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miR128 up-regulation correlates with impaired amyloid β(1-42) degradation in monocytes from patients with sporadic Alzheimer's disease

Alzheimers disease (AD), the most common form of dementia in elderly individuals, is characterized by neurofibrillary tangles, extracellular amyloid-β (Aβ) plaques and neuroinflammation. New evidence has shown that the lysosomal system might be a crossroad in which etiological factors in AD pathogenesis converge. This study shows that several lysosomal enzymes, including Cathepsin B, D, S, β-Galactosidase, α-Mannosidase, and β-Hexosaminidase, were less expressed in monocytes and lymphocytes from patients with a clinical diagnosis of AD dementia compared with cells from healthy controls. In vitro experiments of gain and loss of function suggest that down-regulation is a direct consequence of miR-128 up-regulation found in AD-related cells. The present study also demonstrates that miR-128 inhibition in monocytes from AD patients improves Aβ(1-42) degradation. These results could contribute to clarify the molecular mechanisms that affect the imbalanced Aβ production/clearance involved in the pathogenesis of AD.

Rat Brain Cortex Mitochondria Release Group II Secretory Phospholipase A2 under Reduced Membrane Potential

Activation of brain mitochondrial phospholipase(s) A2 (PLA2) might contribute to cell damage and be involved in neurodegeneration. Despite the potential importance of the phenomenon, the number, identities, and properties of these enzymes are still unknown. Here, we demonstrate that isolated mitochondria from rat brain cortex, incubated in the absence of respiratory substrates, release a Ca2+-dependent PLA2 having biochemical properties characteristic to secreted PLA2 (sPLA2) and immunoreacting with the antibody raised against recombinant type IIA sPLA2 (sPLA2-IIA). Under identical conditions, no release of fumarase in the extramitochondrial medium was observed. The release of sPLA2 from mitochondria decreases when mitochondria are incubated in the presence of respiratory substrates such as ADP, malate, and pyruvate, which causes an increase of transmembrane potential determined by cytofluorimetric analysis using DiOC6(3) as a probe. The treatment of mitochondria with the uncoupler carbonyl cyanide 3-chlorophenylhydrazone slightly enhances sPLA2 release. The increase of sPLA2 specific activity after removal of mitochondrial outer membrane indicates that the enzyme is associated with mitoplasts. The mitochondrial localization of the enzyme has been confirmed by electron microscopy in U-251 astrocytoma cells and by confocal laser microscopy in the same cells and in PC-12 cells, where the structurally similar isoform type V-sPLA2 has mainly nuclear localization. In addition to sPLA2, mitochondria contain another phospholipase A2 that is Ca2+-independent and sensitive to bromoenol lactone, associated with the outer mitochondrial membrane. We hypothesize that, under reduced respiratory rate, brain mitochondria release sPLA2-IIA that might contribute to cell damage.

The effect of S-adenosyl-l-methionine on ischemia-induced disturbances of brain phospholipid in the gerbil

Brain ischemia was produced in gerbils (Meriones unguiculatus) by the bilateral ligation of the carotid arteries with reported procedures. Changes in the energy status of brain demonstrated that carotid ligation was effective. At different time intervals from ligation, groups of ferbils were given either saline or S-Adenosyl-l-methionine (SAMe) by the intraventricular (i.v.) route (1.6 mg/Kg body wt. twice, at each 10 min interval), or by the intraperitoneal (i.p.) administration (200 mg/Kg body wt.) or subcutaneously (s.c.) with 40 mg/Kg body wt, daily, for two weeks. Control animals, with and without SAMe, together with the ischemic groups, were decapitated directly into liquid nitrogen, 10 min after ligation. Brain neutral and polar lipid, together with free fatty acids, which were all labeled in vivo by the intraventricular injection of [1-14C]arachidonic acid 2 hr prior to ligation, were extracted, purified and separated by conventional procedures. SAMe when injected i.v. or i.p. noticeably corrected the changes in polar lipid by reversing the decrease of brain phosphatidylcholine and choline plasmalogen, as well as of their labeling, which was due to ischemia. Concurrently with this action, SAMe treatment (i.v. and i.p.) also provided to some extent to re-establish the normal level of labeling of ethanolamine lipids. When SAMe was given s.c., no effect was present. SAMe had no effect on the increase of free fatty acid and diglyceride due to ischemia. The prevention by SAMe of the changes of choline lipids suggests that a stimulation of the methyltransferase reaction may occur in the ischemic brain, due to increased substrate (SAMe) availability. This effect may be important for cell survival, since membrane phospholipid derangements alter the properties of the membrane.

Receptor-Mediated Degradation of Choline Plasmalogens and Glycerophospholipid Methylation: A New Hypothesis

The stimulation of receptors on the cell surface initiates biochemical and physical changes in membranes that lead to biological responses by the cells. The biochemical and physical changes include changes in levels of cyclic nucleotides, phosphorylation of proteins in membranes, increased membrane disorder (fluidity), and increased fluxes of Ca2+, Na+, and other ions. Changes in lipid metabolism associated with receptor stimulation may include the release of arachidonic acid and formation of metabolites and changes in phospholipid N-methylation and in polyphosphoinositide metabolism. The large number of studies on the association of phospholipid N-methylation with receptor stimulation and adenylate cyclase suggest that an important biological mechanism is involved. An overall hypothesis linking receptor stimulation directly with increased activity of AdoMet: PtdEtn methyltransferase and phospholipase A2 was proposed (Hirata and Axelrod, 1980; Mato and Alemany, 1983). This hypothesis is no longer tenable because of difficulties of others with reproduction of the results, problems inherent in the methodology, and errors in the interpretation of the results. Most previous studies failed to recognize that stopping a reaction with acid causes the hydrolysis of plasmalogens to lysoGpl. The presence of lyso compounds was instead interpreted as evidence for phospholipase A2 activity.

The coumarin derivative AD6 inhibits the release of arachidonic acid by interfering with phospholipase A2 activity in human platelets stimulated with thrombin

AD6 is a coumarin derivative which is able to inhibit platelet aggregation and release due to various agonists as adrenaline, PAF, Ca++ ionophore and others. It has been demonstrated that this compound reduces the production of free arachidonate and diglyceride from human platelets pulse-labeled with radioactive arachidonic acid thus suggesting a possible interference with the activity of phospholipase A2 and/or phospholipase C. The present report indicates that the drug has no effect on the increase of the labeling of phosphatidic acid which takes place when platelets pulse-labeled with arachidonic acid are stimulated with thrombin. Furthermore, AD6 is not able to cause changes on the metabolism of phosphoinositides monitored using platelets pre-labeled with [3H] inositol. These observations exclude the possibility that AD6 interferes with phospholipase C activity. Experiments with platelets pulse-labeled with arachidonate suggest that AD6 inhibits phospholipase(s) A2 activity or modulate negatively one or more processes involved in its activation.

Activation of phospholipase A2 and β-thromboglobulin release in human platelets: Comparative effects of thrombin and fluoroaluminate stimulation

Several reports have suggested that the activity of platelet phospholipase A2 is modulated by GTP-binding protein(s) whose nature and properties need to be defined. Fluoroaluminate is known to activate G-proteins and this leads to a number of cellular responses including the activation of phospholipases. This paper demonstrates that human platelets, prelabelled with [3H]arachidonic acid, produce free arachidonic acid when stimulated with fluoroaluminate and this effect is time- and dose-dependent. The production of arachidonic acid is not inhibited by neomycin, a PI-cycle inhibitor, but is completely abolished by mepacrine, an inhibitor of both phospholipase A2 and C. At low concentration of fluoroaluminate (10 mM NaF) phospholipase A2 but not phospholipase C is activated. In addition, fluoroaluminate treatment releases beta-thromboglobulin (beta-TG) and this effect is not inhibited by acetylsalicylic acid. Under identical conditions both neomycin and mepacrine suppress the release of arachidonic acid and beta-TG induced by thrombin. Sodium nitroprusside, which increases cGMP levels in platelets, inhibits arachidonic acid liberation and beta-TG release in thrombin-stimulated platelets but has no effect in fluoroaluminate-treated platelets; cGMP was reported to suppress phospholipase C activation. These results are consistent with the hypothesis that, in thrombin-stimulated platelets, the liberation of arachidonic acid and beta-TG are strictly dependent on the activation of phospholipase C. We have also provided evidence for the existence of a phospholipase A2 activated by a G-protein which is independent from the degradation of phosphoinositides and, contrary to phospholipase C, it is not down regulated by cGMP.

AD6 (8-monochloro-3-beta-diethylamino-ethyl-4-methyl-7-ethoxycarbonyl-methoxy coumarin) inhibits the release of arachidonic acid in human platelets stimulated by thrombin

The coumarin derivative AD6 is known to inhibit platelet aggregation and release and it possesses vasodilatory properties on coronary arteries of laboratory animals. Furthermore, the inhibition of the production of TxB2 from endogenous substrates after stimulation of human platelets with collagen has been demonstrated. The present report demonstrates that AD6 inhibits the production of labeled arachidonic acid and diglycerides from phospholipids of platelets stimulated with thrombin. This effect is dose-dependent and is already evident at a concentration of the drug (25 microM) which is unable to prevent the aggregation. Apparently, AD6 inhibits the release of arachidonic acid from phosphatidylinositol and choline phosphoglycerides which are the main sources of the substrate for the synthesis of prostaglandins and thromboxanes.

Evidence that cytosolic phospholipase A2 is down-regulated by protein kinase C in intact human platelets stimulated with fluoroaluminate

We reported that protein kinase C (PKC) inhibitors increase the release of arachidonic acid induced by fluoroaluminate (AlF4 −), an unspecific G‐protein activator, in intact human platelets. Now we demonstrate that this effect is independent of the extracellular Ca2+ concentration and that AlF4 −‐induced release of AA is abolished by BAPTA, an intracellular Ca2+ chelator, even in the presence of GF 109203X, a specific and potent PKC inhibitor. This compound also blocks the liberation of the secretory phospholipase A2 in the extracellular medium, indicating that this enzyme is not involved in the potentiation of arachidonic acid by PKC inhibitors. On the other hand, the latter effect is completely abolished by treatment of platelets with AACOCF3, a specific inhibitor of cytosolic phospholipase A2 (cPLA2). These observations indicate that cPLA2 is responsible for the AlF4 −‐induced release of arachidonic acid by a mechanism that is down‐regulated by PKC.

Caspase 3 activation and PARP cleavage in lymphocytes from newborn babies of diabetic mothers with unbalanced glycaemic control.

Several epidemiological studies showed that gestational diabetes mellitus is the most frequent metabolic disorder of pregnancy, the pathogenesis of which has yet to be completely clarified.

Serine base exchange enzyme in porcine lyophilised platelets: enzyme properties and modulation by AlF4- and different types of heparin.

Phosphatidylserine is one of the PKC modulators and thus it may play an important role in signal transduction. Regulation of the synthesis of this phospholipid is not yet clarified. The contrasting reports are possibly related to the existence of different enzymes which, in mammalian tissues, catalyse the exchange between free serine and the nitrogen base of a membrane phospholipid. This study demonstrates that serine base exchange reactions of commercially available lyophilised porcine platelets exhibit similar pH optima, temperature and Ca2+ dependence as observed in fresh tissues. Analysis of fatty acids composition of the three phospholipid classes involved in base exchange reactions also demonstrated a similarity with fresh platelets. Serine and ethanolamine base exchange enzyme activities were assayed in parallel in platelet lysate subjected to preincubation at various temperatures (30-60°C). When dithioerithrol was omitted from the incubation medium, the two base exchange reactions were inhibited with a similar temperature-dependent pattern. Addition of the reducing agent enhanced the sensitivity to preincubation only for the serine base exchange reaction which was inhibited by 80% after preincubation at 45°C. With respect to its regulation, porcine platelet serine base exchange enzyme(s) was inhibited by fluoroalluminate, a widely used G-protein activator, and stimulated by unfractionated heparin. Low mol. wt. heparin did not influence enzyme activity. Unfractionated heparin greatly stimulated SBEE activity assayed at pH 7.4, a pH value far from the optimal pH.