Selenium deficiency is associated with endoplasmic reticulum stress in a rat model of cardiac malfunction

Metal-Binding Proteins Cross-Linking with Endoplasmic Reticulum Stress in Cardiovascular Diseases

The endoplasmic reticulum (ER), an essential organelle in eukaryotic cells, is widely distributed in myocardial cells. The ER is where secreted protein synthesis, folding, post-translational modification, and transport are all carried out. It is also where calcium homeostasis, lipid synthesis, and other processes that are crucial for normal biological cell functioning are regulated. We are concerned that ER stress (ERS) is widespread in various damaged cells. To protect cells' function, ERS reduces the accumulation of misfolded proteins by activating the unfolded protein response (UPR) pathway in response to numerous stimulating factors, such as ischemia or hypoxia, metabolic disorders, and inflammation. If these stimulatory factors are not eliminated for a long time, resulting in the persistence of the UPR, it will aggravate cell damage through a series of mechanisms. In the cardiovascular system, it will cause related cardiovascular diseases and seriously endanger human health. Furthermore, there has been a growing number of studies on the antioxidative stress role of metal-binding proteins. We observed that a variety of metal-binding proteins can inhibit ERS and, hence, mitigate myocardial damage.

Selenium Deficiency Induces Pathological Cardiac Lipid Metabolic Remodeling and Inflammation

SCOPE

Selenium (Se) disequilibrium is closely involved in many cardiac diseases, although its in vivo mechanism remains uncertain. Therefore, a pig model was created in order to generate a comprehensive picture of cardiac response to dietary Se deficiency.

METHODS AND RESULTS

A total of 24 pigs were divided into two equal groups, which were fed a diet with either 0.007 mg/kg Se or 0.3 mg/kg Se for 16 weeks. Se deficiency caused cardiac oxidative stress by blocking glutathione and thioredoxin systems and increased thioredoxin domain-containing protein S-nitrosylation. Energy production was disordered as free fatty acids were overloaded, the tricarboxylic acid cycle was strengthened, and three respiratory chain proteins enhanced S-nitrosylation. Excess free fatty acids led to increased synthesis of diacylglycerol, phosphatidylcholine, and phosphatidylethanolamine, where the latter two are vulnerable to oxidation and caused an increase in malondialdehyde. Moreover, increased palmitic acid enhanced de novo ceramide synthesis and accumulation. Additionally, Se deficiency initiated inflammation via cytosolic DNA-sensing pathways, which activated downstream interferon regulatory factor 7 and nuclear factor kappa B.

CONCLUSIONS

The present study identified a lipid metabolic vulnerability and inflammation initiation pathways via Se deficiency, which may provide targets for human redox imbalance-induced cardiac disease treatment. This article is protected by copyright. All rights reserved.

Selenium deficiency causes apoptosis through endoplasmic reticulum stress in swine small intestine

Selenium (Se) plays a crucial role in intestinal health. However, the specific mechanism by which deficiency of Se causes intestinal damage remains unclear. This study was to explore whether Se deficiency can cause ER stress and induce apoptosis in swine small intestine. We established the Se deficiency swine model in vivo and the intestinal epithelial (IPEC-J2) cell Se deficiency model in vitro. The results of morphological observation showed that Se deficiency caused structural damage in intestinal villi and the decrease of goblet cell structure. The apoptotic characteristics such as nucleolar condensation, mitochondrial swelling, and apoptotic bodies were observed in the IPEC-J2 cells. The results of acridine orange/ethidium bromide and mitochondrial membrane potential fluorescence staining in vitro showed that there were more apoptotic cells in the Se-deficiency group than that in the control group. The protein and/or mRNA expression levels of Bax, Bcl-2, caspase 3, caspase 8, caspase 9, cytc, PERK, ATF6, IRE, XBP1, CHOP, GRP78, which are related to ER stress-apoptosis pathway, were significantly increased in the Se-deficient group which compared with the control group in vivo and in vitro were consistent. These results indicated that Se deficiency induced ER stress and increased the apoptosis in swine small intestine and IPEC-J2 cells and then caused the damage in swine small intestinal tissue. Besides, the results of gene expressions in our experiment proved that ER stress induced by Se deficiency promoted apoptosis. These results filled the blank in the mechanism of Se deficiency-induced intestinal injury in swine.

Keshan Disease: A Potentially Fatal Endemic Cardiomyopathy in Remote Mountains of China

Keshan disease (KD) as an endemic, highly lethal cardiomyopathy, first reported in northeast China's Keshan County in 1935. The clinical manifestations of patients with KD include primarily congestive heart failure, acute heart failure, and cardiac arrhythmia. Even though some possible etiologies, such as viral infection, fungal infection, microelement deficiency, and malnutrition, have been reported, the exact causes of KD remain poorly known. The endemic areas where KD is found are remote and rural, and many are poor and mountainous places where people are the most socioeconomically disadvantaged in terms of housing, income, education, transportation, and utilization of health services. To date, KD is a huge burden to and severely restricts the economic development of the local residents and health systems of the endemic areas. Although efforts have been made by the government to control, treat, and interrupt disease transmission, the cure for or complete eradication of KD still requires global attention. For this reason, in this review, we systematically describe the etiological hypothesis, clinical manifestations, incidence characteristics, and treatment of KD, to facilitate the better understanding of and draw more attention to this non-representative cardiovascular disease, with the aim of accelerating its elimination.

Selenoprotein Gpx3 knockdown induces myocardial damage through Ca2+ leaks in chickens

Glutathione peroxidase 3 (Gpx3) is a pivotal selenoprotein that acts as an antioxidant. However, the role of Gpx3 in maintaining the normal metabolism of cardiomyocytes remains to be elucidated in more detail. Herein, we employed a model of Gpx3 interference in chicken embryos in vivo and Gpx3 knockdown chicken cardiomyocytes in vitro. Real-time PCR, western blotting and fluorescent staining were performed to detect reactive oxygen species (ROS), the calcium (Ca²⁺) concentration, endoplasmic reticulum (ER) stress, myocardial contraction, inflammation and heat shock proteins (HSPs). Our results revealed that Gpx3 suppression increased the level of ROS, which induced Ca²⁺ leakage in the cytoplasm by blocking the expression of Ca²⁺ channels. The imbalance of Ca²⁺ homeostasis triggered ER stress and blocked myocardial contraction. Furthermore, we found that Ca²⁺ imbalance in the cytoplasm induced severe inflammation, and HSPs might play a protective role throughout these processes. In conclusion, Gpx3 suppression induces myocardial damage through the activation of Ca²⁺-dependent ER stress.

Cul5-type Ubiquitin Ligase KLHDC1 Contributes to the Elimination of Truncated SELENOS Produced by Failed UGA/Sec Decoding

The UGA codon signals protein translation termination, but it can also be translated into selenocysteine (Sec, U) to produce selenocysteine-containing proteins (selenoproteins) by dedicated machinery. As Sec incorporation can fail, Sec-containing longer and Sec-lacking shorter proteins co-exist. Cul2-type ubiquitin ligases were recently shown to destabilize such truncated proteins; however, which ubiquitin ligase targets truncated proteins for degradation remained unclear. We report that the Cul5-type ubiquitin ligase KLHDC1 targets truncated SELENOS, a selenoprotein, for proteasomal degradation. SELENOS is involved in endoplasmic reticulum (ER)-associated degradation, which is linked to reactive oxygen species (ROS) production, and the knockdown of KLHDC1 in U2OS cells decreased ER stress-induced cell death. Knockdown of SELENOS increased the cell population with lower ROS levels. Our findings reveal that, in addition to Cul2-type ubiquitin ligases, KLHDC1 is involved in the elimination of truncated oxidoreductase-inactive SELENOS, which would be crucial for maintaining ROS levels and preventing cancer development.

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KLHDC1 is a Cul5-type ubiquitin ligase

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KLHDC1 targets immature SELENOS for proteasomal degradation

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KLHDC1 knockdown in U2OS cells decreases ER stress-induced cell death

Assessing the Efficacy of Dietary Selenomethionine Supplementation in the Setting of Cardiac Ischemia/Reperfusion Injury

Oxidative stress is a major hallmark of cardiac ischemia/reperfusion (I/R) injury. This partly arises from the presence of activated phagocytes releasing myeloperoxidase (MPO) and its production of hypochlorous acid (HOCl). The dietary supplement selenomethionine (SeMet) has been shown to bolster endogenous antioxidant processes as well as readily react with MPO-derived oxidants. The aim of this study was to assess whether supplementation with SeMet could modulate the extent of cellular damage observed in an in vitro cardiac myocyte model exposed to (patho)-physiological levels of HOCl and an in vivo rat model of cardiac I/R injury. Exposure of the H9c2 cardiac myoblast cell line to HOCl resulted in a dose-dependent increase in necrotic cell death, which could be prevented by SeMet supplementation and was attributed to SeMet preventing the HOCl-induced loss of mitochondrial inner trans-membrane potential, and the associated cytosolic calcium accumulation. This protection was credited primarily to the direct oxidant scavenging ability of SeMet, with a minor contribution arising from the ability of SeMet to bolster cardiac myoblast glutathione peroxidase (GPx) activity. In vivo, a significant increase in selenium levels in the plasma and heart tissue were seen in male Wistar rats fed a diet supplemented with 2 mg kg⁻¹ SeMet compared to controls. However, SeMet-supplementation demonstrated only limited improvement in heart function and did not result in better heart remodelling following I/R injury. These data indicate that SeMet supplementation is of potential benefit within pathological settings where excessive HOCl is known to be generated but has limited efficacy as a therapeutic agent for the treatment of heart attack.

Efficacy of Long-term Selenium Supplementation in the Treatment of Chronic Keshan Disease with Congestive Heart Failure

Few effective treatments for chronic Keshan disease have been available till now. The efficacy of long-term selenium supplementation in the treatment of chronic Keshan disease with congestive heart failure is inconclusive. This study aimed to determine whether selenium supplementation is associated with a decreased risk of cardiac death in chronic Keshan disease with congestive heart failure by ten years of follow-up. A retrospective long-term follow-up analysis was performed on a monitored cohort consisting of 302 chronic Keshan disease patients with a mean age of 40.8±11.4 years. Of the 302 chronic Keshan disease patients, 170 (56.3%) were given selenium supplementation until the end point of follow-up. Cox proportional hazards regression models were used to identify the independent predictors of cardiac events. Our results showed that during the follow-up, there were 101 deaths of patients with chronic Keshan disease in the selenium supplementation group (101/170, 59.4%) and 98 in non-selenium supplementation group (98/132, 74.2%). Multivariate analyses suggested that selenium supplementation was associated with a decreased risk of cardiac death (HR 0.39, 95% CI 0.28-0.53) after adjustment for baseline age, sex, cigarette smoking, family history of Keshan disease, body mass index (BMI), heart rate, electrocardiogram (ECG) abnormalities, blood pressure, initial cardiothoracic ratio, left ventricular ejection fractions (LVEF) and whole-blood selenium concentration. Our ten-year follow-up analysis indicated that selenium supplementation, specifically combined with the use of angiotensin-converting enzyme inhibitor and beta blocker therapy, improved the survival of patients with chronic Keshan disease with congestive heart failure. BMI, selenium deficiency, male, combined ECG abnormalities, LVEF, and fast heart rate increased the risk of cardiac events.

Excessive Selenium Supplementation Induced Oxidative Stress and Endoplasmic Reticulum Stress in Chicken Spleen

Excessive selenium (Se) intake is harmful for animals and humans. The aim of the present study was to examine the effect of long-term excessive Se supplementation on oxidative stress and endoplasmic reticulum (ER) stress-related injuries in chicken spleen. A total of 180 1-day-old chickens were randomly divided into four groups with different Se dietary contents (0.2 mg/kg Se, 5 mg/kg Se, 10 mg/kg Se, or 15 mg/kg Se) for 45 days. Then, the levels of antioxidative enzymes, GPx, SOD, and MDA as well as the expression levels of GRP78, ARF6, caspase 3, caspase 12, and Bcl 2 in the spleen were determined at days 15, 30, and 45, respectively. The results showed that excessive Se treatment decreased the activities of GPx and SOD (P < 0.05) but increased the levels of MDA (P < 0.05) in a dose- and time-dependent manner. In addition, the ER stress genes GRP78 and ATF6 were highly expressed (P < 0.05), and the apoptosis genes caspase 3 and caspase 12 were increased, but Bcl 2 was decreased by Se treatment (P < 0.05). Correlation analysis showed that there was a high correlation between these biomarkers, which indicated that ER stress and ER stress-related apoptosis were correlated with oxidative stress. These results showed the important role of oxidative stress and ER stress in Se-related immune injuries in chicken.

Assessing Cardiac Metabolism: A Scientific Statement From the American Heart Association

In a complex system of interrelated reactions, the heart converts chemical energy to mechanical energy. Energy transfer is achieved through coordinated activation of enzymes, ion channels, and contractile elements, as well as structural and membrane proteins. The heart's needs for energy are difficult to overestimate. At a time when the cardiovascular research community is discovering a plethora of new molecular methods to assess cardiac metabolism, the methods remain scattered in the literature. The present statement on "Assessing Cardiac Metabolism" seeks to provide a collective and curated resource on methods and models used to investigate established and emerging aspects of cardiac metabolism. Some of those methods are refinements of classic biochemical tools, whereas most others are recent additions from the powerful tools of molecular biology. The aim of this statement is to be useful to many and to do justice to a dynamic field of great complexity.

Ameliorative Effects of Selenium on Cadmium-Induced Oxidative Stress and Endoplasmic Reticulum Stress in the Chicken Kidney

The harmful influences of dietary cadmium (Cd) on the chicken kidney and the protective role of selenium (Se) against Cd-induced nephrotoxicity in the chicken are relatively unexplored subjects. The aim of this study was to investigate the ameliorative role of Se on the effects of Cd-induced oxidative stress, endoplasmic reticulum stress, and apoptosis in chicken kidneys. For this study, 100-day-old chickens received Se (as 10 mg Na2SeO3/kg dry weight of diet), Cd (as 150 mg CdCl2/kg dry weight of diet), or Cd + Se in their diets for 60 days. Then, the histopathological changes, Cd and Se contents, levels of oxidative stress, inducible nitric oxide synthase-nitric oxide (iNOS-NO) system activity, levels of endoplasmic reticulum (ER) stress, results of the terminal deoxynucleotidyl transferase dUTP nick end labeling (TUNEL) assay of apoptosis, and expression levels of Bcl-2 and caspase 3 in the kidney were examined. The results showed that Cd exposure caused histopathological and ultrastructural damage and apoptosis of the kidneys. Cd administration significantly increased the accumulation of Cd, the malondialdehyde (MDA) content, NO production, iNOS activity, iNOS expression levels, expression levels of ER stress-related genes (GRP78, GRP94, ATF4, ATF6, and IRE) and the pro-apoptosis gene caspase 3, and the rate of apoptosis. Cd administration markedly decreased the Se content, superoxide dismutase (SOD) and glutathione peroxidase (GPx) activities, and anti-apoptosis gene Bcl-2 expression levels. Co-treatment with Se and Cd obviously reduced the accumulation of Cd, Cd-induced histopathological and ultrastructural changes, oxidative stress, iNOS-NO system activity, ER stress, caspase 3 expression levels, and the rate of apoptosis in the kidneys. These results suggested that Cd exposure caused renal injury and that Se ameliorated Cd-induced nephrotoxicity in chickens.

Involvement of caspases and their upstream regulators in myocardial apoptosis in a rat model of selenium deficiency-induced dilated cardiomyopathy

Keshan disease is an endemic dilated cardiomyopathy (DCM) which is closely related with selenium-deficient diet in China. In the previous study, we reported that the low selenium status plays a pivotal role in the myocardial apoptosis in the DCM rats, however, the underlying mechanism remains unclear. The present study aimed to determine whether the intrinsic, extrinsic pathways and the upstream regulators were involved in the myocardial apoptosis of selenium deficiency-induced DCM rats. Therefore, the rat model of endemic DCM was induced by a selenium-deficient diet for 12 weeks. Accompanied with significant dilation and impaired systolic function of left ventricle, an enhanced myocardial apoptosis was detected by TUNEL assay. Western blot analysis showed remarkably increased protein levels of cleaved caspase-3, caspase-8, caspase-9, and cytosolic cytochrome c released from the mitochondria. In addition, the immunoreactivities of p53 and Bax were significantly up-regulated, while the anti-apoptotic Bcl-2 family members Bcl-2 and Bcl-X(L) were down-regulated. Furthermore, appropriate selenium supplement for another 4 weeks could partially reverse all the above changes. In conclusion, the intrinsic, extrinsic pathways and the upstream regulators such as p53, Bax, Bcl-2, and Bcl-X(L )were all involved in selenium deficiency-induced myocardial apoptosis.