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Intestinal anastomotic healing (AH) is critical in colorectal surgery, since disruptive AH leads to anastomotic leakage, a feared postoperative complication. Macrophages are innate immune cells and are instrumental in orchestrating intestinal wound healing, displaying a functional dichotomy as effectors of both tissue injury and repair. The aim of this study was to investigate the phase-specific function and plasticity of macrophages during intestinal AH. Transgenic CD11b diphtheria toxin receptor (CD11b-DTR) mice were used to deplete intestinal macrophages in a temporally controlled manner. Distal colonic end-to-end anastomoses were created in CD11b-DTR, and wild-type mice and macrophages were selectively depleted during either the inflammatory (day 0–3), proliferative (day 4–10), or reparative (day 11–20) phase of intestinal AH, respectively. For each time point, histological and functional analysis as well as gene set enrichment analysis (GSEA) of RNA-sequencing data were performed. Macrophage depletion during the inflammatory phase significantly reduced the associated inflammatory state without compromising microscopic AH. When intestinal macrophages were depleted during the proliferative phase, AH was improved, despite significantly reduced perianastomotic neoangiogenesis. Lastly, macrophages were depleted during the reparative phase and GSEA revealed macrophage-dependent pathways involved in collagen remodeling, cell proliferation, and extracellular matrix composition. However, AH remained comparable at this late timepoint. These results demonstrate that during intestinal AH, macrophages elicit phase-specific effects, and that therapeutic interventions must critically balance their dual and timely defined role., Finanziert durch den Open-Access-Publikationsfonds der Westfälischen Wilhelms-Universität Münster (WWU Münster).

The interactions of fibroblast-like synoviocyte (FLS)-derived pro-inflammatory cytokines/chemokines and immune cells support the recruitment and activation of inflammatory cells in RA. Here, we show for the first time that the classical myokine myostatin (GDF-8) is involved in the recruitment of Th17 cells to inflammatory sites thereby regulating joint inflammation in a mouse model of TNFalpha-mediated chronic arthritis. Mechanistically, myostatin-deficiency leads to decreased levels of the chemokine CCL20 which is associated with less infiltration of Th17 cells into the inflamed joints. In vitro, myostatin alone or in combination with IL-17A enhances the secretion of CCL20 by FLS whereas myostatin-deficiency reduces CCL20 secretion, associated with an altered transmigration of Th17 cells. Thus, the communication between activated FLS and Th17 cells through myostatin and IL-17A may likely contribute to a vicious cycle of inflammation, accounting for the persistence of joint inflammation in chronic arthritis. Blockade of the CCL20–CCR6 axis by inhibition of myostatin may, therefore, be a promising treatment option for chronic inflammatory diseases such as arthritis., Finanziert über die DEAL-Vereinbarung mit Wiley 2019-2022.

Background. Granulocyte Macrophage-Colony Stimulating Factor (GM-CSF) has been shown to induce clinical response and remission in patients with active Crohn’s disease (CD). Moreover the beneficial role of GM-CSF was shown in a mouse model of acute colitis induced by Dextran Sodium Sulfate (DSS). Since it is known that GM-CSF has pleiotropic effects on monocytes and since those cells represent the exclusive source of macrophages in inflamed intestinal mucosa we characterized GM-CSF treated mouse monocytes in vitro and analyzed their function in vivo in a model of chronic DSS colitis. Methods. Mouse bone marrow-derived monocyte precursors were treated for 48 hours with GM-CSF in vitro and phenotypical changes were assessed by real-time polymerase chain reaction (qRT-PCR) and flow cytometry. Functional properties were evaluated in mixed lymphocyte reactions (MLR), by phagocytosis assays, adherence to plastic surface, cytokine production upon lipopolysaccharide (LPS) stimulation and measurement of reactive oxygen species (ROS) production. Therapeutic effects of GM-CSF-treated monocytes were evaluated in a model of chronic colitis induced by repeated oral administration of DSS (2%) on three days per week. GM-CSF treated monocytes were administered i.v. one day prior start of the third DSS treatment cycle and the severity of developed colitis was evaluated by body weight change, colon length, histology and expression of inflammatory markers. The distribution of injected GM-CSF-monocytes across intestine was evaluated by in vivo near infrared imaging. Results. We found that GM-CSF-treated monocytes express higher levels of anti-inflammatory molecules on mRNA and protein levels (e.g. IL1-Ra, IL4-R and ARG1). Functionally, GM-CSF promotes ROS production of the cells but reduces phagocytosis and adherence. In MLR we observed an induction of Foxp3 in naive T cells. Clinically, in chronic DSS-induced colitis, treatment of mice with GM-CSF-monocytes showed an overall better outcome compared to mice treated with control monocytes. This encompasses body weight, colon length, mRNA expression of inflammatory marker molecules (e.g. IL6 and TNF) and histological observations. Using in vivo imaging technology we found that a higher percentage of GM-CSF treated monocytes enter the inflamed intestine compared to control monocytes. In addition, GM-CSF-monocytes persisted longer at sides of inflammation. Conclusion. We showed that the beneficial effects of GM-CSF in CD are probably due to its modifying action especially on monocytes and concomitant anti-inflammatory alterations in phenotype and function of macrophages developed from these cells in an experimental model of colitis.