The Liver X receptor (LXR) is an important regulator of carbohydrate and lipid metabolism in humans and mice. We have recently shown that activation of LXR regulates cellular fuel utilization in adipocytes. In contrast, the role of LXR in human adipocyte lipolysis, the major function of human white fat cells, is not clear. In the present study, we stimulated in vitro differentiated human and murine adipocytes with the LXR agonist GW3965 and observed an increase in basal lipolysis. Microarray analysis of human adipocyte mRNA following LXR activation revealed an altered gene expression of several lipolysis-regulating proteins, which was also confirmed by quantitative real-time PCR. We show that expression and intracellular localization of perilipin1 (PLIN1) and hormone-sensitive lipase (HSL) are affected by GW3965. Although LXR activation does not influence phosphorylation status of HSL, HSL activity is required for the lipolytic effect of GW3965. This effect is abolished by PLIN1 knockdown. In addition, we demonstrate that upon activation, LXR binds to the proximal regions of the PLIN1 and HSL promoters. By selective knock-down of either LXR isoform, we show that LXRα is the major isoform mediating the lipolysis-related effects of LXR. In conclusion, the present study demonstrates that activation of LXRα up-regulates basal human adipocyte lipolysis. This is at least partially mediated through LXR binding to the PLIN1 promoter and down-regulation of PLIN1 expression.
"Quantitative PCR and western blot confirmed the EBF1 RNAi microarray data (i.e., a significant 30%–40% downregulation in the mRNA and protein expression of key lipolytic genes, including PLIN1 and LIPE) (Figures 4C and S4C). A combined decrease in the expression of PLIN1 and LIPE can result in increased lipolysis in human adipocytes provided that the ratio between LIPE and PLIN1 is increased at the lipid droplet surface (Stenson et al., 2011). In order to dissect mechanisms by which EBF1 controls basal lipolysis, human adipocytes were transfected with siRNAs targeting EBF1, PLIN1, or both (Figure 4C). "
[Show abstract][Hide abstract] ABSTRACT: White adipose tissue (WAT) morphology characterized by hypertrophy (i.e., fewer but larger adipocytes) associates with increased adipose inflammation, lipolysis, insulin resistance, and risk of diabetes. However, the causal relationships and the mechanisms controlling WAT morphology are unclear. Herein, we identified EBF1 as an adipocyte-expressed transcription factor with decreased expression/activity in WAT hypertrophy. In human adipocytes, the regulatory targets of EBF1 were enriched for genes controlling lipolysis and adipocyte morphology/differentiation, and in both humans and murine models, reduced EBF1 levels associated with increased lipolysis and adipose hypertrophy. Although EBF1 did not affect adipose inflammation, TNFα reduced EBF1 gene expression. High-fat diet intervention in Ebf1(+/-) mice resulted in more pronounced WAT hypertrophy and attenuated insulin sensitivity compared with wild-type littermate controls. We conclude that EBF1 is an important regulator of adipose morphology and fat cell lipolysis and may constitute a link between WAT inflammation, altered lipid metabolism, adipose hypertrophy, and insulin resistance.
"The liver X receptor (LXR) is known as an important regulator of carbohydrate and adipose tissue metabolism in humans and mice. LXR includes two isoforms LXR alpha and LXR beta, as both of them express in human adipose tissue (Korach-Andre et al. 2011; Stenson et al. 2011). Serum response factor (SRF) is a member of the MADS box family of TFs originally named for its role in mediating the effects of serum stimulation. "
[Show abstract][Hide abstract] ABSTRACT: Adipose tissue plays important roles in whole body energy homeostasis and is now known to be a very important and active endocrine organ. The transcriptional regulatory network of adipose tissue metabolism is complex and much yet to be known. To identify transcriptional profile in adipose tissue, expressed sequence tag (EST) analysis using Digital Differential Display (DDD) was employed. The results of EST analysis were re-evaluated by microarray data using COXPRESdb (an available expression data repository). To uncover transcriptional regulatory mechanisms which play key roles in the adipose tissue metabolism, transcriptional regulatory network analysis was applied, using the promoter analysis and interaction network toolset. Sixty-five transcripts were found to be more frequent in adipose tissue in comparison to the other tissues. COXPRESdb result showed that 62 % of the identified over-expressed genes in adipose tissue by DDD had expression level greater than 1 (in base 2 logarithm). Based on coincidence of regulatory sites, candidate TFs were identified including TFs that previously known to be involved in adipose tissue metabolism (SP1, KROX, STAT1, LRF, VDR, LXR, SRF and HIF1) and TFs, such as CKROX, ZF5, ETF, AP-2, AP-2alpha, PAX-5, SPZ1, RBPJ and CACD, that had not been recognized previously. This work yielded several TF candidates activating in adipose tissue metabolism. These findings open a new avenue for future research on promoter occupancy and TF perturbation.
[Show abstract][Hide abstract] ABSTRACT: MicroRNAs (miRNAs) are small non-coding RNAs that regulate gene expression and have multiple effects in various tissues including adipose inflammation, a condition characterized by increased local release of the pro-lipolytic cytokine tumor necrosis factor-alpha (TNF-α). Whether miRNAs regulate adipocyte lipolysis is unknown. We set out to determine whether miRNAs affect adipocyte lipolysis in human fat cells. To this end, eleven miRNAs known to be present in human adipose tissue were over-expressed in human in vitro differentiated adipocytes followed by assessments of TNF-α and glycerol levels in conditioned media after 48 h. Three miRNAs (miR-145, -26a and let-7d) modulated both parameters in parallel. However, while miR-26a and let-7d decreased, miR-145 increased both glycerol release and TNF-α secretion. Further studies were focused therefore on miR-145 since this was the only stimulator of lipolysis and TNF-α secretion. Time-course analysis demonstrated that miR-145 over-expression up-regulated TNF-α expression/secretion followed by increased glycerol release. Increase in TNF-α production by miR-145 was mediated via activation of p65, a member of the NF-κB complex. In addition, miR-145 down-regulated the expression of the protease ADAM17, resulting in an increased fraction of membrane bound TNF-α, which is the more biologically active form of TNF-α. MiR-145 overexpression also increased the phosphorylation of activating serine residues in hormone sensitive lipase and decreased the mRNA expression of phosphodiesterase 3B, effects which are also observed upon TNF-α treatment in human adipocytes. We conclude that miR-145 regulates adipocyte lipolysis via multiple mechanisms involving increased production and processing of TNF-α in fat cells.
PLoS ONE 01/2014; 9(1):e86800. DOI:10.1371/journal.pone.0086800 · 3.23 Impact Factor
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