Cytoskeletal pathology induced by ethanol

Targeting the cytoskeleton as a therapeutic approach to substance use disorders

Substance use disorders (SUD) are chronic relapsing disorders governed by continually shifting cycles of positive drug reward experiences and drug withdrawal-induced negative experiences. A large body of research points to plasticity within systems regulating emotional, motivational, and cognitive processes as drivers of continued compulsive pursuit and consumption of substances despite negative consequences. This plasticity is observed at all levels of analysis from molecules to networks, providing multiple avenues for intervention in SUD. The cytoskeleton and its regulatory proteins within neurons and glia are fundamental to the structural and functional integrity of brain processes and are potentially the major drivers of the morphological and behavioral plasticity associated with substance use. In this review, we discuss preclinical studies that provide support for targeting the brain cytoskeleton as a therapeutic approach to SUD. We focus on the interplay between actin cytoskeleton dynamics and exposure to cocaine, methamphetamine, alcohol, opioids, and nicotine and highlight preclinical studies pointing to a wide range of potential therapeutic targets, such as nonmuscle myosin II, Rac1, cofilin, prosapip 1, and drebrin. These studies broaden our understanding of substance-induced plasticity driving behaviors associated with SUD and provide new research directions for the development of SUD therapeutics.

Increased hepatocellular protein carbonylation in human end-stage alcoholic cirrhosis

OBJECTIVE

Oxidative stress is a significant contributing factor in the pathogenesis of alcoholic liver disease (ALD). In the murine models of chronic alcohol consumption, induction of oxidative stress results in increased peroxidation of polyunsaturated fatty acids to form highly reactive electrophilic α/β unsaturated aldehydes that post-translationally modify proteins altering activity. Data are presented here suggesting that oxidative stress and the resulting carbonylation of hepatic proteins is an ongoing process involved in alcohol-induced cirrhosis.

METHODS

Using age-matched pooled hepatic tissue obtained from healthy humans and patients with end stage cirrhotic ALD, overall carbonylation was assessed by immunohistochemistry and LC-MS/MS of streptavidin purified hepatic whole cell extracts treated with biotin hydrazide. Identified carbonylated proteins were further evaluated using bioinformatics analyses.

RESULTS

Using immunohistochemistry and Western blotting, protein carbonylation was increased in end stage ALD occurring primarily in hepatocytes. Mass spectrometric analysis revealed a total of 1224 carbonylated proteins in normal hepatic and end-stage alcoholic cirrhosis tissue. Of these, 411 were unique to cirrhotic ALD, 261 unique to normal hepatic tissue and 552 common to both groups. Bioinformatic pathway analysis of hepatic carbonylated proteins revealed a propensity of long term EtOH consumption to increase post-translational carbonylation of proteins involved in glutathione homeostatic, glycolytic and cytoskeletal pathways. Western analysis revealed increased expression of GSTA4 and GSTπ in human ALD. Using LC-MS/MS analysis, a nonenaldehyde post-translational modification was identified on Lysine 235 of the cytoskeletal protein vimentin in whole cell extracts prepared from human end stage ALD hepatic tissue.

CONCLUSIONS

These studies are the first to use LC-MS/MS analysis of carbonylated proteins in human ALD and begin exploring possible mechanistic links with end-stage alcoholic cirrhosis and oxidative stress.

Emerging roles of actin cytoskeleton regulating enzymes in drug addiction: actin or reactin'?

Neurons rely on their cytoskeleton to give them shape and stability, and on cytoskeletal dynamics for growth and synaptic plasticity. Because drug addiction is increasingly seen as the inappropriate learning of strongly reinforcing stimuli, the role of the cytoskeleton in shaping drug memories has been of increasing interest in recent years. Does the cytoskeleton have an active role in shaping these memories, and to what extent do alterations in the cytoskeleton reflect the acute actions of drug exposure, or homeostatic reactions to the chronic exposure to drugs of abuse? Here we will review recent advances in understanding the role of the cytoskeleton in the development of drug addiction, with a focus on actin filaments, as they have been studied in greater detail.

Morphometric and biochemical characteristics of short-term effects of ethanol on rat cardiac muscle

Alcoholism is a very important cause of congestive cardiomyopathy in man. The aim of this study was to examine a short-term effect of ethanol in rat cardiac muscle, using histologic, morphometric and biochemical methods. Experiments were carried out in Wistar male albino rats, divided into two groups: the control group consisting of eight animals receiving tap water, and the experimental group comprising eight animals received ethyl alcohol for ten days, in a single daily dose of 3 g ethanol/kg body weight, per os, using esophageal intubation. The mean volume weighted nuclear volume of cardiac myocytes was estimated by point sampled intercept method, by objective x 100. The mean cubed nuclear intercept length was multiplied by pi and divided by 3. For biochemical analysis, a 10% water tissue homogenate from the left ventricle was made. In the experimental group, the mean volume-weighted nuclear volume (15.08 +/- 5.20 microm3) was significantly lower than in the control group (51.32 +/- 7.83 microm3) (p < 0.001). The treatment of experimental animals with ethanol caused significant increase of aldolase (p < 0.0001) and aspartate transaminase (p < 0.05) activity in the rat cardiac tissue; at the same time, the enzyme activity of creatine phosphokinase, alanine transaminase and alkaline phosphatase were not changed in the experimental group compared to the control values. The amount of the glucose in the cardiac muscle was greater in the experimental group compared to the control animals. Our results suggest that there is depression of cardiomyocyte nuclei in experimental animals treated with ethanol. Alcohol intake results in the loss of Krebs cycle enzymes and as a consequence there is greater utilization of fatty acids for energy production.

Altering the state of phosphorylation of rat liver keratin intermediate filaments by ethanol treatment in vivo changes their structure

Dephosphorylation of keratin intermediate filaments (IF) in livers from ethanol-fed rats relative to controls occurs concurrently with a reorganization of the distribution of IF in the cells. One possible molecular mechanism for this reorganization is a phosphorylation-induced conformational change in the keratin that propagates as a change in the polymerization of the keratin subunits. To test this hypothesis, the structure of liver keratin IF, from both control and alcohol-fed rats, was explored by circular dichroism (CD), tryptophan fluorescence quenching, and 13C nuclear magnetic resonance (NMR). Keratin IF were isolated from livers of control rats and from livers of rats that had ethanol included in their feed for 6-40 weeks. A significant decrease in the intensity of the CD spectrum of keratin IF from livers of ethanol-treated animals, relative to controls, was observed. These data suggested either that a change in conformation or an increase in conformational motility in the keratin IF from ethanol-treated animals occurred as a result of the ethanol-induced dephosphorylation. 13C NMR data were obtained to distinguish between these two possibilities. An increase in resonance intensity of some 13C NMR resonances was observed in the keratin IF from livers of ethanol-treated animals, relative to controls. The CD and NMR data were therefore consistent with an increase in conformational motility of the rod domain in these keratin IF. No significant change was observed in the quenching of tryptophan fluorescence by KI. The change in protein dynamics detected in these experiments could be the molecular basis for the alteration of keratin IF organization in alcoholic hepatitis.

Alterations of hepatocellular intermediate filaments during extrahepatic cholestasis in rat liver

Intermediate filaments (IF) maintain the structural and functional integrity of cells. To investigate whether IF change as a consequence of increased mechanical pressure and what the significance of such alterations is for the integrity of hepatocytes, we investigated alterations of IF in rat liver following common bile duct ligation (CBDL). Immunofluorescence of cytokeratin 18 was performed on extracted cryostat sections which were also used for electron microscopy. Ultrathin sections of mildly extracted liver tissue were applied to reveal the relationship between IF and intercellular junctions and cytoplasmic organelles. Our results showed that hepatocellular IF underwent striking changes during CBDL. The so-called pericanalicular sheath disappeared and IF were rigidly rearranged at the cell periphery, appearing as honeycomb-like structures. Increased amounts of IF were found in close association with increased numbers of desmosomes at the lateral membranes of hepatocytes, and electron-dense desmosome-like bodies were even observed in the ectoplasm at bile canaliculi. Rearrangement of IF in the cytoplasm resulted in segregation of subcellular compartments. The increased density of the IF network and desmosomes are compensatory mechanisms of hepatocytes to resist increased mechanical load and disperse the tension. However, the intracellular rearrangement of IF leading to segregation of subcellular compartments may also have distinct effects on hepatocellular metabolic functions.

Ethanol retards gastric epithelial restoration in monolayer cultures

The purpose of this study was to clarify the effect of ethanol on confluent monolayer gastric epithelial cells that had a round cell-free area in the center of the culture dish. Restoration of such "wounding" was evaluated quantitatively every 12 hr using a computer image analyzer with and without ethanol. Without ethanol, restoration was achieved within 48 hr. Exposure to ethanol retarded cellular restoration significantly. Staining for actin and myosin in the control group revealed the presence of lamellipodia and stress fibers. However, in the ethanol group narrowed lamellipodia and few stress fibers were observed. In conclusion, ethanol retarded the migration and proliferation of cultured gastric mucosal cells after in vitro wounding, possibly by damaging the cytoskeletal system.

Site-specificity of ethanol-induced dephosphorylation of rat hepatocyte keratins 8 and 18: A 31P NMR study

Chronic feeding of ethanol to rats results in disorganization of the keratin intermediate filament network within hepatocytes. Previous studies from this laboratory have shown that intermediate filament organization in cultured cells is related to the phosphorylation state of the proteins. Therefore, we have examined the phosphorylation state of hepatocyte keratins from control and ethanol-fed rats. Feeding ethanol to rats results in dephosphorylation of one site on keratin 8 and one site on keratin 18 at all time points beginning with 6 weeks of ethanol treatment. Dephosphorylation was detected by phosphate analysis and by two-dimensional electrophoresis in which a change in isoelectric point of keratins from ethanol-fed rats was observed. These observations indicate that dephosphorylation of keratins in ethanol-fed animals may be an early step in alcoholic hepatitis which has occurred by 6 weeks of ethanol treatment. To further characterize keratin dephosphorylation in ethanol-fed rats, we used 31P NMR spectroscopy to classify the dephosphorylation site(s). Hepatocyte keratins were purified and solubilized in 9.5 M urea, 10 mM Tris-Cl, pH 8.1. 31P NMR spectra were obtained at 109 MHz, in 10 mm tubes at 30 degrees C. Samples of hepatocyte keratins were phosphorylated with A-kinase, protein kinase C, casein kinase II or Ca/CAM kinase and these samples were analyzed by 31P NMR spectroscopy. The resulting spectra were used as standards to compare the 31P chemical shifts of the resonances produced by these kinases with the phosphorus resonances of control and experimental samples. The 31P NMR spectrum of control hepatocyte keratins shows three resonances at 0.7, 4 and 5 ppm. In vitro phosphorylation by A-kinase produces a resonance at 4 ppm which is distinctly different from the resonance produced by each of the other kinases. In hepatocyte keratins from ethanol-fed animals, the resonance at 4 ppm was missing from the spectrum. These observations indicate that the keratin site that is dephosphorylated in ethanol-fed rats is characterized by the same 31P chemical shift as the keratin site that is phosphorylated by A-kinase.

Effect of ethanol treatment on indices of cumulative oxidative stress

The effect of ethanol exposure upon several parameters relating to oxidative stress has been examined in brain and liver. A single administration of either acetaldehyde or ethanol was able to enhance rates of generation of reactive oxygen species in liver but this effect was not apparent in the cerebral cortex. Glutamine synthetase is especially sensitive to inactivation by free radicals and evidence for cumulative oxidative damage to this enzyme was found in liver and to a lesser extent in cerebral cortex. This enzyme was depressed in liver after both a single injection of acetaldehyde or ethanol, or after more extended dosing. The liver was also more susceptible than cerebral cortex, to pro-oxidant effects as judged by depression of glutathione after acute dosing with either solvent. Enzyme inhibition representing temporally summated oxidative events may be a more sensitive procedure than direct measurement of rates of formation of active oxygen species and may find especially utility in the detection of prolonged low level pro-oxidant activity.

Chronic ethanol treatment of rats and the myocardial β-adrenoceptors

We examined the effect of chronic treatment with ethanol on the dynamics of beta-adrenoceptor binding in left ventricular myocardium of rats. After treatment with BAAM (20 mg/kg i.p.), an irreversible inhibitor of beta-adrenoceptors, the inhibition of beta-adrenoceptor binding was less, and the recovery of receptor binding was faster in chronically ethanol-treated rats compared to the control animals given equicaloric dextrin maltose treatment. When intracellular beta-adrenoceptor recycling was inhibited with colchicine, cytoplasmic left ventricular beta-adrenoceptor binding was greater in ethanol-treated compared to dextrin maltose-treated animals. We conclude that the previously reported decreased functional activity of the beta-adrenoceptor-mediated system probably reflects the contribution of ethanol-mediated effects not entirely restricted to the receptor-binding mechanisms.

Evolution of several cytoskeletal proteins of astrocytes in primary culture: effect of prenatal alcohol exposure

In the present work we have analyzed, using immunoblotting and immunofluorescence techniques, the evolution of several cytoskeletal proteins during the development of astrocytes in primary culture. The effect of prenatal exposure to alcohol on these proteins was also evaluated. Microtubular protein alpha-tubulin decreased approximately 47% from 4 to 7 days after which its content remained practically constant. Immunofluorescence studies showed also that the content of alpha-tubulin was greater at day 4 of culture. This increase in fluorescence was coincident with the presence of globular particles which were found in interphase astrocytes and stained with both anti alpha- and anti-beta tubulin. These structures appeared only in proliferating cells. Glial fibrillary acidic protein (GFAP) and vimentin were analyzed as intermediate filament (IF) proteins. GFAP, in cytoskeletal preparations, increased regularly for 14 days followed by a decrease to day 21. In contrast, vimentin showed a progressive increase throughout the entire culture period. Fluorescence studies revealed some differences between the IF distribution patterns of GFAP and vimentin. In astrocytes obtained from rats prenatally exposed to ethanol, decreases in the amounts of all the cytoskeletal proteins studied were found during the entire culture period. In these cells a striking disorganization of cytoskeleton was also observed. The alcohol-induced decrease of GFAP in cultured astrocytes was also found when this protein was studied in preparations from whole brain developed "in vivo".

Ethanol treatment induces a delayed segmentation anomaly in the chick embryo

A repeatable somite anomaly is described that results from the incubation of cultured chick embryos in the presence of ethanol. The anomaly comprises a misalignment of approximately five consecutive pairs of somites such that one of each pair is displaced cranially by up to one-half a somite length. The appearance of the malformation is delayed by approximately six somite pairs after the beginning of treatment. These characteristics were shared by embryos treated at the stage of gastrulation (no somites yet present) up to embryos possessing ten pairs of somites at treatment time. The deleterious effect did not appear to result from a disruption in the mechanics of the segmentation process itself, since isolated segmental plates were able to form normal intersomitic clefts in the presence of ethanol. Similarly, there were apparently no alterations in the compaction process that occurs at the cranial end of the segmental plate, since both the contractile and adhesive components were unaffected, as judged by the distributions of actin and fibronectin. The potential mechanisms of the anomaly are discussed with reference to similar segmental defects produced by heat shock. In view of earlier results indicating that cells in the primitive streak at gastrulation are sensitive to the presence of ethanol, it is proposed that this somite anomaly is due to a disruption in the contribution of these mesoderm cells to the segmental plate.

Evidence for nonrandom regression of dendrites of Purkinje neurons during aging

This study examined dendritic networks of Purkinje neurons for randomness of age-related changes in cerebella from Fischer 344 rats at three ages. Terminal dendritic segments were studied in relation to their distance from the neuronal soma (path length). The data indicated that the terminal dendritic segments furthest from the cell body were preferentially affected during aging and there was a redistribution of the remaining terminal segments in cells from rats of the intermediate age group. The data also suggested that dendritic regrowth occurred in proximal regions of networks from rats in the oldest group.

Interaction of intermediate filaments with nuclear lamina and cell periphery

Ultrastructural observations of the cytoskeleton suggest that the connection of the intermediate filaments (IFs) to actin microfilaments (MFs) at the plasma membrane and the nuclear lamina inside the nuclear membrane link signals received at the cell periphery to the nucleus. When these connections are viewed in three dimensions using detergent extracted cytoskeletal preparations from tissue cultures or slices made from tissue, the IFs are seen to run without interruption from the cell periphery to the nucleus and back. The IFs form side to side connections with the nuclear lamina and pore complexes. The nucleus and the centrioles are supported and held suspended in these extracted cells where all organelles and cytosol have been removed. The IFs are particularly dense in the ectoplasm where they form a sheet and provide the scaffolding which maintains the shape of the extracted cells. The IFs in the ectoplasm are attached to desmoplakin at cell-cell desmosome adhesions and to MFs where the cells are attached to the fibronectin substratum possibly through integrin linkages at adhesion plaques. This was graphically shown by immunogold labelling of IF cells treated with nickel. In this way, it was possible to visualize the loss of the cell-cell connections at desmosomes and the disruption of the IF-MF connections in the ectoplasm. The MFs after losing their connections with the IFs, redistribute to cover the entire cell periphery. The nickel treatment of primary liver cell cultures lead to the loss of several functions including formation of the bile canaliculus, the ability to secrete fluorescein diacetate and the ability to take up horseradish peroxidase (HRP) by endocytosis. These observations support the conclusion that the IF-MF connections at the cell periphery provide both structural and functional polarity of the liver cells including uptake and secretion and the formation of bile canaliculi.

A cytokeratin immunohistochemical study of alcoholic liver disease: evidence that hepatocytes can express 'bile duct-type' cytokeratins

A cytokeratin immunohistochemical study was performed on 40 liver biopsies diagnosed as alcoholic liver disease to further investigate the cytoskeletal changes occurring in this disease. On paraffin sections of 29 cases, a variable number of hepatocytes were reactive with a polyclonal antiserum that normally stains only bile ducts. Using monoclonal antibodies specific for a single cytokeratin polypeptide on cryostat sections, a variable number of hepatocytes were immunoreactive for cytokeratin no. 7 in 23 cases and also for cytokeratin no. 19 in seven cases. Both these polypeptides are restricted to bile duct cells in the normal liver. The number of hepatocytes positive for bile duct-type cytokeratins increased and their location changed with the severity of the disease. Mallory bodies were reactive with monoclonal antibodies CAM 5.2 and anti-cytokeratin no. 18 but unreactive with anti-cytokeratin no. 8. except in one case. In two cases, Mallory bodies reactive with both monoclonal antibodies anti-cytokeratin no. 7 and anti-cytokeratin no. 19 were found. These results clearly indicate that hepatocytes in alcoholic liver disease can express immunoreactivity for bile duct-type cytokeratins. Our data also demonstrate heterogeneity in the composition of Mallory bodies. Whether hepatocytes expressing bile duct-type cytokeratins are the precursors of Mallory body-containing cells is not clear at present.

Selective rearrangement of cytokeratin filaments in cultured liver epithelial cells induced by nickel

Rearrangements of intermediate filaments (IFs) in the liver cells involve cytokeratins, i.e., Mallory body formation. However, rearrangements of IFs observed in cell culture characteristically involve vimentin or both vimentin and cytokeratin. We report here that nickel treatment of a liver epithelial cell line (T51B) in vitro selectively induced cytokeratin filaments to accumulate in a juxtanuclear location as the cells rounded up. After withdrawal of nickel from the culture medium, vimentin filaments remained attached to the cell periphery as the cells spread out again, but the cytokeratin filaments remained aggregated in a perinuclear position without reestablishing all peripheral connections. Thus, the rearrangement of cytokeratin filaments involved partial loss of the peripheral attachments in this model.