Institute for Infection and Immunity, St. George's University of London, London, United Kingdom.
Institute of Cellular Medicine, Newcastle University, Newcastle upon Tyne, United Kingdom.
Am J Physiol Cell Physiol. 2019 Nov 1;317(5):C983-C992. doi: 10.1152/ajpcell.00193.2019. Epub 2019 Aug 21.
The airway epithelium maintains differential glucose concentrations between the airway surface liquid (ASL, ~0.4 mM) and the blood/interstitium (5-6 mM), which is important for defense against infection. Glucose primarily moves from the blood to the ASL via paracellular movement, down its concentration gradient, across the tight junctions. However, there is evidence that glucose can move transcellularly across epithelial cells. Using a Förster resonance energy transfer sensor for glucose, we investigated intracellular glucose concentrations in airway epithelial cells and the role of hexokinases in regulating intracellular glucose concentrations in normoglycemic and hyperglycemic conditions. Our findings indicated that in airway epithelial cells (H441 or primary human bronchial epithelial cells) exposed to 5 mM glucose (normoglycemia), intracellular glucose concentration is in the micromolar range. Inhibition of facilitative glucose transporters (GLUTs) with cytochalasin B reduced intracellular glucose concentration. When cells were exposed to 15 mM glucose (hyperglycemia), intracellular glucose concentration was reduced. Airway cells expressed hexokinases I, II, and III. Inhibition with 3-bromopyruvate decreased hexokinase activity by 25% and elevated intracellular glucose concentration, but levels remained in the micromolar range. Exposure to hyperglycemia increased glycolysis, glycogen, and sorbitol. Thus, glucose enters the airway cell via GLUTs and is then rapidly processed by hexokinase-dependent and hexokinase-independent metabolic pathways to maintain low intracellular glucose concentrations. We propose that this prevents transcellular transport and aids the removal of glucose from the ASL and that the main route of entry for glucose into the ASL is via the paracellular pathway.
气道上皮细胞维持气道表面液（ASL，约 0.4mM）和血液/间质（5-6mM）之间的葡萄糖浓度差，这对于抵御感染很重要。葡萄糖主要通过细胞旁运动，沿着浓度梯度，穿过紧密连接，从血液中移动到 ASL。然而，有证据表明葡萄糖可以穿过上皮细胞进行跨细胞转运。我们使用葡萄糖的Förster 共振能量转移传感器，研究了气道上皮细胞中的细胞内葡萄糖浓度，以及己糖激酶在调节正常血糖和高血糖条件下细胞内葡萄糖浓度中的作用。我们的研究结果表明，在暴露于 5mM 葡萄糖（正常血糖）的气道上皮细胞（H441 或原代人支气管上皮细胞）中，细胞内葡萄糖浓度处于微摩尔范围。细胞松弛素 B 抑制易化葡萄糖转运蛋白（GLUTs）可降低细胞内葡萄糖浓度。当细胞暴露于 15mM 葡萄糖（高血糖）时，细胞内葡萄糖浓度降低。气道细胞表达己糖激酶 I、II 和 III。用 3-溴丙酮酸抑制己糖激酶活性降低了 25%，并升高了细胞内葡萄糖浓度，但仍处于微摩尔范围。暴露于高血糖会增加糖酵解、糖原和山梨醇。因此，葡萄糖通过 GLUTs 进入气道细胞，然后被己糖激酶依赖和非依赖的代谢途径快速处理，以维持低细胞内葡萄糖浓度。我们提出，这可以防止跨细胞转运，并有助于从 ASL 中去除葡萄糖，并且葡萄糖进入 ASL 的主要途径是通过细胞旁途径。
