細胞間の通信は、細胞内外の様々な生理活性を制御するために重要です。本稿では、単一細胞分泌物の時空間的な性質を測定するためのプロトコルについて説明します。これを達成するためには、学際的なアプローチは、生細胞イメージングとラベルフリーnanoplasmonic検知を統合が使用されます。
Inter-cellular communication is an integral part of a complex system that helps in maintaining basic cellular activities. As a result, the malfunctioning of such signaling can lead to many disorders. To understand cell-to-cell signaling, it is essential to study the spatial and temporal nature of the secreted molecules from the cell without disturbing the local environment. Various assays have been developed to study protein secretion, however, these methods are typically based on fluorescent probes which disrupt the relevant signaling pathways. To overcome this limitation, a label-free technique is required.
In this paper, we describe the fabrication and application of a label-free localized surface plasmon resonance imaging (LSPRi) technology capable of detecting protein secretions from a single cell. The plasmonic nanostructures are lithographically patterned onto a standard glass coverslip and can be excited using visible light on commercially available light microscopes. Only a small fraction of the coverslip is covered by the nanostructures and hence this technique is well suited for combining common techniques such as fluorescence and bright-field imaging.
A multidisciplinary approach is used in this protocol which incorporates sensor nanofabrication and subsequent biofunctionalization, binding kinetics characterization of ligand and analyte, the integration of the chip and live cells, and the analysis of the measured signal. As a whole, this technology enables a general label-free approach towards mapping cellular secretions and correlating them with the responses of nearby cells.
細胞間の通信は、細胞の内側と外側の両方の多くの生理活性の調節のために不可欠です。タンパク質および小胞の様々なその後、このような分化、創傷治癒、免疫応答、遊走、および増殖などの複雑な細胞プロセスを誘発することが分泌され得る。細胞間シグナル伝達経路の1-5誤動作は、癌、アテローム性動脈硬化症を含む多くの疾患に関与しています、および糖尿病、いくつかの名前を付けます。
最適な細胞分泌アッセイは、空間的および時間的に関連するシグナル伝達経路に影響を与えることなく、目的の分泌タンパク質をマッピングすることができるべきです。このようにして、濃度プロファイルと受信細胞の応答との間の因果関係を推測することができます。残念ながら、最も一般的に使用される蛍光ベースの技術の多くは、これらの基準を満たしていません。蛍光融合タンパク質は、被検体Wをタグ付けするために使用することができセルをithinが、分泌経路を妨害することができ、又は分泌場合、定量化が困難である細胞外へ拡散グローをもたらします。蛍光immunosandwichベースのアッセイは、細胞分泌物を検出するために最も一般的に使用される技術であるが、典型的には個々の細胞の単離を必要とする。また6-11、検知抗体の導入は、典型的には、実験や抗体標識の大きさを停止または終了150kDaのIgGについては、下流のシグナル伝達に障害となっています。
これらの障害物のそれはラベルフリー技術は、画像タンパク質分泌および既存のラベルフリー技術の中で利用されるプラズモン共鳴(SPR)の表面と、局在表面プラズモン共鳴(LSPR)センサは、優れた候補であることが好ましいからである。12-17これらセンサー広くタンパク質、エキソソームおよび他のバイオマーカーの分析物結合の研究のために使用されている。LSPRの場合は18〜24、プラズモンnanostructuresガラスカバースリップ上にリソグラフィでパターン化し、標準的な広視野顕微鏡の構成を介して可視光を用いて励起することができます。それらのナノスケールのフットプリントに、ガラス基板の大部分は、25-28。例えば、生細胞の顕微鏡との統合に適した明視野でよく、これらのプローブを作製する蛍光顕微鏡のような一般的な画像化技術のために利用可能である我々は、リアルタイム測定を示しましたそれぞれ、225ミリ秒と10ミクロンの空間的および時間的解像度で官能金プラズモンナノ構造を用いて、ハイブリドーマ細胞からの抗体分泌物。基本的なチップ構成は 、図1に示されている。顕微鏡28の出力光路は、画像及びナノ構造の指定された配列の部分占有率の定量決意にファイバ光学的に結合分析装置( 図2に使用されるCCDカメラの間に分割され)。
protoc同時に、標準的な明視野顕微鏡を用いて細胞の応答を監視しながら、本論文では、オール単一細胞分泌物のリアルタイム測定のための実験計画について説明します。学際的なアプローチは、ナノ構造体の製造、分析物の高親和性結合のためのナノ構造体の官能化、商業表面プラズモン共鳴(SPR)測定器を使用して、両方の最小化、非特異的結合と特徴づける運動速度定数の表面の最適化、細胞株の統合が含ま基板と、画像やスペクトルデータの解析へ。私たちは、この技術は、細胞の分泌物と細胞を受けたとの因果関係の時空マッピングを可能にする技術であることを期待しています。
The LSPR imaging technique described in this work has numerous advantages over more traditional methodologies for detecting cell secretions. First, the time resolution of our technique is on the order of seconds whereas the commercial alternative, an immunosandwhich assay known as EliSpot, has a typical time resolution of 2 to 3 days.7,32 As a result we were able to resolve sudden changes in the rate of protein secretion, such as that shown in Figure 6. Second, having arrays distributed over the chip allows for the secreted signal to be tracked in space and time which enables more rigorous comparisons to diffusion-based models of cell secretion. In addition, arrays like the control array shown in Figure 6 can be used to subtract out global changes in the image that typically arise from instrumental factors such as focus drift. Third, our technique requires no modification of the cells. If desired, the experiment can incorporate commonly used tags such as fluorescent proteins, but if there is concern that such tags may negatively affect cell viability or homeostasis the label-free nature of our approach does not require them. Fourth, using the spectroscopic data we have demonstrated that quantitative information regarding the fractional occupancy of surface bound ligands can be calculated.
There are numerous alternative methods to EBL for fabricating metallic nanoparticles. However, we have found that the EBL provides considerable flexibility for optimizing nanostructure and array dimensions to best suit the optics and the cells under investigation. Also critical is the fact that the chips can be readily regenerated by plasma ashing. In this way, a typical chip can be used dozens of times. Biofunctionalization details must be modified for the specific application. The protocol presented here conjugated the surface with relatively small c-myc peptide ligands. Larger ligands such as whole antibodies typically require more spacing and thus a higher SPO to SPN/SPC ratio. Regardless, a well formed SAM layer is essential for preventing non-specific binding in live-cell experiments. In general, larger molecular weight analytes are more readily detected by LSPR. Thus, in its single-cell manifestation, this technique may not be appropriate for detecting the secretion of small proteins, such as cytokines.
The current setup has been used for studying individual non-adherent cells. There are significant number of secreted signaling proteins and vesicles to which the results reported in this work are directly applicable. For example carcinoembryonic antigen (CEA) which for decades now has been a diagnostic marker for cancer. Colon cancer cells are known to secrete CEA at the rates of thousands of molecules/cell/hr and the molecular weight is 180 kDa which exceeds that of IgG antibodies. CEA is believed to be involved in autocrine and paracrine signaling pathways but the spatio-temporal nature of these secretions have never been measured. Our technique can directly address these signaling questions. An extension of this work will be to measure the spatio-temporal nature of CEA secretion from single cells.33 Future work will also focus on integrating LSPRi with two and three dimensional cell cultures of adherent cells. By incorporating multiplexed arrays capable of detecting a number of secreted proteins in parallel, this technique has the potential to open a new window into cell secretions and how they influence neighboring cells.
The authors have nothing to disclose.
The authors have nothing to disclose.
25mm diameter glass coverslips | Bioscience Tools | CSHP-No1.5-25 | 170±5 µm is optimal |
Poly-methyl methacrylate | Microchem | PMMA 950 A4 | |
Ethyl lactate methyl metacrylate | Microchem | MMA EL6 | |
Electron beam evaporator | Temescal | FC-2000 | |
Electron beam lithography | Raith | Series 150 | |
Ethanol | Sigma-Aldrich | 459836 | |
Acetone | Sigma-Aldrich | 320110 | |
CR-7 chromium etchant | Cyantek | CR-7 | |
Scanning electron microscope | Zeiss | Ultra 55 | |
Atomic force microscope | Veeco | Nanoscope III | |
Plasma ashing system | Technics | Series 85 RIE | |
SH-(CH2)8-EG3-OH (SPO) | Prochimia | TH 001-m8.n3-0.2 | |
SH-(CH2)11-EG3-COOH (SPC) | Prochimia | TH 003m11n3-0.1 | |
SH-(CH2)11-EG3-NH2 (SPN) | Prochimia | TH 002-m11.n3-0.2 | |
Surface plasmon resonance system | Biorad | XPR36 | |
Bare gold chip | Biorad | GLC chip | Plasma ashed to remove the monolayer |
1-Ethyl-3-(3-dimethylaminopropyl) carbodiimide | Thermo | 22980 | |
N-hydroxysuccinimide (NHS) | Thermo | 24510 | |
Pentylamine-Biotin | Thermo | 21345 | |
Ethanolamine | Sigma-Aldrich | E9508 | |
Neutraavidin | Thermo | 31000 | |
Phosphate buffered saline | Thermo | 28374 | |
Tween 20 | Sigma-Aldrich | P2287 | |
Inverted microscope | Zeiss | Axio Observer | Microscope is equipped with 40X oil immersion objective; CO2 and humidity incubation from Pecon GmbH |
CCD camera | Hamamatsu | Orca R2 | Thermoelectrically cooled (16 bit) |
Spectrometer | Ocean Optics | QE65Pro | |
Spectrasuite | Ocean Optics | version1.4 | |
c-myc peptide HyNic Tag | Solulink | SP-E003 | |
monoclonal anti-c-myc antibody | Sigma-Aldrich | M4439 | |
Hybridoma cell line | ATCC | CRL-1729 | |
Antibiotic Antimycotic Solution (100×) | Sigma-Aldrich | A5955 | |
Serum free media RPMI 1640 | Invitrogen | 11835-030 | |
Fetal bovine serum | ATCC | 30-2020 | |
Rhodamine DHPE | Life Technologies | L-1392 |