Oxidative stress-mediated early senescence contributes to the short replicative life span of human peritoneal mesothelial cells

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.

Mechanisms of carboplatin- and paclitaxel-dependent induction of premature senescence and pro-cancerogenic conversion of normal peritoneal mesothelium and fibroblasts

Carboplatin (CPT) and paclitaxel (PCT) are the optimal non-surgical treatment of epithelial ovarian cancer (EOC). Although their growth-restricting influence on EOC cells is well known, their impact on normal peritoneal cells, including mesothelium (PMCs) and fibroblasts (PFBs), is poorly understood. Here, we investigated whether, and if so, by what mechanism, CPT and PCT induce senescence of omental PMCs and PFBs. In addition, we tested whether PMC and PFB exposure to the drugs promotes the development of a pro-cancerogenic phenotype. The results showed that CPT and PCT induce G2/M growth arrest-associated senescence of normal peritoneal cells and that the strongest induction occurs when the drugs act together. PMCs senesce telomere-independently with an elevated p16 level and via activation of AKT and STAT3. In PFBs, telomeres shorten along with an induction of p21 and p53, and their senescence proceeds via the activation of ERK1/2. Oxidative stress in CPT + PCT-treated PMCs and PFBs is extensive and contributes causatively to their premature senescence. Both PMCs and PFBs exposed to CPT + PCT fuel the proliferation, migration, and invasion of established (A2780, OVCAR-3, SKOV-3) and primary EOCs, and this activity is linked with an overproduction of multiple cytokines altering the cancer cell transcriptome and controlled by p38 MAPK, NF-κB, STAT3, Notch1, and JAK1. Collectively, our findings indicate that CPT and PCT lead to iatrogenic senescence of normal peritoneal cells, which paradoxically and opposing therapeutic needs alters their phenotype towards pro-cancerogenic. It cannot be excluded that these adverse outcomes of chemotherapy may contribute to EOC relapse in the case of incomplete tumor eradication and residual disease initiation. © 2023 The Pathological Society of Great Britain and Ireland.

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.

Basal cell adhesion molecule promotes metastasis-associated processes in ovarian cancer

BACKGROUND

Basal cell adhesion molecule (BCAM) is a laminin α5 (LAMA5) binding membrane-bound protein with a putative role in cancer. Besides full-length BCAM1, an isoform lacking most of the cytoplasmic domain (BCAM2), and a soluble form (sBCAM) of unknown function are known. In ovarian carcinoma (OC), all BCAM forms are abundant and associated with poor survival, yet BCAM's contribution to peritoneal metastatic spread remains enigmatic.

METHODS

Biochemical, omics-based and real-time cell assays were employed to identify the source of sBCAM and metastasis-related functions of different BCAM forms. OC cells, explanted omentum and a mouse model of peritoneal colonisation were used in loss- and gain-of-function experiments.

RESULTS

We identified ADAM10 as a major BCAM sheddase produced by OC cells and identified proteolytic cleavage sites proximal to the transmembrane domain. Recombinant soluble BCAM inhibited single-cell adhesion and migration identically to membrane-bound isoforms, confirming its biological activity in OC. Intriguingly, this seemingly anti-tumorigenic potential of BCAM contrasts with a novel pro-metastatic function discovered in the present study. Thus, all queried BCAM forms decreased the compactness of tumour cell spheroids by inhibiting LAMA5 - integrin β1 interactions, promoted spheroid dispersion in a three-dimensional collagen matrix, induced clearance of mesothelial cells at spheroid attachment sites in vitro and enhanced invasion of spheroids into omental tissue both ex vivo and in vivo.

CONCLUSIONS

Membrane-bound BCAM as well as sBCAM shed by ADAM10 act as decoys rather than signalling receptors to modulate metastasis-related functions. While BCAM appears to have tumour-suppressive effects on single cells, it promotes the dispersion of OC cell spheroids by regulating LAMA5-integrin-β1-dependent compaction and thereby facilitating invasion of metastatic target sites. As peritoneal dissemination is majorly mediated by spheroids, these findings offer an explanation for the association of BCAM with a poor clinical outcome of OC, suggesting novel therapeutic options.

Proteome-Wide Differential Effects of Peritoneal Dialysis Fluid Properties in an In Vitro Human Endothelial Cell Model

To replace kidney function, peritoneal dialysis (PD) utilizes hyperosmotic PD fluids with specific physico-chemical properties. Their composition induces progressive damage of the peritoneum, leading to vasculopathies, decline of membrane function, and PD technique failure. Clinically used PD fluids differ in their composition but still remain bioincompatible. We mapped the molecular pathomechanisms in human endothelial cells induced by the different characteristics of widely used PD fluids by proteomics. Of 7894 identified proteins, 3871 were regulated at least by 1 and 49 by all tested PD fluids. The latter subset was enriched for cell junction-associated proteins. The different PD fluids individually perturbed proteins commonly related to cell stress, survival, and immune function pathways. Modeling two major bioincompatibility factors of PD fluids, acidosis, and glucose degradation products (GDPs) revealed distinct effects on endothelial cell function and regulation of cellular stress responses. Proteins and pathways most strongly affected were members of the oxidative stress response. Addition of the antioxidant and cytoprotective additive, alanyl-glutamine (AlaGln), to PD fluids led to upregulation of thioredoxin reductase-1, an antioxidant protein, potentially explaining the cytoprotective effect of AlaGln. In conclusion, we mapped out the molecular response of endothelial cells to PD fluids, and provided new evidence for their specific pathomechanisms, crucial for improvement of PD therapies.

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.

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.

Deciphering the Molecular Mechanism of Spontaneous Senescence in Primary Epithelial Ovarian Cancer Cells

Spontaneous senescence of cancer cells remains a puzzling and poorly understood phenomenon. Here we comprehensively characterize this process in primary epithelial ovarian cancer cells (pEOCs). Analysis of tumors from ovarian cancer patients showed an abundance of senescent cells in vivo. Further, serially passaged pEOCs become senescent after a few divisions. These senescent cultures display trace proliferation, high expression of senescence biomarkers (SA--Gal, -H2A.X), growth-arrest in the G₁ phase, increased level of cyclins D1, D2, decreased cyclin B1, up-regulated p16, p21, and p53 proteins, eroded telomeres, reduced activity of telomerase, predominantly non-telomeric DNA damage, activated AKT, AP-1, and ERK1/2 signaling, diminished JNK, NF-B, and STAT3 pathways, increased formation of reactive oxygen species, unchanged activity of antioxidants, increased oxidative damage to DNA and proteins, and dysfunctional mitochondria. Moreover, pEOC senescence is inducible by normal peritoneal mesothelium, fibroblasts, and malignant ascites via the paracrine activity of GRO-1, HGF, and TGF-1. Collectively, pEOCs undergo spontaneous senescence in a mosaic, telomere-dependent and telomere-independent manner, plausibly in an oxidative stress-dependent mechanism. The process may also be activated by extracellular stimuli. The biological and clinical significance of pEOC senescence remains to be explored.

Mechanisms and significance of therapy-induced and spontaneous senescence of cancer cells

In contrast to the well-recognized replicative and stress-induced premature senescence of normal somatic cells, mechanisms and clinical implications of senescence of cancer cells are still elusive and uncertain from patient-oriented perspective. Moreover, recent years provided multiple pieces of evidence that cancer cells may undergo senescence not only in response to chemotherapy or ionizing radiation (the so-called therapy-induced senescence) but also spontaneously, without any external insults. Since the molecular nature of the latter process is poorly recognized, the significance of spontaneously senescent cancer cells for tumor progression, therapy effectiveness, and patient survival is purely speculative. In this review, we summarize the most up-to-date research regarding therapy-induced and spontaneous senescence of cancer cells, by delineating the most important discoveries regarding the occurrence of these phenomena in vivo and in vitro. This review provides data collected from studies on various cancer cell models, and the narration is presented from the broader perspective of the most critical findings regarding the senescence of normal somatic cells.

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.

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.

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.

Evidence for a Mesothelial Origin of Body Cavity Effusion Lymphomas

Background

Primary effusion lymphoma (PEL) is a Kaposi's sarcoma herpes virus (KSHV)-induced lymphoma that typically arises in body cavities of HIV-infected patients. PEL cells are often co-infected with Epstein-Barr virus (EBV). "PEL-like" lymphoma is a KSHV-unrelated lymphoma that arises in body cavities of HIV-negative patients. "PEL-like" lymphoma is sometimes EBV positive. The derivation of PEL/"PEL-like" cells is unclear.

Methods

Mesothelial cells were cultured from body cavity effusions of 23 patients. Cell proliferation, cytokine secretion, marker phenotypes, KSHV/EBV infection, and clonality were evaluated by standard methods. Gene expression was measured by quantitative polymerase chain reaction and immunoblotting. A mouse model of PEL (3 mice/group) was used to evaluate tumorigenicity.

Results

We found that the mesothelia derived from six effusions of HIV-infected patients with PEL or other KSHV-associated diseases contained rare KSHV + or EBV + mesothelial cells. After extended culture (16-17 weeks), some mesothelial cells underwent a trans-differentiation process, generating lymphoid-type CD45 + /B220 + , CD5 + , CD27 + , CD43 + , CD11c + , and CD3 - cells resembling "B1-cells," most commonly found in mouse body cavities. These "B1-like" cells were short lived. However, long-term KSHV + EBV - and EBV + KSHV - clonal cell lines emerged from mesothelial cultures from two patients that were clonally distinct from the monoclonal or polyclonal B-cell populations found in the patients' original effusions.

Conclusions

Mesothelial-to-lymphoid transformation is a newly identified in vitro process that generates "B1-like" cells and is associated with the emergence of long-lived KSHV or EBV-infected cell lines in KSHV-infected patients. These results identify mesothelial cultures as a source of PEL cells and lymphoid cells in humans.

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.

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.

Synthetic resveratrol analogue, 3,3',4,4',5,5'-hexahydroxy-trans-stilbene, accelerates senescence in peritoneal mesothelium and promotes senescence-dependent growth of gastrointestinal cancers

3,3′,4,4′,5,5′-Hexahydroxy-trans-stilbene (M8) is a synthetic resveratrol derivative, advertised as a candidate drug highly effective against numerous malignancies. Because multiple tumors prone to M8 frequently metastasize into the peritoneal cavity, this study was aimed at establishing the effect of M8 on the growth and senescence of human peritoneal mesothelial cells (HPMCs), the largest cell population within the peritoneum, actively involved in the intraperitoneal spread of cancer. The study showed that M8, used at the highest non-toxic dose of 10 μM, impairs proliferation and accelerates senescence in cultured HPMCs via an oxidative stress-dependent mechanism. At the same time, soluble factors released to the environment by HPMCs that senesced prematurely in response to M8 promoted growth of colorectal and pancreatic carcinomas in vitro. These findings indicate that M8 may indirectly—through the modification of normal (mesothelial) cells phenotype—facilitate an expansion of cancer cells, which challenges the postulated value of this stilbene in chemotherapy.

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

Senescence bystander effect refers to a phenomenon in which senescent cells elicit the development of senescence phenotype in their nearby young counterparts. In this paper we examined the mechanism of senescence bystander effect triggered by senescent human peritoneal mesothelial cells (HPMCs) in proliferating HPMCs and peritoneal fibroblasts (HPFBs). The results showed that conditioned medium (CM) derived from senescent HPMCs elicited a senescence response (growth inhibition coupled with increased expression of senescence-associated β-galactosidase and accumulation of histone γ-H2A.X) in either early-passage HPMCs or HPFBs. Samples of CM from senescent HPMCs contained increased amounts of numerous soluble mediators of which only transforming growth factor-β1 (TGF-β1) was able to induce senescence phenotype in the both types of peritoneal cells, likely through an induction of reactive oxygen species (ROS) and p38 mitogen-activated protein kinase (MAPK). At the same time, senescent HPMCs released increased amounts of thrombospondin-1 (TSP-1), a major activator of TGF-β1. Significantly, TSP-1 itself was unable to induce senescence phenotype in HPMCs or in HPFBs. The experiments employing anti-TSP-1 antibodies and specific TSP-1 blocking peptide revealed that neutralization of TSP-1 in CM prevented TGF-β1-dependent development of senescence phenotype. Collectively, our findings indicate that senescent HPMCs exhibit senescence-promoting activity toward neighboring young cells (HPMCs and HPFBs), and this effect is, at least partly, related to TSP-1-dependent activation and further ROS- and p38 MAPK-related activity of TGF-β1.

Mesothelial cell: a multifaceted model of aging

Human peritoneal mesothelial cells (HPMCs) dominate within the peritoneal cavity and thus play a central role in a variety of intraperitoneal processes, including the transport of water and solutes, inflammation, host response, angiogenesis, and extracellular matrix remodeling. In addition, they contribute to the development of abdominal adhesions, peritonitis, endometriosis, cancer cell metastases, and peritoneal dialysis complications. For less than a decade the primary cultures of omental HPMCs have also been used as an experimental tool in studies on cellular aging. This paper provides the first comprehensive overview of the current state of art on molecular mechanisms underlying HPMC senescence in vitro. Special attention is paid to the causes of the very fast dynamics of HPMC senescence, and in particular to the role of non-telomeric DNA damage, the autocrine activity of TGF-β1, and the causative effects of oxidative stress. In addition, some clinical manifestations of HPMC senescence will be discussed, including its interplay with organismal aging, peritoneal dialysis, and cancer progression.

High adhesion of tumor cells to mesothelial monolayers derived from peritoneal wash of disseminated gastrointestinal cancers

The role of the mesothelial layer in the peritoneal spreading of cancer cells is only partially clarified. Here we attempted to better define the mesothelial contribution to the tumor cell adhesion using a direct adhesion test applied to human primary cultures of mesothelial cells (HPMCs) derived from the peritoneal washes of patients with gastric and colorectal cancers. Gastric and colon carcinoma cells were seeded on different mesothelial monolayers and quantitative fluorescence analysis was performed to analyze their growth and adhesive properties. The adhesion of the cancer cells was not affected by the origin of the HPMCs when derived from patients with different cancers or with benign disease. In contrast, the high levels of ICAM1 expression and ROS production, which characterize these senescent mesothelial cells, enhanced the tumor cell adhesion. These results suggest that the mesothelial adhesive properties are dependent on the cell senescence, while are not affected by the tumor environment. The use of peritoneal washes as a source to isolate HPMCs provides a practical and reliable tool for the in vitro analysis of the mesothelial conditions affecting the peritoneal carcinomatosis.

Peritoneal fibrosis and high transport are induced in mildly pre-injured peritoneum by 3,4-dideoxyglucosone-3-ene in mice

Peritoneal dialysis (PD) solution contains high concentrations of glucose and glucose degradation products (GDPs). One of several GDPs--3,4-dideoxyglucosone-3-ene (3,4-DGE)--was recently identified as the most reactive and toxic GDP in PD fluids. In vitro, 3,4-DGE has been shown to induce mesothelial cell damage; however, its role in peritoneal fibrosis in vivo remains unclear. In the present study, we intraperitoneally administered chlorhexidine gluconate (CG) for mild peritoneal injury, and we then injected 3,4-DGE [38 μmol/L (low concentration) or 145 μmol/L (high concentration)] 5 times weekly for 4 weeks. Significant thickening of the parietal peritoneal membrane was observed only when treatment with low or high concentrations of 3,4-DGE occurred after CG administration, but not when either CG or 3,4-DGE alone was given. The combination of CG and 3,4-DGE also caused upregulation of messenger RNA expression of transforming growth factor β1, connective tissue growth factor, fibronectin, collagen type 1 α1 chain, alpha smooth muscle actin (α-SMA), vascular endothelial growth factor 164, NADPH oxidase 1 and 4, p22phox, p47phox, and gp91phox in peritoneal tissue. Treatment with CG alone was sufficient to cause significant F4/80-positive macrophage infiltration, appearance of α-SMA-positive cells, and vessel formation in the submesothelial layer. Addition of 3,4-DGE markedly enhanced those changes and induced apoptosis, mainly in leukocytes. The concentration of 3,4-DGE in the abdominal cavity declined more rapidly in CG-treated mice than in PBS-treated mice. Peritoneal membrane permeability determined by peritoneal equilibration test showed high transport conditions in peritoneum treated with both CG and 3,4-DGE. These results indicate that, when mild peritoneal damage is already present, 3,4-DGE causes peritoneal thickening and fibrosis, resulting in deterioration of peritoneal membrane function.

Resveratrol delays replicative senescence of human mesothelial cells via mobilization of antioxidative and DNA repair mechanisms

Resveratrol (3,4',5-trihydroxy-trans-stilbene; RVT) is a natural phytoestrogen known to modulate the rate of senescence in cultured cells. The mechanism by which RVT affects this process is still elusive. In this paper we used human peritoneal mesothelial cells (HPMCs) to examine the effect of RVT (0.5 and 10 μM) on their growth and senescence, with particular emphasis paid to parameters associated with oxidative stress. The results showed that RVT used at a concentration of 0.5 μM (but not at 10 μM) markedly improved HPMC growth capacity, as evidenced by elevated expression of PCNA antigen, augmented fraction of cells in the S phase of the cell cycle, and increased number of divisions achieved before senescence. These effects coincided with diminished expression and activity of senescence-associated β-galactosidase but were not associated with changes in the telomere length and an incidence of apoptosis. Moreover cells exposed to 0.5 μM RVT were characterized by increased release of reactive oxygen species, which was accompanied by up-regulated biogenesis of mitochondria and collapsed mitochondrial membrane potential. At the same time, they displayed increased activity of superoxide dismutase and reduced DNA damage (8-OH-dG and γ-H2A.X level). The efficiency of 8-OH-dG repair was increased which could be related to increased activity of DNA glycosylase I (hOgg1). As shown using RT-PCR, expression of hOgg1 mRNA in these cells was markedly elevated. Collectively, our results indicate that delayed senescence of HPMCs exposed to RVT may be associated with mobilization of antioxidative and DNA repair mechanisms.

Resveratrol and its synthetic derivatives exert opposite effects on mesothelial cell-dependent angiogenesis via modulating secretion of VEGF and IL-8/CXCL8

We examined the effect of resveratrol (RVT) and its two derivatives (3,3′,4,4′-tetrahydroxy-trans-stilbene and 3,3′,4,4′,5,5′-hexahydroxy-trans-stilbene) on human peritoneal mesothelial cell (HPMC)-dependent angiogenesis in vitro. To this end, angiogenic activity of endothelial cells (HUVEC, HMVEC, and HMEC-1) was monitored upon their exposure to conditioned medium (CM) from young and senescent HPMCs treated with stilbenes or to stilbenes themselves. Results showed that proliferation and migration of endothelial cells were inhibited in response to indirect (HPMC-dependent) or direct RVT activity. This effect was associated with decreased secretion of VEGF and IL-8/CXCL8 by HPMCs treated with RVT, which confirmed the experiments with recombinant forms of these angiogenic agents. Angiogenic activity of endothelial cells treated with CM from HPMCs exposed to RVT analogues was more effective. Improved migration was particularly evident in cells exposed to CM from senescent HPMCs. Upon direct treatment, RVT derivatives stimulated proliferation (but not migration) of HUVECs, and failed to affect the behaviour of HMVEC and HMEC-1 cells. These compounds stimulated production of VEGF and IL-8/CXCL8 by HPMCs. Studies with neutralizing antibodies against angiogenic factors revealed that augmented angiogenic reactions of endothelial cells exposed to CM from HPMC treated with RVT analogues were related to enhanced production of VEGF and IL-8/CXCL8. Collectively, these findings indicate that RVT and its synthetic analogues divergently alter the secretion of the angiogenic factors by HPMCs, and thus modulate HPMC-dependent angiogenic responses in the opposite directions. This may have implications for the attempts of practical employment of the stilbenes for treatment of pathologies proceeding with abnormal vascularisation of the peritoneal tissue.

Thiols stabilize cobblestone morphology of cultured mesothelial cells

Cellular thiols including GSH (glutathione) and L-Cys (L-cysteine) are essential for cell signalling, growth and differentiation. L-Cys is derived from the extracellular thiol pool and is the rate-limiting compound for intracellular GSH biosynthesis. The present study investigated the effect of thiol-supplemented medium on cell growth, phenotype and total GSH of cultured hPMCs (human peritoneal mesothelial cells). Cells were cultured in medium M199 supplemented with 2% serum, with 'plus' or without 'minus' L-Cys and compared with medium supplemented with either β-ME (β-mercaptoethanol) (0.25 mmol/l) or the receptor tyrosine kinase ligand EGF (epidermal growth factor, 100 ng/ml). β-ME produced a disproportionate increase in total GSH compared with L-Cys and other thiols tested [(procysteine (2-oxothiazolidine-4-carboxylic acid) or NAC (N-acetyl-L-cysteine)], while growth and morphology were identical. Cell behaviour of primary hPMCs is characterized by the transition of fibroblastoid to cobblestone morphology during early passage. L-Cys and β-ME promoted a rapid MET (mesenchymal-to-epithelial transition) within 3 days of culture, confirmed by the presence of cobblestone cells, intact organelles, abundant microvilli, primary cilia and cortical actin. In contrast, EGF produced a biphasic response consisting of delayed growth and retention of a fibroblastoid morphology. During a rapid log phase of growth, MET was accompanied by rapid catch-up growth. Thiols may stabilize the epithelial phenotype by engaging redox-sensitive receptors and transcription factors that modulate differentiation. These data may benefit researchers working on thiol-mediated cell differentiation and strategies to regenerate damage to serosal membranes.

Isolation of mouse mesenchymal stem cells with normal ploidy from bone marrows by reducing oxidative stress in combination with extracellular matrix

BACKGROUND

Isolation of mouse MSCs (mMSCs) with normal ploidy from bone marrow remains challenging. mMSCs isolated under 20% O(2) are frequently contaminated by overgrown hematopoietic cells, and could also be especially vulnerable to oxidative damage, resulting in chromosomal instability. Culture under low oxygen or extracellular matrix (ECM) improves proliferation of MSCs in several species. We tested the hypothesis that culture under low oxygen in combination with ECM prepared from mouse embryonic fibroblast (MEF-ECM) could be used to purify proliferative mMSCs, and to reduce oxidative damage and maintain their chromosomal stability.

RESULTS

Optimization of culture conditions under 20% O(2) resulted in immortalization of mMSCs, showing extensive chromosome abnormalities, consistent with previous studies. In contrast, culture under low oxygen (2% O(2)) improved proliferation of mMSCs and reduced oxidative damage, such that mMSCs were purified simply by plating at low density under 2% O(2). MEF-ECM reduced oxidative damage and enhanced proliferation of mMSCs. However, these isolated mMSCs still exhibited high frequency of chromosome abnormalities, suggesting that low oxygen or in combination with MEF-ECM was insufficient to fully protect mMSCs from oxidative damage. Notably, antioxidants (alpha -phenyl-t-butyl nitrone (PBN) and N-acetylcysteine (NAC)) further reduced DNA damage and chromosomal abnormalities, and increased proliferation of mMSCs. mMSCs isolated by the combination method were successfully used to generate induced pluripotent stem (iPS) cells by ectopic expression of Oct4, Sox2, Klf4 and c-Myc.

CONCLUSIONS

We have developed a technique that allows to reduce the number of karyotypic abnormalities for isolation of primary mMSCs and for limited culture period by combination of low oxygen, MEF-ECM, antioxidants and low density plating strategy. The effectiveness of the new combination method is demonstrated by successful generation of iPS cells from the isolated mMSCs. However, a culture system for mMSCs still is needed to prevent all the anomalies, especially after a long-term culture period.

A comprehensive review on mesenchymal stem cell growth and senescence

In recent years mesenchymal stem cells (MSCs) have generated a great deal of excitement as an attractive alternative to embryonic stem cells (ESCs) in cell-based regenerative medicine. In contrast to cells of embryonic origin, however, the clinical application of MSCs is heavily restricted by their finite ability of self-renewal, in which they resemble the rest of the somatic cells. Yet the mechanisms controlling MSC proliferation and senescence remain unclear. This review summarizes recent advances in our understanding of the factors affecting MSC expansion in vitro and discusses the pattern of their senescence with particular emphasis on the role of telomere shortening, activation of effectory pathways, and oxidative stress. The issues associated with MSC growth and senescence will be shown in the context of other somatic cells, and all of the parallels and disparities will be delineated precisely.

Senescent peritoneal mesothelial cells promote ovarian cancer cell adhesion: the role of oxidative stress-induced fibronectin

Adhesion of ovarian cancer cells to the peritoneal mesothelium is a key step in the malignant progression of the disease. In an in vitro study, we showed that the adherence of ovarian cancer cells (of the OVCAR-3, SKOV-3, and A2780 cell lines) to senescent human omentum-derived peritoneal mesothelial cells (HOMCs) was greater than to early passage cells. The process was mediated primarily by the increased interaction of the alpha5beta1 integrin on cancer cells with HOMC-associated fibronectin (FN). In comparison with early passage HOMCs, senescent cells exhibited increased FN mRNA expression levels and produced significantly more FN. To assess the effect of senescence-associated oxidative stress on FN release, HOMCs were rendered senescent by exposure to an oxidant, tert-butyl hydroperoxide. Treatment with tert-butyl hydroperoxide resulted in a significant increase in HOMC FN mRNA and protein expression levels. The effect of oxidative stress on FN synthesis was found to be mediated by transforming growth factor-beta1, whose signaling pathway was controlled at upstream and downstream levels by p38 MAPK. The activity of p38 MAPK increased markedly in senescent HOMCs. Treatment of HOMCs with antioxidants significantly attenuated senescence-associated increases in p38 MAPK activity, production of both transforming growth factor-beta1 and FN, and ovarian cancer cell adhesion. These data indicate that oxidative stress that accompanies senescence may increase FN production by HOMCs and thus facilitate binding and dissemination of ovarian cancer cells.

Vulnerability to oxidative stress and different patterns of senescence in human peritoneal mesothelial cell strains

Both the ascites fluid-derived mesothelial cell line LP-9 and primary cultures of human omentum-derived mesothelial cells (HOMCs) are commonly used in experimental studies. However, they seem to have a different replicative potential in vitro. In the present study, we have attempted to determine the causes of this discrepancy. HOMCs were found to divide fewer times and enter senescence earlier than LP-9 cells. This effect was coupled with earlier increases in the expression of senescence-associated-beta-galactosidase and cell cycle inhibitors p16INK4a and p21WAF1. Moreover, almost 3 times as many early-passage HOMCs as LP-9 cells bore senescence-associated DNA damage foci. In sharp contrast to LP-9 cells, the foci present in HOMCs localized predominantly outside the telomeres, and the HOMC telomere length did not significantly shorten during senescence. Compared with LP-9 cells, HOMCs were found to enter senescence with significantly lower levels of lipofuscin and damaged DNA, and markedly decreased glutathione contents. In addition, early-passage HOMCs generated significantly more reactive oxygen species either spontaneously or in response to exogenous oxidants. These results indicate that compared with LP-9 cells, HOMCs undergo stress-induced telomere-independent premature senescence, which may result from increased vulnerability to oxidative DNA injury.