Adiponectin Knockout Mice Research Articles

Adiponectin and Adiponectin Receptors

Metabolic syndrome is thought to result from obesity and obesity-linked insulin resistance. Obesity in adulthood is characterized by adipocyte hypertrophy. Adipose tissue participates in the regulation of energy homeostasis as an important endocrine organ that secretes a number of biologically active "adipokines."Heterozygous peroxisome proliferator-activated receptor-gamma knockout mice were protected from high-fat diet induced obesity, adipocyte hypertrophy, and insulin resistance. Systematic gene profiling analysis of these mice revealed that adiponectin/Acrp30 was overexpressed. Functional analyses including generation of adiponectin transgenic or knockout mice have revealed that adiponectin serves as an insulin-sensitizing adipokine. In fact, obesity-linked down-regulation of adiponectin was a mechanism whereby obesity could cause insulin resistance and diabetes. Recently, we have cloned adiponectin receptors in the skeletal muscle (AdipoR1) and liver (AdipoR2), which appear to comprise a novel cell-surface receptor family. We showed that AdipoR1 and AdipoR2 serve as receptors for globular and full-length adiponectin and mediate increased AMP-activated protein kinase, peroxisome proliferator-activated receptor-alpha ligand activities, and glucose uptake and fatty-acid oxidation by adiponectin. Obesity decreased expression levels of AdipoR1/R2, thereby reducing adiponectin sensitivity, which finally leads to insulin resistance, the so-called "vicious cycle." Most recently, we showed that osmotin, which is a ligand for the yeast homolog of AdipoR (PHO36), activated AMPK via AdipoR in C2C12 myocytes. This may facilitate efficient development of adiponectin receptor agonists. Adiponectin receptor agonists and adiponectin sensitizers should serve as versatile treatment strategies for obesity-linked diseases such as diabetes and metabolic syndrome.

Adiponectin Stimulates Angiogenesis in Response to Tissue Ischemia through Stimulation of AMP-activated Protein Kinase Signaling

Obesity is a risk factor for the development of cardiovascular diseases that are associated with impaired angiogenesis. Adiponectin is an adipocyte-specific adipocytokine with anti-atherogenic and anti-diabetic properties, and its plasma levels are reduced in association with obesity-linked diseases. Here, we investigated whether adiponectin regulates angiogenesis in response to tissue ischemia using adiponectin knock-out (KO) mice. Angiogenic repair of ischemic hind limbs was impaired in adiponectin-KO mice compared with wild-type (WT) mice as evaluated by laser Doppler flow method and capillary density analyses. Adenovirus-mediated supplement of adiponectin accelerated angiogenic repair in both adiponectin-KO and WT mice. Intramuscular injection of an adenovirus encoding dominant-negative AMP-activated kinase diminished the improvement in limb perfusion seen in WT mice and abolished the adiponectin-induced enhancement of perfusion. These data indicate that adiponectin can function to stimulate angiogenesis in response to ischemic stress by promoting AMP-activated kinase signaling. Therefore, adiponectin may be useful in the treatment for obesity-related vascular deficiency diseases.

Serum adiponectin levels predict the effect of short-term dietary interventions on insulin sensitivity in humans.

Fat-rich diets can acutely induce insulin resistance. Data from adiponectin knock-out mice suggest that this effect might be increased in the absence of adiponectin. In the present study we tested whether plasma adiponectin concentrations influence changes in insulin sensitivity induced by a short-term dietary intervention in humans. We analysed data from 27 healthy, non-obese men with normal glucose tolerance. These men ate a diet high in fat and a diet high in carbohydrates for three days each. The high-fat diet induced a significant drop in insulin sensitivity (determined by euglycaemic-hyperinsulinaemic clamp) compared to baseline (0.100+/-0.009 vs 0.083+/-0.007 micro mol.kg(-1).min(-1).(pmol.l(-1)), p=0.01). The drop in insulin sensitivity was more pronounced in subjects with low serum adiponectin (0.094+/-0.011 vs 0.077+/-0.010 micro mol.kg(-1).min(-1).(pmol.l(-1)), p=0.02) than in subjects with high serum adiponectin (0.103+/-0.011 vs 0.090+/-0.040 micro mol.kg(-1).min(-1).(pmol.l(-1)), p=0.16). In the whole group the high-carbohydrate, low-fat diet did not cause an increase in insulin sensitivity (0.095+/-0.007 vs 0.102+/-0.009 micro mol.kg(-1).min(-1).(pmol.l(-1)), p=0.06). However, insulin sensitivity was significantly increased in the subgroup with low serum adiponectin levels (0.084+/-0.013 vs 0.099+/-0.018 micro mol.kg(-1).min(-1).(pmol.l(-1)), p=0.01). In an additional multivariate analysis post-intervention insulin sensitivity was predicted by pre-intervention insulin sensitivity ( p<0.001) and adiponectin concentrations ( p=0.001). These data indicate that the reduction in insulin sensitivity achieved by a short-term high-fat diet is more pronounced in non-obese subjects with low serum adiponectin. Thus it is possible that the restriction of dietary fat and a diet high in carbohydrates might be particularly effective in subjects with low adiponectin such as obese or Type 2 diabetic individuals.

Adiponectin as a potential key player in metabolic syndrome: Insights into atherosclerosis, diabetes and cancer

The adipose tissue produces and secretes many bioactive substances, collectively referred to as adipocytokines. Adiponectin is an adipocytokine, which we identified by screening the adipose-specific genes from human fat. Plasma concentration of adiponectin is reduced in visceral obesity. Adiponectin accumulated in injured vascular wall, and exhibited anti-atherogenic moieties. Adiponectin knockout mice exhibit a more severe insulin resistance. The human mutation of adiponectin gene accompanying hypoadiponectinemia is strongly associated with both atherosclerotic vascular diseases and type 2 diabetes. We conclude that hypoadiponectinemia stands upstream of the pathophysiology of metabolic syndrome leading to atherosclerosis.

Importance of Adipocytokines in Obesity-Related Diseases

To elucidate the biological characteristics of adipose tissue, we analyzed the gene expression profile of visceral and subcutaneous fat. Unexpectedly, adipose tissue, especially visceral fat, expressed a variety of genes for secretory proteins. About 30% of the genes expressed in visceral adipose tissue encoded secretory proteins and most were biologically active molecules, which we called adipocytokines. We found plasminogen activator inhibitor type 1 and heparin binding EGF-like growth factor. Production of these atherogenic adipocytokines was shown to increase with the accumulation of visceral fat, which may be one of the mechanisms of vascular disease in visceral obesity. We found a unique and novel collagen-like protein, adiponectin, encoded by the most abundantly expressed gene in adipose tissue, termed apM1 (adipose most abundant gene transcript-1). Plasma levels of adiponectin ranged from 0.3 to approximately 3 mg/dl but were decreased in patients with visceral obesity, type 2 diabetes and coronary artery disease (CAD). Screening for mutations in the adiponectin gene revealed that patients carrying a missense mutation showed markedly decreased plasma levels of adiponectin and had CAD. These data suggest that hypoadiponectinemia may be considered an important risk factor for CAD. Cell biology studies revealed that adiponectin has a potent inhibitory effect on the expression of adhesion molecules in endothelial cells and an inhibitory effect on the expression in macrophages. In order to confirm these antidiabetic and antiatherogenic functions of adiponectin, we developed adiponectin knockout mice. Adiponectin knockout mice showed severe insulin resistance and impaired glucose metabolism when fed a high-fat, high-sucrose diet. Knockout mice also developed intimal thickening in response to endothelial injury.

Enhanced carbon tetrachloride-induced liver fibrosis in mice lacking adiponectin

Background & Aims : Obesity is one of the risk factors for liver fibrosis, in which plasma adiponectin, an adipocytokine, levels are decreased. Hepatic stellate cells play central roles in liver fibrosis. When they are activated, they undergo transformation to myofibroblast-like cells. Adiponectin suppresses the proliferation and migration of vascular smooth muscle cells, whose characteristics are similar to those of hepatic stellate cells. Adiponectin could have biological significances in liver fibrosis. Methods : The role of adiponectin on liver fibrosis induced by the administration of carbon tetrachloride twice a week for 12 weeks was tested by using adiponectin-knockout mice and an adenovirus-mediated adiponectin-expression system. We also investigated the effect of adiponectin in activated hepatic stellate cells. Results : When mice were administered carbon tetrachloride (300 μL/kg body weight) twice a week for 12 weeks, knockout mice showed extensive liver fibrosis with an enhanced expression of transforming growth factor-β1 and connective tissue growth factor compared with wild-type mice ( P < 0.05). Injection of adenovirus producing adiponectin (AdADN) before carbon tetrachloride (1000 μL/kg body weight) treatment prevented liver fibrosis in wild-type mice ( P < 0.001). Injection of AdADN at 6 weeks attenuated liver fibrosis even though carbon tetrachloride was given for an additional 6 weeks (total of 12 weeks). In cultured hepatic stellate cells, adiponectin suppressed platelet-derived growth factor-induced proliferation and migration and attenuated the effect of transforming growth factor-β1 on the gene expression of transforming growth factor-β1 and connective tissue growth factor and on nuclear translocation of Smad2. Conclusions : The findings indicate that adiponectin attenuates liver fibrosis and could be a novel approach in its prevention.

Dual roles of adiponectin/Acrp30 in vivo as an anti-diabetic and anti-atherogenic adipokine.

Genome-wide scanning is a powerful tool to identify susceptible chromosome loci, however, individual chromosomal regions still have many candidate genes. Although cDNA microarray analysis provides valuable information for identifying genes involved in pathogenesis, expression levels of many genes are changed. A novel approach for identification of therapeutic targets is the combination of genome-wide scanning and the use of DNA chips, as shown in Fig. (1). Using DNA chips, we screened for secreted molecules, the expressions of which were changed in adipose tissues from mice rendered insulin resistance. Decreased expression of one of these molecules, adiponectin/Acrp30, correlates strongly with insulin resistance. Interestingly, recent genome-wide scans have mapped a susceptibility locus for type 2 diabetes and metabolic syndrome to chromosome 3q27, where adiponectin gene is located. Decreasing serum adiponectin levels are associated with increased risk for type 2 diabetes. Interestingly, adiponectin was decreased in insulin resistant rodent models both of obesity and lipoatrophy, and replenishment of adiponectin ameliorated their insulin resistance. Moreover, adiponectin transgenic mice ameliorated insulin resistance and diabetes Adiponectin knockout mice showed insulin resistance and glucose intolerance. In muscle and liver, adiponectin activated AMP kinase and PPARalpha pathways thereby increasing beta-oxidation of lipids, leading to decreased TG content, which ameliorated insulin resistance under a high-fat diet. Despite similar plasma glucose and lipid levels on an apoE deficient background, adiponectin transgenic apoE deficient mice showed amelioration of atherosclerosis, which was associated with decreased expressions of class A scavenger receptor and tumor necrosis factor alpha. Finally, cDNA encoding adiponectin receptors (AdipoR1 and R2) have been identified by expression cloning, which facilitates the understanding of molecular mechanisms of adiponectin actions and obesity-linked diseases such as diabetes and atherosclerosis and the designing of novel antidiabetic and anti-atherogenic drugs with AdipoR1 and R2 as molecular targets.

Adiponectin: stability in plasma over 36 hours and within-person variation over 1 year.

Adiponectin (Arcp30, AdipoQ, apM1, or GBP28), a novel 247-amino acid peptide, is secreted predominantly by adipocytes and accounts for ∼0.05% of total serum proteins (1)(2)(3)(4). It is induced early in adipocyte differentiation (1), consists of an N-terminal collagenous and a C-terminal globular domain, and shares homology to subunits of complement factor C1q (1)(3). Adiponectin expression is reduced in obesity and type 2 diabetes, and plasma concentrations of adiponectin are inversely related to body weight and insulin concentrations (5)(6)(7)(8). Treatment with adiponectin improves insulin sensitivity in mouse models of insulin resistance (9)(10), and in adiponectin knockout mice, adiponectin substitution can reverse diet-induced insulin resistance (11). Adiponectin is also inversely associated with other traditional cardiovascular risk factors, such as blood pressure, heart rate, total cholesterol, LDL-cholesterol, and triglycerides (12)(13). In addition, recent studies suggest that it may have antiatherogenic and antiinflammatory properties (14)(15)(16)(17)(18)(19). Adiponectin may therefore be an important blood biomarker to assess in large-scale epidemiologic studies of several chronic diseases. To gain a reliable risk estimate with a single blood measurement, the within-person variability over time should be small compared with the between-person variability (20). In addition, the stability of a valid biological marker should not be substantially affected by length of storage or temperature (21)(22)(23)(24)(25). Ideally, serum or plasma from whole blood should be separated immediately and stored in deep freeze. In large epidemiologic studies, however, blood specimens are often collected at different times and locations and transported on ice over several hours or days to central laboratories for processing and storage. The aims of the present study were to evaluate the stability of …