Molecular characterization and NF-κB-regulated transcription of selenoprotein S from the Bama mini-pig

Current views on selenoprotein S in the pathophysiological processes of diabetes-induced atherosclerosis: potential therapeutics and underlying biomarkers

Atherosclerotic cardiovascular disease (ASCVD) consistently ranks as the primary mortality factor among diabetic people. A thorough comprehension of the pathophysiological routes and processes activated by atherosclerosis (AS) caused by diabetes mellitus (DM), together with the recognition of new contributing factors, could lead to the discovery of crucial biomarkers and the development of innovative drugs against atherosclerosis. Selenoprotein S (SELENOS) has been implicated in the pathology and progression of numerous conditions, including diabetes, dyslipidemia, obesity, and insulin resistance (IR)-all recognized contributors to endothelial dysfunction (ED), a precursor event to diabetes-induced AS. Hepatic-specific deletion of SELENOS accelerated the onset and progression of obesity, impaired glucose tolerance and insulin sensitivity, and increased hepatic triglycerides (TG) and diacylglycerol (DAG) accumulation; SELENOS expression in subcutaneous and omental adipose tissue was elevated in obese human subjects, and act as a positive regulator for adipogenesis in 3T3-L1 preadipocytes; knockdown of SELENOS in Min6 β-cells induced β-cell apoptosis and reduced cell proliferation. SELENOS also participates in the early stages of AS, notably by enhancing endothelial function, curbing the expression of adhesion molecules, and lessening leukocyte recruitment-actions that collectively reduce the formation of foam cells. Furthermore, SELENOS forestalls the apoptosis of vascular smooth muscle cells (VSMCs) and macrophages, mitigates vascular calcification, and alleviates inflammation in macrophages and CD4+ T cells. These actions help stifle the creation of unstable plaque characterized by thinner fibrous caps, larger necrotic cores, heightened inflammation, and more extensive vascular calcification-features seen in advanced atherosclerotic lesion development. Additionally, serum SELENOS could function as a potential biomarker, and SELENOS single nucleotide polymorphisms (SNPs) rs4965814, rs28628459, and rs9806366, might be effective gene markers for atherosclerosis-related diseases in diabetes. This review accentuates the pathophysiological processes of atherosclerosis in diabetes and amasses current evidence on SELENOS's potential therapeutic benefits or as predictive biomarkers in the various stages of diabetes-induced atherosclerosis.

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.

Comparative Transcriptome Analysis Provides Insight into Spatio-Temporal Expression Characteristics and Genetic Regulatory Network in Postnatal Developing Subcutaneous and Visceral Fat of Bama Pig

The depot differences between Subcutaneous Fat (SAF) and Visceral Fat (VAF) are critical for human well-being and disease processes in regard to energy metabolism and endocrine function. Miniature pigs (Sus scrofa) are ideal biomedical models for human energy metabolism and obesity due to the similarity of their lipid metabolism with that of humans. However, the regulation of differences in fat deposition and development remains unclear. In this study, the development of SAF and VAF was characterized and compared in Bama pig during postnatal development (infancy, puberty and adulthood), using RNA sequencing techniques (RNA-Seq). The transcriptome of SAF and VAF was profiled and isolated from 1-, 3- and 6 months-old pigs and identified 23,636 expressed genes, of which 1,165 genes were differentially expressed between the depots and/or developmental stages. Upregulated genes in SAF showed significant function and pathway enrichment in the central nervous system development, lipid metabolism, oxidation-reduction process and cell adhesion, whereas genes involved in the immune system, actin cytoskeleton organization, male gonad development and the hippo signaling pathway were preferentially expressed in VAF. Miner analysis of short time-series expression demonstrated that differentiation in gene expression patterns between the two depots corresponded to their distinct responses in sexual development, hormone signaling pathways, lipid metabolism and the hippo signaling pathway. Transcriptome analysis of SAF and VAF suggested that the depot differences in adipose tissue are not only related to lipid metabolism and endocrine function, but are closely associated with sexual development and organ size regulation.

Hepatic galectin-3 is associated with lipid droplet area in non-alcoholic steatohepatitis in a new swine model

Non-alcoholic fatty liver disease (NAFLD) is currently a growing epidemic disease that can lead to cirrhosis and hepatic cancer when it evolves into non-alcoholic steatohepatitis (NASH), a gap not well understood. To characterize this disease, pigs, considered to be one of the most similar to human experimental animal models, were used. To date, all swine-based settings have been carried out using rare predisposed breeds or long-term experiments. Herein, we fully describe a new experimental swine model for initial and reversible NASH using cross-bred animals fed on a high saturated fat, fructose, cholesterol, cholate, choline and methionine-deficient diet. To gain insight into the hepatic transcriptome that undergoes steatosis and steatohepatitis, we used RNA sequencing. This process significantly up-regulated 976 and down-regulated 209 genes mainly involved in cellular processes. Gene expression changes of 22 selected transcripts were verified by RT-qPCR. Lipid droplet area was positively associated with CD68, GPNMB, LGALS3, SLC51B and SPP1, and negatively with SQLE expressions. When these genes were tested in a second experiment of NASH reversion, LGALS3, SLC51B and SPP1 significantly decreased their expression. However, only LGALS3 was associated with lipid droplet areas. Our results suggest a role for LGALS3 in the transition of NAFLD to NASH.

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.

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.

Function analysis of Mef2c promoter in muscle differentiation

Regeneration of adult skeletal muscle following injury occurs through the activation of satellite cells that proliferates, differentiates, and fuses with injured myofibers. Myocyte enhancer factor 2 (MEF2) proteins are reported to have the potential contributions to adult muscle regeneration. To further understand Mef2c gene, the promoter of pig Mef2c gene was analyzed in this paper. Quantitative real-time PCR (qRT-PCR) revealed the expression pattern of Mef2c gene in muscle of eight tissues. The Mef2c promoter had the higher transcriptional activity in differentiated C2C12 cells than that in proliferating C2C12 cells, which was accompanied by the upregulation of mRNA expression of Mef2c gene. Function deletion and mutation analyses showed that MyoD and MEF2 binding sites within the Mef2c promoter were responsible for the regulation of Mef2c transcription. MEF2C could upregulate the transcriptional activities of Mef2c promoter constructs, which contained a 3'-end nucleotide sequence with p300 binding site. The electrophoretic mobility shift assays and chromatin immunoprecipitation assays determined the MyoD binding site in Mef2c promoter. These results advanced our knowledge of the promoter of the pig Mef2c gene, and the study of Mef2c promoter regulator elements helped to elucidate the regulation mechanisms of Mef2c in muscle differentiation or muscle repair and regeneration.

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.

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.

Transcriptome analysis on the inflammatory cell infiltration of nonalcoholic steatohepatitis in bama minipigs induced by a long-term high-fat, high-sucrose diet

Long-term adherence to a high-fat, high-calorie diet influences human health and causes obesity, metabolic syndrome and nonalcoholic steatohepatitis (NASH). Inflammation plays a key role in the development of NASH; however, the mechanism of inflammation induced by over-nutrition remains largely unknown. In this study, we fed Bama minipigs a high-fat, high-sucrose diet (HFHSD) for 23 months. The pigs exhibited characteristics of metabolic syndrome and developed steatohepatitis with greatly increased numbers of inflammatory cells, such as lymphocytes (2.27-fold, P<0.05), Kupffer cells (2.59-fold, P<0.05), eosinophils (1.42-fold, P<0.05) and neutrophils (2.77-fold, P<0.05). High-throughput RNA sequencing (RNA-seq) was performed to explore the systemic transcriptome of the pig liver during inflammation. Approximately 18.2 gigabases of raw sequence data were generated, and over 303 million high-quality reads were assembled into 21,126 unigenes. RNA-seq data analysis showed that 822 genes were differentially expressed in liver (P<0.05) between the HFHSD and control groups. Kyoto Encyclopedia of Genes and Genomes (KEGG) analysis showed that the process of inflammation involved the inflammatory signal transduction-related toll-like receptor, MAPK, and PPAR signaling pathways; the cytokine-related chemokine signaling, cytokine-cytokine receptor interaction, and IL2, IL4, IL6, and IL12 signaling pathways; the leukocyte receptor signaling-related T cell, B cell, and natural killer cell signaling pathways; inflammatory cell migration and invasion- related pathways; and other pathways. Moreover, we identified several differentially expressed inflammation-related genes between the two groups, including FOS, JUN, TLR7, MYC, PIK3CD, VAV3, IL2RB and IL4R, that could be potential targets for further investigation. Our study suggested that long-term HFHSD induced obesity and liver inflammation, providing basic insight into the molecular mechanism of this condition and laying the groundwork for further studies on obesity and steatohepatitis.

Molecular cloning and characterization of the promoter region of the porcine apolipoprotein E gene

Apolipoprotein E (APOE), a component of lipoproteins plays an important role in the transport and metabolism of cholesterol, and is associated with hyperlipoproteinemia and Alzheimer's disease. In order to further understand the characterization of APOE gene, the promoter of APOE gene of Landrace pigs was analyzed in the present study. The genomic structure and amino acid sequence in pigs were analyzed and found to share high similarity in those of human but low similarity in promoter region. Real-time PCR revealed the APOE gene expression pattern of pigs in diverse tissues. The highest expression level was observed in liver, relatively low expression in other tissues, especially in stomach and muscle. Furthermore, the promoter expressing in Hepa 1-6 was significantly better at driving luciferase expression compared with C2C12 cell. After analysis of porcine APOE gene promoter regions, potential transcription factor binding sites were predicted and two GC signals, a TATA box were indicated. Results of promoter activity analysis indicated that one of potential regulatory elements was located in the region -669 to -259, which was essential for a high expression of the APOE gene. Promoter mutation and deletion analysis further suggested that the C/EBPA binding site within the APOE promoter was responsible for the regulation of APOE transcription. Electrophoretic mobility shift assays also showed the binding site of the transcription factor C/EBPA. This study advances our knowledge of the promoter of the porcine APOE gene.

Transcriptome profiling identifies differentially expressed genes in postnatal developing pituitary gland of miniature pig

In recent years, Tibetan pig and Bama pig are popularly used as animal models for medical researches. However, little genomic information is available for the two breeds, particularly regarding gene expression pattern at the whole-transcriptome level. In this study, we characterized the pituitary transcriptome profile along their postnatal developmental stages within and between the two breeds in order to illustrate the differential dynamics and functions of differentially expressed genes. We obtained a total of ∼300 million 80-bp paired-end reads, detected 15 715 previously annotated genes. Most of the genes (90.33%) were shared between the two breeds with the main functions in metabolic process. Four hormone genes (GH, PRL, LHB, and FSHB) were detected in all samples with extremely high levels of expression. Functional differences between the three developmental stages (infancy, puberty and adulthood) in each breed were dominantly presented by the gene expressions at the first stage. That is, Bama pig was over-represented in the genes involved in the cellular process, while Tibetan pig was over-represented in the genes represented by the reproductive process. The identified SNPs indicated that the divergence between the miniature pig breeds and the large pig (Duroc) were greater than that between the two miniature pig breeds. This study substantially expands our knowledge concerning the genes transcribed in the pig pituitary gland and provides an overview of pituitary transcriptome dynamics throughout the period of postnatal development.

Molecular cloning, tissue distribution and ontogenetic expression of Xiang pig chemerin and its involvement in regulating energy metabolism through Akt and ERK1/2 signaling pathways

Chemerin, as a new member of adipokines family, is highly expressed in adipose tissue in rodent and its expression increases with obesity. Moreover, chemerin has been reported to have significant relationship with metabolic syndrome and insulin sensitivity. Here, the gene encoding chemerin from Xiang pig was cloned. The open reading frame of this cDNA encodes 163 deduced amino acid residues. The putative protein has a N-terminal signaling peptide and a nuclear localization signal profile which are highly conserved among the vertebrate orthologs. Both chemerin and chemerinR are highly expressed in lung, kidney and small intestine in adult Xiang pig. Besides these tissues, chemerin is abundant in liver and backfat, and chemerinR is abundant in spleen and skeletal muscle. We also investigated the age-dependent expression of chemerin in suckling Xiang piglets in various tissues, which showed an interaction between age and segments in abundance of chemerin and chemerinR from day 1 to day 21. For chemerinR, it was abundant in skeletal muscle of both adult and fetal Xiang pig. Further, we treated differentiated C2C12 cells with chemerin. The result showed that chemerin regulated energy metabolism partly through Akt and ERK1/2 signaling pathway. Taken together, our findings provide basic molecular information for the deeper investigation on the function of chemerin.