Abstract 548: Molecular Mechanism Behind Protein S Deficiency in Obese Patients

Abstract

Introduction: Protein S is a vitamin K-dependent plasma protein, produced mainly in the liver; Protein S circulates in the blood at a concentration of 450 nM. Protein S is an anticoagulant, serving as a cofactor for APC and TFPI, and as an inhibitor of Factor IX (FIXa). Protein S deficiency causes deep vein thrombosis (DVT), increased risk of inflammation and, because DVT is a complication commonly observed in obese individuals, Protein S deficiency might be associated with obesity. Aim: To identify a correlation between Protein S deficiency and obesity, and identify the probable molecular mechanism behind the Protein S deficiency in the obese subjects. Methods: Immunoblots, ELISA, EMSA, CHIP, aPTT assay, and thrombin generation assay. Results: By ELISA, we measured a decrease in Protein S level in obese mice compared with wild type mice. In obesity, the liver becomes hypoxic, thus, we hypothesized that hypoxia and hypoxia inducible factor 1 alpha (HIF1α) may regulate Protein S expression in obesity. We found that a high fat diet induced HIF1α stability in mice. HIF1α levels were inversely proportional to Protein S levels, suggesting that HIF1α is a negative regulator of Protein S expression. We further identified a putative HIF1α binding site in the Protein S promoter, and, by using in vitro and in vivo assays, we demonstrated that HIF1α binds directly to the Protein S promoter and suppresses transcription. We further confirmed HIF1α-mediated Protein S transcriptional regulation in vivo, Plasma Protein S levels are increased in the liver-specific HIF1α knockout mouse whereas, liver-specific overexpression of HIF1α reduced the concentration of Protein S in the plasma. Conclusion: We conclude that HIF1α regulates Protein S expression in mouse liver and in obesity. Inhibition of HIF1α or intravenous injection of Protein S may reduce the occurrence of DVT in obese individuals.