Lingyan Xu

A Genome-Wide Association Study Confirms Previously Reported Loci for Type 2 Diabetes in Han Chinese

Background Genome-wide association study (GWAS) has identified more than 30 loci associated with type 2 diabetes (T2D) in Caucasians. However, genomic understanding of T2D in Asians, especially Han Chinese, is still limited. Methods and Principal Findings A two-stage GWAS was performed in Han Chinese from Mainland China. The discovery stage included 793 T2D cases and 806 healthy controls genotyped using Illumina Human 660- and 610-Quad BeadChips; and the replication stage included two independent case-control populations (a total of 4445 T2D cases and 4458 controls) genotyped using TaqMan assay. We validated the associations of KCNQ1 (rs163182, p = 2.085×10−17, OR 1.28) and C2CD4A/B (rs1370176, p = 3.677×10−4, OR 1.124; rs1436953, p = 7.753×10−6, OR 1.141; rs7172432, p = 4.001×10−5, OR 1.134) in Han Chinese. Conclusions and Significance Our study represents the first GWAS of T2D with both discovery and replication sample sets recruited from Han Chinese men and women residing in Mainland China. We confirmed the associations of KCNQ1 and C2CD4A/B with T2D, with the latter for the first time being examined in Han Chinese. Arguably, eight more independent loci were replicated in our GWAS.

Deletion of steroid receptor coactivator-3 gene ameliorates hepatic steatosis

BACKGROUND & AIMS Excess dietary fat can cause hepatic steatosis, which can progress into severe liver disorders including steatohepatitis and cirrhosis. Steroid receptor coactivator-3 (SRC-3), a member of the p160 coactivator family, is reported as a key regulator of adipogenesis and energy homeostasis. We sought to determine the influence of SRC-3 on hepatic steatosis and the mechanism beneath. METHODS The influence of siRNA-mediated SRC-3 silencing on hepatic lipid accumulation was assessed in HepG2 cells. The molecular mechanism of SRC-3 regulation of hepatic lipid metabolism was also studied. Moreover, the effect of SRC-3 ablation on hepatic steatosis was examined in SRC-3 deficient mice. RESULTS In this study, we report that SRC-3 ablation reduces palmitic acid-induced lipid accumulation in HepG2 cells. Moreover, deletion of SRC-3 ameliorates hepatic steatosis and inflammation response in mice fed a high fat diet (HFD). These metabolic improvements can presumably be explained by the reduction in chicken ovalbumin upstream promoter transcription factor II (COUP-TFII) expression and the subsequent elevation in peroxisome proliferator-activated receptor α (PPARα) level. At the molecular level, SRC-3 interacts with retinoic receptor α (RARα) to activate COUP-TFII expression under all-trans retinoic acid (ARTA) treatment. CONCLUSIONS These findings indicate a crucial role for SRC-3 in regulating hepatic lipid metabolism and provide the possible novel inner mechanisms.

Role of forkhead box protein A3 in age-associated metabolic decline.

Significance This paper reports that the transcription factor forkhead box protein A3 (Foxa3) is directly involved in the development of age-associated obesity and insulin resistance. Mice that lack the Foxa3 gene remodel their fat tissues, store less fat, and burn more energy as they age. These mice also live significantly longer. We show that Foxa3 suppresses a key metabolic cofactor, PGC1α, which is involved in the gene programs that turn on energy expenditure in adipose tissues. Overall, these findings suggest that Foxa3 contributes to the increased adiposity observed during aging, and that it can be a possible target for the treatment of metabolic disorders. Aging is associated with increased adiposity and diminished thermogenesis, but the critical transcription factors influencing these metabolic changes late in life are poorly understood. We recently demonstrated that the winged helix factor forkhead box protein A3 (Foxa3) regulates the expansion of visceral adipose tissue in high-fat diet regimens; however, whether Foxa3 also contributes to the increase in adiposity and the decrease in brown fat activity observed during the normal aging process is currently unknown. Here we report that during aging, levels of Foxa3 are significantly and selectively up-regulated in brown and inguinal white fat depots, and that midage Foxa3-null mice have increased white fat browning and thermogenic capacity, decreased adipose tissue expansion, improved insulin sensitivity, and increased longevity. Foxa3 gain-of-function and loss-of-function studies in inguinal adipose depots demonstrated a cell-autonomous function for Foxa3 in white fat tissue browning. Furthermore, our analysis revealed that the mechanisms of Foxa3 modulation of brown fat gene programs involve the suppression of peroxisome proliferator activated receptor γ coactivtor 1 α (PGC1α) levels through interference with cAMP responsive element binding protein 1-mediated transcriptional regulation of the PGC1α promoter. Overall, our data demonstrate a role for Foxa3 in energy expenditure and in age-associated metabolic disorders.

Selection of Reference Genes for qRT-PCR in High Fat Diet-Induced Hepatic Steatosis Mice Model

With the epidemic proportions of obesity worldwide and the concurrent prevalence of hepatic steatosis, there is an urgent need for better understanding the intrinsic mechanism of hepatic steatosis, especially the changes of gene expression underlying the development of hepatic steatosis and its associated abnormal liver function. Quantitative real-time PCR (qRT-PCR) is a sensitive and highly reproducible technique of gene expression analysis. However, for accurate and reliable gene expression results, it is vital to have an internal control gene expressed at constant levels under all the experimental conditions being analyzed for. In this study, the authors validated candidate reference genes suitable for qRT-PCR profiling experiments using livers from control mice and high fat diet-induced obese mice. Cross-validation of expression stability of ten selected reference genes using three popular algorithms, GeNorm, NormFinder, and BestKeeper found HPRT1 and GAPDH as most stable reference genes. Thus, HPRT1 and GAPDH are recommended as stable reference genes most suitable for gene expression studies in the development of hepatic steatosis.

The transcriptional coactivator PGC1α protects against hyperthermic stress via cooperation with the heat shock factor HSF1

Heat shock proteins (HSPs) are required for the clearance of damaged and aggregated proteins and have important roles in protein homeostasis. It has been shown that the heat shock transcription factor, HSF1, orchestrates the transcriptional induction of these stress-regulated chaperones; however, the coregulatory factors responsible for the enhancement of HSF1 function on these target genes have not been fully elucidated. Here, we demonstrate that the cold-inducible coactivator, PGC1α, also known for its role as a regulator of mitochondrial and peroxisomal biogenesis, thermogenesis and cytoprotection from oxidative stress, regulates the expression of HSPs in vitro and in vivo and modulates heat tolerance. Mechanistically, we show that PGC1α physically interacts with HSF1 on HSP promoters and that cells and mice lacking PGC1α have decreased HSPs levels and are more sensitive to thermal challenges. Taken together, our findings suggest that PGC1α protects against hyperthermia by cooperating with HSF1 in the induction of a transcriptional program devoted to the cellular protection from thermal insults.

The Winged Helix Transcription Factor Foxa3 Regulates Adipocyte Differentiation and Depot-Selective Fat Tissue Expansion

ABSTRACT Conversion of mesenchymal stem cells into terminally differentiated adipocytes progresses sequentially through regulated transcriptional steps. While it is clear that the late phases of adipocyte maturation are governed by the nuclear receptor peroxisome proliferator-activated receptor gamma (PPARγ), less is known about the transcriptional control of the initial stages of differentiation. To identify early regulators, we performed a small interfering RNA (siRNA) screen of Forkhead-box genes in adipocytes and show here for the first time that the winged helix factor Foxa3 promotes adipocyte differentiation by cooperating with C/EBPβ and -δ to transcriptionally induce PPARγ expression. Furthermore, we demonstrate that mice with genetic ablation of Foxa3 have a selective decrease in epididymal fat depot and a cell-autonomous defect to induce PPARγ specifically in their visceral adipocytes. In obese subjects, FOXA3 is differentially expressed in visceral and subcutaneous adipose depots. Overall, our study implicates Foxa3 in the regulation of adipocyte differentiation and depot-selective adipose tissue expansion.

Chemokine (C-C Motif) Ligand 20, a Potential Biomarker for Graves' Disease, Is Regulated by Osteopontin

Context Graves’ disease (GD) is a common autoimmune disease involving the thyroid gland. The altered balance of pro- and anti-inflammatory cytokines plays an important role in the pathogenesis of GD. Chemokine (C-C motif) ligand 20 (CCL20) is important for interleukin-17 (IL-17) signal activation and a potent chemoattractant for Th17 cells. Meanwhile, Osteopontin (OPN), a broadly expressed pleiotropic cytokine, has been implicated in GD through inducing Th1-involved response to enhance the production of proinflammatory cytokines and chemokines, but little is known about the role of OPN in regulating CCL20 and IL-17 signaling. Objective This study sought to explore the possibility of CCL20 level as a biomarker for GD, as well as investigate the role of OPN in regulating CCL20 production. Methods Fifty untreated GD patients, fifteen euthyroid GD patients, twelve TRAb-negative GD patients and thirty-five healthy control donors were recruited. OPN, CCL20 and other clinical GD diagnosis parameters were measured. CD4+T cells were isolated from peripheral blood mononuclear cells (PBMCs) using antibody-coated magnetic beads. Enzyme-linked immune-sorbent assay and quantitative polymerase chain reaction were used to determine CCL20 expression level. Results We found that the plasma CCL20 level was enhanced in GD patients and decreased in euthyroid and TRAb-negative GD patients. In addition, CCL20 level correlated with GD clinical diagnostic parameters and plasma OPN level. Moreover, we demonstrated that recombinant OPN and plasma from untreated GD patients increased the expression of CCL20 in CD4+T cells, which could be blocked by OPN antibody. Furthermore, we found that the effect of OPN on CCL20 expression was mediated by β3 integrin receptor, IL-17, NF-κB and MAPK pathways. Conclusions These results demonstrated that CCL20 might serve as a biomarker for GD and suggested the possible role of OPN in induction of CCL20 expression.

Forkhead box A3 mediates glucocorticoid receptor function in adipose tissue

Significance This paper shows a previously unidentifed relationship between the transcription factor forkhead box a3 (Foxa3) and the glucocorticoid receptor (GR) by demonstrating, for the first time to our knowledge, that Foxa3 is a target of GR and that it is required for GR transcriptional function in fat depots. Via animal studies we show that the absence of the Foxa3 gene protects the fat depot from the expansion associated with chronic exposure to glucocorticoids, drugs widely used in medical practice to treat inflammatory disease and autoimmune disorders. Overall our findings suggest that Foxa3 can be a potential target for the prevention of glucocorticoid-induced pathological side effects in adipose tissues. Glucocorticoids (GCs) are widely prescribed anti-inflammatory agents, but their chronic use leads to undesirable side effects such as excessive expansion of adipose tissue. We have recently shown that the forkhead box protein A3 (Foxa3) is a calorie-hoarding factor that regulates the selective enlargement of epididymal fat depots and suppresses energy expenditure in a nutritional- and age-dependent manner. It has been demonstrated that Foxa3 levels are elevated in adipose depots in response to high-fat diet regimens and during the aging process; however no studies to date have elucidated the mechanisms that control Foxa3’s expression in fat. Given the established effects of GCs in increasing visceral adiposity and in reducing thermogenesis, we assessed the existence of a possible link between GCs and Foxa3. Computational prediction analysis combined with molecular studies revealed that Foxa3 is regulated by the glucocorticoid receptor (GR) in preadipocytes, adipocytes, and adipose tissues and is required to facilitate the binding of the GR to its target gene promoters in fat depots. Analysis of the long-term effects of dexamethasone treatment in mice revealed that Foxa3 ablation protects mice specifically against fat accretion but not against other pathological side effects elicited by this synthetic GC in tissues such as liver, muscle, and spleen. In conclusion our studies provide the first demonstration, to our knowledge, that Foxa3 is a direct target of GC action in adipose tissues and point to a role of Foxa3 as a mediator of the side effects induced in fat tissues by chronic treatment with synthetic steroids.

Loss of steroid receptor co-activator-3 attenuates carbon tetrachloride-induced murine hepatic injury and fibrosis.

Hepatic fibrosis, a disease characterized by altered accumulation of extracellular matrix, can cause cirrhosis and liver failure. There is growing interest in the impact of co-activators on hepatic fibrogenesis. Here, we provided genetic evidence that mice lacking steroid receptor co-activator-3 (SRC-3) were protected against carbon tetrachloride (CCl4)-induced acute liver necrosis and chronic hepatic fibrosis. After acute CCl4 treatment, SRC-3−/− mice showed attenuated profibrotic response and hepatocyte apoptosis, whereas hepatocyte proliferation was elevated in SRC-3−/− mice versus SRC-3+/+ mice. Similarly, chronically CCl4-treated SRC-3−/− mice showed significant weakening of inflammatory infiltrates, hepatic stellate cell activation and collagen accumulation in the liver compared with SRC-3+/+ mice. Further investigation revealed that TGFβ1/Smad signaling pathway was impaired in the absence of SRC-3. Moreover, the expression levels of SRC-3, as assessed in human tissue microarray of liver diseases, correlated positively with degrees of fibrosis. These data revealed that SRC-3−/− mice were resistant to CCl4-induced acute and chronic hepatic damage and TGFβ1/Smad signaling was suppressed in the lack of SRC-3. Our results established an essential involvement of SRC-3 in liver fibrogenesis, which might provide new clues to the future treatment of hepatic fibrosis.

SRC-3 deficient mice developed fat redistribution under high-fat diet.

An emerging concept suggests that an aberrant distributed body fat is closely linked to the occurrence of metabolic abnormalities. Mice deficient in steroid receptor coactivator-3 (SRC-3) are shown to be protected against high-fat diet (HFD) induced obesity but little is known about whether visceral (VAT) and subcutaneous adipose tissue (SCAT) distribute differently in SRC-3−/− mice versus SRC-3+/+ mice. Here we reported that under HFD, fat redistributed between VAT and subcutaneous area of SRC-3−/− mice. When VAT/SCAT weight ratio (VAT/SCAT ratio) was calculated, SRC-3−/− mice had significantly elevated VAT/SCAT ratio in HFD versus normal diet (ND), while VAT/SCAT ratio was similar in SRC-3+/+ mice under ND and HFD. Serological changes in SRC-3−/− mice paralleled the altered fat distribution. In SRC-3−/− mice, assays on gene expression revealed an increase in adipogenesis in VAT versus SCAT and an elevation in thermogenesis and lipolysis in SCAT versus VAT, which could explain the preferential fat accumulation in SRC-3−/− VAT. Our results presented in vivo evidence that SRC-3 deficiency could lead to fat redistribution under HFD in mice and provided new clues to researches on the pathogenesis of fat redistribution.