[Show abstract][Hide abstract] ABSTRACT: Obesity associated with unhealthy diet and lack of exercise is shown to contribute to the onset and/or aggravation of the metabolic syndrome and diabetes, thus placing affected individuals at increased risk of cardiovascular disease and cancer. Plasma adiponectin levels are decreased in obesity, which causes insulin resistance and diabetes. Therefore, we identified adiponectin receptors (AdipoRs) as the therapeutic target. It was suggested that, similarly to caloric restriction and exercise, activation of the AdipoRs may have the potential not only to improve lifestyle-related diseases but to contribute to prolonged the shortened lifespan on a high caloric unhealthy diet. To this end, we have identified "AdipoRon" as an adiponectin receptor agonist. Indeed, AdipoRon ameliorated diabetes associated with obesity as well as to increase exercise endurance, thus prolonging shortened lifespan of obese mice fed on a high fat diet. Additionally, we have recently determined the crystal structures of the human AdipoRs. The seven-transmembrane helices of AdipoRs are structurally distinct from those of G-protein coupled receptors. It is expected that these findings will contribute not only to the elucidation of the AdipoR-related signal transduction but to the development and optimization of AdipoR-targeted therapeutics for obesity-related diseases such as diabetes.
[Show abstract][Hide abstract] ABSTRACT: Adiponectin stimulation of its receptors, AdipoR1 and AdipoR2, increases the activities of 5' AMP-activated protein kinase (AMPK) and peroxisome proliferator-activated receptor (PPAR), respectively, thereby contributing to healthy longevity as key anti-diabetic molecules. AdipoR1 and AdipoR2 were predicted to contain seven transmembrane helices with the opposite topology to G-protein-coupled receptors. Here we report the crystal structures of human AdipoR1 and AdipoR2 at 2.9 and 2.4 Å resolution, respectively, which represent a novel class of receptor structure. The seven-transmembrane helices, conformationally distinct from those of G-protein-coupled receptors, enclose a large cavity where three conserved histidine residues coordinate a zinc ion. The zinc-binding structure may have a role in the adiponectin-stimulated AMPK phosphorylation and UCP2 upregulation. Adiponectin may broadly interact with the extracellular face, rather than the carboxy-terminal tail, of the receptors. The present information will facilitate the understanding of novel structure-function relationships and the development and optimization of AdipoR agonists for the treatment of obesity-related diseases, such as type 2 diabetes.
[Show abstract][Hide abstract] ABSTRACT: The adiponectin receptors (AdipoR1 and AdipoR2) are membrane proteins with seven transmembrane helices. These receptors regulate glucose and fatty acid metabolism, thereby ameliorating type 2 diabetes. The full-length human AdipoR1 and a series of N-terminally truncated mutants of human AdipoR1 and AdipoR2 were expressed in insect cells. In small-scale size exclusion chromatography, the truncated mutants AdipoR1Δ88 (residues 89–375) and AdipoR2Δ99 (residues 100–386) eluted mostly in the intact monodisperse state, while the others eluted primarily as aggregates. However, gel filtration chromatography of the large-scale preparation of the tag-affinity-purified AdipoR1Δ88 revealed the presence of an excessive amount of the aggregated state over the intact state. Since aggregation due to contaminating nucleic acids may have occurred during the sample concentration step, anion-exchange column chromatography was performed immediately after affinity chromatography, to separate the intact AdipoR1Δ88 from the aggregating species. The separated intact AdipoR1Δ88 did not undergo further aggregation, and was successfully purified to homogeneity by gel filtration chromatography. The purified AdipoR1Δ88 and AdipoR2Δ99 proteins were characterized by thermostability assays with 7-diethylamino-3-(4-maleimidophenyl)-4-methyl coumarin, thin layer chromatography of bound lipids, and surface plasmon resonance analysis of ligand binding, demonstrating their structural integrities. The AdipoR1Δ88 and AdipoR2Δ99 proteins were crystallized with the anti-AdipoR1 monoclonal antibody Fv fragment, by the lipidic mesophase method. X-ray diffraction data sets were obtained at resolutions of 2.8 and 2.4 Å, respectively.
Full-text · Article · Jan 2015 · Journal of Structural and Functional Genomics
[Show abstract][Hide abstract] ABSTRACT: The discovery of adiponectin and subsequently the receptors it acts upon have lead to a great surge forward in the understanding of the development of insulin resistance and obesity-linked diseases. Adiponectin is a hormone that is derived from adipose tissue and is reduced in obesity-linked diseases including insulin resistance/type 2 diabetes and atherosclerosis. Adiponectin exerts its effects by binding to adiponectin receptors, two of which, AdipoR1 and AdipoR2, have been cloned. This has enabled researchers to carry out detailed studies elucidating the role played by these receptors and the metabolic pathways that are involved following their activation. Such studies have clearly shown that the stimulation of these receptors is associated with glucose homeostasis and ongoing research into their role will clarify the underlying molecular mechanisms of adiponectin. Such knowledge can then be used to provide therapeutic targets aimed at managing obesity-linked diseases including type 2 diabetes and metabolic syndrome.
[Show abstract][Hide abstract] ABSTRACT: Adiponectin secreted from adipocytes binds to adiponectin receptors AdipoR1 and AdipoR2, and exerts antidiabetic effects via activation of AMPK and PPAR-α pathways, respectively. Levels of adiponectin in plasma are reduced in obesity, which causes insulin resistance and type 2 diabetes. Thus, orally active small molecules that bind to and activate AdipoR1 and AdipoR2 could ameliorate obesity-related diseases such as type 2 diabetes. Here we report the identification of orally active synthetic small-molecule AdipoR agonists. One of these compounds, AdipoR agonist (AdipoRon), bound to both AdipoR1 and AdipoR2 in vitro. AdipoRon showed very similar effects to adiponectin in muscle and liver, such as activation of AMPK and PPAR-α pathways, and ameliorated insulin resistance and glucose intolerance in mice fed a high-fat diet, which was completely obliterated in AdipoR1 and AdipoR2 double-knockout mice. Moreover, AdipoRon ameliorated diabetes of genetically obese rodent model db/db mice, and prolonged the shortened lifespan of db/db mice on a high-fat diet. Thus, orally active AdipoR agonists such as AdipoRon are a promising therapeutic approach for the treatment of obesity-related diseases such as type 2 diabetes.
[Show abstract][Hide abstract] ABSTRACT: Aims/hypothesis:
Monocyte chemoattractant protein-1 (MCP-1)/chemokine (C-C motif) ligand (CCL) 2 (CCL2) secreted from white adipose tissue (WAT) in obesity has been reported to contribute to tissue macrophage accumulation and insulin resistance by inducing a chronic inflammatory state. MCP-1 has been shown to be elevated in the fatty liver of lipoatrophic A-ZIP-transgenic (A-ZIP-Tg) mice. Treatment of these mice with the CC chemokine receptor (CCR) 2 antagonist has been shown to ameliorate the hyperglycaemia, hyperinsulinaemia and hepatomegaly, in conjunction with reducing liver inflammation. However, since CCR2 antagonists can block not only MCP-1 but also MCP-2 (CCL8) and MCP-3 (CCL7), it remains unclear whether MCP-1 secreted from the liver could contribute to hyperglycaemia, hyperinsulinaemia and hepatomegaly in conjunction with liver inflammation, as well as to the M1 and M2 states of macrophage polarisation.
To address these issues, we analysed the effects of targeted disruption of MCP-1 in A-ZIP-Tg mice.
MCP-1 deficiency alone or per se resulted in a significant amelioration of insulin resistance in A-ZIP-Tg mice, which was associated with a suppression of extracellular signal-regulated protein kinase (ERK)-1/2 and p38 mitogen-activated protein kinase (p38MAPK) phosphorylation in liver. Although MCP-1 deficiency did not reduce the expression of macrophage markers, it increased the expression of the genes encoding M2 macrophage markers such as Arg1 and Chi3l3, as well as significantly reducing the triacylglycerol content of livers from A-ZIP-Tg mice. CONCLUSIONS/ INTERPRETATION: Our data clearly indicated that MCP-1 deficiency improved insulin resistance and hepatic steatosis in A-ZIP-Tg mice and was associated with switching macrophage polarisation and suppressing ERK-1/2 and p38MAPK phosphorylation.
[Show abstract][Hide abstract] ABSTRACT: Adiponectin is a cytokine secreted by adipocytes, whose plasma levels are decreased in obesity. Adiponectin has insulin-sensitizing, antiatherogenic, and antidiabetogenic effects. It has been shown that adiponectin may also exert antineoplastic activity through suppression of tumor proliferation and neoangiogenesis and through induction of apoptosis. Recently, low adiponectin serum concentration has been found in obesity-related malignancies, including endometrial cancer. In addition, the expression of adiponectin receptors (AdipoR1 and AdipoR2) has been documented in several human cancer tissues, but the expression has previously not been assessed in human endometrial cancer tissues. In this study, we analyzed the immunohistochemical expression of AdipoR1 and AdipoR2 in a series of surgically resected human endometrioid adenocarcinoma tissues from a total of 141 cases. Decreased AdipoR1 or AdipoR2 expression was significantly associated with histological higher grade (P=0.0026 and 0.0004, respectively). Decreased expression of AdipoR1 was associated with myometrial invasion and lymph node metastasis of endometrioid adenocarcinoma (P=0.0039 and P=0.0069, respectively). AdipoR1 and AdipoR2 immunoexpression was significantly associated with the expression of the progesterone receptor, although it was not significantly correlated with the expression of the estrogen receptor, Ki-67 or p53. Our present study raises the possibility that decreased expression of adiponectin receptors is implicated in the development, invasion, and metastasis of human endometrioid adenocarcinoma. Our findings, moreover, indicate that adiponectin receptors could be considered as therapeutic targets for endometrioid adenocarcinoma. In adiponectin receptor-positive endometrioid adenocarcinoma, we think adiponectin-based anticancer therapy is useful; however, in histological high-grade endometrioid adenocarcinoma, in which the expression levels of adiponectin receptors are relatively low, adiponectin therapy supported by adiponectin receptor induction is needed.
No preview · Article · May 2012 · International journal of gynecological pathology: official journal of the International Society of Gynecological Pathologists
[Show abstract][Hide abstract] ABSTRACT: We studied the molecular mechanism of obesity-induced insulin resistance and adipogenesis. Plasma adiponectin and adiponectin receptor (AdipoR1) in muscle are down-regulated in obesity. Analysis of muscle-specific AdipoR1 knockout mice revealed the pivotal role of adiponectin/AdipoR1 in the regulation of mitochondrial biogenesis via AMPK- and SIRT1-mediated PGC-1α activation as well as Ca(2+)-dependent up-regulation of PGC-1α expression. Reduced adiponectin/AdipoR1 signals in muscle in obesity appear to cause PGC-1α inactivation as well as down-regulation and consequently impaired mitochondrial biogenesis and insulin resistance. In the epigenetic analysis of adipogenesis, we demonstrated that adipocyte-specific formaldehyde-assisted isolation of regulatory elements (FAIRE) peaks are associated with genes up-regulated by adipogenesis, whereas preadipocyte-specific FAIRE peaks are associated with genes down-regulated by adipogenesis. Computational motif analyses of adipocyte-specific FAIRE peaks confirmed PPARγ and CCAAT-enhancer binding proteins (C/EBPs) on the top list, consistent with their crucial roles in adipogenic transcription, and also revealed NFIA and NFIB to be important regulators of proper adipocyte differentiation.
Preview · Article · Apr 2012 · Cold Spring Harbor Symposia on Quantitative Biology
[Show abstract][Hide abstract] ABSTRACT: To identify a novel susceptibility locus for type 2 diabetes, we performed an imputation-based, genome-wide association study (GWAS) in a Japanese population using newly obtained imputed-genotype data for 2 229 890 single-nucleotide polymorphisms (SNPs) estimated from previously reported, directly genotyped GWAS data in the same samples (stage 1: 4470 type 2 diabetes versus 3071 controls). We directly genotyped 43 new SNPs with P-values of <10(-4) in a part of stage-1 samples (2692 type 2 diabetes versus 3071 controls), and the associations of validated SNPs were evaluated in another 11 139 Japanese individuals (stage 2: 7605 type 2 diabetes versus 3534 controls). Combined meta-analysis using directly genotyped data for stages 1 and 2 revealed that rs515071 in ANK1 and rs7656416 near MGC21675 were associated with type 2 diabetes in the Japanese population at the genome-wide significant level (P < 5 × 10(-8)). The association of rs515071 was also observed in European GWAS data (combined P for all populations = 6.14 × 10(-10)). Rs7656416 was in linkage disequilibrium to rs6815464, which had recently been identified as a top signal in a meta-analysis of East Asian GWAS for type 2 diabetes (r(2) = 0.76 in stage 2). The association of rs7656416 with type 2 diabetes disappeared after conditioning on rs6815464. These results indicate that the ANK1 locus is a new, common susceptibility locus for type 2 diabetes across different ethnic groups. The signal of association was weaker in the directly genotyped data, so the improvement in signal indicates the importance of imputation in this particular case.
No preview · Article · Mar 2012 · Human Molecular Genetics
[Show abstract][Hide abstract] ABSTRACT: Identification of regulatory elements within the genome is crucial for understanding the mechanisms that govern cell type-specific gene expression. We generated genome-wide maps of open chromatin sites in 3T3-L1 adipocytes (on day 0 and day 8 of differentiation) and NIH-3T3 fibroblasts using formaldehyde-assisted isolation of regulatory elements coupled with high-throughput sequencing (FAIRE-seq). FAIRE peaks at the promoter were associated with active transcription and histone modifications of H3K4me3 and H3K27ac. Non-promoter FAIRE peaks were characterized by H3K4me1+/me3-, the signature of enhancers, and were largely located in distal regions. The non-promoter FAIRE peaks showed dynamic change during differentiation, while the promoter FAIRE peaks were relatively constant. Functionally, the adipocyte- and preadipocyte-specific non-promoter FAIRE peaks were, respectively, associated with genes up-regulated and down-regulated by differentiation. Genes highly up-regulated during differentiation were associated with multiple clustered adipocyte-specific FAIRE peaks. Among the adipocyte-specific FAIRE peaks, 45.3% and 11.7% overlapped binding sites for, respectively, PPARγ and C/EBPα, the master regulators of adipocyte differentiation. Computational motif analyses of the adipocyte-specific FAIRE peaks revealed enrichment of a binding motif for nuclear family I (NFI) transcription factors. Indeed, ChIP assay showed that NFI occupy the adipocyte-specific FAIRE peaks and/or the PPARγ binding sites near PPARγ, C/EBPα, and aP2 genes. Overexpression of NFIA in 3T3-L1 cells resulted in robust induction of these genes and lipid droplet formation without differentiation stimulus. Overexpression of dominant-negative NFIA or siRNA-mediated knockdown of NFIA or NFIB significantly suppressed both induction of genes and lipid accumulation during differentiation, suggesting a physiological function of these factors in the adipogenic program. Together, our study demonstrates the utility of FAIRE-seq in providing a global view of cell type-specific regulatory elements in the genome and in identifying transcriptional regulators of adipocyte differentiation.
[Show abstract][Hide abstract] ABSTRACT: Ca2+/calmodulin (CaM)-dependent protein kinase (CaMK) kinase (CaMKK) is a member of the CaMK cascade that mediates the response
to intracellular Ca2+ elevation. CaMKK phosphorylates and activates CaMKI and CaMKIV, which directly activate transcription factors. In this study,
we determined the 2.4 Å crystal structure of the catalytic kinase domain of the human CaMKKβ isoform complexed with its selective
inhibitor, STO-609. The structure revealed that CaMKKβ lacks the αD helix and that the equivalent region displays a hydrophobic
molecular surface, which may reflect its unique substrate recognition and autoinhibition. Although CaMKKβ lacks the activation
loop phosphorylation site, the activation loop is folded in an active-state conformation, which is stabilized by a number
of interactions between amino acid residues conserved among the CaMKK isoforms. An in vitro analysis of the kinase activity confirmed the intrinsic activity of the CaMKKβ kinase domain. Structure and sequence analyses
of the STO-609-binding site revealed amino acid replacements that may affect the inhibitor binding. Indeed, mutagenesis demonstrated
that the CaMKKβ residue Pro274, which replaces the conserved acidic residue of other protein kinases, is an important determinant for the selective inhibition
by STO-609. Therefore, the present structure provides a molecular basis for clarifying the known biochemical properties of
CaMKKβ and for designing novel inhibitors targeting CaMKKβ and the related protein kinases.
Preview · Article · Jun 2011 · Journal of Biological Chemistry
[Show abstract][Hide abstract] ABSTRACT: AMP-activated protein kinase (AMPK) is a serine/threonine kinase that functions as a sensor to maintain energy balance at both the cellular and the whole-body levels and is therefore a potential target for drug design against metabolic syndrome, obesity and type 2 diabetes. Here, the crystal structure of the phosphorylated-state mimic T172D mutant kinase domain from the human AMPK α2 subunit is reported in the apo form and in complex with a selective inhibitor, compound C. The AMPK α2 kinase domain exhibits a typical bilobal kinase fold and exists as a monomer in the crystal. Like the wild-type apo form, the T172D mutant apo form adopts the autoinhibited structure of the `DFG-out' conformation, with the Phe residue of the DFG motif anchored within the putative ATP-binding pocket. Compound C binding dramatically alters the conformation of the activation loop, which adopts an intermediate conformation between DFG-out and DFG-in. This induced fit forms a compound-C binding pocket composed of the N-lobe, the C-lobe and the hinge of the kinase domain. The pocket partially overlaps with the putative ATP-binding pocket. These three-dimensional structures will be useful to guide drug discovery.
No preview · Article · May 2011 · Acta Crystallographica Section D Biological Crystallography
[Show abstract][Hide abstract] ABSTRACT: We conducted a genome-wide association study of type 2 diabetes (T2D) using 459,359 SNPs in a Japanese population with a three-stage study design (stage 1, 4,470 cases and 3,071 controls; stage 2, 2,886 cases and 3,087 controls; stage 3, 3,622 cases and 2,356 controls). We identified new associations in UBE2E2 on chromosome 3 and in C2CD4A-C2CD4B on chromosome 15 at genome-wide significant levels (rs7612463 in UBE2E2, combined P = 2.27 × 10⁻⁹; rs7172432 in C2CD4A-C2CD4B, combined P = 3.66 × 10⁻⁹). The association of these two loci with T2D was replicated in other east Asian populations. In the European populations, the C2CD4A-C2CD4B locus was significantly associated with T2D, and a combined analysis of all populations gave P = 8.78 × 10⁻¹⁴, whereas the UBE2E2 locus did not show association to T2D. In conclusion, we identified two new loci at UBE2E2 and C2CD4A-C2CD4B associated with susceptibility to T2D.
[Show abstract][Hide abstract] ABSTRACT: Adiponectin is an anti-diabetic adipokine. Its receptors possess a seven-transmembrane topology with the amino terminus located intracellularly, which is the opposite of G-protein-coupled receptors. Here we provide evidence that adiponectin induces extracellular Ca(2+) influx by adiponectin receptor 1 (AdipoR1), which was necessary for subsequent activation of Ca(2+)/calmodulin-dependent protein kinase kinase beta (CaMKKbeta), AMPK and SIRT1, increased expression and decreased acetylation of peroxisome proliferator-activated receptor gamma coactivator-1alpha (PGC-1alpha), and increased mitochondria in myocytes. Moreover, muscle-specific disruption of AdipoR1 suppressed the adiponectin-mediated increase in intracellular Ca(2+) concentration, and decreased the activation of CaMKK, AMPK and SIRT1 by adiponectin. Suppression of AdipoR1 also resulted in decreased PGC-1alpha expression and deacetylation, decreased mitochondrial content and enzymes, decreased oxidative type I myofibres, and decreased oxidative stress-detoxifying enzymes in skeletal muscle, which were associated with insulin resistance and decreased exercise endurance. Decreased levels of adiponectin and AdipoR1 in obesity may have causal roles in mitochondrial dysfunction and insulin resistance seen in diabetes.
[Show abstract][Hide abstract] ABSTRACT: Apolipoprotein E (apoE) and its receptor, very low density lipoprotein receptor (VLDLR), are involved in fat accumulation in adipocytes. Here, we investigated the effect of a peroxisome proliferator-activated receptor (PPAR) gamma agonist, rosiglitazone, on regulation of VLDLR expression both in white adipose tissue (WAT) of obese mice and in cultured adipocytes. Furthermore, to determine whether rosiglitazone directly regulates transcription of the VLDLR gene, we carried out luciferase assay with a reporter gene containing mouse VLDLR promoter region, electrophoretic mobility shift assay, and chromatin immunoprecipitation assay. Four-day treatment with rosiglitazone increased the expression of VLDLR in WAT of ob/ob mice. Moreover, rosiglitazone increased the expression of VLDLR in cultured adipocytes. The PPAR-responsive element (PPRE)-directed mutagenesis analyses revealed that the PPRE motif in the VLDLR promoter region plays a significant role in transcriptional activation of the VLDLR gene in adipocytes. In addition, electrophoretic mobility shift assay and chromatin immunoprecipitation assay demonstrated that endogenous PPARgamma directly binds to this functional PPRE motif in the VLDLR promoter region. We also investigated the effects of rosiglitazone on insulin sensitivity and lipid accumulation in both ob/ob mice and apoE-deficient ob/ob mice. Rosiglitazone ameliorated insulin sensitivity in both ob/ob mice and apoE-deficient ob/ob mice, possibly through decreasing the expression of monocyte chemoattractant protein-1 (MCP-1), increasing the expression of superoxide dismutase 1 (SOD1) in WAT, and increasing plasma adiponectin concentration. In ob/ob mice, body weight and WAT weight were significantly higher in the mice treated with rosiglitazone than those treated with vehicle. However, in apoE-deficient ob/ob mice, no significant difference in body weight or WAT weight was observed between the vehicle-treated group and the rosiglitazone-treated group. Moreover, rosiglitazone did not increase body weight and WAT weight in VLDLR-deficient mice. These findings indicate that rosiglitazone directly increases VLDLR expression, thereby enhancing apoE-VLDLR-dependent lipid accumulation in adipocytes.
[Show abstract][Hide abstract] ABSTRACT: Knowledge of the regulatory factors associated with down-regulation of adiponectin gene expression and up-regulation of PAI-1 gene expression is crucial to understand the pathophysiological basis of obesity and metabolic diseases, and could establish new treatment strategies for these conditions. We showed that expression of 5-HT(2A) receptors was up-regulated in hypertrophic 3T3-L1 adipocytes, which exhibited decreased expression of adiponectin and increased expression of PAI-1. 5-HT(2A) receptor antagonists and suppression of 5-HT(2A) receptor gene expression enhanced adiponectin expression. Activation of Gq negatively regulated adiponectin expression, and inhibition of mitogen-activated protein kinase reversed the Gq-induced effect. Moreover, the 5-HT(2A) receptor blockade reduced PAI-1 expression. These findings indicate that antagonism of 5-HT(2A) receptors in adipocytes could improve the obesity-linked decreases in adiponectin expression and increases in PAI-1 expression.