钾通道亚型对肠道物质吸收和转运的调节及其在肥胖发生中的作用

Obesity is associated with a high risk of many diseases, such as cardiovascular diseases, diabetes mellitus and cancers. Although obesity is a multiple factors-induced metabolic disease, it is mainly resulted from an unbalance between energy intake and expenditure. Energy intake depends on the amount of nutrients absorbed by the brush border membrane of small intestinal epithelial cells (IEC) and on the amount of nutrients transported by mesenteric capillaries and lacteals. Excessive intake of glucose and fatty acid is the major source for accumulated fat. The Na+-dependent uptake of glucose and fatty acid into IEC is driven by the transmembrane gradient and membrane potential (Em). Since Em is primarily determined by plasmalemmal voltage-gated K+ (Kv) channels, inhibition of Kv channels in IEC would induce membrane depolarization and inhibit the nutrient absorption by reducing the driving force for Na+. Moreover, food intake increases intestinal mucosal blood flow to facilitate transportation of absorbed nutrients, which is controlled by mesenteric vascular resistance. Inhibition of Kv channels in mesenteric artery smooth muscle cells (MASMC) would induce membrane depolarization, increase mesenteric vascular resistance, and ultimately limit transportation of absorbed nutrients to other tissues for storage. We recently identified multiple functional Kv channel isoforms in animal IEC and MASMC. Blockade of these channels induced membrane depolarization, attenuated Na+-dependent nutrient uptake in small intestine, and caused mesenteric vasoconstriction. Furthermore, ingestion of Kv channel blocker significantly reduced the weight gain in mice. Therefore, we hypothesize that altered expression and activity of Kv channels in IEC and MASMC may be associated with the development of obesity. We will test the hypothesis by focusing on three specific aims: 1) To characterize the electrophysiological and pharmacological properties of Kv channels and isoforms in IEC and to specify their molecular identity, localization and role in mediating Na+-dependent nutrient absorption, 2) To determine whether Kv channels in MASMC regulate mesenteric vascular resistance and nutrient transportation, and 3) To determine whether blockade of Kv channels inhibits weight gain in animals, and to elucidate the molecular mechanisms of intestinal Kv channels associated with obesity. Successful execution of this project will greatly enhance our knowledge about the expression, localization and function of Kv channel isoforms in IEC and MASMC. Pharmacological intervention designed to minimize the intestinal absorption and circulatory transportation of ingested nutrients by blocking Kv channels would be an effective strategy for obesity prevention or therapy.

肥胖可诱导严重机体疾病。尽管肥胖是多因素代谢性疾病,但能量摄入过多或消耗减少是导致肥胖的主要因素。能量摄入依赖于小肠上皮的吸收功能及肠系膜血管的转运功能,并受细胞膜钾通道的调节。阻断钾通道将引起细胞膜去极化而减少营养物质在小肠上皮的电源依赖性吸收，并导致肠系膜血管平滑肌收缩和物质转运的减慢。而钾通道在物质的吸收和转运中的作用被长期忽视,人们对此所知甚少。我们在近期的初步动物实验中发现,阻断钾通道亚型可选择性减少小鼠小肠对营养物质的吸收和转运,并使其体重与对照组相比明显减轻。因此本课题将基于我们的初步动物实验结果,应用动物细胞、组织及整体实验,和人体组织、细胞及现代分子生物学和电生理学技术, 来全面阐明钾通道在调节肠道营养物质的吸收和转运及其在肥胖发生中的作用。本项目有望发现新的抗肥胖机制,从而发展选择性抑制能量摄取过多而较少影响其它正常营养成份摄入的减肥新药。

能量摄入过多或消耗减少是导致肥胖的主要原因。能量摄入依赖于小肠上皮的吸收功能及肠系膜血管的转运功能，并受细胞膜电位和钾离子通道的调节。而钾通道在物质的吸收和转运中的作用被长期忽视，人们对此所知甚少。因此，本课题基于我们的前期预实验结果，应用动物细胞、组织和整体实验，以及现代细胞及分子生物学和电生理学技术，研究钾通道在调节肠道营养物质的吸收和转运及其在肥胖发生中的作用。我们阐明了小肠黏膜细胞上钾通道亚型Kv1.1 及Kv1.3，对电源依赖性物质吸收过程的调节作用及其分子机制。发现钾通道亚型阻断剂，不影响正常小鼠的体重及血糖，却能降低糖尿病肥胖的体重增长和高血糖，具有潜在的应用前景。我们还阐明了吸收入血后的葡萄糖产生的高渗透压，主要通过激动血管内皮细胞膜上的K+通道亚型SKca和IKca引起内皮细胞依赖的超极化（EDH），并通过激活细胞膜上的Na+-K+ ATP酶，导致血管平滑肌细胞膜的超极化反应，进而抑制平滑肌细胞膜上的电压依赖性的钙通道 (VGCC)，使细胞外Ca2+内流减少最终使血管舒张。因此，我们从细胞膜离子通道和转换器的角度，发现了新的抗肥胖和抗糖尿病机制，从而为发展选择性抑制能量摄取过多，但又较少影响其它正常营养成分摄入的减肥和抗糖尿病的新药研发，提供了潜在的药物治疗靶点。