Tytgat Institute for Liver and Intestinal Research, Department of Gastroenterology and Hepatology, Academic Medical Center, Amsterdam, The Netherlands.
Microbiology and Systems Biology, The Netherlands Organization for Applied Scientific Research (TNO), Zeist, The Netherlands.
Gastroenterology. 2017 Oct;153(4):1026-1039. doi: 10.1053/j.gastro.2017.06.004. Epub 2017 Jun 15.
BACKGROUND & AIMS: Visceral hypersensitivity is one feature of irritable bowel syndrome (IBS). Bacterial dysbiosis might be involved in the activation of nociceptive sensory pathways, but there have been few studies of the role of the mycobiome (the fungal microbiome) in the development of IBS. We analyzed intestinal mycobiomes of patients with IBS and a rat model of visceral hypersensitivity.
We used internal transcribed spacer 1-based metabarcoding to compare fecal mycobiomes of 18 healthy volunteers with those of 39 patients with IBS (with visceral hypersensitivity or normal levels of sensitivity). We also compared the mycobiomes of Long-Evans rats separated from their mothers (hypersensitive) with non-handled (normally sensitive) rats. We investigated whether fungi can cause visceral hypersensitivity using rats exposed to fungicide (fluconazole and nystatin). The functional relevance of the gut mycobiome was confirmed in fecal transplantation experiments: adult maternally separated rats were subjected to water avoidance stress (to induce visceral hypersensitivity), then given fungicide and donor cecum content via oral gavage. Other rats subjected to water avoidance stress were given soluble β-glucans, which antagonize C-type lectin domain family 7 member A (CLEC7A or DECTIN1) signaling via spleen-associated tyrosine kinase (SYK), a SYK inhibitor to reduce visceral hypersensitivity, or vehicle (control). The sensitivity of mast cells to fungi was tested with mesenteric windows (ex vivo) and the human mast cell line HMC-1.
α diversity (Shannon index) and mycobiome signature (stability selection) of both groups of IBS patients differed from healthy volunteers, and the mycobiome signature of hypersensitive patients differed from that of normally sensitive patients. We observed mycobiome dysbiosis in rats that had been separated from their mothers compared with non-handled rats. Administration of fungicide to hypersensitive rats reduced their visceral hypersensitivity to normal levels of sensitivity. Administration of cecal mycobiomes from rats that had been separated from their mothers (but not non-handled mycobiome) restored hypersensitivity to distension. Administration of soluble β-glucans or a SYK inhibitor reduced visceral hypersensitivity, compared with controls. Particulate β-glucan (a DECTIN-1 agonist) induced mast cell degranulation in mesenteric windows and HMC-1 cells responded to fungal antigens by release of histamine.
In an analysis of patients with IBS and controls, we associated fungal dysbiosis with IBS. In studies of rats, we found fungi to promote visceral hypersensitivity, which could be reduced by administration of fungicides, soluble β-glucans, or a SYK inhibitor. The intestinal fungi might therefore be manipulated for treatment of IBS-related visceral hypersensitivity.
内脏敏感性是肠易激综合征（IBS）的特征之一。细菌失调可能参与伤害感受感觉途径的激活，但关于真菌群落（真菌微生物组）在 IBS 发展中的作用的研究较少。我们分析了 IBS 患者和内脏高敏感大鼠模型的肠道真菌群落。
我们使用基于内部转录间隔区 1 的代谢条形码比较了 18 名健康志愿者和 39 名 IBS 患者（内脏高敏感或正常敏感）的粪便真菌群落。我们还比较了与未处理（正常敏感）大鼠分离的长耳大鼠的真菌群落。我们使用暴露于杀真菌剂（氟康唑和制霉菌素）的大鼠来研究真菌是否会导致内脏高敏感。粪便移植实验证实了肠道真菌群落的功能相关性：成年母子分离大鼠接受水回避应激（诱导内脏高敏感），然后通过口服灌胃给予杀真菌剂和供体盲肠内容物。其他接受水回避应激的大鼠给予可溶性β-葡聚糖，通过脾相关酪氨酸激酶（SYK）拮抗 C 型凝集素结构域家族 7 成员 A（CLEC7A 或 DECTIN1）信号，使用 SYK 抑制剂减少内脏高敏感，或使用载体（对照）。通过肠系膜窗（离体）和人肥大细胞系 HMC-1 测试肥大细胞对真菌的敏感性。
两组 IBS 患者的 α 多样性（香农指数）和真菌群落特征（稳定性选择）均与健康志愿者不同，高敏感患者的真菌群落特征与正常敏感患者不同。与未处理的大鼠相比，与母亲分离的大鼠的真菌群落失调。给予杀真菌剂可使高敏感大鼠的内脏高敏感恢复到正常水平。给予与母亲分离的大鼠的盲肠真菌群落（而非未处理的真菌群落）可恢复对扩张的高敏感性。与对照组相比，给予可溶性β-葡聚糖或 SYK 抑制剂可降低内脏高敏感。颗粒状β-葡聚糖（DECTIN-1 激动剂）可诱导肠系膜窗和 HMC-1 细胞中的肥大细胞脱颗粒，肥大细胞通过释放组胺对真菌抗原产生反应。
在对 IBS 患者和对照者的分析中，我们将真菌失调与 IBS 相关联。在大鼠研究中，我们发现真菌可促进内脏高敏感，给予杀真菌剂、可溶性β-葡聚糖或 SYK 抑制剂可降低内脏高敏感。因此，肠道真菌可能被操纵用于治疗与 IBS 相关的内脏高敏感。
