Hallmarks Of Cellular Senescence Research Articles

Hallmarks of cellular senescence: biology, mechanisms, regulations.

Cellular senescence is a process in which the cell cycle becomes permanently arrested, thereby inhibiting cell division, proliferation and growth. Various cellular stresses, such as DNA damage, telomere shortening and oxidative stress, can trigger cellular senescence. Physiologically, cellular senescence contributes to tissue development, repair and critical biological processes such as embryogenesis, whereas, pathologically, it plays a key role in diverse disease subsets. To this end, elucidating the underlying mechanisms and molecular regulation of senescence is crucial. Here, in this Review, we explore recent key findings on cellular senescence in experimental and human disease models, focusing on its molecular mechanisms, regulation and future research directions to advance the field and facilitate therapeutic translation.

Use of Telomere Length as a Biomarker in Idiopathic Pulmonary Fibrosis.

Telomere shortening, a hallmark of cellular aging, is associated with poor outcomes in idiopathic pulmonary fibrosis (IPF). This study aimed to explore the relationships between telomere length (TL), pulmonary function tests, and telomere-related gene (TRG) mutations in a real-world IPF population. We included IPF patients from two Belgian academic hospitals, collecting demographic and clinical data. TL was measured using Flow-FISH and expressed as a percentile. Short TL was defined as below the 10th percentile (P10), and very short TL as below the 1st percentile (P1). We analysed 143 patients (106 men, 74%), with a median age of 70years. Thirty patients (21%) met the European Respiratory Society (ERS) criteria for familial pulmonary fibrosis (FPF). Short TL was found in 74 patients (50%), predominantly in men (p < 0.05). Patients with short TL experienced a greater decline in lung function over 24months compared to those with normal TL (-4% vs + 3% FVC, p < 0.05; -7% vs -3% DLCO, p < 0.05). Patients with very short TL were younger at diagnosis and tended to have a more pronounced FVC decline (-5% vs -1%, p = 0.06). TRG variants were identified in 16 individuals, occurring more frequently in those with short (14/27, 52%) or very short TL (10/20, 50%). Short TL is common in both sporadic and familial IPF and serves as a predictive biomarker for accelerated lung function decline. Additionally, the presence of short TL is indicative of an underlying TRG mutation.

RNA G-quadruplex (rG4) exacerbates cellular senescence by mediating ribosome pausing.

Loss of protein homeostasis is a hallmark of cellular senescence, and ribosome pausing plays a crucial role in the collapse of proteostasis. However, our understanding of ribosome pausing in senescent cells remains limited. In this study, we utilized ribosome profiling and G-quadruplex RNA immunoprecipitation sequencing techniques to explore the impact of RNA G-quadruplex (rG4) on the translation efficiency in senescent cells. Our results revealed a reduction in the translation efficiency of rG4-rich genes in senescent cells and demonstrated rG4 structures within coding sequence (CDS) can impede translation both in vivo and in vitro. Moreover, we observed a significant increase in the abundance of rG4 structures in senescent cells, and the stabilization of the rG4 structures further exacerbated cellular senescence. Mechanistically, the RNA helicase DHX9 functions as a key regulator of rG4 abundance, and its reduced expression in senescent cells contributing to increased ribosome pausing. Additionally, we also observed an increased abundance of rG4, an imbalance in protein homeostasis, and reduced DHX9 expression in aged mice. In summary, our findings reveal a novel biological role for rG4 and DHX9 in the regulation of translation and proteostasis, which may have implications for delaying cellular senescence and the aging process.

Increased chromatin accessibility underpins senescence.

Senescence is a cellular state induced by various stressors or extracellular signals, but a universal pathway that triggers this process irrespective of the initial stressor has yet to be identified. Recent data indicate that chromatin opening, particularly in the noncoding genome, is a hallmark of cellular senescence. We propose a model in which this increased chromatin accessibility mediated by transcription factors downstream of the senescence-inducing stressors acts as a decisive factor to commit cells toward the senescence fate. Engagement toward senescence is then determined by the balance between mechanisms that increase or decrease chromatin accessibility and can be influenced by modulating the activity of specific histone-modifying complexes. Traits of senescent cells, such as increased nuclear and nucleolar size, the secretion of pro-inflammatory cytokines, reduced rRNA biogenesis, telomere dysfunction, expression of retrotransposons and endogenous retroviruses, as well as DNA damage, can all be attributed to increased chromatin accessibility. This concept suggests potential targets to tilt the balance toward the senescence response in the context of future therapies against cancer and age-related diseases.

Younger Age Is Associated with Favorable Outcomes in Adult Dogs with Hemangiosarcoma Receiving Adjuvant Doxorubicin Chemotherapy: Results from the PRO-DOX Study.

Canine hemangiosarcoma is a common and aggressive vascular malignancy predominantly affecting dogs over six years of age. Despite surgical resection followed by adjuvant chemotherapy, median survival remains around 4-6 months. Propranolol, a beta-adrenergic receptor (b-AR) antagonist, has shown efficacy in human angiosarcoma, a tumor with similar clinical and morphological characteristics, when combined with chemotherapy. To determine if propranolol could be repurposed as an effective adjunct to chemotherapy, we conducted a phase I clinical study evaluating the safety and efficacy of propranolol combined with doxorubicin (PRO-DOX) in 20 dogs with stage 1 or stage 2 splenic hemangiosarcoma.Plasma from 19 dogs was analyzed for propranolol pharmacokinetics and RNA was extracted from tumors from 13 of the dogs for transcriptional profiling. Although propranolol did not appear to influence treatment outcomes, our results revealed long-term survival in young adult dogs (less than 6 years of age), suggesting the possibility of a better response to doxorubicin. Faster clearance of 4-OH propranolol also correlated with long-term survival in younger dogs, but this appeared to be associated with drug metabolism due to age rather than effects of the drug on survival outcomes. Gene expression analysis identified distinct age-associated tumor signatures, with young dogs exhibiting increased immune-related gene expression and older dogs showing elevated expression of genes associated with the cell cycle and the DNA damage response and repair. These findings highlight several hallmarks of cellular aging in hemangiosarcoma that may influence treatment responses and long-term survival. Our findings suggest that young adult dogs with splenic hemangiosarcoma treated with doxorubicin have a better prognosis and underscore the need for further research into age-related molecular mechanisms of disease. These insights could refine therapeutic strategies and clinical decision-making in hemangiosarcoma management.

Nuclear Profilin-1 for DNA Damage Repair Is Involved in Phagocytic Impairment of Senescent Microglia.

Accumulation of DNA damage is a hallmark of cellular senescence and plays a critical role in brain aging. Although the DNA damage repair mechanisms are crucial in cellular senescence, they are not well understood in microglia. In this study, we found that profilin-1 (PFN1), an actin-binding protein, relocates from the cytoplasm to the nucleus in response to DNA double-strand breaks (DSBs) induced by doxorubicin. This nuclear PFN1 subsequently translocates back to the cytoplasm during the recovery period. In response to DSBs, we detected enhanced expression of genes associated with nonhomologous end joining (NHEJ), but not with homologous recombination (HR), along with increased nuclear F-actin accumulation. However, this repair process is compromised when PFN1 is either knocked down or its nuclear transport is blocked. Notably, in DNA damage-induced senescent microglia, increased nuclear localization of PFN1 and nuclear F-actin formation are associated with phagocytic dysfunction. Both exvivo aged microglia and publicly available single-cell RNA sequencing data from aged mouse brains recapitulate the invitro findings described above. Despite cytochalasin D treatment for actin depolymerization, the return of PFN1 to the cytoplasm was not facilitated due to its aggregation. We propose that PFN1 plays an important role in DNA damage repair in microglia. In addition, the dysregulation of the nucleocytoplasmic balance of PFN1 alongside DNA damage accumulation may contribute to the phagocytic impairment of microglia in the aged brain.

Phosphorylation-driven regulation of SIRT1 in muscle senescence: Insights from molecular dynamics simulation and experimental validation.

Phosphorylation-driven regulation of SIRT1 in muscle senescence: Insights from molecular dynamics simulation and experimental validation.

Alleviation of Aging‐Related Hallmarks in a Mouse Model of Progeria via a Nanoparticle‐Based Artificial Transcription Factor

Abstract The increasing demand for precise and safe modulation of cellular rejuvenation and reprogramming has driven the development of innovative nanotechnologies capable of achieving unprecedented control over cell fate and function. Among these, biomimetic nanoparticles stand out due to their enhanced biocompatibility, improved targeting capabilities, prolonged circulation time, and multifunctionality. These attributes position them as promising tools for advancing drug delivery, personalized medicine, and targeted therapies for various diseases. In this study, a novel nanoparticle‐based artificial transcription factor developed, termed Oct4‐nanoscript, specifically designed to emulate the function of the Oct4 gene. This results support that the Oct4‐nanoscript exhibits high‐affinity DNA binding, efficient nuclear localization, and robust activation of Oct4 target genes. Furthermore, partial reprogramming induced by Oct4‐nanoscript significantly reduced DNA damage and restored key epigenetic marks, hallmarks of cellular aging. In a Hutchinson‐Gilford Progeria Syndrome (HGPS) mouse model, the Oct4‐nanoscript effectively rescued age‐related pathological features and extended lifespan. This non‐viral, stable, and highly specific biomimetic nanoparticle platform for emulating Oct4 gene function presents a promising therapeutic strategy for age‐related diseases, including HGPS. These findings advance the field of regenerative medicine, offering a foundation for developing innovative therapies targeting complex biological challenges.

Mitochondrial DNA released by senescent tumor cells enhances PMN-MDSC-driven immunosuppression through the cGAS-STING pathway.

Mitochondrial DNA released by senescent tumor cells enhances PMN-MDSC-driven immunosuppression through the cGAS-STING pathway.

Alteration of telomere length and mtDNA copy number in interstitial lung disease associated with rheumatoid arthritis

Interstitial lung disease (ILD) is a common extra-articular manifestation of rheumatoid arthritis (RA). The inflammatory response in lung disease is characterized by severe oxidative stress, which enhances cellular senescence. Telomeric shortening and mitochondria dysregulation represent two hallmarks of cellular senescence. The maintenance of telomere length (TL) and mitochondrial DNA (mtDNA) copy number is preserved by many proteins, such as TERF1 and TFAM, respectively. Our aim was to evaluate the TL, the mtDNA copy number and the expression of two regulator gene factors in RA patients with (RA-ILD) and without lung involvement (RA-NILD). Eighty-five RA patients and 21 healthy subjects were enrolled. Relative TL, mtDNA copy number, and expression analysis of TERF1 and TFAM genes were measured using qPCR assay. All RA patients present a statistically significant telomere shortening; in particular, RA-ILD patients show shorter TL compared to both controls and RA-NILD. Patients with Usual Interstitial Pneumonia pattern show a more evident shortening of TL. Lastly, both RA-ILD and RA-NILD patients present a significant decrease in mtDNA copy number compared to controls. The analysis of regulatory genes showed an increase in TERF1 expression in RA patients compared to controls, also after stratification in the two subgroups, and a decrease in TFAM expression in RA patients compared to controls. These results show that the alteration of TL and mtDNA copy number in RA patients is more evident in the presence of ILD. The hypothesis is that, in these patients, oxidative stress could accelerate the shortening of telomeres and the decrease of mtDNA copy number.

NEAT1 regulates BMSCs aging through disruption of FGF2 nuclear transport

BackgroundThe aging of bone marrow mesenchymal stem cells (BMSCs) impairs bone tissue regeneration, contributing to skeletal disorders. LncRNA NEAT1 is considered as a proliferative inhibitory role during cellular senescence, but the relevant mechanisms remain insufficient. This study aims to elucidate how NEAT1 regulates mitotic proteins during BMSCs aging.MethodsBMSCs were isolated from alveolar bone of human volunteers aged 26–33 (young) and 66–78 (aged). NEAT1 expression and distribution changes during aging process were observed using fluorescence in situ hybridization (FISH) in young (3 months) and aged (18 months) mice or human BMSCs. Subsequent RNA pulldown and proteomic analyses, along with single-cell analysis, immunofluorescence, RNA immunoprecipitation (RIP), and co-immunoprecipitation (Co-IP), were conducted to investigate that NEAT1 impairs the nuclear transport of mitotic FGF2 and contributes to BMSCs aging.ResultsWe reveal that NEAT1 undergoes significant upregulated and shifts from nucleus to cytoplasm in bone marrow and BMSCs during aging process. In which, the expression correlates with nuclear DNA content during karyokinesis, suggesting a link to mitogenic factor. Within NEAT1 knockdown, hallmarks of cellular aging, including senescence-associated secretory phenotype (SASP), p16, and p21, were significantly downregulated. RNA pulldown and proteomic analyses further identify NEAT1 involved in osteoblast differentiation, mitotic cell cycle, and ribosome biogenesis, highlighting its role in maintaining BMSCs differentiation and proliferation. Notably, as an essential growth factor of BMSCs, Fibroblast Growth Factor 2 (FGF2) directly abundant binds to NEAT1 and the sites enriched with nuclear localization motifs. Importantly, NEAT1 decreased the interaction between FGF2 and Karyopherin Subunit Beta 1 (KPNB1), influencing the nuclear transport of mitogenic FGF2.ConclusionsOur findings position NEAT1 as a critical regulator of mitogenic protein networks that govern BMSC aging. Targeting NEAT1 might offer novel therapeutic strategies to rejuvenate aged BMSCs.

Immune therapeutic strategies for the senescent tumor microenvironment.

Senescent cells can either to promote immunosuppressive tumor microenvironment or facilitate immune surveillance. Despite the revolutionary impact of cancer immunotherapy, durable responses in solid tumors, particularly in advanced stages, remain limited. Recent studies have shed light on the influence of senescent status within the tumor microenvironment (TME) on therapy resistance and major efforts are needed to overcome these challenges. This review summarizes recent advancements in targeting cellular senescence, with a particular focus on immunomodulatory approaches on the hallmarks of cellular senescence.

Morphological and Metabolic Features of Brain Aging in Rodents, Ruminants, Carnivores, and Non-Human Primates

Brain aging in mammals is characterized by morphological and functional changes in neural cells. Macroscopically, this process, leading to progressive cerebral volume loss and functional decline, includes memory and motor neuron deficits, as well as behavioral disorders. Morphologically, brain aging is associated with aged neurons and astrocytes, appearing enlarged and flattened, and expressing enhanced pH-dependent β-galactosidase activity. Multiple mechanisms are considered hallmarks of cellular senescence in vitro, including cell cycle arrest, increased lysosomal activity, telomere shortening, oxidative stress, and DNA damage. The most common markers for senescence identification were identified in (i) proteins implicated in cell cycle arrest, such as p16, p21, and p53, (ii) increased lysosomal mass, and (iii) increased reactive oxygen species (ROS) and senescence-associated secretory phenotype (SASP) expression. Finally, dysfunctional autophagy, a process occurring during aging, contributes to altering brain homeostasis. The brains of mammals can be studied at cellular and subcellular levels to elucidate the mechanisms on the basis of age-related and degenerative disorders. The aim of this review is to summarize and update the most recent knowledge about brain aging through a comparative approach, where similarities and differences in some mammalian species are considered.

Connecting the Dots: Telomere Shortening and Rheumatic Diseases.

Telomeres, repetitive sequences located at the extremities of chromosomes, play a pivotal role in sustaining chromosomal stability. Telomerase is a complex enzyme that can elongate telomeres by appending telomeric repeats to chromosome ends and acts as a critical factor in telomere dynamics. The gradual shortening of telomeres over time is a hallmark of cellular senescence and cellular death. Notably, telomere shortening appears to result from the complex interplay of two primary mechanisms: telomere shelterin complexes and telomerase activity. The intricate interplay of genetic, environmental, and lifestyle influences can perturb telomere replication, incite oxidative stress damage, and modulate telomerase activity, collectively resulting in shifts in telomere length. This age-related process of telomere shortening plays a considerable role in various chronic inflammatory and oxidative stress conditions, including cancer, cardiovascular disease, and rheumatic disease. Existing evidence has shown that abnormal telomere shortening or telomerase activity abnormalities are present in the pathophysiological processes of most rheumatic diseases, including different disease stages and cell types. The impact of telomere shortening on rheumatic diseases is multifaceted. This review summarizes the current understanding of the link between telomere length and rheumatic diseases in clinical patients and examines probable telomere shortening in peripheral blood mononuclear cells and histiocytes. Therefore, understanding the intricate interaction between telomere shortening and various rheumatic diseases will help in designing personalized treatment and control measures for rheumatic disease.

The miR-30-5p/TIA-1 axis directs cellular senescence by regulating mitochondrial dynamics

Senescent cells exhibit a diverse spectrum of changes in their morphology, proliferative capacity, senescence-associated secretory phenotype (SASP) production, and mitochondrial homeostasis. These cells often manifest with elongated mitochondria, a hallmark of cellular senescence. However, the precise regulatory mechanisms orchestrating this phenomenon remain predominantly unexplored. In this study, we provide compelling evidence for decreases in TIA-1, a pivotal regulator of mitochondrial dynamics, in models of both replicative senescence and ionizing radiation (IR)-induced senescence. The downregulation of TIA-1 was determined to trigger mitochondrial elongation and enhance the expression of senescence-associated β-galactosidase, a marker of cellular senescence, in human foreskin fibroblast HS27 cells and human keratinocyte HaCaT cells. Conversely, the overexpression of TIA-1 mitigated IR-induced cellular senescence. Notably, we identified the miR-30-5p family as a novel factor regulating TIA-1 expression. Augmented expression of the miR-30-5p family was responsible for driving mitochondrial elongation and promoting cellular senescence in response to IR. Taken together, our findings underscore the significance of the miR-30-5p/TIA-1 axis in governing mitochondrial dynamics and cellular senescence.

Age-related changes in human skeletal muscle transcriptome and proteome are more affected by chronic inflammation and physical inactivity than primary aging.

Evaluation of the influence of primary and secondary aging on the manifestation of molecular and cellular hallmarks of aging is a challenging and currently unresolved issue. Our study represents the first demonstration of the distinct role of primary aging and chronic inflammation/physical inactivity - the most important drivers of secondary aging, in the regulation of transcriptomic and proteomic profiles in human skeletal muscle. To achieve this purpose, young healthy people (n = 15), young (n = 8) and older (n = 37) patients with knee/hip osteoarthritis, a model to study the effect of long-term inactivity and chronic inflammation on the vastus lateralis muscle, were included in the study. It was revealed that widespread and substantial age-related changes in gene expression in older patients relative to young healthy people (~4000 genes regulating mitochondrial function, proteostasis, cell membrane, secretory and immune response) were related to the long-term physical inactivity and chronic inflammation rather than primary aging. Primary aging contributed mainly to the regulation of genes (~200) encoding nuclear proteins (regulators of DNA repair, RNA processing, and transcription), mitochondrial proteins (genes encoding respiratory enzymes, mitochondrial complex assembly factors, regulators of cristae formation and mitochondrial reactive oxygen species production), as well as regulators of proteostasis. It was found that proteins associated with aging were regulated mainly at the post-transcriptional level. The set of putative primary aging genes and their potential transcriptional regulators can be used as a resource for further targeted studies investigating the role of individual genes and related transcription factors in the emergence of a senescent cell phenotype.

GPI-anchored Gas1 protein regulates cytosolic proteostasis in budding yeast.

The decline in protein homeostasis (proteostasis) is a hallmark of cellular aging and aging-related diseases. Maintaining a balanced proteostasis requires a complex network of molecular machineries that govern protein synthesis, folding, localization, and degradation. Under proteotoxic stress, misfolded proteins that accumulate in cytosol can be imported into mitochondria for degradation through the "mitochondrial as guardian in cytosol" (MAGIC) pathway. Here, we report an unexpected role of Gas1, a cell wall-bound glycosylphosphatidylinositol (GPI)-anchored β-1,3-glucanosyltransferase in the budding yeast, in differentially regulating MAGIC and ubiquitin-proteasome system (UPS). Deletion of GAS1 inhibits MAGIC but elevates protein ubiquitination and UPS-mediated protein degradation. Interestingly, we found that the Gas1 protein exhibits mitochondrial localization attributed to its C-terminal GPI anchor signal. But this mitochondria-associated GPI anchor signal is not required for mitochondrial import and degradation of misfolded proteins through MAGIC. By contrast, catalytic inactivation of Gas1 via the gas1-E161Q mutation inhibits MAGIC but not its mitochondrial localization. These data suggest that the glucanosyltransferase activity of Gas1 is important for regulating cytosolic proteostasis.

High-throughput assessment of cellular senescence.

High-throughput assessment of cellular senescence.

Telomerase-Mediated Anti-Ageing Interventions.

The ageing process involves a gradual decline of chromosome integrity throughout an organism's lifespan. Telomeres are protective DNA-protein complexes that cap the ends of linear chromosomes in eukaryotic organisms. Telomeric DNA consists of long stretches of short "TTAGGG" repeats that are conserved across most eukaryotes including humans. Telomeres shorten progressively with each round of DNA replication due to the inability of conventional DNA polymerase to completely replicate the chromosome ends, known as the "end-replication problem". The telomerase enzyme counteracts the telomeric DNA loss by de novo addition of telomeric repeats onto chromosomal ends. Germline and stem cells maintain significant levels of telomerase activity to maintain telomere length and can divide almost indefinitely. However, the differentiation of stem cells accompanies the inactivation of telomerase gene expression, resulting in the progressive shortening of telomeres in somatic cells over successive divisions. Critically short telomeres elicit and sustain a persistent DNA damage response leading to permanent growth arrest of cells known as cellular senescence, a hallmark of cellular ageing. The accumulation of senescent cells in tissues and organs contributes to organismal ageing. Thus, the prevention of telomere shortening is a promising means to delay or even reverse cellular ageing. In this chapter, we summarize potential anti-ageing interventions that mitigate telomere shortening through increasing telomerase level or activity and discuss these strategies' risks, benefits, and future outlooks.

Generation of somatic de novo structural variation as a hallmark of cellular senescence in human lung fibroblasts

Cellular senescence is characterized by replication arrest in response to stress stimuli. Senescent cells accumulate in aging tissues and can trigger organ-specific and possibly systemic dysfunction. Although senescent cell populations are heterogeneous, a key feature is that they exhibit epigenetic changes. Epigenetic changes such as loss of repressive constitutive heterochromatin could lead to subsequent LINE-1 derepression, a phenomenon often described in the context of senescence or somatic evolution. LINE-1 elements decode the retroposition machinery and reverse transcription generates cDNA from autonomous and non-autonomous TEs that can potentially reintegrate into genomes and cause structural variants. Another feature of cellular senescence is mitochondrial dysfunction caused by mitochondrial damage. In combination with impaired mitophagy, which is characteristic of senescent cells, this could lead to cytosolic mtDNA accumulation and, as a genomic consequence, integrations of mtDNA into nuclear DNA (nDNA), resulting in mitochondrial pseudogenes called numts. Thus, both phenomena could cause structural variants in aging genomes that go beyond epigenetic changes. We therefore compared proliferating and senescent IMR-90 cells in terms of somatic de novo numts and integrations of a non-autonomous composite retrotransposons - the so-called SVA elements—that hijack the retropositional machinery of LINE-1. We applied a subtractive and kinetic enrichment technique using proliferating cell DNA as a driver and senescent genomes as a tester for the detection of nuclear flanks of de novo SVA integrations. Coupled with deep sequencing we obtained a genomic readout for SVA retrotransposition possibly linked to cellular senescence in the IMR-90 model. Furthermore, we compared the genomes of proliferative and senescent IMR-90 cells by deep sequencing or after enrichment of nuclear DNA using AluScan technology. A total of 1,695 de novo SVA integrations were detected in senescent IMR-90 cells, of which 333 were unique. Moreover, we identified a total of 81 de novo numts with perfect identity to both mtDNA and nuclear hg38 flanks. In summary, we present evidence for possible age-dependent structural genomic changes by paralogization that go beyond epigenetic modifications. We hypothesize, that the structural variants we observe potentially impact processes associated with replicative aging of IMR-90 cells.