Abstract 164: Adult Cardiac Fibroblasts Null for Sphingosine Kinase-1 Exhibit Dysregulation of Inflammatory Proteins
Background: The possible role of sphingosine kinase/S1P in the regulation of mediator cytokines that induce inflammation in the heart has not been studied during oxidative stress.
Methods and Aim: We cultured cardiac fibroblasts (AMCF) isolated from adult mouse hearts to determine whether sphingosine kinase regulates interleukin-1β and/or hypoxia-induced inflammatory proteins such as inducible nitric oxide synthase (iNOS) and cyclooxygenase-2 (COX-2).
Results: In AMCF IL-1β is a weak inducer of iNOS and NO accumulation. Hypoxia alone has no significant effect on iNOS or COX-2 activation. However, IL-1β treatment in combination with hypoxia readily stimulates iNOS and NO production. Similarly, IL-β and hypoxia trigger de novo COX-2 synthesis. We also show for the first time that sphingosine kinase (SphK) is highly expressed in AMCF compared to adult mouse cardiac myocytes. While hypoxia does not alter SphK activity compared to normoxic AMCF, IL1β enhances SphK activity versus control. Using SphK-1 knockout mice we demonstrate that SphK-1 is the major isoform expressed in AMCF, since the bulk of SphK activity was abrogated in the knockout mice. Moreover, we found that iNOS expression and NO production were not impaired but rather enhanced in SphK-1 null AMCF during hypoxia and IL1β stimulation.
Conclusion: Thus, SphK-1 supresses pro-inflammatory responses. These are the first data showing that the SphK-1/S1P signaling pathways play a prosurvival regulatory role in the inflammatory response induced by oxidative stress in cardiac fibroblasts.