Department of Biomedical and Clinical Sciences [BKV), Linköping University, Linköping, Sweden.
Division of Gastroenterology and Hepatology, Department of Biomedical and Clinical Sciences [BKV), Faculty of Health Science, Linköpings University, Linköping, Sweden.
J Crohns Colitis. 2020 Jul 30;14(7):962-973. doi: 10.1093/ecco-jcc/jjaa020.
Diarrhoea is a common, debilitating symptom of gastrointestinal disorders. Pathomechanisms probably involve defects in trans-epithelial water transport, but the role of aquaporin [AQP] family water channels in diarrhoea-predominant diseases is unknown. We investigated the involvement of AQPs in the pathobiology of collagenous colitis [CC], which features chronic, watery diarrhoea despite overtly normal intestinal epithelial cells [IECs].
We assessed the expression of all AQP family members in mucosal samples of CC patients before and during treatment with the corticosteroid drug budesonide, steroid-refractory CC patients and healthy controls. Samples were analysed by genome-wide mRNA sequencing [RNA-seq] and quantitative real-time PCR [qPCR]. In some patients, we performed tissue microdissection followed by RNA-seq to explore the IEC-specific CC transcriptome. We determined changes in the protein levels of the lead candidates in IEC by confocal microscopy. Finally, we investigated the regulation of AQP expression by corticosteroids in model cell lines.
Using qPCR and RNA-seq, we identified loss of AQP8 expression as a hallmark of active CC, which was reverted by budesonide treatment in steroid-responsive but not refractory patients. Consistently, decreased AQP8 mRNA and protein levels were observed in IECs of patients with active CC, and steroid drugs increased AQP8 expression in model IECs. Moreover, low APQ8 expression was strongly associated with higher stool frequency in CC patients.
Down-regulation of epithelial AQP8 may impair water resorption in active CC, resulting in watery diarrhoea. Our results suggest that AQP8 is a potential drug target for the treatment of diarrhoeal disorders.
腹泻是胃肠道疾病常见且使人虚弱的症状。发病机制可能涉及跨上皮水转运缺陷，但水通道蛋白（AQP）家族水通道在以腹泻为主的疾病中的作用尚不清楚。我们研究了 AQP 在胶原性结肠炎（CC）发病机制中的作用，尽管肠上皮细胞（IEC）明显正常，但 CC 仍表现为慢性水样腹泻。
我们通过基因组范围的 mRNA 测序（RNA-seq）和定量实时 PCR（qPCR）评估了皮质类固醇药物布地奈德治疗前后、皮质类固醇难治性 CC 患者和健康对照者黏膜样本中所有 AQP 家族成员的表达情况。在一些患者中，我们进行了组织微切割，然后进行 RNA-seq 以探索特定于 IEC 的 CC 转录组。我们通过共聚焦显微镜确定了主要候选蛋白在 IEC 中的变化。最后，我们研究了皮质激素对模型细胞系中 AQP 表达的调节作用。
使用 qPCR 和 RNA-seq，我们确定 AQP8 表达缺失是 CC 活动期的一个标志，布地奈德治疗可使皮质激素反应性但非难治性患者的表达恢复。一致地，在活动期 CC 患者的 IEC 中观察到 AQP8 mRNA 和蛋白水平降低，皮质类固醇药物增加了模型 IEC 中的 AQP8 表达。此外，AQP8 表达降低与 CC 患者粪便频率增加密切相关。
上皮 AQP8 的下调可能会损害活动期 CC 中的水吸收，导致水样腹泻。我们的结果表明，AQP8 可能是治疗腹泻性疾病的潜在药物靶点。
