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Seldin MM, Lei X, Tan SY, Stanson KP, Wei Z, Wong GW. Skeletal muscle-derived myonectin activates the mammalian target of rapamycin (mTOR) pathway to suppress autophagy in liver. J Biol Chem 2013; 288:36073-82. [PMID: 24187137 DOI: 10.1074/jbc.m113.500736] [Citation(s) in RCA: 82] [Impact Index Per Article: 7.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/13/2022] Open
Abstract
Cells turn on autophagy, an intracellular recycling pathway, when deprived of nutrients. How autophagy is regulated by hormonal signals in response to major changes in metabolic state is not well understood. Here, we provide evidence that myonectin (CTRP15), a skeletal muscle-derived myokine, is a novel regulator of cellular autophagy. Starvation activated liver autophagy, whereas nutrient supplementation following food deprivation suppressed it; the former and latter correlated with reduced and increased expression and circulating levels of myonectin, respectively, suggestive of a causal link. Indeed, recombinant myonectin administration suppressed starvation-induced autophagy in mouse liver and cultured hepatocytes, as indicated by the inhibition of LC3-dependent autophagosome formation, p62 degradation, and expression of critical autophagy-related genes. Reduction in protein degradation is mediated by the PI3K/Akt/mTOR signaling pathway; inhibition of this pathway abrogated the ability of myonectin to suppress autophagy in cultured hepatocytes. Together, our results reveal a novel skeletal muscle-liver axis controlling cellular autophagy, underscoring the importance of hormone-mediated tissue cross-talk in maintaining energy homeostasis.
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Affiliation(s)
- Marcus M Seldin
- From the Department of Physiology and Center for Metabolism and Obesity Research, The Johns Hopkins University School of Medicine, Baltimore, Maryland 21205
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102
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Tan BK, Chen J, Adya R, Ramanjaneya M, Patel V, Randeva HS. Metformin increases the novel adipokine adipolin/CTRP12: role of the AMPK pathway. J Endocrinol 2013; 219:101-8. [PMID: 23946431 DOI: 10.1530/joe-13-0277] [Citation(s) in RCA: 23] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/08/2022]
Abstract
Adipolin is a novel adipokine with anti-inflammatory and glucose-lowering properties. Lower levels of adipolin are found in obese and diabetic mice. Polycystic ovary syndrome (PCOS) is a pro-inflammatory state associated with obesity and diabetes. To date, there are no human studies on adipolin. Therefore, we measured serum (ELISA) and adipose tissue adipolin mRNA expression (RT-PCR) and protein concentrations (western blotting) in PCOS and control subjects. We also investigated the ex vivo effect of glucose and metformin on adipolin protein production in human subcutaneous adipose tissue explants. We report novel data that serum and subcutaneous adipose tissue adipolin mRNA expression and protein concentrations were significantly lower in women with PCOS compared with control subjects. Furthermore, Spearman's rank analysis showed that serum adipolin concentrations were significantly negatively correlated with BMI, waist-to-hip ratio, and glucose (P<0.05). However, when subjected to multiple regression analysis, none of these variables were predictive of serum adipolin concentrations (P>0.05). Also, subcutaneous adipose tissue adipolin mRNA expression and protein concentrations were only significantly negatively correlated with glucose (P<0.05). No significant correlations were found with omental adipose tissue adipolin mRNA expression and protein concentrations (P>0.05). Moreover, glucose profoundly reduced and metformin significantly increased adipolin protein production in human adipose tissue explants respectively. Importantly, metformin's effects appear to be via the AMP-activated protein kinase signaling pathway.
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Affiliation(s)
- Bee K Tan
- Warwick Medical School, University of Warwick, Coventry CV4 7AL, UK
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103
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104
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Nonneman DJ, Shackelford SD, King DA, Wheeler TL, Wiedmann RT, Snelling WM, Rohrer GA. Genome-wide association of meat quality traits and tenderness in swine1,2. J Anim Sci 2013; 91:4043-50. [DOI: 10.2527/jas.2013-6255] [Citation(s) in RCA: 46] [Impact Index Per Article: 4.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/13/2022] Open
Affiliation(s)
- D. J. Nonneman
- USDA-ARS, U.S. Meat Animal Research Center, Clay Center, NE 68933
| | | | - D. A. King
- USDA-ARS, U.S. Meat Animal Research Center, Clay Center, NE 68933
| | - T. L. Wheeler
- USDA-ARS, U.S. Meat Animal Research Center, Clay Center, NE 68933
| | - R. T. Wiedmann
- USDA-ARS, U.S. Meat Animal Research Center, Clay Center, NE 68933
| | - W. M. Snelling
- USDA-ARS, U.S. Meat Animal Research Center, Clay Center, NE 68933
| | - G. A. Rohrer
- USDA-ARS, U.S. Meat Animal Research Center, Clay Center, NE 68933
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105
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Peterson JM, Seldin MM, Wei Z, Aja S, Wong GW. CTRP3 attenuates diet-induced hepatic steatosis by regulating triglyceride metabolism. Am J Physiol Gastrointest Liver Physiol 2013; 305:G214-24. [PMID: 23744740 PMCID: PMC3742855 DOI: 10.1152/ajpgi.00102.2013] [Citation(s) in RCA: 96] [Impact Index Per Article: 8.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 01/31/2023]
Abstract
CTRP3 is a secreted plasma protein of the C1q family that helps regulate hepatic gluconeogenesis and is downregulated in a diet-induced obese state. However, the role of CTRP3 in regulating lipid metabolism has not been established. Here, we used a transgenic mouse model to address the potential function of CTRP3 in ameliorating high-fat diet-induced metabolic stress. Both transgenic and wild-type mice fed a high-fat diet showed similar body weight gain, food intake, and energy expenditure. Despite similar adiposity to wild-type mice upon diet-induced obesity (DIO), CTRP3 transgenic mice were strikingly resistant to the development of hepatic steatosis, had reduced serum TNF-α levels, and demonstrated a modest improvement in systemic insulin sensitivity. Additionally, reduced hepatic triglyceride levels were due to decreased expression of enzymes (GPAT, AGPAT, and DGAT) involved in triglyceride synthesis. Importantly, short-term daily administration of recombinant CTRP3 to DIO mice for 5 days was sufficient to improve the fatty liver phenotype, evident as reduced hepatic triglyceride content and expression of triglyceride synthesis genes. Consistent with a direct effect on liver cells, recombinant CTRP3 treatment reduced fatty acid synthesis and neutral lipid accumulation in cultured rat H4IIE hepatocytes. Together, these results establish a novel role for CTRP3 hormone in regulating hepatic lipid metabolism and highlight its protective function and therapeutic potential in attenuating hepatic steatosis.
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Affiliation(s)
- Jonathan M. Peterson
- 1Department of Physiology, Johns Hopkins University School of Medicine, Baltimore, Maryland; ,3Center for Metabolism and Obesity Research, Johns Hopkins University School of Medicine, Baltimore, Maryland; and ,4Department of Health Sciences, School of Public Health, East Tennessee State University, Johnson City, Tennessee
| | - Marcus M. Seldin
- 1Department of Physiology, Johns Hopkins University School of Medicine, Baltimore, Maryland; ,3Center for Metabolism and Obesity Research, Johns Hopkins University School of Medicine, Baltimore, Maryland; and
| | - Zhikui Wei
- 1Department of Physiology, Johns Hopkins University School of Medicine, Baltimore, Maryland; ,3Center for Metabolism and Obesity Research, Johns Hopkins University School of Medicine, Baltimore, Maryland; and
| | - Susan Aja
- 2Department of Neuroscience, Johns Hopkins University School of Medicine, Baltimore, Maryland; ,3Center for Metabolism and Obesity Research, Johns Hopkins University School of Medicine, Baltimore, Maryland; and
| | - G. William Wong
- 1Department of Physiology, Johns Hopkins University School of Medicine, Baltimore, Maryland; ,3Center for Metabolism and Obesity Research, Johns Hopkins University School of Medicine, Baltimore, Maryland; and
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106
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Bell-Anderson KS, Funnell AP, Williams H, Mat Jusoh H, Scully T, Lim WF, Burdach JG, Mak KS, Knights AJ, Hoy AJ, Nicholas HR, Sainsbury A, Turner N, Pearson RC, Crossley M. Loss of Krüppel-like factor 3 (KLF3/BKLF) leads to upregulation of the insulin-sensitizing factor adipolin (FAM132A/CTRP12/C1qdc2). Diabetes 2013; 62:2728-37. [PMID: 23633521 PMCID: PMC3717849 DOI: 10.2337/db12-1745] [Citation(s) in RCA: 37] [Impact Index Per Article: 3.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 02/02/2023]
Abstract
Krüppel-like factor 3 (KLF3) is a transcriptional regulator that we have shown to be involved in the regulation of adipogenesis in vitro. Here, we report that KLF3-null mice are lean and protected from diet-induced obesity and glucose intolerance. On a chow diet, plasma levels of leptin are decreased, and adiponectin is increased. Despite significant reductions in body weight and adiposity, wild-type and knockout animals show equivalent energy intake, expenditure, and excretion. To investigate the molecular events underlying these observations, we used microarray analysis to compare gene expression in Klf3(+/+) and Klf3(-/-) tissues. We found that mRNA expression of Fam132a, which encodes a newly identified insulin-sensitizing adipokine, adipolin, is significantly upregulated in the absence of KLF3. We confirmed that KLF3 binds the Fam132a promoter in vitro and in vivo and that this leads to repression of promoter activity. Further, plasma adipolin levels were significantly increased in Klf3(-/-) mice compared with wild-type littermates. Boosting levels of adipolin via targeting of KLF3 offers a novel potential therapeutic strategy for the treatment of insulin resistance.
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Affiliation(s)
- Kim S Bell-Anderson
- School of Molecular Bioscience, University of Sydney, Sydney, New South Wales, Australia.
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107
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Peterson JM, Wei Z, Seldin MM, Byerly MS, Aja S, Wong GW. CTRP9 transgenic mice are protected from diet-induced obesity and metabolic dysfunction. Am J Physiol Regul Integr Comp Physiol 2013; 305:R522-33. [PMID: 23842676 DOI: 10.1152/ajpregu.00110.2013] [Citation(s) in RCA: 91] [Impact Index Per Article: 8.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/06/2023]
Abstract
CTRP9 is a secreted multimeric protein of the C1q family and the closest paralog of the insulin-sensitizing adipokine, adiponectin. The metabolic function of this adipose tissue-derived plasma protein remains largely unknown. Here, we show that the circulating levels of CTRP9 are downregulated in diet-induced obese mice and upregulated upon refeeding. Overexpressing CTRP9 resulted in lean mice that dramatically resisted weight gain induced by a high-fat diet, largely through decreased food intake and increased basal metabolism. Enhanced fat oxidation in CTRP9 transgenic mice resulted from increases in skeletal muscle mitochondrial content, expression of enzymes involved in fatty acid oxidation (LCAD and MCAD), and chronic AMPK activation. Hepatic and skeletal muscle triglyceride levels were substantially decreased in transgenic mice. Consequently, CTRP9 transgenic mice had a greatly improved metabolic profile with markedly reduced fasting insulin and glucose levels. The high-fat diet-induced obesity, insulin resistance, and hepatic steatosis observed in wild-type mice were prevented in transgenic mice. Consistent with the in vivo data, recombinant protein significantly enhanced fat oxidation in L6 myotubes via AMPK activation and reduced lipid accumulation in H4IIE hepatocytes. Collectively, these data establish CTRP9 as a novel metabolic regulator and a new component of the metabolic network that links adipose tissue to lipid metabolism in skeletal muscle and liver.
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Affiliation(s)
- Jonathan M Peterson
- Department of Physiology, Johns Hopkins University School of Medicine, Baltimore, Maryland, USA
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108
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Akiyama H, Otani M, Sato S, Toyosawa S, Furukawa S, Wakisaka S, Maeda T. A novel adipokine C1q/TNF-related protein 1 (CTRP1) regulates chondrocyte proliferation and maturation through the ERK1/2 signaling pathway. Mol Cell Endocrinol 2013; 369:63-71. [PMID: 23348620 DOI: 10.1016/j.mce.2013.01.002] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 07/30/2012] [Revised: 11/19/2012] [Accepted: 01/07/2013] [Indexed: 01/22/2023]
Abstract
Adipose tissue-derived adipokines play important roles as regulators of skeletal growth and development. CTRP1, a paralog of adiponectin, is a member of the C1q and tumor necrosis factor (TNF)-related protein (CTRP) superfamily. It is expressed at high levels in adipose tissue and has recently emerged as a novel adipokine. In the present study, we provide the first evidence for a physiological role of the CTRP1 in chondrocyte proliferation and maturation using a mouse chondrocytic cell line, N1511. The CTRP1 protein was strongly expressed and predominantly distributed in the reserve and proliferative chondrocytes in the fetal growth plate and its mRNA decreased during the maturation of N1511 chondrocytes. Recombinant CTRP1 promoted proliferation of immature proliferating N1511 chondrocytes in a dose-dependent manner, whereas it inhibited maturation of maturing N1511 chondrocytes. The stimulatory effect of CTRP1 on chondrocyte proliferation was associated with activation of the extracellular signal-regulated kinases 1/2 (ERK1/2) signaling pathway. On the other hand, the inhibitory effect of CTRP1 on chondrocyte maturation is associated with suppression of the ERK1/2 pathway. These results suggest a novel physiological role for CTRP1 in endochondral ossification.
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Affiliation(s)
- Hironori Akiyama
- Department of Radiology, Graduate School of Dentistry, Osaka University, Suita, Osaka, Japan
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109
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A central role for C1q/TNF-related protein 13 (CTRP13) in modulating food intake and body weight. PLoS One 2013; 8:e62862. [PMID: 23638159 PMCID: PMC3636217 DOI: 10.1371/journal.pone.0062862] [Citation(s) in RCA: 46] [Impact Index Per Article: 4.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/18/2012] [Accepted: 03/26/2013] [Indexed: 11/19/2022] Open
Abstract
C1q/TNF-related protein 13 (CTRP13), a hormone secreted by adipose tissue (adipokines), helps regulate glucose metabolism in peripheral tissues. We previously reported that CTRP13 expression is increased in obese and hyperphagic leptin-deficient mice, suggesting that it may modulate food intake and body weight. CTRP13 is also expressed in the brain, although its role in modulating whole-body energy balance remains unknown. Here, we show that CTRP13 is a novel anorexigenic factor in the mouse brain. Quantitative PCR demonstrated that food restriction downregulates Ctrp13 expression in mouse hypothalamus, while high-fat feeding upregulates expression. Central administration of recombinant CTRP13 suppressed food intake and reduced body weight in mice. Further, CTRP13 and the orexigenic neuropeptide agouti-related protein (AgRP) reciprocally regulate each other's expression in the hypothalamus: central delivery of CTRP13 suppressed Agrp expression, while delivery of AgRP increased Ctrp13 expression. Food restriction alone reduced Ctrp13 and increased orexigenic neuropeptide gene (Npy and Agrp) expression in the hypothalamus; in contrast, when food restriction was coupled to enhanced physical activity in an activity-based anorexia (ABA) mouse model, hypothalamic expression of both Ctrp13 and Agrp were upregulated. Taken together, these results suggest that CTRP13 and AgRP form a hypothalamic feedback loop to modulate food intake and that this neural circuit may be disrupted in an anorexic-like condition.
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110
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Wei Z, Seldin MM, Natarajan N, Djemal DC, Peterson JM, Wong GW. C1q/tumor necrosis factor-related protein 11 (CTRP11), a novel adipose stroma-derived regulator of adipogenesis. J Biol Chem 2013; 288:10214-29. [PMID: 23449976 DOI: 10.1074/jbc.m113.458711] [Citation(s) in RCA: 56] [Impact Index Per Article: 5.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/26/2023] Open
Abstract
C1q/TNF-related proteins (CTRPs) are a family of secreted regulators of glucose and lipid metabolism. Here, we describe CTRP11, a novel and phylogenetically conserved member of the C1q family. Our studies revealed that white and brown adipose are major tissues that express CTRP11, and its expression is acutely regulated by changes in metabolic state. Within white adipose tissue, CTRP11 is primarily expressed by stromal vascular cells. As a secreted multimeric protein, CTRP11 forms disulfide-linked oligomers. Although the conserved N-terminal Cys-28 and Cys-32 are dispensable for the assembly of higher-order oligomeric structures, they are unexpectedly involved in modulating protein secretion. When co-expressed, CTRP11 forms heteromeric complexes with closely related CTRP10, CTRP13, and CRF (CTRP14) via the C-terminal globular domains, combinatorial associations that potentially generate functionally distinct complexes. Functional studies revealed a role for CTRP11 in regulating adipogenesis. Ectopic expression of CTRP11 or exposure to recombinant protein inhibited differentiation of 3T3-L1 adipocytes. The expression of peroxisome proliferator-activated receptor-γ and CAAT/enhancer binding protein-α, which drive the adipogenic gene program, was markedly suppressed by CTRP11. Impaired adipogenesis was caused by a CTRP11-mediated decrease in p42/44-MAPK signaling and inhibition of mitotic clonal expansion, a process essential for adipocyte differentiation in culture. These results implicate CTRP11 as a novel secreted regulator of adipogenesis and highlight the potential paracrine cross-talk between adipocytes and cells of the stromal vascular compartment in maintaining adipose tissue homeostasis.
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Affiliation(s)
- Zhikui Wei
- Department of Physiology and Center for Metabolism and Obesity Research, Johns Hopkins University School of Medicine, Baltimore, Maryland 21205, USA
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111
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Enomoto T, Shibata R, Ohashi K, Kambara T, Kataoka Y, Uemura Y, Yuasa D, Murohara T, Ouchi N. Regulation of adipolin/CTRP12 cleavage by obesity. Biochem Biophys Res Commun 2012; 428:155-9. [DOI: 10.1016/j.bbrc.2012.10.031] [Citation(s) in RCA: 19] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/04/2012] [Accepted: 10/05/2012] [Indexed: 12/29/2022]
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112
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Abstract
The integrated control of animal physiology requires intimate tissue crosstalk, a vital task mediated by circulating humoral factors. As one type of these factors, adipose tissue-derived adipokines have recently garnered attention as important regulators of systemic insulin sensitivity and metabolic homeostasis. However, the realization that skeletal muscle also secretes a variety of biologically and metabolically active polypeptide factors (collectively called myokines) has provided a new conceptual framework to understand the critical role skeletal muscle plays in coordinating whole-body energy balance. Here, we highlight recent progress made in the myokine field and discuss possible roles of myonectin, which we have recently identified as a potential postprandial signal derived from skeletal muscle to integrate metabolic processes in other tissues, such as adipose and liver; one of its roles is to promote fatty acid uptake into cells. Myonectin is also likely an important mediator in inter-tissue crosstalk.
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113
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Wei Z, Lei X, Seldin MM, Wong GW. Endopeptidase cleavage generates a functionally distinct isoform of C1q/tumor necrosis factor-related protein-12 (CTRP12) with an altered oligomeric state and signaling specificity. J Biol Chem 2012; 287:35804-14. [PMID: 22942287 DOI: 10.1074/jbc.m112.365965] [Citation(s) in RCA: 34] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Adipose tissue-derived adipokines are an important class of secreted metabolic regulators that mediate tissue cross-talk to control systemic energy balance. We recently described C1q/TNF-related protein-12 (CTRP12), a novel insulin-sensitizing adipokine that regulates glucose metabolism in liver and adipose tissue. However, the biochemical properties of CTRP12 and its naturally occurring cleaved isoform have not been characterized. Here, we show that CTRP12 is a secreted hormone subjected to multiple functionally relevant posttranslational modifications at highly conserved residues. For example, Asn(39) is glycosylated, whereas Cys(85) mediates the assembly of higher order oligomeric structure. Endopeptidase cleavage at Lys(91) generates a cleaved globular gCTRP12 isoform, the expression of which is increased by insulin. PCSK3/furin was identified as the major proprotein convertase expressed by adipocytes that mediates the endogenous cleavage of CTRP12. Cleavage at Lys(91) is context-dependent: mutation of the charged Arg(93) to Ala on the P2' position enhanced cleavage, and triple mutations (K90A/K91A/R93A) abolished cleavage. Importantly, the two isoforms of CTRP12 differ in oligomeric structures and are functionally distinct. The full-length protein forms trimers and larger complexes, and the cleaved isoform consisted of predominantly dimers. Whereas full-length fCTRP12 strongly activated Akt signaling in H4IIE hepatocytes and 3T3-L1 adipocytes, gCTRP12 preferentially activated MAP kinase (ERK1/2 and p38 MAPK) signaling. Further, only fCTRP12 improved insulin-stimulated glucose uptake in adipocytes. These results reveal a novel mechanism controlling signaling specificity and function of a hormone via cleavage-dependent alteration in oligomeric state.
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Affiliation(s)
- Zhikui Wei
- Department of Physiology and Center for Metabolism and Obesity Research, Johns Hopkins University School of Medicine, Baltimore, Maryland 21205, USA
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114
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Anti-inflammatory and anti-atherogenic properties of adiponectin. Biochimie 2012; 94:2137-42. [PMID: 22713764 DOI: 10.1016/j.biochi.2012.06.008] [Citation(s) in RCA: 159] [Impact Index Per Article: 13.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/18/2012] [Accepted: 06/06/2012] [Indexed: 12/27/2022]
Abstract
Obesity-related disorders, such as insulin resistance, hypertension and atherosclerosis, are associated with chronic inflammation. Adiponectin is an adipocyte-derived secreted factor that is down-regulated in obese states. Adiponectin exerts the protective actions on obesity-linked diseases, such as insulin resistance and atherosclerosis by attenuating chronic inflammation in its target organs. Adiponectin also exerts the salutary effects on vascular disorders by directly acting on vascular component cells including endothelial cells, smooth muscle cells and macrophages. This review will focus on the role of adiponectin in control of inflammatory responses and atherogenic processes.
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115
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Ouchi N, Walsh K. Cardiovascular and metabolic regulation by the adiponectin/C1q/tumor necrosis factor-related protein family of proteins. Circulation 2012; 125:3066-8. [PMID: 22653085 DOI: 10.1161/circulationaha.112.114181] [Citation(s) in RCA: 37] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/16/2022]
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116
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Campello RS, Alves-Wagner ABT, Abdulkader F, Mori RCT, Machado UF. Carbohydrate- and lipid-enriched meals acutely disrupt glycemic homeostasis by inducing transient insulin resistance in rats. Can J Physiol Pharmacol 2012; 90:537-45. [PMID: 22510071 DOI: 10.1139/y2012-056] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
Chronic intake of high-carbohydrate or high-lipid diets is a well-known insulin resistance inducer. This study investigates the immediate effect (1-6 h) of a carbohydrate- or lipid-enriched meal on insulin sensitivity. Fasted rats were refed with standard, carbohydrate-enriched (C), or lipid-enriched (L) meal. Plasma insulin, glucose, and non-esterified fatty acids (NEFA) were measured at 1, 2, 4, and 6 h of refeeding. The glucose-insulin index showed that either carbohydrates or lipids decreased insulin sensitivity at 2 h of refeeding. At this time point, insulin tolerance tests (ITTs) and glucose tolerance tests (GTTs) detected insulin resistance in C rats, while GTT confirmed it in L rats. Reduced glycogen and phosphorylated AKT and GSK3 content revealed hepatic insulin resistance in C rats. Reduced glucose uptake in skeletal muscle subjected to the fatty acid concentration that mimics the high NEFA level of L rats suggests insulin resistance in these animals is mainly in muscle. In conclusion, carbohydrate- or lipid-enriched meals acutely disrupt glycemic homeostasis, inducing a transient insulin resistance, which seems to involve liver and skeletal muscle, respectively. Thus, the insulin resistance observed when those types of diets are chronically consumed may be an evolution of repeated episodes of this transient insulin resistance.
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Affiliation(s)
- Raquel Saldanha Campello
- Department of Physiology and Biophysics, Institute of Biomedical Sciences, University of Sao Paulo, Brazil.
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117
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Seldin MM, Peterson JM, Byerly MS, Wei Z, Wong GW. Myonectin (CTRP15), a novel myokine that links skeletal muscle to systemic lipid homeostasis. J Biol Chem 2012; 287:11968-80. [PMID: 22351773 DOI: 10.1074/jbc.m111.336834] [Citation(s) in RCA: 269] [Impact Index Per Article: 22.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/11/2022] Open
Abstract
Skeletal muscle plays important roles in whole-body glucose and fatty acid metabolism. However, muscle also secretes cytokines and growth factors (collectively termed myokines) that can potentially act in an autocrine, a paracrine, and/or an endocrine manner to modulate metabolic, inflammatory, and other processes. Here, we report the identification and characterization of myonectin, a novel myokine belonging to the C1q/TNF-related protein (CTRP) family. Myonectin transcript was highly induced in differentiated myotubes and predominantly expressed by skeletal muscle. Circulating levels of myonectin were tightly regulated by the metabolic state; fasting suppressed, but refeeding dramatically increased, its mRNA and serum levels. Although mRNA and circulating levels of myonectin were reduced in a diet-induced obese state, voluntary exercise increased its expression and circulating levels. Accordingly, myonectin transcript was up-regulated by compounds (forskolin, epinephrine, ionomycin) that raise cellular cAMP or calcium levels. In vitro, secreted myonectin forms disulfide-linked oligomers, and when co-expressed, forms heteromeric complexes with other members of the C1q/TNF-related protein family. In mice, recombinant myonectin administration reduced circulating levels of free fatty acids without altering adipose tissue lipolysis. Consistent with this, myonectin promoted fatty acid uptake in cultured adipocytes and hepatocytes, in part by up-regulating the expression of genes (CD36, FATP1, Fabp1, and Fabp4) that promote lipid uptake. Collectively, these results suggest that myonectin links skeletal muscle to lipid homeostasis in liver and adipose tissue in response to alterations in energy state, revealing a novel myonectin-mediated metabolic circuit.
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Affiliation(s)
- Marcus M Seldin
- Department of Physiology and Center for Metabolism and Obesity Research, Johns Hopkins University School of Medicine, Baltimore, Maryland 21205, USA
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