Histochem Cell Biol (2012) 137:205–216 DOI 10.1007/s00418-011-0888-x O R I G I N A L P A P E R The lipid droplet coat protein perilipin 5 also localizes to muscle mitochondria Madeleen Bosma · Ronnie Minnaard · Lauren M. Sparks · Gert Schaart · Mario Losen · Marc H. de Baets · Hans Duimel · Sander Kersten · Perry E. Bickel · Patrick Schrauwen · Matthijs K. C. Hesselink Accepted: 13 November 2011 / Published online: 30 November 2011 © The Author(s) 2011. This article is published with open access at Springerlink.com Abstract Perilipin 5 (PLIN5/OXPAT) is a lipid droplet (LD) coat protein mainly present in tissues with a high fat- oxidative capacity, suggesting a role for PLIN5 in facilitat- ing fatty acid oxidation. Here, we investigated the role of PLIN5 in fat oxidation in skeletal muscle. In human skele- tal muscle, we observed that PLIN5 (but not PLIN2) pro- tein content correlated tightly with OXPHOS content and in rat muscle PLIN5 content correlated with mitochondrial M. Bosma · L. M. Sparks · P. Schrauwen Department of Human Biology, NUTRIM School for Nutrition, Toxicology and Metabolism, Maastricht University Medical Centre, 6200MD Maastricht, The Netherlands R. Minnaard · G. Schaart · M. K. C. Hesselink (&) Department of Human Movement Sciences, NUTRIM School for Nutrition, Toxicology and Metabolism, Maastricht University Medical Centre, 6200MD Maastricht, The Netherlands e-mail: matthijs.hesselink@maastrichtuniversity.nl M. Losen · M. H. de Baets Department of Neuroscience, School of Mental Health and Neuroscience, Maastricht University Medical Centre, 6200MD Maastricht, The Netherlands H. Duimel Electron Microscopy Unit, Department of Molecular Cell Biology, Maastricht University Medical Centre, 6200MD Maastricht, The Netherlands S. Kersten Nutrition, Metabolism and Genomics Group, Division of Human Nutrition, Wageningen University, 6700EV Wageningen, The Netherlands P. E. Bickel Division of Endocrinology, Department of Internal Medicine, Center for Metabolic and Degenerative Diseases, Brown Foundation Institute of Molecular Medicine, University of Texas Health Science Center at Houston, Houston, TX, USA respiration rates on a lipid-derived substrate. This prompted us to examine PLIN5 protein expression in skeletal muscle mitochondria by means of immunogold electron micros- copy and Western blots in isolated mitochondria. These data show that PLIN5, in contrast to PLIN2, not only local- izes to LD but also to mitochondria, possibly facilitating fatty acid oxidation. Unilateral overexpression of PLIN5 in rat anterior tibialis muscle augmented myocellular fat stor- age without increasing mitochondrial density as indicated by the lack of change in protein content of Wve components of the OXPHOS system. Mitochondria isolated from PLIN5 overexpressing muscles did not possess increased fatty acid respiration. Interestingly though, 14C-palmitate oxi- dation assays in muscle homogenates from PLIN5 over- expressing muscles revealed a 44.8% (P = 0.05) increase in complete fatty acid oxidation. Thus, in mitochondrial isola- tions devoid of LD, PLIN5 does not augment fat oxidation, while in homogenates containing PLIN5-coated LD, fat oxi- dation is higher upon PLIN5 overexpression. The presence of PLIN5 in mitochondria helps to understand why PLIN5, in contrast to PLIN2, is of speciWc importance in fat oxidative tissues. Our data suggests involvement of PLIN5 in directing fatty acids from the LD to mitochondrial fatty acid oxidation. Keywords PLIN5 · OXPAT · Perilipin · Lipid droplet · Fatty acid oxidation · Mitochondria Introduction Perilipin 5 (aliases include OXPAT, lipid storage droplet protein 5, myocardial lipid droplet protein and PAT-1) is a lipid droplet (LD) coat protein that belongs to the perilipin family of proteins. Although the tissue distribution of this protein family diVers considerably between members, all 123