Abstract 3063: Impaired Mitochondrial Dynamics: A Novel Mechanism for Lipotoxic Heart Disease
To assess the contribution of increased fatty acid uptake and utilization to mitochondrial dysfunction and proliferation in diabetic hearts, we investigated mice with cardiomyocyte-restricted overexpression of long-chain acyl-CoA synthetase 1 (MHC-ACS). In vivo PET confirmed a 2-fold increase in myocardial palmitate uptake in MHC-ACS (p<0.05). At 24 weeks, mitochondrial volume density was increased by 50% (p<0.05). Although mitochondrial size was identical at birth, mitochondrial size in MHC-ACS hearts failed to increase, resulting in persistently smaller mitochondria (3wk: −72%, 8wk: −71%, 24wk: −72%; all p<0.05), which had increased superoxide production. To determine if these changes were secondary to impaired mitochondrial dynamics we stably overexpressed ACS1 in L6 myoblasts, and labeled mitochondria with Mito RFP or Mito GFP to visualize the mitochondrial network and determine rates of mitochondrial fusion. Incubation of L6 cells with 150μM palmitate caused mitochondrial fragmentation in 60% of vector-infected cells, which was more pronounced in ACS1 overexpressing cells (90%; p<0.05 vs. vector-infected). PEG fusion assays revealed normal mitochondrial fusion in serum-incubated cells which was prevented in the presence of palmitate. Palmitate-induced fusion defects were reversible when cells were placed in palmitate-free media. In MHC-ACS hearts, phospholipid precursors ceramide (+260%; p<0.05) and diacylglycerol (+40%; p<0.05) were increased. In mitochondria, the predominant 18:2 side chains of cardiolipin were replaced by 22:6 side chains, and the content of phosphatidyl-choline (+46%), -ethanolamine (+64%), and -serine (+51%; all p<0.05) was increased. Thus, increased cardiac FA uptake remodels mitochondrial phospholipids, impairs mitochondrial fusion and leads to fragmentation of the mitochondrial network, which represents a novel mechanism for lipid-induced mitochondrial dysfunction in the heart.