Bioluminescence determination of active caspase-3 in single apoptotic cells

Miniaturized bioluminescence technology for single-cell quantification of caspase-3/7

Correct determination of the instantaneous level and changes of relevant proteins inside individual cells is essential for correct interpretation and understanding of physiological, diagnostic, and therapeutic events. Thus, single-cell analyses are important for quantification of natural cellular heterogeneity, which cannot be evaluated from averaged data of a cell population measurements. Here, we developed an original highly sensitive and selective instrumentation and methodology based on homogeneous single-step bioluminescence assay to quantify caspases and evaluate their heterogeneity in individual cells. Individual suspended cells are selected under microscope and reliably transferred into the 7 µl detection vials by a micromanipulator. The sensitivity of the method is given by implementation of photomultiplying tube with a cooled photocathode working in the photon counting mode. By optimization of our device and methodology, the limits of detection and quantitation were decreased down to 2.1 and 7.0 fg of recombinant caspase-3, respectively. These masses are lower than average amounts of caspase-3/7 in individual apoptotic and even non-apoptotic cells. As a proof of concept, the content of caspase-3/7 in single treated and untreated HeLa cells was determined to be 154 and 25 fg, respectively. Based on these results, we aim to use the technology for investigations of non-apoptotic functions of caspases.

A single-cell analytical approach to quantify activated caspase-3/7 during osteoblast proliferation, differentiation, and apoptosis

The protein heterogeneity at the single-cell level has been recognized to be vital for an understanding of various life processes during animal development. In addition, the knowledge of accurate quantity of relevant proteins at cellular level is essential for appropriate interpretation of diagnostic and therapeutic results. Some low-copy-number proteins are known to play a crucial role during cell proliferation, differentiation, and also in apoptosis. The fate decision is often based on the concentration of these proteins in the individual cells. This is likely to apply also for caspases, cysteine proteases traditionally associated with cell death via apoptosis but recently being discovered also as important factors in cell proliferation and differentiation. The hypothesis was tested in bone-related cells, where modulation of fate from apoptosis to proliferation/differentiation and vice versa is particularly challenging, e.g., towards anti-osteoporotic treatments and anti-cancer strategies. An ultrasensitive and highly selective method based on bioluminescence photon counting was used to quantify activated caspase-3/7 in order to demonstrate protein-level heterogeneity in individual cells within one population and to associate quantitative measurements with different cell fates (proliferation, differentiation, apoptosis). The results indicate a gradual increase of caspase-3/7 activation from the proliferative status to differentiation (more than three times) and towards apoptosis (more than six times). The findings clearly support one of the putative key mechanisms of non-apoptotic functions of pro-apoptotic caspases based on fine-tuning of their activation levels.

Parallel single-cell analysis of active caspase-3/7 in apoptotic and non-apoptotic cells

Analysing the chemical content of individual cells has already been proven to reveal unique information on various biological processes. Single-cell analysis provides more accurate and reliable results for biology and medicine than analyses of extracts from cell populations, where a natural heterogeneity is averaged. To meet the requirements in the research of important biologically active molecules, such as caspases, we have developed a miniaturized device for simultaneous analyses of individual cells. A stainless steel body with a carousel holder enables high-sensitivity parallel detections in eight microvials. The holder is mounted in front of a photomultiplier tube with cooled photocathode working in photon counting mode. The detection of active caspase-3/7, central effector caspases in apoptosis, in single cells is based on the bioluminescence chemistry commercially available as Caspase-Glo^® 3/7 reagent developed by Promega. Individual cells were captured from a culture medium under microscope and transferred by micromanipulator into detection microvial filled with the reagent. As a result of testing, the limits of detection and quantification were determined to be 0.27/0.86 of active caspase-3/7 content in an average apoptotic cell and 0.46/2.92 for non-apoptotic cells. Application potential of this technology in laboratory diagnostics and related medical research is discussed. Graphical abstract Miniaturized device for simultaneous analyses of individual cells.

Application of inductively coupled plasma mass spectrometry in the study of apoptosis: determination of caspase-3 using a gold nanoparticle tag

Apoptosis is a main type of cell death in which caspase-3 plays a key role. In this work, a simple, fast and sensitive immunoassay for caspase-3 is established by using inductively coupled plasma mass spectrometry (ICP-MS) detection and signal enhancement gold nanoparticle (Au-NP) labelling of the secondary antibody (IgG). After the immunoreaction of caspase-3, primary antibody and Au-NP labeled IgG, the concentration of caspase-3 was determined by ICP-MS analysis of the Au-NPs released from the immunocomplex. Under the optimized conditions, a limit of detection (LOD, 3σ) of 0.42 ng mL(-1) (0.31 nM) was obtained for caspase-3, with a dynamic range of 1-200 ng mL(-1) and a relative standard deviation of 4.1% (c = 5 ng mL(-1), n = 11). The proposed method has good specificity towards caspase-3. To demonstrate the application potential of the proposed method, the cell lysates of Hg(2+)-induced HepG2 cells were analyzed, and it was found that the concentration of caspase-3 increased when increasing the incubation concentration of Hg(2+). This method is easy, sensitive and selective, and has excellent capability of tolerating a complex biological matrix, indicating the potential of the ICP-MS-based assay in the study of apoptosis.

Recent advances in the development of single cell analysis--a review

Development of techniques for the analysis of the content of individual cells represents an important direction in modern bioanalytical chemistry. While the analysis of chromosomes, organelles, or location of selected proteins has been traditionally the domain of microscopic techniques, the advances in miniaturized analytical systems bring new possibilities for separations and detections of molecules inside the individual cells including smaller molecules such as hormones or metabolites. It should be stressed that the field of single cell analysis is very broad, covering advanced optical, electrochemical and mass spectrometry instrumentation, sensor technology and separation techniques. The number of papers published on single cell analysis has reached several hundred in recent years. Thus a complete literature coverage is beyond the limits of a journal article. The following text provides a critical overview of some of the latest developments with the main focus on mass spectrometry, microseparation methods, electrophoresis in capillaries and microfluidic devices and respective detection techniques for performing single cell analyses.