ABSTRACT
Impaired oxidative phosphorylation is suggested as a factor behind insulin resistance of skeletal muscle in type 2 diabetes. The role of oxidative phosphorylation in adipose tissue was elucidated from results of Affymetrix gene profiling in subcutaneous and visceral adipose tissue of eight nonobese healthy, eight obese healthy, and eight obese type 2 diabetic women. Downregulation of several genes in the electron transport chain was the most prominent finding in visceral fat of type 2 diabetic women independent of obesity, but the gene pattern was distinct from that previously reported in skeletal muscle in type 2 diabetes. A similar but much weaker effect was observed in subcutaneous fat. Tumor necrosis factor-alpha (TNF-alpha) is a major factor behind inflammation and insulin resistance in adipose tissue. TNF-alpha treatment decreased mRNA expression of electron transport chain genes and also inhibited fatty acid oxidation when differentiated human preadipocytes were treated with the cytokine for 48 h. Thus, type 2 diabetes is associated with a tissue- and region-specific downregulation of oxidative phosphorylation genes that is independent of obesity and at least in part mediated by TNF-alpha, suggesting that impaired oxidative phosphorylation of visceral adipose tissue has pathogenic importance for development of type 2 diabetes.
Subject(s)
Diabetes Mellitus, Type 2/genetics , Gene Expression Profiling , Intra-Abdominal Fat/metabolism , Obesity/genetics , Adult , Cells, Cultured , Diabetes Mellitus, Type 2/metabolism , Down-Regulation/drug effects , Electron Transport/genetics , Fatty Acids/metabolism , Female , Humans , Intra-Abdominal Fat/drug effects , Middle Aged , Oligonucleotide Array Sequence Analysis , Oxidation-Reduction/drug effects , Tumor Necrosis Factor-alpha/pharmacologyABSTRACT
CONTEXT: Low-grade inflammation in adipose tissue may contribute to insulin resistance in obesity. However, the roles of individual inflammatory mediators in adipose tissue are poorly understood. OBJECTIVES: The objective of this study was to determine which inflammation markers are most overexpressed at the gene level in adipose tissue in human obesity and how this relates to corresponding protein secretion. DESIGN: We examined gene expression profiles in 17 lean and 20 obese subjects. The secretory pattern of relevant corresponding proteins was examined in human s.c. adipose tissue or isolated fat cells in vitro and in vivo in several obese or lean cohorts. RESULTS: In ranking gene expression, defined pathways associated with obesity and immune and defense responses scored high. Among seven markedly overexpressed chemokines, only monocyte chemoattractant protein 1 (MCP1) was released from adipose tissue and isolated fat cells in vitro. In obesity, the secretion and expression of MCP1 in adipose tissue pieces were more than 6- and 2-fold increased, respectively, but there was no change in circulating MCP1 levels. There was no net release of MCP1, but there was a net release of leptin, in vivo from adipose tissue into the circulation. CONCLUSIONS: Obesity is associated with the increased expression of several chemokine genes in adipose tissue. However, only MCP1 is secreted into the extracellular space, where it primarily acts as a local factor, because little or no spillover into the circulation occurs. MCP1 influences the function of adipocytes, is a recruitment factor for macrophages, and may be a crucial link among chemokines between adipose tissue inflammation and insulin resistance.
Subject(s)
Adipose Tissue/physiopathology , Chemokine CCL2/physiology , Chemokines/physiology , Obesity/physiopathology , Adult , Body Mass Index , Chemokine CCL2/biosynthesis , Chemokines/biosynthesis , Female , Homeostasis/physiology , Humans , Immunity/physiology , Inflammation Mediators/physiology , Insulin Resistance , Male , Oligonucleotide Array Sequence Analysis , Proteins/metabolism , Reverse Transcriptase Polymerase Chain ReactionABSTRACT
The COQ2 gene in Saccharomyces cerevisiae encodes a Coq2 (p-hydroxybenzoate:polyprenyl transferase), which is required in the biosynthetic pathway of CoQ (ubiquinone). This enzyme catalyses the prenylation of p-hydroxybenzoate with an all-trans polyprenyl group. We have isolated cDNA which we believe encodes the human homologue of COQ2 from a human muscle and liver cDNA library. The clone contained an open reading frame of length 1263 bp, which encodes a polypeptide that has sequence homology with the Coq2 homologues in yeast, bacteria and mammals. The human COQ2 gene, when expressed in yeast Coq2 null mutant cells, rescued the growth of this yeast strain in the absence of a non-fermentable carbon source and restored CoQ biosynthesis. However, the rate of CoQ biosynthesis in the rescued cells was lower when compared with that in cells rescued with the yeast COQ2 gene. CoQ formed when cells were incubated with labelled decaprenyl pyrophosphate and nonaprenyl pyrophosphate, showing that the human enzyme is active and that it participates in the biosynthesis of CoQ.
Subject(s)
Alkyl and Aryl Transferases/genetics , Gene Expression Regulation, Enzymologic/genetics , Ubiquinone/biosynthesis , Alkyl and Aryl Transferases/deficiency , Alkyl and Aryl Transferases/metabolism , Amino Acid Sequence/genetics , Base Sequence/genetics , Cloning, Molecular/methods , Genetic Complementation Test/methods , Humans , Liver/chemistry , Liver/metabolism , Mitochondrial Proteins/genetics , Molecular Sequence Data , Muscle, Skeletal/chemistry , Muscle, Skeletal/metabolism , Mutation/genetics , Organ Specificity/genetics , Predictive Value of Tests , Protein Sorting Signals/genetics , RNA, Messenger/genetics , Saccharomyces cerevisiae/chemistry , Saccharomyces cerevisiae/enzymology , Saccharomyces cerevisiae/genetics , Saccharomyces cerevisiae/growth & development , Saccharomyces cerevisiae Proteins/genetics , Sequence Analysis, DNA/methodsABSTRACT
The steroid hormone (NR3) subfamily of nuclear receptors was until recently believed to be restricted to deuterostomes. However, a novel nuclear receptor belonging to the NR3 subfamily was recently identified in the Drosophila melanogaster genome, indicating the existence of an ancestor before the evolutionary split of deuterostomes and protostomes. This receptor, termed the Drosophila estrogen-related receptor (dERR), most closely resembles the human and mouse estrogen-related receptors (ERRs) in both the DNA binding domain (DBD) (approximately 85% identical) and the ligand binding domain (LBD) (approximately 35% identical). Here we describe the functional analysis and rational design of ligand responsive dERR mutants created by protein engineering of the LBD. On the basis of homology modeling, three amino acid residues in the LBD were identified and mutated to enable ligand-dependent suppression of transcriptional activity. Our results show that the Y295A/T333I/Y365L triple mutant is significantly suppressed by the known ERR inverse agonists 4-hydroxytamoxifen (OHT) and diethylstilbestrol (DES), in comparison to the wild-type dERR receptor, which was inefficiently suppressed by these substances. The coactivator mGRIP-1 (mouse glucocorticoid receptor interacting protein 1) was shown to significantly increase the activity of the triple mutant in transfection experiments, and the addition of OHT resulted in an efficient suppression of the activity. Accordingly, the ability to functionally interact with a coactivator is still maintained by the Y295A/T333I/Y365L mutant. These findings demonstrate the potential of using rational design and engineering of the LBD to study the function of a nuclear receptor lacking identified ligands.
