Chronic ethanol exposure in rats affects rabs-dependent hepatic trafficking of apolipoprotein E and transferrin

Alcohol and Prostate Cancer: Time to Draw Conclusions

It has been a long-standing debate in the research and medical societies whether alcohol consumption is linked to the risk of prostate cancer (PCa). Many comprehensive studies from different geographical areas and nationalities have shown that moderate and heavy drinking is positively correlated with the development of PCa. Nevertheless, some observations could not confirm that such a correlation exists; some even suggest that wine consumption could prevent or slow prostate tumor growth. Here, we have rigorously analyzed the evidence both for and against the role of alcohol in PCa development. We found that many of the epidemiological studies did not consider other, potentially critical, factors, including diet (especially, low intake of fish, vegetables and linoleic acid, and excessive use of red meat), smoking, family history of PCa, low physical activity, history of high sexual activities especially with early age of first intercourse, and sexually transmitted infections. In addition, discrepancies between observations come from selectivity criteria for control groups, questionnaires about the type and dosage of alcohol, and misreported alcohol consumption. The lifetime history of alcohol consumption is critical given that a prostate tumor is typically slow-growing; however, many epidemiological observations that show no association monitored only current or relatively recent drinking status. Nevertheless, the overall conclusion is that high alcohol intake, especially binge drinking, is associated with increased risk for PCa, and this effect is not limited to any type of beverage. Alcohol consumption is also directly linked to PCa lethality as it may accelerate the growth of prostate tumors and significantly shorten the time for the progression to metastatic PCa. Thus, we recommend immediately quitting alcohol for patients diagnosed with PCa. We discuss the features of alcohol metabolism in the prostate tissue and the damaging effect of ethanol metabolites on intracellular organization and trafficking. In addition, we review the impact of alcohol consumption on prostate-specific antigen level and the risk for benign prostatic hyperplasia. Lastly, we highlight the known mechanisms of alcohol interference in prostate carcinogenesis and the possible side effects of alcohol during androgen deprivation therapy.

Ethanol exposure inhibits hepatocyte lipophagy by inactivating the small guanosine triphosphatase Rab7

Alcohol consumption is a well-established risk factor for the onset and progression of fatty liver disease. An estimated 90% of heavy drinkers are thought to develop significant liver steatosis. For these reasons, an increased understanding of the molecular basis for alcohol-induced hepatic steatosis is important. It has become clear that autophagy, a catabolic process of intracellular degradation and recycling, plays a key role in hepatic lipid metabolism. We have shown that Rab7, a small guanosine triphosphatase known to regulate membrane trafficking, acts as a key orchestrator of hepatocellular lipophagy, a selective form of autophagy in which lipid droplets (LDs) are specifically targeted for turnover by the autophagic machinery. Nutrient starvation results in Rab7 activation on the surface of the LD and lysosomal compartments, resulting in the mobilization of triglycerides stored within the LDs for energy production. Here, we examine whether the steatotic effects of alcohol exposure are a result of perturbations to the Rab7-mediated lipophagic pathway. Rats chronically fed an ethanol-containing diet accumulated significantly higher levels of fat in their hepatocytes. Interestingly, hepatocytes isolated from these ethanol-fed rats contained juxtanuclear lysosomes that exhibited impaired motility. These changes are similar to those we observed in Rab7-depleted hepatocytes. Consistent with these defects in the lysosomal compartment, we observed a marked 80% reduction in Rab7 activity in cultured hepatocytes as well as a complete block in starvation-induced Rab7 activation in primary hepatocytes isolated from chronic ethanol-fed animals. Conclusion: A mechanism is supported whereby ethanol exposure inhibits Rab7 activity, resulting in the impaired transport, targeting, and fusion of the autophagic machinery with LDs, leading to an accumulation of hepatocellular lipids and hepatic steatosis. (Hepatology Communications 2017;1:140-152).

Downregulation of the small GTPase SAR1A: a key event underlying alcohol-induced Golgi fragmentation in hepatocytes

The hepatic asialoglycoprotein receptor (ASGP-R) is posttranslationally modified in the Golgi en route to the plasma membrane, where it mediates clearance of desialylated serum glycoproteins. It is known that content of plasma membrane-associated ASGP-R is decreased after ethanol exposure, although the mechanisms remain elusive. Previously, we found that formation of compact Golgi requires dimerization of the largest Golgi matrix protein giantin. We hypothesize that ethanol-impaired giantin function may be related to altered trafficking of ASGP-R. Here we report that in HepG2 cells expressing alcohol dehydrogenase and hepatocytes of ethanol-fed rats, ethanol metabolism results in Golgi disorganization. This process is initiated by dysfunction of SAR1A GTPase followed by altered COPII vesicle formation and impaired Golgi delivery of the protein disulfide isomerase A3 (PDIA3), an enzyme that catalyzes giantin dimerization. Additionally, we show that SAR1A gene silencing in hepatocytes mimics the effect of ethanol: dedimerization of giantin, arresting PDIA3 in the endoplasmic reticulum (ER) and large-scale alterations in Golgi architecture. Ethanol-induced Golgi fission has no effect on ER-to-Golgi transportation of ASGP-R, however, it results in its deposition in cis-medial-, but not trans-Golgi. Thus, alcohol-induced deficiency in COPII vesicle formation predetermines Golgi fragmentation which, in turn, compromises the Golgi-to-plasma membrane transportation of ASGP-R.

Alcohol induces Golgi fragmentation in differentiated PC12 cells by deregulating Rab1-dependent ER-to-Golgi transport

In the present study, we analyze the effects of ethanol on the Golgi structure and membrane transport in differentiated PC12 cells, which are used as a model of neurons. Chronic exposure to moderate doses of ethanol induces Golgi fragmentation, a common characteristic of many neurodegenerative diseases. Alcohol impaired the lateral linking of stacks without causing microtubule damage. Extensive immunocytochemical and western blot analyses of representative Golgi proteins showed that few, but important, proteins are significantly affected. Thus, alcohol exposure induced a significant ER-to-Golgi transport delay, the retention of the GTPase Rab1 in the Golgi membranes and the accumulation of tethering factor p115 in the cytosol. These modifications would explain the observed fragmentation. The amount of p115 and the stacking protein GRASP65 increased in alcohol-treated cells, which might be a mechanism to reverse Golgi damage. Importantly, the overexpression of GTP-tagged Rab1 but not of a dominant-negative Rab1 mutant, restored the Golgi morphology, suggesting that this protein is the main target of alcohol. Taken together, our results support the view that alcohol and neurodegenerative diseases such as Parkinson have similar effects on intracellular trafficking and provide new clues on the neuropathology of alcoholism.

Protein Traffic Is an Intracellular Target in Alcohol Toxicity

Eukaryotic cells comprise a set of organelles, surrounded by membranes with a unique composition, which is maintained by a complex synthesis and transport system. Cells also synthesize the proteins destined for secretion. Together, these processes are known as the secretory pathway or exocytosis. In addition, many molecules can be internalized by cells through a process called endocytosis. Chronic and acute alcohol (ethanol) exposure alters the secretion of different essential products, such as hormones, neurotransmitters and others in a variety of cells, including central nervous system cells. This effect could be due to a range of mechanisms, including alcohol-induced alterations in the different steps involved in intracellular transport, such as glycosylation and vesicular transport along cytoskeleton elements. Moreover, alcohol consumption during pregnancy disrupts developmental processes in the central nervous system. No single mechanism has proved sufficient to account for these effects, and multiple factors are likely involved. One such mechanism indicates that ethanol also perturbs protein trafficking. The purpose of this review is to summarize our understanding of how ethanol exposure alters the trafficking of proteins in different cell systems, especially in central nervous system cells (neurons and astrocytes) in adult and developing brains.

Pathogenesis of alcoholic liver disease: interactions between parenchymal and non-parenchymal cells

The development of alcoholic liver disease (ALD) is a complex process involving both the parenchymal and non-parenchymal cells in the liver. The impact of ethanol on hepatocytes can be characterized as a condition of organelle stress with multifactorial changes in hepatocellular function accumulating during ethanol exposure. These changes include oxidative stress, mitochondrial dysfunction, decreased methylation capacity, endoplasmic reticulum stress, impaired vesicular trafficking and altered proteasome function. Injury to hepatocytes is attributed, in part, to ethanol metabolism by the hepatocytes. Changes in the structural integrity of hepatic sinusoidal endothelial cells, as well as enhanced inflammation in the liver during ethanol exposure are also important contributors to injury. Activation of hepatic stellate cells initiates the deposition of extracellular matrix proteins characteristic of fibrosis. Kupffer cells, the resident macrophages in the liver, are particularly critical to the onset of ethanol-induced liver injury. Chronic ethanol exposure sensitizes Kupffer cells to activation by lipopolysaccharides via toll-like receptor 4. This sensitization enhances the production of inflammatory mediators, such as tumor necrosis factor-α and reactive oxygen species that contribute to hepatocyte dysfunction, necrosis and apoptosis of hepatocytes and the generation of extracellular matrix proteins leading to fibrosis. In this review we provide an overview of the complex interactions between parenchymal and non-parenchymal cells in the liver during the progression of ethanol-induced liver injury.

Down-regulation of liver Galbeta1, 4GlcNAc alpha2, 6-sialyltransferase gene by ethanol significantly correlates with alcoholic steatosis in humans

Hepatic steatosis and steatohepatitis are frequent results of long-term ethanol exposure. We have previously demonstrated that long-term ethanol down-regulates Galbetal, 4GlcNAc alpha2, 6-sialyltransferase (ST6Gal1), leading to defective glycosylation of a number of proteins including apolipoprotein (apo) E and apo J and the appearance of asialoconjugates in the blood of continuously alcohol-fed animals as well as in human alcoholics. In the current study, we have explored the possibility of whether ethanol-induced down-regulation of ST6Gal1 could contribute toward alcoholic steatosis in human alcoholics presumably because of impaired lipid and lipoprotein transport caused by this down-regulation. Real-time quantitative polymerase chain reaction analyses of liver samples from nondrinkers, moderate drinkers, and heavy drinkers as well as from subjects with and without alcoholic liver disease revealed direct evidence that the down-regulation of ST6Gal1 may be due to ethanol per se. The ST6Gal1 messenger RNA level was reduced by as much as 70% in moderate and heavy drinkers as well as in patients with alcoholic liver disease, but was not changed in subjects with liver disease due to causes other than alcohol exposure. Biochemical and histopathologic analysis demonstrated that the liver total cholesterol was increased by more than 30% (P < .05) and 75% (P < .01), respectively, in moderate and heavy drinkers compared with nondrinkers, with even more dramatic changes in triglyceride levels. Significantly, there was a strong inverse correlation between ST6Gal1 messenger RNA level and liver lipid deposit (F = 8.68, P < .001) by statistical analysis. Thus, it is suggested that alcohol-mediated down-regulation of hepatic ST6Gal1 gene leads to defective glycosylation of lipid-carrying apolipoproteins such as apo E and apo J, resulting in defective intracellular lipid and lipoprotein transport, which in turn may contribute to alcoholic steatosis.

Liver Galbeta1,4GlcNAc alpha2,6-sialyltransferase is down-regulated in human alcoholics: possible cause for the appearance of asialoconjugates

Galbetal,4GlcNAc alpha2,6-sialyltransferase (ST6GalI) mediates the glycosylation of proteins and lipids to form functionally important glycoproteins and glycolipids in the Golgi compartment. Our previous work demonstrated that long-term ethanol feeding in rats caused a marked 59% decrease in ST6GalI activity as well as ST6GalI messenger RNA (mRNA) level in the liver that was due to decreased stability of the mRNA. Clinical observations show that down-regulation of ST6GalI gene and consequent impaired activity of ST6GalI seems to be the major cause for the appearance of asialoconjugates in the blood of long-term alcoholics. The plasma carbohydrate-deficient transferrin (CDT) and sialic acid index of plasma apolipoprotein J were also altered in the alcoholic group compared with the nondrinkers. We have now investigated how alcohol affects the gene regulation of ST6GalI and the possible mechanism in postmortem human liver specimens taken from nondrinkers, moderate alcohol drinkers, and heavy alcohol drinkers. Real-time polymerase chain reaction analyses of the liver RNA extract showed that ST6GalI mRNA level was progressively decreased by 49% in moderate drinkers (P < .01) and by 69% in heavy drinkers (P < .01) compared with nondrinkers. Western blot analysis showed that liver ST6GalI protein level was negligibly decreased in moderate drinkers but decreased by 30% (P < .05) in heavy drinkers compared with nondrinkers. We further demonstrated a single ST6GalI mRNA-binding protein complex in the normal human liver extract, which progressively decreased in the liver extracts of moderate and heavy alcohol drinkers. Thus, it is concluded that the appearance of asialoconjugates in alcoholics is possibly due to the down-regulation of ST6GalI gene expression.

Chronic ethanol feeding to rats decreases adiponectin secretion by subcutaneous adipocytes

Chronic ethanol feeding to mice and rats decreases serum adiponectin concentration and adiponectin treatment attenuates chronic ethanol-induced liver injury. Although it is clear that lowered adiponectin has pathophysiological importance, the mechanisms by which chronic ethanol decreases adiponectin are not known. Here, we have investigated the impact of chronic ethanol feeding on adiponectin expression and secretion by adipose tissue. Rats were fed a 36% Lieber-DeCarli ethanol-containing liquid diet or pair-fed control diet for 4 wk. Chronic ethanol feeding decreased adiponectin mRNA but had no effect on adiponectin protein in subcutaneous adipose tissue. Chronic ethanol feeding also reduced adiponectin secretion by isolated subcutaneous and retroperitoneal adipocytes despite the maintenance of equivalent intracellular concentrations of adiponectin between subcutaneous adipocytes from ethanol- and pair-fed rats. Treatment with brefeldin A suppressed adiponectin secretion by subcutaneous adipocytes from pair-fed rats but had little effect after ethanol feeding. In subcutaneous adipocytes from pair-fed rats, adiponectin was enriched in endoplasmic reticulum (ER)/Golgi relative to plasma membrane; however, after chronic ethanol feeding, adiponectin was equally distributed between plasma membrane and ER/Golgi fractions. In conclusion, chronic ethanol feeding impaired adiponectin secretion by subcutaneous and retroperitoneal adipocytes; impaired secretion likely contributes to decreased adiponectin concentrations after chronic ethanol feeding.

Chronic ethanol consumption upregulates the cytosolic and plasma membrane sialidase genes, but down regulates lysosomal membrane sialidase gene in rat liver

We have previously shown that chronic ethanol feeding stimulates liver cytosolic sialidase (CS) and plasma membrane sialidase (PMS), whereas it decreases lysosomal membrane sialidase (LMS) activities with concomitant alterations in their relative synthetic rate in rat. To understand the molecular mechanism(s) for these changes, we have evaluated the effect of ethanol administration in male Wistar rats as a function of increasing dietary ethanol concentration after 8 weeks of pair-feeding on (i) the expression of CS, PMS, and LMS genes by real-time quantitative polymerase chain reaction method; (ii) their relative transcription rates by nuclear run-on assay; and (iii) the actual amount of these sialidase proteins in the liver fractions of the respective groups by Western blot method. We have demonstrated that the animals fed with 10.6%, 20.8%, and 36% of total calories as ethanol showed a 20% (P<.05), 34% (P<.01), and 69% (P<.01) increase in CS mRNA level, and 22% (P<.05), 26% (P<.01), and 47% (P<.01) increase in PMS mRNA level, but a decrease in LMS mRNA level by 35% (P<.05), 50% (P<.01), and 80% (P<.01), respectively, as compared to controls. Western blot analyses of CS, PMS, and LMS in the liver subfractions showed that changes in protein levels of CS, LMS, and PMS were consistent with the corresponding changes in the respective mRNA levels. Thus, the upregulation of CS and PMS, but not LMS which is down regulated by chronic ethanol, may account for the appearance of asialoconjugates in alcoholics.

Ethanol destabilizes liver Gal beta l, 4GlcNAc alpha2,6-sialyltransferase, mRNA by depleting a 3'-untranslated region-specific binding protein

Asialoconjugates are viable biomarkers for alcohol abuse. We previously showed that chronic ethanol feeding down-regulated liver Gal beta l, 4GlcNAc alpha2,6-sialyltransferase (ST6Gal l) mRNA by destabilizing it. Since RNA-binding proteins are known to stabilize many eukaryotic mRNAs by interacting with the 3'-untranslated region (UTR), we have delineated the possible mechanism by which ethanol destabilizes ST6Gal l mRNA. Using (32)P-labeled RNA probes generated from a 2.7-kb 3'-UTR of ST6Gal l mRNA, we identified a liver cytosolic 41-kDa specific binding protein that interacts with its 3'-UTR domain and protects it from degradation in normal rat liver but disappears after chronic ethanol treatment. Mapping of the binding region revealed that four RNA probes of 80-base pair (bp) length spanning the 304 bp of the 3'-UTR of ST6Gal l mRNA showed equal binding intensity. The corresponding cDNA sequences for the four 80-bp RNA probes share the 13-bp consensus sequence. Mutagenesis analysis identified that four nucleotides, AG and TC, among the consensus sequences were critical for the RNA-protein interaction. Therefore, 5'-CAGCCTCCTCCCT-3' serves as a cis-element critically involved in this interaction. The RNA-protein complex formation progressively decreased with increasing dietary ethanol, resulting in its virtual disappearance with 36% of the dietary calories as ethanol. Concomitantly, the same ethanol diet decreased sialic acid index of plasma apolipoprotein J by 45% (p < 0.05). Thus, depletion of a binding protein that specifically interacts with its 3'-UTR region of ST6Gal l mRNA may account for its destabilization and consequent appearance of asialoconjugates as alcohol biomarkers.

Chronic ethanol feeding increases activation of NADPH oxidase by lipopolysaccharide in rat Kupffer cells: role of increased reactive oxygen in LPS-stimulated ERK1/2 activation and TNF-alpha production

Reactive oxygen species (ROS) contribute to the development of chronic ethanol-induced liver injury. Although ROS modulate the activity of many signal transduction pathways, the molecular targets of ROS during ethanol exposure are not well understood. Here, we investigated whether specific ROS-sensitive signal transduction pathways contribute to increased tumor necrosis factor alpha (TNF-alpha) production by Kupffer cells after chronic ethanol feeding to rats. Lipopolysaccharide (LPS) rapidly increased ROS production, measured by dihydrorhodamine fluorescence, in Kupffer cells from ethanol- and pair-fed rats, and ROS production was 2.5-fold greater in ethanol-fed compared with pair-fed. Pretreatment with diphenyleneiodonium (DPI), which inhibits reduced nicotinamide adenine dinucleotide phosphate (NADPH) oxidase, normalized ROS production in Kupffer cells from ethanol-fed rats. LPS rapidly increased Rac1-guanosinetriphosphatase (GTPase) activity and p67(phox) translocation to the plasma membrane in Kupffer cells from pair-fed rats. After ethanol feeding, Rac1-GTPase activity was already increased over pair-fed at baseline and remained elevated over pair-fed after LPS stimulation. Further, LPS-stimulated p67(phox) translocation to the plasma membrane was enhanced after chronic ethanol feeding. LPS-stimulated extracellular signal-regulated kinase (ERK)1/2 and p38 phosphorylation, two signaling pathways regulated by ROS, were increased twofold in Kupffer cells from ethanol-fed rats compared with pair-fed controls. However, only LPS-stimulated ERK1/2 phosphorylation was inhibited by DPI, which also reduced LPS-stimulated TNF-alpha production in Kupffer cells from pair- and ethanol-fed rats. These results demonstrate that chronic ethanol feeding increases LPS-stimulated NADPH oxidase-dependent production of ROS in Kupffer cells. Further, ERK1/2 is an important target of NADPH oxidase-derived ROS in Kupffer cells, contributing to enhanced LPS-stimulated TNF-alpha production by Kupffer cells after chronic ethanol feeding.

Effects of chronic ethanol administration on the activities and relative synthetic rates of myelin and synaptosomal plasma membrane-associated sialidase in the rat brain

In an attempt to understand the possible mechanism of chronic ethanol-induced generation of asialoconjugates in the brain and consequent behavioral abnormalities, we have studied the effects of chronic ethanol feeding to rats on the plasma membrane sialidase status in the various subcellular fractions of the brain. We determined sialidase activity using 3H-monosialoganglioside (3H-GM3), 2'-(4-methylumbelliferyl)-alpha-D-N-acetylneuraminic acid (4-MU-NeuAC) substrates and Amplex Red (Sialidase) kit. We determined the plasma membrane sialidase protein by Western blot using the anti-plasma membrane sialidase. We also determined its relative synthetic rate (RSR) by the 60 min incorporation of intracranially infused [35S]-methionine (50 microCi/100 g) into immunoprecipitable plasma membrane sialidase. Chronic ethanol administration stimulated the sialidase activity in the total brain homogenate as well as the myelin and synaptosomal membrane fractions, respectively, in all the three experimental models. Chronic ethanol also increased the concentration of the rat brain plasma membrane sialidase protein relative to that of glyceraldehyde-3-phosphate dehydrogenase by 2.4-, 1.62- and 1.51-fold in the total brain homogenate, myelin and synaptosomal membrane fractions, respectively. These increases in plasma membrane sialidase activity and its protein content were due to concomitant increases in their relative synthetic rates by 115% (p < 0.01) and 72% (p < 0.01) in the myelin and synaptosomal membrane fractions, respectively. Thus, our studies clearly show that chronic ethanol induced deglycosylation of brain gangliosides is in part, due to specific up-regulation of plasma membrane sialidase in the myelin and synaptosomal membrane fractions of the brain. This increase in plasma membrane sialidase may be responsible for chronic-ethanol-induced physiological and neurological impairment in the brain, presumably due to deglycosylation of gangliosides that are essential for crucial cellular and metabolic activities.

Decreased insulin-dependent glucose transport by chronic ethanol feeding is associated with dysregulation of the Cbl/TC10 pathway in rat adipocytes

Heavy alcohol consumption is an independent risk factor for type 2 diabetes. Although the exact mechanism by which alcohol contributes to the increased risk is unknown, impaired glucose disposal is a likely target. Insulin-stimulated glucose disposal in adipocytes is regulated by two separate and independent pathways, the PI3K pathway and the Cbl/TC10 pathway. Previous studies suggest that chronic ethanol feeding impairs insulin-stimulated glucose transport in adipocytes in a PI3K-independent manner. In search of potential targets of ethanol that would affect insulin-stimulated glucose transport, we investigated the effects of 4-wk ethanol feeding to male Wistar rats on the Cbl/TC10 pathway in isolated adipocytes. Chronic ethanol feeding inhibited insulin-stimulated cCbl phosphorylation compared with pair feeding. Insulin receptor and Akt/PKB phosphorylation were not affected by ethanol feeding. Chronic ethanol exposure also impaired cCbl and TC10 recruitment to a lipid raft fraction isolated from adipocytes by detergent extraction. Furthermore, chronic ethanol feeding increased the amount of activated TC10 and filamentous actin in adipocytes at baseline and abrogated the ability of insulin to further activate TC10 or polymerize actin. These results demonstrate that the impairment in insulin-stimulated glucose transport observed in adipocytes after chronic ethanol feeding to rats is associated with a disruption of insulin-mediated Cbl/TC10 signaling and actin polymerization.

Chronic ethanol feeding controls the activities of various sialidases by regulating their relative synthetic rates in the rat liver

We have determined the concentration effects of feeding for 8 weeks 10.8%, 21.6%, and 36% dietary ethanol calories on the activities and relative synthetic rates (RSRs) of various subcellular sialidases of rat liver. The hepatic RSRs of each species of sialidase was determined based on the ratio of 1-hour incorporation of [35S]-methionine into immunoprecipitable sialidase as percent of the incorporation into total protein in each subcellular fraction. Ganglioside sialidase activities in the hepatic subcellular fractions were also determined. Ethanol feeding at 36% dietary calories caused an increase in the ganglioside sialidase activity of the plasma membrane sialidase (PMS) by 232% (P < .01) and that of cytosolic sialidase (CS) by 184% (P < .05), but decreased the lysosomal membrane sialidase (LMS) by 54% (P < .01) when compared with the control animals. The specificity of each antisialidase antibody was verified by immunoblots. The RSR of PMS was increased by 40% (P < .01), 67% (P < .01), and 220% (P < .01) in the 10.8%, 21.6%, and 36% ethanol groups, respectively. Similarly, the RSR of CS was increased by 17% (P < .01), 19% (P < .01), and 63% (P < .01), respectively, in these ethanol groups. In contrast, the RSR of LMS was inhibited by 36% (P < .01), 34% (P < .01), and 69% (P < .01), respectively, in these ethanol groups. Intralysosomal sialidase failed to hydrolyze gangliosides. Thus, PMS and CS, but not LMS or intralysosomal sialidase, may play important roles in ethanol-modulated desialylation of gangliosides and consequent liver injury and behavioral alterations.

Ethanol perturbs the secretory pathway in astrocytes

Ethanol exposure induces retention of glycoproteins in growing astrocytes. We examined the intracellular sites at which this retention occurs and investigated whether this effect is accompanied by alterations in the Golgi complex and microtubular system. We studied the effects of ethanol on the Golgi complex structure, as well as on the secretory pathway functionality by monitoring both the transport of the VSV-G protein and the protein levels of several molecules involved in the regulation of this pathway. Ethanol was found to delay VSV-G transport, modify Golgi complex morphology, and reduce the number of secretory vesicles. Moreover, ethanol affected the levels of mannosidase II, p58, betaCOP, rbet1, and several Rab GTPases. It also affected microtubule organization and polymerization and the levels of the motor proteins kinesin and dynein. Most of these effects were dose-dependent. These alterations, together with those previously reported concerning biosynthesis of glycoconjugates, provide novel insights into how ethanol impairs brain development.

Ethanol-induced alterations in Rab proteins: possible implications for pituitary dysfunction

Chronic exposure of pubertal male rats to ethanol results in a decline in serum testosterone, increased gonadotropins, pituitary luteinizing hormone (LH) and follicle stimulating hormone (FSH) content, and decreased or inappropriately normal serum LH and FSH levels, suggesting impaired secretory release of gonadotropins. The molecular mechanisms behind this disorder are undefined, but a disruption of vesicle-mediated secretory processes is possible because intracellular protein trafficking pathways are involved in secretion of glycoproteins such as FSH and LH. Because small GTP-binding proteins of Rab family have been implicated as key regulators of membrane and protein trafficking in mammalian cells, this study was designed to test if ethanol-impaired pituitary FSH and LH secretion is associated with changes in Rab proteins, particularly Rab1B, Rab3B, Rab6, and Rab11. Male Sprague-Dawley rats 35 days old were pair-fed a Lieber-DeCarli diet with ethanol or without ethanol for 5 to 60 days. After ethanol exposure, serum testosterone levels decreased while LH and FSH were inappropriately unchanged. Immunohistochemical staining showed decreased Rab1B, Rab3B, and Rab11 protein levels in ethanol-treated pituitaries. Immunoblotting showed that ethanol induced a transient reduction in Rab6 after 5 days of ethanol exposure, whereas Rab3B decreased after 20 days, Rab11 after 30 days, and Rab1B after 60 days. Despite these changes in Rab proteins, mRNA levels were unaffected by ethanol exposure. We concluded that reductions in key Rab proteins may lead to altered vesicle trafficking and may play a role in disruption of pituitary FSH and LH secretion caused by ethanol.