Mitochondrial association of alpha-synuclein causes oxidative stress

α-Synuclein is a neuron-specific protein that contributes to the pathology of Parkinson’s disease via mitochondria-related mechanisms. The present study investigated possible interaction of α-synuclein with mitochondria and consequences of such interaction. Using SHSY cells overexpressing α-synuclein A53T mutant or wild-type, as well as isolated rat brain mitochondria, the present study shows that α-synuclein localizes at the mitochondrial membrane. In both SHSY cells and isolated mitochondria, interaction of α-synuclein with mitochondria causes release of cytochrome c, increase of mitochondrial calcium and nitric oxide, and oxidative modification of mitochondrial components. These findings suggest a pivotal role for mitochondria in oxidative stress and apoptosis induced by α-synuclein. Received 27 December 2007; received after revision 7 February 2008; accepted 8 February 2008     

Visualization of the mitochondria ofToxoplasma gondii-infected mouse fibroblasts by the cationic permeant fluorescent dye rhodamine 123

Summary The mitochondria of living mouse fibroblasts infected withToxoplasma gondii were monitored with the cationic permeant fluorescent dye rhodamine 123. Fluorescence microscopy revealed that host cell mitochondria accumulated at the cytoplasmic surface of parasitophorous vacuoles and increased the dye uptake in the periparasitophorous vacuole asT. gondii multiplied.The author wishes gratefully to acknowledge the work of Miss Mayumi Kato and Mr. Isao Kimata in preparing the photographs. The publication cost was supported by a grant of the Ohyama Health Foundation.     

Protective effect of N-(2-propynyl)-2-(5-benzyloxy-indolyl) methylamine (PF9601N) on mitochondrial permeability transition

PF9601N, N-(2-propynyl)-2-(5-benzyloxy-indolyl) methylamine, an monoamine oxidase (MAO) B inhibitor, has shown neuroprotective properties against dopaminergic toxins. To elucidate the mechanisms involved in this protection, the effect of PF9601N on mitochondria was assessed. PF9601N prevents mitochondrial swelling, drop in the electrical potential and oxidation of sulfhydryl groups, glutathione and pyridine nucleotides induced by Ca²⁺. These observations demonstrate the protective effect of PF9601N on the induction of mitochondrial permeability transition. This protection is due to the interaction of the secondary protonated amino group in the molecule with pore-forming structures and to its antioxidant property, rather than to inhibition of MAO B activity. PF9601N also prevents the release of cytochrome c from mitochondria, suggesting its potential inhibitory effect on mitochondria-mediated apoptosis. The low IC⁵⁰ value for this inhibition, in comparison with deprenyl, make it a more efficient compound than propargylamines and other amines in protecting the bioenergetic functions of mitochondria. Received 9 March 2006; received after revision 10 April 2006; accepted 21 April 2006     

Injection of a soluble sperm fraction into sea-urchin eggs triggers the cortical reaction

Summary Fertilization membranes from around unfertilized sea-urchin eggs after microinjection of a soluble spermatozoa fraction isosmotic with seawater. This demonstrates that the spermatozoon contains a chemical that triggers an increase in cytosolic calcium, leading to exocytosis of cortical granules. It also demonstrates that the triggering mechanism does not require an externally-activated egg-membrane process. Further experiments show that the chemical trigger is not calcium.     

Evidence of a direct action of triiodothyronine (T3) on the cell membrane of GH3 cells: an electrophysiological approach

Summary Electrophysiological experiments demonstrate that triiodothyronine (T₃) exerts a direct effect on the membrane of a strain of cultured rat pituitary tumor cells, GH₃/B₆. These cells respond to pressure application of T₃ (2–5 nl, concentration 1·10^–10 M) with an increase in the membrane resistance (R_m) and a hyperpolarization. Spontaneously firing cells become silent.     

Influence of bistramide A on the twitch tension in rat atrial heart muscle

Bistramide A, a new toxin isolated from the UrochordateLissoclinum bistratum Sluiter, was applied to rat auricular heart muscle bundles. At a stimulation frequency of 0.2 Hz, the toxin induces a dose-dependent reduction of the stimulated twitch tension force; it decreases and shortens the duration of the plateau and the slow repolarizing phase of the action potential. In the control solution, switching from a stimulation frequency of 0.2 Hz to 1 Hz decreases the force with which a positive potentiation develops either at a maintained high frequency or after switching from 1 Hz to 0.2 Hz. Bistramide A reduces both the force evoked at 1 Hz and the potentiation. The data suggest that Bistramide A blocks Na⁺ conductance; inhibits Ca⁺⁺ channels in a time-and frequency-dependent manner; reduces Na⁺–Ca⁺⁺ exchange activity; but does not modify the ability of the sarcoplasmic reticulum to be refilled although the rate of Ca⁺⁺ accumulation is decreased.     

Deciduogenic effects of mediators of the polyphosphatidylinositol pathway in pseudopregnant mice

Intraluminal injections (15 l) of either concanavalin A (125 g) or ionophore A 23187 (0.01 mol) induced a decidual cell reaction (DCR) in the uterus of day 4.5 pseudopregnant mice. However, when these agents were administered in different combinations with each other or with CaCl₂ (15 mol) and phorbol-12-myristate-13-acetate (1.6 nmol), interacting effects occurred to either enhance or inhibit each of the others' independent deciduogenic capacities. The results suggest that the polyphosphatidylinositol pathway and Ca²⁺ are involved in the induction of the DCR in mice with complex interactions occurring between the active components of the pathway to modulate the outcome of the transformation process.     

Mechanism of inhibition of IgE-dependent histamine release from rat mast cells by xestobergsterol A from the Okinawan marine spongeXestospongia bergquistia

Histamine release from rat peritoneal mast cells induced by anti-IgE was essentially complete within 4–5 min. Xestobergsterol A and B, which are constituents of the Okinawan marine spongeXestospongia bergquistia Fromont, dose-dependently inhibited anti-IgE-induced histamine release from rat mast cells. The IC₅₀ values of xestobergsterol A and B for histamine release in mast cells activated by anti-IgE were 0.07 and 0.11 M, respectively. Anti-IgE stimulated PI-PLC activity in a mast cell membrane preparation. Xestobergsterol A dose-dependently inhibited the generation of IP3 and membrane-bound PI-PLC activity. Moreover, xestobergsterol A inhibited Ca²⁺-mobilization from intracellular Ca²⁺-stores as well as histamine release in mast cells activated by anti-IgE. On the other hand, xestobergsterol B did not inhibit the membrane-bound and cytosolic PI-PLC activity, IP3 generation or the initial rise in [Ca²⁺]_i in mast cells activated by anti-IgE. These results suggest that the mechanism of inhibition by xestobergsterol A of the initial rise in [Ca²⁺]_i, of the generation of IP3, and of histamine release induced by anti-IgE, was through the inhibition of PI-PLC activity.     

Differential insult-dependent recruitment of the intrinsic mitochondrial pathway during neuronal programmed cell death

Programmed cell death contributes to neurological diseases and may involve mitochondrial dysfunction with redistribution of apoptogenic proteins. We examined neuronal death to elucidate whether the intrinsic mitochondrial pathway and the crosstalk between caspase-dependent/-independent injury was differentially recruited by stressors implicated in neurodegeneration. After exposure of cultured cerebellar granule cells to various insults, the progression of injury was correlated with mitochondrial involvement, including the redistribution of intermembrane space (IMS) proteins, and patterns of protease activation. Injury occurred across a continuum from Bax- and caspase-dependent (trophic- factor withdrawal) to Bax-independent, calpain-dependent (excitotoxicity) injury. Trophic-factor withdrawal produced classical recruitment of the intrinsic pathway with activation of caspase-3 and redistribution of cytochrome c, whereas excitotoxicity induced early redistribution of AIF and HtrA2/Omi, elevation of intracellular calcium and mitochondrial depolarization. Patterns of engagement of neuronal programmed cell death and the redistribution of mitochondrial IMS proteins were canonical, reflecting differential insult-dependencies. Received 14 August 2008; received after revision 02 October 2008; accepted 23 October 2008