细胞内胆汁酸动态实时监控使用遗传编码的FRET为基础的胆汁酸传感器
Summary
We provide a detailed protocol to study bile acid dynamics in living cells using a genetically encoded BAS FRET sensor. This Bile Acid Sensor represents a unique tool to study (regulation of) bile acid transport and FXR activation in a wide range of cell types.
Abstract
Förster Resonance Energy Transfer (FRET) has become a powerful tool for monitoring protein folding, interaction and localization in single cells. Biosensors relying on the principle of FRET have enabled real-time visualization of subcellular signaling events in live cells with high temporal and spatial resolution. Here, we describe the application of a genetically encoded Bile Acid Sensor (BAS) that consists of two fluorophores fused to the farnesoid X receptor ligand binding domain (FXR-LBD), thereby forming a bile acid sensor that can be activated by a large number of bile acids species and other (synthetic) FXR ligands. This sensor can be targeted to different cellular compartments including the nucleus (NucleoBAS) and cytosol (CytoBAS) to measure bile acid concentrations locally. It allows rapid and simple quantitation of cellular bile acid influx, efflux and subcellular distribution of endogenous bile acids without the need for labeling with fluorescent tags or radionuclei. Furthermore, the BAS FRET sensors can be useful for monitoring FXR ligand binding. Finally, we show that this FRET biosensor can be combined with imaging of other spectrally distinct fluorophores. This allows for combined analysis of intracellular bile acid dynamics and i) localization and/or abundance of proteins of interest, or ii) intracellular signaling in a single cell.
Introduction
荧光共振能量转移（FRET）被广泛地用于获得与高时空分辨率的1活细胞更好地了解细胞功能。在FRET，从激发供体荧光团的能量被转移到受体荧光团。 FRET效率强烈依赖于供体和受体荧光团和它们的取向之间的距离，因此，影响的两种荧光团的构象变化敏感的读出。这一现象被利用，以产生基于FRET的生物传感器为小分子成像。改变它们的浓度可以监测作为增加/减少在所述受体与供体荧光团2的发光强度的比率。例如，基于FRET的钙生物传感器允许在活细胞中3快速和稳定的检测的游离钙离子浓度。对基于FRET的生物传感器的其它优点是成像在单个活细胞，T继承人的非侵入性，他们有能力将针对不同类型的细胞和细胞室4。
细胞内胆汁酸动力学的许多方面仍然知之甚少。例如，鲜为人知的是，游离态和结合胆汁酸转运的机制基础调节。现有的技术来监测这种运输主要是利用荧光素酶为基础的记者，放射性标记的胆汁酸，或荧光胆汁酸类似物。后者需要修改的胆汁酸，可能影响其性能。荧光素酶为基础的记者有时间分辨率差。此外，这些技术导致样品损失，是不适用的成像在单个细胞。因此，这将是有益的使用方法，使转运活性的活单细胞成像使用FRET生物传感器，特别是因为它包括比例检测5,6的优点。虽然CF变种P / YFP形式最经常使用的FRET对，采用魔橙和mCherry携带自联合诱导突变已导致FRET工具箱新颖传感器，包括一个红移胆汁酸传感器 7的膨胀的新策略。
我们以前创建的基因编码FRET胆汁酸传感器（BAS），它由一个供体荧光团（天蓝色）和受体荧光（黄水晶）的融合与法尼醇X受体（FXR）配体结合结构域（FXR-LBD）和含有肽的LXXLL模8。这与FXR-LBD肽同伙在胆汁酸依赖性。一旦FXR激活，柠檬色和蔚蓝之间的距离将改变由于构象变化。在哺乳动物细胞系，FXR激活导致在茶晶/天蓝色的比例清楚地检测到增加，而纯化的传感器的工作原理在相反的方向，并导致在FXR活化降低的FRET比率。该传感器（CytoBAS）允许监测细胞内胆汁酸的动态。由羧基末端加成亚细胞靶向基序下，BAS构建体可以靶向至核（NucleoBAS）和过氧化物酶体（PeroxiBAS），允许胆汁酸的浓度在不同的细胞区室的测量。虽然增加了过氧化物酶体靶向母题不会损害其回应胆汁酸，细胞渗透性FXR配体没有引起任何FRET内过氧化物酶体8 PeroxiBAS的变化。作为该差异的性质是未知的，该协议如下聚焦在CytoBAS和NucleoBAS。
使用这种基因编码FRET传感器的最近表现在含肝胆汁酸转运体的Na + /牛磺胆酸钠共转运多肽（NTCP）和有机溶质转运α/β（OSTαβ）8个单元 。 NTCP是主要的肝胆汁酸进口商和OSTαβ是基底肠胆酸转运体可作为进口商和出口商依赖于电化学胆汁酸浓度梯度9，10个功能两者。最近的数据表明，在由NTCP和/或OSTαβ胆汁酸运输，在FRET比率作为配体-FXR-LBD相互作用的结果健壮和快速的响应可以被观察到。
在这里，我们将详细介绍协议的方法来测量FRET如共聚焦显微镜分析和荧光激活细胞分选（FACS），突出关键环节，解决潜在的问题，并讨论替代方法。使用该基因编码的FRET传感器，与FXR-LBD胆汁酸相互作用可以量化，并直接在活细胞中监测并提供了一种快速，简单的可视化胆汁酸运输和动态实时的方法。编码CytoBAS和NucleoBAS哺乳动物表达质粒是市售的。因此，该生物传感器可进一步向了解胆汁酸转运或激活FXR，并提供了一个深入了解胆汁酸生物学和信号传导的化合物。
Protocol
Representative Results
Discussion
这里，我们提出了详细的方案的使用一种新的遗传编码的胆汁酸传感器能够监测胆汁酸转运的时空动力学在活细胞的。该生物传感器包括稠合到FXR-LBD，从而形成基于FRET的胆汁酸传感器（BAS）和天蓝色茶晶荧光蛋白。
具有与细胞培养和FACS或（共焦）显微基本经验当胆汁酸传感器是相对简单和使用方便。然而，某些方面可能需要一些故障排除。当使用与胆汁酸转运组合胆汁酸?…
Divulgations
The authors have nothing to disclose.
Acknowledgements
This work was supported by ERC starting grants (ERC-2011-StG 280255 and ERC-2013-StG 337479) and by the Netherlands Organization for Health Research and Development (Vidi 91713319).
Materials
| CytoBAS | Addgene | 62860 | |
| NucleoBAS | Addgene | 62861 | |
| Dulbecco's modified Eagles media (DMEM) | Lonza | BE12-614F | High glucose without L-glutamine |
| Penicillin-Streptomycin (pen/strep) | Lonza | 17-602E | |
| L-glutamine (200mM) | Lonza | 17-605E | |
| Fetal Bovine Serum (FBS) | Invitrogen | 102-70 | |
| Trypsin-EDTA (10x) | Lonza | CC-5012 | |
| T-25 cell culture flask | VWR international | 392-0253 | Laminin coated |
| T-175 cell culture flask | VWR international | 392-0238 | Laminin coated |
| 6-well plate | VWR international | 734-0229 | Poly-L-lysine and Laminin coated |
| 10cm dish | VWR international | 392-0243 | Laminin coated |
| Diethylaminoethyl (DEAE) – Dextran | Sigma-Aldrich | D9885 | |
| Polyethylenimine (PEI) | Brunschwig | 23966-2 | |
| G418 (geneticin) 50 mg/ml | Invitrogen | 10131-027 | |
| Hygromycin B, 50 mg / ml | Invitrogen | 10687-010 | |
| Cloning cylinder (6×8 mm) | Bellco | 2090-00608 | |
| L-15 Leibovitz culture medium | Invitrogen | 21083-027 | No phenol red |
| Polystyrene round bottom tube (5 ml) Facs tube | Falcon BD | 352008 | No cap, non-sterile |
| Falcon 2063 tubes (5 ml) | Falcon BD | 352063 | Snap cap, sterile |
| Nunc Lab-Tek 8 well coverglass | Thermo scientific | 155409 | Sterile |
| Charcoal-filtered FBS | Life technologies | 12676011 | |
| GW4064 | Sigma-Aldrich | G5172 | |
| TCDCA | Sigma-Aldrich | T6260 | |
| CDCA | Sigma-Aldrich | C9377 | |
| Other chemicals | Sigma-Aldrich | n.v.t. |
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