Phenotypic change and accumulation of smooth muscle cells in strictures in Crohn's disease: relevance to local angiotensin II system

Intestinal stricture lesions in Crohn's disease are characterized as submucosal fibromuscular accumulation. There has been a controversy about whether the fibrogenic cells in stricture lesions in Crohn's disease originate from a smooth muscle cell or a fibroblast lineage. In the present study, we aimed to elucidate: (1) the origin of the fibrogenic cells in stricture lesions; and (2) the roles of the local angiotensin II system, including mast cell chymase, in stricture formation. Methanol-Carnoy's-fixed colonic tissues, obtained from the stricture sites of 18 patients with Crohn's disease, were analyzed by immunostaining for vimentin, smooth muscle actin (1A4 and CGA7), angiotensin II type-1 receptor, angiotensin II-converting enzyme, and mast cell tryptase and chymase. As controls, unaffected (normal) portions of 11 colonic tumor specimens were also investigated. Submucosal fibromuscular accumulation was seen in every stricture lesion. The majority of mesenchymal cells accumulated in the stricture lesions were moderately differentiated intestinal smooth muscle cells [vimentin(+), 1A4(+), and CGA7(+)]. Moreover, occasional intestinal smooth muscle cells in the muscular layers, adjacent to the site of the submucosal fibromuscular response, showed distinct positivity for vimentin, indicating phenotypic modulation toward an immature, or dedifferentiated state. These smooth muscle cells accumulated in the stricture lesions were positive for angiotensin II type-1 receptor. Abundant chymase-positive mast cells were distributed in these lesions. These results suggest that the proliferation and migration of moderately differentiated intestinal smooth muscle cells from the muscular layers are the major pathologicalmechanisms in stricture formation in Crohn's disease, and the angiotensin II system is involved in this process.