High-energy Femoral Neck Fractures in Young Patients

Femoral neck fractures in physiologically young patients typically occur from high-energy axial loading forces through the thigh with the hip in an abducted position. These fractures have a high rate of associated head, chest, abdominal, and musculoskeletal injuries. High-energy hip fractures differ from traditional geriatric hip fractures regarding incidence, mechanism, management algorithms, and complications. After adequate resuscitation, goals of treatment include anatomic reduction and stable fixation while maintaining vascularity of the femoral head, which can be achieved through a variety of different techniques. Prompt recognition and treatment of these fractures is crucial to achieve a successful outcome because these injuries are often associated with complications such as osteonecrosis, fixation failure, and nonunion.

A human obesity-associated MC4R mutation with defective Gq/11α signaling leads to hyperphagia in mice

Melanocortin 4 receptor (MC4R) mutations are the most common cause of human monogenic obesity and are associated with hyperphagia and increased linear growth. While MC4R is known to activate Gsα/cAMP signaling, a substantial proportion of obesity-associated MC4R mutations do not affect MC4R/Gsα signaling. To further explore the role of specific MC4R signaling pathways in the regulation of energy balance, we examined the signaling properties of one such mutant, MC4R (F51L), as well as the metabolic consequences of MC4RF51L mutation in mice. The MC4RF51L mutation produced a specific defect in MC4R/Gq/11α signaling and led to obesity, hyperphagia, and increased linear growth in mice. The ability of a melanocortin agonist to acutely inhibit food intake when delivered to the paraventricular nucleus (PVN) was lost in MC4RF51L mice, as well as in WT mice in which a specific Gq/11α inhibitor was delivered to the PVN; this provided evidence that a Gsα-independent signaling pathway, namely Gq/11α, significantly contributes to the actions of MC4R on food intake and linear growth. These results suggest that a biased MC4R agonist that primarily activates Gq/11α may be a potential agent to treat obesity with limited untoward cardiovascular and other side effects.

Using Spinal Anesthesia and a Fracture Table for Closed Reduction of an Obturator Foramen Hip Dislocation: A Case Report

CASE

A 37-year-old man with a right obturator foramen hip dislocation underwent closed reduction under spinal anesthesia with the use of a fracture traction table.

CONCLUSION

This novel technique provides surgeons and anesthesiologists an alternative method of treating obturator foramen hip dislocations that provides a more controlled reduction and less need for assistants.

The role of selenoproteins in neutrophils during inflammation

Polymorphonuclear neutrophils (PMNs)-derived ROS are involved in the regulation of multiple functions of PMNs critical in both inflammation and its timely resolution. Selenium is an essential trace element that functions as a gatekeeper of cellular redox homeostasis in the form of selenoproteins. Despite their well-studied involvement in regulating functions of various immune cells, limited studies have focused on the regulation of selenoproteins in PMN and their associated functions. Ex-vivo treatment of murine primary bone marrow derived PMNs with bacterial endotoxin lipopolysaccharide (LPS) indicated temporal regulation of several selenoprotein genes at the mRNA level. However, only glutathione peroxidase 4 (Gpx4) was significantly upregulated, while Selenof, Selenow, and Gpx1 were significantly downregulated in a temporal manner at the protein level. Exposure of PMNs isolated from tRNASec (Trsp)fl/fl S100A8Cre (TrspN) PMN-specific selenoprotein knockout mice, to the Gram-negative bacterium, Citrobacter rodentium, showed decreased bacterial growth, reduced phagocytosis, as well as impaired neutrophil extracellular trap (NET) formation ability, when compared to the wild-type PMNs. Increased extracellular ROS production upon LPS stimulation was also observed in TrspN PMNs that was associated with upregulation of Alox12, Cox2, and iNOS, as well as proinflammatory cytokines such as TNFα and IL-1β. Our data indicate that the inhibition of selenoproteome expression results in alteration of PMN proinflammatory functions, suggesting a potential role of selenoproteins in the continuum of inflammation and resolution.

Selenophosphate synthetase 1 deficiency exacerbates osteoarthritis by dysregulating redox homeostasis

Aging and mechanical overload are prominent risk factors for osteoarthritis (OA), which lead to an imbalance in redox homeostasis. The resulting state of oxidative stress drives the pathological transition of chondrocytes during OA development. However, the specific molecular pathways involved in disrupting chondrocyte redox homeostasis remain unclear. Here, we show that selenophosphate synthetase 1 (SEPHS1) expression is downregulated in human and mouse OA cartilage. SEPHS1 downregulation impairs the cellular capacity to synthesize a class of selenoproteins with oxidoreductase functions in chondrocytes, thereby elevating the level of reactive oxygen species (ROS) and facilitating chondrocyte senescence. Cartilage-specific Sephs1 knockout in adult mice causes aging-associated OA, and augments post-traumatic OA, which is rescued by supplementation of N-acetylcysteine (NAC). Selenium-deficient feeding and Sephs1 knockout have synergistic effects in exacerbating OA pathogenesis in mice. Therefore, we propose that SEPHS1 is an essential regulator of selenium metabolism and redox homeostasis, and its dysregulation governs the progression of OA.

Osteoarthritis is caused by the gradual accumulation of oxidative stress in cartilage. Here, the authors show that dysregulation of the selenium metabolic pathway underlies a shift in redox homeostasis in chondrocytes, leading to chronic osteoarthritic changes in joints.

Macrophage Selenoproteins Restrict Intracellular Replication of Francisella tularensis and Are Essential for Host Immunity

The essential micronutrient Selenium (Se) is co-translationally incorporated as selenocysteine into proteins. Selenoproteins contain one or more selenocysteines and are vital for optimum immunity. Interestingly, many pathogenic bacteria utilize Se for various biological processes suggesting that Se may play a role in bacterial pathogenesis. A previous study had speculated that Francisella tularensis, a facultative intracellular bacterium and the causative agent of tularemia, sequesters Se by upregulating Se-metabolism genes in type II alveolar epithelial cells. Therefore, we investigated the contribution of host vs. pathogen-associated selenoproteins in bacterial disease using F. tularensis as a model organism. We found that F. tularensis was devoid of any Se utilization traits, neither incorporated elemental Se, nor exhibited Se-dependent growth. However, 100% of Se-deficient mice (0.01 ppm Se), which express low levels of selenoproteins, succumbed to F. tularensis-live vaccine strain pulmonary challenge, whereas 50% of mice on Se-supplemented (0.4 ppm Se) and 25% of mice on Se-adequate (0.1 ppm Se) diet succumbed to infection. Median survival time for Se-deficient mice was 8 days post-infection while Se-supplemented and -adequate mice was 11.5 and >14 days post-infection, respectively. Se-deficient macrophages permitted significantly higher intracellular bacterial replication than Se-supplemented macrophages ex vivo, corroborating in vivo observations. Since Francisella replicates in alveolar macrophages during the acute phase of pneumonic infection, we hypothesized that macrophage-specific host selenoproteins may restrict replication and systemic spread of bacteria. F. tularensis infection led to an increased expression of several macrophage selenoproteins, suggesting their key role in limiting bacterial replication. Upon challenge with F. tularensis, mice lacking selenoproteins in macrophages (TrspM) displayed lower survival and increased bacterial burden in the lung and systemic tissues in comparison to WT littermate controls. Furthermore, macrophages from TrspM mice were unable to restrict bacterial replication ex vivo in comparison to macrophages from littermate controls. We herein describe a novel function of host macrophage-specific selenoproteins in restriction of intracellular bacterial replication. These data suggest that host selenoproteins may be considered as novel targets for modulating immune response to control a bacterial infection.

Identification of Signaling Pathways for Early Embryonic Lethality and Developmental Retardation in Sephs1-/- Mice

Selenophosphate synthetase 1 (SEPHS1) plays an essential role in cell growth and survival. However, the underlying molecular mechanisms remain unclear. In the present study, the pathways regulated by SEPHS1 during gastrulation were determined by bioinformatical analyses and experimental verification using systemic knockout mice targeting Sephs1. We found that the coagulation system and retinoic acid signaling were most highly affected by SEPHS1 deficiency throughout gastrulation. Gene expression patterns of altered embryo morphogenesis and inhibition of Wnt signaling were predicted with high probability at E6.5. These predictions were verified by structural abnormalities in the dermal layer of Sephs1^−/− embryos. At E7.5, organogenesis and activation of prolactin signaling were predicted to be affected by Sephs1 knockout. Delay of head fold formation was observed in the Sephs1^−/− embryos. At E8.5, gene expression associated with organ development and insulin-like growth hormone signaling that regulates organ growth during development was altered. Consistent with these observations, various morphological abnormalities of organs and axial rotation failure were observed. We also found that the gene sets related to redox homeostasis and apoptosis were gradually enriched in a time-dependent manner until E8.5. However, DNA damage and apoptosis markers were detected only when the Sephs1^−/− embryos aged to E9.5. Our results suggest that SEPHS1 deficiency causes a gradual increase of oxidative stress which changes signaling pathways during gastrulation, and afterwards leads to apoptosis.

Female Mice with Selenocysteine tRNA Deletion in Agrp Neurons Maintain Leptin Sensitivity and Resist Weight Gain While on a High-Fat Diet

The role of the essential trace element selenium in hypothalamic physiology has begun to come to light over recent years. Selenium is used to synthesize a family of proteins participating in redox reactions called selenoproteins, which contain a selenocysteine residue in place of a cysteine. Past studies have shown that disrupted selenoprotein expression in the hypothalamus can adversely impact energy homeostasis. There is also evidence that selenium supports leptin signaling in the hypothalamus by maintaining proper redox balance. In this study, we generated mice with conditional knockout of the selenocysteine tRNA^[Ser]Sec gene (Trsp) in an orexigenic cell population called agouti-related peptide (Agrp)-positive neurons. We found that female Trsp^AgrpKO mice gain less weight while on a high-fat diet, which occurs due to changes in adipose tissue activity. Female Trsp^AgrpKO mice also retained hypothalamic sensitivity to leptin administration. Male mice were unaffected, however, highlighting the sexually dimorphic influence of selenium on neurobiology and energy homeostasis. These findings provide novel insight into the role of selenoproteins within a small yet heavily influential population of hypothalamic neurons.

Selenium and the 15kDa Selenoprotein Impact Colorectal Tumorigenesis by Modulating Intestinal Barrier Integrity

Selenoproteins play important roles in many cellular functions and biochemical pathways in mammals. Our previous study showed that the deficiency of the 15 kDa selenoprotein (Selenof) significantly reduced the formation of aberrant crypt foci (ACF) in a mouse model of azoxymethane (AOM)-induced colon carcinogenesis. The objective of this study was to examine the effects of Selenof on inflammatory tumorigenesis, and whether dietary selenium modified these effects. For 20 weeks post-weaning, Selenof-knockout (KO) mice and littermate controls were fed diets that were either deficient, adequate or high in sodium selenite. Colon tumors were induced with AOM and dextran sulfate sodium. Surprisingly, KO mice had drastically fewer ACF but developed a similar number of tumors as their littermate controls. Expression of genes important in inflammatory colorectal cancer and those relevant to epithelial barrier function was assessed, in addition to structural differences via tissue histology. Our findings point to Selenof's potential role in intestinal barrier integrity and structural changes in glandular and mucin-producing goblet cells in the mucosa and submucosa, which may determine the type of tumor developing.

Selenium-dependent metabolic reprogramming during inflammation and resolution

Trace element selenium (Se) is incorporated as the 21st amino acid, selenocysteine, into selenoproteins through tRNA^[Ser]Sec. Selenoproteins act as gatekeepers of redox homeostasis and modulate immune function to effect anti-inflammation and resolution. However, mechanistic underpinnings involving metabolic reprogramming during inflammation and resolution remain poorly understood. Bacterial endotoxin lipopolysaccharide (LPS) activation of murine bone marrow–derived macrophages cultured in the presence or absence of Se (as selenite) was used to examine temporal changes in the proteome and metabolome by multiplexed tandem mass tag–quantitative proteomics, metabolomics, and machine-learning approaches. Kinetic deltagram and clustering analysis indicated that addition of Se led to extensive reprogramming of cellular metabolism upon stimulation with LPS enhancing the pentose phosphate pathway, tricarboxylic acid cycle, and oxidative phosphorylation, to aid in the phenotypic transition toward alternatively activated macrophages, synonymous with resolution of inflammation. Remodeling of metabolic pathways and consequent metabolic adaptation toward proresolving phenotypes began with Se treatment at 0 h and became most prominent around 8 h after LPS stimulation that included succinate dehydrogenase complex, pyruvate kinase, and sedoheptulokinase. Se-dependent modulation of these pathways predisposed bone marrow–derived macrophages to preferentially increase oxidative phosphorylation to efficiently regulate inflammation and its timely resolution. The use of macrophages lacking selenoproteins indicated that all three metabolic nodes were sensitive to selenoproteome expression. Furthermore, inhibition of succinate dehydrogenase complex with dimethylmalonate affected the proresolving effects of Se by increasing the resolution interval in a murine peritonitis model. In summary, our studies provide novel insights into the role of cellular Se via metabolic reprograming to facilitate anti-inflammation and proresolution.

Adaptive Thermogenesis in a Mouse Model Lacking Selenoprotein Biosynthesis in Brown Adipocytes

Selenoproteins are a class of proteins with the selenium-containing amino acid selenocysteine (Sec) in their primary structure. Sec is incorporated into selenoproteins via recoding of the stop codon UGA, with specific cis and trans factors required during translation to avoid UGA recognition as a stop codon, including a Sec-specific tRNA, tRNA[Ser]Sec, encoded in mice by the gene Trsp. Whole-body deletion of Trsp in mouse is embryonically lethal, while targeted deletion of Trsp in mice has been used to understand the role of selenoproteins in the health and physiology of various tissues. We developed a mouse model with the targeted deletion of Trsp in brown adipocytes (Trspf/f-Ucp1-Cre+/-), a cell type predominant in brown adipose tissue (BAT) controlling energy expenditure via activation of adaptive thermogenesis, mostly using uncoupling protein 1 (Ucp1). At room temperature, Trspf/f-Ucp1-Cre+/- mice maintain oxygen consumption and Ucp1 expression, with male Trspf/f-Ucp1-Cre+/- mice accumulating more triglycerides in BAT than both female Trspf/f-Ucp1-Cre+/- mice or Trspf/f controls. Acute cold exposure neither reduced core body temperature nor changed the expression of selenoprotein iodothyronine deiodinase type II (Dio2), a marker of adaptive thermogenesis, in Trspf/f-Ucp1-Cre+/- mice. Microarray analysis of BAT from Trspf/f-Ucp1-Cre+/- mice revealed glutathione S-transferase alpha 3 (Gsta3) and ELMO domain containing 2 (Elmod2) as the transcripts most affected by the loss of Trsp. Male Trspf/f-Ucp1-Cre+/- mice showed mild hypothyroidism while downregulating thyroid hormone-responsive genes Thrsp and Tshr in their BATs. In summary, modest changes in the BAT of Trspf/f-Ucp1-Cre +/- mice implicate a mild thyroid hormone dysfunction in brown adipocytes.

The Essential Role of Selenoproteins in the Resolution of Citrobacter rodentium-Induced Intestinal Inflammation

Enteropathogenic Escherichia coli (EPEC) leads to adverse colonic inflammation associated with poor resolution of inflammation and loss of epithelial integrity. Micronutrient trace element selenium (Se) is incorporated into selenoproteins as the 21st amino acid, selenocysteine (Sec). Previous studies have shown that such an incorporation of Sec into the selenoproteome is key for the anti-inflammatory functions of Se in macrophages and other immune cells. An intriguing mechanism underlying the anti-inflammatory and pro-resolving effects of Se stems from the ability of selenoproteins to skew arachidonic acid metabolism from pro-inflammatory mediators, prostaglandin E₂ (PGE₂) toward anti-inflammatory mediators derived from PGD₂, such as 15-deoxy-Δ^{12, 14}- prostaglandin J₂ (15d-PGJ₂), via eicosanoid class switching of bioactive lipids. The impact of Se and such an eicosanoid-class switching mechanism was tested in an enteric infection model of gut inflammation by C. rodentium, a murine equivalent of EPEC. C57BL/6 mice deficient in Se (Se-D) experienced higher mortality when compared to those on Se adequate (0.08 ppm Se) and Se supplemented (0.4 ppm Se) diets following infection. Decreased survival was associated with decreased group 3 innate lymphoid cells (ILC3s) and T helper 17 (Th17) cells in colonic lamina propria of Se-D mice along with deceased expression of epithelial barrier protein Zo-1. Inhibition of metabolic inactivation of PGE₂ by 15-prostaglandin dehydrogenase blocked the Se-dependent increase in ILC3 and Th17 cells in addition to reducing epithelial barrier integrity, as seen by increased systemic levels of FITC-dextran following oral administration; while 15d-PGJ₂ administration in Se-D mice alleviated the effects by increasing ILC3 and Th17 cells. Mice lacking selenoproteins in monocyte/macrophages via the conditional deletion of the tRNA^[Sec] showed increased mortality post infection. Our studies indicate a crucial role for dietary Se in the protection against inflammation following enteric infection via immune mechanisms involving epithelial barrier integrity.

Selenophosphate synthetase 1 and its role in redox homeostasis, defense and proliferation

Selenophosphate synthetase (SEPHS) synthesizes selenophosphate, the active selenium donor, using ATP and selenide as substrates. SEPHS was initially identified and isolated from bacteria and has been characterized in many eukaryotes and archaea. Two SEPHS paralogues, SEPHS1 and SEPHS2, occur in various eukaryotes, while prokaryotes and archaea have only one form of SEPHS. Between the two isoforms in eukaryotes, only SEPHS2 shows catalytic activity during selenophosphate synthesis. Although SEPHS1 does not contain any significant selenophosphate synthesis activity, it has been reported to play an essential role in regulating cellular physiology. Prokaryotic SEPHS contains a cysteine or selenocysteine (Sec) at the catalytic domain. However, in eukaryotes, SEPHS1 contains other amino acids such as Thr, Arg, Gly, or Leu at the catalytic domain, and SEPHS2 contains only a Sec. Sequence comparisons, crystal structure analyses, and ATP hydrolysis assays suggest that selenophosphate synthesis occurs in two steps. In the first step, ATP is hydrolyzed to produce ADP and gamma-phosphate. In the second step, ADP is further hydrolyzed and selenophosphate is produced using gamma-phosphate and selenide. Both SEPHS1 and SEPHS2 have ATP hydrolyzing activities, but Cys or Sec is required in the catalytic domain for the second step of reaction. The gene encoding SEPHS1 is divided by introns, and five different splice variants are produced by alternative splicing in humans. SEPHS1 mRNA is abundant in rapidly proliferating cells such as embryonic and cancer cells and its expression is induced by various stresses including oxidative stress and salinity stress. The disruption of the SEPHS1 gene in mice or Drosophila leads to the inhibition of cell proliferation, embryonic lethality, and morphological changes in the embryos. Targeted removal of SEPHS1 mRNA in insect, mouse, and human cells also leads to common phenotypic changes similar to those observed by in vivo gene knockout: the inhibition of cell growth/proliferation, the accumulation of hydrogen peroxide in mammals and an unidentified reactive oxygen species (ROS) in Drosophila, and the activation of a defense system. Hydrogen peroxide accumulation in SEPHS1-deficient cells is mainly caused by the down-regulation of genes involved in ROS scavenging, and leads to the inhibition of cell proliferation and survival. However, the mechanisms underlying SEPHS1 regulation of redox homeostasis are still not understood.

The intricate role of selenium and selenoproteins in erythropoiesis

Selenium (Se) is incorporated as the 21st amino acid selenocysteine (Sec) into the growing polypeptide chain of proteins involved in redox gatekeeper functions. Erythropoiesis presents a particular problem to redox regulation as the presence of iron, heme, and unpaired globin chains lead to high levels of free radical-mediated oxidative stress, which are detrimental to erythroid development and can lead to anemia. Under homeostatic conditions, bone marrow erythropoiesis produces sufficient erythrocytes to maintain homeostasis. In contrast, anemic stress induces an alternative pathway, stress erythropoiesis, which rapidly produces new erythrocytes at extramedullary sites, such as spleen, to alleviate anemia. Previous studies suggest that dietary Se protects erythrocytes from such oxidative damage and the absence of selenoproteins causes hemolysis of erythrocytes due to oxidative stress. Furthermore, Se deficiency or lack of selenoproteins severely impairs stress erythropoiesis exacerbating the anemia in rodent models and human patients. Interestingly, erythroid progenitors develop in close proximity with macrophages in structures referred to as erythroblastic islands (EBIs), where macrophage expression of selenoproteins appears to be critical for the expression of heme transporters to facilitate export of heme from macrophage stores to the developing erythroid cells. Here we review the role of Se and selenoproteins in the intrinsic development of erythroid cells in addition to their role in the development of the erythropoietic niche that supports the functional role of EBIs in erythroid expansion and maturation in the spleen during recovery from anemia.

Selenoproteins in colon cancer

Selenocysteine-containing proteins (selenoproteins) have been implicated in the regulation of various cell signaling pathways, many of which are linked to colorectal malignancies. In this in-depth excurse into the selenoprotein literature, we review possible roles for human selenoproteins in colorectal cancer, focusing on the typical hallmarks of cancer cells and their tumor-enabling characteristics. Human genome studies of single nucleotide polymorphisms in various genes coding for selenoproteins have revealed potential involvement of glutathione peroxidases, thioredoxin reductases, and other proteins. Cell culture studies with targeted down-regulation of selenoproteins and studies utilizing knockout/transgenic animal models have helped elucidate the potential roles of individual selenoproteins in this malignancy. Those selenoproteins, for which strong links to development or progression of colorectal cancer have been described, may be potential future targets for clinical interventions.

Selenoproteins regulate stress erythroid progenitors and spleen microenvironment during stress erythropoiesis

Micronutrient selenium (Se) plays a key role in redox regulation through its incorporation into selenoproteins as the 21st amino acid selenocysteine (Sec). Because Se deficiency appears to be a cofactor in the anemia associated with chronic inflammatory diseases, we reasoned that selenoproteins may contribute to erythropoietic recovery from anemia, referred to as stress erythropoiesis. Here, we report that loss of selenoproteins through Se deficiency or by mutation of the Sec tRNA (tRNA[Sec]) gene (Trsp) severely impairs stress erythropoiesis at 2 stages. Early stress erythroid progenitors failed to expand and properly differentiate into burst-forming unit-erythroid cells , whereas late-stage erythroid progenitors exhibited a maturation defect that affected the transition of proerythroblasts to basophilic erythroblasts. These defects were, in part, a result of the loss of selenoprotein W (SelenoW), whose expression was reduced at both transcript and protein levels in Se-deficient erythroblasts. Mutation of SelenoW in the bone marrow cells significantly decreased the expansion of stress burst-forming unit-erythroid cell colonies, which recapitulated the phenotypes induced by Se deficiency or mutation of Trsp Similarly, mutation of SelenoW in murine erythroblast (G1E) cell line led to defects in terminal differentiation. In addition to the erythroid defects, the spleens of Se-deficient mice contained fewer red pulp macrophages and exhibited impaired development of erythroblastic island macrophages, which make up the niche supporting erythroblast development. Taken together, these data reveal a critical role of selenoproteins in the expansion and development of stress erythroid progenitors, as well as the erythroid niche during acute anemia recovery.

Radioactive 75Se Labeling and Detection of Selenoproteins

The trace element selenium (Se) is incorporated into proteins as the amino acid selenocysteine (Sec), which is cotranslationally inserted into specific proteins in response to a UGA codon. Proteins containing Sec at these specific positions are called selenoproteins. Most selenoproteins function as oxidoreductases, while some serve other important functions. There are 25 known selenoprotein genes in humans and 24 in mice. The use of Sec allows selenoproteins to be detected by a convenient method involving metabolic labeling with ⁷⁵Se. Labeling of cells and whole animals are used for the examination of selenoprotein expression profiles and the investigation of selenoprotein functions. In mammals, nonspecific ⁷⁵Se insertion is very low, and sensitivity and specificity of selenoprotein detection approaches that of Western blotting. This method allows for the examination of selenoprotein expression and Se metabolism in model and non-model organisms. Herein, we describe experimental protocols for analyzing selenoproteins by metabolic labeling with ⁷⁵Se both in vitro and in vivo. As an example, the procedure for metabolic labeling of HEK293T human embryonic kidney cells is described in detail. This approach remains a method of choice for the detection of selenoproteins in diverse settings.

The RNA-binding protein Secisbp2 differentially modulates UGA codon reassignment and RNA decay

Dual-assignment of codons as termination and elongation codons is used to expand the genetic code. In mammals, UGA can be reassigned to selenocysteine during translation of selenoproteins by a mechanism involving a 3΄ untranslated region (UTR) selenocysteine insertion sequence (SECIS) and the SECIS-binding protein Secisbp2. Here, we present data from ribosome profiling, RNA-Seq and mRNA half-life measurements that support distinct roles for Secisbp2 in UGA-redefinition and mRNA stability. Conditional deletions of the Secisbp2 and Trsp (tRNA^Sec) genes in mouse liver were compared to determine if the effects of Secisbp2 loss on selenoprotein synthesis could be attributed entirely to the inability to incorporate Sec. As expected, tRNA^Sec depletion resulted in loss of ribosome density downstream of all UGA-Sec codons. In contrast, the absence of Secisbp2 resulted in variable effects on ribosome density downstream of UGA-Sec codons that demonstrate gene-specific differences in Sec incorporation. For several selenoproteins in which loss of Secisbp2 resulted in greatly diminished mRNA levels, translational activity and Sec incorporation efficiency were shown to be unaffected on the remaining RNA. Collectively, these results demonstrate that Secisbp2 is not strictly required for Sec incorporation and has a distinct role in stabilizing mRNAs that can be separated from its effects on UGA-redefinition.

Potential Role of the 15kDa Selenoprotein in Colorectal Inflammation

Previously, systemic knockout (KO) of the ER-resident 15kDa selenoprotein (Sep15, SelenoF) protected mice against the formation of chemically-induced pre-neoplastic lesions and suggested modulation of inflammatory pathways. Our objective is to elucidate the potential role of SelenoF in the early steps of colon tumorigenesis by assaying gene expression of KO mice and littermate controls (WT) that were either treated with 2% dextran sulfate sodium (DSS) to induce colitis or given water (control). Based on previous results, we hypothesize that SelenoF expression is inversely correlated with a protective interferon (IFN)-γ pro-inflammatory response. Microarray analyses of colonic mucosa suggest that knockout of SelenoF expression itself caused more significant gene expression changes than DSS treatment (inflammation). Gene pathway analyses indicated galectin-6 was the highest up-regulated gene in DSS-treated (133-fold) and untreated (30-fold) KO compared to WT mice. The top significantly changed network included genes involved in the differentiation of T-lymphocytes. Colonic gene expression changes in SelenoF-KO mice, as validated with qPCR, included up-regulation of guanylate-binding protein 1 (p=0.004), and a down-regulation of T-box transcription factor 21 (p=0.08). Interestingly, a decrease in IFN-γ levels (p=0.026) was detected in the serum of KO compared to WT mice, whereas the opposite trend was shown in colonic mucosa. Thus, our preliminary analyses indicate that SelenoF may indeed influence the expression of inflammatory genes in the colon. Its contribution to the regulation of colitis will continue to be elucidated.

The utilization of selenocysteine-tRNA[Ser]Sec isoforms is regulated in part at the level of translation in vitro

The tRNA for the 21st proteinogenic amino acid, selenocysteine, exists in mammalian cells as 2 isoforms differing by a single 2'-O-methylribosyl moiety at position 34 (Um34). These isoforms contain either 5-methoxycarbonylmethyluridine (mcm⁵U) or 5-methoxycarbonylmethyl-2'-O-methyluridine (mcm⁵Um) at position 34. The accumulation of the mcm⁵Um isoform is tightly correlated with the expression of nonessential "stress response" selenoproteins such as glutathione peroxidase 1 (GPX1). The expression of essential selenoproteins, such as thioredoxin reductase 1 (TXNRD1), is not affected by changes in Sec-tRNA^[Ser]Sec isoform accumulation. In this work we used purified mcm⁵U and mcm⁵Um Sec-tRNA^[Ser]Sec isoforms to analyze possible differences in binding to the selenocysteine-specific elongation factor, EEFSEC, and the translation of GPX1 and TXNRD1in vitro. Our results indicate that no major distinction between mcm⁵U and mcm⁵Um isoforms is made by the translation machinery, but a small consistent increase in GPX1 translation is associated with the mcm⁵Um isoform. These results implicate fundamental differences in translation efficiency in playing a role in regulating selenoprotein expression as a function of isoform accumulation.

Selenoprotein Gene Nomenclature

The human genome contains 25 genes coding for selenocysteine-containing proteins (selenoproteins). These proteins are involved in a variety of functions, most notably redox homeostasis. Selenoprotein enzymes with known functions are designated according to these functions: TXNRD1, TXNRD2, and TXNRD3 (thioredoxin reductases), GPX1, GPX2, GPX3, GPX4, and GPX6 (glutathione peroxidases), DIO1, DIO2, and DIO3 (iodothyronine deiodinases), MSRB1 (methionine sulfoxide reductase B1), and SEPHS2 (selenophosphate synthetase 2). Selenoproteins without known functions have traditionally been denoted by SEL or SEP symbols. However, these symbols are sometimes ambiguous and conflict with the approved nomenclature for several other genes. Therefore, there is a need to implement a rational and coherent nomenclature system for selenoprotein-encoding genes. Our solution is to use the root symbol SELENO followed by a letter. This nomenclature applies to SELENOF (selenoprotein F, the 15-kDa selenoprotein, SEP15), SELENOH (selenoprotein H, SELH, C11orf31), SELENOI (selenoprotein I, SELI, EPT1), SELENOK (selenoprotein K, SELK), SELENOM (selenoprotein M, SELM), SELENON (selenoprotein N, SEPN1, SELN), SELENOO (selenoprotein O, SELO), SELENOP (selenoprotein P, SeP, SEPP1, SELP), SELENOS (selenoprotein S, SELS, SEPS1, VIMP), SELENOT (selenoprotein T, SELT), SELENOV (selenoprotein V, SELV), and SELENOW (selenoprotein W, SELW, SEPW1). This system, approved by the HUGO Gene Nomenclature Committee, also resolves conflicting, missing, and ambiguous designations for selenoprotein genes and is applicable to selenoproteins across vertebrates.

Glutathione peroxidase 4 and vitamin E cooperatively prevent hepatocellular degeneration

The selenoenzyme glutathione peroxidase 4 (Gpx4) is an essential mammalian glutathione peroxidase, which protects cells against detrimental lipid peroxidation and governs a novel form of regulated necrotic cell death, called ferroptosis. To study the relevance of Gpx4 and of another vitally important selenoprotein, cytosolic thioredoxin reductase (Txnrd1), for liver function, mice with conditional deletion of Gpx4 in hepatocytes were studied, along with those lacking Txnrd1 and selenocysteine (Sec) tRNA (Trsp) in hepatocytes. Unlike Txnrd1- and Trsp-deficient mice, Gpx4^−/− mice died shortly after birth and presented extensive hepatocyte degeneration. Similar to Txnrd1-deficient livers, Gpx4^−/− livers manifested upregulation of nuclear factor (erythroid-derived)-like 2 (Nrf2) response genes. Remarkably, Gpx4^−/− pups born from mothers fed a vitamin E-enriched diet survived, yet this protection was reversible as subsequent vitamin E deprivation caused death of Gpx4-deficient mice ~4 weeks thereafter. Abrogation of selenoprotein expression in Gpx4^−/− mice did not result in viable mice, indicating that the combined deficiency aggravated the loss of Gpx4 in liver. By contrast, combined Trsp/Txnrd1-deficient mice were born, but had significantly shorter lifespans than either single knockout, suggesting that Txnrd1 plays an important role in supporting liver function of mice lacking Trsp. In sum our study demonstrates that the ferroptosis regulator Gpx4 is critical for hepatocyte survival and proper liver function, and that vitamin E can compensate for its loss by protecting cells against deleterious lipid peroxidation.

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Conditional Gpx4 loss causes hepatocellular degeneration and early death of mice.

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Dietary vitamin E supplementation rescues death of liver-specific Gpx4 null mice.

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Nutritional vitamin E content in diet may severely impact experimental outcome.

Selenoprotein Expression in Macrophages Is Critical for Optimal Clearance of Parasitic Helminth Nippostrongylus brasiliensis

The plasticity of macrophages is evident in helminthic parasite infections, providing protection from inflammation. Previously we demonstrated that the micronutrient selenium induces a phenotypic switch in macrophage activation from a classically activated (pro-inflammatory; M1/CAM) toward an alternatively activated (anti-inflammatory; M2/AAM) phenotype, where cyclooxygenase (COX)-dependent cyclopentenone prostaglandin J2 (15d-PGJ2) plays a key role. Here, we hypothesize that dietary selenium modulates macrophage polarization toward an AAM phenotype to assist in the increasing clearance of adult Nippostrongylus brasiliensis, a gastrointestinal nematode parasite. Mice on a selenium-adequate (0.08 ppm) diet significantly augmented intestinal AAM presence while decreasing adult worms and fecal egg production when compared with infection of mice on selenium-deficient (<0.01 ppm) diet. Further increase in dietary selenium to supraphysiological levels (0.4 ppm) had very little or no impact on worm expulsion. Normal adult worm clearance and enhanced AAM marker expression were observed in the selenium-supplemented Trsp(fl/fl)Cre(WT) mice that express selenoproteins driven by tRNA(Sec) (Trsp), whereas N. brasiliensis-infected Trsp(fl/fl)Cre(LysM) selenium-supplemented mice showed a decreased clearance, with lowered intestinal expression of several AAM markers. Inhibition of the COX pathway with indomethacin resulted in delayed worm expulsion in selenium-adequate mice. This was rescued with 15d-PGJ2, which partially recapitulated the effect of selenium supplementation on fecal egg output in addition to increasing markers of AAMs in the small intestine. Antagonism of PPARγ blocked the effect of selenium. These results suggest that optimal expression of selenoproteins and selenium-dependent production of COX-derived endogenous prostanoids, such as Δ(12)-PGJ2 and 15d-PGJ2, may regulate AAM activation to enhance anti-helminthic parasite responses.

Dietary Selenium Levels Affect Selenoprotein Expression and Support the Interferon-γ and IL-6 Immune Response Pathways in Mice

Selenium is an essential element that is required to support a number of cellular functions and biochemical pathways. The objective of this study was to examine the effects of reduced dietary selenium levels on gene expression to assess changes in expression of non-selenoprotein genes that may contribute to the physiological consequences of selenium deficiency. Mice were fed diets that were either deficient in selenium or supplemented with selenium in the form of sodium selenite for six weeks. Differences in liver mRNA expression and translation were measured using a combination of ribosome profiling, RNA-Seq, microarrays, and qPCR. Expression levels and translation of mRNAs encoding stress-related selenoproteins were shown to be up-regulated by increased selenium status, as were genes involved in inflammation and response to interferon-γ. Changes in serum cytokine levels were measured which confirmed that interferon-γ, as well as IL-6, were increased in selenium adequate mice. Finally, microarray and qPCR analysis of lung tissue demonstrated that the selenium effects on immune function are not limited to liver. These data are consistent with previous reports indicating that adequate selenium levels can support beneficial immune responses, and further identify the IL-6 and interferon-γ pathways as being responsive to dietary selenium intake.

Expression of Selenoproteins Is Maintained in Mice Carrying Mutations in SECp43, the tRNA Selenocysteine 1 Associated Protein (Trnau1ap)

Selenocysteine tRNA 1 associated protein (Trnau1ap) has been characterized as a tRNA^[Ser]Sec-binding protein of 43 kDa, hence initially named SECp43. Previous studies reported its presence in complexes containing tRNA^[Ser]Sec implying a role of SECp43 as a co-factor in selenoprotein expression. We generated two conditionally mutant mouse models targeting exons 3+4 and exons 7+8 eliminating parts of the first RNA recognition motif or of the tyrosine-rich domain, respectively. Constitutive inactivation of exons 3+4 of SECp43 apparently did not affect the mice or selenoprotein expression in several organs. Constitutive deletion of exons 7+8 was embryonic lethal. We therefore generated hepatocyte-specific Secp43 knockout mice and characterized selenoprotein expression in livers of mutant mice. We found no significant changes in the levels of ⁷⁵Se-labelled hepatic proteins, selenoprotein levels as determined by Western blot analysis, enzymatic activity or selenoprotein mRNA abundance. The methylation pattern of tRNA^[Ser]Sec remained unchanged. Truncated Secp43 ^Δ7,8mRNA increased in Secp43-mutant livers suggesting auto-regulation of Secp43 mRNA abundance. We found no signs of liver damage in Secp433-mutant mice, but neuron-specific deletion of exons 7+8 impaired motor performance, while not affecting cerebral selenoprotein expression or cerebellar development. These findings suggest that the targeted domains in the SECp43 protein are not essential for selenoprotein biosynthesis in hepatocytes and neurons. Whether the remaining second RNA recognition motif plays a role in selenoprotein biosynthesis and which other cellular process depends on SECp43 remains to be determined.