Rapid nongenomic modulation by neurosteroids of dendritic spines in the hippocampus: Androgen, oestrogen and corticosteroid.

Memories are stored in synapses that consist of axon terminals and dendritic spines. Dendritic spines are postsynaptic structures of synapses and are essential for synaptic plasticity and cognition. Therefore, extensive investigations concerning the functions and structures of spines have been performed. Sex steroids and stress steroids have been shown to modulate hippocampal synapses. Although the rapid modulatory action of sex steroids on synapses has been studied in hippocampal neurones over several decades, the essential molecular mechanisms have not been fully understood. Here, a description of kinase-dependent signalling mechanisms is provided that can explain the rapid nongenomic modulation of dendritic spinogenesis in rat and mouse hippocampal slices by the application of sex steroids, including dihydrotestosterone, testosterone, oestradiol and progesterone. We also indicate the role of synaptic (classic) sex steroid receptors that trigger these rapid synaptic modulations. Moreover, we describe rapid nongenomic spine modulation by applying corticosterone, which is an acute stress model of the hippocampus. The explanations for the results obtained are mainly based on the optical imaging of dendritic spines. Comparisons are also performed with results obtained from other types of imaging, including electron microscopic imaging. Relationships between spine modulation and modulation of cognition are discussed. We recognise that most of rapid effects of exogenously applied oestrogen and androgen were observed in steroid-depleted conditions, including acute slices of the hippocampus, castrated male animals and ovariectomised female animals. Therefore, the previously observed effects can be considered as a type of recovery event, which may be essentially similar to hormone replacement therapy under hormone-decreased conditions. On the other hand, in gonadally intact young animals with high levels of endogenous sex hormones, further supplementation of sex hormones might not be effective, whereas the infusion of blockers for steroid receptors or kinases may be effective, with respect to suppressing sex hormone functions, thus providing useful information regarding molecular mechanisms.

Hippocampal synthesis of estrogens and androgens which are paracrine modulators of synaptic plasticity: synaptocrinology.

Hippocampal pyramidal neurons and granule neurons of adult male rats are equipped with a complete machinery for the synthesis of pregnenolone, dehydroepiandrosterone, testosterone, dihydrotestosterone and 17beta-estradiol. Both estrogens and androgens are synthesized in male hippocampus. These brain steroids are synthesized by cytochrome P450s (P450scc, P45017alpha and P450arom), hydroxysteroid dehydrogenases and reductases from endogenous cholesterol. The expression levels of enzymes are as low as 1/300-1/1000 of those in endocrine organs. Synthesis is dependent on the acute Ca(2+) influx upon neuron-neuron communication via NMDA receptors. Estradiol is particularly important because estradiol rapidly modulates neuronal synaptic transmission such as long-term potentiation via synaptic estrogen receptors. Xenoestrogens may also act via estrogen-driven signaling pathways.

Neurosteroid synthesis by cytochrome p450-containing systems localized in the rat brain hippocampal neurons: N-methyl-D-aspartate and calcium-dependent synthesis.

Neurosteroidogenesis has not been well elucidated due to the very low level of steroidogenic proteins in the brain. Here we report the first demonstration of the neuronal localization of neurosteroidogenic systems as well as the regulation of neurosteroidogenic activity in the adult rat hippocampus. Significant localization of cytochrome P450scc was observed in pyramidal neurons and granule neurons by means of immunohistochemical staining of slices. We also observed the colocalization, in hippocampal neurons, of P450scc with redox partners, hydroxysteroid sulfotransferase and steroidogenic acute regulatory protein. The distributions of astroglial cells and oligodendroglial cells showed very different patterns from that of the P450scc-containing cells. The expression of P450scc, redox partners, the sulfotransferase, and steroidogenic acute regulatory protein was also confirmed by Western blot analysis. The process of active neurosteroidogenesis was stimulated by exposing neurons to N-methyl-D-aspartate. Upon stimulation with N-methyl-D-aspartate, Ca(2+) influx through the N-methyl-D-aspartate subtype of glutamate receptors occurred, and significant net production of pregnenolone and pregnenolone sulfate was observed in the hippocampus. This neurosteroid production was considerably suppressed by the addition of antagonists of N-methyl-D-aspartate receptors, by Ca(2+) depletion, or by the addition of an inhibitor of P450scc. Upon stimulation with N-methyl-D-aspartate, the processing of full-length steroidogenic acute regulatory protein (37-kDa) to the truncated 30-kDa steroidogenic acute regulatory protein was observed. Taken together, these observations imply that hippocampal neurons synthesize neurosteroids. This synthesis may be stimulated and regulated by glutamate-mediated synaptic communication.

Effect of microsome-liposome fusion on the rotational mobility of cytochrome P450IIB4 in rabbit liver microsomes.

Membrane fusion of microsomes with soybean phospholipid vesicles was performed at pH 6.5 to investigate the effect of lipid-enrichment in the membrane on the rotational mobility of cytochrome P450. Rotational diffusion of cytochrome P450 in the microsomal membrane of phenobarbital-induced rabbit liver was measured by detecting the decay of absorption anisotropy after photolysis of the heme CO complex by a vertically polarized laser flash. The fusion procedures yielded three separate fractions upon sucrose density gradient centrifugation with lipid-to-protein ratio in weight (L/P) as follows: 1.5 in the bottom fraction, 2.2 in the middle fraction, and 3.9 in the top fraction. In each fraction, co-existence of mobile and immobile cytochrome P450 was observed. The percentage of rotationally mobile P450 (with the mean rotational relaxation time of phi=505-828 micros) in each of the different bands was found to be 59% in the bottom fraction, 61% in the middle fraction, and 68% in the top fraction. This increase in mobile population of P450 due to lipid-enrichment indicates that aggregated proteins in microsomal membranes dissociate with increasing L/P which is inversely proportional to the protein concentration in the membrane. With freeze-fracture electron microscopy, it was shown that the average distance increased between intramembrane particles by lipid-enrichment. Thus, the significant immobile population (32%) of P450 in microsomal membranes can be explained by nonspecific protein aggregation which is a consequence of the low L/P of 0.8. The decrease in the mobile population in the bottom fraction compared with intact microsomes was shown to be due to the pH 6.5 incubation used for fusion.

Digital fluorescence imaging of trafficking of endosomes containing low-density lipoprotein in brain astroglial cells.

We have used digital fluorescence microscopy to examine transport of LDL-containing endosomes in rat brain astroglial cells to show that individual middle endosomes undergo rapid transitions between forward/backward movements and immobile states over short distances. The population of rapidly moving endosomes (>0.04 microm/sec) was 35. 9%, and the remaining endosomes were slowly moving or temporarily immobile (<0.04 microm/sec). The averaged motion was, however, a very slow perinuclear motion with a velocity of 3.25 microm/h. This small velocity is mainly due to frequent changing of directions in movements, requiring 6 h for a significant concentration around the circumference of the cell nuclei. The application of both anti-dynein antibodies and vanadate in permeabilized cells resulted in peripherally concentrated distribution of endosomes, probably due to inhibition of perinuclear motion by dynein-like motor proteins. These results imply that both dynein-like and kinesin-like proteins bind to the same endosome resulting in both perinuclear and peripherally directed movements.

Effects of neurosteroids on Ca(2+) signaling mediated by recombinant N-methyl-D-aspartate receptor expressed in Chinese hamster ovary cells.

Pregnenolone sulfate (PREGS) potentiates the N-methyl-D-aspartate (NMDA) receptor-mediated Ca(2+)-signals in cultured hippocampal neurons. The NMDA receptor family has several different subunits whose expression in neurons has distinct spatial and temporal patterns. To examine subunit specificity of the PREGS action, we have investigated the effect of PREGS on recombinant GluR epsilon2/zeta1 (NR2B/NR1) type NMDA receptors stabley expressed in Chinese hamster ovary cells using heat shock promoters. PREGS enhanced the Ca(2+) influx through the GluR epsilon2/zeta1 receptors in a dose-dependent manner. The EC(50) of PREGS for the GluR epsilon2/zeta1 receptors was 8.6 microM. Other sulfated neurosteroids, dehydroepiandrosterone sulfate (DHEAS), 17beta-estradiol sulfate and 3alpha-ol-5beta-pregnan-20-one sulfate (3alpha5betaS), inhibited the positive modulatory effect of PREGS on the GluR epsilon2/zeta1 NMDA receptors. Ifenprodil, a specific inhibitor of GluR epsilon2 subunit, abolished the NMDA-induced Ca(2+) influx even in the presence of PREGS. These results imply that PREGS positively modulates the Ca(2+) influx through the GluR epsilon2/zeta1 receptors which are expressed from the embryonic period.

Real-time fluorescence analysis on molecular mechanisms for regulation of cytochrome P450scc activity upon steroidogenic stimulation in adrenocortical cells.

Real-time fluorescence analysis revealed that the activity of cytochrome P450scc was related to Ca2+ signals arising from extracellular NADPH, ACTH and ATP stimulation in adrenocortical fasciculata cells. The side-chain cleavage reaction by cytochrome P450scc was measured with 3beta-hydroxy-22,23-bisnor-5-cholenyl ether (cholesterol-resorufin) by observing the distinct increase in fluorescence upon conversion of cholesterol-resorufin to resorufin and pregnenolone. Adrenocorticotropic hormone (ACTH) induced a relatively small stimulation of the P450scc activity. A significant production of resorufin was revealed after stimulation of cell cultures with 100 pM, 1 nM of ACTH for 3 h. On the other hand, extracellular NADPH was found to rapidly and greatly stimulate the resorufin production in intact cells immediately after the addition of 50-500 microM NADPH. The extracellular NADPH stimulation was prevented by the addition of thapsigargin and EGTA which abolished Ca2+ oscillations induced by NADPH. Suramin, a specific antagonist of the P2y type ATP receptor, also completely abolished the NADPH-induced cholesterol-resorufin conversion. These results imply that extracellular NADPH (membrane impermeable) produced Ca2+ oscillations through its binding to ATP receptor thereby stimulating the activity of P450scc. The application of 45-500 microM extracellular ATP to cells did not, however, significantly increase the resorufin production. These three stimulators produced very different types of Ca2+ signals. ACTH induced mainly a series of Ca2+ spikes superimposed on a long-lasting basal Ca2+ elevation. The Ca2+ signals induced by NADPH showed predominantly a series of Ca2+ spikes without elevation of the basal Ca2+ concentration. Only long-lasting Ca2+ elevation was induced by extracellular ATP. The stimulation of cytochrome P450scc may thus be correlated with the different patterns of Ca2+ signals.

Dynamic mobility of genetically expressed fusion protein between cytochrome P4501A1 and NADPH-cytochrome P450 reductase in yeast microsomes.

A fusion protein of rat liver CYP1A1 with NADPH-cytochrome P450 reductase was expressed genetically in yeast microsomal membranes. This flavo-cytochrome is active in 6-hydroxylation of zoxazolamine. Rotational diffusion of the fusion protein was examined by observing the flash-induced absorption anisotropy r(t) of the P450.CO complex. Theoretical analysis of r(t) was performed based on a "rotation-about-membrane normal" model. The absorption anisotropy decayed within 2 ms to a time-independent value r(3). Forty percent of the fusion protein rotated with a rotational relaxation time phi of 1.35 ms. Treatment with high salt increased the mobile population of the fusion protein to 62% with phi = 0.96 ms. The mobile population of the fusion protein is close to that of CYP1A1 coexpressed with the P450 reductase and greater than that of CYP1A1 alone [Iwase et al. (1991) Biochemistry 30, 8347-8351]. The large mobile population of the fusion protein provides evidence that CYP1A1 is mobilized by forming associations with P450 reductase in microsomal membranes.

Calcium ion as a second messenger for o-nitrophenylsulfenyl-adrenocorticotropin (NPS-ACTH) and ACTH in bovine adrenal steroidogenesis.

o-Nitrophenyl sulfenyl-modified ACTH (NPS-ACTH) stimulated steroidogenesis acutely in bovine fasciculata-reticularis cells without increase in cellular cAMP synthesis. Application of NPS-ACTH to the cultured cells induced Ca2+ signals in individual cells as detected by video-enhanced microscopic fluorescence measurements. The percentage of Ca2+ signaling cells corresponded well with the increase of steroidogenesis induced by NPS-ACTH below 1 nM. Treatment of the cells with nicardipine, a Ca2+ channel blocker, suppressed the Ca2+ signals except for the transient increase just after the addition of NPS-ACTH and also blocked completely the stimulative effect on the steroidogenesis of NPS-ACTH below 1 nM. At a dosage of NPS-ACTH higher than 10 nM, the stimulative effect of steroidogenesis was partly suppressed by nicardipine and also by AA-861, a lipoxygenase inhibitor. The action of NPS-ACTH might be mediated by both Ca2+ and lipoxygenase metabolite(s) of arachidonic acid as dual second messengers. The effect of ACTH in pM range on the steroidogenesis was suppressed completely by the treatment with nicardipine and AA-861 at the same time, indicating that the action was mediated by both Ca2+ and the lipoxygenase metabolite(s) but not by cAMP. cAMP plays a significant role as a second messenger for ACTH action only at ACTH concentrations greater than 10 pM.

Removal of airborne bacteria by filtration using a composite microporous membrane made of a pyridinium-type polymer showing strong affinity with microbial cells.

A composite microporous membrane made of poly(N-benzyl-4-vinylpyridinium chloride) that showed strong affinity with bacterial cells was prepared as a filter material for removing airborne bacteria. Thickness, pore diameter and porosity of the membrane were 0.72 mm, 14.5 microm and 63%, respectively. Electron micrographic analysis revealed that the membrane consisted of a very large number of connected beads of 1.4 microm in diameter made of the pyridinium-type polymer. Filtration using the membrane was performed easily at low flow rates with insignificant pressure drop across the membrane. Filtration at 63.7 cm/sec gave 99.98% and 99.996% removal (3.7 and 4.4 log10-unit reduction in concentration) of Escherichia coli and Pseudomonas aeruginosa, respectively. Staphylococcus aureus was not detected in filtrates. Since pores of the membrane were much larger than these bacteria, the efficient removal was best explained in terms of the affinity of the polymer with bacterial cells.

Monoclonal antibody 14F7, which recognizes a stage-specific immature oligodendrocyte surface molecule, inhibits oligodendrocyte differentiation mediated in co-culture with astrocytes.

Cells at an intermediate stage of oligodendrocyte lineage are not only well characterized by biochemical studies but also are likely to relate to the outcome of physiological events. To elucidate the molecular events leading to the development of oligodendrocyte lineage cells, we have raised monoclonal antibodies against stage-specific immature oligodendrocytes, which have previously been isolated by a novel oligodendrocyte-lineage cell culture technique (Sakurai et al.: J Neurosci Res 52:17-26, 1998). We have isolated a mouse monoclonal antibody termed 14F7 which predominantly labels stage-specific immature oligodendrocytes and have found that the expression of 14F7 immunoreactivity in the developing neonatal rat forebrain is closely associated with cells expressing the oligodendrocyte progenitor marker A2B5 and to immature oligodendrocyte expressing O4 antigen. 14F7+ cells were distributed in the ventricular and subventricular zone and the nearby forming corpus callosum as non-myelinating cells. In contrast to cell culture observations, 14F7+ cells were seen only in oligodendrocyte lineage cells. For instance, dissociated cell culture studies indicated that 14F7 labels a cell surface molecule, and its cellular distribution is coincident with all of O4+ cells and A2B5+ cells, and even A2B5- cells. By contrast, 14F7-positive cells did not label astrocytes and, furthermore, did not label myelin basic protein (MBP)-positive oligodendrocytes. 14F7 recognized a 48-kDa protein on sodium dodecyl sulfate polyacrylamide gel electrophoresis. 14F7 immunoreactivity was detectable in rat brain as early as embryonic day 18. Furthermore, in these cells, the total time for differentiation was extended, and on maturation, these cells subsequently expressed an array of myelin-specific proteins, which normally occurs by direct contact with type-1 astrocytes. However, in the presence of 14F7, stage-specific oligodendrocytes co-cultured with astrocytes completely failed to express MBP. These data suggest that the 14F7 antigen is a novel cell surface molecule that is expressed in the intermediate stage of oligodendrocyte-lineage cells, and it is expected that it regulates the differentiation of oligodendrocyte throughout development.

Time resolved study of effect of chlorpromazine on mobility of cytochrome P-450 and phospholipids in the inner membrane of adrenocortical mitochondria.

The effects of chlorpromazine on the mobility of cytochrome P-450 and the fluidity of lipid membranes have been investigated in bovine adrenocortical submitochondrial particles (SMP). Rotational diffusion of the cytochrome was measured by observing the decay of absorption anisotropy, ra(t), after photolysis of the heme.CO complex by a vertically polarized laser flash. Analysis of ra(t) was based on a 'rotation-about-membrane-normal' model. The anisotropy decayed within 2 ms to a time independent value r3. The presence of chlorpromazine decreased the mobile population of cytochrome P-450 from 28 to 23%. The rotational relaxation time phi a of the mobile population (approximately 1100 microseconds) was, however, not significantly changed by chlorpromazine. The lipid fluidity was examined by observing time-resolved fluorescence anisotropy, rf(t), of 1,6-diphenyl 1,3,5-hexatriene (DPH). The anisotropy rf(t) decayed within 70 ns to a time independent value r infinity. The motion of DPH was analyzed based on a 'wobbling-in-cone' model. The presence of chlorpromazine decreased the cone angle from 42 degrees to 39 degrees, while the rotational relaxation time phi f (approximately 2 ns) was not significantly changed by the presence of chlorpromazine. These results demonstrate that chlorpromazine decreased the mobility of not only lipids but also membrane proteins.

Digital fluorescence imaging of elementary steps of neurosteroid synthesis in rat brain glial cells.

With fluorescence microscopic imaging, we have examined Ca2+ signaling, LDL uptake and distribution of cytochrome P450 scc on individual rat brain glial cells in order to investigate the molecular mechanisms of neurosteroid synthesis. Astrocytes and oligodendrocytes were cultured from newborn rat brain. Ca2+ signaling was observed in Calcium Green-1 loaded astrocytes upon neurotransmitter stimulations using video-enhanced microscopy. Upon stimulation of serotonin and glutamate, we observed typically three types of Ca2+ signaling which were Ca2+ oscillations, a transient increase in Ca2+ concentration and Ca2+ oscillations superimposed on a transient Ca2+ increase. On the other hand, histamine and ATP induced only a transient increase in Ca2+ without oscillatory response. Uptake of octadecyl rhodamine (R18) labeled LDL by astrocytes and oligodendrocytes was observed in the time scale of 30 min with confocal laser scanning microscopy. Some localization of LDL in the cytoplasm was observed for astrocytes. For oligodendrocytes, incorporated LDL was distributed over the entire cytoplasmic region of both cell body and multiple branched cell processes. The presence of a significant amount of cytochrome P450 scc was demonstrated with immunofluorescence staining in both astrocytes and oligodendrocytes. The density of P450 scc in both glial cells was suggested to be around 1% of that in bovine adrenocortical fasciculata cells. The results lead to an improved quantitative picture of neurosteroid synthesis in glial cells.

Adrenocorticotropin induces calcium oscillations in adrenal fasciculata cells: single cell imaging.

With fluorescence microscopic imaging, we have demonstrated that the Ca2+ signaling occurred in individual Calcium Green-1 loaded bovine adrenal fasciculata cells upon stimulation with adrenocorticotropin (ACTH) at physiological concentration of 0.1-100 pM. We observed three patterns of Ca2+ signaling which were Ca2+ oscillations (33%), step-like increase in Ca2+ concentration (10%), and Ca2+ oscillations superimposed on step-like increase in Ca2+ (57%). The oscillation in intracellular Ca2+ concentration occurred with a frequency around 0.04 Hz. When Ca2+ signaling upon ACTH stimulation was inhibited by the treatment with EGTA, the corticoid production was considerably suppressed. The results suggest that the Ca2+ signaling is a probable candidate of the second messenger for ACTH-induced steroid hormone synthesis in zona fasciculata cells.

Dynamic interactions of rabbit liver cytochromes P450IA2 and P450IIB4 with cytochrome b5 and NADPH-cytochrome P450 reductase in proteoliposomes.

Purified liver microsomal cytochrome P450IA2 or P450IIB4 was co-reconstituted with cytochrome b5 or NADPH-cytochrome P450 reductase in phosphatidylcholine-phosphatidylethanolamine-phosphatidylserine vesicles at a lipid to P450 weight ratio of 2 by cholate dialysis procedures. The proteoliposomes catalyzed drug oxidation. Rotational diffusion of cytochrome P450 was measured by observing the decay of absorption anisotropy, r(t), after photolysis of the heme.CO complex. Analysis of r(t) was based on a "rotation-about-membrane normal" model. The absorption anisotropy decayed within 1 ms to a time-independent value, r3. Different rotational mobility for the two cytochrome P450s was observed. Though 20% of cytochrome P450IA2 was immobile, all cytochrome P450IIB4 molecules were rotating. The rotational relaxation time, phi, of the mobile population was 237 microseconds for cytochrome P450IA2 and 160 microseconds for cytochrome P450IIB4. The two cytochrome P450s have shown very different interactions with cytochrome b5 and NADPH-cytochrome P450 reductase. By the presence of the redox partner, the mobile population of cytochrome P450IA2 was increased significantly from 80% to 96% (plus cytochrome b5) and to 89% (plus NADPH-cytochrome P450 reductase) due to dissociation of P450 oligomers. On the other hand, the mobility of cytochrome P450IIB4 was not considerably affected by the presence of cytochrome b5 or NADPH-cytochrome P450 reductase as judged by little difference in phi and r3, keeping the mobile population of 100%. These results imply that cytochrome P450IA2 forms a transient association with cytochrome b5 and NADPH-cytochrome P450 reductase.(ABSTRACT TRUNCATED AT 250 WORDS)

Rotation and membrane topology of genetically expressed methylcholanthrene-inducible cytochrome P-450IA1 lacking the N-terminal hydrophobic segment in yeast microsomes.

A modified rat liver cytochrome P-450IA1, lacking amino acids 2-30, a proposed membrane anchor for cytochrome P-450, was expressed genetically in yeast microsomal membranes. This truncated cytochrome is practically active in the deethylation of 7-ethoxycoumarin. A full-length cytochrome P-450IA1 was also expressed in yeast microsomes. Rotational diffusion of P-450IA1 was examined by observing the flash-induced absorption anisotropy r(t) of the P-450.CO complex. The anisotropy decayed to a time-independent value within a 2-ms time range. Since the decay curve has the characteristics of a slow rotation of membrane-embedded cytochrome, the theoretical analysis of r(t) was performed based on a "rotation-about-membrane normal" model. 41% of the shortened P-450IA1 was rotating with the rotational relaxation time phi of 1020 microseconds, whereas 27% of the full-length P-450IA1 was mobile with phi = 1101 microseconds. The high salt treatment did not remove the shortened cytochrome from the membrane and also did not drastically weaken the interactions of the cytochrome with the membrane, as judged from the slow rotation characteristics (phi = 830 microseconds). These results demonstrate that the N-terminal shortened P-450IA1 is incorporated properly into the yeast microsomal membrane and that the N-terminal hydrophobic segment is not solely responsible for attachment to the membrane, providing evidence that additional segments of P-450IA1 are involved in the membrane binding.