Unique Regulation of Adipose Triglyceride Lipase (ATGL) by Perilipin 5, a Lipid Droplet-associated Protein

Abstract

Lipolysis is a critical metabolic pathway contributing to energy homeostasis through degradation of triacylglycerides stored in lipid droplets (LDs), releasing fatty acids. Neutral lipid lipases act at the oil/water interface. In mammalian cells, LD surfaces are coated with one or more members of the perilipin protein family, which serve important functions in regulating lipolysis. We investigated mechanisms by which three perilipin proteins control lipolysis by adipocyte triglyceride lipase (ATGL), a key lipase in adipocytes and non-adipose cells. Using a cell culture model, we examined interactions of ATGL and its co-lipase CGI-58 with perilipin 1 (perilipin A), perilipin 2 (adipose differentiation-related protein), and perilipin 5 (LSDP5) using multiple techniques as follows: anisotropy Forster resonance energy transfer, coimmunoprecipitation, [32 P]orthophosphate radiolabeling, and measurement of lipolysis. The results show that ATGL interacts with CGI-58 and perilipin 5; the latter is selectively expressed in oxidative tissues. Both proteins independently recruited ATGL to the LD surface, but with opposite effects; interaction of ATGL with CGI-58 increased lipolysis, whereas interaction of ATGL with perilipin 5 decreased lipolysis. In contrast, neither perilipin 1 nor 2 interacted directly with ATGL. Activation of protein kinase A (PKA) increased [ 32 P]orthophosphate incorporation into perilipin 5 by 2-fold, whereas neither ATGL nor CGI-58 was labeled under the incubation conditions. Cells expressing both ectopic perilipin 5 and ATGL showed a 3-fold increase in lipolysis following activation of PKA. Our studies establish perilipin 5 as a novel ATGL partner and provide evidence that the protein composition of perilipins at the LD surface regulates lipolytic activity of ATGL. Hydrolysis of triacylglycerol (TAG)3 stored in the lipid droplet (LD) compartment provides a convenient source of cellular fuel for energy production during conditions such as fasting. However, lipolysis can contribute to the build up of toxic lipid intermediates and/or oxidized lipids in pathological conditions when cellular lipid homeostasis is altered, e.g. with obesity (1). Therefore, TAG hydrolysis must be carefully controlled to meet tissue-specific requirements for energy or lipid substrates in both adipose and non-adipose tissues. A better understanding of the mechanisms by which cells control lipid mobilization is needed to design novel approaches for intervention and prevention of the pathophysiological consequences of obesity.During the past 10 years, key players in the lipolytic pathway of adipocytes were identified through the study of transgenic mouse models (2-8). Phenotypic analysis of hormone-sensitive lipase null mice suggested the existence of another lipase (7), leading to the identification of adipose triglyceride lipase (ATGL) (6, 9, 10). Characterization of ATGL null mice helped to establish the respective roles of these two lipases in the lipolytic cascade (7). Complete lipolysis requires three enzyme reactions t...

Myonectin (CTRP15), a Novel Myokine That Links Skeletal Muscle to Systemic Lipid Homeostasis

“…Adipose Tissue and 3T3-L1 Adipocyte Lipolysis-Experiments were performed as described previously (30). Food was removed from mice 2 h prior to the isolation of epididymal fat pads.…”

Perilipin 5 restores the formation of lipid droplets in activated hepatic stellate cells and inhibits their activation

“…53 At the molecular level, independent work from groups strongly supports the idea that Plin5 plays as a scaffold for three major key lipolytic players: abhd5, ATGL, and HSL in hydrolysis of TG in LDs. [40][41][42][43] It has been shown that the C-terminus of Plin5 serves as an ATGL and abhd5 binding domain. 54 ATGL and abhd5 competitively bind Plin5.…”

“…Phosphorylation of Plin5 by protein kinase A fuels lipolysis by stimulating its interaction with ATGL. 43 On the other hand, AMPK acts as a nutrient sensor 55 and an anti-lipolytic factor by phosphorylating and inactivating HSL 56 and blocking its translocation to LDs. 57 Protein kinase A and AMPK played opposite roles in regulation of lipid content in HSC and in the inhibition of HSC activation.…”

Perilipins 2 and 3 lack a carboxy-terminal domain present in perilipin 1 involved in sequestering ABHD5 and suppressing basal lipolysis

“…Our studies focused on perilipins 2 and 3, because perilipin 4 is a much longer protein (1,357aa compared with perilipin 1, which has 522 aa in humans) with a very distinct domain architecture, and perilipin 5 has already been shown to bind both ABHD5 and ATGL in a mutually exclusive manner (25)(26)(27).…”