Fatty Acid Signaling: The New Function of Intracellular Lipases

Abstract

Until recently, intracellular triacylglycerols (TAG) stored in the form of cytoplasmic lipid droplets have been considered to be only passive “energy conserves”. Nevertheless, degradation of TAG gives rise to a pleiotropic spectrum of bioactive intermediates, which may function as potent co-factors of transcription factors or enzymes and contribute to the regulation of numerous cellular processes. From this point of view, the process of lipolysis not only provides energy-rich equivalents but also acquires a new regulatory function. In this review, we will concentrate on the role that fatty acids liberated from intracellular TAG stores play as signaling molecules. The first part provides an overview of the transcription factors, which are regulated by fatty acids derived from intracellular stores. The second part is devoted to the role of fatty acid signaling in different organs/tissues. The specific contribution of free fatty acids released by particular lipases, hormone-sensitive lipase, adipose triacylglycerol lipase and lysosomal lipase will also be discussed.

Lipid droplet functions beyond energy storage

“…The LD core can accumulate the precursors of molecules important for intercellular communication, such as steroid hormones and FA signals [70, 71]. In specialized endocrine cells of the gonads and adrenals, cholesteryl esters stored in LDs provide an important source of cholesterol for the mitochondrial biosynthesis of several different steroid hormones [72].…”

Perfluorooctanoic acid exposure alters polyunsaturated fatty acid composition, induces oxidative stress and activates the AKT/AMPK pathway in mouse epididymis

“…Fatty acids are precursor molecules for the synthesis of lipids, which influence membrane fluidity, lipid raft structures, and signal transduction (Papackova and Cahova, 2015). Omega-3 and omega-6 polyunsaturated fatty acids (PUFA) are two fatty acid families necessary in vertebrates and obtained through hydrolysis of TG from food (Funari et al, 2003;Thomas et al, 2004).…”

Ozone Exposure Increases Circulating Stress Hormones and Lipid Metabolites in Humans

“…Endogenous and ingested free fatty acids are reesterified in adipose tissue as triacylglycerides for storage (35). During a stress response, circulating epinephrine and cortisol through b-adrenergic and glucocorticoid receptors, respectively, can increase hormone-sensitive lipase-mediated lipolysis of adipose triglycerides into free fatty acids and glycerol (35). Ozoneinduced elevation of free fatty acids in the serum could lead to uptake of these lipid metabolites by the peripheral tissues, including liver and muscle, for oxidation.…”

“…This is likely induced through stress hormone-mediated adipose lipolysis. Endogenous and ingested free fatty acids are reesterified in adipose tissue as triacylglycerides for storage (35). During a stress response, circulating epinephrine and cortisol through b-adrenergic and glucocorticoid receptors, respectively, can increase hormone-sensitive lipase-mediated lipolysis of adipose triglycerides into free fatty acids and glycerol (35).…”