Nuclear envelope alterations generate an aging-like epigenetic pattern in mice deficient in Zmpste24 metalloprotease

The histone acylation reader ENL/AF9 regulates aging in Drosophila melanogaster

Histone acylation plays a pivotal role in modulating gene expression, ensuring proper neurogenesis and responsiveness to various signals. Recently, the evolutionary conserved YAF9, ENL, AF9, TAF41, SAS5 (YEATS) domain found in four human paralogs, has emerged as a new class of histone acylation reader with a preference for the bulkier crotonyl group lysine over acetylation. Despite advancements, the role of either histone crotonylation or its readers in neurons remains unclear. In this study, we employed Drosophila melanogaster to investigate the role of ENL/AF9 (dENL/AF9) in the nervous system. Pan-neuronal dENL/AF9 knockdown not only extended the lifespan of flies but also enhanced their overall fitness during aging, including improved sleep quality and locomotion. Moreover, a decreased activity of dENL/AF9 in neurons led to an up-regulation of catalase gene expression which combined with reduced levels of malondialdehyde (MDA) and an enhanced tolerance to oxidative stress in aging flies. This study unveiled a novel function of histone crotonylation readers in aging with potential implications for understanding age-related conditions in humans.

Impact of Combined Baricitinib and FTI Treatment on Adipogenesis in Hutchinson-Gilford Progeria Syndrome and Other Lipodystrophic Laminopathies

Hutchinson-Gilford progeria syndrome (HGPS) is a rare genetic disease that causes premature aging symptoms, such as vascular diseases, lipodystrophy, loss of bone mineral density, and alopecia. HGPS is mostly linked to a heterozygous and de novo mutation in the LMNA gene (c.1824 C > T; p.G608G), resulting in the production of a truncated prelamin A protein called "progerin". Progerin accumulation causes nuclear dysfunction, premature senescence, and apoptosis. Here, we examined the effects of baricitinib (Bar), an FDA-approved JAK/STAT inhibitor, and a combination of Bar and lonafarnib (FTI) treatment on adipogenesis using skin-derived precursors (SKPs). We analyzed the effect of these treatments on the differentiation potential of SKPs isolated from pre-established human primary fibroblast cultures. Compared to mock-treated HGPS SKPs, Bar and Bar + FTI treatments improved the differentiation of HGPS SKPs into adipocytes and lipid droplet formation. Similarly, Bar and Bar + FTI treatments improved the differentiation of SKPs derived from patients with two other lipodystrophic diseases: familial partial lipodystrophy type 2 (FPLD2) and mandibuloacral dysplasia type B (MADB). Overall, the results show that Bar treatment improves adipogenesis and lipid droplet formation in HGPS, FPLD2, and MADB, indicating that Bar + FTI treatment might further ameliorate HGPS pathologies compared to lonafarnib treatment alone.

Common factors among three types of cells aged in mice

The greatest risk factor for the formation of numerous significant chronic disorders is aging. Understanding the core molecular underpinnings of aging can help to slow down the inevitable process. Systematic study of gene expression or DNA methylation data is possible at the transcriptomics and epigenetics levels. DNA methylation and gene expression are both affected by aging. Gene expression is an important element in the aging of Homo sapiens. In this work, we evaluated the expression of differentially expressed genes (DEGs), proteins, and transcription factors (TFs) in three different types of cells in mice: antibody-secreting cells, cardiac mesenchymal stromal cells, and skeletal muscle cells. The goal of this article is to uncover a common cause during aging among these cells in order to increase understanding about establishing complete techniques for preventing aging and improving people's quality of life. We conducted a comprehensive network-based investigation to establish which genes and proteins are shared by the three different types of aged cells. Our findings clearly indicated that aging induces gene dysregulation in immune, pharmacological, and apoptotic pathways. Furthermore, our research developed a list of hub genes with differential expression in aging responses that should be investigated further to discover viable anti-aging treatments.

Role of mitophagy in the hallmarks of aging

Aging, subjected to scientific scrutiny, is extensively defined as a time-dependent decline in functions that involves the majority of organisms. The time-dependent accretion of cellular lesions is generally a universal trigger of aging, while mitochondrial dysfunction is a sign of aging. Dysfunctional mitochondria are identified and removed by mitophagy, a selective form of macroautophagy. Increased mitochondrial damage resulting from reduced biogenesis and clearance may promote the aging process. The primary purpose of this paper is to illustrate in detail the effects of mitophagy on aging and emphasize the associations between mitophagy and other signs of aging, including dietary restriction, telomere shortening, epigenetic alterations, and protein imbalance. The evidence regarding the effects of these elements on aging is still limited. And although the understanding of relationship between mitophagy and aging has been long-awaited, to analyze details of such a relationship remains the main challenge in aging studies.

Lamin A to Z in normal aging

Almost since the discovery that mutations in the LMNA gene, encoding the nuclear structure components lamin A and C, lead to Hutchinson-Gilford progeria syndrome, people have speculated that lamins may have a role in normal aging. The most common HPGS mutation creates a splice variant of lamin A, progerin, which promotes accelerated aging pathology. While some evidence exists that progerin accumulates with normal aging, an increasing body of work indicates that prelamin A, a precursor of lamin A prior to C-terminal proteolytic processing, accumulates with age and may be a driver of normal aging. Prelamin A shares properties with progerin and is also linked to a rare progeroid disease, restrictive dermopathy. Here, we describe mechanisms underlying changes in prelamin A with aging and lay out the case that this unprocessed protein impacts normative aging. This is important since intervention strategies can be developed to modify this pathway as a means to extend healthspan and lifespan.

New Insights into the Role of Histone Changes in Aging

Aging is the progressive decline or loss of function at the cellular, tissue, and organismal levels that ultimately leads to death. A number of external and internal factors, including diet, exercise, metabolic dysfunction, genome instability, and epigenetic imbalance, affect the lifespan of an organism. These aging factors regulate transcriptome changes related to the aging process through chromatin remodeling. Many epigenetic regulators, such as histone modification, histone variants, and ATP-dependent chromatin remodeling factors, play roles in chromatin reorganization. The key to understanding the role of gene regulatory networks in aging lies in characterizing the epigenetic regulators responsible for reorganizing and potentiating particular chromatin structures. This review covers epigenetic studies on aging, discusses the impact of epigenetic modifications on gene expression, and provides future directions in this area.

The Nuclear Lamina: Protein Accumulation and Disease

Cellular health is reliant on proteostasis-the maintenance of protein levels regulated through multiple pathways modulating protein synthesis, degradation and clearance. Loss of proteostasis results in serious disease and is associated with aging. One proteinaceous structure underlying the nuclear envelope-the nuclear lamina-coordinates essential processes including DNA repair, genome organization and epigenetic and transcriptional regulation. Loss of proteostasis within the nuclear lamina results in the accumulation of proteins, disrupting these essential functions, either via direct interactions of protein aggregates within the lamina or by altering systems that maintain lamina structure. Here we discuss the links between proteostasis and disease of the nuclear lamina, as well as how manipulating specific proteostatic pathways involved in protein clearance could improve cellular health and prevent/reverse disease.

The Role of Dot1l in Prenatal and Postnatal Murine Chondrocytes and Trabecular Bone

Osteoarthritis and osteoporosis are widely prevalent and have far-reaching public health implications. There is increasing evidence that epigenetics, in particular, histone 3 lysine 79 methyltransferase DOT1L, plays an important role in the cartilage and bone biology. In this study, we evaluated the role of Dot1l in the articular cartilage, growth plate, and trabecular bone utilizing conditional KO mouse models. We generated chondrocyte-specific constitutive and inducible conditional Dot1l KO mouse lines using Col2a1-Cre and Acan-CreER systems. Prenatal deletion of Dot1l in mouse chondrocytes led to perinatal mortality, accelerated ossification, and dysregulation of Col10a1 expression. Postnatal deletion of Dot1l in mouse chondrocytes resulted in trabecular bone loss decreased extracellular matrix production, and disruption of the growth plate. In addition, pharmacological inhibition of DOT1L in a progeria mouse model partially rescued the abnormal osseous phenotype. In conclusion, Dot1l is important in maintaining the growth plate, extracellular matrix production, and trabecular bone. © 2019 The Authors. JBMR Plus published by Wiley Periodicals, Inc. on behalf of American Society for Bone and Mineral Research.

Chromatin regulation by Histone H4 acetylation at Lysine 16 during cell death and differentiation in the myeloid compartment

Histone H4 acetylation at Lysine 16 (H4K16ac) is a key epigenetic mark involved in gene regulation, DNA repair and chromatin remodeling, and though it is known to be essential for embryonic development, its role during adult life is still poorly understood. Here we show that this lysine is massively hyperacetylated in peripheral neutrophils. Genome-wide mapping of H4K16ac in terminally differentiated blood cells, along with functional experiments, supported a role for this histone post-translational modification in the regulation of cell differentiation and apoptosis in the hematopoietic system. Furthermore, in neutrophils, H4K16ac was enriched at specific DNA repeats. These DNA regions presented an accessible chromatin conformation and were associated with the cleavage sites that generate the 50 kb DNA fragments during the first stages of programmed cell death. Our results thus suggest that H4K16ac plays a dual role in myeloid cells as it not only regulates differentiation and apoptosis, but it also exhibits a non-canonical structural role in poising chromatin for cleavage at an early stage of neutrophil cell death.

Hutchinson-Gilford Progeria Syndrome: Challenges at Bench and Bedside

The structural nuclear proteins known as "lamins" (A-type and B-type) provide a scaffold for the compartmentalization of genome function that is important to maintain genome stability. Mutations in the LMNA gene -encoding for A-type lamins- are associated with over a dozen of degenerative disorders termed laminopathies, which include muscular dystrophies, lipodystrophies, neuropathies, and premature ageing diseases such as Hutchinson Gilford Progeria Syndrome (HGPS). This devastating disease is caused by the expression of a truncated lamin A protein named "progerin". To date, there is no effective treatment for HGPS patients, who die in their teens from cardiovascular disease. At a cellular level, progerin expression impacts nuclear architecture, chromatin organization, response to mechanical stress, and DNA transactions such as transcription, replication and repair. However, the current view is that key mechanisms behind progerin toxicity still remain to be discovered. Here, we discuss new findings about pathological mechanisms in HGPS, especially the contribution of replication stress to cellular decline, and therapeutic strategies to ameliorate progerin toxicity. In particular, we present evidence for retinoids and calcitriol (hormonal vitamin D metabolite) being among the most potent compounds to ameliorate HGPS cellular phenotypes in vitro, providing the rationale for testing these compounds in preclinical models of the disease in the near term, and in patients in the future.

Next-Generation Sequencing and Quantitative Proteomics of Hutchinson-Gilford progeria syndrome-derived cells point to a role of nucleotide metabolism in premature aging

Hutchinson-Gilford progeria syndrome (HGPS) is a very rare fatal disease characterized for accelerated aging. Although the causal agent, a point mutation in LMNA gene, was identified more than a decade ago, the molecular mechanisms underlying HGPS are still not fully understood and, currently, there is no cure for the patients, which die at a mean age of thirteen. With the aim of unraveling non-previously altered molecular pathways in the premature aging process, human cell lines from HGPS patients and from healthy parental controls were studied in parallel using Next-Generation Sequencing (RNAseq) and High-Resolution Quantitative Proteomics (iTRAQ) techniques. After selection of significant proteins and transcripts and crosschecking of the results a small set of protein/transcript pairs were chosen for validation. One of those proteins, ribose-phosphate pyrophosphokinase 1 (PRPS1), is essential for nucleotide synthesis. PRPS1 loss-of-function mutants present lower levels of purine. PRPS1 protein and transcript levels are detected as significantly decreased in HGPS cell lines vs. healthy parental controls. This modulation was orthogonally confirmed by targeted techniques in cell lines and also in an animal model of Progeria, the ZMPSTE24 knock-out mouse. In addition, functional experiments through supplementation with S-adenosyl-methionine (SAMe), a metabolite that is an alternative source of purine, were done. Results indicate that SAMe has a positive effect in the proliferative capacity and reduces senescence-associated Beta-galactosidase staining of the HPGS cell lines. Altogether, our data suggests that nucleotide and, specifically, purine-metabolism, are altered in premature aging, opening a new window for the therapeutic treatment of the disease.

Changes at the nuclear lamina alter binding of pioneer factor Foxa2 in aged liver

Increasing evidence suggests that regulation of heterochromatin at the nuclear envelope underlies metabolic disease susceptibility and age-dependent metabolic changes, but the mechanism is unknown. Here, we profile lamina-associated domains (LADs) using lamin B1 ChIP-Seq in young and old hepatocytes and find that, although lamin B1 resides at a large fraction of domains at both ages, a third of lamin B1-associated regions are bound exclusively at each age in vivo. Regions occupied by lamin B1 solely in young livers are enriched for the forkhead motif, bound by Foxa pioneer factors. We also show that Foxa2 binds more sites in Zmpste24 mutant mice, a progeroid laminopathy model, similar to increased Foxa2 occupancy in old livers. Aged and Zmpste24-deficient livers share several features, including nuclear lamina abnormalities, increased Foxa2 binding, de-repression of PPAR- and LXR-dependent gene expression, and fatty liver. In old livers, additional Foxa2 binding is correlated to loss of lamin B1 and heterochromatin (H3K9me3 occupancy) at these loci. Our observations suggest that changes at the nuclear lamina are linked to altered Foxa2 binding, enabling opening of chromatin and de-repression of genes encoding lipid synthesis and storage targets that contribute to etiology of hepatic steatosis.

Aging Hallmarks: The Benefits of Physical Exercise

World population has been continuously increasing and progressively aging. Aging is characterized by a complex and intraindividual process associated with nine major cellular and molecular hallmarks, namely, genomic instability, telomere attrition, epigenetic alterations, a loss of proteostasis, deregulated nutrient sensing, mitochondrial dysfunction, cellular senescence, stem cell exhaustion, and altered intercellular communication. This review exposes the positive antiaging impact of physical exercise at the cellular level, highlighting its specific role in attenuating the aging effects of each hallmark. Exercise should be seen as a polypill, which improves the health-related quality of life and functional capabilities while mitigating physiological changes and comorbidities associated with aging. To achieve a framework of effective physical exercise interventions on aging, further research on its benefits and the most effective strategies is encouraged.

Mandibuloacral dysplasia: A premature ageing disease with aspects of physiological ageing

Mandibuloacral dysplasia (MAD) is a rare genetic condition characterized by bone abnormalities including localized osteolysis and generalized osteoporosis, skin pigmentation, lipodystrophic signs and mildly accelerated ageing. The molecular defects associated with MAD are mutations in LMNA or ZMPSTE24 (FACE1) gene, causing type A or type B MAD, respectively. Downstream of LMNA or ZMPSTE24 mutations, the lamin A precursor, prelamin A, is accumulated in cells and affects chromatin dynamics and stress response. A new form of mandibuloacral dysplasia has been recently associated with mutations in POLD1 gene, encoding DNA polymerase delta, a major player in DNA replication. Of note, involvement of prelamin A in chromatin dynamics and recruitment of DNA repair factors has been also determined under physiological conditions, at the border between stress response and cellular senescence. Here, we review current knowledge on MAD clinical and pathogenetic aspects and highlight aspects typical of physiological ageing.

Hallmarks of progeroid syndromes: lessons from mice and reprogrammed cells

Ageing is a process that inevitably affects most living organisms and involves the accumulation of macromolecular damage, genomic instability and loss of heterochromatin. Together, these alterations lead to a decline in stem cell function and to a reduced capability to regenerate tissue. In recent years, several genetic pathways and biochemical mechanisms that contribute to physiological ageing have been described, but further research is needed to better characterize this complex biological process. Because premature ageing (progeroid) syndromes, including progeria, mimic many of the characteristics of human ageing, research into these conditions has proven to be very useful not only to identify the underlying causal mechanisms and identify treatments for these pathologies, but also for the study of physiological ageing. In this Review, we summarize the main cellular and animal models used in progeria research, with an emphasis on patient-derived induced pluripotent stem cell models, and define a series of molecular and cellular hallmarks that characterize progeroid syndromes and parallel physiological ageing. Finally, we describe the therapeutic strategies being investigated for the treatment of progeroid syndromes, and their main limitations.

Summary: This Review defines the molecular and cellular hallmarks of progeroid syndromes according to the main cellular and animal models, and discusses the therapeutic strategies developed to date.

The Biology of Aging and Cancer: A Brief Overview of Shared and Divergent Molecular Hallmarks

Aging is the inevitable time-dependent decline in physiological organ function and is a major risk factor for cancer development. Due to advances in health care, hygiene control and food availability, life expectancy is increasing and the population in most developed countries is shifting to an increasing proportion of people at a cancer susceptible age. Mechanisms of aging are also found to occur in carcinogenesis, albeit with shared or divergent end-results. It is now clear that aging and cancer development either share or diverge in several disease mechanisms. Such mechanisms include the role of genomic instability, telomere attrition, epigenetic changes, loss of proteostasis, decreased nutrient sensing and altered metabolism, but also cellular senescence and stem cell function. Cancer cells and aged cells are also fundamentally opposite, as cancer cells can be thought of as hyperactive cells with advantageous mutations, rapid cell division and increased energy consumption, while aged cells are hypoactive with accumulated disadvantageous mutations, cell division inability and a decreased ability for energy production and consumption. Nonetheless, aging and cancer are tightly interconnected and many of the same strategies and drugs may be used to target both, while in other cases antagonistic pleiotrophy come into effect and inhibition of one can be the activation of the other. Cancer can be considered an aging disease, though the shared mechanisms underpinning the two processes remain unclear. Better understanding of the shared and divergent pathways of aging and cancer is needed.

Nucleolar expansion and elevated protein translation in premature aging

Premature aging disorders provide an opportunity to study the mechanisms that drive aging. In Hutchinson-Gilford progeria syndrome (HGPS), a mutant form of the nuclear scaffold protein lamin A distorts nuclei and sequesters nuclear proteins. We sought to investigate protein homeostasis in this disease. Here, we report a widespread increase in protein turnover in HGPS-derived cells compared to normal cells. We determine that global protein synthesis is elevated as a consequence of activated nucleoli and enhanced ribosome biogenesis in HGPS-derived fibroblasts. Depleting normal lamin A or inducing mutant lamin A expression are each sufficient to drive nucleolar expansion. We further show that nucleolar size correlates with donor age in primary fibroblasts derived from healthy individuals and that ribosomal RNA production increases with age, indicating that nucleolar size and activity can serve as aging biomarkers. While limiting ribosome biogenesis extends lifespan in several systems, we show that increased ribosome biogenesis and activity are a hallmark of premature aging.

HGPS is a premature aging disease caused by mutations in the nuclear protein lamin A. Here, the authors show that cells from patients with HGPS have expanded nucleoli and increased protein synthesis, and report that nucleoli also expand as aging progresses in cells derived from healthy individuals.

Hutchinson-Gilford Progeria Syndrome: A premature aging disease caused by LMNA gene mutations

Products of the LMNA gene, primarily lamin A and C, are key components of the nuclear lamina, a proteinaceous meshwork that underlies the inner nuclear membrane and is essential for proper nuclear architecture. Alterations in lamin A and C that disrupt the integrity of the nuclear lamina affect a whole repertoire of nuclear functions, causing cellular decline. In humans, hundreds of mutations in the LMNA gene have been identified and correlated with over a dozen degenerative disorders, referred to as laminopathies. These diseases include neuropathies, muscular dystrophies, lipodystrophies, and premature aging diseases. This review focuses on one of the most severe laminopathies, Hutchinson-Gilford Progeria Syndrome (HGPS), which is caused by aberrant splicing of the LMNA gene and expression of a mutant product called progerin. Here, we discuss current views about the molecular mechanisms that contribute to the pathophysiology of this devastating disease, as well as the strategies being tested in vitro and in vivo to counteract progerin toxicity. In particular, progerin accumulation elicits nuclear morphological abnormalities, misregulated gene expression, defects in DNA repair, telomere shortening, and genomic instability, all of which limit cellular proliferative capacity. In patients harboring this mutation, a severe premature aging disease develops during childhood. Interestingly, progerin is also produced in senescent cells and cells from old individuals, suggesting that progerin accumulation might be a factor in physiological aging. Deciphering the molecular mechanisms whereby progerin expression leads to HGPS is an emergent area of research, which could bring us closer to understanding the pathology of aging.

Prostate Cancer: Is It a Battle Lost to Age?

Age is often considered an important non-modifiable risk factor for a number of diseases, including prostate cancer. Some prominent risk factors of prostate cancer include familial history, ethnicity and age. In this review, various genetic and physiological characteristics affected due to advancing age will be analysed and correlated with their direct effect on prostate cancer.

Epigenetic Mechanisms of Longevity and Aging

Aging is an inevitable outcome of life, characterized by progressive decline in tissue and organ function and increased risk of mortality. Accumulating evidence links aging to genetic and epigenetic alterations. Given the reversible nature of epigenetic mechanisms, these pathways provide promising avenues for therapeutics against age-related decline and disease. In this review, we provide a comprehensive overview of epigenetic studies from invertebrate organisms, vertebrate models, tissues, and in vitro systems. We establish links between common operative aging pathways and hallmark chromatin signatures that can be used to identify "druggable" targets to counter human aging and age-related disease.

Life stress, glucocorticoid signaling, and the aging epigenome: Implications for aging-related diseases

Life stress has been associated with accelerated cellular aging and increased risk for developing aging-related diseases; however, the underlying molecular mechanisms remain elusive. A highly relevant process that may underlie this association is epigenetic regulation. In this review, we build upon existing evidence to propose a model whereby exposure to life stress, in part via its effects on the hypothalamic-pituitary axis and the glucocorticoid signaling system, may alter the epigenetic landscape across the lifespan and, consequently, influence genomic regulation and function in ways that are conducive to the development of aging-related diseases. This model is supported by recent studies showing that life stressors and stress-related phenotypes can accelerate epigenetic aging, a measure that is based on DNA methylation prediction of chronological age and has been associated with several aging-related disease phenotypes. We discuss the implications of this model for the prevention and treatment of aging-related diseases, as well as the challenges and limitations of this line of research.

Olive Oil and the Hallmarks of Aging

Aging is a multifactorial and tissue-specific process involving diverse alterations regarded as the "hallmarks of aging", which include genomic instability, telomere attrition, epigenetic alterations, loss of proteostasis, deregulated nutrient sensing, mitochondrial dysfunction, cellular senescence, stem cell exhaustion and altered intracellular communication. Virtually all these hallmarks are targeted by dietary olive oil, particularly by virgin olive oil, since many of its beneficial effects can be accounted not only for the monounsaturated nature of its predominant fatty acid (oleic acid), but also for the bioactivity of its minor compounds, which can act on cells though both direct and indirect mechanisms due to their ability to modulate gene expression. Among the minor constituents of virgin olive oil, secoiridoids stand out for their capacity to modulate many pathways that are relevant for the aging process. Attenuation of aging-related alterations by olive oil or its minor compounds has been observed in cellular, animal and human models. How olive oil targets the hallmarks of aging could explain the improvement of health, reduced risk of aging-associated diseases, and increased longevity which have been associated with consumption of a typical Mediterranean diet containing this edible oil as the predominant fat source.

NF-κB activation impairs somatic cell reprogramming in ageing

Ageing constitutes a critical impediment to somatic cell reprogramming. We have explored the regulatory mechanisms that constitute age-associated barriers, through derivation of induced pluripotent stem cells (iPSCs) from individuals with premature or physiological ageing. We demonstrate that NF-κB activation blocks the generation of iPSCs in ageing. We also show that NF-κB repression occurs during cell reprogramming towards a pluripotent state. Conversely, ageing-associated NF-κB hyperactivation impairs the generation of iPSCs by eliciting the reprogramming repressor DOT1L, which reinforces senescence signals and downregulates pluripotency genes. Genetic and pharmacological NF-κB inhibitory strategies significantly increase the reprogramming efficiency of fibroblasts from Néstor-Guillermo progeria syndrome and Hutchinson-Gilford progeria syndrome patients, as well as from normal aged donors. Finally, we demonstrate that DOT1L inhibition in vivo extends lifespan and ameliorates the accelerated ageing phenotype of progeroid mice, supporting the interest of studying age-associated molecular impairments to identify targets of rejuvenation strategies.

iTRAQ-based analysis of progerin expression reveals mitochondrial dysfunction, reactive oxygen species accumulation and altered proteostasis

INTRODUCTION

Nuclear accumulation of a mutant form of the nuclear protein Lamin-A, called Progerin (PG) or Lamin AΔ50, occurs in Hutchinson-Gilford Progeria Syndrome (HGPS) or Progeria, an accelerated aging disease. One of the main symptoms of this genetic disorder is a loss of sub-cutaneous fat due to a dramatic lipodystrophy.

METHODS

We stably induced the expression of human PG and GFP -Green Fluorescent Protein- as control in 3T3L1 cells using a lentiviral system to study the effect of PG expression in the differentiation capacity of this cell line, one of the most used adipogenic models. Quantitative proteomics (iTRAQ) was done to study the effect of the PG accumulation. Several of the modulated proteins were validated by immunoblotting and real-time PCR. Mitochondrial function was analyzed by measurement of a) the mitochondrial basal activity, b) the superoxide anion production and c) the individual efficiency of the different complex of the respiratory chain.

RESULTS

We found that over-expression PG by lentiviral gene delivery leads to a decrease in the proliferation rate and to defects in adipogenic capacity when compared to the control. Quantitative proteomics analysis showed 181 proteins significantly (p<0.05) modulated in PG-expressing preadipocytes. Mitochondrial function is impaired in PG-expressing cells. Specifically, we have detected an increase in the activity of the complex I and an overproduction of Superoxide anion. Incubation with Reactive Oxygen Species (ROS) scavenger agents drives to a decrease in autophagic proteolysis as revealed by LC3-II/LC3-I ratio.

CONCLUSION

PG expression in 3T3L1 cells promotes changes in several Biological Processes, including structure of cytoskeleton, lipid metabolism, calcium regulation, translation, protein folding and energy generation by the mitochondria. Our data strengthen the contribution of ROS accumulation to the premature aging phenotype and establish a link between mitochondrial dysfunction and loss of proteostasis in HGPS.

Aging and DNA methylation

In this Opinion article, we summarize how changes in DNA methylation occur during aging in mammals and discuss examples of how such events may contribute to the aging process. We explore mechanisms that could facilitate DNA methylation changes in a site-specific manner and highlight a model in which region-specific DNA hypermethylation during aging is facilitated in a competitive manner by destabilization of the Polycomb repressive complex.

Can changes in histone acetylation contribute to memory formation?

Neuronal histone acetylation has been postulated to be a mnemonic substrate and a target for memory enhancers and neuropsychiatric drugs. Here we critically evaluate this view and examine the apparent conflict between the proposed instructive role for histone acetylation in memory-related transcription and the insights derived from genomic and genetic studies in other systems. We next discuss the suitability of activity-dependent neuronal histone acetylation as a mnemonic substrate and debate alternative interpretations of current evidence. We believe that further progress in our understanding of the role of histone acetylation and other epigenetic modifications in neuronal plasticity, memory, and neuropsychiatric disorders requires a clear discrimination between cause and effect so that novel epigenetics-related processes can be distinguished from classical transcriptional mechanisms.

Epigenetic involvement in Hutchinson-Gilford progeria syndrome: a mini-review

Hutchinson-Gilford progeria syndrome (HGPS) is a rare human genetic disease that leads to a severe premature ageing phenotype, caused by mutations in the LMNA gene. The LMNA gene codes for lamin-A and lamin-C proteins, which are structural components of the nuclear lamina. HGPS is usually caused by a de novo C1824T mutation that leads to the accumulation of a dominant negative form of lamin-A called progerin. Progerin also accumulates physiologically in normal ageing cells as a rare splicing form of lamin-A transcripts. From this perspective, HGPS cells seem to be good candidates for the study of the physiological mechanisms of ageing. Progerin accumulation leads to faster cellular senescence, stem cell depletion and the progeroid phenotype. Tissues of mesodermic origin are especially affected by HGPS. HGPS patients usually have a bad quality of life and, with current treatments, their life expectancy does not exceed their second decade at best. Though progerin can be expressed in almost any tissue, when death occurs, it is usually due to cardiovascular complications. In HGPS, severe epigenetic alterations have been reported. Histone-covalent modifications are radically different from control specimens, with the tendency to lose the bipartition into euchromatin and heterochromatin. This is reflected in an altered spatial compartmentalization and conformation of chromatin within the nucleus. Moreover, it seems that microRNAs and microRNA biosynthesis might play a role in HGPS. Exemplary in this connection is the suggested protective effect of miR-9 on the central nervous system of affected individuals. This mini-review will report on the state of the art of HGPS epigenetics, and there will be a discussion of how epigenetic alterations in HGPS cells can alter the cellular metabolism and lead to the systemic syndrome.

Prelamin A causes progeria through cell-extrinsic mechanisms and prevents cancer invasion

Defining the relationship between ageing and cancer is a crucial but challenging task. Mice deficient in Zmpste24, a metalloproteinase mutated in human progeria and involved in nuclear prelamin A maturation, recapitulate multiple features of ageing. However, their short lifespan and serious cell-intrinsic and cell-extrinsic alterations restrict the application and interpretation of carcinogenesis protocols. Here we present Zmpste24 mosaic mice that lack these limitations. Zmpste24 mosaic mice develop normally and keep similar proportions of Zmpste24-deficient (prelamin A accumulating) and Zmpste24-proficient (mature lamin A containing) cells throughout life, revealing that cell-extrinsic mechanisms are preeminent for progeria development. Moreover, prelamin A accumulation does not impair tumour initiation and growth, but it decreases the incidence of infiltrating oral carcinomas. Accordingly, silencing of ZMPSTE24 reduces human cancer cell invasiveness. Our results support the potential of cell-based and systemic therapies for progeria and highlight ZMPSTE24 as a new anticancer target.

Using zebrafish models to explore genetic and epigenetic impacts on evolutionary developmental origins of aging

Can we reset, reprogram, rejuvenate, or reverse the organismal aging process? Certain genetic manipulations could at least reset and reprogram epigenetic dynamics beyond phenotypic plasticity and elasticity in cells, which can be manipulated further into organisms. However, in a whole complex aging organism, how can we rejuvenate intrinsic resources and infrastructures in an intact and noninvasive manner? The incidence of diseases increases exponentially with age, accompanied by progressive deteriorations of physiological functions in organisms. Aging-associated diseases are sporadic but essentially inevitable complications arising from senescence. Senescence is often considered the antithesis of early development, but yet there may be factors and mechanisms in common between these 2 phenomena to rejuvenate over the dynamic process of aging. The association between early development and late-onset disease with advancing age is thought to come from a consequence of developmental plasticity, the phenomenon by which one genotype can give rise to a range of physiologically and/or morphologically adaptive states based on diverse epigenotypes in response to intrinsic or extrinsic environmental cues and genetic perturbations. We hypothesized that the future aging process can be predictive based on adaptivity during the early developmental period. Modulating the thresholds and windows of plasticity and its robustness by molecular genetic and chemical epigenetic approaches, we have successfully conducted experiments to isolate zebrafish mutants expressing apparently altered senescence phenotypes during their embryonic and/or larval stages ("embryonic/larval senescence"). Subsequently, at least some of these mutant animals were found to show a shortened life span, whereas others would be expected to live longer into adulthood. We anticipate that previously uncharacterized developmental genes may mediate the aging process and play a pivotal role in senescence. On the other hand, unexpected senescence-related genes might also be involved in the early developmental process and its regulation. The ease of manipulation using the zebrafish system allows us to conduct an exhaustive exploration of novel genes, genotypes, and epigenotypes that can be linked to the senescence phenotype, which facilitates searching for the evolutionary and developmental origins of aging in vertebrates.

The hallmarks of aging

Aging is characterized by a progressive loss of physiological integrity, leading to impaired function and increased vulnerability to death. This deterioration is the primary risk factor for major human pathologies, including cancer, diabetes, cardiovascular disorders, and neurodegenerative diseases. Aging research has experienced an unprecedented advance over recent years, particularly with the discovery that the rate of aging is controlled, at least to some extent, by genetic pathways and biochemical processes conserved in evolution. This Review enumerates nine tentative hallmarks that represent common denominators of aging in different organisms, with special emphasis on mammalian aging. These hallmarks are: genomic instability, telomere attrition, epigenetic alterations, loss of proteostasis, deregulated nutrient sensing, mitochondrial dysfunction, cellular senescence, stem cell exhaustion, and altered intercellular communication. A major challenge is to dissect the interconnectedness between the candidate hallmarks and their relative contributions to aging, with the final goal of identifying pharmaceutical targets to improve human health during aging, with minimal side effects.

Detection of nuclear envelope alterations in senescence

Gene mutations that cause defects in the nuclear envelope are responsible for progeroid syndromes, characterized by exacerbated cell senescence and accelerated aging. Consequently, morphological abnormalities of the nucleus represent a cellular phenotype whose analysis allows for both the characterization of the consequences of particular mutations and the assessment of the impact of approaches aimed at reversing their pathological effects. To obtain reliable results, systematic and reproducible procedures are required. Here, we describe a simple fluorescence microscopy-based protocol to detect nuclear envelope alterations in the study of cellular senescence.

Age-related susceptibility to apoptosis in human retinal pigment epithelial cells is triggered by disruption of p53-Mdm2 association

PURPOSE

Relatively little is known about the contribution of p53/Mdm2 pathway in apoptosis of retinal pigment epithelial (RPE) cells or its possible link to dysfunction of aging RPE or to related blinding disorders such as age-related macular degeneration (AMD).

METHODS

Age-associated changes in p53 activation were evaluated in primary RPE cultures from human donor eyes of various ages. Apoptosis was evaluated by activation of caspases and DNA fragmentation. Gene-specific small interfering RNA was used to knock down expression of p53.

RESULTS

We observed that the basal rate of p53-dependent apoptosis increased in an age-dependent manner in human RPE. The age-dependent increase in apoptosis was linked to alterations in several aspects of the p53 pathway. p53 phosphorylation Ser15 was increased through the stimulation of ATM-Ser1981. p53 acetylation Lys379 was increased through the inhibition of SIRT1/2. These two posttranslational modifications of p53 blocked the sequestration of p53 by Mdm2, thus resulting in an increase in free p53 and of p53 stimulation of apoptosis through increased expression of PUMA (p53 upregulated modulator of apoptosis) and activation of caspase-3. Aged RPE also had reduced expression of antiapoptotic Bcl-2, which contributed to the increase in apoptosis. Of particular interest in these studies was that pharmacologic treatments to block p53 phosphorylation, acetylation, or expression were able to protect RPE cells from apoptosis.

CONCLUSIONS

Our studies suggest that aging in the RPE leads to alterations of specific checkpoints in the apoptotic pathway, which may represent important molecular targets for the treatment of RPE-related aging disorders such as AMD.

Potential therapeutic approaches for modulating expression and accumulation of defective lamin A in laminopathies and age-related diseases

Scientific understanding of the genetic components of aging has increased in recent years, with several genes being identified as playing roles in the aging process and, potentially, longevity. In particular, genes encoding components of the nuclear lamina in eukaryotes have been increasingly well characterized, owing in part to their clinical significance in age-related diseases. This review focuses on one such gene, which encodes lamin A, a key component of the nuclear lamina. Genetic variation in this gene can give rise to lethal, early-onset diseases known as laminopathies. Here, we analyze the literature and conduct computational analyses of lamin A signaling and intracellular interactions in order to examine potential mechanisms for altering or slowing down aberrant Lamin A expression and/or for restoring the ratio of normal to aberrant lamin A. The ultimate goal of such studies is to ameliorate or combat laminopathies and related diseases of aging, and we provide a discussion of current approaches in this review.

Nuclear lamina defects cause ATM-dependent NF-κB activation and link accelerated aging to a systemic inflammatory response

Alterations in the architecture and dynamics of the nuclear lamina have a causal role in normal and accelerated aging through both cell-autonomous and systemic mechanisms. However, the precise nature of the molecular cues involved in this process remains incompletely defined. Here we report that the accumulation of prelamin A isoforms at the nuclear lamina triggers an ATM- and NEMO-dependent signaling pathway that leads to NF-κB activation and secretion of high levels of proinflammatory cytokines in two different mouse models of accelerated aging (Zmpste24(-/-) and Lmna(G609G/G609G) mice). Causal involvement of NF-κB in accelerated aging was demonstrated by the fact that both genetic and pharmacological inhibition of NF-κB signaling prevents age-associated features in these animal models, significantly extending their longevity. Our findings provide in vivo proof of principle for the feasibility of pharmacological modulation of the NF-κB pathway to slow down the progression of physiological and pathological aging.

Reprogramming aging and progeria

The aging rate of an organism depends on the ratio of tissue degeneration to tissue repair. As a consequence, molecular alterations that tip this balance toward degeneration cause accelerated aging. Conversely, interventions can be pursued to reduce tissue degeneration or to increase tissue repair with the aim of delaying the onset of age-associated manifestations. Recent studies on the biology of stem cells in aging have revealed the influence of systemic factors on their functionality and demonstrated the feasibility of reprogramming aged and progeroid cells. These results illustrate the reversibility of some aspects of the aging process and encourage the search for new anti-aging and anti-progeria interventions.

Splicing-directed therapy in a new mouse model of human accelerated aging

Hutchinson-Gilford progeria syndrome (HGPS) is caused by a point mutation in the LMNA gene that activates a cryptic donor splice site and yields a truncated form of prelamin A called progerin. Small amounts of progerin are also produced during normal aging. Studies with mouse models of HGPS have allowed the recent development of the first therapeutic approaches for this disease. However, none of these earlier works have addressed the aberrant and pathogenic LMNA splicing observed in HGPS patients because of the lack of an appropriate mouse model. Here, we report a genetically modified mouse strain that carries the HGPS mutation. These mice accumulate progerin, present histological and transcriptional alterations characteristic of progeroid models, and phenocopy the main clinical manifestations of human HGPS, including shortened life span and bone and cardiovascular aberrations. Using this animal model, we have developed an antisense morpholino-based therapy that prevents the pathogenic Lmna splicing, markedly reducing the accumulation of progerin and its associated nuclear defects. Treatment of mutant mice with these morpholinos led to a marked amelioration of their progeroid phenotype and substantially extended their life span, supporting the effectiveness of antisense oligonucleotide-based therapies for treating human diseases of accelerated aging.

Hot topics in epigenetic mechanisms of aging: 2011

Aging is a complex process that results in compromised biological functions of the organism and increased susceptibility to disease and death. Although the molecular basis of aging is currently being investigated in many experimental contexts, there is no consensus theory to fully explain the aging process. Epigenetic factors, including DNA methylation, histone modifications, and microRNA expression, may play central roles in controlling changes in gene expression and genomic instability during aging. In this Hot Topic review, we first examine the mechanisms by which these epigenetic factors contribute to aging in diverse eukaryotic species including experimental models of yeasts, worms, and mammals. In a second section, we will emphasize in the mammalian epigenetic alterations and how they may affect human longevity by altering stem cell function and/or somatic cell decline. The field of aging epigenetics is ripe with potential, but is still in its infancy, as new layers of complexity are emerging in the epigenetic network. As an example, we are only beginning to understand the relevance of non-coding genome to organism aging or the existence of an epigenetic memory with transgenerational inheritance. Addressing these topics will be fundamental for exploiting epigenetics phenomena as markers of aging-related diseases or as therapeutic targets.

Cell autonomous and systemic factors in progeria development

Progeroid laminopathies are accelerated aging syndromes caused by defects in nuclear envelope proteins. Accordingly, mutations in the LMNA gene and functionally related genes have been described to cause HGPS (Hutchinson–Gilford progeria syndrome), MAD (mandibuloacral dysplasia) or RD (restrictive dermopathy). Functional studies with animal and cellular models of these syndromes have facilitated the identification of the molecular alterations and regulatory pathways involved in progeria development. We have recently described a novel regulatory pathway involving miR-29 and p53 tumour suppressor which has provided valuable information on the molecular components orchestrating the response to nuclear damage stress. Furthermore, by using progeroid mice deficient in ZMPSTE24 (zinc metalloprotease STE24 homologue) involved in lamin A maturation, we have demonstrated that, besides these abnormal cellular responses to stress, dysregulation of the somatotropic axis is responsible for some of the alterations associated with progeria. Consistent with these observations, pharmacological restoration of the somatotroph axis in these mice delays the onset of their progeroid features, significantly extending their lifespan and supporting the importance of systemic alterations in progeria progression. Finally, we have very recently identified a novel progeroid syndrome with distinctive features from HGPS and MAD, which we have designated NGPS (Néstor–Guillermo progeria syndrome) (OMIM #614008). This disorder is caused by a mutation in BANF1, a gene encoding a protein with essential functions in the assembly of the nuclear envelope, further illustrating the importance of the nuclear lamina integrity for human health and providing additional support to the study of progeroid syndromes as a valuable source of information on human aging.

Histone H4 lysine 16 hypoacetylation is associated with defective DNA repair and premature senescence in Zmpste24-deficient mice

Specific point mutations in lamin A gene have been shown to accelerate aging in humans and mice. Particularly, a de novo mutation at G608G position impairs lamin A processing to produce the mutant protein progerin, which causes the Hutchinson Gilford progeria syndrome. The premature aging phenotype of Hutchinson Gilford progeria syndrome is largely recapitulated in mice deficient for the lamin A-processing enzyme, Zmpste24. We have previously reported that Zmpste24 deficiency results in genomic instability and early cellular senescence due to the delayed recruitment of repair proteins to sites of DNA damage. Here, we further investigate the molecular mechanism underlying delayed DNA damage response and identify a histone acetylation defect in Zmpste24(-/-) mice. Specifically, histone H4 was hypoacetylated at a lysine 16 residue (H4K16), and this defect was attributed to the reduced association of a histone acetyltransferase, Mof, to the nuclear matrix. Given the reversible nature of epigenetic changes, rescue experiments performed either by Mof overexpression or by histone deacetylase inhibition promoted repair protein recruitment to DNA damage sites and substantially ameliorated aging-associated phenotypes, both in vitro and in vivo. The life span of Zmpste24(-/-) mice was also extended with the supplementation of a histone deacetylase inhibitor, sodium butyrate, to drinking water. Consistent with recent data showing age-dependent buildup of unprocessable lamin A in physiological aging, aged wild-type mice also showed hypoacetylation of H4K16. The above results shed light on how chromatin modifications regulate the DNA damage response and suggest that the reversal of epigenetic marks could make an attractive therapeutic target against laminopathy-based progeroid pathologies.

Aging and chronic DNA damage response activate a regulatory pathway involving miR-29 and p53

Aging is a multifactorial process that affects most of the biological functions of the organism and increases susceptibility to disease and death. Recent studies with animal models of accelerated aging have unveiled some mechanisms that also operate in physiological aging. However, little is known about the role of microRNAs (miRNAs) in this process. To address this question, we have analysed miRNA levels in Zmpste24-deficient mice, a model of Hutchinson-Gilford progeria syndrome. We have found that expression of the miR-29 family of miRNAs is markedly upregulated in Zmpste24(-/-) progeroid mice as well as during normal aging in mouse. Functional analysis revealed that this transcriptional activation of miR-29 is triggered in response to DNA damage and occurs in a p53-dependent manner since p53(-/-) murine fibroblasts do not increase miR-29 expression upon doxorubicin treatment. We have also found that miR-29 represses Ppm1d phosphatase, which in turn enhances p53 activity. Based on these results, we propose the existence of a novel regulatory circuitry involving miR-29, Ppm1d and p53, which is activated in aging and in response to DNA damage.

NO points to epigenetics in vascular development

Our understanding of epigenetic mechanisms important for embryonic vascular development and cardiovascular differentiation is still in its infancy. Although molecular analyses, including massive genome sequencing and/or in vitro/in vivo targeting of specific gene sets, has led to the identification of multiple factors involved in stemness maintenance or in the early processes of embryonic layers specification, very little is known about the epigenetic commitment to cardiovascular lineages. The object of this review will be to outline the state of the art in this field and trace the perspective therapeutic consequences of studies aimed at elucidating fundamental epigenetic networks. Special attention will be paid to the emerging role of nitric oxide in this field.

Rejuvenating somatotropic signaling: a therapeutical opportunity for premature aging?

We have recently reported that progeroid Zmpste24-/- mice, which exhibit multiple defects that phenocopy Hutchinson-Gilford progeria syndrome, show a profound dysregulation of somatotropic axis, mainly characterized by the occurrence of very high circulating levels of growth hormone (GH) and a drastic reduction in insulin-like growth factor-1 (IGF-1). We have also shown that restoration of the proper GH/IGF-1 balance in Zmpste24-/- mice by treatment with recombinant IGF-1 delays the onset of many progeroid features in these animals and significantly extends their lifespan. Here, we summarize these observations and discuss the importance of GH/IGF-1 balance in longevity as well as its modulation as a putative therapeutic strategy for the treatment of human progeroid syndromes.