Localization of estrogen receptor ERα, ERβ and GPR30 on myenteric neurons of the gastrointestinal tract and their role in motility

Estrogen is well known to have a modulatory role on gastrointestinal tract, particularly through its interaction with nuclear estrogen receptors (ERs), alpha and beta (ER alpha/beta). Recent functional studies also indicate that estrogen can activate a G-protein coupled estrogen receptor, GPR30, or GPER1. The present study was designed to identify either the presence or absence of nuclear ERs and GPR30 in the myenteric plexus of the stomach, duodenum, jejunum, ileum and colon of female and male mice. Immunofluorescence staining revealed a high expression of GPR30 in the cytoplasm but not within the nucleus of enteric neurons in female and male mice. ER beta localization was similar to GPR30, where it was expressed in cytoplasm of enteric neurons, but was absent from nuclei, opening up the possibility that ER beta and GPR30 might work together to manifest estrogenic effects. Comparatively, ER alpha was mainly located in the nuclei of enteric neurons. ER alpha, ER beta and GPR30 were also expressed in the cytoplasm of glial cells in the stomach and small intestine, but levels were lower in the colon. The expression nuclear:cytoplasm ratio of ER alpha was higher in male than female mice, which might relate to sex-dependent translocation of ER alpha from cytoplasm to nucleus in response to known plasma levels of estrogen. A functional study using isolated ileal segments showed that ER alpha, ER beta and GPR30 are involved in the neuronal-mediated contractions in female tissues, but only ER alpha was involved in male tissues. This may indicate although expression level was similar between males and females, the downstream mechanisms of ER beta and GPR30 could be different between sexes. The present study provides a rationale for the action of estrogen to modulate gastrointestinal function in health and disease in different sexes.