The Peritoneum: Health, Disease, and Perspectives regarding Tissue Engineering and Cell Therapies.

There are several pathologies associated with the peritoneum, such as mesothelioma and peritonitis. Moreover, the peritoneum is widely used in ultrafiltration procedures, i.e., peritoneal dialysis, presenting advantages over hemodialysis. On the other hand, ultrafiltration failure may lead to dialysis-induced fibrosis and hypervolemia. Therefore, the pathophysiological study of this tissue is of extreme biomedical importance. Studies investigating the biology of the cells dwelling in the peritoneum wall provide evidence of their plasticity and progenitor features. For instance, both mesothelial and submesothelial cells present characteristics similar to mesenchymal stem cells, including osteogenic and adipogenic differentiation potential, support of extramedullary hematopoiesis, modulation of inflammatory responses, and regulation of tumor progression. Indeed, the participation of each cell type in peritoneal pathological and physiological phenomena is still under debate, especially regarding a possible differentiation pathway connecting these peritoneal cells. The primary aim of this review is to raise this discussion. In order to do so, we will firstly provide an overview of the peritoneum anatomy, histology, and ontology, and finally we will address how a better understanding of peritoneal cell biology may contribute to future cell therapy and tissue engineering approaches.

The involvement of the spleen during chronic phase of Schistosoma mansoni infection in galectin-3-/- mice.

Schistosoma mansoni synthesizes glycoconjugates which interact with galectin-3, eliciting an intense humoral immune response. Moreover, it was demonstrated that galectin-3 regulates B cell differentiation into plasma cells. Splenomegaly is a hallmark event characterized by polyclonal B cell activation and enhancement of antibody production. Here, we investigated whether galectin-3 interferes with spleen organization and B cell compartment during chronic schistosomiasis, using wild type (WT) and galectin-3-/- mice. In chronically-infected galectin-3-/- mice the histological architecture of the spleen, including white and red pulps, was disturbed with heterogeneous lymphoid follicles, an increased number of plasma cells (CD19-B220-/lowCD138+) and a reduced number of macrophages (CD19-B220-Mac-1+CD138-) and B lymphocytes (CD19+B220+/highCD138-), compared with the WT infected mice. In the absence of galectin-3 there was an increase of annexin-V+PI- cells and a major presence of apoptotic cells in spleen compared with WT infected mice. In spleen of WT infected mice galectin-3 was largely expressed in lymphoid follicles and extrafollicular sites. Thus, we propose that galectin-3 plays a role in splenic architecture, controlling distinct events such as apoptosis, macrophage activity, B cell differentiation and plasmacytogenesis in the course of S. mansoni infection.

Interplay of cysteinyl leukotrienes and TGF-ß in the activation of hepatic stellate cells from Schistosoma mansoni granulomas.

Hepatic stellate cells (HSCs) have a critical role in liver physiology, and in the pathogenesis of liver inflammation and fibrosis. Here, we investigated the interplay between leukotrienes (LT) and TGF-ß in the activation mechanisms of HSCs from schistosomal granulomas (GR-HSCs). First, we demonstrated that GR-HSCs express 5-lipoxygenase (5-LO), as detected by immunolocalization in whole cells and confirmed in cell lysates through western blotting and by mRNA expression through RT-PCR. Moreover, mRNA expression of 5-LO activating protein (FLAP) and LTC(4)-synthase was also documented, indicating that GR-HSCs have the molecular machinery required for LT synthesis. Morphological analysis of osmium and Oil-Red O-stained HSC revealed large numbers of small lipid droplets (also known as lipid bodies). We observed co-localization of lipid droplet protein marker (ADRP) and 5-LO by immunofluorescence microscopy. We demonstrated that GR-HSCs were able to spontaneously release cysteinyl-LTs (CysLTs), but not LTB(4,) into culture supernatants. CysLT production was highly enhanced after TGF-ß-stimulation. Moreover, the 5-LO inhibitor zileuton and 5-LO gene deletion were able to inhibit the TGF-ß-stimulated proliferation of GR-HSCs, suggesting a role for LTs in HSC activation. Here, we extend the immunoregulatory function of HSC by demonstrating that HSC from liver granulomas of schistosome-infected mouse are able to release Cys-LTs in a TGF-ß-regulated manner, potentially impacting pathogenesis and liver fibrosis in schistosomiasis.

Bone marrow subendosteal microenvironment harbours functionally distinct haemosupportive stromal cell populations.

In adult animals, bone marrow is the major site of blood cell production, which is controlled by interactions between the local stroma and blood cell progenitors. The endosteal/subendosteal environment comprises bone-lining and adjacent reticular cells and sustains haemopoietic stem cell (HSC) self-renewal, proliferation and differentiation. We have questioned the specific role of each of these stroma cells in controlling HSC fate. We have isolated two distinct stroma-cell populations containing subendosteal reticulocytes (F-RET) and osteoblasts (F-OST) from periosteum-free fragments of murine femurs by a two-step collagenase-digestion procedure. Both populations produce similar extracellular matrix (collagen I, laminin, fibronectin, decorin), except for collagen IV, which is low in F-OST. They also express osteogenic markers: osteopontin, osteonectin, bone sialoprotein and alkaline phosphatase (ALP). The quantity and activity of ALP are however higher in F-OST. When co-cultured with bone marrow mononuclear cells or lineage-negative haemopoietic progenitors, F-OST stroma induces low proliferation and high maintenance of early haemopoietic progenitors, whereas F-RET stroma induces high short-term proliferation and differentiation. Analysis by reverse transcription/polymerase chain reaction has revealed higher levels of Jagged-1 expression by F-OST cells than by the F-RET population. Thus, two adjacent stroma cells (subendosteal and endosteal) play distinct roles in controlling the stem-cell capacity and fate of HSC and probably contribute distinctly to HSC niche formation.

Haemopoietic progenitors in the adult mouse omentum: permanent production of B lymphocytes and monocytes.

The coelome-associated lympho-myeloid tissues, including the omentum, are derived from early embryo haemopoietic tissue of the splanchnopleura, and produce B lymphocytes and macrophages. They are reactive in pathologies involving coelomic cavities, in which they can expand in situ the cells of inflammatory infiltrates. We have addressed the question of the role of the adult omentum in permanent basal production of early lymphopoietic progenitors (pro-B/pre-B cells), through characterisation of omentum cells ex vivo, and study of their in vitro differentiation. We have shown that the murine omentum produces early haemopoietic progenitors throughout life, including B-cell progenitors prior to the Ig gene recombination expressing RAG-1 and lambda5, as well as macrophages. Their production is stroma-dependent. The omentum stroma can supply in vitro the cytokines (SDF-1alpha, Flt3 ligand and IL-7) and the molecular environment required for generation of these two cell lineages. Omentum haemopoietic progenitors are similar to those observed in foetal blood cell production, rather than to progenitors found in the adult haemopoietic tissue in the bone marrow--in terms of phenotype expression and differentiation capacity. We conclude that a primitive pattern of haemopoiesis observed in the early embryo is permanently preserved and functional in the adult omentum, providing production of cells engaged in nonspecific protection of abdominal intestinal tissue and of the coelomic cavity.

Connexin expression and gap-junction-mediated cell interactions in an in vitro model of haemopoietic stroma.

In addition to the steady-state production of all blood cells, bone marrow can respond to an increased requirement for one or several cell lineages. The hormonal controls involved may act directly on blood cell progenitors or indirectly through modification of the haemopoietic environment. Intercellular gap junctions formed by connexins (Cx) provide direct communication among adjacent cells and the functional integration of multicellular systems. Since haemopoietic stroma is determinant for blood cell production, we have questioned whether gap-junction-dependent controls of haemopoiesis are sensitive to hormones and vitamins. We have analysed the expression, synthesis, cell distribution and formation of functional gap junctions in the murine bone-marrow stroma cell line S-17, and between stromal cells and blood cell progenitors. Nine Cxs were identified by reverse transcription/polymerase chain reaction, and only Cx43 by Western blot and immunofluorescence. All of the studied parameters were sensitive to intrinsic controls dependent upon the pattern of cell growth and modulated by exogenous controls mediated by retinol and steroids. Positive or negative modulation was specific for different Cxs. FACS analysis showed communication among the stromal cells and between stromal cells and myeloid (Mac1+) but not lymphoid (B220+) progenitors. Calcein transfer modulation did not correspond to the modulation of Cx43 expression and formation of connexons, suggesting the participation of other Cxs. Thus, functional gap junctions among haemopoietic stroma cells and between stroma and haematopoietic cells in the bone marrow may be modulated in response to hormonal stimuli, potentially controlling overall blood cell production.