Consequences of mutations and inborn errors of selenoprotein biosynthesis and functions

Expanding the Frontiers of Guardian Antioxidant Selenoproteins in Cardiovascular Pathophysiology

Significance: Physiological levels of reactive oxygen and nitrogen species (ROS/RNS) function as fundamental messengers for many cellular and developmental processes in the cardiovascular system. ROS/RNS involved in cardiac redox-signaling originate from diverse sources, and their levels are tightly controlled by key endogenous antioxidant systems that counteract their accumulation. However, dysregulated redox-stress resulting from inefficient removal of ROS/RNS leads to inflammation, mitochondrial dysfunction, and cell death, contributing to the development and progression of cardiovascular disease (CVD). Recent Advances: Basic and clinical studies demonstrate the critical role of selenium (Se) and selenoproteins (unique proteins that incorporate Se into their active site in the form of the 21st proteinogenic amino acid selenocysteine [Sec]), including glutathione peroxidase and thioredoxin reductase, in cardiovascular redox homeostasis, representing a first-line enzymatic antioxidant defense of the heart. Increasing attention has been paid to emerging selenoproteins in the endoplasmic reticulum (ER) (i.e., a multifunctional intracellular organelle whose disruption triggers cardiac inflammation and oxidative stress, leading to multiple CVD), which are crucially involved in redox balance, antioxidant activity, and calcium and ER homeostasis. Critical Issues: This review focuses on endogenous antioxidant strategies with therapeutic potential, particularly selenoproteins, which are very promising but deserve more detailed and clinical studies. Future Directions: The importance of selective selenoproteins in embryonic development and the consequences of their mutations and inborn errors highlight the need to improve knowledge of their biological function in myocardial redox signaling. This could facilitate the development of personalized approaches for the diagnosis, prevention, and treatment of CVD. Antioxid. Redox Signal. 40, 369-432.

Analysis of the Clinical Features and Imaging Findings of Pontocerebellar Hypoplasia Type 2D Caused by Mutations in SEPSECS Gene

Pontocerebellar hypoplasia type 2D (PCH2D) caused by SEPSECS gene mutations is very rare and only described in a few case reports. In this study, we analyzed the clinical features and imaging findings of these individuals, so as to provide references for the clinic. We reported a case of PCH2D caused by a new complex heterozygote mutation in SEPSECS gene, and reviewed the literatures to summarize the clinical features and imaging findings and compare the differences between early-onset patients (EOPs) and late-onset patients (LOPs). Of 23 PCH2D patients, 19 cases were early-onset and 4 cases were late-onset, with average ages of 4.1 ± 4.0 years and 21.8 ± 9.4 years, females were more prevalent (14/19). EOPs mainly distributed in Arab countries (10/14) and Finland (4/14), while LOPs in East Asia (3/3). EOPs develop severe initial symptoms at the average age of 4.1 ± 7.8 months or shortly after birth, while LOPs experienced mild developmental delay in infancy. Microcephaly (10/11), intellectual disability (10/11), decreased motor function (10/11), and spastic or dystonic quadriplegia (8/10) were the common clinical features of EOPs and LOPs. EOPs also presented with visual impairment (5/7), seizures (4/7), neonatal irritability/opisthotonus (3/7), tremors/myoclonus (3/7), dysmorphic features (3/7), and other symptoms. EOPs were characterized by cerebellar symptoms (4/4). Magnetic resonance imaging (MRI) revealed progressive cerebellar atrophy followed by less pronounced cerebral atrophy, and there was no pons atrophy in LOPs. Most patients of PCH2D were severe early-onset, and a few were late-onset with milder symptoms. EOPs and LOPs shared some common clinical features and MRI findings, but also had their own characteristics.

A homozygous mutation in the human selenocysteine tRNA gene impairs UGA recoding activity and selenoproteome regulation by selenium

The selenocysteine (Sec) tRNA (tRNA[Ser]Sec) governs Sec insertion into selenoproteins by the recoding of a UGA codon, typically used as a stop codon. A homozygous point mutation (C65G) in the human tRNA[Ser]Sec acceptor arm has been reported by two independent groups and was associated with symptoms such as thyroid dysfunction and low blood selenium levels; however, the extent of altered selenoprotein synthesis resulting from this mutation has yet to be comprehensively investigated. In this study, we used CRISPR/Cas9 technology to engineer homozygous and heterozygous mutant human cells, which we then compared with the parental cell lines. This C65G mutation affected many aspects of tRNA[Ser]Sec integrity and activity. Firstly, the expression level of tRNA[Ser]Sec was significantly reduced due to an altered recruitment of RNA polymerase III at the promoter. Secondly, selenoprotein expression was strongly altered, but, more surprisingly, it was no longer sensitive to selenium supplementation. Mass spectrometry analyses revealed a tRNA isoform with unmodified wobble nucleotide U34 in mutant cells that correlated with reduced UGA recoding activities. Overall, this study demonstrates the pleiotropic effect of a single C65G mutation on both tRNA phenotype and selenoproteome expression.

Selenium, Iodine and Iron-Essential Trace Elements for Thyroid Hormone Synthesis and Metabolism

The adequate availability and metabolism of three essential trace elements, iodine, selenium and iron, provide the basic requirements for the function and action of the thyroid hormone system in humans, vertebrate animals and their evolutionary precursors. Selenocysteine-containing proteins convey both cellular protection along with H₂O₂-dependent biosynthesis and the deiodinase-mediated (in-)activation of thyroid hormones, which is critical for their receptor-mediated mechanism of cellular action. Disbalances between the thyroidal content of these elements challenge the negative feedback regulation of the hypothalamus-pituitary-thyroid periphery axis, causing or facilitating common diseases related to disturbed thyroid hormone status such as autoimmune thyroid disease and metabolic disorders. Iodide is accumulated by the sodium-iodide-symporter NIS, and oxidized and incorporated into thyroglobulin by the hemoprotein thyroperoxidase, which requires local H₂O₂ as cofactor. The latter is generated by the dual oxidase system organized as 'thyroxisome' at the surface of the apical membrane facing the colloidal lumen of the thyroid follicles. Various selenoproteins expressed in thyrocytes defend the follicular structure and function against life-long exposure to H₂O₂ and reactive oxygen species derived therefrom. The pituitary hormone thyrotropin (TSH) stimulates all processes required for thyroid hormone synthesis and secretion and regulates thyrocyte growth, differentiation and function. Worldwide deficiencies of nutritional iodine, selenium and iron supply and the resulting endemic diseases are preventable with educational, societal and political measures.

Identification of Key Candidate Genes for Beak Length Phenotype by Whole-Genome Resequencing in Geese

The domestic goose is an important economic animal in agriculture and its beak, a trait with high heritability, plays an important role in promoting food intake and defending against attacks. In this study, we sequenced 772 420-day-old Xingguo gray geese (XGG) using a low-depth (~1 ×) whole-genome resequencing strategy. We detected 12,490,912 single nucleotide polymorphisms (SNPs) using the standard GATK and imputed with STITCH. We then performed a genome-wide association study on the beak length trait in XGG. The results indicated that 57 SNPs reached genome-wide significance levels for the beak length trait and were assigned to seven genes, including TAPT1, DHX15, CCDC149, LGI2, SEPSECS, ANAPC4, and Slc34a2. The different genotypes of the most significant SNP (top SNP), which was located upstream of LGI2 and explained 7.24% of the phenotypic variation in beak length, showed significant differences in beak length. Priority-based significance analysis concluded that CCDC149, LGI2, and SEPSECS genes in the most significant quantitative trait locus interval were the most plausible positional and functional candidate genes for beak length development in the XGG population. These findings not only enhance our understanding of the genetic mechanism of the beak length phenotype in geese, but also lay the foundation for further studies to facilitate the genetic selection of traits in geese.

Inherited Selenocysteine Transfer RNA Mutation: Clinical and Hormonal Evaluation of 2 Patients

INTRODUCTION

Iodothyronine deiodinases are selenoproteins with the amino acid selenocysteine (Sec) introduced into the position of a TGA stop codon by a complex machinery involving tRNA^[Ser]Sec when a cis-acting Sec-insertion sequence element is present in the 3' end of the mRNA. Recently, a variant in the TRU-TCA1-1 gene encoding for tRNA^[Ser]Sec was reported, which resulted in reduced expression of stress-related selenoproteins. The proband presented with multisystem symptoms, euthyroid hyperthyroxinemia, and selenium deficiency. Here, we describe 2 new members of a family harboring the same tRNA^[Ser]Sec variant.

CASE PRESENTATION

A 13-year-old patient was seen for Hashimoto's disease with high FT3 (4.6 pg/mL, normal range 2-4.2 pg/mL) and normal FT4 and TSH concentrations. He had no clinical complaints. During a 6-year clinical and hormonal follow-up, the index patient was not treated, FT3 decreased, FT4 increased, and serum TSH stayed in the normal range resulting in a euthyroid hyperthyroxinemia. Reverse T3 concentration was significantly increased at the last visit (19 years and 4 months). At the last evaluation, the total selenium level was low (91 μg/L, normal range 95-125). DNA sequencing identified a germinal homozygous variant (C65G) in the TRU-TCA1-1 gene. During follow-up, no additional clinical symptom was observed in the absence of any treatment. The same germinal tRNA^[Ser]Sec variant was identified at heterozygous state in his father, who had normal thyroid function tests except a moderately increased reverse T3 concentration, with increased total selenium (143 μg/L) level. In both patients, the expression of stress-related selenoprotein GPX3 was in the low-normal range (168 and 180 IU/L, respectively, normal range: 150-558 IU/L). We did not find any significant biological abnormalities evocative of other selenoprotein deficiencies.

DISCUSSION/CONCLUSION

We report on 2 members of a family with a variant in the TRU-TCA1-1 gene encoding for tRNA^[Ser]Sec. Our study suggests that this tRNA^[Ser]Sec variant is not exclusively causative of disruption in selenoprotein synthesis.

Pathogenic Variants in Selenoproteins and Selenocysteine Biosynthesis Machinery

Selenium is incorporated into selenoproteins as the 21st amino acid selenocysteine (Sec). There are 25 selenoproteins encoded in the human genome, and their synthesis requires a dedicated machinery. Most selenoproteins are oxidoreductases with important functions in human health. A number of disorders have been associated with deficiency of selenoproteins, caused by mutations in selenoprotein genes or Sec machinery genes. We discuss mutations that are known to cause disease in humans and report their allele frequencies in the general population. The occurrence of protein-truncating variants in the same genes is also presented. We provide an overview of pathogenic variants in selenoproteins genes from a population genomics perspective.

Selenium Deficiency Due to Diet, Pregnancy, Severe Illness, or COVID-19-A Preventable Trigger for Autoimmune Disease

The trace element selenium (Se) is an essential part of the human diet; moreover, increased health risks have been observed with Se deficiency. A sufficiently high Se status is a prerequisite for adequate immune response, and preventable endemic diseases are known from areas with Se deficiency. Biomarkers of Se status decline strongly in pregnancy, severe illness, or COVID-19, reaching critically low concentrations. Notably, these conditions are associated with an increased risk for autoimmune disease (AID). Positive effects on the immune system are observed with Se supplementation in pregnancy, autoimmune thyroid disease, and recovery from severe illness. However, some studies reported null results; the database is small, and randomized trials are sparse. The current need for research on the link between AID and Se deficiency is particularly obvious for rheumatoid arthritis and type 1 diabetes mellitus. Despite these gaps in knowledge, it seems timely to realize that severe Se deficiency may trigger AID in susceptible subjects. Improved dietary choices or supplemental Se are efficient ways to avoid severe Se deficiency, thereby decreasing AID risk and improving disease course. A personalized approach is needed in clinics and during therapy, while population-wide measures should be considered for areas with habitual low Se intake. Finland has been adding Se to its food chain for more than 35 years-a wise and commendable decision, according to today's knowledge. It is unfortunate that the health risks of Se deficiency are often neglected, while possible side effects of Se supplementation are exaggerated, leading to disregard for this safe and promising preventive and adjuvant treatment options. This is especially true in the follow-up situations of pregnancy, severe illness, or COVID-19, where massive Se deficiencies have developed and are associated with AID risk, long-lasting health impairments, and slow recovery.

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.

Serum Selenium Status as a Diagnostic Marker for the Prognosis of Liver Transplantation

The trace element selenium (Se) is taken up from the diet and is metabolized mainly by hepatocytes. Selenoprotein P (SELENOP) constitutes the liver-derived Se transporter. Biosynthesis of extracellular glutathione peroxidase (GPx3) in kidney depends on SELENOP-mediated Se supply. We hypothesized that peri-operative Se status may serve as a useful prognostic marker for the outcome in patients undergoing liver transplantation due to hepatocellular carcinoma. Serum samples from liver cancer patients were routinely collected before and after transplantation. Concentrations of serum SELENOP and total Se as well as GPx3 activity were determined by standardized tests and related to survival, etiology of cirrhosis/carcinoma, preoperative neutrophiles, lymphocytes, thyrotropin (TSH) and Child-Pugh and Model for End-Stage Liver Disease (MELD) scores. A total of 221 serum samples from 79 transplanted patients were available for analysis. The Se and SELENOP concentrations were on average below the reference ranges of healthy subjects. Patients with ethanol toxicity-dependent etiology showed particularly low SELENOP and Se concentrations and GPx3 activity. Longitudinal analysis indicated declining Se concentrations in non-survivors. We conclude that severe liver disease necessitating organ replacement is characterized by a pronounced Se deficit before, during and after transplantation. A recovering Se status after surgery is associated with positive prognosis, and an adjuvant Se supplementation may, thus, support convalescence.

SECISBP2 is a novel prognostic predictor that regulates selenoproteins in diffuse large B-cell lymphoma

The overexpression of glutathione peroxidase 4 (GPX4; an enzyme that suppresses peroxidation of membrane phospholipids) is considered a poor prognostic predictor of diffuse large B-cell lymphoma (DLBCL). However, the mechanisms employed in GPX4 overexpression remain unknown. GPX4 is translated as a complete protein upon the binding of SECISBP2 to the selenocysteine insertion sequence (SECIS) on the 3'UTR of GPX4 mRNA. In this study, we investigated the expression of SECISBP2 and its subsequent regulation of GPX4 and TXNRD1 in DLBCL patients. Moreover, we determined the significance of the expression of these selenoproteins in vitro using MD901 and Raji cells. SECISBP2 was positive in 45.5% (75/165 cases) of DLBCL samples. The SECISBP2-positive group was associated with low overall survival (OS) as compared to the SECISBP2-negative group (P = 0.006). Similarly, the SECISBP2 and GPX4 or TXNRD1 double-positive groups (P < 0.001), as well as the SECISBP2, GPX4, and TXNRD1 triple-positive group correlated with poor OS (P = 0.001), suggesting that SECISBP2 may serve as an independent prognostic predictor for DLBCL (hazard ratio (HR): 2.693, P = 0.008). In addition, western blotting showed a decrease in GPX4 and TXNRD1 levels in SECISBP2-knockout (KO) MD901 and Raji cells. Oxidative stress increased the accumulation of reactive oxygen species in SECISBP2-KO cells (MD901; P < 0.001, Raji; P = 0.020), and reduced cell proliferation (MD901; P = 0.001, Raji; P = 0.030), suggesting that SECISBP2-KO suppressed resistance to oxidative stress. Doxorubicin treatment increased the rate of cell death in SECISBP2-KO cells (MD901; P < 0.001, Raji; P = 0.048). Removal of oxidative stress inhibited the altered cell death rate. Taken together, our results suggest that SECISBP2 may be a novel therapeutic target in DLBCL.

Selenium in Endocrinology-Selenoprotein-Related Diseases, Population Studies, and Epidemiological Evidence

Selenium (Se), apart from iodine, iron, and calcium, is one of the nutrient-derived key elements strongly affecting the endocrine system. However, no specific hormonal "feedback" regulation for Se status has yet been identified, in contrast to the fine-tuned hormone network regulating Ca2+ and phosphate balance or hepcidin-related iron status. Since its discovery as an essential trace element, the effects of Se excess or deficiency on the endocrine system or components of the hypothalamic-pituitary-periphery feedback circuits, the thyroid hormone axis, glucoregulatory and adrenal hormones, male and female gonads, the musculoskeletal apparatus, and skin have been identified. Analysis of the Se status in the blood or via validated biomarkers such as the hepatically derived selenoprotein P provides valuable diagnostic insight and a rational basis for decision making on required therapeutic or preventive supplementation of risk groups or patients. Endocrine-related epidemiological and interventional evidence linking Se status to beneficial or potentially adverse actions of selected selenoproteins mediating most of the (patho-) physiological effects are discussed in this mini-review. Autoimmune thyroid disease, diabetes and obesity, male fertility, as well as osteoporosis are examples for which observational or interventional studies have indicated Se effects. The currently prevailing concept relating Se and selenoproteins to "oxidative stress," reactive oxygen species, radical hypotheses, and related strategies of pharmacological approaches based on various selenium compounds will not be the focus. The crucial biological function of several selenoproteins in cellular redox-regulation and specific enzyme reactions in endocrine pathways will be addressed and put in clinical perspective.

Nano-selenium Supplementation Increases Selenoprotein (Sel) Gene Expression Profiles and Milk Selenium Concentration in Lactating Dairy Cows

Supplementation with selenium is common for dairy cows, but the importance of selenium source is not clear. This study aimed to compare nano-selenium (Nano-Se) and sodium selenite supplements for dairy cows on lactation performance, milk Se levels and selenoprotein (Sel) gene expression. Twelve multiparous Holstein cows were randomly divided into two groups: a control group fed a basal diet plus 0.30 mg Se/kg of DM as sodium selenite or Nano-Se for 30 days. Dry matter intake, milk yield and composition were not affected by dietary Se source (P > 0.05); however, the milk total Se levels and milk glutathione peroxidase (GSH-Px) activities were higher with Nano-Se supplementation than sodium selenite (P < 0.05). At the end of the experiment, Nano-Se supplementation significantly increased plasma Se levels and GSH-Px activity, compared with the sodium selenite supplement. The mRNA expression levels of glutathione peroxidase 1, 2 and 4; thioredoxin reductase 2 and 3; and selenoproteins W, T, K and F were markedly upregulated (P < 0.05) in the mammary gland of the Nano-Se group. Thus, the source of selenium plays an important role in the antioxidant status and in particular the Sel gene expression in the mammary glands of dairy cows, both being stimulated by nano sources.

Selenium sources differ in their potential to alleviate the cadmium-induced testicular dysfunction

Cadmium (Cd), a major environmental contaminant, is closely associated with male reproductive health. Selenium (Se) has been recognized as an effective chemo-protectant against Cd toxicity, but the underlying mechanisms remain unclear. The objective of present study was to illustrate the toxic effect of Cd on testis, and then compare the antagonistic effect among different Se sources on growth performance, testicular damage, ion homeostasis, antioxidative potential, and the expression of selenotranscriptome and biosynthetic related factors in Cd-treated chicken. Male chickens were fed with (Ⅰ) Control group: basal diet; (Ⅱ) Cd group: basal diet with 140 mg/kg CdCl₂; (Ⅲ) YSe + Cd group: basal diet with 140 mg/kg CdCl₂ and 3 mg/kg Yeast-Se; (Ⅳ) NSe + Cd group: basal diet with 140 mg/kg CdCl₂ and 1 mg/kg Nano-Se; (Ⅴ) SSe + Cd group: basal diet with 140 mg/kg CdCl₂ and 3 mg/kg Na₂SeO₃. It was observed that different Se treatments dramatically alleviated Cd-induced testicular developmental disorder, ion homeostasis disorder, hormone secretion disorder and oxidative stress. Simultaneously, Se mitigated Cd-induced testicular toxicity by regulating selenoprotein biosynthetic related factors to promote selenoprotein transcription. Finally, this study indicated that dietary supplementation of Yeast-Se produced an acceptable Se form to protect testis from Cd exposure.

Identification of Resistance to Exogenous Thyroxine in Humans

Background: Thyroxine (T4) to triiodothyronine (T3) deiodination in the hypothalamus/pituitary is mediated by deiodinase type-2 (D2) activity. Dio2^(-/-) mice show central resistance to exogenous T4. Patients with resistance to exogenous thyroxine (RETH) have not been described. The aim of this study was to identify hypothyroid patients with thyrotropin (TSH) unresponsiveness to levothyroxine (LT4) and to characterize the clinical, hormonal, and genetic features of human RETH. Methods: We investigated hypothyroid patients with elevated TSH under LT4 treatment at doses leading to clinical and/or biochemical hyperthyroidism. TSH and free T4 (fT4) were determined by chemiluminescence, and total T4, T3, and reverse T3 (rT3) by radioimmunoassay. TSH/fT4 ratio at inclusion and T3/T4, rT3/T4, and T3/rT3 ratios at follow-up were compared with those from patients with resistance to thyroid hormone (RTH) due to thyroid hormone receptor-β (THRB) mutations. DIO2, including the Ala92-D2 polymorphism, selenocysteine binding protein 2 (SECISBP2), and THRB were fully sequenced. Results: Eighteen hypothyroid patients (nine of each sex, 3-59 years) treated with LT4 showed elevated TSH (15.5 ± 4.7 mU/L; reference range [RR]: 0.4-4.5), fT4 (20.8 ± 2.4 pM; RR: 9-20.6), and TSH/fT4 ratio (0.74 ± 0.25; RR: 0.03-0.13). Despite increasing LT4 doses from 1.7 ± 1.0 to 2.4 ± 1.7 μg/kg/day, TSH remained elevated (6.9 ± 2.7 mU/L). Due to hyperthyroid symptoms, LT4 doses were reduced, and TSH increased again to 7.9 ± 3.2 mU/L. In the euthyroid/hyperthyrotropinemic state, T3/T4 and T3/rT3 ratios were decreased (9.2 ± 2.4, RR: 11.3-15.3 and 2.5 ± 1.4, RR: 7.5-8.5, respectively) whereas rT3/T4 was increased (0.6 ± 0.2; RR: 0.43-0.49), suggesting reduced T4 to T3 and increased T4 to rT3 conversion. These ratios were serum T4-independent and were not observed in RTH patients. Genetic testing was normal. The Ala92-D2 polymorphism was present in 7 of 18 patients, but the allele dose did not correlate with RETH. Conclusions: Human RETH is characterized by iatrogenic thyrotoxicosis and elevated TSH/fT4 ratio. In the euthyroid/hyperthyrotropinemic state, it is confirmed by decreased T3/T4 and T3/rT3 ratios, and elevated rT3/T4 ratio. This phenotype may guide clinicians to consider combined T4+T3 therapy in a targeted fashion. The absence of germline DIO2 mutations suggests that aberrant post-translational D2 modifications in pituitary/hypothalamus or defects in other genes regulating the T4 to T3 conversion pathway could be involved in RETH.

Tolerance to Selenoprotein Loss Differs between Human and Mouse

Mouse has emerged as the most common model organism in biomedicine. Here, we analyzed the tolerance to the loss-of-function (LoF) of selenoprotein genes, estimated from mouse knockouts and the frequency of LoF variants in humans. We found not only a general correspondence in tolerance (e.g., GPX1, GPX2) and intolerance (TXNRD1, SELENOT) to gene LoF between humans and mice but also important differences. Notably, humans are intolerant to the loss of iodothyronine deiodinases, whereas their deletion in mice leads to mild phenotypes, and this is consistent with phenotype differences in selenocysteine machinery loss between these species. In contrast, loss of TXNRD2 and GPX4 is lethal in mice but may be tolerated in humans. We further identified the first human SELENOP variants coding for proteins varying in selenocysteine content. Finally, our analyses suggested that premature termination codons in selenoprotein genes trigger nonsense-mediated decay, but do this inefficiently when UGA codon is gained. Overall, our study highlights differences in the physiological importance of selenoproteins between human and mouse.

Effective Immune Functions of Micronutrients against SARS-CoV-2

The third coronavirus outbreak in the last two decades has caused significant damage to the world's economy and community health. The highly contagious COVID-19 infection has affected millions of people to date and has led to hundreds of thousands of deaths worldwide. Aside from the highly infectious nature of SARS-CoV-2, the lack of a treatment or vaccine has been the main reason for its spread. Thus, it has become necessary to find alternative methods for controlling SARS-CoV-2. For the present review, we conducted an online search for different available nutrition-based therapies for previously known coronavirus infections and RNA-based virus infections as well as general antiviral therapies. These treatments have promise for combating COVID-19, as various nutrients and minerals play direct and indirect roles in the control and prevention of this newly emerged viral infection. The patients' nutritional status with COVID-19 must be analyzed before administering any treatment, and nutritional supplements should be given to the affected individuals along with routine treatment. We suggest a potential interventional role of nutrients to strengthen the immune system against the emerging infection caused by COVID-19.

Bioinformatics of Selenoproteins

Significance: Bioinformatics has brought important insights into the field of selenium research. The progress made in the development of computational tools in the last two decades, coordinated with growing genome resources, provided new opportunities to study selenoproteins. The present review discusses existing tools for selenoprotein gene finding and other bioinformatic approaches to study the biology of selenium. Recent Advances: The availability of complete selenoproteomes allowed assessing a global distribution of the use of selenocysteine (Sec) across the tree of life, as well as studying the evolution of selenoproteins and their biosynthetic pathway. Beyond gene identification and characterization, human genetic variants in selenoprotein genes were used to examine adaptations to selenium levels in diverse human populations and to estimate selective constraints against gene loss. Critical Issues: The synthesis of selenoproteins is essential for development in mice. In humans, several mutations in selenoprotein genes have been linked to rare congenital disorders. And yet, the mechanism of Sec insertion and the regulation of selenoprotein synthesis in mammalian cells are not completely understood. Future Directions: Omics technologies offer new possibilities to study selenoproteins and mechanisms of Sec incorporation in cells, tissues, and organisms.

Human Disorders Affecting the Selenocysteine Incorporation Pathway Cause Systemic Selenoprotein Deficiency

Significance: Generalized selenoprotein deficiency has been associated with mutations in SECISBP2, SEPSECS, and TRU-TCA1-1, 3 factors that are crucial for incorporation of the amino acid selenocysteine (Sec) into at least 25 human selenoproteins. SECISBP2 and TRU-TCA1-1 defects are characterized by a multisystem phenotype due to deficiencies of antioxidant and tissue-specific selenoproteins, together with abnormal thyroid hormone levels reflecting impaired hormone metabolism by deiodinase selenoenzymes. SEPSECS mutations are associated with a predominantly neurological phenotype with progressive cerebello-cerebral atrophy. Recent Advances: The recent identification of individuals with defects in genes encoding components of the selenocysteine insertion pathway has delineated complex and multisystem disorders, reflecting a lack of selenoproteins in specific tissues, oxidative damage due to lack of oxidoreductase-active selenoproteins and other pathways whose nature is unclear. Critical Issues: Abnormal thyroid hormone metabolism in patients can be corrected by triiodothyronine (T3) treatment. No specific therapies for other phenotypes (muscular dystrophy, male infertility, hearing loss, neurodegeneration) exist as yet, but their severity often requires supportive medical intervention. Future Directions: These disorders provide unique insights into the role of selenoproteins in humans. The long-term consequences of reduced cellular antioxidant capacity remain unknown, and future surveillance of patients may reveal time-dependent phenotypes (e.g., neoplasia, aging) or consequences of deficiency of selenoproteins whose function remains to be elucidated. The role of antioxidant therapies requires evaluation. Antioxid. Redox Signal. 33, 481-497.

Sedaghatian-type spondylometaphyseal dysplasia: Whole exome sequencing in neonatal dry blood spots enabled identification of a novel variant in GPX4

Accumulation of lipid peroxides causes membrane damage and cell death. Glutathione peroxidase 4 (GPX4) acts as a hydroperoxidase which prevents accumulation of toxic oxidized lipids and blocks ferroptosis, an iron-dependent, non-apoptotic mode of cell death. GPX4 deficiency causes Sedaghatian-type spondylo-metaphyseal dysplasia (SSMD), a lethal autosomal recessive disorder, featuring skeletal dysplasia, cardiac arrhythmia and brain anomalies with only three pathogenic GPX4 variants reported in two SSMD patients. Our objective was to identify the underlying genetic cause of neonatal death of two siblings presenting with hypotonia, cardiorespiratory failure and SSMD. Whole exome sequencing (WES) was performed in DNA samples from two siblings and their parents. Since "critical samples" were not available from the patients, DNA was extracted from dry blood spots (DBS) retrieved from the Israeli newborn-screening center. Sanger sequencing and segregation analysis followed the WES. Homozygous novel GPX4 variant, c.153_160del; p.His52fs*1 causing premature truncation of GPX4 was detected in both siblings; their parents were heterozygotes. Segregation analysis confirmed autosomal recessive inheritance. This report underscores the importance of DBS WES in identifying the genes and mutations causing devastating rare diseases. Obtaining critical samples from a dying patient is crucial for enabling genetic diagnosis.

The Biochemical Profile of Post-Mortem Brain from People Who Suffered from Epilepsy Reveals Novel Insights into the Etiopathogenesis of the Disease

Epilepsy not-otherwise-specified (ENOS) is one of the most common causes of chronic disorders impacting human health, with complex multifactorial etiology and clinical presentation. Understanding the metabolic processes associated with the disorder may aid in the discovery of preventive and therapeutic measures. Post-mortem brain samples were harvested from the frontal cortex (BA8/46) of people diagnosed with ENOS cases (n = 15) and age- and sex-matched control subjects (n = 15). We employed a targeted metabolomics approach using a combination of proton nuclear magnetic resonance (¹H-NMR) and direct injection/liquid chromatography tandem mass spectrometry (DI/LC-MS/MS). We accurately identified and quantified 72 metabolites using ¹H-NMR and 159 using DI/LC-MS/MS. Among the 212 detected metabolites, 14 showed significant concentration changes between ENOS cases and controls (p < 0.05; q < 0.05). Of these, adenosine monophosphate and O-acetylcholine were the most commonly selected metabolites used to develop predictive models capable of discriminating between ENOS and unaffected controls. Metabolomic set enrichment analysis identified ethanol degradation, butyrate metabolism and the mitochondrial beta-oxidation of fatty acids as the top three significantly perturbed metabolic pathways. We report, for the first time, the metabolomic profiling of postmortem brain tissue form patients who died from epilepsy. These findings can potentially expand upon the complex etiopathogenesis and help identify key predictive biomarkers of ENOS.

Functional Biomarkers for the Selenium Status in a Human Nutritional Intervention Study

Soils in Germany are commonly low in selenium; consequently, a sufficient dietary supply is not always ensured. The extent of such provision adequacy is estimated by the optimal effect range of biomarkers, which often reflects the physiological requirement. Preceding epidemiological studies indicate that low selenium serum concentrations could be related to cardiovascular diseases. Inter alia, risk factors for cardiovascular diseases are physical inactivity, overweight, as well as disadvantageous eating habits. In order to assess whether these risk factors can be modulated, a cardio-protective diet comprising fixed menu plans combined with physical exercise was applied in the German MoKaRi (modulation of cardiovascular risk factors) intervention study. We analyzed serum samples of the MoKaRi cohort (51 participants) for total selenium, GPx activity, and selenoprotein P at different timepoints of the study (0, 10, 20, 40 weeks) to explore the suitability of these selenium-associated markers as indicators of selenium status. Overall, the time-dependent fluctuations in serum selenium concentration suggest a successful change in nutritional and lifestyle behavior. Compared to baseline, a pronounced increase in GPx activity and selenoprotein P was observed, while serum selenium decreased in participants with initially adequate serum selenium content. SELENOP concentration showed a moderate positive monotonic correlation (r = 0.467, p < 0.0001) to total Se concentration, while only a weak linear relationship was observed for GPx activity versus total Se concentration (r = 0.186, p = 0.021). Evidently, other factors apart from the available Se pool must have an impact on the GPx activity, leading to the conclusion that, without having identified these factors, GPx activity should not be used as a status marker for Se.

Gained in translation: The power of digging deep into disease models

Mutations affecting the SECISBP2 protein necessary for selenocysteine incorporation are linked to human disease, but with a wide range of clinical outcomes. To gain insight into this diversity, Zhao et al. dissect the phenotypic and molecular consequences of two specific mutations in the Secisbp2 gene that partially disrupt selenoprotein synthesis. They observe surprising tissue-dependent effects, emphasizing the complexities of translational science.

The Study on Polymorphism of TrxR and Nrf2/HO-1 Signaling Pathway in Kaschin-Beck Disease

Kaschin-Beck disease (KBD) is an endemic, chronic, and degenerative osteoarthropathy, which seriously impairs the quality of patients' life. We detected the expression of TrxR by ELISA and found that TrxR was lower in KBD than in normal control group significantly (P < 0.001); this result indicated that TrxR must be related to KBD. We retrieved cSNPs in NCBI SNP database and used three bioinformatics programmers, including SIFT, PolyPhen, and SNP3d, to help select the researched nsSNP. Then, we used PCR-RFLP to analyze the relationship between the SNP site rs5746841 in TrxR2 gene and susceptibility of KBD and detected the expression of Nrf2 and HO-1 by western blot. The results showed that the genotype of rs5746841 in 93 normal controls and 103 KBD subjects were C/C totally, but A/A and A/C were not found, which indicated preliminarily that there was no correlation between rs5746841 in TrxR2 gene and susceptibility of KBD. The expression of TrxR was lower in KBD than in normal control group significantly, while the expressions of Nrf2 and HO-1 were higher in KBD than in normal control group. These results indicated that the low expression of selenoprotein TrxR may be a candidate factor of KBD, which related to Nrf2/HO-1 signaling pathway.

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.

Targeting ferroptosis: A novel therapeutic strategy for the treatment of mitochondrial disease-related epilepsy

BACKGROUND

Mitochondrial disease is a family of genetic disorders characterized by defects in the generation and regulation of energy. Epilepsy is a common symptom of mitochondrial disease, and in the vast majority of cases, refractory to commonly used antiepileptic drugs. Ferroptosis is a recently-described form of iron- and lipid-dependent regulated cell death associated with glutathione depletion and production of lipid peroxides by lipoxygenase enzymes. Activation of the ferroptosis pathway has been implicated in a growing number of disorders, including epilepsy. Given that ferroptosis is regulated by balancing the activities of glutathione peroxidase-4 (GPX4) and 15-lipoxygenase (15-LO), targeting these enzymes may provide a rational therapeutic strategy to modulate seizure. The clinical-stage therapeutic vatiquinone (EPI-743, α-tocotrienol quinone) was reported to reduce seizure frequency and associated morbidity in children with the mitochondrial disorder pontocerebellar hypoplasia type 6. We sought to elucidate the molecular mechanism of EPI-743 and explore the potential of targeting 15-LO to treat additional mitochondrial disease-associated epilepsies.

METHODS

Primary fibroblasts and B-lymphocytes derived from patients with mitochondrial disease-associated epilepsy were cultured under standardized conditions. Ferroptosis was induced by treatment with the irreversible GPX4 inhibitor RSL3 or a combination of pharmacological glutathione depletion and excess iron. EPI-743 was co-administered and endpoints, including cell viability and 15-LO-dependent lipid oxidation, were measured.

RESULTS

EPI-743 potently prevented ferroptosis in patient cells representing five distinct pediatric disease syndromes with associated epilepsy. Cytoprotection was preceded by a dose-dependent decrease in general lipid oxidation and the specific 15-LO product 15-hydroxyeicosatetraenoic acid (15-HETE).

CONCLUSIONS

These findings support the continued clinical evaluation of EPI-743 as a therapeutic agent for PCH6 and other mitochondrial diseases with associated epilepsy.