Hypoxia-Induced Neuroinflammation and Learning-Memory Impairments in Adult Zebrafish Are Suppressed by Glucosamine

Behavioral neuroscience in zebrafish: unravelling the complexity of brain-behavior relationships

This paper reviews the utility of zebrafish (Danio rerio) as a model system for exploring neurobehavioral phenomena in preclinical research, focusing on physiological processes, disorders, and neurotoxicity biomarkers. A comprehensive review of the current literature was conducted to summarize the various behavioral characteristics of zebrafish. The study examined the etiological agents used to induce neurotoxicity and the biomarkers involved, including Aβ42, tau, MMP-13, MAO, NF-Кβ, and GFAP. Additionally, the different zebrafish study models and their responses to neurobehavioral analysis were discussed. The review identified several key biomarkers of neurotoxicity in zebrafish, each impacting different aspects of neurogenesis, inflammation, and neurodegeneration. Aβ42 was found to alter neuronal growth and stem cell function. Tau's interaction with tubulin affected microtubule stability and led to tauopathies under pathological conditions. MMP-13 was linked to oxidative assault and sensory neuron degeneration. MAO plays a role in neurotransmitter metabolism and neurotoxicity conversion. NF-Кβ was involved in pro-inflammatory pathways, and GFAP was indicative of neuroinflammation and astroglial activation. Zebrafish provide a valuable model for neurobehavioral research, adhering to the "3Rs" philosophy. Their neurotoxicity biomarkers offer insights into the mechanisms of neurogenesis, inflammation, and neurodegeneration. This model system aids in evaluating physiological and pathological conditions, enhancing our understanding of neurobehavioral phenomena and potential therapeutic interventions.

Protective effect of increased O-GlcNAc cycling against 6-OHDA induced Parkinson's disease pathology

This study aimed to elucidate the role of O-GlcNAc cycling in 6-hydroxydopamine (6-OHDA)-induced Parkinson's disease (PD)-like neurodegeneration and the underlying mechanisms. We observed dose-dependent downregulation of O-GlcNAcylation, accompanied by an increase in O-GlcNAcase following 6-OHDA treatment in both mouse brain and Neuro2a cells. Interestingly, elevating O-GlcNAcylation through glucosamine (GlcN) injection provided protection against PD pathogenesis induced by 6-OHDA. At the behavioral level, GlcN mitigated motor deficits induced by 6-OHDA, as determined using the pole, cylinder, and apomorphine rotation tests. Furthermore, GlcN attenuated 6-OHDA-induced neuroinflammation and mitochondrial dysfunction. Notably, augmented O-GlcNAcylation, achieved through O-GlcNAc transferase (OGT) overexpression in mouse brain, conferred protection against 6-OHDA-induced PD pathology, encompassing neuronal cell death, motor deficits, neuroinflammation, and mitochondrial dysfunction. These collective findings suggest that O-GlcNAcylation plays a crucial role in the normal functioning of dopamine neurons. Moreover, enhancing O-GlcNAcylation through genetic and pharmacological means could effectively ameliorate neurodegeneration and motor impairment in an animal model of PD. These results propose a potential strategy for safeguarding against the deterioration of dopamine neurons implicated in PD pathogenesis.

Forskolin rescues hypoxia-induced cognitive dysfunction in zebrafish with potential involvement of O-GlcNAc cycling regulation

Repeated sublethal hypoxia exposure induces brain inflammation and affects the initiation and progression of cognitive dysfunction. Experiments from the current study showed that hypoxic exposure downregulates PKA/CREB signaling, which is restored by forskolin (FSK), an adenylate cyclase activator, in both Neuro2a (N2a) cells and zebrafish brain. FSK significantly protected N2a cells from hypoxia-induced cell death and neurite shrinkage. Intraperitoneal administration of FSK for 5 days on zebrafish additionally led to significant recovery from hypoxia-induced social interaction impairment and learning and memory (L/M) deficit. FSK suppressed hypoxia-induced neuroinflammation, as indicated by the observed decrease in NF-κB activation and GFAP expression. We further investigated the potential effect of FSK on O-GlcNAcylation changes induced by hypoxia. Intriguingly FSK induced marked upregulation of the protein level of O-GlcNAc transferase catalyzing addition of the GlcNAc group to target proteins, accompanied by elevated O-GlcNAcylation of nucleocytoplasmic proteins. The hypoxia-induced O-GlcNAcylation decrease in the brain of zebrafish was considerably restored following FSK treatment. Based on the collective results, we propose that FSK rescues hypoxia-induced cognitive dysfunction, potentially through regulation of HBP/O-GlcNAc cycling.

Caffeine-induced protein kinase A activation restores cognitive deficits induced by sleep deprivation by regulating O-GlcNAc cycling in adult zebrafish

Sleep deprivation (SD) is widely acknowledged as a significant risk factor for cognitive impairment. In this study, intraperitoneal caffeine administration significantly ameliorated the learning and memory (L/M) deficits induced by SD and reduced aggressive behaviors in adult zebrafish. SD led to a reduction in protein kinase A (PKA) phosphorylation, phosphorylated-cAMP response element-binding protein (p-CREB), and c-Fos expression in zebrafish brain. Notably, these alterations were effectively reversed by caffeine. In addition, caffeine mitigated neuroinflammation induced by SD, as evident from suppression of the SD-mediated increase in glial fibrillary acidic protein (GFAP) and nuclear factor-κB (NF-κB) activation. Caffeine restored normal O-GlcNAcylation and O-GlcNAc transferase (OGT) levels while reversing the increased expression of O-GlcNAcase (OGA) in zebrafish brain after SD. Intriguingly, rolipram, a selective phosphodiesterase 4 (PDE4) inhibitor, effectively mitigated cognitive deficits, restored p-CREB and c-Fos levels, and attenuated the increase in GFAP in brain induced by SD. In addition, rolipram reversed the decrease in O-GlcNAcylation and OGT expression as well as elevation of OGA expression following SD. Treatment with H89, a PKA inhibitor, significantly impaired the L/M functions of zebrafish compared with the control group, inducing a decrease in O-GlcNAcylation and OGT expression and, conversely, an increase in OGA expression. The H89-induced changes in O-GlcNAc cycling and L/M dysfunction were effectively reversed by glucosamine treatment. H89 suppressed, whereas caffeine and rolipram promoted O-GlcNAc cycling in Neuro2a cells. Our collective findings underscore the interplay between PKA signaling and O-GlcNAc cycling in the regulation of cognitive function in the brain, offering potential therapeutic targets for cognitive deficits associated with SD.NEW & NOTEWORTHY Our observation highlights the intricate interplay between cAMP/PKA signaling and O-GlcNAc cycling, unveiling a novel mechanism that potentially governs the regulation of learning and memory functions. The dynamic interplay between these two pathways provides a novel and nuanced perspective on the molecular foundation of learning and memory regulation. These insights open avenues for the development of targeted interventions to treat conditions that impact cognitive function, including SD.

SARS-CoV-2 Infection to Premature Neuronal Aging and Neurodegenerative Diseases: Is there any Connection with Hypoxia?

The pandemic of coronavirus disease-2019 (COVID-19), caused by SARS-CoV-2, has become a global concern as it leads to a spectrum of mild to severe symptoms and increases death tolls around the world. Severe COVID-19 results in acute respiratory distress syndrome, hypoxia, and multi- organ dysfunction. However, the long-term effects of post-COVID-19 infection are still unknown. Based on the emerging evidence, there is a high possibility that COVID-19 infection accelerates premature neuronal aging and increases the risk of age-related neurodegenerative diseases in mild to severely infected patients during the post-COVID period. Several studies correlate COVID-19 infection with neuronal effects, though the mechanism through which they contribute to the aggravation of neuroinflammation and neurodegeneration is still under investigation. SARS-CoV-2 predominantly targets pulmonary tissues and interferes with gas exchange, leading to systemic hypoxia. The neurons in the brain require a constant supply of oxygen for their proper functioning, suggesting that they are more vulnerable to any alteration in oxygen saturation level that results in neuronal injury with or without neuroinflammation. We hypothesize that hypoxia is one of the major clinical manifestations of severe SARS-CoV-2 infection; it directly or indirectly contributes to premature neuronal aging, neuroinflammation, and neurodegeneration by altering the expression of various genes responsible for the survival of the cells. This review focuses on the interplay between COVID-19 infection, hypoxia, premature neuronal aging, and neurodegenerative diseases and provides a novel insight into the molecular mechanisms of neurodegeneration.

Causal associations between common musculoskeletal disorders and dementia: a Mendelian randomization study

Introduction

Dementia and musculoskeletal disorders (MSDs) are major public health problems. We aimed to investigate the genetic causality of common MSDs and dementia.

Methods

Two-sample Mendelian randomization (MR) was used in this study. MR analysis based on gene-wide association study (GWAS) data on osteoarthritis (OA), dementia with Lewy bodies, and other MSDs and dementia types were obtained from the Genetics of Osteoarthritis consortium, IEU-open GWAS project, GWAS catalog, and FinnGen consortium. Rigorously selected single-nucleotide polymorphisms were regarded as instrumental variables for further MR analysis. Inverse-variance weighted, MR-Egger regression, weight median, simple mode, and weight mode methods were used to obtain the MR estimates. Cochran's Q test, MR-Egger and MR-Pleiotropy Residual Sum and Outlier analysis, and the leave-one-out test were applied for sensitivity testing.

Results

The inverse-variance weighted method showed that hip OA was genetically associated with a lower risk of dementia, unspecified dementia, dementia in Alzheimer's disease, and vascular dementia. Kneehip OA was inversely associated with unspecified dementia and vascular dementia. Rheumatoid arthritis, juvenile idiopathic arthritis and seronegative rheumatoid arthritis were inversely associated with frontotemporal dementia, and rheumatoid arthritis was inversely associated with unspecified dementia. Simultaneously, ankylosing spondylitis was an independent risk factor for dementia, dementia with Lewy bodies, and dementia in Alzheimer's disease. Sensitivity tests showed that heterogeneity and horizontal pleiotropy did not exist in these associations. The leave-one-out test showed that these associations were stable.

Conclusion

We found that some MSDs were associated with the risk of dementia and provide evidence for the early detection of dementia in patients with MSDs and for the impact of inflammation on the central nervous system.

Repeated sleep deprivation decreases the flux into hexosamine biosynthetic pathway/O-GlcNAc cycling and aggravates Alzheimer's disease neuropathology in adult zebrafish

This study investigated chronic and repeated sleep deprivation (RSD)-induced neuronal changes in hexosamine biosynthetic pathway/O-linked N-acetylglucosamine (HBP/O-GlcNAc) cycling of glucose metabolism and further explored the role of altered O-GlcNAc cycling in promoting neurodegeneration using an adult zebrafish model. RSD-triggered degenerative changes in the brain led to impairment of memory, neuroinflammation and amyloid beta (Aβ) accumulation. Metabolite profiling of RSD zebrafish brain revealed a significant decrease in glucose, indicating a potential association between RSD-induced neurodegeneration and dysregulated glucose metabolism. While RSD had no impact on overall O-GlcNAcylation levels in the hippocampus region, changes were observed in two O-GlcNAcylation-regulating enzymes, specifically, a decrease in O-GlcNAc transferase (OGT) and an increase in O-GlcNAcase (OGA). Glucosamine (GlcN) treatment induced an increase in O-GlcNAcylation and recovery of the OGT level that was decreased in the RSD group. In addition, GlcN reversed cognitive impairment by RSD. GlcN reduced neuroinflammation and attenuated Aβ accumulation induced by RSD. Repeated treatment of zebrafish with diazo-5-oxo-l-norleucine (DON), an inhibitor of HBP metabolism, resulted in cognitive dysfunction, neuroinflammation and Aβ accumulation, similar to the effects of RSD. The pathological changes induced by DON were restored to normal upon treatment with GlcN. Both the SD and DON-treated groups exhibited a common decrease in glutamate and γ-aminobutyric acid compared to the control group. Overexpression of OGT in zebrafish brain rescued RSD-induced neuronal dysfunction and neurodegeneration. RSD induced a decrease in O-GlcNAcylation of amyloid precursor protein and increase in β-secretase activity, which were reversed by GlcN treatment. Based on the collective findings, we propose that dysregulation of HBP and O-GlcNAc cycling in brain plays a crucial role in RSD-mediated progression of neurodegeneration and Alzheimer's disease pathogenesis. Targeting of this pathway may, therefore, offer an effective regulatory approach for treatment of sleep-associated neurodegenerative disorders.

Hexosamine biosynthetic pathway and O-GlcNAc cycling of glucose metabolism in brain function and disease

Impaired brain glucose metabolism is considered a hallmark of brain dysfunction and neurodegeneration. Disruption of the hexosamine biosynthetic pathway (HBP) and subsequent O-linked N-acetylglucosamine (O-GlcNAc) cycling has been identified as an emerging link between altered glucose metabolism and defects in the brain. Myriads of cytosolic and nuclear proteins in the nervous system are modified at serine or threonine residues with a single N-acetylglucosamine (O-GlcNAc) molecule by O-GlcNAc transferase (OGT), which can be removed by β-N-acetylglucosaminidase (O-GlcNAcase, OGA). Homeostatic regulation of O-GlcNAc cycling is important for the maintenance of normal brain activity. Although significant evidence linking dysregulated HBP metabolism and aberrant O-GlcNAc cycling to induction or progression of neuronal diseases has been obtained, the issue of whether altered O-GlcNAcylation is causal in brain pathogenesis remains uncertain. Elucidation of the specific functions and regulatory mechanisms of individual O-GlcNAcylated neuronal proteins in both normal and diseased states may facilitate the identification of novel therapeutic targets for various neuronal disorders. The information presented in this review highlights the importance of HBP/O-GlcNAcylation in the neuronal system and summarizes the roles and potential mechanisms of O-GlcNAcylated neuronal proteins in maintaining normal brain function and initiation and progression of neurological diseases.

Habitual glucosamine use, APOE genotypes, and risk of incident cause-specific dementia in the older population

BACKGROUND

The relationship of glucosamine use with incident dementia in the older population remains uncertain. We aimed to evaluate the longitudinal association between habitual glucosamine supplement and the risk of cause-specific dementia and examine the possible effect modifiers on this association.

METHODS

The study included 214,945 participants over the age of 60 who had available information on glucosamine use and did not have dementia at baseline in the UK Biobank. The APOE genotypes were determined by a combination variant of rs429358 and rs7412. The primary outcome was incident vascular dementia, incident Alzheimer's disease, and incident frontotemporal dementia, respectively.

RESULTS

Over a median follow-up duration of 12 years, 1039, 1774, and 122 participants developed vascular dementia, Alzheimer's disease, and frontotemporal dementia, respectively. Overall, habitual glucosamine use was significantly associated with a lower risk of incident vascular dementia (adjusted HR, 0.82; 95%CI, 0.70-0.96), but not significantly associated with incident Alzheimer's disease (adjusted HR, 1.02; 95%CI, 0.92-1.14) and incident frontotemporal dementia (adjusted HR, 0.95; 95%CI, 0.63-1.43). Moreover, the inverse association between habitual glucosamine use and incident vascular dementia was more pronounced in participants with concomitant supplement of calcium (P-interaction = 0.011), and those without concomitant supplement of zinc (P-interaction = 0.018). However, APOE ε4 dosage and baseline cognitive function did not significantly modify the relationships of glucosamine use with incident vascular dementia or Alzheimer's disease (All P-interactions > 0.05).

CONCLUSIONS

Regardless of APOE genotypes and baseline cognitive function, habitual glucosamine use was significantly inversely associated with incident vascular dementia in the older population.

Association of regular glucosamine use with incident dementia: evidence from a longitudinal cohort and Mendelian randomization study

BACKGROUND

Emerging data suggests the neuroprotective and anti-neuroinflammatory effects of glucosamine. We aimed to examine the association between regular glucosamine use and risk of incident dementia, including dementia subtypes.

METHODS

We conducted large-scale observational and two-sample Mendelian randomization (MR) analyses. Participants in UK Biobank having accessible data for dementia incidence and who did not have dementia at baseline were included in the prospective cohort. Through the Cox proportional hazard model, we examined the risks of incident all-cause dementia, Alzheimer's disease (AD), and vascular dementia among glucosamine users and non-users. To further test the causal association between glucosamine use and dementia, we conducted a 2-sample MR utilizing summary statistics from genome-wide association studies (GWAS). The GWAS data were obtained from observational cohort participants of mostly European ancestry.

RESULTS

During a median follow-up of 8.9 years, there were 2458 cases of all-cause dementia, 924 cases of AD, and 491 cases of vascular dementia. In multivariable analysis, the hazard ratios (HR) of glucosamine users for all-cause dementia, AD, and vascular dementia were 0.84 (95% CI 0.75-0.93), 0.83 (95% CI 0.71-0.98), and 0.74 (95% CI 0.58-0.95), respectively. The inverse associations between glucosamine use and AD appeared to be stronger among participants aged below 60 years than those aged above 60 years (p = 0.04 for interaction). The APOE genotype did not modify this association (p > 0.05 for interaction). Single-variable MR suggested a causal relationship between glucosamine use and lower dementia risk. Multivariable MR showed that taking glucosamine continued to protect against dementia after controlling for vitamin, chondroitin supplement use and osteoarthritis (all-cause dementia HR 0.88, 95% CI 0.81-0.95; AD HR 0.78, 95% CI 0.72-0.85; vascular dementia HR 0.73, 95% CI 0.57-0.94). Single and multivariable inverse variance weighted (MV-IVW) and MR-Egger sensitivity analyses produced similar results for these estimations.

CONCLUSIONS

The findings of this large-scale cohort and MR analysis provide evidence for potential causal associations between the glucosamine use and lower risk for dementia. These findings require further validation through randomized controlled trials.

Cyclooxygenase‑2 contributes to the hypoxia‑induced aggravation of the neuroinflammation response stimulated by lipopolysaccharide in microglia

Hypoxia and neuroinflammation are key risk factors involved in various pathophysiological neural disorders. Hypoxia can aggravate neuroinflammation in vitro and in vivo; however, the underlying mechanisms remain unknown. In the present study, hypoxia [either 3 or 1% oxygen (O₂)] increased lipopolysaccharide (LPS)-induced expression of the IL-6, IL-1β and TNF-α proinflammatory cytokines in BV2 cells. At the molecular level, both hypoxia and FG-4592, an hypoxia inducible factor 1 pathway activator, effectively induced cyclooxygenase-2 (COX-2) expression. The COX-2 inhibitor celecoxib significantly reduced the expression of cytokines induced by LPS under hypoxic conditions. Additionally, the administration of celecoxib inhibited the activation of microglia as well as cytokine expression in mice administered with hypoxia exposure and LPS injection. The present data demonstrated that COX-2 is involved in the hypoxia-induced aggravation of neuroinflammation stimulated by LPS.

Animal Inflammation-Based Models of Neuropsychiatric Disorders

Mounting evidence links psychiatric disorders to central and systemic inflammation. Experimental (animal) models of psychiatric disorders are important tools for translational biopsychiatry research and CNS drug discovery. Current experimental models, most typically involving rodents, continue to reveal shared fundamental pathological pathways and biomarkers underlying the pathogenetic link between brain illnesses and neuroinflammation. Recent data also show that various proinflammatory factors can alter brain neurochemistry, modulating the levels of neurohormones and neurotrophins in neurons and microglia. The role of "active" glia in releasing a wide range of proinflammatory cytokines also implicates glial cells in various psychiatric disorders. Here, we discuss recent animal inflammation-related models of psychiatric disorders, focusing on their translational perspectives and the use of some novel promising model organisms (zebrafish), to better understand the evolutionally conservative role of inflammation in neuropsychiatric conditions.

Resetting Proteostasis of CIRBP with ISRIB Suppresses Neural Stem Cell Apoptosis under Hypoxic Exposure

Neurological disorders are often progressive and lead to disabilities with limited available therapies. Epidemiological evidence implicated that prolonged exposure to hypoxia leads to neurological damage and a plethora of complications. Neural stem cells (NSCs) are a promising tool for neurological damage therapy in terms of their unique properties. However, the literature on the outcome of NSCs exposed to severe hypoxia is scarce. In this study, we identified a responsive gene that reacts to multiple cellular stresses, marked cold-inducible RNA-binding protein (CIRBP), which could attenuate NSC apoptosis under hypoxic pressure. Interestingly, ISRIB, a small-molecule modulator of the PERK-ATF4 signaling pathway, could prevent the reduction and apoptosis of NSCs in two steps: enhancing the expression of CIRBP through the protein kinase R- (PKR-) like endoplasmic reticulum kinase (PERK) and activating transcription factor 4 (ATF4) axis. Taken together, CIRBP was found to be a critical factor that could protect NSCs against apoptosis induced by hypoxia, and ISRIB could be acted upstream of the axis and may be recruited as an open potential therapeutic strategy to prevent or treat hypoxia-induced brain hazards.

Insight into the Effects of High-Altitude Hypoxic Exposure on Learning and Memory

The earth land area is heterogeneous in terms of elevation; about 45% of its land area belongs to higher elevation with altitude above 500 meters compared to sea level. In most cases, oxygen concentration decreases as altitude increases. Thus, high-altitude hypoxic stress is commonly faced by residents in areas with an average elevation exceeding 2500 meters and those who have just entered the plateau. High-altitude hypoxia significantly affects advanced neurobehaviors including learning and memory (L&M). Hippocampus, the integration center of L&M, could be the most crucial target affected by high-altitude hypoxia exposure. Based on these points, this review thoroughly discussed the relationship between high-altitude hypoxia and L&M impairment, in terms of hippocampal neuron apoptosis and dysfunction, neuronal oxidative stress disorder, neurotransmitters and related receptors, and nerve cell energy metabolism disorder, which is of great significance to find potential targets for medical intervention. Studies illustrate that the mechanism of L&M damaged by high-altitude hypoxia should be further investigated based on the entire review of issues related to this topic.

Hizikia fusiforme functional oil (HFFO) prevents neuroinflammation and memory deficits evoked by lipopolysaccharide/aluminum trichloride in zebrafish

Background

Oxidative stress, cholinergic deficiency, and neuroinflammation are hallmarks of most neurodegenerative disorders (NDs). Lipids play an important role in brain development and proper functioning. Marine-derived lipids have shown good memory-improving potentials, especially those from fish and microalgae. The cultivated macroalga Hizikia fusiforme is healthy food and shows benefits to memory, but the study is rare on the brain healthy value of its oil. Previously, we had reported that the Hizikia fusiforme functional oil (HFFO) contains arachidonic acid, 11,14,17-eicosatrienoic acid, phytol, and other molecules displaying in vitro acetylcholinesterase inhibitory and nitroxide scavenging activity; however, the in vivo effect remains unclear. In this study, we further investigated its potential effects against lipopolysaccharides (LPS)- or aluminum trichloride (AlCl3)-induced memory deficiency in zebrafish and its drug-related properties in silica.

Methods

We established memory deficit models in zebrafish by intraperitoneal (i.p.) injection of lipopolysaccharides (LPS) (75 ng) or aluminum trichloride (AlCl3) (21 μg), and assessed their behaviors in the T-maze test. The interleukin-1β (IL-1β), tumor necrosis factor-α (TNF-α), acetylcholine (ACh), and malondialdehyde (MDA) levels were measured 24 h after the LPS/AlCl3 injection as markers of inflammation, cholinergic activity, and oxidative stress. Furthermore, the interaction of two main components, 11,14,17-eicosatrienoic acid and phytol, was investigated by molecular docking, with the important anti-inflammatory targets nuclear factor kappa B (NF-κB) and cyclooxygenase 2 (COX-2). Specifically, the absorption, distribution, metabolism, excretion, and toxicity (ADMET) and drug-likeness properties of HFFO were studied by ADMETlab.

Results

The results showed that HFFO reduced cognitive deficits in zebrafish T-maze induced by LPS/AlCl3. While the LPS/AlCl3 treatment increased MDA content, lowered ACh levels in the zebrafish brain, and elevated levels of central and peripheral proinflammatory cytokines, these effects were reversed by 100 mg/kg HFFO except for MDA. Moreover, 11,14,17-eicosatrienoic acid and phytol showed a good affinity with NF-κB, COX-2, and HFFO exhibited acceptable drug-likeness and ADMET profiles in general.

Conclusion

Collectively, this study's findings suggest HFFO as a potent neuroprotectant, potentially valuable for the prevention of memory impairment caused by cholinergic deficiency and neuroinflammation.

Fish Behavior as a Neural Proxy to Reveal Physiological States

Behaviors are the integrative outcomes of the nervous system, which senses and responds to the internal physiological status and external stimuli. Teleosts are aquatic organisms which are more easily affected by the surrounding environment compared to terrestrial animals. To date, behavioral tests have been widely used to assess potential environmental risks using fish as model animals. In this review, we summarized recent studies regarding the effects of internal and external stimuli on fish behaviors. We concluded that behaviors reflect environmental and physiological changes, which have possible implications for environmental and physiological assessments.

Comparative Transcriptome Analysis of Organ-Specific Adaptive Responses to Hypoxia Provides Insights to Human Diseases

The common carp is a hypoxia-tolerant fish, and the understanding of its ability to live in low-oxygen environments has been applied to human health issues such as cancer and neuron degeneration. Here, we investigated differential gene expression changes during hypoxia in five common carp organs including the brain, the gill, the head kidney, the liver, and the intestine. Based on RNA sequencing, gene expression changes under hypoxic conditions were detected in over 1800 genes in common carp. The analysis of these genes further revealed that all five organs had high expression-specific properties. According to the results of the GO and KEGG, the pathways involved in the adaptation to hypoxia provided information on responses specific to each organ in low oxygen, such as glucose metabolism and energy usage, cholesterol synthesis, cell cycle, circadian rhythm, and dopamine activation. DisGeNET analysis showed that some human diseases such as cancer, diabetes, epilepsy, metabolism diseases, and social ability disorders were related to hypoxia-regulated genes. Our results suggested that common carp undergo various gene regulations in different organs under hypoxic conditions, and integrative bioinformatics may provide some potential targets for advancing disease research.

Zebrafish for modeling stroke and their applicability for drug discovery and development

INTRODUCTION

The global health burden of stroke is significant and few therapeutic treatment options currently exist for patients. Pre-clinical research relies heavily on rodent stroke models but the limitations associated with using these systems alone has meant translation of drug compounds to the clinic has not been greatly successful to date. Zebrafish disease modeling offers a potentially complementary platform for pre-clinical compound screening to aid the drug discovery process for translational stroke research.

AREAS COVERED

In this review, the authors introduce stroke and describe the issues associated with the current pre-clinical drug development pipeline and the advantages that zebrafish disease modeling can offer. Existing zebrafish models of ischemic and hemorrhagic stroke are reviewed. Examples of how zebrafish models have been utilized for drug discovery in other disease disciplines are also discussed.

EXPERT OPINION

Zebrafish disease modeling holds the capacity and potential to significantly enhance the stroke drug development pipeline. However, for this system to be more widely accepted and incorporated into translational stroke research, continued improvement of the existing zebrafish stroke models, as well as focussed collaboration between zebrafish and stroke researchers, is essential.

Pre-Exposure to Environmental Enrichment Protects against Learning and Memory Deficits Caused by Infrasound Exposure

With the development of industrialization in recent years, infrasound has become an important component of public noise. To date, diverse studies have revealed the negative effects of infrasound on the central nervous system (CNS), especially the learning and memory ability. It is widely reported that environmental enrichment (EE) ameliorates the learning and memory deficits in different models of brain injury. Therefore, the present study was designed to determine the possible benefits of pre-exposure to EE in preventing functional deficits following infrasound exposure and their related mechanism. Adult male rats were given enriched or standard housing for 30 days. Following enrichment, the rats were exposed to 16 Hz, 130 dB infrasound for 14 days, and then their learning and memory ability was assessed. Changes to neuroinflammation, apoptosis, and oxidative stress in the hippocampus were also detected. Our results showed that the infrasound-induced deficit in learning and memory was attenuated significantly in EE pre-exposed rats. Pre-exposure to EE could induce a decrease in proinflammatory cytokines and increased anti-inflammatory cytokines and antioxidant properties in the hippocampus. Moreover, pre-exposure to EE also exerted antiapoptosis functions by upregulating the B-cell lymphoma/leukemia-2 (Bcl-2) level and downregulating the P53 level in the hippocampus. In conclusion, the results of the present study suggested that EE is neuroprotective when applied before infrasound exposure, resulting in an improved learning and memory ability by enhancing antioxidant, anti-inflammatory, and antiapoptosis capacities.

The mechanism and effects of remdesivir-induced developmental toxicity in zebrafish: Blood flow dysfunction and behavioral alterations

The antiviral drug remdesivir has been used to treat the growing number of coronavirus disease 2019 (COVID-19) patients. However, the drug is mainly excreted through urine and feces and introduced into the environment to affect non-target organisms, including fish, which has raised concerns about potential ecotoxicological effects on aquatic organisms. Moreover, studies on the ecological impacts of remdesivir on aquatic environments have not been reported. Here, we aimed to explore the toxicological impacts of microinjection of remdesivir on zebrafish early embryonic development and larvae and the associated mechanism. We found that 100 μM remdesivir delayed epiboly and impaired convergent movement of embryos during gastrulation, and dose-dependent increases in mortality and malformation were observed in remdesivir-treated embryos. Moreover, 10-100 μM remdesivir decreased blood flow and swimming velocity and altered the behavior of larvae. In terms of molecular mechanisms, eighty differentially expressed genes (DEGs) were identified by transcriptome analysis in the remdesivir-treated group. Some of these DEGs, such as manf, kif3a, hnf1ba, rgn, prkcz, egr1, fosab, nr4a1, and ptgs2b, were mainly involved in early embryonic development, neuronal developmental disorders, vascular disease and the blood flow pathway. These data reveal that remdesivir can impair early embryonic development, blood flow and behavior of zebrafish embryos/larvae, probably due to alterations at the transcriptome level. This study suggests that it is important to avoid the discharge of remdesivir to aquatic ecosystems and provides a theoretical foundation to hinder remdesivir-induced ecotoxicity to aquatic environments.

Neuroprotective and Proneurogenic Effects of Glucosamine in an Internal Carotid Artery Occlusion Model of Ischemia

Neuroprotective, antineuroinflammatory, and proneurogenic effects of glucosamine, a naturally occurring amino sugar, have been reported in various animal models of brain injury including cerebral ischemia and hypoxic brain damage. Given that clinical translation of therapeutic candidates identified in animal models of ischemic stroke has remained unsatisfactory in general, possibly due to inadequacy of existing models, we sought to study the effects of glucosamine in a recently developed, clinical condition mimicking mouse model of internal cerebral artery occlusion. In this model of mild to moderate striatal damage, glucosamine ameliorated behavioral dysfunction, rescued ischemia-induced striatal damage, and suppressed ischemia-induced upregulation of proinflammatory genes in striatal tissue. Further, in ex vivo neurosphere assay involving neural stem cells/neural progenitor cells from subventricular zone, glucosamine increased the number of large neurospheres, along with enhancing mRNA levels of the proliferation markers Nestin, NeuroD1, and Sox2. Lastly, coronal brain sections containing the striatal region with subventricular zone showed increased number of BrdU positive cells and DCX positive cells, a marker for newly differentiating and immature neurons, in glucosamine-treated ischemic mice. Cumulatively, the results confirming neuroprotective, antineuroinflammatory, and proneurogenic effects of glucosamine enhance drug repurposing potential of glucosamine in cerebral ischemia.

Repeated hypoxia exposure induces cognitive dysfunction, brain inflammation, and amyloidβ/p-Tau accumulation through reduced brain O-GlcNAcylation in zebrafish

Repetitive hypoxia (RH) exposure affects the initiation and progression of cognitive dysfunction, but little is known about the mechanisms of hypoxic brain damage. In this study, we show that sublethal RH increased anxiety, impaired learning and memory (L/M), and triggered downregulation of brain levels of glucose and several glucose metabolites in zebrafish, and that supplementation of glucose or glucosamine (GlcN) restored RH-induced L/M impairment. Fear conditioning (FC)-induced brain activation of and PKA/CREB signaling was abrogated by RH, and this effect was reversed by GlcN supplementation. RH was associated with decreased brain O-GlcNAcylation and an increased O-GlcNAcase (OGA) level. RH increased brain inflammation and p-Tau and amyloid β accumulation, and these effects were suppressed by GlcN. Our observations collectively suggest that changes in O-GlcNAc flux during hypoxic exposure could be an important causal factor for neurodegeneration, and that supplementation of the HBP/O-GlcNAc flux may be a potential novel therapeutic or preventive target for addressing hypoxic brain damage.

Glucosamine promotes seizure activity via activation of the PI3K/Akt pathway in epileptic rats

CONTEXT

Glucosamine is an amino monosaccharide with a small molecular weight and has a protective effect against various neurological diseases including multiple sclerosis and encephalomyelitis. Interestingly, low-dose glucosamine has exhibited anti-epilepsy activity. Recent studies have shown that the activation of the protein kinase B (Akt) signaling pathway may promote epilepsy. Glucosamine can increase the level of Akt phosphorylation in the brain tissue, which may aggravate epilepsy. Hence, we speculate that a higher dose of glucosamine may aggravate epilepsy via AKT signaling.

OBJECTIVE

To investigate the effect of glucosamine on the behavior and electrophysiology of epileptic rats through PI3K/Akt pathway.

METHODS

Glucose (2.0 g/kg) and glucosamine (0, 0.5, 1.0, and 2.0 g/kg) were added to 2 mL of drinking water, respectively. An acute seizure rat model of lithium-pilocarpine and PTZ-kindling were constructed to observe the effects of different doses of glucosamine on epileptic behavior and hippocampal electrical activity. Meanwhile, the changes in Akt were detected by western blot.

RESULTS

Epileptic seizures were induced by a single dose of pilocarpine or PTZ and 2.0 g/kg of glucosamine significantly prolonged the duration and severity of epileptic seizures, enhanced hippocampal electrical activity energy density, and increased phosphorylated AKT levels. A glucosamine dose of 2.0 g/kg also significantly increased the total onset energy density. Furthermore, 2.0 g/kg glucosamine facilitated the development of the chronic PTZ-kindling process.

CONCLUSIONS

Glucosamine may exacerbate acute and chronic epileptic seizures via activation of the PI3K/Akt pathway in rats with experimental epilepsy.

Zebrafish as a Model for In-Depth Mechanistic Study for Stroke

Stroke is one of the world's leading causes of death and disability, posing enormous burden to the society. However, the pathogenesis and mechanisms that underlie brain injury and brain repair remain largely unknown. There's an unmet need of in-depth mechanistic research in this field. Zebrafish (Danio rerio) is a powerful tool in brain science research mainly due to its small size and transparent body, high genome synteny with human, and similar nervous system structures. It can be used to establish both hemorrhagic and ischemic stroke models easily and effectively through different ways. After the establishment of stroke model, research methods including behavioral test, in vivo imaging, and drug screening are available to explore mechanisms that underlie the brain injury and brain repair after stroke. This review focuses on the advantages and the feasibility of zebrafish stroke model, and will also introduce the key methods available for stroke studies in zebrafish, which may drive future mechanistic studies in the pursuit of discovering novel therapeutic targets for stroke patients.

Neuroglobin alleviates arsenic-induced neuronal damage

People who drink water contaminated with arsenic for a long time develop neuritis, cerebellar symptoms, and deficits in memory and intellectual function. Arsenic induces oxidative stress and promotes apoptosis through multiple signalling pathways in nerve cells. Neuroglobin (Ngb), as a key mediator, is considered to be protective against oxidative stress. In this study, we aimed to study the effects of Ngb knockdown in arsenite-treated rat neurons on levels of apoptosis markers and reactive oxygen species and serum Ngb levels of subjects from arsenic-endemic regions in China. We discovered that arsenic-induced apoptosis and reactive oxygen species production were enhanced in Ngb-knocked-down rat neurons. Silencing of Ngb aggravated the arsenic-induced decrease in the rate of Bcl-2/Bax and the levels of Bcl-2 protein following arsenite treatment. The results also showed that serum Ngb levels were independently negatively correlated with arsenic concentration in drinking water. Furthermore, the serum Ngb levels of four groups (245 individuals) according to different degree exposure to arsenic were 815.18 ± 89.52, 1247.97 ± 117.18, 774.79 ± 91.55, and 482.72 ± 49.30 pg/mL, respectively. Taken together, it can be deduced that Ngb has protective effects against arsenic-induced apoptosis by eliminating reactive oxygen species.

Improving Age-Related Cognitive Decline through Dietary Interventions Targeting Mitochondrial Dysfunction

Aging is inevitable and it is one of the major contributors to cognitive decline. However, the mechanisms underlying age-related cognitive decline are still the object of extensive research. At the biological level, it is unknown how the aging brain is subjected to progressive oxidative stress and neuroinflammation which determine, among others, mitochondrial dysfunction. The link between mitochondrial dysfunction and cognitive impairment is becoming ever more clear by the presence of significant neurological disturbances in human mitochondrial diseases. Possibly, the most important lifestyle factor determining mitochondrial functioning is nutrition. Therefore, with the present work, we review the latest findings disclosing a link between nutrition, mitochondrial functioning and cognition, and pave new ways to counteract cognitive decline in late adulthood through diet.

Hypoxia-Induced S100A8 Expression Activates Microglial Inflammation and Promotes Neuronal Apoptosis

S100 calcium-binding protein A8 (S100A8), a danger-associated molecular pattern, has emerged as an important mediator of the pro-inflammatory response. Some S100 proteins play a prominent role in neuroinflammatory disorders and increase the secretion of pro-inflammatory cytokines in microglial cells. The aim of this study was to determine whether S100A8 induced neuronal apoptosis during cerebral hypoxia and elucidate its mechanism of action. In this study, we reported that the S100A8 protein expression was increased in mouse neuronal and microglial cells when exposed to hypoxia, and induced neuroinflammation and neuronal apoptosis. S100A8, secreted from neurons under hypoxia, activated the secretion of tumor necrosis factor (TNF-α) and interleukin-6 (IL-6) through phosphorylation of extracellular-signal-regulated kinase (ERK) and c-Jun N-terminal kinase (JNK) in microglia. Also, phosphorylation of ERK via the TLR4 receptor induced the priming of the NLRP3 inflammasome. The changes in Cyclooxygenase-2 (COX-2) expression, a well-known inflammatory activator, were regulated by the S100A8 expression in microglial cells. Knockdown of S100A8 levels by using shRNA revealed that microglial S100A8 expression activated COX-2 expression, leading to neuronal apoptosis under hypoxia. These results suggested that S100A8 may be an important molecule for bidirectional microglia-neuron communication and a new therapeutic target for neurological disorders caused by microglial inflammation during hypoxia.

A comparison between chemical and gas hypoxia as models of global ischemia in zebrafish (Danio rerio)

BACKGROUND

Zebrafish models for neurovascular diseases offer new methods for elucidation of molecular pathways to tissue damage. External fertilization and high fecundity provide opportunities for transgenics and other forms of genetic manipulation that are more accessible than offered by mammalian models of disease. Furthermore, behavioral analyses of zebrafish allow for connection of molecular pathways to organismal outputs such as locomotion, learning, and memory. Unfortunately, a zebrafish model of hypoxia-ischemia has been slow to catch on, possibly due to hypoxia exposure protocols that are challenging to reproduce and result in high mortality.

METHODS

In this study, we have introduced a predictable and simple method of hypoxia induction, the addition of sodium sulfite to aquarium water. The effects of this treatment on zebrafish locomotion were compared to those of zebrafish exposed to hypoxia induced by nitrogen gas bubbling, a method used in previous reports.

RESULTS

We found that hypoxia induced by sodium sulfite significantly impaired locomotion in the hours following treatment, and its effects did not differ from those caused by nitrogen gas hypoxia.

CONCLUSION

These results indicate that hypoxia by sodium sulfite represents an effective and easily reproducible method for the study of hypoxia-ischemia in zebrafish.

Glucosamine-mediated immunomodulation after stroke is sexually dimorphic

Growing evidence suggests that galectin-3 (Gal-3) is instrumental in orchestrating innate immune response and microglia activation following different brain pathologies. However, its role remains controversial. We recently showed that a readily available natural product glucosamine may act as a strong modulator of Gal-3. Glucosamine is a naturally occurring sugar and a precursor in the synthesis of glycosylated proteins. It is often used as a supplement to treat symptoms of various inflammatory conditions. Our recent work suggests that by increasing the synthesis and availability of Gal-3 ligands and/or by regulating its expression levels, glucosamine may significantly modulate Gal-3 signaling. Because evidence suggests that Gal-3 might be differentially regulated after ischemic injury in the brains of female mice, here we examined and compared the immunomodulatory potential of glucosamine in male and female stroke. The mice were subjected to transient middle cerebral artery occlusion (MCAO), followed by different reperfusion periods. The short-term 5 days treatment with glucosamine (150 ​mg/kg i.p.) was initiated 2 ​hrs after stroke. To visualize the effects of glucosamine treatment on post-stroke inflammation, we took advantage of a transgenic mouse model bearing the dual reporter system luciferase/GFP under transcriptional control of a murine TLR2 promoter (TLR2-luc-GFP) allowing in vivo bioluminescence imaging of innate immune response and microglial activation. We report that after stroke, both, male and female mice strongly up-regulate the TLR2 bioluminescence signals from activated microglia, however, the observed in vivo immunomodulatory effects of glucosamine after stroke were sex-dependent. Analysis of cytokine profiles at protein level, in glucosamine-treated male mice 72hsr after stroke, revealed down regulation of pro-inflammatory cytokines, an increase in levels of anti-inflammatory cytokines including IL-4, IL13 and colony stimulating factors MCFC and GM-CSF and a significant decrease in the size of ischemic lesion in male mice. Conversely, in female mice glucosamine markedly increases the pro-inflammatory signaling and exacerbates ischemic injury. Analysis of the downstream signaling target of glucosamine/Gal-3 revealed that glucosamine administration restored PPAR-γ activity in male but not in female mice 3 days following MCAO. Together, our results suggest that glucosamine acts as a fine tuner of post-ischemic inflammation in a sex dependent-manner and may have therapeutic potential after stroke in males. Based on our results propose that targeting immune system after stroke may require adapted sex-specific therapeutic approaches.

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Immunomodulatory effects of glucosamine are sex dependent.

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Glucosamine differentially modulates galectin-3/IL4R signaling in male and female mice.

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Glucosamine restores PPAR-gamma transcriptional activity in male mice and protects against stroke in male mice.

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Glucosamine increases inflammatory signaling and exacerbates ischemic injury in female mice.

Sleep deprivation impairs learning and memory by decreasing protein O-GlcNAcylation in the brain of adult zebrafish

Sleep is an evolutionarily conserved physiological process implicated in the consolidation of learning and memory (L/M). Here, we report that sleep deprivation (SD)-induced cognitive deficits in zebrafish are mediated through reduction in O-GlcNAcylation of brain. Microarray-based gene expression profiling of zebrafish brain demonstrated significant changes in genes involved in metabolism by SD or fear conditioning (FC), compared to the control group. In particular, it was observed that a marked decrease in the number of genes involved in carboxylic acid and organic acid metabolic processes in the brains of SD group compared to control group. SD downregulated O-GlcNAc transferase (OGT) and O-GlcNAcylation, while the expression of O-GlcNAcase was upregulated. FC activated protein kinase A (PKA) and phosphorylated cAMP response element binding protein (p-CREB), an effect that was greatly inhibited by SD. Moreover, FC upregulated expressions of OGT and increased O-GlcNAcylation in the brains of normal but not SD zebrafish. Intriguingly, upregulation of O-GlcNAcylation by glucosamine restored defects in L/M functions and PKA/p-CREB activity in SD group. Our findings highlight the O-GlcNAcylation changes in the brain during the L/M process and further provide a foundation for future studies seeking the molecular and biochemical mechanisms by which HBP of glucose metabolism affects cognitive function.

Midbrain and cerebral inflammatory and glutamatergic adaptations during chronic hypercapnia in goats

Cognitive impairment is associated with multiple human diseases that have in common chronic hypercapnia. However, the mechanisms leading to chronic hypercapnia-induced cognitive decline are not known. We have previously shown chronic hypercapnia through exposure to increased inspired CO₂ (6% InCO₂) in conscious goats caused an immediate (within hours) and sustained decline in cognitive performance during a shape discrimination test. Herein, within the same goats, we assessed markers of neuroinflammation and glutamate receptor expression/phosphorylation within CNS regions important for cognitive function following 24 hours (h) or 30 days (d) of chronic hypercapnia. Within 24 h, chronic hypercapnia increased expression of the inflammatory cytokine IL-1β in the orbitofrontal cortex and medial prefrontal cortex, but at 30d IL-1β levels were not different relative to time-matched goats exposed to room-air. Additionally, Iba1 expression (a marker of microglial activation) was unaltered by chronic hypercapnia in all regions tested. Finally, levels of the total and phosphorylated AMPA receptor subunit GluR₂ were reduced within the hippocampus at both 24 h and 30 d of hypercapnia, and reduced following 30 d within the anterior insular cortex. These data suggest that chronic hypercapnia leads to CNS site-dependent acute inflammatory responses and shifts in select glutamate receptor expression/phosphorylation in brain regions contributing to cognitive function. Such changes may be indicative of alterations in glutamatergic receptor-mediated signaling and neuronal dysfunction that contribute to declines in cognitive function associated with human diseases defined or marked by chronic CO₂ retention.

Chronic Exposure to High Altitude: Synaptic, Astroglial and Memory Changes

Long-term operations carried out at high altitude (HA) by military personnel, pilots, and astronauts may trigger health complications. In particular, chronic exposure to high altitude (CEHA) has been associated with deficits in cognitive function. In this study, we found that mice exposed to chronic HA (5000 m for 12 weeks) exhibited deficits in learning and memory associated with hippocampal function and were linked with changes in the expression of synaptic proteins across various regions of the brain. Specifically, we found decreased levels of synaptophysin (SYP) (p < 0.05) and spinophilin (SPH) (p < 0.05) in the olfactory cortex, post synaptic density−95 (PSD-95) (p < 0.05), growth associated protein 43 (GAP43) (p < 0.05), glial fibrillary acidic protein (GFAP) (p < 0.05) in the cerebellum, and SYP (p < 0.05) and PSD-95 (p < 0.05) in the brainstem. Ultrastructural analyses of synaptic density and morphology in the hippocampus did not reveal any differences in CEHA mice compared to SL mice. Our data are novel and suggest that CEHA exposure leads to cognitive impairment in conjunction with neuroanatomically-based molecular changes in synaptic protein levels and astroglial cell marker in a region specific manner. We hypothesize that these new findings are part of highly complex molecular and neuroplasticity mechanisms underlying neuroadaptation response that occurs in brains when chronically exposed to HA.

Cell Proliferation in the Isolated Brains of Adult Zebrafish Incubated in Artificial Cerebrospinal Fluid

The high rate of cell proliferation in the zebrafish brain allows one to perform reliable studies on cellular molecules associated with cell proliferation. In this study, we show that 5-bromo-2'-deoxyuridine (BrdU)-labeled cells were detected in the isolated brains of adult zebrafish that were incubated in oxygenated artificial cerebrospinal fluid (aCSF) in vitro. The number of BrdU-labeled cells shown in the in vitro preparation was close to that in the in vivo study and was modified by treatment with various pharmacological agents, such as valproic acid. In parallel to cell proliferation, protein expression and neural activity could also be measured in the isolated brains maintained in aCSF.

Acute ingestion of rosemary water: Evidence of cognitive and cerebrovascular effects in healthy adults

BACKGROUND

The use of herbal extracts and supplements to enhance health and wellbeing is increasing in western society.

AIMS

This study investigated the impact of the acute ingestion of a commercially available water containing an extract and hydrolat of rosemary ( Rosmarinus officinalis L. syn. Salvia rosmarinus Schleid.). Aspects of cognitive functioning, mood and cerebrovascular response measured by near-infrared spectroscopy provided the dependent variables.

METHODS

Eighty healthy adults were randomly allocated to consume either 250 mL of rosemary water or plain mineral water. They then completed a series of computerised cognitive tasks, followed by subjective measures of alertness and fatigue. Near-infrared spectroscopy monitored levels of total, oxygenated and deoxygenated haemoglobin at baseline and throughout the cognitive testing procedure.

RESULTS

Analysis of the data revealed a number of statistically significant, small, beneficial effects of rosemary water on cognition, consistent with those found previously for the inhalation of the aroma of rosemary essential oil. Of particular interest here are the cerebrovascular effects noted for deoxygenated haemoglobin levels during cognitive task performance that were significantly higher in the rosemary water condition. This represents a novel finding in this area, and may indicate a facilitation of oxygen extraction at times of cognitive demand.

CONCLUSION

Taken together the data suggest potential beneficial properties of acute consumption of rosemary water. The findings are discussed in terms of putative metabolic and cholinergic mechanisms.