Transcription factor activating enhancer-binding protein-2beta. A negative regulator of adiponectin gene expression

ACSL4 Directs Intramuscular Adipogenesis and Fatty Acid Composition in Pigs

Simple Summary

In the livestock industry, intramuscular fat content is an important indicator of the meat quality of domestic animals. The variations of the Acyl-CoA Synthetase Long-Chain Family Member 4 (ACSL4) gene locus are associated with intramuscular fat content in different pig populations, but the detailed molecular function of ACSL4 in pig intramuscular adipogenesis remains obscure. Our study reveals the function of ACSL4 in pig intramuscular adipogenesis and provides new clues for improving the palatability of meat and enhancing the nutritional value of pork for human health.

Abstract

The intramuscular fat is a major quality trait of meat, affecting sensory attributes such as flavor and texture. Several previous GWAS studies identified Acyl-CoA Synthetase Long Chain Family Member 4 (ACSL4) gene as the candidate gene to regulate intramuscular fat content in different pig populations, but the underlying molecular function of ACSL4 in adipogenesis within pig skeletal muscle is not fully investigated. In this study, we isolated porcine endogenous intramuscular adipocyte progenitors and performed ACSL4 loss- and gain-of-function experiments during adipogenic differentiation. Our data showed that ACSL4 is a positive regulator of adipogenesis in intramuscular fat cells isolated from pigs. More interestingly, the enhanced expression of ACSL4 in pig intramuscular adipocytes could increase the cellular content of monounsaturated and polyunsaturated fatty acids, such as gamma-L eicosapentaenoic acid (EPA), docosahexaenoic acid (DHA). The above results not only confirmed the function of ACSL4 in pig intramuscular adipogenesis and meat quality attributes, but also provided new clues for the improvement of the nutritional value of pork for human health.

A human specific Alu DNA cassette is found flanking the genes of transcription factor AP2

Objective

Alu elements are retroposons that invaded the primate genome and shaped its biology. Some Alus inserted recently and are polymorphic in the human population. It is these Alus that are being sought after in disease association studies and regulatory biology. Discovering polymorphic Alus in the human genome can open areas of new research in these fields.

Results

Using the polymerase chain reaction on genomic DNA, we identified a polymorphic Alu in the flanking region of the TFAP2B and TFAP2D genes. The new insert was found in higher frequency in Europeans (0.4) and Asians (0.38) and lower frequency in Africans (0.25). We also show this Alu to be part of a 3 Alu cassette that is human specific. The TFAP2B and TFAP2D genes encode members of the transcription factor AP-2, which plays a role in organ development. The insertion of this Alu cassette flanking the transcription factor genes distinguishes humans from the primates. This cassette can possibly affect the regulation of both genes or alternately provoke genomic deletions, which we have shown in this study. Its presence in such a location is intriguing and unquestionably opens an investigational window in disease association studies and in the field of gene regulation.

Electronic supplementary material

The online version of this article (10.1186/s13104-019-4247-7) contains supplementary material, which is available to authorized users.

Alterations of adiponectin gene expression and DNA methylation in adipose tissues and blood cells are associated with gestational diabetes and neonatal outcome

Background

Adiponectin critically contributes to metabolic homeostasis, especially by insulin-sensitizing action. Gestational diabetes mellitus (GDM) is characterized by insulin resistance leading to materno-fetal hyperglycemia and detrimental birth outcomes. By investigating paired subcutaneous (SAT) and visceral adipose tissue (VAT) as well as blood (cell) samples of GDM-affected (n = 25) vs. matched control (n = 30) mother-child dyads of the prospective “EaCH” cohort study, we addressed whether alterations of adiponectin plasma, mRNA, and DNA methylation levels are associated with GDM and offspring characteristics.

Results

Hypoadiponectinemia was present in women with GDM, even after adjustment for body mass index (BMI). This was accompanied by significantly decreased mRNA levels in both SAT and VAT (P < 0.05), independent of BMI. Maternal plasma adiponectin showed inverse relations with glucose and homeostatic model assessment of insulin resistance (both P < 0.01). In parallel to reduced mRNA expression in GDM, significant (P < 0.05) yet small alterations in locus-specific DNA methylation were observed in maternal fat (~ 2%) and blood cells (~ 1%). While newborn adiponectin levels were similar between groups, DNA methylation in GDM offspring was variously altered (~ 1–4%; P < 0.05).

Conclusions

Reduced adiponectin seems to be a pathogenic co-factor in GDM, even independent of BMI, affecting materno-fetal metabolism. While altered maternal DNA methylation patterns appear rather marginally involved, functional, diagnostic, and/or predictive implications of cord blood DNA methylation should be further evaluated.

Electronic supplementary material

The online version of this article (10.1186/s13148-018-0567-z) contains supplementary material, which is available to authorized users.

AP-2β inhibits hepatocellular carcinoma invasion and metastasis through Slug and Snail to suppress epithelial-mesenchymal transition

Transcription factor AP-2β plays an important role in human cancer, but its clinical significance in hepatocellular carcinogenesis is largely unknown.

Methods: AP-2β expression was detected in human hepatocellular cancer (HCC) tissues and cell lines. The effects of AP-2β on HCC proliferation, migration, invasion, tumor formation and metastasis were evaluated by MTT, colony formation and transwell assays in vitro and mouse experiments in vivo. The association between AP-2β and miR-27a/EMT markers in HCC cell lines and tissues was analyzed.

Results: AP-2β expression was decreased in HCC tissues and cell lines. Reduced expression of AP-2β was significantly associated with more advanced tumor stages and larger tumor sizes. The overexpression of AP-2β reduced HCC proliferation, migration, invasion, tumor formation and metastasis in vitro and in vivo. Additionally, AP-2β overexpression increased the sensitivity of HCC cells to cisplatin. Moreover, AP-2β modulates the levels of EMT markers through Slug and Snail in HCC cell lines and tissues. Furthermore, oncogenic miR-27a inhibits AP-2β expression by binding to the AP-2β 3′ untranslated region (UTR) and reverses the tumor suppressive role of AP-2β.

Conclusion: These results suggested that AP-2β is lowly expressed in HCC by inhibiting EMT signaling to regulate HCC cell growth and migration. Therefore, AP-2β in the novel miR-27a/AP-2β/Slug/EMT regulatory axis enhances the chemotherapeutic drug sensitivity of HCC and might represent a potential target for evaluating the treatment and prognosis of human HCC.

Genes regulated by potassium channel tetramerization domain containing 15 (Kctd15) in the developing neural crest

Neural crest (NC) development is controlled precisely by a regulatory network with multiple signaling pathways and the involvement of many genes. The integration and coordination of these factors are still incompletely understood. Overexpression of Wnt3a and the BMP antagonist Chordin in animal cap cells from Xenopus blastulae induces a large number of NC specific genes. We previously suggested that Potassium Channel Tetramerization Domain containing 15 (Kctd15) regulates NC formation by affecting Wnt signaling and the activity of transcription factor AP-2. In order to advance understanding of the function of Kctd15 during NC development, we performed DNA microarray assays in explants injected with Wnt3a and Chordin, and identified genes that are affected by Kctd15 overexpression. Among the many genes identified, we chose Duf domain containing protein 1 (ddcp1), Platelet-Derived Growth Factor Receptor a (pdgfra), Complement factor properdin (cfp), Zinc Finger SWIM-Type Containing 5 (zswim5), and complement component 3 (C3) to examine their expression by whole mount in situ hybridization. Our work points to a possible role for Kctd15 in the regulation of NC formation and other steps in embryonic development.

Obesity susceptibility loci in Qataris, a highly consanguineous Arabian population

OBJECTIVES

In Qataris, a population characterized by a small size and a high rate of consanguinity, between two-thirds to three-quarters of adults are overweight or obese. We investigated the relevance of 23 obesity-related loci in the Qatari population.

METHODS

Eight-hundred-four individuals assessed to be third generation Qataris were included in the study and assigned to 3 groups according to their body mass index (BMI): 190 lean (BMI < 25 kg/m(2)); 131 overweight (25 kg/m(2) ≤ BMI < 30 kg/m(2)) and 483 obese (BMI ≥ 30 kg/m(2)). Genomic DNA was isolated from peripheral blood and genotyped by TaqMan.

RESULTS

Two loci significantly associated with obesity in Qataris: the TFAP2B variation (rs987237) (A allele versus G allele: chi-square = 10.3; P = 0.0013) and GNPDA2 variation (rs10938397) (A allele versus G allele: chi-square = 6.15; P = 0.013). The TFAP2B GG genotype negatively associated with obesity (OR = 0.21; P = 0.0031). Conversely, the GNDPA2 GG homozygous genotype associated with higher risk of obesity in subjects of age < 32 years (P = 0.0358).

CONCLUSION

We showed a different genetic profile associated with obesity in the Qatari population compared to Western populations. Studying the genetic background of Qataris is of primary importance as the etiology of a given disease might be population-specific.

Adipocytokines levels at delivery, functional variation of TFAP2β, and maternal and neonatal anthropometric parameters

OBJECTIVE

Adipocytokines participate in the regulation of glucose metabolism and fetal development. The transcription factor activating protein 2B (TFAP2β) has been associated with adipocytokine regulation, and gene variations with type 2 diabetes and obesity. This study investigated associations between maternal TFAP2B variation, adipocytokine levels, and maternal and neonatal anthropometric characteristics.

DESIGN AND METHODS

A population-based sample of women was followed from delivery to 6 months postpartum. Adiponectin, leptin, and interleukin-6 levels at delivery, and maternal as well as neonatal anthropometric variables were assessed. The TFAP2β intron 1 variable number tandem repeat (VNTR) was genotyped.

RESULTS

Maternal interleukin-6 correlated positively with leptin at delivery, with peripartum weight changes and weight of newborn males, adjusted for potential confounders. Leptin at delivery was associated with TFAP2β intron 1 VNTR genotype, adjusted for confounders, maternal weight and negatively with birth weight among female neonates. A path model suggested a link between TFAP2β genotype, leptin levels, and newborn females' weight.

CONCLUSIONS

The present results stress a role for the TFAP2 β in adiposity-related conditions and intrauterine growth. The association between neonatal birth weight and maternal adipocytokine levels, together with the observed sex effect, call for further studies on the mechanisms behind neuroendocrine fetal programming.

Genetic polymorphisms of the main transcription factors for adiponectin gene promoter in regulation of adiponectin levels: association analysis in three European cohorts

Adiponectin serum concentrations are an important biomarker in cardiovascular epidemiology with heritability etimates of 30–70%. However, known genetic variants in the adiponectin gene locus (ADIPOQ) account for only 2%–8% of its variance. As transcription factors are thought to play an under-acknowledged role in carrying functional variants, we hypothesized that genetic polymorphisms in genes coding for the main transcription factors for the ADIPOQ promoter influence adiponectin levels. Single nucleotide polymorphisms (SNPs) at these genes were selected based on the haplotype block structure and previously published evidence to be associated with adiponectin levels. We performed association analyses of the 24 selected SNPs at forkhead box O1 (FOXO1), sterol-regulatory-element-binding transcription factor 1 (SREBF1), sirtuin 1 (SIRT1), peroxisome-proliferator-activated receptor gamma (PPARG) and transcription factor activating enhancer binding protein 2 beta (TFAP2B) gene loci with adiponectin levels in three different European cohorts: SAPHIR (n = 1742), KORA F3 (n = 1636) and CoLaus (n = 5355). In each study population, the association of SNPs with adiponectin levels on log-scale was tested using linear regression adjusted for age, sex and body mass index, applying both an additive and a recessive genetic model. A pooled effect size was obtained by meta-analysis assuming a fixed effects model. We applied a significance threshold of 0.0033 accounting for the multiple testing situation. A significant association was only found for variants within SREBF1 applying an additive genetic model (smallest p-value for rs1889018 on log(adiponectin) = 0.002, β on original scale = −0.217 µg/ml), explaining ∼0.4% of variation of adiponectin levels. Recessive genetic models or haplotype analyses of the FOXO1, SREBF1, SIRT1, TFAPB2B genes or sex-stratified analyses did not reveal additional information on the regulation of adiponectin levels. The role of genetic variations at the SREBF1 gene in regulating adiponectin needs further investigation by functional studies.

Snail, a transcriptional regulator, represses adiponectin expression by directly binding to an E-box motif in the promoter

OBJECTIVE

Adiponectin is a hormone that modulates many metabolic processes and is exclusively expressed in adipose tissue. However, complete understanding of the factors that regulate adiponectin expression is lacking. The following were investigated: (1) functional analysis of the human adiponectin promoter, (2) putative adiponectin repressor sequence activity in 3T3-L1 adipocytes using promoter mutagenesis, (3) whether Snail, an E-box binding transcription factor, binds this repressor sequence, (4) if Snail regulates adiponectin expression in 3T3-L1 pre-adipocytes.

MATERIALS/METHODS

To further understand how adiponectin expression is regulated, we isolated the human adiponectin promoter and analyzed its activity after serial deletions.

RESULTS

We found a negative cis-regulatory element located in the adiponectin proximal promoter sequence (-174 to -152 bp), which contained an E-box site (CAACTG). The DNA binding activity of this putative negative regulatory factor was found to be sequence-specific and the binding activity is decreased during adipocyte differentiation time-dependently. Affinity chromatography identified the zinc-finger transcription factor Snail (SNAI1) as the putative negative regulatory factor. Chromatin immunoprecipitation assay and electrophoretic mobility shift assay confirmed that Snail binds to this negative cis-regulatory element in pre-adipocytes, exclusively. Inhibition of Snail expression using small interfering RNA techniques increased adiponectin expression in 3T3-L1 adipocytes, while overexpression of Snail reduced adiponectin expression. Furthermore, we observed an inverse relation between the expression of Snail and the expression of CCAAT-enhancer-binding protein alpha and peroxisome proliferator-activated receptor gamma, which are transcription factors that regulate adipogenesis.

CONCLUSIONS

Snail is a novel regulator of adiponectin expression and probably has a role in regulating adipogenesis.

Sex differences in human adipose tissues - the biology of pear shape

Women have more body fat than men, but in contrast to the deleterious metabolic consequences of the central obesity typical of men, the pear-shaped body fat distribution of many women is associated with lower cardiometabolic risk. To understand the mechanisms regulating adiposity and adipose tissue distribution in men and women, significant research attention has focused on comparing adipocyte morphological and metabolic properties, as well as the capacity of preadipocytes derived from different depots for proliferation and differentiation. Available evidence points to possible intrinsic, cell autonomous differences in preadipocytes and adipocytes, as well as modulatory roles for sex steroids, the microenvironment within each adipose tissue, and developmental factors. Gluteal-femoral adipose tissues of women may simply provide a safe lipid reservoir for excess energy, or they may directly regulate systemic metabolism via release of metabolic products or adipokines. We provide a brief overview of the relationship of fat distribution to metabolic health in men and women, and then focus on mechanisms underlying sex differences in adipose tissue biology.

Screening for adiponectin secretion regulators

Adiponectin is an adipokine secreted from adipocytes and plays important roles in the suppression of metabolic syndromes that can result in type 2 diabetes, obesity, and atherosclerosis. Adiponectin is a promising drug target because a number of studies have shown that upregulation of adiponectin has a number of therapeutic benefits. Extensive efforts have revealed various adiponectin regulators, such as cytokines, transcription factors, and drugs. Cytokines, such as tumor necrosis factor α, IL-6, and IL-18, downregulate adiponectin production. On the other hand, transcription factors such as peroxisome proliferator-activated receptor-γ (PPARγ), CCAAT-enhancer-binding protein α, and forkhead box O1 (FoxO1) upregulate adiponectin expression, although the activating transcription factor 3 and cAMP response element-binding protein downregulate it. Although a number of therapeutic drugs have been reported as adiponectin secretion regulators, most of them act through PPARγ-dependent mechanisms, leaving PPARγ-derived side effects as a concern. Using high-throughput screening, we have identified PPARγ-independent adiponectin secretion regulators as potential drug candidates with a novel mechanism of action.

Childhood environmental and genetic predictors of adulthood obesity: the cardiovascular risk in young Finns study

CONTEXT

Obesity from childhood to adulthood is associated with adverse health later in life. Increased youth BMI is a risk factor for later obesity, but it is unknown whether identification of other risk factors, including recently discovered genetic markers, would help to identify children at risk of developing adult obesity.

OBJECTIVES

Our objective was to examine the childhood environmental and genetic predictors of adult obesity.

DESIGN, SETTING, AND PARTICIPANTS

We followed 2119 individuals of the Cardiovascular Risk in Young Finns Study for up to 27 yr since baseline (1980, age 3-18 yr).

MAIN OUTCOME MEASURE

We evaluated adult obesity [body mass index (BMI) ≥ 30 kg/m(2)].

RESULTS

The independent predictors (P < 0.05) of adult obesity included childhood BMI, C-reactive protein (CRP), family income (inverse), mother's BMI, and polymorphisms near genes TFAP2B, LRRN6C, and FLJ35579. A risk assessment based on childhood BMI, mother's BMI, and family income was superior in predicting obesity compared with the approach using data only on BMI (C-statistics 0.751 vs. 0.772, P = 0.0015). Inclusion of data on childhood CRP and novel genetic variants for BMI did not incrementally improve C-value (0.779, P = 0.16). A nonlaboratory risk score (childhood BMI, mother's BMI, and family income) predicted adult obesity in all age groups between 3-18 yr (P always <0.001).

CONCLUSIONS

Childhood BMI, CRP, family income (inversely), mother's BMI, and polymorphisms near genes FLJ35779, TFAP2B, and LRRN6C are independently related to adulthood obesity. However, because genetic risk markers and CRP only marginally improve the prediction, our results indicate that children at high risk of adult obesity can be identified using a simple non-laboratory-based risk assessment.

Relation of the expression of transcriptional factor TFAP2B to that of adipokines in subcutaneous and omental adipose tissues

To determine the potential role of the transcriptional factor-activating enhancer-binding protein-2beta (TFAP2B) in the regulation of expression of adipokines, adiponectin, leptin, and interleukin-6 (IL-6) in vivo, we quantified the mRNA expression levels of these adipokines and TFAP2B in visceral (omental) and abdominal subcutaneous adipose tissues of 66 individuals with variable degree of adiposity and studied their correlations with BMI and their plasma concentrations. We found that BMI correlated negatively with plasma adiponectin levels and positively with those of leptin. Adiponection mRNA expression in subcutaneous fat correlated negatively with BMI, whereas leptin mRNA levels in the omentum correlated with plasma leptin levels and BMI. In contrast, IL-6 mRNA levels in subcutaneous and omental fat did not correlate with BMI. IL-6 mRNA levels in the omental fat correlated with plasma IL-6 levels. Whereas TFAP2B mRNA expression did not correlate with BMI, it correlated negatively with adiponectin expression in the subcutaneous adipose tissue. Furthermore, TFAP2B mRNA expression correlated negatively with leptin and positively with IL-6 expression in both subcutaneous and omental adipose tissues. These relationships are consistent with our in vitro observations and indicate that TFAP2B seems to regulate the expression of various adipokines in vivo.

Prolactin regulatory element-binding protein involved in cAMP-mediated suppression of adiponectin gene

Adiponectin (ApN) has several protective effects against diabetes and atherosclerosis. However, the detailed mechanisms of the regulation of the ApN gene have not yet been clarified. Prolactin regulatory element-binding (PREB) protein has been identified as a factor that regulates insulin gene expression in the pancreas. PREB is located not only in the pancreas but also in adipose tissue; however, its role in adipose tissue is not known. To analyse the effects of PREB on ApN gene transcription, we employed a reporter gene assay and electrophoretic mobility shift assay (EMSA). In the cells expressing or knocking down the PREB, ApN expression was determined. PREB was located mainly in the nuclei of adipose tissue and its cell line, 3T3-L1 cells. The nuclear extract contained ApN promoter-binding activity that was super-shifted by PREB antiserum in EMSA studies. In the 3T3-L1 cells, the co-expression of PREB and the ApN promoter inhibited the activity of the latter. The addition of cAMP to the cells increased PREB expression in a dose-dependent manner. A deletional analysis of the ApN promoter showed that the PREB-responsive cis-element in the ApN promoter mediated the transcriptional effect of PREB, whereas a mutant of this motif in the ApN promoter abrogated the effect of PREB, as well as that of cAMP. Furthermore, cells expressing or knocking down PREB exhibited decreased and increased ApN expression, respectively. These results demonstrate that PREB may contribute to the regulation of ApN gene transcription, in response to cAMP activation in adipocytes.

Transcription factor AP-2beta inhibits expression and secretion of leptin, an insulin-sensitizing hormone, in 3T3-L1 adipocytes

BACKGROUND

We have previously reported an association between the activator protein-2beta (AP-2beta) transcription factor gene and type 2 diabetes. This gene is preferentially expressed in adipose tissue, and subjects with a disease-susceptible allele of AP-2beta showed stronger AP-2beta expression in adipose tissue than those without the susceptible allele. Furthermore, overexpression of AP-2beta led to lipid accumulation and induced insulin resistance in 3T3-L1 adipocytes.

RESULT

We found that overexpression of AP-2beta in 3T3-L1 adipocytes decreased the promoter activity of leptin, and subsequently decreased both messenger RNA (mRNA) and protein expression and secretion. Furthermore, knockdown of endogenous AP-2beta by RNA-interference increased mRNA and protein expression of leptin. Electrophoretic mobility shift and chromatin immunoprecipitation assays revealed specific binding of AP-2beta to leptin promoter regions in vitro and in vivo. In addition, site-directed mutagenesis of the AP-2-binding site located between position +34 and +42 relative to the transcription start site abolished the inhibitory effect of AP-2beta. Our results clearly showed that AP-2beta directly inhibited insulin-sensitizing hormone leptin expression by binding to its promoter.

CONCLUSION

AP-2beta modulated the expression of leptin through direct interaction with its promoter region.

Transcriptional and post-translational regulation of adiponectin

Adiponectin is an adipose-tissue-derived hormone with anti-diabetic, anti-atherogenic and anti-inflammatory functions. Adiponectin circulates in the bloodstream in trimeric, hexameric and high-molecular-mass species, and different forms of adiponectin have been found to play distinct roles in the regulation of energy homoeostasis. The serum levels of adiponectin are negatively correlated with obesity and insulin resistance, yet the underlying mechanisms remain elusive. In the present review, we summarize recent progress made on the mechanisms regulating adiponectin gene transcription, multimerization and secretion. We also discuss the potential relevance of these studies to the development of new clinical therapy for insulin resistance, Type 2 diabetes and other obesity-related metabolic disorders.

AP-2gamma promotes proliferation in breast tumour cells by direct repression of the CDKN1A gene

Overexpression of the activator protein (AP)-2gamma transcription factor in breast tumours has been identified as an independent predictor of poor outcome and failure of hormone therapy. To understand further the function of AP-2gamma in breast carcinoma, we have used an RNA interference and gene expression profiling strategy with the MCF-7 cell line as a model. Gene expression changes between control and silenced cells implicate AP-2gamma in the control of cell cycle progression and developmental signalling. A function for AP-2gamma in cell cycle control was verified using flow cytometry: AP-2gamma silencing led to a partial G1/S arrest and induction of the cyclin-dependent kinase inhibitor, p21cip/CDKN1A. Reporter and chromatin immunoprecipitation assays demonstrated a direct, functional interaction by AP-2gamma at the CDKN1A proximal promoter. AP-2gamma silencing coincided with acquisition of an active chromatin conformation at the CDKN1A locus and increased gene expression. These data provide a mechanism whereby AP-2gamma overexpression can promote breast epithelial proliferation and, coupled with previously published data, suggest how loss of oestrogen regulation of AP-2gamma may contribute to the failure of hormone therapy in patients.

Transcription factor AP-2beta inhibits glucose-induced insulin secretion in cultured insulin-secreting cell-line

AIM

We previously identified the transcription factor activating enhancer-binding protein-2beta (AP-2beta) gene as a new candidate for conferring susceptibility to type 2 diabetes. To ascertain the possible involvement of AP-2beta in the pathogenesis of type 2 diabetes we examined the effects of AP-2beta on glucose-induced insulin secretion.

METHODS

We measured the insulin secretion stimulated by glucose, tolbutamide, or KCl in the HIT-T15 cells infected with adenovirus vectors encoding AP-2beta or LacZ (control).

RESULTS

We identified clear expression of AP-2beta in isolated rat pancreatic islets and in HIT-T15 cells. Glucose-induced increase in insulin secretion was significantly inhibited in AP-2beta-overexpressing cells (LacZ, 5.0+/-0.8 ng h(-1)mg(-1) protein; AP-2beta, 1.7+/-0.2 ng h(-1)mg(-1) protein; P=0.0015), whereas insulin expression was the same in both types of cells. Tolbutamide-induced insulin secretion was also suppressed in the AP-2beta-overexpressing cells, but KCl-induced insulin secretion was not affected by AP-2beta overexpression. In addition, Kir6.2 and glucokinase expression was significantly decreased in the AP-2beta-overexpressing cells.

CONCLUSION

We identified for the first time that AP-2beta expressed and functioned in insulin-secreting cell-line HIT-T15. These results suggest that AP-2beta contributes to susceptibility to type 2 diabetes by inhibiting glucose-induced insulin secretion in pancreatic beta cells.

The transcription factor TFAP2B is associated with insulin resistance and adiposity in healthy adolescents

Insulin resistance and central adiposity are strong risk indicators for type 2 diabetes and coronary heart disease. An important role for adipose tissue in the etiology and progression of these conditions has recently become more evident. A transcription factor, TFAP2B, has been shown to participate in the regulation of adipocyte metabolism, by facilitating glucose uptake and lipid accumulation, while simultaneously reducing insulin sensitivity, and recently a direct function for TFAP2B as an inhibitor of adiponectin expression was observed. In this study, we have investigated how insulin resistance, plasma adiponectin, and central adiposity, in a normal population of adolescents, are affected by genetic variability in TFAP2B. Our results show that both insulin sensitivity, as measured from levels of fasting glucose and insulin, and central adiposity, estimated by subscapular skinfold thickness, were significantly associated to genetic variability in TFAP2B. This association was restricted to males only, where carriers of the 4-repeat allele of intron 2 had higher insulin sensitivity and lower subscapular skinfold thickness. Levels of adiponectin did not show any association to the TFAP2B polymorphism, but was negatively correlated to central adiposity in females. These results suggest that reduction of TFAP2B expression could have a protective effect against future risk of complications associated with decreased insulin sensitivity and central adiposity, such as type 2 diabetes and coronary heart disease.

Genome-wide association scan meta-analysis identifies three Loci influencing adiposity and fat distribution

To identify genetic loci influencing central obesity and fat distribution, we performed a meta-analysis of 16 genome-wide association studies (GWAS, N = 38,580) informative for adult waist circumference (WC) and waist-hip ratio (WHR). We selected 26 SNPs for follow-up, for which the evidence of association with measures of central adiposity (WC and/or WHR) was strong and disproportionate to that for overall adiposity or height. Follow-up studies in a maximum of 70,689 individuals identified two loci strongly associated with measures of central adiposity; these map near TFAP2B (WC, P = 1.9x10(-11)) and MSRA (WC, P = 8.9x10(-9)). A third locus, near LYPLAL1, was associated with WHR in women only (P = 2.6x10(-8)). The variants near TFAP2B appear to influence central adiposity through an effect on overall obesity/fat-mass, whereas LYPLAL1 displays a strong female-only association with fat distribution. By focusing on anthropometric measures of central obesity and fat distribution, we have identified three loci implicated in the regulation of human adiposity.

Transcription factor activating protein-2beta: a positive regulator of monocyte chemoattractant protein-1 gene expression

We previously reported an association between the activating protein (AP)-2beta transcription factor gene and type 2 diabetes. This gene is preferentially expressed in adipose tissue, and subjects with a disease-susceptible allele of AP-2beta showed stronger AP-2beta expression in adipose tissue than those without the susceptible allele. Furthermore, overexpression of AP-2beta leads to lipid accumulation by enhancing glucose transport and inducing insulin resistance in 3T3-L1 adipocytes. In this study, we found that overexpression of AP-2beta in 3T3-L1 adipocytes accelerated the promoter activity of monocyte chemoattractant protein-1 (MCP-1) and subsequently increased both mRNA and protein expression and protein secretion. Furthermore, knockdown of endogenous AP-2beta by RNA interference reduced the mRNA and the protein expression of MCP-1. EMSAs and chromatin immunoprecipitation assays revealed specific binding of AP-2beta to MCP-1 promoter regions, in vitro and in vivo. Additionally, site-directed mutagenesis of the AP-2 binding site located at -137 to -129 relative to the transcription start site markedly diminished MCP-1 promoter activity, whereas other putative AP-2 binding sites did not. Our results clearly show that AP-2beta directly enhanced MCP-1 secretion by binding to its promoter. Thus, we propose that AP-2beta positively regulates MCP-1 expression; subsequently contributes to the infiltration of macrophages to adipose tissue; and leads to insulin resistance, type 2 diabetes, and cardiovascular diseases.

Involvement of protein kinase D in phosphorylation and increase of DNA binding of activator protein 2 alpha to downregulate ATP-binding cassette transporter A1

BACKGROUND

Activator protein (AP) 2alpha negatively regulates expression of ABCA1 gene through Ser-phosphorylation of AP2alpha (Circ Res. 2007;101:156-165). Potential specific Ser-phosphorylation sites for this reaction were investigated in human AP2alpha.

METHODS AND RESULTS

The phosphorylation was shown mediated by PKD, and Ser258 and Ser326 were found in its specific phosphorylation sequence segment in AP2alpha. PKD phosphorylated Ser258 more than Ser326 and induced its binding to the ABCA1 promoter. These reactions and AP2alpha-induced suppression of the ABCA1 promoter activity were reversed by mutation of Ser258 more than Ser326 mutation. Knockdown of PKD by siRNA reduced the AP2alpha Ser-phosphorylation, and increased ABCA1 expression and HDL biogenesis. Gö6983 inhibited PKD more selectively than PKC in THP-1 and HEK 293 cells and in mice, and increased ABCA1 expression, HDL biogenesis, and plasma HDL level.

CONCLUSIONS

PKD phosphorylates AP2alpha to negatively regulate expression of ABCA1 gene to increase HDL biogenesis. The major functional phosphorylation of AP2alpha was identified at Ser258 by PKD, in the AP2alpha basic domain highly conserved among species and all 5 subtypes of AP2. PKD/AP2 system can be a potent pharmacological target for prevention of atherosclerosis.

Nutrigenomics, beta-cell function and type 2 diabetes

INTRODUCTION

The present investigation was designed to investigate the accuracy and precision of lactate measurement obtained with contemporary biosensors (Chiron Diagnostics, Nova Biomedical) and standard enzymatic photometric procedures (Sigma Diagnostics, Abbott Laboratories, Analyticon).

MATERIALS AND METHODS

Measurements were performed in vitro before and after the stepwise addition of 1 molar sodium lactate solution to samples of fresh frozen plasma to systematically achieve lactate concentrations of up to 20 mmol/l.

RESULTS

Precision of the methods investigated varied between 1% and 7%, accuracy ranged between 2% and -33% with the variability being lowest in the Sigma photometric procedure (6%) and more than 13% in both biosensor methods.

CONCLUSION

Biosensors for lactate measurement provide adequate accuracy in mean with the limitation of highly variable results. A true lactate value of 6 mmol/l was found to be presented between 4.4 and 7.6 mmol/l or even with higher difference. Biosensors and standard enzymatic photometric procedures are only limited comparable because the differences between paired determinations presented to be several mmol. The advantage of biosensors is the complete lack of preanalytical sample preparation which appeared to be the major limitation of standard photometry methods.