Bile acids are well-recognized stimuli of glucagon-like peptide-1 (GLP-1) secretion. This action has been attributed to activation of the G protein–coupled bile acid receptor GPBAR1 (TGR5), although other potential bile acid sensors include the nuclear farnesoid receptor and the apical sodium-coupled bile acid transporter ASBT. The aim of this study was to identify pathways important for GLP-1 release and to determine whether bile acids target their receptors on GLP-1–secreting L-cells from the apical or basolateral compartment. Using transgenic mice expressing fluorescent sensors specifically in L-cells, we observed that taurodeoxycholate (TDCA) and taurolithocholate (TLCA) increased intracellular cAMP and Ca2+. In primary intestinal cultures, TDCA was a more potent GLP-1 secretagogue than taurocholate (TCA) and TLCA, correlating with a stronger Ca2+ response to TDCA. Using small-volume Ussing chambers optimized for measuring GLP-1 secretion, we found that both a GPBAR1 agonist and TDCA stimulated GLP-1 release better when applied from the basolateral than from the luminal direction and that luminal TDCA was ineffective when intestinal tissue was pretreated with an ASBT inhibitor. ASBT inhibition had no significant effect in nonpolarized primary cultures. Studies in the perfused rat gut confirmed that vascularly administered TDCA was more effective than luminal TDCA. Intestinal primary cultures and Ussing chamber–mounted tissues from GPBAR1-knockout mice did not secrete GLP-1 in response to either TLCA or TDCA. We conclude that the action of bile acids on GLP-1 secretion is predominantly mediated by GPBAR1 located on the basolateral L-cell membrane, suggesting that stimulation of gut hormone secretion may include postabsorptive mechanisms.

The prion protein (PrP) binds copper and has antioxidant activity enhancing the survival of neurones in culture. The ability of the PrP to bind other cations was tested and it was found that only manganese could substitute for copper. Although initially manganeseloaded PrP exhibited similar structure and activity to copper-loaded PrP, after aging, manganese-loaded PrP became proteinase resistant and lost function. It was also found that manganese could be incorporated into PrP expressed by astrocytes and that this PrP was partially proteinase resistant. These results show that it is possible to generate proteinase-resistant PrP from cells and suggest a possible mechanism for the formation of the scrapie isoform of the PrP as generated in sporadic prion disease.

Enteroendocrine cells (EECs) produce hormones such as glucagon-like peptide-1 (GLP-1) and peptideYY (PYY) that regulate food absorption, insulin secretion and appetite. Based on the success of GLP-1 based therapies for type 2 diabetes and obesity, EECs are themselves the focus of drug discovery programmes to enhance gut hormone secretion. The aim of this study was to identify the transcriptome and peptidome of human EECs, and to provide a cross-species comparison between humans and mice. By RNA sequencing of human EECs purified by flow cytometry after cell fixation and staining, we present a first transcriptomic analysis of human EEC populations, and demonstrate strong correlation with murine counterparts. RNA sequencing was deep enough to enable identification of low abundance transcripts such as G-protein coupled receptors and ion channels, revealing expression in human EECs of GPCRs previously found to play roles in post-prandial nutrient detection. By liquid chromatography mass spectrometry (LC-MS) we profiled the gradients of peptide hormones along the human and mouse gut, including their sequences and post-translational modifications. The transcriptomic and peptidomic profiles of human and mouse EECs, and cross-species comparison, will be valuable tools for drug discovery programmes and for understanding human metabolism and the endocrine impacts of bariatric surgery.