ABSTRACT
Plasma level of the protein VAP-1/SSAO (Vascular Adhesion Protein-1/Semicarbazide-Sensitive Amine Oxidase) is increased in diabetes and/or obesity and may be related to vascular complications associated to these pathologies. The aim of this work was to complete a preceding study where we described the role played by some hormones or metabolites, implicated in diabetes and/or obesity, in the regulation of the release of VAP-1/SSAO by 3T3-L1 adipocytes. Here we focused on the previously observed effect produced by TNFalpha in the release of VAP-1/SSAO and studied the effect of a beta-adrenergic compound, isoproterenol. Both compounds stimulated the release of VAP-1/SSAO to the culture medium but had a different effect on the VAP-1/SSAO membrane form. While TNFalpha produced a decrease on VAP-1/SSAO membrane form content, isoproterenol did not modify it. We thus observed two different ways of regulation of the release of VAP-1/SSAO by 3T3-L1 adipocytes by metabolites implicated in diabetes and adipose tissue physiopathology. Our work permits a better understanding of this increased plasma VAP-1/SSAO levels observed in diabetes.
Subject(s)
Adipocytes/drug effects , Adrenergic beta-Agonists/pharmacology , Amine Oxidase (Copper-Containing)/metabolism , Cell Adhesion Molecules/metabolism , Isoproterenol/pharmacology , Tumor Necrosis Factor-alpha/pharmacology , 3T3-L1 Cells , Adipocytes/enzymology , Adipocytes/metabolism , Amine Oxidase (Copper-Containing)/analysis , Animals , Blotting, Western , Cell Culture Techniques , Cell Fractionation , Dose-Response Relationship, Drug , Electrophoresis, Polyacrylamide Gel , Mice , SolubilityABSTRACT
Plasma level of the protein SSAO/VAP-1 (samicarbazide-sensitive amine oxidase / vascular-adhesion protein-1) is increased in diabetes and/or obesity and may be related to vascular complications associated to these pathologies. The aim of this work was to complete a preceding study where we described the role played by some hormones or metabolites, implicated in diabetes and/or obesity, in the regulation of the release of VAP-1/SSAO by 3T3-L1 adipocytes. Here we focused on the previously observed effect produced by TNFa in the release of VAP-1/SSAO and studied the effect of a beta-adrenergic compound, isoproterenol. Both compounds stimulated the release of VAP-1/SSAO to the culture medium but had a different effect on the SSAO/VAP-1 membrane form. While TNFa produced a decrease on SSAO/VAP-1 membrane form content, isoproterenol did not modify it. We thus observed two different ways of regulation of the release of SSAO/VAP-1 by 3T3-L1 adipocytes by metabolites implicated in diabetes and adipose tissue physiopathology. Our work permits a better understanding of this increased plasma SSAO/VAP-1 levels observed in diabetes
Los niveles plasmáticos de la proteina SSAO/VAP-1 están aumentados en la diabetes y la obesidad, lo que podría estar relacionado con las complicaciones vasculares asociadas a estas patologías. En continuidad con trabajos anteriores acerca del papel de algunas hormonas o metabolitos, implicados en la diabetes y obesidad. Se estudia en este trabajo el efecto producido por el TNFa y del agonista beta-adrenérgico, isoproterenol en la regulación de la liberación de VAP-1/SSAO por adipocitos 3T3-L1. Ambos compuestos estimularon la liberación de VAP-1/SSAO al medio de cultivo, pero tuvieron un efecto diferente sobre la isoforma ligada a la membrana de SSAO/VAP-1. Así, mientras que el TNFa produjo una disminución significativa en la actividad SSAO/VAP-1 ligada a la membrana, no se modificó por el isoproterenol. Además, observamos dos maneras diferentes de regulación de la liberación de SSAO/VAP-1 por adipocitos 3T3-L1 a través de metabolitos implicados en diabetes y fisiopatología del tejido adiposo. Nuestro trabajo permite un mejor entendimiento de estos niveles plasmáticos aumentados de SSAO/VAP-1 observados en diabetes
Subject(s)
Animals , Mice , Adipocytes , Adrenergic beta-Agonists/pharmacokinetics , Amine Oxidase (Copper-Containing) , Cell Adhesion Molecules , Isoproterenol/pharmacology , Blotting, Western , Cell Adhesion Molecules/metabolism , Cell Fractionation , 3T3-L1 Cells , Adipocytes/enzymology , Adipocytes/metabolism , Amine Oxidase (Copper-Containing)/analysis , Amine Oxidase (Copper-Containing)/metabolism , Dose-Response Relationship, Drug , Electrophoresis, Polyacrylamide Gel , SolubilityABSTRACT
AIMS/HYPOTHESIS: Vascular adhesion protein-1 (VAP-1), which is identical to semicarbazide-sensitive amine oxidase (SSAO), is a dual-function membrane protein with adhesion properties and amine oxidase activity. A soluble form of VAP-1 is found in serum, where concentrations are enhanced in diabetes and obesity. In vitro, soluble VAP-1 enhances lymphocyte adhesion to endothelial cells, thus possibly participating in the enhanced lymphocyte adhesion capacity that is implicated in the cardiovascular complications associated with diabetes or obesity. In both, the tissue origin of the soluble VAP-1/SSAO is unknown. We examined whether adipose tissue, which has abundant expression of VAP-1/SSAO, is a source of soluble VAP-1. METHODS: We detected VAP-1/SSAO in plasma of diabetic animals, with or without VAP-1 immunoprecipitation, and in culture medium from 3T3-L1 adipocytes and human adipose tissue explants. VAP-1 protein glycosylation was measured. RESULTS: Diabetic and obese animals have increased plasma SSAO activity associated with VAP-1 protein. We also found that 3T3-L1 adipocytes and human adipose tissue explants release a soluble form of VAP-1/SSAO, which derives from the membrane. The release of soluble VAP-1 was enhanced by exposure of murine and human adipocytes to TNF-alpha and blocked by batimastat, a metalloprotease inhibitor. Partial ablation of adipose tissue reduced plasma SSAO activity in normal and diabetic rats. CONCLUSIONS/INTERPRETATION: Adipose cells are a source of soluble VAP-1/SSAO released by shedding of the membrane form. The release of SSAO is regulated by TNF-alpha and insulin. By releasing VAP-1/SSAO, adipose cells could contribute to the atherogenesis and vascular dysfunction associated with diabetes and obesity.
Subject(s)
Adipocytes/metabolism , Amine Oxidase (Copper-Containing)/metabolism , Cell Adhesion Molecules/metabolism , Metalloproteases/metabolism , 3T3 Cells , Adipocytes/cytology , Adipocytes/enzymology , Animals , Humans , Male , Mice , Neuraminidase/pharmacology , Obesity/physiopathology , Rats , Rats, Wistar , Rats, ZuckerABSTRACT
It has been recently reported that insulin recruits a novel signaling machinery to lipid rafts required for insulin-stimulated GLUT4 translocation [Baumann, A., Ribon, V., Kanzaki, M., Thurmond, D. C., Mora, S., Shigematsu, S., Bickel, P. E., Pessin, J. E. & Saltiel, A. R. (2001) Nature 407, 202-207, 2000; Chiang, S. H., Baumann, C. A., Kanzaki, M., Thurmond, D. C., Watson, R. T., Neudauer, C. L., Macara, I. G., Pessin, J. E. & Saltiel, A. R. (2001) Nature 410, 944-948]. We have assessed the role of lipid rafts on GLUT4 traffic in adipose cells. High GLUT4 levels were detected in caveolae from adipocytes by two approaches, the mechanical isolation of purified caveolae from plasma membrane lawns and the immunogold analysis of plasma membrane lawns followed by freeze-drying. The role of lipid rafts in GLUT4 trafficking was studied by adding nystatin or filipin at concentrations that specifically disrupt caveolae morphology and inhibit caveolae function without altering clathrin-mediated endocytosis. These caveolae inhibitors did not affect the insulin-stimulated glucose transport. However, they blocked both the GLUT4 internalization and the down-regulation of glucose transport triggered by insulin removal in 3T3-L1 adipocytes. Our data indicate that lipid rafts are crucial for GLUT4 internalization after insulin removal. Given that high levels of GLUT4 were detected in caveolae from insulin-treated adipose cells, this transporter may be internalized from caveolae or caveolae may operate as an obligatory transition station before internalization.
