Influence of annexin A7 on Insulin Sensitivity

Abstract

Background: Insulin sensitivity is impaired by PGE2, a major product of cyclooxygenase-2 (COX-2), which thus interferes with cellular glucose uptake following a glucose load. As shown in erythrocytes, PGE2 formation is inhibited by annexin A7. The present study defined the role of annexin A7 in glucose metabolism. Methods: Gene-targeted mice lacking annexin A7 (annexinA7-/-) were compared to wild type mice (annexinA7+/+). 6-Keto-prostaglandin-F1α (6-Keto-PGF1α) was determined by ELISA to estimate COX-2 activity in serum. Hepatic COX activity was determined by an ELISA assay. Glucose and insulin serum concentrations were determined following an intraperitoneal glucose load and glucose serum levels after intraperitoneal injection of insulin. Experiments were done without and with pretreatment of the mice with COX inhibitor aspirin. Results: The serum 6-Keto-PGF1α level and hepatic COX activity were significantly higher in annexinA7-/- than in annexinA7+/+ mice. The intraperitoneal glucose tolerance test revealed decreased glucose tolerance in annexinA7-/- mice compared to annexinA7+/+ mice. Intraperitoneal insulin injection decreased the serum glucose level in both genotypes, an effect significantly less pronounced in annexinA7-/- than in annexinA7+/+ mice. Intraperitoneal glucose administration resulted in higher serum insulin concentrations in annexinA7-/- than in annexinA7+/+ mice. Aspirin pretreatment lowered the increase in insulin concentration following glucose injection in both genotypes and virtually abrogated the differences in serum insulin between the genotypes. Moreover, aspirin pretreatment improved glucose tolerance in annexinA7-/- mice. Conclusions: Annexin A7 influences insulin sensitivity of cellular glucose uptake and thus glucose tolerance. These effects depend on COX activity.