Negative and positive regulation of astrocyte DNA synthesis by ethanol

Gliogenesis and glial pathology in depression

Recent research has changed the perception of glia from being no more than silent supportive cells of neurons to being dynamic partners participating in brain metabolism and communication between neurons. This discovery of new glial functions coincides with growing evidence of the involvement of glia in the neuropathology of mood disorders. Unanticipated reductions in the density and number of glial cells are reported in fronto-limbic brain regions in major depression and bipolar illness. Moreover, age-dependent decreases in the density of glial fibrillary acidic protein (GFAP) - immunoreactive astrocytes and levels of GFAP protein are observed in the prefrontal cortex of younger depressed subjects. Since astrocytes participate in the uptake, metabolism and recycling of glutamate, we hypothesize that an astrocytic deficit may account for the alterations in glutamate/GABA neurotransmission in depression. Reductions in the density and ultrastructure of oligodendrocytes are also detected in the prefrontal cortex and amygdala in depression. Pathological changes in oligodendrocytes may be relevant to the disruption of white matter tracts in mood disorders reported by diffusion tensor imaging. Factors such as stress, excess of glucocorticoids, altered gene expression of neurotrophic factors and glial transporters, and changes in extracellular levels of neurotransmitters released by neurons may modify glial cell number and affect the neurophysiology of depression. Therefore, we will explore the role of these events in the possible alteration of glial number and activity, and the capacity of glia as a promising new target for therapeutic medications. Finally, we will consider the temporal relationship between glial and neuronal cell pathology in depression.

MAP kinase signaling in diverse effects of ethanol

Chronic ethanol abuse is associated with liver injury, neurotoxicity, hypertension, cardiomyopathy, modulation of immune responses and increased risk for cancer, whereas moderate alcohol consumption exerts protective effect on coronary heart disease. However, the signal transduction mechanisms underlying these processes are not well understood. Emerging evidences highlight a central role for mitogen activated protein kinase (MAPK) family in several of these effects of ethanol. MAPK signaling cascade plays an essential role in the initiation of cellular processes such as proliferation, differentiation, development, apoptosis, stress and inflammatory responses. Modulation of MAPK signaling pathway by ethanol is distinctive, depending on the cell type; acute or chronic; normal or transformed cell phenotype and on the type of agonist stimulating the MAPK. Acute exposure to ethanol results in modest activation of p42/44 MAPK in hepatocytes, astrocytes, and vascular smooth muscle cells. Acute ethanol exposure also results in potentiation or prolonged activation of p42/44MAPK in an agonist selective manner. Acute ethanol treatment also inhibits serum stimulated p42/44 MAPK activation and DNA synthesis in vascular smooth muscle cells. Chronic ethanol treatment causes decreased activation of p42/44 MAPK and inhibition of growth factor stimulated p42/44 MAPK activation and these effects of ethanol are correlated to suppression of DNA synthesis, impaired synaptic plasticity and neurotoxicity. In contrast, chronic ethanol treatment causes potentiation of endotoxin stimulated p42/44 MAPK and p38 MAPK signaling in Kupffer cells leading to increased synthesis of tumor necrosis factor. Acute exposure to ethanol activates pro-apoptotic JNK pathway and anti-apoptotic p42/44 MAPK pathway. Apoptosis caused by chronic ethanol treatment may be due to ethanol potentiation of TNF induced activation of p38 MAPK. Ethanol induced activation of MAPK signaling is also involved in collagen expression in stellate cells. Ethanol did not potentiate serum stimulated or Gi-protein dependent activation of p42/44 MAPK in normal hepatocytes but did so in embryonic liver cells and transformed hepatocytes leading to enhanced DNA synthesis. Ethanol has a 'triangular effect' on MAPK that involve direct effects of ethanol, its metabolically derived mediators and oxidative stress. Acetaldehyde, phosphatidylethanol, fatty acid ethyl ester and oxidative stress, mediate some of the effects seen after ethanol alone whereas ethanol modulation of agonist stimulated MAPK signaling appears to be mediated by phosphatidylethanol. Nuclear MAPKs are also affected by ethanol. Ethanol modulation of nuclear p42/44 MAPK occurs by both nuclear translocation of p42/44 MAPK and its activation in the nucleus. Of interest is the observation that ethanol caused selective acetylation of Lys 9 of histone 3 in the hepatocyte nucleus. It is plausible that ethanol modulation of cross talk between phosphorylation and acetylations of histone may regulate chromatin remodeling. Taken together, these recent developments place MAPK in a pivotal position in relation to cellular actions of ethanol. Furthermore, they offer promising insights into the specificity of ethanol effects and pharmacological modulation of MAPK signaling. Such molecular signaling approaches have the potential to provide mechanism-based therapy for the management of deleterious effects of ethanol or for exploiting its beneficial effects.

Effects of ethanol and ipsapirone on the development of midline raphe glial cells and astrocytes

Previously, results of studies from our laboratory have shown that the offspring of ethanol-fed female rats have a significant decrease in serotonin (5-HT) neurons and glia that contain S100B, an essential trophic factor for the development of 5-HT neurons. The deficiency of S100B-immunopositive glia was detected during the vulnerable period in 5-HT neuron development and in brain areas proximal to these neurons. The reductions of both 5-HT neurons and S100B-positive glia were prevented by maternal treatment with a 5-HT(1A) agonist (i.e., ipsapirone or buspirone). In the current study, we investigated whether the offspring of ethanol-fed rats had a general decrease in the density of glial cells in the brain areas that contain 5-HT neurons, and we determined whether these changes were prevented by maternal treatment with ipsapirone between gestational days (GDs) 13 and 20. We estimated the density of vimentin-positive glia of the midline raphe glial structure (MRGS) at GD 20 and postnatal day (PND) 5 and of glial fibrillary acidic protein (GFAP)-positive astrocytes proximal to the dorsal and median raphe at PNDs 5 and 19. The results of this study provide evidence that in utero ethanol exposure is associated with a reduced density of GFAP-immunopositive astrocytes proximal to the dorsal and median raphe. Maternal ipsapirone treatment significantly increased astroglial density in the dorsal raphe at PNDs 5 and 19 and in the median raphe at PND 5, such that it either prevented (dorsal raphe, PNDs 5 and 19) or blunted (median raphe, PND 5) the effects of ethanol.

Dual mechanisms for ethanol-induced inhibition of monocyte chemotactic protein-3 mRNA expression in activated glial cells

The differential display of mRNA technique was used to screen the expressed genes in control and 50 mM chronic ethanol-treated rat C6 glial cells, with and without activation by lipopolysaccharide (LPS) combined with phorbol 12-myristate 13-acetate (PMA). One differentially expressed transcript was identified as that corresponding to the chemokine monocyte chemotactic protein (MCP)-3. MCP-3 is a broadly active chemokine that functions in chemoattraction and activation of monocytes, T lymphocytes, eosinophils, basophils, natural killer cells, and dendritic cells. Steady-state MCP-3 mRNA levels were elevated 6-fold after 24-h stimulation of control cells but less than 3-fold after stimulation of 9-day chronic ethanol-exposed cells. One- and 5-day exposures to 50 mM ethanol were not effective at reducing steady-state MCP-3 mRNA levels in stimulated cells, whereas 1-day exposure to >150 mM ethanol was effective. Stimulation with tumor necrosis factor-alpha elevated MCP-3 mRNA in C6 glial cells to a lesser extent than with LPS plus PMA, but the effects of ethanol were consistent. To gain insight into possible mechanisms for ethanol-induced reductions in steady-state MCP-3 mRNA, additional studies examined nuclear MCP-3 RNA levels and MCP-3 mRNA degradation. MCP-3 RNA content was greatly reduced in isolated nuclei from acute and chronic ethanol-exposed cells, suggesting transcriptional inhibition. On the other hand, acute ethanol exposure enhanced degradation of preexisting MCP-3 mRNA, indicating message destabilization. Thus, the results are consistent with a dual mechanism for ethanol-induced reductions in steady-state MCP-3 mRNA levels.

Astrocyte-mediated trophic support of developing serotonin neurons: effects of ethanol, buspirone, and S100B

Previously, this laboratory demonstrated that the development of serotonin (5-HT) neurons and S100B-immunopositive glia proximal to these neurons is impaired in the offspring of ethanol-fed rats. However, maternal treatment with a 5-HT(1A) agonist, e.g., buspirone or ipsapirone, between gestational days 13 and 20 prevented most of the ethanol-associated changes to developing 5-HT neurons and S100B-immunopositive glia in offspring. The present in vitro studies examined the hypothesis that the protective effects of a 5-HT(1A) agonist on ethanol-exposed, developing 5-HT neurons are mediated in part by astrocyte-produced factors such as S100B. Primary cultures of fetal 5-HT neurons were maintained in conditioned medium (CM) that was obtained from ethanol- and buspirone-treated astrocytes. In order to assess the potential contribution of S100B to the protective effects of buspirone, a mouse monoclonal antibody to S100B was added to the CM to block the biological effects of this protein. These studies demonstrated that CM, obtained from ethanol-treated astrocytes, was unable to support normal development of 5-HT neurons; there was a significant reduction in the number of 5-HT neurons/well. However, CM that was obtained from astrocytes that were co-treated with buspirone and ethanol prevented the ethanol-associated reduction, and the protective effects of buspirone required S100B. We also investigated whether exogenous S100B could protect 5-HT neurons from damage caused by direct exposure to ethanol. Direct exposure of fetal brainstem neurons to ethanol in chemically-defined medium was associated with a significant reduction in the number of 5-HT immunopositive neurons/well. However, exogenous S100B protected 5-HT neurons from the ethanol-associated reduction. Our observations suggest that the protective effects of buspirone on ethanol-exposed, developing 5-HT neurons are mediated in part by the astrocyte-produced factor S100B.

Does trimetazidine exert cytoprotective activity on astrocytes subjected to hypoxia in vitro?

The aim of the present study was to establish whether trimetazidine (TMZ) is capable of protecting astrocytes against hypoxic injury. Using the model of astrocyte cell culture we tried to observe the cells treated with TMZ before, during and after hypoxia simulated in vitro. Cell viability was determined by Live/Dead (viability/cytotoxicity) Assay Kit and MTT conversion test. Apoptotic cell death was distinguished by a method using fluorescence microscopy with Hoechst 33342. The effect of the drug on the DNA synthesis was evaluated by measuring the incorporation of [3H]thymidine into DNA of astrocytes. TMZ stimulates the proliferation of astrocytes most significant one when the astrocytes are exposed to the drug in normoxia, hypoxia and/or re-oxygenation. Adding TMZ into cultures during re-oxygenation and hypoxial re-oxygenation significantly decreases the number of dead and apoptotic cells. Our experiment has proved that TMZ exerts the most significantly cytoprotective effect on astrocytes in vitro when added during hypoxia and/or re-oxygenation. We may conclude that the protective effect of TMZ depends on the sequence of drug adding and hypoxia/ re-oxygenation onset.

Potential involvement of S100B in the protective effects of a serotonin-1a agonist on ethanol-treated astrocytes

Previously, this laboratory found that the offspring of rats that consumed ethanol on a chronic basis prior to parturition exhibited a significant reduction in serotonin (5-HT) neurons and in astrocytes proximal to these neurons. This laboratory also showed that maternal treatment with a 5-HT(1A) agonist during the latter part of gestation prevented the reduction of 5-HT neurons and most of the astrocyte abnormalities. The present in vitro studies extended our prior in vivo work by examining the potential involvement of S100B with the protective effects of a 5-HT(1A) agonist, i.e., buspirone, on astrocytes. Astrocyte cultures were either maintained in chemically defined media in the presence and absence of ethanol and buspirone or in conditioned media that was generated by ethanol- and buspirone-treated astrocytes. A mouse monoclonal antibody to S100B was used to assess the potential involvement of S100B with the protective effects of buspirone. Additional in vitro studies measured the direct effects of S100B and ethanol on astrocyte proliferation. These investigations demonstrate that in vitro ethanol exposure reduces the number of astrocytes, and that treatment with the 5-HT(1A) agonist buspirone prevents the ethanol-associated reduction in astrocyte number. The protective effects of buspirone appear to be mediated by factors that are secreted by astrocytes; such factors likely include S100B. In addition, added S100B prevents an ethanol-associated reduction in [(3)H]-thymidine incorporation into proliferating astrocytes.

Quantitative immunocytochemistry of glia in the cerebellar cortex of old ethanol-fed rats

It is clear from results of studies in this laboratory that chronic ethanol consumption causes regression of the extensive Purkinje neuron (PN) dendritic arbor. There are, however, a paucity of studies on the effects of chronic ethanol consumption on glia cells that reside in the molecular layer of the cerebellar cortex with PN dendrites. The purpose of the present study was to investigate the possibility that chronic ethanol consumption in old F344 rats results in gliosis within the molecular layer of the cerebellar cortex. Ten 12-month-old, male, F344 rats received a liquid diet containing 35% ethanol for 40 weeks. Pair-fed controls (n=10) received a liquid diet in which maltose dextrins were substituted for ethanol. Chow-fed rats (n=10) served as controls for age. At the end of the treatment period, rats were euthanized and perfused through the aorta, and cerebella were prepared for immunocytochemistry. Free floating sections were stained with (1) glial fibrillary acidic protein antibody for labeling of Bergmann glial cells and fibers, (2) OX-42 antibody for labeling of microglia, and (3) 0.5% cresyl violet for estimates of molecular layer volume. Results indicate that the densities of Bergmann glial cell processes and microglia within the cerebellar molecular layer are not altered by ethanol consumption.

Immortalized hypothalamic luteinizing hormone-releasing hormone (LHRH) neurons induce a functional switch in the growth factor responsiveness of astroglia: involvement of basic fibroblast growth factor

Recent evidence indicates that astroglial-derived growth factors (GFs) participate in the development of luteinizing hormone-releasing hormone (LHRH) neurons, but it is still unknown whether LHRH neurons may exert a reciprocal modulation of glial cell function. Using immortalized hypothalamic LHRH (GT1-1) neurons in co-culture with glial cells, we have recently shown that basic fibroblast growth factor (bFGF) plays a prominent role in the glial-induced acquisition of the mature LHRH phenotype by GT1-1 cells. We have resorted to this model and combined biochemical and morphological approaches to study whether the response of glial cells to a number of GFs (including bFGF, insulin-like growth factor I, IGF-I, epidermal growth factor, EGF and insulin) expressed during LHRH neuron differentiation, is modulated by co-culture with pure LHRH neurons. Pre-treatment of hypothalamic astrocytes with an inactive ('priming') dose of bFGF for 12 h powerfully increased astroglia proliferative response to IGF-I (10 ng/ml), EGF (10 g/ml) and insulin (10 microg/ml), inducing a 65-100% increase in the [3H]thymidine incorporation compared to untreated cultures. When astroglial cells and developing GT1-1 neurons were co-cultured for 5 days in vitro (DIV), the [3H]thymidine incorporation was significantly higher than in astroglial cells cultured without neurons. Application of the different GFs to the co-culture for either 12 or 24 h further stimulated DNA synthesis to various extent according to the GF applied and the time of application. Localization of the proliferating cells by dual immunohistochemical staining, followed by cell counting and bromodeoxiuridine (BrdU) labeling index calculation, revealed that the incorporation of BrdU was restricted to the nuclei of LHRH-immunopositive neurons. Such changes were accompanied by extensive morphological alterations of astroglial and LHRH fiber networks, whereas neutralization of bFGF activity in GT1-1 neuron-glial co-cultures by a bFGF-antibody, dramatically counteracted the observed effects. The functional switch of astroglia proliferative response to GFs coupled to the potent morphological and functional modifications of developing glia and pure LHRH neurons observed in vitro, support a bidirectional interaction between immortalized LHRH neurons and astroglial cells and identify bFGF as a key player in this crosstalk.

Differential fibronectin expression in activated C6 glial cells treated with ethanol

The central nervous system is particularly susceptible to alcohol effects and toxicity. Glial cells constitute the most common cell type in the brain and play critical roles in normal brain function and during infection and injury. Astrocytes in particular seem to be important targets for alcohol neurotoxicity during both development and in adulthood. To gain more insight into alcohol-mediated effects on astrocytes at the molecular level, gene expression in rat C6 glial cells was studied in the presence or absence of ethanol. The differential display of mRNA technique was used to screen the expressed genes in ethanol-treated rat C6 cells before and after treatment with lipopolysaccharide (LPS) combined with phorbol-12-myristate-13-acetate (PMA), conditions that mimic an infectious inflammatory state and cause immunologic activation. The present data show that fibronectin appeared as a major gene whose expression is increased in C6 cells by LPS plus PMA stimulation and decreased by chronic ethanol exposure, both in mRNA and protein levels. Fibronectin is a dimeric glycoprotein found in the extracellular matrix of most tissues, in the blood, and on cell surfaces and is involved in many cellular processes. These results show that chronic exposure to ethanol is associated with changes in astrocyte properties during immunologic activation that reduce fibronectin expression. The discovery of astrocyte fibronectin expression as a potential regulated target for chronic alcohol abuse may be useful in understanding, preventing, and treating some brain disorders associated with alcohol abuse and alcoholism.

Light ethanol consumption enhances liver regeneration after partial hepatectomy in rats

BACKGROUND & AIMS

The effects of "social drinking" on the liver have yet to be fully documented. The aim of this study was to document the effects of daily light, moderate, and heavy ethanol exposure on hepatic regenerative activity in the rat.

METHODS

Adult male Sprague-Dawley rats underwent daily gavages with 1.0 (light), 2. 0 (moderate), or 4.0 (heavy) g/kg of ethanol or tap water (controls) for 30 days before 70% partial hepatectomy (PHx). Hepatic regenerative activity was then documented on days 1, 3, 5, and 7 after PHx.

RESULTS

Compared with controls, restitution of liver mass, [(3)H]thymidine incorporation, and proliferating cell nuclear antigen expression were decreased in the heavy (-10%, -60%, and -36%, respectively), unchanged in the moderate (-4%, -8%, and -16%, respectively), and increased in the light (+6%, +38%, and +29%, respectively) ethanol groups. Messenger RNA differential display of resected livers at PHx identified a band present only in the light ethanol group that encodes a unique 47-kilodalton protein with growth-promoting features designated light ethanol-induced stimulatory protein.

CONCLUSIONS

The results indicate that light ethanol consumption enhances hepatic regenerative activity after PHx in rats. Further studies are required to determine the mechanism involved and whether social drinking has beneficial or adverse effects on the natural history of acute or chronic liver disease in humans.

Promitogenic effects of ethanol, methanol, and ethanolamine in insulin-treated fibroblasts

The zinc-dependent potentiating effect of ethanol (EtOH) on insulin-stimulated DNA synthesis was studied with a focus on the possible site of EtOH action and the ability of other alcohols to elicit similar promitogenic effects. In serum-starved (27 hr) NIH 3T3 fibroblasts, 200-300 mM methanol (MeOH) and 0.1-1.5 mM ethanolamine (Etn), but not 3- to 9-carbon normal alcohols, enhanced the effect of insulin on DNA synthesis to varying extents. The promitogenic effects of EtOH and MeOH, but not that of Etn, required the presence of 15-25 microM zinc. The potentiating effects of Etn were enhanced by 5 mM choline (Cho) and inhibited by 1-3 mM hemicholinium-3 (HC-3), an inhibitor of Cho transporter and Cho kinase. In the presence of 15 microM zinc, 40 mM EtOH, which had no effect on its own, inhibited the potentiating effects of Cho and enhanced the inhibitory effects of HC-3 on synergistic stimulation of DNA synthesis by Etn and insulin. On the other hand, both Cho and HC-3 partially inhibited the promitogenic effect of 80 mM EtOH in the presence of 25 microM zinc. After a 10-min incubation, EtOH decreased the amount of cell-associated [(14)C]Cho in the absence but not in the presence of HC-3. After a 40-min incubation, Cho (5 mM) partially inhibited the cellular uptake as well as the metabolism of [(14)C]Etn. Whereas after the 40-min incubation 80 mM EtOH had no effects on Etn metabolism, in the absence of Cho it decreased the amount of cell-associated [(14)C]Etn. However, EtOH had no detectable effects on cell association of [(14)C]Etn after the 10-min incubation. The results suggest that in NIH 3T3 fibroblasts EtOH is a remarkably specific promitogen, and that it may act via a cell membrane site(s), also regulated by Cho (agonist) and HC-3 (antagonist), which can influence membrane binding and the promitogenic activity of Etn.

Ethanol has multiple effects on DNA synthesis in fibroblasts depending on the presence of secreted growth regulators and zinc as well as the level of protein kinase C activation

Earlier we showed that in serum-starved (27 h), washed mouse fibroblasts and other cell lines 40-80 mM concentrations of ethanol (EtOH) potentiate, in a zinc (Zn2+)-dependent manner, the combined stimulatory effects of calcium (Ca2+) and insulin (Ins) on DNA synthesis. We now report that the promitogenic EtOH effects require removal of the used medium at least 6 h prior to treatments with EtOH, Zn2+, and Ins. If serum-starved (27 h) cells were continuously incubated for another 18-h period without replacing the medium, a secreted cellular factor moderately enhanced the mitogenic effect of Ins and simultaneously blocked the potentiating effect of EtOH on DNA synthesis measured during the last hour of treatments. However, the presence of Ca2+ (2.8 mM) plus Zn2+ (25 microM) or 25-300 nM phorbol 12-myristate 13-acetate (PMA) during the serum starvation period partially restored the promitogenic effect of EtOH. The PMA effect was blocked by the protein kinase C (PKC) inhibitor GF 109203X added for the second (18 h) period. Even at 300 nM, PMA failed to fully downregulate PKC-alpha, the major PKC isoform, over a 28-h period, suggesting that an activated PKC enzyme was involved in the restoration of EtOH effect. When EtOH (40-80 mM) was added for the entire serum starvation period and the incubations were continued for 18 h without removing the medium, EtOH inhibited both the combined actions of Ins and cellular factor as well as the promoting effect of newly added EtOH on Ins-dependent DNA synthesis. Coaddition of Zn2+ and PMA with EtOH prevented these inhibitory effects of EtOH. The results indicate that in mouse fibroblasts EtOH can both enhance and inhibit Ins-dependent DNA synthesis depending on the timing of EtOH treatment as well as the presence of Zn2+, cellular factors, and activators of the PKC system.

Cytotoxicity of short-chain alcohols

Ethanol and other short-chain alcohols elicit a number of cellular responses that are potentially cytotoxic and, to some extent, independent of cell type. Aberrations in phospholipid and fatty acid metabolism, changes in the cellular redox state, disruptions of the energy state, and increased production of reactive oxygen metabolites have been implicated in cellular damage resulting from acute or chronic exposure to short-chain alcohols. Resulting disruptions of intracellular signaling cascades through interference with the synthesis of phosphatidic acid, decreases in phosphorylation potential and lipid peroxidation are mechanisms by which solvent alcohols can affect the rate of cell proliferation and, consequently, cell number. Nonoxidative metabolism of short-chain alcohols, including phospholipase D-mediated synthesis of alcohol phospholipids, and the synthesis of fatty acid alcohol esters are additional mechanisms by which alcohols can affect membrane structure and compromise cell function.