NR2B-containing NMDA receptors contribute to diarrhea-predominant irritable bowel syndrome

Abstract

Colonic mucosal N-methyl-D-aspartate receptors (NMDARs) contribute to visceral hypersensitivity in diarrhea-predominant irritable bowel syndrome (IBS-D) by increasing the production of brain-derived neurotrophic factor (BDNF). We investigated which of the multiple NMDAR subtypes and BDNF isoforms are responsible for this effect. Immunohistochemistry and Western blotting were used to detect levels of colonic mucosal NR2A-D subunits and the precursor (proBDNF) and mature (mBDNF) forms of BDNF in 67 participants. Only NR2B subunit expression was elevated in the colonic mucosa of IBS-D patients, in parallel with increased total BDNF and proBDNF expression. Expression of 15 kDa mBDNF was not detected in the colonic mucosa. NR2B, total BDNF and proBDNF levels correlated with abdominal pain scores. Quantitative real-time PCR and Western blotting showed that NMDAR activation substantially induced total BDNF/proBDNF expression in HT-29 cells, while the NMDAR inhibitor MK-801 and the NR2B subunit antagonist Ro25-6981 each completely blocked these effects. Thus, colonic mucosal NR2B-containing NMDARs may contribute to visceral hypersensitivity in IBS-D patients by upregulating BDNF, especially proBDNF.