Abstract 735: A Novel Class of Sphingolipids Mediate Autophagy and Apoptosis in Models of Ischemia

Abstract

Rationale: Heart failure caused by ischemic cardiomyopathy is the leading cause of death and disability in the USA and world, accounting for 10 million deaths in 2016. Sphingolipids including ceramides and sphingosine-1-phosphate have been demonstrated to play roles in myocardial injury. In general, these lipids are synthesized from serine palmitoyltransferase (SPT) derived using serine and palmitoyl-CoA. While the standard SPT enzyme exists as a heterodimer of two subunits, Sptlc1 and Sptlc2, a new subunit was recently discovered, Sptlc3, which enables the SPT complex to use myristoyl-CoA, thereby synthesizing a previously underappreciated group of atypical sphingolipids. We previously demonstrated that these atypical lipids are a major component of myocardial sphingolipid pools. Furthermore, in contrast to canonical sphingolipids, the atypical lipids promote cardiomyocyte apoptosis. Therefore, the goal of this research is to determine the contribution of these novel lipids to cardiomyocyte apoptosis and therefore whether they may contribute to ischemic injury. Objectives: To determine the contribution of Sptlc3 and atypical sphingolipids to cardiomyocyte apoptosis and ischemic injury and to assess the potential relevance of Sptlc3 to human HF. Methods: Murine primary cardiac fibroblasts and cardiomyocytes were isolated and subject to ischemic induction. Following this, cells were analyzed with TUNEL staining, lipidomic analysis or treatment with a Sptlc3 mimetic. Results: Ischemic cells show significantly increased Sptlc3 expression, non-canonical sphingolipids in the sphingolipid pool and apoptotic cells as compared to their controls. The cells treated with the Sptlc3 mimetic show apoptotic and a non-canonical autophagic pathway being induced in cells. Conclusions: We have identified a novel class of sphingolipids enriched in myocardium of mice with cardiomyopathies. Furthermore, the enzyme that produces these, Sptlc3, is robustly increased in human heart failure. Because the Sptlc3-derived lipids promoted cardiomyocyte apoptosis, we propose that Sptlc3 may mediate myocardial injury in ischemia.