Mesothelial primary cilia of peritoneal and other serosal surfaces

Effects of pharmacological primary cilium disturbance in the context of in vitro 2D and 3D malignant pleura mesothelioma

INTRODUCTION

Primary cilium (PC) is a single non-motile antenna-like organelle composed of a microtubule core axon originating from the mother centriole of the centrosome. The PC is universal in all mammalian cells and protrudes to the extracellular environment receiving mechanochemical cues that it transmits in the cell.

AIM

To investigate the role of PC in mesothelial malignancy in the context of two-dimensional (2D) and three-dimensional (3D) phenotypes.

MATERIALS AND METHODS

The effect of pharmacological deciliation [using ammonium sulphate (AS) or chloral hydrate (CH)] and PC elongation [using lithium chloride (LC)] on cell viability, adhesion, and migration (2D cultures) as well as in mesothelial sphere formation, spheroid invasion and collagen gel contraction (3D cultures) was investigated in benign mesothelial MeT-5A cells and in malignant pleural mesothelioma (MPM) cell lines, M14K (epithelioid) and MSTO (biphasic), and primary malignant pleural mesothelioma cells (pMPM).

RESULTS

Pharmacological deciliation or elongation of the PC significantly affected cell viability, adhesion, migration, spheroid formation, spheroid invasion and collagen gel contraction in MeT-5A, M14K, MSTO cell lines and in pMPM cells compared to controls (no drug treatment).

CONCLUSIONS

Our findings indicate a pivotal role of the PC in functional phenotypes of benign mesothelial cells and MPM cells.

The Development of Peritoneal Metastasis from Gastric Cancer and Rationale of Treatment According to the Mechanism

In the present article, we describe the normal structure of the peritoneum and review the mechanisms of peritoneal metastasis (PM) from gastric cancer (GC). The structure of the peritoneum was studied by a double-enzyme staining method using alkaline-phosphatase and 5′-nucreotidase, scanning electron microscopy, and immunohistological methods. The fundamental structure consists of three layers, mesothelial cells and a basement membrane (layer 1), macula cribriformis (MC) (layer 2), and submesothelial connective tissue containing blood vessels and initial lymphatic vessels, attached to holes in the MC (layer 3). Macro molecules and macrophages migrate from mesothelial stomata to the initial lymphatic vessels through holes in the MC. These structures are characteristically found in the diaphragm, omentum, paracolic gutter, pelvic peritoneum, and falciform ligament. The first step of PM is spillage of cancer cells (peritoneal free cancer cells; PFCCs) into the peritoneal cavity from the serosal surface of the primary tumor or cancer cell contamination from lymphatic and blood vessels torn during surgical procedures. After PFCCs adhere to the peritoneal surface, PMs form by three processes, i.e., (1) trans-mesothelial metastasis, (2) trans-lymphatic metastasis, and (3) superficial growing metastasis. Because the intraperitoneal (IP) dose intensity is significantly higher when generated by IP chemotherapy than by systemic chemotherapy, IP chemotherapy has a great role in the treatment of PFCCs, superficial growing metastasis, trans-lymphatic metastasis and in the early stages of trans-mesothelial metastasis. However, an established trans-mesothelial metastasis has its own interstitial tissue and vasculature which generate high interstitial pressure. Accordingly, it is reasonable to treat established trans-mesothelial metastasis by bidirectional chemotherapy from both IP and systemic chemotherapy.

Mesothelial Cells

♦ Background

The introduction of peritoneal dialysis (PD) as a modality of renal replacement therapy has provoked much interest in the biology of the peritoneal mesothelial cell. Mesothelial cells isolated from omental tissue have immunohistochemical markers that are identical to those of mesothelial stem cells, and omental mesothelial cells can be cultivated in vitro to study changes to their biologic functions in the setting of PD.

♦ Method

The present article describes the structure and function of mesothelial cells in the normal peritoneum and details the morphologic changes that occur after the introduction of PD. Furthermore, this article reviews the literature of mesothelial cell culture and the limitations of in vitro studies.

♦ Results

The mesothelium is now considered to be a dynamic membrane that plays a pivotal role in the homeostasis of the peritoneal cavity, contributing to the control of fluid and solute transport, inflammation, and wound healing. These functional properties of the mesothelium are compromised in the setting of PD. Cultures of peritoneal mesothelial cells from omental tissue provide a relevant in vitro model that allows researchers to assess specific molecular pathways of disease in a distinct population of cells. Structural and functional attributes of mesothelial cells are discussed in relation to long-term culture, proliferation potential, age of tissue donor, use of human or animal in vitro models, and how the foregoing factors may influence in vitro data.

♦ Conclusions

The ability to propagate mesothelial cells in culture has resulted, over the past two decades, in an explosion of mesothelial cell research pertaining to PD and peritoneal disorders. Independent researchers have highlighted the potential use of mesothelial cells as targets for gene therapy or transplantation in the search to provide therapeutic strategies for the preservation of the mesothelium during chemical or bacterial injury.

Peritoneal Mesothelial Cell Culture and Biology

The peritoneal mesothelium is composed of an extensive monolayer of mesothelial cells that lines the body's serous cavity and internal organs and was previously thought to act principally as a protective nonadhesive lubricating surface to facilitate intracoelomic movement. With the introduction of peritoneal dialysis over three decades ago, there has been much interest in the cell biology of peritoneal mesothelial cells. Independent studies have highlighted specific properties of the peritoneal mesothelial cell, including antigen presentation, regenerative properties, clearance of fibrin; synthesis of cytokines, growth factors, and matrix proteins; and secretion of lubricants to protect the tissue from abrasion, adhesion, infection, and tumor dissemination. It is now evident that the mesothelium is not merely a passive membrane but, rather, a dynamic membrane that contributes substantially to the structural, functional, and homeostatic properties of the peritoneum. Since peritoneal mesothelial cells in culture possess immunohistochemical markers identical to mesothelial stem cells, the culture of mesothelial cells offers researchers an essential tool to assess their morphologic, structural, and functional properties. This review will discuss current procedures to isolate peritoneal mesothelial cells from human omental specimens, animal sources, and spent dialysate. Furthermore, the functional and morphologic properties of mesothelial cells are discussed, together with the potential use of mesothelial cell culture in research and clinical applications.

Pathophysiology of colorectal peritoneal carcinomatosis: Role of the peritoneum

Colorectal cancer (CRC) is the third most common cancer and the fourth most common cause of cancer-related death worldwide. Besides the lymphatic and haematogenous routes of dissemination, CRC frequently gives rise to transcoelomic spread of tumor cells in the peritoneal cavity, which ultimately leads to peritoneal carcinomatosis (PC). PC is associated with a poor prognosis and bad quality of life for these patients in their terminal stages of disease. A loco-regional treatment modality for PC combining cytoreductive surgery and hyperthermic intraperitoneal peroperative chemotherapy has resulted in promising clinical results. However, this novel approach is associated with significant morbidity and mortality. A comprehensive understanding of the molecular events involved in peritoneal disease spread is paramount in avoiding unnecessary toxicity. The emergence of PC is the result of a molecular crosstalk between cancer cells and host elements, involving several well-defined steps, together known as the peritoneal metastatic cascade. Individual or clumps of tumor cells detach from the primary tumor, gain access to the peritoneal cavity and become susceptible to the regular peritoneal transport. They attach to the distant peritoneum, subsequently invade the subperitoneal space, where angiogenesis sustains proliferation and enables further metastatic growth. These molecular events are not isolated events but rather a continuous and interdependent process. In this manuscript, we review current data regarding the molecular mechanisms underlying the development of colorectal PC, with a special focus on the peritoneum and the role of the surgeon in peritoneal disease spread.

Transition of mesothelial cell to fibroblast in peritoneal dialysis: EMT, stem cell or bystander?

Long-term peritoneal dialysis (PD) can lead to fibrotic changes in the peritoneum, characterized by loss of mesothelial cells (MCs) and thickening of the submesothelial area with an accumulation of collagen and myofibroblasts. The origin of myofibroblasts is a central question in peritoneal fibrosis that remains unanswered at present. Numerous clinical and experimental studies have suggested that MCs, through epithelial-mesenchymal transition (EMT), contribute to the pool of peritoneal myofibroblasts. However, recent work has placed significant doubts on the paradigm of EMT in organ fibrogenesis (in the kidney particularly), highlighting the need to reconsider the role of EMT in the generation of myofibroblasts in peritoneal fibrosis. In particular, selective cell isolation and lineage-tracing experiments have suggested the existence of progenitor cells in the peritoneum, which are able to switch to fibroblast-like cells when stimulated by the local environment. These findings highlight the plastic nature of MCs and its contribution to peritoneal fibrogenesis. In this review, we summarize the key findings and caveats of EMT in organ fibrogenesis, with a focus on PD-related peritoneal fibrosis, and discuss the potential of peritoneal MCs as a source of myofibroblasts.

Wt1 and β-catenin cooperatively regulate diaphragm development in the mouse

The developing diaphragm consists of various differentiating cell types, many of which are not well characterized during organogenesis. One important but incompletely understood tissue, the diaphragmatic mesothelium, is distinctively present from early stages of development. Congenital Diaphragmatic Hernia (CDH) occurs in humans when diaphragm tissue is lost during development, resulting in high morbidity and mortality postnatally. We utilized a Wilms Tumor 1 (Wt1) mutant mouse model to investigate the involvement of the mesothelium in normal diaphragm signaling and development. Additionally, we developed and characterized a Wt1(CreERT2)-driven β-catenin loss-of-function model of CDH after finding that canonical Wnt signaling and β-catenin are reduced in Wt1 mutant mesothelium. Mice with β-catenin loss or constitutive activation induced in the Wt1 lineage are only affected when tamoxifen injection occurs between E10.5 and E11.5, revealing a critical time-frame for Wt1/ β-catenin activity. Conditional β-catenin loss phenocopies the Wt1 mutant diaphragm defect, while constitutive activation of β-catenin on the Wt1 mutant background is sufficient to close the diaphragm defect. Proliferation and apoptosis are affected, but primarily these genetic manipulations appear to lead to a change in normal diaphragm differentiation. Our data suggest a fundamental role for mesothelial signaling in proper formation of the diaphragm.

Ultrastructure of lymphatic stomata in the tunica vaginalis of humans

Lymphatic stomata are small openings of lymphatic capillaries on the surface of the mesothelium that lines the serous cavity and have the function of active absorption. They play an important role in physiological and pathological conditions. The cavity of the tunica vaginalis is a typical serous cavity of the testis, but the lymphatic stomata of the tunica vaginalis of humans have never been reported. Here, we studied their ultrastructure by scanning and transmission electron microscopy. The submesothelial connective tissue with foramina was investigated after the mesothelial cells were digested using NaOH solution. We found the lymphatic stomata in cuboidal mesothelial cell regions of the parietal layer of the tunica vaginalis of humans with a diameter of about 1-2 μm. Sometimes, closed lymphatic stomata could be observed. Our study is the first to report the existence of lymphatic stomata of the tunica vaginalis of humans. We found that the tunica vaginalis cavity is connected with the lymphatic system through the stomata, which might provide a morphological basis for the drainage of hydrocele and tumor metastasis of the tunica vaginalis of humans.

Biology of the peritoneum in normal homeostasis and after surgical trauma

The peritoneum is a serous membrane, which has a protective function for the contents of the abdominal cavity. It maintains homeostasis by allowing exchange of molecules and production of peritoneal fluid, thus providing an environment in which intra-abdominal organs can function properly. When traumatized, whether by surgery or due to inflammatory processes, a series of responses come into action to regenerate the injured part of the peritoneum. The inflammatory reaction causes influx of inflammatory cells but also activates resident mesothelial cells, ultimately leading to a fibrinous exudate. Depending on the severity of the trauma this exudate is transient due to fibrinolysis, or becomes more dense as a result of fibroblasts persisting, leading to fibrinous adhesions. A pivotal role is taken by the enzyme plasmin and its promotors and inhibitors; it is mainly the tissue-type plasminogen activator/plasminogen activator inhibitor ratio which determines the rate of fibrinolysis and therefore the rate of adhesion formation. The rate of injury determines the rate and extent of the inflammatory response to that injury; in its turn the inflammatory reaction determines the extent of adhesion formation. One should realize this when performing intra-abdominal surgery, which is in fact operating inside the peritoneal organ.

The Peritoneal Mesothelium Covering the Genital Tract and its Ligaments in the Female Pig Shows Signs of Active Function

The aim of this study was to describe the surface features of the peritoneal mesothelium covering the genital tract and adjacent ligaments of the sow to find signs of biosynthetic activation of cells. Surface features of the serosa covering the genital tract and adjacent ligaments from 14 cyclic sows, 7 in the follicular phase and 7 in the luteal phase of the estrous cycle, were examined by histology and scanning electron microscopy. Five additional sows, three in the follicular phase and two in the luteal phase of the estrous cycle, were examined by transmission electron microscopy (TEM). In this study, the presence of cells of the oviductal epithelium in the serosa of the infundibulum and the ampulla, as well as indications of a high functional activity of the mesothelial cells in the areas studied were two aspects that differed from the findings of previous works. Presence of endosalpingeal cells was observed in the serosal surface, showing cyclical variations with a predominance of either ciliated cells during the follicular phase or secretory cells during the luteal phase. Signs of high functional activity of the mesothelial cells included the predominance of cuboidal over flattened cells, a cytoplasm richly supplied with organelles, a dense microvillous coat, numerous primary cilia, and many secretory structures on the surface of cells. These results indicate that the serosa covering the genital area and the adjacent ligaments in the sow has an active epithelium whose coordinating role between reproductive tissues may be far more significant than previously thought.

Functional and molecular characterization of a peritoneal dialysis model in the C57BL/6J mouse

BACKGROUND

Animal models are important for understanding the physiology and pathophysiology of peritoneal transport during peritoneal dialysis (PD). Mechanistic investigations of rat and rabbit models of PD are mostly based on intervention studies using pharmacologic agents or blocking antibodies. These models may be limited by the time-course, lack of specificity, or side effects of such interventions. Genetically modified mice could provide an attractive alternative to the above models. In this study, we have characterized PD parameters and tested the effect of gender and dialysate volume and/or osmolality in the C57BL/6J mouse.

METHODS

Mice were submitted to a 2-hour peritoneal equilibration test in order to obtain permeability parameters. The expression of the water channel aquaporin-1 (AQP1) and endothelial NO synthase (eNOS) was investigated at the protein (immunoblotting, immunostaining) and mRNA [real-time reverse-transcription-polymerase chain reaction (RT-PCR)] levels. The potential effect of gender on these parameters was also studied.

RESULTS

Exposure of mice to 2 mL of 3.86% glucose dialysate yielded equilibration curves for urea and glucose, a sodium sieving, and a net ultrafiltration (UF) that were remarkably similar to those obtained in rats. The increase in dialysate volume (from 2 mL to 3 mL and 6 mL) resulted in a higher ultrafiltration and, for the highest volume, an increase in the diffusive mass transport coefficient (MTAC) for urea. The increase in dialysate glucose concentration (from 1.36% to 3.86% and 7%) resulted in increased sodium sieving and higher UF, whereas the MTAC for urea was unchanged. In comparison with males, females had a similar peritoneal transport rate for small solutes but a significantly lower sodium sieving, reflecting a lower AQP1 mRNA and protein expression in the peritoneum.

CONCLUSION

These data demonstrate the structural and functional similarity between mouse and rat models of PD, and further emphasize the relevance of mouse models to understand PD in humans. They also suggest that gender may influence water transport and AQP1 expression in the peritoneum.