Adipocyte DIO2 Expression Increases in Human Obesity but Is Not Related to Systemic Insulin Sensitivity

Understanding the Roles of Selenium on Thyroid Hormone-Induced Thermogenesis in Adipose Tissue

Brown adipose tissue (BAT) and white adipose tissue (WAT) are known to regulate lipid metabolism. A lower amount of BAT compared to WAT, along with adipose tissue dysfunction, can result in obesity. Studies have shown that selenium supplementation protects against adipocyte dysfunction, decreases WAT triglycerides, and increases BAT triiodothyronine (T3). In this review, we discuss the relationship between selenium and lipid metabolism regulation through selenoprotein deiodinases and the role of deiodinases and thyroid hormones in the induction of adipose tissue thermogenesis. Upon 22 studies included in our review, we found that studies investigating the relationship between selenium and deiodinases demonstrated that selenium supplementation affects the iodothyronine deiodinase 2 (DIO2) protein and the expression of its associated gene, DIO2, proportionally. However, its effect on DIO1 is inconsistent while its effect on DIO3 activity is not detected. Studies have shown that the activity of deiodinases especially DIO2 protein and DIO2 gene expression is increased along with other browning markers upon white adipose tissue browning induction. Studies showed that thermogenesis is stimulated by the thyroid hormone T3 as its activity is correlated to the expression of other thermogenesis markers. A proposed mechanism of thermogenesis induction in selenium supplementation is by autophagy control. However, more studies are needed to establish the role of T3 and autophagy in adipose tissue thermogenesis, especially, since some studies have shown that thermogenesis can function even when T3 activity is lacking and studies related to autophagy in adipose tissue thermogenesis have contradictory results.

Endoplasmic reticulum-resident selenoproteins and their roles in glucose and lipid metabolic disorders

Glucose and lipid metabolic disorders (GLMDs), such as diabetes, dyslipidemia, metabolic syndrome, nonalcoholic fatty liver disease, and obesity, are significant public health issues that negatively impact human health. The endoplasmic reticulum (ER) plays a crucial role at the cellular level for lipid and sterol biosynthesis, intracellular calcium storage, and protein post-translational modifications. Imbalance and dysfunction of the ER can affect glucose and lipid metabolism. As an essential trace element, selenium contributes to various human physiological functions mainly through 25 types of selenoproteins (SELENOs). At least 10 SELENOs, with experimental and/or computational evidence, are predominantly found on the ER membrane or within its lumen. Two iodothyronine deiodinases (DIOs), DIO1 and DIO2, regulate the thyroid hormone deiodination in the thyroid and some external thyroid tissues, influencing glucose and lipid metabolism. Most of the other eight members maintain redox homeostasis in the ER. Especially, SELENOF, SELENOM, and SELENOS are involved in unfolded protein responses; SELENOI catalyzes phosphatidylethanolamine synthesis; SELENOK, SELENON, and SELENOT participate in calcium homeostasis regulation; and the biological significance of thioredoxin reductase 3 in the ER remains unexplored despite its established function in the thioredoxin system. This review examines recent research advances regarding ER SELENOs in GLMDs and aims to provide insights on ER-related pathology through SELENOs regulation.

The correlation between iodine and metabolism: a review

Iodine is involved in the synthesis of thyroid hormones and plays a crucial role in human life. Both iodine deficiency and excess are common issues in certain populations. Iodine also has extrathyroidal effects on organs that can uptake it independently of thyroid hormones. Recently, multiple clinical studies have shown a connection between iodine intake and metabolic disorders, such as metabolic syndrome, obesity, diabetes, hypertension, and dyslipidemia. However, the results of these studies have been inconsistent, and the mechanisms behind these associations are still not well understood. Therefore, in this review, we aim to examine the recent research progress regarding the relationship between iodine and metabolic disorders, along with the relevant mechanisms.

Selenium and Selenoproteins in Health

Selenium is a trace mineral that is essential for health. After being obtained from food and taken up by the liver, selenium performs various physiological functions in the body in the form of selenoproteins, which are best known for their redox activity and anti-inflammatory properties. Selenium stimulates the activation of immune cells and is important for the activation of the immune system. Selenium is also essential for the maintenance of brain function. Selenium supplements can regulate lipid metabolism, cell apoptosis, and autophagy, and have displayed significant alleviating effects in most cardiovascular diseases. However, the effect of increased selenium intake on the risk of cancer remains unclear. Elevated serum selenium levels are associated with an increased risk of type 2 diabetes, and this relationship is complex and nonlinear. Selenium supplementation seems beneficial to some extent; however, existing studies have not fully explained the influence of selenium on various diseases. Further, more intervention trials are needed to verify the beneficial or harmful effects of selenium supplementation in various diseases.

Deiodinases control local cellular and systemic thyroid hormone availability

Iodothyronine deiodinases (DIO) are a family of selenoproteins controlling systemic and local availability of the major thyroid hormone l-thyroxine (T4), a prohormone secreted by the thyroid gland. T4 is activated to the active 3,3'-5-triiodothyronine (T3) by two 5'-deiodinases, DIO1 and DIO2. DIO3, a 5-deiodinase selenoenzyme inactivates both the prohormone T4 and its active form T3. DIOs show species-specific different patterns of temporo-spatial expression, regulation and function and exhibit different mechanisms of reaction and inhibitor sensitivities. The main regulators of DIO expression and function are the thyroid hormone status, several growth factors, cytokines and altered pathophysiological conditions. Selenium (Se) status has a modest impact on DIO expression and translation. DIOs rank high in the priority of selenium supply to various selenoproteins; thus, their function is impaired only during severe selenium deficiency. DIO variants, polymorphisms, SNPs and rare mutations have been identified. Development of DIO isozyme selective drugs is ongoing. A first X-ray structure has been reported for DIO3. This review focusses on the biochemical characteristics and reaction mechanisms, the relationships between DIO selenoproteins and their importance for local and systemic provision of the active hormone T3. Nutritional, pharmacological, and environmental factors and inhibitors, such as endocrine disruptors, impact DIO functions.

Selenium status and type 2 diabetes risk

Optimal selenium (Se) status is necessary for overall health. That status can be affected by food intake pattern, age, sex, and health status. At nutritional levels of intake, Se functions metabolically as an essential constituent of some two dozen selenoproteins, most, if not all, of which have redox functions. Insufficient dietary intake of Se reduces, to varying degrees, the expression of these selenoproteins. Recent clinical and animal studies have indicated that both insufficient and excessive Se intakes may increase risk of type 2 diabetes mellitus (T2D), perhaps by way of selenoprotein actions. In this review, we discuss the current evidence linking Se status and T2D risk, and the roles of 14 selenoproteins and other proteins involved in selenoprotein biosynthesis. Understanding such results can inform the setting of safe and adequate Se intakes.

Identification of potential models for predicting progestin insensitivity in patients with endometrial atypical hyperplasia and endometrioid endometrial cancer based on ATAC-Seq and RNA-Seq integrated analysis

Objective: The aim of this study was to establish predictive models based on the molecular profiles of endometrial lesions, which might help identify progestin-insensitive endometrial atypical hyperplasia (EAH) or endometrioid endometrial cancer (EEC) patients before progestin-based fertility-preserving treatment initiation.

Methods: Endometrial lesions from progestin-sensitive (PS, n = 7) and progestin-insensitive (PIS, n = 7) patients were prospectively collected before progestin treatment and then analyzed by ATAC-Seq and RNA-Seq. Potential chromatin accessibility and expression profiles were compared between the PS and PIS groups. Candidate genes were identified by bioinformatics analyses and literature review. Then expanded samples (n = 35) were used for validating bioinformatics data and conducting model establishment.

Results: ATAC-Seq and RNA-Seq data were separately analyzed and then integrated for the subsequent research. A total of 230 overlapping differentially expressed genes were acquired from ATAC-Seq and RNA-Seq integrated analysis. Further, based on GO analysis, REACTOME pathways, transcription factor prediction, motif enrichment, Cytoscape analysis and literature review, 25 candidate genes potentially associated with progestin insensitivity were identified. Finally, expanded samples were used for data verification, and based on these data, three predictive models comprising 9 genes (FOXO1, IRS2, PDGFC, DIO2, SOX9, BCL11A, APOE, FYN, and KLF4) were established with an overall predictive accuracy above 90%.

Conclusion: This study provided potential predictive models that might help identify progestin-insensitive EAH and EEC patients before fertility-preserving treatment.

Adipose Tissue and Skeletal Muscle Expression of Genes Associated with Thyroid Hormone Action in Obesity and Insulin Resistance

Background: Thyroid hormone (TH) regulates metabolic pathways which may interfere with insulin action. There is limited knowledge on adipose tissue (AT) and skeletal muscle (SM) expression of genes associated with TH action in relation to insulin sensitivity. The aim of this study was to analyze AT and SM expression of the genes associated with TH action in subjects with different degree of insulin sensitivity and the regulation of these genes by insulin and free fatty acids (FFA). Methods: The study group comprised 72 euthyroid male subjects: 36 normal weight subjects and 36 overweight/obese subjects. Two-hour hyperinsulinemic-euglycemic clamp and tissue biopsies were performed. In the subgroup of 20 subjects, 9 normal weight subjects and 11 overweight/obese subjects, clamp was prolonged to 6 hours and another clamp with Intralipid/heparin infusion was performed after 1 week. Tissue biopsies were performed before and after each clamp. Results: Overweight/obese subjects had higher AT DIO2, DIO3, and NCOR1, lower AT THRA and PPARGC1A, higher SM NCOR1, and lower SM DIO2, DIO3, PPARGC1A, and ATP2A2 expression. In AT, DIO2 and PPARGC1A increased, whereas NCOR1 and FOXO1 decreased after the clamp only in normal weight individuals. DIO3 decreased in both groups. In SM, NCOR1 decreased, whereas PPARGC1A and ATP2A2 increased after the clamp only in normal weight individuals. Tissue THRA and THRB decreased in both groups. Intralipid/heparin abolished these effects. Conclusions: Alterations in AT and SM expression of TH-related gene indicate a decreased tissue TH action in obesity. Inability to increase TH-related gene expression in obesity and during FFA oversupply may contribute to the aggravation of lipotoxicity.

Relationship between Serum Kallistatin and Afamin and Anthropometric Factors Associated with Obesity and of Being Overweight in Patients after Myocardial Infarction and without Myocardial Infarction

Extensive clinical and epidemiological evidence has linked obesity to a broad spectrum of cardiovascular disease (CVD), including coronary disease, heart failure, hypertension, cerebrovascular disease, atrial fibrillation, ventricular arrhythmias, and sudden death. In addition, increasing knowledge of regulatory peptides has allowed an assessment of their role in various non-communicable diseases, including CVD. The study assessed the concentration of kallistatin and afamin in the blood serum of patients after a myocardial infarction and without a cardiovascular event, and determined the relationship between the concentration of kallistatin and afamin and the anthropometric indicators of being overweight and of obesity in these groups. Serum kallistatin and afamin were quantified by ELISA tests in a cross-sectional study of 160 patients who were divided into two groups: study group (SG) (n = 80) and another with no cardiovascular event (CG) (n = 80). Serum kallistatin concentration was significantly higher in the SG (p < 0.001), while the level of afamin was significantly lower in this group (p < 0.001). In addition, a positive correlation was observed in the SG between the afamin concentration and the waist to hip ratio (WHR), lipid accumulation product (LAP) and the triglyceride glucose index (TyG index). In the CG, the concentration of kallistatin positively correlated with the LAP and TyG index, while the concentration of afamin positively correlated with all the examined parameters: body mass index (BMI), waist circumference (WC), hip circumference (HC), waist to hip ratio (WHtR), visceral adiposity index (VAI), LAP and TyG index. Serum kallistatin and afamin concentrations are associated with the anthropometric parameters related to being overweight and to obesity, especially to those describing the visceral distribution of adipose tissue and metabolic disorders related to excessive fatness.

Effect of exercise on peritoneal microenvironment and progression of ovarian cancer

Ovarian cancer is one of the deadliest gynecological malignancies and lacks treatments that do not significantly impact patient health-related quality of life. Exercise has been associated with reduced cancer risk and improved clinical outcomes; however the underlying molecular mechanisms are unknown. In this study, we utilized a treadmill-running exercise model to investigate the effects of exercise on high-grade serous ovarian carcinoma (HGSOC) progression and chemotherapy outcomes. We found that treadmill-running suppressed peritoneal colonization of tumors in a syngeneic mouse ovarian cancer model. Acute exercise stimulated the production of CCL2 and IL-15 in the peritoneal microenvironment while downregulating CCL22, VEGF, and CCL12. Using a co-culture model, we demonstrated the role of CCL2 in mediating the activity of peritoneal cells to inhibit cancer cell viability. We showed that the activation of M1 macrophages may contribute to the exercise-induced changes in the peritoneal microenvironment. We identified that chronic exercise modulates gene expression of intraperitoneal fat tissues related to lipid formation, thermogenesis, browning, and inflammation, which can contribute to inhibiting the colonization of metastatic ovarian cancer. Treadmill running also lowered blood urea nitrogen levels and reduced incidence of neutropenia and thrombocytopenia during chemotherapy in a mouse model, suggesting the potential beneficial effects of exercise in improving chemotherapy outcomes. Our data provided new insights into the acute and chronic effects of physical activity on ovarian cancer at the molecular and in vivo levels.

Selenium, as selenite, prevents adipogenesis by modulating selenoproteins gene expression and oxidative stress-related genes

OBJECTIVES

The aim of this study was to assess the effect of the micronutrient selenium, as inorganic selenite, on adipocytes differentiation, and to identify underlying molecular mechanisms to advance the understanding of basic cellular mechanisms associated with adipogenesis.

METHODS

The effect of sodium selenite (Na₂SeO₃) on cell viability (bromide 3-[4,5-dimethylthiazol-2-yl]-2,5-difeniltetrazol [MTT] assay) in preadipocytes, lipid accumulation (oil red O [ORO] assay) and intracellular reactive oxygen species (ROS, [NBT assay]) in mature adipocytes, as well as explore molecular mechanisms via gene expression analyses (real-time quantitative polymerase chain reaction), before and after differentiation, was investigated using 3T3-L1 murine preadipocytes.

RESULTS

Selenite (100, 200, and 400 nM) significantly decreased lipid accumulation during differentiation compared with untreated adipocytes (P < 0.05, 0.001, and 0.01, respectively). Preadipocytes exposure (48 h) to selenite caused an increase in glutathione peroxidase 1 (Gpx1) gene expression in a dose-dependent manner. Adipogenesis significantly increased intracellular reactive oxygen species levels (P < 0.05) while decreasing gene expression of antioxidant enzymes (Gpx1: P < 0.05) and significantly increasing gene expression of regulators of lipid catabolism (type II iodothyronine deiodinase [Dio2], P < 0.01) and markers of differentiation (eg, selenium-binding protein 1 [Selenbp1], peroxisome proliferator activated receptor gamma [Pparg], CCAAT/enhancer binding protein alpha [Cebpa], and fatty acid binding protein 4 [Fab4]) compared with preadipocytes (P < 0.01, 0.01, 0.01, and 0.001, respectively). Selenite exposure (200 nM) caused a significant increase in Gpx1, selenoprotein W (Selenow) and selenoprotein P (Selenop) gene expression, in adipocytes compared with untreated ones (P < 0.01, 0.001, and 0.05, respectively) with a significant decrease in heme oxygenase 1 (Ho-1), cyclooxygenase 2 (Cox2), Dio2, and Fabp4 gene expression (P < 0.001, 0.05, 0.05, and 0.01, respectively).

CONCLUSIONS

Selenium, as selenite, prevented adipogenesis through increasing antioxidant selenoprotein expression, leading to decreased inflammatory markers and, subsequently, to a decrease in differentiation and lipid deposition. These findings, if demonstrated in vivo, could provide valuable data for novel dietary approaches to prevent obesity.

Integrative analysis of histomorphology, transcriptome and whole genome resequencing identified DIO2 gene as a crucial gene for the protuberant knob located on forehead in geese

Background

During domestication, remarkable changes in behavior, morphology, physiology and production performance have taken place in farm animals. As one of the most economically important poultry, goose owns a unique appearance characteristic called knob, which is located at the base of the upper bill. However, neither the histomorphology nor the genetic mechanism of the knob phenotype has been revealed in geese.

Results

In the present study, integrated radiographic, histological, transcriptomic and genomic analyses revealed the histomorphological characteristics and genetic mechanism of goose knob. The knob skin was developed, and radiographic results demonstrated that the knob bone was obviously protuberant and pneumatized. Histologically, there were major differences in structures in both the knob skin and bone between geese owing knob (namely knob-geese) and those devoid of knob (namely non-knob geese). Through transcriptome analysis, 592 and 952 genes differentially expressed in knob skin and bone, and significantly enriched in PPAR and Calcium pathways in knob skin and bone, respectively, which revealed the molecular mechanisms of histomorphological differences of the knob between knob- and non-knob geese. Furthermore, integrated transcriptomic and genomic analysis contributed to the identification of 17 and 21 candidate genes associated with the knob formation in the skin and bone, respectively. Of them, DIO2 gene could play a pivotal role in determining the knob phenotype in geese. Because a non-synonymous mutation (c.642,923 G > A, P265L) changed DIO2 protein secondary structure in knob geese, and Sanger sequencing further showed that the AA genotype was identified in the population of knob geese, and was prevalent in a crossing population which was artificially selected for 10 generations.

Conclusions

This study was the first to uncover the knob histomorphological characteristics and genetic mechanism in geese, and DIO2 was identified as the crucial gene associated with the knob phenotype. These data not only expand and enrich our knowledge on the molecular mechanisms underlying the formation of head appendages in both mammalian and avian species, but also have important theoretical and practical significance for goose breeding.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12864-021-07822-9.

Growth performance, physiological parameters, and transcript levels of lipid metabolism-related genes in hybrid yellow catfish (Tachysurus fulvidraco ♀ × Pseudobagrus vachellii ♂) fed diets containing Siberian ginseng

In high-density aquaculture, fish health can suffer because of excessive feeding, which causes fatty liver disease. Siberian ginseng (Acanthopanax senticosus) has been used as a feed additive to promote animal growth, immunity, and lipid metabolism. In this study, we explored the effects of A. senticosus on the physiology of hybrid yellow catfish (Tachysurus fulvidraco ♀ × Pseudobagrus vachellii ♂). A control group and five groups fed diets containing A. senticosus (0.5, 1, 2, 4, and 8 g A. senticosus/kg feed) were established and maintained for 8 weeks. Dietary supplementation with A. senticosus at 4 g/kg promoted growth of the hybrid yellow catfish. Serum total cholesterol (TC) and triacylglycerol (TG) levels at 2 g/kg A. senticosus (TC: 1.31 mmol/L; TG: 1.08 mmol/L) were significantly lower than in the control group (TC: 1.51 mmol/L; TG: 1.41 mmol/L), and 4 g/kg A. senticosus (17.20 μmol/g tissue) reduced the liver TG level compared with the control group (21.36 μmol/g tissue) (P <0.05). Comparative transcriptomic analysis of liver tissue between the control group and the group showing optimum growth (4 g/kg A. senticosus) revealed 820 differentially expressed genes and 44 significantly enriched pathways, especially lipid metabolism pathways such as unsaturated fatty acid and fatty acid metabolism. The transcript levels of five lipid metabolism-related genes were determined by quantitative real-time PCR. The results showed that 2–4 g/kg A. senticosus supplementation reduced the FADS2, ELOVL2, CYP24a, and PLPP3 transcript levels and 4 g/kg A. senticosus increased the DIO2 transcript level (P <0.05), leading to altered synthesis of TG and thyroxine and reduced fat deposition in the liver. Our results show that dietary A. senticosus affects the regulation of fat metabolism and promotes the growth of hybrid yellow catfish. A. senticosus is a healthy feed additive, and the appropriate dietary supplementation rate is 2–4 g/kg.

Cardiac Autonomic Neuropathy: A Progressive Consequence of Chronic Low-Grade Inflammation in Type 2 Diabetes and Related Metabolic Disorders

Cardiac autonomic neuropathy (CAN) is one of the earliest complications of type 2 diabetes (T2D), presenting a silent cause of cardiovascular morbidity and mortality. Recent research relates the pathogenesis of cardiovascular disease in T2D to an ensuing chronic, low-grade proinflammatory and pro-oxidative environment, being the hallmark of the metabolic syndrome. Metabolic inflammation emerges as adipose tissue inflammatory changes extending systemically, on the advent of hyperglycemia, to reach central regions of the brain. In light of changes in glucose and insulin homeostasis, dysbiosis or alteration of the gut microbiome (GM) emerges, further contributing to inflammatory processes through increased gut and blood-brain barrier permeability. Interestingly, studies reveal that the determinants of oxidative stress and inflammation progression exist at the crossroad of CAN manifestations, dictating their evolution along the natural course of T2D development. Indeed, sympathetic and parasympathetic deterioration was shown to correlate with markers of adipose, vascular, and systemic inflammation. Additionally, evidence points out that dysbiosis could promote a sympatho-excitatory state through differentially affecting the secretion of hormones and neuromodulators, such as norepinephrine, serotonin, and γ-aminobutyric acid, and acting along the renin-angiotensin-aldosterone axis. Emerging neuronal inflammation and concomitant autophagic defects in brainstem nuclei were described as possible underlying mechanisms of CAN in experimental models of metabolic syndrome and T2D. Drugs with anti-inflammatory characteristics provide potential avenues for targeting pathways involved in CAN initiation and progression. The aim of this review is to delineate the etiology of CAN in the context of a metabolic disorder characterized by elevated oxidative and inflammatory load.

Emerging functions of adipokines in linking the development of obesity and cardiovascular diseases

Increasing evidence shows that obesity is the critical factor in shaping cardio-metabolic phenotypes. However, the pathogenic mechanisms remain incompletely clarified. According to the published reports, adipose tissue communicates with several diverse organs, such as heart, lungs, and kidneys through the secretion of various cytokines named adipokines. The adipocytes isolated from obese mice or humans are dysfunctional with aberrant production of pro-inflammatory adipokines, which subsequently induce both acute and chronic inflammatory reaction and facilitate the process of cardio-metabolic disorder complications. Furthermore, the microenvironment within adipose tissue under obese status also influence the secretion of adipokines. Recently, given that several important adipokines have been completely researched and causally involved in various diseases, we could make a conclusion that adipokines play an essential role in modulating the development of cardio-metabolic disorder diseases, whereas several novel adipokines continue to be explored and elucidated. In the present review, we summarized the current knowledge of the microenvironment of adipose tissue and the published mechanisms whereby adipocytes affects obesity and cardiovascular diseases. On the other hand, we also provide the evidence to elucidate the functions of adipokines in controlling and regulating the inflammatory reactions which contribute to obesity and cardiovascular disease.

Unique Genetic and Histological Signatures of Mouse Pericardial Adipose Tissue

Obesity is a major risk factor for a plethora of metabolic disturbances including diabetes and cardiovascular disease. Accumulating evidence is showing that there is an adipose tissue depot-dependent relationship with obesity-induced metabolic dysfunction. While some adipose depots, such as subcutaneous fat, are generally metabolically innocuous, others such as visceral fat, are directly deleterious. A lesser known visceral adipose depot is the pericardial adipose tissue depot. We therefore set out to examine its transcriptional and morphological signature under chow and high-fat fed conditions, in comparison with other adipose depots, using a mouse model. Our results revealed that under chow conditions pericardial adipose tissue has uncoupling-protein 1 gene expression levels which are significantly higher than classical subcutaneous and visceral adipose depots. We also observed that under high-fat diet conditions, the pericardial adipose depot exhibits greatly upregulated transcript levels of inflammatory cytokines. Our results collectively indicate, for the first time, that the pericardial adipose tissue possesses a unique transcriptional and histological signature which has features of both a beige (brown fat-like) but also pro-inflammatory depot, such as visceral fat. This unique profile may be involved in metabolic dysfunction associated with obesity.

Selenium and Selenoproteins in Adipose Tissue Physiology and Obesity

Selenium (Se) homeostasis is tightly related to carbohydrate and lipid metabolism, but its possible roles in obesity development and in adipocyte metabolism are unclear. The objective of the present study is to review the current data on Se status in obesity and to discuss the interference between Se and selenoprotein metabolism in adipocyte physiology and obesity pathogenesis. The overview and meta-analysis of the studies on blood Se and selenoprotein P (SELENOP) levels, as well as glutathione peroxidase (GPX) activity in obese subjects, have yielded heterogenous and even conflicting results. Laboratory studies demonstrate that Se may modulate preadipocyte proliferation and adipogenic differentiation, and also interfere with insulin signaling, and regulate lipolysis. Knockout models have demonstrated that the selenoprotein machinery, including endoplasmic reticulum-resident selenoproteins together with GPXs and thioredoxin reductases (TXNRDs), are tightly related to adipocyte development and functioning. In conclusion, Se and selenoproteins appear to play an essential role in adipose tissue physiology, although human data are inconsistent. Taken together, these findings do not support the utility of Se supplementation to prevent or alleviate obesity in humans. Further human and laboratory studies are required to elucidate associations between Se metabolism and obesity.

Beneficial Metabolic Effects of Chitosan and Chitosan Oligosaccharide on Epididymal WAT Browning and Thermogenesis in Obese Rats

Many anti-obesity chemicals have been withdrawn from the market due to serious adverse reactions, and the researchers have turned their attention to low-toxic natural products. Previous studies have demonstrated that chitosan (CTS) and chitosan oligosaccharide (COS) were low-toxic natural products for the use of weight loss. However, it is still unclear whether CTS and COS have positive effects on the thermogenesis. In this study, CTS and COS significantly reduced the weight gain of rats without affecting food intake and effectively inhibited adipose tissue hypertrophy and hyperplasia. Consistently, CTS and COS significantly increased the thermogenic capacity of obese rats induced by high-fat diet (HFD) and increased the expression of browning genes and proteins (UCP1, PGC1α, PRMD16, and ATF2) in white adipose tissue (WAT) and brown adipose tissue (BAT). In vitro, COS inhibited the formation of mature adipocytes and increased the expression of browning genes. In conclusion, COS and CTS was used to explore the function and mechanism on thermogenesis, and CTS and COS can increase the browning of WAT and the thermogenesis of BAT to inhibit obesity. This effect may be achieved by promoting the expression of browning and thermogenic genes, providing new ideas for the utilization of COS and CTS.