title: Decrease in intramuscular lipid droplets and translocation of HSL in response to muscle contraction and epinephrine.
abstract: A better understanding of skeletal muscle lipid metabolism is needed to identify the molecular mechanisms relating intramuscular triglyceride (IMTG) to muscle metabolism and insulin sensitivity. An increasing number of proteins have been reported to be associated with intracellular triglyceride (TG), among them the PAT family members: perilipin, ADRP (for adipocyte differentiation-related protein), and TIP47 (for tail-interacting protein of 47 kDa). Hormone-sensitive lipase (HSL) is thought to be the major enzyme responsible for IMTG hydrolysis in skeletal muscle. In adipocytes, regulation of HSL by intracellular redistribution has been demonstrated. The existence of such regulatory mechanisms in skeletal muscle has long been hypothesized but has never been demonstrated. The aim of this study was to characterize the PAT family proteins associated with IMTG and to investigate the effect of epinephrine stimulation or muscle contraction on skeletal muscle TG content and HSL intracellular distribution. Rat soleus muscles were either incubated with epinephrine or electrically stimulated for 15 min. Single muscle fibers were used for morphological analysis by confocal and transmission electron microscopy. We show a decrease in IMTG in response to both lipolytic stimuli. Furthermore, we identify two PAT family proteins, ADRP and TIP47, associated with IMTG. Finally, we demonstrate HSL translocation to IMTG and ADRP after stimulation with epinephrine or contraction.
authors.affiliation: Copenhagen Muscle Research Center, Department of Medical Physiology, Panum Institute, University of Copenhagen, Copenhagen N, Denmark. cprats@mfi.ku.dk
authors.forename: Clara
authors.initials: C
authors.lastname: Prats
authors.forename: Morten
authors.initials: M
authors.lastname: Donsmark
authors.forename: Klaus
authors.initials: K
authors.lastname: Qvortrup
authors.forename: Constantine
authors.initials: C
authors.lastname: Londos
authors.forename: Carole
authors.initials: C
authors.lastname: Sztalryd
authors.forename: Cecilia
authors.initials: C
authors.lastname: Holm
authors.forename: Henrik
authors.initials: H
authors.lastname: Galbo
authors.forename: Thorkil
authors.initials: T
authors.lastname: Ploug
mesh_terms: D000818:Animals; D001692:Biological Transport; D004837:Epinephrine / Q000494:pharmacology*; D008055:Lipids / Q000737:chemistry*; D008297:Male; D018613:Microscopy, Confocal; D046529:Microscopy, Electron, Transmission; D009119:Muscle Contraction; D018482:Muscle, Skeletal / Q000378:metabolism; D021381:Protein Transport; D051381:Rats; D017208:Rats, Wistar; D002787:Sterol Esterase / Q000378:metabolism*; D013997:Time Factors; D014662:Vasoconstrictor Agents / Q000494:pharmacology
chemical_list: D008055:Lipids; D014662:Vasoconstrictor Agents; D002787:Sterol Esterase; D004837:Epinephrine