Differential expression of adipokines due to hypoxia in brown and white adipocytes

Abstract

Background: Adipose tissue, consisting of white and brown adipocytes, comprises an important endocrine regulator, secreting hormones specified as adipokines. While recent studies demonstrated that adipose tissue responds to hypoxia, the different roles of regulation in brown and white adipocytes are still unclear. In this study the effect of hypoxia on murine brown and white adipocyte cell lines was analyzed. Methods: In cultured adipocytes hypoxia was induced chemically with desferoxamine and cobaldchlorid or physically in an atmosphere of 1% oxygen. Vitality and differentiation was tested by oil-red-staining. Western Blot analysis was performed for hypoxia inducible factor 1 alpha (HIF 1 alpha) in nuclear protein extracts. In corresponding cellular protein extracts HIF 1 alpha regulated proteins (leptin, adiponectin, vascular endothelial growth factor (VEGF) and angiotensinogen) were evaluated by western blot. Results: Chemical as well as physical hypoxia inhibits differentiation of the brown and white adipocyte cell lines. Hypoxia leads to increased HIF 1 alpha-activation in brown and white adipocytes. The expression of adiponectin increased in white adipocytes and decreased in the brown adipocytes under hypoxic conditions. In contrast the amount of leptin was increased in brown and white adipocytes. VEGF- and angiotensinogen-expression did not change in both cell types following hypoxic stimulation. Conclusions: Hypoxia induces similar activation of HIF 1 alpha but differential protein expression in brown and white adipocytes. Different expression of adipokines under hypoxic conditions in the two cell types may represent diverging roles in hypoxia and thus requires an approach distinguishing between these cells for further investigations.