Background

Previous studies have demonstrated that Luteolin has a positive effect on epithelial barrier integrity by promoting the function of tight protein, however, little is known about the underline mechanism of Luteolin. In this study, we constructed Caco-2 cell monolayer to explore the effects and the regulation mechanism of Luteolin in intestinal epithelial barrier integrity.

Methods

Caco-2 cells were co-treated with TNF-α, Interferon-γ (IFN-γ) and Luteolin for 24 h. Overexpression or knockdown of SHP-1 was applied to study the effects of protein phosphoserine phosphatase-1 (SHP-1) on epithelial barrier integrity. Cell viability was tested by 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) assay. Barrier function was detected by trans-epithelial electrical resistance (TEER) and FITC-dextran assay. The expression levels of SHP-1, phosphorylation signal transducer and activator of transcription 3 (p-STAT3), STAT3 and tight junction proteins were measured by qRT-PCR or western blot. In vivo model of ulcerative colitis was established to detect the function of Luteolin in ulcerative colitis.

Results

We clarified that Luteolin protected intestinal epithelial barrier function of Caco-2 monolayers by increasing the resistance values and tight junction (TJ) protein expression. The expression of OCLN, CLDN1, and ZO1 was increased by Luteolin, while the expression of CLDN2 was decreased. Furthermore, Luteolin significantly alleviated the symptom of ulcerative colitis in DSS-induced mice. The in vitro cell model proved that overexpression of SHP-1 promotes the epithelial barrier function and knockdown of SHP-1 or STAT3 activation destroyed the protective effects of Luteolin on the expression of TJ proteins.

Conclusion

We found that the treatment of Luteolin promoted epithelial barrier function and Luteolin might preserve intestinal epithelial barrier function through suppression of STAT3 signaling pathway by SHP-1.

中文翻译：

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木犀草素通过 SHP-1/STAT3 通路缓解溃疡性结肠炎

 背景

先前的研究表明，木犀草素通过促进紧密蛋白的功能，对上皮屏障的完整性产生积极影响，然而，人们对木犀草素的潜在机制知之甚少。本研究构建Caco-2细胞单层，探讨木犀草素对肠上皮屏障完整性的影响及调节机制。

 方法

Caco-2 细胞与 TNF-α、干扰素-γ (IFN-γ) 和木犀草素共同处理 24 小时。应用 SHP-1 的过表达或敲低来研究蛋白磷酸丝氨酸磷酸酶-1 (SHP-1) 对上皮屏障完整性的影响。通过 3-(4,5-二甲基噻唑-2-基)-2,5-二苯基溴化四唑 (MTT) 测定法测试细胞活力。通过跨上皮电阻（TEER）和FITC-葡聚糖测定检测屏障功能。通过qRT-PCR或蛋白质印迹测量SHP-1、磷酸化信号转导子和转录激活子3（p-STAT3）、STAT3和紧密连接蛋白的表达水平。建立溃疡性结肠炎体内模型，检测木犀草素在溃疡性结肠炎中的作用。

 结果

我们阐明木犀草素通过增加电阻值和紧密连接 (TJ) 蛋白表达来保护 Caco-2 单层的肠上皮屏障功能。木犀草素增加了 OCLN、CLDN1 和 ZO1 的表达，而减少了 CLDN2 的表达。此外，木犀草素显着减轻了 DSS 诱导的小鼠溃疡性结肠炎的症状。体外细胞模型证明，SHP-1的过度表达可促进上皮屏障功能，敲低SHP-1或STAT3的激活则破坏了木犀草素对TJ蛋白表达的保护作用。

 结论

我们发现木犀草素的治疗促进了上皮屏障功能，并且木犀草素可能通过 SHP-1 抑制 STAT3 信号通路来保护肠上皮屏障功能。