Metformin suppresses expression of the selenoprotein P gene via an AMP-activated kinase (AMPK)/FoxO3a pathway in H4IIEC3 hepatocytes

Relationship between the changes in hepatokine levels and metabolic effects after laparoscopic sleeve gastrectomy in severely obese patients

PURPOSE

To clarify the relationships between the changes in hepatokines and weight loss, and between these changes and the metabolic effects, and the roles played by these changes, after laparoscopic sleeve gastrectomy (LSG).

METHODS

We recruited 25 Japanese patients with severe obesity, who underwent LSG. We measured two hepatokines: selenoprotein P (SeP) and leukocyte cell-derived chemotaxin 2 (LECT2), at the baseline, and then 6 months and 1 year after LSG. Finally, we compared the changes in the hepatokines with the parameters of type 2 diabetes (T2D) and non-alcoholic steatohepatitis (NASH).

RESULTS

Changes in LECT2 were correlated with the percentage of total weight loss (ρ = - 0.499, P = 0.024) and the decrease in total fat area (ρ = 0.559, P = 0.003). The changes in SeP were correlated with those in hemoglobin A1c (ρ = 0.526, P = 0.043) and the insulinogenic index (ρ = 0.638, P = 0.010) in T2D patients. In patients with NASH, the LECT2 levels were correlated with liver steatosis (ρ = 0.601).

CONCLUSIONS

SeP levels decrease in association with HbA1c reduction, whereas LECT2 levels are associated with reductions in fat mass and NASH scores after LSG. Hepatokines may be involved in the pathology of obesity and its complications.

Expanding the Frontiers of Guardian Antioxidant Selenoproteins in Cardiovascular Pathophysiology

Significance: Physiological levels of reactive oxygen and nitrogen species (ROS/RNS) function as fundamental messengers for many cellular and developmental processes in the cardiovascular system. ROS/RNS involved in cardiac redox-signaling originate from diverse sources, and their levels are tightly controlled by key endogenous antioxidant systems that counteract their accumulation. However, dysregulated redox-stress resulting from inefficient removal of ROS/RNS leads to inflammation, mitochondrial dysfunction, and cell death, contributing to the development and progression of cardiovascular disease (CVD). Recent Advances: Basic and clinical studies demonstrate the critical role of selenium (Se) and selenoproteins (unique proteins that incorporate Se into their active site in the form of the 21st proteinogenic amino acid selenocysteine [Sec]), including glutathione peroxidase and thioredoxin reductase, in cardiovascular redox homeostasis, representing a first-line enzymatic antioxidant defense of the heart. Increasing attention has been paid to emerging selenoproteins in the endoplasmic reticulum (ER) (i.e., a multifunctional intracellular organelle whose disruption triggers cardiac inflammation and oxidative stress, leading to multiple CVD), which are crucially involved in redox balance, antioxidant activity, and calcium and ER homeostasis. Critical Issues: This review focuses on endogenous antioxidant strategies with therapeutic potential, particularly selenoproteins, which are very promising but deserve more detailed and clinical studies. Future Directions: The importance of selective selenoproteins in embryonic development and the consequences of their mutations and inborn errors highlight the need to improve knowledge of their biological function in myocardial redox signaling. This could facilitate the development of personalized approaches for the diagnosis, prevention, and treatment of CVD. Antioxid. Redox Signal. 40, 369-432.

Sulforaphane decreases serum selenoprotein P levels through enhancement of lysosomal degradation independent of Nrf2

Selenoprotein P (SeP) is a major selenoprotein in serum predominantly produced in the liver. Excess SeP impairs insulin secretion from the pancreas and insulin sensitivity in skeletal muscle, thus inhibition of SeP could be a therapeutic strategy for type 2 diabetes. In this study, we examine the effect of sulforaphane (SFN), a phytochemical of broccoli sprouts and an Nrf2 activator, on SeP expression in vitro and in vivo. Treatment of HepG2 cells with SFN decreases inter- and intra-cellular SeP levels. SFN enhances lysosomal acidification and expression of V-ATPase, and inhibition of this process cancels the decrease of SeP by SFN. SFN activates Nrf2 in the cells, while Nrf2 siRNA does not affect the decrease of SeP by SFN or lysosomal acidification. These results indicate that SFN decreases SeP by enhancing lysosomal degradation, independent of Nrf2. Injection of SFN to mice results in induction of cathepsin and a decrease of SeP in serum. The findings from this study are expected to contribute to developing SeP inhibitors in the future, thereby contributing to treating and preventing diseases related to increased SeP.

"Alphabet" Selenoproteins: Implications in Pathology

Selenoproteins are a group of proteins containing selenium in the form of selenocysteine (Sec, U) as the 21st amino acid coded in the genetic code. Their synthesis depends on dietary selenium uptake and a common set of cofactors. Selenoproteins accomplish diverse roles in the body and cell processes by acting, for example, as antioxidants, modulators of the immune function, and detoxification agents for heavy metals, other xenobiotics, and key compounds in thyroid hormone metabolism. Although the functions of all this protein family are still unknown, several disorders in their structure, activity, or expression have been described by researchers. They concluded that selenium or cofactors deficiency, on the one hand, or the polymorphism in selenoproteins genes and synthesis, on the other hand, are involved in a large variety of pathological conditions, including type 2 diabetes, cardiovascular, muscular, oncological, hepatic, endocrine, immuno-inflammatory, and neurodegenerative diseases. This review focuses on the specific roles of selenoproteins named after letters of the alphabet in medicine, which are less known than the rest, regarding their implications in the pathological processes of several prevalent diseases and disease prevention.

Functional analysis of selenok, selenot and selenop promoters and their regulation by selenium in yellow catfish Pelteobagrus fulvidraco

The selenok, selenot and selenop are three key selenoproteins involved in stress response. Our study, using the yellow catfish Pelteobagrus fulvidraco as the experimental animal, obtained the 1993-bp, 2000-bp and 1959-bp sequences of selenok, selenot and selenop promoters, respectively, and predicted the binding sites of several transcriptional factors on their promoters, such as Forkhead box O 4 (FoxO4), activating transcription factor 4 (ATF4), Kruppel-like factor 4 (KLF4) and nuclear factor erythroid 2-related factor 2 (NRF2). Selenium (Se) increased the activities of the selenok, selenot and selenop promoters. FoxO4 and Nrf2 can directly bind with selenok promoter and controlled selenok promoter activities positively; KLF4 and Nrf2 can directly bind with selenot promoter and controlled selenot promoter activities positively; FoxO4 and ATF4 can directly bind to selenop promoter and regulated selenop promoter activities positively. Se promoted FoxO4 and Nrf2 binding to selenok promoter, KLF4 and Nrf2 binding to selenot promoter, and FoxO4 and ATF4 binding to selenop promoter. Thus, we provide the first evidence for FoxO4 and Nrf2 bindnig elements in selenok promoter, KLF4 and Nrf2 binding elements in selenot promoter, and FoxO4 and ATF4 binding elements in selenop promoter, and offer novel insight into regulatory mechanism of these selenoproteins induced by Se.

High throughput drug screening identifies resveratrol as suppressor of hepatic SELENOP expression

INTRODUCTION

Selenium (Se) is an essential trace element that exerts its effects mainly as the proteinogenic amino acid selenocysteine within a small set of selenoproteins. Among all family members, selenoprotein P (SELENOP) constitutes a particularly interesting protein as it serves as a biomarker and serum Se transporter from liver to privileged tissues. SELENOP expression is tightly regulated by dietary Se intake, inflammation, hypoxia and certain substances, but a systematic drug screening has hitherto not been performed.

METHODS

A compound library of 1861 FDA approved clinically relevant drugs was systematically screened for interfering effects on SELENOP expression in HepG2 cells using a validated ELISA method. Dilution experiments were conducted to characterize dose-responses. A most potent SELENOP inhibitor was further characterized by RNA-seq analysis to assess effect-associated biochemical pathways.

RESULTS

Applying a 2-fold change threshold, 236 modulators of SELENOP expression were identified. All initial hits were replicated as biological triplicates and analyzed for effects on cell viability. A set of 38 drugs suppressed SELENOP expression more than three-fold, among which were cancer drugs, immunosuppressants, anti-infectious drugs, nutritional supplements and others. Considering a 90% cell viability threshold, resveratrol, vidofludimus, and antimony potassium-tartrate were the most potent substances with suppressive effects on extracellular SELENOP concentrations. Resveratrol suppressed SELENOP levels dose-dependently in a concentration range from 0.8 μM to 50.0 μM, without affecting cell viability, along with strong effects on key genes controlling metabolic pathways and vesicle trafficking.

CONCLUSION

The results highlight an unexpected direct effect of the plant stilbenoid resveratrol, known for its antioxidative and health-promoting effects, on the central Se transport protein. The suppressive effects on SELENOP may increase liver Se levels and intracellular selenoprotein expression, thereby conferring additional protection to hepatocytes at the expense of systemic Se transport. Further physiological effects from this interaction require analyses in vivo and by clinical studies.

Circulating selenoprotein P levels predict glucose-lowering and insulinotropic effects of metformin, but not alogliptin: A post-hoc analysis

AIMS/INTRODUCTION

Selenoprotein P (SeP; encoded by SEPP1 in humans) is a hepatokine that causes impaired insulin secretion and insulin resistance. Metformin downregulates SELENOP promoter activity through an adenosine monophosphate-activated kinase-forkhead box protein O3a pathway in hepatocytes. This study aimed to test our hypothesis that circulating SeP levels are associated with the glucose-lowering effect of metformin in humans.

MATERIALS AND METHODS

A total of 84 participants with poorly controlled type 2 diabetes were randomly assigned to receive metformin (1,000 mg, twice daily) or a dipeptidyl peptidase-4 inhibitor, alogliptin (25 mg, once daily) for 12 weeks. We tested metformin and alogliptin on SeP levels and factors associated therewith as a post-hoc analysis.

RESULTS

Both metformin and aloglipitin did not change the SeP levels. Although metformin significantly increased the insulin secretory index secretory units of islets in transplantation only in participants with higher baseline SeP (>3.87), both agents similarly reduced fasting plasma glucose and glycated hemoglobin. SeP levels at baseline were correlated negatively with changes in SeP (r = -0.484, P = 0.004) and fasting plasma glucose (r = -0.433, P = 0.011), and positively with changes in C-peptide immunoreactivity (r = 0.420, P = 0.017) and secretory units of islets in transplantation (r = 0.388, P = 0.028) in the metformin, but not alogliptin, group.

CONCLUSIONS

Higher baseline levels of SeP significantly predicted metformin-mediated, but not alogliptin-mediated, glucose-lowering and insulinotropic effects. Serum SeP levels might be a novel biomarker for predicting the outcomes of metformin therapy, which might be helpful in tailoring diabetes medication.

Emerging roles of selenium on metabolism and type 2 diabetes

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

Forkhead box protein O1 (FoxO1) knockdown accelerates the eicosapentaenoic acid (EPA)-mediated Selenop downregulation independently of sterol regulatory element-binding protein-1c (SREBP-1c) in H4IIEC3 hepatocytes

Selenoprotein P is upregulated in type 2 diabetes, causing insulin and exercise resistance. We have previously reported that eicosapentaenoic acid (EPA) negatively regulates Selenop expression by suppressing Srebf1 in H4IIEC3 hepatocytes. However, EPA downregulated Srebf1 long before downregulating Selenop. Here, we report additional novel mechanisms for the Selenop gene regulation by EPA. EPA upregulated Foxo1 mRNA expression, which was canceled with the ERK1/2 inhibitor, but not with the PKA inhibitor. Foxo1 knockdown by siRNA initiated early suppression of Selenop, but not Srebf1, by EPA. However, EPA did not affect the nuclear translocation of the FoxO1 protein. Neither ERK1/2 nor PKA inhibitor affected FoxO1 nuclear translocation. In summary, FoxO1 knockdown accelerates the EPA-mediated Selenop downregulation independent of SREBP-1c in hepatocytes. EPA upregulates Foxo1 mRNA via the ERK1/2 pathway without altering its protein and nuclear translocation. These findings suggest redundant and conflicting transcriptional networks in the lipid-induced redox regulation.

Cyclosporine A Downregulates Selenoprotein P Expression via a Signal Transducer and Activator of Transcription 3-Forkhead Box Protein O1 Pathway in Hepatocytes In Vitro

Cyclosporine A (CsA) is an immunosuppressant applied worldwide for preventing graft rejection and autoimmune diseases. However, CsA elevates oxidative stress, which can lead to liver injuries. The present study aimed to clarify the mechanisms underlying the CsA-mediated oxidative stress. Among the redox proteins, CsA concentration-dependently downregulated Selenop-encoding selenoprotein P, a major circulating antioxidant protein reducing reactive oxygen species, in hepatocytes cell lines and primary hepatocytes. The luciferase assay identified the CsA-responsive element in the SELENOP promoter containing a putative binding site for forkhead box protein O (FoxO) 1. The CsA-mediated suppression on the SELENOP promoter was independent of the nuclear factor of activated T-cell, a classic target repressed by CsA. A chromatin immunoprecipitation assay showed that CsA suppressed the FoxO1 binding to the SELENOP promoter. Foxo1 knockdown significantly downregulated Selenop expression in H4IIEC3 cells. Furthermore, CsA downregulated FoxO1 by inactivating its upstream signal transducer and activator of transcription 3 (STAT3). Knockdown of Stat3 downregulated Foxo1 and Selenop expression in hepatocytes. These findings revealed a novel mechanism underlying CsA-induced oxidative stress by downregulating the STAT3-FoxO1-Selenop pathway in hepatocytes. SIGNIFICANCE STATEMENT: This study shows that Cyclosporine A (CsA) downregulates Selenop, an antioxidant protein, by suppressing the signal transducer and activator of transcription 3-forkhead box protein O1 pathway in hepatocytes, possibly one of the causations of CsA-induced oxidative stress in hepatocytes. The present study sheds light on the previously unrecognized CsA-redox axis.

Cyclosporine A downregulates selenoprotein P expression via a STAT3-FoxO1 pathway in hepatocytes in vitro

Cyclosporine A (CsA) is a worldwide applied immunosuppressant for preventing graft rejection and autoimmune diseases. However, CsA elevates oxidative stress leading to liver injuries. The present study aimed to clarify the mechanisms underlying the CsA-mediated oxidative stress. Among the redox proteins, CsA concentration-dependently downregulated Selenop encoding selenoprotein P (SeP), a major circulating antioxidant protein reducing reactive oxygen species (ROS), in hepatocytes cell lines and primary hepatocytes. The luciferase assay identified the CsA-responsive element in the SELENOP promoter containing a putative binding site for FoxO1. The CsA-mediated suppression on the SELENOP promoter was independent of NFAT, a classic target repressed by CsA. A ChIP assay showed that CsA suppressed the FoxO1 binding to the SELENOP promoter. Foxo1 knockdown significantly downregulated Selenop expression in H4IIEC3 cells. Furthermore, CsA downregulated FoxO1 by inactivating its upstream signal transducer and activator of transcription 3 (STAT3). Knockdown of Stat3 downregulated Foxo1 and Selenop expression in hepatocytes. These findings revealed a novel mechanism underlying CsA-induced oxidative stress via downregulating the STAT3-FoxO1-Selenop pathway in hepatocytes. Significance Statement Our study shows that CsA downregulates Selenop, an antioxidant protein, via suppressing the STAT3-FoxO1 pathway in hepatocytes, possibly one of the causations of CsA-induced oxidative stress in hepatocytes. The present study sheds light on the previously unrecognized CsA-redox axis.

Selenium and Selenoproteins at the Intersection of Type 2 Diabetes and Thyroid Pathophysiology

Type 2 diabetes (T2D) is considered one of the largest global public-health concerns, affecting approximately more than 400 million individuals worldwide. The pathogenesis of T2D is very complex and, among the modifiable risk factors, selenium (Se) has recently emerged as a determinant of T2D pathogenesis and progression. Selenium is considered an essential element with antioxidant properties, and is incorporated into the selenoproteins involved in the antioxidant response. Furthermore, deiodinases, the enzymes responsible for homeostasis and for controlling the activity of thyroid hormones (THs), contain Se. Given the crucial action of oxidative stress in the onset of insulin resistance (IR) and T2D, and the close connection between THs and glucose metabolism, Se may be involved in these fundamental relationships; it may cover a dual role, both as a protective factor and as a risk factor of T2D, depending on its basal plasma concentration and the individual’s diet intake. In this review we discuss the current evidence (from experimental, observational and randomized clinical studies) on how Se is associated with the occurrence of T2D and its influence on the relationship between thyroid pathophysiology, IR and T2D.

Pharmacological Induction of Fetal Hemoglobin in β-Thalassemia and Sickle Cell Disease: An Updated Perspective

A significant amount of attention has recently been devoted to the mechanisms involved in hemoglobin (Hb) switching, as it has previously been established that the induction of fetal hemoglobin (HbF) production in significant amounts can reduce the severity of the clinical course in diseases such as β-thalassemia and sickle cell disease (SCD). While the induction of HbF using lentiviral and genome-editing strategies has been made possible, they present limitations. Meanwhile, progress in the use of pharmacologic agents for HbF induction and the identification of novel HbF-inducing strategies has been made possible as a result of a better understanding of γ-globin regulation. In this review, we will provide an update on all current pharmacological inducer agents of HbF in β-thalassemia and SCD in addition to the ongoing research into other novel, and potentially therapeutic, HbF-inducing agents.

Lauric acid impairs insulin-induced Akt phosphorylation by upregulating SELENOP expression via HNF4α induction

Selenoprotein P (SeP; encoded by SELENOP in humans, Selenop in rodents) is a hepatokine that is upregulated in the liver of humans with type 2 diabetes. Excess SeP contributes to the onset of insulin resistance and various type 2 diabetes-related complications. We have previously reported that the long-chain saturated fatty acid, palmitic acid, upregulates Selenop expression, whereas the polyunsaturated fatty acids (PUFAs) downregulate it in hepatocytes. However, the effect of medium-chain fatty acids (MCFAs) on Selenop is unknown. Here we report novel mechanisms that underlie the lauric acid-mediated Selenop gene regulation in hepatocytes. Lauric acid upregulated Selenop expression in Hepa1-6 hepatocytes and mice liver. A luciferase promoter assay and computational analysis of transcription factor-binding sites identified the hepatic nuclear factor 4α (HNF4α) binding site in the SELENOP promoter. A chromatin immunoprecipitation (ChIP) assay showed that lauric acid increased the binding of HNF4α to the SELENOP promoter. The knockdown of Hnf4α using siRNA canceled the upregulation of lauric acid-induced Selenop. Thus, the lauric acid-induced impairment of Akt phosphorylation brought about by insulin was rescued by the knockdown of either Hnf4α or Selenop. These results provide new insights into the regulation of SeP by fatty acids and suggest that SeP may mediate MCFA-induced hepatic insulin signal reduction.

EGCG-derived polymeric oxidation products enhance insulin sensitivity in db/db mice

The present study investigated the influence of epigallocatechin-3-gallate (EGCG) and its autoxidation products on insulin sensitivity in db/db mice. Compared to EGCG, autoxidation products of EGCG alleviated diabetic symptoms by suppressing the deleterious renal axis of the renin-angiotensin system (RAS), activating the beneficial hepatic axis of RAS, and downregulating hepatic and renal SELENOP and TXNIP. A molecular weight fraction study demonstrated that polymeric oxidation products were of essential importance. The mechanism of action involved coating polymeric oxidation products on the cell surface to protect against cholesterol loading, which induces abnormal RAS. Moreover, polymeric oxidation products could regulate RAS and SELENOP at doses that were far below cytotoxicity. The proof-of-principal demonstrations of EGCG-derived polymeric oxidation products open a new avenue for discovering highly active polymeric oxidation products based on the oxidation of naturally occurring polyphenols to manage diabetes and other diseases involving abnormal RAS.

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EGCG autoxidation forms polymeric oxidation products.

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The polymeric oxidation products are coated on the surface of cells or tissues.

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The surface coating regulates RAS, SELENOP, and TXNIP in db/db mice.

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The surface coating increases insulin sensitivity in db/db mice.

Safety of selenium exposure and limitations of selenoprotein maximization: Molecular and epidemiologic perspectives

Recent evidence from laboratory and epidemiologic studies has shed a different light on selenium health effects and its recommended range of environmental exposure, compared with earlier research. Specifically, epidemiologic studies in Western populations have shown adverse effects of selenium exposure at low levels, sometimes below or slightly above selenium intakes needed to maximize selenoprotein expression and activity. In addition, three recent lines of evidence in molecular and biochemical studies suggest some potential drawbacks associated with selenoprotein maximization: 1) the possibility that selenoprotein upregulation is a compensatory response to oxidative challenge, induced by selenium itself or other oxidants; 2) the capacity of selenoproteins to trigger tumor growth in some circumstances; and 3) the deleterious metabolic effects of selenoproteins and particularly of selenoprotein P. The last observation provides a toxicological basis to explain why in humans selenium intake levels as low as 60 μg/day, still in the range of selenium exposure upregulating selenoprotein expression, might start to increase risk of type 2 diabetes. Overall, these new pieces of evidence from the literature call into question the purported benefit of selenoprotein maximization, and indicate the need to reassess selenium dietary reference values and upper intake level. This reassessment should clarify which range of selenoprotein upregulation follows restoration of adequate selenium availability and which range is driven by a compensatory response to selenium toxicity and oxidative stress.

Effects of eicosapentaenoic acid on serum levels of selenoprotein P and organ-specific insulin sensitivity in humans with dyslipidemia and type 2 diabetes

Aim

Selenoprotein P (SeP, encoded by SELENOP in humans) is a hepatokine that causes insulin resistance in the liver and skeletal muscle. It was found that polyunsaturated fatty acid eicosapentaenoic acid (EPA) downregulates Selenop expression by inactivating SREBP‐1c. The present study aimed to examine the effect of EPA for 12 weeks on circulating SeP levels and insulin sensitivity in humans with type 2 diabetes.

Methods

A total of 20 participants with dyslipidemia and type 2 diabetes were randomly assigned to an EPA (900 mg, twice daily) group and a control group. The primary endpoint was a change in serum SeP levels. Organ‐specific insulin sensitivity in the liver (HGP and %HGP), skeletal muscle (Rd), and adipose tissue (FFA and %FFA) were assessed using a hyperinsulinemic‐euglycemic clamp study with stable isotope‐labeled glucose infusion.

Results

Serum SeP levels were not changed in either group at the end of the study. In the EPA group, the changes in SeP levels were positively correlated with the change in serum EPA levels (r = 0.709, P = 0.022). Treatment with EPA significantly enhanced %FFA but not %HGP and Rd. The change in serum EPA levels was significantly positively correlated with the change in %HGP, and negatively correlated with changes in Rd.

Conclusions

The change in serum EPA levels was positively correlated with serum SeP levels, hepatic insulin sensitivity, and negatively with skeletal muscle insulin sensitivity in humans with type 2 diabetes. The EPA‐induced enhancement of hepatic insulin sensitivity might be associated with a mechanism independent of serum SeP levels.

Metformin inhibits hepatocellular carcinoma development by inducing apoptosis and pyroptosis through regulating FOXO3

This study aimed to expand our understanding of metformin (Met) in inhibiting hepatocellular carcinoma (HCC) progression and to investigate its underlying mechanism. Met was administrated to HCC cells at 5, 10, and 20 μM, after which the cell phenotype was evaluated. RNA-seq cluster analysis was used to screen for target genes modulated by Met. Luciferase activity and ChIP assays were performed to detect the effect of FOXO3 on the transcriptional activation of NLRP3. We evaluated the effect of Met and FOXO3 and on the growth of HCC cells in vivo. Met inhibited HCC cell proliferation and promoted apoptosis. Met also induced pyroptosis of HCC cells. FOXO3 was significantly upregulated by Met treatment, and FOXO3 activated transcription of NLRP3. Cells after Met treatment together with FOXO3 knockdown have a stronger colony formation and migration ability but a lower apoptosis rate compared to the Met treatment alone group. In vivo, Met inhibited HCC tumor growth. The tumors in Met treatment and FOXO3 knockdown group grew faster than in Met treatment group. Thus, Met attenuates HCC cell development by inducing apoptosis and pyroptosis. This effect of metformin is partially dependent on FOXO3 which can activate the transcription of NLRP3.

Suppressor of cytokine signalling-2 controls hepatic gluconeogenesis and hyperglycemia by modulating JAK2/STAT5 signalling pathway

Hepatic gluconeogenesis plays a crucial role in maintaining blood glucose homeostasis in mammals. Globe knockout of suppressor of cytokine signalling-2 (SOCS2), a feedback inhibitor of cytokine signalling, has been shown resistant to high-fat-diet (HFD)-induced hepatic steatosis with impaired glucose tolerance in mice. However, the underlying mechanism of SOCS2 regulates hepatic glucose homeostasis still undefined. In the present study, we demonstrated that the hepatic SOCS2 expression is markedly reduced in fasted C57BL/6 J mice or db/db mice. Moreover, hepatic SOCS2 expression levels are induced by metformin treatment. Ablation of SOCS2 attenuates suppressing effects of metformin on gluconeogenesis in hepatocytes. Gain- and loss-of-function studies indicated that SOCS2 regulates hepatic gluconeogenic genes expression and glucose output by mediating JAK2/STAT5 signalling pathway in db/db mice. Mechanistically, we observed that SOCS2 inactivates STAT5 by attenuating the interaction between JAK2 and STAT5, which in turn reduces hepatic gluconeogenesis. The present study reveals a critical role of SOCS2 in regulating hepatic gluconeogenesis. The inhibitory effect of metformin on gluconeogenesis is mediated, at least in part, by upregulating SOCS2 and therefore reducing hepatic gluconeogenic genes expression. SOCS2 may represent a new therapeutic target for the treatment of diabetes.

Identification of a novel endogenous long non-coding RNA that inhibits selenoprotein P translation

Selenoprotein P (SELENOP) is a major plasma selenoprotein that contains 10 Sec residues, which is encoded by the UGA stop codon. The mRNA for SELENOP has the unique property of containing two Sec insertion sequence (SECIS) elements, which is located in the 3' untranslated region (3'UTR). Here, we coincidentally identified a novel gene, CCDC152, by sequence analysis. This gene was located in the antisense region of the SELENOP gene, including the 3'UTR region in the genome. We demonstrated that this novel gene functioned as a long non-coding RNA (lncRNA) that decreased SELENOP protein levels via translational rather than transcriptional, regulation. We found that the CCDC152 RNA interacted specifically and directly with the SELENOP mRNA and inhibited its binding to the SECIS-binding protein 2, resulting in the decrease of ribosome binding. We termed this novel gene product lncRNA inhibitor of SELENOP translation (L-IST). Finally, we found that epigallocatechin gallate upregulated L-IST in vitro and in vivo, to suppress SELENOP protein levels. Here, we provide a new regulatory mechanism of SELENOP translation by an endogenous long antisense ncRNA.

Elevated circulating Selenoprotein P levels in patients with polycystic ovary syndrome

Selenoprotein P (SeP), an hepatokine that is primarily produced by liver, has been reported to affect glucose metabolism. In this study, we aimed to measure and compare serum SeP values in patients with polycystic ovary syndrome (PCOS) and a healthy control group, and to investigate whether there was a relationship between SeP values and insulin resistance in patients with PCOS. This prospective case-control study included 40 patients with PCOS and 39 healthy women (non-PCOS) matched for age and body mass index. SeP levels were significantly higher in the PCOS group compared with the healthy controls (7.48 ± 3.80 vs. 5.17 ± 3.20 mg/ml, p = .005). Serum insulin, hs-CRP, HOMA-IR, FBG, total-testosterone, and free-testosterone levels were higher in women with PCOS than in controls. In an unadjusted model and after adjusting for potential confounders, SeP had increased odds for PCOS (p = .007). ROC curve analysis showed that the area under the ROC curves were 0.691 (95% CI: 0.576-0.806, p < .003) for SeP levels. The optimal cut-off value of SeP for detecting PCOS was ≥5.87 mgl/ml. We showed, for the first time, that serum SeP levels were increased significantly in PCOS, Our results suggest that there is a potential link between PCOS and SeP levelsIMPACT STATEMENTWhat is already known on this subject? Selenoprotein deficiency causes various dysfunctions associated with oxidative stress, but recent studies found that increased SeP levels were associated with insulin resistance. Circulating SeP levels have been found to be increased in patients with type 2 diabetes mellitus (T2DM).What the results of this study add? Our study is the first in the literature to examine the relationship between SeP levels and the presence of PCOS. Serum SeP levels were increased significantly in PCOS.What the implications are of these findings for clinical practice and/or further research? SeP seemed to have a role in PCOS. SeP can be used to predict metabolic disorders associated with PCOS and to determine treatment methods.

Dietary Marginal and Excess Selenium Increased Triglycerides Deposition, Induced Endoplasmic Reticulum Stress and Differentially Influenced Selenoproteins Expression in the Anterior and Middle Intestines of Yellow Catfish Pelteobagrus fulvidraco

Selenium (Se) is an essential micro-mineral and plays important roles in antioxidant responses, and also influences lipid metabolism and selenoprotein expression in vertebrates, but the effects and mechanism remain unknown. The study was undertaken to decipher the insights into dietary Se influencing lipid metabolism and selenoprotein expression in the anterior and middle intestine (AI and MI) of yellow catfish Pelteobagrus fulvidraco. Yellow catfish (weight: 8.27 ± 0.03 g) were fed a 0.03- (M-Se), 0.25- (A-Se), or 6.39- (E-Se) mg Se/kg diet for 12 wk. AI and MI were analyzed for triglycerides (TGs) and Se concentrations, histochemistry and immunofluorescence, enzyme activities, and gene and protein levelsassociated with antioxidant responses, lipid metabolism, endoplasmic reticulum (ER) stress, and selenoproteome. Compared to the A-Se group, M-Se and E-Se diets significantly decreased weight gain (WG) and increased TGs concentration in the AI and MI. In the AI, compared with A-Se group, M-Se and E-Se diets significantly increased activities of fatty acid synthase, expression of lipogenic genes, and suppressed lipolysis. In the MI, compared to the A-Se group, M-Se and E-Se diets significantly increased activities of lipogenesis and expression of lipogenic genes. Compared with A-Se group, E-Se diet significantly increased glutathione peroxidase (GPX) activities in the AI and MI, and M-Se diet did not significantly reduce GPX activities in the AI and MI. Compared with the A- Se group, E-Se diet significantly increased glutathione peroxidase (GPX) activities in the plasma and liver, and M-Se diet significantly reduced GPX activities in the plasma and liver. Compared with the A-Se group, M-Se and E-Se groups also increased glucose-regulated protein 78 (GRP78, ER stress marker) protein expression of the intestine. Dietary Se supplementation also differentially influenced the expression of the 28 selenoproteins in the AI and MI, many of which possessed antioxidant characteristics. Compared with the A-Se group, the M-Se group significantly decreased mRNA levels of txnrd2 and txnrd3, but made no difference on mRNA levels of these seven GPX proteins in the MI. Moreover, we characterized sterol regulatory element binding protein 1c (SREBP1c) binding sites of three ER-resident proteins (selenom, selenon, and selenos) promoters, and found that Se positively controlled selenom, selenon, and selenos expression via SREBP1c binding to the selenom, selenon, and selenos promoter. Thus, dietary marginal and excess Se increased TGs deposition of yellow catfish P. fulvidraco, which might be mediated by ER-resident selenoproteins expression and ER stress.

Alcohol Intake Is Associated With Elevated Serum Levels of Selenium and Selenoprotein P in Humans

Selenoprotein P is a hepatokine with antioxidative properties that eliminate a physiologic burst of reactive oxygen species required for intracellular signal transduction. Serum levels of selenoprotein P are elevated during aging and in people with type 2 diabetes, non-alcoholic fatty liver disease, and hepatitis C. However, how serum levels of full-length selenoprotein P are regulated largely remains unknown, especially in the general population. To understand the significance of serum selenoprotein P levels in the general population, we evaluated intrinsic and environmental factors associated with serum levels of full-length selenoprotein P in 1,183 subjects participating in the Shika-health checkup cohort. Serum levels of selenium were positively correlated with liver enzymes and alcohol intake and negatively correlated with body mass index. Serum levels of selenoprotein P were positively correlated with age, liver enzymes, and alcohol intake. In multiple regression analyses, alcohol intake was positively correlated with serum levels of both selenium and selenoprotein P independently of age, gender, liver enzymes, and fatty liver on ultrasonography. In conclusion, alcohol intake is associated with elevated serum levels of selenium and selenoprotein P independently of liver enzyme levels and liver fat in the general population. Moderate alcohol intake may exert beneficial or harmful effects on health, at least partly by upregulating selenoprotein P. These findings increase our understanding of alcohol-mediated redox regulation and form the basis for the adoption of appropriate drinking guidelines.

Therapeutic strategies targeting FOXO transcription factors

FOXO proteins are transcription factors that are involved in numerous physiological processes and in various pathological conditions, including cardiovascular disease, cancer, diabetes and chronic neurological diseases. For example, FOXO proteins are context-dependent tumour suppressors that are frequently inactivated in human cancers, and FOXO3 is the second most replicated gene associated with extreme human longevity. Therefore, pharmacological manipulation of FOXO proteins is a promising approach to developing therapeutics for cancer and for healthy ageing. In this Review, we overview the role of FOXO proteins in health and disease and discuss the pharmacological approaches to modulate FOXO function.

Selenoprotein P; P for Plasma, Prognosis, Prophylaxis, and More

Selenoprotein P (SeP) is one of the 25 human selenocysteine (Sec)-containing proteins, and is generally thought to function as a plasma carrier of the trace element selenium in the body. Recent studies, however, indicate unsuspected pivotal roles of SeP in human diseases, particularly in type 2 diabetes mellitus (T2DM) and pulmonary arterial hypertension (PAH). In this review, we will summarize the characteristics of SeP and recent advances in the field, especially focusing on the emerging roles of SeP in pathophysiological conditions. We will also discuss potential medical/pharmaceutical applications targeting SeP.

Hepatokine Selenoprotein P-Mediated Reductive Stress Causes Resistance to Intracellular Signal Transduction

Significance: Selenoprotein P functions as a redox protein through its intrinsic thioredoxin domain and by distributing selenium to intracellular glutathione peroxidases, that is, glutathione peroxidase 1 and 4. Recent Advances: Selenoprotein P was rediscovered as a hepatokine that causes the pathology of type 2 diabetes and aging-related diseases, including exercise resistance in the skeletal muscle, insulin secretory failure in pancreatic β cells, angiogenesis resistance in vascular endothelial cells, and myocardial ischemic-reperfusion injury. It was unexpected for the antioxidant selenoprotein P to cause insulin resistance, because oxidative stress associated with obesity and fatty liver is a causal factor for hepatic insulin resistance. Critical Issues: Oxidative stress induced by the accumulation of reactive oxygen species (ROS) has a causal role in the development of insulin resistance, whereas ROS themselves function as intracellular second messengers that promote insulin signal transduction. ROS act both positively and negatively in insulin signaling depending on their concentrations. It might be possible that selenoprotein P causes "reductive stress" by eliminating a physiological ROS burst that is required for insulin signal transduction, thereby causing insulin resistance. In a large-scale intervention study, selenium supplementation that upregulates selenoprotein P was paradoxically associated with an increased risk for diabetes in humans. This review discusses the molecular mechanisms underlying the selenoprotein P-mediated resistance to angiogenesis and to exercise. Future Directions: Selenoprotein P may be the first identified intrinsic factor that induces reductive stress, causing resistance to intracellular signal transduction, which may be the therapeutic target against sedentary-lifestyle-associated diseases, such as diabetes and obesity.

Higher Serum Selenoprotein P Level as a Novel Inductor of Metabolic Complications in Psoriasis

Selenoprotein P (SeP), a member of hepatokines, is involved in the development of various metabolic diseases closely related to psoriasis, but it has not been explored in that dermatosis so far. The study aimed to evaluate the clinical value of serum SeP concentrations in patients with psoriasis and its interplay between disease activity, metabolic or inflammatory parameters and systemic therapy. The study included thirty-three patients with flared plaque-type psoriasis and fifteen healthy volunteers. Blood samples were collected before and after three months of treatment with methotrexate or acitretin. Serum SeP levels were evaluated using the immune–enzymatic method. SeP concentration was significantly higher in patients with psoriasis than in the controls (p < 0.05). Further, in patients with severe psoriasis, SeP was significantly increased, compared with the healthy volunteers before treatment, and significantly decreased after (p < 0.05, p = 0.041, respectively). SeP positively correlated with C-reactive protein and platelets and negatively with red blood counts (p = 0.008, p = 0.013, p = 0.022, respectively). Therapy resulted in a significant decrease in SeP level. Selenoprotein P may be a novel indicator of inflammation and the metabolic complications development in psoriatics, especially with severe form or with concomitant obesity. Classic systemic therapy has a beneficial effect on reducing the risk of comorbidities by inhibiting SeP.

Acute Hyperenergetic, High-Fat Feeding Increases Circulating FGF21, LECT2, and Fetuin-A in Healthy Men

BACKGROUND

Hepatokines such as fibroblast growth factor 21 (FGF21), leukocyte cell-derived chemotaxin 2 (LECT2), fetuin-A, fetuin-B, and selenoprotein P (SeP) are liver-derived proteins that are modulated by chronic energy status and metabolic disease. Emerging data from rodent and cell models indicate that hepatokines may be sensitive to acute nutritional manipulation; however, data in humans are lacking.

OBJECTIVE

The aim was to investigate the influence of hyperenergetic, high-fat feeding on circulating hepatokine concentrations, including the time course of responses.

METHODS

In a randomized, crossover design, 12 healthy men [mean ± SD: age, 24 ± 4 y; BMI (kg/m2), 24.1 ± 1.5] consumed a 7-d hyperenergetic, high-fat diet [HE-HFD; +50% energy, 65% total energy as fat (32% saturated, 26% monounsaturated, 8% polyunsaturated)] and control diet (36% total energy as fat), separated by 3 wk. Whole-body insulin sensitivity was assessed before and after each diet using oral-glucose-tolerance tests. Fasting plasma concentrations of FGF21 (primary outcome), LECT2, fetuin-A, fetuin-B, SeP, and related metabolites were measured after 1, 3, and 7 d of each diet. Hepatokine responses were analyzed using 2-factor repeated-measures ANOVA and subsequent pairwise comparisons.

RESULTS

Compared with the control, the HE-HFD increased circulating FGF21 at 1 d (105%) and 3 d (121%; P ≤ 0.040), LECT2 at 3 d (17%) and 7 d (32%; P ≤ 0.004), and fetuin-A at 7 d (7%; P = 0.028). Plasma fetuin-B and SeP did not respond to the HE-HFD. Whole-body insulin sensitivity was reduced after the HE-HFD by 31% (P = 0.021).

CONCLUSIONS

Acute high-fat overfeeding augments circulating concentrations of FGF21, LECT2, and fetuin-A in healthy men. Notably, the time course of response varies between proteins and is transient for FGF21. These findings provide further insight into the nutritional regulation of hepatokines in humans and their interaction with metabolic homeostasis. This study was registered at clinicaltrials.gov as NCT03369145.

Selenoprotein P as a significant regulator of pancreatic β cell function

Selenoprotein P (SeP; encoded by SELENOP) is selenium (Se)-rich plasma protein that is mainly produced in the liver. SeP functions as a Se-transport protein to deliver Se from the liver to other tissues, such as the brain and testis. The protein plays a pivotal role in Se metabolism and antioxidative defense, and it has been identified as a 'hepatokine' that causes insulin resistance in type 2 diabetes. SeP levels are increased in type 2 diabetes patients, and excess SeP impairs insulin signalling, promoting insulin resistance. Furthermore, increased levels of SeP disturb the functioning of pancreatic β cells and inhibit insulin secretion. This review focuses on the biological function of SeP and the molecular mechanisms associated with the adverse effects of excess SeP on pancreatic β cells' function, particularly with respect to redox reactions. Interactions between the liver and pancreas are also discussed.

Selenoprotein P as an in vivo redox regulator: disorders related to its deficiency and excess

Selenoprotein P (encoded by SELENOP) contains the essential trace element selenium in the form of selenocysteine, which is an analog of cysteine that contains selenium instead of sulfur. Selenoprotein P is a major selenium-containing protein in human plasma and is mainly synthesized in the liver. It functions as a selenium-transporter to maintain antioxidative selenoenzymes in several tissues, such as the brain and testis, and plays a pivotal role in selenium-metabolism and antioxidative defense. A decrease of selenoprotein P and selenoproteins causes various dysfunctions related to oxidative stress. On the other hand, recent studies indicate that excess selenoprotein P exacerbates glucose metabolism and promotes type 2 diabetes. This review focuses on the biological functions of selenoprotein P, particularly its role in selenium-metabolism and antioxidative defense. Furthermore, the effects of excess selenoprotein P on glucose metabolism, and resulting diseases are described. The development of a therapeutic agent that targets excess selenoprotein P is discussed.

Diagnostic and Prognostic Significance of Serum Levels of SeP (Selenoprotein P) in Patients With Pulmonary Hypertension

OBJECTIVE

Despite the recent progress in upfront combination therapy for pulmonary arterial hypertension (PAH), useful biomarkers for the disorder still remain to be developed. SeP (Selenoprotein P) is a glycoprotein secreted from various kinds of cells including pulmonary artery smooth muscle cells to maintain cellular metabolism. We have recently demonstrated that SeP production from pulmonary artery smooth muscle cells is upregulated and plays crucial roles in the pathogenesis of PAH. However, it remains to be elucidated whether serum SeP levels could be a useful biomarker for PAH. Approach and Results: We measured serum SeP levels and evaluated their prognostic impacts in 65 consecutive patients with PAH and 20 controls during follow-up (mean, 1520 days; interquartile range, 1393-1804 days). Serum SeP levels were measured using a newly developed sol particle homogeneous immunoassay. The patients with PAH showed significantly higher serum SeP levels compared with controls. Higher SeP levels (cutoff point, 3.47 mg/L) were associated with the outcome (composite end point of all-cause death and lung transplantation) in patients with PAH (hazard ratio, 4.85 [1.42-16.6]; P<0.01). Importantly, we found that the absolute change in SeP of patients with PAH (ΔSeP) in response to the initiation of PAH-specific therapy significantly correlated with the absolute change in mean pulmonary artery pressure, pulmonary vascular resistance (ΔPVR), and cardiac index (ΔCI; R=0.78, 0.76, and -0.71 respectively, all P<0.0001). Moreover, increase in ΔSeP during the follow-up predicted poor outcome of PAH.

CONCLUSIONS

Serum SeP is a novel biomarker for diagnosis and assessment of treatment efficacy and long-term prognosis in patients with PAH.

Selenoprotein P Promotes the Development of Pulmonary Arterial Hypertension: Possible Novel Therapeutic Target

BACKGROUND

Excessive proliferation and apoptosis resistance of pulmonary artery smooth muscle cells (PASMCs) are key mechanisms of pulmonary arterial hypertension (PAH). Despite the multiple combination therapy, a considerable number of patients develop severe pulmonary hypertension (PH) because of the lack of diagnostic biomarker and antiproliferative therapies for PASMCs.

METHODS

Microarray analyses were used to identify a novel therapeutic target for PAH. In vitro experiments, including lung and serum samples from patients with PAH, cultured PAH-PASMCs, and high-throughput screening of 3336 low-molecular-weight compounds, were used for mechanistic study and exploring a novel therapeutic agent. Five genetically modified mouse strains, including PASMC-specific selenoprotein P (SeP) knockout mice and PH model rats, were used to study the role of SeP and therapeutic capacity of the compounds for the development of PH in vivo.

RESULTS

Microarray analysis revealed a 32-fold increase in SeP in PAH-PASMCs compared with control PASMCs. SeP is a widely expressed extracellular protein maintaining cellular metabolism. Immunoreactivity of SeP was enhanced in the thickened media of pulmonary arteries in PAH. Serum SeP levels were also elevated in patients with PH compared with controls, and high serum SeP predicted poor outcome. SeP-knockout mice ( SeP^-/-) exposed to chronic hypoxia showed significantly reduced right ventricular systolic pressure, right ventricular hypertrophy, and pulmonary artery remodeling compared with controls. In contrast, systemic SeP-overexpressing mice showed exacerbation of hypoxia-induced PH. Furthermore, PASMC-specific SeP^-/- mice showed reduced hypoxia-induced PH compared with controls, whereas neither liver-specific SeP knockout nor liver-specific SeP-overexpressing mice showed significant differences with controls. Altogether, protein levels of SeP in the lungs were associated with the development of PH. Mechanistic experiments demonstrated that SeP promotes PASMC proliferation and resistance to apoptosis through increased oxidative stress and mitochondrial dysfunction, which were associated with activated hypoxia-inducible factor-1α and dysregulated glutathione metabolism. It is important to note that the high-throughput screening of 3336 compounds identified that sanguinarine, a plant alkaloid with antiproliferative effects, reduced SeP expression and proliferation in PASMCs and ameliorated PH in mice and rats.

CONCLUSIONS

These results indicate that SeP promotes the development of PH, suggesting that it is a novel biomarker and therapeutic target of the disorder.

Genome-Wide RNAi Screen Identifies PMPCB as a Therapeutic Vulnerability in EpCAM+ Hepatocellular Carcinoma

Hepatocellular carcinoma (HCC) is a genetically heterogeneous disease for which a dominant actionable molecular driver has not been identified. Patients with the stem cell-like EpCAM+AFP+ HCC subtype have poor prognosis. Here, we performed a genome-wide RNAi screen to identify genes with a synthetic lethal interaction with EpCAM as a potential therapeutic target for the EpCAM+AFP+ HCC subtype. We identified 26 candidate genes linked to EpCAM/Wnt/β-catenin signaling and HCC cell growth. We further characterized the top candidate PMPCB, which plays a role in mitochondrial protein processing, as a bona fide target for EpCAM+ HCC. PMPCB blockage suppressed EpCAM expression and Wnt/β-catenin signaling via mitochondria-related reactive oxygen species production and FOXO activities, resulting in apoptosis and tumor suppression. These results indicate that a synthetic lethality screen is a viable strategy to identify actionable drivers of HCC and identify PMPCB as a therapeutically vulnerable gene in EpCAM+ HCC subpopulations. SIGNIFICANCE: This study identifies PMPCB as critical to mitochondrial homeostasis and a synthetic lethal candidate that selectively kills highly resistant EpCAM+ HCC tumors by inactivating the Wnt/β-catenin signaling pathway.

Induction of Selenoprotein P mRNA during Hepatitis C Virus Infection Inhibits RIG-I-Mediated Antiviral Immunity

Patients infected with hepatitis C virus (HCV) have an increased risk of developing type 2 diabetes. HCV infection is linked to various liver abnormalities, potentially contributing to this association. We show that HCV infection increases the levels of hepatic selenoprotein P (SeP) mRNA (SEPP1 mRNA) and serum SeP, a hepatokine linked to insulin resistance. SEPP1 mRNA inhibits type I interferon responses by limiting the function of retinoic-acid-inducible gene I (RIG-I), a sensor of viral RNA. SEPP1 mRNA binds directly to RIG-I and inhibits its activity. SEPP1 mRNA knockdown in hepatocytes causes a robust induction of interferon-stimulated genes and decreases HCV replication. Clinically, high SeP serum levels are significantly associated with treatment failure of direct-acting antivirals in HCV-infected patients. Thus, SeP regulates insulin resistance and innate immunity, possibly inducing immune tolerance in the liver, and its upregulation may explain the increased risk of type 2 diabetes in HCV-infected patients.

Metformin induces the AP-1 transcription factor network in normal dermal fibroblasts

Metformin is a widely-used treatment for type 2 diabetes and is reported to extend health and lifespan as a caloric restriction (CR) mimetic. Although the benefits of metformin are well documented, the impact of this compound on the function and organization of the genome in normal tissues is unclear. To explore this impact, primary human fibroblasts were treated in culture with metformin resulting in a significant decrease in cell proliferation without evidence of cell death. Furthermore, metformin induced repositioning of chromosomes 10 and 18 within the nuclear volume indicating altered genome organization. Transcriptome analyses from RNA sequencing datasets revealed that alteration in growth profiles and chromosome positioning occurred concomitantly with changes in gene expression profiles. We further identified that different concentrations of metformin induced different transcript profiles; however, significant enrichment in the activator protein 1 (AP-1) transcription factor network was common between the different treatments. Comparative analyses revealed that metformin induced divergent changes in the transcriptome than that of rapamycin, another proposed mimetic of CR. Promoter analysis and chromatin immunoprecipitation assays of genes that changed expression in response to metformin revealed enrichment of the transcriptional regulator forkhead box O3a (FOXO3a) in normal human fibroblasts, but not of the predicted serum response factor (SRF). Therefore, we have demonstrated that metformin has significant impacts on genome organization and function in normal human fibroblasts, different from those of rapamycin, with FOXO3a likely playing a role in this response.

Identification of Novel Therapeutic Targets for Pulmonary Arterial Hypertension

Pulmonary arterial hypertension (PAH) and chronic thromboembolic pulmonary hypertension (CTEPH) are fatal diseases; however, their pathogenesis still remains to be elucidated. We have recently screened novel pathogenic molecules and have performed drug discovery targeting those molecules. Pulmonary artery smooth muscle cells (PASMCs) in patients with PAH (PAH-PASMCs) have high proliferative properties like cancer cells, which leads to thickening and narrowing of distal pulmonary arteries. Thus, we conducted a comprehensive analysis of PAH-PASMCs and lung tissues to search for novel pathogenic proteins. We validated the pathogenic role of the selected proteins by using tissue-specific knockout mice. To confirm its clinical significance, we used patient-derived blood samples to evaluate the potential as a biomarker for diagnosis and prognosis. Finally, we conducted a high throughput screening and found inhibitors for the pathogenic proteins.

Metformin-induced anticancer activities: recent insights

Metformin is a widely used antidiabetic drug, and there is evidence among diabetic patients that metformin is a chemopreventive agent against multiple cancers. There is also evidence in human studies that metformin is a cancer chemotherapeutic agent, and several clinical trials that use metformin alone or in combination with other drugs are ongoing. In vivo and in vitro cancer cell culture studies demonstrate that metformin induces both AMPK-dependent and AMPK-independent genes/pathways that result in inhibition of cancer cell growth and migration and induction of apoptosis. The effects of metformin in cancer cells resemble the patterns observed after treatment with drugs that downregulate specificity protein 1 (Sp1), Sp3 and Sp4 or by knockdown of Sp1, Sp3 and Sp4 by RNA interference. Studies in pancreatic cancer cells clearly demonstrate that metformin decreases expression of Sp1, Sp3, Sp4 and pro-oncogenic Sp-regulated genes, demonstrating that one of the underlying mechanisms of action of metformin as an anticancer agent involves targeting of Sp transcription factors. These observations are consistent with metformin-mediated effects on genes/pathways in many other tumor types.

Selenium, selenoprotein P, and Alzheimer's disease: is there a link?

The essential trace element, selenium (Se), is crucial to the brain but it may be potentially neurotoxic, depending on dosage and speciation; Se has been discussed for decades in relation to Alzheimer's disease (AD). Selenoprotein P (SELENOP) is a secreted heparin-binding glycoprotein which serves as the main Se transport protein in mammals. In vivo studies showed that this protein might have additional functions such as a contribution to redox regulation. The current review focuses on recent research on the possible role of SELENOP in AD pathology, based on model and human studies. The review also briefly summarizes results of epidemiological studies on Se supplementation in relation to brain diseases, including PREADViSE, EVA, and AIBL. Although mainly positive effects of Se are assessed in this review, possible detrimental effects of Se supplementation or exposure, including potential neurotoxicity, are also mentioned. In relation to AD, various roles of SELENOP are discussed, i.e. as the means of Se delivery to neurons, as an antioxidant, in cytoskeleton assembly, in interaction with redox-active metals (copper, iron, and mercury) and with misfolded proteins (amyloid-beta and hyperphosphorylated tau-protein).

The relationship between gestational diabetes mellitus and selenoprotein-P plasma 1 (SEPP1) gene polymorphisms

Our aim is to demonstrate any correlation between gestational diabetes mellitus (GDM) and polymorphism of the selenoprotein P (SEPP1) gene encoding the SEPP1 protein, having a role in the insulin resistance in GDM. Forty pregnant women with GDM and 40 healthy pregnant women were included in the study. In both groups, single nucleotide polymorphisms (SNPs), specifically, rs4987017, rs13154178, rs146125471, rs28919926, and rs16872762 were studied. There was no difference between the groups in terms of polymorphism rs146125471, rs28919926, or rs16872762 (p > .05). There was a significant difference in SNP rs13154178 polymorphism between the two groups (p < .01). When rs13154178 gene polymorphism was compared with AA homozygous individuals, fasting blood glucose levels were significantly higher in carriers of either polymorphism than in those with no polymorphism (p < .001). We suggest rs13154178 gene polymorphism may lead to GDM in the Turkish society.

Pathophysiological significance of hepatokine overproduction in type 2 diabetes

Currently, many studies draw attention to novel secretory factors, such as adipokines or myokines, derived from the tissues that were not originally recognized as endocrine organs. The liver may contribute to the onset of various kinds of pathologies of type 2 diabetes by way of the production of secretory proteins "hepatokines." Using the comprehensive gene expression analyses in human livers, we have rediscovered selenoprotein P and LECT2 as hepatokines involved in the onset of dysregulated glucose metabolism. Overproduction of selenoprotein P, previously reported as a transport protein of selenium, induces insulin resistance and hyperglycemia in type 2 diabetic condition. Selenoprotein P also contributes to vascular complications of type 2 diabetes directly by inducing VEGF resistance in vascular endothelial cells. Notably, selenoprotein P impairs health-promoting effects of exercise by inhibiting ROS/AMPK/PGC-1α pathway in the skeletal muscle through its receptor LRP1. Overproduction of LECT2, previously reported as a neutrophil chemotactic protein, links obesity to insulin resistance in the skeletal muscle. Further studies would develop novel diagnostic or therapeutic procedures targeting hepatokines to combat over-nutrition-related diseases such as type 2 diabetes.

Metformin induces FOXO3-dependent fetal hemoglobin production in human primary erythroid cells

Induction of red blood cell (RBC) fetal hemoglobin (HbF; α2γ2) ameliorates the pathophysiology of sickle cell disease (SCD) by reducing the concentration of sickle hemoglobin (HbS; α2β^S2) to inhibit its polymerization. Hydroxyurea (HU), the only US Food and Drug Administration (FDA)-approved drug for SCD, acts in part by inducing HbF; however, it is not fully effective, reflecting the need for new therapies. Whole-exome sequence analysis of rare genetic variants in SCD patients identified FOXO3 as a candidate regulator of RBC HbF. We validated these genomic findings through loss- and gain-of-function studies in normal human CD34⁺ hematopoietic stem and progenitor cells induced to undergo erythroid differentiation. FOXO3 gene silencing reduced γ-globin RNA levels and HbF levels in erythroblasts, whereas overexpression of FOXO3 produced the opposite effect. Moreover, treatment of primary CD34⁺ cell-derived erythroid cultures with metformin, an FDA-approved drug known to enhance FOXO3 activity in nonerythroid cells, caused dose-related FOXO3-dependent increases in the percentage of HbF protein and the fraction of HbF-immunostaining cells (F cells). Combined HU and metformin treatment induced HbF additively and reversed the arrest in erythroid maturation caused by HU treatment alone. HbF induction by metformin in erythroid precursors was dependent on FOXO3 expression and did not alter expression of BCL11A, MYB, or KLF1. Collectively, our data implicate FOXO3 as a positive regulator of γ-globin expression and identify metformin as a potential therapeutic agent for SCD.

Green tea extracts reduce leukocyte cell-Derived chemotaxin 2 and selenoprotein P levels in the livers of C57BL/6J mice fed a high-fat diet

Epidemiological studies suggest that green tea extracts (GTEs), including catechins such as epigallocatechin gallate and epicatechin gallate, have a beneficial effect on obesity, hyperglycemia, insulin resistance, endothelial dysfunction, and inflammation. Although several studies have shown that catechins directly modulate the cellular and molecular alterations in the liver tissue, the contributions of indirect mechanisms underlying these systemic effects of catechins remain unclear. In this study, we report that, in the C57BL/6J mouse liver, GTEs reduce high-fat diet-induced increases in the levels of hepatokines, liver-derived secretary proteins such as leukocyte cell-derived chemotaxin 2 and selenoprotein P production, which have been shown to induce systemic adverse effects, including several metabolic diseases. These findings suggest that the systemic effects of GTEs involve the regulation of hepatokine production as an indirect mechanism.

Association of expression of selenoprotein P in mRNA and protein levels with metabolic syndrome in subjects with cardiovascular disease: Results of the Selenegene study

BACKGROUND

Selenoprotein P (SeP) is involved in transporting selenium from the liver to target tissues. Because SeP confers protection against disease by reducing chronic oxidative stress, the present study aimed to assess the level of SeP in the serum of patients with metabolic syndrome (MetS) with a history of cardiovascular disease (CVD).

METHODS

A cross-sectional study was conducted in 63 and 71 subjects with and without MetS in the presence of documented CVD. All demographic, anthropometric and cardiometabolic variables (lipids, blood glucose, blood pressure) were assessed. Lifestyle-related factors and personal history and familial CVD risk factors were recorded. The expression of SELP in mRNA and protein levels in the serum was measured, and MetS was determined using ATPIII criteria. Binary logistic regression analysis demonstrated MetS and SeP to be dependent and independent variables, respectively.

RESULTS

Mean of systolic and diastolic blood pressure, triglyceride, high-density lipoprotein-cholesterol, fasting blood sugar, body mass index and waist circumference were higher among subjects with MetS (p = 0.05). The mean of selenium was higher among subjects with MetS, whereas the mean of SeP was lower among subjects with MetS (p < 0.001). In the unadjusted model, the SeP had decreased odds for MetS [odds ratio (OR) = 0.995; 95% confidence interval (CI) = 0.989-1.00] (p < 0.04). Furthermore, the association between MetS and SeP levels remained marginally significant even after adjusting for potential confounders such as age, gender, family history, smoking status and nutrition. SeP and waist circumference show a significant relationship (OR =0.995; 95% CI = 0.990-1.00) (p < 0.033).

CONCLUSIONS

We have demonstrated a significant decrease in circulating SeP levels according to MetS status in patients with documented cardiovascular disease.

Selenoprotein P-neutralizing antibodies improve insulin secretion and glucose sensitivity in type 2 diabetes mouse models

Selenoprotein P (SeP) functions as a selenium (Se)-supply protein. SeP is identified as a hepatokine, promoting insulin resistance in type 2 diabetes. Thus, the suppression of Se-supply activity of SeP might improve glucose metabolism. Here, we develop an anti-human SeP monoclonal antibody AE2 as with neutralizing activity against SeP. Administration of AE2 to mice significantly improves glucose intolerance and insulin resistance that are induced by human SeP administration. Furthermore, excess SeP administration significantly decreases pancreas insulin levels and high glucose-induced insulin secretion, which are improved by AE2 administration. Epitope mapping reveals that AE2 recognizes a region of human SeP adjacent to the first histidine-rich region (FHR). A polyclonal antibody against the mouse SeP FHR improves glucose intolerance and insulin secretion in a mouse model of diabetes. This report describes a novel molecular strategy for the development of type 2 diabetes therapeutics targeting SeP.

Selenoprotein P is secreted by the liver and when present in excess it promotes development of type 2 diabetes. Here the authors develop neutralizing antibodies to target human and mouse selenoprotein P, and show that they improve insulin secretion and glucose tolerance in mouse models.

AMPK activation ameliorates D-GalN/LPS-induced acute liver failure by upregulating Foxo3A to induce autophagy

BACKGROUND AND AIM

Acute liver failure (ALF) is an uncommon but serious disease still carrying a high mortality. This study aimed to investigate the mechanism of AMPK on D-GalN/LPS-induced ALF.

METHODS

In this study, we utilized intraperitoneal injection of D-GalN/LPS to induce ALF model, and analyzed the expression of AMPK, inflammatory cytokines (TNF-α, IL-1β and IL-6), Foxo3A and autophagy-related genes (Atg-5, Beclin-1, Atg-7) by real-time quantitative polymerase chain reaction (RT-PCR) in liver tissue. We also examined the level of alanine aminotransferase (ALT) and aspartate aminotransferase (AST) in serum of ALF mice. AMPK activation and inhibition of autophagy were induced by AICAR and 3-MA, respectively. Silence and overexpression of Foxo3A were performed by si-Foxo3A and pcDNA-Foxo3A, respectively. Lastly, the BMDM-conditioned medium (BMDM-CM) derived from BMDMs treated with AICAR and LPS were used to explore the effect of AMPK and Foxo3A on hepatocytes.

RESULT

The expression of AMPK was decreased in liver tissue and the level of ALT and AST were increased in serum of D-GalN/LPS-induced ALF mice. AMPK activation ameliorated ALF by inhibiting inflammation (downregulated TNF-α, IL-1β and IL-6 expression), activating autophagy (increased Atg-5, Beclin-1 and Atg-7 expression) and upregulating Foxo3A expression. Silence of Foxo3A decreased AMPK-activated autophagy, but overexpressing Foxo3A attenuated liver failure by activating autophagy. In addition, AMPK activation alleviated liver failure in vitro.

CONCLUSION

Thus, AMPK/Foxo3A/autophagy pathway may be an effective treatment approach to ameliorate ALF.

Eicosapentaenoic acid down-regulates expression of the selenoprotein P gene by inhibiting SREBP-1c protein independently of the AMP-activated protein kinase pathway in H4IIEC3 hepatocytes

Selenoprotein P (encoded by SELENOP in humans, Selenop in rat), a liver-derived secretory protein, induces resistance to insulin and vascular endothelial growth factor (VEGF) in type 2 diabetes. Suppression of selenoprotein P may provide a novel therapeutic approach to treating type 2 diabetes; however, few drugs inhibiting SELENOP expression in hepatocytes have been identified. The present findings demonstrate that eicosapentaenoic acid (EPA) suppresses SELENOP expression by inactivating sterol regulatory element-binding protein-1c (SREBP-1c, encoded by Srebf1 in rat) in H4IIEC3 hepatocytes. Treatment with EPA caused concentration- and time-dependent reduction in SELENOP promoter activity. EPA activated AMP-activated protein kinase (AMPK); however, the inhibitory effect of EPA on SELENOP promoter activity was not canceled with an AMPK inhibitor compound C and dominant-negative AMPK transfection. Deletion mutant promoter assays and computational analysis of transcription factor-binding sites conserved among the species resulted in identification of a sterol regulatory element (SRE)-like site in the SELENOP promoter. A chromatin immunoprecipitation (ChIP) assay revealed that EPA decreases binding of SREBP-1c to the SELENOP promoter. Knockdown of Srebf1 resulted in a significant down-regulation of Selenop expression. Conversely, SREBP-1c overexpression inhibited the suppressive effect of EPA. These data provide a novel mechanism of action for EPA involving improvement of systemic insulin sensitivity through the regulation of selenoprotein P production independently of the AMPK pathway and suggest an additional approach to developing anti-diabetic drugs.