Flow-cytometric analysis of mitochondria-associated fluorescence in young and old human fibroblasts

Glucose Dialysate Induces Mitochondrial DNA Damage in Peritoneal Mesothelial Cells

Background

It is known that peritoneal mesothelial cells (PMCs) are denuded in patients undergoing long-term continuous ambulatory peritoneal dialysis (CAPD); the mechanism of damage is not well known. A high quantity of glucose loaded onto PMCs in these patients may generate toxic radicals during the mitochondrial metabolism, leading to mitochondrial DNA damage that accumulates due to the incomplete repair system of this DNA.

Objective

To study damage to the PMCs of long-term CAPD patients, and to examine whether glucose overload accelerates this damage in vitro.

Design

Descriptive clinical and in vitro study.

Participants

Stable CAPD patients and nonuremic patients undergoing elective abdominal surgery.

Methods

( 1 ) Clinical Samples: 13 peritoneal tissue samples from CAPD patients and 5 omental tissue samples from patients with normal renal function were investigated. PMCs in dialysate effluent were collected from another 13 stable CAPD patients. ( 2 ) In Vitro Samples: Primary cultured PMCs were incubated for up to 144 hours in medium containing one of the following: 5.6 mmol/L glucose (control), 56 mmol/L glucose (G), 222 mmol/L glucose (high G), or 222 mmol/L mannitol (high M; osmolar control for high G). The tissues and cells of clinical and in vitro samples were stained for light and immunoelectron microscopy with anti–8-hydroxy-2'-deoxyguanosine (anti–8-OH-dG) antibody, a marker of oxidative DNA damage. In vitro cells were also studied using transmission electron microscopy. Cellular ATP content, mitochondrial membrane potential, and intracellular generation of reactive oxygen species (ROS) were analyzed by luciferase–luciferin system, or by flow cytometry using rhodamine 123 and 2',7'-dichlorodihydrofluorescein diacetate (DCFH-DA).

Results

Biopsy specimens showed strong cytoplasmic staining with 8-OH-dG in patients on long-term CAPD, but only faint staining in patients with end-stage renal disease before the initiation of CAPD, and no staining in patients with normal renal function. Dialysate effluent showed strong granular staining with 8-OH-dG in most PMCs in all long-term CAPD patients, but only faint and focal staining in patients at the start and after 3 – 5 months of CAPD. In vitro experiments also showed strong granular staining by 8-OH-dG in most PMCs cultured in high G, weak staining in G and high M, and no staining in the control. Immunoelectron microscopy revealed the localization of 8-OH-dG to mitochondria. Transmission electron microscopy showed swelling of mitochondria, with decreased cristae, in PMCs cultured in high G. However, only partial expansion of mitochondria was seen in G and high M, and no changes were seen in the control. Cellular ATP content and mitochondrial membrane potential were reduced early, followed by an increase when cultured in high G. Intracellular ROS production was also increased in PMCs cultured in high G and high M.

Conclusions

These data suggest that high-glucose peritoneal dialysate may promote oxidative mitochondrial DNA damage in PMCs in CAPD patients.

Fluorescence-activated cell sorting analysis of mitochondrial content, membrane potential, and matrix oxidant burden in human lymphoblastoid cell lines

Fluorescence-activated cell sorting (FACS) permits specific biologic parameters of cellular populations to be quantified in a high-throughput fashion based on their unique fluorescent properties. Relative quantitation of mitochondrial-localized dyes in human cells using FACS analysis allows sensitive analysis of a variety of mitochondrial parameters including mitochondrial content, mitochondrial membrane potential, and matrix oxidant burden. Here, we describe protocols that utilize FACS analysis of human lymphoblastoid cell lines (LCL) for relative quantitation of mitochondrial-localized fluorescent dye intensity. The specific dyes described include MitoTracker Green FM to assess mitochondrial content, tetramethylrhodamine ethyl ester (TMRE) to assess mitochondrial membrane potential, and MitoSOX Red to assess mitochondrial matrix oxidant burden. Representative results of FACS-based mitochondrial analyses demonstrate the variability of these three basic mitochondrial parameters in LCLs from healthy individuals, as well as the sensitivity of applying FACS analysis of LCLs to study the effects of pharmacologic induction and scavenging of oxidant stress.

Mitochondrial dysfunction in platelets and hippocampi of senescence-accelerated mice

Senescence-accelerated mice (SAM) strains are useful models to understand the mechanisms of age-dependent degeneration. In this study, measurements of the mitochondrial membrane potential (Deltapsi(m)) of platelets and the Adenosine 5(')-triphosphate (ATP) content of hippocampi and platelets were made, and platelet mitochondria were observed in SAMP8 (faster aging mice) and SAMR1 (aging resistant control mice) at 2, 6 and 9 months of age. In addition, an Abeta-induced (Amyloid beta-protein) damage model of platelets was established. After the addition of Abeta, the Deltapsi(m) of platelets of SAMP8 at 1 and 6 months of age were measured. We found that platelet Deltapsi(m), and hippocampal and platelet ATP content of SAMP8 mice decreased at a relatively early age compared with SAMR1. The platelets of 6 month-old SAMP8 showed a tolerance to Abeta-induced damages. These results suggest that mitochondrial dysfunction might be one of the mechanisms leading to age-associated degeneration in SAMP mice at an early age and the platelets could serve as a biomarker for detection of mitochondrial function and age related disease.

Mitochondrial function in fibroblasts with aging in culture and/or Alzheimer's disease

Mitochondrial membrane potentials (MMP) reflect the functional state of the mitochondria within cells. Our recently published method provides a quantitative estimate of the MMP of populations of mitochondrial-like particles (MLP) within living cells at 37 degrees C using the combination of conventional fluorescence microscopy, 3D-deconvolution and exhaustive photon reassignment (EPR). Although the method does not provide an absolute measure of MMP, these relative MMP allow direct comparison between various mitochondria in cells at various ages in culture and in different cell lines from multiple patients. Fibroblasts lines from four Alzheimer's disease (AD) patients bearing the presenilin-1 (PS-1) mutation and four appropriate controls were evaluated at different ages in culture. The results showed a large variation in the relative MMP, cell size and sum of relative MMP of all MLP within each cell or within each cell line. Nevertheless, combining the values of relative MMP for the cell lines in each group revealed changes in distribution with age in culture. The relative MMP decreased while the cell sizes and sum of relative MMP within each cell increased with age in fibroblasts. Values did not differ between controls and the AD patients bearing PS-1 mutation at any age in cultures. This new, sensitive and quantitative estimate of relative MMP indicates that under non-stressed conditions relative MMP change with aging in culture, but relative MMP do not differ between controls and AD subjects.

Senescence-associated changes in respiration and oxidative phosphorylation in primary human fibroblasts

Limitation of lifespan in replicative senescence is related to oxidative stress, which is probably both the cause and consequence of impaired mitochondrial respiratory function. The respiration of senescent human diploid fibroblasts was analysed by high-resolution respirometry. To rule out cell-cycle effects, proliferating and growth-arrested young fibroblasts were used as controls. Uncoupled respiration, as normalized to citrate synthase activity, remained unchanged, reflecting a constant capacity of the respiratory chain. Oligomycin-inhibited respiration, however, was significantly increased in mitochondria of senescent cells, indicating a lower coupling of electron transport with phosphorylation. In contrast, growth-arrested young fibroblasts exhibited a higher coupling state compared with proliferating controls. In intact cells, partial uncoupling may lead to either decreased oxidative ATP production or a compensatory increase in routine respiration. To distinguish between these alternatives, we subtracted oligomycin-inhibited respiration from routine respiration, which allowed us to determine the part of respiratory activity coupled with ATP production. Despite substantial differences in the respiratory control ratio, ranging from 4 to 11 in the different experimental groups, a fixed proportion of respiratory capacity was maintained for coupled oxidative phosphorylation in all the experimental groups. This finding indicates that the senescent cells fully compensate for increased proton leakage by enhanced electron-transport activity in the routine state. These results provide a new insight into age-associated defects in mitochondrial function and compensatory mechanisms in intact cells.

Mitochondrial membrane potential and ageing in Podospora anserina

Some filamentous fungi exhibit a limited vegetative growth with modifications in the mitochondria, suggesting the involvement of mitochondria in the process of ageing. Nevertheless, the relationship between the ability to grow or the fate of these cells relative to their mitochondrial membrane potential (Psi(mt)) level has not been investigated. Using flow cytometric analysis, we have assessed Psi(mt) in young and senescent cultures of wild type strains and mitochondrial or nuclear mutant strains of Podospora anserina that present very long or brief life span. When we compared two distinct populations of cells obtained from the same strain, we can show a correlation not only between Psi(mt) and ageing, but also between Psi(mt) and the frequency of regeneration and/or the life span. However, this relationship is not observed when we compared the cells obtained from different physiological states or mutants strains. These results allow us to suggest that the Psi(mt) modifications during senescence could be only one of the possible consequences of the process and are not the factor driving towards death. We also show that the driving force of Psi(mt) is principally maintained by the alternative pathway during ageing, suggesting a role of the alternative oxidase pathway.

Human epidermal cells progressively lose their cardiolipins during ageing without change in mitochondrial transmembrane potential

Mitochondria dysfunction is considered to be a major cause of the modifications that occur during cell ageing. For this reason, cardiolipin, a suitable marker of the chondriome, as well as the mitochondrial transmembrane potential were examined in keratinocytes obtained from 9- to 75-year-old women. The study was carried out by flow cytometry using two fluorescent mitochondria probes: nonyl acridine orange, which binds specifically to cardiolipin, and rhodamine 123, which is incorporated mainly in response to transmembrane potential. Cardiolipin levels in cells from elderly donors (75 years old) would be 57% lower (r = 0.540; P = 0.0002) than those in children (9 years old), while the inner transmembrane potential remained unchanged (r = 0.0394; P = 0.8017). The stability of the membrane potential may be explained by either or both of the following hypotheses: (i) the same pool of organelles able to maintain membrane potential is conserved even when cardiolipin levels decrease (ii) mitochondria membrane potential does indeed decrease with age but is compensated by glycolysis energy production. Finally, it may be stated that the fluorescent probes nonyl acridine orange and rhodamine 123 might be of interest in testing the phenotype of senescent cells and would be useful in screening the role of certain specific genes in cell ageing.

Assessment of ram sperm mitochondrial function by quantitative determination of sperm rhodamine 123 accumulation

A simple procedure is described for determining the functional state of ram sperm mitochondria by quantitative measurement of sperm rhodamine 123 (R 123) accumulation. Sperm were incubated with 1 microgram/ml R 123, and the accumulated R 123 was measured fluorimetrically after release from washed sperm by detergent lysis. Ram sperm R 123 uptake was maximal after 30 min of incubation and responded to changes in both sperm (P < 0.01) and R 123 (P < 0.01) concentration. There was a linear relationship (r = 0.98) between R 123 uptake and the proportion of cold-shocked sperm present in a sperm sample. R 123 uptake was unaffected by 20 mM 2-deoxyglucose or by 10 mM malonate (the latter being sufficient to reduce O2 uptake; P < 0.01). R 123 accumulation in ram sperm was reduced by 6 mg/ml sodium pentobarbitone (P < 0.05), by 1 microM 2,4-dinitrophenol (P < 0.01), and by 0.05% Triton X-100 (P < 0.01). It is concluded that quantitative estimation of R 123 uptake complements oxygen uptake in detecting mitochondrial dysfunction in ram sperm. While it is largely unaffected by inhibition of glycolysis, and is less sensitive than oxygen uptake to trichloroacetic acid cycle inhibition, R 123 uptake is sensitive to factors directly reducing the mitochondrial membrane potential of ram sperm. It may therefore by useful in the evaluation of the effects of such membrane-mediated injuries as cold shock and freezing damage on ram sperm mitochondria.

Evidence for and against the causal involvement of mitochondrial DNA mutation in mammalian ageing

Current experimental evidence on the role of mitochondrial DNA mutation in ageing is assessed alongside reports implicating other genetic and non-genetic causes, including inter-relationships between the mitochondrial and nuclear genomes and their potential effect on mitochondrial structure and function. The role of a 5-kb mtDNA deletion, identified as age-dependent in a variety of human and other mammalian species, is specifically evaluated in the context of its functional effect in mitotic and non-mitotic adult tissue. Downstream effects of mitochondrial decline are considered in terms of the maintenance of ATP production. Associated sequelae then are discussed specifically with reference to restrictions in the supply of ribose moieties for DNA and RNA synthesis, and to disruption of NADPH production and hence cellular anti-oxidant defences.

Simultaneous use of rhodamine 123, phycoerythrin, Texas red, and allophycocyanin for the isolation of human hematopoietic progenitor cells

The supravital, mitochondrial specific dye Rhodamine 123 (R123) was used in conjunction with three monoclonal antibodies to isolate a population of human bone marrow (BM) cells enriched for hematopoietic progenitor cells. BM cells stained with phycoerythrin-HLA-DR, Texas red-CD34, allophycocyanin-CD15, and R123 were fractionated using four-color immunofluorescence cell sorting. Cells expressing CD34 but not HLA-DR and CD15 (CD34+ HLA-DR- CD15-) were subdivided according to their reactivity with R123 into quiescent, R123 dull (R+) or cycling, R123 bright (R++) subpopulations. Morphological analysis and hematopoietic progenitor cell assays indicated that CD34+ HLA-DR- CD15- R+ cells contained larger numbers of blast cells and colony forming units than CD34+ HLA-DR- CD15- R++ cells. The flow cytometer settings used to accommodate the detection of the R123 fluorescence in combination with that of three other fluorochromes are described.

Retention of the mitochondrial probe rhodamine 123 in normal lymphocytes and leukemic cells in relation to the cell cycle

The cationic fluorochrome rhodamine 123 (R123) is specifically taken up by mitochondria of live cells where it is retained due to the mitochondrial transmembrane potential. After pulse exposure of human normal quiescent or proliferating lymphocytes, human lymphocytic leukemic MOLT cells, and mice leukemic L1210 cells to 10 micrograms/ml of R123, the dye release was studied using flow cytometry. Two distinct phases of R123 release, each following first-order kinetics, were apparent; the half-time of retention for the rapidly and slowly released fractions of R123 was 0.8-1.1 and 2.8-4.2 h, respectively. Simultaneous supravital cell staining with R123 and Hoechst 33342 made it possible to correlate retention of R123 with cell position in the cell cycle. No significant differences were observed in the rate of R123 release from cells in G1 vs S or vs G2 + M phases of the cycle. The data rule out a possibility that the release of R123 is due to periodic depolarization of the mitochondria in the cell as may be postulated by cell cycle models that assume a transient passage of cells through resting phase following division. The observed similar rates of R123 release regardless of cell type or cell cycle phase suggest that the factors affecting the exchange are similar in normal lymphocytes vs leukemic cells and unrelated to cell proliferation rate or phase of the cell cycle. Two distinct rates of R123 release indicate the presence of two kinds of binding sites differing in affinity to the dye.

Analysis of the membrane potential of rat- and mouse-liver mitochondria by flow cytometry and possible applications

Washed and purified rat- or mouse-liver mitochondria exhibiting high membrane integrity and metabolic activity were studied by flow cytometry. The electrophoretic accumulation/redistribution of cationic lipophilic probes, rhodamine 123, safranine O and a cyanine derivative, 3,3'-dihexyloxadicarbocyanine iodide, during the energization process was studied and was consistent with the generation of a negative internal membrane potential. An exception to this was nonylacridine orange which spontaneously bound to the mitochondrial membrane by hydrophobic interactions via its hydrocarbon chain. Energized purified mitochondria stained with potentiometric dyes exhibited both higher fluorescence and population homogeneity than the non-energized or deenergized (nigericin plus valinomycin) mitochondria. By contrast, under non-energized or deenergized conditions, the mitochondrial population exhibited fluorescence intensity heterogeneity related to the residual membrane potential; two subpopulations were evident, one of low fluorescence which may be related to the autofluorescence of the mitochondria (plus non-specific dye binding) and a second population which exhibited high fluorescence. Flow cytometry of the unpurified, simply washed, rat-liver mitochondria stained with rhodamine 123, a classically used dye, provided evidence of their heterogeneity in terms of light-scattering properties and membrane-potential-related fluorescence. One third of the washed mitochondria were found to be non-functional by such assays. The fluorescence of purified rat-liver mitochondria due to the membrane potential built up by endogenous substrates indicates heterogeneity of the mitochondrial population with respect to levels of endogenous substrates. The low-angle light scattering increases upon energization and provides some original information about the shape and modification of the inner mitochondrial conformation accompanying the energization. The heterogeneity of the rat liver mitochondrial population, from a structural, metabolic (existence of endogenous substrates) and functional (active and non-active mitochondrial population dispersion) point of view could thus be demonstrated by flow-cytometry analysis. Two animal models were examined with regard to the alteration of the mitochondrial membrane potential under the effects of drugs (rat-liver mitochondria), and the effects of ammonium toxicity (mouse-liver mitochondria). These results are promising and open new perspectives in the study of mitochondriopathies.

Mitochondrial antigenic structure and enzyme activity in ageing human diploid fibroblasts

It has been proposed that cellular ageing may be caused by loss of mitochondrial function due to the action of free radicals. To investigate this hypothesis, antigenic structures of the mitochondrial inner membrane/matrix and of the outer mitochondrial membrane of human diploid fibroblasts were monitored by immunoblotting at four stages during cellular lifespan in vitro. At the same time, specific activities of the enzymes oligomycin-sensitive ATPase (O-S ATPase), malate dehydrogenase (MDH) and glutamate dehydrogenase (GDH) were assayed to assess the functional capacity of cellular oxidative phosphorylation and of the tricarboxylic acid cycle. No changes were found with ageing in inner mitochondrial membrane-associated matrix components, or in the activities of O-S ATPase and MDH. However GDH activity increased significantly with ageing in vitro, possibly indicating greater amino acid utilization for energy production in older cells. There was loss of an outer mitochondrial membrane antigen, of approximate molecular weight 60 kilodaltons (kDa), in the oldest cells tested, which may influence outer membrane transport capacity late in the cellular lifespan. Overall, the results fail to provide support for the hypothesis that ageing primarily results from free radical-induced impairment of mitochondrial function.

Activated monocytes induce arthritis-associated changes in mitochondria of cultured synovial fibroblasts

We have recently shown that synovial fibroblasts cultured from patients with reactive or rheumatoid arthritis exhibit increased autofluorescence when compared with controls. Morphological studies suggested that this increase was related to the anomalous structure of mitochondria in cells cultured from rheumatoid or non-rheumatoid inflammatory synovial tissue. The present study describes attempts to find an explanation for these observations. The effects of conditioned media of cultured mononuclear cells were tested on normal synovial fibroblasts. Conditioned media of monocytes stimulated with lipopolysaccharide or poly-IC induced an increase in the cellular autofluorescence and changes in the morphology of mitochondria in normal fibroblasts. These changes were indistinguishable from those seen in synovial fibroblasts cultured from various arthritides. Indomethacin or gold salts did not abolish the effects of monocyte-conditioned media. Abnormal mitochondria could not be induced in the presence of cycloheximide. This study describes a new aspect of monocyte-fibroblast interactions during rheumatoid and non-rheumatoid inflammation of synovial tissue.

Fura-2 measurement of cytosolic free Ca2+ in monolayers and suspensions of various types of animal cells

The fluorescent indicator fura-2 has been applied to a variety of cell types in order to set up appropriate conditions for measurements of the cytosolic concentration of free ionized Ca2+ [( Ca2+]i) in both cell suspensions and single cells analyzed in a conventional fluorimeter or in a fluorescence microscope equipped for quantitative analyses (with or without computerized image analyses), respectively. When the usual procedure for fluorescence dye loading (i.e., incubation at 37 degrees C with fura-2 acetoxy-methyl ester) was used, cells often exhibited a nonhomogeneous distribution of the dye, with marked concentration in multiple small spots located preferentially in the perinuclear area. These spots (studied in detail in human skin fibroblasts), were much more frequent in attached than in suspended cells, and were due to the accumulation (most probably by endocytosis) of the dye within acidic organelles after hydrolysis by lysosomal enzyme(s). When loading with fura-2 was performed at low (15 degrees C) temperature, no spots appeared, and cells remained diffusely labeled even after subsequent incubation at 32-37 degrees C for up to 2 h. Homogeneous distribution of the dye is a prerequisite for appropriate [Ca2+]i measurement. In fact, comparison of the results obtained in human skin fibroblasts labeled at either 37 or 15 degrees C demonstrated in spotty cells a marked apparent blunting of Ca2+ transients evoked by application of bradykinin. Additional problems were encountered when using fura-2. Leakage of the dye from loaded cells to the extracellular medium markedly affected the measurements in cell suspensions. This phenomenon was found to depend on the cell type, and to markedly decrease when temperature was lowered, suggesting the involvement of a facilitated transport. Calibration of fluorescence signals in terms of absolute [Ca2+]i was complicated by the increased fluorescence of fura-2 in the intracellular environment. To solve this problem we propose an in situ calibration procedure based on measurements carried out on cells in which [Ca2+]i was massively lowered (by loading the probe in a Ca2+-free medium) or increased (by treatment with the Ca2+ ionophore ionomycin, applied in a medium containing 3 mM Ca2+). These results provide explanations and, at least partial, solutions to the major problems encountered when using fura-2, and should thus be of help in clarifying the proper usage of the dye in [Ca2+]i measurements.

Permissive role of n-6 polyunsaturated fatty acids on carbohydrate oxidation in human infant skin fibroblasts: one possible mechanism of their intervention on coronary heart disease and diabetes

Many publications indicate the beneficial effect of n-6 polyunsaturated fatty acids (n-6 PUFAs) in the control of coronary heart disease and diabetes, although the mechanism is not clear. Some of our previous results suggest that, in contrast to other lipids, n-6 PUFAs could have a permissive effect on carbohydrate oxidation. To check this hypothesis, we determined pyruvate dehydrogenase (PDH, decarboxylase: EC 1.2.4.1) activity in infant skin fibroblasts (ISF) incubated 6 hours in the presence of 0.25 mM linoleic (LI) or arachidonic (AR) acid, compared to oleic acid (OL) and control ISF incubated without addition of fatty acids. The four groups of cells were preincubated 36 hours either in the presence of fetal bovine serum (FBS), or in the presence of lipoprotein-deprived serum (LPDS).

RESULTS

(1) When the ISF were maintained in the medium containing FBS, the two PUFAs had little inhibitory effect on PDH activity, in contrast with the effect of OL. (2) When the ISF were kept in the lipoprotein-deficient medium, PDH activity was low in controls and in the OL cells, but the addition of LI or AR increased the activity. This suggests the role of n-6 PUFAs in enhancing carbohydrate oxidation, under certain conditions.

Increased uptake and retention of rhodamine 123 by mitochondria of old human fibroblasts

Binding of the fluorescent dye R123 by a variety of mammalian cells has been shown to be dependent on the high transmembrane potential maintained in functional mitochondria. Recent studies in our laboratory have shown that old human fibroblasts (HF) bind and retain more R123 than young HF. In an effort to determine whether this difference in R123 uptake indeed reflected a difference in mitochondrial transmembrane potential, drugs known to disrupt the transmembrane potential of mitochondria were used to monitor the R123-mitochondria interaction of young and old HF. Distinct differences indicating that old HF maintain a higher mitochondrial transmembrane potential were observed. More significantly, perhaps this difference reflects an age-related change(s) in the structure and/or function of mitochondria.