The ability to deposit triacylglycerol (TG) within specifi c cellular organelles is an evolutionary conserved process present in virtually every mammalian cell and in most microorganisms ( 1-3 ). TG storage within lipid droplets (LDs) not only represents an energy reservoir, but is also an important source for the generation of membrane and signaling lipids ( 4 ). However, excessive accumulation of lipids is a hallmark of many metabolic disorders including obesity, hepatic steatosis, and cardiac steatosis ( 5-7 ). Apart from that, fatty acid (FA) esterifi cation and deposition within neutral lipids protect cells from the harmful excess of nonesterifi ed FAs also referred to as lipotoxicity ( 8,9 ). The LD surface is characterized by the presence of various hydrophobic proteins including members of the so-called PAT family ( 1, 10 ) (designation derived from perilipin, adipophilin, and tail-interacting protein of 47 kDa ) and neutral lipid hydrolases, which are involved in TG breakdown and the release of FAs and glycerol.

Background: Perilipin 5 (Plin5) protects cardiac lipid droplets from uncontrolled lipolysis. Results: Plin5-mediated inhibition of lipid droplet triglyceride breakdown is reversed by the action of protein kinase A (PKA) depending on serine 155 of Plin5. Conclusion:The lipolytic barrier function of Plin5 is under regulation of PKA. Significance: Regulation of Plin5 is implicated in the development of lipolysis-related cardiac disease.

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Aims Lipotoxic cardiomyopathy in diabetic and obese patients typically encompasses increased cardiac fatty acid (FA) uptake eventually surpassing the mitochondrial oxidative capacity. Lowering FA utilization via inhibition of lipolysis represents a strategy to counteract the development of lipotoxic heart dysfunction. However, defective cardiac triacylglycerol (TAG) catabolism and FA oxidation in humans (and mice) carrying mutated ATGL alleles provokes lipotoxic heart dysfunction questioning a therapeutic approach to decrease cardiac lipolysis. Interestingly, decreased lipolysis via cardiac overexpression of Perilipin 5 (Plin5), a binding partner of ATGL, is compatible with normal heart function and lifespan despite massive cardiac lipid accumulation. Herein, we decipher mechanisms that protect Plin5 transgenic mice from the development of heart dysfunction. Methods and results We generated mice with cardiac-specific overexpression of Plin5 encoding a serine-155 to alanine exchange (Plin5-S155A) of the protein kinase A phosphorylation site, which has been suggested as a prerequisite to stimulate lipolysis and may play a crucial role in the preservation of heart function. Plin5-S155A mice showed a substantial increase in cardiac TAG and ceramide levels, which was comparable to mice overexpressing non-mutated Plin5. Lipid accumulation was compatible with normal heart function even under mild stress. Plin5-S155A mice showed reduced cardiac FA oxidation but normal ATP production and changes in the Plin5-S155A phosphoproteome compared to Plin5 transgenic mice. Interestingly, mitochondrial recruitment of dynamin-related protein 1 (Drp1) was markedly reduced in cardiac muscle of Plin5-S155A and Plin5 transgenic mice accompanied by decreased phosphorylation of mitochondrial fission factor, a mitochondrial receptor of Drp1. Conclusions This study suggests that low cardiac lipolysis is associated with reduced mitochondrial fission and may represent a strategy to combat the development of lipotoxic heart dysfunction.

Murine hepatic carboxylesterase 2c (Ces2c) and the presumed human ortholog carboxylesterase 2 (CES2) have been implicated in the development of nonalcoholic fatty liver disease (NAFLD) in mice and obese humans. These studies demonstrated that Ces2c hydrolyzes triglycerides (TGs) in hepatocytes. Interestingly, Ces2c/CES2 is most abundantly expressed in the intestine, indicating a role of Ces2c/CES2 in intestinal TG metabolism. Here we show that Ces2c is an important enzyme in intestinal lipid metabolism in mice. Intestine‐specific Ces2c overexpression (Ces2cint) provoked increased fatty acid oxidation (FAO) in the small intestine accompanied by enhanced chylomicron clearance from the circulation. As a consequence, high‐fat diet–fed Ces2cint mice were resistant to excessive diet‐induced weight gain and adipose tissue expansion. Notably, intestinal Ces2c overexpression increased hepatic insulin sensitivity and protected mice from NAFLD development. Although lipid absorption was not affected in Ces2cint mice, fecal energy content was significantly increased. Mechanistically, we demonstrate that Ces2c is a potent neutral lipase, which efficiently hydrolyzes TGs and diglycerides (DGs) in the small intestine, thereby generating fatty acids (FAs) for FAO and monoglycerides (MGs) and DGs for potential re‐esterification. Consequently, the increased availability of MGs and DGs for re‐esterification and primordial apolipoprotein B48 particle lipidation may increase chylomicron size, ultimately mediating more efficient chylomicron clearance from the circulation. Conclusion: This study suggests a critical role for Ces2c in intestinal lipid metabolism and highlights the importance of intestinal lipolysis to protect mice from the development of hepatic insulin resistance, NAFLD, and excessive diet‐induced weight gain during metabolic stress.