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...
