Epithelial-To-Mesenchymal Transition Induced by Freund’s Adjuvant Treatment in Rat Mesothelial Cells: A Morphological and Immunocytochemical Study

Abstract

Intraperitoneal injection of Freund's adjuvant induces acute peritonitis. By the time of the Freund's adjuvant treatment the flat, simple squamous epithelial cells became rounded, cuboidal shaped, many of them have lost their connection with the neighbouring cells and detached from the basement membrane. The macrophage markers' (ED1, OX43 and CD68) expression also increased in the mesothelial cells and more mesothelin and anti-ED1 double-labelled cells were found freely present close to the surface. The cytokeratin expression of the mesothelial cells has gradually decreased. At the 5th day of the inflammation practically there was no cytokeratin labelling present in the mesothelial cells and the mesothelin expression has significantly decreased. Parallel to this mesothelial cells started to express vimentin, a characteristic mesenchymal intermediate filament protein indicating that they gradually lost their epithelial character and gained mesenchymal phenotype. These results strongly suggest that under the effect of Freund's adjuvant treatment (inflammation) mesothelial cells can undergo epithelial-to-mesenchymal transition and differentiate into phagocytotic (macrophage-like) cells. Studying the caveolae/caveolin-1 on the plasma membrane of mesothelial cells we found that the Freund's adjuvant treatment has changed the cellular distribution of caveolin-1: as the inflammation progressed strong caveolin-1 labelling was found inside of the cytoplasm (in perinuclear localization) indicating that inflammation induced the caveolae internalization. These results indicate that caveolae/caveolin-1 might play important regulatory role in signal transduction leading to trasdifferentiation.

Transforming growth factor-β1 induces fibrosis in rat meningeal mesothelial cells via the p38 signaling pathway

“…1). Keratin and vimentin are commonly used markers for identifying mesothelial cells (16,17). Keratin and vimentin were predominantly localized in the cytoplasm, which is consistent with the characteristics of mesothelial cells.…”

Estrogen Receptor Alpha Is Expressed in Mesenteric Mesothelial Cells and Is Internalized in Caveolae upon Freund's Adjuvant Treatment

“…Our previous light microscopical data revealed that mesothelial cells lose their epithelial character (decreased cytokeratin, E-cadherin expression) upon Freund's adjuvant treatment and obtain a mesenchymal phenotype by expressing vimentin [26] . The inflammatory stimuli changed remarkably the ultrastructure of mesothelial cells as well.…”

“…In a previous paper we have shown that rat mesenteric mesothelial cells undergo EMT upon inflammatory stimuli induced by Freund's adjuvant treatment [26] . In the present paper we furnish additional evidence for the inflammatory response of the tissue by showing that the morphological changes at the ultrastructural level were in correlation with the expression levels of pro-inflammatory cytokines (IL 1α, 1β and IL-6) measured in mesothelial cells.…”

“…In our previously published papers we showed that mesothelial cells that form a continuous squamous epithelial layer on the two sides of the mesentery undergo epithelial-mesenchymal transition (EMT) upon Freund's adjuvant treatment [26] . It has also been proved that upon inflammatory stimuli mesothelial cells can assume a macrophage character demonstrated by the expression of the macrophage marker, ED1 [27] and they can serve as a source of activated macrophages during inflammatory events [28] .…”

Inflammatory Cytokinesinduce EMT in Mesenteric Mesothelial Cells, and Transdifferentiate Them into Macrophages

“…DURING INFLAMMATION INDUCED EMT During inflammation-induced EMT mesenteric mesothelial cells start to express macrophage markers (OX43, ED1) as well [12,52], suggesting that they might be transformed into macrophage-like cells [53]. Our previous data showed that under inflammatory stimuli the number of peritoneal macrophages dramatically increased [54].…”