Farnesoid X receptor (FXR) is the master regulator of bile acid (BA) homeostasis because it controls BA synthesis, influx, efflux, and detoxification in the gut/liver axis. Deregulation of BA homeostasis has been linked to hepatocellular carcinoma (HCC), and spontaneous hepatocarcinogenesis has been observed in FXR-null mice. This dreaded liver neoplasm has been associated with both FXR gene deletion and BA-mediated metabolic abnormalities after inactivation of FXR transcriptional activity. In the present study, we addressed the hypothesis that intestinal selective FXR reactivation would be sufficient to restore the fibroblast growth factor 15 (FGF15)/ cholesterol-7alpha-hydroxylase (Cyp7a1) enterohepatic axis and eventually provide protection against HCC. To this end, we generated FXR-null mice with re-expression of constitutively active FXR in enterocytes (FXR 2/2 iVP16FXR) and corresponding control mice (FXR 2/2 iVP16). In FXR-null mice, intestinal selective FXR reactivation normalized BA enterohepatic circulation along with up-regulation of intestinal FXR transcriptome and reduction of hepatic BA synthesis. At 16 months of age, intestinal FXR reactivation protected FXR-null mice from spontaneous HCC development that occurred in otherwise FXR-null mice. Activation of intestinal FXR conferred hepatoprotection by restoring hepatic homeostasis, limiting cellular proliferation through reduced cyclinD1 expression, decreasing hepatic inflammation and fibrosis (decreased signal transducer and activator of transcription 3 activation and curtailed collagen deposition). Conclusion: Intestinal FXR is sufficient to restore BA homeostasis through the FGF15 axis and prevent progression of liver damage to HCC even in the absence of hepatic FXR. Intestinal-selective FXR modulators could stand as potential therapeutic intervention to prevent this devastating hepatic malignancy, even if carrying a somatic FXR mutation. (HEPATOLOGY 2015;61:161-170) See Editorial on Page 21 H epatocellular carcinoma (HCC) is the fifthmost prevalent type of cancer and the secondleading cause of cancer-related death, with over Abbreviations: AKR1B7, aldo-keto reductase 1b7; ALDH1B1, aldehyde dehydrogenase 1 family member B1; ALT, alanine aminotransferase; ANG1, angiogenin 1; ANOVA, analysis of variance; AST, aspartate aminotransferase; BA, bile acid; CA, cholic acid; CCND1 and E1, cyclinD1 and E1; CLD, chronic liver disease; CYP3A11, cytochrome P450 isoform 3A11; CYP7A1, cholesterol-7alpha-hydroxylase; ERK1/2, extracellular signal-regulated protein kinases 1 and 2; FGF15, fibroblast growth factor 15; FGFR4, FGF receptor 4; FRS2, FGF receptor substrate 2; FXR, farnesoid X receptor; GSTM1, glutathione S-transferase mu1; IBABP, ileal bile acid-binding protein; JNK, c-Jun (NH2)-terminal kinase; HCC, hepatocellular carcinoma; KO, knockout; IFN-g, interferon gamma; IHC, immunohistochemistry; IL-6, interleukin-6; b-MCA, beta-muricholic acid; MRP, multidrug resistance-associated protein; NF-jB, nuclear factor kappa B; NRF2, nuclear factor erythroid 2-r...

Cholesterol homeostasis is critical for cellular proliferation. Liver X receptor (LXR) ␣ and ␤ are the nuclear receptors responsible for regulation of cholesterol metabolism. In physiological conditions, high intracellular cholesterol levels cause increased synthesis of oxysterols, which activate LXR, thus triggering a transcriptional response for cholesterol secretion and catabolism. Here we employed a mouse model of partial hepatectomy (PH) to dissect the molecular pathways connecting cholesterol homeostasis, cellular proliferation, and LXR. First, we show that hepatic cholesterol content increases after PH, whereas the entire LXR transcriptome is down-regulated. Although LXR messenger RNA (mRNA) levels are unmodified, LXR target genes are significantly down-regulated on day 1 after PH and restored to control levels on day 7, when the liver reaches normal size. The inactivation of LXR following PH is related to the reduced oxysterol availability by way of decreased synthesis, and increased sulfation and secretion. On the contrary, cholesterol synthesis is up-regulated, and extracellular matrix remodeling is enhanced. Second, we show that reactivation of LXR by way of a synthetic ligand determines a negative modulation of hepatocyte proliferation. This effect is sustained by the reactivation of hepatic cholesterol catabolic and secretory pathways, coupled with a significant reduction of cholesterol biosynthesis. Our data unveil a previously unrecognized and apparently paradoxical scenario of LXR modulation. During liver regeneration LXR activity is abated in spite of increasing intracellular cholesterol levels. Turning off LXR-transcriptional pathways is crucial to guaranteeing the requisite intracellular cholesterol levels of regenerating hepatocytes. In line with this hypothesis, pharmacological LXR reactivation during PH significantly reduces liver regeneration capacity. (HEPATOLOGY 2010;51:1334-1344 C holesterol is not only the precursor of steroid hormones but also a regulator of embryonic development and cell proliferation, being a key component of the cell membrane. 1,2 Thus, there is a need of coordinate tuning of cholesterol metabolism and lipogenic gene expression during membrane synthesis, cellular differentiation, and proliferation. Proliferating cells satisfy their cholesterol demand by increasing their uptake of exogenous cholesterol 3 through an increase in low-density lipoprotein receptor. 4 When cholesterol synthesis is inhibited by HMG-CoA reductase inhibitor, cell growth is reduced, 5 whereas the subsequent addition of choles-

Tumours can be viewed as aberrant tissues or organs sustained by tumorigenic stem-like cells that engage into dysregulated histo/organogenetic processes. Paragangliomas, prototypical organoid tumours constituted by dysmorphic variants of the vascular and neural tissues found in normal paraganglia, provide a model to test this hypothesis. To understand the origin of paragangliomas, we built a biobank comprising 77 cases, 18 primary cultures, 4 derived cell lines, 80 patient-derived xenografts and 11 cell-derived xenografts. We comparatively investigated these unique complementary materials using morphofunctional, ultrastructural and flow cytometric assays accompanied by microRNA studies. We found that paragangliomas contain stem-like cells with hybrid mesenchymal/vasculoneural phenotype, stabilized and expanded in the derived cultures. The viability and growth of such cultures depended on the downregulation of the miR-200 and miR-34 families, which allowed high PDGFRA and ZEB1 protein expression levels. Both tumour tissue- and cell culture-derived xenografts recapitulated the vasculoneural paraganglioma structure and arose from mesenchymal-like cells through a fixed developmental sequence. First, vasculoangiogenesis organized the microenvironment, building a perivascular niche which in turn supported neurogenesis. Neuroepithelial differentiation was associated with severe mitochondrial dysfunction, not present in cultured paraganglioma cells, but acquired in vivo during xenograft formation. Vasculogenesis was the Achilles’ heel of xenograft development. In fact, imatinib, that targets endothelial-mural signalling, blocked paraganglioma xenograft formation (11 xenografts from 12 cell transplants in the control group versus 2 out of 10 in the treated group, P = 0.0015). Overall our key results were unaffected by the SDHx gene carrier status of the patient, characterized for 70 out of 77 cases. In conclusion, we explain the biphasic vasculoneural structure of paragangliomas and identify an early and pharmacologically actionable phase of paraganglioma organization.Electronic supplementary materialThe online version of this article (10.1007/s00401-017-1799-2) contains supplementary material, which is available to authorized users.