Human Genetic Disorders Resulting in Systemic Selenoprotein Deficiency.

Selenium, a trace element fundamental to human health, is incorporated as the amino acid selenocysteine (Sec) into more than 25 proteins, referred to as selenoproteins. Human mutations in SECISBP2, SEPSECS and TRU-TCA1-1, three genes essential in the selenocysteine incorporation pathway, affect the expression of most if not all selenoproteins. Systemic selenoprotein deficiency results in a complex, multifactorial disorder, reflecting loss of selenoprotein function in specific tissues and/or long-term impaired selenoenzyme-mediated defence against oxidative and endoplasmic reticulum stress. SEPSECS mutations are associated with a predominantly neurological phenotype with progressive cerebello-cerebral atrophy. Selenoprotein deficiency due to SECISBP2 and TRU-TCA1-1 defects are characterized by abnormal circulating thyroid hormones due to lack of Sec-containing deiodinases, low serum selenium levels (low SELENOP, GPX3), with additional features (myopathy due to low SELENON; photosensitivity, hearing loss, increased adipose mass and function due to reduced antioxidant and endoplasmic reticulum stress defence) in SECISBP2 cases. Antioxidant therapy ameliorates oxidative damage in cells and tissues of patients, but its longer term benefits remain undefined. Ongoing surveillance of patients enables ascertainment of additional phenotypes which may provide further insights into the role of selenoproteins in human biological processes.

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

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

Impaired exercise performance is independent of inflammation and cellular stress following genetic reduction or deletion of selenoprotein S.

Selenoprotein S (Seps1) can be protective against oxidative, endoplasmic reticulum (ER), and inflammatory stress. Seps1 global knockout mice are less active, possess compromised fast muscle ex vivo strength, and, depending on context, heightened inflammation. Oxidative, ER, and inflammatory stress modulates contractile function; hence, our aim was to investigate the effects of Seps1 gene dose on exercise performance. Seps1-/- knockout, Seps1-/+ heterozygous, and wild-type mice were randomized to 3 days of incremental, high-intensity treadmill running or a sedentary control group. On day 4, the in situ contractile function of fast tibialis anterior (TA) muscles was determined. Seps1 reduction or deletion compromised exercise capacity, decreasing distance run. TA strength was also reduced. In sedentary Seps1-/- knockout mice, TA fatigability was greater than wild-type mice, and this was ameliorated with exercise. Whereas, in Seps1+/- heterozygous mice, exercise compromised TA endurance. These impairments in exercise capacity and TA contractile function were not associated with increased inflammation or a dysregulated redox state. Seps1 is highly expressed in muscle fibers and blood vessels. Interestingly, Nos1 and Vegfa mRNA transcripts were decreased in TA muscles from Seps1-/- knockout and Seps1-/+ heterozygous mice. Impaired exercise performance with Seps1 reduction or deletion cannot be attributed to heightened cellular stress, but it may potentially be mediated, in part, by the effects of Seps1 on the microvasculature.

Deficiency of selenoprotein S, an endoplasmic reticulum resident oxidoreductase, impairs the contractile function of fast-twitch hindlimb muscles.

Selenoprotein S (Seps1) is an endoplasmic reticulum (ER) resident antioxidant implicated in ER stress and inflammation. In human vastus lateralis and mouse hindlimb muscles, Seps1 localization and expression were fiber-type specific. In male Seps1+/- heterozygous mice, spontaneous physical activity was reduced compared with wild-type littermates ( d = 1.10, P = 0.029). A similar trend was also observed in Seps1-/- knockout mice ( d = 1.12, P = 0.051). Whole body metabolism, body composition, extensor digitorum longus (EDL), and soleus mass and myofiber diameter were unaffected by genotype. However, in isolated fast EDL muscles from Seps1-/- knockout mice, the force frequency curve (FFC; 1-120 Hz) was shifted downward versus EDL muscles from wild-type littermates ( d = 0.55, P = 0.002), suggestive of reduced strength. During 4 min of intermittent, submaximal (60 Hz) stimulation, the genetic deletion or reduction of Seps1 decreased EDL force production ( d = 0.52, P < 0.001). Furthermore, at the start of the intermittent stimulation protocol, when compared with the 60-Hz stimulation of the FFC, EDL muscles from Seps1-/- knockout or Seps1+/- heterozygous mice produced 10% less force than those from wild-type littermates ( d = 0.31, P < 0.001 and d = 0.39, P = 0.015). This functional impairment was associated with reduced mRNA transcript abundance of thioredoxin-1 ( Trx1), thioredoxin interacting protein ( Txnip), and the ER stress markers Chop and Grp94, whereas, in slow soleus muscles, Seps1 deletion did not compromise contractile function and Trx1 ( d = 1.38, P = 0.012) and Txnip ( d = 1.27, P = 0.025) gene expression was increased. Seps1 is a novel regulator of contractile function and cellular stress responses in fast-twitch muscles.

Stable expression and function of the inositol 1,4,5-triphosphate receptor requires palmitoylation by a DHHC6/selenoprotein K complex.

Calcium (Ca(2+)) is a secondary messenger in cells and Ca(2+) flux initiated from endoplasmic reticulum (ER) stores via inositol 1,4,5-triphosphate (IP3) binding to the IP3 receptor (IP3R) is particularly important for the activation and function of immune cells. Previous studies demonstrated that genetic deletion of selenoprotein K (Selk) led to decreased Ca(2+) flux in a variety of immune cells and impaired immunity, but the mechanism was unclear. Here we show that Selk deficiency does not affect receptor-induced IP3 production, but Selk deficiency through genetic deletion or low selenium in culture media leads to low expression of the IP3R due to a defect in IP3R palmitoylation. Bioinformatic analysis of the DHHC (letters represent the amino acids aspartic acid, histidine, histidine, and cysteine in the catalytic domain) family of enzymes that catalyze protein palmitoylation revealed that one member, DHHC6, contains a predicted Src-homology 3 (SH3) domain and DHHC6 is localized to the ER membrane. Because Selk is also an ER membrane protein and contains an SH3 binding domain, immunofluorescence and coimmunoprecipitation experiments were conducted and revealed DHHC6/Selk interactions in the ER membrane that depended on SH3/SH3 binding domain interactions. DHHC6 knockdown using shRNA in stably transfected cell lines led to decreased expression of the IP3R and impaired IP3R-dependent Ca(2+) flux. Mass spectrophotometric and bioinformatic analyses of the IP3R protein identified two palmitoylated cysteine residues and another potentially palmitoylated cysteine, and mutation of these three cysteines to alanines resulted in decreased IP3R palmitoylation and function. These findings reveal IP3R palmitoylation as a critical regulator of Ca(2+) flux in immune cells and define a previously unidentified DHHC/Selk complex responsible for this process.

Selenoprotein O deficiencies suppress chondrogenic differentiation of ATDC5 cells.

Selenoprotein O (Sel O) is a selenium-containing protein, but its function is still unclear. In the present study, we observed that the mRNA and protein expression levels of Sel O increased during chondrogenic induction of ATDC5 cells. The effects of Sel O on chondrocyte differentiation were then examined through shRNA-mediated gene silencing technique. The expression of Sel O was significantly suppressed at both mRNA and protein levels in a stable cell line transfected with a Sel O-specific target shRNA construct. Thereafter, we demonstrated that Sel O deficiencies suppress chondrogenic differentiation of ATDC5 cells. Sel O deficiencies inhibited expression of chondrogenic gene Sox9, Col II, and aggrecan. Sel O-deficient cells also accumulated a few cartilage glycosaminoglycans (GAGs) and decreased the activity of alkaline phosphatase (ALP). In addition, Sel O deficiencies inhibited chondrocyte proliferation through delayed cell cycle progression by suppression of cyclin D1 expression. Moreover, Sel O deficiencies induced chondrocyte death through cell apoptosis. In summary, we describe the expression patterns and the essential roles of Sel O in chondrocyte viability, proliferation, and chondrogenic differentiation. Additionally, Sel O deficiency-mediated impaired chondrogenesis may illustrate the mechanisms of Se deficiency in the pathophysiological process of the endemic osteoarthropathy.

Pro178 and Pro183 of selenoprotein S are essential residues for interaction with p97(VCP) during endoplasmic reticulum-associated degradation.

During endoplasmic reticulum (ER)-associated degradation, p97(VCP) is recruited to the ER membrane through interactions with transmembrane proteins, such as selenoprotein S (SelS), selenoprotein K (SelK), hrd1, and gp78. SelS has a single-spanning transmembrane domain and protects cells from ER stress-induced apoptosis through interaction with p97(VCP). The cytosolic tail of SelS consists of a coiled-coil domain, a putative VCP-interacting motif (VIM), and an unpronounced glycine- and proline-rich secondary structure. To understand the regulatory mechanism of SelS during ER stress, we investigated the interaction of the protein with p97(VCP) using mouse neuroblastoma cells and human embryonic kidney 293 cells. The SelS expression level increased when ER stress was induced. In addition, the effect of ER stress was enhanced, and recruitment of p97(VCP) to the ER membrane was inhibited in SelS knockdown cells. The effect of SelS knockdown was rescued by ectopic expression of SelS U188C. p97(VCP) interacted with SelS U188C and was recruited to the ER membrane. The expression of SelS[ΔVIM], which is a VIM deletion mutant of SelS, also showed both a recovery effect and an interaction with p97(VCP) in cells. However, mutants in which the proline residue positions 178 or 183 of SelS were changed to alanine or were deleted did not interact with p97(VCP). The proline mutants did not rescue ER stress in SelS knockdown cells. These results suggest that both Pro(178) and Pro(183) of SelS play important roles in the translocation of p97(VCP) to the ER membrane and protect cells from ER stress.

Deficiency of the 15-kDa selenoprotein led to cytoskeleton remodeling and non-apoptotic membrane blebbing through a RhoA/ROCK pathway.

The 15-kDa selenoprotein (Sep15) has been implicated in etiology of some types of cancer. Herein, inducible RNAi cell lines were established and cell morphology and motility were analyzed. The majority of Sep15-deficient cells (>95%) formed membrane blebs in a dynamic manner. Blebbing cells transformed cell morphology from a normal flat spindle shape to a spherical morphology. In blebbing cells, actin fibers moved to the cell periphery, covering and obscuring visualization of α-tubulin. Bleb formation was suppressed by the inhibitors of Rho-associated protein kinase (ROCK), RhoA or myosin light chain (MLC), restoring blebbing cells to wild-type morphology. RhoA activation and phosphorylation of myosin phosphatase target subunit 1 was induced by Sep15 knockdown. Sep15-deficient cells were non-apoptotic, and displayed a distinct relative localization of F-actin and α-tubulin from typical apoptotic blebbing cells. Our data suggest that Sep15 in Chang liver cells regulates the pathway that antagonizes RhoA/ROCK/MLC-dependent non-apoptotic bleb formation.

Transcriptional activation of antioxidants may compensate for selenoprotein deficiencies in Amblyomma maculatum (Acari: Ixodidae) injected with selK- or selM-dsRNA.

The Gulf-Coast tick, Amblyomma maculatum, possesses an elaborate set of selenoproteins, which prevent the deleterious effects from oxidative stress that would otherwise occur during feeding. In the current work, we examined the role of selenoprotein K (SelK) and selenoprotein M (SelM) in feeding A. maculatum by bioinformatics, transcriptional gene expression, RNA interference and antioxidant assays. The transcriptional expression of SelK did not vary significantly in salivary glands or midguts throughout the bloodmeal. However, there was a 58-fold increase in transcript levels of SelM in tick midguts. Ticks injected with selK-dsRNA or selM-dsRNA did not reveal any observable differences in egg viability but oviposition was reduced. Surprisingly, salivary antioxidant activity was higher in selenoprotein knockouts compared with controls, which is probably the result of compensatory transcriptional expression of genes involved in combating reactive oxygen species. In fact, quantitative real-time PCR data suggest that the transcriptional expression of catalase increased in ticks injected with selM-double-stranded RNA. Additionally, the transcriptional expression of selN decreased ∼90% in both SelK/SelM knockdowns. These data indicate that SelK and SelM are salivary antioxidants but are not essential for tick survival or reproduction and are compensated by other antioxidant systems.

Selenoprotein N deficiency in mice is associated with abnormal lung development.

Mutations in the human SEPN1 gene, encoding selenoprotein N (SepN), cause SEPN1-related myopathy (SEPN1-RM) characterized by muscle weakness, spinal rigidity, and respiratory insufficiency. As with other members of the selenoprotein family, selenoprotein N incorporates selenium in the form of selenocysteine (Sec). Most selenoproteins that have been functionally characterized are involved in oxidation-reduction (redox) reactions, with the Sec residue located at their catalytic site. To model SEPN1-RM, we generated a Sepn1-knockout (Sepn1(-/-)) mouse line. Homozygous Sepn1(-/-) mice are fertile, and their weight and lifespan are comparable to wild-type (WT) animals. Under baseline conditions, the muscle histology of Sepn1(-/-) mice remains normal, but subtle core lesions could be detected in skeletal muscle after inducing oxidative stress. Ryanodine receptor (RyR) calcium release channels showed lower sensitivity to caffeine in SepN deficient myofibers, suggesting a possible role of SepN in RyR regulation. SepN deficiency also leads to abnormal lung development characterized by enlarged alveoli, which is associated with decreased tissue elastance and increased quasi-static compliance of Sepn1(-/-) lungs. This finding raises the possibility that the respiratory syndrome observed in patients with SEPN1 mutations may have a primary pulmonary component in addition to the weakness of respiratory muscles.

Satellite cell loss and impaired muscle regeneration in selenoprotein N deficiency.

Selenoprotein N (SelN) deficiency causes a group of inherited neuromuscular disorders termed SEPN1-related myopathies (SEPN1-RM). Although the function of SelN remains unknown, recent data demonstrated that it is dispensable for mouse embryogenesis and suggested its involvement in the regulation of ryanodine receptors and/or cellular redox homeostasis. Here, we investigate the role of SelN in satellite cell (SC) function and muscle regeneration, using the Sepn1(-/-) mouse model. Following cardiotoxin-induced injury, SelN expression was strongly up-regulated in wild-type muscles and, for the first time, we detected its endogenous expression in a subset of mononucleated cells by immunohistochemistry. We show that SelN deficiency results in a reduced basal SC pool in adult skeletal muscles and in an imperfect muscle restoration following a single injury. A dramatic depletion of the SC pool was detected after the first round of degeneration and regeneration that totally prevented subsequent regeneration of Sepn1(-/-) muscles. We demonstrate that SelN deficiency affects SC dynamics on isolated single fibres and increases the proliferation of Sepn1(-/-) muscle precursors in vivo and in vitro. Most importantly, exhaustion of the SC population was specifically identified in muscle biopsies from patients with mutations in the SEPN1 gene. In conclusion, we describe for the first time a major physiological function of SelN in skeletal muscles, as a key regulator of SC function, which likely plays a central role in the pathophysiological mechanism leading to SEPN1-RM.

Selenoprotein K knockout mice exhibit deficient calcium flux in immune cells and impaired immune responses.

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

Roles of the 15-kDa selenoprotein (Sep15) in redox homeostasis and cataract development revealed by the analysis of Sep 15 knockout mice.

The 15-kDa selenoprotein (Sep15) is a thioredoxin-like, endoplasmic reticulum-resident protein involved in the quality control of glycoprotein folding through its interaction with UDP-glucose:glycoprotein glucosyltransferase. Expression of Sep15 is regulated by dietary selenium and the unfolded protein response, but its specific function is not known. In this study, we developed and characterized Sep15 KO mice by targeted removal of exon 2 of the Sep15 gene coding for the cysteine-rich UDP-glucose:glycoprotein glucosyltransferase-binding domain. These KO mice synthesized a mutant mRNA, but the shortened protein product could be detected neither in tissues nor in Sep15 KO embryonic fibroblasts. Sep15 KO mice were viable and fertile, showed normal brain morphology, and did not activate endoplasmic reticulum stress pathways. However, parameters of oxidative stress were elevated in the livers of these mice. We found that Sep15 mRNA was enriched during lens development. Further phenotypic characterization of Sep15 KO mice revealed a prominent nuclear cataract that developed at an early age. These cataracts did not appear to be associated with severe oxidative stress or glucose dysregulation. We suggest that the cataracts resulted from an improper folding status of lens proteins caused by Sep15 deficiency.

Selenium Deficiency in COVID-19-A Possible Long-Lasting Toxic Relationship.

In the last two years, there has been a surge in the number of publications on the trace element selenium (Se) and selenocysteine-containing selenoproteins in human health, largely due to the pandemic and the multiple roles that this micronutrient and Se-dependent selenoproteins play in various aspects of the disease [...].

Selenoprotein K deficiency-induced apoptosis: A role for calpain and the ERS pathway.

Selenoprotein K (SELENOK), an endoplasmic reticulum (ER) resident protein, is regulated by dietary selenium and expressed at a relatively high level in neurons. SELENOK has been shown to participate in oxidation resistance, calcium (Ca2+) flux regulation, and the ER-associated degradation (ERAD) pathway in immune cells. However, its role in neurons has not been elucidated. Here, we demonstrated that SELENOK gene knockout markedly enhanced ER stress (ERS) and increased apoptosis in neurons. SELENOK gene knockout elicited intracellular Ca2+ flux and activated the m-calpain/caspase-12 cascade, thus inducing neuronal apoptosis both in vivo and in vitro. In addition, SELENOK knockout significantly reduced cognitive ability and increased anxiety in 7-month-old mice. Our findings reveal an unexpected role of SELENOK in regulating ERS-induced neuronal apoptosis.

Loss of Selenoprotein Iodothyronine Deiodinase 3 Expression Correlates with Progression of Complete Hydatidiform Mole to Gestational Trophoblastic Neoplasia.

To investigate if differences in imprinting at tropho-microRNA (miRNA) genomic clusters can distinguish between pre-gestational trophoblastic neoplasia cases (pre-GTN) and benign complete hydatidiform mole (CHM) cases at the time of initial uterine evacuation. miRNA sequencing was performed on frozen tissue from 39 CHM cases including 9 GTN cases. DIO3, DLK1, RTL1, and MEG 3 mRNA levels were assessed by qRT-PCR. Protein abundance was assessed by Western blot for DIO3, DLK1, and RTL1. qRT-PCR and Western blot were performed for selenoproteins and markers of oxidative stress. Immunohistochemistry (IHC) was performed for DIO3 on an independent validation set of clinical samples (n = 42) and compared to normal placenta controls across gestational ages. Relative expression of the 14q32 miRNA cluster was lower in pre-GTN cases. There were no differences in protein abundance of DLK1 or RTL1. Notably, there was lower protein expression of DIO3 in pre-GTN cases (5-fold, p < 0.03). There were no differences in mRNA levels of DIO3, DLK1, RTL1 or MEG 3. mRNA levels were higher in all CHM cases compared to normal placenta. IHC showed syncytiotrophoblast-specific DIO3 immunostaining in benign CHM cases and normal placenta, while pre-GTN cases of CHM lacked DIO3 expression. We describe two new biomarkers of pre-GTN CHM cases: decreased 14q32 miRNA expression and loss of DIO3 expression by IHC. Differences in imprinting between benign CHM and pre-GTN cases may provide insight into the fundamental development of CHM.

Upregulated ethanolamine phospholipid synthesis via selenoprotein I is required for effective metabolic reprogramming during T cell activation.

OBJECTIVE: T cell activation triggers metabolic reprogramming to meet increased demands for energy and metabolites required for cellular proliferation. Ethanolamine phospholipid synthesis has emerged as a regulator of metabolic shifts in stem cells and cancer cells, which led us to investigate its potential role during T cell activation. METHODS: As selenoprotein I (SELENOI) is an enzyme participating in two metabolic pathways for the synthesis of phosphatidylethanolamine (PE) and plasmenyl PE, we generated SELENOI-deficient mouse models to determine loss-of-function effects on metabolic reprogramming during T cell activation. Ex vivo and in vivo assays were carried out along with metabolomic, transcriptomic, and protein analyses to determine the role of SELENOI and the ethanolamine phospholipids synthesized by this enzyme in cell signaling and metabolic pathways that promote T cell activation and proliferation. RESULTS: SELENOI knockout (KO) in mouse T cells led to reduced de novo synthesis of PE and plasmenyl PE during activation and impaired proliferation. SELENOI KO did not affect T cell receptor signaling, but reduced activation of the metabolic sensor AMPK. AMPK was inhibited by high [ATP], consistent with results showing SELENOI KO causing ATP accumulation, along with disrupted metabolic pathways and reduced glycosylphosphatidylinositol (GPI) anchor synthesis/attachment CONCLUSIONS: T cell activation upregulates SELENOI-dependent PE and plasmenyl PE synthesis as a key component of metabolic reprogramming and proliferation.

Selenoproteins that function in cancer prevention and promotion.

Of the many health benefits attributed to selenium, the one that has received the most attention is its role in cancer prevention. Selenium-containing proteins (selenoproteins) have been shown in recent years to have roles in cancer prevention. However, selenoproteins have diverse functions and their view as antioxidants is oversimplified. Some selenoproteins appear to have a split personality in having roles both in preventing and promoting cancer. The contrasting roles of one selenoprotein, thioredoxin reductase 1, in cancer are discussed in detail, but as also noted, at least one other selenoprotein may also have such a dual function. In addition, we discuss examples of inhibition of cancer development by selenoprotein deficiency in mouse models. These studies highlight the complex nature of selenium in relation to cancer.

Oxidative stress in SEPN1-related myopathy: from pathophysiology to treatment.

OBJECTIVE: Mutations of the selenoprotein N gene (SEPN1) cause SEPN1-related myopathy (SEPN1-RM), a novel early-onset muscle disorder formerly divided into four different nosological categories. Selenoprotein N (SelN) is the only selenoprotein involved in a genetic disease; its function being unknown, no treatment is available for this potentially lethal disorder. Our objective was to clarify the role of SelN and the pathophysiology of SEPN1-RM to identify therapeutic targets. METHODS: We established and analyzed an ex vivo model of SelN deficiency using fibroblast and myoblast primary cultures from patients with null SEPN1 mutations. DCFH assay, OxyBlot, Western blot, Fura-2, and cell survival studies were performed to measure intracellular oxidant activity, oxidative stress markers, calcium handling, and response to exogenous treatments. RESULTS: SelN-depleted cells showed oxidative/nitrosative stress manifested by increased intracellular oxidant activity (reactive oxygen species and nitric oxide) and/or excessive oxidation of proteins, including the contractile proteins actin and myosin heavy chain II in myotubes. SelN-devoid myotubes showed also Ca(2+) homeostasis abnormalities suggesting dysfunction of the redox-sensor Ca(2+) channel ryanodine receptor type 1. Furthermore, absence of SelN was associated with abnormal susceptibility to H(2)O(2)-induced oxidative stress, demonstrated by increased cell death. This cell phenotype was restored by pretreatment with the antioxidant N-acetylcysteine. INTERPRETATION: SelN plays a key role in redox homeostasis and human cell protection against oxidative stress. Oxidative/nitrosative stress is a primary pathogenic mechanism in SEPN1-RM, which can be effectively targeted ex vivo by antioxidants. These findings pave the way to SEPN1-RM treatment, which would represent a first specific pharmacological treatment for a congenital myopathy.

Congenital muscular dystrophies: toward molecular therapeutic interventions.

Congenital muscular dystrophies (CMDs) are a clinically and genetically heterogeneous group of neuromuscular disorders that typically present at birth or in early infancy with hypotonia, weakness, and histologic evidence of a dystrophic myopathy. CMD biochemical types include various abnormalities of alpha-dystroglycan O-mannosyl glycosylation as well as defects in integrin matrix receptors, the extracellular matrix proteins laminin-alpha(2) and collagen VI, nuclear proteins such as lamin A/C, and a protein of the endoplasmic reticulum, selenoprotein N. Current therapies are directed mostly at supportive care; however, recent advances in biotechnology and increased knowledge of the pathophysiology underlying the various CMD types have helped identify potential therapeutic strategies directed at genetic, molecular, and biochemical pathways involved in these disorders. In this article, we review our current understanding of the molecular pathogenesis of several CMD types and how these mechanisms may be therapeutically targeted.