Perilipin 5, a lipid droplet-associated protein, provides physical and metabolic linkage to mitochondria

Abstract

Cellular energy homeostasis of oxidative tissue relies on a critical balance between fatty acid (FA) uptake from the environment and consumption by mitochondria oxidation. These processes are controlled by complex regulatory mechanisms that ensure energy needs are met while preventing buildup of toxic lipid intermediates and/or oxidized lipids. Transient formation of lipid droplets (LD) may protect mitochondria from lipotoxicity in physiological conditions such as fasting. However, with chronic excess FA levels as observed in obesity, LDs not only cease to be protective but may also contribute to pathology ( 1 ). Distinct features of cardiomyopathy appear in obese and diabetic type 2 patients, including accumulation of lipid droplets and long chain fatty acyl compounds (ceramides, acyl carnitines, and CoAs) in cardiomyocytes, which are Abstract Maintaining cellular lipid homeostasis is crucial to oxidative tissues, and it becomes compromised in obesity. Lipid droplets (LD) play a central role in lipid homeostasis by mediating fatty acid (FA) storage in the form of triglyceride, thereby lowering intracellular levels of lipids that mediate cellular lipotoxicity. LDs and mitochondria have interconnected functions, and anecdotal evidence suggests they physically interact. However, the mechanisms of interaction have not been identifi ed. Perilipins are LD-scaffolding proteins and potential candidates to play a role in their interaction with mitochondria. We examined the contribution of LD perilipin composition to the physical and metabolic interactions between LD and mitochondria using multiple techniques: confocal imaging, electron microscopy (EM), and lipid storage and utilization measurements. Using neonatal cardiomyocytes, reconstituted cell culture models, and rodent heart tissues, we found that perilipin 5 (Plin5) recruits mitochondria to the LD surface through a C-terminal region. Compared with control cells, Plin5-expressing cells show decreased LD hydrolysis, decreased palmitate ␤ -oxidation, and increased palmitate incorporation into triglycerides in basal conditions, whereas in stimulated conditions, LD hydrolysis inhibition is lifted and FA released for ␤ -oxidation. These results suggest that Plin5 regulates oxidative LD hydrolysis and controls local FA fl ux to protect mitochondria against excessive exposure to FA Abbreviations: AA, amino acid; ADFP, adipose differentiationrelated protein; ASM, acid-soluble metabolite; CHO-K1, Chinese hamster ovary; EM, electron microscopy; ER, endoplasmic reticulum; LD, lipid droplet; OCR, oxygen consumption rate; Plin1, perilipin 1, perilipin A; Plin2, perilipin 2, ADFP; Plin5, perilipin 5, Lipid Storage Droplet Protein 5; PPAR ␣ , peroxisome proliferator-activated receptor ␣ ; RNAi, RNA interference; TIP47, tail interacting protein. This work was supported by American Diabetes Association Career Development Award 1-05-CD-17 (C.S.); by National Institutes of Health Grant 1RO1-DK-075017 (C.S.); by American Heart Association Grant-in-Aid 11GRNT7600027 (C.S.); by the Ger...

Mfn2 is critical for brown adipose tissue thermogenic function

“…While initial studies identified SNAP23, a SNARE protein implicated in LD fusion, as a key element for LD–mitochondria interactions (Jagerstrom et al , 2009), a number of recent studies have also demonstrated that perilipins, one of the canonical LD membrane proteins, could act as modulators of LD–mitochondria interactions (Wang et al , 2011; Ramos et al , 2014; Yu et al , 2015). Accordingly, and as supported by our results, perilipins were often found in mitochondrial extracts from muscle, heart, and BAT (Wang et al , 2011; Bosma et al , 2012; Yu et al , 2015). Further, experiments using perilipin 5 (PLIN5) demonstrate that perilipin overexpression is enough to alter the docking of mitochondria to the lipid droplet (Wang et al , 2011).…”

“…Further, experiments using perilipin 5 (PLIN5) demonstrate that perilipin overexpression is enough to alter the docking of mitochondria to the lipid droplet (Wang et al , 2011). In particular, the C‐terminal domain of perilipin proteins seems to be key for LD–mitochondria interactions (Wang et al , 2011). Perilipin 1 (PLIN1) is a predominant perilipin in adipose tissues, and its expression is almost exclusive to WAT and BAT (for review, see Bickel et al , 2009).…”

The role of triacylglycerol in cardiac energy provision

“…LDs [141], controlling both LD-TAG-derived FA release and facilitating its delivery to mitochondria for -oxidation [141,143,144]. Together, these observations indicate that mTAG pool turnover may dictate rates of FA oxidation as the majority of FA cycles through mTAG.…”

“…ATGL overexpression maintained cardiac energetics (ATP; PCr:ATP) and function in high fat fed mice, but exogenous NEFA oxidation was halved, suggesting preferential utilisation of endogenous lipids from the mTAG pool [139]. Perilipin-5 (PLIN5) binds ATGL on the LD surface [140], shielding TAG from lipolysis; ectopic PLIN5 expression increased mTAG levels and decreased FA oxidation, again suggesting rates of FA oxidation may be determined by mTAG-FA turnover [141,142]. PLIN5 is also present on mitochondria, where it facilitates the tightly-coupled association of mitochondria with…”

Lipid-induced cardiovascular diseases

“…Feeding unsaturated FA, protects against saturated FA-induced cell death by sequestering lipids in intracellular droplets [85,86] Perlipins regulate FA-storage to regulate and maintain normal oxidative balance [87,88] MicroRNA FA-induced changes in miR regulation results in insulin resistance [89] Mitochondrial function FA-induced mitochondrial fragmentation and increased reactive oxygen species (ROS) [90] * FA: fatty acid; TAG: triacylglycerol; WD: western diet…”