[Abstract unavailable

Human Protein Reference Database (HPRD) is an object database that integrates a wealth of information relevant to the function of human proteins in health and disease. Data pertaining to thousands of protein-protein interactions, posttranslational modifications, enzyme/substrate relationships, disease associations, tissue expression, and subcellular localization were extracted from the literature for a nonredundant set of 2750 human proteins. Almost all the information was obtained manually by biologists who read and interpreted >300,000 published articles during the annotation process. This database, which has an intuitive query interface allowing easy access to all the features of proteins, was built by using open source technologies and will be freely available at http://www.hprd.org to the academic community. This unified bioinformatics platform will be useful in cataloging and mining the large number of proteomic interactions and alterations that will be discovered in the postgenomic era.

The insulin-sensitizing hormone, adiponectin, belongs to the expanding C1q/TNF (tumour necrosis factor) family of proteins. We recently identified a family of adiponectin paralogues designated as CTRP (C1q/TNF-related protein) 1–7, and in the present study describe CTRP10. In the present study, we show that CTRP1, CTRP2, CTRP3, CTRP5 and CTRP7 transcripts are expressed predominantly by adipose tissue. In contrast, placenta and eye expressed the highest levels of CTRP6 and CTRP10 transcripts respectively. Expression levels of CTRP1, CTRP2, CTRP3, CTRP6 and CTRP7 transcripts are up-regulated in 8-week-old obese (ob/ob)mice relative to lean controls. Treatment of mice with a PPAR-γ (peroxisome-proliferator-activated receptor-γ) agonist, rosiglitazone, increased the expression of CTRP1 and decreased CTRP6 transcript levels. All CTRPs are secreted glycoproteins when expressed in mammalian cells. CTRP1, CTRP2, CTRP3, CTRP5 and CTRP6 circulate in the blood and are potential endocrine hormones; their serum levels vary according to the sex and genetic background of mice. Importantly, serum levels of CTRP1 and CTRP6 are increased in adiponectin-null mice. Like adiponectin, all secreted CTRP proteins form trimers as their basic structural units. CTRP3, CTRP5, CTRP6 and CTRP10 trimers are further assembled into higher-order oligomeric complexes via disulfide bonding mediated by their N-terminal cysteine residues. Besides forming homo-oligomers, CTRP1/CTRP6, CTRP2/CTRP7 and adiponectin/CTRP2 are secreted as heterotrimers, thus providing a mechanism to potentially generate functionally distinct ligands. Functional characterization of one such family member, CTRP1, showed that it specifically activates Akt and p44/42-MAPK (mitogen-activated protein kinase) signalling pathways in differentiated mouse myotubes. Moreover, injection of recombinant CTRP1 into mice significantly reduced their serum glucose levels. Thus at least CTRP1 may be considered a novel adipokine. In summary, these molecular, biochemical and functional data provide an important framework to further address the physiological functions and mechanisms of the action of this family of secreted glycoproteins in normal and disease states.

Background: Skeletal muscle-derived myokines modulate metabolic, inflammatory, and other processes. Results: Myonectin, a novel myokine whose expression and circulating levels are regulated by diet, metabolic state, and exercise, functions to control lipid metabolism. Conclusion: Myonectin is a potential nutrient-responsive metabolic regulator secreted by muscle. Significance: Myonectin links muscle to systemic lipid metabolism via its action on adipocytes and hepatocytes, providing insight into complex tissue cross-talk.

Biochemical, genetic, and animal studies in recent years have established a critical role for the adipokine Acrp30͞adiponectin in controlling whole-body metabolism, particularly by enhancing insulin sensitivity in muscle and liver, and by increasing fatty acid oxidation in muscle. We describe a widely expressed and highly conserved family of adiponectin paralogs designated as C1q͞ tumor necrosis factor-␣-related proteins (CTRPs) 1-7. In the present study, we focus on mCTRP2, the mouse paralog most similar to adiponectin. At nanomolar concentrations, bacterially produced mCTRP2 rapidly induced phosphorylation of AMP-activated protein kinase, acetyl-CoA carboxylase, and mitogen-activated protein kinase in C2C12 myotubes, which resulted in increased glycogen accumulation and fatty acid oxidation. The discovery of a family of adiponectin paralogs has implications for understanding the control of energy homeostasis and could provide new targets for pharmacologic intervention in metabolic diseases such as diabetes and obesity.

All mammals produce heparin, a negatively charged glycosaminoglycan that is a major constituent of the secretory granules of mast cells which are found in the peritoneal cavity and most connective tissues. Although heparin is one of the most studied molecules in the body, its physiological function has yet to be determined. Here we describe transgenic mice, generated by disrupting the N-deacetylase/N-sulphotransferase-2 gene, that cannot express fully sulphated heparin. The mast cells in the skeletal muscle that normally contain heparin lacked metachromatic granules and failed to store appreciable amounts of mouse mast-cell protease (mMCP)-4, mMCP-5 and carboxypeptidase A (mMC-CPA), even though they contained substantial amounts of mMCP-7. We developed mast cells from the bone marrow of the transgenic mice. Although these cultured cells contained high levels of various protease transcripts and had substantial amounts of mMCP-6 protein in their granules, they also failed to express mMCP-5 and mMC-CPA. Our data show that heparin controls, through a post-translational mechanism, the levels of specific cassettes of positively charged proteases inside mast cells.

Adiponectin is a major insulin-sensitizing, multimeric hormone derived from adipose tissue that acts on muscle and liver to regulate whole-body glucose and lipid metabolism. Here, we describe a novel and highly conserved paralog of adiponectin designated as C1q/TNF-related protein (CTRP) 9. Of all the CTRP paralogs, CTRP9 shows the highest degree of amino acid identity to adiponectin in its globular C1q domain. CTRP9 is expressed predominantly in adipose tissue and females expresses higher levels of the transcript than males. Moreover, its expression levels in ob/ob mice changed in an age-dependent manner, with significant up-regulation in younger mice. CTRP9 is a secreted glycoprotein with multiple post-translational modifications in its collagen domain that include hydroxylated prolines and hydroxylated and glycosylated lysines. It is secreted as multimers (predominantly trimers) from transfected cells and circulates in the mouse serum with levels varying according to sex and metabolic state of mice. Furthermore, CTRP9 and adiponectin can be secreted as heterooligomers when cotransfected into mammalian cells, and in vivo, adiponectin/CTRP9 complexes can be reciprocally coimmunoprecipitated from the serum of adiponectin and CTRP9 transgenic mice. Biochemical analysis demonstrates that adiponectin and CTRP9 associate via their globular C1q domain, and this interaction does not require their conserved N-terminal cysteines or their collagen domains. Furthermore, we show that adiponectin and CTRP9 form heterotrimers. In cultured myotubes, CTRP9 specifically activates AMPK, Akt, and p44/42 MAPK signaling pathways. Adenovirus-mediated overexpression of CTRP9 in obese (ob/ob) mice significantly lowered serum glucose levels. Collectively, these results suggest that CTRP9 is a novel adipokine, and further study of CTRP9 will yield novel mechanistic insights into its physiological and metabolic function.

Adipose tissue-derived adipokines play important roles in controlling systemic insulin sensitivity and energy balance. Our recent efforts to identify novel metabolic mediators produced by adipose tissue have led to the discovery of a highly conserved family of secreted proteins, designated as C1q/TNFrelated proteins 1-10 (CTRP1 to -10). However, physiological functions regulated by CTRPs are largely unknown. Here we provide the first in vivo functional characterization of CTRP3. We show that circulating levels of CTRP3 are inversely correlated with leptin levels; CTRP3 increases with fasting, decreases in diet-induced obese mice with high leptin levels, and increases in leptin-deficient ob/ob mice. A modest 3-fold elevation of plasma CTRP3 levels by recombinant protein administration is sufficient to lower glucose levels in normal and insulin-resistant ob/ob mice, without altering insulin or adiponectin levels. The glucose-lowering effect in mice is linked to activation of the Akt signaling pathway in liver and a marked suppression of hepatic gluconeogenic gene expression. Consistent with its effects in mice, CTRP3 acts directly and independently of insulin to regulate gluconeogenesis in cultured hepatocytes. In humans, alternative splicing generates two circulating CTRP3 isoforms differing in size and glycosylation pattern. The two human proteins form hetero-oligomers, an association that does not require interdisulfide bond formation and appears to protect the longer isoform from proteolytic cleavage. Recombinant human CTRP3 also reduces glucose output in hepatocytes by suppressing gluconeogenic enzyme expression. This study provides the first functional evidence linking CTRP3 to hepatic glucose metabolism and establishes CTRP3 as a novel adipokine.As the largest endocrine organ, adipose tissue secretes many bioactive molecules that circulate in blood, collectively termed adipokines (1). These proteins include leptin, adiponectin, resistin, retinol-binding protein 4 (RBP4), omentin, and vaspin (2-7). Adipokines play important roles in energy homeostasis; their circulating levels are often dysregulated in conditions of obesity and/or diabetes (1). Adiponectin, the most highly expressed and intensely studied adipokine, has insulin-sensitizing, anti-inflammatory, and antiatherogenic properties (8). Allelic polymorphisms and reduced plasma adiponectin levels are tightly linked to insulin resistance and type 2 diabetes (8). A large body of evidence implicates adiponectin as a major insulin-sensitizing adipokine as well as an important biomarker and therapeutic target for obesity-associated metabolic diseases (1, 8). However, variable and relatively mild metabolic dysfunctions in adiponectin knock-out mice suggest the existence of additional metabolic regulators sharing overlapping function with adiponectin (9 -12). Our efforts to identify such mediators produced by adipose tissue have led to the discovery of a highly conserved family of secreted proteins, designated as C1q/TNF-related proteins 1-10 (CTRP1 to -10) (...