Proceedings of The Physiological Society
AstraZeneca (2010) Proc Physiol Soc 18, C07 and PC07
Expression of 7TM chemo-sensors in isolated enteroendocrine cells
M. S. Engelstoft1, K. L. Egerod1, T. Schwartz1
1. Laboratory for Molecular Pharmacology, University of Copenhagen, Copenhagen, Denmark.
The secretion of peptide hormones from enteroendocrine cells is controlled by a mixture of different stimuli: neurotransmitters, neuropeptides, nutrients, metabolites and paracrine and luminal messengers - most of which act through 7TM, G protein coupled receptors (1). Enteroendocrine cells have been isolated and characterized based on genetic tagging using promoter elements for GLP-1, GIP and ghrelin (2-4). Here, enteroendocrine cells were isolated from transgenic mice expressing GFP under the control of regulatory elements for CCK and their expression of peptide precursors and 7TM receptors were characterized by QPCR. Immunohistochemistry demonstrated that the GFP expression was restricted to classical enteroendocrine cells which included CCK cells but which was not restricted to these. QPCR analysis of isolated FACS purified cells showed that the GFP labelled cells besides CCK also expressed for example somato-statin. A comprehensive QPCR analysis of 7TM receptor expression demonstrated that this mixed population of enteroendocrine cells - as expected - expressed a number of proposed chemosensors for nutrients and metabolites of which the short chain fatty acid receptor GPR41 was very prominent along with the long chain fatty acid receptors GPR40 and GPR120 as well as the proposed OEA receptor GPR119 were highly enriched as compared to the ordinary enterocytes. Certain, specific subtypes of monoaminergic receptors were clearly, highly enriched as compared to others from the same families - of these the 5HT5b receptor was an unexpected curiosity. Among the neuropeptides receptors the gastrin releasing peptide receptor (BB2) was - as expected - highly enriched and, for example a high level of the galanin R1 receptor expression was also observed. Among the receptors for paracrine substances a number of different somatostatin receptor subtypes were, for example, expressed in the enteroendocrine cells. A number of orphan receptors were also highly enriched in the enteroendocrine cells. It is concluded that even this rather mixed population of enteroendocrine cells express a surprisingly selective repertoire of 7TM receptors and receptor subtypes. Some of these have previously been shown also to be expressed in more pure populations of enteroendocrine cells (2-4). It remains to be shown which of these 7TM receptors will best serve as targets for novel therapeutics to function as regulators of the release of physiological mixtures of GI tract hormones.
Where applicable, experiments conform with Society ethical requirements