Yang Wang

BACKGROUND: CPT1 (carnitine palmitoyltransferase 1) is a rate-limiting enzyme for long-chain fatty acid oxidation. In adult hearts, CPT1b predominates, while CPT1a is coexpressed at lower levels. Pathological stress on the heart induces CPT1a expression, coinciding with a reduction in fatty acid oxidation, yet the role of CPT1a in pathological remodeling is unknown. METHODS: CPT1 isoform expression was assayed in the myocardium of patients with heart failure with nonischemic cardiomyopathy and a preclinical mouse model of heart failure. Mice were subjected to afterload stress via transverse aortic constriction (TAC) or sham surgery (sham) with cardiac-specific CPT1a knockdown or cardiac-specific, adeno-associated virus serotype 9 (AAV9)–mediated CPT1a overexpression (AAV9.cTnT [cardiac troponin T].Cpt1a) versus empty virus or PBS infusions as controls. MicroRNA 370, known to suppress hepatic CPT1a, was assayed and overexpressed to determine if microRNA 370 regulates cardiac CPT1a expression. RESULTS: CPT1a protein was elevated and microRNA 370 reduced in the myocardium of male and female patients with nonischemic cardiomyopathy, as well as in failing mouse hearts. AAV9–mediated microRNA 370 overexpression in mouse hearts suppressed CPT1a expression and attenuated the response of CPT1a to TAC. Preventing CPT1a upregulation in response to TAC in cardiac-specific CPT1a knockout mice exacerbated adverse remodeling, severe dysfunction, and increased mortality. In contrast, CPT1a overexpression (2.8-fold) attenuated impaired ejection fraction (by 54%) versus control TAC hearts ( P <0.05). Delivery of AAV9.cTnT.Cpt1a 4 weeks after TAC surgery led to significant rescue of ejection fraction and mitigated the exacerbated dysfunction of cardiac-specific CPT1a knockout mice TAC hearts. RNA-seq revealed a novel function of CPT1a in suppressing hypertrophic, profibrotic, and cell death gene programs in both sham and TAC hearts, irrespective of changes in fatty acid oxidation, with reduced histone acetylation. CONCLUSIONS: The effects of CPT1a in the heart extend beyond fatty acid oxidation including noncanonical regulation of gene programs. CPT1a upregulation occurs in nonischemic cardiomyopathy and is a critical cardioprotective adaptation to pathological stress.

BACKGROUND: Movement of circulating lipids into tissues and arteries requires transfer across the endothelial cell (EC) barrier. This process allows the heart to obtain fatty acids, its chief source of energy, and apoB-containing lipoproteins to cross the arterial endothelial barrier, leading to cholesterol accumulation in the subendothelial space. Multiple studies have established elevated postprandial TRLs (triglyceride-rich lipoproteins) as an independent risk factor for cardiovascular disease. We explored how chylomicrons affect ECs and transfer their fatty acids across the EC barrier. METHODS: We had reported that media from chylomicron-treated ECs lead to lipid droplet formation in macrophages. To determine the responsible component of this media, we assessed whether removing the extracellular vesicles (EVs) would obviate this effect. EVs from control and treated cells were then characterized by protein, lipid, and microRNA content. We also studied the EV-induced transcription changes in macrophages and ECs and whether knockdown of SR-BI (scavenger receptor-BI) altered these responses. In addition, using chylomicrons labeled with [ ¹³ C]oleate, we studied the uptake and release of this labeled by ECs. RESULTS: Chylomicron treatment of ECs led to an inflammatory response that included production of EVs that drove macrophage lipid droplet accumulation. The EVs contained little free fatty acids and triglycerides, but abundant phospholipids and diacylglycerols. In concert with this, [ ¹³ ]C labeled chylomicron triglycerides exited ECs primarily in phospholipids. EVs from chylomicron-treated versus untreated ECs were larger, more abundant, and contained specific microRNAs. Treatment of macrophages and naive ECs with media from chylomicron-treated ECs increased expression of inflammatory genes. CONCLUSIONS: EC chylomicron metabolism produces EVs that increase macrophage inflammation and create LDs. Media containing these EVs also increases EC inflammation, illustrating an autocrine inflammatory process. Fatty acids within chylomicron triglycerides are converted to phospholipids within EVs. Thus, EC uptake of chylomicrons constitutes an important pathway for vascular inflammation and tissue lipid acquisition.