Epigenetic Modification of Phenotype in Intestinal Smooth Muscle Cells
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Inflammation causes proliferation of intestinal smooth muscle cells (ISMC), contributing to the thickened intestinal wall and the dysmotility symptoms observed in inflammatory bowel disease (IBD). A unique consequence of Crohn’s disease (CD), a subset of IBD characterized by chronic, transmural intestinal inflammation, is the formation of obstructive strictures attributable to ISMC hyperplasia. In vitro, prolonged proliferation of ISMC results in loss of their normal contractile phenotype, including decreased expression of contractile markers and the neurotrophin glial cell-line derived neurotrophic factor (GDNF). In other diseases of smooth muscle hyperplasia, epigenetic modifications, including DNA methylation and histone acetylation, affect smooth muscle phenotype and contribute to impaired tissue function. Any epigenetic role in regulating gene expression and the contractile phenotype of ISMC is unknown. Repeated passage ISMC were treated with trichostatin A (TSA) and 5-azacytidine (AZA), which inhibit enzymes that deacetylate histones and methylate DNA, respectively, and the outcomes on phenotype were assessed. TSA and AZA treatment decreased the enhanced growth response of repeated passage ISMC, and increased the expression of contractile markers, SMA and SM22. Repeated passage cells treated with TSA and AZA increased expression of muscarinic receptor 3, myosin light chain kinase 2, and showed an increased response to carbachol stimulation. TSA and AZA treatment also increased GDNF expression, and improved the neurotrophic function of repeated passage ISMC. Compared to low passage ISMC, repeated passage cells had increased DNA methyltransferase 1 (DNMT1) and histone deacetylase 2 (HDAC2) expression. ISMC from human strictures showed a decreased contractile phenotype, with increased levels of DNMT1 and HDAC5. Repeated passage human ISMC also had decreased expression of contractile markers SMA and SM22, mimicking the rat model. These findings suggest that the altered contractile phenotype of ISMC is associated with epigenetic changes, including increased DNA methylation and histone deacetylation. Furthermore, this evidence supports a potential therapeutic role for improving the contractility of ISMC, and restoring proper motility in CD patients.