Diabetic cardiomyopathy (DbCM), which consists of cardiac hypertrophy and failure in the absence of traditional risk factors, is a major contributor to increased heart failure risk in type 2 diabetes patients. In rodent models of DbCM, cardiac hypertrophy and dysfunction have been shown to depend upon saturated fatty acid (SFA) oversupply and de novo sphingolipid synthesis. However, it is not known whether these effects are mediated by bulk SFAs and sphingolipids or by individual lipid species. In this report, we demonstrate that a diet high in SFA induced cardiac hypertrophy, left ventricular systolic and diastolic dysfunction, and autophagy in mice. Furthermore, treatment with the SFA myristate, but not palmitate, induced hypertrophy and autophagy in adult primary cardiomyocytes. De novo sphingolipid synthesis was required for induction of all pathological features observed both in vitro and in vivo, and autophagy was required for induction of hypertrophy in vitro. Finally, we implicated a specific ceramide N-acyl chain length in this process and demonstrated a requirement for (dihydro)ceramide synthase 5 in cardiomyocyte autophagy and myristate-mediated hypertrophy. Thus, this report reveals a requirement for a specific sphingolipid metabolic route and dietary SFAs in the molecular pathogenesis of lipotoxic cardiomyopathy and hypertrophy. IntroductionObesity and diabetes present two of the most important health challenges facing the Western world at this time. Patients suffering from type 2 diabetes (T2D) are subject to a number of major health risks, including a greatly increased risk of heart failure (1). This is due in part to the development of diabetic cardiomyopathy (DbCM), which occurs independently of other traditional risk factors (2). DbCM promotes cardiac remodeling and impairs cardiac function (1). Importantly, individuals with T2D and the metabolic syndrome present with dyslipidemia, and recent studies have suggested that DbCM may occur as a result of lipid overload and subsequent lipotoxic events (ref. 2, reviewed in ref. 3). In particular, oversupply of saturated fatty acids (SFAs) has been implicated in this process.Previous studies of lipotoxic DbCM in rodents have relied on several important transgenic models. The B6.Cg-Lep ob /J (ob/ob) and B6.BKS(D)-Lepr db /J (db/db) mouse models, which lack the genes encoding leptin and the leptin receptor, respectively, are both very popular models that develop obesity and a DbCM-like cardiac phenotype (reviewed in ref. 4). Other less common models, including the Atgl-knockout mouse and the LpL GPI transgenic mouse, also induce lipotoxic cardiomyopathy by perturbing cardiac lipid uptake, handling, or metabolism (reviewed in ref. 4). While these transgenic models robustly induce lipid overload in cardiomyocytes, the very disruptions that produce lipotoxic DbCM also drastically alter patterns of lipid uptake and handling in a nonphysiologic way. In contrast, wild-type mice fed standard lard-based high-fat diets (LBD) failed to develop a DbCM-like phenotyp...

Acid sphingomyelinase plays a key role in palmitic acid-amplified inflammatory signaling triggered by lipopolysaccharide at low concentrations in macrophages.

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Metabolic disease, including obesity and type 2 diabetes, constitutes a major emerging health crisis in Western nations. Although the symptoms and clinical pathology and physiology of these conditions are well understood, the molecular mechanisms underlying the disease process have largely remained obscure. Sphingolipids, a lipid class with both signaling and structural properties, have recently emerged as key players in most major tissues affected by diabetes and are required components in the molecular etiology of this disease. Indeed, sphingolipids have been shown to mediate loss of insulin sensitivity, to promote the characteristic diabetic pro-inflammatory state, and to induce cell death and dysfunction in important organs such as the pancreas and heart. Furthermore, plasma sphingolipid levels are emerging as potential biomarkers for the decompensation of insulin resistance to frank type 2 diabetes. Despite these discoveries, the roles of specific sphingolipid species and sphingolipid metabolic pathways remain obscure, and newly developed experimental approaches must be employed to elucidate the detailed molecular mechanisms necessary for rational drug development and other clinical applications.

Background: Myristate is a novel potential substrate for sphingoid base synthesis. Results: Myocardial sphingoid base synthesis utilizes myristate; these sphingolipids are functionally non-redundant with canonical sphingoid bases. Conclusion: d16:0 and d16:1 sphingolipids constitute an appreciable proportion of cardiac dihydrosphingosine and dihydroceramide, with distinct biological roles. Significance: This pool of sphingolipids may play a heretofore unsuspected role in myocardial pathology or protection.