restriction (CR), a reduction in calorie intake without malnutrition, retards aging in several animal models from worms to mammals. Developing CR mimetics, compounds that reproduce the longevity benefits of CR without its side effects, is of widespread interest. Here, we employed the Connectivity Map to identify drugs with overlapping gene expression profiles with CR. Eleven statistically significant compounds were predicted as CR mimetics using this bioinformatics approach. We then tested rapamycin, allantoin, trichostatin A, LY-294002 and geldanamycin in Caenorhabditis elegans. An increase in lifespan and healthspan was observed for all drugs except geldanamycin when fed to wild-type worms, but no lifespan effects were observed in eat-2 mutant worms, a genetic model of CR, suggesting that life-extending effects may be acting via CR-related mechanisms. We also treated daf-16 worms with rapamycin, allantoin or trichostatin A, and a lifespan extension was observed, suggesting that these drugs act via DAF-16-independent mechanisms, as would be expected from CR mimetics. Supporting this idea, an analysis of predictive targets of the drugs extending lifespan indicates various genes within CR and longevity networks. We also assessed the transcriptional profile of worms treated with either rapamycin or allantoin and found that both drugs use several specific pathways that do not overlap, indicating different modes of action for each compound. The current work validates the capabilities of this bioinformatic drug repositioning method in the context of longevity and reveals new putative CR mimetics that warrant further studies.