Department of Medicine, Penn State Milton S. Hershey Medical Center, Hershey, PA, United States.
Department of Internal Medicine, University of Nebraska Medical Center, Omaha, NE, United States.
Front Immunol. 2024 Jul 16;15:1348010. doi: 10.3389/fimmu.2024.1348010. eCollection 2024.
Defective intestinal epithelial tight junction (TJ), characterized by an increase in intestinal TJ permeability, has been shown to play a critical role in the pathogenesis of inflammatory bowel disease (IBD). Tumor necrosis factor-α (TNF-α) is a key pro-inflammatory cytokine involved in the immunopathology of IBD and has been shown to cause an increase in intestinal epithelial TJ permeability. Although TNF-α antibodies and other biologics have been advanced for use in IBD treatment, these therapies are associated with severe side effects and have limited efficacy, and there is an urgent need for therapies with benign profiles and high therapeutic efficacy. Probiotic bacteria have beneficial effects and are generally safe and represent an important class of potential therapeutic agents in IBD. (LA) is one of the most used probiotics for wide-ranging health benefits, including in gastrointestinal, metabolic, and inflammatory disorders. A specific strain of LA, LA1, was recently demonstrated to have protective and therapeutic effects on the intestinal epithelial TJ barrier. However, the mechanisms of actions of LA1 remain largely unknown.
The primary aim of this study was to investigate microbial-epithelial interactions and novel signaling pathways that regulate the effect of LA1 on TNF-α-induced increase in intestinal epithelial TJ permeability, using cell culture and animal model systems.
Pre-treatment of filter-grown Caco-2 monolayers with LA1 prevented the TNF-α-induced increase in intestinal epithelial TJ permeability by inhibiting TNF-α-induced activation of NF-κB p50/p65 and myosin light chain kinase (MLCK) gene and kinase activity in a TLR-2-dependent manner. LA1 produced a TLR-2- and MyD88-dependent activation of NF-κB p50/p65 in immune cells; however, LA1, in intestinal cells, inhibited the NF-κB p50/p65 activation in a TLR-2-dependent but MyD88-independent manner. In addition, LA1 inhibition of NF-κB p50/p65 and MLCK gene was mediated by TLR-2 pathway activation of phosphatidylinositol 3-kinase (PI3K) and IKK-α phosphorylation. Our results demonstrated novel intracellular signaling pathways by which LA1/TLR-2 suppresses the TNF-α pathway activation of NF-κB p50/p65 in intestinal epithelial cells and protects against the TNF-α-induced increase in intestinal epithelial TJ permeability.
有缺陷的肠道上皮紧密连接（TJ），其特征是肠道 TJ 通透性增加，已被证明在炎症性肠病（IBD）的发病机制中起关键作用。肿瘤坏死因子-α（TNF-α）是一种关键的促炎细胞因子，参与 IBD 的免疫病理学，并且已被证明可引起肠道上皮 TJ 通透性增加。尽管 TNF-α 抗体和其他生物制剂已被推进用于 IBD 治疗，但这些疗法与严重的副作用相关，且疗效有限，因此迫切需要具有良性特征和高治疗效果的疗法。益生菌具有有益作用，通常是安全的，是 IBD 中一类重要的潜在治疗药物。（LA）是一种用于广泛健康益处的最常用益生菌，包括胃肠道、代谢和炎症性疾病。最近证明，LA 的一种特定菌株 LA1 对肠道上皮 TJ 屏障具有保护和治疗作用。然而，LA1 的作用机制在很大程度上仍然未知。
本研究的主要目的是使用细胞培养和动物模型系统，研究微生物-上皮相互作用和调节 LA1 对 TNF-α诱导的肠道上皮 TJ 通透性增加的新型信号通路。
在 TNF-α诱导的 Caco-2 单层细胞培养物中，LA1 的预处理通过抑制 TLR-2 依赖性 TNF-α诱导的 NF-κB p50/p65 和肌球蛋白轻链激酶（MLCK）基因和激酶活性，防止 TNF-α诱导的肠道上皮 TJ 通透性增加。LA1 在免疫细胞中产生 TLR-2 和 MyD88 依赖性 NF-κB p50/p65 激活；然而，LA1 在肠道细胞中以 TLR-2 依赖性但 MyD88 非依赖性方式抑制 NF-κB p50/p65 的激活。此外，LA1 通过 TLR-2 途径激活磷脂酰肌醇 3-激酶（PI3K）和 IKK-α磷酸化来抑制 NF-κB p50/p65 和 MLCK 基因。我们的研究结果证明了 LA1/TLR-2 通过抑制 NF-κB p50/p65 在肠道上皮细胞中的 TNF-α通路激活来抑制肠道上皮 TJ 通透性增加的新型细胞内信号通路。
