Cloning of a Protein That Mediates Transcriptional Effects of Fatty Acids in Preadipocytes

Abstract

Exposure of preadipocytes to long chain fatty acids induces expression of several gene markers of adipocyte differentiation. This report describes the cloning, from a preadipocyte library, of a cDNA encoding a fatty acid-activated receptor, FAAR. The cDNA had the characteristics and ligand-binding domains of nuclear hormone receptors and encoded a 440 amino acid protein related to peroxisome proliferator-activated receptors, PPAR. The deduced protein sequence was 88% homologous to that of hNUC I, isolated from human osteosarcoma cells. FAAR mRNA was abundant in adipose tissue, intestine, brain, heart, and skeletal muscles and less abundant in kidney, liver, testis, and spleen. The mRNA was undetectable in growing Ob1771 and 3T3-F442A preadipocytes, was strongly induced early during differentiation, and was increased by fatty acid. Transcription assays using hybrid receptor showed strong stimulation by fatty acid and weaker induction by fibrates. Transfection of 3T3-C2 fibroblasts, with a FAAR expression vector, conferred fatty acid inducibility of the adipocyte lipid-binding protein and the fatty acid transporter. Transcriptional induction of these genes exhibited inducer specificity identical to that described in preadipocytes. In summary, the data indicate that FAAR is likely a mediator of fatty acid transcriptional effects in preadipocytes.

Regulation of lipid accumulation in 3T3-L1 cells: insulin-independent and combined effects of fatty acids and insulin

“…This appears to be the first study to report lipid accumulation in adipocyte lineage cells in response to physiological concentrations of FA, in the absence of the influence of a complex hormone 'cocktail'. Linoleic and oleic acids are considered to be ligands for PPAR-g (Amri et al, 1995;Forman et al, 1997;Margetic et al, 2002;Ferré, 2004;Kokta et al, 2004), however there appear to be no other in vitro adipocyte lineage cell studies, which have investigated PPAR-g expression or lipid accumulation in the absence of insulin. The strategy of the current study was to provide FA in the media at approximately physiological concentrations, as building blocks for lipid synthesis.…”

“…During differentiation of preadipocytes to adipocytes, PPAR-g, PPAR-a and CCAAT/enhancer-binding protein factors (C/EBP) a, b, d and z are important transcription factors involved in the regulation of this mechanism (Lee et al, 1999;Kersten et al, 2000;Lacasa et al, 2001); PPAR-g being activated prior to the activation of C/EBP-a. PPAR-g is also required for survival of mature adipocytes (Imai et al, 2004), and is activated by a variety of factors, including glucocorticoids (Wu et al, 1996), unsaturated FA such as oleic acid, linoleic acid, eicosapentaenoic acid and arachidonic acid (Amri et al, 1995) and insulin-sensitising reagents such as thiazolidinidiones (Spiegelman, 1998;Torii et al, 1998;Yamauchi et al, 2001;Li and Lazar, 2002). Hence, insulin is thought to be a factor in the increased expression of PPAR-g. PPAR-g activation also results in the initiation of expression of GLUT-4.…”

Integrative physiology of human adipose tissue

“…Important stimuli for differentiation include insulin and fatty acids. Fatty acids act through members of the peroxisome proliferator-activated receptor (PPAR) family, PPARd (also known as fatty acid-activated receptor, FAAR 38 ) and particularly PPARg. The natural ligand for PPARg is probably a fatty acid derivative.…”

Regulation of Peroxisome Proliferator-activated Receptor γ Activity by Mitogen-activated Protein Kinase

“…PPAR␥ is expressed predominantly in mouse white and brown fat, with lower levels in liver, whereas PPAR␣ is present in heart, kidney, and liver (5, 6). PPAR␦ expression is ubiquitous (7,8).Ectopic expression of either PPAR␣ or PPAR␥ in NIH-3T3 cells is sufficient to induce adipocyte differentiation in the presence of PPAR␥ activators (9, 10). The rapid induction of PPAR␥ during adipocyte differentiation and its enriched expression in adipose tissues suggest that PPAR␥ is responsible for the initiation and maintenance of the adipocyte phenotype in vivo (9).…”

“…PPAR␥ is expressed predominantly in mouse white and brown fat, with lower levels in liver, whereas PPAR␣ is present in heart, kidney, and liver (5, 6). PPAR␦ expression is ubiquitous (7,8).…”