Pontentiometric cyanine dyes are sensitive probes for mitochondria in intact plant cells : kinetin enhances mitochondrial fluorescence

Recent Development of Advanced Fluorescent Molecular Probes for Organelle-Targeted Cell Imaging

Fluorescent molecular probes are very powerful tools that have been generally applied in cell imaging in the research fields of biology, pathology, pharmacology, biochemistry, and medical science. In the last couple of decades, numerous molecular probes endowed with high specificity to particular organelles have been designed to illustrate intracellular images in more detail at the subcellular level. Nowadays, the development of cell biology has enabled the investigation process to go deeply into cells, even at the molecular level. Therefore, probes that can sketch a particular organelle's location while responding to certain parameters to evaluate intracellular bioprocesses are under urgent demand. It is significant to understand the basic ideas of organelle properties, as well as the vital substances related to each unique organelle, for the design of probes with high specificity and efficiency. In this review, we summarize representative multifunctional fluorescent molecular probes developed in the last decade. We focus on probes that can specially target nuclei, mitochondria, endoplasmic reticulums, and lysosomes. In each section, we first briefly introduce the significance and properties of different organelles. We then discuss how probes are designed to make them highly organelle-specific. Finally, we also consider how probes are constructed to endow them with additional functions to recognize particular physical/chemical signals of targeted organelles. Moreover, a perspective on the challenges in future applications of highly specific molecular probes in cell imaging is also proposed. We hope that this review can provide researchers with additional conceptual information about developing probes for cell imaging, assisting scientists interested in molecular biology, cell biology, and biochemistry to accelerate their scientific studies.

Could the kinetin riboside be used to inhibit human prostate cell epithelial-mesenchymal transition?

The epithelial-mesenchymal transition (EMT) is a molecular process connected to higher expression of vimentin and increased activity of transcription factors (Snail, Twist) which restrains E-cadherin. EMT has been linked to prostate cancer metastatic potential, therapy resistance, and poor outcomes. Kinetin riboside (9-(b-dribofuranosyl)-6-furfurylaminopurine, KR) is a naturally occurring cytokinin, which induces apoptosis and shows strong antiproliferative activity against various human cancer cell lines. To establish the effect of KR on human prostate cell lines, expression of, e.g. AR, E-, N-cadherins, Vimentin, Snail, Twist, and MMPs, was analysed at mRNA and protein levels using Western Blot and RT-PCR and/or RQ-PCR techniques. KR inhibited the growth of human prostate cancer cells, but also, to a small extent, of normal cells. This effect depended on the type of the cells and their androgen sensitivity. KR also decreased the level of p-Akt, which takes part in androgen signalling modulation. The antiapoptotic Bcl-2 protein was down-regulated in cancer cell lines, while that of Bax is up-regulated upon KR exposure. KR contributed to re-expression of the E-cadherin as well as to significant changes in cell migration. Taken together, our results indicate for the first time that KR can be proposed as a factor for signalling pathways regulation that participates in the inhibition of development of aggressive forms of prostate cancer, and may alter the approach to therapeutic interventions. We propose KR as a potent inhibitor of EMT in human prostate cells.

Pulsing of membrane potential in individual mitochondria: a stress-induced mechanism to regulate respiratory bioenergetics in Arabidopsis

Mitochondrial ATP synthesis is driven by a membrane potential across the inner mitochondrial membrane; this potential is generated by the proton-pumping electron transport chain. A balance between proton pumping and dissipation of the proton gradient by ATP-synthase is critical to avoid formation of excessive reactive oxygen species due to overreduction of the electron transport chain. Here, we report a mechanism that regulates bioenergetic balance in individual mitochondria: a transient partial depolarization of the inner membrane. Single mitochondria in living Arabidopsis thaliana root cells undergo sporadic rapid cycles of partial dissipation and restoration of membrane potential, as observed by real-time monitoring of the fluorescence of the lipophilic cationic dye tetramethyl rhodamine methyl ester. Pulsing is induced in tissues challenged by high temperature, H(2)O(2), or cadmium. Pulses were coincident with a pronounced transient alkalinization of the matrix and are therefore not caused by uncoupling protein or by the opening of a nonspecific channel, which would lead to matrix acidification. Instead, a pulse is the result of Ca(2+) influx, which was observed coincident with pulsing; moreover, inhibitors of calcium transport reduced pulsing. We propose a role for pulsing as a transient uncoupling mechanism to counteract mitochondrial dysfunction and reactive oxygen species production.

Organelle-selective energy transfer: a fluorescent indicator of intracellular environment

A dye cassette fluoresces green (ca 520 nm) in the cytoplasm, endoplasmic reticulum (ER), and lysosomes, but red in mitochondria, that is, it illustrates 'organelle specific energy transfer'. This phenomenon may open new horizons in intracellular imaging.

Nanoparticle phagocytosis and cellular stress: involvement in cellular imaging and in gene therapy against glioma

In gene therapy against glioma, targeting tumoral tissue is not an easy task. We used the tumor infiltrating property of microglia in this study. These cells are well adapted to this therapy since they can phagocyte nanoparticles and allow their visualization by MRI. Indeed, while many studies have used transfected microglia containing a suicide gene and other internalized nanoparticles to visualize microglia, none have combined both approaches during gene therapy. Microglia cells were transfected with the TK-GFP gene under the control of the HSP(70) promoter. First, the possible cellular stress induced by nanoparticle internalization was checked to avoid a non-specific activation of the suicide gene. Then, MR images were obtained on tubes containing microglia loaded with superparamagnetic nanoparticles (VUSPIO) to characterize their MR properties, as well as their potential to track cells in vivo. VUSPIO were efficiently internalized by microglia, were found non-toxic and their internalization did not induce any cellular stress. VUSPIO relaxivity r(2) was 224 mM(-1).s(-1). Such results could generate a very high contrast between loaded and unloaded cells on T(2)-weighted images. The intracellular presence of VUSPIO does not prevent suicide gene activity, since TK is expressed in vitro and functional in vivo. It allows MRI detection of gene modified macrophages during cell therapy strategies.

Distribution of phytoplasmas in infected plants as revealed by real-time PCR and bioimaging

Phytoplasmas are cell wall-less bacteria inhabiting the phloem and utilizing it for their spread. Infected plants often show changes in growth pattern and a reduced crop yield. A quantitative real-time polymerase chain reaction (Q-PCR) assay and a bioimaging method were developed to quantify and localize phytoplasmas in situ. According to the Q-PCR assay, phytoplasmas accumulated disproportionately in source leaves of Euphorbia pulcherrima and, to a lesser extent, in petioles of source leaves and in stems. However, phytoplasma accumulation was small or nondetectable in sink organs (roots and sink leaves). For bioimaging, infected plant tissue was stained with vital fluorescence dyes and examined using confocal laser scanning microscopy. With a DNA-sensitive dye, the pathogens were detected exclusively in the phloem, where they formed dense masses in sieve tubes of Catharanthus roseus. Sieve tubes were identified by counterstaining with aniline blue for callose and multiphoton excitation. With a potentiometric dye, not all DNA-positive material was stained, suggesting that the dye stained metabolically active phytoplasmas only. Some highly infected sieve tubes contained phytoplasmas that were either inactive or dead upon staining.

Sensitive and reliable JC-1 and TOTO-3 double staining to assess mitochondrial transmembrane potential and plasma membrane integrity: interest for cell death investigations

BACKGROUND

Apoptosis is currently studied by flow cytometry with mitochondrial membrane potential (Deltapsimt) and membrane integrity fluorochromes. Rhodamine 123 and DiOC6(3) remain controversial to identify cells displaying a low Deltapsimt. JC-1 constitutes a good Deltapsimt indicator, due to a fluorescence shift from green to orange emission, according to the increase in Deltapsimt. Nevertheless, it is not feasible to analyze it simultaneously with propidium iodide. Among available fluorescent probes, TOTO-3 seems to be a good candidate for double staining with JC-1.

METHODS

Cell death of HaCaT cells was induced by H2O2 and FasL. Samples were stained with DiOC6(3)/IP or JC-1/TOTO-3 then analyzed by flow cytometry. Results were supported by confocal microscopy analyses of mitochondrial membrane potential. Moreover, cell morphology was determined on the sorted subpopulations defined on the basis of staining (JC-1 versus TOTO-3).

RESULTS

We found that JC-1 is a more efficient mitochondrial probe than DiOC6(3). After stress induction, the fluorescence level of JC-1 and TOTO-3 clearly defined three fluorescent subpopulations, respectively: (1) JC-1high and TOTO-3low, (2) JC-1low and TOTO-3medium, and (3) JC-1low and TOTO-3high. Their morphologic aspects after cell sorting indicated that they corresponded to three functional states (intact, apoptotic, and necrotic cells), and data were supported by caspase activity measurements.

CONCLUSIONS

We propose a reliable and efficient staining, with JC-1 and TOTO-3 to discriminate three functional cellular states: intact, apoptotic, and necrotic/late apoptotic cells by flow cytometry.

Progesterone induces hyperpolarization after a transient depolarization phase in human spermatozoa

Progesterone (P4) induces a membrane depolarization and various ion fluxes (chloride efflux, sodium and calcium influxes), which are required for the human sperm acrosome reaction (AR). By use of the potentiometric fluorescent dye DiSC3(5) and two different technical approaches, the present study aimed to quantify and further analyze P4-induced modifications in membrane potential in capacitated human spermatozoa. Spectrofluorimetric analysis revealed that the mean resting membrane potential of sperm was -58 +/- 2 mV (n = 12). When 10 microM P4 was added, the sperm membrane depolarized by approximately +15 mV, partly driven by a Cl- efflux. It subsequently repolarized to reach a significant lower potential than the initial resting potential in two thirds of the tested samples. The flow cytometry analysis showed a heterogeneous resting membrane potential and revealed that the depolarization-hyperpolarization events concerned only subpopulations, between 3% and 40% of the sperm cells according to the samples (n = 7). We hypothesize that P4 has a beneficial effect on the ability of zona pellucida to promote the AR in a sperm subpopulation by increasing the number of hyperpolarized cells presenting a membrane potential that is compatible with the opening of T-type calcium channels by subsequent zona pellucida-induced depolarization.

Current status of flow cytometry in cell and molecular biology

This review summarizes recent developments in flow cytometry (FC). It gives an overview of techniques currently available, in terms of apparatus and sample handling, a guide to evaluating applications, an overview of dyes and staining methods, an introduction to internet resources, and a broad listing of classic references and reviews in various fields of interest, as well as some recent interesting articles.

Mitochondrial contribution to the anoxic Ca2+ signal in maize suspension-cultured cells

Anoxia induces a rapid elevation of the cytosolic Ca2+ concentration ([Ca2+]cyt) in maize (Zea mays L.) cells, which is caused by the release of the ion from intracellular stores. This anoxic Ca2+ release is important for gene activation and survival in O2-deprived maize seedlings and cells. In this study we examined the contribution of mitochondrial Ca2+ to the anoxic [Ca2+]cyt elevation in maize cells. Imaging of intramitochondrial Ca2+ levels showed that a majority of mitochondria released their Ca2+ in response to anoxia and took up Ca2+ upon reoxygenation. We also investigated whether the mitochondrial Ca2+ release contributed to the increase in [Ca2+]cyt under anoxia. Analysis of the spatial association between anoxic [Ca2+]cyt changes and the distribution of mitochondrial and other intracellular Ca2+ stores revealed that the largest [Ca2+]cyt increases occurred close to mitochondria and away from the tonoplast. In addition, carbonylcyanide p-trifluoromethoxyphenyl hydrazone treatment depolarized mitochondria and caused a mild elevation of [Ca2+]cyt under aerobic conditions but prevented a [Ca2+]cyt increase in response to a subsequent anoxic pulse. These results suggest that mitochondria play an important role in the anoxic elevation of [Ca2+]cyt and participate in the signaling of O2 deprivation.

Compartmentation of lactate and glucose metabolism in C6 glioma cells. A 13c and 1H NMR study

13C and 1H NMR spectroscopy was used to investigate the metabolism of L-lactate and D-glucose in C6 glioma cells. The changing of lactate and glucose concentration in the extracellular medium of C6 glioma cells incubated with 5.5 mM glucose and 11 mM lactate indicated a net production of lactate as the consequence of an active aerobic glycolysis. The 13C enrichments of various metabolites were determined after 4-h cell incubation in media containing both substrates, each of them being alternatively labeled in the form of either [3-13C]L-lactate or [1-13C]D-glucose. Using 11 mM [3-13C]L-lactate, the enrichment of glutamate C4, 69%, was found higher than that of alanine C3, 32%, when that of acetyl-CoA C2 was 78%. These results indicated that exogenous lactate was the major substrate for the oxidative metabolism of the cells. Nevertheless, an active glycolysis occurred, leading to a net lactate production. This lactate was, however, metabolically different from the exogenous lactate as both lactate species did not mix into a unique compartment. The results were actually consistent with the concept of the existence of two pools of both lactate and pyruvate, wherein one pool was closely connected with exogenous lactate and was the main fuel for the oxidative metabolism, and the other pool was closely related to aerobic glycolysis.

Correlation of Rapid Cell Death with Metabolic Changes in Fungus-Infected, Cultured Parsley Cells

To study in detail the hypersensitive reaction, one of the major defense responses of plants against microbial infection, we used a model system of reduced complexity with cultured parsley (Petroselinum crispum) cells infected with the phytopathogenic fungus Phytophthora infestans. Experimental conditions were established to maintain maximal viability of the cultured cells during co-cultivation with fungal germlings, and a large proportion of the infected parsley cells responded to fungal infection with rapid cell death, thereby exhibiting major features of the hypersensitive reaction in whole-plant-pathogen interactions. Rapid cell death clearly correlated with termination of further growth and development of the fungal pathogen. Thus, the system fulfilled important prerequisites for investigating cell-death-related metabolic changes in individual infected cells. Using cytochemical methods, we monitored the increase of mitochondrial activity in single infected cells and the intracellular accumulation of reactive oxygen species prior to the occurrence of rapid cell death. We obtained strong correlative evidence for the involvement of these intracellularly accumulating reactive oxygen species in membrane damage and in the resulting abrupt collapse of the cell.

Structurally modified trimethine thiacarbocyanine dyes. Effect of N-alkyl substituents on antineoplastic behavior

The effect of dye localization and dye distribution on the antineoplastic behavior of photosensitizers was investigated with a homologous series of trimethine thiacarbocyanine dyes in L1210 leukemia and A549 lung carcinoma cells. These dyes were synthesized with N-alkyl groups of different sizes (ethyl to octadecyl) to vary their lipophilic properties without compromising their photophysics. While dyes with smaller N-alkyl groups (ethyl to decyl) were already cytotoxic in the dark, longer chain cyanines exhibited antineoplastic activity only after exposure to light. Results from this study indicate that the switch from dark cytotoxicity to phototoxicity occurred when dyes, due to a decrease in cationic character with increasing size of alkyl substituents, were no longer able to cross the plasma membrane. Dark cytotoxicity decreased with increasing size of N-alkyl groups and was cell-line independent. On the other hand, photodynamic damage varied by several orders of magnitude depending on the cell line and the length of the alkyl substituents. The most effective photosensitizer was the dioctadecyl dye which achieved a 4- to 5-log reduction of leukemia cells, although it had very modest triplet and singlet oxygen quantum yields of 0.008 and 0.006, respectively. This study also showed that photobiological performance can be improved greatly by optimizing dye binding properties via structural modifications.

Confocal laser scanning microscopy of mitochondria within microspore tetrads of plants using rhodamine 123 as a fluorescent vital stain

The present study demonstrates that rhodamine 123 penetrates the callose walls surrounding plant microspores before they are released from tetrads. The stain accumulates in active mitochondria due to the electrical potential across the mitochondrial membrane. Accumulation of dye does not occur in mitochondria of fixed cells and fades quickly when mitochondrial activity is inhibited by exposure to carbonyl cyanide m-chlorophenyl hydrazone. Rhodamine can be used as a viability test for microspores still within tetrads, thus making it possible to determine when during development genes leading to pollen sterility are expressed. Rhodamine 123 is excited by blue (550 nm) light and can thus be used with confocal laser scanning microscopy. Anthers of Nicotiana tabacum, Oenothera villaricae, Silene dioica and Lycopersicum esculentum were studied here.

Small lipid-soluble cations are not membrane voltage probes for Neurospora or Saccharomyces

Small lipid-soluble cations, such as tetraphenylphosphonium (TPP+) and tetraphenylarsonium (TPA+) are frequently used as probes of membrane voltage (delta psi, or Vm) for small animal cells, organelles, and vesicles. Because much controversy has accompanied corresponding measurements on 'walled' eukaryotic cells (plants, fungi), we studied their transport and relation to Vm in the large-celled fungus Neurospora crassa-where Vm can readily be determined with microelectrodes-as well as in the most commonly used model eukaryotic cell, the yeast Saccharomyces cerevisiae. We found no reasonable conditions under which the distribution of TPP+ or TPA+, between the cytoplasm (i) and extracellular solution (o), can serve to estimate Vm, even roughly, in either of these organisms. When applied at probe concentrations (i.e., < or = 100 microM, which did not depolarize the cells nor deplete ATP), TPP+ stabilized at ratios (i/o) below 30 in both organisms. That would imply apparent Vm values positive to -90 mV, in the face of directly measured Vm values (in Neurospora) negative to -180 mV. When applied at moderate or high concentrations (1-30 mM), TPP+ and TPA+ induced several phases of depolarization and changes of membrane resistance (Rm), as well as depletion of cytoplasmic energy stores. Only the first phase depolarization, occurring within the perfusion-turnover time and accompanied by a nearly proportionate decline of Rm, could have resulted from TPP+ or TPA+ currents per se. And the implied currents were small. Repeated testing, furthermore, greatly reduced the depolarizing effects of these lipid-soluble ions, implicating an active cellular response to decrease membrane permeability.

Mitochondrial dysfunction in yeast expressing the cytoplasmic male sterility T-urf13 gene from maize: analysis at the population and individual cell level

The urf13TW gene, which is derived from the mitochondrial T-urf13 gene responsible for Texas cytoplasmic male sterility in maize, was expressed in Saccharomyces cerevisiae by targeting its translation product into mitochondria. Analysis by oxygraphy at the population level revealed that in the presence of methomyl the oxygen uptake of intact yeast cells carrying the targeted protein is strongly stimulated only with ethanol as respiratory substrate and not with glycerol, lactate, pyruvate, or acetate. When malate is the substrate oxidized by isolated mitochondria, interaction between the targeted protein and methomyl results in significant inhibition of oxygen uptake. This inhibition is eliminated and oxygen uptake is stimulated by subsequent addition of NAD+. Using 3,3'-dihexyloxacarbocyanine iodide [DiOC6(3)] as probe, interactive laser scanning and flow cytometry, which permit analysis at the individual cell level, demonstrated that specific staining of the mitochondrial compartment is obtained and that DiOC6(3) fluorescence serves as a measure of the membrane potential. Finally, it was shown that, as in T cytoplasm maize mitochondria, HmT toxin and methomyl dissipate the membrane potential of yeast mitochondria that carry the foreign protein. Furthermore, the results suggest that the HmT toxin and methomyl response is related to the plasmid copy number per cell and that the deleterious effect induced by HmT toxin is stronger than that of methomyl.

Flow Cytometric Analysis of Rhodamine 123 Fluorescence during Modulation of the Membrane Potential in Plant Mitochondria

The fluorescent dye rhodamine 123, which selectively accumulates in mitochondria based on the membrane potential, was used with flow cytometry to evaluate variations in activity of mitochondria isolated from plant tissues. In the presence of succinate and ATP, potato (Solanum tuberosum L.) tuber mitochondrial activity was affected by metabolic inhibitors and compounds that modify the membrane potential. The more uniform the mitochondrial population, the higher the observed membrane potential. The reactive population corresponds to the proportion of intact mitochondria (94-97%) defined by classic methods. Changes in the light-scattering properties are more related to internal modifications affecting the inner membrane-matrix system of the mitochondria during metabolic modulation than to specific volume change or outer membrane surface modifications. We tested our approach using an Arum maculatum preparation that contains three different types of mitochondria and demonstrated the validity of the light-scatter measurements to distinguish the alpha, beta, and [ill] mitochondria and to measure their ability to built up a membrane potential in the presence of succinate. These results demonstrate clearly that flow cytometric techniques using rhodamine 123 can be employed to study the activity in isolated plant mitochondria.

Monitoring by epifluorescence microscopy of organelle DNA fate during pollen development in five angiosperm species

The fates of mitochondrial and plastid nucleoids during pollen development in six angiosperm species (Antirrhinum majus, Glycine max, Medicago sativa, Nicotiana tabacum, Pisum sativum, and Trifolium pratense) were examined using epifluorescence microscopy after double staining with 4',6-diamidino-2- phenylindole (DAPI) to stain DNA and with a potentiometric dye (either DiOC7 or rhodamine 123) for visualization of metabolically active mitochondria. From the pollen mother cell stage to the microspore stage of pollen development, mitochondria and plastids both contained DNA detectable by DAPI staining. However, during the further maturation preceding anthesis, mitochondrial DNA became undetectable cytologically in either the generative or the vegetative cell of mature pollen; even in germinated pollen tubes containing hundreds of metabolically active mitochondria undergoing cytoplasmic streaming, vital staining with DAPI failed to reveal mitochondrial DNA. By the mature pollen stage, plastid DNA also became undetectable by DAPI staining in the vegetative cell. However, in the generative cell of mature pollen the timing of plastid DNA disappearance as detected by DAPI varied with the species. Plastid DNA remained detectable only in the generative cells of pollen grains from species known or suspected to have biparental transmission of plastids. The apparent absence of cytologically detectable organelle genomes in living pollen was further examined using molecular methods by hybridizing organelle DNA-specific probes to digests of total DNA from mature pollen and from other organs of A. majus and N. tabacum, both known to be maternal for organelle inheritance. Mitochondrial DNA was detected in pollen of both species; thus the cytological alteration of mitochondrial genomes during pollen development does not correspond with total mtDNA loss from the pollen. Plastid DNA was detectable with molecular probes in N. tabacum pollen but not in A. majus pollen. Since the organelle DNA detected by molecular methods in mature pollen may lie solely in the vegetative cell, further study of the basis of maternal inheritance of mitochondria and plastids will require molecular methods which distinguish vegetative cell from reproductive cell organelle genomes. The biological effect of the striking morphological alteration of organelle genomes during later stages of pollen development, which leaves them detectable by molecular methods but not by DAPI staining, is as yet unknown.

The activity of powdery-mildew haustoria after feeding the host cells with different sugars, as measured with a potentiometric cyanine dye

The biotrophic parasite Erysiphe graminis f. sp. hordei produces haustoria within the cells of its host Hordeum vulgare. To determine the physiological activity of these haustoria, the electric potential across the membranes in the mitochondria of the haustorium was studied. The membrane potential was estimated with the fluorescent potentiometric cyanine dye 3,3'-dibutyloxacarbocyanine iodide. The addition of depolarizing agents (carbonylcyanide m-chlorophenylhydrazone, 2,4-dinitrophenol or KCN) to infected cells resulted in an increase of fluorescence after the addition of low concentrations or a decrease of fluorescence after the addition of higher concentrations. When the infected host cell was fed with increasing concentrations of D-glucose (25, 50, 75 mM), corresponding decreases of fluorescence were measured immediately in the mitochondria of the fungal haustoria. Sucrose induced a similar reduction of fluorescence about 20 min late. D-Galactose and D-fructose induced a somewhat smaller reduction of fluorescence, L-glucose and D-glucitol had no effect. The results indicate that haustoria take up glucose from the host cells immediately. Sucrose, D-galactose and D-fructose seem to require time to be metabolized before their products reach the fungal haustorium or mitochondria.