Department of Microbiology and Immunology, Lewis Katz School of Medicine, Temple University, Philadelphia, PA, United States.
Front Immunol. 2021 Feb 26;12:638867. doi: 10.3389/fimmu.2021.638867. eCollection 2021.
The human microbiota is the community of microorganisms that live upon or within their human host. The microbiota consists of various microorganisms including bacteria, fungi, viruses, and archaea; the gut microbiota is comprised mostly of bacteria. Many bacterial species within the gut microbiome grow as biofilms, which are multicellular communities embedded in an extracellular matrix. Studies have shown that the relative abundances of bacterial species, and therefore biofilms and bacterial byproducts, change during progression of a variety of human diseases including gastrointestinal, autoimmune, neurodegenerative, and cancer. Studies have shown the location and proximity of the biofilms within the gastrointestinal tract might impact disease outcome. Gram-negative enteric bacteria secrete the amyloid curli, which makes up as much as 85% of the extracellular matrix of enteric biofilms. Curli mediates cell-cell attachment and attachment to various surfaces including extracellular matrix components such as fibronectin and laminin. Structurally, curli is strikingly similar to pathological and immunomodulatory human amyloids such as amyloid-β, which has been implicated in Alzheimer's disease, α-synuclein, which is involved in Parkinson's disease, and serum amyloid A, which is secreted during the acute phase of inflammation. The immune system recognizes both bacterial amyloid curli and human amyloids utilizing the same receptors, so curli also induces inflammation. Moreover, recent work indicates that curli can participate in the self-assembly process of pathological human amyloids. Curli is found within biofilms of commensal enteric bacteria as well as invasive pathogens; therefore, evidence suggests that curli contributes to complex human diseases. In this review, we summarize the recent findings on how bacterial biofilms containing curli participate in the pathological and immunological processes in gastrointestinal diseases, systemic autoimmune diseases, and neurodegenerative diseases.
人体微生物群是生活在人类宿主表面或内部的微生物群落。微生物群由各种微生物组成，包括细菌、真菌、病毒和古菌；肠道微生物群主要由细菌组成。肠道微生物组中的许多细菌物种以生物膜的形式生长，生物膜是嵌入细胞外基质中的多细胞群落。研究表明，在包括胃肠道、自身免疫、神经退行性和癌症在内的多种人类疾病的进展过程中，细菌物种的相对丰度（因此生物膜和细菌副产物）发生变化。研究表明，生物膜在胃肠道中的位置和接近度可能会影响疾病结果。革兰氏阴性肠道细菌分泌淀粉样卷曲，占肠道生物膜细胞外基质的 85%。卷曲介导细胞-细胞附着和附着到各种表面，包括细胞外基质成分，如纤连蛋白和层粘连蛋白。结构上，卷曲与病理性和免疫调节性人类淀粉样蛋白非常相似，如淀粉样蛋白-β，其与阿尔茨海默病有关，α-突触核蛋白与帕金森病有关，血清淀粉样蛋白 A 在炎症急性期分泌。免疫系统利用相同的受体识别细菌淀粉样卷曲和人类淀粉样蛋白，因此卷曲也会引起炎症。此外，最近的工作表明，卷曲可以参与病理性人类淀粉样蛋白的自组装过程。卷曲存在于共生肠道细菌和侵袭性病原体的生物膜中；因此，有证据表明卷曲有助于复杂的人类疾病。在这篇综述中，我们总结了最近的发现，即含有卷曲的细菌生物膜如何参与胃肠道疾病、系统性自身免疫性疾病和神经退行性疾病中的病理和免疫过程。
