Department of Veterinary Biomedical Sciences, Western College of Veterinary Medicine, University of Saskatchewan , Saskatoon , Canada.
Department of Large Animal Clinical Sciences, Western College of Veterinary Medicine, University of Saskatchewan , Saskatoon , Canada.
Am J Physiol Gastrointest Liver Physiol. 2019 Apr 1;316(4):G495-G508. doi: 10.1152/ajpgi.00348.2018. Epub 2019 Jan 10.
Brachyspira spp. cause diarrheal disease in multiple animal species by colonization of the colon, resulting in colitis, mucus induction, and disrupted ion transport. Unique to spirochete pathogenesis is the immense production of mucus, resulting in a niche mucin environment likely favoring spirochete colonization. Mucin rheological properties are heavily influenced by anionic secretion, and loss of secretory function has been implicated in diseases such as cystic fibrosis. Here, the effects on the agonist-induced electrogenic anionic secretory response by infectious colonic spirochete bacteria Brachyspira hyodysenteriae and Brachyspira hampsonii were assessed in the proximal, apex, and distal sections of colon in Ussing chambers. Activation of secretion via isoproterenol, carbachol, and forskolin/3-isobutyl-1-methylxanthine demonstrated a significantly decreased change in short-circuit current ( I) in Brachyspira-infected pigs in all sections. Tissue resistances did not account for this difference, rather, it was attributed to a decrease in anionic secretion as indicated by a decrease in bumetanide inhibitable I. Quantitative RT-PCR and Western blot analyses determined that the major anionic channels of the epithelium were downregulated in diarrheic pigs paired with altered mucin gene expression. The investigated cytokines were not responsible for the downregulation of anion channel gene transcripts. Although IL-1α was upregulated in all segments, it did not alter cystic fibrosis transmembrane conductance regulator (CFTR) mRNA expression in Caco-2 monolayers. However, a whole cell Brachyspira hampsonii lysate significantly reduced CFTR mRNA expression in Caco-2 monolayers. Together, these findings indicate that these two Brachyspira spp. may directly cause a decreased anionic secretory response in the porcine colon, supporting an altered mucin environment likely favoring spirochete colonization. NEW & NOTEWORTHY This research demonstrates for the first time that the niche mucin environment produced by two infectious spirochete spp. is supported by a decrease in the electrogenic anionic secretory response throughout the porcine colon. Our findings suggest that the host's cytokine response is not likely responsible for the decrease in anionic secretory function. Rather, it appears that Brachyspira spp. directly impede ion channel transcription and translation, potentially altering colonic mucin rheological properties, which may favor spirochete colonization.
短螺旋体属细菌引起多种动物的腹泻病，通过结肠定殖导致结肠炎、黏液诱导和离子转运紊乱。螺旋体发病机制的独特之处在于大量黏液的产生，导致黏液环境有利于螺旋体的定殖。黏蛋白流变学特性受阴离子分泌的强烈影响，分泌功能丧失与囊性纤维化等疾病有关。在这里，通过在 Ussing 室中评估感染性结肠螺旋体细菌短螺旋体属和哈姆普雷螺旋体在结肠近端、顶端和远端对激动剂诱导的电致阴离子分泌反应的影响。异丙肾上腺素、卡巴胆碱和 forskolin/3-异丁基-1-甲基黄嘌呤的激活显示，在所有节段中，感染短螺旋体属的猪的短电路电流（ I）变化明显减少。组织电阻不能解释这种差异，而是归因于阴离子分泌减少，如布美他尼抑制的 I 减少所示。定量 RT-PCR 和 Western blot 分析确定，在腹泻猪中上皮的主要阴离子通道下调与黏蛋白基因表达改变相关。研究的细胞因子不是阴离子通道基因转录物下调的原因。虽然所有节段的 IL-1α 均上调，但它没有改变 Caco-2 单层细胞中的囊性纤维化跨膜电导调节剂（CFTR）mRNA 表达。然而，整个细胞哈姆普雷螺旋体属的裂解物显著降低了 Caco-2 单层细胞中的 CFTR mRNA 表达。总之，这些发现表明这两种短螺旋体属可能直接导致猪结肠中阴离子分泌反应减少，支持可能有利于螺旋体定殖的改变的黏蛋白环境。
这项研究首次表明，两种感染性螺旋体属在猪结肠中产生的黏蛋白微环境是通过整个猪结肠中电致阴离子分泌反应的减少来支持的。我们的研究结果表明，宿主的细胞因子反应不太可能是阴离子分泌功能下降的原因。相反，短螺旋体属似乎直接阻碍离子通道的转录和翻译，可能改变结肠黏蛋白的流变学特性，从而有利于螺旋体的定殖。
