Deficient PKR in RAX/PKR Association Ameliorates Ethanol-Induced Neurotoxicity in the Developing Cerebellum

Photobiomodulation using an 830-nm laser alleviates hippocampal reactive gliosis and cognitive dysfunction in a mouse model of adolescent chronic alcohol exposure

Chronic alcoholism is known to have detrimental effects on the brain, including cognitive impairment, neurotransmitter imbalances, and brain atrophy. The hippocampus, crucial for spatial memory and cognitive functions, is particularly susceptible to alcohol-induced changes. Photobiomodulation (PBM), a non-invasive therapeutic method that utilizes red or near-infrared light, has shown promising applications in the central and peripheral nervous systems. Near-infrared (NIR) light, in particular, has been shown to prevent apoptosis, and neuroinflammation, as well as to improve cognitive functions. In this study, we aimed to investigate whether 830-nm laser irradiation could mitigate cognitive deficits in a chronic alcohol mouse model. Chronic alcoholism was induced in C57BL/6 mice through continuous ethanol gavage for 4 weeks at a dosage of 5 g/kg/day. Gavaging was performed 3 times per week for 4 weeks. Mice were transcranial irradiated by 830-nm laser, following making a chronic alcohol mouse model. Laser irradiation (50 mW/cm2) was performed 5 times per week for 3 weeks. To verify memory and cognitive defeats of a chronic alcohol mouse model, we performed animal behavior tasks such as Morris water maze, Y maze, and novel objective recognition. Our results confirmed the cognitive impairment in the chronic alcohol mouse model compared to the control group in conducted tasks. However, cognitive and spatial memory significantly improved following 830-nm laser irradiation. Additionally, we confirmed whether the behavior tasks result from histological changes. We performed immunofluorescence staining in the hippocampus region (CA3, CA1 and hilus) using astrocyte (GFAP) and microglia (Iba1) markers. As a result, reactive astrocyte was significantly increased in the chronic alcohol mouse model compared to control mice, whereas the number of GFAP-positive cells was significantly reduced by 830-nm laser irradiation. These findings indicate that chronic alcohol exposure induces spatial memory and cognitive impairment, which can be effectively rescued through near-infrared laser irradiation.

Recent breakthroughs in understanding the cerebellum's role in fetal alcohol spectrum disorder: A systematic review

Exposure to alcohol during fetal development can lead to structural and functional abnormalities in the cerebellum, a brain region responsible for motor coordination, balance, and specific cognitive functions. In this systematic review, we comprehensively analyze a vast body of research conducted on vertebrate animals and humans over the past 13 years. We identified studies through PubMed and screened them following PRISMA guidelines. Data extraction and quality analysis were conducted using Covidence systematic review software. A total of 108 studies met our inclusion criteria, with the majority (79 studies) involving vertebrate animal models and 29 studies focusing on human subjects. Animal models included zebrafish, mice, rats, sheep, and non-human primates, investigating the impact of ethanol on cerebellar structure, gene/protein expression, physiology, and cerebellar-dependent behaviors. Additionally, some animal studies explored potential therapeutic interventions against ethanol-induced cerebellar damage. The human studies predominantly adopted cohort designs, exploring the effects of prenatal alcohol exposure on cerebellar structure and function. Certain human studies delved into innovative cerebellar-based diagnostic approaches for fetal alcohol spectrum disorder (FASD). The collective findings from these studies clearly indicate that the cerebellum is involved in various neurophysiological deficits associated with FASD, emphasizing the importance of evaluating both cerebellar structure and function in the diagnostic process for this condition. Moreover, this review sheds light into potential therapeutic strategies that can mitigate prenatal alcohol exposure-induced cerebellar damage.

Assessment of Ethanol Exposure from Hand Sanitizer Use and Potential for Developmental Toxicity in Nursing Infants

Ingestion of ethanol during pregnancy is known to have detrimental effects on the fetus. Although the potential developmental effects of maternal ethanol intake during lactation are less well characterized, public health guidelines recommend avoidance of alcohol or, if alcohol is consumed, to allow for 1–2 h to pass before nursing. A proposal to classify ethanol as potentially harmful to breast‐fed children warrants an investigation of the potential adverse neurodevelopmental effects of low‐dose ethanol exposure during lactation. There currently are no studies that have examined neurodevelopmental outcomes from lactational exposure to ethanol from the use of topical products that contain ethanol, such as alcohol‐based hand sanitizers (ABHS). Furthermore, the epidemiological literature of lactational ethanol exposures from maternal alcohol consumption is limited in design, provides equivocal evidence of neurological effects in infants, and is insufficient to characterize a dose–response relationship for developmental effects. Toxicological studies that observed neurodevelopmental effects in pups from ethanol via lactation did so at exceedingly high doses that also caused maternal toxicity. In this investigation, blood ethanol concentrations (BECs) of breastfeeding women following typical‐to‐intense ABHS use were computationally predicted and compared to health benchmarks to quantify the risk for developmental outcomes. Margins of 2.2 to 1000 exist between BECs associated with ABHS use compared to BECs associated with neurotoxicity adverse effect levels in the toxicology literature or oral ethanol intake per public health guidelines. Neurodevelopmental effects are not likely to occur in infants due to ABHS use by breastfeeding women, even when ABHSs are used at intense frequencies.

Adverse neurodevelopmental effects of ethanol exposure are supported by toxicological studies; ethanol as a potential “lactation hazard” needs evaluation. A lactation hazard may not be applicable for all ethanol‐containing products, such as hand sanitizers. Furthermore, internal dose assessments of hand sanitizer use are lacking. Computationally modeled blood ethanol concentrations following hand sanitizer use are lower than concentrations associated with toxicological and guideline benchmarks. Therefore, there is low potential for the use of ethanol‐containing hand sanitizers to be a lactation hazard.

Resveratrol inhibits neural apoptosis and regulates RAX/P-PKR expression in retina of diabetic rats

PURPOSE

This study was to investigate the effect of resveratrol (RSV) administration on diabetes-induced neural apoptosis and on RNA-dependent-protein-kinase (PKR)-associated protein X (RAX), PKR and phosphorylated PKR (P-PKR) expression and distribution in retina of diabetic rats.

METHODS

Retina was obtained from normal and diabetic Sprague-Dawley rats with or without RSV (5 and 10 mg/kg/d) treatment at 30-, 32-, 34- and 36-weeks. Apoptosis of retinal neural cells and distribution of RAX/P-PKR was assessed by TUNEL and immunofluorescence methods. Expression of RAX, PKR and P-PKR was evaluated by qRT-PCR and western-blotting methods.

RESULTS

Our study showed that the TUNEL-positive cells were mainly localized in ganglion cells layer (GCL), inner nuclear layer (INL) and outer nuclear layer (ONL) of the diabetic rat's retina at 30-, 32-, 34- and 36-weeks. RSV administration effectively suppressed the neural apoptosis in GCL, INL and ONL. Almost no TUNEL-positive cells were observed in retina of normal control and RSV-treated normal control rats. Our study also showed that the expression level of RAX, P-PKR in diabetic rats retina at 30-, 32-, 34-, and 36-weeks was elevated. With supplementation of 5 and 10 mg/kg/d RSV, the expression level of RAX and P-PKR was decreased (P < 0.05). The expression level of RAX and P-PKR in the retina of normal control rats was not altered by RSV. The expression level of PKR was not altered by streptozotocin injection and RSV treatment.

CONCLUSIONS

Our results suggested that RSV attenuates retinal neural apoptosis in diabetic rats retina may be via regulation RAX/P-PKR expression.

The Potential Role of Protein Kinase R as a Regulator of Age-Related Neurodegeneration

There is a growing evidence describing a decline in adaptive homeostasis in aging-related diseases affecting the central nervous system (CNS), many of which are characterized by the appearance of non-native protein aggregates. One signaling pathway that allows cell adaptation is the integrated stress response (ISR), which senses stress stimuli through four kinases. ISR activation promotes translational arrest through the phosphorylation of the eukaryotic translation initiation factor 2 alpha (eIF2α) and the induction of a gene expression program to restore cellular homeostasis. However, depending on the stimulus, ISR can also induce cell death. One of the ISR sensors is the double-stranded RNA-dependent protein kinase [protein kinase R (PKR)], initially described as a viral infection sensor, and now a growing evidence supports a role for PKR on CNS physiology. PKR has been largely involved in the Alzheimer’s disease (AD) pathological process. Here, we reviewed the antecedents supporting the role of PKR on the efficiency of synaptic transmission and cognition. Then, we review PKR’s contribution to AD and discuss the possible participation of PKR as a player in the neurodegenerative process involved in aging-related pathologies affecting the CNS.

Ethanol, neurosteroids and cellular stress responses: Impact on central nervous system toxicity, inflammation and autophagy

Alcohol intake can impair brain function, in addition to other organs such as the liver and kidney. In the brain ethanol can be detrimental to memory formation, through inducing the integrated stress response/endoplasmic reticulum stress/unfolded protein response and the molecular mechanisms linking stress to other events such as NOD-, LRR- and pyrin domain-containing protein 3 (NLRP3) inflammation and autophagy. This literature review aims to provide an overview of our current understanding of the molecular mechanisms involved in ethanol-induced damage with endoplasmic reticulum stress, integrated stress response, NLRP3 inflammation and autophagy, while discussing the impact of neurosteroids and oxysterols, including allopregnanolone, 25-hydroxycholesterol and 24S-hydroxycholesterol, on the central nervous system.

4-Phenylbutyric Acid Protects Against Ethanol-Induced Damage in the Developing Mouse Brain

BACKGROUND

Ethanol (EtOH) exposure during pregnancy may result in fetal alcohol spectrum disorders (FASD). One of the most deleterious consequences of EtOH exposure is neuronal loss in the developing brain. Previously, we showed that EtOH exposure induced neuroapoptosis in the brain of postnatal day 4 (PD4) mice but not PD12 mice. This differential susceptibility may result from an insufficient cellular stress response system such as unfolded protein response (also known as endoplasmic reticulum [ER] stress) in PD4 mice. In this study, we compared the effect of EtOH on ER stress in PD4 and PD12 mice and determined whether the inhibition of ER stress could protect the developing brain against EtOH damage.

METHODS

We used a third-trimester equivalent mouse model of FASD. PD4 and PD12 C57BL/6 mice were subcutaneously injected with saline (control), EtOH, EtOH plus 4-phenylbutyric acid (4-PBA), a chemical chaperone known as ER stress inhibitor, and 4-PBA alone. The expression of apoptosis marker, ER stress markers, and markers for glial cell activation was examined in the cerebral cortex.

RESULTS

EtOH induced neuroapoptosis and increased the expression of ER stress markers, such as activating transcription factor 6, 78-kDa glucose-regulated protein, inositol-requiring enzyme 1α, mesencephalic astrocyte-derived neurotrophic factor, and caspase-12 in PD4 but not PD12 mice. EtOH exposure also activated microglia and astrocytes. Interestingly, treatment with 4-PBA attenuated EtOH-induced neuroapoptosis. Moreover, 4-PBA inhibited the expression of the aforementioned ER stress markers and EtOH-induced glial activation in PD4 mice.

CONCLUSIONS

ER stress plays an important role in EtOH-induced damage to the developing brain. Inhibition of ER stress is neuroprotective and may provide a new therapeutic strategy for treating FASD.

Impacts on prenatal development of the human cerebellum: a systematic review

PURPOSE

The cerebellum is essential for normal neurodevelopment and is particularly susceptible for intra-uterine disruptions. Although some causal prenatal exposures have been identified, the origin of neurodevelopmental disorders remains mostly unclear. Therefore, a systematic literature search was conducted to provide an overview of parental environmental exposures and intrinsic factors influencing prenatal cerebellar growth and development in humans.

MATERIALS AND METHODS

The literature search was limited to human studies in the English language and was conducted in Embase, Medline, Cochrane, Web of Science, Pubmed and GoogleScholar. Eligible studies were selected by three independent reviewers and study quality was scored by two independent reviewers.

RESULTS

The search yielded 3872 articles. We found 15 eligible studies reporting associations between cerebellar development and maternal smoking (4), use of alcohol (3), in vitro fertilization mediums (1), mercury (1), mifepristone (2), aminopropionitriles (1), ethnicity (2) and cortisol levels (1). No studies reported on paternal factors.

CONCLUSIONS

Current literature on associations between parental environmental exposures, intrinsic factors and human cerebellar development is scarce. Yet, this systematic review provided an essential overview of human studies demonstrating the vulnerability of the cerebellum to the intra-uterine environment.

Ethanol-Induced Neurodegeneration and Glial Activation in the Developing Brain

Ethanol induces neurodegeneration in the developing brain, which may partially explain the long-lasting adverse effects of prenatal ethanol exposure in fetal alcohol spectrum disorders (FASD). While animal models of FASD show that ethanol-induced neurodegeneration is associated with glial activation, the relationship between glial activation and neurodegeneration has not been clarified. This review focuses on the roles of activated microglia and astrocytes in neurodegeneration triggered by ethanol in rodents during the early postnatal period (equivalent to the third trimester of human pregnancy). Previous literature indicates that acute binge-like ethanol exposure in postnatal day 7 (P7) mice induces apoptotic neurodegeneration, transient activation of microglia resulting in phagocytosis of degenerating neurons, and a prolonged increase in glial fibrillary acidic protein-positive astrocytes. In our present study, systemic administration of a moderate dose of lipopolysaccharides, which causes glial activation, attenuates ethanol-induced neurodegeneration. These studies suggest that activation of microglia and astrocytes by acute ethanol in the neonatal brain may provide neuroprotection. However, repeated or chronic ethanol can induce significant proinflammatory glial reaction and neurotoxicity. Further studies are necessary to elucidate whether acute or sustained glial activation caused by ethanol exposure in the developing brain can affect long-lasting cellular and behavioral abnormalities observed in the adult brain.

Effects of Ethanol on the Cerebellum: Advances and Prospects

Alcohol abuse causes cerebellar dysfunction and cerebellar ataxia is a common feature in alcoholics. Alcohol exposure during development also impacts the cerebellum. Children with fetal alcohol spectrum disorder (FASD) show many symptoms associated specifically with cerebellar deficits. However, the cellular and molecular mechanisms are unclear. This special issue discusses the most recent advances in the study of mechanisms underlying alcoholinduced cerebellar deficits. The alteration in GABAA receptor-dependent neurotransmission is a potential mechanism for ethanol-induced cerebellar dysfunction. Recent advances indicate ethanol-induced increases in GABA release are not only in Purkinje cells (PCs), but also in molecular layer interneurons and granule cells. Ethanol is shown to disrupt the molecular events at the mossy fiber - granule cell - Golgi cell (MGG) synaptic site and granule cell parallel fibers - PCs (GPP) synaptic site, which may be responsible for ethanol-induced cerebellar ataxia. Aging and ethanol may affect the smooth endoplasmic reticulum (SER) of PC dendrites and cause dendritic regression. Ethanol withdrawal causes mitochondrial damage and aberrant gene modifications in the cerebellum. The interaction between these events may result in neuronal degeneration, thereby contributing to motoric deficit. Ethanol activates doublestranded RNA (dsRNA)-activated protein kinase (PKR) and PKR activation is involved ethanolinduced neuroinflammation and neurotoxicity in the developing cerebellum. Ethanol alters the development of cerebellar circuitry following the loss of PCs, which could result in modifications of the structure and function of other brain regions that receive cerebellar inputs. Lastly, choline, an essential nutrient is evaluated for its potential protection against ethanol-induced cerebellar damages. Choline is shown to ameliorate ethanol-induced cerebellar dysfunction when given before ethanol exposure.

Endoplasmic Reticulum Stress and Ethanol Neurotoxicity

Ethanol abuse affects virtually all organ systems and the central nervous system (CNS) is particularly vulnerable to excessive ethanol exposure. Ethanol exposure causes profound damages to both the adult and developing brain. Prenatal ethanol exposure induces fetal alcohol spectrum disorders (FASD) which is associated with mental retardation and other behavioral deficits. A number of potential mechanisms have been proposed for ethanol-induced brain damage; these include the promotion of neuroinflammation, interference with signaling by neurotrophic factors, induction of oxidative stress, modulation of retinoid acid signaling, and thiamine deficiency. The endoplasmic reticulum (ER) regulates posttranslational protein processing and transport. The accumulation of unfolded or misfolded proteins in the ER lumen triggers ER stress and induces unfolded protein response (UPR) which are mediated by three transmembrane ER signaling proteins: pancreatic endoplasmic reticulum kinase (PERK), inositol-requiring enzyme 1 (IRE1), and activating transcription factor 6 (ATF6). UPR is initiated to protect cells from overwhelming ER protein loading. However, sustained ER stress may result in cell death. ER stress has been implied in various CNS injuries, including brain ischemia, traumatic brain injury, and aging-associated neurodegeneration, such as Alzheimer's disease (AD), Huntington's disease (HD), Amyotrophic lateral sclerosis (ALS), and Parkinson's disease (PD). However, effects of ethanol on ER stress in the CNS receive less attention. In this review, we discuss recent progress in the study of ER stress in ethanol-induced neurotoxicity. We also examine the potential mechanisms underlying ethanol-mediated ER stress and the interaction among ER stress, oxidative stress and autophagy in the context of ethanol neurotoxicity.

Exposure of neonatal rats to alcohol has differential effects on neuroinflammation and neuronal survival in the cerebellum and hippocampus

Background

Fetal alcohol exposure is a leading cause of preventable birth defects, yet drinking during pregnancy remains prevalent worldwide. Studies suggest that activation of the neuroimmune system plays a role in the effects of alcohol exposure during the rodent equivalent to the third trimester of human pregnancy (i.e., first week of neonatal life), particularly by contributing to neuronal loss. Here, we performed a comprehensive study investigating differences in the neuroimmune response in the cerebellum and hippocampus, which are important targets of third trimester-equivalent alcohol exposure.

Methods

To model heavy, binge-like alcohol exposure during this period, we exposed rats to alcohol vapor inhalation during postnatal days (P)3–5 (blood alcohol concentration = 0.5 g/dL). The cerebellar vermis and hippocampus of rat pups were analyzed for signs of glial cell activation and neuronal loss by immunohistochemistry at different developmental stages. Cytokine production was measured by reverse transcriptase polymerase chain reaction during peak blood alcohol concentration and withdrawal periods. Additionally, adolescent offspring were assessed for alterations in gait and spatial memory.

Results

We found that this paradigm causes Purkinje cell degeneration in the cerebellar vermis at P6 and P45; however, no signs of neuronal loss were found in the hippocampus. Significant increases in pro-inflammatory cytokines were observed in both brain regions during alcohol withdrawal periods. Although astrocyte activation occurred in both the hippocampus and cerebellar vermis, microglial activation was observed primarily in the latter.

Conclusions

These findings suggest that heavy, binge-like third trimester-equivalent alcohol exposure has time- and brain region-dependent effects on cytokine levels, morphological activation of microglia and astrocytes, and neuronal survival.

Electronic supplementary material

The online version of this article (doi:10.1186/s12974-015-0382-9) contains supplementary material, which is available to authorized users.