Regulation of a Novel Intestinal NHE Isoform (NHE8)

新型肠道 NHE 亚型 (NHE8) 的调节

• 批准号: 7146729
• 负责人: Fayez Khalaf Ghishan
• 金额: $ 30.96万
• 依托单位: UNIVERSITY OF ARIZONA
• 依托单位国家: 美国
• 财政年份: 2006
• 资助国家: 美国
• 起止时间: 2006-08-01 至 2011-07-31
• 项目状态: 已结题
• 来源: https://reporter.nih.gov/project-details/7146729
• 关键词: age difference; epidermal growth factor; gastrointestinal absorption /transport; genetic transcription; genetically modified animals; glucocorticoids; laboratory mouse; laboratory rat; protein isoforms; protein structure function; second messengers; sodium hydrogen exchanger; tumor necrosis factor alpha

DESCRIPTION (provided by applicant): The gastrointestinal tract undergoes significant morphological and functional changes during maturation to meet the increasing demands for nutrient transport. The major function of the gastrointestinal tract is to transport nutrients and fluids to maintain adequate electrolyte homeostasis. The gastrointestinal tract of a 1- year-old infant handles approximately 3 liters of fluid per day, resulting in only 50 grams of daily stool output, indicating the complex transport capacity of the gastrointestinal tract during early life. Our previous studies have shown that expression of the intestinal sodium/hydrogen exchangers (NHE2 and NHE3) is low during early life, and increases significantly with maturation. Moreover, the phenotypes of knockout mouse models of NHE2 and NHE3 show minimal perturbations in fluid and electrolyte balance, indicating the presence of another NHE(s) during this period of maturation. Our study demonstrates that NHE8 is expressed in the apical membrane of epithelial cells in the gastrointestinal tract, at high levels during early life, and decreasing into adulthood. This localization is similar to the finding that NHE8 is expressed apically in the renal epithelium. Therefore, the proposed studies are designed to test the hypothesis that NHE8 represents a unique, novel NHE, which is important in electrolyte homeostasis during the suckling and weaning periods of development. We plan to explore five specific aims to determine the physiological role of NHE8 and its regulation in physiological and pathological conditions. Specific Aim 1 is designed to characterize functional and pharmacological properties of NHE8. Our second Specific Aim is designed to determine NHE8 expression along the cephalo-caudal and crypt-villus axes in the rat intestine and in NHE2/3 knock-out mice. We will also seek to further strengthen our supposition that NHE8 is expressed on the brush-border membrane of intestinal epithelial cells. In Specific Aim 3, we plan to investigate the transcriptional mechanisms of NHE8 regulation under basal conditions and as regulated by EGF and glucocorticoids. Our preliminary data show that NHE8 gene expression is regulated by these physiological effectors. EGF and glucocorticoids are important for functional maturation of the gastrointestinal tract, and have been shown to regulate intestinal NHEs. Furthermore, known intestinal NHEs are regulated during inflammation and we plan to follow up on our preliminary observation that NHE8 is regulated during endotoxemia (e.g. LPS administration) and by TNFa exposure. Therefore our Specific Aim 4 is designed to determine the mechanism responsible for acute and chronic effects of TNFa on NHES protein and gene expression. Specific Aim 5 is designed to define the mechanisms involved in the acute regulation of NHES by second messengers (cyclic nucleotides and intracellular calcium). Overall, the proposed studies are likely to have a significant impact on our understanding of the molecular mechanisms controlling electroneutral NaCI absorption in early life and its relationship to various perturbations of intestinal homeostasis.

描述(申请人提供)：胃肠道在成熟过程中经历了显著的形态和功能变化，以满足日益增长的营养运输需求。胃肠道的主要功能是运输营养物质和液体，以维持足够的电解质平衡。一岁婴儿的胃肠道每天处理大约3升液体，导致每天的粪便产量只有50克，这表明早期生命中胃肠道的复杂运输能力。我们以前的研究表明，肠道钠氢交换器(NHE2和NHE3)在生命早期的表达水平很低，随着生命的成熟表达显著增加。此外，NHE2和NHE3基因敲除小鼠模型的表型显示出液体和电解质平衡的微小扰动，表明在这一成熟期存在另一种NHE(S)。我们的研究表明，NHE8在胃肠道上皮细胞的顶膜中表达，在生命早期高水平表达，并在成年后逐渐减少。这一定位类似于NHE8在肾上皮细胞顶端表达的发现。因此，建议的研究旨在检验NHE8代表一种独特的、新颖的NHE的假设，NHE8在哺乳期和断奶期的电解质平衡中非常重要。我们计划探索五个特定的目标来确定NHE8的生理作用及其在生理和病理条件下的调节。具体目标1旨在表征NHE8的功能和药理特性。我们的第二个特定目标是确定NHE8在大鼠肠道和NHE2/3基因敲除小鼠的头尾和隐窝绒毛轴线上的表达。我们还将寻求进一步加强我们的假设，即NHE8表达在肠上皮细胞的刷状缘膜上。在具体目标3中，我们计划研究NHE8在基础条件下以及在EGF和糖皮质激素调控下的转录机制。我们的初步数据表明，NHE8基因的表达受这些生理效应因子的调控。EGF和糖皮质激素对胃肠道功能成熟很重要，已被证明对肠道NHEs有调节作用。此外，已知的肠道NHEs在炎症过程中受到调节，我们计划跟进我们的初步观察，即NHE8在内毒素血症(例如，内毒素注射)和TNFa暴露期间受到调节。因此，我们的特定目标4旨在确定TNFa对NHES蛋白和基因表达的急性和慢性影响的机制。具体目标5旨在确定第二信使(环核苷酸和细胞内钙)对NHES的急性调节机制。总体而言，拟议的研究可能会对我们理解早期生命中控制电子中性粒细胞NaCI吸收的分子机制及其与肠道内环境平衡的各种扰动的关系产生重大影响。