Whey protein powder with milk fat globule membrane attenuates Alzheimer's disease pathology in 3×Tg-AD mice by modulating neuroinflammation through the peroxisome proliferator-activated receptor γ signaling pathway.

Whey protein powder (PP), which is mainly derived from bovine milk, is rich in milk fat globule membrane (MFGM). The MGFM has been shown to play a role in promoting neuronal development and cognition in the infant brain. However, its role in Alzheimer's disease (AD) has not been elucidated. Here, we showed that the cognitive ability of 3×Tg-AD mice (a triple-transgenic mouse model of AD) could be improved by feeding PP to mice for 3 mo. In addition, PP ameliorated amyloid peptide deposition and tau hyperphosphorylation in the brains of AD mice. We found that PP could alleviate AD pathology by inhibiting neuroinflammation through the peroxisome proliferator-activated receptor γ (PPARγ)-nuclear factor-κB signaling pathway in the brains of AD mice. Our study revealed an unexpected role of PP in regulating the neuroinflammatory pathology of AD in a mouse model.

Different Effects and Mechanisms of Selenium Compounds in Improving Pathology in Alzheimer's Disease.

Owing to the strong antioxidant capacity of selenium (Se) in vivo, a variety of Se compounds have been shown to have great potential for improving the main pathologies and cognitive impairment in Alzheimer's disease (AD) models. However, the differences in the anti-AD effects and mechanisms of different Se compounds are still unclear. Theoretically, the absorption and metabolism of different forms of Se in the body vary, which directly determines the diversification of downstream regulatory pathways. In this study, low doses of Se-methylselenocysteine (SMC), selenomethionine (SeM), or sodium selenate (SeNa) were administered to triple transgenic AD (3× Tg-AD) mice for short time periods. AD pathology, activities of selenoenzymes, and metabolic profiles in the brain were studied to explore the similarities and differences in the anti-AD effects and mechanisms of the three Se compounds. We found that all of these Se compounds significantly increased Se levels and antioxidant capacity, regulated amino acid metabolism, and ameliorated synaptic deficits, thus improving the cognitive capacity of AD mice. Importantly, SMC preferentially increased the expression and activity of thioredoxin reductase and reduced tau phosphorylation by inhibiting glycogen synthase kinase-3 beta (GSK-3ß) activity. Glutathione peroxidase 1 (GPx1), the selenoenzyme most affected by SeM, decreased amyloid beta production and improved mitochondrial function. SeNa improved methionine sulfoxide reductase B1 (MsrB1) expression, reflected in AD pathology as promoting the expression of synaptic proteins and restoring synaptic deficits. Herein, we reveal the differences and mechanisms by which different Se compounds improve multiple pathologies of AD and provide novel insights into the targeted administration of Se-containing drugs in the treatment of AD.

Knockdown of the SELENOK gene induces ferroptosis in cervical cancer cells.

Selenoprotein K (SELENOK) is one of the endoplasmic reticulum (ER) proteins that mainly functions in the regulation of ER stress, calcium flux, and antioxidant defense. Reactive oxygen species (ROS) is one of the key indicators of ferroptosis, and SELENOK inhibition could disrupt ROS balance, and consequently might cause ferroptosis. However, there are no previous studies about the mechanism of SELENOK in ferroptosis by regulating ROS. In this study, we report the effect of SELENOK inhibition on cell proliferation, viability, iron recycling-associated proteins, ROS, antioxidant enzymes, and lipid peroxidation of cervical cancer cells (HeLa cells). The results showed that ROS levels and iron-dependent lipid peroxidation were significantly enhanced, whereas cell viability and proliferation were significantly downregulated, and resulted in marked reductions in tumor size after SELENOK knockdown. SELENOK knockdown also caused steep decreases in glutathione peroxidase 4/glutathione levels and deterioration in ROS scavenging ability, and exacerbated ferroptosis in HeLa cells. Our findings elucidated that SELENOK knockdown could shrink tumor size by regulating ferroptosis, which might provide a theoretical basis for treating cervical cancer.

SELENOM Knockout Induces Synaptic Deficits and Cognitive Dysfunction by Influencing Brain Glucose Metabolism.

Selenium, a trace element associated with memory impairment and glucose metabolism, mainly exerts its function through selenoproteins. SELENOM is a selenoprotein located in the endoplasmic reticulum (ER) lumen. Our study demonstrates for the first time that SELENOM knockout decreases synaptic plasticity and causes memory impairment in 10-month-old mice. In addition, SELENOM knockout causes hyperglycaemia and disturbs glucose metabolism, which is essential for synapse formation and transmission in the brain. Further research reveals that SELENOM knockout leads to inhibition of the brain insulin signaling pathway [phosphatidylinositol 3-kinase (PI3K)/AKT/mTOR/p70 S6 kinase pathway], which may impair synaptic plasticity in mice. High-fat diet (HFD) feeding suppresses the brain insulin signaling pathway in SELENOM knockout mice and leads to earlier onset of cognitive impairment at 5 months of age. In general, our study demonstrates that SELENOM knockout induces synaptic deficits via the brain insulin signaling pathway, thus leading to cognitive dysfunction in mice. These data strongly suggest that SELENOM plays a vital role in brain glucose metabolism and contributes substantially to synaptic plasticity.

Application of orthokeratology on myopia control and its effect on ocular surface and meibomian gland function in Chinese myopic adolescents.

Purpose: This study aimed to investigate the influence of orthokeratology (OK) on myopia control and ocular surface and meibomian gland function in myopic adolescents. Methods: A prospective study was conducted over a 12-month period. The subjects were classified into two groups, namely, the OK lens group and the frame glasses control group. Axial length, corneal curvature, ocular surface, and meibomian gland parameters were measured at baseline, 1, 3, 6, and 12 months after wearing OK lenses. Results: The axial length growth rate in the OK group was significantly slower than in the control group (P < 0.01). The naked eye vision and the ocular surface disease index (OSDI) scores recorded 1, 3, 6, and 12 months after wearing OK lenses were significantly higher than the scores recorded before wearing OK lenses. There was no significant difference in other ocular parameters at each follow-up time point compared with pre-wearing (P > 0.05). After using the OK lens for 6 months, the OSDI score and corneal fluorescein staining (CFS) score increased significantly (P < 0.001), but there were no significant differences in other parameters among the groups. No infectious keratitis occurred during the study. Conclusion: These results provide evidence that the use of OK lenses can control the axial growth and progress rate of myopia compared with frame glasses. During the 12-month follow-up, although wearing OK lenses may have aggravated dry eye symptoms, each patient's ocular surface and meibomian gland function did not change significantly, indicating that the use of OK lenses is a relatively safe modality for the control of myopia in adolescents.

Reversal of Lipid Metabolism Dysregulation by Selenium and Folic Acid Co-Supplementation to Mitigate Pathology in Alzheimer's Disease.

Aberrant lipid metabolism is reported to be closely related to the pathogenesis of neurodegenerative diseases, such as Alzheimer's disease (AD). Selenium (Se) and folate are two ideal and safe nutritional supplements, whose biological effects include regulating redox and homocysteine (Hcy) homeostasis in vivo. Here, to achieve effective multitarget therapy for AD, we combined Se and folic acid in a co-supplementation regimen (Se-FA) to study the therapeutic potential and exact mechanism in two transgenic mouse models of AD (APP/Tau/PSEN and APP/PS1). In addition to a reduction in Aß generation and tau hyperphosphorylation, a restoration of synaptic plasticity and cognitive ability was observed in AD mice upon Se-FA administration. Importantly, by using untargeted metabolomics, we found that these improvements were dependent on the modulation of brain lipid metabolism, which may be associated with an antioxidant effect and the promotion of Hcy metabolism. Thus, from mechanism to effects, this study systematically investigated Se-FA as an intervention for AD, providing important mechanistic insights to inform its potential use in clinical trials.

Selenomethionine Improves Mitochondrial Function by Upregulating Mitochondrial Selenoprotein in a Model of Alzheimer's Disease.

Alzheimer's disease (AD), the most common neurodegenerative disease in elderly humans, is pathologically characterized by amyloid plaques and neurofibrillary tangles. Mitochondrial dysfunction that occurs in the early stages of AD, which includes dysfunction in mitochondrial generation and energy metabolism, is considered to be closely associated with AD pathology. Selenomethionine (Se-Met) has been reported to improve cognitive impairment and reduce amyloid plaques and neurofibrillary tangles in 3xTg-AD mice. Whether Se-Met can regulate mitochondrial dysfunction in an AD model during this process remains unknown.In this study, the N2a-APP695-Swedish (N2aSW) cell and 8-month-old 3xTg-AD mice were treated with Se-Met in vitro and in vivo. Our study showed that the numbers of mitochondria were increased after treatment with Se-Met. Se-Met treatment also significantly increased the levels of NRF1 and Mfn2, and decreased those of OPA1 and Drp1. In addition, the mitochondrial membrane potential was significantly increased, while the ROS levels and apoptosis rate were significantly decreased, in cells after treatment with Se-Met. The levels of ATP, complex IV, and Cyt c and the activity of complex V were all significantly increased. Furthermore, the expression level of SELENO O was increased after Se-Met treatment. Thus, Se-Met can maintain mitochondrial dynamic balance, promote mitochondrial fusion or division, restore mitochondrial membrane potential, promote mitochondrial energy metabolism, inhibit intracellular ROS generation, and reduce apoptosis. These effects are most likely mediated via upregulation of SELENO O. In summary, Se-Met improves mitochondrial function by upregulating mitochondrial selenoprotein in these AD models.

Selenoprotein K deficiency-induced apoptosis: A role for calpain and the ERS pathway.

Selenoprotein K (SELENOK), an endoplasmic reticulum (ER) resident protein, is regulated by dietary selenium and expressed at a relatively high level in neurons. SELENOK has been shown to participate in oxidation resistance, calcium (Ca2+) flux regulation, and the ER-associated degradation (ERAD) pathway in immune cells. However, its role in neurons has not been elucidated. Here, we demonstrated that SELENOK gene knockout markedly enhanced ER stress (ERS) and increased apoptosis in neurons. SELENOK gene knockout elicited intracellular Ca2+ flux and activated the m-calpain/caspase-12 cascade, thus inducing neuronal apoptosis both in vivo and in vitro. In addition, SELENOK knockout significantly reduced cognitive ability and increased anxiety in 7-month-old mice. Our findings reveal an unexpected role of SELENOK in regulating ERS-induced neuronal apoptosis.

Roles of Selenoproteins in Brain Function and the Potential Mechanism of Selenium in Alzheimer's Disease.

Selenium (Se) and its compounds have been reported to have great potential in the prevention and treatment of Alzheimer's disease (AD). However, little is known about the functional mechanism of Se in these processes, limiting its further clinical application. Se exerts its biological functions mainly through selenoproteins, which play vital roles in maintaining optimal brain function. Therefore, selenoproteins, especially brain function-associated selenoproteins, may be involved in the pathogenesis of AD. Here, we analyze the expression and distribution of 25 selenoproteins in the brain and summarize the relationships between selenoproteins and brain function by reviewing recent literature and information contained in relevant databases to identify selenoproteins (GPX4, SELENOP, SELENOK, SELENOT, GPX1, SELENOM, SELENOS, and SELENOW) that are highly expressed specifically in AD-related brain regions and closely associated with brain function. Finally, the potential functions of these selenoproteins in AD are discussed, for example, the function of GPX4 in ferroptosis and the effects of the endoplasmic reticulum (ER)-resident protein SELENOK on Ca2+ homeostasis and receptor-mediated synaptic functions. This review discusses selenoproteins that are closely associated with brain function and the relevant pathways of their involvement in AD pathology to provide new directions for research on the mechanism of Se in AD.

Corrigendum: Selenomethionine Improves Mitochondrial Function by Upregulating Mitochondrial Selenoprotein in a Model of Alzheimer's Disease.

[This corrects the article DOI: 10.3389/fnagi.2021.750921.].

Selenium Restores Synaptic Deficits by Modulating NMDA Receptors and Selenoprotein K in an Alzheimer's Disease Model.

Aims: Strong evidence has implicated synaptic failure as a direct contributor to cognitive decline in Alzheimer's disease (AD), and selenium (Se) supplementation has demonstrated potential for AD treatment. However, the exact roles of Se and related selenoproteins in mitigating synaptic deficits remain unclear. Results: Our data show that selenomethionine (Se-Met), as the major organic form of Se in vivo, structurally restored synapses, dendrites, and spines, leading to improved synaptic plasticity and cognitive function in triple transgenic AD (3 × Tg-AD) mice. Furthermore, we found that Se-Met ameliorated synaptic deficits by inhibiting extrasynaptic N-methyl-d-aspartate acid receptors (NMDARs) and stimulating synaptic NMDARs, thereby modulating calcium ion (Ca2+) influx. We observed that a decrease in selenoprotein K (SELENOK) levels was closely related to AD, and a similar disequilibrium was found between synaptic and extrasynaptic NMDARs in SELENOK knockout mice and AD mice. Se-Met treatment upregulated SELENOK levels and restored the balance between synaptic and extrasynaptic NMDAR expression in AD mice. Innovation: These findings establish a key signaling pathway linking SELENOK and NMDARs with synaptic plasticity regulated by Se-Met, and thereby provide insight into mechanisms by which Se compounds mediate synaptic deficits in AD. Conclusion: Our study demonstrates that Se-Met restores synaptic deficits through modulating Ca2+ influx mediated by synaptic and extrasynaptic NMDARs in 3 × Tg-AD mice, and suggests a potentially functional interaction between SELENOK and NMDARs. Antioxid. Redox Signal. 35, 863-884.

Genome-wide identification of the expansin gene family reveals that expansin genes are involved in fibre cell growth in cotton.

BACKGROUND: Expansins (EXPs), a group of proteins that loosen plant cell walls and cellulosic materials, are involved in regulating cell growth and diverse developmental processes in plants. However, the biological functions of this gene family in cotton are still unknown. RESULTS: In this paper, we identified a total of 93 expansin genes in Gossypium hirsutum. These genes were classified into four subfamilies, including 67 GhEXPAs, 8 GhEXPBs, 6 GhEXLAs, and 12 GhEXLBs, and divided into 15 subgroups. The 93 expansin genes are distributed over 24 chromosomes, excluding Ghir_A02 and Ghir_D06. All GhEXP genes contain multiple exons, and each GhEXP protein has multiple conserved motifs. Transcript profiling and qPCR analysis revealed that the expansin genes have distinct expression patterns among different stages of cotton fibre development. Among them, 3 genes (GhEXPA4o, GhEXPA1A, and GhEXPA8h) were highly expressed in the initiation stage, 9 genes (GhEXPA4a, GhEXPA13a, GhEXPA4f, GhEXPA4q, GhEXPA8f, GhEXPA2, GhEXPA8g, GhEXPA8a, and GhEXPA4n) had high expression during the fast elongation stage, and GhEXLA1c and GhEXLA1f were preferentially expressed in the transition stage of fibre development. CONCLUSIONS: Our results provide a solid basis for further elucidation of the biological functions of expansin genes in relation to cotton fibre development and valuable genetic resources for future crop improvement.

Cognitive improvement and synaptic deficit attenuation by a multifunctional carbazole-based cyanine in AD mice model through regulation of Ca2+/CaMKII/CREB signaling pathway.

Accumulation of ß-amyloid (Aß) peptide and hyperphosphorylated tau in the brain is one of the pathological characteristics of Alzheimer's disease (AD) and attractive therapeutic targets in its treatment. In the present study, the cognitive ability of 4-month-old 3 × Tg-AD mice significantly improved after 40 days treatment with intraperitoneal injection of 2.25 mg/kg of SLOH, which is a multifunctional carbazole-based cyanine fluorophore. It reduced Aß deposition, tau levels and its hyperphosphorylation by modulating AKT and promoting protein phosphatase 2A activity in the brain as well as in the primary neurons of 3 × Tg-AD mice. Moreover, SLOH attenuated synaptic deficit both in vitro and in vivo by regulating the Ca2+/CaMKII/CREB signaling pathway. These findings strongly suggest that SLOH owns a high therapeutic potential to treat early onset AD.

Transcriptomic Insights into the Response of the Olfactory Bulb to Selenium Treatment in a Mouse Model of Alzheimer's Disease.

Alzheimer's disease (AD) is a devastating neurodegenerative disorder characterized by the presence of extracellular senile plaques primarily composed of Aß peptides and intracellular neurofibrillary tangles (NFTs) composed of hyperphosphorylated tau proteins. Olfactory dysfunction is an early clinical phenotype in AD and was reported to be attributable to the presence of NFTs, senile Aß plaques in the olfactory bulb (OB). Our previous research found that selenomethionine (Se-Met), a major form of selenium (Se) in organisms, effectively increased oxidation resistance as well as reduced the generation and deposition of Aß and tau hyperphosphorylation in the olfactory bulb of a triple transgenic mouse model of AD (3×Tg-AD), thereby suggesting a potential therapeutic option for AD. In this study, we further investigated changes in the transcriptome data of olfactory bulb tissues of 7-month-old triple transgenic AD (3×Tg-AD) mice treated with Se-Met (6 µg/mL) for three months. Comparison of the gene expression profile between Se-Met-treated and control mice revealed 143 differentially expressed genes (DEGs). Among these genes, 21 DEGs were upregulated and 122 downregulated. The DEGs were then annotated against the Gene Ontology (GO) and Kyoto Encyclopedia of Genes and Genomes (KEGG) databases. The results show that upregulated genes can be roughly classified into three types. Some of them mainly regulate the regeneration of nerves, such as Fabp7, Evt5 and Gal; some are involved in improving cognition and memory, such as Areg; and some are involved in anti-oxidative stress and anti-apoptosis, such as Adcyap1 and Scg2. The downregulated genes are mainly associated with inflammation and apoptosis, such as Lrg1, Scgb3a1 and Pglyrp1. The reliability of the transcriptomic data was validated by quantitative real time polymerase chain reaction (qRT-PCR) for the selected genes. These results were in line with our previous study, which indicated therapeutic effects of Se-Met on AD mice, providing a theoretical basis for further study of the treatment of AD by Se-Met.

Comparison of the effects of selenomethionine and selenium-enriched yeast in the triple-transgenic mouse model of Alzheimer's disease.

Alzheimer's disease (AD) is a complex, multifactorial neurodegenerative disease that exhibits multiple pathogeneses and heterogeneity. Selenium (Se) is an essential trace element for human and animal nutrition. It has been shown that supplementation with two organic forms of Se, Se-enriched yeast (Se-yeast) and selenomethionine (Se-Met), could improve cognitive impairment, reverse synaptic deficits and mitigate tau pathology in triple-transgenic (3× Tg) AD mice. Se-yeast is well known for its high Se-Met content, which may mediate its anti-AD effects. In addition, a large amount of the physiological and biochemical mechanisms of these two Se drugs in the amelioration AD pathology remains unknown. In this study, the content of Se-yeast aside from Se was analyzed, and the effects of Se-Met and Se-yeast on 3× Tg-AD mice were investigated and compared. The results showed that both Se-Met and Se-yeast not only significantly increased the Se levels, enhanced the antioxidant capacity and improved the cognitive decline in the model, but also decreased the Aß and tau pathologies in the brain tissue of the AD mice. Moreover, the ability of Se-Met to increase the Se levels in different tissues of the AD mice was more significant than that of Se-yeast. However, the positive effect of Se-yeast on improving the cognitive ability of the AD mice was better than that of Se-Met, likely due to the various elements, vitamins and other nutrients in Se-yeast. Collectively, these results suggest that Se-yeast has potential as a clinical health product or drug for AD but that Se-Met, as a pure organic Se compound, is more suitable for studying the therapeutic mechanism of Se because of its comprehensive effects on AD.

Selenium-enriched yeast inhibited ß-amyloid production and modulated autophagy in a triple transgenic mouse model of Alzheimer's disease.

As the most common cause of progressive intellectual failure in elderly humans, Alzheimer's disease (AD) is pathologically featured by amyloid plaques, synaptic loss, and neurofibrillary tangles. The amyloid plaques are mainly aggregates of amyloid ß-peptide (Aß), a primary factor contributing to the pathogenesis of AD. Elimination or reduction of the level of Aß is considered an important strategy in AD treatment. The pharmacotherapeutic efficacy of selenium (Se), an essential biological trace element for mammalian species, has been confirmed in a number of experimental models of neurodegenerative diseases. Selenium-enriched yeast (Se-yeast) is commonly used as a nutritional supplement for Se. In this study, we investigated the effects and underlying mechanisms of Se-yeast on Aß pathology in a 4-month-old triple transgenic mouse model of AD (3×Tg-AD mice). The administration of Se-yeast attenuated the deposition of Aß in the brains of AD mice, which was concomitant with decreased levels of LC3II. The Se-yeast treatment decreased the level of amyloid-protein precursor (APP), downregulated the activity of AMP-activated protein kinase (AMPK) and upregulated the activity of AKT/mTOR/p70S6K. Furthermore, the levels of p62 also significantly decreased, and the cathepsin D levels increased, accompanied by increased turnover of Aß and APP in Se-yeast-treated AD mice. In addition to decreasing the generation of Aß, Se-yeast also inhibited the initiation of autophagy by modulating the AMPK/AKT/mTOR/p70S6K signaling pathway and enhanced autophagic clearance, thus reducing the burden of Aß accumulation in the brains of AD mice. Our results further highlight the potential therapeutic effects of Se-yeast on AD.

Selenomethionine Attenuates the Amyloid-ß Level by Both Inhibiting Amyloid-ß Production and Modulating Autophagy in Neuron-2a/AßPPswe Cells.

Alzheimer's disease (AD) is a complex and progressive neurological disorder, and amyloid-ß (Aß) has been recognized as the major cause of AD. Inhibiting Aß production and/or enhancing the clearance of Aß to reduce its levels are still the effective therapeutic strategies pursued in anti-AD research. In previous studies, we have reported that selenomethionine (Se-Met), a major form of selenium in animals and humans with significant antioxidant capacity, can reduce both amyloid-ß (Aß) deposition and tau hyperphosphorylation in a triple transgenic mouse model of AD. In this study, a Se-Met treatment significantly decreased the Aß levels in Neuron-2a/AßPPswe (N2asw) cells, and the anti-amyloid effect of Se-Met was attributed to its ability to inhibit Aß generation by suppressing the activity of BACE1. Furthermore, both the LC3-II/LC3-I ratio and the number of LC3-positive puncta were significantly decreased in Se-Met-treated cells, suggesting that Se-Met also promoted Aß clearance by modulating the autophagy pathway. Subsequently, Se-Met inhibited the initiation of autophagy through the AKT-mTOR-p70S6K signaling pathway and enhanced autophagic turnover by promoting autophagosome-lysosome fusion and autophagic clearance. Our results further highlight the potential therapeutic effects of Se-Met on AD.

Long-Term Dietary Supplementation with Selenium-Enriched Yeast Improves Cognitive Impairment, Reverses Synaptic Deficits, and Mitigates Tau Pathology in a Triple Transgenic Mouse Model of Alzheimer's Disease.

Alzheimer's disease (AD) is a progressive neurodegenerative disorder characterized by multiple histopathological changes in the brain and by impairments in memory and cognitive function. Currently, there is no effective treatment that can halt or reverse the progression of this disease. Here, we explored the effects of 3 months of treatment with selenium-enriched yeast (Se-yeast), which is commonly used as a source of organic selenium (Se) for nutrition, on cognitive dysfunction and neuropathology in the triple transgenic mouse model of AD (3×Tg-AD mice). As the results revealed that Se-yeast significantly improved the spatial learning and memory retention of 3×Tg-AD mice, promoted neuronal activity, attenuated the activation of astrocytes and microglia, mitigated synaptic deficits, and reduced the levels of total tau and phosphorylated tau though inhibiting the activity of GSK-3ß, dietary supplementation with Se-yeast exerted multiple beneficial effects on the prevention or treatment of AD. These findings provide evidence of a potentially viable compound for AD treatment.

Selenomethionine Mitigates Cognitive Decline by Targeting Both Tau Hyperphosphorylation and Autophagic Clearance in an Alzheimer's Disease Mouse Model.

Tau pathology was recently identified as a key driver of disease progression and an attractive therapeutic target in Alzheimer's disease (AD). Selenomethionine (Se-Met), a major bioactive form of selenium (Se) in organisms with significant antioxidant capacity, reduced the levels of total tau and hyperphosphorylated tau and ameliorated cognitive deficits in younger triple transgenic AD (3xTg-AD) mice. Whether Se-Met has a similar effect on tau pathology and the specific mechanism of action in older 3xTg-AD mice remains unknown. Autophagy is a major self-degradative process to maintain cellular homeostasis and function. Autophagic dysfunction has been implicated in the pathogenesis of multiple age-dependent diseases, including AD. Modulation of autophagy has been shown to retard the accumulation of misfolded and aggregated proteins and to delay the progression of AD. Here, we found that 3xTg-AD mice showed significant improvement in cognitive ability after a 3-month treatment with Se-Met beginning at 8 months of age. In addition to attenuating the hyperphosphorylation of tau by modulating the activity of Akt/glycogen synthase kinase-3ß and protein phosphatase 2A, Se-Met-induced reduction of tau was also mediated by an autophagy-based pathway. Specifically, Se-Met improved the initiation of autophagy via the AMP-activated protein kinase-mTOR (mammalian target of rapamycin) signaling pathway and enhanced autophagic flux to promote the clearance of tau in 3xTg-AD mice and primary 3xTg neurons. Thus, our results demonstrate for the first time that Se-Met mitigates cognitive decline by targeting both the hyperphosphorylation of tau and the autophagic clearance of tau in AD mice. These data strongly support Se-Met as a potent nutraceutical for AD therapy.SIGNIFICANCE STATEMENT Selenium has been widely recognized as a vital trace element abundant in the brain with effects of antioxidant, anticancer, and anti-inflammation. In this study, we report that selenomethionine rescues spatial learning and memory impairments in aged 3xTg-AD mice via decreasing the level of tau protein and tau hyperphosphorylation. We find that selenomethionine promotes the initiation of autophagy via the AMPK-mTOR pathway and enhances autophagic flux, thereby facilitating tau clearance in vivo and in vitro We have now identified an additional, novel mechanism by which selenomethionine improves the cognitive function of AD mice. Specifically, our data suggest the effect of selenium/selenomethionine on an autophagic pathway in Alzheimer's disease.

Selenomethionine promoted hippocampal neurogenesis via the PI3K-Akt-GSK3ß-Wnt pathway in a mouse model of Alzheimer's disease.

The maintenance of neural system integrity and function is the ultimate goal for the treatment of neurodegenerative disease such as Alzheimer's disease (AD). Neurogenesis plays an integral role in the maintenance of neural and cognitive functions, and its dysfunction is regarded as a major cause of cognitive impairment in AD. Moreover, the induction of neurogenesis by targeting endogenous neural stem cells (NSCs) is considered as one of the most promising treatment strategies. Our previous studies demonstrated that selenomethionine (Se-Met) was able to reduce ß-amyloid peptide (Aß) deposition, decrease Tau protein hyperphosphorylation and markedly improve cognitive functions in triple transgenic (3xTg) AD mice. In this study, we reported that the therapeutic effect of Se-Met on AD could also be due to neurogenesis modulation. By using the cultured hippocampal NSCs from 3xTg AD mice, we discovered that Se-Met (1-10 µM) with low concentration could promote NSC proliferation, while the one with a high concentration (50,100 µM) inhibiting proliferation. In subsequent studies, we also found that Se-Met activated the signaling pathway of PI3K/Akt, and thereby inhibited the GSK3ß activity, which would further activated the ß-catenin/Cyclin-D signaling pathway and promote NSC proliferation. Besides, after the induction of Se-Met, the number of neurons differentiated from NSCs significantly increased, and the number of astrocytes decreased. After a 90-day treatment with Se-Met (6 µg/mL), the number of hippocampal neurons in 4-month-old AD mice increased significantly, while the one of astrocyte saw a sharp drop. Thus, Se-Met treatment promoted NSCs differentiation into neurons, and subsequently repaired damaged neural systems in AD mice. Being consistent with our in vitro studies, Se-Met acts through the PI3K-Akt- GSK3ß-Wnt signaling pathway in vivo. This study provides an unparalleled evidence that selenium (Se) compounds are, to some extent, effective in promoting neurogenesis, and therefore we propose a novel mechanism for Se-Met treatment in AD.