PPARα activators and fasting induce the expression of adipose differentiation-related protein in liver

Abstract

The adipose differentiation-related protein (ADFP)/adipophilin belongs to a family of PAT (for perilipin, ADFP, and TIP47) proteins that associate on the surface of lipid droplets (LDs). Except for LD association, a clear role for ADFP has not been found. We demonstrate that ADFP is transcriptionally regulated by peroxisome proliferator-activated receptor a (PPARa) in mouse liver and rat and human hepatoma cells through a highly conserved direct repeat-1(DR-1) element. Although the ADFP mRNA is highly increased by a synthetic PPARa agonist, the ADFP protein is only substantially increased in cells containing LDs, such as hepatocytes incubated with fatty acids, and in livers of fasted mice. ADFP is induced by fasting even in the absence of a functional PPARa, in marked contrast to the PPARa target gene acyl-coenzyme A oxidase-1. Activation of LXRs, which stimulates LD formation through the activation of lipogenesis, does not affect ADFP mRNA levels. TIP47, another PAT member known to be expressed in liver, was unaffected by all treatments. This constitutively expressed PAT member seems to be less transcriptionally regulated than ADFP.These observations suggest that ADFP is primarily a fasting-induced protein in liver that coats the newly synthesized triacylglycerol-containing LDs formed during fasting. Most tissues are able to store triacylglycerol (TAG), cholesteryl esters (CEs), or lipids in relatively small (,1 mm diameter) lipid droplets (LDs) that can be used as an energy source or for membrane biogenesis (1). Although the interior of those LDs consists largely of neutral lipids, numerous proteins have recently been extracted together with the LD fractions isolated from two different cell lines (2, 3), suggesting that LDs should be viewed more as active intracellular compartments.Vimentin (4), perilipin (5, 6), and mouse adipose differentiation-related protein (ADFP; adipophilin in humans) (7) were the first proteins experimentally demonstrated to associate with the LD surface. This cellular location was more recently also experimentally confirmed for tailinteracting protein of 47 kDa (TIP47) (8, 9) and S3-12 (10). Perilipin, ADFP, and TIP47 exhibit high sequence identity within an N-terminal motif termed PAT-1 (for perilipin, ADFP, and TIP47) and a more distally located PAT-2 domain (9, 11). The N-terminus of S3-12 shares limited identity with the PAT-1 motif, but the protein shares sequence homology with ADFP and TIP47 in the PAT2 domain and the C terminus (12). S3-12 and the PAT proteins have amphipathic 11-mer helical repeats in common. These repeats are also found in other lipid binding proteins, such as synucleins, apolipoproteins, phosphate cytidyltransferases, and dehydrins (13). The PAT proteins and S3-12 are expressed in distinct tissues, suggesting that they have evolved to fine-tune lipid metabolism according to the particular needs of these tissues (12).At present, the LD-associating properties have only been thoroughly studied for ADFP and perilipin (14, 15). Perilipin expression is c...

OXPAT/PAT-1 Is a PPAR-Induced Lipid Droplet Protein That Promotes Fatty Acid Utilization

“…The PPAR family (␣, ␤, and ␥) of nuclear receptor transcription factors controls the expression of multiple genes involved in cellular fatty acid uptake, utilization, and storage (40). Moreover, three members of the PAT family are known targets of the PPAR system (36,(41)(42)(43)(44)(45). Northern blotting and immunoblotting with cDNA and antibody reagents described above confirm that OXPAT mRNA and protein are increased markedly (ϳ15-fold) in gastrocnemius muscle of MCK-PPAR␣ mice ( Fig.…”

“…Recent work has demonstrated that the other members of the PAT family, with the exception of TIP47, are induced in response to PPAR␥ ligand administration (36,41,43) in mice. Adipophilin expression is induced in liver of PPAR␣ agonist-treated mice (45). Several lines of evidence presented herein indicate that OXPAT is also a bona fide PPAR target gene.…”

Glucagon regulates intracellular distribution of adipose differentiation-related protein during triacylglycerol accumulation in the liver

“…It is well known that the addition of fatty acid to various cells induces ADRP expression and LD formation and that PPAR-RXR heterodimers are involved in mRNA expression of the ADRP gene (19)(20)(21)(22)(23)(24)(25). We tested the effect of fatty acids on the distribution of ADRP using HuH-7 hepatocytes, but we did not observe ADRP distribution in the iLD fractions by…”

“…The expression of Adrp mRNA is induced not only in adipocytes but also in many other types of cells upon lipid accumulation (17)(18)(19)(20)(21). It is reported that peroxisome-proliferator activated protein (PPAR)-retinoid X receptor (RXR) heterodimers are responsible for ADRP transcription, while PPAR ␥ is the major subtype in adipose tissue and the placenta ( 22,23 ), PPAR ␦ is crucial in macrophages ( 19 ), and PPAR ␣ acts in the liver ( 20,24 ).…”

Transcriptome Analysis of K-877 (a Novel Selective PPARα Modulator (SPPARMα))-Regulated Genes in Primary Human Hepatocytes and the Mouse Liver

“…Importantly, these genes were also induced by fenofibric acid treatment. In addition, nine of these 11 genes (except for AADAC and SLC25A42) have been reported to be direct PPAR target genes [11][12][13][14][15][16] . Arylacetamide deacetylase (AADAC) and SLC25A42 are involved in VLDL assembly 17) and coenzyme A transport 18) , respectively, and are important for determining the fatty acid fate.…”