title: Functional compensation for adipose differentiation-related protein (ADFP) by Tip47 in an ADFP null embryonic cell line.
abstract: Ectopic accumulation of lipid droplets in non-adipose tissues correlates with the degree of insulin resistance in these tissues. Emerging evidence indicates that lipid droplets are specialized organelles that participate in lipid metabolism and intracellular trafficking. These properties are thought to derive from the lipid droplet-associated PAT protein family (perilipin, ADFP, and Tip47). The functions of the ubiquitously distributed adipose differentiation-related protein (ADFP) and Tip47 remain unknown. To evaluate the roles of ADFP and Tip47 in lipid biogenesis and metabolism, ADFP null and wild type (wt) clonal cell lines were established from ADFP null and wt mice, respectively. In ADFP null cells, Tip47 was identified as the sole lipid droplet-associated protein from the PAT family by mass spectroscopy, which was further confirmed by immunoblotting and immunocytochemistry. Following incubation with oleic acid, ADFP null cells were able to form lipid droplets to the same extent as wt cells. No statistical differences between the two cell types were observed in NEFA uptake or lipolysis. Small interference RNAs (siRNAs) against Tip47 were found to down-regulate protein levels for Tip47 by 85%. ADFP null cells treated with Tip47 siRNA retained the ability to form lipid droplets but to a lesser extent and shunted the utilization of exogenously added NEFA from triglycerides to phospholipids. These data support the hypothesis that Tip47 plays an important role in lipid metabolism. Tip47 and ADFP in peripheral tissues may play a critical role in regulating the formation and turnover, and hence metabolic consequences, of ectopic fat.
authors.affiliation: Geriatric Research, Education and Clinical Center, Baltimore Veterans Affairs Health Care Center, Department of Medicine, School of Medicine, University of Maryland, Baltimore, Maryland 21201, USA. csztalry@grecc.umaryland.edu
authors.forename: Carole
authors.initials: C
authors.lastname: Sztalryd
authors.forename: Ming
authors.initials: M
authors.lastname: Bell
authors.forename: Xinyue
authors.initials: X
authors.lastname: Lu
authors.forename: Pamela
authors.initials: P
authors.lastname: Mertz
authors.forename: Sabrina
authors.initials: S
authors.lastname: Hickenbottom
authors.forename: Benny H-J
authors.initials: BH
authors.lastname: Chang
authors.forename: Lawrence
authors.initials: L
authors.lastname: Chan
authors.forename: Alan R
authors.initials: AR
authors.lastname: Kimmel
authors.forename: Constantine
authors.initials: C
authors.lastname: Londos
mesh_terms: D017667:Adipocytes / Q000166:cytology* / Q000378:metabolism; D000273:Adipose Tissue / Q000166:cytology / Q000378:metabolism*; D000818:Animals; D002454:Cell Differentiation; D002460:Cell Line; D002855:Chromatography, Thin Layer; D004622:Embryo, Mammalian / Q000166:cytology / Q000378:metabolism*; D005347:Fibroblasts / Q000166:cytology / Q000378:metabolism*; D015151:Immunoblotting; D007124:Immunoenzyme Techniques; D050356:Lipid Metabolism; D008066:Lipolysis; D013058:Mass Spectrometry; D008565:Membrane Proteins / Q000235:genetics / Q000502:physiology*; D051379:Mice; D018345:Mice, Knockout; D000070780:Perilipin-2; D010743:Phospholipids / Q000378:metabolism; D011257:Pregnancy Proteins / Q000235:genetics / Q000502:physiology*; D034741:RNA, Small Interfering / Q000494:pharmacology; D014280:Triglycerides / Q000378:metabolism
chemical_list: D008565:Membrane Proteins; D000070780:Perilipin-2; D010743:Phospholipids; C000602983:Plin2 protein, mouse; D011257:Pregnancy Proteins; D034741:RNA, Small Interfering; D014280:Triglycerides