Selenoprotein S (SELENOS) is a potential prognostic biomarker for brain lower grade glioma

BACKGROUND

Selenium, an essential micronutrient, primarily exists as selenocysteine in various selenoproteins. Selenoprotein S (SELENOS) is crucial in the development of human cancer. This study aimed to explore the correlation between SELENOS gene expression and the prognosis of brain lower-grade glioma (LGG).

METHODS

SELENOS protein and mRNA expression in human normal and tumor tissues were explored through the HPA database. SELENOS expression differences between normal and tumor tissues, along with its prognostic significance in gliomas, were analyzed using the TCGA, GTEx datasets, while the CGGA dataset was used to further assess its prognostic potential in a Chinese cohort. The association between SELENOS expression and tumor immune infiltration was also assessed. Multivariate and univariate Cox models were used to screen for clinicopathological parameters associated with SELENOS expression. The GDSC datasets was utilized to explore the connection between SELENOS and chemotherapeutic responses in LGG. A protein-protein interaction network for SELENOS was created. SELENOS expression in LGG cell lines were determined by Western blotting and qRT-PCR, and its functions were ascertained by routine in vitro experiments.

RESULTS

SELENOS was upregulated in 11 cancers and downregulated in 10 cancers relative to the corresponding normal tissues, and correlated significantly with the prognosis, especially for GBM, LGG and GBMLGG. Furthermore, It displayed a positive correlation with immune cell infiltration levels in LGG. Multivariate and Univariate Cox analyses confirmed that the impact of SELENOS on the prognosis of LGG is the combined result of factors such as age and tumor grade. The expression of SELENOS was significantly negatively correlated with temozolomide IC50 in LGG. We found that SELENOS interacts with 10 proteins, which are upregulated in LGG compared to human normal tissues. The expression of these interactors is positively correlated with SELENOS expression and LGG survival/prognosis. In vitro experiments confirmed the aberrant expression of SELENOS in LGG cell lines, and siRNA-mediated knockdown of SELENOS reduced the proliferation, viability, invasion and migration of LGG cells, and induced apoptosis.

CONCLUSIONS

SELENOS is a potential prognostic marker and therapeutic target for LGG, and its low expression is associated with favorable prognosis in LGG.

Selenium alleviates pancreatic fibrosis in chickens caused by mercuric chloride: Involvement of the MAPK signaling pathway and selenoproteins

Mercuric chloride (HgCl2) is a widespread inorganic mercury with digestive toxicity. The pancreas is an important digestive organ in animals, and pancreatic fibrosis (PF) is a major pathological feature of chronic pancreatitis, which can be caused by heavy metals. Selenium (Se) is an essential trace element for the animal organism, performing biological functions in the form of selenoproteins, as well as alleviating the toxicity of heavy metals. In this study, we explored the specific mechanisms underlying the protective effect of Se on HgCl2-induced pancreatic injury in chickens. Morphological observation and serum biochemical analysis showed that Se attenuated HgCl2-caused pancreatic tissue damage and elevated glucose concentration and α-amylase activity. Next, the expression of oxidative stress indicators such as MDA and GSH-Px as well as inflammation-related markers including IL-1β, IL-6, and TNF-α were detected. Results showed that Se had an inhibitory effect on HgCl2-induced oxidative stress and inflammation. Furthermore, we found that Se alleviated HgCl2-induced PF by detecting the expression of markers related to PF including TGF-β1, α-SMA, COL1A1, and FN1. Mechanistically, Se attenuated HgCl2-induced PF via the MAPK signaling pathway. Importantly, several selenoproteins, especially those with antioxidant activity, were involved in the protective effect of Se on HgCl2 toxicity. In conclusion, our findings demonstrated that Se inhibited HgCl2-induced oxidative stress and inflammation and alleviated chicken PF through the MAPK signaling pathway, in which some antioxidant selenoproteins were involved.

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.

Selenium and selenoproteins role in Parkinson's disease: Is there a link between selenoproteins and accumulated alpha-synuclein?

BACKGROUND

While Parkinson's disease (PD) etiology is not clear yet, accumulated alpha-synuclein is proposed to induce neurodegeneration. Selenium (Se) and its functional proteins play a key role in aggregation of misfolded proteins. However, their implications in neurodegenerative process are unclear.

AIM

Diagnosing Se and selenoprotein P (SelP), selenoprotein S (SelS) proportions in serum of PD patients to compare with healthy controls, whether the changes in their concentration could be a biomarker for PD.

METHODS

Se concentration was investigated in 30 PD patients and 30 controls using atomic absorption spectrometry. Also, alpha-Synuclein, SelP, and SelS levels were evaluated by ELISA. The parameters were compared in PD patients and controls. Also, the variations within the case group according to their age, disorder stage, and drug administration were evaluated.

RESULTS

PD subjects had higher Se concentration. The mean SelP in PD patients was lower from controls, whilst SelS levels were higher. Also, the concentration of alpha-synuclein was higher in PD patients. However, age, stage (except UPDRS III), and disorder duration had no influence on the Se and selenoproteins level, whilst there was a direct association between alpha-synuclein levels and disorder stage. Also, alpha-synuclein proportions in subjects using levodopa was significantly higher.

CONCLUSION

Our results suggest that serum levels of Se and SelP could be a biomarker or risk factor for PD. Although SelS interferes to reduce aggregated proteins, its pathway in PD is not clearly understood. Future studies could focus on how SelS can reduce on alpha-synuclein aggregation. Thus, other studies should be performed on this issue to induce the selenoproteins in PD.

A Comprehensive Review on GLP-1 Signaling Pathways in the Management of Diabetes Mellitus - Focus on the Potential Role of GLP-1 Receptors Agonists and Selenium among Various Organ Systems

Diabetes Mellitus develops when the body becomes unable to fuel its cells with glucose, which results in the accumulation of sugar excess in the bloodstream. Because it has diverse pathophysiological impacts on the body, diabetes mellitus represents a significant issue of concern in an attempt to find suitable treatment modalities and medications for afflicted diabetic patients. Glucagon-like peptide 1 (GLP-1) plays a pivotal role in the incretin effect, emerging as a prospective treatment for diabetes mellitus and a promising means of regenerating pancreatic cells, whether directly or through its receptor agonists. It has been shown that GLP-1 efficiently increases insulin production, lowers blood sugar levels in patients with type 2 diabetes mellitus, and decreases appetite, craving, and hunger, therefore amplifying the sensation of fullness and satiety. Moreover, since they are all dependent on GLP-1 effect, intricate signaling pathways share some similarities during specific phases, although the pathways continue to exhibit significant divergence engendered by specific reactions and effects in each organ, which encompasses the rationale behind observed differences. This triggers an expanding range of GLP-1 R agonists, creating new unforeseen research and therapeutic application prospects. This review aims to explain the incretin effect, discuss how GLP-1 regulates blood glucose levels, and how it affects different body organs, as well as how it transmits signals, before introducing selenium's role in the incretin impact.

GSK3β Inhibition by Phosphorylation at Ser389 Controls Neuroinflammation

The inhibition of Glycogen Synthase Kinase 3 β (GSK3β) by Ser⁹ phosphorylation affects many physiological processes, including the immune response. However, the consequences of GSK3β inhibition by alternative Ser³⁸⁹ phosphorylation remain poorly characterized. Here we have examined neuroinflammation in GSK3β Ser³⁸⁹ knock-in (KI) mice, in which the phosphorylation of Ser³⁸⁹ GSK3β is impaired. The number of activated microglia/infiltrated macrophages, astrocytes, and infiltrated neutrophils was significantly higher in these animals compared to C57BL/6J wild-type (WT) counterparts, which suggests that the failure to inactivate GSK3β by Ser³⁸⁹ phosphorylation results in sustained low-grade neuroinflammation. Moreover, glial cell activation and brain infiltration of immune cells in response to lipopolysaccharide (LPS) failed in GSK3β Ser³⁸⁹ KI mice. Such effects were brain-specific, as peripheral immunity was not similarly affected. Additionally, phosphorylation of the IkB kinase complex (IKK) in response to LPS failed in GSK3β Ser³⁸⁹ KI mice, while STAT3 phosphorylation was fully conserved, suggesting that the NF-κB signaling pathway is specifically affected by this GSK3β regulatory pathway. Overall, our findings indicate that GSK3β inactivation by Ser³⁸⁹ phosphorylation controls the brain inflammatory response, raising the need to evaluate its role in the progression of neuroinflammatory pathologies.

Selenoprotein S: A versatile disordered protein

Selenoprotein S (selenos) is a small, intrinsically disordered membrane protein that is associated with various cellular functions, such as inflammatory processes, cellular stress response, protein quality control, and signaling pathways. It is primarily known for its contribution to the ER-associated degradation (ERAD) pathway, which governs the extraction of misfolded proteins or misassembled protein complexes from the ER to the cytosol for degradation by the proteasome. However, selenos's other cellular roles in signaling are equally vital, including the control of transcription factors and cytokine levels. Consequently, genetic polymorphisms of selenos are associated with increased risk for diabetes, dyslipidemia, and cardiovascular diseases, while high expression levels correlate with poor prognosis in several cancers. Its inhibitory role in cytokine secretion is also exploited by viruses. Since selenos binds multiple protein complexes, however, its specific contributions to various cellular pathways and diseases have been difficult to establish. Thus, the precise cellular functions of selenos and their interconnectivity have only recently begun to emerge. This review aims to summarize recent insights into the structure, interactome, and cellular roles of selenos.

Emerging roles of selenium on metabolism and type 2 diabetes

Selenium is recognized as an essential element for human health and enters human body mainly via diet. Selenium is a key constituent in selenoproteins, which exert essential biological functions, including antioxidant and anti-inflammatory effects. Several selenoproteins including glutathione peroxidases, selenoprotein P and selenoprotein S are known to play roles in the regulation of type 2 diabetes. Although there is a close association between certain selenoproteins with glucose metabolism or insulin resistance, the relationship between selenium and type 2 diabetes is complex and remains uncertain. Here we review recent advances in the field with an emphasis on roles of selenium on metabolism and type 2 diabetes. Understanding the association between selenium and type 2 diabetes is important for developing clinical practice guidelines, establishing and implementing effective public health policies, and ultimately combating relative health issues.

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.

Potential involvement of the microbiota-gut-brain axis in the neurotoxicity of triphenyl phosphate (TPhP) in the marine medaka (Oryzias melastigma) larvae

Triphenyl phosphate (TPhP), a prevalent pollutant in the aquatic environment, has been reported to induce neurotoxicity (e.g., a suppression in locomotor activity) in fish larvae, posing a great threat to fish populations. However, the underlying mechanism was not fully revealed. In this study, the Oryzias melastigma larvae (21 dph) were exposed to waterborne TPhP (20 and 100 μg/L) for 7 days and a decreased locomotor activity was found. After exposure, the brain transcriptome and communities of gut microbiota were investigated to explore the potential mechanism underlying the suppressed locomotor activity by TPhP. The results showed that 1160 genes in the brain were dysregulated by TPhP, of which 24 genes were identified as being highly associated with the neural function and development (including nerve regeneration, neuronal growth and differentiation, brain ion homeostasis, production of neurotransmitters and etc), suggesting a general impairment in the central nervous system. Meanwhile, TPhP caused disorders in the gut microbiota. The relative abundance of Gammaproteobacteria and Alphaproteobacteria, which can influence the brain functions of host via the microbiota-gut-brain axis, were significantly altered by TPhP. Furthermore, the Redundancy analysis (RDA) revealed positive correlations between the intestinal genera Ruegeria, Roseivivax and Nautella and the dysregulated brain genes by TPhP. These results suggest that TPhP might impair the central nervous system of the O. melastigma larvae not only directly but also through the microbiota-gut-axis (indirectly), contributing to the suppressed locomotor activity. These findings enrich our mechanistic understanding of the toxicity of TPhP in fish larvae and shed preliminary light on the involvement of microbiota-gut-brain axis in the neurotoxicity of environmental pollutants.

Hepatic deficiency of selenoprotein S exacerbates hepatic steatosis and insulin resistance

Nonalcoholic fatty liver disease (NAFLD) is closely associated with insulin resistance (IR) and type 2 diabetes mellitus (T2DM), which are all complex metabolic disorders. Selenoprotein S (SelS) is an endoplasmic reticulum (ER) resident selenoprotein involved in regulating ER stress and has been found to participate in the occurrence and development of IR and T2DM. However, the potential role and mechanism of SelS in NAFLD remains unclear. Here, we analyzed SelS expression in the liver of high-fat diet (HFD)-fed mice and obese T2DM model (db/db) mice and generated hepatocyte-specific SelS knockout (SelS^H-KO) mice using the Cre-loxP system. We showed that hepatic SelS expression levels were significantly downregulated in HFD-fed mice and db/db mice. Hepatic SelS deficiency markedly increased ER stress markers in the liver and caused hepatic steatosis via increased fatty acid uptake and reduced fatty acid oxidation. Impaired insulin signaling was detected in the liver of SelS^H-KO mice with decreased phosphorylation levels of insulin receptor substrate 1 (IRS1) and protein kinase B (PKB/Akt), which ultimately led to disturbed glucose homeostasis. Meanwhile, our results showed hepatic protein kinase Cɛ (PKCɛ) activation participated in the negative regulation of insulin signaling in SelS^H-KO mice. Moreover, the inhibitory effect of SelS on hepatic steatosis and IR was confirmed by SelS overexpression in primary hepatocytes in vitro. Thus, we conclude that hepatic SelS plays a key role in regulating hepatic lipid accumulation and insulin action, suggesting that SelS may be a potential intervention target for the prevention and treatment of NAFLD and T2DM.

Endoplasmic Reticulum Stress-Associated Neuronal Death and Innate Immune Response in Neurological Diseases

Neuronal death and inflammatory response are two common pathological hallmarks of acute central nervous system injury and chronic degenerative disorders, both of which are closely related to cognitive and motor dysfunction associated with various neurological diseases. Neurological diseases are highly heterogeneous; however, they share a common pathogenesis, that is, the aberrant accumulation of misfolded/unfolded proteins within the endoplasmic reticulum (ER). Fortunately, the cell has intrinsic quality control mechanisms to maintain the proteostasis network, such as chaperone-mediated folding and ER-associated degradation. However, when these control mechanisms fail, misfolded/unfolded proteins accumulate in the ER lumen and contribute to ER stress. ER stress has been implicated in nearly all neurological diseases. ER stress initiates the unfolded protein response to restore proteostasis, and if the damage is irreversible, it elicits intracellular cascades of death and inflammation. With the growing appreciation of a functional association between ER stress and neurological diseases and with the improved understanding of the multiple underlying molecular mechanisms, pharmacological and genetic targeting of ER stress are beginning to emerge as therapeutic approaches for neurological diseases.

Missense mutation in selenocysteine synthase causes cardio-respiratory failure and perinatal death in mice which can be compensated by selenium-independent GPX4

Selenoproteins are a small family of proteins containing the trace element selenium in form of the rare amino acid selenocysteine (Sec), which is decoded by the UGA codon. In humans, a number of pathogenic variants in genes encoding distinct selenoproteins or selenoprotein biosynthesis factors have been identified. Pathogenic variants in selenocysteine synthase (SEPSECS), which catalyzes the last step in Sec-tRNA[Ser]Sec biosynthesis, were reported in children suffering from progressive cerebello-cerebral atrophy. To understand the pathomechanism associated with SEPSECS deficiency, we generated a novel mouse model recapitulating the respective human pathogenic p.Y334C variant in the murine Sepsecs gene (SepsecsY334C). Unlike in patients, pups homozygous for the p.Y334C variant died perinatally with signs of cardio-respiratory failure. Perinatal death is reminiscent of the Sedaghatian spondylometaphyseal dysplasia disorder in humans, which is caused by pathogenic variants in the gene encoding the selenoprotein and key ferroptosis regulator glutathione peroxidase 4 (GPX4). Protein expression levels of distinct selenoproteins in SepsecsY334C/Y334C mice were found to be generally reduced in brain and isolated cortical neurons, while transcriptomics analysis uncovered an upregulation of NRF2-regulated genes. Crossbreeding of SepsecsY334C/Y334C mice with mice harboring a targeted mutation of the catalytically active Sec to Cys in GPX4 rescued perinatal death of SepsecsY334C/Y334C mice, showing that the cardio-respiratory defects of SepsecsY334C/Y334C mice were caused by the lack of GPX4. Like in SepsecsY334C/Y334C mice, selenoprotein expression levels remained low and NRF2-regulated genes remained highly expressed in these compound mutant mice, indicating that selenium-independent GPX4, along with a sustained antioxidant response are sufficient to compensate for dysfunctional Sec-tRNA[Ser]Sec biosynthesis. Our findings imply that children with pathogenic variants in SEPSECS or GPX4 may even benefit from treatments that incompletely compensate for impaired GPX4 activity.

How cytosolic compartments play safeguard functions against neuroinflammation and cell death in cerebral ischemia

Ischemic stroke is the second leading cause of mortality and disability globally. Neuronal damage following ischemic stroke is rapid and irreversible, and eventually results in neuronal death. In addition to activation of cell death signaling, neuroinflammation is also considered as another pathogenesis that can occur within hours after cerebral ischemia. Under physiological conditions, subcellular organelles play a substantial role in neuronal functionality and viability. However, their functions can be remarkably perturbed under neurological disorders, particularly cerebral ischemia. Therefore, their biochemical and structural response has a determining role in the sequel of neuronal cells and the progression of disease. However, their effects on cell death and neuroinflammation, as major underlying mechanisms of ischemic stroke, are still not understood. This review aims to provide a comprehensive overview of the contribution of each organelle on these pathological processes after ischemic stroke.

Upregulated Long Non-coding RNA ALMS1-IT1 Promotes Neuroinflammation by Activating NF-κB Signaling in Ischemic Cerebral Injury

BACKGROUND

ALMS1-IT1, a recently identified lncRNA, has been proven to play a crucial role in regulating tumor progression and predicting the survival time of tumor patients. Data analysis from the Human Body Map (HBM) revealed that ALMS1-IT1 is expressed mainly in brain tissues.

METHODS

In this study, the role of ALMS1-IT in regulating neuro-inflammation and functional recovery was investigated after ischemic cerebral damage. To this end, the rat model of transient middle cerebral artery occlusion (tMCAO) was constructed, the cell model of oxygen-glucose deprivation (OGD) was established using BV2 microglial cells, and the aberrant expression of ALMS1-IT1 was assessed in brain tissues. After ALMS1- IT1 knockdown through intrathecal injection of Lv-shALMS1-IT1, neuro-inflammatory response and functional tests including a modified neurological severity score (mNSS) and a foot-fault test were assessed.

RESULTS

The level of ALMS1-IT1 was promptly enhanced at 12 hours (h) following MCAO, peaking at 48 h, and remaining high at day 14 compared to the sham group. Pro-inflammatory cytokines (IL-1β, IL-6, and TNF- α) were increased after MCAO, whereas ALMS1-IT1 inhibition suppressed the expression of IL-1β, IL-6 and TNF-α in MCAO rats. The results from mNSS and foot-fault test showed that ALMS1-IT1 knockdown significantly improved spatial learning and sensorimotor function of MCAO rats. Mechanistically, ALMS1-IT1 knockdown suppressed the activation of NF-κB signaling in vitro and in vivo, as evidenced by decreased p65 expression and p65 nuclear translocation. ALMS1-IT1 overexpression facilitated pro-inflammatory cytokines expression in microglia, whereas the effect was blocked by treatment with JSH-23 (a specific NF-κB inhibitor).

CONCLUSION

These data demonstrated that ALMS1-IT1 inhibition improved neurological function of MCAO rats, at least in part by repressing NF-κB-dependent neuro-inflammation.

Identification of VIMP as a gene inhibiting cytokine production in human CD4+ effector T cells

Many players regulating the CD4+ T cell-mediated inflammatory response have already been identified. However, the critical nodes that constitute the regulatory and signaling networks underlying CD4 T cell responses are still missing. Using a correlation-network-guided approach, here we identified VIMP (VCP-interacting membrane protein), one of the 25 genes encoding selenoproteins in humans, as a gene regulating the effector functions of human CD4 T cells, especially production of several cytokines including IL2 and CSF2. We identified VIMP as an endogenous inhibitor of cytokine production in CD4 effector T cells via both the E2F5 transcription regulatory pathway and the Ca2+/NFATC2 signaling pathway. Our work not only indicates that VIMP might be a promising therapeutic target for various inflammation-associated diseases but also shows that our network-guided approach can significantly aid in predicting new functions of the genes of interest.

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.

Regulation of GSK3β by Ser389 Phosphorylation During Neural Development

GSK3β is a constitutively active kinase that promotes cell death, which requires strict regulatory mechanisms. Although Akt-mediated phosphorylation at Ser9 is the default mechanism to inactivate GSK3β, phosphorylation of GSK3β at Ser389 by p38 MAPK has emerged as an alternative inhibitory pathway that provides cell protection and repair in response to DNA damage. Phosphorylation of Ser389 GSK3β has been detected in adult brain, where it has been related to neuronal survival and behavior. However, the use of this pathway to regulate GSK3β in the neonatal developing brain is unknown. In this study, we show that phosphorylation of GSK3β at Ser389 in the brain is developmentally regulated, with the highest levels corresponding to the first 2 weeks of age. Moreover, we found that the phosphorylation of GSK3β at Ser389 is the preferential mechanism for inactivating brain GSK3β in 2-week-old mice. Importantly, we show that phospho-Ser389 GSK3β expression is predominant in neuronal cell cultures from neonatal brain relative to other cell populations. However, phospho-Ser389 GSK3β is triggered by DNA double-strand breaks in all developing neural cell types examined. Thus, the phosphorylation of GSK3β on Ser389 could be a central regulatory mechanism to restrain GSK3β during neurogenesis early in life.

Role of Selenoproteins in Redox Regulation of Signaling and the Antioxidant System: A Review

Selenium is a vital trace element present as selenocysteine (Sec) in proteins that are, thus, known as selenoproteins. Humans have 25 selenoproteins, most of which are functionally characterized as oxidoreductases, where the Sec residue plays a catalytic role in redox regulation and antioxidant activity. Glutathione peroxidase plays a pivotal role in scavenging and inactivating hydrogen and lipid peroxides, whereas thioredoxin reductase reduces oxidized thioredoxins as well as non-disulfide substrates, such as lipid hydroperoxides and hydrogen peroxide. Selenoprotein R protects the cell against oxidative damage by reducing methionine-R-sulfoxide back to methionine. Selenoprotein O regulates redox homeostasis with catalytic activity of protein AMPylation. Moreover, endoplasmic reticulum (ER) membrane selenoproteins (SelI, K, N, S, and Sel15) are involved in ER membrane stress regulation. Selenoproteins containing the CXXU motif (SelH, M, T, V, and W) are putative oxidoreductases that participate in various cellular processes depending on redox regulation. Herein, we review the recent studies on the role of selenoproteins in redox regulation and their physiological functions in humans, as well as their role in various diseases.

Cell-Type Specific Analysis of Selenium-Related Genes in Brain

Selenoproteins are a unique class of proteins that play key roles in redox signaling in the brain. This unique organ is comprised of a wide variety of cell types that includes excitatory neurons, inhibitory neurons, astrocytes, microglia, and oligodendrocytes. Whereas selenoproteins are known to be required for neural development and function, the cell-type specific expression of selenoproteins and selenium-related machinery has yet to be systematically investigated. Due to advances in sequencing technology and investment from the National Institutes of Health (NIH)-sponsored BRAIN initiative, RNA sequencing (RNAseq) data from thousands of cortical neurons can now be freely accessed and searched using the online RNAseq data navigator at the Allen Brain Atlas. Hence, we utilized this newly developed tool to perform a comprehensive analysis of the cell-type specific expression of selenium-related genes in brain. Select proteins of interest were further verified by means of multi-label immunofluorescent labeling of mouse brain sections. Of potential significance to neural selenium homeostasis, we report co-expression of selenoprotein P (SELENOP) and selenium binding protein 1 (SELENBP1) within astrocytes. These findings raise the intriguing possibility that SELENBP1 may negatively regulate astrocytic SELENOP synthesis and thereby limit downstream Se supply to neurons.

Selenoprotein S protects against high glucose-induced vascular endothelial apoptosis through the PKCβII/JNK/Bcl-2 pathway

Vascular endothelial apoptosis is closely associated with the pathogenesis and progression of diabetic macrovascular diseases. Selenoprotein S (SelS) participates in the protection of vascular endothelial and smooth muscle cells from oxidative and endoplasmic reticulum stress-induced injury. However, whether SelS can protect vascular endothelium from high glucose (HG)-induced apoptosis and the underlying mechanism remains unclear. The present study preliminarily analyzed aortic endothelial apoptosis and SelS expression in diabetic rats in vivo and the effects of HG on human umbilical vein endothelial cell (HUVEC) apoptosis and SelS expression in vitro. Subsequently, SelS expression was up- or downregulated in HUVECs using the pcDNA3.1-SelS recombinant plasmid and SelS-specific small interfering RNAs, and the effects of high/low SelS expression on HG-induced HUVEC apoptosis and a possible molecular mechanism were analyzed. As expected, HG induced vascular endothelial apoptosis and upregulated endothelial SelS expression in vivo and in vitro. SelS overexpression in HUVECs suppressed HG-induced increase in apoptosis and cleaved caspase3 level, accompanied by reduced protein kinase CβII (PKCβII), c-JUN N-terminal kinase (JNK), and B-cell lymphoma/leukemia-2 (Bcl-2) phosphorylation. In contrast, inhibiting SelS expression in HUVECs further aggravated HG-induced increase in apoptosis and cleaved caspase3 level, which was accompanied by increased PKCβII, JNK, and Bcl-2 phosphorylation. Pretreatment with PKC activators blocked the protective effects of SelS and increased the apoptosis and cleaved caspase3 level in HUVECs. In summary, SelS protects vascular endothelium from HG-induced apoptosis, and this was achieved through the inhibition of PKCβII/JNK/Bcl-2 pathway to eventually inhibit caspase3 activation. SelS may be a promising target for the prevention and treatment of diabetic macrovascular complications.

Association of genetic polymorphisms of SelS with Type 2 diabetes in a Chinese population

Background: Selenoprotein S (SelS) gene expression is positively correlated to triglyceride (TG) concentrations and is associated with diabetes in animal model. However, the relationship between genetic polymorphisms of SelS and Type 2 diabetes (T2DM) remains unclear. Methods: In the present study, we genotyped four single nucleotide polymorphisms (rs12910524, rs1384565, rs2101171, rs4965814) of SelS gene using TaqMan genotyping method in a case-control study (1947 T2DM patients and 1639 control subjects). Results: We found both rs1384565 CC genotype (12.1 compared with 6.6%, P<0.001) and C allele (35.2 compared with 24.4%, P<0.001) were more frequent in the T2DM patients than in the controls. Logistic regression analysis suggested after adjustment of other confounders, the difference remained significant between the two groups (CC compared with TT, P=0.002, OR = 1.884, 95% CI: 1.263-2.811; CT compared with TT, P<0.001, OR = 1.764, 95% CI: 1.412-2.204). Conclusion: The present study suggested that genetic polymorphisms of SelS were associated with T2DM in a Chinese population.

Selenoprotein S protects against adipocyte death through mediation of the IRE1α-sXBP1 pathway

As the most conserved branch of the unfolded protein response (UPR), the inositol-requiring enzyme 1a (IRE1a)/X-box binding protein 1 (XBP1) pathway plays crucial roles in cell survival and cell death by upregulating UPR-associated genes involved in protein entry into the endoplasmic reticulum (ER) and ER-associated degradation (ERAD). Selenoprotein S (SelS) is localized to the ER membrane and involved in ERAD. Although SelS plays an important role in restoring ER stress, the SelS-dependent protective mechanisms against cell death remain unclear. Here, using an inducible SelS knockdown (KD) 3T3-L1 cell model, we showed that SelS KD resulted adipocyte death, which was associated with imbalance of the Bcl-2 family members. Furthermore, SelS KD decreased spliced XBP1 (sXBP1), increased IRE1α and p-JNK, suggesting a role of SelS in the modulation of the IRE1α-sXBP1 pathway. Moreover, adipocyte death induced by SelS suppression can be inhibited by overexpression of sXBP1. Thus, it is proposed that SelS promotes cell survival through the IRE1α-XBP1 signaling pathway.

Selenoprotein S inhibits inflammation-induced vascular smooth muscle cell calcification

Vascular calcification is a prominent feature of many diseases including atherosclerotic cardiovascular disease (CVD), leading to high morbidity and mortality rates. A significant association of selenoprotein S (SelS) gene polymorphism with atherosclerotic CVD has been reported in epidemiologic studies, but the underlying mechanism is far from clear. To investigate the role of SelS in inflammation-induced vascular calcification, osteoblastic differentiation and calcification of vascular smooth muscle cells (VSMCs) induced by lipopolysaccharide (LPS) or tumor necrosis factor (TNF)-α were compared between the cells with and without SelS knockdown. LPS or TNF-α induced osteoblastic differentiation and calcification of VSMCs, as showed by the increases of runt-related transcription factor 2 (Runx2) protein levels, Runx2 and type I collagen mRNA levels, alkaline phosphatase activity, and calcium deposition content. These changes were aggravated when SelS was knocked down by small interfering RNA. Moreover, LPS activated both classical and alternative pathways of nuclear factor-κB (NF-κB) signaling in calcifying VSMCs, which were further enhanced under SelS knockdown condition. SelS knockdown also exacerbated LPS-induced increases of proinflammatory cytokines TNF-α and interleukin-6 expression, as well as increases of endoplasmic reticulum (ER) stress markers glucose-regulated protein 78 and inositol-requiring enzyme 1α expression in calcifying VSMCs. In conclusion, the present study suggested that SelS might inhibit inflammation-induced VSMC calcification probably by suppressing activation of NF-κB signaling pathways and ER stress. Our findings provide new understanding of the role of SelS in vascular calcification, which will be potentially beneficial to the prevention of atherosclerotic CVD.

Selenoprotein S Attenuates Tumor Necrosis Factor-α-Induced Dysfunction in Endothelial Cells

Endothelial dysfunction, partly induced by inflammatory mediators, is known to initiate and promote several cardiovascular diseases. Selenoprotein S (SelS) has been identified in endothelial cells and is associated with inflammation; however, its function in inflammation-induced endothelial dysfunction has not been described. We first demonstrated that the upregulation of SelS enhances the levels of nitric oxide and endothelial nitric oxide synthase in tumor necrosis factor- (TNF-) α-treated human umbilical vein endothelial cells (HUVECs). The levels of TNF-α-induced endothelin-1 and reactive oxygen species are also reduced by the upregulation of SelS. Furthermore, SelS overexpression blocks the TNF-α-induced adhesion of THP-1 cells to HUVECs and inhibits the increase in intercellular adhesion molecule-1 and vascular cell adhesion molecule-1. Moreover, SelS overexpression regulates TNF-α-induced inflammatory factors including interleukin-1β, interleukin-6, interleukin-8, and monocyte chemotactic protein-1 and attenuates the TNF-α-induced activation of p38 mitogen-activated protein kinase (MAPK) and nuclear factor-κB (NF-κB) pathways. Conversely, the knockdown of SelS with siRNA results in an enhancement of TNF-α-induced injury in HUVECs. These findings suggest that SelS protects endothelial cells against TNF-α-induced dysfunction by inhibiting the activation of p38 MAPK and NF-κB pathways and implicates it as a possible modulator of vascular inflammatory diseases.

Selenoprotein S Reduces Endoplasmic Reticulum Stress-Induced Phosphorylation of Tau: Potential Role in Selenate Mitigation of Tau Pathology

Previous studies demonstrated that selenium in the form of sodium selenate reduces neurofibrillary tangle formation in Alzheimer's disease models. Hyperphosphorylation of tau, which leads to formation of neurofibrillary tangles in Alzheimer's disease, is increased by endoplasmic reticulum (ER) stress. Selenoprotein S (SelS) is part of an ER membrane complex that removes misfolded proteins from the ER as a means to reduce ER stress. Selenate, as with other forms of selenium, will increase selenoprotein expression. We therefore proposed that increased SelS expression by selenate would contribute to the beneficial actions of selenate in Alzheimer's disease. SelS expression increased with ER stress and decreased under conditions of elevated glucose concentrations in the SH-SY5Y neuronal cell line. Reducing expression of SelS with siRNA promoted cell death in response to ER stress. Selenate increased SelS expression, which significantly correlated with decreased tau phosphorylation. Restricting SelS expression during ER stress conditions increased tau phosphorylation, and also promoted aggregation of phosphorylated tau in neurites and soma. In human postmortem brain, SelS expression coincided with neurofibrillary tangles, but not with amyloid-β plaques. These results indicate that selenate can alter phosphorylation of tau by increasing expression of SelS in Alzheimer's disease and potentially other neurodegenerative disorders.

Selenoprotein S: a therapeutic target for diabetes and macroangiopathy?

Inflammatory response, oxidative stress, and endoplasmic reticulum (ER) stress are important pathophysiological bases of the occurrence and development of diabetes mellitus (DM) and macroangiopathy complications. Selenoprotein S (SELENOS) is involved in the regulation of these mechanisms; therefore, its association with DM and macroangiopathy has gradually received attention from scholars worldwide. SELENOS has different biological functions in different tissues and organs: it exerts antioxidant protection and has anti-ER stress effects in the pancreas and blood vessels, while it promotes the occurrence and development of insulin resistance in the liver, adipose tissue, and skeletal muscle. In addition, studies have confirmed that some SELENOS gene polymorphisms can influence the inflammatory response and are closely associated with the risk for developing DM and macroangiopathy. Therefore, comprehensive understanding of the association between SELENOS and inflammation, oxidative stress, and ER stress may better elucidate and supplement the pathogenic mechanisms of DM and macroangiopathy complications. Furthermore, in-depth investigation of the association of SELENOS function in different tissues and organs with DM and macroangiopathy may facilitate the development of new strategies for the prevention and treatment of DM and macrovascular complications. Here, we summarize the consensus and controversy regarding functions of SELENOS on currently available evidence.

A Reduction in Selenoprotein S Amplifies the Inflammatory Profile of Fast-Twitch Skeletal Muscle in the mdx Dystrophic Mouse

Excessive inflammation is a hallmark of muscle myopathies, including Duchenne muscular dystrophy (DMD). There is interest in characterising novel genes that regulate inflammation due to their potential to modify disease progression. Gene polymorphisms in Selenoprotein S (Seps1) are associated with elevated proinflammatory cytokines, and in vitro SEPS1 is protective against inflammatory stress. Given that SEPS1 is highly expressed in skeletal muscle, we investigated whether the genetic reduction of Seps1 exacerbated inflammation in the mdx mouse. F1 male mdx mice with a heterozygous Seps1 deletion (mdx:Seps1-/+) were generated. The mdx:Seps1-/+ mice had a 50% reduction in SEPS1 protein expression in hindlimb muscles. In the extensor digitorum longus (EDL) muscles, mRNA expression of monocyte chemoattractant protein 1 (Mcp-1) (P = 0.034), macrophage marker F4/80 (P = 0.030), and transforming growth factor-β1 (Tgf-β1) (P = 0.056) were increased in mdx:Seps1-/+ mice. This was associated with a reduction in muscle fibre size; however, ex vivo EDL muscle strength and endurance were unaltered. In dystrophic slow twitch soleus muscles, SEPS1 reduction had no effect on the inflammatory profile nor function. In conclusion, the genetic reduction of Seps1 appears to specifically exacerbate the inflammatory profile of fast-twitch muscle fibres, which are typically more vulnerable to degeneration in dystrophy.

Sinomenine activates astrocytic dopamine D2 receptors and alleviates neuroinflammatory injury via the CRYAB/STAT3 pathway after ischemic stroke in mice

Background

Astrocyte-mediated neuroinflammation plays a critical role in ischemic stroke-induced secondary cerebral injury. Previous studies have suggested that the dopamine D2 receptor (DRD2) acts as a key target in regulating the neuroinflammatory response. However, the underlying molecular mechanisms are still unknown, and effective DRD2 agonists are lacking. In the present study, we examined the anti-inflammatory and neuroprotective effects of sinomenine (Sino), a monomeric compound with potential immunoregulatory properties in nervous system.

Methods

TTC staining, apoptosis assay, evaluation of brain edema, and neurological assessment were performed in the middle cerebral artery occlusion (MCAO) mouse model. Primary astrocytes exposed to oxygen glucose deprivation (OGD) were used in the in vitro experiments. Quantitative PCR was applied to assess the levels of inflammatory cytokines. Multi-labeling immunofluorescence, Western blot, co-immunoprecipitation, and electrophoretic mobility shift assay (EMSA) were also used to investigate the molecular mechanisms underlying the Sino-mediated anti-inflammatory effects in vivo and in vitro.

Results

Sino remarkably attenuated the cerebral infarction and neuronal apoptosis, reduced the levels of inflammatory cytokines, and alleviated neurological deficiency in MCAO mice. Sino significantly inhibited astrocytic activation and STAT3 phosphorylation as well as increased DRD2 and αB-crystallin (CRYAB) expression after MCAO. In vitro, Sino blocked OGD-induced activation of STAT3 and generation of pro-inflammatory cytokines in primary astrocytes, and these effects were significantly abolished by either DRD2 or CRYAB knockdown. Additionally, Sino induced up-regulation and nuclear translocation of CRYAB in astrocytes and enhanced the interaction between CRYAB and STAT3, which further inhibited the activation and DNA-binding activity of STAT3.

Conclusions

Our study demonstrates that Sino activates astrocytic DRD2 and thereby suppresses neuroinflammation via the CRYAB/STAT3 pathway, which sheds some light on a promising therapeutic strategy for ischemic stroke.

Electronic supplementary material

The online version of this article (doi:10.1186/s12974-016-0739-8) contains supplementary material, which is available to authorized users.

The source of circulating selenoprotein S and its association with type 2 diabetes mellitus and atherosclerosis: a preliminary study

Background

Selenoprotein S (SelS) is a transmembrane protein that is expressed in the liver, skeletal muscle, adipose tissue, pancreatic islets, kidney, and blood vessels. In addition to its transmembrane localization, SelS is also secreted from hepatoma HepG2 cells (but not L6 skeletal muscle cells, 3T3-L1 adipocytes, Min6 pancreatic β cells and human embryonic kidney 293 cells) and has been detected in the serum of some human subjects, with a detection rate of 31.1 %. These findings prove that serum SelS is secreted by hepatocytes. However, whether vascularly expressed SelS can be secreted has not been reported. Transmembrane SelS has been suggested to play different roles in the pathogenesis and progression of diabetes mellitus (DM) and atherosclerosis (AS), but the association of secreted SelS with DM and macroangiopathy remains unclear.

Research design and methods

Supernatants were collected from human umbilical vein endothelial cells (HUVECs), human aortic vascular smooth muscle cells (HA/VSMCs) and human hepatoma HepG2 cells that were untransfected or transfected with the indicated plasmid and concentrated for western blotting. Serum samples were collected from 158 human subjects with or without type 2 DM (T2DM) and/or AS. Serum SelS levels were measured using an enzyme-linked immunosorbent assay.

Results

Secreted SelS was only detected in the supernatants of hepatoma HepG2 cells. The SelS detection rate among the 158 human serum samples was 100 %, and the average SelS level was 64.81 ng/dl. The serum SelS level in the isolated DM subjects was lower than the level in the healthy control subjects (52.66 ± 20.53 vs 70.40 ± 21.38 ng/dl). The serum SelS levels in the DM complicated with SAS subjects (67.73 ± 21.41 ng/dl) and AS subjects (71.69 ± 27.00 ng/dl) were significantly increased compared with the serum SelS level in the isolated DM subjects. There was a positive interaction effect between T2DM and AS on the serum SelS level (P = 0.002). Spearman correlation analysis showed that the serum SelS level was negatively correlated with fasting plasma glucose.

Conclusions

Vascular endothelial and vascular smooth muscle cells could not secrete SelS. Serum SelS was primarily secreted by hepatocytes. SelS was universally detected in human serum samples, and the serum SelS level was associated with T2DM and its macrovascular complications. Thus, regulating liver and serum SelS levels might become a new strategy for the prevention and treatment of DM and its macrovascular complications.

Electronic supplementary material

The online version of this article (doi:10.1186/s12933-016-0388-3) contains supplementary material, which is available to authorized users.

Importance of selenium and selenoprotein for brain function: From antioxidant protection to neuronal signalling

Multiple biological functions of selenium manifest themselves mainly via 25 selenoproteins that have selenocysteine at their active centre. Selenium is vital for the brain and seems to participate in the pathology of disorders such as Alzheimer's disease, Parkinson's disease, amyotrophic lateral sclerosis and epilepsy. Since selenium was shown to be involved in diverse functions of the central nervous system, such as motor performance, coordination, memory and cognition, a possible role of selenium and selenoproteins in brain signalling pathways may be assumed. The aim of the present review is to analyse possible relations between selenium and neurotransmission. Selenoproteins seem to be of special importance in the development and functioning of GABAergic (GABA, γ-aminobutyric acid) parvalbumin positive interneurons of the cerebral cortex and hippocampus. Dopamine pathway might be also selenium dependent as selenium shows neuroprotection in the nigrostriatal pathway and also exerts toxicity towards dopaminergic neurons under higher concentrations. Recent findings also point to acetylcholine neurotransmission involvement. The role of selenium and selenoproteins in neurotransmission might not only be limited to their antioxidant properties but also to inflammation, influencing protein phosphorylation and ion channels, alteration of calcium homeostasis and brain cholesterol metabolism. Moreover, a direct signalling function was proposed for selenoprotein P through interaction with post-synaptic apoliprotein E receptors 2 (ApoER2).

Endoplasmic reticulum stress in brain ischemia

Endoplasmic reticulum (ER) stress is an intricate mechanism that mediates numerous responses during brain ischemia, thus being essential to determine the fate of neurons. In recent years, studies of the mechanisms of brain ischemic injury have centered on ER stress, glutamate excitotoxicity, dysfunction of mitochondria, inflammatory reactions, calcium overload and death receptor pathways. The role of ER stress is highly important. In addition to resulting in neuronal cell death through calcium toxicity and apoptotic pathways, ER stress also triggers a series of adaptive responses including unfolded protein response (UPR), autophagy, the expression of pro-survival proteins and the enhancement of ER self-repair ability, leading to less ischemic brain damage. This paper provides an overview of recent advances in understanding of the relations between ER stress and brain ischemia.

Selenium, selenoproteins and neurodegenerative diseases

A review of selenium's essential role in normal brain function and its potential involvement in neurodegenerative diseases.

Selenoprotein S is a marker but not a regulator of endoplasmic reticulum stress in intestinal epithelial cells

Selenoproteins are candidate mediators of selenium-dependent protection against tumorigenesis and inflammation in the gut. Expression and roles of only a limited number of intestinal selenoproteins have been described so far. Selenoprotein S (SelS) has been linked to various inflammatory diseases and is suggested to be involved in endoplasmic reticulum (ER) homeostasis regulation and antioxidative protection in a cell-type-dependent manner, but its protein expression, regulation, and function in the gut are not known. We here analyzed the expression and localization of SelS in the healthy and inflamed gut and studied its regulation and function in intestinal epithelial cell lines. SelS was expressed in the intestinal epithelium of the small and large intestine and colocalized with markers of Paneth cells and macrophages. It was upregulated in inflamed ileal tissue from Crohn's disease patients and in two models of experimental colitis in mice. We detected SelS in colorectal cell lines, where it colocalized with the ER marker calnexin. SelS protein expression was unaffected by enterocytic differentiation but increased in response to selenium supplementation and after treatment with the ER stress inducer tunicamycin. On the other hand, depletion of SelS in LS174T, HT29, and Caco-2 cells by RNA interference did not cause or modulate ER stress and had no effect on hydrogen peroxide-induced cell death. In summary, we introduce SelS as a novel marker of Paneth cells and intestinal ER stress. Although it is upregulated in Crohn's disease, its role in disease etiology remains to be established.

Genome-wide linkage analysis of congenital heart defects using MOD score analysis identifies two novel loci

Background

Congenital heart defects (CHD) is the most common cause of death from a congenital structure abnormality in newborns and is often associated with fetal loss. There are many types of CHD. Human genetic studies have identified genes that are responsible for the inheritance of a particular type of CHD and for some types of CHD previously thought to be sporadic. However, occasionally different members of the same family might have anatomically distinct defects — for instance, one member with atrial septal defect, one with tetralogy of Fallot, and one with ventricular septal defect. Our objective is to identify susceptibility loci for CHD in families affected by distinct defects. The occurrence of these apparently discordant clinical phenotypes within one family might hint at a genetic framework common to most types of CHD.

Results

We performed a genome-wide linkage analysis using MOD score analysis in families with diverse CHD. Significant linkage was obtained in two regions, at chromosome 15 (15q26.3, P_empirical = 0.0004) and at chromosome 18 (18q21.2, P_empirical = 0.0005).

Conclusions

In these two novel regions four candidate genes are located: SELS, SNRPA1, and PCSK6 on 15q26.3, and TCF4 on 18q21.2. The new loci reported here have not previously been described in connection with CHD. Although further studies in other cohorts are needed to confirm these findings, the results presented here together with recent insight into how the heart normally develops will improve the understanding of CHD.

Alternative transcripts and 3'UTR elements govern the incorporation of selenocysteine into selenoprotein S

Selenoprotein S (SelS) is a 189 amino acid trans-membrane protein that plays an important yet undefined role in the unfolded protein response. It has been proposed that SelS may function as a reductase, with the penultimate selenocysteine (Sec¹⁸⁸) residue participating in a selenosulfide bond with cysteine (Cys¹⁷⁴). Cotranslational incorporation of Sec into SelS depends on the recoding of the UGA codon, which requires a Selenocysteine Insertion Sequence (SECIS) element in the 3′UTR of the transcript. Here we identify multiple mechanisms that regulate the expression of SelS. The human SelS gene encodes two transcripts (variants 1 and 2), which differ in their 3′UTR sequences due to an alternative splicing event that removes the SECIS element from the variant 1 transcript. Both transcripts are widely expressed in human cell lines, with the SECIS-containing variant 2 mRNA being more abundant. In vitro experiments demonstrate that the variant 1 3′UTR does not allow readthrough of the UGA/Sec codon. Thus, this transcript would produce a truncated protein that does not contain Sec and cannot make the selenosulfide bond. While the variant 2 3′UTR does support Sec insertion, its activity is weak. Bioinformatic analysis revealed two highly conserved stem-loop structures, one in the proximal part of the variant 2 3′UTR and the other immediately downstream of the SECIS element. The proximal stem-loop promotes Sec insertion in the native context but not when positioned far from the UGA/Sec codon in a heterologous mRNA. In contrast, the 140 nucleotides downstream of the SECIS element inhibit Sec insertion. We also show that endogenous SelS is enriched at perinuclear speckles, in addition to its known localization in the endoplasmic reticulum. Our results suggest the expression of endogenous SelS is more complex than previously appreciated, which has implications for past and future studies on the function of this protein.

Selenium homeostasis and antioxidant selenoproteins in brain: implications for disorders in the central nervous system

The essential trace element selenium, as selenocysteine, is incorporated into antioxidant selenoproteins such as glutathione peroxidases (GPx), thioredoxin reductases (TrxR) and selenoprotein P (Sepp1). Although comparatively low in selenium content, the brain exhibits high priority for selenium supply and retention under conditions of dietary selenium deficiency. Liver-derived Sepp1 is the major transport protein in plasma to supply the brain with selenium, serving as a "survival factor" for neurons in culture. Sepp1 expression has also been detected within the brain. Presumably, astrocytes secrete Sepp1, which is subsequently taken up by neurons via the apolipoprotein E receptor 2 (ApoER2). Knock-out of Sepp1 or ApoER2 as well as neuron-specific ablation of selenoprotein biosynthesis results in neurological dysfunction in mice. Astrocytes, generally less vulnerable to oxidative stress than neurons, are capable of up-regulating the expression of antioxidant selenoproteins upon brain injury. Occurrence of neurological disorders has been reported occasionally in patients with inadequate nutritional selenium supply or a mutation in the gene encoding selenocysteine synthase, one of the enzymes involved in selenoprotein biosynthesis. In three large trials carried out among elderly persons, a low selenium status was associated with faster decline in cognitive functions and poor performance in tests assessing coordination and motor speed. Future research is required to better understand the role of selenium and selenoproteins in brain diseases including hepatic encephalopathy.

Contrasting roles of dietary selenium and selenoproteins in chemically induced hepatocarcinogenesis

Selenium (Se) has long been known for its cancer prevention properties, but the molecular basis remains unclear. The principal questions in assessing the effect of dietary Se in cancer are whether selenoproteins, small molecule selenocompounds, or both, are involved, and under which conditions and genotypes Se may be protective. In this study, we examined diethylnitrosamine-induced hepatocarcinogenesis in mice lacking a subset of selenoproteins due to expression of a mutant selenocysteine tRNA gene (Trsp (A37G) mice). To uncouple the effects of selenocompounds and selenoproteins, these animals were examined at several levels of dietary Se. Our analysis revealed that tumorigenesis in Trsp (A37G) mice maintained on the adequate Se diet was increased. However, in the control, wild-type mice, both Se deficiency and high Se levels protected against tumorigenesis. We further found that the Se-deficient diet induced severe neurological phenotypes in Trsp A37G mice. Surprisingly, a similar phenotype could be induced in these mice at high dietary Se intake. Overall, our results show a complex role of Se in chemically induced hepatocarcinogenesis, which involves interaction among selenoproteins, selenocompounds and toxins, and depends on genotype and background of the animals.

Genetic variation in selenoprotein genes, lifestyle, and risk of colon and rectal cancer

Background

Associations between selenium and cancer have directed attention to role of selenoproteins in the carcinogenic process.

Methods

We used data from two population-based case-control studies of colon (n = 1555 cases, 1956 controls) and rectal (n = 754 cases, 959 controls) cancer. We evaluated the association between genetic variation in TXNRD1, TXNRD2, TXNRD3, C11orf31 (SelH), SelW, SelN1, SelS, SepX, and SeP15 with colorectal cancer risk.

Results

After adjustment for multiple comparisons, several associations were observed. Two SNPs in TXNRD3 were associated with rectal cancer (rs11718498 dominant OR 1.42 95% CI 1.16,1.74 pACT 0.0036 and rs9637365 recessive 0.70 95% CI 0.55,0.90 pACT 0.0208). Four SNPs in SepN1 were associated with rectal cancer (rs11247735 recessive OR 1.30 95% CI 1.04,1.63 pACT 0.0410; rs2072749 GGvsAA OR 0.53 95% CI 0.36,0.80 pACT 0.0159; rs4659382 recessive OR 0.58 95% CI 0.39,0.86 pACT 0.0247; rs718391 dominant OR 0.76 95% CI 0.62,0.94 pACT 0.0300). Interaction between these genes and exposures that could influence these genes showed numerous significant associations after adjustment for multiple comparisons. Two SNPs in TXNRD1 and four SNPs in TXNRD2 interacted with aspirin/NSAID to influence colon cancer; one SNP in TXNRD1, two SNPs in TXNRD2, and one SNP in TXNRD3 interacted with aspirin/NSAIDs to influence rectal cancer. Five SNPs in TXNRD2 and one in SelS, SeP15, and SelW1 interacted with estrogen to modify colon cancer risk; one SNP in SelW1 interacted with estrogen to alter rectal cancer risk. Several SNPs in this candidate pathway influenced survival after diagnosis with colon cancer (SeP15 and SepX1 increased HRR) and rectal cancer (SepX1 increased HRR).

Conclusions

Findings support an association between selenoprotein genes and colon and rectal cancer development and survival after diagnosis. Given the interactions observed, it is likely that the impact of cancer susceptibility from genotype is modified by lifestyle.

GSK-3β inhibitors suppressed neuroinflammation in rat cortex by activating autophagy in ischemic brain injury

Previous studies have shown that GSK-3β inhibitor could reduce infarct volume after ischemia brain injury. However, the underlying mechanisms of GSK-3β inhibitor involving neuroprotection remain poorly understood. In the present study, we demonstrated that GSK-3β inhibitor suppressed insult-induced neuroinflammation in rat cortex by increasing autophagy activation in ischemic injury. Male rats were subjected to pMCAO (permanent middle cerebral artery occlusion) followed by treating with SB216763, a GSK-3β inhibitor. We found that insult-induced inflammatory response was significantly decreased by intraperitoneal infusion of SB216763 in rat cortex. A higher level of autophagy was also detected after SB216763 treatment. In the cultured primary microglia, SB216763 activated autophagy and suppressed inflammatory response. Importantly, inhibition of autophagy by Beclin1-siRNA increased inflammatory response in the SB216763-treated microglia. These data suggest that GSK-3β inhibitor suppressed neuroinflammation by activating autophagy after ischemic brain injury, thus offering a new target for prevention of ischemic brain injury.