Differential roles for cyclin-dependent kinase inhibitors p21 and p16 in the mechanisms of senescence and differentiation in human fibroblasts

Reduced DNMT1 expression associated with TP53 promoter hypomethylation mediate enhanced granulosa cell senescence during ovarian aging

BACKGROUND

The effects of granulose cell (GC) senescence on premature ovarian insufficiency/premature ovarian failure have been extensively examined, the association between GC senescence and ovarian aging remains to be clarified.

METHODS

Human and mouse GCs from young/control and old/advanced maternal age (AMA) groups were collected, and GC senescence was determined. The role of the DNMT1-p53 axis in GC senescence during ovarian aging was examined and validated in a KGN cell senescence model.

RESULTS

SA-beta-gal-positive GCs were significantly increased in the AMA group, accompanied by activation of the p53-p21 pathway, which was also found in GCs from aged mice and H2O2-induced senescent KGN cells. Pyrosequencing methylation analysis revealed that increased expression of p53 was associated with decreased average methylation levels of CpG sites (-1031, -1019, -1012 and -1008) within the P53 promoter CpG island in senescenct GCs and KGN cells. We further found that decreased DNA-methyltransferase 1 (DNMT1) expression was responsible for the reduced methylation levels of the CpG sites.

CONCLUSION

Decreased DNMT1 with hypomethylation of the CpG sites within the P53 promoter CpG island in GCs is involved in ovarian aging.

Progressive hippocampal senescence and persistent memory deficits in traumatic brain Injury: A role of delayed testosterone

Cellular senescence is a stable, pro-inflammatory cell cycle arrest that has been recently implicated in the persistent memory deficits experienced with repetitive mild traumatic brain injury (rmTBI). Testosterone (T) treatment immediately following traumatic brain injury (TBI) mitigates cognitive deficits and cellular dysfunction known to induce cellular senescence. However, it has yet to be elucidated whether the therapeutic window for T treatment can be extended to a subacute time post-injury. This study examined the progression of hippocampal cellular senescence after rmTBI and evaluated the effects of subacute T on persistent memory deficits and cellular senescence post-injury. Changes in senescence-associated markers in the hippocampus were quantified at 5- and 9-weeks post-injury (WPI). An age-independent progressive increase in senescence-associated gene expression was observed for Cdkn2a, Cdkn1a, and p53 protein levels, along with a decrease in Sirt1 gene expression. Acute and persistent cognitive deficits were observed in the rmTBI rats as compared to sham rats. Serum T levels were significantly decreased at 4 WPI. Testosterone administration at 5 WPI ameliorated these persistent memory deficits. Moreover, subacute T treatment reduced rmTBI-induced levels of Cdkn2a 4 weeks post-treatment. This study indicates that rmTBI results in a progressive cellular senescence pathology that may contribute to the underlying mechanisms of persistent cognitive symptoms. Therapeutically targeting cellular senescence within this extended temporal window holds implications for patients dealing with the chronic cognitive ramifications of rmTBI.

Changing landscape of hematopoietic and mesenchymal cells and their interactions during aging and in age-related skeletal pathologies

Aging profoundly impacts mesenchymal and hematopoietic lineage cells, including their progenitors-the skeletal stem cells (SSCs) and hematopoietic stem cells (HSCs), respectively. SSCs are crucial for skeletal development, homeostasis, and regeneration, maintaining bone integrity by differentiating into osteoblasts, adipocytes, and other lineages that contribute to the bone marrow (BM) microenvironment. Meanwhile, HSCs sustain hematopoiesis and immune function. With aging, SSCs and HSCs undergo significant functional decline, partly driven by cellular senescence-a hallmark of aging characterized by irreversible growth arrest, secretion of pro-inflammatory factors (senescence associated secretory phenotype, SASP), and impaired regenerative potential. In SSCs, senescence skews lineage commitment toward adipogenesis at the expense of osteogenesis, contributing to increased bone marrow adiposity , reduced bone quality, and osteoporosis. Similarly, aged HSCs exhibit diminished self-renewal, biased differentiation, and heightened inflammation, compromising hematopoietic output and immune function. In this review, we examine the age-related cellular and molecular changes in SSCs and HSCs, their lineage decisions in the aging microenvironment, and the interplay between skeletal and hematopoietic compartments. We also discuss the role of senescence-driven alterations in BM homeostasis and how targeting cellular aging mechanisms may offer therapeutic strategies for mitigating age-related skeletal and hematopoietic decline.

Sirt6 deficiency promotes senescence and age-associated intervertebral disc degeneration in mice

Intervertebral disc degeneration is a major risk factor contributing to chronic low back and neck pain. While the etiological factors for disc degeneration vary, age is still one of the most important risk factors. Recent studies have shown the promising role of SIRT6 in mammalian aging and skeletal tissue health, however its role in the intervertebral disc health remains unexplored. We investigated the contribution of SIRT6 to disc health by studying the age-dependent spinal phenotype of mice with conditional deletion of Sirt6 in the disc (AcanCreERT2; Sirt6fl/fl). Histological studies showed a degenerative phenotype in knockout mice compared to Sirt6fl/fl control mice at 12 months, which became pronounced at 24 months. RNA-Seq analysis of NP and AF tissues, in vitro quantitative histone analysis, and RNA-seq with ATAC-seq multiomic studies revealed that SIRT6-loss resulted in changes in acetylation and methylation status of specific Histone 3 lysine residues and affected DNA accessibility and transcriptomic landscape. A decrease in autophagy and an increase in DNA damage were also noted in Sirt6-deficient cells. Further mechanistic insights revealed that loss of SIRT6 increased senescence and SASP burden in the disc characterized by increased p21, p19, γH2AX, IL-6, IL-1β, and TGF-β abundance. Taken together, our study highlights the contribution of SIRT6 in modulating DNA damage, autophagy, and cell senescence and its importance in maintaining disc health during aging, thereby underscoring it as a potential therapeutic target to treat intervertebral disc degeneration.

Aging and injury drive neuronal senescence in the dorsal root ganglia

Aging negatively impacts central nervous system function; however, there is limited information about the cellular impact of aging on peripheral nervous system function. Importantly, injury to vulnerable peripheral axons of dorsal root ganglion (DRG) neurons results in somatosensory dysfunction, such as pain, at higher rates in aged individuals. Cellular senescence is common to both aging and injury and contributes to the aged pro-inflammatory environment. We discovered DRG neuron senescence in the context of aging and pain-inducing peripheral nerve injury in young (~3 months) and aged (~24 months) male and female mice. Senescent neurons were dynamic and heterogeneous in their expression of multiple senescence markers, including pro-inflammatory factor IL6. Senescence marker-expressing neurons had nociceptor-like profiles, included high-firing phenotypes and displayed increased excitability after IL6 application. Furthermore, elimination of senescent cells resulted in improvement of nociceptive behaviors in nerve-injured mice. Finally, male and female post-mortem human DRG contained senescent neurons that increased with age (~32 years old versus 65 years old). Overall, we describe a susceptibility of the peripheral nervous system to neuronal senescence-a potential targetable mechanism to treat sensory dysfunction, such as chronic pain, particularly in aged populations.

Downregulating FGGY carbohydrate kinase domain containing promotes cell senescence by activating the p53/p21 signaling pathway in colorectal cancer

Carbohydrate kinases serve an oncogenic role in several types of cancer; however, the function of FGGY carbohydrate kinase domain containing (FGGY) in colorectal cancer (CRC) remains unknown. The present study investigated the function and possible molecular mechanisms of FGGY in CRC. The results showed that elevated levels of FGGY mRNA and protein were observed in CRC tissues, and a higher expression of FGGY was associated with advanced N stage and reduced overall survival time in patients with CRC. Silencing FGGY inhibited the viability of CRC cells by inducing cell cycle arrest and promoting apoptosis in vitro, thereby attenuating tumor growth in a xenograft mouse model. FGGY knockdown also enriched the senescence‑associated heterochromatin foci (SAHF) pathway and p53 pathway, as further confirmed by enhancing senescence‑associated β‑galactosidase (SA‑β‑gal) activity, with increased levels of SAHF‑associated proteins HP1γ and trimethylation of H3K9 (H3k9me3) in CRC cells, as well as upregulation of p53 and its downstream protein p21. Furthermore, p53 knockout rescued FGGY knockdown‑mediated reductions in cell viability, SA‑β‑gal activity, and the levels of HP1γ and H3k9me3 in CRC cells. These findings indicated that FGGY could act as a newly identified potential oncogene in CRC, partially through regulating the p53/p21 signaling pathway and altering cell senescence.

Hemin-induced transient senescence via DNA damage response: a neuroprotective mechanism against ferroptosis in intracerebral hemorrhage

Intracerebral hemorrhage (ICH) poses acute fatality and long-term neurological risks, in part due to hemin and iron accumulation from hemoglobin breakdown. We observed that hemin induces DNA double-strand breaks (DSBs), prompting a senescence-like phenotype in neurons, necessitating a deeper exploration of cellular responses. Using experimental ICH models and human ICH patient tissue, we elucidate hemin-mediated DNA damage response (DDR) inducing transient senescence and delayed expression of heme oxygenase (HO-1). HO-1 co-localizes with senescence-associated β-Galactosidase (SA-β-Gal) in ICH patient tissues, emphasizing the clinical relevance of inducible HO-1 expression in senescent cells. We reveal a reversible senescence state protective against acute cell death by hemin, while repeat exposure leads to long-lasting senescence. Inhibiting early senescence expression increases cell death, supporting the protective role of senescence against hemin toxicity. Hemin-induced senescence is attenuated by a pleiotropic carbon nanoparticle that is a catalytic mimic of superoxide dismutase, but this treatment increased lipid peroxidation, consistent with ferroptosis from hemin breakdown released iron. When coupled with iron chelator deferoxamine (DEF), the nanoparticle reduces hemin-induced senescence and upregulates factors protecting against ferroptosis. Our study suggests transient senescence induced by DDR as an early potential neuroprotective mechanism in ICH, but the risk of iron-related toxicity supports a multi-pronged therapeutic approach.

AMP-activated protein kinase (AMPK) is essential for tendon homeostasis and prevents premature senescence and ectopic calcification

Tendinopathy is a debilitating tendon disorder affecting millions of people, characterized by pain, swelling, and diminished biomechanical properties. While the precise mechanisms underlying tendon homeostasis remain unclear, metabolic regulation plays a critical role. In this study, we combine transcriptomic analysis of human tendinopathic samples with a conditional mouse model in which Prkaa1 (encoding AMPKα1) is selectively deleted in tendon progenitors to elucidate the role of AMPK signaling in tendon homeostasis. RNA sequencing of diseased human tendons revealed downregulation of key metabolic genes, including several involved in the mitochondrial electron transport chain and AMPK signaling pathways, alongside an increase in markers associated with senescence and a secretory inflammatory profile. In parallel, mice with loss of Prkaa1 function exhibited normal postnatal development; however, by one month of age, tendons demonstrated widespread transcriptional alterations related to cell cycle regulation and ECM organization. By three months, AMPKα1-deficient tendons showed significant reductions in mechanical strength and increased expression of senescence markers p21 and p16, progressing to prominent ectopic calcification with age. In vitro studies further confirmed that tendon fibroblasts lacking AMPKα1 have altered ECM substrate adhesion profiles. Importantly, voluntary exercise partially rescued these deficits by enhancing ECM organization and reducing senescence marker expression. Collectively, our findings demonstrate that AMPKα1 is critical for maintaining energy balance, regulating ECM remodeling, and preventing premature cellular senescence in tendon. These insights highlight AMPK signaling as a promising therapeutic target and underscore the beneficial role of exercise in mitigating tendinopathic changes.

Dose-dependent effects of curcumin on 22Rv1 prostate cancer cell line

BACKGROUND

Prostate cancer (PCa) is the second most frequent cancer type in the male population over 66 years. Curcumin is a polyphenolic natural compound extract from the rhizomes of Curcuma longa Linn (Zingiberaceae family) which showed important anticancer effects by inhibiting cell proliferation and inducing apoptosis in several cancer types. Recently, some studies reported that oral curcumin lowered PSA levels, but it did not modify the clinical outcomes in patients with prostate cancer who received intermittent androgen deprivation (IAD). Other studies reported that high concentrations of curcumin were toxic for patients.

METHODS AND RESULTS

In this study we showed that low doses of curcumin can induce senescence-like effects in 22Rv1 cell line while higher concentrations have cytotoxic effects. Five,15 and 30 µM curcumin blocked cell cycle in G2/M phase but only 15 and 30 µM curcumin induced cell death. In addition, an increased expression of p21, a known senescence marker, was detected in 22Rv1 cells treated with curcumin in every experimental condition. However, the expression of p16, another known senescence marker, increased only to 30 µM curcumin.

CONCLUSION

In the context of personalized approach in PCa care, we suggest that the appropriate concentration of curcumin used in combination with radiotherapy or with androgen deprivation therapy (ADT) could be taken into consideration.

Comparative analysis of transcriptomic profiles of mesenchymal stem cells at the onset of senescence and after exposure to acute exogenous oxidative stress

Cellular senescence can be triggered by a wide range of stress-inducing factors, including environmental and internal damaging events, such as oxidative stress. Moreover, stressed and senescent cells exhibit modifications in their transcriptional expression profile, but little is known regarding the common genes and pathways regulating these processes. Here, we analyzed the effects of long-term culture as well as exogenous acute oxidative stress on the transcriptional program of Wharton's jelly mesenchymal stem cells (WJ-MSCs). We demonstrate that, exposure to H2O2 compromised genomic stability and mitochondrial function in early passage WJ-MSCs, potentially initiating senescence to prevent cellular transformation. On the other hand, prolonged in vitro expansion of WJ-MSCs activated processes linked to integrins and extracellular matrix organization, possibly indicating the unfavorable consequences that senescence has on tissue integrity. Additionally, cells entering senescence and oxidative stressed young WJ-MSCs over-activated transcription factors related to permanent proliferative arrest and suppressed anti-senescence factors. Common differentially expressed genes in the late passage and H2O2-treated WJ-MSCs were implicated in DNA damage response and cell cycle arrest, which are known to trigger a senescent phenotype. Notably, the TP53INP1 gene emerged as a significantly upregulated gene in both late passage and H2O2-treated young WJ-MSCs, marking it as a potent senescence indicator. Silencing TP53INP1 mitigated the senescent phenotype, a role that appeared to be facilitated by autophagy regulation. Taken together, our results shed light on how transcriptomic changes govern MSCs' senescence program and identify key molecular drivers that could prove crucial for WJ-MSCs-based clinical applications.

Multiple synergistic anti-aging effects of vascular cell adhesion molecule 1 functionalized nanoplatform to improve age-related neurodegenerative diseases

Aging is a critical factor in the onset and progression of neurodegenerative diseases and cognitive decline, with aging-related neuroinflammation and cellular senescence being major contributors. In the aging brain, the cerebral vascular endothelium overexpresses vascular cell adhesion molecule 1 (VCAM1), activating microglia and leading to neuroinflammation and cognitive impairment. Quercetin, a natural neuroprotective agent widely used for treating neurodegenerative diseases, their therapeutic efficacy, however, is limited by its poor water solubility and inability to penetrate the blood-brain barrier (BBB). To address these challenges, we developed a multifunctional micellar platform (Anti-VCAM1-GM1@Q) to improve age-related neurodegenerative diseases. The micelles incorporate anti-VCAM1 antibodies to target cerebral vascular endothelial cells and block VCAM1. Additionally, monosialoganglioside (GM1) was utilized to deliver quercetin due to its biparental properties, high BBB permeability, and neuroprotective effects. Anti-VCAM1-GM1@Q micelles demonstrated strong anti-aging properties. They improved quercetin's bioavailability, effectively penetrated the BBB, targeted cerebral vascular endothelial cells, and reduced neuroinflammation. In animal models, these micelles provided effective neuroprotection, improved memory function and age-related cognitive impairment, and mitigated age-related neurodegeneration. Notably, this system exhibited remarkable treatment efficacy and high safety, indicating substantial potential for clinical translational applications.

Differential activation of p53-Lamin A/C and p16-RB mediated senescence pathways in trophoblast from pregnancies complicated by type A2 Gestational Diabetes Mellitus

Gestational diabetes mellitus (GDM) increases maternal risks such as hypertension and future type 2 diabetes while also contributing to fetal complications such as large-for-gestational-age infants and stillbirth. The placenta which is crucial for fetal development, exhibits structural and functional changes in GDM, but the impact of these alterations on placental trophoblast function remains unclear. During their differentiation villous cytotrophoblast display several characteristics of senescent cells however the role of senescence pathways in placental function remains unexplored in GDM. Here we investigate whether placental senescence pathways are altered in GDM, utilizing term villous tissue and primary trophoblasts to assess molecular changes, and determined fetal sex-based differences. Our data suggest that both p21 and p16 mediated senescence pathways are activated during trophoblast differentiation and are dysregulated in GDM placenta in a sexually dimorphic manner. We also provide evidence for increased activation of p53-Lamin A/C and p16-RB pathways in trophoblast from GDM placentas. Reduced expression of p21 and its downstream effects on GCM1 expression and βhCG secretion outline how altered physiological senescence can affect trophoblast differentiation and function. This is a seminal study highlighting how placental senescence pathways are altered in pregnancies complicated by GDM.

Gut microbial-derived phenylacetylglutamine accelerates host cellular senescence

Gut microbiota plays a crucial role in the host health in the aging process. However, the mechanisms for how gut microbiota triggers cellular senescence and the consequent impact on human aging remain enigmatic. Here we show that phenylacetylglutamine (PAGln), a metabolite linked to gut microbiota, drives host cellular senescence. Our findings indicate that the gut microbiota alters with age, which leads to increased production of phenylacetic acid (PAA) and its downstream metabolite PAGln in older individuals. The PAGln-induced senescent phenotype was verified in both cellular models and mouse models. Further experiments revealed that PAGln induces mitochondrial dysfunction and DNA damage via adrenoreceptor (ADR)-AMP-activated protein kinase (AMPK) signaling. Blockade of ADRs as well as senolytics therapy impede PAGln-induced cellular senescence in vivo, implying potential anti-aging therapies. This combined evidence reveals that PAGln, a naturally occurring metabolite of human gut microbiota, mechanistically accelerates host cellular senescence.

EBP50 regulates senescence and focal adhesion in endometrial carcinoma

Ezrin-radixin-moesin (ERM)-binding phosphoprotein 50 (EBP50) is a multifunctional scaffold protein that is highly expressed in polarized epithelial cells. Here, we focused on the functional roles of EBP50 in endometrial carcinoma (Em Ca). We analyzed immunohistochemical sections from 121 Em Ca and 30 normal samples. We also characterized EBP50 overexpression or knockout (KO) Em Ca cell lines. High levels of membranous (Me) EBP50 expression were observed in endometrial tissues from normal menstrual cycles, in contrast to the transient upregulation of cytoplasmic (Cyt) EBP50 in tissues in the proliferative phase; this was probably in response to estrogenic effects. There was a significant stepwise reduction of Me-EBP50 expression from grade (G) 1 to G3 Em Cas, which was consistent with the loss of glandular structures. Conversely, Cyt-EBP50 levels increased with in the higher tumor grades. Low Me-EBP50 expression was significantly associated with tumor lymphovascular invasion and short overall survival. Whereas EBP50 KO led to senescence and reduced proliferation and motility, overexpression elicited the opposite phenotypes. Moreover, the number of focal adhesions (FAs), which mediate cell migration, was significantly increased in EBP50 overexpressing cells but decreased in the KO cells. In conclusion, Me- and/or Cyt-EBP50 expression contributes to acceleration of cell motility through enhancement of FA formation, and inhibits senescence to promote cytokinesis. Together, these effects contribute to Em Ca aggressiveness.

Regulatory Network Inference of Induced Senescent Midbrain Cell Types Reveals Cell Type-Specific Senescence-Associated Transcriptional Regulators

Cellular senescence of brain cell types has become an increasingly important perspective for both aging and neurodegeneration, specifically in the context of Parkinson's Disease (PD). The characterization of classical hallmarks of senescence is a widely debated topic, whereby the context in which a senescence phenotype is being investigated, such as the cell type, the inducing stressor, and/or the model system, is an extremely important aspect to consider when defining a senescent cell. Here, we describe a cell type-specific profile of senescence through the investigation of various canonical senescence markers in five human midbrain cell lines using chronic 5-Bromodeoxyuridine (BrdU) treatment as a model of DNA damage-induced senescence. We used principal component analysis (PCA) and subsequent regulatory network inference to define both unique and common senescence profiles in the cell types investigated, as well as revealed senescence-associated transcriptional regulators (SATRs). Functional characterization of one of the identified regulators, transcription factor AP4 (TFAP4), further highlights the cell type-specificity of the expression of the various senescence hallmarks. Our data indicates that SATRs modulate cell type-specific profiles of induced senescence in key midbrain cell types that play an important role in the context of aging and PD.

Current Methodologies to Assess Cellular Senescence in Cancer

Cellular senescence plays a critical role in cancer, acting as both a tumor-suppressive and tumor-promoting mechanism. Senescent cells undergo stable cell-cycle arrest in response to various stressors, including DNA damage and oncogenic signaling, and exhibit a complex secretory phenotype known as the senescence-associated secretory phenotype (SASP), which can impact the tumor microenvironment. The hallmarks of senescence include cell-cycle arrest, secretion of pro-inflammatory factors, structural changes, and metabolic alterations. These features, while initially suppressing tumorigenesis, can later contribute to cancer progression under certain conditions. Methods for studying senescence in preclinical models include in vitro assays, ex vivo tissue analysis, and in vivo detection techniques. Emerging therapeutic strategies focus on exploiting senescence for cancer treatment, particularly through the use of senolytic agents that selectively eliminate senescent cells and senomorphic compounds that modulate SASP activity. However, the identification of reliable and universal biomarkers for senescence remains a challenge, necessitating a multimarker approach to accurately detect and characterize senescent cells in various contexts.

Studying Cellular Senescence Using the Model Organism Drosophila melanogaster

Cellular senescence, a complex biological process characterized by irreversible cell cycle arrest, contributes significantly to the development and progression of aging and of age-related diseases. Studying cellular senescence in vivo can be challenging due to the high heterogeneity and dynamic nature of senescent cells. Recently, Drosophila melanogaster has emerged as a powerful model organism for studying aging and cellular senescence due to its tractability and short lifespan, as well as due to the conservation of age-related genes and of key age-related pathways with mammals. Consequently, several research studies have utilized Drosophila to investigate the cellular mechanisms and pathways implicated in cellular senescence. Herein, we provide an overview of the assays that can be applied to study the different features of senescent cells in D. melanogaster tissues, highlighting the benefits of this model in aging research. We also emphasize the importance of selecting appropriate biomarkers for the identification of senescent cells, and the need for further understanding of the aging process including a more accurate identification and detection of senescent cells at the organismal level; a far more complex process as compared to single cells.

Rejuvenating aged osteoprogenitors for bone repair

Aging is marked by a decline in tissue regeneration, posing significant challenges to an increasingly older population. Here, we investigate age-related impairments in calvarial bone healing and introduce a novel two-part rejuvenation strategy to restore youthful repair. We demonstrate that aging negatively impacts the calvarial bone structure and its osteogenic tissues, diminishing osteoprogenitor number and function and severely impairing bone formation. Notably, increasing osteogenic cell numbers locally fails to rescue repair in aged mice, identifying the presence of intrinsic cellular deficits. Our strategy combines Wnt-mediated osteoprogenitor expansion with intermittent fasting, which leads to a striking restoration of youthful levels of bone healing. We find that intermittent fasting improves osteoprogenitor function, benefits that can be recapitulated by modulating NAD+-dependent pathways or the gut microbiota, underscoring the multifaceted nature of this intervention. Mechanistically, we identify mitochondrial dysfunction as a key component in age-related decline in osteoprogenitor function and show that both cyclical nutrient deprivation and Nicotinamide mononucleotide rejuvenate mitochondrial health, enhancing osteogenesis. These findings offer a promising therapeutic avenue for restoring youthful bone repair in aged individuals, with potential implications for rejuvenating other tissues.

Cellular senescence as a key contributor to secondary neurodegeneration in traumatic brain injury and stroke

Traumatic brain injury (TBI) and stroke pose major health challenges, impacting millions of individuals globally. Once considered solely acute events, these neurological conditions are now recognized as enduring pathological processes with long-term consequences, including an increased susceptibility to neurodegeneration. However, effective strategies to counteract their devastating consequences are still lacking. Cellular senescence, marked by irreversible cell-cycle arrest, is emerging as a crucial factor in various neurodegenerative diseases. Recent research further reveals that cellular senescence may be a potential driver for secondary neurodegeneration following brain injury. Herein, we synthesize emerging evidence that TBI and stroke drive the accumulation of senescent cells in the brain. The rationale for targeting senescent cells as a therapeutic approach to combat neurodegeneration following TBI/stroke is outlined. From a translational perspective, we emphasize current knowledge and future directions of senolytic therapy for these neurological conditions.

Single Cell MALDI-MSI Analysis of Lipids and Proteins within a Replicative Senescence Fibroblast Model

In this study, we evaluate lipids and select proteins in human lung fibroblasts (hLFs) to interrogate changes occurring due to aging and senescence. To study single cell populations, a comparison of cells adhered onto slides using poly-d-lysine versus centrifugal force deposition was first analyzed to determine whether specific alterations were observed between preparations. The poly-d-lysine approach was then utilized to interrogate the lipidome of the cell populations and further evaluate potential applications of the MALDI-immunohistochemistry (IHC) platform for single-cell-level analyses. Two protein markers of senescence, vimentin and p21, were both observed within the fibroblast populations and quantified. Lipidomic analysis of the fibroblasts found 12 lipids significantly altered because of replicative senescence, including fatty acids, such as stearic acid, and ceramide phosphoethanolamine species (CerPE). Similar to previous reports, alterations were detected in putative fatty acid building blocks, ceramides, among other lipid species. Altogether, our results reveal the ability to detect lipids implicated in senescence and show alterations to protein expression between normal and senescent fibroblast populations, including differences between young and aged cells. This report is the first time that the MALDI-IHC system has been utilized at a single-cell level to analyze both protein expression and lipid profiles in cultured cells, with a particular focus on changes associated with aging and senescence.

mTOR potentiates senescent phenotypes and primary cilia formation after cisplatin-induced G2 arrest in retinal pigment epithelial cells

Cisplatin, a platinum-based anticancer drug, is used to treat several types of cancer. Despite its effectiveness, cisplatin-induced side effects have often been reported. Although cisplatin-induced toxicities, such as apoptosis and/or necrosis, have been well studied, the fate of cells after exposure to sublethal doses of cisplatin needs further elucidation. Treatment with a sublethal dose of cisplatin induced cell cycle arrest at the G2 phase in retinal pigment epithelial cells. Following cisplatin withdrawal, the cells irreversibly exited the cell cycle and became senescent. Notably, the progression from the G2 to the G1 phase occurred without mitotic entry, a phenomenon referred to as mitotic bypass, resulting in the accumulation of cells containing 4N DNA content. Cisplatin-exposed cells exhibited morphological changes associated with senescence, including an enlarged size of cell and nucleus and increased granularity. In addition, the senescent cells possessed primary cilia and persistent DNA lesions. Senescence induced by transient exposure to cisplatin involves mTOR activation. Although transient co-exposure with an mTORC1 inhibitor rapamycin did not prevent mitotic bypass and entry into senescence, it delayed the progression of senescence and attenuated senescent phenotypes, resulting in shorter primary cilia formation. Conclusively, cisplatin induces senescence in retinal pigment epithelial cells by promoting mTOR activation.

Oxygen matters: Unraveling the role of oxygen in the neuronal response to cisplatin

BACKGROUND AND AIMS

Cell culture is a fundamental experimental tool for understanding cell physiology. However, translating these findings to in vivo settings has proven challenging. Replicating donor tissue conditions, including oxygen levels, is crucial for achieving meaningful results. Nevertheless, oxygen culture conditions are often overlooked, particularly in the context of chemotherapy-induced neurotoxicity.

METHODS

In this study, we investigated the role of oxygen levels in primary neuronal cultures by comparing neuronal performance under cisplatin exposure (1 μg/mL) in supraphysiological normoxia (representing atmospheric conditions in a standard incubator; 18.5% O2) and physioxia (representing physiologic oxygen conditions in nervous tissue; 5% O2). Experiments were also conducted to assess survival, neurite development, senescence marker expression, and proinflammatory cytokine secretion.

RESULTS

Under control conditions, both oxygen concentration conditions exhibited similar behaviors. However, after cisplatin administration, sensory neurons cultured under supraphysiological normoxic conditions show higher mortality, exhibit an evolutionarily proinflammatory cytokine profile over time, and activate apoptotic-regulated neuron death markers. In contrast, under physiological conditions, neurons treated with cisplatin exhibited senescence marker expression and an attenuated inflammatory secretome.

INTERPRETATION

These results underscore the critical role of oxygen in neuronal culture, particularly in studying compounds where neuronal damage is mechanistically linked to oxidative stress. Even at identical doses of evaluated neurotoxic drugs, distinct cellular phenotypic fates can emerge, impacting translatability to the in vivo setting.

The cell cycle inhibitor p21CIP1 is essential for irinotecan-induced senescence and plays a decisive role in re-sensitization of temozolomide-resistant glioblastoma cells to irinotecan

BACKGROUND AND PURPOSE

Standard of care for glioblastomas includes radio-chemotherapy with the monoalkylating compound temozolomide. Temozolomide induces primarily senescence, inefficiently killing glioblastoma cells. Recurrences are inevitable. Although recurrences presumably arise from cells evading/escaping TMZ-induced senescence, becoming resistant, they are often again treated with TMZ. As an alternative treatment, irinotecan could be used. Our aim was to examine to what extent and conditions the topoisomerase I inhibitor irinotecan induces senescence and to analyze the underlying mechanism.

RESULTS

Multiple glioblastoma lines with different genetic signatures for p53, p21CIP1, p16INK4A, p14ARF, and PTEN were used. By means of LN229 glioblastoma clones which escaped from temozolomide-induced senescence, thus, being potentially recurrence-forming, we show that this escape is accompanied by increased p21CIP1 protein levels in temozolomide-unexposed senescence-evading clones and inability of temozolomide to induce p21CIP1. In contrast, irinotecan was still able to induce p21CIP1 and could elevate senescence and cell death. In combination with the senolytic drug BV6, irinotecan-induced senescence was significantly reduced. Differential response clusters were also observed in paired samples of newly diagnosed and recurrent patients' tumors. This can partially explain a significantly prolonged progression-free time until surgery for recurrence in patients additionally treated with irinotecan after temozolomide consolidation and upon the first onset of recurrence.

CONCLUSIONS

p21CIP1 is essentially involved in induction and maintenance of irinotecan-induced senescence. Neither p16INK4A, p14ARF, nor PTEN contribute to senescence, if p21CIP1 cannot be induced. Based on the positive results of the irinotecan/BV6 treatment, combatting recurrent glioblastomas by targeting senescence cell antiapoptotic pathways (SCAPs) should be considered.

Distribution and impact of p16INK4A+ senescent cells in elderly tissues: a focus on senescent immune cell and epithelial dysfunction

Cellular senescence, recognized as a key hallmark of aging, leads to the accumulation of senescent cells in various tissues over time. While the detrimental effects of these cells on age-related pathological conditions are well-documented, there is still limited information about how senescent cells are distributed in normal tissues of both young and aged organs. Our research indicates that fully senescent p16INK4A+ cells are rarely identified in the parenchyma of organic tissues and in the stromal cells crucial for structural maintenance, such as fibroblasts and smooth muscle cells. Instead, p16INK4A+ cells are more commonly found in immune cells, whether they reside in the organ or are infiltrating. Notably, p16INK4A+ senescent T cells have been observed to induce apoptosis and inflammation in colonic epithelial cells through Granzyme A-PARs signaling, compromising the integrity of the epithelial lining. This study showed that the senescence of immune cells could affect the phenotypical change of the parenchymal cells in the elderly and suggests that targeting immunosenescence might be a strategy to control functional decline in this population.

Senescence-like Phenotype After Chronic Exposure to Isoproterenol in Primary Quiescent Immune Cells

Chronic stress is associated with a higher risk for carcinogenesis as well as age-related diseases and immune dysfunction. There is evidence showing that psychological stress can contribute to premature immunosenescence. Therefore, the question arose whether chronic exposure to catecholamine could drive immune cells into senescence. Peripheral blood mononuclear cells were isolated from whole blood. After repeated ex vivo treatment with isoproterenol, an epinephrine analog, well-established senescence biomarkers were assessed. We found (i) DNA double-strand break induction, (ii) telomere shortening, (iii) failure to proliferate, (iv) higher senescence-associated β-galactosidase activity, (v) decreases in caspases 3 and 7 activity, and (vi) strong upregulation of the proteoglycan versican accompanied by increased cellular adhesion suggesting the induction of a senescence-like phenotype. These results emphasize the complexity of the effect of isoproterenol on multiple cellular processes and provide insights into the molecular mechanisms of stress leading to immunosenescence.

Prostaglandin E2 regulates senescence and post-senescence neoplastic escape in primary human keratinocytes

Aging of the epidermis partially occurs as a consequence of epidermal cell senescence, a non-proliferative state in which cells remain metabolically active and acquire changes in their secretome. We previously reported that senescent normal human epidermal keratinocytes (NHEKs) have two opposite outcomes: either cell death by excess of autophagic activity or escape from senescence to give rise to post-senescence neoplastic emerging (PSNE) cells. In this study, we investigated the role of PTGS2, the inducible enzyme of the prostaglandin biosynthesis pathway, in the onset of NHEK senescence and in the switch from senescence to pre-transformation. We provide evidence that the PTGS2/PGE2/EP4 pathway plays a critical role in NHEK senescence as well as in senescence escape. We show that treating proliferating NHEKs with prostaglandin E2 (PGE2) or with an agonist of one of its receptors, EP4, induced the establishment of the senescent phenotype, according to several markers including the senescence-associated β-galactosidase activity. Conversely, treating already senescent NHEKs with an antagonist of EP4, or knocking-down PTGS2 by siRNA resulted in the decrease of the percentage of senescence-associated β-galactosidase-positive cells. We also demonstrate that the PSNE frequency was significantly decreased upon PTGS2 silencing by siRNA, pharmacological PTGS2 inhibition, or treatment by an EP4 antagonist, while on the contrary treatments with PGE2 or EP4 agonist increased the PSNE frequency. These results indicate that the PTGS2/PGE2/EP4 pathway is required to induce and maintain the senescent phenotype of NHEKs, and that PGE2 level is a potential determinant of the initial steps of the age-related oncogenic process.

The role of cardiomyocyte senescence in cardiovascular diseases: A molecular biology update

Cardiovascular diseases (CVD) are the leading cause of death worldwide, and advanced age is a main contributor to the prevalence of CVD. Cellular senescence is an irreversible state of cell cycle arrest that occurs in old age or after cells encounter various stresses. Senescent cells not only result in the reduction of cellular function, but also produce senescence-associated secretory phenotype (SASP) to affect surrounding cells and tissue microenvironment. There is increasing evidence that the gradual accumulation of senescent cardiomyocytes is causally involved in the decline of cardiovascular system function. To highlight the role of senescent cardiomyocytes in the pathophysiology of age-related CVD, we first introduced that senescent cardiomyoyctes can be identified by structural changes and several senescence-associated biomarkers. We subsequently provided a comprehensive summary of existing knowledge, outlining the compelling evidence on the relationship between senescent cardiomyocytes and age-related CVD phenotypes. In addition, we discussed that the significant therapeutic potential represented by the prevention of accelerated senescent cardiomyocytes, and the current status of some existing geroprotectors in the prevention and treatment of age-related CVD. Together, the review summarized the role of cardiomyocyte senescence in CVD, and explored the molecular knowledge of senescent cardiomyocytes and their potential clinical significance in developing senescent-based therapies, thereby providing important insights into their biology and potential therapeutic exploration.

Body Composition and Senescence: Impact of Polyphenols on Aging-Associated Events

Aging is a dynamic and progressive process characterized by the gradual accumulation of cellular damage. The continuous functional decline in the intrinsic capacity of living organisms to precisely regulate homeostasis leads to an increased susceptibility and vulnerability to diseases. Among the factors contributing to these changes, body composition-comprised of fat mass and lean mass deposits-plays a crucial role in the trajectory of a disability. Particularly, visceral and intermuscular fat deposits increase with aging and are associated with adverse health outcomes, having been linked to the pathogenesis of sarcopenia. Adipose tissue is involved in the secretion of bioactive factors that can ultimately mediate inter-organ pathology, including skeletal muscle pathology, through the induction of a pro-inflammatory profile such as a SASP, cellular senescence, and immunosenescence, among other events. Extensive research has shown that natural compounds have the ability to modulate the mechanisms associated with cellular senescence, in addition to exhibiting anti-inflammatory, antioxidant, and immunomodulatory potential, making them interesting strategies for promoting healthy aging. In this review, we will discuss how factors such as cellular senescence and the presence of a pro-inflammatory phenotype can negatively impact body composition and lead to the development of age-related diseases, as well as how the use of polyphenols can be a functional measure for restoring balance, maintaining tissue quality and composition, and promoting health.

p53 dependence of senescence markers p21v1 and p21v2 in aging and acute injury

The senescence phenotype is heterogeneous, as observed by the context-dependent differential expression of senescence markers. Here, we provide evidence to demonstrate an inverse relationship in the expression pattern of the two murine variants of p21 (p21v1, and p21v2) in aging and hemorrhagic shock. While an upregulation of p21v1 was observed following hemorrhagic shock injury, p21v2 was upregulated in the aged mouse. We further show that the p21v1 response is, at least, partially independent of p53.

Carbon monoxide attenuates cellular senescence-mediated pulmonary fibrosis via modulating p53/PAI-1 pathway

PURPOSE

Idiopathic pulmonary fibrosis (IPF) is a fatal progressive condition often requiring lung transplantation. Accelerated senescence of type II alveolar epithelial cells (AECII) plays a crucial role in pulmonary fibrosis progression through the secretion of the senescence-associated secretory phenotype (SASP). Low-dose carbon monoxide (CO) possesses anti-inflammatory, anti-oxidative, and anti-aging properties. This study aims to explore the preventive effects of CO-releasing molecule 2 (CORM2) in a bleomycin-induced pulmonary fibrosis model.

METHODS

We established an pulmonary fibrosis model in C57BL/6J mice and evaluated the impact of CORM2 on fibrosis pathology using Masson's trichrome staining, fluorescence staining, and pulmonary function tests. Fibrogenic marker expression and SASP secretion in tissues and AECII cells were analyzed using qRT-PCR, Western blot, and ELISA assays both in vivo and in vitro. Additionally, we investigated DNA damage and cellular senescence through immunofluorescence and SA-β-gal staining.

RESULTS

CORM2 showed a preventive effect on bleomycin-induced lung fibrosis by improving pulmonary function and reducing the expression of fibrosis-related genes, such as TGF-β, α-SMA, Collagen I/III. CORM2 decreased the DNA damage response by inhibiting γ-H2AX, p53, and p21. We identified PAI-1 as a new target gene that was downregulated by CORM2, and which was associated with cellular senescence and fibrosis. CORM2 effectively inhibited cellular senescence and delayed EMT occurrence in AECII cells.

CONCLUSION

Our study highlights the potential of CORM2 in preventing DNA damage-induced cellular senescence in bleomycin-induced pulmonary fibrosis through modulation of the p53/PAI-1 signaling pathway. These findings underscore the promising prospects of CORM2 in targeting cellular senescence and the p53/PAI-1 pathway as a potential preventive strategy for IPF.

Exercise activates AMPK in mouse and human pancreatic islets to decrease senescence

Beta (β)-cell senescence contributes to type 2 diabetes mellitus (T2DM). While exercise is vital for T2DM management and significantly affects cellular ageing markers, its effect on β-cell senescence remains unexplored. Here, we show that short-term endurance exercise training (treadmill running, 1 h per day for 10 days) in two male and female mouse models of insulin resistance decreases β-cell senescence. In vivo and in vitro experiments revealed that this effect is mediated, at least in part, by training-induced increases in serum glucagon, leading to activation of 5'-AMP-activated protein kinase (AMPK) signalling in β-cells. AMPK activation resulted in the nuclear translocation of NRF2 and decreased expression of senescence markers and effectors. Remarkably, human islets from male and female donors with T2DM treated with serum collected after a 10-week endurance exercise training programme showed a significant decrease in the levels of senescence markers. These findings indicate that exercise training decreases senescence in pancreatic islets, offering promising therapeutic implications for T2DM.

Lens capsule advanced glycation end products induce senescence in epithelial cells: Implications for secondary cataracts

Posterior capsule opacification (PCO) is a common complication after cataract surgery. Residual lens epithelial cells (LECs) on the anterior lens capsule, after cataract surgery, migrate to the posterior lens capsule and undergo transdifferentiation into myofibroblast-like cells. Those cells synthesize excessive amounts of extracellular matrix and contribute to fibrosis during PCO. Cellular senescence, a phenomenon that increases with aging, has been implicated in several fibrotic diseases. Here, we have investigated the prevalence of senescent LECs within the lens posterior capsule and the ability of advanced glycation end products (AGEs) in lens capsules to induce senescence, contributing to PCO. Aged lens capsules from pseudophakic human cadaver eyes showed the presence of senescent LECs. In human capsular bags, LECs showed an age-dependent increase in senescence after 28 days of culture. Human LECs cultured on aged lens capsules for 3 days underwent senescence; this effect was not seen in LECs cultured on young lens capsules. Human LECs cultured on an AGE-modified extracellular matrix (ECM-AGEs) showed an AGE-concentration-dependent increase in the expression of senescence markers and reactive oxygen species (ROS) levels. Treatment with a RAGE antagonist and ROS inhibitor reduced the expression of senescence and fibrotic markers. Additionally, conditioned media from ECM-AGEs-treated cells induced the expression of fibrotic markers in naïve LECs. Together, these suggest that AGEs in the capsule induce senescence of LECs, which triggers the mesenchymal transition of neighboring non-senescent LECs and contributes to PCO.

SIRT6 loss causes intervertebral disc degeneration in mice by promoting senescence and SASP status

Intervertebral disc degeneration is a major risk factor contributing to chronic low back and neck pain. While the etiological factors for disc degeneration vary, age is still one of the most important risk factors. Recent studies have shown the promising role of SIRT6 in mammalian aging and skeletal tissue health, however its role in the intervertebral disc health remains unexplored. We investigated the contribution of SIRT6 to disc health by studying the age-dependent spinal phenotype of mice with conditional deletion of Sirt6 in the disc (Acan CreERT2 ; Sirt6 fl/fl ). Histological studies showed a degenerative phenotype in knockout mice compared to Sirt6 fl/fl control mice at 12 months which became pronounced at 24 months. RNA-Seq analysis of NP and AF tissues, quantitative histone analysis, and in vitro multiomics employing RNA-seq with ATAC-seq revealed that SIRT6-loss resulted in changes in acetylation and methylation status of specific Histone 3 lysine residues, thereby affecting DNA accessibility and transcriptomic landscape. A decrease in autophagy and an increase in DNA damage were also noted in Sirt6-deficient cells. Further mechanistic insights revealed that loss of SIRT6 increased senescence and SASP burden in the disc characterized by increased p21, γH2AX, IL-6, and TGF-β abundance. Taken together our study highlights the contribution of SIRT6 in modulating DNA damage, autophagy and cell senescence, and its importance in maintaining disc health during aging thereby underscoring it as a potential therapeutic target to treat intervertebral disc degeneration.

Systematic transcriptomic analysis and temporal modelling of human fibroblast senescence

Cellular senescence is a diverse phenotype characterised by permanent cell cycle arrest and an associated secretory phenotype (SASP) which includes inflammatory cytokines. Typically, senescent cells are removed by the immune system, but this process becomes dysregulated with age causing senescent cells to accumulate and induce chronic inflammatory signalling. Identifying senescent cells is challenging due to senescence phenotype heterogeneity, and senotherapy often requires a combinatorial approach. Here we systematically collected 119 transcriptomic datasets related to human fibroblasts, forming an online database describing the relevant variables for each study allowing users to filter for variables and genes of interest. Our own analysis of the database identified 28 genes significantly up- or downregulated across four senescence types (DNA damage induced senescence (DDIS), oncogene induced senescence (OIS), replicative senescence, and bystander induced senescence) compared to proliferating controls. We also found gene expression patterns of conventional senescence markers were highly specific and reliable for different senescence inducers, cell lines, and timepoints. Our comprehensive data supported several observations made in existing studies using single datasets, including stronger p53 signalling in DDIS compared to OIS. However, contrary to some early observations, both p16 and p21 mRNA levels rise quickly, depending on senescence type, and persist for at least 8-11 days. Additionally, little evidence was found to support an initial TGFβ-centric SASP. To support our transcriptomic analysis, we computationally modelled temporal protein changes of select core senescence proteins during DDIS and OIS, as well as perform knockdown interventions. We conclude that while universal biomarkers of senescence are difficult to identify, conventional senescence markers follow predictable profiles and construction of a framework for studying senescence could lead to more reproducible data and understanding of senescence heterogeneity.

To target cellular senescence in diabetic kidney disease: the known and the unknown

Cellular senescence represents a condition of irreversible cell cycle arrest, characterized by heightened senescence-associated beta-galactosidase (SA-β-Gal) activity, senescence-associated secretory phenotype (SASP), and activation of the DNA damage response (DDR). Diabetic kidney disease (DKD) is a significant contributor to end-stage renal disease (ESRD) globally, with ongoing unmet needs in terms of current treatments. The role of senescence in the pathogenesis of DKD has attracted substantial attention with evidence of premature senescence in this condition. The process of cellular senescence in DKD appears to be associated with mitochondrial redox pathways, autophagy, and endoplasmic reticulum (ER) stress. Increasing accumulation of senescent cells in the diabetic kidney not only leads to an impaired capacity for repair of renal injury, but also the secretion of pro-inflammatory and profibrotic cytokines and growth factors causing inflammation and fibrosis. Current treatments for diabetes exhibit varying degrees of renoprotection, potentially via mitigation of senescence in the diabetic kidney. Targeting senescent cell clearance through pharmaceutical interventions could emerge as a promising strategy for preventing and treating DKD. In this paper, we review the current understanding of senescence in DKD and summarize the possible therapeutic interventions relevant to senescence in this field.

Regulation of cell function and identity by cellular senescence

During aging and in some contexts, like embryonic development, wound healing, and diseases such as cancer, senescent cells accumulate and play a key role in different pathophysiological functions. A long-held belief was that cellular senescence decreased normal cell functions, given the loss of proliferation of senescent cells. This view radically changed following the discovery of the senescence-associated secretory phenotype (SASP), factors released by senescent cells into their microenvironment. There is now accumulating evidence that cellular senescence also promotes gain-of-function effects by establishing, reinforcing, or changing cell identity, which can have a beneficial or deleterious impact on pathophysiology. These effects may involve both proliferation arrest and autocrine SASP production, although they largely remain to be defined. Here, we provide a historical overview of the first studies on senescence and an insight into emerging trends regarding the effects of senescence on cell identity.

Multiparametric identification of putative senescent cells in skeletal muscle via mass cytometry

Senescence is an irreversible arrest of the cell cycle that can be characterized by markers of senescence such as p16, p21, and KI-67. The characterization of different senescence-associated phenotypes requires selection of the most relevant senescence markers to define reliable cytometric methodologies. Mass cytometry (a.k.a. Cytometry by time of flight, CyTOF) can monitor up to 40 different cell markers at the single-cell level and has the potential to integrate multiple senescence and other phenotypic markers to identify senescent cells within a complex tissue such as skeletal muscle, with greater accuracy and scalability than traditional bulk measurements and flow cytometry-based measurements. This article introduces an analysis framework for detecting putative senescent cells based on clustering, outlier detection, and Boolean logic for outliers. Results show that the pipeline can identify putative senescent cells in skeletal muscle with well-established markers such as p21 and potential markers such as GAPDH. It was also found that heterogeneity of putative senescent cells in skeletal muscle can partly be explained by their cell type. Additionally, autophagy-related proteins ATG4A, LRRK2, and GLB1 were identified as important proteins in predicting the putative senescent population, providing insights into the association between autophagy and senescence. It was observed that sex did not affect the proportion of putative senescent cells among total cells. However, age did have an effect, with a higher proportion observed in fibro/adipogenic progenitors (FAPs), satellite cells, M1 and M2 macrophages from old mice. Moreover, putative senescent cells from muscle of old and young mice show different expression levels of senescence-related proteins, with putative senescent cells of old mice having higher levels of p21 and GAPDH, whereas putative senescent cells of young mice had higher levels of IL-6. Overall, the analysis framework prioritizes multiple senescence-associated proteins to characterize putative senescent cells sourced from tissue made of different cell types.

Hemin-Induced Transient Senescence Via DNA Damage Response: A Neuroprotective Mechanism Against Ferroptosis in Intracerebral Hemorrhage

Intracerebral hemorrhage (ICH) poses acute fatality and long-term neurological risks due to hemin and iron accumulation from hemoglobin breakdown. Our observation that hemin induces DNA double-strand breaks (DSBs), prompting a senescence-like phenotype in neurons, necessitating deeper exploration of cellular responses. Using experimental ICH models and human ICH patient tissue, we elucidate hemin-mediated DNA damage response (DDR) inducing transient senescence and delayed expression of heme oxygenase (HO-1). HO-1 co-localizes with senescence-associated β-Galactosidase (SA-β-Gal) in ICH patient tissues, emphasizing clinical relevance of inducible HO-1 expression in senescent cells. We reveal a reversible senescence state protective against acute cell death by hemin, while repeat exposure leads to long-lasting senescence. Inhibiting early senescence expression increases cell death, supporting the protective role of senescence against hemin toxicity. Hemin-induced senescence is attenuated by a pleiotropic carbon nanoparticle that is a catalytic mimic of superoxide dismutase, but this treatment increased lipid peroxidation, consistent with ferroptosis from hemin breakdown released iron. When coupled with iron chelator deferoxamine (DEF), the nanoparticle reduces hemin-induced senescence and upregulates factors protecting against ferroptosis. Our study suggests transient senescence induced by DDR as an early potential neuroprotective mechanism in ICH, but the risk or iron-related toxicity supports a multi-pronged therapeutic approach.

Skeletal phenotypes and molecular mechanisms in aging mice

Aging is an inevitable physiological process, often accompanied by age-related bone loss and subsequent bone-related diseases that pose serious health risks. Research on skeletal diseases caused by aging in humans is challenging due to lengthy study durations, difficulties in sampling, regional variability, and substantial investment. Consequently, mice are preferred for such studies due to their similar motor system structure and function to humans, ease of handling and care, low cost, and short generation time. In this review, we present a comprehensive overview of the characteristics, limitations, applicability, bone phenotypes, and treatment methods in naturally aging mice and prematurely aging mouse models (including SAMP6, POLG mutant, LMNA, SIRT6, ZMPSTE24, TFAM, ERCC1, WERNER, and KL/KL-deficient mice). We also summarize the molecular mechanisms of these aging mouse models, including cellular DNA damage response, senescence-related secretory phenotype, telomere shortening, oxidative stress, bone marrow mesenchymal stem cell (BMSC) abnormalities, and mitochondrial dysfunction. Overall, this review aims to enhance our understanding of the pathogenesis of aging-related bone diseases.

The p21CIP1-CDK4-DREAM axis is a master regulator of genotoxic stress-induced cellular senescence

Cellular senescence, a major driver of aging, can be stimulated by DNA damage, and is counteracted by the DNA repair machinery. Here we show that in p16INK4a-deficient cells, senescence induction by the environmental genotoxin B[a]P or ionizing radiation (IR) completely depends on p21CIP1. Immunoprecipitation-based mass spectrometry interactomics data revealed that during senescence induction and maintenance, p21CIP1 specifically inhibits CDK4 and thereby activates the DREAM complex. Genome-wide transcriptomics revealed striking similarities in the response induced by B[a]P and IR. Among the top 100 repressed genes 78 were identical between B[a]P and IR and 76 were DREAM targets. The DREAM complex transcriptionally silences the main proliferation-associated transcription factors E2F1, FOXM1 and B-Myb as well as multiple DNA repair factors. Knockdown of p21CIP1, E2F4 or E2F5 diminished both, repression of these factors and senescence. The transcriptional profiles evoked by B[a]P and IR largely overlapped with the profile induced by pharmacological CDK4 inhibition, further illustrating the role of CDK4 inhibition in genotoxic stress-induced senescence. Moreover, data obtained by live-cell time-lapse microscopy suggest the inhibition of CDK4 by p21CIP1 is especially important for arresting cells which slip through mitosis. Overall, we identified the p21CIP1/CDK4/DREAM axis as a master regulator of genotoxic stress-induced senescence.

CDC7 inhibition drives an inflammatory response and a p53-dependent senescent-like state in breast epithelial cells

Drugs that block DNA replication prevent cell proliferation, which may result in anticancer activity. The latter is dependent on the drug's mode of action as well as on cell type-dependent responses to treatment. The inhibition of Cell division cycle 7-related protein kinase (CDC7), a key regulator of DNA replication, decreases the efficiency of origin firing and hampers the restarting of paused replication forks. Here, we show that upon prolonged CDC7 inhibition, breast-derived MCF10A cells progressively withdraw from the cell cycle and enter a reversible senescent-like state. This is characterised by the rewiring of the transcriptional programme with the induction of cytokine and chemokine expression and correlates with the accumulation of Cyclic GMP-AMP synthase (cGAS)-positive micronuclei. Importantly, cell fate depends on Cellular tumour antigen p53 (p53) function as cells no longer enter senescence but are funnelled into apoptosis upon p53 knockout. This work uncovers key features of the secondary response to CDC7 inhibitors, which could aid the development of these compounds as anticancer drugs.

RAS-activated PI3K/AKT signaling sustains cellular senescence via P53/P21 axis in experimental models of psoriasis

BACKGROUND

Psoriasis is a chronic immune-mediated skin disease in which upper epidermal keratinocytes exhibit a senescent-like phenotype. In psoriatic skin, a variety of inflammatory cytokines can activate intracellular pathways including phosphatidylinositol 3-kinase (PI3K)/AKT signaling and RAS effectors. AKT and RAS participate to cellular senescence, but currently their role in senescence responses occurring in psoriasis have not yet been investigated.

OBJECTIVE

The role of AKT molecular axis and RAS activation was evaluated in the context of cellular senescence in psoriasis disease.

METHODS

RAS/AKT involvement in senescence was analyzed in psoriatic keratinocytes cultures subjected to multiple passages to promote senescence in vitro, as well as in skin lesions of patients affected by psoriasis. The impact of pharmacological inhibition of PI3K/AKT pathway on senescence and inflammation responses was tested in senescent psoriatic keratinocytes and in a psoriasiform dermatitis murine model induced by RAS overexpression in the upper epidermis of mice.

RESULTS

We found AKT hyperactivation associated to the upregulation of senescence markers, in senescent psoriatic keratinocyte cultures, as well as in skin lesions of psoriatic patients. AKT-induced senescence was sustained by constitutive RAS activation, and down-stream responses were mediated by P53/P21 axis. PI3K/AKT inhibition contrasted senescence processes induced by cytokines in psoriatic keratinocytes. Additionally, RAS-induced psoriasis-like dermatitis in mice was accompanied by AKT upregulation, increase of senescence marker expression and by skin inflammation. In this model, both senescence and inflammation were significantly reduced by selective AKT inhibition.

CONCLUSION

Therefore, targeting RAS-AKT pathway could be a promising novel strategy to counteract multiple psoriasis symptoms.

The Role of Aging and Senescence in Immune Checkpoint Inhibitor Response and Toxicity

Cellular senescence accumulates with age and has been shown to impact numerous physiological and pathological processes, including immune function. The role of cellular senescence in cancer is multifaceted, but the impact on immune checkpoint inhibitor response and toxicity has not been fully evaluated. In this review, we evaluate the impact of cellular senescence in various biological compartments, including the tumor, the tumor microenvironment, and the immune system, on immune checkpoint inhibitor efficacy and toxicity. We provide an overview of the impact of cellular senescence in normal and pathological contexts and examine recent studies that have connected aging and cellular senescence to immune checkpoint inhibitor treatment in both the pre-clinical and clinical contexts. Overall, senescence plays a multi-faceted, context-specific role and has been shown to modulate immune-related adverse event incidence as well as immune checkpoint inhibitor response.

The human colon: Evidence for degenerative changes during aging and the physiological consequences

BACKGROUND

The incidence of constipation increases among the elderly (>65 years), while abdominal pain decreases. Causes include changes in lifestyle (e.g., diet and reduced exercise), disease and medications affecting gastrointestinal functions. Degenerative changes may also occur within the colo-rectum. However, most evidence is from rodents, animals with relatively high rates of metabolism and accelerated aging, with considerable variation in time course. In humans, cellular and non-cellular changes in the aging intestine are poorly investigated.

PURPOSE

To examine all available studies which reported the effects of aging on cellular and tissue functions of human isolated colon, noting the region studied, sex and age of tissue donors and study size. The focus on human colon reflects the ability to access full-thickness tissue over a wide age range, compared with other gastrointestinal regions. Details are important because of natural human variability. We found age-related changes within the muscle, in the enteric and nociceptor innervation, and in the submucosa. Some involve all regions of colon, but the ascending colon appears more vulnerable. Changes can be cell- and sublayer-dependent. Mechanisms are unclear but may include development of "senescent-like" and associated inflammaging, perhaps associated with increased mucosal permeability to harmful luminal contents. In summary, reduced nociceptor innervation can explain diminished abdominal pain among the elderly. Degenerative changes within the colon wall may have little impact on symptoms and colonic functions, because of high "functional reserve," but are likely to facilitate the development of constipation during age-related challenges (e.g., lifestyle, disease, and medications), now operating against a reduced functional reserve.

Senescent glia link mitochondrial dysfunction and lipid accumulation

Senescence is a cellular state linked to ageing and age-onset disease across many mammalian species1,2. Acutely, senescent cells promote wound healing3,4 and prevent tumour formation5; but they are also pro-inflammatory, thus chronically exacerbate tissue decline. Whereas senescent cells are active targets for anti-ageing therapy6-11, why these cells form in vivo, how they affect tissue ageing and the effect of their elimination remain unclear12,13. Here we identify naturally occurring senescent glia in ageing Drosophila brains and decipher their origin and influence. Using Activator protein 1 (AP1) activity to screen for senescence14,15, we determine that senescent glia can appear in response to neuronal mitochondrial dysfunction. In turn, senescent glia promote lipid accumulation in non-senescent glia; similar effects are seen in senescent human fibroblasts in culture. Targeting AP1 activity in senescent glia mitigates senescence biomarkers, extends fly lifespan and health span, and prevents lipid accumulation. However, these benefits come at the cost of increased oxidative damage in the brain, and neuronal mitochondrial function remains poor. Altogether, our results map the trajectory of naturally occurring senescent glia in vivo and indicate that these cells link key ageing phenomena: mitochondrial dysfunction and lipid accumulation.

Differential impact of sex on regulation of skeletal muscle mitochondrial function and protein homeostasis by hypoxia-inducible factor-1α in normoxia

Hypoxia-inducible factor (HIF)-1α is continuously synthesized and degraded in normoxia. During hypoxia, HIF1α stabilization restricts cellular/mitochondrial oxygen utilization. Cellular stressors can stabilize HIF1α even during normoxia. However, less is known about HIF1α function(s) and sex-specific effects during normoxia in the basal state. Since skeletal muscle is the largest protein store in mammals and protein homeostasis has high energy demands, we determined HIF1α function at baseline during normoxia in skeletal muscle. Untargeted multiomics data analyses were followed by experimental validation in differentiated murine myotubes with loss/gain of function and skeletal muscle from mice without/with post-natal muscle-specific Hif1a deletion (Hif1amsd). Mitochondrial oxygen consumption studies using substrate, uncoupler, inhibitor, titration protocols; targeted metabolite quantification by gas chromatography-mass spectrometry; and post-mitotic senescence markers using biochemical assays were performed. Multiomics analyses showed enrichment in mitochondrial and cell cycle regulatory pathways in Hif1a deleted cells/tissue. Experimentally, mitochondrial oxidative functions and ATP content were higher with less mitochondrial free radical generation with Hif1a deletion. Deletion of Hif1a also resulted in higher concentrations of TCA cycle intermediates and HIF2α proteins in myotubes. Overall responses to Hif1amsd were similar in male and female mice, but changes in complex II function, maximum respiration, Sirt3 and HIF1β protein expression and muscle fibre diameter were sex-dependent. Adaptive responses to hypoxia are mediated by stabilization of constantly synthesized HIF1α. Despite rapid degradation, the presence of HIF1α during normoxia contributes to lower mitochondrial oxidative efficiency and greater post-mitotic senescence in skeletal muscle. In vivo responses to HIF1α in skeletal muscle were differentially impacted by sex. KEY POINTS: Hypoxia-inducible factor -1α (HIF1α), a critical transcription factor, undergoes continuous synthesis and proteolysis, enabling rapid adaptive responses to hypoxia by reducing mitochondrial oxygen consumption. In mammals, skeletal muscle is the largest protein store which is determined by a balance between protein synthesis and breakdown and is sensitive to mitochondrial oxidative function. To investigate the functional consequences of transient HIF1α expression during normoxia in the basal state, myotubes and skeletal muscle from male and female mice with HIF1α knockout were studied using complementary multiomics, biochemical and metabolite assays. HIF1α knockout altered the electron transport chain, mitochondrial oxidative function, signalling molecules for protein homeostasis, and post-mitotic senescence markers, some of which were differentially impacted by sex. The cost of rapid adaptive responses mediated by HIF1α is lower mitochondrial oxidative efficiency and post-mitotic senescence during normoxia.

The microRNA Let-7f Induces Senescence and Exacerbates Oxidative Stress in Retinal Pigment Epithelial Cells

This study aims to investigate the role of microRNA let-7f in the dysfunction and degeneration of retinal pigment epithelium (RPE) cells through the induction of senescence and oxidative stress. Furthermore, we explore whether let-7f inhibition can protect these cells against sodium iodate (SI)-induced oxidative stress. Oxidative stress and let-7f expression are reciprocally regulated in retinal pigment epithelial cells. Overexpression of let-7f in ARPE-19 cells induced oxidative stress as demonstrated by increased reactive oxygen species (ROS) production as well as senescence. Inhibition of let-7f successfully protected RPE cells from the detrimental effects induced by SI. In addition, let-7f overexpression induced RPE cellular dysfunction by diminishing their migratory capabilities and reducing the phagocytosis of porcine photoreceptor outer segments (POS). Results were further confirmed in vivo by intravitreal injections of SI and let-7f antagomir in C57BL/6 mice. Our results provide strong evidence that let-7f is implicated in the dysfunction of RPE cells through the induction of senescence and oxidative injury. These findings may help to uncover novel and relevant processes in the pathogenesis of dry AMD.

Induced Pluripotent Stem Cell-Derived Fibroblasts Efficiently Engage Senescence Pathways but Show Increased Sensitivity to Stress Inducers

The risk of aberrant growth of induced pluripotent stem cell (iPSC)-derived cells in response to DNA damage is a potential concern as the tumor suppressor genes TP53 and CDKN2A are transiently inactivated during reprogramming. Herein, we evaluate the integrity of cellular senescence pathways and DNA double-strand break (DSB) repair in Sendai virus reprogrammed iPSC-derived human fibroblasts (i-HF) compared to their parental skin fibroblasts (HF). Using transcriptomics analysis and a variety of functional assays, we show that the capacity of i-HF to enter senescence and repair DSB is not compromised after damage induced by ionizing radiation (IR) or the overexpression of H-RASV12. Still, i-HF lines are transcriptionally different from their parental lines, showing enhanced metabolic activity and higher expression of p53-related effector genes. As a result, i-HF lines generally exhibit increased sensitivity to various stresses, have an elevated senescence-associated secretory phenotype (SASP), and cannot be immortalized unless p53 expression is knocked down. In conclusion, while our results suggest that i-HF are not at a greater risk of transformation, their overall hyperactivation of senescence pathways may impede their function as a cell therapy product.

The NDR family of kinases: essential regulators of aging

Aging is defined as a progressive decline of cognitive and physiological functions over lifetime. Since the definition of the nine hallmarks of aging in 2013 by López-Otin, numerous studies have attempted to identify the main regulators and contributors in the aging process. One interesting group of proteins whose participation has been implicated in several aging hallmarks are the nuclear DBF2-related (NDR) family of serine-threonine AGC kinases. They are one of the core components of the Hippo signaling pathway and include NDR1, NDR2, LATS1 and LATS2 in mammals, along with its highly conserved metazoan orthologs; Trc in Drosophila melanogaster, SAX-1 in Caenorhabditis elegans, CBK1, DBF20 in Saccharomyces cerevisiae and orb6 in Saccharomyces pombe. These kinases have been independently linked to the regulation of widely diverse cellular processes disrupted during aging such as the cell cycle progression, transcription, intercellular communication, nutrient homeostasis, autophagy, apoptosis, and stem cell differentiation. However, a comprehensive overview of the state-of-the-art knowledge regarding the post-translational modifications of and by NDR kinases in aging has not been conducted. In this review, we summarize the current understanding of the NDR family of kinases, focusing on their relevance to various aging hallmarks, and emphasize the growing body of evidence that suggests NDR kinases are essential regulators of aging across species.

Emerging Roles of Vitamin B12 in Aging and Inflammation

Vitamin B12 (cobalamin) is an essential nutrient for humans and animals. Metabolically active forms of B12-methylcobalamin and 5-deoxyadenosylcobalamin are cofactors for the enzymes methionine synthase and mitochondrial methylmalonyl-CoA mutase. Malfunction of these enzymes due to a scarcity of vitamin B12 leads to disturbance of one-carbon metabolism and impaired mitochondrial function. A significant fraction of the population (up to 20%) is deficient in vitamin B12, with a higher rate of deficiency among elderly people. B12 deficiency is associated with numerous hallmarks of aging at the cellular and organismal levels. Cellular senescence is characterized by high levels of DNA damage by metabolic abnormalities, increased mitochondrial dysfunction, and disturbance of epigenetic regulation. B12 deficiency could be responsible for or play a crucial part in these disorders. In this review, we focus on a comprehensive analysis of molecular mechanisms through which vitamin B12 influences aging. We review new data about how deficiency in vitamin B12 may accelerate cellular aging. Despite indications that vitamin B12 has an important role in health and healthy aging, knowledge of the influence of vitamin B12 on aging is still limited and requires further research.