Characterization of proteoglycans produced by rat pleural mesothelial cells in vitro

An integrative histopathologic clustering model based on immuno-matrix elements to predict the risk of death in malignant mesothelioma

Objective

Previous studies have reported a close relationship between malignant mesothelioma (MM) and the immune matricial microenvironment (IMM). One of the major problems in these studies is the lack of adequate adjustment for potential confounders. Therefore, the aim of this study was to identify and quantify risk factors such as IMM and various tumor characteristics and their association with the subtype of MM and survival.

Methods

We examined IMM and other tumor markers in tumor tissues from 82 patients with MM. These markers were evaluated by histochemistry, immunohistochemistry, immunofluorescence, and morphometry. Logistic regression analysis, cluster analysis, and Cox regression analysis were performed.

Results

Hierarchical cluster analysis revealed two clusters of MM that were independent of clinicopathologic features. The high‐risk cluster included MM with high tumor cellularity, high type V collagen (Col V) fiber density, and low CD8⁺ T lymphocyte density in the IMM. Our results showed that the risk of death was increased for patients with MM with high tumor cellularity (OR = 1.63, 95% CI = 1.29‐2.89, P = .02), overexpression of Col V (OR = 2.60, 95% CI = 0.98‐6.84, P = .04), and decreased CD8 T lymphocytes (OR = 1.001, 95% CI = 0.995‐1.007, P = .008). The hazard ratio for the high‐risk cluster was 2.19 (95% CI = 0.54‐3.03, P < .01) for mortality from MM at 40 months.

Conclusion

Morphometric analysis of Col V, CD8⁺ T lymphocytes, and tumor cellularity can be used to identify patients with high risk of death from MM.

Mesothelial cells in tissue repair and fibrosis

Mesothelial cells are fundamental to the maintenance of serosal integrity and homeostasis and play a critical role in normal serosal repair following injury. However, when normal repair mechanisms breakdown, mesothelial cells take on a profibrotic role, secreting inflammatory, and profibrotic mediators, differentiating and migrating into the injured tissues where they contribute to fibrogenesis. The development of new molecular and cell tracking techniques has made it possible to examine the origin of fibrotic cells within damaged tissues and to elucidate the roles they play in inflammation and fibrosis. In addition to secreting proinflammatory mediators and contributing to both coagulation and fibrinolysis, mesothelial cells undergo mesothelial-to-mesenchymal transition, a process analogous to epithelial-to-mesenchymal transition, and become fibrogenic cells. Fibrogenic mesothelial cells have now been identified in tissues where they have not previously been thought to occur, such as within the parenchyma of the fibrotic lung. These findings show a direct role for mesothelial cells in fibrogenesis and open therapeutic strategies to prevent or reverse the fibrotic process.

Electron microscopic alterations of the rat's pleura after experimental haemothorax

The initial signs of pleural reactivity and the subsequent mechanisms of pleural healing still remain unsolved. The visceral and parietal (costal and diaphragmatic) pleura were investigated following an experimental haemothorax (EH) by transmission electron microscopy. Young-adult Wistar rats were divided in five groups and survived 6 hours, 1, 3, 8 and 15 days respectively after EH. Six hours after EH the mesothelial cells had a more prominent lysosomal system and electron-dense material in the vesicles, as in the dilatated intercellular spaces. On the 1st day of the EH the mesothelial cytoplasm formed a thin interrupted band. The extravasal cells built multiple layers over the basal lamina, leading to a thicker submesothelial layer, occupying the superficial position toward the pleural cavity. The activated mesothelial cells covered both pleural sheets on the 3rd day after EH. Eight days after EH different membrane bodies, large apical evaginations, elastic-like formations, an extensive vesicular and cytofilamentous systems characterized the mesothelium. The wider elastic membrane showed thickenings, protrusions, bifurcations and double course. Fifteen days after EH larger zones in both pleural sheets displayed thinner basal lamina, remnants of elastic membrane and a thicker submesothelial layer. In conclusion, different newly formed structures (reversible and stable) retain the tendency of enlargement of the pleural surface in all investigated periods. Simultaneous intercellular and transcellular transport, as an increase of the lysosomal system characterize the passing of the electron-dense material through the mesothelium. The early period (until 3rd day after EH) is characterized by more prominent mesothelial changes, involving activated cells. The initiation of the late period (on the 8th day after EH) begins with the appearance of lamellar bodies and newly formed elastic membrane. The following late changes (on the 15th day after EH) concern predominantly the components of the connective tissue layer, such as collagen accumulations and blood capillaries. The present data suggest that the alterations over the entire pleura are irregular and asynchronous, showing significant morphological differences in both pleura sheets, some of them are diffuse in character, the final ones appear to be stable and ensure incomplete pleural restoration.

Retroviral gene transfer is inhibited by chondroitin sulfate proteoglycans/glycosaminoglycans in malignant pleural effusions

Gene therapy may be an important adjuvant for treating cancer in the pleural space. The initial results of retroviral gene transfer to cancer cells in malignant pleural effusions revealed that transduction was markedly inhibited, and studies to characterize the inhibitory factor(s) were performed. The inhibition was contained within the soluble, rather than cellular, components of the effusions and was demonstrated with amphotropic, gibbon ape leukemia virus, and vesicular stomatitis virus-glycoprotein pseudotyped retroviral vectors. After excluding complement proteins, a series of studies identified chondroitin sulfates (CSs) as the inhibitory substances. First, treatment of the effusions with mammalian hyaluronidase or chondroitinases, but not Streptomyces hyaluronidase, abolished the inhibitory activity. Second, addition of exogenous CS glycosaminoglycans mimicked the inhibition observed with pleural effusions. Third, immunoassays and biochemical analyses of malignant pleural effusion specimens revealed CS in relevant concentrations within pleural fluid. Fourth, proteoglycans/glycosaminoglycans isolated from the effusions inhibited retroviral gene transfer. Analyses of the mechanism of inhibition indicate that the chondroitin sulfates interact with vector in solution rather than at the target cell surface. These results suggest that drainage of the malignant pleural effusion, and perhaps enzymatic pretreatment of the pleural cavity, will be necessary for efficient retroviral vector mediated gene delivery to pleural metastases.

Fetal lung fibroblasts selectively down-regulate proteoglycan synthesis in response to elevated oxygen

Cell proliferation is in part regulated by extracellular matrix. Therefore, it is possible that elevated O2 may indirectly affect lung fibroblast growth via modulation of extracellular matrix. In the present study, we investigated the effect of elevated O2 on the synthesis of glycosaminoglycans (GAGs) and proteoglycans (PGs) by fetal lung fibroblasts. A 48-h exposure to >/=50% O2 reduced the incorporation of [3H]glucosamine and 35SO4 into GAGs by fetal lung fibroblasts. The relative proportion of the individual GAG molecules was not altered by elevated O2. Fibroblasts exposed to 50% O2 secreted less [35S]proteoglycans into the medium than controls. Specifically, the synthesis of the small soluble PG, biglycan, was decreased by exposure to 50% O2. Fetal lung fibroblasts did not synthesize the small chondroitin/dermatan sulfate PG, decorin. Elevated O2 concentrations also reduced the synthesis of membrane- and matrix-associated PGs. Furthermore, exposure of fetal lung fibroblasts to >/=50% O2 resulted in a decreased mRNA expression for biglycan and versican core protein sequences. In contrast, elevated O2 increased the message for type I collagen and fibronectin without affecting that of beta-actin. The inhibitory effect of elevated O2 on biglycan mRNA and protein expression was overcome by incubating the cells in 3% O2 after the 48-h exposure to 50% O2. The latter treatment also reversed the increased mRNA expression of type I collagen associated with elevated O2 but not that of fibronectin. These results demonstrate that fetal lung fibroblasts, in response to elevated oxygen concentrations, selectively down-regulate their GAG and PG synthesis and that this O2 effect is reversible.