Impact of cell cycle dynamics on pathology recognition: Raman imaging study

Confocal Raman imaging combined with fluorescence‐activated cell sorting was used for in vitro studies of cell cultures to look at biochemical differences between the cells in different cell phases. To answer the question what is the impact of the cell cycle phase on discrimination of pathological cells, the combination of several factors was checked: a confluency of cell culture, the cell cycle dynamics and development of pathology. Confluency of 70% and 100% results in significant phenotypic cell changes that can be also diverse for different batches. In 100% confluency cultures, cells from various phases become phenotypically very similar and their recognition based on Raman spectra is not possible. For lower confluency, spectroscopic differences can be found between cell cycle phases (G₀/G₁, S and G₂/M) for control cells and cells incubated with tumor necrosis factor alpha (TNF‐α), but when the mycotoxin cytochalasin B is used the Raman signatures of cell phases are not separable. Generally, this work shows that heterogeneity between control and inflamed cells can be bigger than heterogeneity between cell cycle phases, but it is related to several factors, and not always can be treated as a rule.      

Flow cytometric cell cycle analysis of muscle precursor cells cultured within 3D scaffolds in a perfusion bioreactor

It has been widely demonstrated that perfusion bioreactors improve in vitro three‐dimensional (3D) cultures in terms of high cell density and uniformity of cell distribution; however, the studies reported in literature were primarily based on qualitative analysis (histology, immunofluorescent staining) or on quantitative data averaged on the whole population (DNA assay, PCR). Studies on the behavior, in terms of cell cycle, of a cell population growing in 3D scaffolds in static or dynamic conditions are still absent. In this work, a perfusion bioreactor suitable to culture C₂C₁₂ muscle precursor cells within 3D porous collagen scaffolds was designed and developed and a method based on flowcytometric analyses for analyzing the cell cycle in the cell population was established. Cells were extracted by enzymatic digestion of the collagen scaffolds after 4, 7, and 10 days of culture, and flow cytometric live/dead and cell cycle analyses were performed with Propidium Iodide. A live/dead assay was used for validating the method for cell extraction and staining. Moreover, to investigate spatial heterogeneity of the cell population under perfusion conditions, two stacked scaffolds in the 3D domain, of which only the upstream layer was seeded, were analyzed separately. All results were compared with those obtained from static 3D cultures. The live/dead assay revealed the presence of less than 20% of dead cells, which did not affect the cell cycle analysis. Cell cycle analyses highlighted the increment of cell fractions in proliferating phases (S/G₂/M) owing to medium perfusion in long‐term cultures. After 7–10 days, the percentage of proliferating cells was 8–12% for dynamic cultures and 3–5% for the static controls. A higher fraction of proliferating cells was detected in the downstream scaffold. From a general perspective, this method provided data with a small standard deviation and detected the differences between static and dynamic cultures and between upper and lower scaffolds. Our methodology can be extended to other cell types to investigate the influence of 3D culture conditions on the expression of other relevant cell markers. © 2009 American Institute of Chemical Engineers Biotechnol. Prog., 2009     

Robust synchronization of coupled circadian and cell cycle oscillators in single mammalian cells

Circadian cycles and cell cycles are two fundamental periodic processes with a period in the range of 1 day. Consequently, coupling between such cycles can lead to synchronization. Here, we estimated the mutual interactions between the two oscillators by time‐lapse imaging of single mammalian NIH3T3 fibroblasts during several days. The analysis of thousands of circadian cycles in dividing cells clearly indicated that both oscillators tick in a 1:1 mode‐locked state, with cell divisions occurring tightly 5 h before the peak in circadian Rev‐Erbα‐YFP reporter expression. In principle, such synchrony may be caused by either unidirectional or bidirectional coupling. While gating of cell division by the circadian cycle has been most studied, our data combined with stochastic modeling unambiguously show that the reverse coupling is predominant in NIH3T3 cells. Moreover, temperature, genetic, and pharmacological perturbations showed that the two interacting cellular oscillators adopt a synchronized state that is highly robust over a wide range of parameters. These findings have implications for circadian function in proliferative tissues, including epidermis, immune cells, and cancer.     

Combined analysis of DNA methylation and cell cycle in cancer cells

DNA methylation is a chemical modification of DNA involved in the regulation of gene expression by controlling the access to the DNA sequence. It is the most stable epigenetic mark and is widely studied for its role in major biological processes. Aberrant DNA methylation is observed in various pathologies, such as cancer. Therefore, there is a great interest in analyzing subtle changes in DNA methylation induced by biological processes or upon drug treatments. Here, we developed an improved methodology based on flow cytometry to measure variations of DNA methylation level in melanoma and leukemia cells. The accuracy of DNA methylation quantification was validated with LC-ESI mass spectrometry analysis. The new protocol was used to detect small variations of cytosine methylation occurring in individual cells during their cell cycle and those induced by the demethylating agent 5-aza-2''-deoxycytidine (5AzadC). Kinetic experiments confirmed that inheritance of DNA methylation occurs efficiently in S phase and revealed a short delay between DNA replication and completion of cytosine methylation. In addition, this study suggests that the uncoupling of 5AzadC effects on DNA demethylation and cell proliferation might be related to the duration of the DNA replication phase.     

Cell cycle analysis of synchronized chinese hamster cells using bromodeoxyuridine labeling and flow cytometry

Summary Chinese hamster ovary cells were synchronized into purified populations of viable G1-, S-, G2-, and M-phase cells by a combination of methods, including growth arrest, aphidicolin block, cell cycle progression, mitotic shake-off, and centrifugal elutriation. The DNA content and bromodeoxyuridine (BrdUrd) labeling index were measured in each purified fraction by dual-parameter flow cytometry. The cell cycle distributions determined from the DNA measurements alone (single parameter) were compared with those calculated from both DNA and BrdUrd data (dual parameter). The results show that highly purified cells can be obtained using these methods, but the assessed purity depends on the method of cell cycle analysis. Using the single versus dual parameter measurement to determine cell cycle distributions gave similar results for most phases of the cell cycle, except for cells near the transition from G1- to S-phase and S- to G2-phase. There the BrdUrd labeling index determined by flow cytometry was more sensitive for detecting small amounts of DNA synthesis. As an alternative to flow cytometry, a simple method of measuring BrdUrd labeling index on cell smears was used and gave the same result as flow cytometry. Measuring both DNA content and DNA synthesis improves characterization of synchronized cell populations, especially at the transitions in and out of S-phase, when cells are undergoing dramatic shifts in biochemical activity.     

Selective analysis of antitumor drug interaction with living cancer cells as probed by surface-enhanced Raman spectroscopy

A new technique for the selective measurement of small amounts of antitumor drugs in the nucleus and cytoplasm of a living cancer cell, based on surface-enhanced Raman spectroscopy (SERS), is proposed. The ability to detect SERS signals from very dilute (up to 10^–10 M) solutions of doxorubicin or adriamycin (DOX), and 4O-tetrahydropyranyl-adriamycin (THP-ADM), as well as from their complexes with targets in vitro and in vivo, has been demonstrated. SERS spectra were obtained from a population as well as from single living erythroleukaemic K562 cells treated with DOX. The results of the measurements on the population of cells containing DOX in nuclei or in the cytoplasm are well correlated with the microscopic SERS measurements on the single cells treated with DOX, obtained by selectively recording signals from the living cell nucleus or from the cytoplasm. Possibilities for the application of this new technique in different aspects of cancer research are discussed.Abbreviations DNA deoxyribonucleic acid - DOX doxorubicin - SERS surface-enhanced Raman spectroscopy - THP-ADM 4O-tetrahydropyranyl adriamycin - PBS phosphate buffered saline Offprint requests to: M. Manfait     

Cell cycle kinetic analysis with flow cytometry in pea root meristem synchronized with aphidicolin

Meristematic cells in pea root were synchronized after treatment with aphidicolin. Flow cytometric analysis of DNA content variations revealed a variety of information: ca 50% of the cells were synchronized in the first part of the S phase; kinetic studies of the S-phase traverse revealed an increase of the DNA synthesis rate from early to late S; some of the cells in the meristem were non-cycling, arrested in Gl (19%) and G2 (12%). The possibility of using such a synchronized system in cytogenetic and biomolecular studies is discussed.     

Optofluidic rotation of living cells for single‐cell tomography

Flow cytometry provides a high throughput, multi‐dimensional analysis of cells flowing in suspension. In order to combine this feature with the ability to resolve detailed structures in 3D, we developed an optofluidic device that combines a microfluidic system with a dual beam trap. This allows for the rotation of single cells in a continuous flow, around an axis perpendicular to the imaging plane. The combination of both techniques enables the tomographic reconstruction of the 3D structure of the cell. In addition this method is capable to provide detailed 3D structural data for flow cytometry, as it improves the reconstructed z‐resolution of a standard microscopy system to produce images with isotropic resolution in all three axes.

     

Cell cycle,cell size and mitochondrial activity of hybridoma cells during batch cultivation

Cell cycle, cell size and rhodamine 123 fluorescence in cell populations of two batch cultures were analysed and quantified with a fluorescence-activated cell sorter (FACS). Two cultures derived from either exponential or stationary phase innocula were investigated in order to demonstrate the dependency of the subsequent cell growth on innoculum condition. The results demonstrated that the level of activity of cells in the innoculum culture could have a significant effect on cellular activity during the initial phase of the inoculated culture, as it advances through its growth cycle. Positive correlation was found between the cell size and mitochondrial activity (as measured by rhodamine 123 uptake) with S and G₂ fractions as the cell progressed through the cell cycle. The enumeration of the fractions of cell cycle phases has helped in prediction of the changes in cell numbers following perturbation of the culture condition.     

Spectroscopic study of human lung epithelial cells (A549) in culture: living cells versus dead cells

The noninvasive analysis of living cells grown on 3-dimensional scaffold materials is a key point in tissue engineering. In this work we show the capability of Raman spectroscopy for use as a noninvasive method to distinguish cells at different stages of the cell cycle and living cells from dead cells. The spectral differences between cells in different stages of the cell cycle are characterized mainly by variations in DNA vibrations at 782, 788, and 1095 cm(-1). The Raman spectrum of dead human lung derived (A549 line) cells indicates the breakdown of both phosphodiester bonds and DNA bases. The most sensitive peak for identifying dead cells is the 788 cm(-1) peak corresponding to DNA Obond;Pbond;O backbone stretching. The magnitude of this peak is reduced by 80% in the spectrum of dead cells. Changes in protein peaks suggest significant conformational changes; for example, the magnitude of the 1231 cm(-1) peak assigned to random coils is reduced by 63% for dead cells. The sharp peak of phenylalanine at 1005 cm(-1) drops to half, indicating a decrease of stable proteins associated with cell death. The differences in the 1190-1385 cm(-1) spectral region also suggest a decrease in the amount of nucleic acids and proteins. Using curve fitting, we quantify these spectral differences that can be used as markers of cell death.     

The role of the cell cycle in determining gene expression and productivity in CHO cells

Understanding the relationships between cell cycle and protein expression is critical to the optimisation of media and environmental conditions for successful commercial operation of animal cell culture processes. Using flow cytometry for the analysis of the early phases of synchronised batch cultures, the dependency of product expression on cell cycle related events has been evaluated in a recombinant CHO cell line. Although the production of recombinant protein is initially found to be cell cycle related, the maximum specific protein productivity is only achieved at a later stage of the exponential phase which also sees a maximum in the intracellular protein concentration. Subsequent work suggests that it is the batch phase/medium composition of cultures which is the major determinant of maximum specific productivity in this cell line. Furthermore the effect of the positive association between S phase and specific productivity is subordinate to the effect of batch phase/medium composition on the specific productivity of batch cultures. This revised version was published online in July 2006 with corrections to the Cover Date.     

Fluorescence kinetics in HeLa cells after treatment with cell cycle arrest inducers visualized with Fucci (fluorescent ubiquitination-based cell cycle indicator)

Fucci (fluorescent ubiquitination-based cell cycle indicator) is able to visualize dynamics of cell cycle progression in live cells; G1- and S-/G2-/M-phase cells expressing Fucci emit red and green fluorescence, respectively. This system could be applied to cell kinetic analysis of tumour cells in the field of cancer therapy; however, it is still unclear how fluorescence kinetics change after various treatments, including exposure to anticancer agents. To explore this, we arrested live HeLa cells expressing the Fucci probes at various cell cycle stages and observed the fluorescence, in conjunction with flow cytometric analysis. X-irradiation, HU (hydroxyurea) and nocodazole arrest cells at G2/M boundary, early S-phase and early M-phase, respectively. Although X-irradiation and HU treatment induced similar accumulation kinetics of green fluorescent cells, nocodazole treatment induced an abnormal red fluorescence at M phase, followed by accumulation of both red and green fluorescent cells with 4N DNA content. We conclude that certain agents that disrupt normal cell cycle regulation could cause unexpected fluorescence kinetics in the Fucci system.     

Cell cycle analysis and synchronization of the TN-368 insect cell line

Summary A cell cycle analysis of theTrichoplusia ni (TN-368) insect cell line is described. By means of autoradiography and percent labeled metaphase data, the cell cycle parameters were determined to be as follows: S, 4.5 hr; G₂, 8.5 hr; M, 0.5 hr; G₁, 1.0 hr; the total cell time being 14.5 hr. A synchronization procedure using 50mm thymidine in a double block procedure was used to provide a method of obtaining a large number of cells in particular cell cycle phases, especially S and G₂. This work was supported in part by U.S. Environmental Protection Agency Grant R-802516.     

Non-invasive label-free monitoring the cardiac differentiation of human embryonic stem cells in-vitro by Raman spectroscopy

Background

Online label-free monitoring of in-vitro differentiation of stem cells remains a major challenge in stem cell research. In this paper we report the use of Raman micro-spectroscopy (RMS) to measure time- and spatially-resolved molecular changes in intact embryoid bodies (EBs) during in-vitro cardiogenic differentiation.

Methods

EBs formed by aggregation of human embryonic stem cells (hESCs) were cultured in defined medium to induce differentiation towards cardiac phenotype and maintained in purpose-built micro-bioreactors on the Raman microscope for 5 days (between days 5 and 9 of differentiation) and spatially-resolved spectra were recorded at 24 h intervals.

Results

The Raman spectra showed that the onset of spontaneous beating of EBs at day 7 coincided with an increase in the intensity of the Raman bands at 1340 cm^− 1, 1083 cm^− 1, 937 cm^− 1, 858 cm^− 1, 577 cm^− 1 and 482 cm^− 1. The spectral maps corresponding to these bands had a high positive correlation with the expression of the cardiac-specific α-actinin obtained by immuno-fluorescence imaging of the same EBs. The spectral markers obtained here are also in agreement with previous studies performed on individual live hESC-derived CMs.

Conclusions

The intensity profile of these Raman bands can be used for label-free in-situ monitoring of EBs to estimate the efficacy of cardiogenic differentiation.

General significance

As the acquisition of the time-course Raman spectra did not affect the viability or the differentiation potential of the hESCs, this study demonstrates the feasibility of using RMS for on-line non-invasive continuous monitoring of such processes inside bioreactor culture systems.     

Quantitative analysis of the redox states of cytochromes in a living L929 (NCTC) cell by resonance Raman microspectroscopy

Raman spectra and images of a living L929 (NCTC) cell have been measured with 532 nm excitation. Both reduced and oxidized forms of cytochromes b and c (cyt b and cyt c) have been observed in situ without any pretreatment. The redox states of cyts b and c have been assessed quantitatively with a spectral analysis. It has been found that reduced cyt c is more abundant than oxidized cyt c, while oxidized cyt b is slightly more abundant than reduced cyt b in a living cell. (© 2013 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Stimulus‐dependent dynamics of p53 in single cells

Many biological networks respond to various inputs through a common signaling molecule that triggers distinct cellular outcomes. One potential mechanism for achieving specific input–output relationships is to trigger distinct dynamical patterns in response to different stimuli. Here we focused on the dynamics of p53, a tumor suppressor activated in response to cellular stress. We quantified the dynamics of p53 in individual cells in response to UV and observed a single pulse that increases in amplitude and duration in proportion to the UV dose. This graded response contrasts with the previously described series of fixed pulses in response to γ‐radiation. We further found that while γ‐triggered p53 pulses are excitable, the p53 response to UV is not excitable and depends on continuous signaling from the input‐sensing kinases. Using mathematical modeling and experiments, we identified feedback loops that contribute to specific features of the stimulus‐dependent dynamics of p53, including excitability and input‐duration dependency. Our study shows that different stresses elicit different temporal profiles of p53, suggesting that modulation of p53 dynamics might be used to achieve specificity in this network.     

A new flow cell and chemometric protocol for implementing in-line Raman spectroscopy in chromatography

On-line monitoring tools for downstream chromatographic processing (DSP) of biotherapeutics can enable fast actions to correct for disturbances in the upstream, gain process understanding, and eventually lead to process optimization. While UV/Vis spectroscopy is mostly assessing the protein's amino acid composition and the application of Fourier transform infrared spectroscopy is limited due to strong water interactions, Raman spectroscopy is able to assess the secondary and tertiary protein structure without significant water interactions. The aim of this work is to implement the Raman technology in DSP, by designing an in-line flow cell with a reduced dead volume of 80 μL and a reflector to increase the signal intensity as well as developing a chemometric modeling path. In this context, measurement settings were adjusted and spectra were taken from different chromatographic breakthrough curves of IgG1 in harvest. The resulting models show a small average RMSEP of 0.12 mg/mL, on a broad calibration range from 0 to 2.82 mg/mL IgG1. This work highlights the benefits of model assisted Raman spectroscopy in chromatography with complex backgrounds, lays the fundamentals for in-line monitoring of IgG1, and enables advanced control strategies. Moreover, the approach might be extended to further critical quality attributes like aggregates or could be transferred to other process steps.     

光镊捕获的单个解冻人血红细胞的拉曼光谱研究

红细胞的冰冻与解冻的实施为血液的长期保存提供了有效的方法。在过去的几十年中,红细胞冻存有过数种方法,其中高甘油冻存法比较普遍,因而用此方法保存红细胞是否对红细胞产生了影响及产生了什么影响是值得研究的。作者利用激光光镊拉曼光谱系统,通过拉曼光谱对冻存人血红细胞进行研究;结果显示,红细胞冻存前后的拉曼光谱有一定的变化,解冻提取后也产生了一定的变化,这些变化主要体现在对应拉曼光谱的位置和强度上。研究结果对进一步研究红细胞的冻存具有一定的参考价值。