Physiology and regulation of T2R bitter taste receptors in enteroendocrine cells

肠内分泌细胞T2R苦味受体的生理学和调节

• 批准号: 8820259
• 负责人: Timothy F Osborne
• 金额: $ 42.41万
• 依托单位: SANFORD BURNHAM PREBYS MEDICAL DISCOVERY INSTITUTE
• 依托单位国家: 美国
• 财政年份: 2013
• 资助国家: 美国
• 起止时间: 2013-04-01 至 2016-03-31
• 项目状态: 已结题
• 来源: https://reporter.nih.gov/project-details/8820259
• 关键词: ABCB1 gene; Accidents; Address; Adopted; Agonist; Animals; Area; Biological Assay; Cell Line; Cell Surface Receptors; Cells; Cholecystokinin; Cholesterol; Coupled; Deglutition; Diet; Dietary Cholesterol; Discrimination; Eating; Enterocytes; Enteroendocrine Cell; Enzyme-Linked Immunosorbent Assay; Epithelium; Exons; Family; Food; Gastrins; Gastrointestinal tract structure; Genes; Genetic; Genetic Models; Health; Hepatic; Hormones; Human; In Situ; Individual; Ingestion; Intestinal Secretions; Intestines; Islets of Langerhans; Knock-out; Lovastatin; Lung; Mammals; Measures; Mediating; Methods; Molecular; Monitor; Mus; Mutant Strains Mice; Mutation; Oral; Oral cavity; Organ Culture Techniques; Pancreas; Pathway interactions; Peptides; Physiological; Physiology; Plants; Poison; Polypeptide Hormones; Proteins; Publications; Receptor Cell; Receptor Gene; Receptor Signaling; Regulation; Relative (related person); Rodent; Role; SRE-2 binding protein; Savory; Signal Transduction; Small Intestines; Source; Stomach; Surface; TRPM5 gene; Taste Buds; Taste Perception; Taste aversion; Testing; Tongue; Toxin; Work; absorption; airway epithelium; base; cell motility; cholesterol absorption; design; detection of nutrient; ezetimibe; feeding; glucagon-like peptide; glucagon-like peptide 1; in vivo; monomer; mouse model; novel; oral tissue; peptide hormone; prevent; promoter; receptor; receptor coupling; response; small molecule; sweet receptor; sweet taste perception; transcription factor; uptake

DESCRIPTION (provided by applicant): Mammals recognize bitter constituents in food through individual small "bitter" molecule agonists stimulation of individual cell surface receptors. These taste 2 receptors (T2Rs) are encoded by a family of single-exon g- protein coupled receptor (GPCR) genes and are predominantly expressed in taste receptor cells (TRCs) on the surface of the tongue and surrounding oral tissue. There is a lone GPCR involved in the majority of sweet taste sensing which is a heterodimer of Taste 1 Receptor (T1R) monomers T1R2 and T1R3. The single sweet and the entire family of bitter T2 receptors are also expressed in areas outside of the oral cavity including the lung, pancreas, and small intestine. Their function in the tongue is obviously to allow taste discrimination between differen potential food sources, however, the physiologic role for taste receptors outside of the oral cavity is not intuitively obvious. In recent publications, we showed that activation of intestinal T2R signaling leads to an increase in secretion of polypeptide hormones cholecystokinin (CCK) and glucagon-like-peptide-1 (GLP-1) from enteroendocrine cells and two major actions of CCK are to limit food intake and slow gastric motility. These results suggest intestinal T2Rs may limit absorption of bitter and potentially toxic molecules that are ingested despite the taste aversion in the mouth. We also showed that intestinal expression and activity of the T2Rs is regulated by the sterol regulatory element binding protein -2 (SREBP-2) transcription factor, which is induced when cellular cholesterol levels are low and activates genes required for accumulating new cell cholesterol. Plant enriched diets are both low in cholesterol and have a higher proportion of bitter tasting and potentially toxic substances relative to diets rich in cholesterol-laden animal flesh. Thus, induction of T2R activity through SREBP-2 on low-cholesterol plant diets provides a mechanism to "sensitize" the gut to the presence of potentially toxic molecules to limit their absorption through CCK dependent suppression of both gut motility and food in take. It should be noted that CCK and the gut peptide hormone gastrin have identical carboxyl termini and the ELISA we used in our early studies detects both hormones with similar sensitivity. Thus, gastrin may be the relevant hormone that is induced by T2R signaling in the gut and our current project is designed to address this key issue. We also showed CCK/gastrin increases expression and activity of the ABCB1 efflux transporter, which is known to prevent cellular uptake of a wide range of toxic organic small molecules. This provides a more active mechanism to limit absorption of toxic molecules consumed during a meal or by accident. Taken together, these studies provide a molecular mechanism connecting nutrient sensing with protection from toxin ingestion. The current proposal combines physiologic studies in select mouse models that have mutations in genes encoding critical proteins of the nutrient sensing and toxin efflux pathways to rigorously test the mechanism. We also propose to adopt a novel in situ assay with isolated small intestine to monitor the connection between T2R signaling and toxin efflux directly.

描述(申请人提供)：哺乳动物通过个体小的“苦”分子激动剂刺激个体细胞表面受体来识别食物中的苦味成分。这些味觉2受体(T2Rs)由一个单外显子g蛋白偶联受体(GPCR)基因家族编码，主要表达在舌面和周围口腔组织的味觉受体细胞(TrCs)中。在大多数甜味感受器中都有一个GPCRs，它是味觉1受体(Taste1 Receptor，T1R)单体T1R2和T1R3的异源二聚体。单一的甜味和整个苦味T2受体家族也在口腔以外的区域表达，包括肺、胰腺和小肠。它们在舌头中的功能显然是允许不同潜在食物来源之间的味觉辨别，然而，口腔外味觉感受器的生理作用并不直观。在最近的文献中，我们发现肠道T2R信号的激活导致肠内分泌细胞分泌多肽激素CCK和GLP-1的增加，CCK的两个主要作用是限制摄食量和减慢胃运动。这些结果表明，肠道T2Rs可能会限制 吸收苦味和潜在的有毒分子，尽管口中有厌恶的味道，但仍被摄取。我们还发现，肠道中T2Rs的表达和活性受到固醇调节元件结合蛋白-2(SREBP-2)转录因子的调节，该转录因子在细胞胆固醇水平较低时被诱导，并激活积累新细胞胆固醇所需的基因。与富含胆固醇的动物肉相比，植物强化饮食的胆固醇含量低，苦味和潜在有毒物质的比例更高。因此，在低胆固醇植物饲料中通过SREBP-2诱导T2R活性提供了一种机制，使肠道对潜在有毒分子的存在“敏感”，通过依赖CCK抑制肠道运动和食物摄取来限制它们的吸收。应该注意的是，CCK和胃泌素具有相同的羧基末端，我们在早期研究中使用的ELISA法检测这两种激素具有相似的敏感性。因此，胃泌素可能是肠道中T2R信号诱导的相关激素，我们目前的项目就是为了解决这一关键问题。我们还发现CCK/胃泌素增加了ABCB1外排转运蛋白的表达和活性，众所周知，这可以阻止细胞摄取广泛的有毒有机小分子。这提供了一种更主动的机制，以限制在用餐期间或意外摄入的有毒分子的吸收。综上所述，这些研究提供了一种将营养感知与防止毒素摄入联系起来的分子机制。目前的建议结合了在选定的小鼠模型中进行的生理学研究，这些模型编码营养感知和毒素外流途径的关键蛋白质的基因发生突变，以严格测试这一机制。我们还建议采用一种新的分离小肠的原位检测方法来直接监测T2R信号与毒素外流之间的联系。