Epigenetic modification of intestinal smooth muscle cell phenotype during proliferation.

Inflammation causes proliferation of intestinal smooth muscle cells (ISMC), which contributes to a thickened intestinal wall, and also to stricture formation in Crohn's disease. Proliferation of ISMC both in vitro and in vivo caused decreased expression of marker proteins, but the underlying cause is unclear. Since epigenetic change is important in other systems, we examined this in cell lines from rat colon at either low passage or after extended growth, using immunocytochemistry, immunoblotting and qPCR to evaluate phenotype. Exposure to the HDAC inhibitor trichostatin A or 5-azacytidine, a DNMT inhibitor, reversed the characteristic loss of phenotypic markers among high passage cell lines of ISMC. Expression of smooth muscle actin and SM-22 were markedly increased, as well as functional expression of the neurotrophin GDNF. Increased expression of muscarinic receptor-3 and MLCK was correlated with an upregulated response to cholinergic stimulation. In human ISMC (hISMC) lines from terminal ileum, phenotype was similarly affected by extended proliferation. However, hISMC from resected Crohn's strictures at low passage already displayed a significantly reduced contractile phenotype, compared with patient-matched intrinsic controls, and was associated with increased, patient-specific expression of DNMT1, HDAC2, and HDAC5. Therefore, protracted growth causes epigenetic alterations that account for an altered phenotype of ISMC. A similar process may promote stricture formation in Crohn's disease, where the potential for halting progression or even reversal of disease through control of phenotypic modulation may become a novel treatment option.