Abstract 10918: Increased Plasma Sphingosine-1-Phosphate (S1P) and Its Capacity to Increase Expression of Plasminogen Activator Inhibitor-1 In Adipocytes and Obese Subjects
Concentrations of plasminogen activator inhibitor type-1 (PAI-1), the physiologic inhibitor of fibrinolysis in blood, are increased in obese subjects. One source is adipocytes. Hypoxia is known to develop within adipose tissue as it expands, presumably contributing to increased sphingosine-1-phosphate (S1P), a breakdown product of sphingosine - ubiquitous in cell membranes. We have previously shown that S1P increases expression of PAI-1 in liver and sought in the present study to determine whether hypoxia induces S1P in adipocytes thereby potentially contributing to increased PAI-1 and hence constraints on fibrinolysis associated with obesity. Mouse 3T3-L1 preadipocytes were differentiated and exposed to CoCl2 (150μM) to simulate hypoxia. Assays were performed for PAI-1 mRNA (RT-PCR) and S1P (HPLC). Physiologic concentration of S1P (500-1,000 nM) increased PAI-1 mRNA by 4-fold in 1 hr (n=3, p<0.05). JTE013 (10μM), an S1P2 receptor antagonist, attenuated the response. Adipocytes expressed sphingosine kinase 1 (SphK1) and S1P lyase (SPL), key enzymes involved in S1P production and degradation in the sphingolipid metabolic pathway. Hypoxia for 30 min increased activity of SphK1 by 1.4 fold (n=4, p<0.05), decreased mRNA of SPL by 45% (n=3, p<0.05), reduced cytosolic sphingosine by 49% (n=3, p<0.05), and increased release of S1P into conditioned medium by 8-fold(P<0.01). In adipocytes and mouse white adipose tissue S1P transporters were expressed abundantly, and glibenclamide (100μM), an inhibitor of one (ABCA1), and MK571 (20μM), an inhibitor of another (ABCC1), diminished the release of S1P. In obese patients (BMI≥25, n=45) with uncomplicated dyslipidemia and hypertension plasma S1P was increased (519±107 nM) compared with that in non-obese (25>BMI≥22, n=42)(465±76 nM, p<0.01) and lean (22>BMI, n=24) subjects (440±85 nM, p<0.01). Thus, hypoxia in adipose tissue of obesity can promote elaboration of S1P that binds to S1P2 receptors in an autocrine or paracrine fashion potentially contributing to increased expression of PAI-1 and consequent constraints on fibrinolysis. S1P production and extracellular transport provide an attractive and novel target for therapy designed to attenuate impaired fibrinolysis associated with obesity.
- © 2012 by American Heart Association, Inc.