Rev-Erb␣ (NR1D1) is an orphan nuclear receptor encoded on the opposite strand of the thyroid receptor ␣ gene. Rev-Erb␣ mRNA is induced during adipocyte differentiation of 3T3-L1 cells, and its expression is abundant in rat adipose tissue. Peroxisome proliferator-activated receptor ␥ (PPAR␥) (NR1C3) is a nuclear receptor controlling adipocyte differentiation and insulin sensitivity. Here we show that Rev-Erb␣ expression is induced by PPAR␥ activation with rosiglitazone in rat epididymal and perirenal adipose tissues in vivo as well as in 3T3-L1 adipocytes in vitro. Adipocyte differentiation is a complex biological process, which is reflected at the molecular level by the transcriptional activation of a number of adipocyte-specific genes and by the acquisition of the ability to accumulate cytoplasmic lipid droplets (1-3). The nuclear receptor peroxisome proliferator-activated receptor ␥ (PPAR␥, 1 NR1C3) (4, 5) and members of the CCAAT enhancer-binding protein (C/EBP) family (6 -12) play key roles in this adipogenic process. In addition, the adipocyte differentiation and determination factor-1 (SREBP-1/ADD1) appears to promote adipocyte differentiation by activating the expression of PPAR␥ and increasing the synthesis of endogenous PPAR␥ ligands (13-15). Members of the PPAR family bind as heterodimers with the retinoid X receptors (RXR) to specific response elements termed peroxisome proliferator response elements (PPRE) (for review see Ref. 16). These PPREs usually consist of a direct repeat of the PuGGTCA motif spaced by one nucleotide (DR1). The transcriptional activity of the PPARs is activated by a number of different fatty acid metabolites, most notably products of the cycloxygenase and lipoxygenase pathways. In addition, a large number of synthetic compounds are known to be potent and subtype specific PPAR ligands. For example, thiazolidinedione compounds used as insulin sensitizers in the treatment of type II diabetes are high affinity PPAR␥ ligands (17).Rev-Erb␣ (NR1D1) is another nuclear receptor, the expression of which is induced during adipocyte differentiation (18). Rev-Erb␣ is highly expressed in adipose tissue but also in skeletal muscle, liver and brain (18 -21). Since no ligand has been identified so far, Rev-Erb␣ is considered as an orphan member of the nuclear receptor superfamily. Rev-Erb␣ has been shown to act as a negative regulator of transcription (22) binding either as monomer on nuclear receptor half-site motifs flanked 5Ј by an A/T rich sequence (A/T PuGGTCA), or as a homodimer to a direct repeat of the PuGGTCA motif spaced by two nucleotides (DR2).We have previously shown that PPAR␣ activates the expression of Rev-Erb␣ through an atypical PPRE, a DR-2 element, in the Rev-Erb␣ promoter (23). Transcriptional activation by PPAR␥ through a DR-2 element has so far not been reported. However, since Rev-Erb␣ is induced during the course of adipocyte differentiation, we decided to investigate whether PPAR␥ could be involved in transcriptional induction of RevErb␣ expression in adipocytes. Furth...

The mouse acyl-CoA-binding protein (ACBP) 5 /diazepam binding inhibitor is a 10-kDa intracellular protein consisting of 86 amino acids. It is highly conserved throughout evolution and expressed in all cell types in the eukaryotes investigated (1, 2). This, together with the characteristics of the ACBP promoter (3, 4), implies a housekeeping function of the gene. However, expression levels vary markedly between tissues (5) and in response to different metabolic stimuli (6 -9), thereby indicating that ACBP might perform more specialized functions in some cell types. The ACBP protein binds C 14 -C 22 acyl-CoA esters with high affinity and specificity (10, 11) and has very little or no affinity toward other ligands (11-13). From in vitro studies, ACBP is known to protect acyl-CoA esters from hydrolysis (14 -16) and to relieve acyl-CoA inhibition of a number of enzymes, including long chain acyl-CoA synthetase, acetyl-CoA carboxylase (ACC), adenine nucleotide translocase, fatty acid synthetase (FAS), carnitine palmitoyltransferase, and acyl-CoA:cholesterol acyltransferase (9, 16 -18). In addition, ACBP is known to donate acyl-CoA esters to phospholipid, glycerolipid, and cholesteryl ester (CE) synthesis (14, 18 -21). Finally, proteolytic products of secreted ACBP have been shown to have signaling functions in Dictyostelium as well as mammalian cells (22). Targeted disruption of the yeast ACBP gene (ACB1) revealed that ACBP deficiency results in increased levels of C18:0 acyl-CoA esters and a decrease in the amount of total C26:0 fatty acids, indicating that transport of FA toward elongation is impaired by lack of ACBP. Furthermore, sphingolipid and ceramide amounts were reduced, membrane structure was altered, and vesicular transport was compromised (23-25).The functions of ACBP in lipid metabolism have been further studied in different mammalian cell culture systems and animal models by both knockdown strategies and overexpression of the protein. It has been reported that knockdown of ACBP by small interfering RNA causes growth arrest and lethality in three different mammalian cell lines (26); however, data from our laboratory show that ACBP can be knocked down in many different cell systems without affecting growth and survival (27). 6 Recently, knockdown of ACBP in HepG2 cells was shown to suppress the expression of a number of genes involved in lipid biosynthesis and lead to decreased levels of saturated and monounsaturated fatty acids (28). In 3T3-L1 preadipocytes, knockdown of ACBP caused a mild impairment of adipocyte differentiation and accumulation of triacylglycerol (TAG) (27), whereas overexpression of ACBP in McA-RH7777 rat hepatoma cells resulted in increased intracellular TAG accumulation (29). Overexpression of ACBP in transgenic mice resulted in accumulation of different lipid classes, including TAG in the liver (30). These results suggest *

The acyl-CoA-binding protein (ACBP) is a 10-kDa intracellular protein that specifically binds acyl-CoA esters with high affinity and is structurally and functionally conserved from yeast to mammals. In vitro studies indicate that ACBP may regulate the availability of acylCoA esters for various metabolic and regulatory purposes. The protein is particularly abundant in cells with a high level of lipogenesis and de novo fatty acid synthesis and is significantly induced during adipocyte differentiation. However, the molecular mechanisms underlying the regulation of ACBP expression in mammalian cells have remained largely unknown. Here we report that ACBP is a novel peroxisome proliferator-activated receptor (PPAR)␥ target gene. The rat ACBP gene is directly activated by PPAR␥/retinoid X receptor ␣ (RXR␣) and PPAR␣/RXR␣, but not by PPAR␦/RXR␣, through a PPAR-response element in intron 1, which is functionally conserved in the human ACBP gene. The intronic PPAR-response element (PPRE) mediates induction by endogenous PPAR␥ in murine adipocytes and confers responsiveness to the PPAR␥-selective ligand BRL49653. Finally, we have used chromatin immunoprecipitation to demonstrate that the intronic PPRE efficiently binds PPAR␥/RXR in its natural chromatin context in adipocytes. Thus, the PPRE in intron 1 of the ACBP gene is a bona fide PPAR␥-response element.

Chronic use of heparin as an anti-coagulant for the treatment of thrombosis or embolism invokes many adverse systemic events including thrombocytopenia, vascular reactions and osteoporosis. Here, we addressed whether adverse effects might also be directed to mesenchymal stem cells that reside in the bone marrow compartment. Harvested human bone marrow-derived mesenchymal stem cells (hMSCs) were exposed to varying doses of heparin and their responses profiled. At low doses (<200 ng/ml), serial passaging with heparin exerted a variable effect on hMSC proliferation and multipotentiality across multiple donors, while at higher doses (≥100 µg/ml), heparin supplementation inhibited cell growth and increased both senescence and cell size. Gene expression profiling using cDNA arrays and RNA-seq analysis revealed pleiotropic effects of low-dose heparin on signaling pathways essential to hMSC growth and differentiation (including the TGFβ/BMP superfamily, FGFs, and Wnts). Cells serially passaged in low-dose heparin possess a donor-dependent gene signature that reflects their altered phenotype. Our data indicate that heparin supplementation during the culturing of hMSCs can alter their biological properties, even at low doses. This warrants caution in the application of heparin as a culture supplement for the ex vivo expansion of hMSCs. It also highlights the need for careful evaluation of the bone marrow compartment in patients receiving chronic heparin treatment.