Department of Gastroenterology, Hannover Medical School, Hannover, Germany.
Inflamm Bowel Dis. 2010 Jul;16(7):1149-61. doi: 10.1002/ibd.21183.
A major causative factor of diarrhea in ulcerative colitis (UC) patients is the loss of Na(+) absorptive capacity of the inflamed colonic mucosa. Potential contributing mechanisms include reduced driving force for active transport, and impaired expression, mislocalization, or defective transport function of Na(+) absorptive proteins. We therefore studied the expression, brush border membrane (BBM) localization, and transport capacity of the major intestinal Na(+) absorptive protein, the Na(+)/H(+) exchanger isoform 3 (NHE3) in biopsies from UC patients.
In UC and control biopsies, inflammation was graded histologically, NHE3, tumor necrosis factor alpha (TNF-alpha), villin, as well as other housekeeping genes were analyzed by quantitative real-time polymerase chain reaction (PCR), BBM localization of NHE3 determined by immunohistochemistry, and confocal microscopy. Na(+) absorptive capacity was assessed by (22)Na(+) isotope fluxes and NHE3 transport activity measured microfluorometrically in BCECF-loaded surface colonocytes within isolated crypts.
In mildly, moderately, and severely inflamed sigmoid colon of UC patients, neither NHE3 mRNA expression nor the abundance of NHE3 in the BBM was significantly altered compared to other structural components of the BBM. However, Na(+) absorption was strongly reduced by approximately 80% and acid-activated NHE3 transport activity was significantly decreased in the surface cells of sigmoid colonic crypts even in moderately inflamed mucosa.
In the colonic mucosa of patients with active UC, NHE3 transport capacity was found significantly decreased despite correct NHE3 location and abundance in the brush border, independent of current treatment. These findings suggest functional NHE3 transport as a novel factor for inflammatory diarrhea in UC patients.
溃疡性结肠炎（UC）患者腹泻的一个主要致病因素是炎症结肠黏膜丧失 Na(+)吸收能力。潜在的致病机制包括主动转运驱动力降低，以及 Na(+)吸收蛋白的表达、定位或转运功能受损。因此，我们研究了 UC 患者活检标本中主要肠 Na(+)吸收蛋白 Na(+)/H(+)交换体 3（NHE3）的表达、刷状缘膜（BBM）定位和转运能力。
在 UC 和对照活检标本中，通过组织学分级炎症，采用实时定量聚合酶链反应（PCR）分析 NHE3、肿瘤坏死因子-α（TNF-α）、绒毛蛋白以及其他管家基因，用免疫组织化学法测定 NHE3 的 BBM 定位，并用共聚焦显微镜观察。通过（22）Na(+)同位素通量和 BCECF 加载的分离隐窝内表面结肠细胞中 NHE3 转运活性的微荧光测量评估 Na(+)吸收能力。
在 UC 患者轻度、中度和重度炎症的乙状结肠中，与 BBM 的其他结构成分相比，NHE3 mRNA 表达或 NHE3 在 BBM 中的丰度均无明显改变。然而，即使在中度炎症的黏膜中，Na(+)吸收也明显降低了约 80%，并且表面细胞中的酸激活 NHE3 转运活性显著降低。
在活动期 UC 患者的结肠黏膜中，尽管 NHE3 在刷状缘的位置和丰度正确，但发现 NHE3 转运能力显著降低，这与当前的治疗无关。这些发现表明，NHE3 转运功能是 UC 患者炎症性腹泻的一个新的因素。
