Activation of the Melanocortin-4 Receptor Prevents Oxidative Damage and Mitochondrial Dysfunction in Cultured Hippocampal Neurons Exposed to Ethanol

Activating MC4R Promotes Functional Recovery by Repressing Oxidative Stress-Mediated AIM2 Activation Post-spinal Cord Injury

Spinal cord injury (SCI) is a destructive neurological trauma that induces permanent sensory and motor impairment as well as a deficit in autonomic physiological function. Melanocortin receptor 4 (MC4R) is a G protein-linked receptor that is extensively expressed in the neural system and contributes to inhibiting inflammation, regulating mitochondrial function, and inducing programmed cell death. However, the effect of MC4R in the modulation of oxidative stress and whether this mechanism is related to the role of absent in melanoma 2 (AIM2) in SCI are not confirmed yet. In the current study, we demonstrated that MC4R is significantly increased in the neurons of spinal cords after trauma and oxidative stimulation of cells. Further, activation of MC4R by RO27-3225 effectively improved functional recovery, inhibited AIM2 activation, maintained mitochondrial homeostasis, repressed oxidative stress, and prevented Drp1 translocation to the mitochondria. Meanwhile, treating Drp1 inhibitors would be beneficial in reducing AIM2 activation, and activating AIM2 could abolish the protective effect of MC4R on neuron homeostasis. In conclusion, we demonstrated that MC4R protects against neural injury through a novel process by inhibiting mitochondrial dysfunction, oxidative stress, as well as AIM2 activation, which may serve as an available candidate for SCI therapy.

Hemichannels contribute to mitochondrial Ca2+ and morphology alterations evoked by ethanol in astrocytes

Alcohol, a toxic and psychoactive substance with addictive properties, severely impacts life quality, leading to significant health, societal, and economic consequences. Its rapid passage across the blood-brain barrier directly affects different brain cells, including astrocytes. Our recent findings revealed the involvement of pannexin-1 (Panx1) and connexin-43 (Cx43) hemichannels in ethanol-induced astrocyte dysfunction and death. However, whether ethanol influences mitochondrial function and morphology in astrocytes, and the potential role of hemichannels in this process remains poorly understood. Here, we found that ethanol reduced basal mitochondrial Ca2+ but exacerbated thapsigargin-induced mitochondrial Ca2+ dynamics in a concentration-dependent manner, as evidenced by Rhod-2 time-lapse recordings. Similarly, ethanol-treated astrocytes displayed increased mitochondrial superoxide production, as indicated by MitoSox labeling. These effects coincided with reduced mitochondrial membrane potential and increased mitochondrial fragmentation, as determined by MitoRed CMXRos and MitoGreen quantification, respectively. Crucially, inhibiting both Cx43 and Panx1 hemichannels effectively prevented all ethanol-induced mitochondrial abnormalities in astrocytes. We speculate that exacerbated hemichannel activity evoked by ethanol may impair intracellular Ca2+ homeostasis, stressing mitochondrial Ca2+ with potentially damaging consequences for mitochondrial fusion and fission dynamics and astroglial bioenergetics.

Mitochondria-tau association promotes cognitive decline and hippocampal bioenergetic deficits during the aging

Current studies indicate that pathological modifications of tau are associated with mitochondrial dysfunction, synaptic failure, and cognitive decline in neurological disorders and aging. We previously showed that caspase-3 cleaved tau, a relevant tau form in Alzheimer's disease (AD), affects mitochondrial bioenergetics, dynamics and synaptic plasticity by the opening of mitochondrial permeability transition pore (mPTP). Also, genetic ablation of tau promotes mitochondrial function boost and increased cognitive capacities in aging mice. However, the mechanisms and relevance of these alterations for the cognitive and mitochondrial abnormalities during aging, which is the primary risk factor for AD, has not been explored. Therefore, in this study we used aging C57BL/6 mice (2-15 and 28-month-old) to evaluate hippocampus-dependent cognitive performance and mitochondrial function. Behavioral tests revealed that aged mice (15 and 28-month-old) showed a reduced cognitive performance compared to young mice (2 month). Concomitantly, isolated hippocampal mitochondria of aged mice showed a significant decrease in bioenergetic-related functions including increases in reactive oxygen species (ROS), mitochondrial depolarization, ATP decreases, and calcium handling defects. Importantly, full-length and caspase-3 cleaved tau were preferentially present in mitochondrial fractions of 15 and 28-month-old mice. Also, aged mice (15 and 28-month-old) showed an increase in cyclophilin D (CypD), the principal regulator of mPTP opening, and a decrease in Opa-1 mitochondrial localization, indicating a possible defect in mitochondrial dynamics. Importantly, we corroborated these findings in immortalized cortical neurons expressing mitochondrial targeted full-length (GFP-T4-OMP25) and caspase-3 cleaved tau (GFP-T4C3-OMP25) which resulted in increased ROS levels and mitochondrial fragmentation, along with a decrease in Opa-1 protein expression. These results suggest that tau associates with mitochondria and this binding increases during aging. This connection may contribute to defects in mitochondrial bioenergetics and dynamics which later may conduce to cognitive decline present during aging.

Modulatory role of α-MSH in hippocampal-dependent memory impairment, synaptic plasticity changes, oxidative stress, and astrocyte reactivity induced by short-term high-fat diet intake

High-fat diet (HFD) consumption is associated with cognitive deficits and neurodegenerative diseases. Since the hippocampus is extremely sensitive to pathophysiological changes, neuroinflammation and the concomitant oxidative stress induced by HFD can significantly interfere with hippocampal-dependent functions related to learning and memory. The neuropeptide alpha-melanocyte stimulating hormone (α-MSH) mediates neuroprotective actions in the central nervous system and can reverse the effects of neuroinflammation in cognitive functions that depend on the hippocampus. In this study, we used male Wistar rats to evaluate the effect of short-term HFD intake (5 days) plus a mild immune challenge, Lipopolysaccharide (LPS 10 μg/kg) on contextual fear, changes in structural plasticity, oxidative stress, and astrocyte reactivation in the hippocampus. We also determined the possible modulatory role of α-MSH. HFD consumption was associated with an increase in markers of oxidative stress (Advanced oxidation protein products and Malondialdehyde) in the dorsal hippocampus (DH). We also found changes in hippocampal structural synaptic plasticity, observing a decrease in total spine in the DH after HFD plus LPS. We observed astrocyte proliferation and a significant increase in the percentage of the area occupied by GFAP. Treatment with α-MSH (0.1 μg/0.25 μl) in the DH reversed the effect of short-term HFD plus LPS on contextual fear memory, oxidative stress, and spine density. α-MSH also reduced astrocyte proliferation. Our present results indicate that HFD consumption for a short period sensitizes the central nervous system (CNS) to a subsequent immune challenge and impairs contextual fear memory and that α-MSH could have a modulatory protective effect.

Acetobacter pasteurianus BP2201 alleviates alcohol-induced hepatic and neuro-toxicity and modulate gut microbiota in mice

The excessive consumption of alcohol results in a dysbiosis of the gut microbiota, which subsequently impairs the gut microbiota-brain/liver axes and induces cognitive dysfunction and hepatic injury. This study aimed to investigate the potential effect of Acetobacter pasteurianus BP2201 in reducing the negative effects of alcohol consumption on cognitive function and liver health by modulating the gut microbiota-brain/liver axes. Treatment with A. pasteurianus BP2201 improved alcohol-induced hippocampal damage, suppressed neuroinflammation, promoted neuroprotein expression in the hippocampus and enhanced cognitive function. At the same time, A. pasteurianus BP2201 can also reduce serum lipid levels, relieve oxidative stress, inhibit TLR4/MyD88/NF-κB pathway, reduce the secretion of TNF-α and IL-1β, so as to improve alcoholic liver injury. Concomitantly, the treatment with A. pasteurianus BP2201 leads to a shift in the intestinal microbiota structure towards that of healthy individuals, inhibiting the proliferation of harmful bacteria and promoting the recovery of beneficial bacteria. In addition, it also improves brain cognitive dysfunction and liver health by affecting the gut microbiota-brain/liver axes by promoting the synthesis of relevant amino acids and the metabolism of nucleotide base components. These findings demonstrate the potential of regulating the gut microbiome and gut microbiota-brain/liver axes to mitigate alcohol-induced disease.

Protective Effect of Sargassum fusiforme Fucoidan against Ethanol-Induced Oxidative Damage in In Vitro and In Vivo Models

Our previous studies have evaluated the bioactivities of a fucoidan isolated from Sargassum fusiforme (SF-F). To further investigate the health benefit of SF-F, in the present study, the protective effect of SF-F against ethanol (EtOH)-induced oxidative damage has been evaluated in in vitro and in vivo models. SF-F effectively improved the viability of EtOH-treated Chang liver cells by suppressing apoptosis. In addition, the in vivo test results indicate that SF-F significantly and dose-dependently increased the survival rate of zebrafish treated with EtOH. Further research results show that this action works through decreasing cell death via reduced lipid peroxidation by scavenging intracellular reactive oxygen species in EtOH-stimulated zebrafish. These results indicate that SF-F effectively protected Chang liver cells and zebrafish against EtOH-induced oxidative damage and suggest the potential of SF-F to be used as an ingredient in the functional food industry.

Irisin attenuates ethanol-induced behavioral deficits in mice through activation of Nrf2 and inhibition of NF-κB pathways

This study aims to investigate the effect of irisin on ethanol-induced behavioral deficits and explore the underlying mechanisms. A mouse model of ethanol addiction/withdrawal was constructed through chronic ethanol administration. Depressive-like behaviors were evaluated by the tail suspension test and forced swimming test, and anxiety-like behaviors were evaluated by the marble-burying test and elevated plus maze test. The expression of Nrf2 was measured by western blotting. Levels of inflammatory mediators (NF-κB, TNF-α, IL-1β and IL-6) and oxidative stress factors (ROS, MDA, GSH and SOD) were detected by ELISA. The ethanol-induced PC12/BV2 cell injury model was used to elucidate whether the effect of irisin on ethanol-induced neurological injury was related to anti-inflammatory and antioxidant mechanisms. Ethanol-induced ethanol preference and emotional deficits were improved by chronic irisin treatment; however, these improvements were partly reversed by cotreatment with the Nrf2 inhibitor ML385. Further results implied that the improvement effect of irisin on behavioral abnormalities may be related to its anti-inflammatory and antioxidant effects. In detail, irisin inhibited ethanol-induced abnormal expression of ROS and MDA and upregulated the expression of GSH and SOD. Meanwhile, irisin treatment inhibited ethanol-induced overexpression of NF-κB, TNF-α, IL-1β and IL-6 in the hippocampus and cerebral cortex. The regulation of oxidative stress factors by irisin was reversed after ML385 treatment. In the in vitro study, overexpression of oxidative stress factors in ethanol-treated PC12 cells was inhibited by irisin treatment; however, the prevention was reversed after the knockdown of Nrf2 siRNA. Moreover, ethanol-induced overexpression of inflammatory mediators in BV2 cells was also inhibited by irisin treatment. Irisin improved depressive and anxiety-like behaviors induced by ethanol addiction/withdrawal in mice, and this protection was greatly associated with the NF-κB-mediated anti-inflammatory signaling pathway and Nrf2-mediated antioxidative stress signaling pathway.

From Natural Behavior to Drug Screening: Invertebrates as Models to Study Mechanisms Associated with Alcohol Use Disorders

Humans consume ethanol-containing beverages, which may cause an uncontrollable or difficult-to-control intake of ethanol-containing liquids and may result in alcohol use disorders. How the transition at the molecular level from "normal" ethanol-associated behaviors to addictive behaviors occurs is still unknown. One problem is that the components contributing to normal ethanol intake and their underlying molecular adaptations, especially in neurons that regulate behavior, are not clear. The fruit fly Drosophila melanogaster and the earthworm Caenorhabditis elegans show behavioral similarities to humans such as signs of intoxication, tolerance, and withdrawal. Underlying the phenotypic similarities, invertebrates and vertebrates share mechanistic similarities. For example in Drosophila melanogaster, the dopaminergic neurotransmitter system regulates the positive reinforcing properties of ethanol and in Caenorhabditis elegans, serotonergic neurons regulate feeding behavior. Since these mechanisms are fundamental molecular mechanisms and are highly conserved, invertebrates are good models for uncovering the basic principles of neuronal adaptation underlying the behavioral response to ethanol. This review will focus on the following aspects that might shed light on the mechanisms underlying normal ethanol-associated behaviors. First, the current status of what is required at the behavioral and cellular level to respond to naturally occurring levels of ethanol is summarized. Low levels of ethanol delay the development and activate compensatory mechanisms that in turn might be beneficial for some aspects of the animal's physiology. Repeated exposure to ethanol however might change brain structures involved in mediating learning and memory processes. The smell of ethanol is already a key component in the environment that is able to elicit behavioral changes and molecular programs. Minimal networks have been identified that regulate normal ethanol consumption. Other environmental factors that influence ethanol-induced behaviors include the diet, dietary supplements, and the microbiome. Second, the molecular mechanisms underlying neuronal adaptation to the cellular stressor ethanol are discussed. Components of the heat shock and oxidative stress pathways regulate adaptive responses to low levels of ethanol and in turn change behavior. The adaptive potential of the brain cells is challenged when the organism encounters additional cellular stressors caused by aging, endosymbionts or environmental toxins or excessive ethanol intake. Finally, to underline the conserved nature of these mechanisms between invertebrates and higher organisms, recent approaches to identify drug targets for ethanol-induced behaviors are provided. Already approved drugs regulate ethanol-induced behaviors and they do so in part by interfering with cellular stress pathways. In addition, invertebrates have been used to identify new compounds targeting molecules involved in the regulation in ethanol withdrawal-like symptoms. This review primarily highlights the advances of the last 5 years concerning Drosophila melanogaster, but also provides intriguing examples of Caenorhabditis elegans and Apis mellifera in support.

The Mechanism of TNF-α-Mediated Accumulation of Phosphorylated Tau Protein and Its Modulation by Propofol in Primary Mouse Hippocampal Neurons: Role of Mitophagy, NLRP3, and p62/Keap1/Nrf2 Pathway

Background

Neuroinflammation-induced phosphorylated Tau (p-Tau) deposition in central nervous system contributes to neurodegenerative disorders. Propofol possesses neuroprotective properties. We investigated its impacts on tumor necrosis factor-α (TNF-α)-mediated p-Tau deposition in neurons.

Methods

Mouse hippocampal neurons were exposed to propofol followed by TNF-α. Cell viability, p-Tau, mitophagy, reactive oxygen species (ROS), NOD-like receptor protein 3 (NLRP3), antioxidant enzymes, and p62/Keap1/Nrf2 pathway were investigated.

Results

TNF-α promoted p-Tau accumulation in a concentration- and time-dependent manner. TNF-α (20 ng/mL, 4 h) inhibited mitophagy while increased ROS accumulation and NLRP3 activation. It also induced glycogen synthase kinase-3β (GSK3β) while inhibited protein phosphatase 2A (PP2A) phosphorylation. All these effects were attenuated by 25 μM propofol. In addition, TNF-α-induced p-Tau accumulation was attenuated by ROS scavenger, NLRP3 inhibitor, GSK3β inhibitor, or PP2A activator. Besides, compared with control neurons, 100 μM propofol decreased p-Tau accumulation. It also decreased ROS and NLRP3 activation, modulated GSK3β/PP2A phosphorylation, leaving mitophagy unchanged. Further, 100 μM propofol induced p62 expression, reduced Keap1 expression, triggered the nuclear translocation of Nrf2, and upregulated superoxide dismutase (SOD) and heme oxygenase-1 (HO-1) expression, which was abolished by p62 knockdown, Keap1 overexpression, or Nrf2 inhibitor. Consistently, the inhibitory effect of 100 μM propofol on ROS and p-Tau accumulation was mitigated by p62 knockdown, Keap1 overexpression, or Nrf2 inhibitor.

Conclusions

In hippocampal neurons, TNF-α inhibited mitophagy, caused oxidative stress and NLRP3 activation, leading to GSK3β/PP2A-dependent Tau phosphorylation. Propofol may reduce p-Tau accumulation by reversing mitophagy and oxidative stress-related events. Besides, propofol may reduce p-Tau accumulation by modulating SOD and HO-1 expression through p62/Keap1/Nrf2 pathway.

Activation of the Nrf2 Pathway Prevents Mitochondrial Dysfunction Induced by Caspase-3 Cleaved Tau: Implications for Alzheimer’s Disease

Alzheimer’s disease (AD) is characterized by memory and cognitive impairment, accompanied by the accumulation of extracellular deposits of amyloid β-peptide (Aβ) and the presence of neurofibrillary tangles (NFTs) composed of pathological forms of tau protein. Mitochondrial dysfunction and oxidative stress are also critical elements for AD development. We previously showed that the presence of caspase-3 cleaved tau, a relevant pathological form of tau in AD, induced mitochondrial dysfunction and oxidative damage in different neuronal models. Recent studies demonstrated that the nuclear factor (erythroid-derived 2)-like 2 (Nrf2) plays a significant role in the antioxidant response promoting neuroprotection. Here, we studied the effects of Nrf2 activation using sulforaphane (SFN) against mitochondrial injury induced by caspase-3 cleaved tau. We used immortalized cortical neurons to evaluate mitochondrial bioenergetics and ROS levels in control and SFN-treated cells. Expression of caspase-3 cleaved tau induced mitochondrial fragmentation, depolarization, ATP loss, and increased ROS levels. Treatment with SFN for 24 h significantly prevented these mitochondrial abnormalities, and reduced ROS levels. Analysis of Western blots and rt-PCR studies showed that SFN treatment increased the expression of several Nrf2-related antioxidants genes in caspase-3 cleaved tau cells. These results indicate a potential role of the Nrf2 pathway in preventing mitochondrial dysfunction induced by pathological forms of tau in AD.

Quercetin promotes behavioral recovery and biomolecular changes of melanocortin-4 receptor in mice with ischemic stroke

OBJECTIVES

Ischemic stroke is known as a common causes of disability, lower psychological well-being as well as preventable death. The pathogenesis of ischemic stroke process becomes worse immediately after oxidative stress occurs. One of the flavonoids with antioxidant abilities is quercetin. This study was aimed to investigate quercetin administration on the behavioral functions (motor and sensory) and expression of melanocortin-4 receptor (MC4R) in mice with ischemic stroke.

METHODS

Male ICR mice were divided into sham, stroke, stroke with quercetin 100, 150, and 200 mg/kg. The stroke model was performed by blocking the left common carotid artery for 2 h. Quercetin was intraperitoneally administered daily for seven days. Evaluation was conducted during two weeks after induction using ladder rung walking test and narrow beam test for motoric function and adhesive removal tape test for sensory function. On day-14 mice were sacrificed, MC4R expression in the dorsal striatum was determined using RT-PCR.

RESULTS

Stroke decreased the motor, sensory function and MC4R mRNA expression in dorsal striatum. Quercetin improved motor and sensory function, and upregulated expression of MC4R.

CONCLUSIONS

Quercetin administration after ischemic stroke improves behavioral function, possibly through the upregulation of MC4R in the brain.