title: Identification and characterization of associated with lipid droplet protein 1: A novel membrane-associated protein that resides on hepatic lipid droplets.
abstract: Alcoholic and nonalcoholic liver steatosis and steatohepatitis are characterized by the massive accumulation of lipid droplets (LDs) in the cytosol of hepatocytes. Although LDs are ubiquitous and dynamic organelles found in the cells of a wide range of organisms, little is known about the mechanisms and sites of LD biogenesis. To examine the participation of these organelles in the pathophysiological disorders of steatotic livers, we used a combination of mass spectrometry (matrix-assisted laser desorption ionization-time of flight and LC-MS electrospray) and Western blot analysis to study the composition of LDs purified from rat liver after a partial hepatectomy. Fifty proteins were identified. Adipose differentiation-related protein was the most abundant, but other proteins such as calreticulin, TIP47, Sar1, Rab GTPases, Rho and actin were also found. In addition, we identified protein associated with lipid droplets I ALDI (tentatively named Associated with LD protein 1), a novel protein widely expressed in liver and kidney corresponding to the product of 0610006F02Rik (GI:27229118). Our results show that, upon lipid loading of the cells, ALDI translocates from the endoplasmic reticulum into nascent LDs and indicate that ALDI may be targeted to the initial lipid deposits that eventually form these droplets. Moreover, we used ALDI expression studies to view other processes related to these droplets, such as LD biogenesis, and to analyze LD dynamics. In conclusion, here we report the composition of hepatic LDs and describe a novel bona fide LD-associated protein that may provide new insights into the mechanisms and sites of LD biogenesis.
authors.affiliation: Departament de Biologia Cellular, Facultat de Medicina, Institut d'Investigacions Biomèdiques August Pi Sunyer, Universitat de Barcelona, Casanova 143, Barcelona 08036, Spain.
authors.forename: Silvia
authors.initials: S
authors.lastname: Turró
authors.forename: Mercedes
authors.initials: M
authors.lastname: Ingelmo-Torres
authors.forename: Josep M
authors.initials: JM
authors.lastname: Estanyol
authors.forename: Francesc
authors.initials: F
authors.lastname: Tebar
authors.forename: Manuel A
authors.initials: MA
authors.lastname: Fernández
authors.forename: Cecilia V
authors.initials: CV
authors.lastname: Albor
authors.forename: Katharina
authors.initials: K
authors.lastname: Gaus
authors.forename: Thomas
authors.initials: T
authors.lastname: Grewal
authors.forename: Carlos
authors.initials: C
authors.lastname: Enrich
authors.forename: Albert
authors.initials: A
authors.lastname: Pol
mesh_terms: D000595:Amino Acid Sequence; D000818:Animals; D019556:COS Cells; D002352:Carrier Proteins / Q000235:genetics / Q000378:metabolism*; D002522:Chlorocebus aethiops; D050356:Lipid Metabolism; D008099:Liver / Q000378:metabolism*; D008297:Male; D008565:Membrane Proteins / Q000235:genetics / Q000378:metabolism*; D008969:Molecular Sequence Data; D051381:Rats; D017207:Rats, Sprague-Dawley
chemical_list: D002352:Carrier Proteins; D008565:Membrane Proteins; C515875:Mettl7b protein, rat