Department of Veterinary Biomedical Sciences, Western College of Veterinary Medicine, University of Saskatchewan, Saskatoon, Saskatchewan, Canada.
Department of Large Animal Clinical Sciences, Western College of Veterinary Medicine, University of Saskatchewan, Saskatoon, Saskatchewan, Canada.
Am J Physiol Gastrointest Liver Physiol. 2020 Feb 1;318(2):G288-G297. doi: 10.1152/ajpgi.00011.2019. Epub 2019 Nov 25.
The effect of and spirochetosis on Na transport was assessed in the colon to determine its contribution to diarrheal disease in pigs following experimental infection. Electrogenic and electroneutral Na absorption was assessed in Ussing chambers by radiolabeled Na flux and pharmacological inhibitory studies. Basal radiolabeled Na flux experiments revealed that mucosal-to-serosal flux () was significantly impaired in and -diseased pigs. Inhibition of epithelial sodium channel via amiloride did not significantly reduce electrogenic short-circuit current () in the proximal, apex, and distal colonic segments of diseased pigs over control pigs, suggesting that a loss of electroneutral Na absorption is responsible for diarrheal development. These findings were further supported by significant downregulation of Na/H exchanger (NHE1, NHE2, and NHE3) mRNA expression in the proximal, apex, and distal colonic segments paired with decreased protein expression of the critical NHE3 isoform. The decrease in NHE3 mRNA expression appears not to be attributed to the host's cytokine response as human IL-1α did not modify NHE3 mRNA expression in Caco-2 cells. However, a whole cell lysate significantly downregulated NHE3 mRNA expression and significantly increased p38 phosphorylation in Caco-2 cells. Together these findings provide a likely mechanism for the spirochete-induced malabsorptive diarrhea, indicated by a decrease in electroneutral Na absorption in the porcine colon due to ability to inhibit NHE3 transcription, resulting in diarrheal disease. This research demonstrates that diarrheal disease caused by two infectious spirochete spp. is a result of impaired electroneutral Na absorption via Na/H exchanger 3 (NHE3) in the porcine colon. Our findings suggest that the decrease in NHE3 mRNA and protein is not likely a result of the host's cytokine response. Rather, it appears that these two spp. directly inhibit the transcription and translation of NHE3, resulting in the development of diarrhea.
研究评估了密螺旋体和梨形鞭毛虫感染对猪结肠钠转运的影响，以确定其在感染后引起猪腹泻病的作用。通过放射性标记的钠通量和药物抑制研究，在 Ussing 室评估了电致和电中性钠吸收。基础放射性标记的钠通量实验表明，黏膜至浆膜的通量（）在密螺旋体和梨形鞭毛虫病猪中显著受损。阿米洛利抑制上皮钠通道（ENaC）不能显著降低病变猪的近端、顶端和远端结肠段的电致短路电流（），这表明电中性钠吸收的丧失是腹泻发展的原因。这些发现进一步得到了以下证据的支持：与对照猪相比，近端、顶端和远端结肠段的钠/氢交换器（NHE1、NHE2 和 NHE3）mRNA 表达显著下调，关键的 NHE3 同工型蛋白表达降低。NHE3 mRNA 表达的下调似乎不是由宿主的细胞因子反应引起的，因为人白细胞介素 1α（human IL-1α）不会改变 Caco-2 细胞中的 NHE3 mRNA 表达。然而，全细胞裂解物显著下调了 Caco-2 细胞中的 NHE3 mRNA 表达，并显著增加了 p38 磷酸化。这些发现共同提供了密螺旋体诱导的吸收不良性腹泻的可能机制，表明由于密螺旋体抑制 NHE3 转录的能力，猪结肠中的电中性钠吸收减少，导致腹泻病。这项研究表明，两种感染性密螺旋体引起的腹泻病是由于猪结肠中钠/氢交换器 3（NHE3）的电中性钠吸收受损所致。我们的研究结果表明，NHE3 mRNA 和蛋白的减少不太可能是宿主细胞因子反应的结果。相反，这两种密螺旋体似乎直接抑制 NHE3 的转录和翻译，导致腹泻的发生。
