Peroxisome proliferator-activated receptors (PPARs) are nuclear hormone receptors that regulate genes involved in energy metabolism and inflammation. For biological activity, PPARs require cognate lipid ligands, heterodimerization with retinoic × receptors, and coactivation by PPAR-γ coactivator-1α or PPAR-γ coactivator-1β (PGC-1α or PGC-1β, encoded by Ppargc1a and Ppargc1b, respectively). Here we show that lipolysis of cellular triglycerides by adipose triglyceride lipase (patatin-like phospholipase domain containing protein 2, encoded by Pnpla2; hereafter referred to as Atgl) generates essential mediator(s) involved in the generation of lipid ligands for PPAR activation. Atgl deficiency in mice decreases mRNA levels of PPAR-α and PPAR-δ target genes. In the heart, this leads to decreased PGC-1α and PGC-1β expression and severely disrupted mitochondrial substrate oxidation and respiration; this is followed by excessive lipid accumulation, cardiac insufficiency and lethal cardiomyopathy. Reconstituting normal PPAR target gene expression by pharmacological treatment of Atgl-deficient mice with PPAR-α agonists completely reverses the mitochondrial defects, restores normal heart function and prevents premature death. These findings reveal a potential treatment for the excessive cardiac lipid accumulation and often-lethal cardiomyopathy in people with neutral lipid storage disease, a disease marked by reduced or absent ATGL activity.

Sepsis is a systemic inflammatory response that follows bacterial infection. Cardiac dysfunction is an important consequence of sepsis that affects mortality and has been attributed to either elevated inflammation or suppression of both fatty acid and glucose oxidation and eventual ATP depletion. Moreover, cardiac adrenergic signaling is compromised in septic patients and this aggravates further heart function. While anti-inflammatory therapies are important for the treatment of the disease, administration of anti-inflammatory drugs did not improve survival in septic patients. This review article summarizes findings on inflammatory and other mechanisms that are triggered in sepsis and affect cardiac function and mortality. Particularly, it focuses on the effects of the disease in metabolic pathways, as well as in adrenergic signaling and the potential interplay of the latter with inflammation. It is suggested that therapeutic approaches should include combination of anti-inflammatory treatments, stimulation of energy production, and restoration of adrenergic signaling in the heart.

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.

Rationale Fatty acid oxidation is transcriptionally regulated by peroxisome proliferator-activated receptor (PPAR)α and under normal conditions accounts for 70% of cardiac ATP content. Reduced Ppara expression during sepsis and heart failure leads to reduced fatty acid oxidation and myocardial energy deficiency. Many of the transcriptional regulators of Ppara are unknown. Objective To determine the role of Krüppel-like factor 5 (KLF5) in transcriptional regulation of Ppara. Methods and Results We discovered that KLF5 activates Ppara gene expression via direct promoter binding. This is blocked in hearts of septic mice by c-Jun, which binds an overlapping site on the Ppara promoter and reduces transcription. We generated cardiac myocyte-specific Klf5 knockout mice that showed reduced expression of cardiac Ppara and its downstream fatty acid metabolism-related targets. These changes were associated with reduced cardiac fatty acid oxidation, ATP levels, increased triglyceride accumulation and cardiac dysfunction. Diabetic mice showed parallel changes in cardiac Klf5 and Ppara expression levels. Conclusions Cardiac myocyte KLF5 is a transcriptional regulator of Ppara and cardiac energetics.

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.