The M1 muscarinic acetylcholine receptor in the crypt stem cell compartment mediates intestinal mucosal growth

Abstract

Maintenance of the highly plastic intestinal epithelium relies upon stem cells localized to intestinal crypts. Recent evidence suggests muscarinic acetylcholine signaling impacts epithelial barrier function, proliferation, and apoptosis. We hypothesized that the intestinal crypt base would express specific muscarinic acetylcholine receptors that drive proliferation in this critical region. Intestinal segments spanning the small bowel were procured from wild-type C57Bl/6 mice to determine muscarinic acetylcholine receptor mRNA expression and create sections on laser capture microdissection slides for analysis of crypt base cells. RT-PCR was performed using primers targeting the five muscarinic acetylcholine receptor subtypes (M1–M5), LGR5, BIII-tubulin, and GAPDH. To determine the effects of muscarinic agonism in vivo, osmotic pumps delivering the M1 muscarinic acetylcholine receptor agonist McN-A-343 were implanted into wild type mice for one week. Segments were harvested, histologic sections created, and morphometric and proliferative parameters measured. In full-thickness intestinal samples, muscarinic acetylcholine receptor subtypes M1–M4 were found in all regions, while M5 was localized to the proximal jejunum. In crypt-base cells, the M1 muscarinic acetylcholine receptor subtype was the only subtype found and was present in all regions. LGR5 was present in all laser capture microdissection samples, indicating the capture of intestinal stem cells. In vivo experiments conducted with McN-A-343 revealed significantly increased villus height, crypt depth, and crypt-cell proliferation. The presence of M1 muscarinic acetylcholine receptor mRNA within the stem cell niche in the intestinal crypt base coupled with increased mucosal growth with M1 receptor stimulation in vivo suggests that the cholinergic system, via the M1 muscarinic acetylcholine receptor, is a critical mediator of intestinal mucosal homeostasis.

Impact statement

Localization of a specific subtype of the muscarinic acetylcholine receptor in the crypt stem cell compartment suggests a critical role in intestinal mucosal homeostasis. Here we demonstrate the localization of the M1 muscarinic acetylcholine receptor to the stem cell compartment and demonstrate increase morphometric and proliferative parameters when this is stimulated in vivo. These data provide novel information about this complex signaling microenvironment and offer potential future therapeutic targets for future study.