Chassaing Benoit, Ley Ruth E, Gewirtz Andrew T
Institute for Biomedical Sciences, Center for Inflammation, Immunity & Infection, Georgia State University, Atlanta, Georgia.
Departments of Microbiology and Molecular Biology & Genetics, Cornell University, Ithaca, New York.
Gastroenterology. 2014 Dec;147(6):1363-77.e17. doi: 10.1053/j.gastro.2014.08.033. Epub 2014 Aug 27.
BACKGROUND & AIMS: Mice lacking the receptor Toll-like receptor 5 (TLR5-null mice), which recognizes flagellin, have an altered intestinal microbiota composition compared with wild-type mice; they develop low-grade inflammation and metabolic syndrome and are prone to colitis. The relative roles of intestinal epithelial cell (IEC) vs dendritic cell (DC) TLR5 in mediating these phenotypes are not clear; modification of intestinal microbiota composition has been reported to reflect animal husbandry practices rather than loss of TLR5. We generated mice with specific disruption of Tlr5 in IECs or DCs by using a breeding scheme that allows comparison with cohoused siblings as controls.
We generated C57BL/6 mice with LoxP sites flanking Tlr5. These mice were crossed with mice expressing Cre recombinase, regulated by the villin or CD11c promoters, to generate mice that lacked expression of TLR5 by IECs (TLR5(ΔIEC)) or DCs (TLR5(ΔDC)), respectively. Tlr5(fl/fl) siblings were used as controls. On weaning, mice were housed by sex and genotype or by sex only (genotypes cohoused). Mice were examined for basal phenotypes, including microbiota composition; we also analyzed responses to pathobiont challenge, administration of dextran sodium sulfate, and high-fat diets.
Similar to previous findings from TLR5-null mice, TLR5(ΔIEC) mice had low-grade inflammation (mild splenomegaly, shortened colons, and increased fecal levels of lipocalin 2), metabolic syndrome, and an inability to clear pathobionts and were prone to developing colitis compared with their sibling controls under both housing conditions. Development of this inflammation in the TLR5(ΔIEC) mice was eliminated by administration of antibiotics and associated with alterations in localization of microbiota and levels of fecal lipopolysaccharide and flagellin. The composition of the microbiota clustered more closely according to genotype than housing. Loss of TLR5 from DCs did not associate with development of inflammation-associated phenotypes or alterations in the composition of the microbiota but resulted in complete loss of flagellin-induced production of interleukin-22.
In mice, flagellin activation of TLR5 on DCs leads to production of interleukin-22. Expression of TLR5 on IECs regulates the composition and localization of the intestinal microbiota, preventing diseases associated with intestinal inflammation.
缺乏识别鞭毛蛋白的Toll样受体5的小鼠（Tlr5基因敲除小鼠）与野生型小鼠相比，肠道微生物群组成发生改变；它们会出现低度炎症和代谢综合征，且易患结肠炎。肠道上皮细胞（IEC）与树突状细胞（DC）中的Tlr5在介导这些表型中的相对作用尚不清楚；据报道，肠道微生物群组成的改变反映的是饲养方式，而非Tlr5的缺失。我们通过一种育种方案，培育出IEC或DC中Tlr5特异性缺失的小鼠，并将其与同笼饲养的同胞作为对照进行比较。
我们培育出Tlr5两侧带有LoxP位点的C57BL/6小鼠。这些小鼠与分别由绒毛蛋白或CD11c启动子调控表达Cre重组酶的小鼠杂交，以分别培育出IEC中缺乏TLR5表达的小鼠（TLR5(ΔIEC)）和DC中缺乏TLR5表达的小鼠（TLR5(ΔDC)）。Tlr5(fl/fl)同胞用作对照。断奶时，小鼠按性别和基因型或仅按性别（基因型同笼饲养）进行饲养。检测小鼠的基础表型，包括微生物群组成；我们还分析了对致病共生菌攻击、给予葡聚糖硫酸钠和高脂饮食的反应。
与之前Tlr5基因敲除小鼠的研究结果相似，在两种饲养条件下，与同胞对照相比，TLR5(ΔIEC)小鼠均出现低度炎症（轻度脾肿大、结肠缩短、粪便中lipocalin 2水平升高）、代谢综合征，无法清除致病共生菌，且易患结肠炎。给予抗生素可消除TLR5(ΔIEC)小鼠的这种炎症，且该炎症与微生物群定位、粪便脂多糖和鞭毛蛋白水平的改变有关。微生物群的组成根据基因型聚类比根据饲养方式聚类更紧密。DC中TLR5的缺失与炎症相关表型的发展或微生物群组成的改变无关，但导致鞭毛蛋白诱导的白细胞介素-22产生完全丧失。
在小鼠中，DC上TLR5的鞭毛蛋白激活导致白细胞介素-22的产生。IEC上TLR5的表达调节肠道微生物群的组成和定位，预防与肠道炎症相关的疾病。
