State Key Laboratory of Medicinal Chemical Biology, College of Life Sciences, Frontiers Science Center for Cell Responses, Nankai University, Tianjin, China.
School of Medicine, Nankai University, No. 94 Weijin Road, Tianjin, 300071, China.
J Leukoc Biol. 2024 Oct 1;116(4):738-752. doi: 10.1093/jleuko/qiae074.
Macropinocytosis is a large-scale endocytosis process primarily observed in phagocytes as part of their cellular function to ingest antigens. Once phagocytes encounter gram-negative bacteria, the receptor proteins identify lipopolysaccharides (LPSs), which trigger radical membrane ruffles that gradually change to cup-like structures. The open area of the cups closes to generate vesicles called macropinosomes. The target bacteria are isolated by the cups and engulfed by the cells as the cups close. In addition to its ingestion function, macropinocytosis also regulates the AKT pathway in macrophages. In the current study, we report that macropinocytic cups are critical for LPS-induced AKT phosphorylation (pAKT) and cytokine expression in macrophages. High-resolution scanning electron microscope observations detailed the macropinocytic cup structures induced by LPS stimulation. Confocal microscopy revealed that AKT and the kinase molecule mTORC2 were localized in the cups. The biochemical analysis showed that macropinocytosis inhibition blocked LPS-induced pAKT. RNA sequencing, quantitative polymerase chain reaction, and enzyme-linked immunosorbent assay analyses revealed that the inhibition of macropinocytosis or the AKT pathway causes a decrease in the expression of proinflammatory cytokines interlukin-6 and interlukin-1α. Moreover, activation of the transcription factor nuclear factor κB, which regulates the cytokine expression downstream of the AKT/IκB pathway, was hindered when macropinocytosis or AKT was inhibited. These results indicate that LPS-induced macropinocytic cups function as signal platforms for the AKT pathway to regulate the cytokine expression by modulating nuclear factor κB activity in LPS-stimulated macrophages. Based on these findings, we propose that macropinocytosis may be a good therapeutic target for controlling cytokine expression.
巨胞饮作用是一种主要在吞噬细胞中观察到的大规模内吞作用过程，是其摄取抗原的细胞功能的一部分。一旦吞噬细胞遇到革兰氏阴性菌，受体蛋白识别脂多糖 (LPS)，触发激进的细胞膜皱襞，逐渐变为杯状结构。杯的开口区域关闭，形成称为巨胞饮体的囊泡。当杯关闭时，目标细菌被杯子隔离并被细胞吞噬。除了摄取功能外，巨胞饮作用还调节巨噬细胞中的 AKT 途径。在本研究中，我们报告巨胞饮杯对于 LPS 诱导的巨噬细胞 AKT 磷酸化 (pAKT) 和细胞因子表达至关重要。高分辨率扫描电子显微镜观察详细描述了 LPS 刺激诱导的巨胞饮杯结构。共聚焦显微镜显示 AKT 和激酶分子 mTORC2 定位于杯子中。生化分析表明，巨胞饮作用抑制阻止了 LPS 诱导的 pAKT。RNA 测序、定量聚合酶链反应和酶联免疫吸附测定分析表明，巨胞饮作用或 AKT 途径的抑制导致促炎细胞因子白细胞介素-6 和白细胞介素-1α的表达减少。此外，当抑制巨胞饮作用或 AKT 时，调节 AKT/IκB 途径下游细胞因子表达的转录因子核因子 κB 的激活受到阻碍。这些结果表明，LPS 诱导的巨胞饮杯作为 AKT 途径的信号平台，通过调节 LPS 刺激的巨噬细胞中核因子 κB 的活性来调节细胞因子表达。基于这些发现，我们提出巨胞饮作用可能是控制细胞因子表达的一个很好的治疗靶点。
