Mesothelial cell: a multifaceted model of aging

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.

Biocompatible Nanocomposites for Postoperative Adhesion: A State-of-the-Art Review

To reduce and prevent postsurgical adhesions, a variety of scientific approaches have been suggested and applied. This includes the use of advanced therapies like tissue-engineered (TE) biomaterials and scaffolds. Currently, biocompatible antiadhesive constructs play a pivotal role in managing postoperative adhesions and several biopolymer-based products, namely hyaluronic acid (HA) and polyethylene glycol (PEG), are available on the market in different forms (e.g., sprays, hydrogels). TE polymeric constructs are usually associated with critical limitations like poor biocompatibility and mechanical properties. Hence, biocompatible nanocomposites have emerged as an advanced therapy for postoperative adhesion treatment, with hydrogels and electrospun nanofibers among the most utilized antiadhesive nanocomposites for in vitro and in vivo experiments. Recent studies have revealed that nanocomposites can be engineered to generate smart three-dimensional (3D) scaffolds that can respond to different stimuli, such as pH changes. Additionally, nanocomposites can act as multifunctional materials for the prevention of adhesions and bacterial infections, as well as tissue healing acceleration. Still, more research is needed to reveal the clinical potential of nanocomposite constructs and the possible success of nanocomposite-based products in the biomedical market.

BET Protein Inhibitor JQ1 Ameliorates Experimental Peritoneal Damage by Inhibition of Inflammation and Oxidative Stress

Peritoneal dialysis (PD) is a current replacement therapy for end-stage kidney diseases (ESKDs). However, long-term exposure to PD fluids may lead to damage of the peritoneal membrane (PM) through mechanisms involving the activation of the inflammatory response and mesothelial-to-mesenchymal transition (MMT), leading to filtration failure. Peritoneal damage depends on a complex interaction among external stimuli, intrinsic properties of the PM, and subsequent activities of the local innate-adaptive immune system. Epigenetic drugs targeting bromodomain and extra-terminal domain (BET) proteins have shown beneficial effects on different experimental preclinical diseases, mainly by inhibiting proliferative and inflammatory responses. However the effect of BET inhibition on peritoneal damage has not been studied. To this aim, we have evaluated the effects of treatment with the BET inhibitor JQ1 in a mouse model of peritoneal damage induced by chlorhexidine gluconate (CHX). We found that JQ1 ameliorated the CHX-induced PM thickness and inflammatory cell infiltration. Moreover, JQ1 decreased gene overexpression of proinflammatory and profibrotic markers, together with an inhibition of the nuclear factor-κB (NF-κB) pathway. Additionally, JQ1 blocked the activation of nuclear factor erythroid 2-related factor 2 (NRF2) and restored changes in the mRNA expression levels of NADPH oxidases (NOX1 and NOX4) and NRF2/target antioxidant response genes. To corroborate the in vivo findings, we evaluated the effects of the BET inhibitor JQ1 on PD patients' effluent-derived primary mesothelial cells and on the MeT-5A cell line. JQ1 inhibited tumor necrosis factor-α (TNF-α)-induced proinflammatory gene upregulation and restored MMT phenotype changes, together with the downmodulation of oxidative stress. Taken together, these results suggest that BET inhibitors may be a potential therapeutic option to ameliorate peritoneal damage.

Novel Aspects of the Immune Response Involved in the Peritoneal Damage in Chronic Kidney Disease Patients under Dialysis

Chronic kidney disease (CKD) incidence is growing worldwide, with a significant percentage of CKD patients reaching end-stage renal disease (ESRD) and requiring kidney replacement therapies (KRT). Peritoneal dialysis (PD) is a convenient KRT presenting benefices as home therapy. In PD patients, the peritoneum is chronically exposed to PD fluids containing supraphysiologic concentrations of glucose or other osmotic agents, leading to the activation of cellular and molecular processes of damage, including inflammation and fibrosis. Importantly, peritonitis episodes enhance peritoneum inflammation status and accelerate peritoneal injury. Here, we review the role of immune cells in the damage of the peritoneal membrane (PM) by repeated exposure to PD fluids during KRT as well as by bacterial or viral infections. We also discuss the anti-inflammatory properties of current clinical treatments of CKD patients in KRT and their potential effect on preserving PM integrity. Finally, given the current importance of coronavirus disease 2019 (COVID-19) disease, we also analyze here the implications of this disease in CKD and KRT.

Adipose tissue at single-cell resolution

Adipose tissue exhibits remarkable plasticity with capacity to change in size and cellular composition under physiological and pathophysiological conditions. The emergence of single-cell transcriptomics has rapidly transformed our understanding of the diverse array of cell types and cell states residing in adipose tissues and has provided insight into how transcriptional changes in individual cell types contribute to tissue plasticity. Here, we present a comprehensive overview of the cellular atlas of adipose tissues focusing on the biological insight gained from single-cell and single-nuclei transcriptomics of murine and human adipose tissues. We also offer our perspective on the exciting opportunities for mapping cellular transitions and crosstalk, which have been made possible by single-cell technologies.

Cell Type-Specific Anti-Adhesion Properties of Peritoneal Cell Treatment with Plasma-Activated Media (PAM)

Postoperative abdominal adhesions are responsible for serious clinical disorders. Administration of plasma-activated media (PAM) to cell type-specific modulated proliferation and protein biosynthesis is a promising therapeutic strategy to prevent pathological cell responses in the context of wound healing disorders. We analyzed PAM as a therapeutic option based on cell type-specific anti-adhesive responses. Primary human peritoneal fibroblasts and mesothelial cells were isolated, characterized and exposed to different PAM dosages. Cell type-specific PAM effects on different cell components were identified by contact- and marker-independent Raman imaging, followed by thorough validation by specific molecular biological methods. The investigation revealed cell type-specific molecular responses after PAM treatment, including significant cell growth retardation in peritoneal fibroblasts due to transient DNA damage, cell cycle arrest and apoptosis. We identified a therapeutic dose window wherein specifically pro-adhesive peritoneal fibroblasts were targeted, whereas peritoneal mesothelial cells retained their anti-adhesive potential of epithelial wound closure. Finally, we demonstrate that PAM treatment of peritoneal fibroblasts reduced the expression and secretion of pro-adhesive cytokines and extracellular matrix proteins. Altogether, we provide insights into biochemical PAM mechanisms which lead to cell type-specific pro-therapeutic cell responses. This may open the door for the prevention of pro-adhesive clinical disorders.

The Epithelial-Mesenchymal Transition Initiated by Malignant Ascites Underlies the Transmesothelial Invasion of Ovarian Cancer Cells

The role of the epithelial-mesenchymal transition (EMT) in ovarian cancer cell progression is unquestioned. In this report, we describe that malignant ascites, fluid that accumulates in the peritoneal cavity in a large group of patients with ovarian cancer, stimulate EMT in two representative ovarian cancer cell lines (A2780, SKOV-3). In addition, we identify the ascites-derived mediators of EMT and signaling pathways initiated in the cancer cells that underlie this phenomenon. Finally, we demonstrate that EMT induced in the cancer cells in response to the malignant ascites contributes to their increased transmesothelial invasion. Altogether, our study provides new insight into the mechanistic aspects of the malignant ascites-dependent exacerbation of the intraperitoneal progression of ovarian cancer.

Epithelial-to-Mesenchymal Transition and Migration of Human Peritoneal Mesothelial Cells Undergoing Senescence

BACKGROUND

Epithelial-to-mesenchymal transition (EMT) of human peritoneal mesothelial cells (HPMCs) contributes to fibrotic thickening of the peritoneum that develops in patients on peritoneal dialysis (PD). The process is thought to be largely mediated by transforming growth factor-beta (TGF-β). As TGF-β has also been implicated in senescence of HPMCs, we have performed an exploratory study to examine if senescent HPMCs can undergo EMT.

METHODS

Omentum-derived HPMCs were rendered senescent by repeated passages in culture. Features of EMT were assessed by immunostaining and quantitative polymerase chain reaction (qPCR) at various stages of the HPMC lifespan and after treatment with or without TGF-β. The motility of HPMCs was assessed in a scratch wound migration assay.

RESULTS

Replicative senescence of HPMCs was associated with a gradual increase in the constitutive expression of EMT markers, including increased production of extracellular matrix proteins. However, senescent HPMCs also retained epithelial cell features such as cytokeratin, calretinin, and E-cadherin and showed decreased, rather than increased, motility. In contrast, exposure to TGF-β resulted in an up-regulation of mesenchymal markers and down-regulation of epithelial markers. Such effects of TGF-β occurred both in young and senescent cells, although they were less pronounced in senescence.

CONCLUSIONS

Senescence of HPMCs is associated with spontaneous development of several EMT features. At the same time, senescent HPMCs preserve epithelial cell-like characteristics and are less prone to develop a full EMT phenotype in response to TGF-β. These observations may support the concept of cellular senescence being antagonistically pleiotropic with regard to EMT.

Aging Increases Susceptibility to Ovarian Cancer Metastasis in Murine Allograft Models and Alters Immune Composition of Peritoneal Adipose Tissue

Ovarian cancer, the most deadly gynecological malignancy in U.S. women, metastasizes uniquely, spreading through the peritoneal cavity and often generating widespread metastatic sites before diagnosis. The vast majority of ovarian cancer cases occur in women over 40 and the median age at diagnosis is 63. Additionally, elderly women receive poorer prognoses when diagnosed with ovarian cancer. Despite age being a significant risk factor for the development of this cancer, there are little published data which address the impact of aging on ovarian cancer metastasis. Here we report that the aged host is more susceptible to metastatic success using two murine syngeneic allograft models of ovarian cancer metastasis. This age-related increase in metastatic tumor burden corresponds with an increase in tumor infiltrating lymphocytes (TILs) in tumor-bearing mice and alteration of B cell-related pathways in gonadal adipose tissue. Based on this work, further studies elucidating the status of B cell TILs in mouse models of metastasis and human tumors in the context of aging are warranted.

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.

The peritoneal "soil" for a cancerous "seed": a comprehensive review of the pathogenesis of intraperitoneal cancer metastases

Various types of tumors, particularly those originating from the ovary and gastrointestinal tract, display a strong predilection for the peritoneal cavity as the site of metastasis. The intraperitoneal spread of a malignancy is orchestrated by a reciprocal interplay between invading cancer cells and resident normal peritoneal cells. In this review, we address the current state-of-art regarding colonization of the peritoneal cavity by ovarian, colorectal, pancreatic, and gastric tumors. Particular attention is paid to the pro-tumoral role of various kinds of peritoneal cells, including mesothelial cells, fibroblasts, adipocytes, macrophages, the vascular endothelium, and hospicells. Anatomo-histological considerations on the pro-metastatic environment of the peritoneal cavity are presented in the broader context of organ-specific development of distal metastases in accordance with Paget's "seed and soil" theory of tumorigenesis. The activity of normal peritoneal cells during pivotal elements of cancer progression, i.e., adhesion, migration, invasion, proliferation, EMT, and angiogenesis, is discussed from the perspective of well-defined general knowledge on a hospitable tumor microenvironment created by the cellular elements of reactive stroma, such as cancer-associated fibroblasts and macrophages. Finally, the paper addresses the unique features of the peritoneal cavity that predispose this body compartment to be a niche for cancer metastases, presents issues that are topics of an ongoing debate, and points to areas that still require further in-depth investigations.

Telomere length profiles in primary human peritoneal mesothelial cells are consistent with senescence

Mesothelial cell (MC) senescence contributes to malignancy and tissue fibrosis. The role of telomere erosion in MC senescence remains controversial, with evidence for both telomere-dependent and telomere-independent mechanisms reported. Single telomere length analysis revealed considerable telomere length heterogeneity in freshly isolated human peritoneal MCs, reflecting a heterogeneous proliferative history and providing high-resolution evidence for telomere-dependent senescence. By contrast the attenuated replicative lifespan, lack of telomere erosion and induction of p16 expression in in vitro-aged cells was consistent with stress-induced senescence. Given the potential pathophysiological impact of senescence in mesothelial tissues, high-resolution MC telomere length analysis may provide clinically useful information.

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.

Characterisation of Cultured Mesothelial Cells Derived from the Murine Adult Omentum

The human omentum has been long regarded as a healing patch, used by surgeons for its ability to immunomodulate, repair and vascularise injured tissues. A major component of the omentum are mesothelial cells, which display some of the characteristics of mesenchymal stem/stromal cells. For instance, lineage tracing studies have shown that mesothelial cells give rise to adipocytes and vascular smooth muscle cells, and human and rat mesothelial cells have been shown to differentiate into osteoblast- and adipocyte-like cells in vitro, indicating that they have considerable plasticity. However, so far, long-term cultures of mesothelial cells have not been successfully established due to early senescence. Here, we demonstrate that mesothelial cells isolated from the mouse omentum could be cultured for more than 30 passages. While epithelial markers were downregulated over passages in the mesothelial cells, their mesenchymal profile remained unchanged. Early passage mesothelial cells displayed clonogenicitiy, expressed several stem cell markers, and up to passage 5 and 13, respectively, could differentiate along the adipogenic and osteogenic lineages, demonstrating stem/progenitor characteristics and differentiation potential.

Diverse properties of the mesothelial cells in health and disease

Mesothelial cells (MCs) form the superficial anatomic layer of serosal membranes, including pleura, pericardium, peritoneum, and the tunica of the reproductive organs. MCs produce a protective, non-adhesive barrier against physical and biochemical damages. MCs express a wide range of phenotypic markers, including vimentin and cytokeratins. MCs play key roles in fluid transport and inflammation, as reflected by the modulation of biochemical markers such as transporters, adhesion molecules, cytokines, growth factors, reactive oxygen species and their scavengers. MCs synthesize extracellular matrix related molecules, and the surface of MC microvilli secretes a highly hydrophilic protective barrier, "glycocalyx", consisting mainly of glycosaminoglycans. MCs maintain a balance between procoagulant and fibrinolytic activation by producing a whole range of regulators, can synthetize fibrin and therefore form adhesions. Synthesis and recognition of hyaluronan and sialic acids might be a new insight to explain immunoactive and immunoregulatory properties of MCs. Epithelial to mesenchymal transition of MCs may involve serosal repair and remodeling. MCs might also play a role in the development and remodeling of visceral adipose tissue. Taken together, MCs play important roles in health and disease in serosal cavities of the body. The mesothelium is not just a membrane and should be considered as an organ.

Acetylcholine and acetylcarnitine transport in peritoneum: Role of the SLC22A4 (OCTN1) transporter

A suitable experimental tool based on proteoliposomes for assaying Organic Cation Transporter Novel member 1 (OCTN1) of peritoneum was pointed out. OCTN1, recently acknowledged as acetylcholine transporter, was immunodetected in rat peritoneum. Transport was assayed following flux of radiolabelled TEA, acetylcholine or acetylcarnitine in proteoliposomes reconstituted with peritoneum extract. OCTN1 mediated, besides TEA, also acetylcholine and a slower acetylcarnitine transport. External sodium inhibited acetylcholine uptake but not its release from proteoliposomes. Differently, sodium did not affect acetylcarnitine uptake. These results suggested that physiologically, acetylcholine should be released while acetylcarnitine was taken up by peritoneum cells. Transport was impaired by OCTN1 inhibitors, butyrobetaine, spermine, and choline. Biotin was also found as acetylcholine transport inhibitor. Anti-OCTN1 antibody specifically inhibited acetylcholine transport confirming the involvement of OCTN1. The transporter was also immunodetected in human mesothelial primary cells. Extract from these cells was reconstituted in proteoliposomes. Transport features very similar to those found with rat peritoneum were observed. Validation of the proteoliposome model for peritoneal transport study was then achieved assaying transport in intact mesothelial cells. TEA, butyrobetaine and Na(+) inhibited acetylcholine transport in intact cells while efflux was Na(+) insensitive. Therefore transport features in intact cells overlapped those found in proteoliposomes.

Senescence-Associated Changes in Proteome and O-GlcNAcylation Pattern in Human Peritoneal Mesothelial Cells

INTRODUCTION

Senescence of peritoneal mesothelial cells represents a biological program defined by arrested cell growth and altered cell secretory phenotype with potential impact in peritoneal dialysis. This study aims to characterize cellular senescence at the level of global protein expression profiles and modification of proteins with O-linked N-acetylglucosamine (O-GlcNAcylation).

METHODS

A comparative proteomics analysis between young and senescent human peritoneal mesothelial cells (HPMC) was performed using two-dimensional gel electrophoresis. O-GlcNAc status was assessed by Western blot under normal conditions and after modulation with 6-diazo-5-oxo-L-norleucine (DON) to decrease O-GlcNAcylation or O-(2-acetamido-2-deoxy-D-glucopyranosylidene) amino N-phenyl carbamate (PUGNAc) to increase O-GlcNAcylation.

RESULTS

Comparison of protein pattern of senescent and young HPMC revealed 29 differentially abundant protein spots, 11 of which were identified to be actin (cytoplasmic 1 and 2), cytokeratin-7, cofilin-2, transgelin-2, Hsp60, Hsc70, proteasome β-subunits (type-2 and type-3), nucleoside diphosphate kinase A, and cytosolic 5'(3')-deoxyribonucleotidase. Although the global level of O-GlcNAcylation was comparable, senescent cells were not sensitive to modulation by PUGNAc.

DISCUSSION

This study identified changes of the proteome and altered dynamics of O-GlcNAc regulation in senescent mesothelial cells. Whereas changes in cytoskeleton-associated proteins likely reflect altered cell morphology, changes in chaperoning and housekeeping proteins may have functional impact on cellular stress response in peritoneal dialysis.

Visceral Adipose Tissue Mesothelial Cells: Living on the Edge or Just Taking Up Space?

Visceral adiposity and pathological adipose tissue remodeling, a result of overnutrition, are strong predictors of metabolic health in obesity. Factors intrinsic to visceral adipose depots are likely to play a causal role in eliciting the detrimental effects of this tissue on systemic nutrient homeostasis. The visceral adipose-associated mesothelium, a monolayer of epithelial cells of mesodermal origin that line the visceral serosa, has recently attracted attention for its role in metabolic dysfunction. Here we highlight and consolidate literature from various fields of study that points to the visceral adipose-associated mesothelium as a potential contributor to adipose development and remodeling. We propose a hypothesis in which adipose mesothelial cells represent a visceral depot-specific determinant of adipose tissue health in obesity.

The Mesothelial Origin of Carcinoma Associated-Fibroblasts in Peritoneal Metastasis

Solid tumors are complex and unstructured organs that, in addition to cancer cells, also contain other cell types. Carcinoma-associated fibroblasts (CAFs) represent an important population in the tumor microenviroment and participate in several stages of tumor progression, including cancer cell migration/invasion and metastasis. During peritoneal metastasis, cancer cells detach from the primary tumor, such as ovarian or gastrointestinal, disseminate through the peritoneal fluid and colonize the peritoneum. Tumor cells metastasize by attaching to and invading through the mesothelial cell (MC) monolayer that lines the peritoneal cavity, then colonizing the submesothelial compact zone where CAFs accumulate. CAFs may derive from different sources depending on the surrounding metastatic niche. In peritoneal metastasis, a sizeable subpopulation of CAFs originates from MCs through a mesothelial-to-mesenchymal transition (MMT), which promotes adhesion, invasion, vascularization and subsequent tumor growth. The bidirectional communication between cancer cells and MC-derived CAFs via secretion of a wide range of cytokines, growth factors and extracellular matrix components seems to be crucial for the establishment and progression of the metastasis in the peritoneum. This manuscript provides a comprehensive review of novel advances in understanding how peritoneal CAFs provide cancer cells with a supportive microenvironment, as well as the development of future therapeutic approaches by interfering with the MMT in the peritoneum.

Specificity of cytochemical and fluorescence methods of senescence-associated β-galactosidase detection for ageing driven by replication and time

Senescence-associated β-galactosidase (SA-β-Gal) is a widely used marker of senescent cells in vitro and in vivo. In this report, young and senescent human peritoneal mesothelial cells (HPMCs) and fragments of the omentum, from which these cells were isolated, were subjected to simultaneous examination of SA-β-Gal using two methods, i.e. cytochemical and fluorescent methods. The results obtained were confronted with the cumulative number of population doublings (CPD) and the calendar age of the tissue donor. The study showed that senescence of HPMCs proceeds with either an increased percentage of SA-β-Gal-positive cells or increased enzyme activity. Cytochemical SA-β-Gal staining in early-passage cultures negatively correlated with CPD values but not with donor age in both cell cultures and omentum specimens. Conversely, SA-β-Gal activity measured with the fluorescence method rose in proportion to the calendar age of the donor either in early-passage cultures or in primary cell isolates from omental tissue. At the same time it was not related to the CPD values. These findings may suggest that with respect to at least peritoneal mesothelial cells, the cytochemical and fluorescent methods of SA-β-Gal detection, though complementary, are informative for different levels of aging, i.e. the cytochemical approach for senescence in vitro and the fluorescence-based technique for organismal aging in vivo.