The lysosomal proteome of senescent cells contributes to the senescence secretome

Targeting lysosomal quality control as a therapeutic strategy against aging and diseases

Previously, lysosomes were primarily referred to as the digestive organelles and recycling centers within cells. Recent discoveries have expanded the lysosomal functional scope and revealed their critical roles in nutrient sensing, epigenetic regulation, plasma membrane repair, lipid transport, ion homeostasis, and cellular stress response. Lysosomal dysfunction is also found to be associated with aging and several diseases. Therefore, function of macroautophagy, a lysosome-dependent intracellular degradation system, has been identified as one of the updated twelve hallmarks of aging. In this review, we begin by introducing the concept of lysosomal quality control (LQC), which is a cellular machinery that maintains the number, morphology, and function of lysosomes through different processes such as lysosomal biogenesis, reformation, fission, fusion, turnover, lysophagy, exocytosis, and membrane permeabilization and repair. Next, we summarize the results from studies reporting the association between LQC dysregulation and aging/various disorders. Subsequently, we explore the emerging therapeutic strategies that target distinct aspects of LQC for treating diseases and combatting aging. Lastly, we underscore the existing knowledge gap and propose potential avenues for future research.

Integrating bulk and single-cell transcriptomics to elucidate the role and potential mechanisms of autophagy in aging tissue

PURPOSE

Autophagy is frequently observed in tissues during the aging process, yet the tissues most strongly correlated with autophagy during aging and the underlying regulatory mechanisms remain inadequately understood. The purpose of this study is to identify the tissues with the highest correlation between autophagy and aging, and to explore the functions and mechanisms of autophagy in the aging tissue microenvironment.

METHODS

Integrated bulk RNA-seq from over 7000 normal tissue samples, single-cell sequencing data from blood samples of different ages, more than 2000 acute myeloid leukemia (AML) bulk RNA-seq, and multiple sets of AML single-cell data. The datasets were analysed using various bioinformatic approaches.

RESULTS

Blood tissue exhibited the highest positive correlation between autophagy and aging among healthy tissues. Single-cell resolution analysis revealed that in aged blood, classical monocytes (C. monocytes) are most closely associated with elevated autophagy levels. Increased autophagy in these monocytes correlated with a higher proportion of C. monocytes, with hypoxia identified as a crucial contributing factor. In AML, a representative myeloid blood disease, enhanced autophagy was accompanied by an increased proportionof C. monocytes. High autophagy levels in monocytes are associated with pro-inflammatory gene upregulation and Reactive Oxygen Species (ROS) accumulation, contributing to tissue aging.

CONCLUSION

This study revealed that autophagy is most strongly correlated with aging in blood tissue. Enhanced autophagy levels in C. monocytes demonstrate a positive correlation with increased secretion of pro-inflammatory factors and elevated production of ROS, which may contribute to a more rapid aging process. This discovery underscores the critical role of autophagy in blood aging and suggests potential therapeutic targets to mitigate aging-related health issues.

Phylloquinone improves endothelial function, inhibits cellular senescence, and vascular inflammation

Phylloquinon (PK) and menaquinones (MK) are both naturally occurring compounds belonging to vitamin K group. Present study aimed to comprehensively analyze the influence of PK in several models of vascular dysfunction to determine whether PK has vasoprotective properties, similar to those previously described for MK. Effects of PK and MK on endothelial dysfunction were studied in ApoE/LDLR-/- mice in vivo, in the isolated aorta incubated with TNF, and in vascular cells as regard inflammation and cell senescence (including replicative and stress-induced models of senescence). Moreover, the vascular conversion of exogenous vitamins to endogenous MK-4 was analyzed. PK, as well as MK, given for 8 weeks in diet (10 mg/kg) resulted in comparable improvement in endothelial function in the ApoE/LDLR-/- mice. Similarly, PK and MK prevented TNF-induced impairment of endothelium-dependent vasorelaxation in the isolated aorta. In in vitro studies in endothelial and vascular smooth muscle cells, we identified that both PK and MK displayed anti-senescence effects via decreasing DNA damage while in endothelial cells anti-inflammatory activity was ascribed to the modulation of NFκB activation. The activity of PK and MK was comparable in terms of their effect on senescence and inflammation. Presence of endogenous synthesis of MK-4 from PK in aorta and endothelial and smooth muscle cells suggests a possible involvement of MK in vascular effects of PK. In conclusion, PK and MK display comparable vasoprotective effects, which may be ascribed, at least in part, to the inhibition of cell senescence and inflammation. The vasoprotective effect of PK in the vessel wall can be related to the direct effects of PK, as well as to the action of MK formed from PK in the vascular wall.

Senescence in the ageing skin: a new focus on mTORC1 and the lysosome

Ageing is defined as the progressive loss of tissue function and regenerative capacity and is caused by both intrinsic factors i.e. the natural accumulation of damage, and extrinsic factors i.e. damage from environmental stressors. Cellular senescence, in brief, is an irreversible exit from the cell cycle that occurs primarily in response to excessive cellular damage, such as from ultraviolet (UV) exposure and oxidative stress, and it has been comprehensively demonstrated to contribute to tissue and organismal ageing. In this review, we will focus on the skin, an organ which acts as an essential protective barrier against injury, insults, and infection. We will explore the evidence for the existence and contribution of cellular senescence to skin ageing. We discuss the known molecular mechanisms driving senescence in the skin, with a focus on the dysregulation of the master growth regulator, mechanistic Target of Rapamycin Complex 1 (mTORC1). We explore the interplay of dysregulated mTORC1 with lysosomes and how they contribute to senescence phenotypes.

Impaired degradation of PLCG1 by chaperone-mediated autophagy promotes cellular senescence and intervertebral disc degeneration

Defects in chaperone-mediated autophagy (CMA) are associated with cellular senescence, but the mechanism remains poorly understood. Here, we found that CMA inhibition induced cellular senescence in a calcium-dependent manner and identified its role in TNF-induced senescence of nucleus pulposus cells (NPC) and intervertebral disc degeneration. Based on structural and functional proteomic screens, PLCG1 (phospholipase C gamma 1) was predicted as a potential substrate for CMA deficiency to affect calcium homeostasis. We further confirmed that PLCG1 was a key mediator of CMA in the regulation of intracellular calcium flux. Aberrant accumulation of PLCG1 caused by CMA blockage resulted in calcium overload, thereby inducing NPC senescence. Immunoassays on human specimens showed that reduced LAMP2A, the rate-limiting protein of CMA, or increased PLCG1 was associated with disc senescence, and the TNF-induced disc degeneration in rats was inhibited by overexpression of Lamp2a or knockdown of Plcg1. Because CMA dysregulation, calcium overload, and cellular senescence are common features of disc degeneration and other age-related degenerative diseases, the discovery of actionable molecular targets that can link these perturbations may have therapeutic value.Abbreviation: ATRA: all-trans-retinoic acid; BrdU: bromodeoxyuridine; CDKN1A/p21: cyclin dependent kinase inhibitor 1A; CDKN2A/p16-INK4A: cyclin dependent kinase inhibitor 2A; CMA: chaperone-mediated autophagy; DHI: disc height index; ER: endoplasmic reticulum; IP: immunoprecipitation; IP3: inositol 1,4,5-trisphosphate; ITPR/IP3R: inositol 1,4,5-trisphosphate receptor; IVD: intervertebral disc; IVDD: intervertebral disc degeneration; KD: knockdown; KO: knockout; Leu: leupeptin; MRI: magnetic resonance imaging; MS: mass spectrometry; N/L: NH4Cl and leupeptin; NP: nucleus pulposus; NPC: nucleus pulposus cells; PI: protease inhibitors; PLC: phospholipase C; PLCG1: phospholipase C gamma 1; ROS: reactive oxygen species; RT-qPCR: real-time quantitative reverse transcription PCR; SA-GLB1/β-gal: senescence-associated galactosidase beta 1; SASP: senescence-associated secretory phenotype; STV: starvation; TMT: tandem mass tag; TNF: tumor necrosis factor; TP53: tumor protein p53; UPS: ubiquitin-proteasome system.

Analysis of the senescence-associated cell surfaceome reveals potential senotherapeutic targets

The accumulation of senescent cells is thought to play a crucial role in aging-associated physiological decline and the pathogenesis of various age-related pathologies. Targeting senescence-associated cell surface molecules through immunotherapy emerges as a promising avenue for the selective removal of these cells. Despite its potential, a thorough characterization of senescence-specific surface proteins remains to be achieved. Our study addresses this gap by conducting an extensive analysis of the cell surface proteome, or "surfaceome", in senescent cells, spanning various senescence induction regimes and encompassing both murine and human cell types. Utilizing quantitative mass spectrometry, we investigated enriched cell surface proteins across eight distinct models of senescence. Our results uncover significant changes in surfaceome expression profiles during senescence, highlighting extensive modifications in cell mechanics and extracellular matrix remodeling. Our research also reveals substantive heterogeneity of senescence, predominantly influenced by cell type and senescence inducer. A key discovery of our study is the identification of four unique cell surface proteins with extracellular epitopes. These proteins are expressed in senescent cells, absent or present at low levels in their proliferating counterparts, and notably upregulated in tissues from aged mice and an Alzheimer's disease mouse model. These proteins stand out as promising candidates for senotherapeutic targeting, offering potential pathways for the detection and strategic targeting of senescent cell populations in aging and age-related diseases.

Senescence detection using reflected light

Senescence is an important cellular program occurring in development, tissue repair, cancer, and aging. Increased senescence is also associated with disease states, including obesity and Type 2 diabetes (T2D). Characterizing and quantifying senescent cells at a single cell level has been challenging and particularly difficult in large primary cells, such as human adipocytes. In this study, we present a novel approach that utilizes reflected light for accurate senescence-associated beta-galactosidase (SABG) staining measurements, which can be integrated with immunofluorescence and is compatible with primary mature adipocytes from both human and mouse, as well as with differentiated 3T3-L1 cells. This technique provides a more comprehensive classification of a cell's senescent state by incorporating multiple criteria, including robust sample-specific pH controls. By leveraging the precision of confocal microscopy to detect X-gal crystals using reflected light, we achieved superior sensitivity over traditional brightfield techniques. This strategy allows for the capture of all X-gal precipitates in SABG-stained samples, revealing diverse X-gal staining patterns and improved detection sensitivity. Additionally, we demonstrate that reflected light outperforms western blot analysis for the detection and quantification of senescence in mature human adipocytes, as it offers a more accurate representation of SABG activity. This detection strategy enables a more thorough investigation of senescent cell characteristics and specifically a deeper look at the relationship between adipocyte senescence and obesity associated disorders, such as T2D.

Quercetin induces senolysis of doxorubicin-induced senescent fibroblasts by reducing autophagy, preventing their pro-tumour effect on osteosarcoma cells

Cellular senescence contributes to ageing and age-related diseases, and multiple therapeutic strategies are being developed to counteract it. Senolytic drugs are being tested in clinical trials to eliminate senescent cells selectively, but their effects and mechanisms are still unclear. Several studies reveal that the upregulation of senescence-associated secretory phenotype (SASP) factors in senescent cells is accompanied by increased autophagic activity to counteract the endoplasmic reticulum (ER) stress. Our study shows that Doxo-induced senescent fibroblasts yield several SASP factors and exhibit increased autophagy. Interestingly, Quercetin, a bioactive flavonoid, reduces autophagy, increases ER stress, and partially triggers senescent fibroblast death. Given the role of senescent cells in cancer progression, we tested the effect of conditioned media from untreated and quercetin-treated senescent fibroblasts on osteosarcoma cells to determine whether senolytic treatment affected tumour cell behaviour. We report that the partial senescent fibroblast clearance, achieved by quercetin, reduced osteosarcoma cell invasiveness, curbing the pro-tumour effects of senescent cells. The reduction of cell autophagic activity and increased ER stress, an undescribed effect of quercetin, emerges as a new vulnerability of Doxo-induced senescent fibroblasts and may provide a potential therapeutic target for cancer treatment, suggesting novel drug combinations as a promising strategy against the tumour.

Therapy-induced senescence in breast cancer: an overview

Outcomes for women with breast cancer have improved dramatically in recent decades. However, many patients present with intrinsic drug resistance and others are initially sensitive to anti-cancer drugs but acquire resistance during the course of their treatment, leading to recurrence and/or metastasis. Drug therapy-induced senescence (TIS) is a form of drug resistance characterised by the induction of cell cycle arrest and the emergence of a senescence-associated secretory phenotype (SASP) that can develop in response to chemo- and targeted- therapies. A wide range of anticancer interventions can lead to cell cycle arrest and SASP induction, by inducing genotoxic stress, hyperactivation of signalling pathways or oxidative stress. TIS can be anti-tumorigenic in the short-term, but pro-tumorigenic in the long-term by creating a pro-inflammatory and immunosuppressive microenvironment. Moreover, the SASP can promote angiogenesis and epithelial-mesenchymal transition in neighbouring cells. In this review, we will describe the characteristics of TIS in breast cancer and detail the changes in phenotype that accompany its induction. We also discuss strategies for targeting senescent cancer cells in order to prevent or delay tumour recurrence.

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.

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.

Cellular senescence in cancer: molecular mechanisms and therapeutic targets

Aging exhibits several hallmarks in common with cancer, such as cellular senescence, dysbiosis, inflammation, genomic instability, and epigenetic changes. In recent decades, research into the role of cellular senescence on tumor progression has received widespread attention. While how senescence limits the course of cancer is well established, senescence has also been found to promote certain malignant phenotypes. The tumor-promoting effect of senescence is mainly elicited by a senescence-associated secretory phenotype, which facilitates the interaction of senescent tumor cells with their surroundings. Targeting senescent cells therefore offers a promising technique for cancer therapy. Drugs that pharmacologically restore the normal function of senescent cells or eliminate them would assist in reestablishing homeostasis of cell signaling. Here, we describe cell senescence, its occurrence, phenotype, and impact on tumor biology. A "one-two-punch" therapeutic strategy in which cancer cell senescence is first induced, followed by the use of senotherapeutics for eliminating the senescent cells is introduced. The advances in the application of senotherapeutics for targeting senescent cells to assist cancer treatment are outlined, with an emphasis on drug categories, and the strategies for their screening, design, and efficient targeting. This work will foster a thorough comprehension and encourage additional research within this field.

Metabolic pathways in immune senescence and inflammaging: Novel therapeutic strategy for chronic inflammatory lung diseases. An EAACI position paper from the Task Force for Immunopharmacology

The accumulation of senescent cells drives inflammaging and increases morbidity of chronic inflammatory lung diseases. Immune responses are built upon dynamic changes in cell metabolism that supply energy and substrates for cell proliferation, differentiation, and activation. Metabolic changes imposed by environmental stress and inflammation on immune cells and tissue microenvironment are thus chiefly involved in the pathophysiology of allergic and other immune-driven diseases. Altered cell metabolism is also a hallmark of cell senescence, a condition characterized by loss of proliferative activity in cells that remain metabolically active. Accelerated senescence can be triggered by acute or chronic stress and inflammatory responses. In contrast, replicative senescence occurs as part of the physiological aging process and has protective roles in cancer surveillance and wound healing. Importantly, cell senescence can also change or hamper response to diverse therapeutic treatments. Understanding the metabolic pathways of senescence in immune and structural cells is therefore critical to detect, prevent, or revert detrimental aspects of senescence-related immunopathology, by developing specific diagnostics and targeted therapies. In this paper, we review the main changes and metabolic alterations occurring in senescent immune cells (macrophages, B cells, T cells). Subsequently, we present the metabolic footprints described in translational studies in patients with chronic asthma and chronic obstructive pulmonary disease (COPD), and review the ongoing preclinical studies and clinical trials of therapeutic approaches aiming at targeting metabolic pathways to antagonize pathological senescence. Because this is a recently emerging field in allergy and clinical immunology, a better understanding of the metabolic profile of the complex landscape of cell senescence is needed. The progress achieved so far is already providing opportunities for new therapies, as well as for strategies aimed at disease prevention and supporting healthy aging.

Iron retardation in lysosomes protects senescent cells from ferroptosis

Ferroptosis, an iron-triggered modality of cellular death, has been reported to closely relate to human aging progression and aging-related diseases. However, the involvement of ferroptosis in the development and maintenance of senescent cells still remains elusive. Here, we established a doxorubicin-induced senescent HSkM cell model and found that both iron accumulation and lipid peroxidation increase in senescent cells. Moreover, such iron overload in senescent cells has changed the expression panel of the ferroptosis-response proteins. Interestingly, the iron accumulation and lipid peroxidation does not trigger ferroptosis-induced cell death. Oppositely, senescent cells manifest resistance to the ferroptosis inducers, compared to the proliferating cells. To further investigate the mechanism of ferroptosis-resistance for senescent cells, we traced the iron flux in cell and found iron arrested in lysosome. Moreover, disruption of lysosome functions by chloroquine and LLOMe dramatically triggered the senescent cell death. Besides, the ferroitinophagy-related proteins FTH1/FTL and NCOA4 knockdown also increases the senescent cell death. Thus, we speculated that iron retardation in lysosome of senescent cells is the key mechanism for ferroptosis resistance. And the lysosome is a promising target for senolytic drugs to selectively clear senescent cells and alleviate the aging related diseases.

Therapy-induced senescent tumor cell-derived extracellular vesicles promote colorectal cancer progression through SERPINE1-mediated NF-κB p65 nuclear translocation

BACKGROUND

Cellular senescence frequently occurs during anti-cancer treatment, and persistent senescent tumor cells (STCs) unfavorably promote tumor progression through paracrine secretion of the senescence-associated secretory phenotype (SASP). Extracellular vesicles (EVs) have recently emerged as a novel component of the SASP and primarily mediate the tumor-promoting effect of the SASP. Of note, the potential effect of EVs released from STCs on tumor progression remains largely unknown.

METHODS

We collected tumor tissues from two cohorts of colorectal cancer (CRC) patients to examine the expression of p16, p21, and SERPINE1 before and after anti-cancer treatment. Cohort 1 included 22 patients with locally advanced rectal cancer (LARC) who received neoadjuvant therapy before surgical resection. Cohort 2 included 30 patients with metastatic CRC (mCRC) who received first-line irinotecan-contained treatment. CCK-8, transwell, wound-healing assay, and tumor xenograft experiments were carried out to determine the impacts of EVs released from STCs on CRC progression in vitro and in vivo. Quantitative proteomic analysis was applied to identify protein cargo inside EVs secreted from STCs. Immunoprecipitation and mass spectrometer identification were utilized to explore the binding partners of SERPINE1. The interaction of SERPINE1 with p65 was verified by co-immunoprecipitation, and their co-localization was confirmed by immunofluorescence.

RESULTS

Chemotherapeutic agents and irradiation could potently induce senescence in CRC cells in vitro and in human CRC tissues. The more significant elevation of p16 and p21 expression in patients after anti-cancer treatment displayed shorter disease-free survival (DFS) for LARC or progression-free survival (PFS) for mCRC. We observed that compared to non-STCs, STCs released an increased number of EVs enriched in SERPINE1, which further promoted the progression of recipient cancer cells. Targeting SERPINE1 with a specific inhibitor, tiplaxtinin, markedly attenuated the tumor-promoting effect of STCs-derived EVs. Additionally, the patients with greater increment of SERPINE1 expression after anti-cancer treatment had shorter DFS for LARC or PFS for mCRC. Mechanistically, SERPINE1 bound to p65, promoting its nuclear translocation and subsequently activating the NF-κB signaling pathway.

CONCLUSIONS

We provide the in vivo evidence of the clinical prognostic implications of therapy-induced senescence. Our results revealed that STCs were responsible for CRC progression by producing large amounts of EVs enriched in SERPINE1. These findings further confirm the crucial role of therapy-induced senescence in tumor progression and offer a potential therapeutic strategy for CRC treatment.

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.

Human Hair Graying Revisited: Principles, Misconceptions, and Key Research Frontiers

Hair graying holds psychosocial importance and serves as an excellent model for studying human pigmentation and aging in an accessible miniorgan. Current evidence suggests that graying results from an interindividually varying mixture of cumulative oxidative and DNA damage, excessive mTORC1 activity, melanocyte senescence, and inadequate production of pigmentation-promoting factors in the hair matrix. Various regulators modulate this process, including genetic factors (DNA repair defects and IRF4 sequence variation, peripheral clock genes, P-cadherin signaling, neuromediators, HGF, KIT ligand secretion, and autophagic flux. This leads to reduced MITF- and tyrosinase-controlled melanogenesis, defective melanosome transfer to precortical matrix keratinocytes, and eventual depletion of hair follicle (HF) pigmentary unit (HFPU) melanocytes and their local progenitors. Graying becomes irreversible only when bulge melanocyte stem cells are also depleted, occurring later in this process. Distinct pigmentary microenvironments are created as the HF cycles: early anagen is the most conducive phase for melanocytic reintegration and activation, and only during anagen can the phenotype of hair graying and repigmentation manifest, whereas the HFPU disassembles during catagen. The temporary reversibility of graying is highlighted by several drugs and hormones that induce repigmentation, indicating potential target pathways. We advise caution in directly applying mouse model concepts, define major open questions, and discuss future human antigraying strategies.

Dajianzhong decoction ameliorated D-gal-induced cognitive aging by triggering mitophagy in vivo and in vitro

ETHNOPHARMACOLOGICAL RELEVANCE

Dajianzhong decoction (DJZ) is a classical famous formula for treating yang-deficiency-syndrome in traditional Chinese medicine and recorded in Jin-Kui-Yao-Lue in Dynasty of Dong Han. Cognitive aging can present similar features of mitochondrial energy deficits to the clinical features of Yang deficiency. However, there is poor understanding of the effects of DJZ treatment on mitophagy in cognitive aging.

AIM OF THE STUDY

The aims of this work were to decipher the effectiveness and mechanism of DJZ against cognitive aging, focusing on mitophagy.

MATERIALS AND METHODS

YFP-Parkin HeLa cells, D-galactose (D-gal) -induced mice (500 mg/kg for 35 d, s. c.) and SH-SY5Y cells (80 mg/ml for 6 h) were established. Firstly, the formation of YFP-Parkin puncta (a well-known mitophagy marker) in YFP-Parkin HeLa cells was employed to discover the mitophagy induction of DJZ. Moreover, the genes and proteins related to PINK1/Parkin pathway and mitochondrial functions were evaluated after treatment with DJZ in vivo (3.5 g/kg or 1.75 g/kg, i. g, 35 d) and in vitro (0.2, 2 and 20 μg/ml, 12 h). Furthermore, the effectiveness of DJZ (3.5 g/kg or 1.75 g/kg, i. g) for alleviating cognitive aging and nerve damage was measured in D-gal mice. Finally, siPINK1 was applied to reverse validation of DJZ in vitro.

RESULTS

The formation of YFP-Parkin puncta in YFP-Parkin HeLa cells was markedly induced by DJZ in a dose-dependent manner. The immunofluorescence intensity of Parkin and the protein expression of Parkin in mitochondrial membrane in D-gal mice were significantly increased after treatment of DJZ. The inhibition of PINK1/Parkin pathway in D-gal-induced mice and SH-SY5Y cells was significantly activated by DJZ. Simultaneously, the impairment of mitochondrial functions induced by D-gal were markedly reversed by DJZ. In addition, DJZ significantly ameliorated the neuropathological injury and cognitive declines in D-gal mice. Finally, after PINK1 was knocked down by siPINK1 in vitro, the neuroprotective effects of DJZ and the Parkin enhancement effect of DJZ were markedly reversed.

CONCLUSION

Our findings firstly showed DJZ could relieve cognitive aging through facilitating PINK1/Parkin-mediated mitophagy to protect against mitochondrial functions, indicating DJZ may be regarded as a promising intervention in cognitive aging.

Mesenchymal stem cells lose the senescent phenotype under 3D cultivation

BACKGROUND

Three-dimensional (3D) cell culture is widely used in various fields of cell biology. In comparison to conventional two-dimensional (2D) cell culture, 3D cell culture facilitates a more accurate replication of the in vivo microenvironment, which is essential for obtaining more relevant results. The application of 3D cell culture techniques in regenerative medicine, particularly in mesenchymal stem cell (MSC)-based research, has been extensively studied. Many of these studies focus on the enhanced paracrine activity of MSCs cultured in 3D environments. However, few focus on the cellular processes that occur during 3D cultivation.

METHODS

In this work, we studied the changes occurring within 3D-cultured MSCs (3D-MSCs). Specifically, we examined the expression of numerous senescent-associated markers, the actin cytoskeleton structure, the architecture of the Golgi apparatus and the localization of mTOR, one of the main positive regulators of replicative senescence. In addition, we assessed whether the selective elimination of senescent cells occurs upon 3D culturing by using cell sorting based on autofluorescence.

RESULTS

Our findings indicate that 3D-MSCs were able to lose replicative senescence markers under 3D cell culture conditions. We observed changes in actin cytoskeleton structure, Golgi apparatus architecture and revealed that 3D cultivation leads to the nuclear localization of mTOR, resulting in a decrease in its active cytoplasmic form. Additionally, our findings provide evidence that 3D cell culture promotes the phenotypic reversion of senescent cell phenotype rather than their removal from the bulk population.

CONCLUSION

These novel insights into the biology of 3D-MSCs can be applied to research in regenerative medicine to overcome replicative senescence and MSC heterogeneity as they often pose significant concerns regarding safety and effectiveness for therapeutic purposes.

Microgravity triggers ferroptosis and accelerates senescence in the MG-63 cell model of osteoblastic cells

In space, cells sustain strong modifications of their mechanical environment. Mechanosensitive molecules at the cell membrane regulate mechanotransduction pathways that induce adaptive responses through the regulation of gene expression, post-translational modifications, protein interactions or intracellular trafficking, among others. In the current study, human osteoblastic cells were cultured on the ISS in microgravity and at 1 g in a centrifuge, as onboard controls. RNAseq analyses showed that microgravity inhibits cell proliferation and DNA repair, stimulates inflammatory pathways and induces ferroptosis and senescence, two pathways related to ageing. Morphological hallmarks of senescence, such as reduced nuclear size and changes in chromatin architecture, proliferation marker distribution, tubulin acetylation and lysosomal transport were identified by immunofluorescence microscopy, reinforcing the hypothesis of induction of cell senescence in microgravity during space flight. These processes could be attributed, at least in part, to the regulation of YAP1 and its downstream effectors NUPR1 and CKAP2L.

Form follows function: Nuclear morphology as a quantifiable predictor of cellular senescence

Enlarged or irregularly shaped nuclei are frequently observed in tissue cells undergoing senescence. However, it remained unclear whether this peculiar morphology is a cause or a consequence of senescence and how informative it is in distinguishing between proliferative and senescent cells. Recent research reveals that nuclear morphology can act as a predictive biomarker of senescence, suggesting an active role for the nucleus in driving senescence phenotypes. By employing deep learning algorithms to analyze nuclear morphology, accurate classification of cells as proliferative or senescent is achievable across various cell types and species both in vitro and in vivo. This quantitative imaging-based approach can be employed to establish links between senescence burden and clinical data, aiding in the understanding of age-related diseases, as well as assisting in disease prognosis and treatment response.

Autophagy-mediated control of ribosome homeostasis in oncogene-induced senescence

Oncogene-induced senescence (OIS) is a persistent anti-proliferative response that acts as a barrier against malignant transformation. During OIS, cells undergo dynamic remodeling, which involves alterations in protein and organelle homeostasis through autophagy. Here, we show that ribosomes are selectively targeted for degradation by autophagy during OIS. By characterizing senescence-dependent alterations in the ribosomal interactome, we find that the deubiquitinase USP10 dissociates from the ribosome during the transition to OIS. This release of USP10 leads to an enhanced ribosome ubiquitination, particularly of small subunit proteins, including lysine 275 on RPS2. Both reinforcement of the USP10-ribosome interaction and mutation of RPS2 K275 abrogate ribosomal delivery to lysosomes without affecting bulk autophagy. We show that the selective recruitment of ubiquitinated ribosomes to autophagosomes is mediated by the p62 receptor. While ribophagy is not required for the establishment of senescence per se, it contributes to senescence-related metabolome alterations and facilitates the senescence-associated secretory phenotype.

Lysosomes in senescence and aging

Dysfunction of lysosomes, the primary hydrolytic organelles in animal cells, is frequently associated with aging and age-related diseases. At the cellular level, lysosomal dysfunction is strongly linked to cellular senescence or the induction of cell death pathways. However, the precise mechanisms by which lysosomal dysfunction participates in these various cellular or organismal phenotypes have remained elusive. The ability of lysosomes to degrade diverse macromolecules including damaged proteins and organelles puts lysosomes at the center of multiple cellular stress responses. Lysosomal activity is tightly regulated by many coordinated cellular processes including pathways that function inside and outside of the organelle. Here, we collectively classify these coordinated pathways as the lysosomal processing and adaptation system (LYPAS). We review evidence that the LYPAS is upregulated by diverse cellular stresses, its adaptability regulates senescence and cell death decisions, and it can form the basis for therapeutic manipulation for a wide range of age-related diseases and potentially for aging itself.

Senescent Cells: Dual Implications on the Retinal Vascular System

Cellular senescence, a state of permanent cell cycle arrest in response to endogenous and exogenous stimuli, triggers a series of gradual alterations in structure, metabolism, and function, as well as inflammatory gene expression that nurtures a low-grade proinflammatory milieu in human tissue. A growing body of evidence indicates an accumulation of senescent neurons and blood vessels in response to stress and aging in the retina. Prolonged accumulation of senescent cells and long-term activation of stress signaling responses may lead to multiple chronic diseases, tissue dysfunction, and age-related pathologies by exposing neighboring cells to the heightened pathological senescence-associated secretory phenotype (SASP). However, the ultimate impacts of cellular senescence on the retinal vasculopathies and retinal vascular development remain ill-defined. In this review, we first summarize the molecular players and fundamental mechanisms driving cellular senescence, as well as the beneficial implications of senescent cells in driving vital physiological processes such as embryogenesis, wound healing, and tissue regeneration. Then, the dual implications of senescent cells on the growth, hemostasis, and remodeling of retinal blood vessels are described to document how senescent cells contribute to both retinal vascular development and the severity of proliferative retinopathies. Finally, we discuss the two main senotherapeutic strategies-senolytics and senomorphics-that are being considered to safely interfere with the detrimental effects of cellular senescence.

Autophagy orchestrates the crosstalk between cells and organs

Over the recent years, it has become apparent that a deeper understanding of cell-to-cell and organ-to-organ communication is necessary to fully comprehend both homeostatic and pathological states. Autophagy is indispensable for cellular development, function, and homeostasis. A crucial aspect is that autophagy can also mediate these processes through its secretory role. The autophagy-derived secretome relays its extracellular signals in the form of nutrients, proteins, mitochondria, and extracellular vesicles. These crosstalk mediators functionally shape cell fate decisions, tissue microenvironment and systemic physiology. The diversity of the secreted cargo elicits an equally diverse type of responses, which span over metabolic, inflammatory, and structural adaptations in disease and homeostasis. We review here the emerging role of the autophagy-derived secretome in the communication between different cell types and organs and discuss the mechanisms involved.

The impact of cellular senescence in human adipose tissue

In the last decades the prevalence of obesity has increased dramatically, and the worldwide epidemic of obesity and related metabolic diseases has contributed to an increased interest for the adipose tissue (AT), the primary site for storage of lipids, as a metabolically dynamic and endocrine organ. Subcutaneous AT is the depot with the largest capacity to store excess energy and when its limit for storage is reached hypertrophic obesity, local inflammation, insulin resistance and ultimately type 2 diabetes (T2D) will develop. Hypertrophic AT is also associated with a dysfunctional adipogenesis, depending on the inability to recruit and differentiate new mature adipose cells. Lately, cellular senescence (CS), an aging mechanism defined as an irreversible growth arrest that occurs in response to various cellular stressors, such as telomere shortening, DNA damage and oxidative stress, has gained a lot of attention as a regulator of metabolic tissues and aging-associated conditions. The abundance of senescent cells increases not only with aging but also in hypertrophic obesity independent of age. Senescent AT is characterized by dysfunctional cells, increased inflammation, decreased insulin sensitivity and lipid storage. AT resident cells, such as progenitor cells (APC), non-proliferating mature cells and microvascular endothelial cells are affected with an increased senescence burden. Dysfunctional APC have both an impaired adipogenic and proliferative capacity. Interestingly, human mature adipose cells from obese hyperinsulinemic individuals have been shown to re-enter the cell cycle and senesce, which indicates an increased endoreplication. CS was also found to be more pronounced in mature cells from T2D individuals, compared to matched non-diabetic individuals, with decreased insulin sensitivity and adipogenic capacity. Factors associated with cellular senescence in human adipose tissue.

Metabolic regulation of endothelial senescence

Endothelial cell (EC) senescence is increasingly recognized as a significant contributor to the development of vascular dysfunction and age-related disorders and diseases, including cancer and cardiovascular diseases (CVD). The regulation of cellular senescence is known to be influenced by cellular metabolism. While extensive research has been conducted on the metabolic regulation of senescence in other cells such as cancer cells and fibroblasts, our understanding of the metabolic regulation of EC senescence remains limited. The specific metabolic changes that drive EC senescence are yet to be fully elucidated. The objective of this review is to provide an overview of the intricate interplay between cellular metabolism and senescence, with a particular emphasis on recent advancements in understanding the metabolic changes preceding cellular senescence. I will summarize the current knowledge on the metabolic regulation of EC senescence, aiming to offer insights into the underlying mechanisms and future research directions.

The Complex Role of Chaperone-Mediated Autophagy in Cancer Diseases

Chaperone-mediated autophagy (CMA) is a process that rapidly degrades proteins labeled with KFERQ-like motifs within cells via lysosomes to terminate their cellular functioning. Meanwhile, CMA plays an essential role in various biological processes correlated with cell proliferation and apoptosis. Previous studies have shown that CMA was initially found to be procancer in cancer cells, while some theories suggest that it may have an inhibitory effect on the progression of cancer in untransformed cells. Therefore, the complex relationship between CMA and cancer has aroused great interest in the application of CMA activity regulation in cancer therapy. Here, we describe the basic information related to CMA and introduce the physiological functions of CMA, the dual role of CMA in different cancer contexts, and its related research progress. Further study on the mechanism of CMA in tumor development may provide novel insights for tumor therapy targeting CMA. This review aims to summarize and discuss the complex mechanisms of CMA in cancer and related potential strategies for cancer therapy.

Iron Metabolism in Cancer and Senescence: A Cellular Perspective

Iron participates in a number of biological processes and plays a crucial role in cellular homeostasis. Alterations in iron metabolism are considered hallmarks of cancer and drivers of aggressive behaviors, such as uncontrolled proliferation, resistance to apoptosis, enhanced metastatic ability, increased cell plasticity and stemness. Furthermore, a dysregulated iron metabolism has been associated with the development of an adverse tumor microenvironment. Alterations in iron metabolism have been described in cellular senescence and in aging. For instance, iron has been shown to accumulate in aged tissues and in age-related diseases. Furthermore, in vitro studies demonstrate increases in iron content in both replicative and stress-induced senescent cells. However, the role, the mechanisms of regulation and dysregulation and the effects of iron metabolism on senescence remain significantly less characterized. In this review, we first provide an overview of iron metabolism and iron regulatory proteins. Then, we summarize alterations in iron homeostasis in cancer and senescence from a cellular point of view.

Exploring the Communication of the SASP: Dynamic, Interactive, and Adaptive Effects on the Microenvironment

Cellular senescence is a complex cell state that can occur during physiological ageing or after exposure to stress signals, regardless of age. It is a dynamic process that continuously evolves in a context-dependent manner. Senescent cells interact with their microenvironment by producing a heterogenous and plastic secretome referred to as the senescence-associated secretory phenotype (SASP). Hence, understanding the cross-talk between SASP and the microenvironment can be challenging due to the complexity of signal exchanges. In this review, we first aim to update the definition of senescence and its associated biomarkers from its discovery to the present day. We detail the regulatory mechanisms involved in the expression of SASP at multiple levels and develop how SASP can orchestrate microenvironment modifications, by focusing on extracellular matrix modifications, neighboring cells' fate, and intercellular communications. We present hypotheses on how these microenvironmental events may affect dynamic changes in SASP composition in return. Finally, we discuss the various existing approaches to targeting SASP and clarify what is currently known about the biological effects of these modified SASPs on the cellular environment.

The Skin Microbiome: Current Landscape and Future Opportunities

Our skin is the largest organ of the body, serving as an important barrier against the harsh extrinsic environment. Alongside preventing desiccation, chemical damage and hypothermia, this barrier protects the body from invading pathogens through a sophisticated innate immune response and co-adapted consortium of commensal microorganisms, collectively termed the microbiota. These microorganisms inhabit distinct biogeographical regions dictated by skin physiology. Thus, it follows that perturbations to normal skin homeostasis, as occurs with ageing, diabetes and skin disease, can cause microbial dysbiosis and increase infection risk. In this review, we discuss emerging concepts in skin microbiome research, highlighting pertinent links between skin ageing, the microbiome and cutaneous repair. Moreover, we address gaps in current knowledge and highlight key areas requiring further exploration. Future advances in this field could revolutionise the way we treat microbial dysbiosis associated with skin ageing and other pathologies.

Comparative analysis of markers for H2O2-induced senescence in renal tubular cells

To address what marker(s) is/are most suitable for determining renal cell senescence, cell area, granularity, cycle shift/arrest, SA-β-Gal, SIRT1 and p16 were evaluated after inducing senescence in HK-2 cells with 0.2-0.8 mM H₂O₂. Only cell area and granularity concentration-dependently increased at all time-points, whereas SA-β-Gal, SIRT1 and p16 showed significant coefficient of determination (R²) at two time-points. Cell granularity had significant correlation coefficient (R) with other six, whereas SA-β-Gal had significant R with five, and cell area, SIRT1 and p16 had significant R with four others. Comparing to SA-β-Gal, other markers had significantly lower fold-changes only at 72-h with 0.8 mM H₂O₂, whereas p16 provided greater fold-changes at 48-h with 0.4 and 0.8 mM H₂O₂. Therefore, cell area, granularity, SA-β-Gal and p16 may serve as the most suitable markers for determining H₂O₂-induced senescence in HK-2 renal cells, whereas other markers can be also used but with inferior quantitative precision.