Bystander senescence in human peritoneal mesothelium and fibroblasts is related to thrombospondin-1-dependent activation of transforming growth factor-β1

Alterations of receptors and insulin-like growth factor binding proteins in senescent cells

The knowledge about cellular senescence expands dynamically, providing more and more conclusive evidence of its triggers, mechanisms, and consequences. Senescence-associated secretory phenotype (SASP), one of the most important functional traits of senescent cells, is responsible for a large extent of their context-dependent activity. Both SASP's components and signaling pathways are well-defined. A literature review shows, however, that a relatively underinvestigated aspect of senescent cell autocrine and paracrine activity is the change in the production of proteins responsible for the reception and transmission of SASP signals, i.e., receptors and binding proteins. For this reason, we present in this article the current state of knowledge regarding senescence-associated changes in cellular receptors and insulin-like growth factor binding proteins. We also discuss the role of these alterations in senescence induction and maintenance, pro-cancerogenic effects of senescent cells, and aging-related structural and functional malfunctions.

Effect of cellular senescence on the response of human peritoneal mesothelial cells to TGF-β

Transforming growth factor β (TGF-β) is implicated in both mesothelial-to-mesenchymal transition (MMT) and cellular senescence of human peritoneal mesothelial cells (HPMCs). We previously showed that senescent HPMCs could spontaneously acquire some phenotypic features of MMT, which in young HPMCs were induced by TGF-β. Here, we used electron microscopy, as well as global gene and protein profiling to assess in detail how exposure to TGF-β impacts on young and senescent HPMCs in vitro. We found that TGF-β induced structural changes consistent with MMT in young, but not in senescent HPMCs. Of all genes and proteins identified reliably in HPMCs across all treatments and states, 4,656 targets represented overlapping genes and proteins. Following exposure to TGF-β, 137 proteins and 46 transcripts were significantly changed in young cells, compared to 225 proteins and only 2 transcripts in senescent cells. Identified differences between young and senescent HPMCs were related predominantly to wound healing, integrin-mediated signalling, production of proteases and extracellular matrix components, and cytoskeleton structure. Thus, the response of senescent HPMCs to TGF-β differs or is less pronounced compared to young cells. As a result, the character and magnitude of the postulated contribution of HPMCs to TGF-β-induced peritoneal remodelling may change with cell senescence.

Prognostic and therapeutic potential of senescent stromal fibroblasts in prostate cancer

The stromal component of the tumour microenvironment in primary and metastatic prostate cancer can influence and promote disease progression. Within the prostatic stroma, fibroblasts are one of the most prevalent cell types associated with precancerous and cancerous lesions; they have a vital role in the structural composition, organization and integrity of the extracellular matrix. Fibroblasts within the tumour microenvironment can undergo cellular senescence, which is a stable arrest of cell growth and a phenomenon that is emerging as a recognized hallmark of cancer. Supporting the idea that cellular senescence has a pro-tumorigenic role, a subset of senescent cells exhibits a senescence-associated secretory phenotype (SASP), which, along with increased inflammation, can promote prostate cancer cell growth and survival. These cellular characteristics make targeting senescent cells and/or modulating SASP attractive as a potential preventive or therapeutic option for prostate cancer.

BRG1 accelerates mesothelial cell senescence and peritoneal fibrosis by inhibiting mitophagy through repression of OXR1

Peritoneal mesothelial cell senescence promotes the development of peritoneal dialysis (PD)-related peritoneal fibrosis. We previously revealed that Brahma-related gene 1 (BRG1) is increased in peritoneal fibrosis yet its role in modulating peritoneal mesothelial cell senescence is still unknown. This study evaluated the mechanism of BRG1 in peritoneal mesothelial cell senescence and peritoneal fibrosis using BRG1 knockdown mice, primary peritoneal mesothelial cells and human peritoneal samples from PD patients. The augmentation of BRG1 expression accelerated peritoneal mesothelial cell senescence, which attributed to mitochondrial dysfunction and mitophagy inhibition. Mitophagy activator salidroside rescued fibrotic responses and cellular senescence induced by BRG1. Mechanistically, BRG1 was recruited to oxidation resistance 1 (OXR1) promoter, where it suppressed transcription of OXR1 through interacting with forkhead box protein p2. Inhibition of OXR1 abrogated the improvement of BRG1 deficiency in mitophagy, fibrotic responses and cellular senescence. In a mouse PD model, BRG1 knockdown restored mitophagy, alleviated senescence and ameliorated peritoneal fibrosis. More importantly, the elevation level of BRG1 in human PD was associated with PD duration and D/P creatinine values. In conclusion, BRG1 accelerates mesothelial cell senescence and peritoneal fibrosis by inhibiting mitophagy through repression of OXR1. This indicates that modulating BRG1-OXR1-mitophagy signaling may represent an effective treatment for PD-related peritoneal fibrosis.

Salivary Gland Bioengineering

Salivary gland dysfunction affects millions globally, and tissue engineering may provide a promising therapeutic avenue. This review delves into the current state of salivary gland tissue engineering research, starting with a study of normal salivary gland development and function. It discusses the impact of fibrosis and cellular senescence on salivary gland pathologies. A diverse range of cells suitable for tissue engineering including cell lines, primary salivary gland cells, and stem cells are examined. Moreover, the paper explores various supportive biomaterials and scaffold fabrication methodologies that enhance salivary gland cell survival, differentiation, and engraftment. Innovative engineering strategies for the improvement of vascularization, innervation, and engraftment of engineered salivary gland tissue, including bioprinting, microfluidic hydrogels, mesh electronics, and nanoparticles, are also evaluated. This review underscores the promising potential of this research field for the treatment of salivary gland dysfunction and suggests directions for future exploration.

Non-Intrinsic, Systemic Mechanisms of Cellular Senescence

Cellular senescence is believed to contribute to aging and disease through the activity of secreted factors that promote inflammation, remodel the extracellular matrix, and adversely modify the behavior of non-senescent cells. While the markers and properties of senescent cells are still under investigation, it is postulated that cellular senescence manifests in vivo as the consequence of cellular damage that accumulates and becomes exacerbated with time. Yet, the notions that senescence has a solely intrinsic and time-dependent nature are questioned by the rapid induction of senescence in young mice and young cells in vitro by exposure to blood from aged animals. Here, we review some of the research on the systemically present factors that increase with age and may contribute to extrinsically induced senescence or "bystander senescence". These include proteins, reactive oxygen species, lipids, and nucleic acids, which may be present in individual soluble form, in vesicles, and in non-membranous multi-component macromolecules.

CD36 Drives Metastasis and Relapse in Acute Myeloid Leukemia

Identifying mechanisms underlying relapse is a major clinical issue for effective cancer treatment. The emerging understanding of the importance of metastasis in hematologic malignancies suggests that it could also play a role in drug resistance and relapse in acute myeloid leukemia (AML). In a cohort of 1,273 AML patients, we uncovered that the multifunctional scavenger receptor CD36 was positively associated with extramedullary dissemination of leukemic blasts, increased risk of relapse after intensive chemotherapy, and reduced event-free and overall survival. CD36 was dispensable for lipid uptake but fostered blast migration through its binding with thrombospondin-1. CD36-expressing blasts, which were largely enriched after chemotherapy, exhibited a senescent-like phenotype while maintaining their migratory ability. In xenograft mouse models, CD36 inhibition reduced metastasis of blasts and prolonged survival of chemotherapy-treated mice. These results pave the way for the development of CD36 as an independent marker of poor prognosis in AML patients and a promising actionable target to improve the outcome of patients.

SIGNIFICANCE

CD36 promotes blast migration and extramedullary disease in acute myeloid leukemia and represents a critical target that can be exploited for clinical prognosis and patient treatment.

Senescent Stromal Cells in the Tumor Microenvironment: Victims or Accomplices?

Cellular senescence is a unique cellular state. Senescent cells enter a non-proliferative phase, and the cell cycle is arrested. However, senescence is essentially an active cellular phenotype, with senescent cells affecting themselves and neighboring cells via autocrine and paracrine patterns. A growing body of research suggests that the dysregulation of senescent stromal cells in the microenvironment is tightly associated with the development of a variety of complex cancers. The role of senescent stromal cells in impacting the cancer cell and tumor microenvironment has also attracted the attention of researchers. In this review, we summarize the generation of senescent stromal cells in the tumor microenvironment and their specific biological functions. By concluding the signaling pathways and regulatory mechanisms by which senescent stromal cells promote tumor progression, distant metastasis, immune infiltration, and therapy resistance, this paper suggests that senescent stromal cells may serve as potential targets for drug therapy, thus providing new clues for future related research.

The Mechanism of miR-21-5p/TSP-1-Mediating Exercise on the Function of Endothelial Progenitor Cells in Aged Rats

(1) Background: The declined function of peripheral circulating endothelial progenitor cells (EPCs) in aging individuals resulted in decreased endothelial cell regeneration and vascular endothelial function. Improving EPCs function in aging individuals plays an important role in preventing cardiovascular diseases. (2) Methods: Thirty aged (18-month-old) male Sprague-Dawley rats were randomly divided into control and exercise groups. An aerobic exercise intervention was performed 5 days/week for 8 weeks. EPCs functions, miR-21-5p, and TSP-1 expressions were detected after the intervention. The senescence rate, proliferation, and migration of EPCs were examined after overexpression of miR-21-5p and inhibition of TSP-1 expression. (3) Results: The senescence rate, proliferation, and migration of EPCs in exercise groups were significantly improved after exercise intervention. The miR-21-5p expression was increased and the TSP-1 mRNA expression was decreased in the EPCs after the intervention. miR-21-5p overexpression can improve EPCs function and inhibit TSP-1 expression but has no effect on senescence rate. Inhibition of TSP-1 expression could improve the function and reduce the senescence rate. (4) Conclusions: Our results indicate that long-term aerobic exercise can improve the functions of EPCs in aging individuals by downregulating TSP-1 expression via miR-21-5p, which reveals the mechanism of exercise in improving cardiovascular function.

Unbiased proteomic analysis of extracellular vesicles secreted by senescent human vascular smooth muscle cells reveals their ability to modulate immune cell functions

Atherosclerosis, a common age-related disease, is characterized by intense immunological activity. Atherosclerotic plaque is composed of endothelial cells, vascular smooth muscle cells (VSMCs), lipids and immune cells infiltrating from the blood. During progression of the disease, VSMCs undergo senescence within the plaque and secrete SASP (senescence-associated secretory phenotype) factors that can actively modulate plaque microenvironment. We demonstrated that senescent VSMCs secrete increased number of extracellular vesicles (senEVs). Based on unbiased proteomic analysis of VMSC-derived EVs and of the soluble fraction of SASP (sSASP), more than 900 proteins were identified in each of SASP compartments. Comparison of the composition of VMSC-derived EVs with the SASP atlas revealed several proteins, including Serpin Family F Member 1 (SERPINF1) and Thrombospondin 1 (THBS1), as commonly upregulated components of EVs secreted by senescent VSMCs and fibroblasts. Among soluble SASP factors, only Growth Differentiation Factor 15 (GDF15) was universally increased in the secretome of senescent VSMCs, fibroblasts, and epithelial cells. Bioinformatics analysis of EV proteins distinguished functionally organized protein networks involved in immune cell function regulation. Accordingly, EVs released by senescent VSMCs induced secretion of IL-17, INFγ, and IL-10 by T cells and of TNFα produced by monocytes. Moreover senEVs influenced differentiation of monocytes favoring mix M1/M2 polarization with proinflammatory characteristics. Altogether, our studies provide a complex, unbiased analysis of VSMC SASP and prove that EVs derived from senescent VSMCs influence the cytokine milieu by modulating immune cell activity. Our results strengthen the role of senescent cells as an important inducer of inflammation in atherosclerosis.

Tumor microenvironment and cellular senescence: Understanding therapeutic resistance and harnessing strategies

The tumor microenvironment (TME) is a major contributor to cancer malignancy including development of therapeutic resistance, a process mediated in part through intercellular crosstalk. Besides diverse soluble factors responsible for pro-survival pathway activation, immune evasion and extracellular matrix (ECM) remodeling further promote cancer resistance. Importantly, therapy-induced senescence (TIS) of cells in the TME is frequently observed in anticancer regimens, an off-target effect that can generate profound impacts on disease progression. By conferring the resistance and fueling the repopulation of remaining cancerous cells, TIS is responsible for tumor relapse and distant metastasis in posttreatment stage. This pathological trajectory can be substantially driven by the pro-inflammatory feature of senescent cells, termed as the senescence-associated secretory phenotype (SASP). Targeting strategies to selectively and efficiently remove senescent cells before they exert non-autonomous but largely deleterious effects, are emerging as an effective solution to prevent drug resistance acquired from a treatment-remodeled TME. In this review, we summarize the TME composition and key activities that affect tissue homeostasis and support treatment resistance. Promising opportunities that allow TME-manipulation and senescent cell-targeting (senotherapy) are discussed, with translational pipelines to overcome therapeutic barriers in clinical oncology projected.

The functional multipotency of transforming growth factor β signaling at the intersection of senescence and cancer

The transforming growth factor β (TGF-β) family of cytokines comprises a group of proteins, their receptors, and effector molecules that, in a coordinated manner, modulate a plethora of physiological and pathophysiological processes. TGF-β1 is the best known and plausibly most active representative of this group. It acts as an immunosuppressant, contributes to extracellular matrix remodeling, and stimulates tissue fibrosis, differentiation, angiogenesis, and epithelial-mesenchymal transition. In recent years, this cytokine has been established as a vital regulator of organismal aging and cellular senescence. Finally, the role of TGF-β1 in cancer progression is no longer in question. Because this protein is involved in so many, often overlapping phenomena, the question arises whether it can be considered a molecular bridge linking some of these phenomena together and governing their reciprocal interactions. In this study, we reviewed the literature from the perspective of the role of various TGF-β family members as regulators of a complex mutual interplay between senescence and cancer. These aspects are then considered in a broader context of remaining TGF-β-related functions and coexisting processes. The main narrative axis in this work is centered around the interaction between the senescence of normal peritoneal cells and ovarian cancer cells. The discussion also includes examples of TGF-β activity at the interface of other normal and cancer cell types.

Transforming Growth Factor Beta 1 and p44/42 Expression in Cardinal Ligament Tissues of Patients with Pelvic Organ Prolapse

Background

Pelvic organ prolapse (POP) is a disease associated with collagen loss and decreased fibroblast proliferation. Transforming growth factor beta 1 (TGF-β1) controls collagen synthesis and degradation in pelvic connective tissue. Although the p44/42 MAPK pathway has been implicated in collagen production and extracellular matrix disorders, its expression in POP remains unknown. This study aimed to investigate TGF-β1 and p44/42 expression in cardinal ligament tissues in patients with POP.

Material/Methods

Cardinal ligament tissues were obtained from 30 patients with POP (POP group) and 30 patients with benign gynecological disorders who had undergone total hysterectomy (control group). The clinical characteristics of the 2 groups were summarized. Immunohistochemical staining and western blotting analysis were performed to measure the expression of TGF-β1, p44/42, phospho-p44/42, MMP9, TIMP1, caspase 3, collagen I, and collagen III in the cardinal ligament tissues.

Results

Patients with POP had significantly lower TGF-β1 and phospho-p44/42 levels than did control patients (P<0.05). The expression of TIMP1, collagen I, and collagen III was significantly lower, and the expression of MMP9 and caspase 3 was significantly higher in the POP group than in the control group (P<0.05). Moreover, the expression of phospho-p44/42 was positively correlated with the expression of TGF-β1, collagen I, and collagen III.

Conclusions

The expression levels of phospho-p44/42 and TGF-β1 were decreased in patients with POP and were positively correlated with collagen expression. Low levels of TGF-β1 and phospho-p44/42 expression in patients with POP may be associated with the occurrence of POP.

Patient-Specific Variables Determine the Extent of Cellular Senescence Biomarkers in Ovarian Tumors In Vivo

The mechanisms and clinical significance of the cellular senescence of tumor cells are a matter of ongoing debate. Recently, the triggers and molecular events underlying spontaneous, replicative senescence of primary epithelial ovarian cancer cells were characterized. In this study, we reanalyzed tumors obtained from ovarian cancer patients with respect to the expression of the senescence biomarkers SA-β-Gal and γ-H2A.X and the proliferative antigen Ki67. The results showed that the tumors displayed strong heterogeneity with respect to the expression of analyzed markers. The expression of SA-β-Gal and γ-H2A.X in the oldest patients (61–85 y.o.) was significantly higher than in the younger age groups. Conversely, the area of Ki67-positive cancer cells was greater in younger individuals. At the same time, there was a positive correlation between SA-β-Gal expression and calendar age in FIGO III–IV and malignant ascites-positive patients. The γ-H2A.X positively correlated with age in the whole group, FIGO III–IV, and ascites-positive patients. Ki67 levels correlated negatively with the age of patients among those same groups. Collectively, our study indicated that organismal aging may determine the development of the senescence phenotype in ovarian tumors, particularly in patients with advanced disease and those accumulating malignant ascites.

Common Genes Involved in Autophagy, Cellular Senescence and the Inflammatory Response in AMD and Drug Discovery Identified via Biomedical Databases

Purpose

Retinal pigment epithelial cell autophagy dysfunction, cellular senescence, and the retinal inflammatory response are key pathogenic factors in age-related macular degeneration (AMD), which has been reviewed in our previously work in 2019. This study aims to identify genes collectively involved in these three biological processes and target drugs in AMD.

Methods

The pubmed2ensembl database was used to perform text mining. The GeneCodis database was applied to analyze gene ontology biological process and the KEGG pathway. The STRING database was used to analyze protein–protein interaction analysis and hub genes were identified by the Cytoscape software. The Drug Gene Interaction Database was used to perform drug–gene interactions.

Results

We identified 62 genes collectively involved in AMD, autophagy, cellular senescence, and inflammatory response, 19 biological processes including 42 genes, 11 enriched KEGG pathways including 37 genes, and 12 hub genes step by step via the above biomedical databases. Finally, five hub genes (IL-6, VEGF-A, TP53, IL-1β, and transforming growth factor [TGF]-β1) and their specific interaction modes were identified, corresponding with 24 target drugs with therapeutic potential for AMD.

Conclusions

IL-6, VEGF-A, TP53, IL-1β, and TGF-β1 are pivotal in autophagy, cellular senescence, and the inflammatory response in AMD, corresponding with 24 drugs with therapeutic potential for AMD, providing definite molecular mechanisms for further research and new possibilities for AMD treatment in the future.

Translational Relevance

IL-6, VEGF-A, TP53, IL-1β, and TGF-β1 may be new targets for AMD gene therapy and drug development.

Where does cellular senescence belong in the pathophysiology of ovarian cancer?

Although ovarian cancer is the leading cause of death from gynecological malignancies, there are still some issues that hamper accurate interpretation of the complexity of cellular and molecular events underlying the pathophysiology of this disease. One of these is cellular senescence, which is the process whereby cells irreversibly lose their ability to divide and develop a phenotype that fuels a variety of age-related diseases, including cancer. In this review, various aspects of cellular senescence associated with intraperitoneal ovarian cancer metastasis are presented and discussed, including mechanisms of senescence in normal peritoneal mesothelial cells; the role of senescent mesothelium in ovarian cancer progression; the effect of drugs commonly used as first-line therapy in ovarian cancer patients on senescence of normal cells; mechanisms of spontaneous senescence in ovarian cancer cells; and, last but not least, other pharmacologic strategies to induce senescence in ovarian malignancies. Collectively, this study shows that cellular senescence is involved in several aspects of ovarian cancer pathobiology. Proper understanding of this phenomenon, particularly its clinical relevance, seems to be critical for oncology patients from both therapeutic and prognostic perspectives.

Thrombospondin-1 in maladaptive aging responses: a concept whose time has come

Numerous age-dependent alterations at the molecular, cellular, tissue and organ systems levels underlie the pathophysiology of aging. Herein, the focus is upon the secreted protein thrombospondin-1 (TSP1) as a promoter of aging and age-related diseases. TSP1 has several physiological functions in youth, including promoting neural synapse formation, mediating responses to ischemic and genotoxic stress, minimizing hemorrhage, limiting angiogenesis, and supporting wound healing. These acute functions of TSP1 generally require only transient expression of the protein. However, accumulating basic and clinical data reinforce the view that chronic diseases of aging are associated with accumulation of TSP1 in the extracellular matrix, which is a significant maladaptive contributor to the aging process. Identification of the relevant cell types that chronically produce and respond to TSP1 and the molecular mechanisms that mediate the resulting maladaptive responses could direct the development of therapeutic agents to delay or revert age-associated maladies.

The ECM path of senescence in aging: components and modifiers

The extracellular matrix (ECM) is a key noncellular component in all organs and tissues. It is composed of a large number of proteins including collagens, glycoproteins (GP), and ECM-associated proteins, which show diversity of biochemical and biophysical functions. The ECM is dynamic both in normal physiology of tissues and under pathological conditions. One cellular phenomenon associated with changes in both ECM components expression and in ECM remodeling enzymes secretion is cellular senescence. It represents a stable state form of cell cycle arrest induced in proliferating cells by various forms of stress. Short-term induction of senescence is essential for tumor suppression and tissue repair. However, long-term presence of senescent cells in tissues may have a detrimental role in promoting tissue damage and aging. Up to date, there is insufficient knowledge about the interplay between the ECM and senescence cells. Since changes in the ECM occur in many physiological and pathological conditions in which senescent cells are present, a better understanding of ECM-senescence interactions is necessary. Here, we will review the functions of the different ECM components and will discuss the current knowledge about their regulation in senescent cells and their influence on the senescence state.

Senescence-related deterioration of intercellular junctions in the peritoneal mesothelium promotes the transmesothelial invasion of ovarian cancer cells

Mechanisms of transmesothelial invasion of ovarian cancer are still poorly understood. Here we examined whether this phenomenon may be determined by an expression of intercellular junctions in peritoneal mesothelial cells (PMCs). Analysis of ovarian tumors showed that cancer cells are localized below an intact layer of PMCs. The PMCs located near the invaded cancer cells displayed low expression of connexin 43, E-cadherin, occludin, and desmoglein, as well as expressed SA-β-Gal, a marker of senescence. Experiments in vitro showed that senescent PMCs exhibited decreased levels of the four tested intercellular junctions, and that the invasion of ovarian cancer cells through the PMCs increased proportionally to the admixture of senescent cells. Intervention studies showed that the expression of connexin 43, E-cadherin, occludin, and desmoglein in senescent PMCs could be restored upon the blockade of p38 MAPK, NF-κB, AKT, JNK, HGF, and TGF-β1. When these molecules were neutralized, the efficiency of the transmesothelial cancer cell invasion was diminished. Collectively, our findings show that the integrity of the peritoneal mesothelium, which is determined by the expression of junctional proteins, is critical for the invasion of ovarian cancer. They also indicate a mechanism by which senescent PMCs may promote the invasive potential of cancer cells.

Thrombospondin-1 regulation of latent TGF-β activation: A therapeutic target for fibrotic disease

Transforming growth factor-β (TGF-β) is a central player in fibrotic disease. Clinical trials with global inhibitors of TGF-β have been disappointing, suggesting that a more targeted approach is warranted. Conversion of the latent precursor to the biologically active form of TGF-β represents a novel approach to selectively modulating TGF-β in disease, as mechanisms employed to activate latent TGF-β are typically cell, tissue, and/or disease specific. In this review, we will discuss the role of the matricellular protein, thrombospondin 1 (TSP-1), in regulation of latent TGF-β activation and the use of an antagonist of TSP-1 mediated TGF-β activation in a number of diverse fibrotic diseases. In particular, we will discuss the TSP-1/TGF-β pathway in fibrotic complications of diabetes, liver fibrosis, and in multiple myeloma. We will also discuss emerging evidence for a role for TSP-1 in arterial remodeling, biomechanical modulation of TGF-β activity, and in immune dysfunction. As TSP-1 expression is upregulated by factors induced in fibrotic disease, targeting the TSP-1/TGF-β pathway potentially represents a more selective approach to controlling TGF-β activity in disease.

Two-Step Senescence-Focused Cancer Therapies

Damaged cells at risk of neoplastic transformation can be neutralized by apoptosis or engagement of the senescence program, which induces permanent cell-cycle arrest and a bioactive secretome that is implicated in tumor immunosurveillance. While from an evolutionary perspective senescence is beneficial in that it protects against malignancies, the accumulation of senescent cells in tissues and organs with aging and at sites of various pathologies is largely detrimental. Because induction of senescence in cancer cells is emerging as a therapeutic concept, it will be important to consider these detrimental effects, including tumor-promoting properties that may drive the formation of secondary tumors or cancer relapse. In this review we discuss the complex relationship between senescence and cancer, and highlight important considerations for therapeutics.

Procancerogenic activity of senescent cells: A case of the peritoneal mesothelium

Human peritoneal mesothelial cells belong to a narrow group of somatic cells in which both the triggers and the mechanisms of senescence have already been well defined. Importantly, senescent mesothelial cells have been found in the peritoneal cavity in vivo. From a clinical point of view, peritoneal mesothelial cells have been recognized as playing a critical role in the intraperitoneal development of tumor metastases. The pro-cancerogenic behavior of mesothelial cells is even more pronounced when the cells exhaust their proliferative capacity and become senescent. In this review, we summarize the current state of art regarding the contribution of peritoneal mesothelial cells in the progression of ovarian, colorectal, and pancreatic carcinomas, with particular attention paid to the cancer-promoting activity of their senescent counterparts. Moreover, we delineate the mechanisms, mediators, and signaling pathways that are engaged by the senescent mesothelial cells to support such vital elements of cancer progression as adhesion, proliferation, migration, invasion, epithelial-mesenchymal transition, and angiogenesis. Finally, we discuss the experimental evidence regarding both natural and synthetic compounds that may either prevent or restrict cancer development by delaying senescence of mesothelial cells.

Copper accumulation in senescent cells: Interplay between copper transporters and impaired autophagy

Cellular senescence is characterized by irreversible growth arrest incurred through either replicative exhaustion or by pro-oncogenic cellular stressors (radioactivity, oxidative stress, oncogenic activation). The enrichment of senescent cells in tissues with age has been associated with tissue dyshomeostasis and age-related pathologies including cancers, neurodegenerative disorders (e.g. Alzheimer's, Parkinson's, etc.) and metabolic disorders (e.g. diabetes). We identified copper accumulation as being a universal feature of senescent cells [mouse embryonic fibroblasts (MEF), human prostate epithelial cells and human diploid fibroblasts] in vitro. Elevated copper in senescent MEFs was accompanied by elevated levels of high-affinity copper uptake protein 1 (Ctr1), diminished levels of copper-transporting ATPase 1 (Atp7a) (copper export) and enhanced antioxidant defence reflected by elevated levels of glutathione (GSH), superoxide dismutase 1 (SOD1) and glutaredoxin 1 (Grx1). The levels of intracellular copper were further increased in senescent MEFs cultured in copper supplemented medium and in senescent Mottled Brindled (Mo^br) MEFs lacking functional Atp7a. Finally, we demonstrated that the restoration/preservation of autophagic-lysosomal degradation in senescent MEFs following rapamycin treatment correlated with attenuation of copper accumulation in these cells despite a further decrease in Atp7a levels. This study for the first time establishes a link between Atp7a and the autophagic-lysosomal pathway, and a requirement for both to effect efficient copper export. Such a connection between cellular autophagy and copper homeostasis is significant, as both have emerged as important facets of age-associated degenerative disease.

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Copper accumulation is a feature of cellular senescence.

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Elevated copper in senescent cells is associated with impaired autophagic-lysosomal function.

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Restoration/preservation of lysosomal function attenuates copper accumulation.

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Both Atp7a and autophagic-lysosomal function are required for copper export.

Innate immunity and cellular senescence: The good and the bad in the developmental and aged brain

Ongoing studies evidence cellular senescence in undifferentiated and specialized cells from tissues of all ages. Although it is believed that senescence plays a wider role in several stress responses in the mature age, its participation in certain physiological and pathological processes throughout life is coming to light. The "senescence machinery" has been observed in all brain cell populations, including components of innate immunity (e.g., microglia and astrocytes). As the beneficial versus detrimental implications of senescence is an open question, we aimed to analyze the contribution of immune responses in regulatory mechanisms governing its distinct functions in healthy (development, organogenesis, danger patrolling events) and diseased brain (glioma, neuroinflammation, neurodeneration), and the putative connection between cellular and molecular events governing the 2 states. Particularly this review offers new insights into the complex roles of senescence both as a chronological event as age advances, and as a molecular mechanism of brain homeostasis through the important contribution of innate immune responses and their crosstalk with neighboring cells in brain parenchyma. We also highlight the impact of the recently described glymphatic system and brain lymphatic vasculature in the interplay between peripheral and central immune surveillance and its potential implication during aging. This will open new ways to understand brain development, its deterioration during aging, and the occurrence of several oncological and neurodegenerative diseases.

Regulation of Cellular Redox Signaling by Matricellular Proteins in Vascular Biology, Immunology, and Cancer

SIGNIFICANCE

In contrast to structural elements of the extracellular matrix, matricellular proteins appear transiently during development and injury responses, but their sustained expression can contribute to chronic disease. Through interactions with other matrix components and specific cell surface receptors, matricellular proteins regulate multiple signaling pathways, including those mediated by reactive oxygen and nitrogen species and H2S. Dysregulation of matricellular proteins contributes to the pathogenesis of vascular diseases and cancer. Defining the molecular mechanisms and receptors involved is revealing new therapeutic opportunities. Recent Advances: Thrombospondin-1 (TSP1) regulates NO, H2S, and superoxide production and signaling in several cell types. The TSP1 receptor CD47 plays a central role in inhibition of NO signaling, but other TSP1 receptors also modulate redox signaling. The matricellular protein CCN1 engages some of the same receptors to regulate redox signaling, and ADAMTS1 regulates NO signaling in Marfan syndrome. In addition to mediating matricellular protein signaling, redox signaling is emerging as an important pathway that controls the expression of several matricellular proteins.

CRITICAL ISSUES

Redox signaling remains unexplored for many matricellular proteins. Their interactions with multiple cellular receptors remains an obstacle to defining signaling mechanisms, but improved transgenic models could overcome this barrier.

FUTURE DIRECTIONS

Therapeutics targeting the TSP1 receptor CD47 may have beneficial effects for treating cardiovascular disease and cancer and have recently entered clinical trials. Biomarkers are needed to assess their effects on redox signaling in patients and to evaluate how these contribute to their therapeutic efficacy and potential side effects. Antioxid. Redox Signal. 27, 874-911.

Oxidative stress contributes to hepatocyte growth factor-dependent pro-senescence activity of ovarian cancer cells

The cancer-promoting activity of senescent peritoneal mesothelial cells (HPMCs) has already been well evidenced both in vitro and in vivo. Here we sought to determine if ovarian cancer cells may activate senescence in HPMCs. The study showed that conditioned medium (CM) from ovarian cancer cells (OVCAR-3, SKOV-3, A2780) inhibited growth and promoted the development of senescence phenotype (increased SA-β-Gal, γ-H2A.X, 53BP1, and decreased Cx43) in HPMCs. An analysis of tumors isolated from the peritoneum of patients with ovarian cancer revealed an abundance of senescent HPMCs in proximity to cancerous tissue. The presence of senescent HPMCs was incidental when fragments of peritoneum free from cancer were evaluated. An analysis of the cells' secretome followed by intervention studies with exogenous proteins and neutralizing antibodies revealed hepatocyte growth factor (HGF) as the mediator of the pro-senescence impact of the cancer cells. The activity of cancerous CM and HGF was associated with an induction of mitochondrial oxidative stress. Signaling pathways involved in the senescence of HPMCs elicited by the cancer-derived CM and HGF included p38 MAPK, AKT and NF-κB. HPMCs that senesced prematurely in response to the cancer-derived CM promoted adhesion of ovarian cancer cells, however this effect was effectively prevented by the cell protection against oxidative stress. Collectively, our findings indicate that ovarian cancer cells can elicit HGF-dependent senescence in HPMCs, which may contribute to the formation of a metastatic niche for these cells within the peritoneal cavity.

Endovenous Laser Ablation of Varicose Veins Preserves Biological Properties of Vascular Endothelium and Modulates Proinflammatory Agent Profile More Favorably Than Classic Vein Stripping

Here we compared effect of serum from varicose patients undergoing endovenous laser ablation (EVLA) and classic vein stripping (CVS) on biological properties of endothelial cells and on the local and systemic profiles of proinflammatory agents. Results showed that serum from EVLA patients improved proliferation and reduced senescence and oxidative stress in the endothelial cells, as compared with the serum from CVS patients. These effects were related to a suppressed activity of TGF-β1, the level of which in the serum from the EVLA patients was decreased. Medium generated by the cells subjected to EVLA serum contained decreased amounts of ICAM-1, VCAM-1, and E-selectin and increased amount of uPA, whereas the serum itself contained decreased concentrations of ICAM-1, E-selectin, and P-selectin and increased concentrations of uPA, PAI-1, and TFPI. Both EVLA and CVS resulted in diversified patients' reaction with respect to a direction of postprocedure changes in proinflammatory factors' serum level. Analysis of proportions showed that the groups differed remarkably in case of ICAM-1 and ET-1, the level of which declined in a higher fraction of patients treated endovenously. Our findings indicate that EVLA preserves better than CVS the functionality of vascular endothelium and modulates better both local and systemic profile of proinflammatory mediators.

Senescent peritoneal mesothelium creates a niche for ovarian cancer metastases

Although both incidence and aggressiveness of ovarian malignancy rise with age, the exact reason for this tendency, in particular the contribution of senescent cells, remains elusive. In this project we found that the patient's age determines the frequency of intraperitoneal metastases of ovarian cancer. Moreover, we documented that senescent human peritoneal mesothelial cells (HPMCs) stimulate proliferation, migration and invasion of ovarian cancer cells in vitro, and that this effect is related to both the activity of soluble agents released to the environment by these cells and direct cell-cell contact. The panel of mediators of the pro-cancerous activity of senescent HPMCs appeared to be cancer cell line-specific. The growth of tumors in a mouse peritoneal cavity was intensified when the cancer cells were co-injected together with senescent HPMCs. This effect was reversible when the senescence of HPMCs was slowed down by the neutralization of p38 MAPK. The analysis of lesions excised from the peritoneum of patients with ovarian cancer showed the abundance of senescent HPMCs in close proximity to the cancerous tissue. Collectively, our findings indicate that senescent HPMCs which accumulate in the peritoneum in vivo may create a metastatic niche facilitating intraperitoneal expansion of ovarian malignancy.

Serum from Varicose Patients Induces Senescence-Related Dysfunction of Vascular Endothelium Generating Local and Systemic Proinflammatory Conditions

Although the role of endothelium in varicose vein development is indisputable, the effect of the pathology on biological properties of endothelial cells remains unclear. Here we examined if the presence of varicose veins affects senescence of endothelial cells (HUVECs) and, if so, what will be the local and systemic outcome of this effect. Experiments showed that HUVECs subjected to serum from varicose patients display improved proliferation, increased expression of senescence marker, SA-β-Gal, and increased generation of reactive oxygen species (ROS), as compared with serum from healthy donors. Both increased SA-β-Gal activity and ROS release were mediated by TGF-β1, the concentration of which in varicose serum was elevated and the activity of which in vitro was prevented using specific neutralizing antibody. Senescent HUVECs exposed to varicose serum generated increased amounts of ICAM-1, VCAM-1, P-selectin, uPA, PAI-1, and ET-1. Direct comparison of sera from varicose and healthy donors showed that pathological serum contained increased level of ICAM-1, VCAM-1, P-selectin, uPA, and ET-1. Calendar age of healthy subjects correlated positively with serum uPA and negatively with P-selectin. Age of varicose patients correlated positively with ICAM-1, VCAM-1, and ET-1. Collectively, our findings indicate that the presence of varicose veins causes a senescence-related dysfunction of vascular endothelium, which leads to the development of local and systemic proinflammatory environment.

Colorectal cancer-promoting activity of the senescent peritoneal mesothelium

Gastrointestinal cancers metastasize into the peritoneal cavity in a process controlled by peritoneal mesothelial cells (HPMCs). In this paper we examined if senescent HPMCs can intensify the progression of colorectal (SW480) and pancreatic (PSN-1) cancers in vitro and in vivo. Experiments showed that senescent HPMCs stimulate proliferation, migration and invasion of SW480 cells, and migration of PSN-1 cells. When SW480 cells were injected i.p. with senescent HPMCs, the dynamics of tumor formation and vascularization were increased. When xenografts were generated using PSN-1 cells, senescent HPMCs failed to favor their growth. SW480 cells subjected to senescent HPMCs displayed up-regulated expression of transcripts for various pro-cancerogenic agents as well as increased secretion of their products. Moreover, they underwent an epithelial-mesenchymal transition in the Smad 2/3-Snail1-related pathway. The search for mediators of senescent HPMC activity showed that increased SW480 cell proliferation was stimulated by IL-6, migration by CXCL8 and CCL2, invasion by IL-6, MMP-3 and uPA, and epithelial-mesenchymal transition by TGF-β1. Secretion of these agents by senescent HPMCs was increased in an NF-κB- and p38 MAPK-dependent mechanism. Collectively, our findings indicate that in the peritoneum senescent HPMCs may create a metastatic niche in which critical aspects of cancer progression become intensified.

Ovarian cancer-derived ascitic fluids induce a senescence-dependent pro-cancerogenic phenotype in normal peritoneal mesothelial cells

PURPOSE

After the seeding ovarian cancer cells into the peritoneal cavity, ascitic fluid creates a microenvironment in which these cells can survive and disseminate. The exact nature of the interactions between malignant ascitic fluids and peritoneal mesothelial cells (HPMCs) in ovarian cancer progression has so far remained elusive. Here we assessed whether malignant ascitic fluids may promote the senescence of HPMCs and, by doing so, enhance the acquisition of their pro-cancerogenic phenotype.

METHODS

Primary omentum-derived HPMCs, ovarian cancer-derived cell lines (A2780, OVCAR-3, SKOV-3), malignant ascitic fluids and benign ascitic fluids from non-cancerous patients were used in this study. Ovarian cancer cell proliferation, as well as HPMC proliferation and senescence, were determined using flow cytometry and β-galactosidase assays, respectively. Ovarian cancer cell migration was quantified using a Transwell assay. The concentrations of soluble agents in ascitic fluids, conditioned media and cell lysates were measured using DuoSet® Immunoassay Development kits.

RESULTS

We found that HPMCs, when exposed to malignant ascitic fluids, exhibited decreased proliferation and increased senescence rates. The malignant ascitic fluids were found to contain elevated levels of HGF, TGF-β1 and GRO-1, of which HGF and GRO-1 were able to induce senescence in HPMCs. We also found that HPMCs subjected to malignant ascitic fluids or exogenously added HGF and GRO-1 stimulated ovarian cancer cell progression, which was manifested by an increased production of HA (adhesion), uPA (proliferation), IL-8 and MCP-1 (migration).

CONCLUSION

Our results indicate that malignant ascitic fluids may contribute to ovarian cancer progression by accelerating the senescence of HPMCs.

Senescent peritoneal mesothelium induces a pro-angiogenic phenotype in ovarian cancer cells in vitro and in a mouse xenograft model in vivo

It is believed that senescent cells contribute to the progression of primary and metastatic tumors, however, the exact mechanisms of this activity remain elusive. In this report we show that senescent human peritoneal mesothelial cells (HPMCs) alter the secretory profile of ovarian cancer cells (A2780, OVCAR-3, SKOV-3) by increasing the release of four angiogenic agents: CXCL1, CXCL8, HGF, and VEGF. Proliferation and migration of endothelial cells subjected to conditioned medium generated by: cancer cells modified by senescent HPMCs; cancer cells co-cultured with senescent HPMCs; and by early-passage HPMCs from aged donors, were markedly intensified. The same was the case for the vascularization, size and number of tumors that developed in the mouse peritoneum upon injection of ovarian cancer cells with senescent HPMCs. When the identified pro-angiogenic proteins were neutralized in conditioned medium from the cancer cells, both aspects of endothelial cell behavior intensified in vitro in response to senescent HPMCs were markedly reduced. The search for mediators of senescent HPMC activity using specific neutralizing antibodies and recombinant exogenous proteins showed that the intensified angiogenic potential of cancer cells was elicited by IL-6 and TGF-β1. At the transcriptional level, increased proliferation and migration of endothelial cells exposed to cancer cells modified by senescent HPMCs was regulated by HIF-1α, NF-κB/p50 and AP-1/c-Jun. Collectively, our findings indicate that senescent HPMCs may promote the progression of ovarian cancer cells by reprogramming their secretory phenotype towards increased production of pro-angiogenic agents and subsequent increase in the angiogenic capabilities of the vascular endothelium.