Role of Myeloid Tet Methylcytosine Dioxygenase 2 in Pulmonary and Peritoneal Inflammation Induced by Lipopolysaccharide and Peritonitis Induced by Escherichia coli

Tet methylcytosine dioxygenase 2 (Tet2) mediates demethylation of DNA. We here sought to determine the expression and function of Tet2 in macrophages upon exposure to lipopolysaccharide (LPS), and in the host response to LPS induced lung and peritoneal inflammation, and during Escherichia (E.) coli induced peritonitis. LPS induced Tet2 expression in mouse macrophages and human monocytes in vitro, as well as in human alveolar macrophages after bronchial instillation in vivo. Bone marrow-derived macrophages from myeloid Tet2 deficient (Tet2fl/flLysMCre) mice displayed enhanced production of IL-1β, IL-6 and CXCL1 upon stimulation with several Toll-like receptor agonists; similar results were obtained with LPS stimulated alveolar and peritoneal macrophages. Histone deacetylation was involved in the effect of Tet2 on IL-6 production, whilst methylation at the Il6 promoter was not altered by Tet2 deficiency. Tet2fl/flLysMCre mice showed higher IL-6 and TNF levels in bronchoalveolar and peritoneal lavage fluid after intranasal and intraperitoneal LPS administration, respectively, whilst other inflammatory responses were unaltered. E. coli induced stronger production of IL-1β and IL-6 by Tet2 deficient peritoneal macrophages but not in peritoneal lavage fluid of Tet2fl/flLysMCre mice after in vivo intraperitoneal infection. Tet2fl/flLysMCre mice displayed enhanced bacterial growth during E. coli peritonitis, which was associated with a reduced capacity of Tet2fl/flLysMCre peritoneal macrophages to inhibit the growth of E. coli in vitro. Collectively, these data suggest that Tet2 is involved in the regulation of macrophage functions triggered by LPS and during E. coli infection.

FC 098MESENCHYMAL STEM CELL EXOSOMES AMELIORATE MICE PERITONEAL FIBROSIS INDUCED BY HUMAN PERITONITIS DIALYSIS EFFLUENT

Background and Aims Peritoneal fibrosis is a severe complication of peritoneal dialysis, but there are few effective therapies for it. The purpose of this study was to investigate the protective effect of exosomes secreted by mouse bone marrow mesenchymal stem cells on peritoneal fibrosis and to reveal the mechanism. Method Forty-two male C57BL/6 mice were randomly divided into a normal group, a control group (2.5% glucose dialysate), a peritonitis-effluent group (The overnight 2.5% glucose dialysate of patients with peritonitis), a high glucose dialysate group (4.25% glucose concentration), a peritonitis-dialysate + exosome group, and a high glucose dialysate + exosome group. The mouse model of peritoneal fibrosis was constructed by intraperitoneal injection of human peritonitis effusion continuously for 42 days. The mice in the exosome treatment group received intraperitoneal injection of mesenchymal stem cell (MSC)-exosomes twice. The level of peritoneal structural and functional damage, inflammation, fibrosis and mesothelial cell damage of peritoneum were detected. Furthermore, the effect of MSC-exosomes was validated in vitro. Results Peritoneal transport was significantly impaired and peritoneal thickness was significantly increased in the peritonitis-effluent group and the high glucose dialysate group after 42 days. The degree of peritoneal inflammation and fibrosis in the two groups was significantly higher than the control group. The results suggested that human peritonitis dialysis effluent could be used to construct a mouse model of peritoneal fibrosis. Masson staining results showed that the fibrosis degree of peritonitis - effluent + exosome group was significantly less than the peritonitis - effluent group. Immunohistochemical analysis showed that the expression levels of mesothelial markers E-cadherin and ZO-1, neutrophil granulocytes (MPO) and macrophages (F4/80), and fibrosis markers collagen I and a-SMA in the peritonitis - effluent + exosome group were significantly lower than those in the peritonitis - effluent group. Similarly, the high glucose dialysate + exosome group mice showed significantly lower levels of peritoneal inflammation and fibrosis than the high glucose dialysate group mice. In vitro experiments showed that exosomes could down-regulate the secretion of IL-1, IL-6 and TGF- by renal tubular cells stimulated by high glucose dialysate, maintain the expression of mesenchymal cell marker (E-cadherin), and inhibit the mesenchymal marker (-SMA), suggesting that exosomes could inhibit the transdifferentiation of peritoneal mesenchymal cell-mesenchymal cells (MMT). Conclusion MSC-exosomes can alleviate peritoneal fibrosis by inhibiting peritoneal mesothelial cell-mesenchymal cell transdifferentiation.

Intraperitoneal oil application causes local inflammation with depletion of resident peritoneal macrophages

Oil is frequently used as a solvent to inject lipophilic substances into the peritoneum of laboratory animals. Although mineral oil causes chronic peritoneal inflammation, little is known whether other oils are better suited. Here we show that olive, peanut, corn or mineral oil causes xanthogranulomatous inflammation with depletion of resident peritoneal macrophages. However, there were striking differences in the severity of the inflammatory response. Peanut and mineral oil caused severe chronic inflammation with persistent neutrophil and monocyte recruitment, expansion of the vasculature and fibrosis. Corn and olive oil provoked no or only mild signs of chronic inflammation. Mechanistically, the vegetal oils were taken up by macrophages leading to foam cell formation and induction of cell death. Olive oil triggered caspase-3 cleavage and apoptosis, which facilitates the resolution of inflammation. Peanut oil and, to a lesser degree, corn oil triggered caspase-1 activation and macrophage pyroptosis, which impairs the resolution of inflammation. As such, intraperitoneal oil administration can interfere with the outcome of subsequent experiments. As a proof-of-principle, intraperitoneal peanut oil injection was compared to its oral delivery in a thioglycolate-induced peritonitis model. The chronic peritoneal inflammation due to peanut oil injection impeded the proper recruitment of macrophages and the resolution of inflammation in this peritonitis model. In summary, the data indicate that it is advisable to deliver lipophilic substances like tamoxifen by oral gavage instead of intraperitoneal injection.