Search

In C. elegans, the conserved transcription factor DAF-16/FOXO is a powerful aging regulator, relaying dire conditions into expression of stress resistance and longevity promoting genes. For some of these functions, including low insulin/IGF signaling (IIS), DAF-16 depends on the protein SMK-1/SMEK, but how SMK-1 exerts this role has remained unknown. We show that SMK-1 functions as part of a specific Protein Phosphatase 4 complex (PP4SMK-1). Loss of PP4SMK-1 hinders transcriptional initiation at several DAF-16-activated genes, predominantly by impairing RNA polymerase II recruitment to their promoters. Search for the relevant substrate of PP4SMK-1 by phosphoproteomics identified the conserved transcriptional regulator SPT-5/SUPT5H, whose knockdown phenocopies the loss of PP4SMK-1. Phosphoregulation of SPT-5 is known to control transcriptional events such as elongation and termination. Here we also show that transcription initiating events are influenced by the phosphorylation status of SPT-5, particularly at DAF-16 target genes where transcriptional initiation appears rate limiting, rendering PP4SMK-1 crucial for many of DAF-16’s physiological roles., The transcription factor DAF-16/FOXO mediates a wide variety of aging-preventive responses by driving the expression of stress resistance and longevity promoting genes. Here the authors show that transcriptional initiation at many DAF-16/FOXO target genes requires the dephosphorylation of SPT-5 by Protein Phosphatase 4.

Aging is a complex phenomenon, where damage accumulation, increasing deregulation of biological pathways, and loss of cellular homeostasis lead to the decline of organismal functions over time. Interestingly, aging is not entirely a stochastic process and progressing at a constant rate, but it is subject to extensive regulation, in the hands of an elaborate and highly interconnected signaling network. This network can integrate a variety of aging-regulatory stimuli, i.e. fertility, nutrient availability, or diverse stresses, and relay them via signaling cascades into gene regulatory events - mostly of genes that confer stress resistance and thus help protect from damage accumulation and homeostasis loss. Transcription factors have long been perceived as the pivotal nodes in this network. Yet, it is well known that the epigenome substantially influences eukaryotic gene regulation, too. A growing body of work has recently underscored the importance of the epigenome also during aging, where it not only undergoes drastic age-dependent changes but also actively influences the aging process. In this review, we introduce the major signaling pathways that regulate age-related decline and discuss the synergy between transcriptional regulation and the epigenetic landscape.

SummaryAging is a major risk factor for human morbidity and mortality. Thus, the identification of compounds that defer aging, also known as ‘geroprotectors’, could greatly improve our health and promote a longer life. Here we screened for geroprotectors, employing the power of human transcriptomics to predict biological age. We used age-stratified human tissue transcriptomes to generate machine-learning-based classifiers capable of distinguishing transcriptomes from young versus old individuals. Then we applied these classifiers to transcriptomes induced by 1300 different compounds in human cell lines and ranked these compounds by their ability to induce a ‘youthful’ transcriptional state. Besides known geroprotectors, several new candidate compounds emerged from this ranking. Testing these in the model organismC. elegans, we identified two Hsp90 inhibitors, Monorden and Tanespimycin, which substantially extended the animals’ lifespan and improved their health. Hsp90 inhibition specifically induces the expression of heat shock proteins, known to improve protein homeostasis. Consistently, Monorden treatment improved the survival ofC. elegansunder proteotoxic stress, and its lifespan benefits were fully dependent on the master regulator of the cytosolic unfolded protein response, the transcription factor HSF-1. Taken together, we present an innovative transcriptomics-based screening approach to discover aging-preventive compounds and highlight Hsp90 inhibitors as powerful geroprotectors that could be of great value, to target the aging process in humans.

Aging strongly influences human morbidity and mortality. Thus, aging-preventive compounds could greatly improve our health and lifespan. Here we screened for such compounds, known as geroprotectors, employing the power of transcriptomics to predict biological age. Using age-stratified human tissue transcriptomes and machine learning, we generated age classifiers and applied these to transcriptomic changes induced by 1,309 different compounds in human cells, ranking these compounds by their ability to induce a "youthful" transcriptional state. Testing the top candidates in C. elegans, we identified two Hsp90 inhibitors, monorden and tanespimycin, which extended the animals' lifespan and improved their health. Hsp90 inhibition induces expression of heat shock proteins known to improve protein homeostasis. Consistently, monorden treatment improved the survival of C. elegans under proteotoxic stress, and its benefits depended on the cytosolic unfolded protein response-inducing transcription factor HSF-1. Taken together, our method represents an innovative geroprotector screening approach and was able to identify a class that acts by improving protein homeostasis. N.S. was supported by funding from the Spanish Ministry of Economy, Industry and Competitiveness (MEIC) to the EMBL partnership, the Centro de Excelencia Severo Ochoa, the CERCA Programme/Generalitat de Catalunya, and an award from the Glenn Foundation for Medical Research. E.A.A.N. was supported by the European Research Council (ERC) and the alumni chapter of Gooische Groningers facilitated by Ubbo Emmius Fonds. C.G.R. was supported by the Swedish Research Council (VR) grant 2015-03740, the COST grant BM1408 (GENiE), and an ICMC project grant

The ability to perceive and respond to harmful conditions is crucial for the survival of any organism. The transcription factor DAF-16/FOXO is central to these responses, relaying distress signals into the expression of stress resistance and longevity promoting genes. However, its sufficiency in fulfilling this complex task has remained unclear. Using C. elegans, we show that DAF-16 does not function alone but as part of a transcriptional regulatory module, together with the transcription factor HLH-30/TFEB. Under harmful conditions, both transcription factors translocate into the nucleus, where they often form a complex, co-occupy target promoters, and co-regulate many target genes. Interestingly though, their synergy is stimulus-dependent: They rely on each other, functioning in the same pathway, to promote longevity or resistance to oxidative stress, but they elicit heat stress responses independently, and they even oppose each other during dauer formation. We propose that this module of DAF-16 and HLH-30 acts by combinatorial gene regulation to relay distress signals into the expression of specific target gene sets, ensuring optimal survival under each given threat., The transcription factor DAF-16/FOXO is a downstream effector of insulin/insulin-like growth factor signaling and plays an important role in stress resistance and longevity. Here, the authors show that DAF-16/FOXO can form a complex with HLH-30/TFEB to synergistically regulate transcription of target genes in response to certain stress stimuli.