Selenium positively affects the proteome of 3 × Tg-AD mice cortex by altering the expression of various key proteins: unveiling the mechanistic role of selenium in AD prevention

The Role of Gut Microbiota in the Neuroprotective Effects of Selenium in Alzheimer's Disease

The objective of the present review was to provide a timely update on the molecular mechanisms underlying the beneficial role of Se in Alzheimer's disease pathogenesis, and discuss the potential role of gut microbiota modulation in this neuroprotective effect. The existing data demonstrate that selenoproteins P, M, S, R, as well as glutathione peroxidases and thioredoxin reductases are involved in regulation of Aβ formation and aggregation, tau phosphorylation and neurofibrillary tangles formation, as well as mitigate the neurotoxic effects of Aβ and phospho-tau. Correspondingly, supplementation with various forms of Se in cellular and animal models of AD was shown to reduce Aβ formation, tau phosphorylation, reverse the decline in brain antioxidant levels, inhibit neuronal oxidative stress and proinflammatory cytokine production, improve synaptic plasticity and neurogenesis, altogether resulting in improved cognitive functions. In addition, most recent findings demonstrate that these neuroprotective effects are associated with Se-induced modulation of gut microbiota. In animal models of AD, Se supplementation was shown to improve gut microbiota biodiversity with a trend to increased relative abundance of Lactobacillus, Bifidobacterium, and Desulfivibrio, while reducing that of Lachnospiracea_NK4A136, Rikenella, and Helicobacter. Moreover, the relative abundance of Se-affected taxa was significantly associated with Aβ accumulation, tau phosphorylation, neuronal oxidative stress, and neuroinflammation, indicative of the potential role of gut microbiota to mediate the neuroprotective effects of Se in AD. Hypothetically, modulation of gut microbiota along with Se supplementation may improve the efficiency of the latter in AD, although further detailed laboratory and clinical studies are required.

Subcellular proteomics insights into Alzheimer's disease development

Alzheimer's disease (AD), one of the most common dementias, is a neurodegenerative disease characterized by cognitive impairment and decreased judgment function. The expected number of AD patient is increasing in the context of the world's advancing medical care and increasing human life expectancy. Since current molecular mechanism studies on AD pathogenesis are incomplete, there is no specific and effective therapeutic agent. Mass spectrometry (MS)-based unbiased proteomics studies provide an effective and comprehensive approach. Many advances have been made in the study of the mechanism, diagnostic markers, and drug targets of AD using proteomics. This paper focus on subcellular level studies, reviews studies using proteomics to study AD-associated mitochondrial dysfunction, synaptic, and myelin damage, the protein composition of amyloid plaques (APs) and neurofibrillary tangles (NFTs), changes in tissue extracellular vehicles (EVs) and exosome proteome, and the protein changes in ribosomes and lysosomes. The methods of sample separation and preparation and proteomic analysis as well as the main findings of these studies are involved. The results of these proteomics studies provide insights into the pathogenesis of AD and provide theoretical resource and direction for future research in AD, helping to identify new biomarkers and drugs targets for AD.

The role of selenium in shaping mice brain metabolome and selenoproteome through the gut-brain axis by combining metabolomics, metallomics, gene expression and amplicon sequencing

Selenium (Se) is a trace element crucial for human health. Recently, the impact of Se supplementation on gut microbiota has been pointed out as well as its influence on the expression of certain selenoproteins and gut metabolites. This study aims to elucidate the link between Se supplementation, brain selenoproteins and brain metabolome as well as the possible connection with the gut-brain axis. To this end, an in vivo study with 40 BALB/c mice was carried out. The study included conventional (n=20) and mice model with microbiota depleted by antibiotics (n=20) under a regular or Se supplemented diet. Brain selenoproteome was determined by a transcriptomic/gene expression profile, while brain metabolome and gut microbiota profiles were accomplished by untargeted metabolomics and amplicon sequencing, respectively. The total content of Se in brain was also determined. The selenoproteins genes Dio and Gpx isoenzymes, SelenoH, SelenoI, SelenoT, SelenoV and SelenoW and 31 metabolites were significantly altered in the brain after Se supplementation in conventional mice, while 11 selenoproteins and 26 metabolites were altered in microbiota depleted mice. The main altered brain metabolites were related to glyoxylate and dicarboxylate metabolism, amino acid metabolism, and gut microbiota that have been previously related with the gut-brain axis (e.g., members of Lachnospiraceae and Ruminococcaceae families). Moreover, specific associations were determined between brain selenoproteome and metabolome, which correlated with the same bacteria, suggesting an intertwined mechanism. Our results demonstrated the effect of Se on brain metabolome through specific selenoproteins gene expression and gut microbiota.

Non-Enzymatic Antioxidants against Alzheimer's Disease: Prevention, Diagnosis and Therapy

Alzheimer's disease (AD) is a neurodegenerative disorder characterized by progressive memory loss and cognitive decline. Although substantial research has been conducted to elucidate the complex pathophysiology of AD, the therapeutic approach still has limited efficacy in clinical practice. Oxidative stress (OS) has been established as an early driver of several age-related diseases, including neurodegeneration. In AD, increased levels of reactive oxygen species mediate neuronal lipid, protein, and nucleic acid peroxidation, mitochondrial dysfunction, synaptic damage, and inflammation. Thus, the identification of novel antioxidant molecules capable of detecting, preventing, and counteracting AD onset and progression is of the utmost importance. However, although several studies have been published, comprehensive and up-to-date overviews of the principal anti-AD agents harboring antioxidant properties remain scarce. In this narrative review, we summarize the role of vitamins, minerals, flavonoids, non-flavonoids, mitochondria-targeting molecules, organosulfur compounds, and carotenoids as non-enzymatic antioxidants with AD diagnostic, preventative, and therapeutic potential, thereby offering insights into the relationship between OS and neurodegeneration.

Mice brain metabolomics after the exposure to a "chemical cocktail" and selenium supplementation through the gut-brain axis

Several environmental pollutants have been shown to damage brain and affect gut microbiota. Limited evidence is available about the impact of "chemical cocktails" (CC) of xenobiotics on brain metabolome and their possible influence in the gut-brain crosstalk. To this end, BALB/c mice were exposed to heavy metals (As, Hg, Cd) and pharmaceuticals (diclofenac and flumequine) under regular rodent diet or supplemented with selenium (Se). Selenium, an antioxidant well-known for its antagonism against the neurotoxicity of several pollutants, modulated several brain metabolic impairments caused by CC (e.g., brain levels of the excitatory amino acid N-acetyl aspartic acid) by influencing mainly the metabolisms of purine, glycosylate and dicarboxylate, glutamate, glycerophospholipid, alanine and aspartate. Numerous associations were obtained between brain metabolites and gut microbes and they changed after Se-supplementation (e.g., Lactobacillus was positively associated with a brain ceramide, phosphoserine, phosphocholine, vitamin D3 derivative, fatty acids, malic acid, amino acids, and urea after the exposure, but not after Se-supplementation). Our results showed numerous evidences about the impact of CC on brain metabolome, the potential role of Se as an antagonist and their impact on the gut-brain axis. Further research is needed to understand the complex mechanism of action implied on CC-brain-microbiota interactions.

Se-Methylselenocysteine (SMC) Improves Cognitive Deficits by Attenuating Synaptic and Metabolic Abnormalities in Alzheimer's Mice Model: A Proteomic Study

Se-methylselenocysteine (SMC) is a major selenocompound in selenium (Se) enriched plants and has been found to ameliorate neuropathology and cognitive deficits in triple-transgenic mice model of Alzheimer's disease (3 × Tg-AD mice). To explore the underlying molecular mechanisms, the present study is designed to elucidate the protein changes in the cortex of SMC-treated 3 × Tg-AD mice. After SMC supplementation, proteomic analysis revealed that 181, 271, and 41 proteins were identified as differentially expressed proteins (DEPs) between 3 × Tg-AD mice vs wild type (AD/WT group), SMC-treated AD mice vs AD (AD + SMC/AD), and AD + SMC/WT group, respectively. Among these, 138 proteins in the diseased group were reversed by SMC treatment. The DEPs in AD/WT group and AD + SMC/AD group were mainly related to metabolism, synapses, and antioxidant proteins, while their levels were decreased in AD mice but up-regulated after treating with SMC. In addition, we found reduced ATP levels and destroyed synaptic structures in the AD mice brains, which were significantly ameliorated upon SMC treatment. Our study suggests that energy metabolism disorders, abnormal amino acid metabolism, synaptic dysfunction, and oxidative stress may be the key pathogenic phenomena of AD. SMC reversed the expression of proteins associated with them, which might be the main mechanism of its intervention in AD.

Response of the critically endangered Przewalski's gazelle (Procapra przewalskii) to selenium deprived environment

Selenium (Se) is an essential mineral nutrient for animals. Se deprivation can lead to many disorders and even death. This study investigated the response of Przewalski's gazelle (P. przewalskii) to Se-deprived environment. We found that Se deprivation in soil and forage not only influenced the mineral contents of the blood and hair in P. przewalskii, but also severely disrupted their blood parameters. We identified significant changes in the abundance of 146 proteins and 25 metabolites (P < 0.05) in serum, including the selenoproteins L8IG93 (glutathione peroxidase) and F4YD09 (Cu/Zn superoxide dismutase). Furthermore, the major known proteins and metabolites associated with the Se stress response in P. przewalskii were Cu/Zn superoxide dismutase, the vitamin K-dependent protein C, the C4b-binding protein alpha chain, complement component C7, lipase linoleic acid, peptidase D, thymidine, pseudo-uridine, L-phenylalanine, L-glutamine, PGA1, and 15-deoxy-delta-12,14-PGJ2. The main signaling pathways involved included complement and coagulation cascades, metabolic pathways, and stress granule formation. Our results indicate that the intake of Se-deficient forage elicited an oxidative stress response in P. przewalskii. These findings provide insights into the response mechanisms of this threatened gazelle to Se stress, and enable the development of conservation strategies to protect populations on the Qinghai-Tibetan Plateau. SIGNIFICANCE: This study is the first to point out the presence of oxidative stress in P. przewalskii in selenium-deficient areas through proteomics and metabolomics studies. These findings should prove helpful for conservation efforts aimed at P. przewalskii populations and maintenance of the integrity of their ecological environment.

Proteomic Profiling of Cerebrum Mitochondria, Myelin Sheath, and Synaptosome Revealed Mitochondrial Damage and Synaptic Impairments in Association with 3 × Tg-AD Mice Model

Alzheimer's disease (AD) is the most common age-associated dementia with complex pathological hallmarks. Mitochondrion, synaptosome, and myelin sheath appear to be vulnerable and play a key role in the pathogenesis of AD. To clarify the early mechanism associated with AD, followed by subcellular components separation, we performed iTRAQ (isobaric tags for relative and absolute quantification)-based proteomics analysis to simultaneously investigate the differentially expressed proteins (DEPs) within the mitochondria, synaptosome, and myelin sheath in the cerebrum of the 6-month-old triple transgenic AD (3 × Tg-AD) and 6-month-old wild-type (WT) mice. A large number of DEPs between the AD and WT mice were identified. Most of them are related to mitochondria and synaptic dysfunction and cytoskeletal protein change. Differential expressions of Lrpprc, Nefl, and Sirpa were verified by Western blot analysis. The results suggest that decreased energy metabolism, impaired amino acid metabolism and neurotransmitter synthesis, increase compensatory fatty acid metabolism, up-regulated cytoskeletal protein expression, and oxidative stress are the early events of AD. Among these, mitochondrial damage, synaptic dysfunction, decreased energy metabolism, and abnormal amino acid metabolism are the most significant events. The results indicate that it is feasible to separate and simultaneously perform proteomics analysis on the three subcellular components.

Systems Biology of Selenium and Complex Disease

Selenium is an essential trace element for maintenance of overall health, whose deficiency and dyshomeostasis have been linked to a variety of diseases and disorders. The majority of previous researches focused on characterization of genes encoding selenoproteins or proteins involved in selenium metabolism as well as their functions. Many studies in humans also investigated the relationship between selenium and complex diseases, but their results have been inconsistent. In recent years, systems biology and "-omics" approaches have been widely used to study complex and global variations of selenium metabolism and function in physiological and different pathological conditions. The present paper reviews recent progress in large-scale and systematic analyses of the relationship between selenium status or selenoproteins and several complex diseases, mainly including population-based cohort studies and meta-analyses, genetic association studies, and some other omics-based studies. Advances in ionomics and its application in studying the interaction between selenium and other trace elements in human health and diseases are also discussed.

Insights into cancer and neurodegenerative diseases through selenoproteins and the connection with gut microbiota - current analytical methodologies

Introduction: Selenium plays many key roles in health especially in connection with cancer and neurodegenerative diseases. However, it needs to be appreciated that the essentiality/toxicity of selenium depends on both, a narrow range of concentration and the chemical specie involved. In this context, selenoproteins are essential biomolecules against these disorders, mainly due to its antioxidant action. To this end, analytical methodologies may allow identifying and quantifying individual selenospecies in human biofluids and tissues. Areas covered: This review focus on the role of selenoproteins in medicine, with special emphasis in cancer and neurodegenerative diseases, considering the possible link with gut microbiota. In particular, this article reviews the analytical techniques and procedures recently developed for the absolute quantification of selenoproteins and selenometabolites in human biofluids and tissues. Expert commentary: The beneficial role of selenium in human health has been extensively studied and reviewed. However, several challenges remain unsolved as discussed in this article: (i) speciation of selenium (especially selenoproteins) in cancer and neurodegenerative disease patients; (ii) supplementation of selenium in humans using functional foods and nutraceuticals; (iii) the link between selenium and selenoproteins expression and the gut microbiota and (iv) analytical methods and pitfalls for the absolute quantification of selenoproteins and selenometabolites.

The Anti-Tumor Agent Sodium Selenate Decreases Methylated PP2A, Increases GSK3βY216 Phosphorylation, Including Tau Disease Epitopes and Reduces Neuronal Excitability in SHSY-5Y Neurons

Selenium application as sodium selenate was repeatedly shown to have anti-carcinogenic properties by increasing levels of the serine/ threonine protein phosphatase 2A (PP2A) in cancer cells. PP2A has a prominent role in cell development, homeostasis, and in neurons regulates excitability. PP2A, GSK3β and Tau reside together in a complex, which facilitates their interaction and (dys)-function as has been reported for several neurological disorders. In this study we recorded maximum increase in total PP2A at 3 µM sodium selenate in a neuron cell line. In conjunction with these data, whole-cell electrophysiological studies revealed that this concentration had maximum effect on membrane potentials, conductance and currents. Somewhat surprisingly, the catalytically active form, methylated PP2A (mePP2A) was significantly decreased. In close correlation to these data, the phosphorylation state of two substrate proteins, sensitive to PP2A activity, GSK3β and Tau were found to be increased. In summary, our data reveal that sodium selenate enhances PP2A levels, but reduces catalytic activity of PP2A in a dose dependent manner, which fails to reduce Tau and GSK3β phosphorylation under physiological conditions, indicating an alternative route in the rescue of cell pathology in neurological disorders.