The fourth scientific workshop of the European Crohn's and Colitis Organization (ECCO) focused on intestinal fibrosis in inflammatory bowel disease (IBD). The objective was to better understand basic mechanisms and markers of intestinal fibrosis as well as to suggest new therapeutic targets to prevent or treat fibrosis. The results of this workshop are presented in three separate manuscripts. This section describes markers of fibrosis in IBD, identifies unanswered questions in the field and provides a framework for future studies addressing the unmet needs in the field of intestinal fibrosis.

1.In this review, the use of precision-cut tissue slices (PCTS) of the liver, kidney, lung and intestine in fibrosis research are evaluated and future possibilities are discussed. 2.In vivo models or techniques that are applicabless to be investigated in PCTS are discussed. 3.It is concluded that the early onset of fibrosis can be induced successfully in PCTS prepared from human and experimental animals. 4.Moreover, precision-cut slices of fibrotic tissue are effective in gaining new knowledge of the mechanisms of fibrosis and of the mode of action of potential antifibrotic drugs. 5.Both healthy and fibrotic human tissue slices will pave the way for the testing of novel therapeutic drugs to treat patients with fibrosis avoiding interspecies extrapolation.

Renal fibrosis is a serious clinical problem resulting in the greatest need for renal replacement therapy. No adequate preventive or curative therapy is available that could be clinically used to target renal fibrosis specifically. The search for new efficacious treatment strategies is therefore warranted. Although in vitro models using homogeneous cell populations have contributed to the understanding of the pathogenetic mechanisms involved in renal fibrosis, these models poorly mimic the complex in vivo milieu. Therefore, we here evaluated a precision-cut kidney slice (PCKS) model as a new, multicellular ex vivo model to study the development of fibrosis and its prevention using anti-fibrotic compounds. Precision-cut slices (200-300 μm thickness) were prepared from healthy C57BL/6 mouse kidneys using a Krumdieck tissue slicer. To induce changes mimicking the fibrotic process, slices were incubated with TGFβ1 (5 ng/ml) for 48 h in the presence or absence of the anti-fibrotic cytokine IFNγ (1 µg/ml) or an IFNγ conjugate targeted to PDGFRβ (PPB-PEG-IFNγ). Following culture, tissue viability (ATP-content) and expression of α-SMA, fibronectin, collagen I and collagen III were determined using real-time PCR and immunohistochemistry. Slices remained viable up to 72 h of incubation, and no significant effects of TGFβ1 and IFNγ on viability were observed. TGFβ1 markedly increased α-SMA, fibronectin and collagen I mRNA and protein expression levels. IFNγ and PPB-PEG-IFNγ significantly reduced TGFβ1-induced fibronectin, collagen I and collagen III mRNA expression, which was confirmed by immunohistochemistry. The PKCS model is a novel tool to test the pathophysiology of fibrosis and to screen the efficacy of anti-fibrotic drugs ex vivo in a multicellular and pro-fibrotic milieu. A major advantage of the slice model is that it can be used not only for animal but also for (fibrotic) human kidney tissue.

Intestinal fibrosis (IF) is a major complication of inflammatory bowel disease. IF research is limited by the lack of relevant in vitro and in vivo models. We evaluated precision-cut intestinal slices (PCIS) prepared from human, rat, and mouse intestine as ex vivo models mimicking the early-onset of (human) IF. Precision-cut intestinal slices prepared from human (h), rat (r), and mouse (m) jejunum, were incubated up to 72 h, the viability of PCIS was assessed by ATP content and morphology, and the gene expression of several fibrosis markers was determined. The viability of rPCIS decreased after 24 h of incubation, whereas mPCIS and hPCIS were viable up to 72 h of culturing. Furthermore, during this period, gene expression of heat shock protein 47 and plasminogen activator inhibitor 1 increased in all PCIS in addition to augmented expression of synaptophysin in hPCIS, fibronectin (Fn2) and TGF-β1 in rPCIS, and Fn2 and connective tissue growth factor (Ctgf) in mPCIS. Addition of TGF-β1 to rPCIS or mPCIS induced the gene expression of the fibrosis markers Pro-collagen1a1, Fn2, and Ctgf in both species. However, none of the fibrosis markers was further elevated in hPCIS. We successfully developed a novel ex vivo model that can mimic the early-onset of fibrosis in the intestine using human, rat, and mouse PCIS. Furthermore, in rat and mouse PCIS, TGF-β1 was able to even further increase the gene expression of fibrosis markers. This indicates that PCIS can be used as a model for the early-onset of IF.

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