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  • Luzindole br Acknowledgments This study was supported by the


    Acknowledgments This study was supported by the Programa Nacional de Innovación para la Competitividad y Productividad-Innóvate Perú (contract number 181-FINCyT-IB-2013) and the World Academy of Science award (No.14-233RG-BIO-LA UNESCO FR324028597).
    Introduction The enzyme Enolase (ENO1, EC. acts in glycolysis to convert 2-phosphoglycerate to phosphoenolpyruvate. Twenty years ago, Shand and West had proposed that next to its glycolytic function Enolase can also inhibit cholesteryl ester hydrolases (CEHs) [1], [2]. The transition of Luzindole macrophages to “foam cells” in the atherosclerotic plaque is accompanied by storage of cholesterol esters in lipid droplets [3], [4]. This process, which can be mimicked experimentally in vitro by loading macrophages with acetyl-LDL or oxidized-LDL, requires enhanced cholesterol esterification activity. Accordingly, cholesterol loading of macrophages results in a marked increase in ENO1 protein [5], [6], which can potentially inhibit CEHs on the surface of lipid droplets [7], [8]. The Liver X Receptor-α and -β (LXRs, NR1H3 and NR1H2, respectively) are members of the nuclear receptor superfamily that play a central role in controlling cholesterol homeostasis [9], [10]. In macrophages, LXRs can decrease the cellular sterol burden by inducing Luzindole of the cholesterol efflux transporters Abca1 and Abcg1[11], [12], and by limiting uptake of LDL-derived cholesterol due to induction of Idol, an E3 ubiquitin ligase that promotes lysosomal degradation of the LDLR [13]. Despite the crucial role of LXRs in cholesterol homeostasis, their effect on cellular cholesterol storage is not well understood. Through transcriptional profiling, we have identified that Enolase is subject to LXR-dependent regulation [14]. Here, we show that Enolase transcript and protein abundance are reduced by LXRs in macrophages and intestine and discuss the impact this may have on mobilization of cholesterol towards efflux pathways.
    Materials and methods
    Discussion We report herein the regulation of Enolase by LXRs. The major finding of this study is that activated LXRs decrease Eno1 expression and corresponding protein levels in murine macrophages and in vivo in a tissue-specific and LXR-dependent manner. Despite being an important metabolic enzyme the regulation of Eno1 expression is poorly understood. Recently, Cai et al. reported that Estrogen-Related Receptors (ERRs) α, β, and γ (NR3B1, 2 and 3, respectively) can bind and drive transcriptional activity of the Eno1 promoter in cooperation with hypoxia-inducible factors under hypoxic conditions [19]. Expression of ENO1 is also highly responsive to proinflammatory signals such as IL- 1β, IL-6, PGE2, or TNF-α in peripheral blood mononuclear cells [20]. These cytokines, largely acting through the NF-κB pathway, increase expression of ENO1 as part of the inflammatory program. Our finding that LXRs are potent repressors of Eno1 expression further illustrates the complex regulation of this enzyme. An important question that emerges from our study relates to the mechanism underlying repression of Eno1 expression by LXRs. LXR binding has been observed by ChIP-seq analysis in the vicinity of the ENO1 gene in human macrophages [21]. However, careful in silico analyses of both human and mouse promoters failed to reveal potential bindings sites (not shown). Alternatively, it is well established that LXR are potent anti-inflammatory factors in macrophages, largely due to their ability to trans-repress inflammatory gene signaling [22], [23]. Accordingly, ligand activated LXRs inhibit expression of NF-κB-responsive genes such as COX2, iNOS and MMP-9 during the inflammatory response [24]. Given that ENO1 gene expression is also enhanced by NF-κB signaling we postulate that repression of Eno1 by LXRs may follow a similar mechanism, an hypothesis that warrants future studies. The question is still open in the context of human macrophages. Preliminary data lead us to confirm that ENO1 regulation by LXRs is present in THP1 human cell line (data not shown) but occurs only at the protein level. This observation suggest that molecular mechanism underlying Eno1 regulation by LXRs is complex and probably organism specific.