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The malignant progression of pancreatic ductal adenocarcinoma (PDAC) is accompanied by a profound desmoplasia, which forces proliferating tumor cells to metabolically adapt to this new microenvironment. We established the PDAC metabolic signature to highlight the main activated tumor metabolic pathways. Comparative transcriptomic analysis identified lipid-related metabolic pathways as being the most highly enriched in PDAC, compared with a normal pancreas. Our study revealed that lipoprotein metabolic processes, in particular cholesterol uptake, are drastically activated in the tumor. This process results in an increase in the amount of cholesterol and an overexpression of the low-density lipoprotein receptor (LDLR) in pancreatic tumor cells. These findings identify LDLR as a novel metabolic target to limit PDAC progression. Here, we demonstrate that shRNA silencing of LDLR, in pancreatic tumor cells, profoundly reduces uptake of cholesterol and alters its distribution, decreases tumor cell proliferation, and limits activation of ERK1/2 survival pathway. Moreover, blocking cholesterol uptake sensitizes cells to chemotherapeutic drugs and potentiates the effect of chemotherapy on PDAC regression. Clinically, high PDAC Ldlr expression is not restricted to a specific tumor stage but is correlated to a higher risk of disease recurrence. This study provides a precise overview of lipid metabolic pathways that are disturbed in PDAC. We also highlight the high dependence of pancreatic cancer cells upon cholesterol uptake, and identify LDLR as a promising metabolic target for combined therapy, to limit PDAC progression and disease patient relapse.

Objective: The kidney has been proposed to play a central role in apo AI catabolism, suggesting that HDL structure is determined, at least in part, by this organ. Here, we aimed at determining the effects of a renal mass reduction on HDL size distribution, lipid content, and apo AI turnover., Methods: We characterized HDL subclasses in rabbits with a 75% reduction of functional renal mass (Nptx group), using enzymatic staining of samples separated on polyacrylamide electrophoresis gels, and also performed kinetic studies using radiolabeled HDL-apo AI in this animal model., Results: Creatinine clearance was reduced to 35% after nephrectomy as compared to the basal values, but without increased proteinuria. A slight, but significant modification of the relative HDL size distribution was observed after nephrectomy, whereas cholesterol plasma concentrations gradually augmented from large HDL2b (+54%) to small HDL3b particles (+150%, P<0.05). Cholesteryl esters were the increased fraction; in contrast, free cholesterol phospholipids and triglycerides of HDL subclasses were not affected by nephrectomy. HDL-apo AI fractional catabolic rates were similar to controls., Conclusion: Reduction of functional renal mass is associated to enrichment of HDL subclasses with cholesteryl esters. Structural abnormalities were not related to a low apo AI turnover, suggesting renal contribution to HDL remodeling beyond being just a catabolic site for these lipoproteins., (Copyright © 2013 Elsevier Inc. All rights reserved.)

Rationale: A crucial step in atherogenesis is the infiltration of the subendothelial space of large arteries by monocytes where they differentiate into macrophages and transform into lipid-loaded foam cells. Macrophages are heterogeneous cells that adapt their response to environmental cytokines. Th1 cytokines promote monocyte differentiation into M1 macrophages, whereas Th2 cytokines trigger an "alternative" M2 phenotype., Objective: We previously reported the presence of CD68(+) mannose receptor (MR)(+) M2 macrophages in human atherosclerotic plaques. However, the function of these plaque CD68(+)MR(+) macrophages is still unknown., Methods and Results: Histological analysis revealed that CD68(+)MR(+) macrophages locate far from the lipid core of the plaque and contain smaller lipid droplets compared to CD68(+)MR(-) macrophages. Interleukin (IL)-4-polarized CD68(+)MR(+) macrophages display a reduced capacity to handle and efflux cellular cholesterol because of low expression levels of the nuclear receptor liver x receptor (LXR)α and its target genes, ABCA1 and apolipoprotein E, attributable to the high 15-lipoxygenase activity in CD68(+)MR(+) macrophages. By contrast, CD68(+)MR(+) macrophages highly express opsonins and receptors involved in phagocytosis, resulting in high phagocytic activity. In M2 macrophages, peroxisome proliferator-activated receptor (PPAR)γ activation enhances the phagocytic but not the cholesterol trafficking pathways., Conclusions: These data identify a distinct macrophage subpopulation with a low susceptibility to become foam cells but high phagocytic activity resulting from different regulatory activities of the PPARγ-LXRα pathways.

Objective: Bexarotene (Targretin) is a clinically used antitumoral agent which exerts its action through binding to and activation of the retinoid-X-receptor (RXR). The most frequent side-effect of bexarotene administration is an increase in plasma triglycerides, an independent risk factor of cardiovascular disease. The molecular mechanism behind this hypertriglyceridemia remains poorly understood., Methods and Results: Using wild-type and LXR alpha/beta-deficient mice, we show here that bexarotene induces hypertriglyceridemia and activates hepatic LXR-target genes of lipogenesis in an LXR-dependent manner, hence exerting a permissive effect on RXR/LXR heterodimers. Interestingly, RNA analysis and Chromatin Immunoprecipitation assays performed in the liver reveal that the in vivo permissive effect of bexarotene on the RXR/LXR heterodimer is restricted to lipogenic genes without modulation of genes controlling cholesterol homeostasis., Conclusions: These findings demonstrate that the hypertriglyceridemic action of bexarotene occurs via the RXR/LXR heterodimer and show that RXR heterodimers can act with a selective permissivity on target genes of specific metabolic pathways in the liver.

Objective: The activity of the antitumoral agent bexarotene (Targretin, Bexarotene) depends on its binding to the nuclear retinoid-X receptor (RXR) and subsequent transcriptional regulation of target genes. Through RXR activation, bexarotene may modulate numerous metabolic pathways involved in atherosclerosis. Here, we investigated the effect of bexarotene on atherosclerosis progression in a dyslipidemic murine model, the human apolipoprotein E2 knockin mouse, that develops essentially macrophage-laden lesions., Methods and Results: Atherosclerotic lesions together with different metabolic pathways involved in atherosclerosis were investigated in mice treated or not with bexarotene. Bexarotene protects from atherosclerosis development in mice, at least in part by improving the circulating cholesterol distribution profile likely via a marked decrease of dietary cholesterol absorption caused by modulation of intestinal expression of genes recently identified as major players in this process, Niemann-Pick-C1-Like1 (NPC1L1) and CD13. This atheroprotection appears despite a strong hypertriglyceridemia. Moreover, bexarotene treatment only modestly modulates inflammatory gene expression in the vascular wall, but markedly enhanced the capacity of macrophages to efflux cellular lipids., Conclusions: These data provide evidence of a favorable pharmacological effect of bexarotene on atherosclerosis despite the induction of hypertriglyceridemia, likely via a beneficial action on intestinal absorption and macrophage efflux.

Roux-en-Y gastric bypass (RYGB), the most effective surgical procedure for weight loss, decreases obesity and ameliorates comorbidities, such as non-alcoholic fatty liver (NAFLD) and cardiovascular (CVD) diseases. Cholesterol is a major CVD risk factor and modulator of NAFLD development, and the liver tightly controls its metabolism. How RYGB surgery modulates systemic and hepatic cholesterol metabolism is still unclear. We studied the hepatic transcriptome of 26 patients with obesity but not diabetes before and 1 year after undergoing RYGB. In parallel, we measured quantitative changes in plasma cholesterol metabolites and bile acids (BAs). RYGB surgery improved systemic cholesterol metabolism and increased plasma total and primary BA levels. Transcriptomic analysis revealed specific alterations in the liver after RYGB, with the downregulation of a module of genes implicated in inflammation and the upregulation of three modules, one associated with BA metabolism. A dedicated analysis of hepatic genes related to cholesterol homeostasis pointed towards increased biliary cholesterol elimination after RYGB, associated with enhancement of the alternate, but not the classical, BA synthesis pathway. In parallel, alterations in the expression of genes involved in cholesterol uptake and intracellular trafficking indicate improved hepatic free cholesterol handling. Finally, RYGB decreased plasma markers of cholesterol synthesis, which correlated with an improvement in liver disease status after surgery. Our results identify specific regulatory effects of RYGB on inflammation and cholesterol metabolism. RYGB alters the hepatic transcriptome signature, likely improving liver cholesterol homeostasis. These gene regulatory effects are reflected by systemic post-surgery changes of cholesterol-related metabolites, corroborating the beneficial effects of RYGB on both hepatic and systemic cholesterol homeostasis. Roux-en-Y gastric bypass (RYGB) is a widely used bariatric surgery procedure with proven efficacy in body weight management, combatting cardiovascular disease (CVD) and non-alcoholic fatty liver disease (NAFLD). RYGB exerts many beneficial metabolic effects, by lowering plasma cholesterol and improving atherogenic dyslipidemia. Using a cohort of patients undergoing RYGB, studied before and 1 year after surgery, we analyzed how RYGB modulates hepatic and systemic cholesterol and bile acid metabolism. The results of our study provide important insights on the regulation of cholesterol homeostasis after RYGB and open avenues that could guide future monitoring and treatment strategies targeting CVD and NAFLD in obesity. [Display omitted] • Body weight management by RYGB surgery has been shown to ameliorate both CVD and NAFLD. • We assessed the hepatic gene expression and plasma metabolite changes in patients after RYGB surgery. • Expression of genes of the alternate BA synthesis and biliary cholesterol elimination pathways are induced after RYGB. • RYGB increases plasma FGF19 and lowers plasma C4 indicating decreased BA synthesis through the classical pathway. • Decreased plasma cholesterol synthesis markers upon RYGB correlate with improved NAFLD histology after surgery. [ABSTRACT FROM AUTHOR]

Abstract: Niemann–Pick C1 like 1 (NPC1L1) is a protein critical for intestinal cholesterol absorption. The nuclear receptors peroxisome proliferator-activated receptor alpha (PPARα) and liver X receptors (LXRα and LXRβ) are major regulators of cholesterol homeostasis and their activation results in a reduced absorption of intestinal cholesterol. The goal of this study was to define the role of PPARα and LXR nuclear receptors in the regulation of NPC1L1 gene expression. We show that LXR activators down-regulate NPC1L1 mRNA levels in the human enterocyte cell line Caco-2/TC7, whereas PPARα ligands have no effect. Furthermore, NPC1L1 mRNA levels are decreased in vivo, in duodenum of mice treated with the LXR agonist T0901317. In conclusion, the present study identifies NPC1L1 as a novel LXR target gene further supporting a crucial role of LXR in intestinal cholesterol homeostasis. [Copyright &y& Elsevier]