Autocrine action of adiponectin on human fat cells prevents the release of insulin resistance-inducing factors

The adipocyte hormone adiponectin is negatively correlated with obesity and insulin resistance and may exert an important antidiabetes function. In this study, primary human skeletal muscle cells were cocultured with human fat cells or incubated with adipocyte-conditioned medium in the presence or absence of the globular domain of adiponectin (gAcrp30) to analyze its capacity to restore normal insulin signaling in the muscle cells. Human skeletal muscle cells cocultured with adipocytes or treated with adipocyte-conditioned medium showed an impaired Akt and glycogen synthase kinase 3 serine phosphorylation in response to insulin. Furthermore, insulin-stimulated GLUT4 translocation was reduced by adipocyte-conditioned medium. Impaired insulin signaling was normalized upon addition of gAcrp30 to the coculture. Further, adipocyte-conditioned medium generated in the presence of gAcrp30 was unable to perturb insulin-stimulated Akt phosphorylation. Concomitant addition of gAcrp30 and adipocyte-conditioned medium to the myocytes failed to restore normal insulin action. Protein array analysis of adipocyte-conditioned medium indicated that the secretion of at least eight different cytokines was diminished in response to gAcrp30. We therefore suggest that adiponectin operates as a key regulator of adipocyte secretory function. This autocrine action may prevent the induction of skeletal muscle insulin resistance and may partly explain the antidiabetes action of this hormone.