Selenium is an essential micronutrient with important functions in human health and relevance to several pathophysiological conditions. The biological effects of selenium are largely mediated by se...

https://www.physiology.org/doi/pdf/10.1152/physrev.00039.2013

Selenoproteins: molecular pathways and physiological roles.

Dietary selenium (]Se), mainly through its incorporation into selenoproteins, plays an important role in inflammation and immunity. Adequate levels of Se are important for initiating immunity, but they are also involved in regulating excessive immune responses and chronic inflammation. Evidence has emerged regarding roles for individual selenoproteins in regulating inflammation and immunity, and this has provided important insight into mechanisms by which Se influences these processes. Se deficiency has long been recognized to negatively impact immune cells during activation, differentiation, and proliferation. This is related to increased oxidative stress, but additional functions such as protein folding and calcium flux may also be impaired in immune cells under Se deficient conditions. Supplementing diets with above-adequate levels of Se can also impinge on immune cell function, with some types of inflammation and immunity particularly affected and sexually dimorphic effects of Se levels in so...

The Role of Selenium in Inflammation and Immunity: From Molecular Mechanisms to Therapeutic Opportunities

Selenium is an essential micronutrient that plays a crucial role in development and a wide variety of physiological processes including effect immune responses The immune system relies on adequate dietary selenium intake and this nutrient exerts its biological effects mostly through its incorporation into selenoproteins The selenoproteome contains 25 members in humans that exhibit a wide variety of functions The development of high-throughput omic approaches and novel bioinformatics tools has led to new insights regarding the effects of selenium and selenoproteins in human immuno-biology Equally important are the innovative experimental systems that have emerged to interrogate molecular mechanisms underlying those effects This review presents a summary of the current understanding of the role of selenium and selenoproteins in regulating immune cell functions and how dysregulation of these processes may lead to inflammation or immune-related diseases

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Selenium, Selenoproteins, and Immunity

The trace element selenium is an essential micronutrient that is required for the biosynthesis of selenocysteine-containing selenoproteins. Most of the known selenoproteins are expressed in the thyroid gland, including some with still unknown functions. Among the well-characterized selenoproteins are the iodothyronine deiodinases, glutathione peroxidases and thioredoxin reductases, enzymes involved in thyroid hormone metabolism, regulation of redox state and protection from oxidative damage. Selenium content in selenium-sensitive tissues such as the liver, kidney or muscle and expression of nonessential selenoproteins, such as the glutathione peroxidases GPx1 and GPx3, is controlled by nutritional supply. The thyroid gland is, however, largely independent from dietary selenium intake and thyroid selenoproteins are preferentially expressed. As a consequence, no explicit effects on thyroid hormone profiles are observed in healthy individuals undergoing selenium supplementation. However, low selenium status correlates with risk of goiter and multiple nodules in European women. Some clinical studies have demonstrated that selenium-deficient patients with autoimmune thyroid disease benefit from selenium supplementation, although the data are conflicting and many parameters must still be defined. The baseline selenium status of an individual could constitute the most important parameter modifying the outcome of selenium supplementation, which might primarily disrupt self-amplifying cycles of the endocrine-immune system interface rectifying the interaction of lymphocytes with thyroid autoantigens. Selenium deficiency is likely to constitute a risk factor for a feedforward derangement of the immune system-thyroid interaction, while selenium supplementation appears to dampen the self-amplifying nature of this derailed interaction.

Selenium, selenoproteins and the thyroid gland: interactions in health and disease

Dietary Selenium in Adjuvant Therapy of Viral and Bacterial Infections

Selenoprotein K (Sel K) is a selenium-containing protein for which no function has been identified. We found that Sel K is an endoplasmic reticulum transmembrane protein expressed at relatively high levels in immune cells and is regulated by dietary selenium. Sel K−/− mice were generated and found to be similar to wild-type controls regarding growth and fertility. Immune system development was not affected by Sel K deletion, but specific immune cell defects were found in Sel K−/− mice. Receptor-mediated Ca2+ flux was decreased in T cells, neutrophils, and macrophages from Sel K−/− mice compared with controls. Ca2+-dependent functions including T cell proliferation, T cell and neutrophil migration, and Fcγ receptor-mediated oxidative burst in macrophages were decreased in cells from Sel K−/− mice compared with that in cells from controls. West Nile virus infections were performed, and Sel K−/− mice exhibited decreased viral clearance in the periphery and increased viral titers in brain. Furthermore, West Nile virus-infected Sel K−/− mice demonstrated significantly lower survival (2 of 23; 8.7%) compared with that of wild-type controls (10 of 26; 38.5%). These results establish Sel K as an endoplasmic reticulum-membrane protein important for promoting effective Ca2+ flux during immune cell activation and provide insight into molecular mechanisms by which dietary selenium enhances immune responses.

Selenoprotein K Knockout Mice Exhibit Deficient Calcium Flux in Immune Cells and Impaired Immune Responses

Selenoprotein P (Sepp1), a glycoprotein rich in selenium, is thought to function in selenium transport throughout the body. The sepp1 gene locus potentially produces three alternative transcripts that differ only in their 5′ untranslated regions (5′UTRs) and not in their protein coding regions, as indicated by transcript information in genomic databases. Here we investigated the distribution, relative expression, and biological significance of these transcript variants. We confirmed the expression of Sepp1 transcript variants using PCR and sequencing. Using 5′-RACE, we identified multiple 5′-termini upstream from three different splice donor sites, and a single splice acceptor site for exon 2. We found regional and temporal changes in variant expression in select adult and neonate murine tissue and brain regions. Distribution of variants in heart and kidney varied with stage of development. Notably, the Sepp1b variant was localized specifically to the hippocampus in brain. Targeted silencing of individual variants using RNAi demonstrated the biological importance for all transcript variants in cell viability. Additionally, we determined that the Sepp1b variant is a specific target for the miR-7 microRNA by means of its unique 5′UTR structure. Our results emphasize the importance of non-coding transcript variations as a regulatory means for Sepp1 expression in different tissues and stages of development. The presence of a variant localized in the hippocampus and regulated by a microRNA may have implications for the known deficits in synaptic function caused by genetic deletion of Sepp1.

Elizabeth D. Nguyen-Wu

Papers

Selenoprotein K Knockout Mice Exhibit Deficient Calcium Flux in Immune Cells and Impaired Immune Responses

Expression and regulation of mouse selenoprotein P transcript variants differing in non-coding RNA.