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Lei Zhou,
Xiaolan Yu,
Qingjie Meng,
Hongqiang Li,
Congcong Niu,
Yun Jiang,
Yuxi Cai,
Minghui Li,
Qiang Li,
Chaoqiang An,
Le Shu,
Ao Chen,
Handong Su,
Yin Tang,
Shen Yin,
Silja Raschke,
Kristin Eckardt,
Jürgen Eckel,
Zaiqing Yang
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ABSTRACT: Obesity is associated with many severe chronic diseases and deciphering its development and molecular mechanisms is necessary for promoting treatment. Previous studies have revealed that mitochondrial content is down-regulated in obesity, diabetes, and nonalcoholic fatty liver disease (NAFLD) and proposed that NAFLD and diabetes are mitochondrial diseases. However, the exact mechanisms underlying these processes remain unclear. In this study, we discovered that resistin down-regulated the content and activities of mitochondria, enhanced hepatic steatosis, and induced insulin resistance in mice. The time course indicated that the change in mitochondrial content was prior to the change in fat accumulation and development of insulin resistance. When the mitochondrial content was maintained, resistin did not stimulate hepatic fat accumulation. The present mutation study found that the residue Thr464 of the p65 subunit of NF-κB was essential for regulating mitochondria. A proximity ligation assay (PLA) revealed that resistin inactivated PGC-1α and diminished the mitochondrial content by promoting the interaction of p65 and PGC-1α. Signaling transduction analysis demonstrated that resistin down-regulated mitochondria via a novel PKC-PKG-p65-PGC-1α signaling pathway. Conclusion: we discovered for the first time, that resistin induced hepatic steatosis through diminishing mitochondrial content. This study revealed a novel pathway for mitochondrial regulation, and suggests that the maintenance of normal mitochondrial content could be a new strategy for treatment of obesity-associated diseases.(HEPATOLOGY 2012.).
Hepatology 11/2012; · 11.66 Impact Factor
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ABSTRACT: PERILIPIN5 (PLIN5) is a newly discovered member of the PAT family that regulates cellular neutral lipid stores and use. It is expressed in highly oxidative tissues and is induced during fasting. Like other members of the PAT family, PERILIPIN5 expression is also regulated by PPARα. However, its induction by fasting is PPARα-independent. So far, the transcriptional regulation of perilipin5, apart from PPARα, remains unclear. In the present study, we investigated the transcriptional regulation of pig perilipin5 and revealed that its promoter activity was up-regulated by C/EBPα. By constructing various progressive deletions and mutants, the binding region of C/EBPα was discovered. Furthermore, the binding site was identified by chromatin immunoprecipitation and luciferase reporter assays. Moreover, over-expression of C/EBPα induced endogenous perilipin5 expression in the pig kidney cell line IBRS2. Data from arrays showed that C/EBPα expression was induced during fasting. Taken together, our results indicate that C/EBPα is an essential regulatory factor for perilipin5 transcription and suggest that fasting stimulates perilipin5 transcription through influencing C/EBPα expression.
Molecular and Cellular Endocrinology 08/2012; 364(1-2):28-35. · 4.19 Impact Factor
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ABSTRACT: Patatin-like phospholipases (PNPLAs) comprise a protein family whose members contain a conserved patatin-like domain with lipid acyl hydrolase activity. The cloning and characterization of full-length cDNAs of PNPLA3 and PNPLA4 in pigs is reported and, for the first time, an alternative splicing variant of porcine PNPLA4, which skips exon 5 of the normal transcript, was identified. Subsequently, tissue expression analysis by quantitative PCR indicated that porcine PNPLA3 was mainly expressed in both adipose and liver whereas porcine PNPLA4 was abundant in liver. Porcine PNPLA3 and PNPLA4 were assigned respectively to chromosome 5p11-p15 and Xp24.
Biotechnology Letters 03/2011; 33(7):1327-37. · 1.68 Impact Factor
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ABSTRACT: Ginkgo biloba, an herbal medication, is capable of lowering glucose, fat, and lipid peroxide in diabetic patients. In the current study, we tested the hypothesis that Ginkgo biloba extract (GBE) prevented hyperinsulinism-induced glucose intolerance in hepatocytes. We investigated the effects of GBE on glucose consumption, glucokinase activity, and mRNA levels of key genes in glucose metabolism and the insulin signaling pathway. To better show its efficacy, we included a control group that was treated with rosiglitazone, a type of thiazolidinedione (TZD). The data indicated that GBE repressed glucose uptake under normal conditions, while it dramatically improved glucose tolerance under insulin-resistant conditions. Furthermore, after analyzing gene expression, we suggest that GBE chiefly exerts its effects by stimulating IRS-2 transcription. It should be noted that, unlike rosiglitazone, GBE did not stimulate excessive glucose uptake as it improved glucose tolerance. It is said that GBE treatment could avoid drug-induced obesity. Our data suggest that GBE has the potential to prevent insulin resistance and is a promising anti-diabetic drug.
Journal of Natural Medicines 01/2011; 65(1):50-6. · 1.39 Impact Factor
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ABSTRACT: The hormone resistin, which was originally shown to induce insulin resistance, has been implicated in the regulation of inflammatory processes, but the molecular mechanism underlying such regulation has not been clearly defined. The goal of our study was to determine whether the expression of COX-2 can be induced by resistin and what the potential signaling pathway involved in this process is. Compared with controls, resistin significantly upregulated COX-2 expression in RAW264.7 macrophage cells. Administration of anti-resistin antibody could significantly reduce this effect. Induction of COX-2 by resistin was also markedly reduced in the presence of either dominant negative mutant IkappaBalpha or PDTC, a pharmacological inhibitor of NF-kappaB. On the other hand, NF-kappaB subunit p65 was upregulated by resistin. Moreover, we found that transforming growth factor-beta-activated kinase 1 (TAK1), a mitogen-activated protein kinase kinase kinase (MAPKKK), could be activated in response to resistin. These results suggest that resistin enhances COX-2 expression in mouse macrophage cells in a TAK1-IKK-NF-kappaB-dependent manner and therefore plays a critical role in inflammatory processes.
Inflammation 09/2009; 33(1):25-33. · 1.75 Impact Factor
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ABSTRACT: The Gq class is one subfamily of the G protein alpha subunits multigene family. It comprises four genes: Gnaq, Gna11, Gna14, and Gna15. In mice and humans, the alpha subunit is an essential component of G protein interaction with receptors and effectors. We report here the cloning and characterization of porcine Gnaq, Gna11, and Gna14. We have cloned the full-length coding sequences of porcine Gnaq, Gna11, and Gna14 (1,080, 1,080, and 1,068 bp, respectively) and then mapped them chromosomally to regions 1q21-27, 2q21-24, and 1q21-27 by radiation hybrid mapping. Tissue distribution analysis indicated that Gnaq and Gna11 were coexpressed in liver, heart, muscle, spleen, adipose tissue, brain, and uterus, but Gna14 mRNA was detected only in kidney and lung. The phylogenetic trees reveal that porcine Gnaq, Gna11, and Gna14 are evolutionarily closer to their human homologs. This is the first report of molecular cloning and characterization of porcine Gnaq, Gna11, and Gna14, which will be helpful for further understanding of the physiological role of Gq class genes in pigs.
Biochemical Genetics 09/2008; 46(7-8):398-405. · 0.86 Impact Factor
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ABSTRACT: Adipocyte-derived factors might play a role in the development of hepatic insulin resistance. Resistin was identified as an adipokine linking obesity and insulin resistance. Resistin is secreted from adipocytes in rodents but in humans it was proposed to originate from macrophages and its impact for insulin resistance has remained elusive. To analyze the role of adipokines in general and resistin as a special adipokine, we cultured the human liver cell line HepG2 with adipocyte-conditioned medium (CM) containing various adipokines such as IL-6 and MCP-1, and resistin. CM and resistin both induce insulin resistance with a robust decrease in insulin-stimulated phosphorylation of Akt and GSK3. Insulin resistance could be prevented by co-treatment with troglitazone but not by co-stimulation with adiponectin. As human adipocytes do not secrete resistin, HepG2 cells were also treated with resistin added into CM. CM with resistin addition induced stronger insulin resistance than CM alone pointing to a specific role of resistin in the initiation of hepatic insulin resistance in humans.
FEBS Letters 10/2007; 581(22):4303-8. · 3.54 Impact Factor
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ABSTRACT: As a beta(2)-adrenergic agonist, clenbuterol decreases body fat, but the molecular mechanism underlying this process is unclear. In the present study, we treated 293T and L-02 cells with clenbuterol and found that clenbuterol downregulates SREBP-1c expression and upregulates CREB1 expression. Considering SREBP-1c has the function of regulating the transcription of several lipogenic enzymes, we considered that the downregulation of SREBP-1c is responsible for body fat reduction by clenbuterol. Many previous studies have found that clenbuterol markedly increases intracellular cAMP levels, therefore, we also investigated whether CREB1 is involved in this process. The data from our experiments indicate that CREB1 overexpression inhibits SREBP-1c transcription, and that this action is antagonized by CREB2, a competitive inhibitor of CREB1. Furthermore, since PPARs are able to repress SREBP-1c transcription, we investigated whether clenbuterol and CREB1 function via a pathway involving PPAR activation. However, our results showed that clenbuterol or CREB1 overexpression suppressed PPARs transcription in 293T and L-02 cells, which suggested that they impair SREBP-1c expression in other ways.
Journal of biochemistry and molecular biology 08/2007; 40(4):525-31. · 2.02 Impact Factor
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ABSTRACT: Visfatin is a newly discovered visceral fat-specific adipocytokine. It is upregulated in obesity and exerts insulin-mimetic effects in various tissues in human and mouse. We reported here the cloning and characterization of porcine visfatin, its three alternate splicing variants. Sequence analysis indicated that variant 1 is the predominant form among species, which contains an open reading frame of 1473 bp encoding a 52-kDa protein of 491 amino acids. While the other two variants were predicted to encode two 3' truncated proteins due to early termination. The nucleotide and amino acid sequences deduced from variant 1 were conservative across species. The porcine visfatin gene was composed of 11 exons at least and had exactly the same exon/intron structure as the human orthologs. Nested PCR showed that variants 1 and 3 were ubiquitously expressed in porcine tissues and that variant 2 was expressed in most tissues examined with exception of testis and liver. The discovery of the three variants of visfatin in porcine would be useful to the further investigation of the function of the visfatin gene.
Domestic Animal Endocrinology 05/2007; 32(3):235-45. · 2.06 Impact Factor
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ABSTRACT: Resistin is a 12.5-kDa cysteine-rich protein secreted from adipose tissue and is an important factor linking obesity with insulin resistance. Here, we investigated the effect of resistin on glucose tolerance in adult human hepatocytes (L-02 cells). In this study, resistin cDNA was transfected into L-02 cells, and glucose concentration and glucokinase activity were determined subsequently. The data indicated resistin impaired, insulin-stimulated glucose utilization, which implied liver was a target tissue of resistin. To understand its molecular mechanism, mRNA levels of key genes in glucose metabolism and insulin signaling pathway were analyzed. The results demonstrated resistin-stimulated expression of glucose-6-phosphatase (G6Pase), sterol regulatory element-binding protein 1c (SREBP1c) and suppressor of cytokine signaling 3 (SOCS-3), repressed expression of peroxisome proliferator-activated receptor gamma (PPARgamma) as well as insulin receptor substrate 2 (IRS-2). Given that glucokinase (GK) activity and glucose transporter 2 (GLUT2) expression were not altered, we presumed that resistin did not effect them. Moreover, resistin lowered mRNA levels of IRS-2 while stimulating SOCS-3 expression, which suggests it impairs glucose tolerance by blocking the insulin signal transduction pathway.
European cytokine network 10/2006; 17(3):189-95. · 1.73 Impact Factor
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ABSTRACT: Resistin, which is a protein that is secreted exclusively by adipocytes, plays an important role in insulin resistance and adipocyte differentiation. Adipocytes express significant amounts of resistin mRNA, while preadipocytes express low levels of resistin mRNA. The mechanism that causes this difference is unclear. Therefore, we studied the mechanism regulating resistin expression and the roles of different transcriptional factors in this process. The results from fluorescent photography and semi-quantitative RT-PCR showed that sterol regulatory element-binding protein 1c (SREBP1c) and cyclic AMP response-element-binding protein (CREB) had no effect on resistin expression. By contrast, CCAAT/enhancer-binding protein-alpha (C/EBPalpha) increased resistin mRNA levels both in 3T3-L1 preadipocytes and in 293T cells. The relative increase in the amount of resistin mRNA in the 293T cells was much larger than that in the 3T3-L1 preadipocytes. Moreover, while C/EBPalpha was necessary for resistin expression, we found that up-regulating C/EBPalpha levels alone was not sufficient to induce a similar level of resistin in preadipocytes to that in adipocytes.
Domestic Animal Endocrinology 03/2006; 30(2):98-107. · 2.06 Impact Factor
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ABSTRACT: To sequence the gene encoding glutamate rich protein (GLURP) and identify the genotypes of geographically different Plasmodium falciparum (P. f) isolates from China.
The gene of R2 repeat region of GLURP was amplified by nested polymerase chain reaction and cloned into T-vector. The nucleotide sequence of GLURP gene was determined by automatic sequencer (Dideoxy termination method) and analyzed by DNA Star software.
At least 7 different GLURP genotypes ranging from 600 bp to 1,500 bp were found in Yunnan and Hainan provinces. R2 region of GLURP gene consisted of several repeat units. Each repeat unit was composed of 19-20 residues which were shown to be highly conserved. GLURP gene was also size polymorphic due to differences in the number of repeat units, whereas the repeat sequence was conserved. Sequence analysis showed that DNA sequences and deduced amino acid sequences were highly homologous among the geographically dispersed isolates or various isolates from the same geographical region. No obvious differences were found in the GLURP gene sequences among geographically different isolates.
GLURP gene is highly structure conserved and size polymorphic, and so is useful in searching for malaria vaccine candidate antigen and developing a genotyping method for malaria research.
Biomedical and Environmental Sciences 04/2002; 15(1):1-7. · 1.35 Impact Factor
