Alcohol, phospholipase A2-associated neuroinflammation, and ω3 docosahexaenoic acid protection

Glymphatic system: a gateway for neuroinflammation

The glymphatic system is a relatively recently identified fluid exchange and transport system in the brain. Accumulating evidence indicates that glymphatic function is impaired not only in central nervous system disorders but also in systemic diseases. Systemic diseases can trigger the inflammatory responses in the central nervous system, occasionally leading to sustained inflammation and functional disturbance of the central nervous system. This review summarizes the current knowledge on the association between glymphatic dysfunction and central nervous system inflammation. In addition, we discuss the hypothesis that disease conditions initially associated with peripheral inflammation overwhelm the performance of the glymphatic system, thereby triggering central nervous system dysfunction, chronic neuroinflammation, and neurodegeneration. Future research investigating the role of the glymphatic system in neuroinflammation may offer innovative therapeutic approaches for central nervous system disorders.

Novel insight into the lipid network of plasma extracellular vesicles reveal sex-based differences in the lipidomic profile of alcohol use disorder patients

BACKGROUND

Alcohol use disorder (AUD) is one of the most common psychiatric disorders, with the consumption of alcohol considered a leading cause of preventable deaths worldwide. Lipids play a crucial functional role in cell membranes; however, we know little about the role of lipids in extracellular vesicles (EVs) as regulatory molecules and disease biomarkers.

METHODS

We employed a sensitive lipidomic strategy to characterize lipid species from the plasma EVs of AUD patients to evaluate functional roles and enzymatic activity networks to improve the knowledge of lipid metabolism after alcohol consumption. We analyzed plasma EV lipids from AUD females and males and healthy individuals to highlight lipids with differential abundance and biologically interpreted lipidomics data using LINEX2, which evaluates enzymatic dysregulation using an enrichment algorithm.

RESULTS

Our results show, for the first time, that AUD females exhibited more significant substrate-product changes in lysophosphatidylcholine/phosphatidylcholine lipids and phospholipase/acyltransferase activity, which are potentially linked to cancer progression and neuroinflammation. Conversely, AUD males suffer from dysregulated ceramide and sphingomyelin lipids involving sphingomyelinase, sphingomyelin phosphodiesterase, and sphingomyelin synthase activity, which relates to hepatotoxicity. Notably, the analysis of plasma EVs from AUD females and males demonstrates enrichment of lipid ontology terms associated with "negative intrinsic curvature" and "positive intrinsic curvature", respectively.

CONCLUSIONS

Our methodological developments support an improved understanding of lipid metabolism and regulatory mechanisms, which contribute to the identification of novel lipid targets and the discovery of sex-specific clinical biomarkers in AUD.

Differential rescue effects of choline chloride and soy isolate on metabolic dysfunction in immature central nervous system neurons: Relevance to fetal alcohol spectrum disorder

Background

Central Nervous System (CNS) abnormalities with insulin resistance and mediated by developmental exposures to ethanol can be avoided or remediated by consumption of dietary soy, which has insulin-sensitizing as well as antioxidant effects. However, choline supplementation has been shown to diminish Fetal Alcohol Spectrum Disorder (FASD) pathologies, and dietary soy contains abundant choline. This study was designed to determine if the therapeutic effects of soy were mediated by or independent of choline.

Methods

Human PNET2 cells exposed to 0 mM or 100 mM ethanol for 48 hours were seeded into 96-well or 12-well plates and treated with vehicle, choline chloride (75 μM), or 1 μM Daidzein+1 μM Genistein (D+G) for 24 h. The cells were then analyzed for viability (Hoechst 33342), mitochondrial function (MTT), and GAPDH, Tau, Acetyl Cholinesterase (AChE), Choline Acetyl Transferase (ChAT), and Aspartyl-Asparaginyl-β-Hydroxylase (ASPH) immunoreactivity.

Results

Choline and D+G significantly increased MTT activity (mitochondrial function) corrected for cell number relative to vehicle in control and ethanol-exposed cultures. Both choline and D+G prevented the ethanol-induced inhibition of GAPDH and ChAT and increased cellular accumulations of Tau. However, D+G significantly increased ASPH expression relative to vehicle and Choline.

Conclusion

Choline and D+G differentially modulated the expression of neuronal proteins, mitochondrial function, and ASPH. Importantly, the prominently increased expression of ASPH by D+G corresponds with the insulin-sensitizer actions of soy isoflavones since ASPH is an insulin-responsive molecule. The findings further suggest that dietary soy may be more effective than choline for reducing ethanol-impaired neuronal migration linked to ASPH inhibition in FASD.

Differential Early Mechanistic Frontal Lobe Responses to Choline Chloride and Soy Isoflavones in an Experimental Model of Fetal Alcohol Spectrum Disorder

Fetal alcohol spectrum disorder (FASD) is the most common preventable cause of neurodevelopmental defects, and white matter is a major target of ethanol neurotoxicity. Therapeutic interventions with choline or dietary soy could potentially supplement public health preventive measures. However, since soy contains abundant choline, it would be important to know if its benefits are mediated by choline or isoflavones. We compared early mechanistic responses to choline and the Daidzein+Genistein (D+G) soy isoflavones in an FASD model using frontal lobe tissue to assess oligodendrocyte function and Akt-mTOR signaling. Long Evans rat pups were binge administered 2 g/Kg of ethanol or saline (control) on postnatal days P3 and P5. P7 frontal lobe slice cultures were treated with vehicle (Veh), Choline chloride (Chol; 75 µM), or D+G (1 µM each) for 72 h without further ethanol exposures. The expression levels of myelin oligodendrocyte proteins and stress-related molecules were measured by duplex enzyme-linked immunosorbent assays (ELISAs), and mTOR signaling proteins and phosphoproteins were assessed using 11-plex magnetic bead-based ELISAs. Ethanol's main short-term effects in Veh-treated cultures were to increase GFAP and relative PTEN phosphorylation and reduce Akt phosphorylation. Chol and D+G significantly modulated the expression of oligodendrocyte myelin proteins and mediators of insulin/IGF-1-Akt-mTOR signaling in both control and ethanol-exposed cultures. In general, the responses were more robust with D+G; the main exception was that RPS6 phosphorylation was significantly increased by Chol and not D+G. The findings suggest that dietary soy, with the benefits of providing complete nutrition together with Choline, could be used to help optimize neurodevelopment in humans at risk for FASD.

Sexually dimorphic organization of open field behavior following moderate prenatal alcohol exposure

BACKGROUND

Prenatal alcohol exposure (PAE) can produce deficits in a wide range of cognitive functions but is especially detrimental to behaviors requiring accurate spatial information processing. In open field environments, spatial behavior is organized such that animals establish "home bases" marked by long stops focused around one location. Progressions away from the home base are circuitous and slow, while progressions directed toward the home base are non-circuitous and fast. The impact of PAE on the organization of open field behavior has not been experimentally investigated.

METHODS

In the present study, adult female and male rats with moderate PAE or saccharin exposure locomoted a circular high walled open field for 30 minutes under lighted conditions.

RESULTS

The findings indicate that PAE and sex influence the organization of open field behavior. Consistent with previous literature, PAE rats exhibited greater locomotion in the open field. Novel findings from the current study indicate that PAE and sex also impact open field measures specific to spatial orientation. While all rats established a home base on the periphery of the open field, PAE rats, particularly males, exhibited significantly less clustered home base stopping with smaller changes in heading between stops. PAE also impaired progression measures specific to distance estimation, while sex alone impacted progression measures specific to direction estimation.

CONCLUSIONS

These findings support the conclusion that adult male rats have an increased susceptibility to the effects of PAE on the organization of open field behavior.

Drinking and smoking polygenic risk is associated with childhood and early-adulthood psychiatric and behavioral traits independently of substance use and psychiatric genetic risk

Alcohol drinking and tobacco smoking are hazardous behaviors associated with a wide range of adverse health outcomes. In this study, we explored the association of polygenic risk scores (PRS) related to drinks per week, age of smoking initiation, smoking initiation, cigarettes per day, and smoking cessation with 433 psychiatric and behavioral traits in 4498 children and young adults (aged 8-21) of European ancestry from the Philadelphia neurodevelopmental cohort. After applying a false discovery rate multiple testing correction accounting for the number of PRS and traits tested, we identified 36 associations related to psychotic symptoms, emotion and age recognition social competencies, verbal reasoning, anxiety-related traits, parents' education, and substance use. These associations were independent of the genetic correlations among the alcohol-drinking and tobacco-smoking traits and those with cognitive performance, educational attainment, risk-taking behaviors, and psychopathology. The removal of participants endorsing substance use did not affect the associations of each PRS with psychiatric and behavioral traits identified as significant in the discovery analyses. Gene-ontology enrichment analyses identified several neurobiological processes underlying mechanisms of the PRS associations we report. In conclusion, we provide novel insights into the genetic overlap of smoking and drinking behaviors in children and young adults, highlighting their independence from psychopathology and substance use.

PARPs in lipid metabolism and related diseases

PARPs and tankyrases (TNKS) represent a family of 17 proteins. PARPs and tankyrases were originally identified as DNA repair factors, nevertheless, recent advances have shed light on their role in lipid metabolism. To date, PARP1, PARP2, PARP3, tankyrases, PARP9, PARP10, PARP14 were reported to have multi-pronged connections to lipid metabolism. The activity of PARP enzymes is fine-tuned by a set of cholesterol-based compounds as oxidized cholesterol derivatives, steroid hormones or bile acids. In turn, PARPs modulate several key processes of lipid homeostasis (lipotoxicity, fatty acid and steroid biosynthesis, lipoprotein homeostasis, fatty acid oxidation, etc.). PARPs are also cofactors of lipid-responsive nuclear receptors and transcription factors through which PARPs regulate lipid metabolism and lipid homeostasis. PARP activation often represents a disruptive signal to (lipid) metabolism, and PARP-dependent changes to lipid metabolism have pathophysiological role in the development of hyperlipidemia, obesity, alcoholic and non-alcoholic fatty liver disease, type II diabetes and its complications, atherosclerosis, cardiovascular aging and skin pathologies, just to name a few. In this synopsis we will review the evidence supporting the beneficial effects of pharmacological PARP inhibitors in these diseases/pathologies and propose repurposing PARP inhibitors already available for the treatment of various malignancies.

Modulation of Poly ADP Ribose Polymerase (PARP) Levels and Activity by Alcohol Binge-Like Drinking in Male Mice

Binge drinking is a frequent pattern of ethanol consumption within Alcohol Use Disorders (AUDs). Binge-like ethanol exposure increases Poly(ADP-ribose) polymerase (PARP) expression and activity. PARP enzymes have been implicated in addiction and serve multiple roles in the cell, including gene expression regulation. In this study, we examined the effects of binge-like alcohol consumption in the prefrontal cortex (PFC) of adult C57BL/6J male mice via a 4-day Drinking-in-the-Dark (DID) paradigm. The role of PARP in associated gene expression and behavioral changes was assessed by administering the PARP inhibitor ABT-888 on the last DID day. We then conducted an RNA-seq analysis of the PFC gene expression changes associated with DID-consumed ethanol or ABT-888 treatment. A separate cohort of mice was inoculated with an HSV-PARP1 vector in the PFC and subject to a DID experiment to verify whether overexpressed PARP1 increased ethanol drinking. We confirmed that alcohol increases Parp1 gene expression and PARP activity in the PFC. RNA-seq showed significantly altered expression of 41 genes by DID-consumed ethanol, and of 48 genes by ABT-888. These results were confirmed by qPCR in 7 of the 10 genes validated, 4 of which have been previously associated with addiction. ABT-888 reduced, and overexpression of PFC PARP1 increased DID ethanol consumption. In our model, alcohol binge drinking induced specific alterations in the PFC expression of genes potentially involved in addiction. Pharmacological PARP inhibition proved effective in reversing these changes and preventing further alcohol consumption. Our results suggest an involvement of ethanol-induced PARP1 in reinforcing binge-like addictive behavior.

Its complicated: The relationship between alcohol and microglia in the search for novel pharmacotherapeutic targets for alcohol use disorders

Alcohol use disorder (AUD) is a chronic relapsing disorder with wide-ranging health consequences. Alcohol targets the central nervous system producing neurodegeneration and subsequent cognitive and behavioral deficits, but the mechanisms behind these effects remain unclear. Recently, evidence has been mounting for the role of neuroimmune activation in the pathogenesis of AUDs, but our nascent state of knowledge about the interaction of alcohol with the neuroimmune system supports that the relationship is complicated. As the resident macrophage of the central nervous system, microglia are a central focus. Human and animal research on the interplay between microglia and alcohol in AUDs has proven to be complex, and though early research focused on a pro-inflammatory phenotype of microglia, the anti-inflammatory and homeostatic roles of microglia must be considered. How these new roles for microglia should be incorporated into our thinking about the neuroimmune system in AUDs is discussed in the context of developing novel pharmacotherapies for AUDs.

PARP inhibition in vivo blocks alcohol-induced brain neurodegeneration and neuroinflammatory cytosolic phospholipase A2 elevations

Chronic alcoholism promotes brain damage that impairs memory and cognition. High binge alcohol levels in adult rats also cause substantial neurodamage to memory-linked regions, notably, the hippocampus (HC) and entorhinal cortex (ECX). Concurrent with neurodegeneration, alcohol elevates poly (ADP-ribose) polymerase-1 (PARP-1) and cytosolic phospholipase A2 (cPLA2) levels. PARP-1 triggers necrosis when excessively activated, while cPLA2 liberates neuroinflammatory ω-6 arachidonic acid. Inhibitors of PARP exert in vitro neuroprotection while suppressing cPLA2 elevations in alcohol-treated HC-ECX slice cultures. Here, we examined in vivo neuroprotection and cPLA2 suppression by the PARP inhibitor, veliparib, in a recognized adult rat model of alcohol-binging. Adult male rats received Vanilla Ensure containing alcohol (ethanol, 7.1 ± 0.3 g/kg/day), or control (dextrose) ± veliparib (25 mg/kg/day), by gavage 3x daily for 4 days. Rats were sacrificed on the morning after the final binge. HC and ECX neurodegeneration was assessed in fixed sections by Fluoro-Jade B (FJB) staining. Dorsal HC, ventral HC, and ECX cPLA2 levels were quantified by immunoblotting. Like other studies using this model, alcohol binges elevated FJB staining in the HC (dentate gyrus) and ECX, indicating neurodegeneration. Veliparib co-treatment significantly reduced dentate gyrus and ECX neurodegeneration by 79% and 66%, respectively. Alcohol binges increased cPLA2 in the ventral HC by 34% and ECX by 72%, which veliparib co-treatment largely prevented. Dorsal HC cPLA2 levels remained unaffected by alcohol binges, consistent with negligible FJB staining in this brain region. These in vivo results support an emerging key role for PARP in binge alcohol-induced neurodegeneration and cPLA2-related neuroinflammation.

Yin-Yang Mechanisms Regulating Lipid Peroxidation of Docosahexaenoic Acid and Arachidonic Acid in the Central Nervous System

Phospholipids in the central nervous system (CNS) are rich in polyunsaturated fatty acids (PUFAs), particularly arachidonic acid (ARA) and docosahexaenoic acid (DHA). Besides providing physical properties to cell membranes, these PUFAs are metabolically active and undergo turnover through the “deacylation-reacylation (Land's) cycle”. Recent studies suggest a Yin-Yang mechanism for metabolism of ARA and DHA, largely due to different phospholipases A₂ (PLA₂s) mediating their release. ARA and DHA are substrates of cyclooxygenases and lipoxygenases resulting in an array of lipid mediators, which are pro-inflammatory and pro-resolving. The PUFAs are susceptible to peroxidation by oxygen free radicals, resulting in the production of 4-hydroxynonenal (4-HNE) from ARA and 4-hydroxyhexenal (4-HHE) from DHA. These alkenal electrophiles are reactive and capable of forming adducts with proteins, phospholipids and nucleic acids. The perceived cytotoxic and hormetic effects of these hydroxyl-alkenals have impacted cell signaling pathways, glucose metabolism and mitochondrial functions in chronic and inflammatory diseases. Due to the high levels of DHA and ARA in brain phospholipids, this review is aimed at providing information on the Yin-Yang mechanisms for regulating these PUFAs and their lipid peroxidation products in the CNS, and implications of their roles in neurological disorders.

Therapeutic potential of PACAP in alcohol toxicity

Alcohol addiction is a worldwide concern as its detrimental effects go far beyond the addicted individual and can affect the entire family as well as the community. Considerable effort is being expended in understanding the neurobiological basis of such addiction in hope of developing effective prevention and/or intervention strategies. In addition, organ damage and neurotoxicological effects of alcohol are intensely investigated. Pharmacological approaches, so far, have only provided partial success in prevention or treatment of alcohol use disorder (AUD) including the neurotoxicological consequences of heavy drinking. Pituitary adenylate cyclase-activating polypeptide (PACAP) is an endogenous 38 amino-acid neuropeptide with demonstrated protection against neuronal injury, trauma as well as various endogenous and exogenous toxic agents including alcohol. In this mini-review, following a brief presentation of alcohol addiction and its neurotoxicity, the potential of PACAP as a therapeutic intervention in toxicological consequences of this devastating disorder is discussed.

Oleoylethanolamide prevents neuroimmune HMGB1/TLR4/NF-kB danger signaling in rat frontal cortex and depressive-like behavior induced by ethanol binge administration

Alcohol abuse is frequently characterized by a specific pattern of intake in binge drinking episodes, inducing neuroinflammation and brain damage. Here, we characterized the temporal profile of neuroinflammation in rats exposed to intragastric binge ethanol administrations (3 times/day × 4 days) and tested the anti-inflammatory/neuroprotective properties of the satiety factor oleoylethanolamide (OEA). Pre-treatment with OEA (5 mg/kg, i.p.) previous each alcohol gavage blocked the expression of high mobility group box 1 (HMGB1) danger signal and the innate immunity Toll-like receptors 4 (TLR4) in frontal cortex, and inhibited the nuclear factor-kappa B (NF-kB) proinflammatory cascade induced by alcohol binge administration. OEA reduced the levels of interleukin-1beta (IL-1β), the monocyte chemoattractant protein-1 (MCP-1), and the enzymes cyclooxygenase-2 (COX-2) and inducible nitric oxide synthase (iNOS) in ethanol binged animals. Elevations in plasma tumor necrosis factor alpha (TNF-α) and IL-1β after ethanol were also inhibited by OEA. OEA also prevented ethanol-induced lipid peroxidation, caspase-8 and pro-apoptotic caspase-3 activation in frontal cortex. Additionally, OEA blocked the rise in blood corticosterone levels after ethanol with no alteration in blood ethanol levels and may affect ethanol-induced gut permeability for endotoxin. Finally, OEA, administered as a pre-treatment during the ethanol binge, exerted antidepressant-like effects during acute withdrawal. Altogether, results highlight a beneficial profile of OEA as a potent anti-inflammatory, antioxidant, neuroprotective and antidepressant-like compound to treat alcohol abuse.

Differential Sphingolipid and Phospholipid Profiles in Alcohol and Nicotine-Derived Nitrosamine Ketone-Associated White Matter Degeneration

BACKGROUND

Alcohol-mediated neurodegeneration is associated with white matter (WM) atrophy due to targeting of myelin and oligodendrocytes. However, variability in disease severity suggests cofactors contribute to WM degeneration. We examined the potential cofactor role of the tobacco-specific nitrosamine, nicotine-derived nitrosamine ketone (NNK), because smoking causes WM atrophy and most heavy drinkers consume tobacco products.

METHODS

This 8-week study of Long Evans rats had 4 treatment groups: control; NNK-2 mg/kg, 3×/wk in weeks 3 to 8; ethanol (EtOH) (chronic-26% caloric + binge-2 g/kg, 3×/wk in weeks 7 to 8); and EtOH + NNK. Exposure effects on WM lipid biochemical profiles and in situ distributions were examined using matrix-assisted laser desorption/ionization imaging mass spectrometry and tandem mass spectrometry.

RESULTS

NNK mainly caused WM fiber degeneration and fiber loss, EtOH caused demyelination, and dual exposures had additive effects. EtOH and EtOH + NNK decreased WM (including corpus callosum) and/or gray matter (hypothalamus, cortex, medial temporal) levels of several phosphatidylserine, phosphatidylinositol, and sphingolipid (sulfatide [ST]) species, while NNK increased or had minimal effect on these lipids. EtOH + NNK had broader and larger inhibitory effects on phospholipids and ST than EtOH or NNK alone. Principal component analysis clustered control with NNK, and EtOH with EtOH + NNK groups, highlighting the independent EtOH- rather than NNK-driven responses.

CONCLUSIONS

Chronic EtOH exposures decreased several phospholipid and sphingolipid species in brain, while concomitant NNK exposures exacerbated these effects. These findings support our hypothesis that tobacco smoking is a pathogenic cofactor in alcohol-mediated WM degeneration.

Ethanol Induced Brain Lipid Changes in Mice Assessed by Mass Spectrometry

Alcohol abuse is a chronic disease characterized by the consumption of alcohol at a level that interferes with physical and mental health and causes serious and persistent changes in the brain. Lipid metabolism is of particular interest due to its high concentration in the brain. Lipids are the main component of cell membranes, are involved in cell signaling, signal transduction, and energy storage. In this study, we analyzed lipid composition of chronically ethanol exposed mouse brains. Juvenile (JUV) and adult (ADU) mice were placed on a daily limited-access ethanol intake model for 52 days. After euthanasia, brains were harvested, and total lipids were extracted from brain homogenates. Samples were analyzed using high resolution mass spectrometry and processed by multivariate and univariate statistical analysis. Significant lipid changes were observed in different classes including sphingolipids, fatty acids, lysophosphatidylcholines, and other glycerophospholipids.

Ethanol-induced changes in poly (ADP ribose) polymerase and neuronal developmental gene expression

Prenatal alcohol exposure has profound effects on neuronal growth and development. Poly-ADP Ribose Polymerase (PARP) enzymes are perhaps unique in the field of epigenetics in that they directly participate in histone modifications, transcription factor modifications, DNA methylation/demethylation and are highly inducible by ethanol. It was our hypothesis that ethanol would induce PARP enzymatic activity leading to alterations in neurodevelopmental gene expression. Mouse E18 cortical neurons were treated with ethanol, PARP inhibitors, and nuclear hormone receptor transcription factor PPARγ agonists and antagonists. Subsequently, we measured PARP activity and changes in Bdnf, OKSM (Oct4, Klf4, Sox2, c-Myc), DNA methylating/demethylating factors, and Pparγ mRNA expression, promoter 5-methylcytosine (5MC) and 5-hydroxymethylcytosine (5HMC), and PPARγ promoter binding. We found that ethanol reduced Bdnf4, 9a, and Klf4 mRNA expression, and increased c-Myc expression. These changes were reversed with a PARP inhibitor. In agreement with its role in DNA demethylation PARP inhibition increased 5MC levels at the c-Myc promoter. In addition, we found that inhibition of PARP enzymatic activity increased PPARγ promoter binding, and this corresponded to increased Bdnf and Klf4 mRNA expression. Our results suggest that PARP participates in DNA demethylation and reduces PPARγ promoter binding. The current study underscores the importance of PARP in ethanol-induced changes to neurodevelopmental gene expression.

Cigarette Smoke-Induced Alterations in Frontal White Matter Lipid Profiles Demonstrated by MALDI-Imaging Mass Spectrometry: Relevance to Alzheimer's Disease

BACKGROUND

Meta-analysis has shown that smokers have significantly increased risks for Alzheimer's disease (AD), and neuroimaging studies showed that smoking alters white matter (WM) structural integrity.

OBJECTIVE

Herein, we characterize the effects of cigarette smoke (CS) exposures and withdrawal on WM myelin lipid composition using matrix assisted laser desorption and ionization-imaging mass spectrometry (MALDI-IMS).

METHODS

Young adult male A/J mice were exposed to air (8 weeks; A8), CS (4 or 8 weeks; CS4, CS8), or CS8 followed by 2 weeks recovery (CS8 + R). Frontal lobe WM was examined for indices of lipid and protein oxidation and lipid profile alterations by MALDI-IMS. Lipid ions were identified by MS/MS with the LIPID MAPS prediction tools database. Inter-group comparisons were made using principal component analysis and R-generated heatmap.

RESULTS

CS increased lipid and protein adducts such that higher levels were present in CS8 compared with CS4 samples. CS8 + R reversed CS8 effects and normalized the levels of oxidative stress. MALDI-IMS demonstrated striking CS-associated alterations in WM lipid profiles characterized by either reductions or increases in phospholipids (phosphatidylinositol, phosphatidylserine, phosphatidylcholine, or phosphatidylethanolamine) and sphingolipids (sulfatides), and partial reversal of CS's inhibitory effects with recovery. The heatmap hierarchical dendrogram and PCA distinguished CS exposure, duration, and withdrawal effects on WM lipid profiles.

CONCLUSION

CS-mediated WM degeneration is associated with lipid peroxidation, protein oxidative injury, and alterations in myelin lipid composition, including shifts in phospholipids and sphingolipids needed for membrane integrity, plasticity, and intracellular signaling. Future goals are to delineate WM abnormalities in AD using MALDI-IMS, and couple the findings with MRI-mass spectroscopy to improve in vivo diagnostics and early detection of brain biochemical responses to treatment.

Adolescent Intermittent Alcohol Exposure: Dysregulation of Thrombospondins and Synapse Formation are Associated with Decreased Neuronal Density in the Adult Hippocampus

BACKGROUND

Adolescent intermittent alcohol exposure (AIE) has profound effects on neuronal function. We have previously shown that AIE causes aberrant hippocampal structure and function that persists into adulthood. However, the possible contributions of astrocytes and their signaling factors remain largely unexplored. We investigated the acute and enduring effects of AIE on astrocytic reactivity and signaling on synaptic expression in the hippocampus, including the impact of the thrombospondin (TSP) family of astrocyte-secreted synaptogenic factors and their neuronal receptor, alpha2delta-1 (α2δ-1). Our hypothesis is that some of the influences of AIE on neuronal function may be secondary to direct effects on astrocytes.

METHODS

We conducted Western blot analysis on TSPs 1 to 4 and α2δ-1 from whole hippocampal lysates 24 hours after the 4th and 10th doses of AIE, then 24 days after the last dose (in adulthood). We used immunohistochemistry to assess astrocyte reactivity (i.e., morphology) and synaptogenesis (i.e., colocalization of pre- and postsynaptic puncta).

RESULTS

Adolescent AIE reduced α2δ-1 expression, and colocalized pre- and postsynaptic puncta after the fourth ethanol (EtOH) dose. By the 10th dose, increased TSP2 levels were accompanied by an increase in colocalized pre- and postsynaptic puncta, while α2δ-1 returned to control levels. Twenty-four days after the last EtOH dose (i.e., adulthood), TSP2, TSP4, and α2δ-1 expression were all elevated. Astrocyte reactivity, indicated by increased astrocytic volume and area, was also observed at that time.

CONCLUSIONS

Repeated EtOH exposure during adolescence results in long-term changes in specific astrocyte signaling proteins and their neuronal synaptogenic receptor. Continued signaling by these traditionally developmental factors in adulthood may represent a compensatory mechanism whereby astrocytes reopen the synaptogenic window and repair lost connectivity, and consequently contribute to the enduring maladaptive structural and functional abnormalities previously observed in the hippocampus after AIE.