Comparison of gene expression between wild-type and SERT knockout ileal mucosa

The serotonin transporter (SERT, SLC6A4), belonging to Na+ and Cl- dependent transporters, functions to regulate the availability of serotonin (5-HT) in various tissues including brain, platelets, and intestine. Alterations in 5-HT levels and/or SERT expression have been implicated in pathophysiological conditions including anxiety-like behavior, obesity, cardiovascular disorders and GI disorders such as IBD, IBS, and diarrhea. Accordingly, SERT deficiency in mice is pleiotropic with many different phenotypic traits. Transgenic mice with global deletion of SERT exhibit increased anxiety, abnormal GI motility, and obesity associated with hyperglycemia. Additionally, these mice are more susceptible to intestinal inflammation. The mechanism by which SERT deficiency underlies GI related disturbances and exacerbates the severity of gut inflammation is not known. Thus, we evaluated the ileal mRNA expression to identify potential intestinal targets that contribute to disease pathogenesis when the SERT gene is non-functional. For these studies, RNA was extracted from ileum mucosa from age matched (9-10 wk) control and SERT KO mice by Trizol and was subjected to Mouse mRNA and OneArray Profiling. Our microarray data revealed 492 significantly upregulated and 293 downregulated genes in SERT KO ileum. Pathway analysis revealed significant enrichment in cell cycle, signaling, chemotaxis, and epithelial transporters. Genes of interest were validated by RT-PCR, which included CYP1A1 (~20 fold decrease, p < 0.05), CLDN8 (~30% decrease, p < 0.05), and HMGCS2 (~7 fold increase, p < 0.05). Similar changes were found in colon. A remarkable decrease in expression of Cyp1a1, which encodes a cytochrome P450 enzyme, provides a novel role of serotonergic pathways in drug and xenobiotic detoxification. CLDN8 encodes for claudin 8, which is downregulated in patients with Crohn’s disease. Deficiency of HMGCS2, the mitochondrial 3-hydroxy-3-methylglutaryl CoA synthase, is linked to hypoglycemia. Our data provides novel clues for differential expression of genes affected by 5-HT and/or SERT deficiency in the intestine. Total RNA from the ileal mucosa of 6 WT and 6 SERT KO mice was pooled pair-wise to create 3 samples from WT and 3 samples from SERT KO mice. Two technical replicates were performed for each sample for 12 total arrays.