Figure 5. Turnover of long-chain fatty acids (LCFAs) within the myocardial triacylglyceride (TAG) pool and their importance in myocardial signaling.

LCFAs, found within the circulation either complexed to albumin or esterified into triacylglyceride rich lipoproteins (TG-lipoprotein), enter the cell via a protein-mediated mechanism across the sarcolemma that is sensitive to CD36 expression. The insulin sensitive fatty acid transport protein 1 (FATP1) and the cardiac-specific FATP6 have also been implicated in LCFA uptake by the heart; however, at present only a direct effect of CD36 expression on TAG dynamics has been demonstrated.¹⁴⁰ Lipoprotein lipase (LPL) is required to liberate LCFA from their esterified form in TG-lipoprotein. After entry into the myocyte LCFA can either enter the mitochondria for oxidation or cycle through the TAG pool (TAG turnover). TAG turnover is defined by the diacylglycerol acyltransferase 1 (DGAT1) dependent on rate (esterification) and the adipose triglyceride lipase (ATGL) dependent on off rate (lipolysis). After LCFA cycling through the TAG pool, LCFA can then be transported into the mitochondria for oxidation or used to initiate gene transcription via peroxisome proliferator–activated receptor α (PPARα). LCFA must first be cycled through the TAG pool to efficiently activate gene transcription.