Impact of Olfr78 Knockout on enteroendocrine cells and on colon homeostasis [scRNA-seq]

The gastrointestinal epithelium constitutes a chemosensory system for microbiota-derived metabolites such as Short Chain Fatty Acids (SCFA). In this study, we investigated spatial distribution of Olfr78, one of the SCFA receptors, in the mouse intestine and studied the transcriptome of colon enteroendocrine cells expressing Olfr78. The receptor is principally detected in the enterochromaffin and L subtypes in the proximal and distal colon, respectively. Using the Olfr78-GFP and VilCre/Olfr78flox transgenic mouse lines, we reveal that loss of epithelial Olfr78 results in impaired enterochromaffin cell differentiation, blocking cells in an undefined secretory lineage state. This is accompanied by reduced defense response to bacteria in colon crypts and mild dysbiosis. Using organoid cultures, we further show that maintenance of enterochromaffin cells involves activation of the Olfr78 receptor via the SCFA ligand acetate. Altogether, this work provides evidence that Olfr78 contributes to colon homeostasis by regulating enterochromaffin cell differentiation. We digested mouse colon from one WT and one Olfr78-GFP KO mice to obtain isolated mesenchymal and epithelial cells for the single-cell RNA sequencing.胃肠道上皮是一套感知微生物群衍生代谢物的化学感应系统，其感知的代谢物包括短链脂肪酸（Short Chain Fatty Acids，SCFA）。本研究针对短链脂肪酸受体之一的Olfr78在小鼠肠道内的空间分布展开探究，并对表达Olfr78的结肠肠内分泌细胞的转录组进行了分析。该受体主要分别于近端结肠的肠嗜铬细胞亚型与远端结肠的L细胞亚型中被检测到。本研究借助Olfr78-GFP与VilCre/Olfr78flox转基因小鼠品系，证实上皮细胞Olfr78的缺失会导致肠嗜铬细胞分化受损，使细胞阻滞于未明确的分泌谱系状态中。该现象同时伴随结肠隐窝对细菌的防御应答减弱，以及轻度菌群失调。通过类器官培养实验，本研究进一步证实，肠嗜铬细胞的维持依赖于Olfr78受体与短链脂肪酸配体乙酸盐的结合激活。综上，本研究证实Olfr78可通过调控肠嗜铬细胞分化，参与维持结肠稳态。本研究通过分离1只野生型（Wild Type，WT）与1只Olfr78-GFP基因敲除（Knock Out，KO）小鼠的结肠组织，获取了分离得到的间充质细胞与上皮细胞，用于单细胞RNA测序实验。