The aims of this study were designed to determine whether liraglutide, a long-acting glucagon-like peptide, could reverse the adverse effects of a diet high in fat that also contained trans-fat and ...high-fructose corn syrup (ALIOS diet). Specifically, we examined whether treatment with liraglutide could reduce hepatic insulin resistance and steatosis as well as improve cardiac function. Male C57BL/6J mice were pair fed or fed ad libitum either standard chow or the ALIOS diet. After 8 wk the mice were further subdivided and received daily injections of either liraglutide or saline for 4 wk. Hyperinsulinemic-euglycemic clamp studies were performed after 6 wk, revealing hepatic insulin resistance. Glucose tolerance and insulin resistance tests were performed at 8 and 12 wk prior to and following liraglutide treatment. Liver pathology, cardiac measurements, blood chemistry, and RNA and protein analyses were performed. Clamp studies revealed hepatic insulin resistance after 6 wk of ALIOS diet. Liraglutide reduced visceral adiposity and liver weight (P < 0.001). As expected, liraglutide improved glucose and insulin tolerance. Liraglutide improved hypertension (P < 0.05) and reduced cardiac hypertrophy. Surprisingly, liver from liraglutide-treated mice had significantly higher levels of fatty acid binding protein, acyl-CoA oxidase II, very long-chain acyl-CoA dehydrogenase, and microsomal triglyceride transfer protein. We conclude that liraglutide reduces the harmful effects of an ALIOS diet by improving insulin sensitivity and by reducing lipid accumulation in liver through multiple mechanisms including, transport, and increase β-oxidation.
Adiponectin is protective against hepatic fibrosis, whereas leptin promotes fibrosis. In HSCs (hepatic stellate cells), leptin signals via a JAK2 (Janus kinase 2)/STAT3 (signal transducer and ...activator of transcription 3) pathway, producing effects that enhance ECM (extracellular matrix) deposition. SOCS-3 (suppressor of cytokine signalling-3) and PTP1B (protein tyrosine phosphatase 1B) are both negative regulators of JAK/STAT signalling, and recent studies have demonstrated a role for adiponectin in regulating SOCS-3 expression. In the present study we investigate mechanisms whereby adiponectin dampens leptin signalling and prevents excess ECM production. We treated culture-activated rat HSCs with recombinant adiponectin, leptin, both or neither, and also treated adiponectin knockout (Ad-/-) and wild-type mice with leptin and/or carbon tetrachloride (CCl4) or saline. We analyse JAK2 and Ob-Rb (long form of the leptin receptor) phosphorylation, and PTP1B expression and activity. We also explore potential mechanisms through which adiponectin regulates SOCS-3-Ob-Rb association. Adiponectin inhibits leptin-stimulated JAK2 activation and Ob-Rb phosphorylation in HSCs, whereas both were increased in Ad-/- mice. Adiponectin stimulates PTP1B expression and activity in vitro, whereas PTP1B expression was lower in Ad-/-mice than in wild-type mice. Adiponectin also promotes SOCS-3-Ob-R association and blocks leptin-stimulated formation of extracellular TIMP-1 (tissue inhibitor of metalloproteinases-1)-MMP-1 (matrix metalloproteinase-1) complexes in vitro. These results suggest two novel mechanisms whereby adiponectin inhibits hepatic fibrosis: (i) by promoting binding of SOCS-3 to Ob-Rb, and (ii) by stimulating PTP1B expression and activity, thus inhibiting JAK2/STAT3 signalling at multiple points.
Background & Aims Epidemiological studies have shown that obesity is a risk factor for hepatocellular carcinoma (HCC). Lower adiponectin levels are associated with poor prognosis in obese HCC ...patients, hence it is plausible that adiponectin acts as a negative regulator of HCC. We investigated the effects of adiponectin on HCC development and its molecular mechanisms. Methods Assays with Huh7 and HepG2 HCC cells were used to examine the signal transduction pathways involved in the protective functions of adiponectin in HCC. These studies were followed by in vivo approaches using HCC xenografts and tumor analysis. Results from in vitro and in vivo findings were corroborated using human HCC tissue microarray and analysis of clinicopathological characteristics. Results Adiponectin increased apoptosis of HCC cells through activation of caspase-3. Adiponectin increased phosphorylation of c-Jun-N-terminal kinase (JNK) and inhibition of c-Jun-N-terminal kinase−phosphorylation inhibited adiponectin-induced apoptosis and caspase-3 activation. Adiponectin increased phosphorylation of 5′-adenosine monophosphate−activated protein kinase and tumor suppressor tuberous sclerosis complex 2 and inhibited mammalian target of rapamycin phosphorylation. Inhibition of 5′-adenosine monophosphate−activated protein kinase phosphorylation not only inhibited adiponectin-induced c-Jun-N-terminal kinase phosphorylation, but also blocked biological effects of adiponectin. Adiponectin substantially reduced liver tumorigenesis in nude mice. Importantly, analysis of adiponectin expression levels in tissue microarray of human HCC patients revealed an inverse correlation of adiponectin expression with tumor size. Conclusions Adiponectin protects against liver tumorigenesis; its reduced expression is associated with poor prognosis in obese patients with HCC.
Obesity is rapidly becoming a pandemic and is associated with increased carcinogenesis. Obese populations have higher circulating levels of leptin in contrast to low concentrations of adiponectin. ...Hence, it is important to evaluate the dynamic role between adiponectin and leptin in obesity‐related carcinogenesis. Recently, we reported the oncogenic role of leptin including its potential to increase tumor invasiveness and migration of hepatocellular carcinoma (HCC) cells. In the present study we investigated whether adiponectin could antagonize the oncogenic actions of leptin in HCC. We employed HCC cell lines HepG2 and Huh7, the nude mice‐xenograft model of HCC, and immunohistochemistry data from tissue‐microarray to demonstrate the antagonistic role of adiponectin on the oncogenic actions of leptin. Adiponectin treatment inhibited leptin‐induced cell proliferation of HCC cells. Using scratch‐migration and electric cell‐substrate impedance‐sensing‐based migration assays, we found that adiponectin inhibited leptin‐induced migration of HCC cells. Adiponectin treatment effectively blocked leptin‐induced invasion of HCC cells in Matrigel invasion assays. Although leptin inhibited apoptosis in HCC cells, we found that adiponectin treatment induced apoptosis even in the presence of leptin. Analysis of the underlying molecular mechanisms revealed that adiponectin treatment reduced leptin‐induced Stat3 and Akt phosphorylation. Adiponectin also increased suppressor of cytokine signaling (SOCS3), a physiologic negative regulator of leptin signal transduction. Importantly, adiponectin significantly reduced leptin‐induced tumor burden in nude mice. In HCC samples, leptin expression significantly correlated with HCC proliferation as evaluated by Ki‐67, whereas adiponectin expression correlated significantly with increased disease‐free survival and inversely with tumor size and local recurrence. Conclusion: Collectively, these data demonstrate that adiponectin has the molecular potential to inhibit the oncogenic actions of leptin by blocking downstream effector molecules. (HEPATOLOGY 2010
Adiponectin is an adipocytokine that was recently shown to be anti‐fibrogenic in hepatic fibrosis. Leptin, on the other hand, promotes hepatic fibrosis. The purpose of the present study was to ...elucidate a mechanism (or mechanisms) whereby adiponectin dampens leptin signaling in activated hepatic stellate cells (HSCs), and prevents excess extracellular matrix production. Activated HSCs, between passages 2 and 5, were cultured and exposed to recombinant human adiponectin and recombinant leptin. Immunoblot analysis for SOCS‐3, TIMP‐1, and the phosphorylated species of Stat3 and adenosine monophosphate‐activated protein kinase (AMPK) were conducted. We also examined MMP‐1 activity by immunosorbant fluorimetric analysis. In HSCs, adiponectin‐induced phosphorylation of AMPK, and subsequently suppressed leptin‐mediated Stat3 phosphorylation and SOCS‐3 induction. Adiponectin also blocked leptin‐stimulated secretion of TIMP‐1, and significantly increased MMP‐1 activity, in vitro. To extend this study, we treated adiponectin knockout mice (Ad−/−) daily with 5 mg/kg recombinant leptin and/or carbon tetrachloride (2 ml/kg) for 6 weeks. Post‐necropsy analysis was performed to examine for inflammation, and histological changes in the Ad−/− and wild‐type mice. There was no significant difference in inflammation, or aminotransferases, between mice receiving carbon tetrachloride and leptin versus carbon tetrachloride alone. As anticipated, the combination of leptin and CCl4 enhanced hepatic fibrosis in both wild‐type and Ad−/− mice, as estimated by amount of collagen in injured livers, but wild‐type mice had significantly higher levels of SOCS‐3 and significantly lower levels of TIMP‐1 mRNA and protein than did adiponectin KO mice exposed to both CCl4 and leptin. We therefore conclude that the protective effects of adiponectin against liver fibrosis require AMPK activation, and may occur through inhibition of the Jak‐Stat signal transduction pathway. J. Cell. Biochem. 110: 1195–1207, 2010. Published 2010 Wiley‐Liss, Inc.
Overexpression of STYK1, a putative serine/threonine and tyrosine receptor protein kinase has been shown to confer tumorigenicity and metastatic potential to normal cells injected into nude mice. ...Mutation of a tyrosine residue in the catalytic STYK1 domain attenuates the tumorigenic potential of tumor cells in vivo, collectively, suggesting an oncogenic role for STYK1.
To investigate the role of STYK1 expression in ovarian cancer, a panel of normal, benign, and ovarian cancer tissues was evaluated for STYK1 immunoreactivity using STYK1 antibodies. In addition, mRNA levels were measured by reverse transcription PCR and real-time PCR of estrogen receptors, GPR30 and STYK1 following treatment of ovarian cell lines with estrogen or G1, a GPR30 agonist, as well as western analysis.
Our data showed higher expression of STYK1 in cancer tissues versus normal or benign. Only normal or benign, and one cancer tissue were STYK1-negative. Moreover, benign and ovarian cancer cell lines expressed STYK1 as determined by RT-PCR. Estradiol treatment of these cells resulted in up- and down-regulation of STYK1 despite estrogen receptor status; whereas G-1, a GPR30-specific agonist, increased STYK1 mRNA levels higher than that of estradiol.
We conclude that STYK1 is expressed in ovarian cancer and is regulated by estrogen through a GPR30 hormone-signaling pathway, to the exclusion of estrogen receptor-alpha.
Glucagon‐like peptide 1 (GLP‐1) is a naturally occurring peptide secreted by the L cells of the small intestine. GLP‐1 functions as an incretin and stimulates glucose‐mediated insulin production by ...pancreatic β cells. In this study, we demonstrate that exendin‐4/GLP‐1 has a cognate receptor on human hepatocytes and that exendin‐4 has a direct effect on the reduction of hepatic steatosis in the absence of insulin. Both glucagon‐like peptide 1 receptor (GLP/R) messenger RNA and protein were detected on primary human hepatocytes, and receptor was internalized in the presence of GLP‐1. Exendin‐4 increased the phosphorylation of 3‐phosphoinositide‐dependent kinase‐1 (PDK‐1), AKT, and protein kinase C ζ (PKC‐ζ) in HepG2 and Huh7 cells. Small interfering RNA against GLP‐1R abolished the effects on PDK‐1 and PKC‐ζ. Treatment with exendin‐4 quantitatively reduced triglyceride stores compared with control‐treated cells. Conclusion: This is the first report that the G protein–coupled receptor GLP‐1R is present on human hepatocytes. Furthermore, it appears that exendin‐4 has the same beneficial effects in vitro as those seen in our previously published in vivo study in ob/ob mice, directly reducing hepatocyte steatosis. Future use for human nonalcoholic fatty liver disease, either in combination with dietary manipulation or other pharmacotherapy, may be a significant advance in treatment of this common form of liver disease. (HEPATOLOGY 2010)
Obesity and insulin resistance (IR) cause a clustering of metabolic abnormalities including non‐alcoholic fatty liver disease (NAFLD), dyslipidemia, hypertension and elevated plasma triglycerides. ...Western diets (WD) containing trans‐fat (TF) and high fructose corn syrup (HFCS) have been shown to increase IR, fat mass and liver lipid accumulation. The Aim of the present study was to determine if liraglutide (LG), a glucagon‐like peptide 1 (GLP‐1) long‐acting analogue could reverse the effects of a WD in mice including reduction in hepatic IR, steatosis and improved cardiac function. Male C57BL6 mice were fed ad libitum either standard chow or a high fat diet containing TF and HFCS for 8 wk, followed by 4 wk of concomitant daily LG injections. After LG injections, within the WD group, LG treatment significantly improved fasting serum glucose levels as compared with saline treated mice (122.2 mg/dL ± 6.17 vs. 166 mg/dL ± 50.73, p<.0001), reduced body weight (29.30 g ±.692 vs. 33.08 g ±4.54, p<.005), reduced liver weight (1.067 g ±.083 vs. 1.217 g ±.108, p<.05) heart weight (.006845 g/cm ± .000302 vs. .00755 g/cm ± .000612). LG liver and heart tissue had significantly higher levels of fatty acid binding protein and microsomal triglyceride transfer protein.
Conclusion
LG reduces the effects of a WD by improving insulin sensitivity and by reducing lipid accumulation in liver and heart through fatty acid uptake and transport.
Grant Funding Source: R01 DK 075397
Understanding and improving the state of the nation's levees has become a national priority following the devastating events surrounding Hurricanes Katrina and Rita. Federal legislation passed in ...2007 created a new national Committee on Levee Safety and spurred the development of the National Levee Database, a central repository of information relating to the location and state of levees across the United States (Water Resources Development Act, 2007). One of the major goals in developing such a database is to improve the safety of America's levees. The National Levee Database, however, does not include features for storing seepage and slope stability data related to numerical analyses of levees. These data are critical in analyzing current levee conditions and predicting future failure scenarios, thus providing a path for further improving the safety of levees. The Levee Analyst is a new GIS data model and set of geoprocessing tools that make it possible to store and manipulate model data associated with seepage and slope stability analyses. The data model provides a concise structure for storing large amounts of levee seepage and slope stability data and also provides a structure that is expandable and compatible with the National Levee Database. The Levee Analyst combines the capabilities of various software systems in providing a data model and suite of tools that assists in further understanding and analyzing the state of America's levees.
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