Association between betatrophin/ANGPTL8 and non-alcoholic fatty liver disease: Animal and human studies. Sci Rep. 2016;6:24013. [PMID: 27045862 PMCID: PMC4820743 DOI: 10.1038/srep24013]

Overview of studies of the vitamin D/vitamin D receptor system in the development of non-alcoholic fatty liver disease

Non-alcoholic fatty liver disease (NAFLD) is the most common chronic liver disease in the world. NAFLD is known to be associated with obesity, type 2 diabetes, metabolic syndrome and increased cardiovascular events: for these reasons, it is becoming a global public health problem and represents an important challenge in terms of prevention and treatment. The mechanisms behind the pathogenesis of NAFLD are multiple and have not yet been completely unraveled; consequently, at moment there are not effective treatments. In the past few years a large body of evidence has been assembled that attributes an important role in hepatic aberrant fat accumulation, inflammation and fibrosis, to the vitamin D/vitamin D receptor (VD/VDR) axis, showing a strong association between hypovitaminosis D and the diagnosis of NAFLD. However, the data currently available, including clinical trials with VD supplementation, still provides a contrasting picture. The purpose of this editorial is to provide an overview of recent advances in the pathogenesis of NAFLD in relation to VD/VDR. Based on recent data from literature, we focused in particular on the hypothesis that VDR itself, independently from its traditional ligand VD, may have a crucial function in promoting hepatic fat accumulation. This might also offer new possibilities for future innovative therapeutic approaches in the management of NAFLD.

Loss of Glycine N-Methyltransferase Associates with Angiopoietin-Like Protein 8 Expression in High Fat-Diet-Fed Mice

Imbalance of lipid metabolism is a main cause of metabolic syndrome leading to life-threatening metabolic diseases. Angiopoietin-like protein 8 (Angptl8) was recently identified as a liver and adipose tissue-released hormone that is one of the molecules involved in triglyceride metabolism. However, the regulatory mechanism of Angptl8 is largely unknown. A high fat diet (HFD)-fed mouse model, which showed high cholesterol, high triglyceride, and high insulin in the blood, revealed the upregulation of hepatic and plasma Angptl8 and the downregulation of hepatic glycine N-methyltransferase (GNMT). The inverse correlation of hepatic Angptl8 and GNMT expression in the livers of HFD-fed mice was also confirmed in a publicly available microarray dataset. The mechanistic study using primary hepatocytes showed that the Angptl8 expression could be induced by insulin treatment in a dose- and time-dependent manner. Inhibition of PI3K/Akt pathway by the specific inhibitors or the dominant-negative Akt blocked the insulin-induced Angptl8 expression. Moreover, knockout of GNMT promoted the Akt activation as well as the Angptl8 expression. These results suggested that GNMT might be involved in insulin-induced Angptl8 expression in HFD-mediated metabolic syndrome.

Angptl8 mediates food-driven resetting of hepatic circadian clock in mice

Diurnal light-dark cycle resets the master clock, while timed food intake is another potent synchronizer of peripheral clocks in mammals. As the largest metabolic organ, the liver sensitively responds to the food signals and secretes hepatokines, leading to the robust regulation of metabolic and clock processes. However, it remains unknown which hepatokine mediates the food-driven resetting of the liver clock independent of the master clock. Here, we identify Angptl8 as a hepatokine that resets diurnal rhythms of hepatic clock and metabolic genes in mice. Mechanistically, the resetting function of Angptl8 is dependent on the signal relay of the membrane receptor PirB, phosphorylation of kinases and transcriptional factors, and consequently transient activation of the central clock gene Per1. Importantly, inhibition of Angptl8 signaling partially blocks food-entrained resetting of liver clock in mice. We have thus identified Angptl8 as a key regulator of the liver clock in response to food.

Decreased circulating levels of ANGPTL8 in Graves' disease patients

BACKGROUND

Angiopoietin-like protein 8 (ANGPTL8), a newly identified hormone, has been recently characterized as a metabolic regulator which can affect energy homeostasis and has interesting potentials as a metabolic disease therapy. However, little is as yet known as to whether circulating ANGPTL8 levels are altered in thyroid dysfunction. This study measured serum ANGPTL8 levels in patients with Graves' disease and explored the correlations between its serum levels and thyroid index in Graves' disease.

METHODS

The concentration of ANGPTL8 was analyzed in blood samples of 128 well-characterized individuals whose anthropometric parameters, biochemical parameters, and thyroid index were measured. The participants were divided into Graves' disease patients (n = 60) and healthy control subjects (n = 68). Logistic regression was used to evaluate the relationship between ANGPTL8 and Graves' disease.

RESULTS

Serum ANGPTL8 levels were more significantly decreased in Graves' disease patients than in healthy control subjects (177.67 ± 135.07 vs 326.41 ± 194.72 pg/mL; p < 0.001). Serum ANGPTL8 was negatively correlated with free triiodothyronine (FT3), free thyroxine (FT4), and thyroid peroxidase antibodies (TPOAb) while being positively correlated with thyrotropin (TSH). Logistic regression analyses demonstrated that serum ANGPTL8 was significantly associated with Graves' disease (p < 0.05).

CONCLUSIONS

Circulating concentrations of ANGPTL8 showed a significant reduction in Graves' disease patients. Thus, it is suggested that thyroid function should be taken into consideration when evaluating the results of ANGPTL8.

Cucurbitacin I induces cancer cell death through the endoplasmic reticulum stress pathway

Endoplasmic reticulum stress (ERS) is usually involved in tumor development and progression, and anticancer agents have recently been recognized to induce ERS. Cucurbitacin-I showed a potent anticancer action by inducing apoptosis through the inhibition of signal transducer and activator of transcription 3 pathway and triggering autophagic cell death. It is not known whether ERS mediates the cancer cell death induced by cucurbitacin-I. Here, we investigated the role of ERS in cucurbitacin-I-treated SKOV3 ovarian cancer cells and PANC-1 pancreatic cancer cells. We confirmed that cucurbitacin-I caused cell death and stirred excessive ERS levels by activating inositol requiring enzyme 1α (IRE1α) and protein kinase R-like endoplasmic reticulum kinase (PERK), as well as PERK downstream factors, including IRE1α and C/EBP homologous protein, but not activating transcription factor 6 (ATF6α) pathway, which was in parallel with the increased Bax and caspase-12-dependent ERS-associated apoptosis, autophagy and autophagy flux levels and caspase-independent nonapoptotic cell death. Furthermore, 4-phenylbutyrate, an ERS inhibitor, suppressed cucurbitacin-I-induced apoptosis, autophagy, autophagy flux, and autophagic cell death. Simultaneously, there are positive correlations among ERS and cucurbitacin-I-induced reactive oxygen species and Ca ²⁺ . Our results suggested that cucurbitacin-I-induced cancer cell death through the excessive ERS and CHOP-Bax and caspase-12-dependent ERS-associated apoptosis, as well as ERS-dependent autophagy, autophagy flux, and caspase-independent nonapoptotic cell death. These novel signaling insights may be useful for developing new, effective anticancer strategies in oncotherapy.

Biological Pathways Leading From ANGPTL8 to Diabetes Mellitus-A Co-expression Network Based Analysis

Angiopoietin like protein 8 (ANGPTL8) is a newly identified hormone with unique nature due to its ability to regulate both glucose and lipid metabolic pathways. It is characterized as an important molecular player of insulin induced nutrient storage and utilization pathway during fasting to re-feeding metabolic transition. Several studies have contributed to increase our knowledge regarding its function and mechanism of action. Moreover, its altered expression levels have been observed in Insulin Resistance, Diabetes Mellitus (Types I & II) and Non Alcohlic Fatty Liver Disease emphasizing its assessment as a drug target. However, there is still a great deal of information that remains to be investigated including its associated biological processes, partner proteins in these processes, its regulators and its association with metabolic pathogenesis. In the current study, the analysis of a transcriptomic data set was performed for functional assessment of ANGPTL8 in liver. Weighted Gene Co-expression Network Analysis coupled with pathway analysis tools was performed to identify genes that are significantly co-expressed with ANGPTL8 in liver and investigate their presence in biological pathways. Gene ontology term enrichment analysis was performed to select the gene ontology classes that over-represent the hepatic ANGPTL8-co-expressed genes. Moreover, the presence of diabetes linked SNPs within the genes set co-expressed with ANGPTL8 was investigated. The co-expressed genes of ANGPTL8 identified in this study (n = 460) provides narrowed down list of molecular targets which are either co-regulated with it and/or might be regulation partners at different levels of interaction. These results are coherent with previously demonstrated roles and regulators of ANGPTL8. Specifically, thirteen co-expressed genes (MAPK8, CYP3A4, PIK3R2, PIK3R4,PRKAB2, G6PC, MAP3K11, FLOT1, PIK3C2G, SHC1, SLC16A2, and RAPGEF1) are also present in the literature curated pathway of ANGPTL8 (WP3915¹). Moreover, the gene-SNP analysis of highly associated biological processes with ANGPTL8 revealed significant genetic signals associated to Diabetes Mellitus and similar phenotypic traits. It provides meaningful insights on the influencing genes involved and co-expressed in these pathways. Findings of this study have implications in functional characterization of ANGPTL8 with emphasis on the identified genes and pathways and their possible involvement in the pathogenesis of Diabetes Mellitus and Insulin Resistance.

Angiopoietin-like 8 (ANGPTL8) expression is regulated by miR-143-3p in human hepatocytes

Angiopoietin-like protein 8 (ANGPTL8) is associated with reduced HDL-cholesterol levels and may contribute to the development of dyslipidemia. Factors regulating ANGPTL8 expression remain poorly understood. Here we analyzed the relationship between miRNA-143-3p and ANGPTL8 in liver cells. Using target prediction algorithms, we identified a putative binding site for miR-143-3p in the ANGPTL8 3' untranslated region (3'UTR). Exogenous miR-143-3p interacted with the ANGPTL8 3'UTR to downregulate its expression compared to scrambled sequence control. Transfection of HepG2 cells with miR-143-3p mimic or siRNA resulted in decreased or increased ANGPTL8 transcript and protein levels, respectively. Treatment of HepG2 cells with 30 mM glucose, 100 nM insulin, or 75 ng/ml lipopolysaccharide to mimic hyperglycemic, hyperinsulinemic, and proinflammatory conditions corresponded with increased miR-143-3p and ANGPTL8 levels. Inhibition of miR-143-3p amplified ANGPTL8 response to these treatments, suggesting that the miRNA acts to suppress ANGPTL8 expression under metabolically distorted conditions. These results, combined with growing evidence supporting a role for ANGPTL8 in the regulation of HDL-C metabolism, provide a better understanding of the molecular mechanisms underlying ANGPTL8 expression.

Betatrophin for diagnosis and prognosis of mothers with gestational diabetes mellitus

Objectives

Betatrophin is a widely used diagnostic marker for type 2 diabetes mellitus (DM), but its clinical utility in diagnosing gestational DM (GDM) is unclear. We evaluated the relationship between betatrophin and the risk of GDM as well as the ability of betatrophin to predict postpartum type 2 DM (PDM).

Methods

In total, 386 patients were categorized into those with and without PDM. All underwent the oral glucose tolerance test while pregnant. Betatrophin was assessed to examine the diagnostic characteristics of GDM.

Results

The betatrophin concentration was remarkably higher in patients with than without GDM. The patients were categorized into three groups; those with a betatrophin concentration of 300 to 600 pg/mL and >600 pg/mL had a higher risk of GDM after adjusting for body mass index, age, homeostatic model assessment–insulin resistance (HOMA-IR) concentration, and betatrophin concentration than those with a betatrophin concentration of <300 pg/mL. The HOMA-IR concentration tended to increase as the betatrophin concentration increased, and betatrophin was independently associated with GDM after adjusting for confounders. The betatrophin concentration was higher among pregnant patients with than without PDM.

Conclusions

Betatrophin has high sensitivity but low specificity for diagnosing GDM and may be a promising predictor of PDM.

Angiopoietin-Like Protein 8 Is a Novel Vitamin D Receptor Target Gene Involved in Nonalcoholic Fatty Liver Pathogenesis

Hepatic vitamin D receptor (VDR) expression is increased in patients with nonalcoholic fatty liver (NAFL) and is required for liver steatosis in an NAFL mouse model. However, how hepatocyte VDR is involved in setting up steatosis remains unclear. The authors transduced human hepatocyte-derived cells with an adenoviral vector encoding human VDR and found that angiopoietin-like protein 8 (ANGPTL8) expression was increased upon VDR activation by vitamin D or lithocholic acid. The mRNA levels of hepatic VDR- and vitamin D-related genes [cytochrome P450 (CYP) 2R1, CYP27A1, and CYP3A4] were higher in NAFL patients compared with normal liver subjects. Noteworthy, hepatic ANGPTL8 mRNA and protein levels were elevated in NAFL patients, and its mRNA correlated with VDR mRNA and with the steatosis grade. Moreover, increases in serum conjugated bile acids, including the VDR agonist glycine-lithocholic acid, were observed in NAFL patients. Additionally, free fatty acids and insulin were able to up-regulate both VDR and ANGPTL8 mRNA in human hepatocytes, whereas ANGPTL8 gene knockdown attenuated free fatty acids-induced triglyceride accumulation in these cells. In conclusion, activated VDR up-regulates ANGPTL8 expression, contributing to triglyceride accumulation in human hepatocytes. Moreover, hepatic ANGPTL8 mRNA positively correlates with VDR mRNA content and the grade of steatosis in NAFL patients, suggesting that this novel pathway may play a key role in the pathogenesis of hepatosteatosis.

CRISPR/Cas9-mediated Angptl8 knockout suppresses plasma triglyceride concentrations and adiposity in rats

Angiopoietin-like protein (ANGPTL)8 is a liver- and adipocyte-derived protein that controls plasma triglyceride (TG) levels. Most animal studies have used mouse models. Here, we generated an Angptl8 KO rat model using a clustered regulatory interspaced short palindromic repeat (CRISPR)/CRISPR-associated protein 9 (Cas9) (CRISPR/Cas9) system to clarify the roles of ANGPTL8 in glucose and lipid metabolism. Compared with WT rats, Angptl8 KO rats had lower body weight and fat content, associated with impaired lipogenesis in adipocytes; no differences existed between the groups in food intake or rectal temperature. Plasma TG levels in both the fasted and refed states were significantly lower in KO than in WT rats, and an oral fat tolerance test showed decreased plasma TG excursion in Angptl8 KO rats. Higher levels of lipase activity in the heart and greater expression of genes related to β-oxidation in heart and skeletal muscle were observed in Angptl8 KO rats. However, there were no significant differences between KO and WT rats in glucose metabolism or the histology of pancreatic β-cells on both standard and high-fat diets. In conclusion, we demonstrated that Angptl8 KO in rats resulted in lower body weight and plasma TG levels without affecting glucose metabolism. ANGPTL8 might be an important therapeutic target for obesity and dyslipidemia.

Association between circulating full-length angiopoietin-like protein 8 and non-high-density lipoprotein cholesterol levels in Chinese non-diabetic individuals: a cross-sectional study

Background

Angiopoietin-like protein 8 (ANGPTL8) is a novel hormone involved in the regulation of lipid metabolism and glucose homeostasis. There are inconsistent results regarding the association between ANGPTL8 and lipids in humans. We aimed to investigate the associations between ANGPTL8 and lipids in people without diabetes.

Methods

This was a cross-sectional study of 107 patients with dyslipidemia and 141 patients without. Dyslipidemia diagnosis was based on Chinese guidelines for the prevention and treatment of dyslipidemia in adults. Total cholesterol (TC), triglycerides (TG), low-density lipoprotein cholesterol, and high-density lipoprotein cholesterol (HDL-C) were examined. Non-HDL-C was calculated by subtracting HDL-C from TC. Circulating full-length ANGPTL8 concentrations were measured using enzyme-linked immunosorbent assay. Associations between log-transformed circulating full-length ANGPTL8 and serum lipids were examined using multivariate linear regression analysis.

Results

Circulating ANGPTL8 concentrations were significantly elevated in patients with dyslipidemia compared with patients without dyslipidemia. Circulating full-length ANGPTL8 concentrations were positively associated with non-HDL-C, TG and TC levels after adjusting for age, gender, body mass index, high-sensitivity C-reactive protein, alanine aminotransferase, and creatinine.

Conclusion

In people without diabetes, circulating full-length ANGPTL8 concentrations in patients with dyslipidemia were significantly elevated compared with non-dyslipidemia, and ANGPTL8 was positively associated with serum non-HDL-C levels.

Electronic supplementary material

The online version of this article (10.1186/s12944-018-0802-9) contains supplementary material, which is available to authorized users.

Apolipoprotein CIII may mediate the impacts of angiopoietin-like protein 8 on triglyceride metabolism

Background

Angiopoietin-like protein 8(ANGPTL8) and apolipoprotein CIII (apoCIII) were found to inhibit the activity of lipoprotein lipase (LPL) and disrupt the clearance of triglyceride-rich lipoproteins (TRLs), leading to hypertriglyceridemia. Whether any relationship exists between these two important modulators of triglyceride metabolism has not been reported. Besides, whether ANGPTL8 concentration is altered in the patients with coronary artery disease (CAD) is still unclear.

Methods

A hospital-based case-control study was conducted. Sixty-eight CAD subjects and fifty-two nonCAD controls were recruited. Plasma apoCIII, ANGPTL8 was measured.

Results

ANGPTL8 and apoCIII concentration exhibited no significant difference between CAD group and nonCAD group. Both ANGPTL8 and apoCIII were significantly correlated with triglyceride level(r = − 0.243, P = 0.008; r = 0.335, P < 0.001, respectively). Regression analysis revealed that apoCIII was an independent contributor to triglyceride level independent of ANGPTL8 concentration (standardized β = 0.230, P < 0.01).

Conclusion

ApoCIII may mediate the effects of ANGPTL8 on triglyceride metabolism.

Association of circulating ANGPTL 3, 4, and 8 levels with medical status in a population undergoing routine medical checkups: A cross-sectional study

Purpose

Angiopoietin-like proteins (ANGPTLs) 3, 4, and 8 reportedly contribute to progression of metabolic disease, a risk factor for cardiovascular disease (CVD). The purpose of this study was to investigate whether circulating ANGPTL levels are associated with CVD risk after adjustment for potential confounding factors.

Methods

We conducted a single center, cross-sectional study of 988 Japanese subjects undergoing routine health checks. Serum ANGPTL3, 4, and 8 levels were measured using an enzyme-linked immunosorbent assay. Using multiple regression analysis we evaluated potential association of circulating ANGPTL3, 4, and 8 levels with general medical status including age, sex, smoking, drinking, obesity, hypertension, impaired glycometabolism, dyslipidemia, hyperuricemia, hepatic impairment, chronic kidney disease, anemia, cardiac abnormality, and inflammation.

Results

Circulating ANGPTL3 levels were relatively high in health-related categories of hepatic impairment and inflammation. Circulating ANGPTL4 levels were also significantly high in impaired glycometabolism or hepatic impairment but decreased in inflammation. Finally, increased ANGPTL8 levels were observed in obesity, impaired glycometabolism and dyslipidemia. Particularly, increased levels of circulating ANGPTL8 were positively correlated with circulating triglycerides and LDL-cholesterol levels and inversely correlated with circulating HDL-cholesterol levels.

Conclusions

Circulating ANGPTL3, 4, and 8 levels reflect some risk factors for CVD development.

Serum Betatrophin Concentrations and the Risk of Incident Diabetes: A Nested Case-Control Study from Chungju Metabolic Disease Cohort

BACKGROUND

Betatrophin is a newly identified hormone derived from the liver and adipose tissue, which has been suggested to regulate glucose and lipid metabolism. Circulating levels of betatrophin are altered in various metabolic diseases, although the results are inconsistent. We aimed to examine whether betatrophin is a useful biomarker in predicting the development of diabetes.

METHODS

A nested case-control study was performed using a prospective Chungju Metabolic disease Cohort Study. During a 4-year follow-up period, we analyzed 167 individuals who converted to diabetes and 167 non-converters, who were matched by age, sex, and body mass index. Serum betatrophin levels were measured by an ELISA (enzyme-linked immunosorbent assay).

RESULTS

Baseline serum betatrophin levels were significantly higher in the converter group compared to the non-converter group (1,315±598 pg/mL vs. 1,072±446 pg/mL, P<0.001). After adjusting for age, sex, body mass index, fasting plasma glucose, systolic blood pressure, total cholesterol, and family history of diabetes, the risk of developing diabetes showed a stepwise increase across the betatrophin quartile groups. Subjects in the highest baseline quartile of betatrophin levels had more than a threefold higher risk of incident diabetes than the subjects in the lowest quartile (relative risk, 3.275; 95% confidence interval, 1.574 to 6.814; P=0.010). However, no significant relationships were observed between serum betatrophin levels and indices of insulin resistance or β-cell function.

CONCLUSION

Circulating levels of betatrophin could be a potential biomarker for predicting new-onset diabetes. Further studies are needed to understand the underlying mechanism of this association.

Angiopoietin-like protein 8/betatrophin correlates with hepatocellular lipid content independent of insulin resistance in non-alcoholic fatty liver disease patients

Aims/Introduction

To explore angiopoietin‐like protein 8 (ANGPTL‐8) levels, and its association with hepatocellular lipid content (HCL) and insulin resistance in patients with different extents of non‐alcoholic fatty liver disease (NAFLD).

Materials and Methods

In 48 adults were recruited, of which 12 had no NAFLD (HCL < 5.5%; group 1), 18 had mild NAFLD (5.5% ≤ HCL < 10.0%; group 2) and 18 had moderate‐to‐severe NAFLD (HCL ≥ 10.0%; group 3). The peripheral insulin sensitivity of all participants was monitored by a hyperinsulinemic‐euglycemic clamp (M value), as well as the magnetic resonance image of HCL. Serum ANGPTL‐8, blood glucose levels and lipid profiles were also recorded in the study.

Results

Group 3 had a worse metabolic profile, and had the highest ANGPTL‐8 level (1,129 ± 351 pg/mL vs 742 ± 252 pg/mL, 765 ± 301 pg/mL, P = 0.001) compared with those in group 1 and group 2. In all metabolic profiles, HCL positively correlated the strongest with ANGPTL‐8 (r = 0.436, P = 0.042). Multivariate stepwise linear regression analysis showed ANGPTL‐8 and alanine aminotransferase were independent determinants of HCL (P = 0.002, P < 0.001, respectively), and these two indexes explained 67.4% of the variation of HCL (P < 0.001).

Conclusions

ANGPTL‐8 was positively correlated with hepatocellular lipid content independent of obesity and insulin resistance, indicating that ANGPTL‐8 might be a new and important important predictor of the severity of NAFLD.

ANGPTL8: An Important Regulator in Metabolic Disorders

Long-term controversy regarding the role of angiopoietin-like protein 8 (ANGPTL8) in beta-cell proliferation and diabetes progression made it a research spotlight. Recently, the controversy was resolved. Although ANGPTL8 could not control beta-cell expansion and islet function, ANGPTL8 was still considered as a novel but atypical member in the ANGPTL family because of its unique structure and crucial effects on lipid metabolism. Besides, ANGPTL8 also participated in some other disorders such as non-alcoholic fatty liver disease and renal dysfunction. Understanding the features of ANGPTL8 may offer new diagnostic and therapeutic approaches to metabolic-related diseases. Therefore, we reviewed most recent findings about ANGPTL8 and aimed to provide an integrated picture of ANGPTL8.

High frequency of type 2 diabetes and impaired glucose tolerance in Japanese subjects with the angiopoietin-like protein 8 R59W variant

BACKGROUND

Angiopoietin-like protein 8 (ANGPTL8) is considered to be metabolically multifunctional. One notable function still to be elucidated definitively is a betatrophic role in protecting and preserving pancreatic beta-cell function. There is, however, a paucity of data regarding the role of ANGPTL8 in the etiology of type 2 diabetes (T2D), but some findings of human research have suggested the potential for significant involvement.

OBJECTIVE

To examine the frequency of T2D and impaired glucose tolerance (IGT) in Japanese subjects with the ANGPTL8 R59W variant.

METHODS

ANGPTL8 R59W (Rs2278426, c.194C > T) was determined by polymerase chain reaction-restriction fragment length polymorphism using the restriction enzyme FokI in 797 consecutive Japanese individuals. Subjects with triglyceride levels greater than or equal to 150 mg/dL were considered to be hypertriglyceridemic.

RESULTS

Genotype frequencies of ANGPTL8 R59W were as follows: wild-type RR (C/C) 53.5%, RW (C/T) 36.6%, and WW (T/T) 9.9%. T2D and IGT were significantly prevalent in WW and RW subjects relative to RR among all 797 subjects (P = .0138) and also in hypertriglyceridemic subjects (P = .0015). In multiple logistic regression models for the existence of T2D and IGT in hypertriglyceridemic subjects, the odds ratio for heterozygote RW and homozygote WW genotypes to wild-type RR was 2.406 (P = .0017) after controlling the risk factors of age, gender, and body mass index as covariates.

CONCLUSIONS

The frequency of ANGPTL8 R59W is significantly higher in Japanese subjects than in other ethnic groups. The rates of T2D and IGT were greater in subjects with the R59W variant. These findings indicate that ANGPTL8 is a participant in diabetes and a potential therapeutic target for T2D prevention, especially in East Asians.

ANGPTL8 negatively regulates NF-κB activation by facilitating selective autophagic degradation of IKKγ

Excessive nuclear factor-κB (NF-κB) activation mediated by tumor necrosis factor α (TNFα) plays a critical role in inflammation. Here we demonstrate that angiopoietin-like 8 (ANGPTL8) functions as a negative feedback regulator in TNFα-triggered NF-κB activation intracellularly. Inflammatory stimuli induce ANGPTL8 expression, and knockdown or knockout of ANGPTL8 potentiates TNFα-induced NF-κB activation in vitro. Mechanistically, upon TNFα stimulation, ANGPTL8 facilitates the interaction of IKKγ with p62 via forming a complex, thus promoting the selective autophagic degradation of IKKγ. Furthermore, the N-terminal domain mediated self-oligomerization of ANGPTL8 is essential for IKKγ degradation and NF-κB activation. In vivo, circulating ANGPTL8 level is high in patients diagnosed with infectious diseases, and the ANGPTL8/p62-IKKγ axis is responsive to inflammatory stimuli in the liver of LPS-injected mice. Altogether, our study suggests the ANGPTL8/p62-IKKγ axis as a negative feedback loop that regulates NF-κB activation, and extends the role of selective autophagy in fine-tuned inflammatory responses.

NF-κB activation mediated by TNFα has a critical role in inflammation; however, the underlying mechanisms await further investigation. Here the authors show that selective autophagy regulates NF-κB activation via an ANGPTL8/p62-IKKγ signaling axis.

Angiopoietin-like protein 8: An attractive biomarker for the evaluation of subjects with insulin resistance and related disorders

Insulin resistance is prevalent worldwide and is associated with many metabolic diseases, in particular, type 2 diabetes mellitus (T2DM), obesity, nonalcoholic fatty liver disease (NAFLD), polycystic ovary syndrome (PCOS) and metabolic syndrome (MetS). Angiopoietin-like protein 8 (ANGPTL8), a newly-identified secreted protein composing of 198 amino acids, is enriched in the liver of human. Considering its promising potential for β-cell proliferation and therapeutic prospect for diabetes, ANGPTL8 has aroused extensive interests. However, a recent collaborative study confirmed that ANGPTL8 didn't stimulate dramatic β-cell regeneration. At present, a controversial scientific discussion on whether and how ANGPTL8 regulate insulin resistance has been ongoing. Interestingly, several in vitro and in vivo studies have suggested the complex roles of ANGPTL8 in insulin resistance. Data resulting from cross-sectional and longitudinal researches in human individuals involving the influence of ANGPTL8 on the development of insulin resistance were controversial. We therefore summarize currently clinical literature to exploit whether this exciting hormone could be applied for clinical application asa potential clinical biomarker to predict insulin resistance and related disorders.

Trans-ancestry Fine Mapping and Molecular Assays Identify Regulatory Variants at the ANGPTL8 HDL-C GWAS Locus

Recent genome-wide association studies (GWAS) have identified variants associated with high-density lipoprotein cholesterol (HDL-C) located in or near the ANGPTL8 gene. Given the extensive sharing of GWAS loci across populations, we hypothesized that at least one shared variant at this locus affects HDL-C. The HDL-C–associated variants are coincident with expression quantitative trait loci for ANGPTL8 and DOCK6 in subcutaneous adipose tissue; however, only ANGPTL8 expression levels are associated with HDL-C levels. We identified a 400-bp promoter region of ANGPTL8 and enhancer regions within 5 kb that contribute to regulating expression in liver and adipose. To identify variants functionally responsible for the HDL-C association, we performed fine-mapping analyses and selected 13 candidate variants that overlap putative regulatory regions to test for allelic differences in regulatory function. Of these variants, rs12463177-G increased transcriptional activity (1.5-fold, P = 0.004) and showed differential protein binding. Six additional variants (rs17699089, rs200788077, rs56322906, rs3760782, rs737337, and rs3745683) showed evidence of allelic differences in transcriptional activity and/or protein binding. Taken together, these data suggest a regulatory mechanism at the ANGPTL8 HDL-C GWAS locus involving tissue-selective expression and at least one functional variant.

Circulating angiopoietin-like 8 (ANGPTL8) is a marker of liver steatosis and is negatively regulated by Prader-Willi Syndrome

ANGPTL8 is a liver-derived protein related to insulin-sensitivity. Its relationship with obesity and liver function in Prader-Willi syndrome (PWS) is unknown. The present study investigated circulating ANGPTL8 in PWS and controls with common obesity, assessing its association to liver steatosis. For this purpose, 20 obese PWS and 20 controls matched for body mass index (BMI), sex and age underwent analysis of ANGPTL8 levels, glucose and lipid metabolism. Liver function tests and degree of liver steatosis by ultrasonography (US), fat-free mass (FFM) and fat mass (FM) by dual-energy x-ray absorptiometry (DEXA) were also assessed. In comparison to controls, obese PWS showed lower values of FFM (p < 0.0001) and higher FM (p = 0.01), while harbouring higher HDL cholesterol, lower triglycerides and OGTT-derived insulin levels, as well as a lower prevalence and severity of liver steatosis. With respect to obese controls, ANGPTL8 levels were significantly lower in PWS (p = 0.007) and overall correlated with transaminase levels and the severity of liver steatosis, as well as FFM (p < 0.05 for all). By a stepwise multivariable regression analysis, ANGPTL8 levels were independently predicted by PWS status (p = 0.01) and liver steatosis (p < 0.05). In conclusion, ANGPTL8 levels are lower in PWS than obese controls and are inversely associated with the severity of liver steatosis. Further studies should investigate the potential genetic basis for this observation.

Relationship of Serum Betatrophin with Nonalcoholic Fatty Liver in a Chinese Population

OBJECTIVE

This study aimed to investigate the association of serum betatrophin with the status and progression of nonalcoholic fatty liver disease (NAFLD).

METHODS

A total of 249 subjects who received ultrasonic examination of liver fat content (LFC) were recruited. Anthropometric and biochemical examinations were performed. Serum betatrophin was measured by ELISA.

RESULTS

Compared with control group, serum betatrophin significantly increased in NAFLD group (P < 0.05). There was significant difference in serum betatrophin among control, low liver fat content (LLFC), and high liver fat content (HLFC) groups (P < 0.01). After adjustment for gender, age, BMI, FPG and HbA1c, the betatrophin positively correlated with LFC (r = 0.185, P < 0.01) and TG (r = 0.195, P < 0.01). Stepwise multiple regression analysis indicated serum betatrophin was independently related to LFC (P < 0.05). Multivariate logistic regression analysis revealed subjects in the highest tertile of serum betatrophin had higher odds of having NAFLD after adjustment for traditional NAFLD risk factors (OR = 2.88, 95%CI: 1.15-7.19) (P<0.05).

CONCLUSION

Serum betatrophin is an independent risk factor for NAFLD and potential non-invasive marker for its progression. Serum betatrophin may be helpful for the early diagnosis of NAFLD and improvement of its prognosis.

Vitamin D modifies the associations between circulating betatrophin and cardiometabolic risk factors among youths at risk for metabolic syndrome

Background

Betatrophin has been recently reported to play a role in glucose homeostasis by inducing beta-cell proliferation in mice. However, studies in human are inconsistent. As a nutritionally-regulated liver-enriched factor, we hypothesize that betatrophin might be regulated by vitamin D, and ignorance of vitamin D status may explain the discrepancy in previous human studies. The aims of this study were to assess the association between circulating betatrophin and glucose homeostasis as well as other cardiometabolic variables in a cohort of youths at risk for metabolic syndrome and test the possible influence of vitamin D status on the association.

Methods

559 subjects aged 14–28 years were recruited from Beijing children and adolescents metabolic syndrome study. All underwent a 2 h-oral glucose tolerance test. Serum levels of betatrophin, 25-hydroxy-vitamin D as well as adipokines including adiponectin and fibroblast growth factor 21 (FGF21) were measured by immunoassays. The relationships between betatrophin and insulin resistance, beta-cell function, other cardiometabolic variables and vitamin D status were evaluated.

Results

Participants in the highest quartile of betatrophin levels had the highest levels of total cholesterol (P < 0.001), triglyceride (P < 0.001) and low-density lipoprotein cholesterol (P < 0.001) and the lowest levels of vitamin D (P = 0.003). After stratification by vitamin D status, betatrophin in subjects with vitamin D deficiency were positively correlated with unfavorable metabolic profiles including high blood pressures, dyslipidemia and hyperglycemia, whereas betatrophin in those with higher vitamin D levels only showed negative association with fasting insulin, 2 h-insulin, and insulin resistance. In addition, adiponectin and FGF21 demonstrated the expected associations with metabolic parameters.

Conclusions

Elevated betatrophin levels were associated with cardiometabolic risk factors in this young population, but the association was largely dependent on vitamin D status. These findings may provide valuable insights in the regulation of betatrophin and help explain the observed discrepancies in literature.

Electronic supplementary material

The online version of this article (doi:10.1186/s12933-016-0461-y) contains supplementary material, which is available to authorized users.

Increased angiopoietin-like protein 8 levels in patients with type 2 diabetes and cardiovascular disease

In the present study, we recruited 124 patients with type 2 diabetes, among which 22 had a history of cardiovascular disease (CVD). The study demonstrated that compared with type 2 diabetes without CVD, those with CVD had remarkably higher levels of angiopoietin-like protein 8 (ANGPTL8). Moreover, the close relationship between ANGPTL8 and CVD was independent of conventional CVD risk factors.