Differential distribution of ghrelin-O-acyltransferase (GOAT) immunoreactive cells in the mouse and rat gastric oxyntic mucosa.

The enzyme that acylates ghrelin was recently identified in mice as the fourth member of the membrane-bound O-acyltransferases superfamily (MBOAT4) and named ghrelin-O-acyltransferase (GOAT). Only one report showed GOAT mRNA expression in ghrelin-expressing cells of the mouse stomach. We investigated the distribution of GOAT protein in peripheral tissues and co-expression with endocrine markers in the gastric mucosa using a custom-made anti-GOAT antibody. Tissues were collected from male Sprague-Dawley rats and C57BL/6 mice. Western blot revealed two immunoreactive bands in rat and mouse gastric corpus mucosal proteins, a 50 kDa band corresponding to the GOAT protein and a 100 kDa band likely corresponding to a dimer. Western blot also detected GOAT in the plasma and levels were strongly increased after 24-h fasting in mice and slightly in rats. GOAT-immunoreactive cells were located in the gastric corpus mucosa and the anterior pituitary gland, whereas other peripheral tissues of rats and mice examined were negative. In mice, GOAT-immunoreactive cells were mainly distributed throughout the middle portion of the oxyntic glands, whereas in rats they were localized mainly in the lower portion of the glands. Double labeling showed that 95+/-1% of GOAT-immunoreactive cells in mice co-labeled with ghrelin, whereas in rats only 56+/-4% of GOAT-positive cells showed co-expression of ghrelin. The remainder of the GOAT-immunopositive cells in rats co-expressed histidine decarboxylase (44+/-3%). No co-localization was observed with somatostatin in rats or mice. These data suggest species differences between rats and mice in gastric GOAT expression perhaps resulting in a different role of the MBOAT4 enzyme in the rat stomach. Detection of GOAT in the plasma raises the possibility that ghrelin octanoylation may occur in the circulation and the fasting-induced increase in GOAT may contribute to the increase of acylated ghrelin after fasting.