Synthesis of the New Cyanine-Labeled Bacterial Lipooligosaccharides for Intracellular Imaging and in Vitro Microscopy Studies
作者:Tung-Cheng Wang、Florent Cochet、Fabio Alessandro Facchini、Lenny Zaffaroni、Christelle Serba、Simon Pascal、Chantal Andraud、Andrea Sala、Flaviana Di Lorenzo、Olivier Maury、Thomas Huser、Francesco Peri
DOI:10.1021/acs.bioconjchem.9b00044
日期:2019.6.19
Endotoxin (lipooligosaccharide, LOS, and lipopolysaccharide, LPS) is the major molecular component of Gram-negative bacteria outer membrane, and very potent pro-inflammatory substance. Visualizing and tracking the distribution of the circulating endotoxin is one of the fundamental approaches to understand the molecular aspects of infection with subsequent inflammatory and immune responses, LPS also being a key player in the molecular dialogue between microbiota and host. While fluorescently labeled LPS has previously been used to track its subcellular localization and colocalization with TLR4 receptor and downstream effectors, our knowledge on lipopolysaccharide (LOS) localization and cellular activity remains almost unexplored. In this study, LOS was labeled with a novel fluorophore, Cy7N, featuring a large Stokes-shifted emission in the deep-red spectrum resulting in lower light scattering and better imaging contrast. The LOS-Cy7N chemical identity was determined by mass spectrometry, and immunoreactivity of the conjugate was evaluated. Interestingly, its application to microscopic imaging showed a faster cell internalization compared to LPS-Alexa488, despite that it is also CD14-dependent and undergoes the same endocytic pathway as LPS toward lysosomal detoxification. Our results suggest the use of the new infrared fluorophore Cy7N for cell imaging of labeled LOS by confocal fluorescence microscopy, and propose that LOS is imported in the cells by mechanisms different from those responsible for LPS uptake.
内毒素(脂寡糖和脂多糖)是革兰氏阴性细菌外膜的主要分子成分,也是非常强效的促炎物质。观察和跟踪循环内毒素的分布是了解感染及其后炎症和免疫反应的分子方面的基本方法之一,LPS 也是微生物群与宿主之间分子对话的关键角色。荧光标记的 LPS 以前曾被用来追踪其亚细胞定位以及与 TLR4 受体和下游效应物的共定位,但我们对脂多糖(LOS)定位和细胞活性的了解几乎还没有。在本研究中,脂多糖被一种新型荧光团 Cy7N 标记,这种荧光团在深红光谱中具有较大的斯托克斯偏移发射,从而降低了光散射,提高了成像对比度。通过质谱分析确定了 LOS-Cy7N 的化学特性,并评估了共轭物的免疫活性。有趣的是,与 LPS-Alexa488 相比,LOS-Cy7N 在显微成像中的应用显示出更快的细胞内化速度,尽管它也依赖于 CD14,并与 LPS 经过相同的内细胞途径进入溶酶体解毒。我们的研究结果表明,可使用新型红外荧光团 Cy7N 通过共聚焦荧光显微镜对标记的 LOS 进行细胞成像,并提出 LOS 进入细胞的机制与 LPS 的摄取机制不同。