Sabrina Bauer

Systemic chemerin is related to inflammation rather than obesity in type 2 diabetes

Background  The adipokine chemerin modulates the function of innate immune cells and may link obesity and inflammation, and therefore, a possible relation of chemerin to inflammatory proteins in obesity and type 2 diabetes (T2D) was analysed. As visceral fat contributes to systemic inflammation, chemerin was measured in portal venous (PVS), hepatic venous (HVS) and systemic venous (SVS) blood of patients with liver cirrhosis.

Serum Galectin-3 Is Elevated in Obesity and Negatively Correlates with Glycosylated Hemoglobin in Type 2 Diabetes

CONTEXT Adipocytes synthesize galectin-3 whose deficiency protects from inflammation associated with metabolic diseases. We aimed to study circulating galectin-3 in obesity and type 2 diabetes (T2D). STUDY DESIGN Galectin-3 was measured by ELISA in the serum of male normal-weight and overweight controls and T2D patients and in T2D patients of both sexes. Because visceral fat contributes to systemic inflammation, galectin-3 was analyzed in paired samples of human and rodent sc and visceral adipose tissue. Visceral adipose tissue adipokines are released to the portal vein, and galectin-3 was analyzed in portal, hepatic, and systemic venous serum (PVS, HVS, and SVS, respectively) of patients with liver cirrhosis and in patients who underwent surgery for nonhepatic diseases. The effect of metformin on adipocyte galectin-3 was analyzed by immunoblot. RESULTS Circulating galectin-3 was similarly elevated in T2D and obesity compared with normal-weight individuals and revealed a body mass index-dependent positive correlation with leptin, resistin, IL-6, and age. In T2D patients, galectin-3 was increased in serum of patients with elevated C-reactive protein and negatively correlated with glycated hemoglobin. Metformin treatment was associated with lower systemic galectin-3. Reduced galectin-3 in metformin-incubated human adipocytes indicated that low galectin-3 may be a direct effect of this drug. Galectin-3 was higher in PVS compared with HVS and SVS, suggesting that the splanchnic region is a major site of galectin-3 synthesis. Low galectin-3 in HVS compared with PVS demonstrated hepatic removal. CONCLUSIONS Systemic galectin-3 is elevated in obesity and negatively correlates with glycated hemoglobin in T2D patients, pointing to a modifying function of galectin-3 in human metabolic diseases.

Circulating levels of chemerin and adiponectin are higher in ulcerative colitis and chemerin is elevated in Crohn's disease

Background: Chemerin is an adipokine that stimulates chemotaxis of cells of the innate immune system. Inflammatory bowel disease (IBD) is linked to an impaired immune response and, therefore, we hypothesized that systemic chemerin may be altered in IBD patients. Methods: Serum was collected from patients with Crohns disease (CD, 230 patients), ulcerative colitis (UC, 80 patients), and healthy controls (HC, 80 probands). Chemerin and adiponectin, which has already been measured in the serum of similar cohorts by others, were determined by enzyme‐linked immunosorbent assay (ELISA). Results: Chemerin was elevated in IBD compared to HC and was higher in male CD than UC patients. Female and male CD patients had lower adiponectin levels compared to UC, and adiponectin was lower in female CD patients compared to female HC. Adiponectin tended to be higher in female and male UC patients compared to HC and this difference became significant in the whole study group. Correlations with disease activity were only found in males. Here, chemerin was higher in CD patients on remission but was reduced in UC with nonactive disease. Adiponectin was higher in UC with inactive disease. Treatment with corticosteroids was linked to elevated adiponectin in male CD patients and higher chemerin in female UC patients. Unlike adiponectin, which was elevated in female serum in all cohorts, chemerin was only higher in female UC patients. Conclusions: These findings further indicate potential regulatory functions of adipokines in intestinal inflammation that are partly gender‐dependent and that may even be associated with the distinct immunopathogenesis of UC and CD. (Inflamm Bowel Dis 2009;)

Sterol regulatory element-binding protein 2 (SREBP2) activation after excess triglyceride storage induces chemerin in hypertrophic adipocytes.

Chemerin is an adipokine whose systemic concentration and adipose tissue expression is increased in obesity. Chemerin is highly abundant in adipocytes, yet the molecular mechanisms mediating its further induction in obesity have not been clarified. Adipocyte hypertrophy contributes to dysregulated adipokine synthesis, and we hypothesized that excess loading with free fatty acids (FFA) stimulates chemerin synthesis. Chemerin was expressed in mature adipocytes, and differentiation of 3T3-L1 cells in the presence of FFA further increased its level. TNF and IL-6 were induced by FFA, but concentrations were too low to up-regulate chemerin. Sterol regulatory element-binding protein 2 (SREBP2) was activated in these cells, indicative for cholesterol shortage. Suppression of cholesterol synthesis by lovastatin led to activation of SREBP2 and increased chemerin, and supplementation with mevalonate reversed this effect. Knockdown of SREBP2 reduced basal and FFA-induced chemerin. EMSA confirmed binding of 3T3-L1 adipocyte nuclear proteins to a SREBP site in the chemerin promotor. SREBP2 was activated and chemerin was induced in adipose tissue of mice fed a high-fat diet, and higher systemic levels seem to be derived from adipocytes. Lipopolysaccharide-mediated elevation of chemerin was similarly effective as induction by FFA, indicating that both mechanisms are equally important. Chemokine-like receptor 1 was not altered by the incubations mentioned above, and higher expression in fat of mice fed a high-fat diet may reflect increased number of adipose tissue-resident macrophages in obesity. In conclusion, the current data show that adipocyte hypertrophy and chronic inflammation are equally important in inducing chemerin synthesis.

Chemerin induces CCL2 and TLR4 in synovial fibroblasts of patients with rheumatoid arthritis and osteoarthritis.

INTRODUCTION Chemerin stimulates migration of leukocytes to sites of inflammation and also increases inflammatory signaling in chondrocytes suggesting a function of chemerin in joint inflammation. Synovial fibroblasts (SF) are critically involved in synovitis and subsequent cartilage destruction. Here, we analyzed whether synovial fibroblasts express chemerin and its receptor CMKLR1. Further, the role of chemerin in synovial fibroblast chemotaxis, proliferation, insulin response and release of inflammatory proteins was studied. METHODS Synovial tissue sections were labeled with chemerin antibody and chemerin was measured in synovial fluid by ELISA. Chemerin mRNA and protein as well as CMKLR1 expression were determined in SFs from patients with osteoarthritis (OA) and rheumatoid arthritis (RA). Effects of chemerin on cytokines, chemokines and matrix metalloproteinases (MMP), and on proliferation, migration and insulin signaling were analyzed appropriately. RESULTS SFs expressed CMKLR1 and chemerin mRNA, and chemerin protein was found in cell supernatants of synovial fibroblasts. Immunohistochemistry detected chemerin in synovial tissue predominantly localized within the lining layer. Chemerin was present in synovial fluids of RA, OA and psoriatic arthritis patients in similar concentrations. Chemerin neither increased IL-6 levels nor MMP-2 or -9 activity in SFs. Also, it did not act as a chemoattractant for these cells. With respect to intracellular signaling, neither basal nor insulin-mediated phosphorylation of Akt was affected. However, chemerin significantly increased TLR4 mRNA and synthesis of CCL2 in SFs while CCL4 and -5 were not altered. Cell proliferation of SFs, however, was modestly reduced by chemerin. CONCLUSIONS These data show that human SFs express both chemerin and its receptor. As chemerin enhanced expression of TLR4 and induced release of CCL2 in SFs, a role of this protein in innate immune system-associated joint inflammation is proposed.

Small-interference RNA-mediated knock-down of aldehyde oxidase 1 in 3T3-L1 cells impairs adipogenesis and adiponectin release

Aldehyde oxidase 1 (AOX1) is highly abundant in the liver and oxidizes aldehydes thereby generating reactive oxygen species. Enzymes involved in detoxification of aldehydes are expressed in adipocytes and alter adipogenesis, therefore the functional role of AOX1 in adipocytes was analyzed. AOX1 mRNA was higher in visceral compared to subcutaneous human adipose tissue but AOX1 protein was detected in both fat depots. AOX1 expression in adipocytes was confirmed by immunohistochemistry and immunoblot. AOX1 was induced during adipocytic differentiation and was downregulated by fenofibrate in differentiated cells. Knock‐down of AOX1 in preadipocytes led to impaired lipid storage and adiponectin release in the differentiated cells. These data indicate that AOX1 is essential for adipogenesis and may link energy and drug metabolism.

Adiponectin upregulates hepatocyte CMKLR1 which is reduced in human fatty liver.

Chemokine-like receptor 1 (CMKLR1) ligands chemerin and resolvin E1 are suggested to have a role in non-alcoholic fatty liver disease (NAFLD). Here, expression of CMKLR1 in liver cells and NAFLD was studied. CMKLR1 was detected in primary human hepatocytes (PHH), Kupffer cells, bile-duct cells and hepatic stellate cells. In human and rodent fatty liver and in fibrotic liver of mice fed a methionine-choline deficient diet CMKLR1 was reduced. Hepatocytes are the major cells in the liver and effects of adipokines, cytokines and lipids on CMKLR1 in PHH were analyzed. Increased cellular triglyceride or cholesterol content, lipopolysaccharide, IL-6, TNF and leptin did not influence CMKLR1 levels in PHH whereas profibrotic TGFβ tended to reduce CMKLR1. Adiponectin strongly upregulated CMKLR1 mRNA and protein in PHH and hepatic CMKLR1 when injected into wild type mice. Further, CMKLR1 was suppressed in the liver of adiponectin deficient mice. These data indicate that low CMKLR1 in NAFLD may partly result from reduced adiponectin activity.

Impaired hepatic removal of interleukin-6 in patients with liver cirrhosis

Systemic concentrations of interleukin-6 (IL-6) are elevated in patients with liver cirrhosis, and impaired hepatic uptake of IL-6 was suggested to contribute to higher levels in these patients. To test this hypothesis IL-6 was measured in portal venous serum (PVS), hepatic venous serum (HVS) and systemic venous serum (SVS) of 41 patients with liver cirrhosis and four patients with normal liver function. IL-6 was higher in PVS than HVS of all blood donors and about 43% of portal vein derived IL-6 was extracted by the healthy liver, and 6.3% by the cirrhotic liver demonstrating markedly impaired removal of IL-6 by the latter. Whereas in patients with CHILD-PUGH stage A IL-6 in HVS was almost 25% lower than in PVS, in patients with CHILD-PUGH stage C IL-6 was similarly abundant in the two blood compartments. Ascites is a common complication in cirrhotic patients and was associated with higher IL-6 levels in all blood compartments without significant differences in hepatic excretion. Hepatic venous pressure gradient did not correlate with the degree of hepatic IL-6 removal excluding hepatic shunting as the principal cause of impaired IL-6 uptake. Furthermore, patients with alcoholic liver cirrhosis had higher IL-6 in all blood compartments than patients with cryptogenic liver cirrhosis. Aetiology of liver cirrhosis did not affect hepatic removal rate indicating higher IL-6 synthesis in patients with alcoholic liver cirrhosis. In summary, the current data provide evidence that impaired hepatic removal of IL-6 is explained by hepatic shunting and liver dysfunction in patients with liver cirrhosis partly explaining higher systemic levels.

Adiponectin induces the transforming growth factor decoy receptor BAMBI in human hepatocytes

Transforming growth factor (TGF) β is the central cytokine in fibrotic liver diseases. We analyzed whether hepatoprotective adiponectin directly interferes with TGFβ1 signaling in primary human hepatocytes (PHH). Adiponectin induces the TGFβ decoy receptor BMP‐and activin‐membrane‐bound inhibitor (BAMBI) in PHH. Overexpression of BAMBI in hepatoma cells impairs TGFβ‐mediated phosphorylation of SMAD2 and induction of connective tissue growth factor. BAMBI is lower in human fatty liver with a higher susceptibility to liver fibrosis and negatively correlates with BMI of the donors. Hepatic BAMBI is reduced in rodent models of liver inflammation and fibrosis. In summary, the current data show that hepatoprotective effects of adiponectin include induction of BAMBI which is reduced in human fatty liver and rodent models of metabolic liver injury.

MMP-9 activity is increased by adiponectin in primary human hepatocytes but even negatively correlates with serum adiponectin in a rodent model of non-alcoholic steatohepatitis

Adiponectin protects from inflammation and fibrosis in metabolic liver disease. In the present study we analyzed whether this adipokine may directly affect the activity of matrix metalloproteinases (MMPs), central regulators of fibrinolysis, in hepatocytes. Global gene expression analysis indicated upregulation of MMP-9 and tissue inhibitor of metalloproteinases-1 (TIMP-1) expression in primary human hepatocytes (PHH) in response to stimulation with adiponectin, and these results were confirmed by real-time RT-PCR. Furthermore, gelatin zymography revealed that MMP-9 activity was significantly induced in supernatants of adiponectin stimulated PHHs. In a murine model of hepatic steatosis and in human steatotic liver samples hepatic MMP-9 activity was not significantly altered. However, in two different murine models of non-alcoholic steatohepatitis (NASH) MMP-9 activity was significantly elevated compared to chow fed control mice. Of note, MMP-9 activity did not or even negatively, respectively, correlate with adiponectin serum levels in these models. The current data indicate that in NASH hepatic inflammation and fibrosis but not hepatic steatosis induce liver MMP-9 activity, and this induction seems to be related to the anti-inflammatory activity of adiponectin rather than its effect on hepatocellular MMP-9 expression.