Mechanism of blood-brain barrier disruption by an Escherichia coli from lambs with severe diarrhea and meningoencephalitis
Introduction
Escherichia coli (E. coli) is an important zoonotic bacterial pathogen. The infection it induces often causes gastrointestinal and respiratory diseases in human and animals [1,2]. In recent years, there have been increasing studies of meningoencephalitis caused by E. coli in humans, but few in animals [3,4]. In previous studies, we found a strain of E. coli that can cause canine meningoencephalitis by breaking the tight junction structure [5]. This finding further provides evidence that E. coli could cause meningoencephalitis in animals. It is well known that E. coli has the potential to induce many problems in young lambs including diarrhea, sepsis, navel ill, joint ill, etc. However, it has not been reported whether E. coli causes meningoencephalitis in lambs.
Meningoencephalitis is an inflammation of the brain and its surrounding protective membranes. It can be caused by many pathogens including bacteria, viruses, fungi, and protozoan etc. The blood-brain barrier (BBB) disruption and neuroinflammation are considered key mechanisms of pathogenic bacteria evading the brain [6,7]. BBB is one of the most important barriers of the central nervous system (CNS), and is the key to preventing the invasion of pathogenic bacteria. The adhesion and invasion of bacteria will destroy the integrity of the BBB, increase the permeability, and eventually cause meningoencephalitis. The structural and functional integrity of BBB are closely related to the expression and arrangement of tight junction (TJ) proteins. ZO-1 and occludin are two key TJ proteins and often used as important indicators to detect the integrity of the BBB [8,9]. In addition, many bacterial products initiate local inflammatory response and enhance the permeability of the BBB. TLRs are pathogen-associated pattern recognition receptors that recognize conserved molecular sequences on pathogens and induce antibacterial immunity. Previous study has showed that TLR4 provides a mechanical link between the bacterial and host immune responses when the CNS is disrupted [10]. In addition, activation of TLR2 can also directly induce the immune response, and regulate the intrinsic structure of TJ [11,12]. As an important signal in the inflammatory response, the NLRP3 inflammasome also plays a key role in maintaining the BBB [13]. The classical NLRP3 inflammasome activation is affected by both signals, the first signal activates the TLR4 signaling pathway and triggers the release of inflammatory cytokines. The second signal promotes the assembly of NLRP3/ASC/Pro-casepase-1 protein complex and induces inflammation. Although certain progress has been made to the understanding of mechanism underlying meningoencephalitis elicited by pathogens, the mechanism on NMGCF-19 invasion of the host brain remains unknown.
In this study, we isolated an E. coli from lambs with diarrhea and neurological symptoms, and demonstrated in mice that the bacteria could disrupt BBB. Preliminary mechanistic investigations found that it may not only have the ability to decrease the expression of TJ proteins that maintains the integrity of BBB, but also have the effect of regulating the inflammatory response, thereby causing meningoencephalitis.
Section snippets
Reagents
Primary antibodies NLRP3, caspase-1, TLR4, ZO-1, occludin and β-tublin were obtained from Cell Signaling Technology Inc. (Beverly, MA, USA). Secondary antibody HRP-labeled goat anti-rabbit IgG was purchased from Santa Cruz (Santa Cruz, USA). Hematoxylin and Eosin (H&E) Staining Kit and BCA Protein Assay Kit were ordered from Shanghai Biyuntian Biotechnology Co.,Ltd (Shanghai, China). The bacterial biochemical test kit was purchased from Hangzhou Microbiological Reagents Limited Company
Disease outbreak in sheep farm in inner Mongolia autonomous region
In early spring, 2019, a disease outbreak occurred on an intensive indoor sheep farm in Inner Mongolia autonomous region. There were approximately 13,000 sheep including 10,000 ewes on the farm. Initially, the neonatal lambs were dull, lethargic, depressed and reluctant to suck. Later on, the affected lambs showed severe diarrhea, dehydrations and weight loss. Some lambs progressed to coma, even showed the neurological disorder such as convulsions with opisthotonos before death. Most of the
Discussion
Bacterial meningoencephalitis is an important central nervous system (CNS) infectious disease that is of great concern to humans and animals [15]. E. coli is an important pathogen causing bacterial meningoencephalitis. The current reports on E. coli meningoencephalitis mainly focused on humans, there were few reports about animals, especially lambs. In this study, a Gram-negative rod-shaped bacillus bacteria from various organs of lambs characterized by diarrhea and nervous system disorder was
Author contribution
All authors have participated and contributed to this manuscript. All the authors have read and confirmed their participation in the manuscript. Concept and design: Xinping Wang, Zecai Zhang, and Weiyu Wang. Acquisition of data: Weiyu Wang, Menglu Cai, Junying Hu, Xu Wang, Xiaoran Chang, and Fan Zhang. Analysis and interpretation: Weiyu Wang, Menglu Cai, Xinping Wang, and Changming Guo. Drafting and editing of the manuscript: Weiyu Wang, Zecai Zhang, and Xinping Wang.
Declaration of competing interest
The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.
Acknowledgement
This study is supported by the National Key Science & Research Program 2017YFD0500104 and 2016YFD0500904.
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These authors contributed equally to this work.