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P021. The urokinase plasminogen activator receptor (uPAR) regulates intestinal macrophage phagocytosis and polarization in experimental colitis

M. Genua1, S. D'Alessio1, J. Cibella1, A. Gandelli1, E. Sala1, C. Correale1, V. Arena2, A. Malesci1, S. Vetrano1, S. Danese1, 1Istituto Clinico Humanitas, Rozzano, Italy, 2Catholic University of Rome, Internal Medicine, Rome, Italy

Background

The urokinase plasminogen activator receptor (uPAR) plays a key role not only in fibrinolysis but also is crucially involved in extracellular matrix degradation and regulates cell migration, adhesion and proliferation. Additionally, uPAR expression is increased in cytokine or bacteria activated macrophages and contributes to the infiltration of inflammatory cells into infected tissues or organs. Since no information exists regarding uPAR in intestinal inflammation, we investigated its role in experimental colitis.

Methods

The dextran sulfate sodium (DSS) and trinitrobenzene sulfonic acid (TNBS) were used as models of colitis. Expression of uPAR in healthy and colitic mice was assessed by Real-Time and western-blot. uPAR expression was investigated by confocal microscopy and flow cytometry. The functional role of uPAR was assessed by the use of uPAR knock out (KO) mice. Colitis disease activity index (DAI) was calculated and intestinal damage evaluated by both endoscopy and histology. The expression of colonic mucosal matrix metalloproteinase (MMPs) along with local inflammatory cytokine production were estimated by Real-Time and ELISA. Macrophage activation and function were assessed by gentamycin protection assay.

Results

The expression levels of uPAR increased during colitis induction both in the DSS and TNBS models, as measured by Real-Time and confirmed by western blot (4–6 times, p < 0.01). Confocal microscopy and FACS analysis identified CD68+ cells as the major cell type expressing high levels of uPAR after colitis induction. KO mice displayed higher weight loss and increased DAI (p < 0.01, for DSS model; p < 0.05, for TNBS model), compared to WT. Histological and endoscopic score were significantly higher in KO mice (p < 0.05). In both models, uPAR absence led to an augmented production of MMP-3, -9 and -12 as well as TNF, IFN-g and IL-6. Functionally, KO lamina-propria macrophages showed a severe impairment in bacterial phagocytosis (p < 0.01) displaying an increased expression of M1 polarization markers such as iNOS and IL-12p40 (p < 0.01).

Conclusion

Our findings reveal uPAR as a key component involved in controlling intestinal inflammation. In particular, uPAR expression is up-regulated during colitis by CD68+ macrophage and its genetic deletion leads to detrimental inflammation. uPAR is required for a correct bacterial handling by lamina-propria macrophages and unveiling the mechanism behind its function could offer a new therapeutic target to control intestinal inflammation.