Background: Intestinal fibrosis is a common complication of IBD. Fibrosis is a consequence of local chronic inflammation and is characterized by an excessive extracellular matrix deposition and loss of normal function. Resident macrophages play a key role in maintaining intestinal homeostasis as well as in injury repair, and their phenotype evolves during the phases of inflammation, remission and wound healing. Stat6 is the chief transcription factor involved in macrophage polarization towards the anti-inflammatory phenotype induced by IL-4 treatment, and we have previously reported that Stat6(−/−) mice develop increased mucosal damage and fibrosis in a model of TNBS-colitis. Our present aim is to analyse the relevance of macrophages on the increased susceptibility of Stat6-KO mice.
Methods: Stat6(−/−) mice received increasing doses of TNBS (0.5, 0.5, 0.75, 0.75, 1 and 1 mg, intrarectally) once a week. Two days after each TNBS administration, they received a suspension of IL4-treated peritoneal macrophages (Mf, 2×106 cells) obtained from wild type (WT) or Stat6(−/−) donors. Seven days after the last dose, mice where sacrificed, and the expression of several markers of fibrosis (Tgf-β, E-Cadherin, Vimentin, Col1a1, α-Sma, Mmp2, Fsp-1 and Timp-1) were analysed by qPCR in colonic tissue.
Results: The fibrotic state in TNBS-treated Stat6(−/−) mice was demonstrated by the increased expression of most of the markers analysed (Vimentin, α-Sma, Mmp2, Timp1, Col1a1).
A significant reduction in mortality was observed in mice receiving a weekly injection of IL4-treated Mf obtained from WT mice (p=0.037), but not in mice administered with Mf obtained from Stat6(−/−) donors (p=0.149). Moreover, mice receiving IL4-treated/WT Mf showed a reduced expression of TNBS-induced fibrotic markers when compared to that observed in mice receiving IL-4-treated/Stat6(−/−) Mf (Figure 1).
Conclusions: Exogenous administration of macrophages with a Stat6-dependent phenotype exerts a protective effect and reverses the increased susceptibility of Stat6(−/−) mice to TNBS-induced colitis and fibrosis.