Downregulated Nuclear Factor E2-Related Factor 2 (Nrf2) Aggravates Cognitive Impairments via Neuroinflammation and Synaptic Plasticity in the Senescence-Accelerated Mouse Prone 8 (SAMP8) Mouse: A Model of Accelerated Senescence

Nrf2 Signaling Pathway: a Potential Therapeutic Target in Combating Oxidative Stress and Neurotoxicity in Chemotherapy-Induced Cognitive Impairment

Chemotherapy-induced cognitive impairment (CICI) is one of the major adverse effects of antineoplastic drugs, which decrease the quality of life in cancer survivors. Extensive experimental and clinical research suggests that chemotherapeutic drugs generate an enormous amount of reactive oxygen species (ROS), contributing to oxidative stress, neuroinflammation, blood-brain barrier (BBB) disruption, and neuronal death, eventually leading to CICI. Despite the progress in exploring different pathological mechanisms of CICI, effective treatment to prevent CICI progression has not been developed yet. Nrf2 is the principal transcription factor that regulates cellular redox balance and inflammation-related gene expression. Emerging evidence suggests that upregulation of Nrf2 and its target genes could suppress oxidative stress, and neuroinflammation, restore BBB integrity, and increase neurogenesis. This review discusses the role of Nrf2 in CICI, how it responds to oxidative stress, inflammation, neurotoxicity, and potential Nrf2 activators that could be used to enhance Nrf2 activation in CICI.

The Role of the Transcription Factor Nrf2 in Alzheimer’s Disease: Therapeutic Opportunities

Alzheimer’s disease (AD) is a common neurodegenerative disorder that affects the elderly. One of the key features of AD is the accumulation of reactive oxygen species (ROS), which leads to an overall increase in oxidative damage. The nuclear factor (erythroid-derived 2)-like 2 (Nrf2) is a master regulator of the antioxidant response in cells. Under low ROS levels, Nrf2 is kept in the cytoplasm. However, an increase in ROS production leads to a translocation of Nrf2 into the nucleus, where it activates the transcription of several genes involved in the cells’ antioxidant response. Additionally, Nrf2 activation increases autophagy function. However, in AD, the accumulation of Aβ and tau reduces Nrf2 levels, decreasing the antioxidant response. The reduced Nrf2 levels contribute to the further accumulation of Aβ and tau by impairing their autophagy-mediated turnover. In this review, we discuss the overwhelming evidence indicating that genetic or pharmacological activation of Nrf2 is as a potential approach to mitigate AD pathology.

Sulforaphane Increase Mitochondrial Biogenesis-Related Gene Expression in the Hippocampus and Suppresses Age-Related Cognitive Decline in Mice

Sulforaphane (SFN) is a potent activator of the transcriptional factor, Nuclear Factor Erythroid 2 (NF-E2)-Related factor 2 (NRF2). SFN and its precursor, glucoraphanin (sulforaphane glucosinolate, SGS), have been shown to ameliorate cognitive function in clinical trials and in vivo studies. However, the effects of SGS on age-related cognitive decline in Senescence-Accelerated Mouse Prone 8 (SAMP8) is unknown. In this study, we determined the preventive potential of SGS on age-related cognitive decline. One-month old SAMP8 mice or control SAM resistance 1 (SAMR1) mice were fed an ad libitum diet with or without SGS-containing broccoli sprout powder (0.3% w/w SGS in diet) until 13 months of age. SGS significantly improved long-term memory in SAMP8 at 12 months of age. Interestingly, SGS increased hippocampal mRNA and protein levels of peroxisome proliferator-activated receptor gamma coactivator-1 alpha (PGC1α) and mitochondrial transcription factor A (TFAM), which are master regulators of mitochondrial biogenesis, both in SAMR1 and SAMP8 at 13 months of age. Furthermore, mRNAs for nuclear respiratory factor-1 (NRF-1) and mitochondrial DNA-encoded respiratory complex enzymes, but not mitochondrial DNA itself, were increased by SGS in SAMP8 mice. These results suggest that SGS prevents age-related cognitive decline by maintaining mitochondrial function in senescence-accelerated mice.

Physical-Exercise-Induced Antioxidant Effects on the Brain and Skeletal Muscle

Erythroid-related nuclear factor 2 (NRF2) and the antioxidant-responsive-elements (ARE) signaling pathway are the master regulators of cell antioxidant defenses, playing a key role in maintaining cellular homeostasis, a scenario in which proper mitochondrial function is essential. Increasing evidence indicates that the regular practice of physical exercise increases cellular antioxidant defenses by activating NRF2 signaling. This manuscript reviewed classic and ongoing research on the beneficial effects of exercise on the antioxidant system in both the brain and skeletal muscle.

MEF2C ameliorates learning, memory, and molecular pathological changes in Alzheimer’s disease in vivo and in vitro

Myocyte enhancer factor 2C (MEF2C) is highly expressed in the nervous system, and regulates neuro-development, synaptic plasticity, and inflammation. However, its mechanism in Alzheimer's disease (AD) is underestimated. In this study, the role and mechanism of MEF2C were investigated in the brain tissue specimens from patients with AD, APPswe/PSEN1dE9 double transgenic (APP/PS1_DT) mice, and SH-SY5Y cells treated with β-amyloid peptide (Aβ). The results indicated that the expression of MEF2C is significantly reduced, and the expression of MEF2C/Aβ in different parts of brain is negatively correlated in patients with AD. Knockdown of MEF2C promotes cell apoptosis and the level of β-amyloid precursor protein cleaving enzyme 1 (BACE) but reduces BACE2 expression. In addition, knockdown of enhances the generation and aggregation of Aβ in the cortex of APP/PS1_DT mice, reduces the expression of synaptic proteins, exacerbates the ability of learning and memory of APP/PS1_DT mice, damages the structure of mitochondria, increases the oxidative stress (OS) level, and inhibits the expression levels of members of the Nrf2-ARE signal pathway. In summary, inhibition of MEF2C exacerbates the toxic effect of Aβ and , damages synaptic plasticity, reduces the ability of learning and memory of APP/PS1 mice, and increases the level of OS via the Nrf2-ARE signal pathway.

Reduced nicotinamide mononucleotide is a new and potent NAD+ precursor in mammalian cells and mice

Nicotinamide adenine dinucleotide (NAD⁺ ) homeostasis is constantly compromised due to degradation by NAD⁺ -dependent enzymes. NAD⁺ replenishment by supplementation with the NAD⁺ precursors nicotinamide mononucleotide (NMN) and nicotinamide riboside (NR) can alleviate this imbalance. However, NMN and NR are limited by their mild effect on the cellular NAD⁺ pool and the need of high doses. Here, we report a synthesis method of a reduced form of NMN (NMNH), and identify this molecule as a new NAD⁺ precursor for the first time. We show that NMNH increases NAD⁺ levels to a much higher extent and faster than NMN or NR, and that it is metabolized through a different, NRK and NAMPT-independent, pathway. We also demonstrate that NMNH reduces damage and accelerates repair in renal tubular epithelial cells upon hypoxia/reoxygenation injury. Finally, we find that NMNH administration in mice causes a rapid and sustained NAD⁺ surge in whole blood, which is accompanied by increased NAD⁺ levels in liver, kidney, muscle, brain, brown adipose tissue, and heart, but not in white adipose tissue. Together, our data highlight NMNH as a new NAD⁺ precursor with therapeutic potential for acute kidney injury, confirm the existence of a novel pathway for the recycling of reduced NAD⁺ precursors and establish NMNH as a member of the new family of reduced NAD⁺ precursors.

Stabilization of Delphinidin in Complex with Sulfobutylether-β-Cyclodextrin Allows for Antinociception in Inflammatory Pain

Aims: Delphinidin (DEL) is a plant-derived antioxidant with clinical potential to treat inflammatory pain but suffers from poor solubility and low bioavailability. The aim of the study was to develop a well-tolerated cyclodextrin (CD)-DEL complex with enhanced bioavailability and to investigate the mechanisms behind its antinociceptive effects in a preclinical model of inflammatory pain. Results: CD-DEL was highly soluble and stable in aqueous solution, and was nontoxic. Systemic administration of CD-DEL reversed mechanical and heat hyperalgesia, while its local application into the complete Freund's adjuvant (CFA)-induced inflamed paw dose-dependently reduced mechanical hyperalgesia, paw volume, formation of the lipid peroxidation product 4-hydroxy-2-nonenal (4-HNE), and tissue migration of CD68⁺ macrophages. CD-DEL also directly prevented 4-HNE-induced mechanical hyperalgesia, cold allodynia, and an increase in the intracellular calcium concentration into transient receptor potential ankyrin 1 expressing cells. Both 4-HNE- and CFA-induced reactive oxygen species (ROS) levels were sensitive to CD-DEL, while its capacity to scavenge superoxide anion radicals (inhibitory concentration 50 [IC₅₀]: 70 ± 5 μM) was higher than that observed for hydroxyl radicals (IC₅₀: 600 ± 50 μM). Finally, CD-DEL upregulated heme oxygenase 1 that was prevented by HMOX-1 siRNA in vitro. Innovation:In vivo application of DEL to treat inflammatory pain is facilitated by complexation with CD. Apart from its antioxidant effects, the CD-DEL has a unique second antioxidative mechanism involving capturing of 4-HNE into the CD cavity followed by displacement and release of the ROS scavenger DEL. Conclusion: CD-DEL has antinociceptive, antioxidative, and anti-inflammatory effects making it a promising formulation for the local treatment of inflammatory pain.

Loss of NRF2 accelerates cognitive decline, exacerbates mitochondrial dysfunction, and is required for the cognitive enhancing effects of Centella asiatica during aging

The water extract of Centella asiatica (CAW) improves cognitive and mitochondrial function and activates the nuclear factor erythroid 2-related factor 2 (NRF2) regulated antioxidant response pathway in aged mice. Here we investigate whether NRF2 activation is required for the cognitive and mitochondrial effects of prolonged CAW exposure during aging. Five-month-old NRF2 knockout (NRF2KO) and wild-type mice were treated with CAW for 1, 7, or 13 months. Each cohort underwent cognitive testing and hippocampal mitochondrial analyses. Age-related cognitive decline was accelerated in NRF2KO mice and while CAW treatment improved cognitive performance in wild-type mice, it had no effect on NRF2KO animals. Hippocampal mitochondrial function also declined further with age in NRF2KO mice and greater hippocampal mitochondrial dysfunction was associated with poorer cognitive performance in both genotypes. Long-term CAW treatment did not affect mitochondrial endpoints in animals of either genotype. These data indicate that loss of NRF2 results in accelerated age-related cognitive decline and worsened mitochondrial deficits. NRF2 also appears to be required for the cognitive enhancing effects of CAW during aging.

Resveratrol Supplementation Attenuates Cognitive and Molecular Alterations under Maternal High-Fat Diet Intake: Epigenetic Inheritance over Generations

Environmental factors such as maternal high-fat diet (HFD) intake can increase the risk of age-related cognitive decline in adult offspring. Epigenetic mechanisms are a possible link between diet effect and neurodegeneration across generations. Here, we found a significant decrease in triglyceride levels in a high-fat diet with resveratrol (RSV) HFD + RSV group and the offspring. Firstly, we obtained better cognitive performance in HFD+RSV groups and their offspring. Molecularly, a significant increase in DNA methylation (5-mC) levels, as well as increased gene expression of DNA methyltransferase 1 (Dnmt1) and Dnmt3a in HFD + RSV F1 group, were found. Furthermore, a significant increase of N6-Methyladenosine methylation (m6A) levels in HFD+RSV F1, as well as changes in gene expression of its enzymes Methyltransferase like 3 (Mettl3) and FTO alpha-ketoglutarate dependent dioxygenase (Fto) were found. Moreover, we found a decrease in gene expression levels of pro-inflammatory markers such as Interleukin 1β (Il1-β), Interleukin 6 (Il-6), Tumor necrosis factor-α (Tnf-α), C-X-C motif chemokine ligand 10 (Cxcl-10), the pro-inflammatory factors monocyte chemoattractant protein 1 (Mcp-1) and Tumor growth factor-β1 (Tgf-β1) in HFD+RSV and HFD+RSV F1 groups. Moreover, there was increased gene expression of neurotrophins such as Neural growth factor (Ngf), Neurotrophin-3 (Nt3), and its receptors Tropomyosin receptor kinase TrkA and TrkB. Likewise, an increase in protein levels of brain-derived neurotrophic factor (BDNF) and phospho-protein kinase B (p-Akt) in HFD+RSV F1 was found. These results suggest that maternal RSV supplementation under HFD intake prevents cognitive decline in senescence-accelerated mice prone 8 (SAMP8) adult offspring, promoting a reduction in triglycerides and leptin plasma levels, changes in the pro-inflammatory profile, and restoring the epigenetic landscape as well as synaptic plasticity.

The effect of dietary phytochemicals on nuclear factor erythroid 2-related factor 2 (Nrf2) activation: a systematic review of human intervention trials

We conducted a systematic review of human trials examining the effects of dietary phytochemicals on Nrf2 activation. In accordance with the PRISMA guidelines, Medline, Embase and CAB abstracts were searched for articles from inception until March 2020. Studies in adult humans that measured Nrf2 activation (gene or protein expression changes) following ingestion of a phytochemical, either alone or in combination were included. The study was pre-registered on the Prospero database (Registration Number: CRD42020176121). Twenty-nine full-texts were retrieved and reviewed for analysis; of these, eighteen were included in the systematic review. Most of the included participants were healthy, obese or type 2 diabetics. Study quality was assessed using the Cochrane Collaboration Risk of Bias Assessment tool. Twelve different compounds were examined in the included studies: curcumin, resveratrol and sulforaphane were the most common (n = 3 each). Approximately half of the studies reported increases in Nrf2 activation (n = 10); however, many were of poor quality and had an unclear or high risk of bias. There is currently limited evidence that phytochemicals activate Nrf2 in humans. Well controlled human intervention trials are needed to corroborate the findings from in vitro and animal studies.

Quercetin improves cognitive disorder in aging mice by inhibiting NLRP3 inflammasome activation

Quercetin is one of the most abundant dietary flavonoid compounds, and its mechanism for combating age-related neurodegenerative diseases is unclear. In this study, quercetin (35 and 70 mg kg^-1, orally administered for 4 weeks) was administered to 7-month-old aging mice (senescence-accelerated mouse prone 8 mice). As a result, it was found that quercetin could improve spatial learning and memory impairment displayed by aging mice in the Morris water maze. The results of immunoblotting reflected the protein expressions of the longevity factor (sirtuin1), inflammasomes (NLRP3 and ASC), synaptic marker (PSD95) and neurotrophic factors (BDNF and NGF) in the hippocampus of the brain. It indicated that the intervention of quercetin could increase the expression of sirtuin1 and prevent neuroinflammation, which was evident from the decrease in the protein levels of the astrocyte marker (GFAP) and inflammatory factors (cleaved-caspase 1, IL-1β and IL-18). In addition, quercetin could reduce the levels of malondialdehyde (MDA) and reactive oxygen species (ROS) in the hippocampus of aging mice. Current data indicated that quercetin might improve neuroinflammation in aging mice by regulating the Sirtuin1/NLRP3 pathway.

Targeting Transcription Factor Nrf2 (Nuclear Factor Erythroid 2-Related Factor 2) for the Intervention of Vascular Cognitive Impairment and Dementia

Vascular cognitive impairment and dementia (VCID) is an age-related, mild to severe mental disability due to a broad panel of cerebrovascular disorders. Its pathobiology involves neurovascular dysfunction, blood-brain barrier disruption, white matter damage, microRNAs, oxidative stress, neuroinflammation, and gut microbiota alterations, etc. Nrf2 (Nuclear factor erythroid 2-related factor 2) is the master regulator of redox status and controls the transcription of a panel of antioxidative and anti-inflammatory genes. By interacting with NF-κB (nuclear factor-κB), Nrf2 also fine-tunes the cellular oxidative and inflammatory balance. Aging is associated with Nrf2 dysfunction, and increasing evidence has proved the role of Nrf2 in mitigating the VCID process. Based on VCID pathobiologies and Nrf2 studies from VCID and other brain diseases, we point out several hypothetical Nrf2 targets for VCID management, including restoration of endothelial function and neurovascular coupling, preservation of blood-brain barrier integrity, reduction of amyloidopathy, promoting white matter integrity, and mitigating oxidative stress and neuroinflammation. Collectively, the Nrf2 pathway could be a promising direction for future VCID research. Targeting Nrf2 would shed light on VCID managing strategies.

Resveratrol Differently Modulates Group I Metabotropic Glutamate Receptors Depending on Age in SAMP8 Mice

Glutamate homeostasis is critical for neurotransmission as this excitatory neurotransmitter has a relevant role in cognition functions through ionotropic and metabotropic glutamate receptors in the central nervous system. During the last years, the role of the group I metabotropic glutamate receptors (mGluRs) in neurodegenerative diseases such as Alzheimer's disease has been intensely investigated. Resveratrol (RSV) is a natural polyphenolic compound that is thought to have neuroprotective properties for human health. However, little is known about the action of this compound on mGluR signaling. Therefore, the aim of this study was to investigate the possible modulation of group I mGluRs in SAMP8 mice five and seven months of age supplemented with RSV in the diet. Data reported herein show that RSV plays a different modulatory action on group I mGluRs: mGluR₅ is downregulated as age increases, independently of RSV presence, and mGluR₁ is upregulated or downregulated by RSV treatment depending on age (i.e., depending on mGluR₅ levels). In addition, a neuroprotective role can be inferred for RSV as lower glutamate levels, higher synapsin levels, and unchanged caspase-3 activity were detected after RSV treatment. In conclusion, our findings indicate that RSV treatment modifies the group I mGluR-mediated glutamatergic system in SAMP8 mice, which could contribute to the beneficial effects of this natural polyphenol.

Comparison of the Protective Effects of Ginsenosides Rb1 and Rg1 on Improving Cognitive Deficits in SAMP8 Mice Based on Anti-Neuroinflammation Mechanism

This present study was designed to investigate the different effects of ginsenosides Rb1 and Rg1 on improving cognitive deficits in 4-month-old SAMP8 mice. Mice were divided into six groups, including the SAMP8 group, the SAMP8 + Donepezil (1.6 mg/kg) group, the SAMP8 + Rb1 (30 and 60 µmol/kg), and SAMP8 + Rg1 (30 and 60 µmol/kg) groups. SAMR1 mice of the same age were used as the control group. Ginsenosides and donepezil were administrated orally to animals for 8 weeks, then the learning and memory ability of mice were measured by using Morris water maze (MWM) test, object recognition test and passive avoidance experiments. The possible mechanisms were studied including the anti-glial inflammation of Rb1 and Rg1 using HE staining, immunohistochemistry and western blot experiments. Results revealed that Rb1 and Rg1 treatment significantly improved the discrimination index of SAMP8 mice in the object recognition test. Rb1 (60 µmol/kg) and Rg1 (30, 60 µmol/kg) could significantly shorten the escape latency in the acquisition test of the MWM test in SAMP8 mice. Furthermore, Rb1 and Rg1 treatments effectively reduced the number of errors in the passive avoidance task in SAMP8 mice. Western blot experiments revealed that Rb1 showed higher effect than Rg1 in decreasing protein expression levels of ASC, caspase-1 and Aβ in the hippocampus of SAMP8 mice, while Rg1 was more effective than Rb1 in decreasing the protein levels of iNOS. In addition, although Rb1 and Rg1 treatments showed significant protective effects in repairing neuronal cells loss and inhibiting the activation of astrocyte and microglia in hippocampus of SAMP8 mice, Rb1 was more effective than Rg1. These results suggest that Rb1 and Rg1 could improve the cognitive impairment in SAMP8 mice, and they have different mechanisms for the treatment of Alzheimer's disease.

Loss of NRF2 leads to impaired mitochondrial function, decreased synaptic density and exacerbated age-related cognitive deficits

Activation of the antioxidant regulatory transcription factor NRF2 (Nuclear factor erythroid-derived 2) regulates cellular bioenergetics and improves neuronal health in aging. Yet how NRF2 participates in maintaining synaptic, mitochondrial and cognitive function has not been fully elucidated. This study investigates how loss of NRF2 affects neuronal metabolism, synaptic density and cognitive performance in aged mice. Dendritic arborization as well as synaptic and mitochondrial gene expression was evaluated in hippocampal neurons isolated from mice lacking NRF2 (NRF2KO) and from wild-type (WT) C57BL6 mice. Mitochondrial function of these neurons was evaluated using the Seahorse XF platform. Additionally learning, memory and executive function were assessed in 20 month old NRF2KO and age-matched WT mice using conditioned fear response (CFR) and odor discrimination reversal learning (ODRL) tests. Hippocampal bioenergetics was profiled using mitochondria isolated from these animals and tissue was harvested for assessment of mitochondrial and synaptic genes. NRF2KO neurons had reduced dendritic complexity and diminished synaptic gene expression. This was accompanied by impaired mitochondrial function and decreased mitochondrial gene expression. Similar mitochondrial deficits were observed in the brains of aged NRF2KO mice. These animals also had significantly impaired cognitive performance and reduced synaptic gene expression as well. These data point to a role for NRF2 in maintaining mitochondrial and cognitive function during aging and suggest that the transcription factor may be a viable target for cognitive enhancing interventions. Because mitochondrial dysfunction and cognitive impairment also occur together in many neurodegenerative conditions there may be broad therapeutic potential of NRF2 activating agents.

Hexavalent chromium-induced toxic effects on the antioxidant levels, histopathological alterations and expression of Nrf2 and MT2 genes in the branchial tissue of Ctenopharyngodon idellus

Ability of hexavalent chromium to accumulate and induce oxidative stress has been studied in the gills of Ctenopharyngodon idellus, with the resulting damage in the form of altered endogenous antioxidant enzyme activity and, histopathology in the tissue. The fish were exposed to 5.3 (C1) and 10.63 mg/L (C2) of hexavalent chromium and were scrutinised on 15th, 30^th and 45th day of toxicant exposure. Oxidative stress studied in terms of lipid peroxidation and glutathione levels and the antioxidant enzymes activity also exhibited alterations. The histopathological modifications in gills announced lesions in the form of hyperplasia, aneurysm, lamellar fusion, focal proliferation, epithelial degeneration and necrosis with loss of lamellae, bringing irreversible damage on 45th day with mean degree of tissue change value of 100.35 ± 10.69. Bioaccumulation of chromium, and increased anomalies in branchial tissue exhibited damage in concentration and time-dependent manner. The ultrastructural anomalies in the cellular morphology in the epithelial cells of filaments and lamellae, exhibited pleomorphic nuclei, swollen mitochondria, extensive vacuolation and loss of microridges in pavement cells. The tissue also displayed altered regulation of Nrf2 and Mt2 following Cr(VI) exposure with maximum downregulation on 45th day by 61 and 53%, respectively. PCA generated two principal components, PC1 (GSH, GST, CAT and SOD) and PC2 (DTC, MDA and Cr(VI) concentration). Thus, it can be concluded that accumulation of Cr(VI) induces alteration in the gene expression of Nrf2 and Mt2 leading to the development of oxidative stress, ensuing various pathological changes creating hindrance in fish survival.

Targeting Mitochondrial Defects to Increase Longevity in Animal Models of Neurodegenerative Diseases

Bioenergetic homeostasis is a vital process maintaining cellular health and has primary importance in neuronal cells due to their high energy demand markedly at synapses. Mitochondria, the metabolic hubs of the cells, are the organelles responsible for producing energy in the form of ATP by using nutrients and oxygen. Defects in mitochondrial homeostasis result in energy deprivation and can lead to disrupted neuronal functions. Mitochondrial defects adversely contribute to the pathogenesis of neurodegenerative diseases such as Alzheimer's (AD) and Parkinson's disease (PD). Mitochondrial defects not only include reduced ATP levels but also increased reactive oxygen species (ROS) leading to cellular damage. Here, we detail the mechanisms that lead to neuronal pathologies involving mitochondrial defects. Furthermore, we discuss how to target these mitochondrial defects in order to have beneficial effects as novel and complementary therapeutic avenues in neurodegenerative diseases. The critical evaluation of these strategies and their potential outcome can pave the way for finding novel therapies for neurodegenerative pathologies.

Nrf2 drives oxidative stress-induced autophagy in nucleus pulposus cells via a Keap1/Nrf2/p62 feedback loop to protect intervertebral disc from degeneration

Intervertebral disc (IVD) degeneration is known to aggravate with age and oxidative stress is implicated in the pathogenesis of many age-related diseases. Nuclear factor (erythroid-derived-2)-like 2 (Nrf2) can confer adaptive protection against oxidative and proteotoxic stress in cells. In this study, we assessed whether Nrf2 can protect against oxidative stress in nucleus pulposus (NP) cells. In addition, we investigated Nrf2 expression in NP tissue samples from patients with different degrees of IVD degeneration and a mouse model of aging and IVD degeneration and the influence of H₂O₂-induced oxidative stress on autophagic pathways in NP cells. Autophagy was assessed by measuring levels of autophagy-related protein (ATG) family members and the autophagic markers, p62 and LC3. We found that expression of Nrf2 progressively decreased in human NP tissue samples of patients with increasing degrees of IVD degeneration. Nrf2 deficiency leads to the degeneration of IVDs during aging. Nrf2 knockout also aggravates IVD degeneration and reduces autophagic gene expression in an induced mouse model of IVD degeneration. The detrimental effects of H₂O₂-induced oxidative stress were increased in autophagy-deficient cells via reduced expression of Atg7 and the Keap1–Nrf2–p62 autophagy pathway. Taken together, these results suggest that excessive oxidative stress causes the upregulation of autophagy, and autophagy acts as an antioxidant feedback response activated by a Keap1-Nrf2-p62 feedback loop in IVD degeneration.

Acupuncture Administration Improves Cognitive Functions and Alleviates Inflammation and Nuclear Damage by Regulating Phosphatidylinositol 3 Kinase (PI3K)/Phosphoinositol-Dependent Kinase 1 (PDK1)/Novel Protein Kinase C (nPKC)/Rac 1 Signaling Pathway in Senescence-Accelerated Prone 8 (SAM-P8) Mice

BACKGROUND Alzheimer's disease (AD) is an age-associated neurodegenerative disorder. This study aimed to investigate effects of acupuncture administration on cognitive function and associated mechanisms. MATERIAL AND METHODS Senescence-accelerated prone 8 (SAM-P8) mice were randomly divided into 3 groups: the SAM-P8 group (P8-CN), the SAM-P8 administrating with acupuncture (P8-Acup) group, and the SAM-P8 administrating without acupuncture (P8-Sham) group. Morris water maze test was conducted to evaluate cognitive functions (memory and learning ability). PDK1, nPKC, and Rac1 inhibitors were used to treat SAM-P8 mice. Transmission electron microscope analysis was used to examine nuclear damage hippocampal tissues. Hematoxylin and eosin (H&E) staining was employed to evaluate inflammation. Western blot was used to detect PI3K, PDK1, nPKC, and Rac 1 expression in hippocampal tissues. RESULTS Acupuncture administration significantly reduced PI3K, PDK1, nPKC, and Rac 1 levels compared to P8-CN group (P<0.05). Both acupuncture and enzyme inhibitors (NSC23766, Rottlerin, OSU03012) significantly improved cognitive functions, reduced inflammation, and alleviated nuclear damages of SAM-P8 mice compared to P8-CN group (P<0.05). Acupuncture significantly enhanced effects of inhibitors on inflammation and nuclear damages compared to inhibitor treatment single (P<0.05). Acupuncture significantly enhanced down-regulative effects of OSU03012 on PI3K and PDK1 levels, increased down-regulative effects of Rottlerin on nPKC and Rac 1 levels and enhanced effects of Rottlerin on Rac 1 compared to P8-CN group (P<0.05). CONCLUSIONS Acupuncture administration improved cognitive functions and alleviated inflammatory response and nuclear damage of SAM-P8 mice, by downregulating PI3K/PDK1/nPKC/Rac 1 signaling pathway. This study could provide potential insight for treating cognitive dysfunction and aging of AD patients.

Differential response to lead toxicity in rat primary microglia and astrocytes

Lead (Pb) is one of the most widely studied occupational and environmental toxins. Chronic exposure to Pb affects neural function in the central nervous system (CNS). Glial cells in the CNS, such as microglia and astrocytes, respond differently to Pb-induced toxicity. However, the underlying mechanism has not yet been identified. We measured the cell viability and intracellular Pb uptake in rat primary microglia and astrocytes using the CCK-8 assay and inductively coupled plasma mass spectrometry, and found that Pb decreased microglial viability at lower dosages than in astrocytes, while Pb uptake was greater in astrocytes. Pb-induced oxidative stress in microglia results in increased production of reactive oxygen species, down-regulation of glutathione, and enhanced Nrf2 protein expression, while there was no obvious change in astrocytes. The role of Nrf2 in Pb-induced oxidative stress has also been confirmed in primary microglia with the use of Nrf2 small interfering RNA and an Nrf2 agonist. These data indicate that primary microglia were more sensitive to Pb exposure than astrocytes, which is associated with an obvious oxidative stress response and up-regulation of Nrf2 might be involved in this process.