Cell senescence: role in aging and age-related diseases

Inhibitory immune checkpoints suppress the surveillance of senescent cells promoting their accumulation with aging and in age-related diseases

The accumulation of pro-inflammatory senescent cells within tissues is a common hallmark of the aging process and many age-related diseases. This modification has been called the senescence-associated secretory phenotype (SASP) and observed in cultured cells and in cells isolated from aged tissues. Currently, there is a debate whether the accumulation of senescent cells within tissues should be attributed to increased generation of senescent cells or to a defect in their elimination from aging tissues. Emerging studies have revealed that senescent cells display an increased expression of several inhibitory immune checkpoint ligands, especially those of the programmed cell death protein-1 (PD-1) ligand-1 (PD-L1) proteins. It is known that the PD-L1 ligands, especially those of cancer cells, target the PD-1 receptor of cytotoxic CD8+ T and natural killer (NK) cells disturbing their functions, e.g., evoking a decline in their cytotoxic activity and promoting their exhaustion and even apoptosis. An increase in the level of the PD-L1 protein in senescent cells was able to suppress their immune surveillance and inhibit their elimination by cytotoxic CD8+ T and NK cells. Senescent cells are known to express ligands for several inhibitory immune checkpoint receptors, i.e., PD-1, LILRB4, NKG2A, TIM-3, and SIRPα receptors. Here, I will briefly describe those pathways and examine whether these inhibitory checkpoints could be involved in the immune evasion of senescent cells with aging and age-related diseases. It seems plausible that an enhanced inhibitory checkpoint signaling can prevent the elimination of senescent cells from tissues and thus promote the aging process.

Natural Products to Promote Vascular Health

Maintaining good vascular health is a major component in healthy ageing as it reduces the risk of cardiovascular diseases. Endothelial dysfunction, in particular, is a key mechanism in the development of major cardiovascular diseases including hypertension, atherosclerosis and diabetes. Recently, endothelial senescence has emerged as a pivotal early event in age-related endothelial dysfunction. Endothelial function is characterized by an imbalance between the endothelial formation of vasoprotective mechanisms, including the formation of nitric oxide (NO) and endothelium-dependent hyperpolarization responses, and an increased level of oxidative stress involving several pro-oxidant enzymes such as NADPH oxidases and, often also, the appearance of cyclooxygenase-derived vasoconstrictors. Pre-clinical studies have indicated that natural products, in particular several polyphenol-rich foods, can trigger activating pathways in endothelial cells promoting an increased formation of NO and endothelium-dependent hyperpolarization. In addition, some can even exert beneficial effects on endothelial senescence. Moreover, some of these products have been associated with the prevention and/or improvement of established endothelial dysfunction in several experimental models of cardiovascular diseases and in humans with cardiovascular diseases. Therefore, intake of certain natural products, such as dietary and plant-derived polyphenol-rich products, appears to be an attractive approach for a healthy vascular system in ageing.

Investigating the Effects of Chelidonic Acid on Oxidative Stress-Induced Premature Cellular Senescence in Human Skin Fibroblast Cells

This study investigated the effects of chelidonic acid (CA) on hydrogen peroxide (H2O2) induced cellular senescence in human skin fibroblast cells (BJ). Cellular senescence is a critical mechanism that is linked to age-related diseases and chronic conditions. CA, a γ-pyrone compound known for its broad pharmacological activity, was assessed for its potential to mitigate oxidative stress and alter senescence markers. A stress-induced premature senescence (SIPS) model was designed in BJ fibroblast cells using the oxidative stress agent H2O2. After this treatment, cells were treated with CA, and the potential effect of CA on senescence was evaluated using senescence-related β-galactosidase, 4',6-diamino-2-phenylindole (DAPI), acridine-orange staining (AO), comet assay, molecular docking assays, gene expression, and protein analysis. These results demonstrate that CA effectively reduces senescence markers, including senescence-associated β-galactosidase activity, DNA damage, lysosomal activity, and oxidative stress indicators such as malondialdehyde. Molecular docking revealed CA's potential interactions with critical proteins involved in senescence signalling pathways, suggesting mechanisms by which CA may exert its effects. Gene expression and protein analyses corroborated the observed anti-senescent effects, with CA modulating p16, p21, and pRB1 expressions and reducing oxidative stress markers. In conclusion, CA appeared to have senolytic and senomorphic potential in vitro, which could mitigate and reverse SIPS markers in BJ fibroblasts.

Challenges and Future Perspectives in Modeling Neurodegenerative Diseases Using Organ-on-a-Chip Technology

Neurodegenerative diseases (NDDs) affect more than 50 million people worldwide, posing a significant global health challenge as well as a high socioeconomic burden. With aging constituting one of the main risk factors for some NDDs such as Alzheimer's disease (AD) and Parkinson's disease (PD), this societal toll is expected to rise considering the predicted increase in the aging population as well as the limited progress in the development of effective therapeutics. To address the high failure rates in clinical trials, legislative changes permitting the use of alternatives to traditional pre-clinical in vivo models are implemented. In this regard, microphysiological systems (MPS) such as organ-on-a-chip (OoC) platforms constitute a promising tool, due to their ability to mimic complex and human-specific tissue niches in vitro. This review summarizes the current progress in modeling NDDs using OoC technology and discusses five critical aspects still insufficiently addressed in OoC models to date. Taking these aspects into consideration in the future MPS will advance the modeling of NDDs in vitro and increase their translational value in the clinical setting.

Senescence and senolysis in cancer: The latest findings

Aging is a life phenomenon that occurs in most living organisms and is a major risk factor for many diseases, including cancer. Cellular senescence is a cellular trait induced by various genomic and epigenetic stresses. Senescent cells are characterized by irreversible cell growth arrest and excessive secretion of inflammatory cytokines (senescence-associated secretory phenotypes, SASP). Chronic tissue microinflammation induced by SASP contributes to the pathogenesis of a variety of age-related diseases, including cancer. Senolysis is a promising new strategy to selectively eliminate senescent cells in order to suppress chronic inflammation, suggesting its potential use as an anticancer therapy. This review summarizes recent findings on the molecular basis of senescence in cancer cells and senolysis.

The role of the immunosuppressive PD-1/PD-L1 checkpoint pathway in the aging process and age-related diseases

The accumulation of senescent cells within tissues is a hallmark of the aging process. Senescent cells are also commonly present in many age-related diseases and in the cancer microenvironment. The escape of abnormal cells from immune surveillance indicates that there is some defect in the function of cytotoxic immune cells, e.g., CD8+ T cells and natural killer (NK) cells. Recent studies have revealed that the expression of programmed death-ligand 1 (PD-L1) protein is abundantly increased in senescent cells. An increase in the amount of PD-L1 protein protects senescent cells from clearance by the PD-1 checkpoint receptor in cytotoxic immune cells. In fact, the activation of the PD-1 receptor suppresses the cytotoxic properties of CD8+ T and NK cells, promoting a state of immunosenescence. The inhibitory PD-1/PD-L1 checkpoint pathway acts in cooperation with immunosuppressive cells; for example, activation of PD-1 receptor can enhance the differentiation of regulatory T cells (Treg), myeloid-derived suppressor cells (MDSC), and M2 macrophages, whereas the cytokines secreted by immunosuppressive cells stimulate the expression of the immunosuppressive PD-L1 protein. Interestingly, many signaling pathways known to promote cellular senescence and the aging process are crucial stimulators of the expression of PD-L1 protein, e.g., epigenetic regulation, inflammatory mediators, mTOR-related signaling, cGAS-STING pathway, and AhR signaling. It seems that the inhibitory PD-1/PD-L1 immune checkpoint axis has a crucial role in the accumulation of senescent cells and thus it promotes the aging process in tissues. Thus, the blockade of the PD-1/PD-L1 checkpoint signaling might be a potential anti-aging senolytic therapy. KEY MESSAGES: Senescent cells accumulate within tissues during aging and age-related diseases. Senescent cells are able to escape immune surveillance by cytotoxic immune cells. Expression of programmed death-ligand 1 (PD-L1) markedly increases in senescent cells. Age-related signaling stimulates the expression of PD-L1 protein in senescent cells. Inhibitory PD-1/PD-L1 checkpoint pathway suppresses clearance of senescent cells.

SuperAgers and centenarians, dynamics of healthy ageing with cognitive resilience

Graceful healthy ageing and extended longevity is the most desired goal for human race. The process of ageing is inevitable and has a profound impact on the gradual deterioration of our physiology and health since it triggers the onset of many chronic conditions like dementia, osteoporosis, diabetes, arthritis, cancer, and cardiovascular disease. However, some people who lived/live more than 100 years called 'Centenarians" and how do they achieve their extended lifespans are not completely understood. Studying these unknown factors of longevity is important not only to establish a longer human lifespan but also to manage and treat people with shortened lifespans suffering from age-related morbidities. Furthermore, older adults who maintain strong cognitive function are referred to as "SuperAgers" and may be resistant to risk factors linked to cognitive decline. Investigating the mechanisms underlying their cognitive resilience may contribute to the development of therapeutic strategies that support the preservation of cognitive function as people age. The key to a long, physically, and cognitively healthy life has been a mystery to scientists for ages. Developments in the medical sciences helps us to a better understanding of human physiological function and greater access to medical care has led us to an increase in life expectancy. Moreover, inheriting favorable genetic traits and adopting a healthy lifestyle play pivotal roles in promoting longer and healthier lives. Engaging in regular physical activity, maintaining a balanced diet, and avoiding harmful habits such as smoking contribute to overall well-being. The synergy between positive lifestyle choices, access to education, socio-economic factors, environmental determinants and genetic supremacy enhances the potential for a longer and healthier life. Our article aims to examine the factors associated with healthy ageing, particularly focusing on cognitive health in centenarians. We will also be discussing different aspects of ageing including genomic instability, metabolic burden, oxidative stress and inflammation, mitochondrial dysfunction, cellular senescence, immunosenescence, and sarcopenia.

Interface between Resolvins and Efferocytosis in Health and Disease

Acute inflammation resolution acts as a vital process for active host response, tissue support, and homeostasis maintenance, during which resolvin D (RvD) and E (RvE) as mediators derived from omega-3 polyunsaturated fatty acids display specific and stereoselective anti-inflammations like restricting neutrophil infiltration and pro-resolving activities. On the other side of the coin, potent macrophage-mediated apoptotic cell clearance, namely efferocytosis, is essential for successful inflammation resolution. Further studies mentioned a linkage between efferocytosis and resolvins. For instance, resolvin D1 (RvD1), which is endogenously formed from docosahexaenoic acid within the inflammation resolution, thereby provoking efferocytosis. There is still limited information regarding the mechanism of action of RvD1-related efferocytosis enhancement at the molecular level. The current review article was conducted to explore recent data on how the efferocytosis process and resolvins relate to each other during the inflammation resolution in illness and health. Understanding different aspects of this connection sheds light on new curative approaches for medical conditions caused by defective efferocytosis and disrupted inflammation resolution.

SIRT1 safeguards adipogenic differentiation by orchestrating anti-oxidative responses and suppressing cellular senescence

Adipose tissue is an important endocrine organ that regulates metabolism, immune response and aging in mammals. Healthy adipocytes promote tissue homeostasis and longevity. SIRT1, a conserved NAD+-dependent deacetylase, negatively regulates adipogenic differentiation by deacetylating and inhibiting PPAR-γ. However, knocking out SIRT1 in mesenchymal stem cells (MSCs) in mice not only causes defects in osteogenesis, but also results in the loss of adipose tissues, suggesting that SIRT1 is also important for adipogenic differentiation.Here, we report that severe impairment of SIRT1 function in MSCs caused significant defects and cellular senescence during adipogenic differentiation. These were observed only when inhibiting SIRT1 during adipogenesis, not when SIRT1 inhibition was imposed before or after adipogenic differentiation. Cells generate high levels of reactive oxygen species (ROS) during adipogenic differentiation. Inhibiting SIRT1 during differentiation resulted in impaired oxidative stress response. Increased oxidative stress with H2O2 or SOD2 knockdown phenocopied SIRT1 inhibition. Consistent with these observations, we found increased p16 levels and senescence associated β-galactosidase activities in the inguinal adipose tissue of MSC-specific SIRT1 knockout mice. Furthermore, previously identified SIRT1 targets involved in oxidative stress response, FOXO3 and SUV39H1 were both required for healthy adipocyte formation during differentiation. Finally, senescent adipocytes produced by SIRT1 inhibition showed decreased Akt phosphorylation in response to insulin, a lack of response to adipocytes browning signals, and increased survival for cancer cells under chemotherapy drug treatments. These findings suggest a novel safeguard function for SIRT1 in regulating MSC adipogenic differentiation, distinct from its roles in suppressing adipogenic differentiation.

Antimullerian Hormone, a Marker of Ovarian Reserve, Is Protective Against Presence and Severity of NASH in Premenopausal Women

BACKGROUND & AIMS

Antimüllerian hormone (AMH) is a marker of ovarian reserve with emerging data linking lower levels to some metabolic and inflammatory diseases in women. Whether AMH levels influence nonalcoholic fatty liver disease (NAFLD) is unknown.

METHODS

Leveraging the NASH Clinical Research Network we determined the association of AMH levels within 6 months of liver biopsy with presence and severity of histologic measures of NAFLD in premenopausal women. Outcomes included presence of nonalcoholic steatohepatitis (NASH), presence and severity of fibrosis, and NAFLD Activity Score and its components. Logistic and ordinal logistic regression models were adjusted for age, race/ethnicity, homeostatic model assessment for insulin resistance, body mass index, dyslipidemia, polycystic ovary syndrome, estrogen-progestin use, and menstrual cyclicity.

RESULTS

Median cohort age was 35 years; 73% were white and 24% Hispanic. Thirty-three percent had diabetes, 81% had obesity, and 95% had dyslipidemia. On biopsy 71% had NASH, 68% had any fibrosis, and 15% had advanced fibrosis. On adjusted analysis (n = 205), higher AMH quartiles were inversely associated with NAFLD histology including prevalent NASH (adjusted odds ratio [AOR], 0.64; 95% confidence interval [CI], 0.41-1.00), NAFLD Activity Score ≥5 (AOR, 0.52; 95% CI, 0.35-0.77), Mallory hyaline (AOR, 0.54; 95% CI, 0.35-0.82), and higher fibrosis stage (AOR, 0.70; 95% CI, 0.51-0.98). The protective effects of AMH were more pronounced among women without polycystic ovary syndrome (n = 164), including lower odds of NASH (AOR, 0.53; 95% CI, 0.32-0.90) and any NASH fibrosis (AOR, 0.54; 95% CI, 0.32-0.93).

CONCLUSIONS

AMH may reflect a unique biomarker of NASH in premenopausal women and findings suggest a novel link between reproductive aging and histologic severity of NAFLD in women.

The chemotherapeutic agent doxorubicin induces brain senescence, with modulation by APOE genotype

Many cancer patients experience serious cognitive problems related to their treatment, which can greatly affect their quality of life. The molecular mechanisms of this cancer chemotherapy-induced cognitive impairment (CICI) are unknown, thus slowing the development of preventative approaches. We hypothesized that cancer chemotherapies could induce cellular senescence in the brain, creating a pro-inflammatory environment and damaging normal brain communication. We tested this hypothesis using the common chemotherapeutic agent doxorubicin in two independent mouse models. In the first model, we used mice that express tdTomato under the pdkn2a (p16) promoter; p16 is a regulator of cellular senescence, and its upregulation is denoted by the presence of fluorescently tagged cells. Two weeks after exposure to three doses of 5 mg/kg doxorubicin, the number of tdTomato positive cells were increased nearly three-fold in both the cerebral cortex and the hippocampus. tdTomato staining co-localized with neurons, microglia, oligodendrocyte precursor cells, and endothelial cells, but not astrocytes. In the second model, we used APOE knock-in mice, since the APOE4 allele is a risk factor for CICI in humans and mouse models. We isolated RNA from the cerebral cortex of APOE3 and APOE4 mice from one to 21 days after a single dose of 10 mg/kg doxorubicin. Using NanoString analysis of over 700 genes related to neuroinflammation and RT-qPCR analysis of cerebral cortex transcripts, we found two-fold induction of four senescence-related genes at three weeks in the APOE4 mice compared to the APOE3 control mice: p21(cdkn1a), p16, Gadd45a, and Egr1. We conclude that doxorubicin promotes cellular senescence pathways in the brain, supporting the hypothesis that drugs to eliminate senescent cells could be useful in preventing CICI.

Trend of incidence rate of age-related diseases: results from the National Health Insurance Service-National Sample Cohort (NHIS-NSC) database in Korea: a cross- sectional study

BACKGROUND

This study aimed to identify and select age-related diseases (ARDs) in Korea, which is about to have a super-aged society, and to elucidate patterns in their incidence rates.

METHODS

The National Health Insurance Service-National Sample Cohort, comprising 1 million health insurance and medical benefit beneficiaries in Korea from 2002 to 2019, was utilized. We selected 14 diseases with high disease burden and prevalence among Koreans from the 92 diseases defined in the Global Burden of Diseases, Injuries, and Risk Factors Study as ARDs. The annual incidence rate represented the number of patients newly diagnosed with an ARD each year from 2006 to 2019, excluding those with a history of ARD diagnosis from 2002 to 2005. The incidence rate by age was categorized into 10-year units based on age as of 2019. The number of patients with ARDs in each age group was used as the numerator, and the incidence rate for each age group was calculated with the age group as the denominator.

RESULTS

Regarding the annual incidence rates of ARDs from 2006 to 2019, chronic obstructive pulmonary disease, congestive heart failure, and ischemic heart disease decreased annually, whereas dyslipidemia, chronic kidney disease, cataracts, hearing loss, and Parkinson's disease showed a significant increase. Hypertension, diabetes, cerebrovascular disease, osteoporosis, osteoarthritis, and age-related macular degeneration initially displayed a gradual decrease in incidence but exhibited a tendency to increase after 2015. Concerning age-specific incidence rates of ARDs, two types of curves emerged. The first type, characterized by an exponential increase with age, was exemplified by congestive heart failure. The second type, marked by an exponential increase peaking between ages 60 and 80, followed by stability or decrease, was observed in 13 ARDs, excluding congestive heart failure. However, hypertension, ischemic heart disease, cerebrovascular disease, chronic obstructive pulmonary disease, and hearing loss in men belonged to the first type.

CONCLUSIONS

From an epidemiological perspective, there are similar characteristics in age-specific ARDs that increase with age, reaching a peak followed by a plateau or decrease in Koreans.

A multi-omics integrative approach unravels novel genes and pathways associated with senescence escape after targeted therapy in NRAS mutant melanoma

Therapy Induced Senescence (TIS) leads to sustained growth arrest of cancer cells. The associated cytostasis has been shown to be reversible and cells escaping senescence further enhance the aggressiveness of cancers. Chemicals specifically targeting senescent cells, so-called senolytics, constitute a promising avenue for improved cancer treatment in combination with targeted therapies. Understanding how cancer cells evade senescence is needed to optimise the clinical benefits of this therapeutic approach. Here we characterised the response of three different NRAS mutant melanoma cell lines to a combination of CDK4/6 and MEK inhibitors over 33 days. Transcriptomic data show that all cell lines trigger a senescence programme coupled with strong induction of interferons. Kinome profiling revealed the activation of Receptor Tyrosine Kinases (RTKs) and enriched downstream signaling of neurotrophin, ErbB and insulin pathways. Characterisation of the miRNA interactome associates miR-211-5p with resistant phenotypes. Finally, iCell-based integration of bulk and single-cell RNA-seq data identifies biological processes perturbed during senescence and predicts 90 new genes involved in its escape. Overall, our data associate insulin signaling with persistence of a senescent phenotype and suggest a new role for interferon gamma in senescence escape through the induction of EMT and the activation of ERK5 signaling.

Cellular senescence exacerbates features of aging in the eyes

Aging is a process often associated with various age-related diseases. Senescence is one of the hallmarks of aging, and senescent cells acquire a complex, often pro-inflammatory, secretory phenotype termed the senescence-associated secretory phenotype (SASP). Here we show that ocular surface cells from human cornea become senescent upon X-irradiation, characterized by increased SA-β-gal activity, decreased cell proliferation, increased expression of p16, and disruption of epithelial barrier. Comprehensive transcriptomic and proteomic analysis revealed that human senescent ocular cells acquire a SASP that disrupts epithelial barrier function. During aging in mice, senescent ocular cells accumulate, resulting in decreased epithelial barrier and chronic inflammation. Lacrimal gland excision, which leads to symptoms of dry eye (DE), resulted in corneal opacity associated with severe angiogenesis only in aged mice but not in young mice, and early senolytic treatment protected old DE mice from corneal opacity. In conclusion, senescent cells alter the ocular microenvironment through their SASP and eliminating these cells could represent a potential approach to alleviate symptoms associated with aged ocular surface.

Impact of menopause on relapse rate and disability level in patients with multiple sclerosis (MS): a systematic review and meta-analysis

BACKGROUND

Menopause is a physiologic phase in women's lives. Findings regarding multiple sclerosis (MS) course through menopause are diverse. So, we designed this systematic review and meta-analysis to estimate the impact of menopause on relapse rate, and disability status in women with MS.

METHODS

PubMed, Scopus, EMBASE, Web of Science, and google scholar were systematically searched by two independent researchers on January 1st, 2023. They also evaluated conference abstracts, and references of the included studies. In addition, data regarding the total number of participants, name of the first author of the publication, publication year, country of origin, disease duration, disease type, annual relapse rate, and Expanded Disability Status Scale (EDSS) before and after menopause were recorded.

RESULTS

A literature search revealed 1024 records. Twenty-one full texts were evaluated, and finally, four studies were included for meta-analysis. Mean ARR before menopause ranged between 0.21 and 0.37, and after menopause ranged between 0.13 and 0.08. The SMD of mean ARR ranged between - 1.04, and - 0.29, while the pooled SMD was estimated as -0.52(95% CI: -0.88, -0.15) (I2 = 73.6%, P = 0.02). The mean EDSS before menopause ranged between 1.5 and 2, and after menopause ranged between 2 and 3.1. The SMD of EDSS ranged between 0.46, and 0.71. The pooled SMD of EDSS change (after menopause-before menopause) estimated as 0.56(95% CI: 0.38, 0.73)(I2 = 0, P = 0.4).

CONCLUSION

The result of this systematic review and meta-analysis show that menopause can be associated with relapse rate reduction, unlike increase in disease-related disability in women with MS.

Myofibroblast senescence promotes arrhythmogenic remodeling in the aged infarcted rabbit heart

Progressive tissue remodeling after myocardial infarction (MI) promotes cardiac arrhythmias. This process is well studied in young animals, but little is known about pro-arrhythmic changes in aged animals. Senescent cells accumulate with age and accelerate age-associated diseases. Senescent cells interfere with cardiac function and outcome post-MI with age, but studies have not been performed in larger animals, and the mechanisms are unknown. Specifically, age-associated changes in timecourse of senescence and related changes in inflammation and fibrosis are not well understood. Additionally, the cellular and systemic role of senescence and its inflammatory milieu in influencing arrhythmogenesis with age is not clear, particularly in large animal models with cardiac electrophysiology more similar to humans than previously studied animal models. Here, we investigated the role of senescence in regulating inflammation, fibrosis, and arrhythmogenesis in young and aged infarcted rabbits. Aged rabbits exhibited increased peri-procedural mortality and arrhythmogenic electrophysiological remodeling at the infarct border zone (IBZ) compared to young rabbits. Studies of the aged infarct zone revealed persistent myofibroblast senescence and increased inflammatory signaling over a 12-week timecourse. Senescent IBZ myofibroblasts in aged rabbits appear to be coupled to myocytes, and our computational modeling showed that senescent myofibroblast-cardiomyocyte coupling prolongs action potential duration (APD) and facilitates conduction block permissive of arrhythmias. Aged infarcted human ventricles show levels of senescence consistent with aged rabbits, and senescent myofibroblasts also couple to IBZ myocytes. Our findings suggest that therapeutic interventions targeting senescent cells may mitigate arrhythmias post-MI with age.

Aging microenvironment and antitumor immunity for geriatric oncology: the landscape and future implications

The tumor microenvironment (TME) has been extensively investigated; however, it is complex and remains unclear, especially in elderly patients. Senescence is a cellular response to a variety of stress signals, which is characterized by stable arrest of the cell cycle and major changes in cell morphology and physiology. To the best of our knowledge, senescence leads to consistent arrest of tumor cells and remodeling of the tumor-immune microenvironment (TIME) by activating a set of pleiotropic cytokines, chemokines, growth factors, and proteinases, which constitute the senescence-associated secretory phenotype (SASP). On the one hand, the SASP promotes antitumor immunity, which enhances treatment efficacy; on the other hand, the SASP increases immunosuppressive cell infiltration, including myeloid-derived suppressor cells (MDSCs), regulatory T cells (Tregs), M2 macrophages, and N2 neutrophils, contributing to TIME suppression. Therefore, a deeper understanding of the regulation of the SASP and components contributing to robust antitumor immunity in elderly individuals with different cancer types and the available therapies is necessary to control tumor cell senescence and provide greater clinical benefits to patients. In this review, we summarize the key biological functions mediated by cytokines and intercellular interactions and significant components of the TME landscape, which influence the immunotherapy response in geriatric oncology. Furthermore, we summarize recent advances in clinical practices targeting TME components and discuss potential senescent TME targets.

Role of Histone Variant H2A.J in Fine-Tuning Chromatin Organization for the Establishment of Ionizing Radiation-Induced Senescence

PURPOSE

Radiation-induced senescence is characterized by profound changes in chromatin organization with the formation of Senescence-Associated-Heterochromatin-Foci (SAHF) and DNA-Segments-with-Chromatin-Alterations-Reinforcing-Senescence (DNA-SCARS). Importantly, senescent cells also secrete complex combinations of pro-inflammatory factors, referred as Senescence-Associated-Secretory-Phenotype (SASP). Here, we analyzed the epigenetic mechanism of histone variant H2A.J in establishing radiation-induced senescence.

EXPERIMENTAL DESIGN

Primary and genetically-modified lung fibroblasts with down- or up-regulated H2A.J expression were exposed to ionizing radiation and were analyzed for the formation of SAHF and DNA-SCARS by immunofluorescence microscopy. Dynamic changes in chromatin organization and accessibility, transcription factor recruitment, and transcriptome signatures were mapped by ATAC-seq and RNA-seq analysis. The secretion of SASP factors and potential bystander effects were analyzed by ELISA and RT-PCR. Lung tissue of mice exposed to different doses were analyzed by the digital image analysis of H2A.J-immunohistochemistry.

RESULTS

Differential incorporation of H2A.J has profound effects on higher-order chromatin organization and on establishing the epigenetic state of senescence. Integrative analyses of ATAC-seq and RNA-seq datasets indicate that H2A.J-associated changes in chromatin accessibility of regulatory regions decisively modulates transcription factor recruitment and inflammatory gene expression, resulting in an altered SASP secretome. In lung parenchyma, pneumocytes show dose-dependent H2A.J expression in response to radiation-induced DNA damage, therefore contributing to pro-inflammatory tissue reactions.

CONCLUSIONS

The fine-tuned incorporation of H2A.J defines the epigenetic landscape for driving the senescence programme in response to radiation-induced DNA damage. Deregulated H2A.J deposition affects chromatin remodeling, transcription factor recruitment, and the pro-inflammatory secretome. Our findings provide new mechanistic insights into DNA-damage triggered epigenetic mechanisms governing the biological processes of radiation-induced injury.

Untangling senescent and damage-associated microglia in the aging and diseased brain

Microglial homeostasis has emerged as a critical mediator of health and disease in the central nervous system. In their neuroprotective role as the predominant immune cells of the brain, microglia surveil the microenvironment for debris and pathogens, while also promoting neurogenesis and performing maintenance on synapses. Chronological ageing, disease onset, or traumatic injury promotes irreparable damage or deregulated signaling to reinforce neurotoxic phenotypes in microglia. These insults may include cellular senescence, a stable growth arrest often accompanied by the production of a distinctive pro-inflammatory secretory phenotype, which may contribute to age- or disease-driven decline in neuronal health and cognition and is a potential novel therapeutic target. Despite this increased scrutiny, unanswered questions remain about what distinguishes senescent microglia and non-senescent microglia reacting to insults occurring in ageing, disease, and injury, and how central the development of senescence is in their pivot from guardian to assailant. To intelligently design future studies to untangle senescent microglia from other primed and reactionary states, specific criteria must be developed that define this population and allow for comparisons between different model systems. Comparing microglial activity seen in homeostasis, ageing, disease, and injury allows for a more coherent understanding of when and how senescent and other harmful microglial subpopulations should be targeted.

SATB2, coordinated with CUX1, regulates IL-1β-induced senescence-like phenotype in endothelial cells by fine-tuning the atherosclerosis-associated p16INK4a expression

Genome-wide association studies (GWAS) have validated a strong association of atherosclerosis with the CDKN2A/B locus, a locus harboring three tumor suppressor genes: p14ARF , p15INK4b , and p16INK4a . Post-GWAS functional analysis reveals that CUX is a transcriptional activator of p16INK4a via its specific binding to a functional SNP (fSNP) rs1537371 on the atherosclerosis-associated CDKN2A/B locus, regulating endothelial senescence. In this work, we characterize SATB2, another transcription factor that specifically binds to rs1537371. We demonstrate that even though both CUX1 and SATB2 are the homeodomain transcription factors, unlike CUX1, SATB2 is a transcriptional suppressor of p16INK4a and overexpression of SATB2 competes with CUX1 for its binding to rs1537371, which inhibits p16INK4a and p16INK4a -dependent cellular senescence in human endothelial cells (ECs). Surprisingly, we discovered that SATB2 expression is transcriptionally repressed by CUX1. Therefore, upregulation of CUX1 inhibits SATB2 expression, which enhances the binding of CUX1 to rs1537371 and subsequently fine-tunes p16INK4a expression. Remarkably, we also demonstrate that IL-1β, a senescence-associated secretory phenotype (SASP) gene itself and a biomarker for atherosclerosis, induces cellular senescence also by upregulating CUX1 and/or downregulating SATB2 in human ECs. A model is proposed to reconcile our findings showing how both primary and secondary senescence are activated via the atherosclerosis-associated p16INK4a expression.

Prolonged Rather Than Early Childhood Parent-Child Separation Predicts Change in Molecular Markers of Cellular Aging: A Consideration of the Role of Adolescence

Early life adversity is a major risk factor for the onset of psychopathology, and cellular aging may be a mechanism underlying these associations. It is unknown whether and how the pattern (timing and duration) of parent-child separation is associated with accelerated cellular aging, particularly with respect to functional aging and replicative senescence, indexed by mitochondrial DNA copy number (mtDNAcn) elevation and telomere length (TL) attrition. This cohort study included 252 rural adolescents (mean age 11.62 years, SD: 1.56). Nearly one in five participants were persistently separated from both parents since birth. Compared with participants who never separated from their parents, adolescents with prolonged parent-child separation had higher acceleration both in functional aging and replicative senescence of cells. However, that was not the case in adolescents who experienced parent-child separation in early childhood but regained stable parental care during adolescence. These findings indicate that pubertal development reopens a window of opportunity for buffering the adverse biological effect based on significant improvements in the supportiveness of the caregiving environment relative to that in childhood. Translating such knowledge to inform intervention and prevention strategies for youths exposed to adversity is a critical goal for the field.

[Cultured Cells in the Aging Research, Exhibiting Cell Surface Component Functions, Intracellular Signaling, a Novel Adaptor Molecule, Aging Phenotype Expression and Various Aspects of the Cellular Physiology]

Cellular aging is one of the most extraordinary phenomena that mammalian cells undergo in vivo and in vitro. We have been observing their behavior for approximately 4 decades and here would like to summarize some of our salient findings. Normal cells such as human diploid cells exhibit finite growth potential in vitro as well as a set of senescent cell phenotypes. Those changes appear probabilistic and irreversible. In the search of the factor(s) to evoke the features we have observed that cellular glycosaminoglycan molecules plays significant roles in the cell physiology. Besides, CCAAT-box binding transcription factor NF-Y relates to the aging-coupled changes in gene expression, and aging of gastric mucosal cells may relate to a decrease in cytoprotection. As to the intracellular signaling, we have confirmed that the breakdown of phosphatidylinositol bisphosphate is critical for mitogenesis by using micro-injection of its antibody. Subsequently, we have discovered a novel, pivotal adaptor protein Grb2/Ash, a missing link between the receptor tyrosine kinases and their downstream target Ras. The limiting factors for the cellular life span have been considered as telomere shortening and accumulation of cellular and genomic damages. We have observed that telomerase-expressing cells exhibit expanded division potential; yet oxidative stress similarly induces senescent cell phenotypes. Herein we have demonstrated that the treatment of senescent cells with nicotinamide or related reagents elicits unique cellular responses, which might indicate the capability of the cells to recover from the aging.

Identification and validation of biomarkers based on cellular senescence in mild cognitive impairment

Background

Mild cognitive impairment (MCI), a syndrome defined as decline of cognitive function greater than expected for an individual's age and education level, occurs in up to 22.7% of elderly patients in United States, causing the heavy psychological and economic burdens to families and society. Cellular senescence (CS) is a stress response that accompanies permanent cell-cycle arrest, which has been reported to be a fundamental pathological mechanism of many age-related diseases. This study aims to explore biomarkers and potential therapeutic targets in MCI based on CS.

Methods

The mRNA expression profiles of peripheral blood samples from patients in MCI and non-MCI group were download from gene expression omnibus (GEO) database (GSE63060 for training and GSE18309 for external validation), CS-related genes were obtained from CellAge database. Weighted gene co-expression network analysis (WGCNA) was conducted to discover the key relationships behind the co-expression modules. The differentially expressed CS-related genes would be obtained through overlapping among the above datasets. Then, pathway and GO enrichment analyses were performed to further elucidate the mechanism of MCI. The protein-protein interaction network was used to extract hub genes and the logistic regression was performed to distinguish the MCI patients from controls. The hub gene-drug network, hub gene-miRNA network as well as transcription factor-gene regulatory network were used to analyze potential therapeutic targets for MCI.

Results

Eight CS-related genes were identified as key gene signatures in MCI group, which were mainly enriched in the regulation of response to DNA damage stimulus, Sin3 complex and transcription corepressor activity. The receiver operating characteristic curves of logistic regression diagnostic model were constructed and presented great diagnostic value in both training and validation set.

Conclusion

Eight CS-related hub genes - SMARCA4, GAPDH, SMARCB1, RUNX1, SRC, TRIM28, TXN, and PRPF19 - serve as candidate biomarkers for MCI and display the excellent diagnostic value. Furthermore, we also provide a theoretical basis for targeted therapy against MCI through the above hub genes.

Endothelin A receptors contribute to senescence of brain microvascular endothelial cells

Cellular senescence plays a pivotal role in the aging and progression of neurodegenerative diseases, including vascular cognitive impairment and dementia (VCID). In postmortem brains from individuals with VCID, endothelin-1 (ET-1) levels closely correlate with blood barrier breakdown and cerebral hypoperfusion. Brain microvascular endothelial cells (BMVECs), previously thought to have exclusively endothelin B receptors, also possess endothelin A (ETA) receptors; however, the functional significance of this receptor in BMVECs is not known. We hypothesize that ETA receptors mediate BMVEC senescence. Serum-starved human BMVECs (HBEC5i) were incubated with ET-1 (1 µmol/L) in the presence/absence of ETA receptor antagonist BQ-123 (20 µmol/L). Cells were collected for Western blot and quantitative real-time PCR analyses. Treatment of ET-1 increased protein expression of ETA receptor, while it was prevented by the ETA receptor antagonist. ET-1 increased p21, p16, p53, LIF1 and cyclin D1 protein levels, and β-galactosidase accumulation, which were prevented in the presence of ETA blockade. While there was no change in tight junction proteins, ET-1 decreased adherent junction protein vascular endothelial cadherin (VE-cadherin) levels. In conclusion, ET-1 upregulates ETA receptors in BMVECs in an autocrine manner and triggers the activation of senescence. These in vitro findings need to be further studied in vivo to establish the role of ETA receptors in the progression of endothelial senescence in VCID.

Leukocyte telomere length, allelic variations in related genes and risk of coronary heart disease in people with long-standing type 1 diabetes

Background

Type 1 diabetes is associated with accelerated vascular aging and advanced atherosclerosis resulting in increased rates of cardiovascular disease and premature death. We evaluated associations between Leukocyte telomere length (LTL), allelic variations (SNPs) in LTL-related genes and the incidence of coronary heart disease (CHD) in adults with long-standing type 1 diabetes.

Methods

We assessed associations of LTL, measured at baseline by RT–PCR, and of SNPs in 11 LTL-related genes with the risk of coronary heart disease (CHD: myocardial infarction or coronary revascularization) and all-cause death during follow-up in two multicenter French-Belgian prospective cohorts of people with long-standing type 1 diabetes.

Results

In logistic and Cox analyses, the lowest tertile of LTL distribution (short telomeres) at baseline was associated with the prevalence of myocardial infarction at baseline and with increased risk of CHD (Hazard ratio 3.14 (1.39–7.70), p = 0.005, for shorter vs longer tertile of LTL) and all-cause death (Hazard ratio 1.63 (95% CI 1.04–2.55), p = 0.03, for shorter vs combined intermediate and longer tertiles of LTL) during follow-up. Allelic variations in six genes related to telomere biology (TERC, NAF1, TERT, TNKS, MEN1 and BICD1) were also associated with the incidence of CHD during follow-up. The associations were independent of sex, age, duration of diabetes, and a range of relevant confounding factors at baseline.

Conclusions

Our results suggest that short LTL is an independent risk factor for CHD in people with type 1 diabetes.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12933-022-01635-0.

Therapeutic Antiaging Strategies

Aging constitutes progressive physiological changes in an organism. These changes alter the normal biological functions, such as the ability to manage metabolic stress, and eventually lead to cellular senescence. The process itself is characterized by nine hallmarks: genomic instability, telomere attrition, epigenetic alterations, loss of proteostasis, deregulated nutrient sensing, mitochondrial dysfunction, cellular senescence, stem cell exhaustion, and altered intercellular communication. These hallmarks are risk factors for pathologies, such as cardiovascular diseases, neurodegenerative diseases, and cancer. Emerging evidence has been focused on examining the genetic pathways and biological processes in organisms surrounding these nine hallmarks. From here, the therapeutic approaches can be addressed in hopes of slowing the progression of aging. In this review, data have been collected on the hallmarks and their relative contributions to aging and supplemented with in vitro and in vivo antiaging research experiments. It is the intention of this article to highlight the most important antiaging strategies that researchers have proposed, including preventive measures, systemic therapeutic agents, and invasive procedures, that will promote healthy aging and increase human life expectancy with decreased side effects.

Histone H2A ubiquitination resulting from Brap loss of function connects multiple aging hallmarks and accelerates neurodegeneration

Aging is an intricate process characterized by multiple hallmarks including stem cell exhaustion, genome instability, epigenome alteration, impaired proteostasis, and cellular senescence. Whereas each of these traits is detrimental at the cellular level, it remains unclear how they are interconnected to cause systemic organ deterioration. Here we show that abrogating Brap, a BRCA1-associated protein essential for neurogenesis, results in persistent DNA double-strand breaks and elevation of histone H2A mono- and poly-ubiquitination (H2Aub). These defects extend to cellular senescence and proteasome-mediated histone H2A proteolysis with alterations in cells' proteomic and epigenetic states. Brap deletion in the mouse brain causes neuroinflammation, impaired proteostasis, accelerated neurodegeneration, and substantially shortened the lifespan. We further show the elevation of H2Aub also occurs in human brain tissues with Alzheimer's disease. These data together suggest that chromatin aberrations mediated by H2Aub may act as a nexus of multiple aging hallmarks and promote tissue-wide degeneration.

Human gingival mesenchymal stem cells retain their growth and immunomodulatory characteristics independent of donor age

Aging has been reported to deteriorate the quantity and quality of mesenchymal stem cells (MSCs), which affect their therapeutic use in regenerative medicine. A dearth of age-related stem cell research further restricts their clinical applications. The present study explores the possibility of using MSCs derived from human gingival tissues (GMSCs) for studying their ex vivo growth characteristics and differentiation potential with respect to donor age. GMSCs displayed decreased in vitro adipogenesis and in vitro and in vivo osteogenesis with age, but in vitro neurogenesis remained unaffected. An increased expression of p53 and SIRT1 with donor age was correlated to their ability of eliminating tumorigenic events through apoptosis or autophagy, respectively. Irrespective of donor age, GMSCs displayed effective immunoregulation and regenerative potential in a mouse model of LPS-induced acute lung injury. Thus, we suggest the potential of GMSCs for designing cell-based immunomodulatory therapeutic approaches and their further extrapolation for acute inflammatory conditions such as acute respiratory distress syndrome and COVID-19.

Aryl hydrocarbon receptor blocks aging-induced senescence in the liver and fibroblast cells

Aging impairs organismal homeostasis leading to multiple pathologies. Yet, the mechanisms and molecular intermediates involved are largely unknown. Here, we report that aged aryl hydrocarbon receptor-null mice (AhR-/-) had exacerbated cellular senescence and more liver progenitor cells. Senescence-associated markers β-galactosidase (SA-β-Gal), p16^Ink4a and p21^Cip1 and genes encoding senescence-associated secretory phenotype (SASP) factors TNF and IL1 were overexpressed in aged AhR-/- livers. Chromatin immunoprecipitation showed that AhR binding to those gene promoters repressed their expression, thus adjusting physiological levels in AhR+/+ livers. MCP-2, MMP12 and FGF secreted by senescent cells were overproduced in aged AhR-null livers. Supporting the relationship between senescence and stemness, liver progenitor cells were overrepresented in AhR-/- mice, probably contributing to increased hepatocarcinoma burden. These AhR roles are not liver-specific since adult and embryonic AhR-null fibroblasts underwent senescence in culture, overexpressing SA-β-Gal, p16^Ink4a and p21^Cip1. Notably, depletion of senescent cells with the senolytic agent navitoclax restored expression of senescent markers in AhR-/- fibroblasts, whereas senescence induction by palbociclib induced an AhR-null-like phenotype in AhR+/+ fibroblasts. AhR levels were downregulated by senescence in mouse lungs but restored upon depletion of p16^Ink4a-expressing senescent cells. Thus, AhR restricts age-induced senescence associated to a differentiated phenotype eventually inducing resistance to liver tumorigenesis.

The Potential Role of m6A RNA Methylation in the Aging Process and Aging-Associated Diseases

N6-methyladenosine (m⁶A) is the most common and conserved internal eukaryotic mRNA modification. m⁶A modification is a dynamic and reversible post-transcriptional regulatory modification, initiated by methylase and removed by RNA demethylase. m⁶A-binding proteins recognise the m⁶A modification to regulate gene expression. Recent studies have shown that altered m⁶A levels and abnormal regulator expression are crucial in the ageing process and the occurrence of age-related diseases. In this review, we summarise some key findings in the field of m⁶A modification in the ageing process and age-related diseases, including cell senescence, autophagy, inflammation, oxidative stress, DNA damage, tumours, neurodegenerative diseases, diabetes, and cardiovascular diseases (CVDs). We focused on the biological function and potential molecular mechanisms of m⁶A RNA methylation in ageing and age-related disease progression. We believe that m⁶A modification may provide a new target for anti-ageing therapies.

Interleukin-1α: Novel functions in cell senescence and antiviral response

The interleukin-1 proteins are a hub of innate inflammatory signaling that activates diverse aspects of adaptive immunity. Until recently, the IL-1α isoform was relatively incompletely understood compared with IL-1β. This review briefly summarizes novel and surprising aspects of IL-1α biology. IL-1α localizes to the nucleus, cytoplasm, mitochondria, cell membrane or extracellular space in various contexts, with corresponding distinct functions. In particular, we focus on multiple pathways by which IL-1α promotes the senescent cell phenotype, unexpectedly involving signaling molecules including mTOR, GATA4, mitochondrial cardiolipin and caspases-4/5. Finally, I review a novel pathway by which IL-1α promotes antiviral immunity.

Effect of oxidative stress on telomere maintenance in aortic smooth muscle cells

Reactive oxygen species (ROS) and telomere dysfunction are both associated with aging and the development of age-related diseases. Although there is evidence for a direct relationship between ROS and telomere dysfunction as well as an independent association of oxidative stress and telomere attrition with age-related disorders, there has not been sufficient exploration of how the interaction between oxidative stress and telomere function may contribute to the pathophysiology of cardiovascular diseases (CVD). To better understand the complex relationships between oxidative stress, telomerase biology and pathophysiology, we examined the telomere biology of aortic smooth muscle cells (ASMCs) isolated from mutant mouse models of oxidative stress. We discovered that telomere lengths were significantly shorter in ASMCs isolated from superoxide dismutase 2 heterozygous (Sod2^+/-) mice, which exhibit increased arterial stiffness with aging, and the observed telomere attrition occurred over time. Furthermore, the telomere erosion occurred even though telomerase activity increased. In contrast, telomeres remained stable in wild-type and superoxide dismutase 1 heterozygous (Sod1^+/-) mice, which do not exhibit CVD phenotypes. The data indicate that mitochondrial oxidative stress, in particular elevated superoxide levels and decreased hydrogen peroxide levels, induces telomere erosion in the ASMCs of the Sod2^+/- mice. This reduction in telomere length occurs despite an increase in telomerase activity and correlates with the onset of disease phenotype. Our results suggest that the oxidative stress caused by imbalance in mitochondrial ROS, from deficient SOD2 activity as a model for mitochondrial dysfunction results in telomere dysfunction, which may contribute to pathogenesis of CVD.

Nuclear Fragility in Radiation-Induced Senescence: Blebs and Tubes Visualized by 3D Electron Microscopy

Irreparable DNA damage following ionizing radiation (IR) triggers prolonged DNA damage response and induces premature senescence. Cellular senescence is a permanent state of cell-cycle arrest characterized by chromatin restructuring, altered nuclear morphology and acquisition of secretory phenotype, which contributes to senescence-related inflammation. However, the mechanistic connections for radiation-induced DNA damage that trigger these senescence-associated hallmarks are poorly understood. In our in vitro model of radiation-induced senescence, mass spectrometry-based proteomics was combined with high-resolution imaging techniques to investigate the interrelations between altered chromatin compaction, nuclear envelope destabilization and nucleo-cytoplasmic chromatin blebbing. Our findings confirm the general pathophysiology of the senescence-response, with disruption of nuclear lamin organization leading to extensive chromatin restructuring and destabilization of the nuclear membrane with release of chromatin fragments into the cytosol, thereby activating cGAS-STING-dependent interferon signaling. By serial block-face scanning electron microscopy (SBF-SEM) whole-cell datasets were acquired to investigate the morphological organization of senescent fibroblasts. High-resolution 3-dimensional (3D) reconstruction of the complex nuclear shape allows us to precisely visualize the segregation of nuclear blebs from the main nucleus and their fusion with lysosomes. By multi-view 3D electron microscopy, we identified nanotubular channels formed in lamin-perturbed nuclei of senescent fibroblasts; the potential role of these nucleo-cytoplasmic nanotubes for expulsion of damaged chromatin has to be examined.

Occurrence of Oxidative Stress and Premature Senescence in the Anterior Segment of Acute Primary Angle-Closure Eyes

Purpose

To explore whether oxidative stress and premature senescence occur in the anterior segment of acute primary angle-closure (APAC) eyes after increased intraocular pressure.

Methods

The eye samples of 21 APAC patients, 22 age-related cataract patients, and 10 healthy donors were included. Aqueous humor (AqH), iris, and anterior lens capsule samples were collected. The levels of oxidative stress markers and senescence-associated secretory phenotype (SASP)–related cytokines in AqH were estimated using relevant reagent kits and multiplex bead immunoassay technique. The intensity of relevant markers in anterior segment tissues was examined by immunofluorescence- and senescence-associated β-galactosidase (SA-β-gal) staining.

Results

Oxidative stress marker levels elevated significantly in the AqH of APAC eyes. Reactive oxygen species (ROS) and 8-hydroxydeoxyguanosine levels were positively correlated with preoperative peak intraocular pressure and age, whereas reduced glutathione/oxidized glutathione (GSH/GSSH) ratio was negatively correlated with both parameters. The levels of several SASP-related cytokines were markedly increased. ROS and malondialdehyde levels were positively correlated with the levels of some SASP-related cytokines, whereas superoxide dismutase level and GSH/GSSH ratio showed an opposite trend. The number of cells positive for oxidative mitochondrial DNA damage and apoptosis-related markers increased in the iris and anterior lens capsule of the APAC group. Senescence-associated markers (p16, p21, and p53) and SA-β-gal activity were increased in the iris of the APAC group.

Conclusions

Oxidative stress and premature senescence occurred in the anterior segment of APAC patients, suggesting that they may be involved in the development of pathological changes in the anterior segment of APAC eyes.

Regulation of NAD+ metabolism in aging and disease

More than a century after discovering NAD⁺, information is still evolving on the role of this molecule in health and diseases. The biological functions of NAD⁺ and NAD⁺ precursors encompass pathways in cellular energetics, inflammation, metabolism, and cell survival. Several metabolic and neurological diseases exhibit reduced tissue NAD⁺ levels. Significantly reduced levels of NAD⁺ are also associated with aging, and enhancing NAD⁺ levels improved healthspan and lifespan in animal models. Recent studies suggest a causal link between senescence, age-associated reduction in tissue NAD⁺ and enzymatic degradation of NAD⁺. Furthermore, the discovery of transporters and receptors involved in NAD⁺ precursor (nicotinic acid, or niacin, nicotinamide, and nicotinamide riboside) metabolism allowed for a better understanding of their role in cellular homeostasis including signaling functions that are independent of their functions in redox reactions. We also review studies that demonstrate that the functional effect of niacin is partially due to the activation of its cell surface receptor, GPR109a. Based on the recent progress in understanding the mechanism and function of NAD⁺ and NAD⁺ precursors in cell metabolism, new strategies are evolving to exploit these molecules' pharmacological potential in the maintenance of metabolic balance.

Stress and telomere shortening: Insights from cellular mechanisms

Short telomeres confer risk of degenerative diseases. Chronic psychological stress can lead to disease through many pathways, and research from in vitro studies to human longitudinal studies has pointed to stress-induced telomere damage as an important pathway. However, there has not been a comprehensive model to describe how changes in stress physiology and neuroendocrine pathways can lead to changes in telomere biology. Critically short telomeres or the collapse of the telomere structure caused by displacement of telomere binding protein complex shelterin elicit a DNA damage response and lead to senescence or apoptosis. In this narrative review, we summarize the key roles glucocorticoids, reactive oxygen species (ROS) and mitochondria, and inflammation play in mediating the relationship between psychological stress and telomere maintenance. We emphasis that these mediators are interconnected and reinforce each other in positive feedback loops. Telomere length has not been studied across the lifespan yet, but the initial setting point at birth appears to be the most influential point, as it sets the lifetime trajectory, and is influenced by stress. We describe two types of intergenerational stress effects on telomeres - prenatal stress effects on telomeres during fetal development, and 'telotype transmission" -the directly inherited transmission of short telomeres from parental germline. It is clear that the initial simplistic view of telomere length as a mitotic clock has evolved into a far more complex picture of both transgenerational telomere influences, and of interconnected molecular and cellular pathways and networks, as hallmarks of aging where telomere maintenance is a key player interacting with mitochondria. Further mechanistic investigations testing this comprehensive model of stress mediators shaping telomere biology and the telomere-mitochondrial nexus will lead to better understanding from cell to human lifespan aging, and could lead to anti-aging interventions.

TBX2 controls a proproliferative gene expression program in melanoma

Senescence shapes embryonic development, plays a key role in aging, and is a critical barrier to cancer initiation, yet how senescence is regulated remains incompletely understood. TBX2 is an antisenescence T-box family transcription repressor implicated in embryonic development and cancer. However, the repertoire of TBX2 target genes, its cooperating partners, and how TBX2 promotes proliferation and senescence bypass are poorly understood. Here, using melanoma as a model, we show that TBX2 lies downstream from PI3K signaling and that TBX2 binds and is required for expression of E2F1, a key antisenescence cell cycle regulator. Remarkably, TBX2 binding in vivo is associated with CACGTG E-boxes, present in genes down-regulated by TBX2 depletion, more frequently than the consensus T-element DNA binding motif that is restricted to Tbx2 repressed genes. TBX2 is revealed to interact with a wide range of transcription factors and cofactors, including key components of the BCOR/PRC1.1 complex that are recruited by TBX2 to the E2F1 locus. Our results provide key insights into how PI3K signaling modulates TBX2 function in cancer to drive proliferation.

Tgfβ1-Cthrc1 Signaling Plays an Important Role in the Short-Term Reparative Response to Heart Valve Endothelial Injury

OBJECTIVE

Aortic valve disease is a common worldwide health burden with limited treatment options. Studies have shown that the valve endothelium is critical for structure-function relationships, and disease is associated with its dysfunction, damage, or injury. Therefore, therapeutic targets to maintain a healthy endothelium or repair damaged endothelial cells could hold promise. In this current study, we utilize a surgical mouse model of heart valve endothelial cell injury to study the short-term response at molecular and cellular levels. The goal is to determine if the native heart valve exhibits a reparative response to injury and identify the mechanisms underlying this process. Approach and Results: Mild aortic valve endothelial injury and abrogated function was evoked by inserting a guidewire down the carotid artery of young (3 months) and aging (16-18 months) wild-type mice. Short-term cellular responses were examined at 6 hours, 48 hours, and 4 weeks following injury, whereas molecular profiles were determined after 48 hours by RNA-sequencing. Within 48 hours following endothelial injury, young wild-type mice restore endothelial barrier function in association with increased cell proliferation, and upregulation of transforming growth factor beta 1 (Tgfβ1) and the glycoprotein, collagen triple helix repeat containing 1 (Cthrc1). Interestingly, this beneficial response to injury was not observed in aging mice with known underlying endothelial dysfunction.

CONCLUSIONS

Data from this study suggests that the healthy valve has the capacity to respond to mild endothelial injury, which in short term has beneficial effects on restoring endothelial barrier function through acute activation of the Tgfβ1-Cthrc1 signaling axis and cell proliferation.

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.

Biomarkers of geroprotection and cardiovascular health: An overview of omics studies and established clinical biomarkers in the context of diet

The slowdown, inhibition, or reversal of age-related decline (as a composite of disease, dysfunction, and, ultimately, death) by diet or natural compounds can be defined as dietary geroprotection. While there is no single reliable biomarker to judge the effects of dietary geroprotection, biomarker signatures based on omics (epigenetics, gene expression, microbiome composition) are promising candidates. Recently, omic biomarkers started to supplement established clinical ones such as lipid profiles and inflammatory cytokines. In this review, we focus on human data. We first summarize the current take on genetic biomarkers based on epidemiological studies. However, most of the remaining biomarkers that we describe, whether omics-based or clinical, are related to intervention studies. Then, because of their promising potential in the context of dietary geroprotection, we focus on the effects of berry-based interventions, which up to now have been mostly described employing clinical markers. We provide an aggregation and tabulation of all the recent systematic reviews and meta-analyses that we could find related to this topic. Finally, we present evidence for the importance of the "nutribiography," that is, the influence that an individual's history of diet and natural compound consumption can have on the effects of dietary geroprotection.

Telomere shortening causes distinct cell division regimes during replicative senescence in Saccharomyces cerevisiae

Background

Telomerase-negative cells have limited proliferation potential. In these cells, telomeres shorten until they reach a critical length and induce a permanently arrested state. This process called replicative senescence is associated with genomic instability and participates in tissue and organismal ageing. Experimental data using single-cell approaches in the budding yeast model organism show that telomerase-negative cells often experience abnormally long cell cycles, which can be followed by cell cycles of normal duration, before reaching the terminal senescent state. These series of non-terminal cell cycle arrests contribute to the heterogeneity of senescence and likely magnify its genomic instability. Due to their apparent stochastic nature, investigating the dynamics and the molecular origins of these arrests has been difficult. In particular, whether the non-terminal arrests series stem from a mechanism similar to the one that triggers terminal senescence is not known.

Results

Here, we provide a mathematical description of sequences of non-terminal arrests to understand how they appear. We take advantage of an experimental data set of cell cycle duration measurements performed in individual telomerase-negative yeast cells that keep track of the number of generations since telomerase inactivation. Using numerical simulations, we show that the occurrence of non-terminal arrests is a generation-dependent process that can be explained by the shortest telomere reaching a probabilistic threshold length. While the onset of senescence is also triggered by telomere shortening, we highlight differences in the laws that describe the number of consecutive arrests in non-terminal arrests compared to senescence arrests, suggesting distinct underlying mechanisms and cellular states.

Conclusions

Replicative senescence is a complex process that affects cell divisions earlier than anticipated, as exemplified by the frequent occurrence of non-terminal arrests early after telomerase inactivation. The present work unravels two kinetically and mechanistically distinct generation-dependent processes underlying non-terminal and terminal senescence arrests. We suggest that these two processes are responsible for two consequences of senescence at the population level, the increase of genome instability on the one hand, and the limitation of proliferation capacity on the other hand.

Supplementary Information

The online version contains supplementary material available at 10.1186/s13578-021-00693-3.

Radiation-Induced Macrophage Senescence Impairs Resolution Programs and Drives Cardiovascular Inflammation

Radiation is associated with tissue damage and increased risk of atherosclerosis, but there are currently no treatments and a very limited mechanistic understanding of how radiation impacts tissue repair mechanisms. We uncovered that radiation significantly delayed temporal resolution programs that were associated with decreased efferocytosis in vivo. Resolvin D1 (RvD1), a known proresolving ligand, promoted swift resolution and restored efferocytosis in sublethally irradiated mice. Irradiated macrophages exhibited several features of senescence, including increased expression of p16^INK4A and p21, heightened levels of SA-β-gal, COX-2, several proinflammatory cytokines/chemokines, and oxidative stress (OS) in vitro, and when transferred to mice, they exacerbated inflammation in vivo. Mechanistically, heightened OS in senescent macrophages led to impairment in their ability to carry out efficient efferocytosis, and treatment with RvD1 reduced OS and improved efferocytosis. Sublethally irradiated Ldlr ^-/- mice exhibited increased plaque necrosis, p16^INK4A cells, and decreased lesional collagen compared with nonirradiated controls, and treatment with RvD1 significantly reduced necrosis and increased lesional collagen. Removal of p16^INK4A hematopoietic cells during advanced atherosclerosis with p16-3MR mice reduced plaque necrosis and increased production of key intraplaque-resolving mediators. Our results demonstrate that sublethal radiation drives macrophage senescence and efferocytosis defects and suggest that RvD1 may be a new therapeutic strategy to limit radiation-induced tissue damage.

Role of Complement in Regulating Inflammation Processes in Renal and Prostate Cancers

For decades, the complement system, the central pillar of innate immune response, was recognized as a protective mechanism against cancer cells and the manipulation of complement effector functions in cancer setting offered a great opportunity to improve monoclonal antibody-based cancer immunotherapies. Similarly, cellular senescence, the process of cell cycle arrest that allow DNA and tissue repair has been traditionally thought to be able to suppress tumor progression. However, in recent years, extensive research has identified the complement system and cellular senescence as two main inducers of tumour growth in the context of chronic, persistent inflammation named inflammaging. Here, we discuss the data describing the ambivalent role of senescence in cancer with a particular focus on tumors that are strongly dependent on complement activation and can be understood by a new, senescence-related point of view: prostate cancer and renal cell carcinoma.

Perspectives on the dynamic implications of cellular senescence and immunosenescence on macrophage aging biology

An intricate relationship between impaired immune functions and the age-related accumulation of tissue senescent cells is rapidly emerging. The immune system is unique as it undergoes mutually inclusive and deleterious processes of immunosenescence and cellular senescence with advancing age. While factors inducing immunosenescence and cellular senescence may be shared, however, both these processes are fundamentally different which holistically influence the aging immune system. Our understanding of the biological impact of immunosenescence is relatively well-understood, but such knowledge regarding cellular senescence in immune cells, especially in the innate immune cells such as macrophages, is only beginning to be elucidated. Tissue-resident macrophages are long-lived, and while functioning in tissue-specific and niche-specific microenvironments, senescence in macrophages can be directly influenced by senescent host cells which may impact organismal aging. In addition, evidence of age-associated immunometabolic changes as drivers of altered macrophage phenotype and functions such as inflamm-aging is also emerging. The present review describes the emerging impact of cellular senescence vis-à-vis immunosenescence in aging macrophages, its biological relevance with other senescent non-immune cells, and known immunometabolic regulators. Gaps in our present knowledge, as well as strategies aimed at understanding cellular senescence and its therapeutics in the context of macrophages, have been reviewed.

Aging and Cancer: The Waning of Community Bonds

Cancer often arises in the context of an altered tissue landscape. We argue that a major contribution of aging towards increasing the risk of neoplastic disease is conveyed through effects on the microenvironment. It is now firmly established that aged tissues are prone to develop clones of altered cells, most of which are compatible with a normal histological appearance. Such increased clonogenic potential results in part from a generalized decrease in proliferative fitness, favoring the emergence of more competitive variant clones. However, specific cellular genotypes can emerge with reduced cooperative and integrative capacity, leading to disruption of tissue architecture and paving the way towards progression to overt neoplastic phenotypes.