Abstract 276: The Role of Diacylglycerol Acetyltransferase 1 and 2 in Cardiac Metabolism and Function

Abstract

Cardiac triglyceride (TG) plays an important role in myocardial metabolism. TG synthesis is catalyzed by diacylglycerol:acetyltransferase (DGAT). Enhancing cardiac TG synthesis and turnover, by means of overexpression DGAT1, has protected hearts against stresses while blocking the TG turnover causes cardiomyopathy. In the meantime DGAT inhibitors are being developed for lipid lowering therapy, raising concerns whether DGAT inhibition affects cardiac function. Here we determined the role of the two cardiac DGAT isoforms in TG synthesis and turnover in the heart and their contribution to cardiac fatty acid metabolism. Using an inducible cardiac specific DGAT1 deletion mouse (iKO) together with DGAT2-specific inhibitor, we were able to achieve graded inhibition of TG synthesis and turnover as determined by 13 C-NMR spectroscopy of isolated perfused mouse heart. The iKO heart has normal TG level (CON 5.7±1.2 vs. 6.9±0.7 μg/mg wwt) and perfusing hearts with glucose (5.5mM), fatty acids (0.4mM) and lactate (1.2mM) for 1hr did not change the TG content in control (CON, pre-perfusion 3.9 ± 0.6 vs. post-perfusion 4.5 ± 0.7 μg/mg wwt), iKO (3.8±0.6 vs. 4.2±0.5 μg/mg wwt) or iKO+DGAT2 inhibitor (3.8±0.6 vs. 5.0±0.8 μg/mg wwt). Relative to CON, the rate of 13 C labeled fatty acids incorporation into the TG pool decreased by 32% in iKO (AUC 5.170 of 7.547, p<0.05) which was accompanied by an increase the oxidation of exogenous fatty acids (relative FAO: 48.5±5.3 for CON vs. 67.0±4.1% for iKO, p<0.05). Cardiac function, assessed by echocardiography (FS: CON 47.5±1.3 vs. iKO 45.8±3.0%, p>0.05) or by rate pressure product of the isolated perfused heart (CON 39149±1047 vs. iKO 40836±3424 bpm*mmHg, p>0.05) is normal in iKO hearts and remained unchanged after treatment with the DGAT2 inhibitor (37083±8507 bpm*mmHg). Coinhibition of DGAT1 and 2 abrogated 13 C labeled fatty acids incorporation into the TG pool by 58% (AUC 5.042 of 11.82, p<0.05) and suppressed expression of PPARα target genes relative to non-treated control hearts (p<0.05). Taken together, our data show that both DGAT1 and 2 contribute TG synthesis in the heart. Inhibition of both isoforms abrogated TG synthesis and reduced PPARα activity in the heart but did not affect cardiac function in isolated perfused heart.