Distribution of six transplasma membrane NADH-dehydrogenases in rat brain tissue

Clustering of plasma membrane-bound cytochrome b5 reductase within 'lipid raft' microdomains of the neuronal plasma membrane

Plasma membrane redox centres play a major role in neuronal defence against oxidative stress and survival. In cerebellar granule neurons in culture (CGN) a large pool of the flavoproteins are associated with the plasma membrane, and the intensity of CGN green/orange autofluorescence correlated with the levels of expression of cytochrome b(5) reductase. Regionalization of cytochrome b(5) reductase in the plasma membrane of CGN by fluorescence resonance energy transfer points out the close proximity between cytochrome b(5) reductase and the 'lipid raft' markers cholera toxin B and caveolin-2. This study unravels that membrane-bound cytochrome b(5) reductase is largely enriched at interneuronal contact sites in the neuronal soma and associated with 'lipid rafts' of the CGN plasma membrane. We also show that cytochrome b(5) reductase makes a large contribution to the NADH oxidase activity and to the red-shifted flavine fluorescence of purified rat brain synaptic plasma membranes. In conclusion, membrane-bound cytochrome b(5) reductase forms a large mesh of redox centres associated with the neuronal plasma membrane.

Regionalization of plasma membrane-bound flavoproteins of cerebellar granule neurons in culture by fluorescence energy transfer imaging

Flavoproteins are components of plasma membrane redox chains, which have been suggested to play major roles in neuronal activity and survival. We found that the red/orange autofluorescence of mature primary cultures of cerebellar granule neurons (8-9 days in vitro) was largely quenched by millimolar concentrations of dithionite added to the extracellular medium, and pointed out that nearly 50% of this autofluorescence was due to plasma membrane-bound flavoproteins. We report in this work that the lipophilic neuronal plasma membrane markers N-(3-triethylammoniumpropyl)-4-(4-(4-(diethylamino)phenyl)butadienyl)-pyridinium dibromide (RH-414) and N-(3-triethylammoniumpropyl)-4-(6-(4-(diethylamino)phenyl)hexatrienyl)pyridinium dibromide (FM4-64) can form fluorescence energy transfer donor-acceptor pairs with flavoproteins with calculated R (0) values between 3.7 and 4.2 nm. The quantification of the efficiency of fluorescence energy transfer with different concentrations of acceptor dyes has been worked out with re-suspended neurons. Using quantitative images of the neurons in culture, acquired with a CCD camera attached to an epifluorescence microscope, regionalization of the plasma membrane-bound flavoproteins of cerebellar granule neurons has been achieved from the quenching by dithionite of the fluorescence of the acceptor dye. The results unraveled that plasma membrane-bound flavoproteins are largely enriched in interneuronal contact sites forming clusters of 0.5-1 microm diameter size, which appears largely regionalized in the neuron's cell body.

Potential role of nuclear translocation of glyceraldehyde-3-phosphate dehydrogenase in apoptosis and oxidative stress

Recent studies indicating a role of glyceraldehyde-3-phosphate dehydrogenase (GAPDH) in apoptosis or oxidative stress has been reported. Using confocal laser-scanning microscopy, we have investigated the cellular distribution of GAPDH in central nervous system (CNS)-derived cells (neuroblastoma mNB41A3), in non-CNS derived cells (R6 fibroblast) and in an apoptosis-resistant Bcl2 overexpressing cell line (R6-Bcl2). Induction of apoptosis by staurosporine or MG132 and oxidative stress by H(2)O(2) or FeCN enhanced the nuclear translocation of endogenous GAPDH in all cell types, as detected by immunocytochemistry. In apoptotic cells, GAPDH expression is three times higher than in non-apoptotic cells. Consistent with a role for GAPDH in apoptosis, overexpression of a GAPDH-green fluorescent protein (GAPDH-GFP) hybrid increased nuclear import of GAPDH-GFP into transfected cells and the number of apoptotic cells, and made them more sensitive to agents that induce apoptosis. Bcl2 overexpression prevents nuclear translocation of GAPDH and apoptosis in untransfected cells, but not in transfected cells that overexpress GAPDH-GFP. Our observations indicate that nuclear translocation of GAPDH may play a role in apoptosis and oxidative stress, probably related to the activity of GAPDH as a DNA repair enzyme or as a nuclear carrier for pro-apoptotic molecules.

Purification of a dichlorophenol-indophenol oxidoreductase from rat and bovine synaptic membranes: tight complex association of a glyceraldehyde-3-phosphate dehydrogenase isoform, TOAD64, enolase-gamma and aldolase C

NADH-dichlorophenol-indophenol oxidoreductases (PMOs) were purified from synaptic plasma membranes or synaptic vesicles (small recycling vesicles) from both bovine and rat brains and from a neuroblastoma cell line, NB41A3. Several isoforms could be identified in purified plasma membranes and vesicles. Purification of the enzyme activity involved protein extraction with detergents, (NH4)2SO4 precipitation, chromatography under stringent conditions and native PAGE. PMO activity could be attributed to a very tight complex of several proteins that could not be separated except by SDS/PAGE. SDS/PAGE resolved the purified complex into at least five proteins, which could be micro-sequenced and identified unambiguously as hsc70, TOAD64 and glyceraldehyde-3-phosphate dehydrogenase tightly associated with the brain-specific proteins aldolase C and enolase-gamma. Enzyme activity could be purified from both synaptic plasma membranes and recycling vesicles, yields being much greater from the latter source. Highly purified plasma membranes (prepared from a neuroblastoma cell line NB41A3 by iminobiotinylation of intact cells and affinity purification with avidin and anti-avidin antibodies under very stringent conditions) also displayed PMO activity tightly associated with TOAD64. The association of PMO in a tight complex was confirmed by its immunoprecipitation from cellular and membrane extracts of NB41A3 using antibodies directed against any component protein of the complex followed by immunodetection with antibodies directed against the other members. Antibodies also inhibited the enzyme activity synergistically. In addition, induction of the different components of the complex during dichlorophenol-indophenol stress was demonstrated by the S1 RNase-protection assay in synchronized NB41A3 cells. The role of the complex in membrane fusion and cellular response to extracellular oxidative stress during growth and development is discussed.

The plasma membrane NADH-diaphorase is active during selective phases of the cell cycle in mouse neuroblastoma cell line NB41A3. Its relation to cell growth and differentiation

Plasma membrane oxidoreductases have been described in all cells and use extracellular impermeant electron acceptors (DCIP, Ferricyanide) that are reduced by NADH. They appear to regulate the overall cell activity in response to oxidative stress from the cellular environment. An NADH-DCIP reductase has been described at the plasma membrane of NB41A3, a neuroblastoma cell line (Zurbriggen and Dryer (1993) Biochim. Biophys. Acta 1183, 513-520) whose activation with extracellular impermeant substrates promotes cell growth. Elutriation was performed to separate cells and the various fractions were analysed for enzyme activity on intact cells combined with flow cytometry. These studies showed that the enzyme is mostly induced and activated during the G1 and during the G2/M-phases. These observations were further corroborated with specific inhibitors of the cell cycle. A three-fold increase in enzyme activity was observed in the presence of alpha-amanitin, a specific cell cycle inhibitor of the G1-phase. Taxol, a specific inhibitor of the M-phase, also induces a significant increase in enzyme activity. FACS analysis of taxol -treated and alpha-amanitin-treated cells corroborated these data. The cells have been synchronized and the enzyme activity was measured at different time intervals. An activity increase was observed after ca. 2-3 h, that corresponds to a raise in the M-phase, according to FACS data. Furthermore, NTera-2 cells - a human neuroblastoma cell line that differentiates into fully mature neurones in the presence of retinoic acid - exhibit a 50% decrease in the enzyme activity during the G0-phase upon differentiation, compared to undifferentiated cells. Together the data presented in this paper show that this plasma membrane NADH-diaphorase affects cell growth and differentiation and is strongly modulated at various phases of the cell cycle.

Developmental changes in the localization of the transplasma membrane NADH-dehydrogenases in the rat brain

The function of transplasma membrane oxidoreductases (PMO's) has been further studied by means of investigating the postnatal (PN) developmental changes in the tissue localization of six isoenzymes previously characterized (see accompanying paper). The changes were followed in the midbrain for PMO-I, -II, and -V and in the brainstem for PMO-III, -IV and -VI. PMO-I is not observed before PN5 and develops as long vertical fibers located mainly in the pontine nucleus and in the dorsal raphe nucleus until it merges all over the midbrain except for the aqueduct and the superior colliculus after PN10. At that stage it is highly expressed in the trigeminal nucleus and the dorsal raphe, but its expression then strongly decreases and PMO-I disappears almost completely later on. Similarly PMO-II only develops around PN5, first in the dorsal and caudal linear raphe and later on (at PN7) also in the pontine nucleus and in the median raphe; at PN10 PMO-II gradually had vanished from these areas and strongly developed in the dorsal raphe and in the mesencephalic trigeminal nucleus. Later on PMO-II also decreases from these areas. PMO-III slowly develops within the gigantocellular reticular nucleus from PN1 to PN5 and later on reaches the facial nucleus (after PN5), the density of PMO-III in these regions at PN10 being much higher than in the adult. PMO-IV follows a similar developmental pattern in the midbrain, with an optimal density around PN10 also. PMO-V appears only at about PN5, first within the dorsal raphe in parallel fibers and in multipolar neurons. It disappears from the fibers around PN10 and remains present in neurons up to adulthood. PMO-VI appears at early stages within the gigantocellular reticular nucleus and after PN5 within the central gray in vertical fibers. At later stages PMO-VI is found in the spinal trigeminal nucleus, at first within the neuropil then in multipolar neurons that remain present up to adulthood. These datas suggested that the different isoenzymes are expressed at various stages in specific areas. The role of PMO's in neuronal development is discussed.