Studies of cell division (mitosis and cytokinesis) by dynamic secondary ion mass spectrometry ion microscopy: LLC-PK1 epithelial cells as a model for subcellular isotopic imaging

The restriction of calcium influx in metaphase and post-metaphase stages of cell division revealed by imaging secondary ion mass spectrometry (SIMS)

A secondary ion mass spectrometry (SIMS)-based isotopic imaging technique of ion microscopy was used for observing calcium influx in single renal epithelial LLC-PK₁ cells. The CAMECA IMS-3f SIMS instrument, used in the study, is capable of producing isotopic images of single cells at 500 nm spatial resolution. Due to the high-vacuum requirements of the instrument the cells were prepared cryogenically with a freeze-fracture method and frozen freeze-dried cells were used for SIMS analysis. The influx of calcium was imaged directly by exposure of cells to ⁴⁴ Ca stable isotope in the extracellular buffer for 10 min. The ⁴⁴ Ca influx was measured at mass 44 and the distribution of endogenous calcium at mass 40 (⁴⁰ Ca) in the same cell. A direct comparison of interphase cells to cells undergoing division revealed that calcium influx is restricted in metaphase and post-metaphase stages of cell division. This restriction is lifted in late cytokinesis. The net influx of ⁴⁴ Ca in 10 min was approximately half under calcium influx restriction in comparison to interphase cells. Under calcium influx restriction the ⁴⁴ Ca concentration was the same between the mitotic chromosome and the cytoplasm. These observations indicate that the endoplasmic reticulum (ER) calcium uptake is compromised under calcium influx restriction in cells undergoing division.

Delineation of Neuroprotective Effects and Possible Benefits of AntioxidantsTherapy for the Treatment of Alzheimer's Diseases by Targeting Mitochondrial-Derived Reactive Oxygen Species: Bench to Bedside

Alzheimer's disease (AD) is considered the sixth leading cause of death in elderly patients and is characterized by progressive neuronal degeneration and impairment in memory, language, etc. AD is characterized by the deposition of senile plaque, accumulation of fibrils, and neurofibrillary tangles (NFTs) which are responsible for neuronal degeneration. Amyloid-β (Aβ) plays a key role in the process of neuronal degeneration in the case of AD. It has been reported that Aβ is responsible for the production of reactive oxygen species (ROS), depletion of endogenous antioxidants, increase in intracellular Ca²⁺ which further increases mitochondria dysfunctions, oxidative stress, release of pro-apoptotic factors, neuronal apoptosis, etc. Thus, oxidative stress plays a key role in the pathogenesis of AD. Antioxidants are compounds that have the ability to counteract the oxidative damage conferred by ROS. Therefore, the antioxidant therapy may provide benefits and halt the progress of AD to advance stages by counteracting neuronal degeneration. However, despite the beneficial effects imposed by the antioxidants, the findings from the clinical studies suggested inconsistent results which might be due to poor study design, selection of the wrong antioxidant, inability of the molecule to cross the blood-brain barrier (BBB), treatment in the advanced state of disease, etc. The present review insights into the neuroprotective effects and limitations of the antioxidant therapy for the treatment of AD by targeting mitochondrial-derived ROS. This particular article will certainly help the researchers to search new avenues for the treatment of AD by utilizing mitochondrial-derived ROS-targeted antioxidant therapies.

Preserving elemental content in adherent mammalian cells for analysis by synchrotron-based x-ray fluorescence microscopy

Trace metals play important roles in biological function, and x-ray fluorescence microscopy (XFM) provides a way to quantitatively image their distribution within cells. The faithfulness of these measurements is dependent on proper sample preparation. Using mouse embryonic fibroblast NIH/3T3 cells as an example, we compare various approaches to the preparation of adherent mammalian cells for XFM imaging under ambient temperature. Direct side-by-side comparison shows that plunge-freezing-based cryoimmobilization provides more faithful preservation than conventional chemical fixation for most biologically important elements including P, S, Cl, K, Fe, Cu, Zn and possibly Ca in adherent mammalian cells. Although cells rinsed with fresh media had a great deal of extracellular background signal for Cl and Ca, this approach maintained cells at the best possible physiological status before rapid freezing and it does not interfere with XFM analysis of other elements. If chemical fixation has to be chosen, the combination of 3% paraformaldehyde and 1.5 % glutaraldehyde preserves S, Fe, Cu and Zn better than either fixative alone. When chemically fixed cells were subjected to a variety of dehydration processes, air drying was proved to be more suitable than other drying methods such as graded ethanol dehydration and freeze drying. This first detailed comparison for x-ray fluorescence microscopy shows how detailed quantitative conclusions can be affected by the choice of cell preparation method.

ERK Plays a Role in Chromosome Alignment and Participates in M-Phase Progression

Cell division, a prerequisite for cell proliferation, is a process in which each daughter cell inherits one complete set of chromosomes. The mitotic spindle is a dedicated apparatus for the alignment and segregation of chromosomes. Extracellular signal-regulated kinase (ERK) 1/2 plays crucial roles in cell cycle progression, particularly during M-phase. Although, association with the mitotic spindle has been reported, the precise roles played by ERK in the dynamics of the mitotic spindle and in M-phase progression remain to be elucidated. In this study, we used MEK inhibitors U0126 and GSK1120212 to dissect the roles of ERK in M-phase progression and chromosome alignment. Fluorescence microscopy revealed that ERK is localized to the spindle microtubules in a manner independent of Src kinase, which is one of the kinases upstream of ERK at mitotic entry. ERK inhibition induces an increase in the number of prophase cells and a decrease in the number of anaphase cells. Time-lapse imaging revealed that ERK inhibition perturbs chromosome alignment, thereby preventing cells from entering anaphase. These results suggest that ERK plays a role in M-phase progression by regulating chromosome alignment and demonstrate one of the mechanisms by which the aberration of ERK signaling may produce cancer cells.

Mass spectrometry imaging and profiling of single cells

Mass spectrometry imaging and profiling of individual cells and subcellular structures provide unique analytical capabilities for biological and biomedical research, including determination of the biochemical heterogeneity of cellular populations and intracellular localization of pharmaceuticals. Two mass spectrometry technologies-secondary ion mass spectrometry (SIMS) and matrix assisted laser desorption/ionization mass spectrometry (MALDI MS)-are most often used in micro-bioanalytical investigations. Recent advances in ion probe technologies have increased the dynamic range and sensitivity of analyte detection by SIMS, allowing two- and three-dimensional localization of analytes in a variety of cells. SIMS operating in the mass spectrometry imaging (MSI) mode can routinely reach spatial resolutions at the submicron level; therefore, it is frequently used in studies of the chemical composition of subcellular structures. MALDI MS offers a large mass range and high sensitivity of analyte detection. It has been successfully applied in a variety of single-cell and organelle profiling studies. Innovative instrumentation such as scanning microprobe MALDI and mass microscope spectrometers enables new subcellular MSI measurements. Other approaches for MS-based chemical imaging and profiling include those based on near-field laser ablation and inductively-coupled plasma MS analysis, which offer complementary capabilities for subcellular chemical imaging and profiling.

Development of a new bimodal imaging methodology: a combination of fluorescence microscopy and high-resolution secondary ion mass spectrometry

In this paper, we present a new experimental methodology to combine mass spectrometry (NanoSIMS) with fluorescence microscopy to provide subcellular information on the location of small molecules in cultured cells. We demonstrate this by comparing the distribution of 5-bromo-2-deoxyuridine in the same cells given by both NanoSIMS analysis and by fluorescence immunohistochemistry. Fiducial markers in the substrates ensured that the images formed by SIMS mapping of bromine ions could be co-registered exactly with images from fluorescence microscopy. The NanoSIMS was shown to faithfully reproduce the information from fluorescence microscopy, but at a much higher spatial resolution. We then show preliminary SIMS images on the distribution of ATN-224, a therapeutic copper chelator for which there is no fluorescent marker, co-registered with conventional Lysotracker and Hoechst stains on the same cells.

Applying imaging ToF-SIMS and PCA in differentiation of tissue types

Time-of-flight secondary ion mass spectrometry (ToF-SIMS) has proven to be an extremely powerful tool for characterizing chemical distributions within biological cells and tissues. However, differentiating biological samples, e.g., cancerous cells from their normal counterparts or benign tissues from malignant tissues, presents unique challenges to ToF-SIMS. Repeatable differentiation of such samples, especially formalin-fixed paraffin-embedded (FFPE) histological specimens, could be used to improve tissue-based diagnosis and aid in prognosis decisions. In this chapter, we describe a strategy for characterizing and differentiating FFPE tissues. ToF-SIMS was used to image deparaffinized FFPE mouse embryos and differentiate tissue types. The robustness and repeatability of the method was determined by analyzing ten tissue slices from three different embryos over a period of 1 month. Using principal component analysis (PCA) to reduce the spectral data generated by ToF-SIMS, histopathologically identified tissue types of the mouse embryos can be differentiated based on the characteristic differences in their mass spectra.

Single-cell ecophysiology of microbes as revealed by Raman microspectroscopy or secondary ion mass spectrometry imaging

An astonishing diversity of microorganisms thrives on our planet and their activities are fundamental for the functioning of all ecosystems including the human body. Consequently, detailed insights into the functions performed by microorganisms in their natural environment are required to understand human biology and the biology of the world around us and to lay the foundations for targeted manipulation of microbial communities. Isotope-labeling techniques combined with molecular detection tools are frequently used by microbial ecologists to directly link structure and function of microbial communities and to monitor metabolic properties of uncultured microbes at the single-cell level. However, only the recent combination of such techniques with Raman microspectroscopy or secondary ion mass spectrometry enables functional studies of microbes on a single-cell level by using stable isotopes as labels. This review provides an overview of these new techniques and their applications in microbial ecology, which allow us to investigate the ecophysiology of uncultured microbes to an extent that was unimaginable just a few years ago.

Perspectives for imaging mass spectrometry in the proteomics landscape

A number of techniques are used in the field of proteomics that can be combined to get the most molecular information from a specific biological sample, fluid or tissue. Imaging techniques are often used to obtain local information from tissue samples. However, imaging experiments are often staining experiments, which rely on specific or aspecific interactions between fluorescent markers and pre-defined (families of) peptide or protein. Therefore, imaging is often used as a screening or validation tool for the local presence of proteins that have been identified by other means. Imaging mass spectrometry (IMS) combines the advantages of MS and microscopy in a single experiment. It is a technique that does not require any labeling of the analytes and provides a high multiplexing capability combined with the potential for analyte identification. It enables simultaneous detection of potentially all peptides and proteins present at a tissue surface and is used for the determination and identification of tissue-specific disease markers. The workflows of IMS experiments closely resemble those of conventional proteomics. In this review, we describe IMS experiments step-by-step to position and evaluate the role of IMS in a comparative proteomics landscape. We illustrate in a concise review that IMS is a true discovery oriented tool for proteomics that seamlessly integrates in conventional proteomics workflows and can be perceived as either an alternative or complementary proteomics technique.

Surface analysis by imaging mass spectrometry

A review of four MS-based techniques available for molecular surface imaging is presented. The main focus is on the commercially available mass spectrometry imaging techniques: secondary ion mass spectrometry (SIMS), matrix assisted laser desorption ionization mass spectrometry (MALDI-MS), desorption electrospray ionization mass spectrometry (DESI-MS) and laser ablation inductively-coupled plasma mass spectrometry (LA-ICP-MS). A short historical perspective is presented and traditional desorption ionization techniques are also briefly described. The four techniques are compared mainly with respect to their usage for imaging of biological surfaces. MALDI is evaluated as the most successful in life sciences and the only technique usable for imaging of large biopolymers. SIMS is less common but offers superior spatial lateral resolution and DESI is considered to be an emerging alternative approach in mass spectrometry imaging. LA-ICP ionization is unbeatable in terms of limits of detection but does not provide structural information. All techniques are considered extremely useful, representing a new wave of expansion of mass spectrometry into surface science and bioanalysis. A minireview with 121 references.

Quantitative imaging of subcellular calcium stores in mammalian LLC-PK1 epithelial cells undergoing mitosis by SIMS ion microscopy

Quantitative 3-D total calcium gradients, representing subcellular stored calcium, were imaged with a CAMECA IMS-3f SIMS ion microscope in cryogenically prepared frozen freeze-dried LLC-PK1 cells captured in interphase and various stages of mitosis. 39K and 23Na concentrations were also measured in the same cells. Correlative optical (or SEM) and SIMS analysis of cells revealed a redistribution of the interphase Golgi calcium store in prophase and prometaphase cells. In metaphase cells, simultaneous SIMS imaging of total calcium in both the spindle and the non-spindle cytoplasm of individual cells revealed a gradual and dynamic alignment of calcium stores in both half-spindles prior to the onset of anaphase. The anaphase cells revealed the highest local total calcium concentrations in the spindle regions behind the daughter chromosomes and the lowest in the central spindle region. The pericentriolar material in telophase cells contained calcium stores. Quantitatively, a typical metaphase cell with well-aligned calcium stores in the spindle region contained 1.1 mM total calcium in each half-spindle, 0.8 mM total calcium in the non-spindle cytoplasm, and 0.5mM total calcium in the chromosomes. At the submicron scale, the distribution of total calcium was heterogeneous in the chromosomes, metaphase spindle, and non-spindle cytoplasm. An increased binding of calcium to chromosomes is not a physiological requirement for chromosomal condensation in mitosis, since interphase nuclei and mitotic chromosomes contained comparable total calcium concentrations measured per unit volume. A significant reduction of total calcium in the non-spindle cytoplasm was observed in the metaphase, anaphase, and telophase cells, which is indicative of the limited storage of the releasable calcium pool in these specific stages of mitosis. Direct total calcium measurements in subcellular regions confirmed that both the spindle and the non-spindle cytoplasm of metaphase cells contained inositol 1,4,5-trisphosphate (IP3)-sensitive calcium stores sensitive to arginine vasopressin, thapsigargin, and calcium ionophore A23187. The dynamic alignment of calcium stores in both half-spindles may be an integral part of the time-dependent process of a cell's overall preparation for exiting the metaphase stage in mammalian LLC-PK1 cells.

Imaging mass spectrometry: fundamentals and applications to drug discovery

Imaging mass spectrometry (IMS) encompasses a variety of techniques that enable the chemical imaging of analytes, which range in size from atoms and small molecules to intact proteins, directly from biological tissues. IMS is transforming specific areas in biological research with its unique combination of chemical and spatial information. Innovations in instrumentation and imaging protocols will make this approach invaluable at many stages of the drug discovery process, including pharmacological target screening and evaluating the distribution of drug and drug metabolites in cells and tissues. The fundamentals and unique methodology of IMS are discussed, along with exciting new applications to drug discovery science.

Focused ion beam/scanning electron microscopy studies of Porcellio scaber (Isopoda, Crustacea) digestive gland epithelium cells

The focused ion beam (FIB) was used to prepare cross sections of precisely selected regions of the digestive gland epithelium of a terrestrial isopod P. scaber (Isopoda, Crustacea) for scanning electron microscopy (SEM). The FIB/SEM system allows ad libitum selection of a region for gross morphologic to ultrastructural investigation, as the repetition of FIB/SEM operations is unrestricted. The milling parameters used in our work proved to be satisfactory to produce serial two-dimensional (2-D) cuts and/or three-dimensional (3-D) shapes on a submicrometer scale. A final, cleaning mill at lower ion currents was employed to minimize the milling artifacts. After cleaning, the milled surface was free of filament- and ridge-like milling artifacts. No other effects of the cleaning mill were observed.