Modulation of Ganglioside Biosynthesis in Primary Cultured Neurons

Murine cerebellar cells were pulse labeled with [14C]galactose, and the incorporation of radioactivity into gangliosides and neutral glycosphingolipids was examined under different experimental conditions. In the presence of drugs affecting intracellular membrane flow, as well as at 15 degrees C, labeled GlcCer was found to accumulate in the cells, whereas the labeling of higher glycosphingolipids and gangliosides was reduced. Monensin and modulators of the cytoskeleton effectively blocked biosynthesis of the complex gangliosides GM1, GD1a, GD1b, GT1b, and GQ1b, whereas incorporation of radioactivity into neutral glycosphingolipids, such as glucosylceramide and lactosylceramide, as well as GM3, GM2, and GD3 was either increased or unaltered. As monensin has been reported to interfere with the flow of molecules from the cis to the trans stacks of the Golgi apparatus, this result highlights at least one subcompartmentalization of ganglioside biosynthesis within the Golgi system. Inhibitors of energy metabolism affected, predominantly, the biosynthesis of the b-series gangliosides, whereas a reduced temperature (15 degrees C) more effectively blocked incorporation of radiolabel into the a-series gangliosides, a result suggesting the importance of GM3, as the principal branching point, for the regulation of ganglioside biosynthesis.     

Alterations in Phosphatidylcholine Metabolism of Stretch-Injured Cultured Rat Astrocytes

Abstract: The primary objective of this study was to determine the influence of stretch-induced cell injury on the metabolism of cellular phosphatidylcholine (PC). Neonatal rat astrocytes were grown to confluency in Silastic-bottomed tissue culture wells in medium that was usually supplemented with 10 µM unlabeled arachidonate. Cell injury was produced by stretching (5–10 mm) the Silastic membrane with a 50-ms pulse of compressed air. Stretch-induced cell injury increased the incorporation of [³H]choline into PC in an incubation time- and stretch magnitude-dependent manner. PC biosynthesis was increased three- to fourfold between 1.5 and 4.5 h after injury and returned to control levels by 24 h postinjury. Stretch-induced cell injury also increased the activity of several enzymes involved in the hydrolysis [phospholipase A₂ (EC 3.1.1.4) and C (PLC; EC 3.1.4.3)] and biosynthesis [phosphocholine cytidylyltransferase (PCT; EC 2.7.7.15)] of PC. Stretch-induced increases in PC biosynthesis and PCT activity correlated well (r = 0.983) and were significantly reduced by pretrating (1 h) the cells with an iron chelator (deferoxamine) or scavengers of reactive oxygen species such as superoxide dismutase and catalase. The stretch-dependent increase in PC biosynthesis was also reduced by antioxidants (vitamin E, vitamin E succinate, vitamin E phosphate, melatonin, and n-acetylcysteine). Arachidonate-enriched cells were more susceptible to stretch-induced injury because lactate dehydrogenase release and PC biosynthesis were significantly less in non-arachidonate-enriched cells. In summary, the data suggest that stretch-induced cell injury is (a) a result of an increase in the cellular level of hydroxyl radicals produced by an iron-catalyzed Haber-Weiss reaction, (b) due in part to the interaction of oxyradicals with the polyunsaturated fatty acids of cellular phospholipids such as PC, and (c) reversible as long as the cell's membrane repair functions (PC hydrolysis and biosynthesis) are sufficient to repair injured membranes. These results suggest that stretch-induced cell injury in vitro may mimic in part experimental traumatic brain injury in vivo because alterations in cellular PC biosynthesis and PLC activity are similar in both models. Therefore, this in vitro model of stretch-induced injury may supplement or be a reasonable alternative to some in vivo models of brain injury for determining the mechanisms by which traumatic cell injury results in cell dysfunction.     

Alterations in Glial Fibrillary Acidic Protein (GFAP) mRNA Levels in the Hamster Facial Motor Nucleus: Effects of Axotomy and Testosterone

Testosterone propionate (TP) administered at the time of facial nerve injury in the hamster accelerates the rate of regeneration. In this study, we tested the hypothesis that the mechanism by which TP augments peripheral nerve regeneration involves regulation of glial fibrillary acidic protein (GFAP) mRNA in the facial motor nucleus. Castrated male hamsters were subjected to right facial nerve transection, with half the animals implanted subcutaneously with Silastic capsules containing exogenous TP and the remainder sham implanted. Postoperative survival times were 0.25, 1, 2, 4, 7, and 14 d. Qualitative/quantitative analyses of both film and emulsion autoradiograms were accomplished. Axotomy, with or without TP, resulted in a dramatic increase in GFAP mRNA levels by 1 d postoperative on the axotomized side, relative to controls. GFAP mRNA levels remained elevated throughout all postoperative times in both the nonhormone- and TP-treated animals. Qualitative examination of the film autoradiograms indicated a generalized decrease in the amount of GFAP mRNA in the control and axotomized nuclei of TP-treated animals when compared to the control and axotomized nuclei, respectively, of nonhormone-treated animals. Statistical comparison of the values obtained for both the film and emulsion autoradiograms confirmed this impression. Thus, while the injury-induced increases in GFAP mRNA expression were not blocked by TP, the overall extent of the increase was significantly tempered by steroid treatment. These data suggest that hormonal modulation of the astrocytic response to peripheral nerve injury may be a contributing factor in the ability of steroids to enhance the regenerative capacities of injured motor neurons.     

Retracted: Upregulated microRNA-31 inhibits oxidative stress-induced neuronal injury through the JAK/STAT3 pathway by binding to PKD1 in mice with ischemic stroke

Ischemic stroke (IS), which is characterized by high morbidity, disability, and mortality, is recognized as a major cerebrovascular disease. MicroRNA-31 (miR-31) was reported to participate in the progression of brain disease. The present study was conducted in order to investigate the effect of miR-31 on oxidative stress-induced neuronal injury in IS mice with the involvement of protein kinase D1 (PKD1) and the JAK/STAT3 pathway. C57BL/6J mice were used to establish the middle cerebral artery occlusion (MCAO) model. Astrocytes were transfected with miR-31 mimic, miR-31 inhibitor, si-PKD1, or JAK-STAT3 pathway inhibitor. Following the establishment of an oxygen–glucose deprivation (OGD) model, the astrocytes were cocultured with neuronal OGD. Lower miR-31, higher PKD1 expressions, and activated JAK/STAT3 pathway were found in both the MCAO and OGD models. miR-31 could negatively target PKD1. In an MCAO model, overexpressing miR-31 and silencing PKD1 reduced neuronal injury, cerebral infarct volume, neuron loss, and oxidative stress injury, inhibited the activation of JAK/STAT3 pathway and the expressions of PKD1, interleukin (IL)-1β, IL-6, tumor necrosis factor-α, malondialdehyde, 4-HNE, 8-HOdG, caspase-3, and Bax, but increased the superoxide dismutase content. In the OGD model, overexpression of miR-31 and silencing of PKD1 attenuated oxidative stress-induced neuronal injury, and diminished the lactate dehydrogenase leakage and reactive oxygen species level, accompanied by elevated neuronal viability. These results indicate that miR-31 alleviates inflammatory response as well as an oxidative stress-induced neuronal injury in IS mice by downregulating PKD1 and JAK/STAT3 pathway.     

MiR-144通过靶向抑制GRK5表达促进脊髓星形胶质细胞活化

已知miR-144与细胞活化和增殖有关,然而其具体分子机制尚不明确。本研究发现miR-144通过靶向GRK5促进脊髓星形胶质细胞的活化。运用real-time PCR检测脊髓损伤和正常大鼠的脊髓组织及其脊髓星形胶质细胞中miR-144的表达,发现与正常的组织和细胞相比,miR-144在脊髓损伤组织和星形胶质细胞中的表达水平显著降低;Western印迹检测到脊髓损伤大鼠的星形胶质细胞中GFAP蛋白的表达显著低于正常大鼠,而GRK5蛋白的表达高于正常大鼠;MTT分析结果显示转染miR-144可显著提高脊髓损伤大鼠的星形胶质细胞活性,但对细胞增殖无明显作用;酶活性试剂盒分析发现miR-144显著提高了SOD和GSH活性;生物学信息分析和萤光素酶报告基因检测结果显示miR-144能靶向结合GRK5,并下调GRK5的表达;MiR-144 mimic转染或miR-144 mimic与pcDNA-GRK5共转染脊髓损伤的星形胶质细胞,发现miR-144转染能通过激活NF-κB通路消除pcDNA-GRK5引起的细胞活化抑制。综上所述,miR-144通过靶定结合癌基因GRK5来促进脊髓星形胶质细胞细胞的活化。     

Balb/C乳鼠小脑Purkinje细胞原代培养方法

目的建立一种简单、有效的Balb/C乳鼠小脑Purkinje细胞原代培养方法,并初步研究其细胞电生理特性。方法钝性分离生后24h内的乳鼠小脑,采用低浓度胰蛋白酶加机械吹打法获得单细胞悬液,然后用含10%胎牛血清的DMEM/F12培养,24h候更换为1%N2+1%T3+1%谷氨酰胺的DMEM/F12维持培养,3-5d天后进行细胞免疫荧光染色,7-9d天后用全细胞膜片钳单通道法记录钙电流。结果该方法培养的神经元形态典型,细胞学鉴定阳性率高(70%),并能记录到钙通道电流。结论该方法取材容易,操作简便,且培养出的原代Purkinje细胞生长状态较好,神经元的活性较高,可用于电生理研究。     

Differential effect of nitric oxide on glutathione metabolism and mitochondrial function in astrocytes and neurones: implications for neuroprotection/neurodegeneration?

Primary culture rat astrocytes exposed to the long acting nitric oxide donor (Z)-1-[2-aminoethyl)-N-(2-ammonioethyl)amino]diazen-1-ium-1,2-diolate (DETA-NO) for 24 h approximately double their concentration of glutathione (GSH) and show no sign of cell death. In contrast, GSH was depleted by 48%, and significant loss of mitochondrial respiratory chain complex activity and cell death were observed in primary culture rat neurones subjected to DETA-NO for 18 h. Northern blot analysis suggested that mRNA amounts of both subunits of glutamate-cysteine ligase (GCL), the rate-limiting enzyme in GSH synthesis, were elevated in astrocytes following nitric oxide (NO) exposure. This correlated with an increase in astrocytic GCL activity. Neurones on the other hand did not exhibit increased GCL activity when exposed to NO. In addition, the rate of GSH efflux was doubled and gamma-glutamyltranspeptidase (gamma-GT) activity was increased by 42% in astrocytes treated with NO for 24 h. These results suggest that astrocytes, but not neurones, up-regulate GSH synthesis as a defence mechanism against excess NO. It is possible that the increased rate of GSH release and activity of gamma-GT in astrocytes may have important implications for neuroprotection in vivo by optimizing the supply of GSH precursors to neurones in close proximity.     

Possible involvement of a cyclic AMP-dependent mechanism in PACAP-induced proliferation and ERK activation in astrocytes

In cultured astrocytes, PACAP activates extracellular signal-regulated kinase (ERK) and induces cell proliferation at picomolar concentrations. Here, we examined the role of cyclic AMP signaling underlying the effects of PACAP. PACAP38 induced accumulation of cyclic AMP in astrocytes at concentrations as low as 10(-12)M. PACAP38 (10(-12)-10(-9)M)-stimulated cell proliferation was completely abolished by the cyclic AMP antagonist Rp-cAMP, whereas the protein kinase A (PKA) inhibitor H89 had no effect. This PACAP38-mediated effect was also abolished by the ERK kinase inhibitor PD98059, suggesting the involvement of ERK in PACAP-induced proliferation. PACAP38 (10(-12)M)-stimulated phosphorylation of ERK lasted for at least 60 min. This effect was completely abolished by Rp-cAMP but not by H89. Dibutyryl cyclic AMP maximally stimulated the incorporation of thymidine and activation of ERK at 10(-10)M. These results suggest that PACAP-mediated stimulation of ERK activity and proliferation of astrocytes may involve a cyclic AMP-dependent, but PKA-independent, pathway.