Mitochondria are required for pro-ageing features of the senescent phenotype

Suppressed basal mitophagy drives cellular aging phenotypes that can be reversed by a p62-targeting small molecule

Selective degradation of damaged mitochondria by autophagy (mitophagy) is proposed to play an important role in cellular homeostasis. However, the molecular mechanisms and the requirement of mitochondrial quality control by mitophagy for cellular physiology are poorly understood. Here, we demonstrated that primary human cells maintain highly active basal mitophagy initiated by mitochondrial superoxide signaling. Mitophagy was found to be mediated by PINK1/Parkin-dependent pathway involving p62 as a selective autophagy receptor (SAR). Importantly, this pathway was suppressed upon the induction of cellular senescence and in naturally aged cells, leading to a robust shutdown of mitophagy. Inhibition of mitophagy in proliferating cells was sufficient to trigger the senescence program, while reactivation of mitophagy was necessary for the anti-senescence effects of NAD precursors or rapamycin. Furthermore, reactivation of mitophagy by a p62-targeting small molecule rescued markers of cellular aging, which establishes mitochondrial quality control as a promising target for anti-aging interventions.

Mitochondrial Transplantation Promotes Protective Effector and Memory CD4+ T Cell Response During Mycobacterium Tuberculosis Infection and Diminishes Exhaustion and Senescence in Elderly CD4+ T cells

Tuberculosis (TB), caused by Mycobacterium tuberculosis (M.tb), is a major global health concern, particularly affecting those with weakened immune systems, including the elderly. CD4+ T cell response is crucial for immunity against M.tb, but chronic infections and aging can lead to T cell exhaustion and senescence, worsening TB disease. Mitochondrial dysfunction, prevalent in aging and chronic diseases, disrupts cellular metabolism, increases oxidative stress, and impairs T-cell functions. This study investigates the effect of mitochondrial transplantation (mito-transfer) on CD4+ T cell differentiation and function in aged mouse models and human CD4+ T cells from elderly individuals. Mito-transfer in naïve CD4+ T cells is found to promote protective effector and memory T cell generation during M.tb infection in mice. Additionally, it improves elderly human T cell function by increasing mitochondrial mass and altering cytokine production, thereby reducing markers of exhaustion and senescence. These findings suggest mito-transfer as a novel approach to enhance aged CD4+ T cell functionality, potentially benefiting immune responses in the elderly and chronic TB patients. This has broader implications for diseases where mitochondrial dysfunction contributes to T-cell exhaustion and senescence.

P7C3 suppresses astrocytic senescence to protect dopaminergic neurons: Implication in the mouse model of Parkinson's disease

AIMS

Astrocytic senescence is inextricably linked to aging and neurodegenerative disorders, including Parkinson's disease (PD). P7C3 is a small, neuroprotective aminopropyl carbazole compound that exhibits anti-inflammatory properties. However, the effects of P7C3 on astrocytic senescence in PD remain to be elucidated.

METHODS

An in vitro, long culture-induced, replicative senescence cell model and a 1-methyl-4-phenylpyridinium (MPP+)/rotenone-induced premature senescence cell model were used to investigate the effects of P7C3 on astrocytic senescence. An in vivo, 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP)-induced mouse PD model was used to study the role of P7C3 in astrocytic senescence. Immunoblotting, real-time quantitative RT-PCR (qPCR), immunofluorescence, subcellular fractionation assays, and immunohistochemistry were utilized to confirm the effects of P7C3 on astrocytic senescence and elucidate its underlying mechanisms.

RESULTS

This study determined that P7C3 suppressed the senescence-associated secretory phenotype (SASP) in both cell models, as demonstrated by the reduction in the critical senescence marker p16 and proinflammatory factors (IL-6, IL-1β, CXCL10, and MMP9) and increased laminB1 levels, implying that P7C3 inhibited replicative astrocytic senescence and MPP+/rotenone-induced premature astrocytic senescence, Most importantly, we demonstrated that P7C3 prevented the death of dopamine (DA) neurons and reduced the behavioral deficits in the MPTP-induced mouse model of PD, which is accompanied by a decrease in senescent astrocytes in the substantia nigra compacta (SNc). Mechanistically, P7C3 promoted Nrf2/Sirt3-mediated mitophagy and reduced mitochondrial reactive oxygen species (mitoROS) generation, which contributed to the suppression of astrocytic senescence. Furthermore, Sirt3 deficiency obviously abolished the inhibitory effects of P7C3 on astrocytic senescence.

CONCLUSION

This study revealed that P7C3 inhibited astrocytic senescence via increased Nrf2/Sirt3-mediated mitophagy and suppression of mitoROS, which further protected against DA neuronal loss. These observations provide a prospective theoretical basis for P7C3 in the treatment of age-associated neurodegenerative diseases, such as PD.

Delaying Renal Aging: Metformin Holds Promise as a Potential Treatment

Given the rapid aging of the population, age-related diseases have become an excessive burden on global health care. The kidney, a crucial metabolic organ, ages relatively quickly. While the aging process itself does not directly cause kidney damage, the physiological changes that accompany it can impair the kidney's capacity for self-repair. This makes aging kidneys more susceptible to diseases, including increased risks of chronic kidney disease and end-stage renal disease. Therefore, delaying the progression of renal aging and preserving the youthful vitality of the kidney are crucial for preventing kidney diseases. However, effective strategies against renal aging are still lacking due to the underlying mechanisms of renal aging, which have not been fully elucidated. Accumulating evidence suggests that metformin has beneficial effects in mitigating renal aging. Metformin has shown promising anti-aging results in animal models but has not been tested for this purpose yet in clinical trials. These findings indicate the potential of metformin as an anti-renal aging drug. In this review, we primarily discuss the characteristics and mechanisms of kidney aging and the potential effects of metformin against renal aging.

Proximal telomeric decompaction due to telomere shortening drives FOXC1-dependent myocardial senescence

Telomeres, TTAGGGn DNA repeat sequences located at the ends of eukaryotic chromosomes, play a pivotal role in aging and are targets of DNA damage response. Although we and others have demonstrated presence of short telomeres in genetic cardiomyopathic and heart failure cardiomyocytes, little is known about the role of telomere lengths in cardiomyocyte. Here, we demonstrate that in heart failure patient cardiomyocytes, telomeres are shortened compared to healthy controls. We generated isogenic human induced pluripotent stem cell derived cardiomyocytes (hiPSC-CMs) with short telomeres (sTL-CMs) and normal telomeres (nTL-CMs) as model. Compared to nTL-CMs, short telomeres result in cardiac dysfunction and expression of senescent markers. Using Hi-C and RNASeq, we observe that short telomeres induced TAD insulation decrease near telomeric ends and this correlated with a transcription upregulation in sTL-CMs. FOXC1, a key transcription factor involved in early cardiogenesis, was upregulated in sTL-CMs and its protein levels were negatively correlated with telomere lengths in heart failure patients. Overexpression of FOXC1 induced hiPSC-CM aging, mitochondrial and contractile dysfunction; knockdown of FOXC1 rescued these phenotypes. Overall, the work presented demonstrate that increased chromatin accessibility due to telomere shortening resulted in the induction of FOXC1-dependent expression network responsible for contractile dysfunction and myocardial senescence.

Physiological skin oxygen levels: An important criterion for skin cell functionality and therapeutic approaches

The skin is made up of different layers with various gradients, which maintain a complex microenvironment, particularly in terms of oxygen levels. However, all types of skin cells are cultured in conventional incubators that do not reproduce physiological oxygen levels. Instead, they are cultured at atmospheric oxygen levels, a condition that is far removed from physiology and may lead to the generation of free radicals known to induce skin ageing. This review aims to summarize the current literature on the effect of physiological oxygen levels on skin cells, highlight the shortcomings of current in vitro models, and demonstrate the importance of respecting skin oxygen levels. We begin by clarifying the terminology used about oxygen levels and describe the specific distribution of oxygen in the skin. We review and discuss how skin cells adapt their oxygen consumption and metabolism to oxygen levels environment, as well as the changes that are induced, particularly, their redox state, life cycle and functions. We examine the effects of oxygen on both simple culture models and more complex reconstructed skin models. Finally, we present the implications of oxygen modulation for a more therapeutic approach.

Mitochondrial Role on Cellular Apoptosis, Autophagy, and Senescence during Osteoarthritis Pathogenesis

Authors have demonstrated that apoptosis activation is a pathway related to cartilage degradation characteristics of the OA process. Autophagy is an adaptive response to protect cells from various environmental changes, and defects in autophagy are linked to cell death. In this sense, decreased autophagy of chondrocytes has been observed in OA articular cartilage. The aim of this work was to study the role of OA mitochondria in apoptosis, autophagy, and senescence, using OA and Normal (N) transmitochondrial cybrids. Results: OA cybrids incubated with menadione showed a higher percentage of late apoptosis and necrosis than N cybrids. Stimulation of cybrids with staurosporine and IL-1β showed that OA cybrids were more susceptible to undergoing apoptosis than N cybrids. An analysis of the antioxidant response using menadione on gene expression revealed a lower expression of nuclear factor erythroid 2-like 2 and superoxide dismutase 2 in OA than N cybrids. Activation of microtubule-associated protein 1A/1B-light chain 3 was reduced in OA compared to N cybrids. However, the percentage of senescent cells was higher in OA than N cybrids. Conclusion: This work suggests that mitochondria from OA patients could be involved in the apoptosis, autophagy, and senescence of chondrocytes described in OA cartilage.

Senolytic treatment does not mitigate oxidative stress-induced muscle atrophy but improves muscle force generation in CuZn superoxide dismutase knockout mice

Oxidative stress is associated with tissue dysfunctions that can lead to reduced health. Prior work has shown that oxidative stress contributes to both muscle atrophy and cellular senescence, which is a hallmark of aging that may drive in muscle atrophy and muscle contractile dysfunction. The purpose of the study was to test the hypothesis that cellular senescence contributes to muscle atrophy or weakness. To increase potential senescence in skeletal muscle, we used a model of oxidative stress-induced muscle frailty, the CuZn superoxide dismutase knockout (Sod1KO) mouse. We treated 6-month-old wildtype (WT) and Sod1KO mice with either vehicle or a senolytic treatment of combined dasatinib (5 mg/kg) + quercetin (50 mg/kg) (D + Q) for 3 consecutive days every 15 days. We continued treatment for 7 months and sacrificed the mice at 13 months of age. Treatment with D + Q did not preserve muscle mass, reduce NMJ fragmentation, or alter muscle protein synthesis in Sod1KO mice when compared to the vehicle-treated group. However, we observed an improvement in muscle-specific force generation in Sod1KO mice treated with D + Q when compared to Sod1KO-vehicle mice. Overall, these data suggest that reducing cellular senescence via D + Q is not sufficient to mitigate loss of muscle mass in a mouse model of oxidative stress-induced muscle frailty but may mitigate some aspects of oxidative stress-induced muscle dysfunction.

Cellular senescence in lung cancer: Molecular mechanisms and therapeutic interventions

Lung cancer stands as the primary contributor to cancer-related fatalities worldwide, affecting both genders. Two primary types exist where non-small cell lung cancer (NSCLC), accounts for 80-85% and SCLC accounts for 10-15% of cases. NSCLC subtypes include adenocarcinoma, squamous cell carcinoma, and large cell carcinoma. Smoking, second-hand smoke, radon gas, asbestos, and other pollutants, genetic predisposition, and COPD are lung cancer risk factors. On the other hand, stresses such as DNA damage, telomere shortening, and oncogene activation cause a prolonged cell cycle halt, known as senescence. Despite its initial role as a tumor-suppressing mechanism that slows cell growth, excessive or improper control of this process can cause age-related diseases, including cancer. Cellular senescence has two purposes in lung cancer. Researchers report that senescence slows tumor growth by constraining multiplication of impaired cells. However, senescent cells also demonstrate the pro-inflammatory senescence-associated secretory phenotype (SASP), which is widely reported to promote cancer. This review will look at the role of cellular senescence in lung cancer, describe its diagnostic markers, ask about current treatments to control it, look at case studies and clinical trials that show how senescence-targeting therapies can be used in lung cancer, and talk about problems currently being faced, and possible solutions for the same in the future.

Proteomic Analysis Reveals Trilaciclib-Induced Senescence

Trilaciclib, a cyclin-dependent kinase 4/6 inhibitor, was approved as a myeloprotective agent for protecting bone marrow from chemotherapy-induced damage in extensive-stage small cell lung cancer. This is achieved through the induction of a temporary halt in the cell cycle of bone marrow cells. While it has been studied in various cancer types, its potential in hematological cancers remains unexplored. This research aimed to investigate the efficacy of trilaciclib in hematological cancers. Utilizing mass spectrometry-based proteomics, we examined the alterations induced by trilaciclib in the chronic myeloid leukemia cell line, K562. Interestingly, trilaciclib promoted senescence in these cells rather than cell death, as observed in acute myeloid leukemia, acute lymphoblastic leukemia, and myeloma cells. In K562 cells, trilaciclib hindered cell cycle progression and proliferation by stabilizing cyclin-dependent kinase 4/6 and downregulating cell cycle-related proteins, along with the concomitant activation of autophagy pathways. Additionally, trilaciclib-induced senescence was also observed in the nonsmall cell lung carcinoma cell line, A549. These findings highlight trilaciclib's potential as a therapeutic option for hematological cancers and underscore the need to carefully balance senescence induction and autophagy modulation in chronic myeloid leukemia treatment, as well as in nonsmall cell lung carcinoma cell line.

The biomedical application of inorganic metal nanoparticles in aging and aging-associated diseases

Aging and aging-associated diseases (AAD), including neurodegenerative disease, cancer, cardiovascular diseases, and diabetes, are inevitable process. With the gradual improvement of life style, life expectancy is gradually extended. However, the extended lifespan has not reduced the incidence of disease, and most elderly people are in ill-health state in their later years. Hence, understanding aging and AAD are significant for reducing the burden of the elderly. Inorganic metal nanoparticles (IMNPs) predominantly include gold, silver, iron, zinc, titanium, thallium, platinum, cerium, copper NPs, which has been widely used to prevent and treat aging and AAD due to their superior properties (essential metal ions for human body, easily synthesis and modification, magnetism). Therefore, a systematic review of common morphological alternations of senescent cells, altered genes and signal pathways in aging and AAD, and biomedical applications of IMNPs in aging and AAD is crucial for the further research and development of IMNPs in aging and AAD. This review focus on the existing research on cellular senescence, aging and AAD, as well as the applications of IMNPs in aging and AAD in the past decade. This review aims to provide cutting-edge knowledge involved with aging and AAD, the application of IMNPs in aging and AAD to promote the biomedical application of IMNPs in aging and AAD.

Elimination of damaged mitochondria during UVB-induced senescence is orchestrated by NIX-dependent mitophagy

Skin aging is the result of two types of aging, "intrinsic aging" an inevitable consequence of physiologic and genetically determined changes and "extrinsic aging," which is dependent on external factors such as exposure to sunlight, smoking, and dietary habits. UVB causes skin injury through the generation of free radicals and other oxidative byproducts, also contributing to DNA damage. Appearance and accumulation of senescent cells in the skin are considered one of the hallmarks of aging in this tissue. Mitochondria play an important role for the development of cellular senescence, in particular stress-induced senescence of human cells. However, many aspects of mitochondrial physiology relevant to cellular senescence and extrinsic skin aging remain to be unraveled. Here, we demonstrate that mitochondria damaged by UVB irradiation of human dermal fibroblasts (HDF) are eliminated by NIX-dependent mitophagy and that this process is important for cell survival under these conditions. Additionally, UVB-irradiation of human dermal fibroblasts (HDF) induces the shedding of extracellular vesicles (EVs), and this process is significantly enhanced in UVB-irradiated NIX-depleted cells. Our findings establish NIX as the main mitophagy receptor in the process of UVB-induced senescence and suggest the release of EVs as an alternative mechanism of mitochondrial quality control in HDF.

A Brain Anti-Senescence Transcriptional Program Triggered by Hypothalamic-Derived Exosomal microRNAs

In contrast to the hypothesis that aging results from cell-autonomous deterioration processes, the programmed longevity theory proposes that aging arises from a partial inactivation of a "longevity program" aimed at maintaining youthfulness in organisms. Supporting this hypothesis, age-related changes in organisms can be reversed by factors circulating in young blood. Concordantly, the endocrine secretion of exosomal microRNAs (miRNAs) by hypothalamic neural stem cells (htNSCs) regulates the aging rate by enhancing physiological fitness in young animals. However, the specific molecular mechanisms through which hypothalamic-derived miRNAs exert their anti-aging effects remain unexplored. Using experimentally validated miRNA-target gene interactions and single-cell transcriptomic data of brain cells during aging and heterochronic parabiosis, we identify the main pathways controlled by these miRNAs and the cell-type-specific gene networks that are altered due to age-related loss of htNSCs and the subsequent decline in specific miRNA levels in the cerebrospinal fluid (CSF). Our bioinformatics analysis suggests that these miRNAs modulate pathways associated with senescence and cellular stress response, targeting crucial genes such as Cdkn2a, Rps27, and Txnip. The oligodendrocyte lineage appears to be the most responsive to age-dependent loss of exosomal miRNA, leading to significant derepression of several miRNA target genes. Furthermore, heterochronic parabiosis can reverse age-related upregulation of specific miRNA-targeted genes, predominantly in brain endothelial cells, including senescence promoting genes such as Cdkn1a and Btg2. Our findings support the presence of an anti-senescence mechanism triggered by the endocrine secretion of htNSC-derived exosomal miRNAs, which is associated with a youthful transcriptional signature.

Unlocking Mitochondrial Dysfunction-Associated Senescence (MiDAS) with NAD + - a Boolean Model of Mitochondrial Dynamics and Cell Cycle Control

The steady accumulation of senescent cells with aging creates tissue environments that aid cancer evolution. Aging cell states are highly heterogeneous. 'Deep senescent' cells rely on healthy mitochondria to fuel a strong proinflammatory secretome, including cytokines, growth and transforming signals. Yet, the physiological triggers of senescence such as the reactive oxygen species (ROS) can also trigger mitochondrial dysfunction, and sufficient energy deficit to alter their secretome and cause chronic oxidative stress - a state termed Mitochondrial Dysfunction-Associated Senescence (MiDAS). Here, we offer a mechanistic hypothesis for the molecular processes leading to MiDAS, along with testable predictions. To do this we have built a Boolean regulatory network model that qualitatively captures key aspects of mitochondrial dynamics during cell cycle progression (hyper-fusion at the G1/S boundary, fission in mitosis), apoptosis (fission and dysfunction) and glucose starvation (reversible hyper-fusion), as well as MiDAS in response to SIRT3 knockdown or oxidative stress. Our model reaffirms the protective role of NAD + and external pyruvate. We offer testable predictions about the growth factor- and glucose-dependence of MiDAS and its reversibility at different stages of reactive oxygen species (ROS)-induced senescence. Our model provides mechanistic insights into the distinct stages of DNA-damage induced senescence, the relationship between senescence and epithelial-to-mesenchymal transition in cancer and offers a foundation for building multiscale models of tissue aging.

Highlights

Boolean regulatory network model reproduces mitochondrial dynamics during cell cycle progression, apoptosis, and glucose starvation. Model offers a mechanistic explanation for the positive feedback loop that locks in Mitochondrial Dysfunction-Associated Senescence (MiDAS), involving autophagy-resistant, hyperfused, dysfunctional mitochondria. Model reproduces ROS-mediated mitochondrial dysfunction and suggests that MiDAS is part of the early phase of damage-induced senescence. Model predicts that cancer-driving mutations that bypass the G1/S checkpoint generally increase the incidence of MiDAS, except for p53 loss.

The Vital Role of Melatonin and Its Metabolites in the Neuroprotection and Retardation of Brain Aging

While primarily produced in the pineal gland, melatonin's influence goes beyond its well-known role in regulating sleep, nighttime metabolism, and circadian rhythms, in the field of chronobiology. A plethora of new data demonstrates melatonin to be a very powerful molecule, being a potent ROS/RNS scavenger with anti-inflammatory, immunoregulatory, and oncostatic properties. Melatonin and its metabolites exert multiple beneficial effects in cutaneous and systemic aging. This review is focused on the neuroprotective role of melatonin during aging. Melatonin has an anti-aging capacity, retarding the rate of healthy brain aging and the development of age-related neurodegenerative diseases, such as Alzheimer's disease, Parkinson's disease, Huntington's disease, multiple sclerosis, amyotrophic lateral sclerosis, etc. Melatonin, as well as its metabolites, N1-acetyl-N2-formyl-5-methoxykynuramine (AFMK) and N1-acetyl-5-methoxykynuramine (AMK), can reduce oxidative brain damage by shielding mitochondria from dysfunction during the aging process. Melatonin could also be implicated in the treatment of neurodegenerative conditions, by modifying their characteristic low-grade neuroinflammation. It can either prevent the initiation of inflammatory responses or attenuate the ongoing inflammation. Drawing on the current knowledge, this review discusses the potential benefits of melatonin supplementation in preventing and managing cognitive impairment and neurodegenerative diseases.

Senescence and fibrosis in salivary gland aging and disease

Salivary gland hypofunction is highly prevalent in aged and diseased individuals leading to significant discomfort and morbidity. One factor that contributes to salivary gland hypofunction is cellular aging, or senescence. Senescent cells can impair gland function by secreting paracrine-acting growth factors and cytokines, known as senescence-associated secretory phenotype (SASP) factors. These SASP factors stimulate inflammation, propagate the senescent phenotype through the bystander effect, and stimulate fibrosis. As senotherapeutics that target senescent cells have shown effectiveness in limiting disease manifestations in other conditions, there is interest in the use of these drugs to treat salivary gland hypofunction. In this review, we highlight the contribution of senescence and fibrosis to salivary gland pathologies. We also discuss therapeutic approaches to eliminate or modulate the senescent SASP phenotype for treating age-related salivary gland diseases and extending health span.

Spatially resolved transcriptome of the aging mouse brain

Brain aging is associated with cognitive decline, memory loss and many neurodegenerative disorders. The mammalian brain has distinct structural regions that perform specific functions. However, our understanding in gene expression and cell types within the context of the spatial organization of the mammalian aging brain is limited. Here we generated spatial transcriptomic maps of young and old mouse brains. We identified 27 distinguished brain spatial domains, including layer-specific subregions that are difficult to dissect individually. We comprehensively characterized spatial-specific changes in gene expression in the aging brain, particularly for isocortex, the hippocampal formation, brainstem and fiber tracts, and validated some gene expression differences by qPCR and immunohistochemistry. We identified aging-related genes and pathways that vary in a coordinated manner across spatial regions and parsed the spatial features of aging-related signals, providing important clues to understand genes with specific functions in different brain regions during aging. Combined with single-cell transcriptomics data, we characterized the spatial distribution of brain cell types. The proportion of immature neurons decreased in the DG region with aging, indicating that the formation of new neurons is blocked. Finally, we detected changes in information interactions between regions and found specific pathways were deregulated with aging, including classic signaling WNT and layer-specific signaling COLLAGEN. In summary, we established a spatial molecular atlas of the aging mouse brain (http://sysbio.gzzoc.com/Mouse-Brain-Aging/), which provides important resources and novel insights into the molecular mechanism of brain aging.

Cytosolic DNA initiates a vicious circle of aging-related endothelial inflammation and mitochondrial dysfunction via STING: the inhibitory effect of Cilostazol

Endothelial senescence, aging-related inflammation, and mitochondrial dysfunction are prominent features of vascular aging and contribute to the development of aging-associated vascular disease. Accumulating evidence indicates that DNA damage occurs in aging vascular cells, especially in endothelial cells (ECs). However, the mechanism of EC senescence has not been completely elucidated, and so far, there is no specific drug in the clinic to treat EC senescence and vascular aging. Here we show that various aging stimuli induce nuclear DNA and mitochondrial damage in ECs, thus facilitating the release of cytoplasmic free DNA (cfDNA), which activates the DNA-sensing adapter protein STING. STING activation led to a senescence-associated secretory phenotype (SASP), thereby releasing pro-aging cytokines and cfDNA to further exacerbate mitochondrial damage and EC senescence, thus forming a vicious circle, all of which can be suppressed by STING knockdown or inhibition. Using next-generation RNA sequencing, we demonstrate that STING activation stimulates, whereas STING inhibition disrupts pathways associated with cell senescence and SASP. In vivo studies unravel that endothelial-specific Sting deficiency alleviates aging-related endothelial inflammation and mitochondrial dysfunction and prevents the development of atherosclerosis in mice. By screening FDA-approved vasoprotective drugs, we identified Cilostazol as a new STING inhibitor that attenuates aging-related endothelial inflammation both in vitro and in vivo. We demonstrated that Cilostazol significantly inhibited STING translocation from the ER to the Golgi apparatus during STING activation by targeting S162 and S243 residues of STING. These results disclose the deleterious effects of a cfDNA-STING-SASP-cfDNA vicious circle on EC senescence and atherogenesis and suggest that the STING pathway is a promising therapeutic target for vascular aging-related diseases. A proposed model illustrates the central role of STING in mediating a vicious circle of cfDNA-STING-SASP-cfDNA to aggravate age-related endothelial inflammation and mitochondrial damage.

Energy metabolism as therapeutic target for aged wound repair by engineered extracellular vesicle

Aging skin, vulnerable to age-related defects, is poor in wound repair. Metabolic regulation in accumulated senescent cells (SnCs) with aging is essential for tissue homeostasis, and adequate ATP is important in cell activation for aged tissue repair. Strategies for ATP metabolism intervention hold prospects for therapeutic advances. Here, we found energy metabolic changes in aging skin from patients and mice. Our data show that metformin engineered EV (Met-EV) can enhance aged mouse skin repair, as well as ameliorate cellular senescence and restore cell dysfunctions. Notably, ATP metabolism was remodeled as reduced glycolysis and enhanced OXPHOS after Met-EV treatment. We show Met-EV rescue senescence-induced mitochondria dysfunctions and mitophagy suppressions, indicating the role of Met-EV in remodeling mitochondrial functions via mitophagy for adequate ATP production in aged tissue repair. Our results reveal the mechanism for SnCs rejuvenation by EV and suggest the disturbed energy metabolism, essential in age-related defects, to be a potential therapeutic target for facilitating aged tissue repair.

The role of mitochondrial quality control mechanisms in chondrocyte senescence

Chondrocytes are the exclusive cellular constituents of articular cartilage, and their functional status governs the health of the cartilage. The primary factor contributing to the deterioration of cartilage structure and function is chondrocyte senescence. In hypoxia and hypodextrose environment, chondrocytes heavily rely on glycolysis for energy metabolism. Mitochondria, acting as the regulatory hub for chondrocyte energy metabolism, exhibit dysfunction before chondrocyte senescence, indicating their crucial involvement in the process. Previous research has suggested that molecules associated with mitochondrial quality control mechanisms can effectively restore mitochondrial function and alleviate chondrocyte senescence. However, there remains to be clarity regarding the relationship between mitochondrial quality control mechanisms and differences in efficacy among various target molecules, which pose challenges when evaluating them in chondrocytes. By conducting a comprehensive review of the existing literature on mitochondrial quality control mechanisms and chondrocyte senescence, we gain further insights into this intricate relationship while identifying promising targets that could potentially open up novel avenues for the treatment of chondrocyte senescence.

Aging, Cellular Senescence, and Glaucoma

Aging is one of the most serious risk factors for glaucoma, and according to age-standardized prevalence, glaucoma is the second leading cause of legal blindness worldwide. Cellular senescence is a hallmark of aging that is defined by a stable exit from the cell cycle in response to cellular damage and stress. The potential mechanisms underlying glaucomatous cellular senescence include oxidative stress, DNA damage, mitochondrial dysfunction, defective autophagy/mitophagy, and epigenetic modifications. These phenotypes interact and generate a sufficiently stable network to maintain the cell senescent state. Senescent trabecular meshwork (TM) cells, retinal ganglion cells (RGCs) and vascular endothelial cells reportedly accumulate with age and stress and may contribute to glaucoma pathologies. Therapies targeting the suppression or elimination of senescent cells have been found to ameliorate RGC death and improve vision in glaucoma models, suggesting the pivotal role of cellular senescence in the pathophysiology of glaucoma. In this review, we explore the biological links between aging and glaucoma, specifically delving into cellular senescence. Moreover, we summarize the current data on cellular senescence in key target cells associated with the development and clinical phenotypes of glaucoma. Finally, we discuss the therapeutic potential of targeting cellular senescence for the management of glaucoma.

SIRT1-dependent PGC-1α deacetylation by SRT1720 rescues progression of atherosclerosis by enhancing mitochondrial function

Vascular smooth muscle cell (VSMC) senescence promotes atherosclerosis via lipid-mediated mitochondrial dysfunction and oxidative stress. However, the mechanisms of mitochondrial dysfunction and VSMC senescence in atherosclerosis have not been established. Here, we investigated the mechanisms whereby signaling pathways regulated by SRT1720 enhance or regulate mitochondrial functions in atherosclerotic VSMCs to suppress atherosclerosis. Initially, we examined the effect of SRT1720 on oleic acid (OA)-induced atherosclerosis. Atherosclerotic VSMCs exhibited elevated expressions of BODIPY and ADRP (adipose differentiation-related protein) and associated intracellular lipid droplet markers. In addition, the expression of collagen I was upregulated by OA, while the expressions of elastin and α-SMA were downregulated. mtDNA copy numbers, an ATP detection assay, transmission electron microscopy (TEM) imaging of mitochondria, mitochondria membrane potentials (assessed using JC-1 probe), and levels of mitochondrial oxidative phosphorylation (OXPHOS) were used to examine the effects of SRT1720 on OA-induced mitochondrial dysfunction. SRT1720 reduced mtDNA damage and accelerated mitochondria repair in VSMCs with OA-induced mitochondria dysfunction. In addition, mitochondrial reactive oxygen species (mtROS) levels were downregulated by SRT1720 in OA-treated VSMCs. Importantly, SRT1720 significantly increased SIRT1 and PGC-1α expression levels, but VSMCs senescence, inflammatory response, and atherosclerosis phenotypes were not recovered by treating cells with EX527 and SR-18292 before SRT1720. Mechanistically, the upregulations of SIRT1 and PGC-1α deacetylation by SRT1720 restored mitochondrial function, and consequently suppressed VSMC senescence and atherosclerosis-associated proteins and phenotypes. Collectively, this study indicates that SRT1720 can attenuate OA-induced atherosclerosis associated with VSMC senescence and mitochondrial dysfunction via SIRT1-mediated deacetylation of the PGC-1α pathway.

Subcellular structure, heterogeneity, and plasticity of senescent cells

Cellular senescence is a state of permanent growth arrest. It can be triggered by telomere shortening (replicative senescence) or prematurely induced by stresses such as DNA damage, oncogene overactivation, loss of tumor suppressor genes, oxidative stress, tissue factors, and others. Advances in techniques and experimental designs have provided new evidence about the biology of senescent cells (SnCs) and their importance in human health and disease. This review aims to describe the main aspects of SnCs phenotype focusing on alterations in subcellular compartments like plasma membrane, cytoskeleton, organelles, and nuclei. We also discuss the heterogeneity, dynamics, and plasticity of SnCs' phenotype, including the SASP, and pro-survival mechanisms. We advance on the multiple layers of phenotypic heterogeneity of SnCs, such as the heterogeneity between inducers, tissues and within a population of SnCs, discussing the relevance of these aspects to human health and disease. We also raise the main challenges as well alternatives to overcome them. Ultimately, we present open questions and perspectives in understanding the phenotype of SnCs from the perspective of basic and applied questions.

Telomeres, cellular senescence, and aging: past and future

Over half a century has passed since Alexey Olovnikov's groundbreaking proposal of the end-replication problem in 1971, laying the foundation for our understanding of telomeres and their pivotal role in cellular senescence. This review paper delves into the intricate and multifaceted relationship between cellular senescence, the influence of telomeres in this process, and the far-reaching consequences of telomeres in the context of aging and age-related diseases. Additionally, the paper investigates the various factors that can influence telomere shortening beyond the confines of the end-replication problem and how telomeres can exert their impact on aging, even in the absence of significant shortening. Ultimately, this paper stands as a tribute to the pioneering work of Olovnikov, whose seminal contributions established the solid foundation upon which our ongoing explorations of telomeres and the aging process are based.

Emerging roles of senolytics/senomorphics in HIV-related co-morbidities

Human immunodeficiency virus (HIV) is known to cause cellular senescence and inflammation among infected individuals. While the traditional antiretroviral therapies (ART) have allowed the once fatal infection to be managed effectively, the quality of life of HIV patients on prolonged ART use is still inferior. Most of these individuals suffer from life-threatening comorbidities like chronic obstructive pulmonary disease (COPD), pulmonary arterial hypertension (PAH), and diabetes, to name a few. Interestingly, cellular senescence is known to play a critical role in the pathophysiology of these comorbidities as well. It is therefore important to understand the role of cellular senescence in the disease progression and co-morbidity development in HIV-infected individuals. In this respect, use of senolytic/senomorphic drugs as combination therapy with ART would be beneficial for HIV patients. This review provides a critical analysis of the current literature to determine the potential and efficacy of using senolytics/senotherapeutics in managing HIV infection, latency, and associated co-morbidities in humans. The various classes of senolytics have been studied in detail to focus on their potential to combat against HIV infections and associated pathologies with advancing age.

Early onset of pathological polyploidization and cellular senescence in hepatocytes lacking RAD51 creates a pro-fibrotic and pro-tumorigenic inflammatory microenvironment

BACKGROUND AND AIMS

RAD51 recombinase (RAD51) is a highly conserved DNA repair protein and is indispensable for embryonic viability. As a result, the role of RAD51 in liver development and function is unknown. Our aim was to characterize the function of RAD51 in postnatal liver development.

APPROACH AND RESULTS

RAD51 is highly expressed during liver development and during regeneration following hepatectomy and hepatic injury, and is also elevated in chronic liver diseases. We generated a hepatocyte-specific Rad51 deletion mouse model using Alb -Cre ( Rad51 -conditional knockout (CKO)) and Adeno-associated virus 8-thyroxine-binding globulin-cyclization recombination enzyme to evaluate the function of RAD51 in liver development and regeneration. The phenotype in Rad51 -CKO mice is dependent on CRE dosage, with Rad51fl/fl ; Alb -Cre +/+ manifesting a more severe phenotype than the Rad51fl/fl ; Alb -Cre +/- mice. RAD51 deletion in postnatal hepatocytes results in aborted mitosis and early onset of pathological polyploidization that is associated with oxidative stress and cellular senescence. Remarkable liver fibrosis occurs spontaneously as early as in 3-month-old Rad51fl/fl ; Alb -Cre +/+ mice. While liver regeneration is compromised in Rad51 -CKO mice, they are more tolerant of carbon tetrachloride-induced hepatic injury and resistant to diethylnitrosamine/carbon tetrachloride-induced HCC. A chronic inflammatory microenvironment created by the senescent hepatocytes appears to activate ductular reaction the transdifferentiation of cholangiocytes to hepatocytes. The newly derived RAD51 functional immature hepatocytes proliferate vigorously, acquire increased malignancy, and eventually give rise to HCC.

CONCLUSIONS

Our results demonstrate a novel function of RAD51 in liver development, homeostasis, and tumorigenesis. The Rad51 -CKO mice represent a unique genetic model for premature liver senescence, fibrosis, and hepatocellular carcinogenesis.

The Role of Oxidative Stress in Tumorigenesis and Progression

Oxidative stress refers to the imbalance between the production of reactive oxygen species (ROS) and the endogenous antioxidant defense system. Its involvement in cell senescence, apoptosis, and series diseases has been demonstrated. Advances in carcinogenic research have revealed oxidative stress as a pivotal pathophysiological pathway in tumorigenesis and to be involved in lung cancer, glioma, hepatocellular carcinoma, leukemia, and so on. This review combs the effects of oxidative stress on tumorigenesis on each phase and cell fate determination, and three features are discussed. Oxidative stress takes part in the processes ranging from tumorigenesis to tumor death via series pathways and processes like mitochondrial stress, endoplasmic reticulum stress, and ferroptosis. It can affect cell fate by engaging in the complex relationships between senescence, death, and cancer. The influence of oxidative stress on tumorigenesis and progression is a multi-stage interlaced process that includes two aspects of promotion and inhibition, with mitochondria as the core of regulation. A deeper and more comprehensive understanding of the effects of oxidative stress on tumorigenesis is conducive to exploring more tumor therapies.

Epigenetic dynamics of aging and cancer development: current concepts from studies mapping aging and cancer epigenomes

PURPOSE OF REVIEW

This review emphasizes the role of epigenetic processes as incidental changes occurring during aging, which, in turn, promote the development of cancer.

RECENT FINDINGS

Aging is a complex biological process associated with the progressive deterioration of normal physiological functions, making age a significant risk factor for various disorders, including cancer. The increasing longevity of the population has made cancer a global burden, as the risk of developing most cancers increases with age due to the cumulative effect of exposure to environmental carcinogens and DNA replication errors. The classical 'somatic mutation theory' of cancer cause is being challenged by the observation that multiple normal cells harbor cancer driver mutations without resulting in cancer. In this review, we discuss the role of age-associated epigenetic alterations, including DNA methylation, which occur across all cell types and tissues with advancing age. There is an increasing body of evidence linking these changes with cancer risk and prognosis.

SUMMARY

A better understanding about the epigenetic changes acquired during aging is critical for comprehending the mechanisms leading to the age-associated increase in cancer and for developing novel therapeutic strategies for cancer treatment and prevention.

Small airway fibroblasts from patients with chronic obstructive pulmonary disease exhibit cellular senescence

Small airway disease (SAD) is a key early-stage pathology of chronic obstructive pulmonary disease (COPD). COPD is associated with cellular senescence whereby cells undergo growth arrest and express the senescence-associated secretory phenotype (SASP) leading to chronic inflammation and tissue remodeling. Parenchymal-derived fibroblasts have been shown to display senescent properties in COPD, however small airway fibroblasts (SAFs) have not been investigated. Therefore, this study investigated the role of these cells in COPD and their potential contribution to SAD. To investigate the senescent and fibrotic phenotype of SAF in COPD, SAFs were isolated from nonsmoker, smoker, and COPD lung resection tissue (n = 9-17 donors). Senescence and fibrotic marker expressions were determined using iCELLigence (proliferation), qPCR, Seahorse assay, and ELISAs. COPD SAFs were further enriched for senescent cells using FACSAria Fusion based on cell size and autofluorescence (10% largest/autofluorescent vs. 10% smallest/nonautofluorescent). The phenotype of the senescence-enriched population was investigated using RNA sequencing and pathway analysis. Markers of senescence were observed in COPD SAFs, including senescence-associated β-galactosidase, SASP release, and reduced proliferation. Because the pathways driving this phenotype were unclear, we used cell sorting to enrich senescent COPD SAFs. This population displayed increased p21CIP1 and p16INK4a expression and mitochondrial dysfunction. RNA sequencing suggested these senescent cells express genes involved in oxidative stress response, fibrosis, and mitochondrial dysfunction pathways. These data suggest COPD SAFs are senescent and may be associated with fibrotic properties and mitochondrial dysfunction. Further understanding of cellular senescence in SAFs may lead to potential therapies to limit SAD progression.NEW & NOTEWORTHY Fibroblasts and senescence are thought to play key roles in the pathogenesis of small airway disease and COPD; however, the characteristics of small airway-derived fibroblasts are not well explored. In this study we isolate and enrich the senescent small airway-derived fibroblast (SAF) population from COPD lungs and explore the pathways driving this phenotype using bulk RNA-seq.

Connecting epigenetics and inflammation in vascular senescence: state of the art, biomarkers and senotherapeutics

Vascular diseases pose major health challenges, and understanding their underlying molecular mechanisms is essential to advance therapeutic interventions. Cellular senescence, a hallmark of aging, is a cellular state characterized by cell-cycle arrest, a senescence-associated secretory phenotype macromolecular damage, and metabolic dysregulation. Vascular senescence has been demonstrated to play a key role in different vascular diseases, such as atherosclerosis, peripheral arterial disease, hypertension, stroke, diabetes, chronic venous disease, and venous ulcers. Even though cellular senescence was first described in 1961, significant gaps persist in comprehending the epigenetic mechanisms driving vascular senescence and its subsequent inflammatory response. Through a comprehensive analysis, we aim to elucidate these knowledge gaps by exploring the network of epigenetic alterations that contribute to vascular senescence. In addition, we describe the consequent inflammatory cascades triggered by these epigenetic modifications. Finally, we explore translational applications involving biomarkers of vascular senescence and the emerging field of senotherapy targeting this biological process.

Emerging role of senescent microglia in brain aging-related neurodegenerative diseases

Brain aging is a recognized risk factor for neurodegenerative diseases like Alzheimer's disease, Parkinson's disease, and amyotrophic lateral sclerosis (ALS, Lou Gehrig's disease), but the intricate interplay between brain aging and the pathogenesis of these conditions remains inadequately understood. Cellular senescence is considered to contribute to cellular dysfunction and inflammaging. According to the threshold theory of senescent cell accumulation, the vulnerability to neurodegenerative diseases is associated with the rates of senescent cell generation and clearance within the brain. Given the role of microglia in eliminating senescent cells, the accumulation of senescent microglia may lead to the acceleration of brain aging, contributing to inflammaging and increased vulnerability to neurodegenerative diseases. In this review, we propose the idea that the senescence of microglia, which is notably vulnerable to aging, could potentially serve as a central catalyst in the progression of neurodegenerative diseases. The senescent microglia are emerging as a promising target for mitigating neurodegenerative diseases.

Myconoside and Calceolarioside E Restrain UV-Induced Skin Photoaging by Activating NRF2-Mediated Defense Mechanisms

Chronic and excessive ultraviolet (UVA/UVB) irradiation exposure is known as a major contributor to premature skin aging, which leads to excessive reactive oxygen species generation, disturbed extracellular matrix homeostasis, DNA damage, and chronic inflammation. Sunscreen products are the major preventive option against UVR-induced photodamage, mostly counteracting the acute skin effects and only mildly counteracting accelerated aging. Therefore, novel anti-photoaging and photopreventive compounds are a subject of increased scientific interest. Our previous investigations revealed that the endemic plant Haberlea rhodopensis Friv. (HRE) activates the antioxidant defense through an NRF2-mediated mechanism in neutrophiles. In the present study, we aimed to investigate the photoprotective potential of HRE and two of its specialized compounds-the phenylethanoid glycosides myconoside (MYC) and calceolarioside E (CAL)-in UVA/UVB-stimulated human keratinocytes in an in vitro model of photoaging. The obtained data demonstrated that the application of HRE, MYC, and CAL significantly reduced intracellular ROS formation in UVR-exposed HaCaT cells. The NRF2/PGC-1α and TGF-1β/Smad/Wnt signaling pathways were pointed out as having a critical role in the observed CAL- and MYC-induced photoprotective effect. Collectively, CAL is worth further evaluation as a potent natural NRF2 activator and a promising photoprotective agent that leads to the prevention of UVA/UVB-induced premature skin aging.

Cellular Senescence, Mitochondrial Dysfunction, and Their Link to Cardiovascular Disease

Cardiovascular diseases (CVDs), a group of disorders affecting the heart or blood vessels, are the primary cause of death worldwide, with an immense impact on patient quality of life and disability. According to the World Health Organization, CVD takes an estimated 17.9 million lives each year, where more than four out of five CVD deaths are due to heart attacks and strokes. In the decades to come, an increased prevalence of age-related CVD, such as atherosclerosis, coronary artery stenosis, myocardial infarction (MI), valvular heart disease, and heart failure (HF) will contribute to an even greater health and economic burden as the global average life expectancy increases and consequently the world's population continues to age. Considering this, it is important to focus our research efforts on understanding the fundamental mechanisms underlying CVD. In this review, we focus on cellular senescence and mitochondrial dysfunction, which have long been established to contribute to CVD. We also assess the recent advances in targeting mitochondrial dysfunction including energy starvation and oxidative stress, mitochondria dynamics imbalance, cell apoptosis, mitophagy, and senescence with a focus on therapies that influence both and therefore perhaps represent strategies with the most clinical potential, range, and utility.

Mitochondria-Targeted Catalase Does Not Suppress Development of Cellular Senescence during Aging

Cellular senescence is a complex stress response marked by stable proliferative arrest and the secretion of biologically active molecules collectively known as the senescence-associated secretory phenotype (SASP). Mitochondria-derived reactive oxygen species (ROS) have been implicated in aging and age-related processes, including senescence. Stressors that increase ROS levels promote both senescence and the SASP, while reducing mitochondrial ROS or mitochondria themselves can prevent senescence or the SASP. Mitochondrially targeted catalase (mCAT), a transgene that reduces mitochondrial levels of ROS, has been shown to extend the lifespan of murine models and protect against the age-related loss of mitochondrial function. However, it remains unclear whether mCAT can prevent senescence or the SASP. In this study, we investigated the impact of mCAT on senescence in cultured cells and aged mice in order to discover if the lifespan-extending activity of mCAT might be due to the reduction in senescent cells or the SASP. Contrary to expectations, we observed that mCAT does not reduce markers of senescence or the SASP in cultured cells. Moreover, mCAT does not prevent the accumulation of senescent cells or the development of the SASP in adipose tissue from aged mice. These results suggest that mitochondrial ROS may not always play a causal role in the development of senescence during natural aging and underscore the need for a nuanced understanding of the intricate relationship between mitochondrial ROS and cellular senescence.

Impaired Mitochondrial Function and Marrow Failure in Patients Carrying a Variant of the SRSF4 Gene

Serine/arginine-rich splicing factors (SRSFs) are a family of proteins involved in RNA metabolism, including pre-mRNA constitutive and alternative splicing. The role of SRSF proteins in regulating mitochondrial activity has already been shown for SRSF6, but SRSF4 altered expression has never been reported as a cause of bone marrow failure. An 8-year-old patient admitted to the hematology unit because of leukopenia, lymphopenia, and neutropenia showed a missense variant of unknown significance of the SRSF4 gene (p.R235W) found via whole genome sequencing analysis and inherited from the mother who suffered from mild leuko-neutropenia. Both patients showed lower SRSF4 protein expression and altered mitochondrial function and energetic metabolism in primary lymphocytes and Epstein-Barr-virus (EBV)-immortalized lymphoblasts compared to healthy donor (HD) cells, which appeared associated with low mTOR phosphorylation and an imbalance in the proteins regulating mitochondrial biogenesis (i.e., CLUH) and dynamics (i.e., DRP1 and OPA1). Transfection with the wtSRSF4 gene restored mitochondrial function. In conclusion, this study shows that the described variant of the SRSF4 gene is pathogenetic and causes reduced SRSF4 protein expression, which leads to mitochondrial dysfunction. Since mitochondrial function is crucial for hematopoietic stem cell maintenance and some genetic bone marrow failure syndromes display mitochondrial defects, the SRSF4 mutation could have substantially contributed to the clinical phenotype of our patient.

Cellular senescence of renal tubular epithelial cells in acute kidney injury

Cellular senescence represents an irreversible state of cell-cycle arrest during which cells secrete senescence-associated secretory phenotypes, including inflammatory factors and chemokines. Additionally, these cells exhibit an apoptotic resistance phenotype. Cellular senescence serves a pivotal role not only in embryonic development, tissue regeneration, and tumor suppression but also in the pathogenesis of age-related degenerative diseases, malignancies, metabolic diseases, and kidney diseases. The senescence of renal tubular epithelial cells (RTEC) constitutes a critical cellular event in the progression of acute kidney injury (AKI). RTEC senescence inhibits renal regeneration and repair processes and, concurrently, promotes the transition of AKI to chronic kidney disease via the senescence-associated secretory phenotype. The mechanisms underlying cellular senescence are multifaceted and include telomere shortening or damage, DNA damage, mitochondrial autophagy deficiency, cellular metabolic disorders, endoplasmic reticulum stress, and epigenetic regulation. Strategies aimed at inhibiting RTEC senescence, targeting the clearance of senescent RTEC, or promoting the apoptosis of senescent RTEC hold promise for enhancing the renal prognosis of AKI. This review primarily focuses on the characteristics and mechanisms of RTEC senescence, and the impact of intervening RTEC senescence on the prognosis of AKI, aiming to provide a foundation for understanding the pathogenesis and providing potentially effective approaches for AKI treatment.

The Third Annual Symposium of the Midwest Aging Consortium

The geroscience hypothesis suggests that addressing the fundamental mechanisms driving aging biology will prevent or mitigate the onset of multiple chronic diseases, for which the largest risk factor is advanced age. Research that investigates the root causes of aging is therefore of critical importance given the rising healthcare burden attributable to age-related diseases. The third annual Midwest Aging Consortium symposium was convened as a showcase of such research performed by investigators from institutions across the Midwestern United States. This report summarizes the work presented during a virtual conference across topics in aging biology, including immune function in the lung-particularly timely given the Corona Virus Immune Disease-2019 pandemic-along with the role of metabolism and nutrient-regulated pathways in cellular function with age, the influence of senescence on stem cell function and inflammation, and our evolving understanding of the mechanisms underlying observation of sex dimorphism in aging-related outcomes. The symposium focused on early-stage and emerging investigators, while including keynote presentations from leaders in the biology of aging field, highlighting the diversity and strength of aging research in the Midwest.

Cutaneous Redox Senescence

Our current understanding of skin cell senescence involves the role of environmental stressors (UV, O3, cigarette smoke, particulate matter, etc.), lifestyle (diet, exercise, etc.) as well as genetic factors (metabolic changes, hormonal, etc.). The common mechanism of action of these stressors is the disturbance of cellular redox balance characterized by increased free radicals and reactive oxygen species (ROS), and when these overload the intrinsic antioxidant defense system, it can lead to an oxidative stress cellular condition. The main redox mechanisms that activate cellular senescence in the skin involve (1) the oxidative damage of telomeres causing their shortening; (2) the oxidation of proteomes and DNA damage; (3) an a in lysosomal mass through the increased activity of resident enzymes such as senescence-associated β-galactosidase (SA-β-gal) as well as other proteins that are products of lysosomal activity; (4) and the increased expression of SASP, in particular pro-inflammatory cytokines transcriptionally regulated by NF-κB. However, the main targets of ROS on the skin are the proteome (oxi-proteome), followed by telomeres, nucleic acids (DNAs), lipids, proteins, and cytoplasmic organelles. As a result, cell cycle arrest pathways, lipid peroxidation, increased lysosomal content and dysfunctional mitochondria, and SASP synthesis occur. Furthermore, oxidative stress in skin cells increases the activity of p16INK4A and p53 as inhibitors of Rb and CDks, which are important for maintaining the cell cycle. p53 also promotes the inactivation of mTOR-mediated autophagic and apoptotic pathways, leading to senescence. However, these markers alone cannot establish the state of cellular senescence, and multiple analyses are encouraged for confirmation. An updated and more comprehensive approach to investigating skin senescence should include further assays of ox-inflammatory molecular pathways that can consolidate the understanding of cutaneous redox senescence.

A comparison of bone microarchitectural and transcriptomic changes in murine long bones in response to hindlimb unloading and aging

Age- and disuse-related bone loss both result in decreases in bone mineral density, cortical thickness, and trabecular thickness and connectivity. Disuse induces changes in the balance of bone formation and bone resorption like those seen with aging. There is a need to experimentally compare these two mechanisms at a structural and transcriptomic level to better understand how they may be similar or different. Bone microarchitecture and biomechanical properties were compared between 6- and 22-month-old C57BL/6 J male control mice and 6-month-old mice that were hindlimb unloaded (HLU) for 3 weeks. Epiphyseal trabecular bone was the compartment most affected by HLU and demonstrated an intermediate bone phenotype between age-matched controls and aged controls. RNA extracted from whole-bone marrow-flushed tibiae was sequenced and analyzed. Differential gene expression analysis additionally included 4-month-old male mice unloaded for 3 weeks compared to age-matched controls. Gene ontology analysis demonstrated that there were age-dependent differences in differentially expressed genes in young adult mice. Genes related to downregulation of cellular processes were most affected in 4-month-old mice after disuse whereas those related to mitochondrial function were most affected in 6-month-old mice. Cell-cycle transition was downregulated with aging. A publicly available dataset (GSE169292) from 3-month female C57BL/6 N mice unloaded for 7 days was included in ingenuity pathway analysis (IPA) with the other datasets. IPA was used to identify the leading canonical pathways and upstream regulators in each HLU age group. IPA identified "Senescence Pathway" as the second leading canonical pathway enriched in mice exposed to HLU. HLU induced activation of the senescence pathway in 3-month and 4-month-old mice but inhibited it in 6-month-old mice. In conclusion, we demonstrate that hindlimb unloading and aging initiate similar changes in bone microarchitecture and gene expression. However, aging is responsible for more significant transcriptome and tissue-level changes compared to hindlimb unloading.

Cellular Senescence in Craniofacial Tissue Regeneration: Inducers, Biomarkers, and Interventions

Craniofacial defects and dental tissue loss have significant negative impacts on the structure and function of jaws and face, often resulting in psychological issues in patients, emphasizing the urgent need for effective craniofacial tissue reconstruction. Unfortunately, natural regeneration of these tissues is limited. Dental-derived mesenchymal stem cells (MSCs) have emerged as a promising resource for tissue engineering-based therapeutic approaches. However, the clinical outcomes of MSC-based transplantation have not met expectations due to various complex reasons, and cellular senescence is recognized as one of the potential mechanisms contributing to the suboptimal results. The quality of MSC decreases during large-scale in vitro expansion, and it is also influenced by the age and the health status of donors. To address these challenges, extensive efforts have been made to developing strategies to combat senescence in tissue engineering, leveraging on current knowledge of underlying mechanisms. This review aims to elucidate the impact of cell senescence in craniofacial and dental regeneration and provides an overview of state-of-the-art antisenescence strategies. We first discuss the potential factors that trigger cell senescence in craniofacial tissue engineering. Then we describe senescence biomarkers, monitoring methods for senescent MSCs, and their underlying molecular mechanisms. The primary focus of this review is on current strategies to inhibit and alleviate cell senescence in tissue engineering. We summarize the strategies concerning the prevention of cell senescence, senolysis, modulation of the senescent associated secretory phenotype, and reversal of senescent MSCs, offering promising opportunities to overcome the challenges associated with cell senescence in craniofacial tissue engineering.

Mitochondrial Transplantation promotes protective effector and memory CD4+ T cell response during Mycobacterium tuberculosis infection and diminishes exhaustion and senescence in elderly CD4+ T cells

Tuberculosis (TB), caused by the bacterium Mycobacterium tuberculosis (M.tb), remains a significant health concern worldwide, especially in populations with weakened or compromised immune systems, such as the elderly. Proper adaptive immune function, particularly a CD4+ T cell response, is central to host immunity against M.tb. Chronic infections, such as M.tb, as well as aging promote T cell exhaustion and senescence, which can impair immune control and promote progression to TB disease. Mitochondrial dysfunction contributes to T cell dysfunction, both in aging and chronic infections and diseases. Mitochondrial perturbations can disrupt cellular metabolism, enhance oxidative stress, and impair T-cell signaling and effector functions. This study examined the impact of mitochondrial transplantation (mito-transfer) on CD4+ T cell differentiation and function using aged mouse models and human CD4+ T cells from elderly individuals. Our study revealed that mito-transfer in naïve CD4+ T cells promoted the generation of protective effector and memory CD4+ T cells during M.tb infection in mice. Further, mito-transfer enhanced the function of elderly human T cells by increasing their mitochondrial mass and modulating cytokine production, which in turn reduced exhaustion and senescence cell markers. Our results suggest that mito-transfer could be a novel strategy to reestablish aged CD4+ T cell function, potentially improving immune responses in the elderly and chronic TB patients, with a broader implication for other diseases where mitochondrial dysfunction is linked to T cell exhaustion and senescence.

Mitofusin 1 silencing decreases the senescent associated secretory phenotype, promotes immune cell recruitment and delays melanoma tumor growth after chemotherapy

Cellular senescence is a therapy endpoint in melanoma, and the senescence-associated secretory phenotype (SASP) can affect tumor growth and microenvironment, influencing treatment outcomes. Metabolic interventions can modulate the SASP, and mitochondrial energy metabolism supports resistance to therapy in melanoma. In a previous report we showed that senescence, induced by the DNA methylating agent temozolomide, increased the level of fusion proteins mitofusin 1 and 2 in melanoma, and silencing Mfn1 or Mfn2 expression reduced interleukin-6 secretion by senescent cells. Here we expanded these observations evaluating the secretome of senescent melanoma cells using shotgun proteomics, and explored the impact of silencing Mfn1 on the SASP. A significant increase in proteins reported to reduce the immune response towards the tumor was found in the media of senescent cells. The secretion of several of these immunomodulatory proteins was affected by Mfn1 silencing, among them was galectin-9. In agreement, tumors lacking mitofusin 1 responded better to treatment with the methylating agent dacarbazine, tumor size was reduced and a higher immune cell infiltration was detected in the tumor. Our results highlight mitochondrial dynamic proteins as potential pharmacological targets to modulate the SASP in the context of melanoma treatment.

D-Mannose reduces cellular senescence and NLRP3/GasderminD/IL-1β-driven pyroptotic uroepithelial cell shedding in the murine bladder

Aging is a risk factor for disease via increased susceptibility to infection, decreased ability to maintain homeostasis, inefficiency in combating stress, and decreased regenerative capacity. Multiple diseases, including urinary tract infection (UTI), are more prevalent with age; however, the mechanisms underlying the impact of aging on the urinary tract mucosa and the correlation between aging and disease remain poorly understood. Here, we show that, relative to young (8-12 weeks) mice, the urothelium of aged (18-24 months) female mice accumulates large lysosomes with reduced acid phosphatase activity and decreased overall autophagic flux in the aged urothelium, indicative of compromised cellular homeostasis. Aged bladders also exhibit basal accumulation of reactive oxygen species (ROS) and a dampened redox response, implying heightened oxidative stress. Furthermore, we identify a canonical senescence-associated secretory phenotype (SASP) in the aged urothelium, along with continuous NLRP3-inflammasome- and Gasdermin-D-dependent pyroptotic cell death. Consequently, aged mice chronically exfoliate urothelial cells, further exacerbating age-related urothelial dysfunction. Upon infection with uropathogenic E. coli, aged mice harbor increased bacterial reservoirs and are more prone to spontaneous recurrent UTI. Finally, we discover that treatment with D-mannose, a natural bioactive monosaccharide, rescues autophagy flux, reverses the SASP, and mitigates ROS and NLRP3/Gasdermin/interleukin (IL)-1β-driven pyroptotic epithelial cell shedding in aged mice. Collectively, our results demonstrate that normal aging affects bladder physiology, with aging alone increasing baseline cellular stress and susceptibility to infection, and suggest that mannose supplementation could serve as a senotherapeutic to counter age-associated urothelial dysfunction.

Radiation-induced changes in energy metabolism result in mitochondrial dysfunction in salivary glands

Salivary glands are indirectly damaged during radiotherapy for head and neck cancer, resulting in acute and chronic hyposalivation. Current treatments for radiation-induced hyposalivation do not permanently restore function to the gland; therefore, more mechanistic understanding of the damage response is needed to identify therapeutic targets for lasting restoration. Energy metabolism reprogramming has been observed in cancer and wound healing models to provide necessary fuel for cell proliferation; however, there is limited understanding of alterations in energy metabolism reprogramming in tissues that fail to heal. We measured extracellular acidification and oxygen consumption rates, assessed mitochondrial DNA copy number, and tested fuel dependency of irradiated primary salivary acinar cells. Radiation treatment leads to increases in glycolytic flux, oxidative phosphorylation, and ATP production rate at acute and intermediate time points. In contrast, at chronic radiation time points there is a significant decrease in glycolytic flux, oxidative phosphorylation, and ATP production rate. Irradiated salivary glands exhibit significant decreases in spare respiratory capacity and increases in mitochondrial DNA copy number at days 5 and 30 post-treatment, suggesting a mitochondrial dysfunction phenotype. These results elucidate kinetic changes in energy metabolism reprogramming of irradiated salivary glands that may underscore the chronic loss of function phenotype.

Interactions between mitochondrial dysfunction and other hallmarks of aging: Paving a path toward interventions that promote healthy old age

Current research on human aging has largely been guided by the milestone paper "hallmarks of aging," which were first proposed in the seminal 2013 paper by Lopez-Otin et al. Most studies have focused on one aging hallmark at a time, asking whether the underlying molecular perturbations are sufficient to drive the aging process and its associated phenotypes. More recently, researchers have begun to investigate whether aging phenotypes are driven by concurrent perturbations in molecular pathways linked to not one but to multiple hallmarks of aging and whether they present different patterns in organs and systems over time. Indeed, preliminary results suggest that more complex interactions between aging hallmarks must be considered and addressed, if we are to develop interventions that successfully promote healthy aging and/or delay aging-associated dysfunction and diseases. Here, we summarize some of the latest work and views on the interplay between hallmarks of aging, with a specific focus on mitochondrial dysfunction. Indeed, this represents a significant example of the complex crosstalk between hallmarks of aging and of the effects that an intervention targeted to a specific hallmark may have on the others. A better knowledge of these interconnections, of their cause-effect relationships, of their spatial and temporal sequence, will be very beneficial for the whole aging research field and for the identification of effective interventions in promoting healthy old age.

Senescent cells at the crossroads of aging, disease, and tissue homeostasis

Originally identified as an outcome of continuous culture of primary cells, cellular senescence has moved beyond the culture dish and is now a bona fide driver of aging and disease in animal models, and growing links to human disease. This cellular stress response consists of a stable proliferative arrest coupled to multiple phenotypic changes. Perhaps the most important of these is the senescence-associated secretory phenotype, or senescence-associated secretory phenotype -a complex and variable collection of secreted molecules release by senescent cells with a number of potent biological activities. Senescent cells appear in multiple age-associated conditions in humans and mice, and interventions that eliminate these cells can prevent or even reverse multiple diseases in mouse models. Here, we review salient aspects of senescent cells in the context of human disease and homeostasis. Senescent cells increase in abundance during several diseases that associated with premature aging. Conversely, senescent cells have a key role in beneficial processes such as development and wound healing, and thus can help maintain tissue homeostasis. Finally, we speculate on mechanisms by which deleterious aspects of senescent cells might be targeted while retaining homeostatic aspects in order to improve age-related outcomes.

Mitochondria as a sensor, a central hub and a biological clock in psychological stress-accelerated aging

The theory that oxidative damage caused by mitochondrial free radicals leads to aging has brought mitochondria into the forefront of aging research. Psychological stress that encompasses many different experiences and exposures across the lifespan has been identified as a catalyst for accelerated aging. Mitochondria, known for their dynamic nature and adaptability, function as a highly sensitive stress sensor and central hub in the process of accelerated aging. In this review, we explore how mitochondria as sensors respond to psychological stress and contribute to the molecular processes in accelerated aging by viewing mitochondria as hormonal, mechanosensitive and immune suborganelles. This understanding of the key role played by mitochondria and their close association with accelerated aging helps us to distinguish normal aging from accelerated aging, correct misconceptions in aging studies, and develop strategies such as exercise and mitochondria-targeted nutrients and drugs for slowing down accelerated aging, and also hold promise for prevention and treatment of age-related diseases.

Microglial Senescence and Activation in Healthy Aging and Alzheimer's Disease: Systematic Review and Neuropathological Scoring

The greatest risk factor for neurodegeneration is the aging of the multiple cell types of human CNS, among which microglia are important because they are the "sentinels" of internal and external perturbations and have long lifespans. We aim to emphasize microglial signatures in physiologic brain aging and Alzheimer's disease (AD). A systematic literature search of all published articles about microglial senescence in human healthy aging and AD was performed, searching for PubMed and Scopus online databases. Among 1947 articles screened, a total of 289 articles were assessed for full-text eligibility. Microglial transcriptomic, phenotypic, and neuropathological profiles were analyzed comprising healthy aging and AD. Our review highlights that studies on animal models only partially clarify what happens in humans. Human and mice microglia are hugely heterogeneous. Like a two-sided coin, microglia can be protective or harmful, depending on the context. Brain health depends upon a balance between the actions and reactions of microglia maintaining brain homeostasis in cooperation with other cell types (especially astrocytes and oligodendrocytes). During aging, accumulating oxidative stress and mitochondrial dysfunction weaken microglia leading to dystrophic/senescent, otherwise over-reactive, phenotype-enhancing neurodegenerative phenomena. Microglia are crucial for managing Aβ, pTAU, and damaged synapses, being pivotal in AD pathogenesis.

Radiation-Induced Changes in Energy Metabolism Result in Mitochondrial Dysfunction in Salivary Glands

Salivary glands are indirectly damaged during radiotherapy for head and neck cancer, resulting in acute and chronic hyposalivation. Current treatments for radiation-induced hyposalivation do not permanently restore function to the gland; therefore, more mechanistic understanding of the damage response is needed to identify therapeutic targets for lasting restoration. Energy metabolism reprogramming has been observed in cancer and wound healing models to provide necessary fuel for cell proliferation; however, there is limited understanding of alterations in energy metabolism reprogramming in tissues that fail to heal. We measured extracellular acidification and oxygen consumption rates, assessed mitochondrial DNA copy number, and tested fuel dependency of irradiated primary salivary acinar cells. Radiation treatment leads to increases in glycolytic flux, oxidative phosphorylation, and ATP production rate at acute and intermediate time points. In contrast, at chronic radiation time points there is a significant decrease in glycolytic flux, oxidative phosphorylation, and ATP production rate. Irradiated salivary glands exhibit significant decreases in spare respiratory capacity and increases in mitochondrial DNA copy number at days 5 and 30 post-treatment, suggesting a mitochondrial dysfunction phenotype. These results elucidate kinetic changes in energy metabolism reprogramming of irradiated salivary glands that may underscore the chronic loss of function phenotype.

A mitochondria-regulated p53-CCF circuit integrates genome integrity with inflammation

Genomic instability and inflammation are distinct hallmarks of aging, but the connection between them is poorly understood. Understanding their interrelationship will help unravel new mechanisms and therapeutic targets of aging and age-associated diseases. Here we report a novel mechanism directly linking genomic instability and inflammation in senescent cells, through a mitochondria-regulated molecular circuit that connects the p53 tumor suppressor and cytoplasmic chromatin fragments (CCF), a driver of inflammation through the cGAS-STING pathway. Activation or inactivation of p53 by genetic and pharmacologic approaches showed that p53 suppresses CCF accumulation and the downstream inflammatory senescence-associated secretory phenotype (SASP), independent of its effects on cell cycle arrest. p53 activation suppressed CCF formation by promoting DNA repair, reflected in maintenance of genomic integrity, particularly in subtelomeric regions, as shown by single cell genome resequencing. Activation of p53 by pharmacological inhibition of MDM2 in old mice decreased features of SASP in liver, indicating a senomorphic role in vivo . Remarkably, mitochondria in senescent cells suppressed p53 activity by promoting CCF formation and thereby restricting ATM-dependent nuclear DNA damage signaling. These data provide evidence for a mitochondria-regulated p53-CCF circuit in senescent cells that controls DNA repair, genome integrity and inflammatory SASP, and is a potential target for senomorphic healthy aging interventions.