The antidiabetic hormone adiponectin circulates in blood as several oligomeric complexes, and the ratios between them are critical in determining insulin sensitivity. In this study we investigated the role of testosterone in regulating the oligomeric complex distribution of adiponectin. Gel filtration analysis revealed that circulating adiponectin existed as the forms of high molecular weight (HMW), middle molecular weight, and low molecular weight complexes in both human and mice. The concentration of HMW adiponectin in female was significantly higher than that in male, whereas there were no gender differences for the other two forms. Castration induced a dramatic elevation of the HMW form but had no effect on either the middle molecular weight or the low molecular weight form in mice. Testosterone treatment, on the other hand, caused a specific reduction of HMW adiponectin in the circulation. Pulse-chase labeling experiments in rat adipocytes revealed that the three oligomeric forms of adiponectin were secreted into the culture medium at different rates and that testosterone selectively impeded the secretion of HMW adiponectin but not the other two forms. The inhibitory effect of testosterone on secretion of HMW adiponectin was largely restored by the transcription inhibitor actinomycin D, suggesting the involvement of a transcriptional event in this process. The selective inhibition of HMW adiponectin by testosterone might contribute to the sex dimorphism of adiponectin in terms of its oligomeric complex distribution and could partly explain why men have higher risk to insulin resistance and atherosclerosis than women.

The discovery of circulating fetal nucleic acid in maternal plasma has opened up new possibilities for noninvasive prenatal diagnosis. Thus far, a gender-and polymorphism-independent fetalspecific target that can be used for prenatal screening and monitoring in all pregnant women has not been reported. In addition, the origin of such circulating nucleic acid has remained unclear. Here we provide direct evidence that the placenta is an important source of fetal nucleic acid release into maternal plasma by demonstrating that mRNA transcripts from placenta-expressed genes are readily detectable in maternal plasma. The surprising stability of such placental mRNA species in maternal plasma and their rapid clearance after delivery demonstrate that such circulating mRNA molecules are practical markers for clinical use. The measurement of such plasma mRNA markers has provided a gender-independent approach for noninvasive prenatal gene expression profiling and has opened up numerous research and diagnostic possibilities.N oninvasive prenatal diagnosis is a long-sought goal in human genetics. Recent interest in cell-free DNA in plasma and serum (1, 2) has led to the discovery of fetal DNA in maternal plasma (3)(4)(5). This noninvasive source of fetal nucleic acid has already been shown to be clinically valuable in the prenatal investigation of many conditions, including fetal rhesus D status (6, 7), sex-linked diseases (8), and ␤ thalassemia (9). In addition, quantitative aberrations of fetal DNA have been described in many pathological conditions, including preeclampsia (10, 11), fetal chromosomal aneuploidies (12, 13), and hyperemesis gravidarum (14).Despite the promising clinical use of fetal DNA in maternal plasma for noninvasive prenatal diagnosis, a number of challenges remain and several fundamental biological issues about this phenomenon are unresolved. First, in studies reporting the quantitative abnormalities involving fetal DNA in maternal plasma, the Y chromosome is commonly used as a fetal-specific marker in women carrying male fetuses (10-14). The use of such Y-specific markers has limited the application of this technology to the 50% of pregnant women who are carrying male fetuses. The eventual routine clinical application of this technology, e.g., as a screening tool for fetal chromosomal aneuploidies (12, 13), will be catalyzed by the development of a gender-and polymorphism-independent fetal nucleic acid marker, which can be used in all pregnancies. Second, the source of fetal DNA in maternal plasma remains unclear. Although it has been suggested that such fetal DNA could have originated from the placenta (4), no empirical proof of this hypothesis has been put forward to date.Recently, a number of investigators have shown that in addition to DNA, RNA is also present in the plasma of human subjects, particularly those with cancer (15-18). The inherent lability of RNA has made these observations rather surprising. It has been suggested that circulating RNA may be stabilized by being protected in apoptotic ...

Angiopoietin-like protein 4 (ANGPTL4) is a circulating protein predominantly expressed in adipose tissue and liver. Several recent studies demonstrated that ANGPTL4 is the target gene of peroxisome proliferation activators, the agonists of which are widely used as the antidiabetic and lipid-lowering drugs. Here we provide evidence that ANGPTL4 is a blood-borne hormone directly involved in regulating glucose homeostasis, lipid metabolism, and insulin sensitivity. Adenovirus-mediated expression of ANGPTL4 potently decreased blood glucose and improved glucose tolerance, whereas it induced hyperlipidemia, fatty liver, and hepatomegaly in C57 mice. In db͞db diabetic mice, ANGPTL4 treatment reduced hyperglycemia to a normal level, and markedly alleviated glucose intolerance and hyperinsulinemia. Ex vivo studies on primary rat hepatocytes revealed that ANGPTL4 significantly decreased hepatic glucose production and enhanced insulin-mediated inhibition of gluconeogenesis. Serum levels of ANGPTL4 in human subjects inversely correlated with plasma glucose concentrations and HOMA IR, the homeostasis model assessment of insulin resistance. In patients with type 2 diabetes, serum levels of ANGPTL4 were significantly lower than those in healthy subjects, suggesting that the decreased ANGPTL4 could be a causative factor of this disease. These results collectively indicate that ANGPTL4 exerts distinct effects on glucose and lipid metabolism, and that its beneficial effect on glucose homeostasis might be useful for the treatment of diabetes.adipokine ͉ diabetes ͉ fatty liver ͉ metabolism A dipose tissue is now recognized to be an important endocrine organ that secretes a variety of bioactive peptides, known as adipokines (or adipocytokines). Growing evidence suggests that adipokines are critically involved in regulating energy metabolism, systemic insulin sensitivity, cardiovascular tone, and immune response (1, 2). Several adipokines, such as TNF-␣, resistin, and IL6, play causative roles in the pathogenesis of insulin resistance, type 2 diabetes, and thrombotic diseases (1). On the other hand, leptin and adiponectin possess many beneficial functions on energy metabolism and insulin sensitivity. Leptin has long been viewed as an antiobesity hormone (3), whereas adiponectin is an insulin-sensitizing adipokine with direct antidiabetic, antiatherogenic, and antiinflammatory functions (4).Angiopoietin-like protein 4 (ANGPTL4), also known as peroxisome proliferator-activated receptor ␥ (PPAR␥) angiopoietinrelated protein, fasting-induced adipose factor, or hepatic fibrinogen͞angiopoietin-r elated protein, is a recently identified adipokine that is predominantly expressed in adipose tissue and liver (5-7). Mouse ANGPTL4 is composed of an NH 2 -terminal coiled-coil domain and a carboxyl fibronectin-like motif, a structural organization conserved in both angiopoietins and angiopoietin-like proteins (5). ANGPTL4 was originally identified as the target gene of PPAR (5, 6). The agonists of both PPAR␥ and PPAR␣ could enhance ANGPTL4 express...

Adiponectin is a multifunctional adipokine that circulates as several oligomeric complexes in the blood stream. However, the molecular basis that regulates the production of the adiponectin oligomers remains largely elusive. We have shown previously that several conserved lysine residues (positions 68 Here, we investigated the potential roles of these post-translational modifications in oligomeric complex formation of adiponectin. Gel filtration chromatography revealed that adiponectin produced from mammalian cells formed trimeric, hexameric, and high molecular weight (HMW) oligomeric complexes. These three oligomeric forms were differentially glycosylated, with the HMW oligomer having the highest carbohydrate content. Disruption of hydroxylation and glycosylation by substitution of the four conserved lysines with arginines selectively abrogated the intracellular assembly of the HMW oligomers in vitro as well as in vivo. In type 2 diabetic patients, both the ratios of HMW to total adiponectin and the degree of adiponectin glycosylation were significantly decreased compared with healthy controls. Functional studies of adiponectin-null mice revealed that abrogation of lysine hydroxylation/glycosylation markedly decreased the ability of adiponectin to stimulate phosphorylation of AMP-activated protein kinase in liver tissue. Chronic treatment of db/db diabetic mice with wild-type adiponectin alleviated hyperglycemia, hypertriglyceridemia, hepatic steatosis, and insulin resistance, whereas full-length adiponectin without proper post-translational modifications and HMW oligomers showed substantially decreased activities. Taken together, these data suggest that hydroxylation and glycosylation of the lysine residues within the collagenous domain of adiponectin are critically involved in regulating the formation of its HMW oligomeric complex and consequently contribute to the insulin-sensitizing activity of adiponectin in hepatocytes.,Adiponectin, a hormone synthesized by adipocytes, is an abundant serum adipokine with potent insulin-sensitizing activity (1-3). Unlike most other adipokines, the plasma levels of adiponectin are significantly decreased in obese individuals and patients with insulin resistance, type 2 diabetes mellitus (T2DM), 2 and cardiovascular diseases (4 -7). Elevation of circulating adiponectin by either transgenic overexpression or direct supplementation with recombinant adiponectin can alleviate many metabolic abnormalities associated with various insulin-resistant and/or diabetic animal models (8 -12). The globular domain of adiponectin decreases postprandial blood glucose, enhances lipid clearance, and increases insulin sensitivity by enhancing fatty acid ␤-oxidation in skeletal muscle (8). On the other hand, full-length adiponectin generated from mammalian cells enhances the sensitivity of insulin to inhibit hepatic glucose production by suppressing the expression of several key enzymes involved in gluconeogenesis, including phosphoenolpyruvate carboxylase and glucose-6-phosphatase (10).In addit...