Molecular regulation of intestinal calcium absorption

肠道钙吸收的分子调节

• 批准号: RGPIN-2015-05842
• 负责人: Alexander, RTodd
• 金额: $ 2.04万
• 依托单位: University of Alberta
• 依托单位国家: 加拿大
• 项目类别: Discovery Grants Program - Individual
• 财政年份: 2016
• 资助国家: 加拿大
• 起止时间: 2016-01-01 至 2017-12-31
• 项目状态: 已结题
• 来源: https://www.nserc-crsng.gc.ca/ase-oro/Details-Detailles_eng.asp?id=613783
• 关键词: Molecular; regulation; intestinal; calcium; absorption

Calcium (Ca2+) is central to a myriad of physiological processes. Consequently it is maintained within narrow limits in plasma. This is accomplished by dynamic interplay between intestinal absorption, deposition/resorption from bone and by filtration and subsequent reabsorption by the kidney. The first step is intestinal Ca2+ absorption, which occurs via one of two routes. Ca2+ is absorbed via an active transcellular (through the epithelial cell) pathway, or by a passive paracellular pathway (between epithelial cells). When adequate amounts of Ca2+ are present in the diet, passive paracellular absorption predominates. When, dietary Ca2+ is low, transcellular transport is important. This is mediated by a series of transport and carrier events (Fig 1). The duodenum is thought to be the primary site of active transcellular Ca2+ absorption, although emerging evidence, including from my research program, suggests a role for the proximal large bowel. The primary regulator of intestinal Ca2+ absorption is vitamin D, which increases active transintestinal Ca2+ transport. The kidney responds directly to extracellular Ca2+ via the calcium sensing receptor (CaSR). The intestine also expresses the CaSR, however, its role in regulating Ca2+ absorption is unknown. My research program in this area focuses on basic molecular mechanisms regulating intestinal Ca2+ absorption. I use murine models because they: i) permit the study of Ca2+ homeostasis within the context of the whole organism; ii) are readily amenable to pharmacologic and genetic approaches, including over-expression and knockdown of key players; and iii) permit the direct measurement of Ca2+ flux across intestinal epithelium in Ussing chambers where voltage and concentration gradients are tightly controlled,  enabling the interrogation of paracellular and transcellular pathways independently. The main objectives of my research program in intestinal Ca2+ absorption over the next 5 years are three-fold. 1) To determine the importance of proximal large bowel in Ca2+ absorption. We hypothesize the cecum is a site of Ca2+ salvaging minimizing Ca2+ loss. To this end, we will measure Ca2+ absorption across proximal large bowel preparations of mice: i) treated with calciotropic hormones or pharmacological regulators of Ca2+ homeostasis; ii) fed altered Ca2+-containing diets; and iii) genetically modified mice lacking components required for transcellular Ca2+ flux. 2) Using similar approaches we will delineate the molecules responsible for maintaining a positive Ca2+ balance early in life. 3) We will explore the direct effect of serum Ca2+ levels on intestinal Ca2+ absorption and the role of the CaSR in this process. To do so we will use pharmacological modulators of the CaSR and both knockdown and over-express the CaSR in the intestine of mice. These studies will address fundamental mechanisms mediating Ca2+ homeostasis.

钙(Ca~(2+))在多种生理过程中起着中心作用。因此，它在血浆中也保持在狭窄的范围内。这是通过肠道吸收、骨骼的沉积/吸收以及过滤和随后的肾脏重吸收之间的动态相互作用实现的。第一步是肠道对钙的吸收，这通常通过两种途径之一发生。Ca~(2+)通过主动的跨细胞途径(通过上皮细胞)吸收，或通过被动的细胞旁途径吸收(上皮细胞之间)。当饮食中存在足够数量的钙离子时，被动的细胞旁吸收占主导地位。当膳食中的钙离子含量较低时，跨细胞转运就很重要。这是由一系列运输和承运人事件调节的(图1)。十二指肠被认为是活跃的跨细胞钙吸收的主要部位，尽管包括我的研究项目在内的新证据表明，大肠近端也有作用。肠道钙吸收的主要调节剂是维生素D，它增加了主动的跨肠钙转运。肾脏通过钙感应受体(CaSR)直接对细胞外钙离子产生反应。肠道也表达CaSR，但其在调节钙吸收中的作用尚不清楚。 我在这方面的研究重点是调节肠道钙吸收的基本分子机制。我之所以使用小鼠模型，是因为它们：i)允许在整个有机体的背景下研究钙离子动态平衡；ii)易于采用药理学和遗传学方法，包括关键角色的过度表达和击倒；以及iii)允许在电压和浓度梯度受到严格控制的Ussing小室中直接测量跨肠上皮细胞的钙通量，从而能够独立地询问细胞旁和跨细胞途径。 我对未来5年肠道钙离子吸收的研究计划的主要目标有三个。1)确定近端大肠在钙吸收中的重要性。我们假设盲肠是一个挽救钙离子的部位，使钙离子损失最小化。为此，我们将测量近端大肠准备的小鼠对钙的吸收：i)用促钙激素或钙稳态的药物调节剂处理；ii)喂养改变的含钙饮食；iii)转基因小鼠缺乏跨细胞钙流动所需的成分。2)使用类似的方法，我们将描绘出在生命早期负责维持正钙平衡的分子。3)探讨血清钙离子水平对肠道钙吸收的直接影响，以及CaSR在这一过程中的作用。为了做到这一点，我们将使用CaSR的药物调节剂，并在小鼠的肠道中下调和过度表达CaSR。这些研究将解决介导钙稳态的基本机制。