Selenoprotein T Deficiency Leads to Neurodevelopmental Abnormalities and Hyperactive Behavior in Mice

Selenium intake is an effective strategy for the improvement of cognitive decline in low cognition older Americans

Age-related cognitive decline is a prominent concern in older adults and selenium (Se) deficiency has been found to be associated with cognitive deficits. For the first time, the present study explored the association between Se intake and cognitive performance in older people with/without cognitive impairment using the data from the National Health and Nutrition Examination Survey 2011-2014. Weighted linear regression models were conducted to evaluate the association between dietary Se/total Se intakes and cognitive assessments. A total of 2387 participants were included. The significant positive association between dietary Se/total Se intakes and total scores of cognitive functioning tests existed only in the older people with low cognitive performance (p < 0.001), not in those with normal cognitive performance. In conclusion, Se intake was beneficial for cognitive decline only in the low cognition older people but failed in normal cognition older people.

New horizons for the role of selenium on cognitive function: advances and challenges

Cognitive deficits associated with oxidative stress and the dysfunction of the central nervous system are present in some neurodegenerative diseases, such as Alzheimer's disease and Parkinson's disease. Selenium (Se), an essential microelement, exhibits cognition-associated functions through selenoproteins mainly owing to its antioxidant property. Due to the disproportionate distribution of Se in the soil, the amount of Se varies greatly in various foods, resulting in a large proportion of people with Se deficiency worldwide. Numerous cell and animal experiments demonstrate Se deficiency-induced cognitive deficits and Se supplementation-improved cognitive performances. However, human studies yield inconsistent results and the mechanism of Se in cognition still remains elusive, which hinder the further exploration of Se in human cognition. To address the urgent issue, the review summarizes Se-contained foods (plant-based foods, animal-based foods, and Se supplements), brain selenoproteins, mechanisms of Se in cognition (improvement of synaptic plasticity, regulation of Zn2+ level, inhibition of ferroptosis, modulation of autophagy and de novo synthesis of L-serine), and effects of Se on cognitive deficits, as well as consequently sheds light on great potentials of Se in the prevention and treatment of cognitive deficits.

Selenoprotein T, a potential treatment of attention-deficit/hyperactivity disorder and comorbid pain in neonatal 6-OHDA lesioned mice

pathological pain and Attention-deficit/hyperactivity disorder (ADHD) are two complex multifactorial syndromes. The comorbidity of ADHD and altered pain perception is well documented in children, adolescents, and adults. According to pathophysiological investigations, the dopaminergic system's dysfunction provides a common basis for ADHD and comorbid pain. Growing evidence suggests that oxidative stress may be crucial in both pathologies. Recent studies revealed that a small peptide encompassing the redox-active site of selenoprotein T (PSELT), protects dopaminergic neurons and fibers as well as lesioned nerves in animal models. The current study aims to examine the effects of PSELT treatment on ADHD-like symptoms and pain sensitivity, as well as the role of catecholaminergic systems in these effects. Our results demonstrated that intranasal administration of PSELT reduced the hyperactivity in the open field, decreased the impulsivity displayed by 6-OHDA-lesioned male mice in the 5-choice serial reaction time task test and improved attentional performance. In addition, PSELT treatment significantly increased the nociception threshold in both normal and inflammatory conditions. Furthermore, anti-hyperalgesic activity was antagonized with sulpiride pre-treatment, but not by phentolamine, or propranolol pre-treatments. The present study suggests that PSELT reduces the severity of ADHD symptoms in mice and possesses potent antinociceptive effects which could be related to the involvement of D2/D3 dopaminergic receptors.

Selenium Nanoparticles in Protecting the Brain from Stroke: Possible Signaling and Metabolic Mechanisms

Strokes rank as the second most common cause of mortality and disability in the human population across the world. Currently, available methods of treating or preventing strokes have significant limitations, primarily the need to use high doses of drugs due to the presence of the blood-brain barrier. In the last decade, increasing attention has been paid to the capabilities of nanotechnology. However, the vast majority of research in this area is focused on the mechanisms of anticancer and antiviral effects of nanoparticles. In our opinion, not enough attention is paid to the neuroprotective mechanisms of nanomaterials. In this review, we attempted to summarize the key molecular mechanisms of brain cell damage during ischemia. We discussed the current literature regarding the use of various nanomaterials for the treatment of strokes. In this review, we examined the features of all known nanomaterials, the possibility of which are currently being studied for the treatment of strokes. In this regard, the positive and negative properties of nanomaterials for the treatment of strokes have been identified. Particular attention in the review was paid to nanoselenium since selenium is a vital microelement and is part of very important and little-studied proteins, e.g., selenoproteins and selenium-containing proteins. An analysis of modern studies of the cytoprotective effects of nanoselenium made it possible to establish the mechanisms of acute and chronic protective effects of selenium nanoparticles. In this review, we aimed to combine all the available information regarding the neuroprotective properties and mechanisms of action of nanoparticles in neurodegenerative processes, especially in cerebral ischemia.

Low-Se Diet Increased Mitochondrial ROS to Suppress Myoblasts Proliferation and Promote Apoptosis in Broilers via miR-365-3p/SelT Signaling Axis

microRNA (miRNA) controls the post-transcriptional translation of mRNA to affect the expression of many genes participating in functional interaction pathways. Selenoproteins are characterized by their antioxidant activity, wherein selenoprotein T (SelT) is an essential membrane-bound selenoprotein serving as a guardian of intracellular homeostasis. During muscle development and regeneration, myoblasts enter the cell cycle and rapidly proliferate. However, the role of SelT in muscle development and selenium (Se) deficiency-induced muscle damage remains poorly investigated. This study established Se deficient broiler models, chicken embryos models, and cultured chicken primary myoblasts in vitro. We showed that Se deficiency induced skeletal muscle damage in broilers, promoted miR-365-3p expression, and downregulated the level of SelT, significantly. The absence of SelT led to the accumulation of mitochondrial superoxide and downregulated mitochondrial dynamics gene expression, which, in turn, induced the disruption of mitochondria potential and blocked the oxidative phosphorylation (OXPHOS) process. Limited ATP production rate caused by mitochondrial ROS overproduction went along with cell cycle arrest, cell proliferation slowness, and myocyte apoptosis increase. Using Mito-TEMPO for mitochondrial ROS elimination could effectively mitigate the above adverse reactions and significantly restore the proliferation potential of myoblasts. Moreover, we identified miR-365-3p, a miRNA that targeted SelT mRNA to inhibit myoblast proliferation by disrupting intracellular redox balance. The omics analysis results showed that Se deficiency led to the significant enrichment of "cell cycle", "oxidative stress response", and "oxidative phosphorylation" pathway genes. Finally, we proved that the effect of the miR-365-3p/SelT signaling axis on muscle development did exist in the chicken embryo stage. In summary, our findings revealed that miR-365-3p was involved in broiler skeletal muscle damage in Se deficiency by targeting SelT, and SelT, serving as an intracellular homeostasis guardian, resisted mitochondrial oxidative stress, and protected ATP generation, promoting myoblast proliferation and inhibiting apoptosis. This study provides an attractive target for the cultivated meat industry and regenerative medicine.

Functional analysis of selenok, selenot and selenop promoters and their regulation by selenium in yellow catfish Pelteobagrus fulvidraco

The selenok, selenot and selenop are three key selenoproteins involved in stress response. Our study, using the yellow catfish Pelteobagrus fulvidraco as the experimental animal, obtained the 1993-bp, 2000-bp and 1959-bp sequences of selenok, selenot and selenop promoters, respectively, and predicted the binding sites of several transcriptional factors on their promoters, such as Forkhead box O 4 (FoxO4), activating transcription factor 4 (ATF4), Kruppel-like factor 4 (KLF4) and nuclear factor erythroid 2-related factor 2 (NRF2). Selenium (Se) increased the activities of the selenok, selenot and selenop promoters. FoxO4 and Nrf2 can directly bind with selenok promoter and controlled selenok promoter activities positively; KLF4 and Nrf2 can directly bind with selenot promoter and controlled selenot promoter activities positively; FoxO4 and ATF4 can directly bind to selenop promoter and regulated selenop promoter activities positively. Se promoted FoxO4 and Nrf2 binding to selenok promoter, KLF4 and Nrf2 binding to selenot promoter, and FoxO4 and ATF4 binding to selenop promoter. Thus, we provide the first evidence for FoxO4 and Nrf2 bindnig elements in selenok promoter, KLF4 and Nrf2 binding elements in selenot promoter, and FoxO4 and ATF4 binding elements in selenop promoter, and offer novel insight into regulatory mechanism of these selenoproteins induced by Se.

The role of selenoproteins in neurodevelopment and neurological function: Implications in autism spectrum disorder

Selenium and selenoproteins play a role in many biological functions, particularly in brain development and function. This review outlines the role of each class of selenoprotein in human brain function. Most selenoproteins play a large antioxidant role within the brain. Autism spectrum disorder (ASD) has been shown to correlate with increased oxidative stress, and the presumption of selenoproteins as key players in ASD etiology are discussed. Further, current literature surrounding selenium in ASD and selenium supplementation studies are reviewed. Finally, perspectives are given for future directions of selenoprotein research in ASD.

Selenoprotein I (selenoi) as a critical enzyme in the central nervous system

Selenoprotein I (selenoi) is a unique selenocysteine (Sec)-containing protein widely expressed throughout the body. Selenoi belongs to two different protein families: the selenoproteins that are characterized by a redox reactive Sec residue and the lipid phosphotransferases that contain the highly conserved cytidine diphosphate (CDP)-alcohol phosphotransferase motif. Selenoi catalyzes the third reaction of the CDP-ethanolamine branch of the Kennedy pathway within the endoplasmic reticulum membrane. This is not a redox reaction and does not directly involve the Sec residue, making selenoi quite distinct among selenoproteins. Selenoi is also unique among lipid phosphotransferases as the only family member containing a Sec residue near its C-terminus that serves an unknown function. The reaction catalyzed by selenoi involves the transfer of the ethanolamine phosphate group from CDP-ethanolamine to one of two lipid donors, 1,2-diacylglycerol (DAG) or 1-alkyl-2-acylglycerol (AAG), to produce PE or plasmanyl PE, respectively. Plasmanyl PE is subsequently converted to plasmenyl PE by plasmanylethanolamine desaturase. Both PE and plasmenyl PE are critical phospholipids in the central nervous system (CNS), as demonstrated through clinical studies involving SELENOI mutations as well as studies in cell lines and mice. Deletion of SELENOI in mice is embryonic lethal, while loss-of-function mutations in the human SELENOI gene have been found in rare cases leading to a form of hereditary spastic paraplegia (HSP). HSP is an upper motor disease characterized by spasticity of the lower limbs, which is often manifested with other symptoms such as impaired vision/hearing, ataxia, cognitive/intellectual impairment, and seizures. This article will summarize the current understanding of selenoi as a metabolic enzyme and discuss its role in the CNS physiology and pathophysiology.

Emerging roles of ER-resident selenoproteins in brain physiology and physiopathology

The brain has a very high oxygen consumption rate and is particularly sensitive to oxidative stress. It is also the last organ to suffer from a loss of selenium (Se) in case of deficiency. Se is a crucial trace element present in the form of selenocysteine, the 21st proteinogenic amino acid present in selenoproteins, an essential protein family in the brain that participates in redox signaling. Among the most abundant selenoproteins in the brain are glutathione peroxidase 4 (GPX4), which reduces lipid peroxides and prevents ferroptosis, and selenoproteins W, I, F, K, M, O and T. Remarkably, more than half of them are proteins present in the ER and recent studies have shown their involvement in the maintenance of ER homeostasis, glycoprotein folding and quality control, redox balance, ER stress response signaling pathways and Ca2+ homeostasis. However, their molecular functions remain mostly undetermined. The ER is a highly specialized organelle in neurons that maintains the physical continuity of axons over long distances through its continuous distribution from the cell body to the nerve terminals. Alteration of this continuity can lead to degeneration of distal axons and subsequent neuronal death. Elucidation of the function of ER-resident selenoproteins in neuronal pathophysiology may therefore become a new perspective for understanding the pathophysiology of neurological diseases. Here we summarize what is currently known about each of their molecular functions and their impact on the nervous system during development and stress.

Selenoproteins in brain development and function

Expression of selenoproteins is widespread in neurons of the central nervous system. There is continuous evidence presented over decades that low levels of selenium or selenoproteins are linked to seizures and epilepsy indicating a failure of the inhibitory system. Many developmental processes in the brain depend on the thyroid hormone T3. T3 levels can be locally increased by the action of iodothyronine deiodinases on the prohormone T4. Since deiodinases are selenoproteins, it is expected that selenoprotein deficiency may affect development of the central nervous system. Studies in genetically modified mice or clinical observations of patients with rare diseases point to a role of selenoproteins in brain development and degeneration. In particular selenoprotein P is central to brain function by virtue of its selenium transport function into and within the brain. We summarize which selenoproteins are essential for the brain, which processes depend on selenoproteins, and what is known about genetic deficiencies of selenoproteins in humans. This review is not intended to cover the potential influence of selenium or selenoproteins on major neurodegenerative disorders in human.

The Role of Selenoproteins SELENOM and SELENOT in the Regulation of Apoptosis, ER Stress, and Calcium Homeostasis in the A-172 Human Glioblastoma Cell Line

Simple Summary

In this work, we present for the first time the effects of the suppression of the activity of poorly studied selenoproteins SELENOM and SELENOT in human glioblastoma cells, which is extremely important for understanding the functions of these proteins in brain cells. It has been shown that despite the structural similarity of these proteins, they affect the viability of these cancer cells in different ways, affecting various molecular mechanisms of regulation of pro-apoptotic genes, ER stress markers, and their physiological partners, as well as the regulation of cytosolic calcium.

Abstract

It is known that seven mammalian selenoproteins are localized in the endoplasmic reticulum: SELENOM, SELENOT, SELENOF, SELENOK, SELENOS, SELENON, and DIO2. Among them, SELENOM and SELENOT are the least studied; therefore, the study of their function using the widespread method of suppressing the expression of genes encoding these proteins and the activity of the enzymes themselves by RNA interference is of great interest. We have shown that a decrease in the expression of SELENOM and SELENOT mRNA in the A-172 human glioblastoma cell line by more than 10 times and the quantitative content of enzymes by more than 3 times leads to ER stress, expressed as a decrease in the ER capacity for storing Ca²⁺ ions. At the level of regulation of apoptotic processes, SELENOM knockdown leads to an increase in the expression of pro-apoptotic CHOP, GADD34, PUMA, and BIM genes, but a compensatory increase in the levels of SELENOT and antioxidant genes from the group of glutathione peroxidases and thioredoxins did not induce cell death. Knockdown of SELENOT had the opposite effect, reducing the expression of pro-apoptotic proteins and regulating the level of a smaller number of genes encoding antioxidant enzymes, which also did not affect the baseline level of apoptosis in the studied cells. At the same time, ER stress induced by MSA or SeNPs induced a more pronounced pro-apoptotic effect in SELENOT knockdown cells through suppression of the expression of selenium-containing antioxidant proteins. Thus, in this work, for the first time, the mechanisms of fine regulation of the processes of apoptosis, cell proliferation, and ER stress by two ER resident proteins, SELENOM and SELENOT, are touched upon, which is not only fundamental but also applied to clinical importance due to the close relationship between the calcium signaling system of cells, folding proteins-regulators of apoptosis and cell survival pathways.

miR-431-5p Regulates Apoptosis of Cardiomyocytes After Acute Myocardial Infarction via Targeting Selenoprotein T

Acute myocardial infarction (AMI) represents the acute manifestation of coronary artery disease. In recent years, microRNAs (miRNAs) have been extensively studied in AMI. This study focused on the role of miR-431-5p in AMI and its effect on cardiomyocyte apoptosis after AMI. The expression of miR-431-5p was analyzed by quantitative real-time PCR (qRT-PCR). By interfering with miR-431-5p in hypoxia-reoxygenation (H/R)-induced HL-1 cardiomyocytes, the effect of miR-431-5p on cardiomyocyte apoptosis after AMI was examined. The interaction between miR-431-5p and selenoprotein T (SELT) mRNA was verified by dual-luciferase reporter assay. Cell apoptosis was determined by terminal deoxynucleotidyl transferase dUTP nick end labeling (TUNEL) assay and flow cytometry. Cell viability was examined by 3-(4,5)-dimethylthiahiazo(-z-y1)-3,5-di-phenytetrazoliumromide (MTT) assay. The results of qRT-PCR showed that the expression of miR-431-5p in AMI myocardial tissues and H/R-induced HL-1 cardiomyocytes was significantly increased. After interfering with miR-431-5p, the expression of SELT in HL-1 cells was up-regulated, cell apoptosis was decreased, cell viability was increased, and lactate dehydrogenase (LDH) activity was decreased. The dual-luciferase reporter assay confirmed the targeting relationship between miR-431-5p and SELT1 3’ untranslated region (UTR). In H/R-induced HL-1 cells, the simultaneous silencing of SELT and miR-431-5p resulted in a decrease of Bcl-2 expression, an increase of Bax expression, and an increase of cleaved-caspase 3 expression compared with silencing miR-431-5p alone. Also, cell viability was decreased, while LDH activity was increased by the simultaneous silencing of SELT and miR-431-5p. Interfering miR-431-5p protected cardiomyocytes from AMI injury via restoring the expression of SELT, providing new ideas for the treatment of AMI.

Abrogating Oxidative Stress as a Therapeutic Strategy against Parkinson’s Disease: A Mini Review of the Recent Advances on Natural Therapeutic Antioxidant and Neuroprotective Agents

Background:

Reactive oxygen species (ROS) play a vital role in cell signaling when maintained at low concentrations. However, when ROS production exceeds the neutralizing capacity of endogenous antioxidants, oxidative stress is observed, which has been shown to contribute to neurodegenerative diseases such as Parkinson's disease (PD). PD is a progressive disorder characterized by the loss of dopaminergic neurons from the striatum, which leads to motor and nonmotor symptoms. Although the complex interplay of mechanisms responsible are yet to be fully understood, oxidative stress was found to be positively associated with PD. Despite active research, currently proposed regimens mainly focus on regulating dopamine metabolism within the brain, even though these treatments have shown limited long-term efficacy and several side effects. Due to the implication of oxidative stress in the pathophysiology of PD, natural antioxidant compounds have attracted interest as potential therapeutics over the last years, with a more favorable anticipated safety profile due to their natural origin. Therefore, natural antioxidants are currently being explored as promising anti-PD agents.

Objective:

In this mini review, emphasis was given to presently studied natural antioxidant and neuroprotective agents that have shown positive results in PD animal models.

Methods:

For this purpose, recent scientific articles were reviewed and discussed, with the aim to highlight the most up-to-date advances on PD treatment strategies related to oxidative stress.

Results:

A plethora of natural compounds are actively being explored against PD, including kaemferol, icaritin, artemisinin, and α-bisabolol, with promising results. Most of these compounds have shown adequate neuroprotective ability along with redox balance restoration, normalized mitochondrial function and limitation of the oxidative damage.

Conclusion:

In conclusion, natural antioxidants may be the way forward to novel treatments against PD, when the limitations of correct dosing and appropriate combinations are resolved.

Hepatic Proteomic Analysis of Selenoprotein T Knockout Mice by TMT: Implications for the Role of Selenoprotein T in Glucose and Lipid Metabolism

Selenoprotein T (SELENOT, SelT), a thioredoxin-like enzyme, exerts an essential oxidoreductase activity in the endoplasmic reticulum. However, its precise function remains unknown. To gain more understanding of SELENOT function, a conventional global Selenot knockout (KO) mouse model was constructed for the first time using the CRISPR/Cas9 technique. Deletion of SELENOT caused male sterility, reduced size/body weight, lower fed and/or fasting blood glucose levels and lower fasting serum insulin levels, and improved blood lipid profile. Tandem mass tag (TMT) proteomics analysis was conducted to explore the differentially expressed proteins (DEPs) in the liver of male mice, revealing 60 up-regulated and 94 down-regulated DEPs in KO mice. The proteomic results were validated by western blot of three selected DEPs. The elevated expression of Glycogen [starch] synthase, liver (Gys2) is consistent with the hypoglycemic phenotype in KO mice. Furthermore, the bioinformatics analysis showed that Selenot-KO-induced DEPs were mainly related to lipid metabolism, cancer, peroxisome proliferator-activated receptor (PPAR) signaling pathway, complement and coagulation cascades, and protein digestion and absorption. Overall, these findings provide a holistic perspective into SELENOT function and novel insights into the role of SELENOT in glucose and lipid metabolism, and thus, enhance our understanding of SELENOT function.

Cell-penetrating, antioxidant SELENOT mimetic protects dopaminergic neurons and ameliorates motor dysfunction in Parkinson's disease animal models

Parkinson's disease (PD) is a neurodegenerative disorder characterized by motor dysfunction for which there is an unmet need for better treatment options. Although oxidative stress is a common feature of neurodegenerative diseases, notably PD, there is currently no efficient therapeutic strategy able to tackle this multi-target pathophysiological process. Based on our previous observations of the potent antioxidant and neuroprotective activity of SELENOT, a vital thioredoxin-like selenoprotein, we designed the small peptide PSELT from its redox active site to evaluate its antioxidant properties in vivo, and its potential polyfunctional activity in PD models. PSELT protects neurotoxin-treated dopaminergic neurons against oxidative stress and cell death, and their fibers against neurotoxic degeneration. PSELT is cell-permeable and acts in multiple subcellular compartments of dopaminergic neurons that are vulnerable to oxidative stress. In rodent models of PD, this protective activity prevented neurodegeneration, restored phosphorylated tyrosine hydroxylase levels, and led to improved motor skills. Transcriptomic analysis revealed that gene regulation by PSELT after MPP+ treatment negatively correlates with that occurring in PD, and positively correlates with that occurring after resveratrol treatment. Mechanistically, a major impact of PSELT is via nuclear stimulation of the transcription factor EZH2, leading to neuroprotection. Overall, these findings demonstrate the potential of PSELT as a therapeutic candidate for treatment of PD, targeting oxidative stress at multiple intracellular levels.

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.

The Function of Selenium in Central Nervous System: Lessons from MsrB1 Knockout Mouse Models

MsrB1 used to be named selenoprotein R, for it was first identified as a selenocysteine containing protein by searching for the selenocysteine insert sequence (SECIS) in the human genome. Later, it was found that MsrB1 is homologous to PilB in Neisseria gonorrhoeae, which is a methionine sulfoxide reductase (Msr), specifically reducing L-methionine sulfoxide (L-Met-O) in proteins. In humans and mice, four members constitute the Msr family, which are MsrA, MsrB1, MsrB2, and MsrB3. MsrA can reduce free or protein-containing L-Met-O (S), whereas MsrBs can only function on the L-Met-O (R) epimer in proteins. Though there are isomerases existent that could transfer L-Met-O (S) to L-Met-O (R) and vice-versa, the loss of Msr individually results in different phenotypes in mice models. These observations indicate that the function of one Msr cannot be totally complemented by another. Among the mammalian Msrs, MsrB1 is the only selenocysteine-containing protein, and we recently found that loss of MsrB1 perturbs the synaptic plasticity in mice, along with the astrogliosis in their brains. In this review, we summarized the effects resulting from Msr deficiency and the bioactivity of selenium in the central nervous system, especially those that we learned from the MsrB1 knockout mouse model. We hope it will be helpful in better understanding how the trace element selenium participates in the reduction of L-Met-O and becomes involved in neurobiology.

The Neurobiology of Selenium: Looking Back and to the Future

Eighteen years ago, unexpected epileptic seizures in Selenop-knockout mice pointed to a potentially novel, possibly underestimated, and previously difficult to study role of selenium (Se) in the mammalian brain. This mouse model was the key to open the field of molecular mechanisms, i.e., to delineate the roles of selenium and individual selenoproteins in the brain, and answer specific questions like: how does Se enter the brain; which processes and which cell types are dependent on selenoproteins; and, what are the individual roles of selenoproteins in the brain? Many of these questions have been answered and much progress is being made to fill remaining gaps. Mouse and human genetics have together boosted the field tremendously, in addition to traditional biochemistry and cell biology. As always, new questions have become apparent or more pressing with solving older questions. We will briefly summarize what we know about selenoproteins in the human brain, glance over to the mouse as a useful model, and then discuss new questions and directions the field might take in the next 18 years.

Selenoprotein T: An Essential Oxidoreductase Serving as a Guardian of Endoplasmic Reticulum Homeostasis

Significance: Selenoproteins incorporate the essential nutrient selenium into their polypeptide chain. Seven members of this family reside in the endoplasmic reticulum (ER), the exact function of most of which is poorly understood. Especially, how ER-resident selenoproteins control the ER redox and ionic environment is largely unknown. Since alteration of ER function is observed in many diseases, the elucidation of the role of selenoproteins could enhance our understanding of the mechanisms involved in ER homeostasis. Recent Advances: Among selenoproteins, selenoprotein T (SELENOT) is remarkable as the most evolutionarily conserved and the only ER-resident selenoprotein whose gene knockout in mouse is lethal. Recent data indicate that SELENOT contributes to ER homeostasis: reduced expression of SELENOT in transgenic cell and animal models promotes accumulation of reactive oxygen and nitrogen species, depletion of calcium stores, activation of the unfolded protein response and impaired hormone secretion. Critical Issues: SELENOT is anchored to the ER membrane and associated with the oligosaccharyltransferase complex, suggesting that it regulates the early steps of N-glycosylation. Furthermore, it exerts a selenosulfide oxidoreductase activity carried by its thioredoxin-like domain. However, the physiological role of the redox activity of SELENOT is not fully understood. Likewise, the nature of its redox partners needs to be further characterized. Future Directions: Given the impact of ER stress in pathologies such as neurodegenerative, cardiovascular, metabolic and immune diseases, understanding the role of SELENOT and developing derived therapeutic tools such as selenopeptides to improve ER proteostasis and prevent ER stress could contribute to a better management of these diseases.

Roles of selenoprotein T and transglutaminase in active immunization against entomopathogenic fungi in the termite Reticulitermes chinensis

Active immunization can protect individuals from infectious diseases in social insects. It is well established that trace elements are essential to the host immune system, but the related gene functions in insect social immunity are unknown. Here, we found that the levels of three free elements (Se, Ca and Cr) and selenoprotein T (SELT) expression were significantly decreased in the termite Reticulitermes chinensis Snyder during active immunization against the entomopathogenic fungus Metarhizium anisopliae (Metchnikoff) Sorokin. Thus, we further explored the role of the SELT gene in the active immunization of termites. After SELT was significantly silenced by RNAi, the nestmates of fungus-contaminated termites exhibited reduced antifungal activity and increased mortality, along with increased expression of the immune genes transglutaminase (TG) and transferrin (Tsf), indicating that the active immunization of termites was disrupted by SELT silencing. Moreover, the TG-knockdown nestmates of fungus-contaminated termites significantly decreased grooming behavior, antifungal activity and survival, despite the upregulation of SELT expression, also suggesting that the active immunization of termites was disrupted by the silencing of TG. These findings demonstrated that both SELT gene and TG gene play important roles in driving active immunization against the entomopathogenic fungus M. anisopliae in R. chinensis.

Selenoprotein T Promotes Proliferation and G1-to-S Transition in SK-N-SH Cells: Implications in Parkinson's Disease

BACKGROUND

Selenium is prioritized to the brain mainly for selenoprotein expression. Selenoprotein T (SELENOT) protects dopaminergic, postmitotic neurons in a mouse model of Parkinson's disease (PD).

OBJECTIVE

We hypothesized a proliferative role of SELENOT in neural cells.

METHODS

To assess SELENOT status in PD, sedated male C57BL/6 mice at 10-12 wk of age were injected with 6-hydroxydopamine in neurons, and human peripheral blood mononuclear cells were isolated from 9 healthy subjects (56% men, 68-y-old) and 11 subjects with PD (64% men, 63-y-old). Dopaminergic neural progenitor-like SK-N-SH cells with transient SELENOT overexpression or knockdown were maintained in the presence or absence of the antioxidant N-acetyl-l-cysteine and the calcium channel blocker nimodipine. Cell cycle, proliferation, and signaling parameters were determined by immunoblotting, qPCR, and flow cytometry.

RESULTS

SELENOT mRNA abundance was increased (P < 0.05) in SK-N-SH cells treated with 1-methyl-4-phenylpyridinium iodide (3.5-fold) and peripheral blood mononuclear cells from PD patients (1.6-fold). Likewise, SELENOT was expressed in tyrosine hydroxylase-positive dopaminergic neurons of 6-hydroxydopamine-injected mice. Knockdown of SELENOT in SK-N-SH cells suppressed (54%; P < 0.05) 5-ethynyl-2'-deoxyuridine incorporation but induced (17-47%; P < 0.05) annexin V-positive cells, CASPASE-3 cleavage, and G1/S cell cycle arrest. SELENOT knockdown and overexpression increased (88-120%; P < 0.05) and reduced (37-42%; P < 0.05) both forkhead box O3 and p27, but reduced (51%; P < 0.05) and increased (1.2-fold; P < 0.05) cyclin-dependent kinase 4 protein abundance, respectively. These protein changes were diminished by nimodipine or N-acetyl-l-cysteine treatment (24 h) at steady-state levels. While the N-acetyl-l-cysteine treatment did not influence the reduction in the amount of calcium (13%; P < 0.05) by SELENOT knockdown, the nimodipine treatment reversed the decreased amount of reactive oxygen species (33%; P < 0.05) by SELENOT overexpression.

CONCLUSIONS

These cellular and mouse data link SELENOT to neural proliferation, expanding our understanding of selenium protection in PD.

Epitranscriptomic systems regulate the translation of reactive oxygen species detoxifying and disease linked selenoproteins

Here we highlight the role of epitranscriptomic systems in post-transcriptional regulation, with a specific focus on RNA modifying writers required for the incorporation of the 21st amino acid selenocysteine during translation, and the pathologies linked to epitranscriptomic and selenoprotein defects. Epitranscriptomic marks in the form of enzyme-catalyzed modifications to RNA have been shown to be important signals regulating translation, with defects linked to altered development, intellectual impairment, and cancer. Modifications to rRNA, mRNA and tRNA can affect their structure and function, while the levels of these dynamic tRNA-specific epitranscriptomic marks are stress-regulated to control translation. The tRNA for selenocysteine contains five distinct epitranscriptomic marks and the ALKBH8 writer for the wobble uridine (U) has been shown to be vital for the translation of the glutathione peroxidase (GPX) and thioredoxin reductase (TRXR) family of selenoproteins. The reactive oxygen species (ROS) detoxifying selenocysteine containing proteins are a prime examples of how specialized translation can be regulated by specific tRNA modifications working in conjunction with distinct codon usage patterns, RNA binding proteins and specific 3' untranslated region (UTR) signals. We highlight the important role of selenoproteins in detoxifying ROS and provide details on how epitranscriptomic marks and selenoproteins can play key roles in and maintaining mitochondrial function and preventing disease.

Progress in the emerging role of selenoproteins in cardiovascular disease: focus on endoplasmic reticulum-resident selenoproteins

Cardiovascular diseases represent one of the most important health problems of developed countries. One of the main actors involved in the onset and development of cardiovascular diseases is the increased production of reactive oxygen species that, through lipid peroxidation, protein oxidation and DNA damage, induce oxidative stress and cell death. Basic and clinical research are ongoing to better understand the endogenous antioxidant mechanisms that counteract oxidative stress, which may allow to identify a possible therapeutic targeting/application in the field of stress-dependent cardiovascular pathologies. In this context, increasing attention is paid to the glutathione/glutathione-peroxidase and to the thioredoxin/thioredoxin-reductase systems, among the most potent endogenous antioxidative systems. These key enzymes, belonging to the selenoprotein family, have a well-established function in the regulation of the oxidative cell balance. The aim of the present review was to highlight the role of selenoproteins in cardiovascular diseases, introducing the emerging cardioprotective role of endoplasmic reticulum-resident members and in particular one of them, namely selenoprotein T or SELENOT. Accumulating evidence indicates that the dysfunction of different selenoproteins is involved in the susceptibility to oxidative stress and its associated cardiovascular alterations, such as congestive heart failure, coronary diseases, impaired cardiac structure and function. Some of them are under investigation as useful pathological biomarkers. In addition, SELENOT exhibited intriguing cardioprotective effects by reducing the cardiac ischemic damage, in terms of infarct size and performance. In conclusion, selenoproteins could represent valuable targets to treat and diagnose cardiovascular diseases secondary to oxidative stress, opening a new avenue in the field of related therapeutic strategies.

The Thioredoxin-Like Family of Selenoproteins: Implications in Aging and Age-Related Degeneration

The thioredoxin-like (Rdx) family proteins contain four selenoproteins (selenoprotein H, SELENOH; selenoprotein T, SELENOT; selenoprotein V, SELENOV; selenoprotein W, SELENOW) and a nonselenoprotein Rdx12. They share a CxxU or a CxxC (C, cysteine; x, any amino acid; U, selenocysteine) motif and a stretch of eGxFEI(V) sequence. From the evolutionary perspective, SELENOW and SELENOV are clustered together and SELENOH and SELENOT are in another branch. Selenoproteins in the Rdx family exhibit tissue- and organelle-specific distribution and are differentially influenced in response to selenium deficiency. While SELENOH is nucleus-exclusive, SELENOT resides mainly in endoplasmic reticulum and SELENOW in cytosol. SELENOV is expressed essentially only in the testes with unknown cellular localization. SELENOH and SELENOW are more sensitive than SELENOT and SELENOV to selenium deficiency. While physiological functions of the Rdx family of selenoproteins are not fully understand, results from animal models demonstrated that (1) brain-specific SELENOT knockout mice are susceptible to 1-methyl-4-phenylpyridinium-induced Parkinson's disease in association with redox imbalance and (2) adult zebrafishes with heterozygous SELENOH knockout are prone to dimethylbenzanthracene-induced tumorigenesis together with increased DNA damage and oxidative stress. Further animal and human studies are needed to fully understand physiological roles of the Rdx family of selenoproteins in redox regulation, genome maintenance, aging, and age-related degeneration.

Selenoprotein T is a key player in ER proteostasis, endocrine homeostasis and neuroprotection

Selenoprotein T (SELENOT, SELT) is a thioredoxin-like enzyme anchored at the endoplasmic reticulum (ER) membrane, whose primary structure is highly conserved during evolution. SELENOT is abundant in embryonic tissues and its activity is essential during development since its gene knockout in mice is lethal early during embryogenesis. Although its expression is repressed in most adult tissues, SELENOT remains particularly abundant in endocrine organs such as the pituitary, pancreas, thyroid and testis, suggesting an important role of this selenoprotein in hormone production. Our recent studies showed indeed that SELENOT plays a key function in insulin and corticotropin biosynthesis and release by regulating ER proteostasis. Although SELENOT expression is low or undetectable in most cerebral structures, its gene conditional knockout in brain provokes anatomical alterations that impact mice behavior. This suggests that SELENOT also plays an important role in brain development and function. In addition, SELENOT is induced after injury in brain or liver and exerts a cytoprotective effect. Thus, the data gathered during the last ten years of intense investigation of this newly discovered thioredoxin-like enzyme point to an essential function during development and in adult endocrine organs or lesioned brain, most likely by regulating ER redox circuits that control homeostasis and survival of cells with intense metabolic activity.

A selenoprotein T-derived peptide protects the heart against ischaemia/reperfusion injury through inhibition of apoptosis and oxidative stress

AIM

Selenoprotein T (SelT or SELENOT) is a novel thioredoxin-like enzyme whose genetic ablation in mice results in early embryonic lethality. SelT exerts an essential cytoprotective action during development and after injury through its redox-active catalytic site. This study aimed to determine the expression and regulation of SelT in the mammalian heart in normal and pathological conditions and to evaluate the cardioprotective effect of a SelT-derived peptide, SelT43-52(PSELT) encompassing the redox motif which is key to its function, against ischaemia/reperfusion(I/R) injury.

METHODS

We used the isolated Langendorff rat heart model and different analyses by immunohistochemistry, Western blot and ELISA.

RESULTS

We found that SelT expression is very abundant in embryo but is undetectable in adult heart. However, SelT expression was tremendously increased after I/R. PSELT (5 nmol/L) was able to induce pharmacological post-conditioning cardioprotection as evidenced by a significant recovery of contractility (dLVP) and reduction of infarct size (IS), without changes in cardiac contracture (LVEDP). In contrast, a control peptide lacking the redox site did not confer cardioprotection. Immunoblot analysis showed that PSELT-dependent cardioprotection is accompanied by a significant increase in phosphorylated Akt, Erk-1/2 and Gsk3α-β, and a decrement of p38MAPK. PSELT inhibited the pro-apoptotic factors Bax, caspase 3 and cytochrome c and stimulated the anti-apoptotic factor Bcl-2. Furthermore, PSELT significantly reduced several markers of I/R-induced oxidative and nitrosative stress.

CONCLUSION

These results unravel the role of SelT as a cardiac modulator and identify PSELT as an effective pharmacological post-conditioning agent able to protect the heart after ischaemic injury.

Selenium accelerates chicken dendritic cells differentiation and affects selenoproteins expression

Selenium (Se) promotes immune cell differentiation and improves immune response. Antigen-presenting cells such as dendritic cells (DCs) play an important role in immune system, however, the impact of Se on DCs is still unclear. In this study, we successfully induced and cultured chicken DCs from peripheral blood mononuclear cells by incubating mononuclear cells with 50 ng/mL recombinant chicken granulocyte-macrophage colony stimulating factor and 10 ng/mL recombinant chicken interleukin-4 for total 9 days. In + Se group, we added 10^-7 mol/L sodium selenite from the first day of cell culture. The results showed that Se supplementation expedited and increased the expression of cell surface markers including CD11c, CD40, CD86, and MHC II. Principal component analysis showed that the expression of selenoproteins SelW, SelK, Dio3, GPX1, GPX2, SelN, SelS, SelH in chicken DCs was highly correlated, and SelW had highest correlation with the cell surface markers MHC II and CD11c. In conclusion, Se accelerates the differentiation and maturation of chicken DCs. Se regulates the differentiation and maturation of chicken DCs by selenoproteins. Selenoproteins has closely correlated to surface markers of chicken DCs.

Endoplasmic reticulum-resident selenoproteins as regulators of calcium signaling and homeostasis

The human selenoprotein family contains 25 members that share the common feature of containing the amino acid, selenocysteine (Sec). Seven selenoproteins are localized to the endoplasmic reticulum (ER) and exhibit different structural features contributing to a range of cellular functions. Some of these functions are either directly or indirectly related to calcium (Ca²⁺) flux or homeostasis. The presence of the unique Sec residue within these proteins allows some to exert oxidoreductase activity, while the function of the Sec in other ER selenoproteins remains unclear. Some functional insight has been achieved by identifying domains within the ER selenoproteins or through the identification of binding partners. For example, selenoproteins K and N (SELENOK AND SELENON) have been characterized through interactions detected with the inositol 1,4,5-triphosphate receptors (IP3Rs) and the SERCA2b pump, respectively. Others have been linked to chaperone functions related to ER stress or Ca²⁺ homeostasis. This review summarizes the details gathered to date regarding the ER-resident selenoproteins and their effect on Ca²⁺ regulated pathways and outcomes in cells.

Selenoprotein T Exerts an Essential Oxidoreductase Activity That Protects Dopaminergic Neurons in Mouse Models of Parkinson's Disease

AIMS

Oxidative stress is central to the pathogenesis of Parkinson's disease (PD), but the mechanisms involved in the control of this stress in dopaminergic cells are not fully understood. There is increasing evidence that selenoproteins play a central role in the control of redox homeostasis and cell defense, but the precise contribution of members of this family of proteins during the course of neurodegenerative diseases is still elusive.

RESULTS

We demonstrated first that selenoprotein T (SelT) whose gene disruption is lethal during embryogenesis, exerts a potent oxidoreductase activity. In the SH-SY5Y cell model of dopaminergic neurons, both silencing and overexpression of SelT affected oxidative stress and cell survival. Treatment with PD-inducing neurotoxins such as 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) or rotenone triggered SelT expression in the nigrostriatal pathway of wild-type mice, but provoked rapid and severe parkinsonian-like motor defects in conditional brain SelT-deficient mice. This motor impairment was associated with marked oxidative stress and neurodegeneration and decreased tyrosine hydroxylase activity and dopamine levels in the nigrostriatal system. Finally, in PD patients, we report that SelT is tremendously increased in the caudate putamen tissue.

INNOVATION

These results reveal the activity of a novel selenoprotein enzyme that protects dopaminergic neurons against oxidative stress and prevents early and severe movement impairment in animal models of PD.

CONCLUSIONS

Our findings indicate that selenoproteins such as SelT play a crucial role in the protection of dopaminergic neurons against oxidative stress and cell death, providing insight into the molecular underpinnings of this stress in PD.