Comparison of Human and Murine Enteroendocrine Cells by Transcriptomic and Peptidomic Profiling.

Enteroendocrine cells (EECs) produce hormones such as glucagon-like peptide 1 and peptide YY that regulate food absorption, insulin secretion, and appetite. Based on the success of glucagon-like peptide 1-based therapies for type 2 diabetes and obesity, EECs are themselves the focus of drug discovery programs 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 a 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 G-protein-coupled receptors previously found to play roles in postprandial nutrient detection. With liquid chromatography-tandem mass spectrometry, we profiled the gradients of peptide hormones along the human and mouse gut, including their sequences and posttranslational modifications. The transcriptomic and peptidomic profiles of human and mouse EECs and cross-species comparison will be valuable tools for drug discovery programs and for understanding human metabolism and the endocrine impacts of bariatric surgery.

CtBP and associated LSD1 are required for transcriptional activation by NeuroD1 in gastrointestinal endocrine cells.

Gene expression programs required for differentiation depend on both DNA-bound transcription factors and surrounding histone modifications. Expression of the basic helix-loop-helix (bHLH) protein NeuroD1 is restricted to endocrine cells in the gastrointestinal (GI) tract, where it is important for endocrine differentiation. RREB1 (RAS-responsive element binding protein 1), identified as a component of the CtBP corepressor complex, binds to nearby DNA elements to associate with NeuroD and potentiate transcription of a NeuroD1 target gene. Transcriptional activation by RREB1 depends on recruitment of CtBP with its associated proteins, including LSD1, through its PXDLS motifs. The mechanism of transcriptional activation by CtBP has not been previously characterized. Here we found that activation was dependent on the histone H3 lysine 9 (H3K9) demethylase activity of LSD1, which removes repressive methyl marks from dimethylated H3K9 (H3K9Me2), to facilitate subsequent H3K9 acetylation by the NeuroD1-associated histone acetyltransferase, P300/CBP-associated factor (PCAF). The secretin, ß-glucokinase, insulin I, and insulin II genes, four known direct targets of NeuroD1 in intestinal and pancreatic endocrine cells, all show similar promoter occupancy by CtBP-associated proteins and PCAF, with acetylation of H3K9. This work may indicate a mechanism for selective regulation of transcription by CtBP and LSD1 involving their association with specific transcription factors and cofactors to drive tissue-specific transcription.