The Role of Annexin A1 in Insulin Resistance and in Pancreatitis

Background: Annexin A1 (ANXA1) is a glucocorticoid-regulated protein, known for its anti-inflammatory effects1. Possible roles of this protein in glucocorticoid-induced metabolic alterations and in pancreatitis were never investigated. The general aim of this dissertation is to evaluate the effect of ANXA1 deficiency on markers of glucose metabolism and corticosterone levels in a mouse model of glucocorticoid-induced insulin resistance, and on markers of inflammation and pancreatic pathology in a mouse model of cerulein-induced acute and chronic pancreatitis. Glucocorticoid-induced hormonal and metabolic alterations: Male BALBc wild type (WT) and ANXA1 knockout (KO) mice were given regular drinking water or dexamethasone in water at a dose of .3 mg/Kg. Insulin and glucose tolerance tests were conducted after 10 days of the treatment. Feces were collected at multiple time points to measure corticosterone and metabolites through ELISA method. Mice were fasted and sacrificed two weeks after the treatment and glucose and insulin were measured through ELISA. Liver and adipose tissues were collected to study the gene expression of gluconeogenic enzymes and Adipokines, respectively, through PCR. In a separate experiment, mice were treated with 5 IU/Kg of insulin then sacrificed after 10 minutes. Liver, muscle and adipose tissue were collected to study insulin signaling by western blotting. In a third experiment, mice were given ip injections of either PBS or .3 mg/Kg of dexamethasone then sacrificed an hour later. Insulin and other hormones were measured through ELISA. Our findings indicate that chronic dexamethasone induced insulin resistance in WT but not in ANXA1 KO mice. Dexamethasone downregulated liver and muscle AKT phosphorylation on serine in WT mice, but this affect was absent in ANXA1 KO mice. Moreover, dexamethasone acutely suppressed insulin levels in WT but not in ANXA1 KO mice. Overall, this indicates that ANXA1 mediates glucocorticoid-induced hormonal and metabolic changes. Acute and chronic pancreatitis: Acute pancreatitis was induced by treating female BALBc WT and ANXA1 KO mice with 8 and 5 ip injections of PBS or cerulein at a dose of 50 μg/Kg. The same dose of 5 cerulein injections were given twice a week for 5 weeks to induce chronic pancreatitis. Serum Interleukin (IL)-6 and IL-10 were measured through ELISA. Histological markers of pancreatic inflammation and fibrosis were evaluated by H&E and Sirius red staining. Our findings indicate that ANXA1 deficient mice express higher IL-6 induction in acute pancreatitis and higher pancreatic fibrosis in chronic pancreatitis. Conclusion: ANXA1 is an important mediator of the metabolic and hormonal effects of glucocorticoids. Moreover, ANXA1 modulates systemic inflammation in acute pancreatitis and protect from fibrosis in chronic pancreatitis.