RESUMEN
Cellular senescence is a cell fate triggered in response to stress and is characterized by stable cell-cycle arrest and a hypersecretory state. It has diverse biological roles, ranging from tissue repair to chronic disease. The development of new tools to study senescence in vivo has paved the way for uncovering its physiological and pathological roles and testing senescent cells as a therapeutic target. However, the lack of specific and broadly applicable markers makes it difficult to identify and characterize senescent cells in tissues and living organisms. To address this, we provide practical guidelines called "minimum information for cellular senescence experimentation in vivo" (MICSE). It presents an overview of senescence markers in rodent tissues, transgenic models, non-mammalian systems, human tissues, and tumors and their use in the identification and specification of senescent cells. These guidelines provide a uniform, state-of-the-art, and accessible toolset to improve our understanding of cellular senescence in vivo.
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Senescencia Celular , Humanos , Animales , Biomarcadores/metabolismo , Guías como Asunto , Neoplasias/patologíaRESUMEN
Accumulating evidence argues that aging exerts a profound influence on epigenetics, and vice versa. A pair of studies by Merkwirth et al. and Tian et al. now provide insights on how mitochondrial stress experienced by C. elegans larvae propagates a specific and persistent epigenetic response that protects adult cells and extends lifespan.
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Proteínas de Caenorhabditis elegans/genética , Caenorhabditis elegans/metabolismo , Envejecimiento , Animales , Epigénesis Genética , Humanos , Longevidad , Mitocondrias/metabolismoRESUMEN
MYC is a highly pleiotropic transcription factor whose deregulation promotes cancer. In contrast, we find that Myc haploinsufficient (Myc(+/-)) mice exhibit increased lifespan. They show resistance to several age-associated pathologies, including osteoporosis, cardiac fibrosis, and immunosenescence. They also appear to be more active, with a higher metabolic rate and healthier lipid metabolism. Transcriptomic analysis reveals a gene expression signature enriched for metabolic and immune processes. The ancestral role of MYC as a regulator of ribosome biogenesis is reflected in reduced protein translation, which is inversely correlated with longevity. We also observe changes in nutrient and energy sensing pathways, including reduced serum IGF-1, increased AMPK activity, and decreased AKT, TOR, and S6K activities. In contrast to observations in other longevity models, Myc(+/-) mice do not show improvements in stress management pathways. Our findings indicate that MYC activity has a significant impact on longevity and multiple aspects of mammalian healthspan.
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Proteínas Proto-Oncogénicas c-myc/genética , Proteínas Proto-Oncogénicas c-myc/metabolismo , Envejecimiento , Animales , Tamaño Corporal , Femenino , Longevidad , Linfoma/genética , Masculino , Redes y Vías Metabólicas , Ratones , Ratones de la Cepa 129 , Ratones Endogámicos C57BL , TranscriptomaRESUMEN
The genomes of virtually all organisms contain repetitive sequences that are generated by the activity of transposable elements (transposons). Transposons are mobile genetic elements that can move from one genomic location to another; in this process, they amplify and increase their presence in genomes, sometimes to very high copy numbers. In this Review we discuss new evidence and ideas that the activity of retrotransposons, a major subgroup of transposons overall, influences and even promotes the process of ageing and age-related diseases in complex metazoan organisms, including humans. Retrotransposons have been coevolving with their host genomes since the dawn of life. This relationship has been largely competitive, and transposons have earned epithets such as 'junk DNA' and 'molecular parasites'. Much of our knowledge of the evolution of retrotransposons reflects their activity in the germline and is evident from genome sequence data. Recent research has provided a wealth of information on the activity of retrotransposons in somatic tissues during an individual lifespan, the molecular mechanisms that underlie this activity, and the manner in which these processes intersect with our own physiology, health and well-being.
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Envejecimiento/genética , Envejecimiento/patología , Enfermedad/genética , Retroelementos/genética , Animales , Daño del ADN , Silenciador del Gen , Genoma Humano/genética , Genómica , Humanos , Inmunidad InnataRESUMEN
An Amendment to this paper has been published and can be accessed via a link at the top of the paper.
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Retrotransposable elements are deleterious at many levels, and the failure of host surveillance systems for these elements can thus have negative consequences. However, the contribution of retrotransposon activity to ageing and age-associated diseases is not known. Here we show that during cellular senescence, L1 (also known as LINE-1) retrotransposable elements become transcriptionally derepressed and activate a type-I interferon (IFN-I) response. The IFN-I response is a phenotype of late senescence and contributes to the maintenance of the senescence-associated secretory phenotype. The IFN-I response is triggered by cytoplasmic L1 cDNA, and is antagonized by inhibitors of the L1 reverse transcriptase. Treatment of aged mice with the nucleoside reverse transcriptase inhibitor lamivudine downregulated IFN-I activation and age-associated inflammation (inflammaging) in several tissues. We propose that the activation of retrotransposons is an important component of sterile inflammation that is a hallmark of ageing, and that L1 reverse transcriptase is a relevant target for the treatment of age-associated disorders.
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Senescencia Celular/genética , Inflamación/genética , Interferón Tipo I/metabolismo , Elementos de Nucleótido Esparcido Largo/genética , Envejecimiento/genética , Envejecimiento/patología , Animales , Regulación hacia Abajo , Femenino , Fibroblastos/metabolismo , Fibroblastos/patología , Humanos , Inflamación/patología , Lamivudine/farmacología , Masculino , Ratones , Fenotipo , ADN Polimerasa Dirigida por ARN/genética , ADN Polimerasa Dirigida por ARN/metabolismo , Inhibidores de la Transcriptasa Inversa/farmacologíaRESUMEN
LINE-1 retrotransposons are sequences capable of copying themselves to new genomic loci via an RNA intermediate. New studies implicate LINE-1 in a range of diseases, especially in the context of aging, but without an accurate understanding of where and when LINE-1 is expressed, a full accounting of its role in health and disease is not possible. We therefore developed a method-5' scL1seq-that makes use of a widely available library preparation method (10x Genomics 5' single cell RNA-seq) to measure LINE-1 expression in tens of thousands of single cells. We recapitulated the known pattern of LINE-1 expression in tumors-present in cancer cells, absent from immune cells-and identified hitherto undescribed LINE-1 expression in human epithelial cells and mouse hippocampal neurons. In both cases, we saw a modest increase with age, supporting recent research connecting LINE-1 to age related diseases.
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Neoplasias , Retroelementos , Humanos , Animales , Ratones , Retroelementos/genética , Análisis de Expresión Génica de una Sola Célula , Elementos de Nucleótido Esparcido Largo/genética , NeuronasRESUMEN
Sirt6 is a multifunctional enzyme that regulates diverse cellular processes such as metabolism, DNA repair, and aging. Overexpressing Sirt6 extends lifespan in mice, but the underlying cellular mechanisms are unclear. Drosophila melanogaster are an excellent model to study genetic regulation of lifespan; however, despite extensive study in mammals, very little is known about Sirt6 function in flies. Here, we characterized the Drosophila ortholog of Sirt6, dSirt6, and examined its role in regulating longevity; dSirt6 is a nuclear and chromatin-associated protein with NAD+-dependent histone deacetylase activity. dSirt6 overexpression (OE) in flies produces robust lifespan extension in both sexes, while reducing dSirt6 levels shortens lifespan. dSirt6 OE flies have normal food consumption and fertility but increased resistance to oxidative stress and reduced protein synthesis rates. Transcriptomic analyses reveal that dSirt6 OE reduces expression of genes involved in ribosome biogenesis, including many dMyc target genes. dSirt6 OE partially rescues many effects of dMyc OE, including increased nuclear size, up-regulation of ribosome biogenesis genes, and lifespan shortening. Last, dMyc haploinsufficiency does not convey additional lifespan extension to dSirt6 OE flies, suggesting dSirt6 OE is upstream of dMyc in regulating lifespan. Our results provide insight into the mechanisms by which Sirt6 OE leads to longer lifespan.
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Longevidad/genética , Sirtuinas/metabolismo , Envejecimiento/fisiología , Animales , Proteínas de Drosophila/metabolismo , Drosophila melanogaster/metabolismo , Femenino , Expresión Génica/genética , Regulación de la Expresión Génica/genética , Haploinsuficiencia/genética , Histona Desacetilasas/economía , Histona Desacetilasas/metabolismo , Masculino , Sirtuinas/genéticaRESUMEN
Retrotransposons are gene segments that proliferate in the genome, and the Long INterspersed Element 1 (LINE-1 or L1) retrotransposon is active in humans. Although older mammals show enhanced skeletal muscle L1 expression, exercise generally reverses this trend. We hypothesize skeletal muscle L1 expression influences muscle physiology, and additional innovative investigations are needed to confirm this hypothesis.
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Elementos de Nucleótido Esparcido Largo , Músculo Esquelético , Animales , Ejercicio Físico , Humanos , Mamíferos/genética , Músculo Esquelético/metabolismoRESUMEN
Long interspersed nuclear element-1 (L1) is a retrotransposable element that autonomously replicates in the human genome, resulting in DNA damage and genomic instability. Activation of L1 in senescent cells triggers a type I interferon response and age-associated inflammation. Two open reading frames encode an ORF1 protein functioning as messenger RNA chaperone and an ORF2 protein providing catalytic activities necessary for retrotransposition. No function has been identified for the conserved, disordered N-terminal region of ORF1. Using microscopy and NMR spectroscopy, we demonstrate that ORF1 forms liquid droplets in vitro in a salt-dependent manner and that interactions between its N-terminal region and coiled-coil domain are necessary for phase separation. Mutations disrupting blocks of charged residues within the N-terminus impair phase separation, whereas some mutations within the coiled-coil domain enhance phase separation. Demixing of the L1 particle from the cytosol may provide a mechanism to protect the L1 transcript from degradation.
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Elementos de Nucleótido Esparcido Largo , Chaperonas Moleculares , Humanos , Elementos de Nucleótido Esparcido Largo/genética , Sistemas de Lectura Abierta , Dominios Proteicos , ARN MensajeroRESUMEN
Cellular senescence triggered by telomere dysfunction has long been hypothesized to constitute a tumor suppression mechanism. The evidence has come primarily from in vitro cell culture studies, and more indirectly from analysis of tumor specimens. Two recent studies, published in the current issue of Cancer Cell and online at EMBO Reports, provide direct mechanistic evidence in cleverly manipulated mouse cancer models. This work shows that telomere-induced senescence is as effective as apoptosis in reducing cancer incidence and is mediated by the tumor suppressor p53.
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Senescencia Celular/genética , Neoplasias/patología , Telómero , Animales , Humanos , Neoplasias/genéticaRESUMEN
Here we present and develop the hypothesis that the derepression of endogenous retrotransposable elements (RTEs) - "genomic parasites" - is an important and hitherto under-unexplored molecular aging process that can potentially occur in most tissues. We further envision that the activation and continued presence of retrotransposition contribute to age-associated tissue degeneration and pathology. Chromatin is a complex and dynamic structure that needs to be maintained in a functional state throughout our lifetime. Studies of diverse species have revealed that chromatin undergoes extensive rearrangements during aging. Cellular senescence, an important component of mammalian aging, has recently been associated with decreased heterochromatinization of normally silenced regions of the genome. These changes lead to the expression of RTEs, culminating in their transposition. RTEs are common in all kingdoms of life, and comprise close to 50% of mammalian genomes. They are tightly controlled, as their activity is highly destabilizing and mutagenic to their resident genomes.
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Senescencia Celular/genética , Retroelementos/genética , Envejecimiento/genética , Envejecimiento/fisiología , Animales , Senescencia Celular/fisiología , Humanos , Retroelementos/fisiologíaRESUMEN
BACKGROUND: Repetitive elements comprise at least 55% of the human genome with more recent estimates as high as two-thirds. Most of these elements are retrotransposons, DNA sequences that can insert copies of themselves into new genomic locations by a "copy and paste" mechanism. These mobile genetic elements play important roles in shaping genomes during evolution, and have been implicated in the etiology of many human diseases. Despite their abundance and diversity, few studies investigated the regulation of endogenous retrotransposons at the genome-wide scale, primarily because of the technical difficulties of uniquely mapping high-throughput sequencing reads to repetitive DNA. RESULTS: Here we develop a new computational method called RepEnrich to study genome-wide transcriptional regulation of repetitive elements. We show that many of the Long Terminal Repeat retrotransposons in humans are transcriptionally active in a cell line-specific manner. Cancer cell lines display increased RNA Polymerase II binding to retrotransposons than cell lines derived from normal tissue. Consistent with increased transcriptional activity of retrotransposons in cancer cells we found significantly higher levels of L1 retrotransposon RNA expression in prostate tumors compared to normal-matched controls. CONCLUSIONS: Our results support increased transcription of retrotransposons in transformed cells, which may explain the somatic retrotransposition events recently reported in several types of cancers.
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Elementos Transponibles de ADN/genética , Línea Celular Tumoral , Inmunoprecipitación de Cromatina , Mapeo Cromosómico , ARN Polimerasas Dirigidas por ADN/metabolismo , Genoma Humano , Humanos , Masculino , Neoplasias de la Próstata/genética , Neoplasias de la Próstata/patología , Unión Proteica , ARN/genética , ARN/metabolismo , Análisis de Secuencia de ARNRESUMEN
The long interspersed nuclear element-1 (LINE-1 or L1) retrotransposon is the only active autonomously replicating retrotransposon in the human genome. L1 harms the cell by inserting new copies, generating DNA damage, and triggering inflammation. Therefore, L1 inhibition could be used to treat many diseases associated with these processes. Previous research has focused on inhibition of the L1 reverse transcriptase due to the prevalence of well-characterized inhibitors of related viral enzymes. Here we present the L1 endonuclease as another target for reducing L1 activity. We characterize structurally diverse small molecule endonuclease inhibitors using computational, biochemical, and biophysical methods. We also show that these inhibitors reduce L1 retrotransposition, L1-induced DNA damage, and inflammation reinforced by L1 in senescent cells. These inhibitors could be used for further pharmacological development and as tools to better understand the life cycle of this element and its impact on disease processes.
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Endonucleasas , Elementos de Nucleótido Esparcido Largo , Humanos , Elementos de Nucleótido Esparcido Largo/genética , Endonucleasas/metabolismo , Endonucleasas/genética , Endonucleasas/antagonistas & inhibidores , Inhibidores Enzimáticos/farmacología , Inhibidores Enzimáticos/química , Daño del ADN , Bibliotecas de Moléculas Pequeñas/farmacología , Bibliotecas de Moléculas Pequeñas/química , Senescencia Celular/efectos de los fármacos , Desoxirribonucleasa IRESUMEN
Although cancer is an age-related disease, how the processes of aging contribute to cancer progression is not well understood. In this study, we uncovered how mouse B cell lymphoma develops as a consequence of a naturally aged system. We show here that this malignancy is associated with an age-associated clonal B cell (ACBC) population that likely originates from age-associated B cells. Driven by c-Myc activation, promoter hypermethylation and somatic mutations, IgM+ ACBCs clonally expand independently of germinal centers and show increased biological age. ACBCs become self-sufficient and support malignancy when transferred into young recipients. Inhibition of mTOR or c-Myc in old mice attenuates pre-malignant changes in B cells during aging. Although the etiology of mouse and human B cell lymphomas is considered distinct, epigenetic changes in transformed mouse B cells are enriched for changes observed in human B cell lymphomas. Together, our findings characterize the spontaneous progression of cancer during aging through both cell-intrinsic and microenvironmental changes and suggest interventions for its prevention.
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The transcription factor MYC is overexpressed in many human cancers and has a significant causal role in tumor incidence and progression. In contrast, Myc +/- heterozygous mice, which have decreased MYC expression, exhibit a 10-20% increase in lifespan and a decreased incidence or progression of several age-related diseases. Myc heterozygous mice were also reported to have decreased mTOR and IGF1 signaling, two pathways whose reduced activity is associated with longevity in diverse species. Given MYC's downstream role in these pathways, the downregulation of mTOR and IGF1 signaling in Myc heterozygotes suggests the presence of feedback loops within this regulatory network. In this communication we provide further evidence that the reduction of Myc expression in Myc +/- heterozygous mice provokes a female-specific decrease in circulating IGF1 as well as a reduction of IGF1 protein in the liver. In particular, reduced Myc expression led to upregulation of miRNAs that target the Igf1 transcript, thereby inhibiting its translation and leading to decreased IGF1 protein levels. Using Argonaute (AGO)-CLIP-sequencing we found enrichment of AGO binding in the Igf1 transcript at the target sites of let-7, miR-122, and miR-29 in female, but not male Myc heterozygotes. Upregulation of the liver-specific miR-122 in primary hepatocytes in culture and in vivo in mice resulted in significant downregulation of IGF1 protein, but not mRNA. Reduced levels of IGF1 increased GH production in the pituitary through a well-documented negative-feedback relationship. In line with this, we found that IGF1 levels in bone (where miR-122 is not expressed) were unchanged, consistent with the decreased incidence of osteoporosis in female Myc heterozygotes, despite decreased circulating IGF1.
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BACKGROUND: The transcription factor c-myc regulates genes involved in hepatocyte growth, proliferation, metabolism, and differentiation. It has also been assigned roles in liver development and regeneration. In previous studies, we made the unexpected observation that c-Myc protein levels were similar in proliferating fetal liver and quiescent adult liver with c-Myc displaying nucleolar localization in the latter. In order to investigate the functional role of c-Myc in adult liver, we have developed a hepatocyte-specific c-myc knockout mouse, c-mycfl/fl;Alb-Cre. RESULTS: Liver weight to body weight ratios were similar in control and c-myc deficient mice. Liver architecture was unaffected. Conditional c-myc deletion did not result in compensatory induction of other myc family members or in c-Myc's binding partner Max. Floxed c-myc did have a negative effect on Alb-Cre expression at 4 weeks of age. To explore this relationship further, we used the Rosa26 reporter line to assay Cre activity in the c-myc floxed mice. No significant difference in Alb-Cre activity was found between control and c-mycfl/fl mice. c-myc deficient mice were studied in a nonproliferative model of liver growth, fasting for 48 hr followed by a 24 hr refeeding period. Fasting resulted in a decrease in liver mass and liver protein, both of which recovered upon 24 h of refeeding in the c-mycfl/fl;Alb-Cre animals. There was also no effect of reducing c-myc on recovery of liver mass following 2/3 partial hepatectomy. CONCLUSIONS: c-Myc appears to be dispensable for normal liver growth during the postnatal period, restoration of liver mass following partial hepatectomy and recovery from fasting.
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Hígado/embriología , Hígado/crecimiento & desarrollo , Regeneración/fisiología , alfa-Amilasas Salivales/metabolismo , Animales , Femenino , Masculino , Ratones , Ratones Noqueados , alfa-Amilasas Salivales/genéticaRESUMEN
Remarkable progress in ageing research has been achieved over the past decades. General perceptions and experimental evidence pinpoint that the decline of physical function often initiates by cell senescence and organ ageing. Epigenetic dynamics and immunometabolic reprogramming link to the alterations of cellular response to intrinsic and extrinsic stimuli, representing current hotspots as they not only (re-)shape the individual cell identity, but also involve in cell fate decision. This review focuses on the present findings and emerging concepts in epigenetic, inflammatory, and metabolic regulations and the consequences of the ageing process. Potential therapeutic interventions targeting cell senescence and regulatory mechanisms, using state-of-the-art techniques are also discussed.
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Envejecimiento/metabolismo , Senescencia Celular/genética , Epigenómica , Inflamación/genética , Envejecimiento/genética , Diferenciación Celular/genética , Humanos , Inflamación/metabolismoRESUMEN
Human mesenchymal stromal cells (hMSCs) represent an attractive cell source for clinic applications. Besides being multi-potent, recent clinical trials suggest that they secrete both trophic and immunomodulatory factors, allowing allogenic MSCs to be used in a wider variety of clinical situations. The yield of prospective isolation is however very low, making expansion a required step toward clinical applications. Unfortunately, this leads to a significant decrease in their stemness. To identify the mechanism behind loss of multi-potency, hMSCs were expanded until replicative senescence and the concomitant molecular changes were characterized at regular intervals. We observed that, with time of culture, loss of multi-potency was associated with both the accumulation of DNA damage and the respective activation of the DNA damage response pathway, suggesting a correlation between both phenomena. Indeed, exposing hMSCs to DNA damage agents led to a significant decrease in the differentiation potential. We also showed that hMSCs are susceptible to accumulate DNA damage upon in vitro expansion, and that although hMSCs maintained an effective nucleotide excision repair activity, there was a progressive accumulation of DNA damage. We propose a model in which DNA damage accumulation contributes to the loss of differentiation potential of hMSCs, which might not only compromise their potential for clinical applications but also contribute to the characteristics of tissue ageing.
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Células de la Médula Ósea/citología , Daño del ADN , Mesodermo/citología , Células del Estroma , Western Blotting , Ciclo Celular , Diferenciación Celular , Células Cultivadas , Senescencia Celular , Reparación del ADN/genética , Técnica del Anticuerpo Fluorescente , Humanos , Inmunofenotipificación , Estrés Oxidativo , Células del Estroma/citología , Células del Estroma/metabolismo , Células del Estroma/fisiología , Factores de Tiempo , beta-Galactosidasa/genéticaRESUMEN
Supv3L1 is an evolutionarily conserved helicase that plays a critical role in the mitochondrial RNA surveillance and degradation machinery. Conditional ablation of Supv3L1 in adult mice leads to premature aging phenotypes including loss of muscle mass and adipose tissue and severe skin abnormalities. To get insights into the spatial and temporal expression of Supv3L1 in the mouse, we generated knock-in and transgenic strains in which an EGFP reporter was placed under control of the Supv3L1 native promoter. During development, expression of Supv3L1 begins at the blastocyst stage, becomes widespread and strong in all fetal tissues and cell types, and continues during postnatal growth. In mature animals reporter expression is only slightly diminished in most tissues and continues to be highly expressed in the brain, peripheral sensory organs, and testis. Together, these data confirm that Supv3L1 is an important developmentally regulated gene, which continues to be expressed in all mature tissues, particularly the rapidly proliferating cells of testes, but also in the brain and sensory organs. The transgenic mice and cell lines derived from them constitute a valuable tool for the examination of the spatial and temporal aspects of Supv3L1 promoter activity, and should facilitate future screens for small molecules that regulate Supv3L1 expression.