[Experimental research on permeability injury of pulmonary microvascular endothelial cells monolayer induced by tumor necrosis factor]

AIM AND METHODS

To investigate the mechanism of tumor necrosis factor (TNF) induced permeability injury of rat pulmonary microvascular endothelial cells (RPMVEC) monolayer, the effect of TNF on permeability of RPMVEC monolayer was examined with microfilter and the effect of TNF on RPMVEC F-actin was observed with immunocytochemistry. The interfering action of formoterol, anisodamine and cholera toxin on permeability and F-actin changes induced by TNF was also observed.

RESULTS

(1) TNF induced significant increase in permeability of RPMVEC monolayer 30, 60 and 90 minutes after treatment with TNF. (2) F-actin in RPMVEC depolymerized 90 minutes after treatment with TNF. Permeability and F-actin did not change significantly when formoterol, anisodamine or cholera toxin was added separately.

CONCLUSION

TNF can induce permeability injury of RPMVEC monolayer, which is correlated with depolymerization of F-actin. Formoterol, anisodamine and cholera toxin can inhibit the permeability change induced by TNF which may due to their inhibition to the distribution change of F-actin.

Ethanol and oxidative mechanisms in the brain

There is strong evidence showing that chronic and excessive ethanol consumption may enhance oxidative damage to neurons and result in cell death. Although not yet well understood, ethanol may enhance ROS production in brain through a number of pathways including increased generation of hydroxyethyl radicals, induction of CYP2E1, alteration of the cytokine signaling pathways for induction of iNOS and sPLA(2), and production of prostanoids through the PLA(2)/COX pathways. Since many neurodegenerative diseases are also associated with oxidative and inflammatory mechanisms in the brain, it would be important to find out whether chronic and excessive ethanol consumption may exacerbate the progression of these diseases. There is evidence that the polyphenolic antioxidants, especially those extracted from grape skin and seed, may protect the brain from neuronal damage due to chronic ethanol administration. Among the polyphenols from grapes, resveratrol seems to have unique antioxidant properties. The possible use of this compound as a therapeutic agent to ameliorate neurodegenerative processes should be further explored.

Ethanol inhibits cytokine-induced iNOS and sPLA2 in immortalized astrocytes: evidence for posttranscriptional site of ethanol action

Chronic and excessive ethanol consumption is known to alter neuron and glial cell functions in the central nervous system (CNS). Astrocytes comprise the major cell type in the brain. These immune active cells are capable of responding to proinflammatory cytokines and endotoxins, which stimulate transcriptional pathways leading to induction of genes, including the inducible nitric oxide synthase (iNOS) and secretory phospholipase A2 (sPLA2). In this study, we investigate the effects of ethanol on cytokine-induced iNOS and sPLA2 in immortalized astrocytes (DITNC). When DITNC cells were exposed to ethanol (0-200 mM) for 4 h prior to subsequent stimulation with cytokines for 16 h, NO production decreased with increasing ethanol concentrations starting from 50 mM. At ethanol concentrations higher than 100 mM, ethanol also inhibited cytokine-induced sPLA2 release into the culture medium. The inhibitory effect of ethanol on NO production corresponds well with the decrease in iNOS protein and NOS enzyme activity, but not with iNOS and sPLA2 mRNA nor binding of NF-kappaB to DNA. The inhibition of cytokine-induced NO production by ethanol was also dependent on the time of ethanol exposure to the cells, but addition of acetaldehyde up to 200 microM did not elicit any changes. Taken together, these results provide evidence for a posttranscriptional mode of ethanol action on the cytokine induction pathway for NO production in astrocytes.

Region-specific decline in the expression of metabotropic glutamate receptor 7 mRNA in rat brain during aging

Age-dependent changes in the expression of group III metabotropic glutamate receptors (mGluR4 and mGluR7) were studied by quantitative in situ hybridization using male Fisher 344 rats 3, 12 and 25 months of age. Results indicate an early decrease in mGluR7 mRNA level in several cortical areas including the frontal, parietal and temporal cortices. In the hippocampus, mGluR7 mRNA levels decreased in the CA1 region and the lower blade of the dentate gyrus. Moreover, significant decrease was found in the laterodorsal thalamic nucleus at 12 months of age. Other regions such as the caudate putamen and nucleus accumbens showed no age-related changes in mGluR7 mRNA levels. Analysis of emulsion autoradiograms revealed a 36% decrease of mGluR7 mRNA in Purkinje neurons in the 12-month-old group and a 48% decline in the 25-month-old group as compared to the 3-month-old group. A substantial decrease in mGluR4 mRNA level was found in the granule cell layer of the cerebellum during aging. The difference between the young and aged groups exceeded 35%. These region-specific decreases may have important implication in some of the age-related changes in cognitive, motor and/or sensory functions.

[The application of multi-pulse stripping amperometric detection to capillary electrophoresis]

There are some drawbacks in amperometric detection in capillary electrophoresis since there is influence of high voltage from electrophoretic instrument. Three electrodes of electrochemical detection system and electrochemical system of capillary electrophoresis are separately placed in capillary outlet buffer reservoir, which can lead to a reduction in the influence of high voltage in the great degree. A carbon fiber with diameter of 7 microns is used as working electrode, and placed just at the separation capillary outlet. The multi-pulse stripping amperometric detection has 1.1 s deposition step and several stripping steps with 0.02 s, which can increase the detection amperometric current and identify the species of each separated component in some classes by different pulse stripping potentials. This detection technique was applied in the separation of Cu, Zn, Pb, Tl and Cd of 25 mg/L by the capillary electrophoresis, and separation efficiency is over 60 thousands theoretical plates. The limit of the multi-pulse stripping amperometry detection was 0.10 microgram/L for cadmium by using water plug field amplified injection.

Platelet activating factor (PAF) antagonists on cytokine induction of iNOS and sPLA2 in immortalized astrocytes (DITNC)

Platelet-activating factor (PAF, 1-O-alkyl-2-acetyl-sn-glycero-3-phosphocholine) and its receptor are known to play important roles in modulating neuronal plasticity and inflammatory responses, particularly during neuronal injury. PAF receptors are widespread in different brain regions and are present on the cell surface as well as in intracellular membrane compartments. Astrocytes are immune active cells and are responsive to cytokines, which stimulate signaling cascades leading to transcriptional activation of genes and protein synthesis. Our recent studies indicate the ability of cytokines, e.g., tumor necrosis factor-alpha (TNFalpha), interleukin-1beta (IL-1beta) and interferon-gamma (IFNgamma), to induce the inducible nitric oxide (iNOS) and secretory phospholipase A2 (sPLA2) genes in immortalized astrocytes (DITNC) (Li et al., J. Interferon and Cytokine Res. 19: 121-127. 1999). The main objective for this study is to examine the effects of PAF antagonists on cytokine induction of iNOS and sPLA2 in these cells. Results show that BN50730, a synthetic PAF antagonist, but not BN52021, a natural PAF antagonist (ginkolide B) can dose-dependently inhibit cytokine induction of NO production and sPLA2 release. Inhibition of NO production by BN50730 corroborated well with the decrease in iNOS protein and mRNA levels as well as binding of NF-kappaB STAT- 1 to DNA, suggesting that BN50730 action is upstream of the transcriptional process. These results are in agreement with the role of intracellular PAF in regulating the cytokine signaling cascade in astrocytes and further suggest the possible use of BN50730 as a therapeutic agent for suppressing the inflammatory pathways elicited by cytokines.

Studies on the cytosolic phospholipase A2 in immortalized astrocytes (DITNC) revealed new properties of the calcium ionophore, A23187

Besides playing an important role in the maintenance of cell membrane phospholipids, phospholipases A2 (PLA2) are responsible for the release of arachidonic acid (AA) which is a precursor for prostaglandin biosynthesis. The cytosolic PLA2 has been the focus of recent studies, probably due to its ability to respond to protein kinases and changes in intracellular calcium levels. In this study, we examined agents for stimulation of the cytosolic phospholipase A2 in immortalized astrocytes (DITNC). Incubation of DITNC cells with [14C]arachidonic acid (AA) resulted in a time-dependent uptake of the label into phospholipids (PL) and neutral glycerides. In prelabeled cells, release of labeled AA could be stimulated by calcium mobilizing agents such as calcium ionophore A23187 (4-20 microM) and thimerosal (100 microM), and by phorbol myristate acetate (PMA, 100 nM), an agent for activation of protein kinase C. The release of AA could also be stimulated by ATP (200 microM), probably through activation of the purinergic receptor but not by glutamate (1 mM). The stimulated release of AA was dependent on extracellular Ca2+ and was inhibited by mepacrine (50 microM), a non-specific PLA2 inhibitor. Western blot analysis further confirmed the presence of an 85 kDa cPLA2 in both membrane and cytosol fractions of these cells and stimulation by A23187 resulted in translocation of this protein to the membrane fraction. Besides labeled fatty acids, A23187 also stimulated the concomitant release of labeled PL into the culture medium and this event was accompanied by the increased release in lactate dehydrogenase (LDH). Results thus revealed that besides activation of cPLA2, the calcium ionophore A23187 is capable of perturbating cell membrane integrity.

Dietary supplementation of grape polyphenols to rats ameliorates chronic ethanol-induced changes in hepatic morphology without altering changes in hepatic lipids

Increase in oxidative stress after chronic ethanol consumption can result in hepatic injury. Because polyphenolic compounds can offer antioxidant protection to the cardiovascular system, this study was designed to investigate whether dietary supplementation of polyphenols from grapes may ameliorate hepatic injury resulting from chronic ethanol consumption. Male Sprague-Dawley rats were administered the following diets for 2 mo: 1) Lieber-DeCarli (L-D) diet with isocaloric amount of maltose instead of ethanol (Basal), 2) the L-D diet with 50g/L ethanol (EtOH); 3) L-D diet with 50 mg/L of grape polyphenols (GP) and 4) ethanol diet with GP (EtOH + GP). Rats given EtOH or EtOH + GP diets had significantly more hepatic triacylglycerols (P < 0.0001) and lipid peroxidation products (P < 0.01) compared with those given the Basal and GP diets. In addition, ethanol ingestion also decreased significantly (P < 0.01) the proportion of 16:0 and increased 18:0 and 18:1 in hepatic phospholipids, suggesting a perturbation of the de novo fatty acid biosynthesis pathways. However, GP supplementation alone and GP added to the ethanol diet did not alter the lipid changes mediated by ethanol except for the levels of 22:6(n-3) which were significantly (P < 0.05) higher in the EtOH + GP group than in the EtOH group. Despite a lack of gross lipid changes, histologic assessment showed significantly (P < 0.05) less hepatic damage in the GP + EtOH group compared with the EtOH group. These results clearly distinguished ethanol-mediated changes in hepatic morphology from the changes in hepatic lipids and further demonstrated the ability of GP to ameliorate hepatic damage resulting from chronic ethanol consumption.

STR HUMARA locus gene and genotype frequencies in Han and Bei populations in China

For the purpose of the population genetics study of the HUMARA locus, the allele, and genotype frequencies were determined in two Chinese population samples (Han-101, Bei-113) using PCR, PAGE, and silver staining. Fourteen alleles were found. The size of amplified fragments were 258 bp-315 bp. The observed heterozygosities were 0.83 in the Han population and 0.73 in the Bei population respectively. The expected heterozygosities were 0.91 in the Han population and 0.97 in the Bei population respectively. Both populations meet Hardy-Weinberg expectation, Han population x2 = 17.7206, df = 11, p > 0.05; Bei population x2 = 7.4268, df = 10, p > 0.05. The discrimination power were 0.95 in females and 0.89 in males in the Han population, 0.94 in females and 0.88 in males in the Bei population. Thus, the allelic frequency data can be used in the personal identification and parentage testing in the forensic science practice. The PCR test established in this study is robust and reproducible.

Involvement of lipid mediators on cytokine signaling and induction of secretory phospholipase A2 in immortalized astrocytes (DITNC)

Our previous studies demonstrated the ability of proinflammatory cytokines, such as tumor necrosis factor-alpha (TNF-alpha) and interleukin 1beta (IL-1beta), to stimulate NFkappaB/DNA binding and synthesis of secretory phospholipase A2 (sPLA2) in immortalized astrocytes (DITNC). In this study, we examined possible involvement of lipid mediators in the cytokine action. Using [14C]serine to label sphingomyelin and ceramide in these cells, subsequent exposure of cells to cytokines did not result in alteration of sphingomyelin/ceramide ratio. Furthermore, neither exogenous sphingomyelinase nor cell-permeable ceramides could stimulate NFkappaB/DNA binding. On the other hand, C-2 ceramide (0.3 microM) as well as other lipid mediators, such as lysophosphatidylcholine and arachidonic acid, were able to elicit a small increase in sPLA2 and potentiate the induction of sPLA2 by TNF-alpha. When DITNC cells were prelabeled with [32P]Pi, an increase in labeled phosphatidic acid (PA) was observed on treatment of cells with IL-1beta (200 U/mL). However, despite the ability of phorbol myristate acetate (PMA) to stimulate phospholipase D (PLD) and synthesis of phosphatidylethanol (PEt) in these cells, PLD activity was not affected by IL-1beta. With the [32P]labeled cells, however, PA-phosphohydrolase inhibitors, such as chlorpromazine and propranolol, could elicit large increases in labeled PA, indicating active PA metabolism in these cells. Cytokines also caused an increase in levels of diacylglycerol (DG) in these cells, although the source of this lipid pool is presently not understood. Taken together, these results provide evidence for the participation of PA and DG in cytokine signaling activity. Furthermore, although cytokines did not cause the release of ceramide, lipid mediators, such as lysophospholipids, and AA could modulate cytokine-mediated induction of sPLA2 in astrocytes.

Chronic ethanol and iron administration on iron content, neuronal nitric oxide synthase, and superoxide dismutase in rat cerebellum

Excessive chronic ethanol administration to animals has been shown to cause oxidative insults to many body organs, including the liver and brain. In many instances, iron supplementation to the diet may further aggravate ethanol-induced liver damage. However, whether increased dietary iron can enhance the damage in the brain is unknown. In this study, four groups of Sprague-Dawley rats were fed a Lieber-DeCarli liquid diet containing 5% (w/v) ethanol or isocaloric amount of maltase and/or 0.25% (w/v) carbonyl iron for 2 months. At the end of the feeding regimen, iron contents were determined in the plasma, liver, cerebral cortex, and cerebellum. Cerebellar superoxide dismutase (SOD) and nitric oxide synthase (NOS) activities were measured and mRNA levels of MnSOD, CuZnSOD, and nNOS in the cerebellar granule cell layer were quantitated by in situ hybridization. Ethanol treatment alone caused an increase in iron levels in plasma, no change in the liver and cerebral cortex, but a decrease in the cerebellum. Iron supplementation increased liver iron >4-fold but did not alter iron contents in the cerebellum and cortex. All of the mRNA species examined and SOD activity were not affected by either iron or ethanol administration. However, NOS activity in the cerebellum was significantly enhanced by ethanol, whereas iron supplementation had an opposite effect. Our results indicate that iron supplementation to animals consuming ethanol may have tissue-specific effects. Furthermore, ethanol-induced increase in NOS activity in the cerebellum may explain the sensitivity of cerebellar neurons to oxidative insult.

Cytokine induction of iNOS and sPLA2 in immortalized astrocytes (DITNC): response to genistein and pyrrolidine dithiocarbamate

Using an immortalized astrocyte cell line (DITNC), we showed that lipopolysaccharide (LPS), tumor necrosis factor-alpha (TNF-alpha), and interleukin-1beta (IL-1beta) but not interferon-alpha (IFN-alpha) could individually induce secretory phospholipase A2 (sPLA2) mRNA and enzymatic activity. However, induction of inducible nitric oxide synthase (iNOS) mRNA and NO production by cytokines required the presence of IFN-gamma. Using a three-cytokine mixture (TNF-alpha, IL-1beta, and IFN-gamma) that could maximally induce both iNOS and sPLA2, the increase in these mRNA species reached a maximum by 4-8 h, followed by a decline up to 48 h. L-N6-(1-Iminoethyl)lysine acetate (L-NIL) inhibited cytokine-induced NO production with IC50 of 25 microM, but this compound did not affect iNOS mRNA. Furthermore, L-NIL exerted no effect on sPLA2 mRNA or sPLA2 activity. Pyrrolidine dithiocarbamate (PDTC), an inhibitor for NF-kappaB, was more effective in inhibiting iNOS mRNA and NO production than for sPLA2. Surprisingly, genistein inhibited both NO production and sPLA2 activity with IC50 of 72 microM and 88 microM, respectively. On the other hand, daidzein, a genistein analog lacking tyrosine kinase inhibitor activity, was not effective in inhibition of NO production at 250 microM. These results demonstrate distinct pathways for induction of iNOS and sPLA2 in DITNC cells by cytokines and shed new insight on transcriptional regulation for these two mRNA species.

Grape polyphenols protect neurodegenerative changes induced by chronic ethanol administration

Increased oxidative stress in the brain due to chronic ethanol consumption is known to result in a number of neurodegenerative changes. This study was designed to test whether dietary supplementation of grape polyphenols (GP) can offer protection to the neurodegenerative changes resulting from chronic ethanol consumption. Sprague-Dawley rats were fed a Leiber-DeCarli liquid diet with ethanol or isocaloric amount of maltose, and with or without GP for 2 months. Chronic ethanol caused significant decreases in synaptosomal Na,K-ATPase (20.5%) and dopamine uptake (22.8%) activities compared with pair-fed controls. Although GP alone did not alter activities of these membrane-bound proteins, GP supplementation was able to completely protect the decrease in synaptic protein function elicited by chronic ethanol consumption.

Changes in mRNA levels for group I metabotropic glutamate receptors following in utero hypoxia-ischemia

The expression of group I metabotropic glutamate receptors (mGluR1 and mGluR5) and inositol 1,4,5-trisphosphate receptor type 1 (IP3R1) mRNA was studied by in situ hybridization in the developing rat hippocampus after in utero hypoxia-ischemia. In utero hypoxia-ischemia was induced by clamping the uterine blood vessels of near-term fetuses for 10 min. Fetuses were delivered surgically, resuscitated and raised by foster mothers until postnatal day 7 and 14. Results indicated a temporal delay in the expression of mGluR1 mRNA in the dentate gyrus of the ischemic animals. The mGluR1 mRNA level was significantly lower in the ischemic animals at postnatal day 7, but reached a similar level as that of controls at postnatal day 14. In utero hypoxia-ischemia did not change the temporal-spatial expression pattern of either mGluR5 or IP3R1 mRNA in the hippocampus. Between postnatal day 7 and 14, mGluR5 mRNA showed a high and relatively constant expression, whereas IP3R1 mRNA levels were increased in all regions examined. The differences in the expressions of group I mGluRs indicate that these receptors may have different functions during hippocampal development and may play different roles in excitotoxicity.

Prenatal ethanol exposure selectively reduces the mRNA encoding alpha-1 thyroid hormone receptor in fetal rat brain

Some of the developmental defects characteristic of congenital or experimental hypothyroidism are also observed in children or experimental animals prenatally exposed to ethanol, suggesting that a subset of neurological defects attributable to ethanol exposure are produced by interfering with thyroid hormone action. In this article, we tested whether an ethanol treatment regimen known to produce neurological damage in rats can alter the expression of the mRNAs encoding the thyroid hormone receptor isoforms (TR alpha-1, TR alpha-2, and TR beta-1) in the fetal rat brain neocortex and hippocampus. Rats were fed an ethanol-containing diet beginning on gestational day (G) 6 and continuing until sacrifice on G15, G17, or G21; controls included animals pair-fed a liquid control diet or fed lab chow. Ethanol selectively reduced the expression of TR alpha-1 mRNA in the neocortex and hippocampus on G21, compared with pair-fed and control fetuses. In contrast, pair-feeding selectively reduced TR alpha-2 mRNA in both neocortex and hippocampus on G21, and increased TR beta-1 mRNA on G17. These data support the hypothesis that ethanol may interfere with thyroid hormone action during fetal brain development. In addition, these data indicate that ethanol and pair-feeding exert independent effects on thyroid hormone receptor expression in the developing brain.

Dietary supplementation of grape polyphenols and chronic ethanol administration on LDL oxidation and platelet function in rats

Polyphenolic compounds have been implicated as the active ingredients for the cardiac protective effect in red wine. We tested the effects of dietary supplementation of polyphenols from grape (GP) and chronic ethanol administration on low-density-lipoprotein (LDL) oxidation and platelet function in rats. Four groups of young male Sprague-Dawley rats were fed the following diets for 2 months: (I) a high fat Lieber-DeCarli liquid diet with an isocaloric amount of maltose, (II) with 5% ethanol (w/v), (III) with 5 mg/dL of GP, and (IV) ethanol plus GP. Platelet aggregation was induced by thrombin and phorbol myristate acetate (PMA) and LDL oxidation was induced by Cu2+. Chronic ethanol administration resulted in a significant increase in LDL oxidation and this effect was partially protected by supplementation with GP. Although platelet number was not affected by either ethanol or GP administration, platelet aggregation induced by thrombin was reduced in ethanol, GP and ethanol plus GP groups as compared to controls. On the other hand, platelet aggregation induced by PMA was not altered in any groups, suggesting that protein kinase C was not a causal factor for the reduction of aggregatory response induced by thrombin. These results show similar effects of ethanol and GP on platelet aggregation but different effects on LDL oxidation. It can be concluded that dietary supplementation with GP may exert partial protection on oxidative insults such as those elicited by chronic ethanol ingestion.

[Research progress on regulation of vascular endothelial barrier function]

The regulatory mechanisms of vascular endothelial barrier function are complicated. Inflammatory mediators, such as alpha-thrombin, activate phospholipases to mediate generation of IP3 and other second messengers through receptor-coupled G protein. Protein kinase C and myosin light chain kinase are then activated, leading to phosphorylation of myosin light chains, rearrangement of F-actin skeleton, interendothelial cell gap formation and increased endothelial permeability.

Changes in IP3R1 and SERCA2b mRNA levels in the gerbil brain after chronic ethanol administration and transient cerebral ischemia-reperfusion

Despite epidemiological studies indicating a positive relationship between alcohol and stroke, little is known with regard to effect of chronic alcohol on neuronal injury after stroke. In this study, we examined the effect of chronic ethanol on mRNA levels of sarcoplasmic or endoplasmic Ca2+-ATPase (SERCA2b) and inositol 1,4, 5-triphosphate receptor (IP3R1) in gerbils subjected to global cerebral ischemia induced by ligation of both common carotid arteries. Gerbils were given daily by intragastric intubation either a liquid diet containing ethanol (4 g/kg) or the same diet with an isocaloric amount of sucrose for 35 days. They were subsequently subjected to a 5 min ischemic insult followed by reperfusion for 48 h. In agreement with other studies, ischemic insult caused significant decreases (P<0.05) in mRNA levels of both IP3R1 and SERCA2b in the hippocampal CA1 region but not in the dentate gyrus. Nevertheless, despite a significant (P<0.05) decrease in SERCA2b mRNA in the Purkinje neurons, chronic ethanol did not alter the expression of this mRNA species in the hippocampal CA1 neurons nor did it alter the decrease in SERCA2b mRNA due to cerebral ischemic insult. Since IP3R1 and SERCA2b are key mediators for regulation of intracellular Ca2+ stores, the decrease in SERCA2b mRNA but not IP3R1 mRNA in cerebellar neurons may be an important mechanism underlying alteration of calcium homeostasis and cerebellar degeneration upon chronic ethanol consumption.

Effects of ischemic tolerance on mRNA levels of IP3R1, beta-actin, and neuron-specific enolase in hippocampal CA1 area of the gerbil brain

Global cerebral ischemia induced to Mongolian gerbils by ligation of common carotid arteries (CCAs) is known to result in injury to the hippocampal CA1 region. In this study, we examined whether neuronal injury can be depicted by measuring levels of mRNA encoding inositol 1,4,5-trisphosphate receptor type 1 (IP3R1), neuron specific enolase (NSE) and beta-actin and whether these measurements can be use to assess ischemic tolerance. Gerbils were subjected either to cerebral ischemia induced by ligation of both CCAs for 5 min, or to an ischemic tolerance paradigm in which a 2 min ischemic preconditioning was performed 24 hr prior to the 5 min ischemia. At 48 hr after the 5 min ischemic insult, significant decreases in mRNA levels for IP3R1 (26%), NSE (38%) and beta-actin (50%) could be observed in the hippocampal CA1 region. Although levels of mRNA in the preconditioning group were decreased as compared to the sham control, the levels were significantly higher than those in the ischemic group. These results indicate the feasibility of using mRNA measurement as a parameter to assess cerebral ischemic damage. In addition, based on the differences in the decline in mRNA levels between the ischemia group and the preconditioned ischemia group, it can be concluded that this ischemic tolerance paradigm could offer partial protection (around 45%) against the injury due to the 5 min cerebral ischemic insult.

Age differences in the expression of metabotropic glutamate receptor 1 and inositol 1,4,5-trisphosphate receptor in mouse cerebellum

Age differences in the expression of cerebellar metabotropic glutamate receptor 1 (mGluR1) and inositol 1,4,5-trisphosphate receptor (IP3R) were investigated using male C57BL/6NNIA mice 5, 15 and 24 months of age. In situ hybridization for mGluR1 mRNA in the granule cell layer indicated significantly higher mRNA levels in the 24-month-old group as compared to the 5- and 15-month-old groups. However, mRNA levels of individual Purkinje neurons did not show age differences. Western blot analysis using antibody against the predominant isoform, mGluR1a, showed a decline in protein levels in the 24-month-old animals. In situ hybridization for IP3R type 1 mRNA in Purkinje neurons showed a slight but not significant decline in the 24-month-old group. Further assay of [3H]IP3 binding with cerebellar membranes showed significant reduction in Bmax values in the 15- and 24-month-old groups as compared to the 5-month-old group but Kd values were not changed. The decrease in mGluR1a receptor protein together with reduction in IP3R binding sites may play an important role in the decline in cerebellar functions with increasing age.

Induction of basic fibroblast growth factor (bFGF) expression following focal cerebral ischemia

Basic fibroblast growth factor (bFGF) is a biologically active polypeptide with mitogenic, angiogenic, and neurotrophic properties. In the present study, we examined the temporal and spatial expression profiles of bFGF mRNA and protein concentration in a focal cerebral ischemia model induced by transient occlusion of the right middle cerebral artery (MCA) and both common carotid arteries (CCAs). Results of Northern blot analysis shows a transient 2.5-fold increase in the 6.0 kb transcript of bFGF mRNA within the ischemic cortex of rats subjected to 60 min ischemic insult followed by 12 h of reperfusion. Although enhanced expression of bFGF mRNA was also noted in the ipsilateral hippocampus, the temporal induction profile appeared to be different from that of the ischemic cortex. A significant increase in bFGF mRNA was observed as early as 60 min following ischemia and remained elevated for up to 2 weeks after the onset of reperfusion. In situ hybridization studies revealed constitutive expression of bFGF mRNA in discrete brain regions of sham-operated animals. Following 60 min ischemia and 12 h reperfusion, increased expression of bFGF mRNA was observed in the ischemic cortex (both peri-infarct and infarct area). Increased expression of bFGF mRNA within the infarcted area is largely confined rostrally to the outer cortical layers of the infarct, an area with increased density of blood vessels. bFGF-like immunoreactivity was also detected in areas expressing bFGF mRNA. Furthermore, a striking increase in bFGF-like immunoreactivity was observed in the ipsilateral hippocampus. Double-staining with anti-GFAP antibody indicated that the majority of the bFGF-like immunoreactivity was localized in the astrocytes, however, not all astrocytes showed bFGF-like immunoreactivity. Some GFAP negative cell also showed bFGF-like immunoreactivity. In summary, increased expression of both bFGF mRNA and immunoreactivity following ischemia were located in the same brain regions. An increase in bFGF-like immunoreactivity after ischemic insult is likely due to an increase in the expression of its 6.0 kb bFGF mRNA transcripts. Although increased bFGF mRNA was observed in both ischemic cortex and ipsilateral hippocampus after ischemic insult, the temporal expression profiles differed. Results from the present study raise the possibility that increased expression of bFGF in the peri-infarcted area may limit the spread of ischemic injury.

Effects of IL-1 beta on receptor-mediated poly-phosphoinositide signaling pathway in immortalized astrocytes (DITNC)

Astrocytes are known to play multi-functional roles in support of many homeostatic mechanisms in the central nervous system including host defense mechanisms. Despite the ability of cytokines to alter gene expression and cellular activity, their effect on receptor-mediated poly-phosphoinositide (poly-PI) signaling pathway has not been examined in detail. In this study, an immortalized astrocyte cell line (DITNC) was used to test the effect of IL-1 beta exposure on the poly-PI signaling pathway. Similar to primary astrocytes, DITNC cells exhibit P2-purinergic receptor response to ATP and UTP leading to transient increases in inositol 1,4,5-trisphosphate [Ins(1,4,5)P3] and intracellular calcium concentration, [Ca2+]i. Upon exposure of DITNC cells to IL-1 beta (100 U/ml) for 24 hrs, an increased response to the poly-PI agonists was observed. The increase in ATP-mediated Ins(1,4,5)P3 release could not be attributed to a shift in the ATP dose or an alteration of the time profile for the release of Ins(1,4,5)P3. Since the increase in response required a lag time of 4 hr after IL-1 beta exposure, it is unlikely that this effect was due to a direct interaction of IL-1 beta with the purinergic receptor. On the other hand, an increase in ATP response could be observed in DITNC cells exposed to conditioned medium obtained after IL-1 beta treatment. It can be concluded that exposure of astrocytes to cytokines may lead to an increase in receptor-mediated poly-PI signaling activity and this may involve compounds secreted into the culture medium, e.g., the secretory phospholipase A2.

Chronic ethanol inhibits inositol metabolism in specific brain regions

Many neurotransmitters and hormones in the nervous system transmit signals through receptors coupled to the poly-phosphoinositide (PI) signaling pathway. In this study, an in vivo protocol with [3H]inositol was used to examine the effect of chronic ethanol administration on inositol metabolism and poly-PI turnover in the cerebral cortex, hippocampus, and cerebellum of mouse brain. C57BL/6 mice were given a nutritionally complete liquid diet containing either ethanol (5%, w/v) or isocaloric sucrose for 2 months. Mice were injected intracerebrally with [3H]inositol; after 16 or 24 hr, they were injected intraperitoneally with lithium (8 mEq/kg body weight) to inhibit the inositol monophosphatase (IP1) activity. All mice were decapitated 4 hr after lithium injection. Labeled inositol phospholipids accounted for 16 to 23% of total labeled inositol in different regions of control mouse brain, and the percentages in the hippocampus were consistently higher than the cerebral cortex and cerebellum. In control mice, the percentages of labeled IP1 after a 4-hr lithium treatment were 11.5%, 9.9%, and 3.7% for cerebral cortex, hippocampus, and cerebellum, respectively. Chronic ethanol feeding resulted in a significant (p < 0.05) decrease in the percent of labeled IP1 and inositol phospholipids, and this effect was observed in the cerebral cortex and, to a lesser extent, hippocampus but not cerebellum. When ratios of labeled IP1 were expressed against labeled inositol phospholipids as an index of the poly-PI turnover activity, significant decreases in IP/lipid ratios were observed in the cerebral cortex, but not the hippocampus or cerebellum. Although mice killed 24 + 4 hr after the last ethanol feeding would have experienced an 8-hr period of ethanol withdrawal, compared with the 16 + 4-hr group, no differences in IP/lipid ratios were observed between the two time groups. These results illustrate regional differences in the effect of chronic ethanol on inositol metabolism in the brain, but no difference in poly-PI turnover in brain due to ethanol withdrawal.

Membrane lipid metabolism and phospholipase activity in insect Spodoptera frugiperda 9 ovarian cells

Although there is increasing use of insect ovarian Sf9 cells for the production of recombinant proteins, namely, via the baculovirus vector expression system, little is known about the lipids in the cell membrane and whether endogenous phospholipases are present for regulation of the cell membrane lipids. In this study, analysis of membrane lipids of Sf9 cells indicated the presence of phosphatidylethanolamine (PE) (diacyl type) and phosphatidylcholine as major phospholipids, followed by phosphatidylserine and phosphatidylinositol (PI), and only trace amounts of ethanolamine plasmalogen. These phospholipids contain high proportions of monoenoic fatty acids, e.g., 16:1 and 18:1, which comprise more than 70% of the total fatty acids although small amounts of polyunsaturated fatty acids such as 18:2 and 20:4 are also present. When Sf9 cells were incubated in a culture medium containing [14C]oleic acid and [14C]arachidonic acid, a large portion of the labels were incorporated into membrane phospholipids. Using [14C]arachidonoyl-phospholipids as substrates for incubation with cell homogenate and subcellular fractions, results indicate the presence of a ca(2+)-independent phospholipase A (PLA2) in the Sf9 cell cytosol fraction. This PLA2 shows a high preference for hydrolysis of PE and is active at a pH range of 7-9. Unlike the brain cells which contain active phospholipase C (PLC) specific for phosphatidylinositol, only limited amount of diacylglycerol (DAG) was released from [14C]arachidonoyl-PE in the Sf9 cells. Taken together, this study demonstrates active metabolism of membrane phospholipids in Sf9 cells, most likely mediated by acyltransferases and PLA2. Furthermore, despite the absence of PLC for PI, limited amount of DAG could be generated through hydrolysis of PE.