SIZE AND SHAPE TRANSFORMATIONS CORRELATED WITH OXIDATIVE PHOSPHORYLATION IN MITOCHONDRIA. I. SWELLING-SHRINKAGE MECHANISMS IN INTACT MITOCHONDRIA

Mitocentricity

Worldwide, interest in mitochondria is constantly growing, as evidenced by scientific statistics, and studies of the functioning of these organelles are becoming more prevalent than studies of other cellular structures. In this analytical review, mitochondria are conditionally placed in a certain cellular center, which is responsible for both energy production and other non-energetic functions, without which the existence of not only the eukaryotic cell itself, but also the entire organism is impossible. Taking into account the high multifunctionality of mitochondria, such a fundamentally new scheme of cell functioning organization, including mitochondrial management of processes that determine cell survival and death, may be justified. Considering that this issue is dedicated to the memory of V. P. Skulachev, who can be called mitocentric, due to the history of his scientific activity almost entirely aimed at studying mitochondria, this work examines those aspects of mitochondrial functioning that were directly or indirectly the focus of attention of this outstanding scientist. We list all possible known mitochondrial functions, including membrane potential generation, synthesis of Fe-S clusters, steroid hormones, heme, fatty acids, and CO2. Special attention is paid to the participation of mitochondria in the formation and transport of water, as a powerful biochemical cellular and mitochondrial regulator. The history of research on reactive oxygen species that generate mitochondria is subject to significant analysis. In the section "Mitochondria in the center of death", special emphasis is placed on the analysis of what role and how mitochondria can play and determine the program of death of an organism (phenoptosis) and the contribution made to these studies by V. P. Skulachev.

Amphiphilic copolymer fluorescent probe for mitochondrial viscosity detection and its application in living cells

The mitochondrial viscosity measurement with the amphiphilic copolymer fluorescent probe (PP) has been successfully revealed for the first time. PP was synthesized, starting from a hydrophobic rhodamine derivative fluorophore and hydrophilic 2-hydroxyethyl acrylate (HEA) by radical polymerization, which could be used to detect mitochondrial viscosity specifically. The systematic investigation demonstrated that the fluorescence emission of PP with a deep red emission increased about 9-fold when the medium is changed from methanol to 99% glycerol, indicating high viscosity dependence. Moreover, PP could self-assemble into nanospheres with the particle size of about 140 nm in water and the nano-structure enabled PP to enter living cells quickly. Cytotoxicity test showed that the cells survival rate remained above 70% at 70 μg·mL^-1 of PP. Good biocompatibility and low cytotoxicity of PP are promising to provide a high contrast fluorescence imaging. Taken together, the results point the way to development of novel amphiphilic copolymer fluorescent probes-based the detection in solutions, physiology and pathology.

Controlling the rates of biochemical reactions and signaling networks by shape and volume changes

In biological systems, chemical activity takes place in micrometer- and nanometer-sized compartments that constantly change in shape and volume. These ever-changing cellular compartments embed chemical reactions, and we demonstrate that the rates of such incorporated reactions are directly affected by the ongoing shape reconfigurations. First, we show that the rate of product formation in an enzymatic reaction can be regulated by simple volume contraction-dilation transitions. The results suggest that mitochondria may regulate the dynamics of interior reaction pathways (e.g., the Krebs cycle) by volume changes. We then show the effect of shape changes on reactions occurring in more complex and structured systems by using biomimetic networks composed of micrometer-sized compartments joined together by nanotubes. Chemical activity was measured by implementing an enzymatic reaction-diffusion system. During ongoing reactions, the network connectivity is changed suddenly (similar to the dynamic tube formations found inside Golgi stacks, for example), and the effect on the reaction is registered. We show that spatiotemporal properties of the reaction-diffusion system are extremely sensitive to sudden changes in network topology and that chemical reactions can be initiated, or boosted, in certain nodes as a function of connectivity.

Photon correlation spectroscopy of brain mitochondrial populations: Application to traumatic brain injury

Mitochondrial dysfunction and pathology that contribute to a host of neurodegenerative diseases are deduced from changes in ultrastructure, routinely examined by a host of optical techniques. We adapted the technique of photon correlation spectroscopy (PCS) to evaluate calcium-induced structural alterations in isolated viable cortical and hippocampal mitochondria. In detecting calcium-induced reductions in light intensity, PCS was more sensitive than absorbance across varying calcium concentrations. Mitochondrial populations encompass a broad distribution of sizes, confirmed by ultrastructural profiles, both which remain unaffected by calcium exposure. Cortical and hippocampal populations show fractional calcium-induced reductions in light scatter compared to subsequent maximal alamethicin-induced reductions. Although reductions in light scatter (refractive index) have been interpreted as mitochondrial swelling, PCS quantification of the mean mitochondrial radius demonstrates that mitochondrial size is unaffected by calcium exposure, but not alamethicin. Likewise, the population distribution histograms remain stable with calcium exposure, but shift to larger radii after alamethicin exposure. Furthermore, hippocampal mitochondrial populations from a neurodegenerative model of traumatic brain injury, lateral fluid percussion, demonstrate greater calcium-induced reductions in scatter intensity, which are associated with an initial population of large mitochondria becoming smaller. The disparate responses to calcium and subsequent alamethicin of mitochondria at 3 and 24 h after injury attest to an acute disruption of membrane permeability in mitochondria from injured brain. PCS provides quantitative indices of refractive index and size in isolated mitochondrial populations, aiding the evaluation of mitochondria in degenerative diseases.

Maternal antioxidant treatments prevent diabetes-induced alterations of mitochondrial morphology in rat embryos

Previous studies have suggested that production of reactive oxygen species by embryonic mitochondria may have a role in the induction of both high-amplitude mitochondrial swelling and embryonic dysmorphogenesis in diabetic pregnancy. The present study analyzed the relationships between a putative metabolite-induced production of free oxygen radicals, mitochondrial lipid peroxidation, and high-amplitude mitochondrial swelling in embryos during organogenesis. For studies in vitro, day 9 embryos of normal rats were cultured for 48 h with a high concentration of glucose in the absence or presence of alpha-cyano-4-hydroxycinnamic acid (CHC), a mitochondrial pyruvate transport inhibitor. The morphology of mitochondria in the neuroepithelium of the embryos was studied with the aid of transmission electron microscopy. For studies in vivo, normal and diabetic pregnant rats were fed a diet supplemented with the antioxidants alpha-tocopherol (vitamin E) or 2,6-di-tert-butyl-4-methylphenol (BHT), and the ultrastructure of mitochondria in the embryonic neuroepithelium and in the visceral yolk sac was investigated on gestational day 11. Exposure to a high concentration of glucose in vitro or to maternal diabetes in vivo induced high-amplitude swelling of mitochondria in the neuroepithelium of the embryos. The swelling of mitochondria was prevented by addition of CHC to the culture media or by maternal ingestion of antioxidant-supplemented food. In diabetic pregnancy, embryonic mitochondria during organogenesis produce free oxygen radicals that cause mitochondrial lipid peroxidation and swelling and furthermore embryonic dysmorphogenesis. Dietary supplementation with antioxidants to the mother may prevent embryonic malformations in diabetic pregnancy by inhibition of mitochondrial dysfunction.

Altered mitochondrial morphology of rat embryos in diabetic pregnancy

BACKGROUND

Previous studies in vivo and in vitro have suggested that the oxidative metabolism of the embryo may have a role in the teratogenicity of diabetic pregnancy. In particular, the production of reactive oxygen species by the embryonic mitochondria has been implicated in the teratological process. The induction of congenital malformations by the diabetic milieu occurs during the early embryonic development. The present study aimed to estimate the role of the embryonic mitochondria in the teratological process of diabetic pregnancy by studying mitochondrial morphology in the embryos exposed to a diabetic environment in vivo or in vitro during early organogenesis and late fetal development.

METHODS

For studies in vivo embryos of control or streptozotocin-diabetic rats were taken at gestational days 9-11 and subjected to light and electron microscopical analysis. The brain, heart, and liver of day-15 fetuses were also observed. For studies in vitro day-9 embryos of normal rats were cultured in a whole-embryo culture system for 48 hours. The culture media were supplied with high concentration of diabetes-related substrates and metabolites, and their effect on structure of embryonic neuroepithelial cells determined.

RESULTS

The light microscopical observations demonstrated numerous cytoplasmic vacuoles in the ectoderm of day-9 embryos and in the neuroepithelium and blood cells of day-10 and day-11 embryos of diabetic rats. Ultrastructurally, these vacuoles were found to be mitochondria undergoing large-amplitude swelling with loss of matrix density and disturbed cristae. In contrast, no mitochondrial differences were found in the brain, heart, and liver, when day-15 fetuses from normal and diabetic rats were compared. Ultrastructural analysis of day-9 embryos cultured for 48 hours in the presence of high concentrations of D-glucose, pyruvate, beta-hydroxybutyrate, and alpha-ketoisocaproate also showed high-amplitude mitochondrial swelling in the neuroepithelium. The mitochondrial swelling was, however, not found in embryos cultured in a high concentration of L-glucose, excluding simple osmotic effects of the diabetes-related substrates and metabolites.

CONCLUSIONS

The mitochondrial morphological changes appeared in embryos subjected to a diabetic environment during a time period when the congenital malformations in diabetic pregnancy are induced. The results support the notion that embryonic mitochondria are involved in the teratological process of diabetic pregnancy.

Sequential observation of mitochondrial distribution in mouse oocytes and embryos

OBJECTIVE

The purpose of this study was to elucidate changes in the distribution of mitochondria through the cell cycle.

MATERIALS AND METHODS

Mouse oocytes and embryos were recovered sequentially from mice and stained with the vital fluorescent mitochondrial stain rhodamine 123. Mitochondrial staining pattern were classified into three types: aggregation (Ag), homogeneous (H), and perinuclear accumulation (PA).

RESULTS

Sequential observations revealed that mitochondria of oocytes and embryos grown in vivo translocated in the cytoplasm during the cell cycle, showing the H pattern before human chorionic gonadotropin (hCG) administration, the PA pattern 8-9 hr post-hCG, the H pattern again 10-14 hr post-hCG, and the PA pattern again 24 and 31-32 hr post-hCG following fertilization. In the two-cell stage, the Ag pattern was shown 35 hr post-hCG, the H pattern was observed 40 hr post-hCG, and the PA pattern was found 48 hr post-hCG. In the embryos cultured in vitro and showing developmental block, mitochondrial translocation was shown to be inhibited after they aggregated in the early two-cell stage (35 hr post-hCG). Moreover, the translocation of mitochondria was restored by the addition of superoxide dismutase or thioredoxin to the culture medium. Both of these enzymes have already been shown to have the ability to overcome developmental block.

CONCLUSION

The present study revealed that mitochondria translocated in the cell cycle and suggested that there is a close relationship between mitochondrial translocation and developmental arrest.

Status of mitochondria in living human fibroblasts during growth and senescence in vitro: use of the laser dye rhodamine 123

Rhodamine 123, a fluorescent laser dye that is selectively taken up into mitochondria of living cells, was used to examine mitochondrial morphology in early-passage (young), late-passage (old), and progeric human fibroblasts. Mitochondria were readily visualized in all cell types during growth (mid-log) and confluent stages. In all cell strains at confluence, mitochondria became shorter, more randomly aligned, and developed a higher proportion of bead-like forms. Treatment of cells for six days with Tevenel, a chloramphenicol analog that inhibits mitochondrial protein synthesis, brought about a marked depletion of mitochondria and a diffuse background fluorescence. Cyanide produced a rapid release of preloaded mitochondrial fluorescence followed by detachment and killing of cells. Colcemid caused a random coiling and fragmentation of mitochondria particularly in the confluent stage. No gross differences were discernible in mitochondria of the three cell strains in mid-log and confluent states or after these treatments. Butanol-extractable fluorescence after loading with rhodamine 123 was lower in all cell strains in confluent compared to mid-log stages. At confluence all three cell strains had similar rhodamine contents at zero-time and after washout up to 24 h. At the mid-log stage, young cells contained more rhodamine initially and lost it more rapidly than old or progeria cells, in that order. The data indicate no gross derangement in the morphology or number of mitochondria in old and progeria fibroblasts but there is a reduction of protonmotive force evident in these cells at the mid-log stage that may be growth limiting.

Stereological analysis of the mitochondrial compartment of the rabbit parotid gland before and after isoprenaline-induced degranulation

A stereological analysis of the mitochondrial compartment of the rabbit parotid gland has been carried out before and after isoprenaline-induced degranulation. Normally, mitochondria constitute about 5% of acinar cell volume, 6% of intercalcate duct cell volume and 16% of striated duct cell volume. The ratio of inner electron transport membrane to outer limiting membrane is in the range 2.3:1. Two hours after the induction of secretion by isoprenaline a significant (P less than 0.10) increase in the volume fraction of mitochondria in acinar and intercalated duct cells was noted and this may reflect increased oxidative phosphorylation at this time. Other parameters measured suggest that there is some rounding up of mitochondria Another significant feature was an increase in the number of damaged mitochondrial profiles (+80% to +250%, P less than 0.05) after isoprenaline treatment. This finding is discussed in the context of changes in mitochondrial enzyme levels which have been reported in similar situations.

Ultrastructural changes in HEp-2 cells treated with staphylococcal alpha-toxin

The effect of highly purified staphylococcal alpha-toxin on HEp-2 neoplastic cells growing in culture was studied by electron microscopy. In addition to some nuclear modifications, the most significant morphological changes were in mitochondrial structure, alpha-toxin seems to induce a defined sequence of changes in mitochondrial configuration which can be summarized as an earlier phase of 'condensation' of mitochondrial structure and a later phase of mitochondrial swelling with an intermediate 'transitional' configuration. The significance of these findings is discussed in the light of the present state of knowledge of the biological characteristics of staphylococcal alpha-toxin.

Ultrastructural studies of beef heart mitochondria. 3. The inequality of gross morphological change and oxidative phosphorylation

The relationships between membranes and intramembrane compartments of isolated heart mitochondria are inadequately defined to express the induced morphological changes associated with the structural organization. The inner membrane and matrix are the major structural entities which undergo transformation upon alteration of metabolism or incubation conditions. To better express these morphological changes within a mitochondrion, two inner membranes plus enclosed matrix are defined as an inmerix (plural inmerices). Three general morphological forms of mitochondria can be distinguished by the size and shape of inmerices. These are distended, condensed, and coalesced inmerixal configurations. Hypotonic conditions and P(i) in isotonic sucrose generate distended configurations. This P(i) distention is apparently dependent on utilization of energy. It does not occur under anaerobic conditions. Oxidizable substrates generate condensed configurations. ADP and dADP generate coalesced configurations and stop formation of condensed and distended inmerixal configurations in the absence of inhibitors. ADP coalescence is apparently not dependent on an energy input. It occurs under aerobic and anaerobic conditions, and in isotonic and hypotonic media. Atractyloside completely inhibits the effects of ADP on inmerixal membranes whereas oligomycin does not. Distention by P(i) is unaffected by the two inhibitors. Distended inmerices, without added P(i) (12 mM and 62 mM sucrose), are coalesced by ADP. These studies indicate that coalescence of inmerixal membranes probably reflects the consequences of specific stoichiometric binding or translocation of adenine nucleotides.

Ultrastructural changes in dog brains immediately following non-pulsatile extracorporeal circulation and prolonged anaesthesia

The brains of dogs were examined with the electron microscope following non-pulsatile extracorporeal circulation of 1, 2 or 3 hours' duration and following 3 hours of hypotensive anaesthesia with the thoracic and pericardial cavities open. Both extracorporeal circulation and prolonged anaesthesia caused subcellular changes in nerve cells and glia in the cerebral cortex, caudate nucleus and dorsal parietal nucleus of the thalamus. The changes involved either an increase in the numbers of cytoplasmic organelles associated with cell shrinkage or a loss of cytoplasmic organelles associated with cell swelling. The main causative factor during extracorporeal circulation appears to have been non-pulsatile blood flow. Hypotension and reduced cardiac output are thought to have been responsible for the cell changes after prolonged anaesthesia.

Expansion of the inner membrane compartment and its relation to mitochondrial volume and ion transport

Glutaraldehyde has been used to fix mitochondria undergoing rapid volume changes associated with energized ion transport under oscillatory state conditions and valinomycin-induced potassium uptake. Fixation was found to prevent structural changes which normally occur during ion accumulation or loss. By correlating packed volume measurements with electron microscopy, it is shown that changes in volume associated with ion movements reflect changes in the inner membrane compartment and that this compartment can be related to the sucrose inaccessible space. The method can therefore be used to accurately determine volume changes that arise from ion translocation.

Distribution of ions and water between tissue compartments in the perfused left ventricle of the rat heart

Left ventricles from rat hearts were perfused through the coronary blood vessels for periods up to 90 minutes with solution containing radioactively labeled sulfate, sucrose, urea, glycerol, or chloride. Urea and glycerol equilibrate with all of tissue water. By contrast, 35 SO 4 and sucrose- 14 C equilibrate very rapidly with 40% of total water and slowly with an additional 20%; they are excluded from 40% of the tissue water. The two "cellular" compartments (C 2 , which equilibrates slowly with SO 4 and sucrose, and C 3 , from which SO 4 and sucrose are excluded) both lose water when hearts are perfused with a solution made hypertonic with NaCl. Chemical analyses for K, Na, and Cl, and measurements of the rate of equilibration of 36 C1 show that C 2 has low contents of Cl and Na. Experiments in which extracellular NaCl was replaced osmole for osmole by KCl according to the method of Boyle and Conway suggest that the boundaries of C 2 and C 3 may have different ionic permeabilities. These observations indicate that the division of mammalian heart muscle into tissue compartments is more complex than conventionally assumed, a conclusion reached by Bozler for frog heart muscle. They are inconsistent with the usual assumption that cardiac cellular water is homogeneous.

Ultrastructural bases for metabolically linked mechanical activity in mitochondria. I. Reversible ultrastructural changes with change in metabolic steady state in isolated liver mitochondria

By means of a new "quick-sampling" method, micropellets of mouse liver mitochondria were rapidly prepared for electron microscopy during the recording of steady state metabolism. Reversible ultrastructural changes were found to accompany change in metabolic steady states. The most dramatic reversible ultrastructural change occurs when ADP is added to systems in which only phosphate acceptor is deficient, i.e., during the State IV to State III transition as defined by Chance and Williams. After 15 min in State IV, mitochondria display an "orthodox" ultrastructural appearance as is usually observed after fixation within intact tissue. On transition to State III, a dramatic change in the manner of folding of the inner membrane takes place. In addition, the electron opacity of the matrix increases as the volume of the matrix decreases, but total mitochondrial volume does not appear to change during this transition. This conformation is called "condensed." Isolated mitochondria were found to oscillate between the orthodox and condensed conformations during reversible transitions between State III and State IV. Various significant ultrastructural changes in mitochondria also occur during transitions in other functional states, e.g., when substrate or substrate and acceptor is made limiting. Internal structural flexibility is discussed with respect to structural and functional integrity of isolated mitochondria. Reversible changes in the manner of folding of the inner membrane and in the manner of packing of small granules in the matrix as respiration is activated by ADP represent an ultrastructural basis for metabolically linked mechanical activity in tightly coupled mitochondria.

Light-induced volume changes in spinach chloroplasts

A light-dependent mechanism that results in a slow, high-amplitude swelling of spinach chloroplasts in vitro has been discovered. The swelling is readily observed by optical and gravimetric methods, and by the use of an electronic particle counter; all show a 100 per cent increase of chloroplast volume in the light with an approximately 10-minute half-time. The existence of an osmotic mechanism for chloroplast swelling in the dark is confirmed. The volume of illuminated chloroplasts versus NaCl concentration represents the addition of osmotic and light effects. The action of light is enhanced by electron flow cofactors, such as phenazine methosulfate (PMS). However, neither conditions for ATP hydrolysis or synthesis nor NH(4)Cl influence the time course and extent of swelling. Hence, high-amplitude chloroplast swelling is light- (or electron flow), but not energy-dependent. A remarkable inhibitory effect of inorganic phosphate on chloroplast swelling is observed in the light, but not in the dark. Another action of light on chloroplasts is known to result in a shrinkage of chloroplasts which is rapid, reversible, energy-dependent, and requires phosphate. Thus phosphate determines the action of light on chloroplast volume. Since shrinkage is reversible, but swelling is not, it may be that they reflect physiological and deteriorative processes, respectively. Chloroplasts and mitochondria appear to control their volume by similar mechanisms.