Physiology/pathophysiology of intestinal vitC uptake: Cell/molecular mechanisms

 说明(申请人提供)：维生素C是正常人体健康和福祉不可或缺的微量营养素。维生素C缺乏会导致多种临床异常。这种维生素是一种有效的抗氧化剂，也是几种酶的辅因子，细胞内水平较低会导致氧化应激，这是许多人类疾病的驱动因素。因此，旨在优化维生素C体内整体动态平衡的研究非常重要。人类已经失去了内源性合成维生素C的能力，必须通过肠道吸收才能获得。 肠道吸收过程涉及人类钠依赖的维生素C转运体1和2(hSVCT1和hSVCT2)，其中hSVCT1仅在极化的肠细胞的顶膜上表达，而hSVCT2定位于基底侧。这项建议的目的是继续我们对肠道维生素C摄取过程的分子生理学/细胞生物学的研究，并解决其病理生理学的具体方面，以及确定外部/内部因素对摄取过程的影响。我们的新的初步研究表明，微RNA和表观遗传学机制(S)参与了hSVCT1表达的调节，发现了新的hSVCT1相互作用伙伴，并显示出暴露于特定的肠道病原体、促炎细胞因子和细菌内毒素时，维生素C的摄取显著抑制。基于这些发现，我们的工作假设是：i)microRNA和表观遗传机制(S)调节SVCT1的表达和功能；ii)hSVCT1具有相互作用的伙伴，影响其生理/细胞生物学；以及iii) 暴露于肠道病原体、促炎细胞因子和细菌内毒素会显著抑制肠道维生素C的摄取。提出了三个具体的目标来检验这些假说，并将利用最先进的细胞/分子方法。这些研究的结果应该提供关于正常生理条件下肠道维生素C吸收过程的有价值的信息，以及这一过程如何受到特定的病理生理因素的影响。这最终应该有助于我们设计有效的策略，以优化正常的维生素C体内平衡，特别是在缺乏/次优水平的情况下。

 DESCRIPTION (provided by applicant): Vitamin C is an indispensable micronutrient for normal human health and well-being. Vitamin C deficiency leads to a variety of clinical abnormalities. The vitamin acts as a potent antioxidant and a cofactor for several enzymes, with low intracellular levels causing oxidative stress, a driver for many human diseases. Therefore, studies designed to optimize overall vitamin C body homeostasis are important. Humans have lost the ability to synthesis vitamin C endogenously, and must obtain it via intestinal absorption. The intestinal absorption process involves the human sodium-dependent vitamin C transporters-1 & 2 (hSVCT1& hSVCT2), where hSVCT1 is exclusively expressed at the apical membrane of the polarized enterocytes whereas hSVCT2 is localized basolaterally. The objectives of this proposal are to continue our investigations into the molecular physiology/cell biology of intestina vitamin C uptake process, and to address specific aspects of its pathophysiology as well as to determine the effect of external/internal factors on the uptake process. Our new preliminary studies suggest the involvement of microRNA and epigenetic mechanism(s) in the regulation of hSVCT1 expression, identified putative novel hSVCT1 interacting partners, and show a significant inhibition in vitamin C uptake upon exposure to specific enteric pathogens (EPEC and ETEC), pro-inflammatory cytokines, and to bacterial LPS. Based on these findings, our working hypotheses are: i) microRNA and epigenetic mechanism(s) regulate SVCT1 expression and function; ii) hSVCT1 has interacting partners that affect its physiology/cell biology; and iii) exposure to enteric pathogens, pro- inflammatory cytokines, and to bacterial LPS leads to a significant inhibition in intestinal vitamin C uptake. Three specific aims are proposed to test these hypotheses and will utilize state-of- the-art cell/molecular approaches. Results of these investigations should provide valuable information regarding the intestinal vitamin C absorption process under normal physiological conditions, and how this event is affected by specific pathophysiological factors. This should ultimately help us in designing effective strategies to optimize normal vitamin C body homeostasis, especially in conditions of deficiency/sub-optimal levels.