Aldosterone induces interleukin-18 through endothelin-1, angiotensin II, Rho/Rho-kinase, and PPARs in cardiomyocytes

Aldosterone (Aldo) is recognized as an important risk factor for cardiovascular diseases. IL-18 induces myocardial hypertrophy, loss of contractility of cardiomyocytes, and apoptosis leading myocardial dysfunction. However, so far, there have been few reports concerning the interaction between Aldo and IL-18. The present study examined the effects and mechanisms of Aldo on IL-18 expression and the roles of peroxisome proliferator-activated receptor (PPAR) agonists in rat cardiomyocytes. We used cultured rat neonatal cardiomyocytes stimulated with Aldo to measure IL-18 mRNA and protein expression, Rho-kinase, and NF-kappaB activity. We also investigated the effects of PPAR agonists on these actions. Aldo, endothelin-1 (ET-1), and angiotensin II (ANG II) increased IL-18 mRNA and protein expression. Mineralocorticoid receptor antagonists, endothelin A receptor antagonist, and ANG II receptor antagonist inhibited Aldo-induced IL-18 expression. Aldo induced ET-1 and ANG II production in cultured media. Moreover, Rho/Rho-kinase inhibitor and statin inhibited Aldo-induced IL-18 expression. On the other hand, Aldo upregulated the activities of Rho-kinase and NF-kappaB. PPAR agonists attenuated the Aldo-induced IL-18 expression and NF-kappaB activity but not the Rho-kinase activity. Our findings indicate that Aldo induces IL-18 expression through a mechanism that involves, at a minimum, ET-1 and ANG II acting via the Rho/Rho-kinase and PPAR/NF-kappaB pathway. The induction of IL-18 in cardiomyocytes by Aldo, ET-1, and ANG II might, therefore, cause a deterioration of the cardiac function in an autocrine and paracrine fashion. The inhibition of the IL-18 expression by PPAR agonists might be one of the mechanisms whereby the beneficial cardiovascular effects are exerted.     

A presynaptic gain control mechanism fine-tunes olfactory behavior

Early sensory processing can play a critical role in sensing environmental cues. We have investigated the physiological and behavioral function of gain control at the first synapse of olfactory processing in Drosophila. Olfactory receptor neurons (ORNs) express the GABA(B) receptor (GABA(B)R), and its expression expands the dynamic range of ORN synaptic transmission that is preserved in projection neuron responses. Strikingly, each ORN channel has a unique baseline level of GABA(B)R expression. ORNs that sense the aversive odorant CO(2) do not express GABA(B)Rs and do not have significant presynaptic inhibition. In contrast, pheromone-sensing ORNs express a high level of GABA(B)Rs and exhibit strong presynaptic inhibition. Furthermore, pheromone-dependent mate localization is impaired in flies that lack GABA(B)Rs in specific ORNs. These findings indicate that different olfactory receptor channels employ heterogeneous presynaptic gain control as a mechanism to allow an animal's innate behavioral responses to match its ecological needs.     

Characterization of conformational deformation-coupled interaction between immunoglobulin G1 Fc glycoprotein and a low-affinity Fcγ receptor by deuteration-assisted small-angle neutron scattering

A recently developed integrative approach combining varied types of experimental data has been successfully applied to three-dimensional modelling of larger biomacromolecular complexes. Deuteration-assisted small-angle neutron scattering (SANS) plays a unique role in this approach by making it possible to observe selected components in the complex. It enables integrative modelling of biomolecular complexes based on building-block structures typically provided by X-ray crystallography. In this integrative approach, it is important to be aware of the flexible properties of the individual building blocks. Here we examine the ability of SANS to detect a subtle conformational change of a multidomain protein using the Fc portion of human immunoglobulin G (IgG) interacting with a soluble form of the low-affinity Fcγ receptor IIIb (sFcγRIIIb) as a model system. The IgG-Fc glycoprotein was subjected to SANS in the absence and presence of 75%-deuterated sFcγRIIIb, which was matched out in D₂O solution. This inverse contrast-matching technique enabled selective observation of SANS from IgG-Fc, thereby detecting its subtle structural deformation induced by the receptor binding. The SANS data were successfully interpreted by considering previously reported crystallographic data and an equilibrium between free and sFcγRIIIb-bound forms. Our SANS data thus demonstrate the applicability of SANS in the integrative approach dealing with biomacromolecular complexes composed of weakly associated building blocks with conformational plasticity.     

Nitric oxide improves membrane fluidity of erythrocytes in essential hypertension: An electron paramagnetic resonance investigation

It has been shown that rheological abnormality might be an etiological factor in hypertension. Recent studies have revealed that human erythrocytes possess a nitric oxide (NO) synthase and that this activation might be involved in the regulation of rheological properties of erythrocytes. The present study was undertaken to investigate the role of NO in the regulation of membrane functions of erythrocytes in patients with essential hypertension by means of an electron paramagnetic resonance (EPR) and spin-labeling method. The NO donor S-nitroso-N-acetylpenicillamine (SNAP) decreased the order parameter (S) for 5-nitroxide stearate (5-NS) and the peak height ratio (h(0)/h(-1)) for 16-NS obtained from EPR spectra of erythrocyte membranes in a dose-dependent manner. The finding indicated that the NO donor increased the membrane fluidity of erythrocytes. In addition, the effect of SNAP was significantly potentiated by 8-bromo-cyclic guanosine monophosphate. By contrast, the change of the fluidity induced by SNAP was reversed in the presence of L-N(G)-nitroarginine methyl ester and asymmetric dimethyl L-arginine. In patients with essential hypertension, the membrane fluidity of erythrocytes was significantly lower than in the normotensive subjects. The effect of SNAP was more pronounced in essential hypertension than in normotensive subjects. These results showed that NO increased the membrane fluidity and decreased the rigidity of cell membranes. Furthermore, the greater effect of NO on the fluidity in essential hypertension suggests that NO might actively participate in the regulation of rheological behavior of erythrocytes and have a crucial role in the improvement of microcirculation in hypertension.     

GSK-3beta regulates phosphorylation of CRMP-2 and neuronal polarity

Neurons are highly polarized and comprised of two structurally and functionally distinct parts, an axon and dendrites. We previously showed that collapsin response mediator protein-2 (CRMP-2) is critical for specifying axon/dendrite fate, possibly by promoting neurite elongation via microtubule assembly. Here, we showed that glycogen synthase kinase-3beta (GSK-3beta) phosphorylated CRMP-2 at Thr-514 and inactivated it. The expression of the nonphosphorylated form of CRMP-2 or inhibition of GSK-3beta induced the formation of multiple axon-like neurites in hippocampal neurons. The expression of constitutively active GSK-3beta impaired neuronal polarization, whereas the nonphosphorylated form of CRMP-2 counteracted the inhibitory effects of GSK-3beta, indicating that GSK-3beta regulates neuronal polarity through the phosphorylation of CRMP-2. Treatment of hippocampal neurons with neurotrophin-3 (NT-3) induced inactivation of GSK-3beta and dephosphorylation of CRMP-2. Knockdown of CRMP-2 inhibited NT-3-induced axon outgrowth. These results suggest that NT-3 decreases phosphorylated CRMP-2 and increases nonphosphorylated active CRMP-2, thereby promoting axon outgrowth.     

Use of RNA interference-mediated gene silencing and adenoviral overexpression to elucidate the roles of AKT/protein kinase B isoforms in insulin actions

Insulin plays a central role in the regulation of glucose homeostasis in part by stimulating glucose uptake and glycogen synthesis. The serine/threonine protein kinase Akt has been proposed to mediate insulin signaling in several processes. However, it is unclear whether Akt is involved in insulin-stimulated glucose uptake and which isoforms of Akt are responsible for each insulin action. We confirmed that expression of a constitutively active Akt, using an adenoviral expression vector, promoted translocation of glucose transporter 4 (GLUT4) to plasma membrane, 2-deoxyglucose (2-DG) uptake, and glycogen synthesis in both Chinese hamster ovary cells and 3T3-L1 adipocytes. Inhibition of Akt either by adenoviral expression of a dominant negative Akt or by the introduction of synthetic 21-mer short interference RNA against Akt markedly reduced insulin-stimulated GLUT4 translocation, 2-DG uptake, and glycogen synthesis. Experiments with isoform-specific short interference RNA revealed that Akt2, and Akt1 to a lesser extent, has an essential role in insulin-stimulated GLUT4 translocation and 2-DG uptake in both cell lines, whereas Akt1 and Akt2 contribute equally to insulin-stimulated glycogen synthesis. These data suggest a prerequisite role of Akt in insulin-stimulated glucose uptake and distinct functions among Akt isoforms.     

Ultrasound-promoted palladium-catalyzed carbonyl allylation by allylic alcohols with tin(II) chloride in non-polar solvents

Heterogeneous ultrasound-promoted palladium-catalyzed carbonyl allylation by γ-substituted allylic alcohols with tin(II) chloride in non-polar solvents such as diethyl ether, diisopropyl ether and toluene was carried out stepwise (first, the formation of allylic tin intermediates by ultrasonication, followed by the allylation of aldehydes by the intermediates) to produce 1,4-disubstituted 3-buten-1-ols regioselectively in moderate yields. The regioselectivity (-selection) in the ultrasound-promoted reaction is the inverse of that (γ-selection) in the homogeneous palladiumcatalyzed carbonyl allylation in polar solvents such as 1,3-dimethyl-2-imidazolidinone, DMF, DMSO and ethylene glycol. The more bulky the γ-substituent, the higher is the -regioselectivity.