Gut fibrosis with altered colonic contractility in a mouse model of scleroderma

Gastrointestinal involvement occurs in up to 90% of patients with SSc. Animal models of SSc mimic some of the pathophysiological disease processes of SSc. The transgenic (TG) mouse strain TβRIIΔk-fib is characterized by ligand-dependent up-regulation of TGF-β signalling and has been shown to develop skin fibrosis, lung fibrosis and diminished aortic ring contractility and adventitial fibrosis. We investigated if similar changes are observed in the gut tissue in this mouse model.

Colonic tissue was examined using histology and immunohistochemistry analyses. Tissue architecture was examined by haematoxylin and eosin (H&E), picrosirius red and immunohistochemical markers for α-smooth muscle actin (α-SMA), phospho-Smad 2/3 (pSmad2/3), Ki-67, protein gene product 9.5 and S-100. Fibrosis was quantified using the NIS Elements BR 2.30 system and by Sircol assay. Colonic strip contractile responses to potassium chloride (KCl) and carbachol were assessed in isolated organ baths. Confirmatory gut fibroblast and intestinal tissue biochemical assays, including cellular signalling mechanisms, were performed.

H&E staining and staining for α-SMA, Ki-67, pSmad2/3 or neural tissue staining showed no differences between TG and wild-type (WT) mice gut tissue. There was increased collagen deposition in the gut of TG mice. Quantitative PCR results of TG gut fibroblasts showed evidence of up-regulated collagen and CTGF transcription, and non-canonical TGF-β signalling pathways were also up-regulated. The organ bath studies showed diminished colonic strip contractility in TG mice compared with WT control mice to KCl and carbachol.

We have shown that this TG mouse model, previously shown to develop skin and lung, develops colonic fibrosis with associated effects on colonic tissue contractility. This may offer further insight in pathological processes leading to the development of gut fibrosis.