Hypoxia-inducible factor-3alpha functions as an accelerator of 3T3-L1 adipose differentiation

Mint3 as a Potential Target for Cooling Down HIF-1α-Mediated Inflammation and Cancer Aggressiveness

Hypoxia-inducible factor-1α (HIF-1α) is a transcription factor that plays a crucial role in cells adapting to a low-oxygen environment by facilitating a switch from oxygen-dependent ATP production to glycolysis. Mediated by membrane type-1 matrix metalloproteinase (MT1-MMP) expression, Munc-18-1 interacting protein 3 (Mint3) binds to the factor inhibiting HIF-1 (FIH-1) and inhibits its suppressive effect, leading to HIF-1α activation. Defects in Mint3 generally lead to improved acute inflammation, which is regulated by HIF-1α and subsequent glycolysis, as well as the suppression of the proliferation and metastasis of cancer cells directly through its expression in cancer cells and indirectly through its expression in macrophages or fibroblasts associated with cancer. Mint3 in inflammatory monocytes enhances the chemotaxis into metastatic sites and the production of vascular endothelial growth factors, which leads to the expression of E-selectin at the metastatic sites and the extravasation of cancer cells. Fibroblasts express L1 cell adhesion molecules in a Mint3-dependent manner and enhance integrin-mediated cancer progression. In pancreatic cancer cells, Mint3 directly promotes cancer progression. Naphthofluorescein, a Mint3 inhibitor, can disrupt the interaction between FIH-1 and Mint3 and potently suppress Mint3-mediated inflammation, cancer progression, and metastasis without causing marked adverse effects. In this review, we will introduce the potential of Mint3 as a therapeutic target for inflammatory diseases and cancers.

The role of maternal DNA methylation in pregnancies complicated by gestational diabetes

Diabetes in pregnancy is associated with adverse pregnancy outcomes and poses a serious threat to the health of mother and child. Although the pathophysiological mechanisms that underlie the association between maternal diabetes and pregnancy complications have not yet been elucidated, it has been suggested that the frequency and severity of pregnancy complications are linked to the degree of hyperglycemia. Epigenetic mechanisms reflect gene-environment interactions and have emerged as key players in metabolic adaptation to pregnancy and the development of complications. DNA methylation, the best characterized epigenetic mechanism, has been reported to be dysregulated during various pregnancy complications, including pre-eclampsia, hypertension, diabetes, early pregnancy loss and preterm birth. The identification of altered DNA methylation patterns may serve to elucidate the pathophysiological mechanisms that underlie the different types of maternal diabetes during pregnancy. This review aims to provide a summary of existing knowledge on DNA methylation patterns in pregnancies complicated by pregestational type 1 (T1DM) and type 2 diabetes mellitus (T2DM), and gestational diabetes mellitus (GDM). Four databases, CINAHL, Scopus, PubMed and Google Scholar, were searched for studies on DNA methylation profiling in pregnancies complicated with diabetes. A total of 1985 articles were identified, of which 32 met the inclusion criteria and are included in this review. All studies profiled DNA methylation during GDM or impaired glucose tolerance (IGT), while no studies investigated T1DM or T2DM. We highlight the increased methylation of two genes, Hypoxia‐inducible Factor‐3α (HIF3α) and Peroxisome Proliferator-activated Receptor Gamma-coactivator-Alpha (PGC1-α), and the decreased methylation of one gene, Peroxisome Proliferator Activated Receptor Alpha (PPARα), in women with GDM compared to pregnant women with normoglycemia that were consistently methylated across diverse populations with varying pregnancy durations, and using different diagnostic criteria, methodologies and biological sources. These findings support the candidacy of these three differentially methylated genes as biomarkers for GDM. Furthermore, these genes may provide insight into the pathways that are epigenetically influenced during maternal diabetes and which should be prioritized and replicated in longitudinal studies and in larger populations to ensure their clinical applicability. Finally, we discuss the challenges and limitations of DNA methylation analysis, and the need for DNA methylation profiling to be conducted in different types of maternal diabetes in pregnancy.

Association between the Extent of Peripheral Blood DNA Methylation of HIF3A and Accumulation of Adiposity in community-dwelling Women: The Yakumo Study

INTRODUCTION

DNA methylation in the CpG sites of intron 1 of HIF3A is associated with body mass index (BMI). This cross-sectional study investigated correlations between DNA methylation of HIF3A and BMI or adiposity parameters in the Japanese population.

METHOD

DNA methylation of HIF3A was quantified via pyrosequencing.

RESULT

DNA methylation of HIF3A differed only in women; DNA methylation level at cg27146050 was associated with visceral adipose tissue thickness and correlated with BMI and percent (%) body fat after excluding smokers.

CONCLUSION

Peripheral blood DNA methylation at the CpG site (cg27146050) of HIF3A correlated with VAT thickness in Japanese women.

Genetic variants of the hypoxia-inducible factor 3 alpha subunit (Hif3a) gene in the Fat and Lean mouse selection lines

BACKGROUND

Adipose tissue hypoxia and members of the hypoxia-inducible factor alpha (HIFA) are involved in development of obesity. However, the mechanism and functions of HIF3A, one of three HIFA paralogs, in fat deposition have not been sufficiently studied.

METHODS AND RESULTS

In the present study, we investigated whether Hif3a sequence variants are associated with divergent fat deposition in mouse selection lines for fatness and leanness. Sequencing and RFLP were used to analyse sequence variants within Hif3a. To identify candidate regulatory variants, we performed literature screening and used databases and bioinformatics tools like Ensembl, MethPrimer, TargetScanMouse, miRDB, PolyAsite, RISE, LncRRIsearch, RNAfold, PredictProtein, CAIcal, and switches.ELM Resource. There are 90 sequence variants in Hif3a between the two mouse lines. While most Fat line variants locate within intronic regions, Lean line variants are mainly in 3' UTR. We constructed a map of Hif3a potential regulatory regions and identified 39 regulatory variants by integrating data on constrained and regulatory elements, CpGs, and miRNAs and lncRNAs binding sites. Moreover, 3' UTR and two exonic variants may influence mRNA stability, translation rate and protein functionality. We propose as priority candidates for further functional studies a missense (rs37398126) and synonymous (rs37739792) variants, and intronic (rs47471302) variant that overlap conserved element in promoter region and predicted lncRNAs binding site.

CONCLUSION

The results indicate a potential involvement of Hif3a in fat deposition. Additionally, approach used in the present study may serve as a general guideline for constructing an integrative gene map for prioritizing candidate gene variants with phenotypic effects.

HIF3A Inhibition Triggers Browning of White Adipocytes via Metabolic Rewiring

Maintenance of energy balance between intake and expenditure is a prerequisite of human health, disrupted in severe metabolic diseases, such as obesity and type 2 diabetes (T2D), mainly due to accumulation of white adipose tissue (WAT). WAT undergoes a morphological and energetic remodelling toward brown adipose tissue (BAT) and the BAT activation has anti-obesity potential. The mechanisms or the regulatory factors able to activate BAT thermogenesis have been only partially deciphered. Identifying novel regulators of BAT induction is a question of great importance for fighting obesity and T2D. Here, we evaluated the role of Hif3α in murine pre-adipocyte 3T3-L1 cell line, a versatile and well characterized biological model of adipogenesis, by gain- and loss-of function approaches and in thermogenesis-induced model in vivo. HIF3A is regulated by inflammation, it modulates lypolysis in adipose tissue of obese adults, but its role in energy metabolism has not previously been investigated. We characterized gene and protein expression patterns of adipogenesis and metabolic activity in vitro and mechanistically in vivo. Overexpression of Hif3α in differentiating adipocytes increases white fat cells, whereas silencing of Hif3α promotes “browning” of white cells, activating thermogenesis through upregulation of Ucp1, Elovl3, Prdm16, Dio2 and Ppargc1a genes. Investigating cell metabolism, Seahorse Real-Time Cell Metabolism Analysis showed that silencing of Hif3α resulted in a significant increase of mitochondrial uncoupling with a concomitant increase in acetyl-CoA metabolism and Sirt1 and Sirt3 expression. The causal Hif3α/Ucp1 inverse relation has been validated in Cannabinoid receptor 1 (CB1) knockout, a thermogenesis-induced model in vivo. Our data indicate that Hif3α inhibition triggers “browning” of white adipocytes activating the beneficial thermogenesis rewiring energy metabolism in vitro and in vivo. HIF3A is a novel player that controls the energy metabolism with potential applications in developing therapy to fight metabolic disorders, as obesity, T2D and ultimately cancer.

Berberine improves insulin resistance in adipocyte models by regulating the methylation of hypoxia-inducible factor-3α

Methylation of hypoxia-inducible factor-3α (HIF3A) was previously demonstrated to be highly associated with insulin resistance (IR) in patients with gestational diabetes mellitus (GDM). We aimed to study the therapeutic effects of Berberine (BBR) on GDM and the possible mechanisms. The expressions and methylated states of HIF3A in pregnant women with GDM were compared with that in healthy controls. The IR cell models of 3T3-L1 adipocytes was constructed by 1 μmol/l dexamethasone (Dex) and 1 μmol/l insulin (Ins). To evaluate the effects of BBR on IR adipocyte models, cells were subjected to BBR treatment at different concentrations. Transfection of HIF3A siRNA further confirmed the role of HIF3A in the BBR-induced improving effects. Low expression and high methylation of HIF3A gene were frequent in the GDM pregnancies. BBR treatment noticeably increased the glucose usage rates, adiponectin secretion and cell differentiation of IR 3T3-L1 adipocytes. Increased HIF3A expression and decreased methylated state of HIF3A were also found in IR adipocytes. Furthermore, HIF3A silencing not only reversed the effects of BBR on improving insulin sensibility, but also partially abolished the expression alterations of insulin-related genes in IR adipocytes induced by BBR treatment. Our results suggest that BBR improves insulin sensibility in IR adipocyte models, and the improving effects of BBR are possibly realized through the inhibition of HIF3A methylation.

Gene Deletion of Calcium-Independent Phospholipase A2γ (iPLA2γ) Suppresses Adipogenic Differentiation of Mouse Embryonic Fibroblasts

Adipogenic differentiation is a complex process by which fibroblast-like undifferentiated cells are converted into cells that accumulate lipid droplets. We here investigated the effect of gene deletion of calcium-independent phospholipase A₂γ (iPLA₂γ), a membrane-bound PLA₂ enzyme, on adipogenic differentiation in mice. Since iPLA₂γ knockout (KO) mice showed reduced fat volume and weight, we prepared mouse embryonic fibroblasts (MEF) from wild-type (WT) and iPLA₂γ KO mice and examined the effect of iPLA₂γ deletion on in vitro adipogenic differentiation. iPLA₂γ increased during adipogenic differentiation in WT mouse-derived MEFs, and the differentiation was partially abolished in iPLA₂γ KO-derived MEFs. In KO-derived MEFs, the inductions of peroxisome proliferator activator receptor γ (PPARγ) and CAAT/enhancer-binding protein α (C/EBPα) were also reduced during adipogenic differentiation, and the reductions in PPARγ and C/EBPα expressions and the defect in adipogenesis were restored by treatment with troglitazone, a PPARγ ligand. These results indicate that iPLA₂γ might play a critical role in adipogenic differentiation by regulating PPARγ expression.

Genome-wide association study of adipocyte lipolysis in the GENetics of adipocyte lipolysis (GENiAL) cohort

OBJECTIVES

Lipolysis, hydrolysis of triglycerides to fatty acids in adipocytes, is tightly regulated, poorly understood, and, if perturbed, can lead to metabolic diseases including obesity and type 2 diabetes. The goal of this study was to identify the genetic regulators of lipolysis and elucidate their molecular mechanisms.

METHODS

Adipocytes from abdominal subcutaneous adipose tissue biopsies were isolated and were incubated without (spontaneous lipolysis) or with a catecholamine (stimulated lipolysis) to analyze lipolysis. DNA was extracted and genome-wide genotyping and imputation conducted. After quality control, 939 samples with genetic and lipolysis data were available. Genome-wide association studies of spontaneous and stimulated lipolysis were conducted. Subsequent in vitro gene expression analyses were used to identify candidate genes and explore their regulation of adipose tissue biology.

RESULTS

One locus on chromosome 19 demonstrated genome-wide significance with spontaneous lipolysis. 60 loci showed suggestive associations with spontaneous or stimulated lipolysis, of which many influenced both traits. In the chromosome 19 locus, only HIF3A was expressed in the adipocytes and displayed genotype-dependent gene expression. HIF3A knockdown in vitro increased lipolysis and the expression of key lipolysis-regulating genes.

CONCLUSIONS

In conclusion, we identified a genetic regulator of spontaneous lipolysis and provided evidence of HIF3A as a novel key regulator of lipolysis in subcutaneous adipocytes as the mechanism through which the locus influences adipose tissue biology.

Early-life determinants of hypoxia-inducible factor 3A gene (HIF3A) methylation: a birth cohort study

Background

Methylation of the hypoxia-inducible factor 3α gene (HIF3A) has been linked to pregnancy exposures, infant adiposity and later BMI. Genetic variation influences HIF3A methylation levels and may modify these relationships. However, data in very early life are limited, particularly in association with adverse pregnancy outcomes. We investigated the relationship between maternal and gestational factors, infant anthropometry, genetic variation and HIF3A DNA methylation in the Barwon Infant Study, a population-based birth cohort. Methylation of two previously studied regions of HIF3A were tested in the cord blood mononuclear cells of 938 infants.

Results

No compelling evidence was found of an association between birth weight, adiposity or maternal gestational diabetes with methylation at the most widely studied HIF3A region. Male sex (− 4.3%, p < 0.001) and pre-eclampsia (− 5.4%, p = 0.02) negatively associated with methylation at a second region of HIF3A; while positive associations were identified for gestational diabetes (4.8%, p = 0.01) and gestational age (1.2% increase per week, p < 0.001). HIF3A genetic variation also associated strongly with methylation at this region (p < 0.001).

Conclusions

Pre- and perinatal factors impact HIF3A methylation, including pre-eclampsia. This provides evidence that specific pregnancy complications, previously linked to adverse outcomes for both mother and child, impact the infant epigenome in a molecular pathway critical to several vascular and metabolic conditions. Further work is required to understand the mechanisms and clinical relevance, particularly the differing effects of in utero exposure to gestational diabetes or pre-eclampsia.

Electronic supplementary material

The online version of this article (10.1186/s13148-019-0687-0) contains supplementary material, which is available to authorized users.

The transcriptional factors HIF-1 and HIF-2 and their novel inhibitors in cancer therapy

Introduction: Hypoxia is one of the intrinsic features of solid tumors, and it is always associated with aggressive phenotypes, including resistance to radiation and chemotherapy, metastasis, and poor patient prognosis. Hypoxia manifests these unfavorable effects through activation of a family of transcription factors, Hypoxia-inducible factors (HIFs) play a pivotal role in the adaptation of tumor cells to hypoxic and nutrient-deprived conditions by upregulating the transcription of several pro-oncogenic genes. Several advanced human cancers share HIFs activation as a final common pathway. Areas covered: This review highlights the role and regulation of the HIF-1/2 in cancers and alludes on the biological complexity and redundancy of HIF-1/2 regulation. Moreover, this review summarizes recent insights into the therapeutic approaches targeting the HIF-1/2 pathway. Expert opinion: More studies are needed to unravel the extensive complexity of HIFs regulation and to develop more precise anticancer treatments. Inclusion of HIF-1/2 inhibitors to the current chemotherapy regimens has been proven advantageous in numerous reported preclinical studies. The combination therapy ideally should be personalized based on the type of mutations involved in the specific cancers, and it might be better to include two drugs that inhibit HIF-1/2 activity by synergistic molecular mechanisms.

Genome-wide methylation study of whole blood cells DNA in men with congenital hypopituitarism disease

Congenital hypopituitarism (CH) is a relatively rare disease that is characterized by the deficiency of one or more hormones secreted by the pituitary gland, which leads to metabolic disorders, amenorrhea and infertility. However, the underlying molecular mechanisms of CH have not yet been fully elucidated. The present study evaluated the genome-wide methylation level of whole blood DNA in 12 patients with CH and 12 age-matched controls using Illumina Human Methylation 450 array, in order to determine the roles of epigenetic regulation in the pathogenesis of CH. The results demonstrated that the methylation levels of 51 CpG sites were significantly different between the patients with CH and the controls. Functional enrichment analysis identified that the aberrant methylated genes were enriched in gene sets associated with metabolic or cellular process, immune system process and reproduction. In addition, two CpG sites on genes LIM domain kinase 2 (LIMK2) and piwi-like RNA-mediated gene silencing 2 (PIWIL2), which are involved in spermatogenesis and/or testicular development, were identified to be hypermethylated in male patients with CH. The hypermethylation of these sites was further validated in another 40 patients with CH and 40 matched controls with a quantitative bisulfite pyrosequencing method, and the methylation levels of these two loci demonstrated promising diagnostic capacities for CH. The present results suggested that aberrant methylation of genes may be involved in the pathogenesis of CH, and hypermethylation of LIMK2 and PIWIL2 may contribute to the infertility of male patients with CH. Further studies are required to elucidate the underlying mechanisms of the epigenetic regulation of these genes.

Interaction between plasma homocysteine and the MTHFR c.677C > T polymorphism is associated with site-specific changes in DNA methylation in humans

One-carbon metabolism provides a direct link among dietary folate/vitamin B₁₂ exposure, the activity of the enzyme methylenetetrahydrofolate reductase (MTHFR), and epigenetic regulation of the genome via DNA methylation. Previously, it has been shown that the common c.677C > T polymorphism in MTHFR influences global DNA methylation status through a direct interaction with folate status and (indirectly) with total homocysteine (tHcy) levels. To build on that and other more recent observations that have further highlighted associations among MTHFR c.677C > T, tHcy, and aberrations in DNA methylation, we investigated whether the interaction between mildly elevated plasma tHcy and the c.677C > T polymorphism is associated with site-specific changes in DNA methylation in humans. We used data on plasma tHcy levels, c.677C > T polymorphism, and site-specific DNA methylation levels for a total of 915 white women and 335 men from the TwinsUK registry ( n = 610) and the Rotterdam study ( n = 670). We performed methylome-wide association analyses in each cohort to model the interaction between levels of tHcy and c.677C > T genotypes on DNA methylation β values. Our meta-analysis identified 13 probes significantly associated with rs1801133 × tHcy levels [false-discovery rate (FDR) < 0.05]. The most significant associations were with a cluster of probes at the AGTRAP-MTHFR-NPPA/B gene locus on chromosome 1 (FDR = 1.3E-04), with additional probes on chromosomes 2, 3, 4, 7, 12, 16, and 19. Our top 2 hits on chromosome 1 were functionally associated with variability in expression of the TNF receptor superfamily member 8 ( TNFRSF8) gene/locus on that chromosome. This is the first study, to our knowledge, to provide a direct link between perturbations in 1-carbon metabolism, through an interaction of tHcy and the activity of MTHFR enzyme on epigenetic regulation of the genome via DNA methylation.-Nash, A. J., Mandaviya, P. R., Dib, M.-J., Uitterlinden, A. G., van Meurs, J., Heil, S. G., Andrew, T., Ahmadi, K. R. Interaction between plasma homocysteine and the MTHFR c.677C>T polymorphism is associated with site-specific changes in DNA methylation in humans.

Down-Regulation of EPAS1 Transcription and Genetic Adaptation of Tibetans to High-Altitude Hypoxia

Tibetans are well adapted to the hypoxic environments at high altitude, yet the molecular mechanism of this adaptation remains elusive. We reported comprehensive genetic and functional analyses of EPAS1, a gene encoding hypoxia inducible factor 2α (HIF-2α) with the strongest signal of selection in previous genome-wide scans of Tibetans. We showed that the Tibetan-enriched EPAS1 variants down-regulate expression in human umbilical endothelial cells and placentas. Heterozygous EPAS1 knockout mice display blunted physiological responses to chronic hypoxia, mirroring the situation in Tibetans. Furthermore, we found that the Tibetan version of EPAS1 is not only associated with the relatively low hemoglobin level as a polycythemia protectant, but also is associated with a low pulmonary vasoconstriction response in Tibetans. We propose that the down-regulation of EPAS1 contributes to the molecular basis of Tibetans’ adaption to high-altitude hypoxia.

Positive correlation of cg16672562 methylation with obesity-related traits in childhood obesity, and its independence with underlying HIF3A (hypoxia-inducible factor 3a) genetic background

Differential methylations of the HIF3A (hypoxia-inducible factor 3a) gene have been linked to body mass index (BMI). To explore the association of these methylations to childhood obesity, we measured 5 CpG methylation sites (cg27146050, cg46801562, cg22891070, cg16672562 and cg46801675) in intron 1 of the HIF3A gene by pyrosequencing, in the Korean population (mean age: 13.9 yrs, 305 obese cases and 387 controls). Two CpG methylations, cg46801562 and cg16672562, had statistically significant association with childhood obesity (P = 2.09E-9 and 1.66E-7, respectively). Notably, in the case of cg16672562, all correlations were significantly positive with BMI (beta = 0.285, P = 1.652E-13), waist-hip ratio (beta = 0.0028, P = 1.42E-15) and fasting plasma glucose level (beta = 0.0645, P = 2.61E-4), when analyzed by linear regression, with age and sex as covariates. We investigated any genetic effect of cg16672562 methylation by using 14 single nucleotide polymorphisms (SNP) identified by exome sequencing of the HIF3A locus cg16672562 methylation showed no statistically significant changes due to the 14 polymorphisms. In this study, we show that cg16672562 is the most significant blood DNA methylation marker for childhood obesity in the Korean population, and might be independent of any underlying HIF3A genetic background.

Recent progress in genetics, epigenetics and metagenomics unveils the pathophysiology of human obesity

In high-, middle- and low-income countries, the rising prevalence of obesity is the underlying cause of numerous health complications and increased mortality. Being a complex and heritable disorder, obesity results from the interplay between genetic susceptibility, epigenetics, metagenomics and the environment. Attempts at understanding the genetic basis of obesity have identified numerous genes associated with syndromic monogenic, non-syndromic monogenic, oligogenic and polygenic obesity. The genetics of leanness are also considered relevant as it mirrors some of obesity's aetiologies. In this report, we summarize ten genetically elucidated obesity syndromes, some of which are involved in ciliary functioning. We comprehensively review 11 monogenic obesity genes identified to date and their role in energy maintenance as part of the leptin-melanocortin pathway. With the emergence of genome-wide association studies over the last decade, 227 genetic variants involved in different biological pathways (central nervous system, food sensing and digestion, adipocyte differentiation, insulin signalling, lipid metabolism, muscle and liver biology, gut microbiota) have been associated with polygenic obesity. Advances in obligatory and facilitated epigenetic variation, and gene-environment interaction studies have partly accounted for the missing heritability of obesity and provided additional insight into its aetiology. The role of gut microbiota in obesity pathophysiology, as well as the 12 genes associated with lipodystrophies is discussed. Furthermore, in an attempt to improve future studies and merge the gap between research and clinical practice, we provide suggestions on how high-throughput '-omic' data can be integrated in order to get closer to the new age of personalized medicine.

Epigenetic signatures of gestational diabetes mellitus on cord blood methylation

Background

Intrauterine exposure to gestational diabetes mellitus (GDM) confers a lifelong increased risk for metabolic and other complex disorders to the offspring. GDM-induced epigenetic modifications modulating gene regulation and persisting into later life are generally assumed to mediate these elevated disease susceptibilities. To identify candidate genes for fetal programming, we compared genome-wide methylation patterns of fetal cord bloods (FCBs) from GDM and control pregnancies.

Methods and results

Using Illumina’s 450K methylation arrays and following correction for multiple testing, 65 CpG sites (52 associated with genes) displayed significant methylation differences between GDM and control samples. Four candidate genes, ATP5A1, MFAP4, PRKCH, and SLC17A4, from our methylation screen and one, HIF3A, from the literature were validated by bisulfite pyrosequencing. The effects remained significant after adjustment for the confounding factors maternal BMI, gestational week, and fetal sex in a multivariate regression model. In general, GDM effects on FCB methylation were more pronounced in women with insulin-dependent GDM who had a more severe metabolic phenotype than women with dietetically treated GDM.

Conclusions

Our study supports an association between maternal GDM and the epigenetic status of the exposed offspring. Consistent with a multifactorial disease model, the observed FCB methylation changes are of small effect size but affect multiple genes/loci. The identified genes are primary candidates for transmitting GDM effects to the next generation. They also may provide useful biomarkers for the diagnosis, prognosis, and treatment of adverse prenatal exposures.

Electronic supplementary material

The online version of this article (doi:10.1186/s13148-017-0329-3) contains supplementary material, which is available to authorized users.

Endothelial Dysfunction in Obesity

Chronic inflammatory state in obesity causes dysregulation of the endocrine and paracrine actions of adipocyte-derived factors, which disrupt vascular homeostasis and contribute to endothelial vasodilator dysfunction and subsequent hypertension. While normal healthy perivascular adipose tissue (PVAT) ensures the dilation of blood vessels, obesity-associated PVAT leads to a change in profile of the released adipo-cytokines, resulting in a decreased vasorelaxing effect. Adipose tissue inflammation, nitric oxide (NO)-bioavailability, insulin resistance and oxidized low-density lipoprotein (oxLDL) are main participating factors in endothelial dysfunction of obesity. In this chapter, disruption of inter-endothelial junctions between endothelial cells, significant increase in the production of reactive oxygen species (ROS), inflammation mediators, which are originated from inflamed endothelial cells, the balance between NO synthesis and ROS , insulin signaling and NO production, and decrease in L-arginine/endogenous asymmetric dimethyl-L-arginine (ADMA) ratio are discussed in connection with endothelial dysfunction in obesity.

Gender Differences in Adipocyte Metabolism and Liver Cancer Progression

Liver cancer is the third most common cancer type and the second leading cause of deaths in men. Large population studies have demonstrated remarkable gender disparities in the incidence and the cumulative risk of liver cancer. A number of emerging risk factors regarding metabolic alterations associated with obesity, diabetes and dyslipidemia have been ascribed to the progression of non-alcoholic fatty liver diseases (NAFLD) and ultimately liver cancer. The deregulation of fat metabolism derived from excessive insulin, glucose, and lipid promotes cancer-causing inflammatory signaling and oxidative stress, which eventually triggers the uncontrolled hepatocellular proliferation. This review presents the current standing on the gender differences in body fat compositions and their mechanistic linkage with the development of NAFLD-related liver cancer, with an emphasis on genetic, epigenetic and microRNA control. The potential roles of sex hormones in instructing adipocyte metabolic programs may help unravel the mechanisms underlying gender dimorphism in liver cancer and identify the metabolic targets for disease management.

DNA methylation and gene expression of HIF3A: cross-tissue validation and associations with BMI and insulin resistance

Background

Associations between BMI and DNA methylation of hypoxia-inducible factor 3-alpha (HIF3A) in both blood cells and subcutaneous adipose tissue (SAT) have been reported. In this study, we investigated associations between BMI and HIF3A DNA methylation in the blood and SAT from the same individuals, and whether HIF3A gene expression in SAT and skeletal muscle biopsies showed associations with BMI and insulin resistance. Furthermore, we aimed to investigate gender specificity and heritability of these traits.

Methods

We studied 137 first-degree relatives of type 2 diabetes (T2D) patients from 48 families, from whom we had SAT and muscle biopsies. DNA methylation of four CpG sites in the HIF3A promoter was analyzed in the blood and SAT by pyrosequencing, and HIF3A gene expression was analyzed in SAT and muscle by qPCR. An index of whole-body insulin sensitivity was estimated from oral glucose tolerance tests.

Results

BMI was associated with HIF3A methylation at one CpG site in the blood, and there was a positive association between the blood and SAT methylation levels at a different CpG site within the individuals. The SAT methylation level did not correlate with HIF3A gene expression. Interestingly, HIF3A expression in SAT, but not in muscle, associated negatively with BMI and whole-body insulin resistance. We found a significant effect of familiality on HIF3A methylation levels in the blood and HIF3A expression levels in skeletal muscle.

Conclusions

Our findings are in line with the previously reported link between BMI and DNA methylation of HIF3A in the blood. The tissue-specific results of HIF3A gene expression indicate that SAT is the more functional tissue in which a low expression may adversely affect whole-body insulin sensitivity.

Electronic supplementary material

The online version of this article (doi:10.1186/s13148-016-0258-6) contains supplementary material, which is available to authorized users.

Hypoxia-inducible factor 3A gene expression and methylation in adipose tissue is related to adipose tissue dysfunction

Recently, a genome-wide analysis identified DNA methylation of the HIF3A (hypoxia-inducible factor 3A) as strongest correlate of BMI. Here we tested the hypothesis that HIF3A mRNA expression and CpG-sites methylation in adipose tissue (AT) and genetic variants in HIF3A are related to parameters of AT distribution and function. In paired samples of subcutaneous AT (SAT) and visceral AT (VAT) from 603 individuals, we measured HIF3A mRNA expression and analyzed its correlation with obesity and related traits. In subgroups of individuals, we investigated the effects on HIF3A genetic variants on its AT expression (N = 603) and methylation of CpG-sites (N = 87). HIF3A expression was significantly higher in SAT compared to VAT and correlated with obesity and parameters of AT dysfunction (including CRP and leucocytes count). HIF3A methylation at cg22891070 was significantly higher in VAT compared to SAT and correlated with BMI, abdominal SAT and VAT area. Rs8102595 showed a nominal significant association with AT HIF3A methylation levels as well as with obesity and fat distribution. HIF3A expression and methylation in AT are fat depot specific, related to obesity and AT dysfunction. Our data support the hypothesis that HIF pathways may play an important role in the development of AT dysfunction in obesity.

Expression of hypoxia-inducible factor 3α in hepatocellular carcinoma and its association with other hypoxia-inducible factors

The functional role of hypoxia-inducible factor (HIF)-3α in the development of hepatocellular carcinoma (HCC) is not yet fully understood. The aim of the present study was to elucidate the association between HIF-3α expression and the clinicopathological features as well as prognosis of HCC patients. In addition, we investigated the association between HIF-3α expression and the expression of HIF-1α and HIF-2α in tumor tissues. The protein levels of HIF-3α were determined using immunohistochemical analysis of paraffin sections of 126 paired HCC and peritumoral tissues. PLC/PRF/5 cells, a human HCC cell line, were transfected with HIF-1α and HIF-2α vectors and HIF-3α mRNA and protein expression was detected using quantitative polymerase chain reaction and western blot analysis, respectively. The expression of HIF-3α was upregulated in 46.0% (58/126) and downregulated in 42.9% (54/126) of tumor tissues, respectively, when compared to peritumoral tissues. HIF-3α protein expression was not associated with peripheral blood vessel invasion, overall survival, or disease-free survival in HCC patients (P>0.05). In HCC tissues, the levels of HIF-3α protein were positively correlated with HIF-2α, but not with HIF-1α expression in HCC tissues. HIF-3α was upregulated in PLC/PRF/5 and Hep3B cells overexpressed with HIF-1α or HIF-2α. The hypoxic microenvironment of liver cancer did not lead to elevated HIF-3α protein expression, indicating that HIF-3α is regulated differently from HIF-1α in vivo. The correlation between HIF-3α and HIF-2α expression at the cellular and tissue levels indicated that HIF-3α may be a target gene of HIF-2α. The hypoxic microenvironment did not lead to elevation of HIF-3α protein expression in liver cancer; thus, HIF-3α may be a target gene of HIF-2α.

Hypoxia-inducible factor 3 biology: complexities and emerging themes

The hypoxia-inducible factor (HIF) family has three distinct members in most vertebrates. All three HIFs consist of a unique and oxygen-labile α-subunit and a common and stable β-subunit. While HIF-1 and HIF-2 function as master regulators of the transcriptional response to hypoxia, much less is known about HIF-3. The HIF-3α gene gives rise to multiple HIF-3α variants due to the utilization of different promoters, different transcription initiation sites, and alternative splicing. These HIF-3α variants are expressed in different tissues, at different developmental stages, and are differentially regulated by hypoxia and other factors. Recent studies suggest that different HIF-3α variants have different and even opposite functions. There is strong evidence that full-length HIF-3α protein functions as an oxygen-regulated transcription activator and that it activates a unique transcriptional program in response to hypoxia. Many HIF-3α target genes have been identified. While some short HIF-3α variants act as dominant-negative regulators of HIF-1/2α actions, other HIF-3α variants can inhibit HIF-1/2α actions by competing for the common HIF-β. There are also a number of HIF-3α variants yet to be explored. Future studies of these naturally occurring HIF-3α variants will provide new and important insights into HIF biology and may lead to the development of new therapeutic strategies.

HIF3A DNA Methylation Is Associated with Childhood Obesity and ALT

Gene polymorphisms associated so far with body mass index (BMI) can explain only 1.18–1.45% of observed variation in BMI. Recent studies suggest that epigenetic modifications, especially DNA methylation, could contribute to explain part of the missing heritability, and two epigenetic genome-wide analysis studies (EWAS) have reported that Hypoxia Inducible Factor 3 Alpha Subunit (HIF3A) methylation was associated with BMI or BMI change. We therefore assessed whether the HIF3A methylation is associated with obesity and other obesity-related phenotypes in Chinese children. The subjects included 110 severe obese cases aged 7–17y and 110 normal-weight controls matched by age and gender for measurement of blood DNA methylation levels at the HIF3A gene locus using the Sequenom’s MassARRAY system. We observed significantly higher methylation levels in obese children than in controls at positions 46801642 and 46801699 in HIF3A gene (P<0.05), and found positive associations between methylation and alanine aminotransferase (ALT) levels adjusted by gender, age and BMI at the position 46801699 (r = 0.226, P = 0.007). These results suggest that HIF3A DNA methylation is associated with childhood obesity, and has a BMI-independent association with ALT. The results provide evidence for identifying epigenetic factors of elivated ALT and may be useful for risk assessment and personalized medicine of liver diseases such as non-alcoholic fatty liver disease (NAFLD).

HIF3α: the little we know

Hypoxia-inducible factors (HIFs) are key regulators of the transcriptional response to hypoxic stress. Three inducible isoforms of HIF are present in mammals. HIF1α and HIF2α are the best characterized and structurally similar isoforms, while HIF3α is the most distantly related and is less studied. The HIF3α gene undergoes complex regulation and produces a large number of long and short mRNA splice variants, which are translated into different polypeptides. These molecules primarily act as negative regulators of HIF1α and HIF2α activity and transcriptional activators of target genes, according to the variant and the biological context. The present review provides an overview of the available, fragmented and sometimes contradictory information concerning the structure, expression and distinct roles of the HIF3α variants, in both hypoxic adaptation and in hypoxia-unrelated activities. The pathological consequences of HIF3α deregulation are also illustrated.

Epigenome-wide association study (EWAS) of BMI, BMI change and waist circumference in African American adults identifies multiple replicated loci

Obesity is an important component of the pathophysiology of chronic diseases. Identifying epigenetic modifications associated with elevated adiposity, including DNA methylation variation, may point to genomic pathways that are dysregulated in numerous conditions. The Illumina 450K Bead Chip array was used to assay DNA methylation in leukocyte DNA obtained from 2097 African American adults in the Atherosclerosis Risk in Communities (ARIC) study. Mixed-effects regression models were used to test the association of methylation beta value with concurrent body mass index (BMI) and waist circumference (WC), and BMI change, adjusting for batch effects and potential confounders. Replication using whole-blood DNA from 2377 White adults in the Framingham Heart Study and CD4+ T cell DNA from 991 Whites in the Genetics of Lipid Lowering Drugs and Diet Network Study was followed by testing using adipose tissue DNA from 648 women in the Multiple Tissue Human Expression Resource cohort. Seventy-six BMI-related probes, 164 WC-related probes and 8 BMI change-related probes passed the threshold for significance in ARIC (P < 1 × 10(-7); Bonferroni), including probes in the recently reported HIF3A, CPT1A and ABCG1 regions. Replication using blood DNA was achieved for 37 BMI probes and 1 additional WC probe. Sixteen of these also replicated in adipose tissue, including 15 novel methylation findings near genes involved in lipid metabolism, immune response/cytokine signaling and other diverse pathways, including LGALS3BP, KDM2B, PBX1 and BBS2, among others. Adiposity traits are associated with DNA methylation at numerous CpG sites that replicate across studies despite variation in tissue type, ethnicity and analytic approaches.

Progress on hypoxia-inducible factor-3: Its structure, gene regulation and biological function (Review)

Hypoxia inducible factors (HIFs) are transcription factors, which are commonly expressed in mammals, including humans. The HIFs consist of hypoxia-regulated α and oxygen-insensitive β subunits, and are key regulators of gene expression during hypoxia in normal and solid tumor tissues. Three members of the HIF family, HIF-1α, HIF-2α, and HIF-3α, are currently known. HIF-3α differs from HIF-1α and HIF-2α in protein structure and regulation of gene expression. For a long time, HIF-3α was considered as a negative mediator of HIF-regulated genes. HIF-3 has a transcriptional regulatory function, which negatively affects gene expression by competing with HIF-1α and HIF-2α in binding to transcriptional elements in target genes during hypoxia. Previously, certain target genes of HIF-3α have been identified, confirming the role of HIF-3α as a transcription factor. In this review, the protein structure, gene regulation and biological function of HIF-3 are discussed based on the literature.

Impact of age, BMI and HbA1c levels on the genome-wide DNA methylation and mRNA expression patterns in human adipose tissue and identification of epigenetic biomarkers in blood

Increased age, BMI and HbA1c levels are risk factors for several non-communicable diseases. However, the impact of these factors on the genome-wide DNA methylation pattern in human adipose tissue remains unknown. We analyzed the DNA methylation of ∼480 000 sites in human adipose tissue from 96 males and 94 females and related methylation to age, BMI and HbA1c. We also compared epigenetic signatures in adipose tissue and blood. Age was significantly associated with both altered DNA methylation and expression of 1050 genes (e.g. FHL2, NOX4 and PLG). Interestingly, many reported epigenetic biomarkers of aging in blood, including ELOVL2, FHL2, KLF14 and GLRA1, also showed significant correlations between adipose tissue DNA methylation and age in our study. The most significant association between age and adipose tissue DNA methylation was found upstream of ELOVL2. We identified 2825 genes (e.g. FTO, ITIH5, CCL18, MTCH2, IRS1 and SPP1) where both DNA methylation and expression correlated with BMI. Methylation at previously reported HIF3A sites correlated significantly with BMI in females only. HbA1c (range 28-46 mmol/mol) correlated significantly with the methylation of 711 sites, annotated to, for example, RAB37, TICAM1 and HLA-DPB1. Pathway analyses demonstrated that methylation levels associated with age and BMI are overrepresented among genes involved in cancer, type 2 diabetes and cardiovascular disease. Our results highlight the impact of age, BMI and HbA1c on epigenetic variation of candidate genes for obesity, type 2 diabetes and cancer in human adipose tissue. Importantly, we demonstrate that epigenetic biomarkers in blood can mirror age-related epigenetic signatures in target tissues for metabolic diseases such as adipose tissue.

DNA methylation and body-mass index: a genome-wide analysis

BACKGROUND

Obesity is a major health problem that is determined by interactions between lifestyle and environmental and genetic factors. Although associations between several genetic variants and body-mass index (BMI) have been identified, little is known about epigenetic changes related to BMI. We undertook a genome-wide analysis of methylation at CpG sites in relation to BMI.

METHODS

479 individuals of European origin recruited by the Cardiogenics Consortium formed our discovery cohort. We typed their whole-blood DNA with the Infinium HumanMethylation450 array. After quality control, methylation levels were tested for association with BMI. Methylation sites showing an association with BMI at a false discovery rate q value of 0·05 or less were taken forward for replication in a cohort of 339 unrelated white patients of northern European origin from the MARTHA cohort. Sites that remained significant in this primary replication cohort were tested in a second replication cohort of 1789 white patients of European origin from the KORA cohort. We examined whether methylation levels at identified sites also showed an association with BMI in DNA from adipose tissue (n=635) and skin (n=395) obtained from white female individuals participating in the MuTHER study. Finally, we examined the association of methylation at BMI-associated sites with genetic variants and with gene expression.

FINDINGS

20 individuals from the discovery cohort were excluded from analyses after quality-control checks, leaving 459 participants. After adjustment for covariates, we identified an association (q value ≤0·05) between methylation at five probes across three different genes and BMI. The associations with three of these probes--cg22891070, cg27146050, and cg16672562, all of which are in intron 1 of HIF3A--were confirmed in both the primary and second replication cohorts. For every 0·1 increase in methylation β value at cg22891070, BMI was 3·6% (95% CI 2·4-4·9) higher in the discovery cohort, 2·7% (1·2-4·2) higher in the primary replication cohort, and 0·8% (0·2-1·4) higher in the second replication cohort. For the MuTHER cohort, methylation at cg22891070 was associated with BMI in adipose tissue (p=1·72 × 10(-5)) but not in skin (p=0·882). We observed a significant inverse correlation (p=0·005) between methylation at cg22891070 and expression of one HIF3A gene-expression probe in adipose tissue. Two single nucleotide polymorphisms--rs8102595 and rs3826795--had independent associations with methylation at cg22891070 in all cohorts. However, these single nucleotide polymorphisms were not significantly associated with BMI.

INTERPRETATION

Increased BMI in adults of European origin is associated with increased methylation at the HIF3A locus in blood cells and in adipose tissue. Our findings suggest that perturbation of hypoxia inducible transcription factor pathways could have an important role in the response to increased weight in people.

FUNDING

The European Commission, National Institute for Health Research, British Heart Foundation, and Wellcome Trust.

DDIT4/REDD1/RTP801 is a novel negative regulator of Schwann cell myelination

Signals that promote myelination must be tightly modulated to adjust myelin thickness to the axonal diameter. In the peripheral nervous system, axonal neuregulin 1 type III promotes myelination by activating erbB2/B3 receptors and the PI3K/AKT/mTOR pathway in Schwann cells. Conversely, PTEN (phosphatase and tensin homolog on chromosome 10) dephosphorylates PtdIns(3,4,5)P3 and negatively regulates the AKT pathway and myelination. Recently, the DLG1/SAP97 scaffolding protein was described to interact with PTEN to enhance PIP3 dephosphorylation. Here we now report that nerves from mice with conditional inactivation of Dlg1 in Schwann cells display only a transient increase in myelin thickness during development, suggesting that DLG1 is a transient negative regulator of myelination. Instead, we identified DDIT4/RTP801/REDD1 as a sustained negative modulator of myelination. We show that DDIT4 is expressed in Schwann cells and its maximum expression level precedes the peak of AKT activation and of DLG1 activity in peripheral nerves. Moreover, loss of DDIT4 expression both in vitro and in vivo in Ddit4-null mice provokes sustained hypermyelination and enhanced mTORC1 activation, thus suggesting that this molecule is a novel negative regulator of PNS myelination.

The differential role of Hif1β/Arnt and the hypoxic response in adipose function, fibrosis, and inflammation

In obesity, adipocytes distant from vasculature become hypoxic and dysfunctional. This hypoxic response is mediated by hypoxia-inducible factors (Hif1α, Hif2α, and Hif3α) and their obligate partner, Hif1β (Arnt). We show that mice lacking Hif1β in fat (FH1βKO) are lean, exhibit reduced adipocyte size, and are protected from age- and diet-induced glucose intolerance. There is also reduced Vegf and vascular permeability in FH1βKO fat, but diet-induced inflammation and fibrosis is unchanged. Adipocytes from FH1βKO mice have reduced glucose uptake due to decreased Glut1 and Glut4, which is mirrored in 3T3-L1 adipocytes with Hif1β knockdown. Hif1β knockdown cells also fail to respond appropriately to hypoxia with reduced cellular respiration and reduced mitochondrial gene expression. Some, but not all, of these effects are reproduced by Hif1α knockdown. Thus, Hif1β/Arnt regulates glucose uptake, mitochondrial gene expression, and vascular permeability to control adipose mass and function, providing a target for obesity therapy.

Disruption of hypoxia-inducible factor 1 in adipocytes improves insulin sensitivity and decreases adiposity in high-fat diet-fed mice

OBJECTIVE

Obesity, insulin resistance, and type 2 diabetes form a tightly correlated cluster of metabolic disorders in which adipose is one of the first affected tissues. The role of hypoxia and hypoxia-inducible factor 1 (HIF1) in the development of high-fat diet (HFD)-induced obesity and insulin resistance was investigated using animal models.

RESEARCH DESIGN AND METHODS

Mice with adipocyte-specific targeted disruption of the genes encoding the HIF1 obligatory subunits Hif1α or Arnt (Hif1β) were generated using an aP2-Cre transgene with the Cre/LoxP system. The mice were fed an HFD for 12 weeks and their metabolic phenotypes were determined. Gene expression patterns in adipose tissues were also determined by microarray and quantitative PCR.

RESULTS

On an HFD, adipocyte-specific ARNT knockout mice and adipocyte-specific HIF1α knockout mice exhibit similar metabolic phenotypes, including reduced fat formation, protection from HFD-induced obesity, and insulin resistance compared with similarly fed wild-type controls. The cumulative food intake remained similar; however, the metabolic efficiency was lower in adipocyte-specific HIF1α knockout mice. Moreover, indirect calorimetry revealed respiratory exchange ratios were reduced in adipocyte-specific HIF1α knockout mice. Hyperinsulinemic-euglycemic clamp studies demonstrated that targeted disruption of HIF1α in adipocytes enhanced whole-body insulin sensitivity. The improvement of insulin resistance is associated with decreased expression of Socs3 and induction of adiponectin.

CONCLUSIONS

Inhibition of HIF1 in adipose tissue ameliorates obesity and insulin resistance. This study reveals that HIF1 could provide a novel potential therapeutic target for obesity and type 2 diabetes.

Pathogenic obesity and nutraceuticals

Over a decade of intense research in the field of obesity has led to the knowledge that chronic, excessive adipose tissue expansion leads to an increase in the risk for CVD, type 2 diabetes mellitus and cancer. This is primarily thought to stem from the low-grade, systemic inflammatory response syndrome that characterises adipose tissue in obesity, and this itself is thought to arise from the complex interplay of factors including metabolic endotoxaemia, increased plasma NEFA, hypertrophic adipocytes and localised hypoxia. Plasma concentrations of vitamins and antioxidants are lower in obese individuals than in the non-obese, which is hypothesised to negatively affect the development of inflammation and disease in obesity. This paper provides a review of the current literature investigating the potential of nutraceuticals to ameliorate the development of oxidative stress and inflammation in obesity, thereby limiting the onset of obesity complications. Research has found nutraceuticals able to positively modulate the activity of adipocyte cell lines and further positive effects have been found in other aspects of pathogenic obesity. While their ability to affect weight loss is still controversial, it is clear that they have a great potential to reverse the development of overweight and obesity-related comorbidities; this, however, still requires much research especially that utilising well-structured randomised controlled trials.

Quantitative monitoring of lipid accumulation over time in cultured adipocytes as function of culture conditions: toward controlled adipose tissue engineering

Adipose tissue engineering is investigated for native fat substitutes and wound healing model systems. Research and clinical applications of bioartificial fat require a quantitative and objective method to continuously measure adipogenesis in living cultures as opposed to currently used culture-destructive techniques that stain lipid droplet (LD) accumulation. To allow standardization, automatic quantification of LD size is further needed, but currently LD size is measured mostly manually. We developed an image processing-based method that does not require staining to monitor adipose cell maturation in vitro nondestructively using optical micrographs taken consecutively during culturing. We employed our method to monitor LD accumulation in 3T3-L1 and mesenchymal stem cells over 37 days. For each cell type, percentage of lipid area, number of droplets per cell, and droplet diameter were obtained every 2-3 days. In 3T3-L1 cultures, high insulin concentration (10 microg/mL) yielded a significantly different (p < 0.01) time course of all three outcome measures. In mesenchymal stem cell cultures, high fetal bovine serum concentration (12.5%) produced significantly more lipid area (p < 0.01). Our method was able to successfully characterize time courses and extents of adipogenesis and is useful for a wide range of applications testing the effects of biochemical, mechanical, and thermal stimulations in tissue engineering of bioartificial fat constructs.

Hypoxia induces adipogenic differentitation of myoblastic cell lines

Muscle atrophy usually accompanies fat accumulation in the muscle. In such atrophic conditions as back muscles of kyphotic spine and the rotator cuff muscles with torn tendons, blood flow might be diminished. It is known that hypoxia causes trans-differentiation of mesenchymal stem cells derived from bone marrow into adipocytes. However, it has not been elucidated yet if hypoxia turned myoblasts into adipocytes. We investigated adipogenesis in C2C12 and G8 murine myogenic cell line treated by hypoxia. Cells were also treated with the cocktail of insulin, dexamethasone and IBMX (MDI), which has been known to inhibit Wnt signaling and promote adipogenesis. Adipogenic differentiation was seen in both hypoxia and MDI. Adipogenic marker gene expression was assessed in C2C12. CCAAT/enhancer-binding protein (C/EBP) beta, alpha and peroxisome proliferator activating receptor (PPAR) gamma were increased by both hypoxia and MDI. The expression profile of Wnt10b was different between hypoxia and MDI. The mechanism for adipogenesis of myoblasts in hypoxia might be regulated by different mechanism than the modification of Wnt signaling.