The impact of DNA damage, genetic mutation and cellular responses on cancer prevention, longevity and aging: observations in humans and mice

Over the past 5 years, data collected from the mouse suggest that pathways important for either preventing or resolving DNA damage are longevity assurance mechanisms whose critical overall function is somatic cell maintenance, a necessary part of cancer prevention. These pathways include those that reduce DNA damage levels caused by exogenous sources, replication errors and by-products of cellular respiration. Unresolved DNA damage leads to permanent mutations in the genetic code that may be oncogenic. Therefore, pathways that resolve DNA damage are important anti-cancer mechanisms. As an important line of defense, there are a variety of pathways that repair DNA damage. In addition, there are anti-cancer pathways that respond to DNA damage by either preventing cellular replication or inducing cell death. Genes in these pathways, termed longevity assurance genes (LAG), code for proteins that reduce cancer incidence and as a result assures a sufficiently long health span needed for reproduction. Data from mouse models, many that were originally designed to study cancer, are showing that a potential consequence of DNA damage and responses to DNA damage is aging; these models support the hypothesis that at least some aspects of normal aging are the consequence of anticancer mechanisms designed to deal with damaged DNA.     

Menopause and aging: Changes in the immune system—A review

Background

The higher risk of women developing autoimmune diseases suggests that immune system is mediated by sex steroids.

Objective

To review the effects of aging and menopause in immune system.

Methods

A systematic review of in vitro, animal and human studies involving aging and menopause and immune system was carried out. An electronic search based on Internet search engines, MEDLINE (1966–June 2010) and the Cochrane Controlled Clinical Trials Register was done.

Results

After crossing-cleaning the reference lists, a total of 688 studies dealing with immune system and menopause were identified. Of them, 30 were considered selectable. The concept of immunosenescence reflects changes in both cellular and serological immune responses throughout the process of generating specific response to foreign antigens. This may be related with a higher incidence of infectious and chronic diseases. After menopause, there is an increase in pro-inflammatory serum markers (IL1, IL6, TNF-alpha), an increase in response of the immune blood cells to these cytokines, a decrease in CD4 T and B lymphocytes and a decrease in the cytotoxic activity of NK cells. Additionally, IL-6 is a key factor in bone resorption and also seems to be associated with other diseases more common after menopause such as diabetes, atherosclerosis and cardiovascular disease.

Conclusions

Most of the studies suggested that in addition to age, in postmenopausal women, changes of the immune system have been attributed to estrogen deprivation. Furthermore, recent studies point out changes in immune response related to use or cessation of hormone replacement at menopause.     

Biallelic variants in CRIPT cause a Rothmund-Thomson-like syndrome with increased cellular senescence

PurposeRothmund-Thomson syndrome (RTS) is characterized by poikiloderma, sparse hair, small stature, skeletal defects, cancer, and cataracts, resembling features of premature aging. RECQL4 and ANAPC1 are the 2 known disease genes associated with RTS in >70% of cases. We describe RTS-like features in 5 individuals with biallelic variants in CRIPT (OMIM 615789).MethodsTwo newly identified and 4 published individuals with CRIPT variants were systematically compared with those with RTS using clinical data, computational analysis of photographs, histologic analysis of skin, and cellular studies on fibroblasts.ResultsAll CRIPT individuals fulfilled the diagnostic criteria for RTS and additionally had neurodevelopmental delay and seizures. Using computational gestalt analysis, CRIPT individuals showed greatest facial similarity with individuals with RTS. Skin biopsies revealed a high expression of senescence markers (p53/p16/p21) and the senescence-associated ß-galactosidase activity was elevated in CRIPT-deficient fibroblasts. RECQL4- and CRIPT-deficient fibroblasts showed an unremarkable mitotic progression and unremarkable number of mitotic errors and no or only mild sensitivity to genotoxic stress by ionizing radiation, mitomycin C, hydroxyurea, etoposide, and potassium bromate.ConclusionCRIPT causes an RTS-like syndrome associated with neurodevelopmental delay and epilepsy. At the cellular level, RECQL4- and CRIPT-deficient cells display increased senescence, suggesting shared molecular mechanisms leading to the clinical phenotypes.     

Age-related changes in the structure and function of chromatin: a review

Due to rapid advancement in biochemical and biophysical techniques during the last decade, extensive studies have been undertaken to understand the structure and function of chromatin. Several interesting results have been reported regarding the changes in basic organization and function of chromatin during the life time of a eukaryotic cell. The data accumulated so far have been obtained with different organs and organisms and widely differing methods, and the conclusions drawn from them are sometimes contradictory. In this paper, therefore, the available data on the age-associated alterations in the composition, structure and function of chromatin have been discussed, and an attempt has been made to correlate the structural changes in chromatin with alteration in gene expression during aging.     

Human cytomegalovirus infection and T cell immunosenescence: a mini review

The mammalian immune system defends the organism against pathogens, and possibly cancer, but is known to become dysregulated with increasing age. This results in greater morbidity and mortality due to infectious disease in old people. The most important changes occur in T cell immunity, manifested sometimes dramatically as altered clonal expansions of cells of limited antigen specificity and a marked shrinkage of the T cell antigen receptor repertoire. At the same time, it was independently reported that CMV seropositivity was associated with many of the same T cell changes that were being identified as biomarkers of immune ageing. It has now become clear that CMV is commonly the driving force behind the oligoclonal expansions and altered phenotypes and functions of CD8 cells seen in most old people. These changes are much less obvious in centenarians and most extreme in people whom longitudinal studies have shown to possess an "immune risk profile". This is a cluster of immunological parameters of which CMV seropositivity is one component and which predicts incipient mortality in an elderly population. Taken together, these findings suggest the hypothesis that persistence of CMV as a chronic antigenic stressor is a major contributor to immunosenescence and associated mortality.     

Folate, DNA damage and the aging brain

Folate plays an essential role as a methyl donor for the synthesis of DNA nucleotides such as thymine and, via S-adenosylmethionine, for maintenance of methylation of cytosine which is required for control of gene expression and for chromatin structure in critical regions of the genome such as centromeres and the subtelomere. If folate is deficient, damage to nuclear and mitochondrial DNA increases and regenerative potential of normal tissues declines. Folate deficiency may contribute to the high burden of DNA damage consistently observed in neurodegenerative disease by causing excessive incorporation of uracil into the genome and increasing susceptibility to DNA damage by causative agents such as Aβ42 and reactive oxygen species. In this brief review the current evidence that folate deficiency and associated metabolites, such as homocysteine, may accelerate DNA damage and aging of the brain is explored and important knowledge gaps are identified.     

The AIM2 inflammasome: Sensor of pathogens and cellular perturbations

Recognition of pathogens and altered self must be efficient and highly specific to orchestrate appropriate responses while limiting excessive inflammation and autoimmune reaction to normal self. AIM2 is a member of innate immune sensors that detects the presence of DNA, arguably the most conserved molecules in living organisms. However, AIM2 achieves specificity by detecting altered or mislocalized DNA molecules. It can detect damaged DNA, and the aberrant presence of DNA within the cytosolic compartment such as genomic DNA released into the cytosol upon loss of nuclear envelope integrity. AIM2 is also a key sensor of pathogens that detects the presence of foreign DNA accumulating in the cytosol during the life cycle of intracellular pathogens including viruses, bacteria, and parasites. AIM2 activation initiates the assembly of the inflammasome, an innate immune complex that leads to the activation of inflammatory caspases. This triggers the maturation and secretion of the cytokines IL-1β and IL-18. It can also initiate pyroptosis, a proinflammatory form of cell death. The AIM2 inflammasome contributes to physiological responses and diseases. It is a key player in host defenses, but its deregulation can contribute immune-linked diseases, such as autoinflammatory and autoimmune pathologies. Moreover, AIM2 may play a role in cancer development. Recent studies have shown that the detection of self-DNA species by AIM2 is an important factor that contributes to diseases associated with perturbation of cellular homeostasis. Thus, in addition of being a sensor of pathogen associated molecular patterns (PAMPs), the AIM2 inflammasome is emerging as a key guardian of cellular integrity.     

Genome reorganization during cellular senescence

It was previously suggested that aging of dividing cells depends on the reorganization of the cell genome during the division cycle and is determined by chance, intrinsic properties of the genome and environmental factors. A considerable amount of evidence has accumulated supporting the hypothesis. This is reviewed in terms of the reorganization taking place at the different orders of DNA structure.     

Changes in endogenous DNA damage in aging mice in response to butylated hydroxyanisole and oltipraz

The extent of DNA damage (single strand breaks) was measured in the livers of female Swiss-Webster mice up to 24 months of age. The effects of the antioxidants butylated hydroxyanisole (BHA) and oltipraz on this DNA damage were also measured. Oltipraz is an antioxidant which is structurally related to compounds found in cruciferous vegetables. From 6 months on the extent of DNA damage increased, reaching a maximum about 18 months old. Limited administration of both BHA and oltipraz to mice significantly reduced the levels of hepatic DNA damage.     

The emerging role of ECM crosslinking in T cell mobility as a hallmark of immunosenescence in humans

Immunosenescence is thought to result from cellular aging and to reflect exposure to environmental stressors and antigens, including cytomegalovirus (CMV). However, not all of the features of immunosenescence are consistent with this view, and this has led to the emergence of the sister theory of “inflammaging”. The recently discovered diffuse tissue distribution of resident memory T cells (T_RM) which don't recirculate, calls these theories into question. These cells account for most T cells residing in barrier epithelia which sit in and travel through the extracellular matrix (ECM). With almost all studies to date carried out on peripheral blood, the age-related changes of the ECM and their consequences for T cell mobility, which is crucial for the function of these cells, have been largely ignored. We propose an update of the theoretical framework of immunosenescence, based on a novel hypothesis: the increasing stiffness and cross-linking of the senescent ECM lead to a progressive immunodeficiency due to an age-related decrease in T cell mobility and eventually the death of these cells. A key element of this mechanism is the mechanical stress to which the cell cytoplasm and nucleus are subjected during passage through the ECM. This hypothesis is based on an “evo-devo” perspective bringing together some major characteristics of aging, to create a single interpretive framework for immunosenescence.     

Adeno-associated virus and adenovirus coinfection induces a cellular DNA damage and repair response via redundant phosphatidylinositol 3-like kinase pathways

During adeno-associated virus and adenovirus (AAV/Ad) coinfection, accumulation of viral genomes and proteins can alter cellular stress responses. To determine how AAV/Ad coinfection affects the host we screened over 60 cellular proteins for their responses. AAV/Ad coinfections induce a robust DNA damage response (DDR) that is distinct from that induced by Ad infection alone. Using chemical inhibitors, deficient cell lines and siRNA knockdowns of the DDR kinases, ATM, ATR and DNA-PK, we determined that DNA-PK and ATM kinases are the initial transducers of this response. AAV/Ad coinfection induces ATM- and DNA-PK mediated phosphorylation of RPA2, NBS1, H2AX and the checkpoint kinases CHK1/2. Inhibition of one or more of the DDR kinases reduces the level of phosphorylation of downstream targets but does not dramatically reduce Ad or AAV protein expression. However, AAV DNA levels are moderately affected by kinase inhibition. These experiments provide new insights into the cellular responses to AAV/Ad coinfections.     

Repair of persistent strand breaks in the mitochondrial genome

Oxidative DNA damage has been attributed to increased cancer incidence and premature aging phenotypes. Reactive oxygen species (ROS) are unavoidable byproducts of oxidative phosphorylation and are the major contributors of endogenous oxidative damage. To prevent the negative effects of ROS, cells have developed DNA repair mechanisms designed to specifically combat endogenous DNA modifications. The base excision repair (BER) pathway is primarily responsible for the repair of small non-helix distorting lesions and DNA single strand breaks. This repair pathway is found in all organisms, and in mammalian cells, consists of three related sub-pathways: short patch (SP-BER), long patch (LP-BER) and single strand break repair (SSBR). While much is known about nuclear BER, comparatively little is known about this pathway in the mitochondria, particularly the LP-BER and SSBR sub-pathways. There are a number of proteins that have recently been found to be involved in mitochondrial BER, including Cockayne syndrome proteins A and B (CSA and CSB), aprataxin (APTX), tryosyl-DNA phosphodiesterase 1 (TDP1), flap endonuclease 1 (FEN-1) and exonuclease G (EXOG). These significant advances in mitochondrial DNA repair may open new avenues in the management and treatment of a number of neurological disorders associated with mitochondrial dysfunction, and will be reviewed in further detail herein.     

Impaired in vivo CD4+ T cell expansion and differentiation in aged mice is not solely due to T cell defects: decreased stimulation by aged dendritic cells

CD4+ T cells regulate humoral and cell-mediated immune responses, which are progressively impaired in aging, resulting in susceptibility to infections and cancer. Dendritic cells (DCs) are major activators of T cells, providing signals that drive their expansion and differentiation. In this study, we asked if decreased CD4+ T cell responses were influenced by the age of DCs rather than being exclusively due to T cell defects. Old T cells transferred to young recipients expanded and differentiated similarly to young T cells. However, aged recipients were poor stimulators of both old and young T cells, which failed to acquire CD44 expression and produce interferon gamma (IFN-γ). DCs in aged hosts expressed fewer MHC-peptide complexes. The CD86 expression in the DCs of both hosts was similar; however, CD40 levels were reduced in old DCs. Finally, old DCs failed to produce inflammatory cytokines in response to LPS. Our results indicate that the impairment of aged CD4+ T cell function is intimately related to multiple alterations in aged DCs, rather than being caused solely by intrinsic T cell defects, suggesting that the function of aged T cells may be partially rescued in vivo when appropriate stimulation is applied. These findings are relevant to vaccination design for elderly populations.     

2nd German-French DNA repair meeting - DNA damage and repair in ageing and degenerative diseases, Konstanz, Germany, September 20-23, 2009

In September 2009, the French Society of Genetic Toxicology and the German Society for Research on DNA Repair jointly organized the ‘2nd German-French DNA repair meeting - DNA damage and repair in ageing and degenerative diseases’, which was held in Konstanz, Germany. Here we summarize the content of the oral presentations given in the various scientific sessions and of prize-winning posters.     

Immunoproteasomes and immunosenescence

Aging is a complex process which is accompanied with the decline and the reshaping of different functions of the body. In particular the immune system is characterized, during ageing (immunosenescence) by a remodeling of innate immunity (well preserved, up-regulated) and clonotypical immunity (severely altered) and by the occurrence of a chronic inflammatory process (inflammaging) which are, at least in part, genetically controlled. In this scenario, it can be anticipated that a crucial role is played by age-related structural and functional alterations and modifications of proteasomes and immunoproteasomes, the last being a key component of antigen processing and MHC class I antigen presentation. A variety of experimental data are available, suggesting that proteasomes are affected by age, and that in centenarians they are relatively preserved. On the contrary, few data are available on immunoproteasomes, likely as a consequence of the poverty of suitable cellular models. Lymphoblastoid cell lines from EBV immortalized B cells from old donors is envisaged as a possible model for the study of immunoproteasomes in humans and their changes with age. Thus, basic questions such as those related to possible consequences, for immune responses in infectious diseases and cancer, of age-related alterations of antigen processing and presenting, change with age of self-antigen repertoire, and the genetic basis of immunoproteasome activity and its change with age, remain largely unanswered.     

Immunosenescence and inflammaging in the aging process: age-related diseases or longevity?

During aging the immune system (IS) undergoes remarkable changes that collectively are known as immunosenescence. It is a multifactorial and dynamic phenomenon that affects both natural and acquired immunity and plays a critical role in most chronic diseases in older people. For a long time, immunosenescence has been considered detrimental because it may lead to a low-grade, sterile chronic inflammation we proposed to call "inflammaging" and a progressive reduction in the ability to trigger effective antibody and cellular responses against infections and vaccinations. Recently, many scientists revised this negative meaning because it can be considered an essential adaptation/remodeling resulting from the lifelong immunological biography of single individuals from an evolutionary perspective. Inflammaging can be considered an adaptive process because it can trigger an anti-inflammatory response to counteract the age-related pro-inflammatory environment. Centenarians represent a valuable model to study the beneficial changes occurring in the IS with age. These extraordinary individuals reached the extreme limits of human life by slowing down the aging process and, in most cases, delaying, avoiding or surviving the major age-associated diseases. They indeed show a complex and heterogeneous phenotype determined by an improved ability to adapt and remodel in response to harmful stimuli. This review aims to point out the intimate relationship between immunosenescence and inflammaging and how these processes impact unsuccessful aging rather than longevity. We also describe the gut microbiota age-related changes as one of the significant triggers of inflammaging and the sex/gender differences in the immune system of the elderly, contributing to the sex/gender disparity in terms of epidemiology, pathophysiology, symptoms and severity of age-related diseases. Finally, we discuss how these phenomena could influence the susceptibility to COVID-19 infection.     

Can exercise-related improvements in immunity influence cancer prevention and prognosis in the elderly?

Cancer incidence increases with advancing age. Over 60% of new cancers and 70% of cancer deaths occur in individuals aged 65 years or older. One factor that may contribute to this is immunosenescence – a canopy term that is used to describe age-related declines in the normal functioning of the immune system. There are multiple age-related deficits in both the innate and adaptive systems that may play a role in the increased incidence of cancer. These include decreased NK-cell function, impaired antigen uptake and presentation by monocytes and dendritic cells, an increase in ‘inflammaging’, a decline in the number of naïve T-cells able to respond to evolving tumor cells, and an increase in functionally exhausted senescent cells. There is consensus that habitual physical exercise can offer protection against certain types of cancer; however the evidence linking immunological mechanisms, exercise, and reduced cancer risk remain tentative. Multiple studies published over the last two decades suggest that exercise can mitigate the deleterious effects of age on immune function, thus increasing anti-cancer immunity. The potential ameliorative effect of exercise on these mechanisms include evidence that physical activity is able to stimulate greater NK-cell activity, enhance antigen-presentation, reduce inflammation, and prevent senescent cell accumulation in the elderly. Here we discuss the role played by the immune system in preventing and controlling cancer and how aging may retard these anti-cancer mechanisms. We also propose a pathway by which exercise-induced alterations in immunosenescence may decrease the incidence of cancer and help improve prognosis in cancer patients.     

Phytoestrogens and cognitive function: a review

Neuroprotective effects of phytoestrogen compounds (found in soy) have been demonstrated in animal research and cell culture studies. In particular, phytoestrogens have been shown to reduce Alzheimer's Disease (AD) related pathology, potentially alleviating risk of AD progression. In addition to their antioxidant properties, soy products also have the ability to affect cognition via interaction with estrogen receptors. However, observational studies and randomised controlled trials in humans have resulted in inconclusive findings within this domain. There are several possible reasons for these discrepant data. Studies which report no effect of phytoestrogens on cognition have mainly been carried out in European cohorts, with an average low dietary consumption. In contrast, investigation of Asian populations, with a higher general intake of tofu (a non-fermented soy product) have shown negative associations with cognitive function in those over the age of 65. Consideration of type of soy product is important, as in the latter sample, protective effects of tempe (fermented soy) were also observed. Limited data provide evidence that effects of phytoestrogens on cognition may be modified by dosage, duration of consumption and cognitive test used. Additionally, characteristics of the study population including age, gender, ethnicity and menopausal status appear to be mediating variables. Phytoestrogen treatment interventions have also shown time-limited positive effects on cognition. These findings are consistent with estrogen treatment studies, where initial positive short-term cognitive effects may occur, which reverse with long-term continuous use in elderly women. Well controlled, large scale studies are needed to assess the effects of phytoestrogens on the aging brain and provide further understanding of this association.     

From DNA damage to mutations: All roads lead to aging

Damage to the repository of genetic information in cells has plagued life since its very beginning 3–4 billion years ago. Initially, in the absence of an ozone layer, especially damage from solar UV radiation must have been frequent, with other sources, most notably endogenous sources related to cell metabolism, gaining in importance over time. To cope with this high frequency of damage to the increasingly long DNA molecules that came to encode the growing complexity of cellular functions in cells, DNA repair evolved as one of the earliest genetic traits. Then as now, errors during the repair of DNA damage generated mutations, which provide the substrate for evolution by natural selection. With the emergence of multicellular organisms also the soma became a target of DNA damage and mutations. In somatic cells selection against the adverse effects of DNA damage is greatly diminished, especially in postmitotic cells after the age of first reproduction. Based on an abundance of evidence, DNA damage is now considered as the single most important driver of the degenerative processes that collectively cause aging. Here I will first briefly review the evidence for DNA damage as a cause of aging since the beginning of life. Then, after discussing the possible direct adverse effects of DNA damage and its cellular responses, I will provide an overview of the considerable progress that has recently been made in analyzing a major consequence of DNA damage in humans and other complex organisms: somatic mutations and the resulting genome mosaicism. Recent advances in studying somatic mutagenesis and genome mosaicism in different human and animal tissues will be discussed with a focus on the possible mechanisms through which loss of DNA sequence integrity could cause age-related functional decline and disease.     

The decreased exclusion of nuclear eccDNA: From molecular and subcellular levels to human aging and age-related diseases

Extrachromosomal circular DNA (eccDNA) accumulates within the nucleus of eukaryotic cells during physiological aging and in age-related diseases (ARDs) and the accumulation could be caused by the declined exclusion of nuclear eccDNA in these states. This review focuses on the formation of eccDNA and the roles of some main factors, such as nuclear pore complexes (NPCs), nucleoplasmic reticulum (NR), and nuclear actin, in eccDNA exclusion. eccDNAs are mostly formed from non-coding DNA during DNA damage repair. They move to NPCs along nuclear actin and are excluded out of the nucleus through functional NPCs in young and healthy cells. However, it has been demonstrated that defective NPCs, abnormal NPC components and nuclear actin rods are increased in aged cells, various cancers and certain other ARDs such as cardiovascular diseases, premature aging, neurodegenerative diseases and myopathies. Therefore, mainly resulting from the increase of dysfunctional NPCs, the exclusion of nuclear eccDNAs may be reduced and eccDNAs thus accumulate within the nucleus in aging and the aforementioned ARDs. In addition, the protective function of non-coding DNA in tumorigenesis is further discussed.