Abstract 11084: Hypoxia Enhances Sphingosine-1-Phosphate (S1P) Release From Adipocytes and Provokes S1P-mediated Insulin Resistance by Inducing TNF-α Expression in Resident NKT Cells
Background: We have previously shown that natural killer T (NKT) cells, a unique subset of T lymphocytes that recognize non-peptide antigens such as glycosphingolipids and phospholipids, accumulate in adipose tissue in diet-induced obese mice and provoke inflammation and glucose intolerance. We sought to determine the critical determinant and underlying mechanism.
Methods and Results: NKT-cell hybridoma (1B6) was established by fusing sorted mouse NKT cells with BW1100 thymoma cells. 1B6 cells were CD4+CD8- and expressed G protein coupled receptors (S1P1, S1P2, S1P4) for sphingosine-1-phosphate (S1P), a breakdown product of sphingolipid metabolism and regulator of lymphocyte trafficking. Treatment with S1P (1,000 nM) increased mRNA expression of tumor necrosis factor-α (TNF-α), a representative proinflammatory adipocytokine by 97±30 (SD) % (n=3, p<0.05, quantitative RT-PCR). VPC23019 (10 μM), an S1P1/S1P3 receptor antagonist, resulted in decreased mRNA expression of TNF-α induced by S1P. In contrast, FTY720 (20–50 nM), an immunosuppressive S1P receptor modulator, decreased mRNA expression of TNF-α induced by S1P. 3T3-L1 mouse adipocytes were positive for sphingosine kinase 2 (SphK2), a key enzyme for S1P production in the sphingolipid metabolic pathway. Hypoxia with 1% O2 increased SphK2 mRNA expression and SphK enzymatic activity and induced the release of S1P from 3T3-L1 adipocytes into the conditioned medium (HPLC after fluorescent derivatization with o-phthaldialdehyde). Among patients with mild dyslipidemia and/or hypertension plasma S1P level was increased in obese patients (BMI>25) (499±144 nM) as compared to the levels in lean (BMI<25) subjects (452±83 nM, n=126, p<0.05).
Conclusions: These data suggest that hypoxia in adipose tissue induced by obesity promotes the synthesis of S1P, which binds to S1P1 receptor on resident NKT cells in a paracrine fashion. NKT cells activated by adipocyte-derived S1P overexpress adipocytokine TNF-α and induce insulin resistance. Thus, hypoxia-induced adipocyte S1P production and S1P1 receptor on resident NKT cells are indispensable for development of diet-induced insulin resistance. S1P1 receptor on NKT cells is an attractive new target of anti-inflammatory pharmacotherapy.
- © 2010 by American Heart Association, Inc.