Sally Coulter

A Vitamin D Receptor/SMAD Genomic Circuit Gates Hepatic Fibrotic Response

Liver fibrosis is a reversible wound-healing response involving TGFβ1/SMAD activation of hepatic stellate cells (HSCs). It results from excessive deposition of extracellular matrix components and can lead to impairment of liver function. Here, we show that vitamin D receptor (VDR) ligands inhibit HSC activation by TGFβ1 and abrogate liver fibrosis, whereas Vdr knockout mice spontaneously develop hepatic fibrosis. Mechanistically, we show that TGFβ1 signaling causes a redistribution of genome-wide VDR-binding sites (VDR cistrome) in HSCs and facilitates VDR binding at SMAD3 profibrotic target genes via TGFβ1-dependent chromatin remodeling. In the presence of VDR ligands, VDR binding to the coregulated genes reduces SMAD3 occupancy at these sites, inhibiting fibrosis. These results reveal an intersecting VDR/SMAD genomic circuit that regulates hepatic fibrogenesis and define a role for VDR as an endocrine checkpoint to modulate the wound-healing response in liver. Furthermore, the findings suggest VDR ligands as a potential therapy for liver fibrosis.

Intestinal FXR agonism promotes adipose tissue browning and reduces obesity and insulin resistance

The systemic expression of the bile acid (BA) sensor farnesoid X receptor (FXR) has led to promising new therapies targeting cholesterol metabolism, triglyceride production, hepatic steatosis and biliary cholestasis. In contrast to systemic therapy, bile acid release during a meal selectively activates intestinal FXR. By mimicking this tissue-selective effect, the gut-restricted FXR agonist fexaramine (Fex) robustly induces enteric fibroblast growth factor 15 (FGF15), leading to alterations in BA composition, but does so without activating FXR target genes in the liver. However, unlike systemic agonism, we find that Fex reduces diet-induced weight gain, body-wide inflammation and hepatic glucose production, while enhancing thermogenesis and browning of white adipose tissue (WAT). These pronounced metabolic improvements suggest tissue-restricted FXR activation as a new approach in the treatment of obesity and metabolic syndrome.

FGF19 Regulates Cell Proliferation, Glucose and Bile Acid Metabolism via FGFR4-Dependent and Independent Pathways

Fibroblast growth factor 19 (FGF19) is a hormone-like protein that regulates carbohydrate, lipid and bile acid metabolism. At supra-physiological doses, FGF19 also increases hepatocyte proliferation and induces hepatocellular carcinogenesis in mice. Much of FGF19 activity is attributed to the activation of the liver enriched FGF Receptor 4 (FGFR4), although FGF19 can activate other FGFRs in vitro in the presence of the coreceptor βKlotho (KLB). In this report, we investigate the role of FGFR4 in mediating FGF19 activity by using Fgfr4 deficient mice as well as a variant of FGF19 protein (FGF19v) which is specifically impaired in activating FGFR4. Our results demonstrate that FGFR4 activation mediates the induction of hepatocyte proliferation and the suppression of bile acid biosynthesis by FGF19, but is not essential for FGF19 to improve glucose and lipid metabolism in high fat diet fed mice as well as in leptin-deficient ob/ob mice. Thus, FGF19 acts through multiple receptor pathways to elicit pleiotropic effects in regulating nutrient metabolism and cell proliferation.

Hepatic fat loss in advanced nonalcoholic steatohepatitis: Are alterations in serum adiponectin the cause?

Advanced liver fibrosis in nonalcoholic steatohepatitis (NASH) is often accompanied by a reduction in hepatic fat to the point of complete fat loss (burnt‐out NASH), but the mechanisms behind this phenomenon have not been elucidated. Adiponectin is raised in cirrhosis of any cause and has potent antisteatotic activity. In this study we examined 65 patients with advanced biopsy‐proven NASH (fibrosis stage 3‐4) and 54 with mild disease (fibrosis stage 0‐1) to determine if disappearance of steatosis correlated with changes in serum adiponectin. All patents had fasting blood tests and anthropometric measures at the time of liver biopsy. Liver fat was accurately quantitated by morphometry. Serum adiponectin was measured by immunoassay. When compared to those with early disease, patients with advanced NASH were more insulin‐resistant, viscerally obese, and older, but there was no difference in liver fat content or adiponectin levels. Adiponectin had a significant negative correlation with liver fat percentage in the whole cohort (r = −0.28, P < 0.01), driven by patients with advanced NASH (r = −0.40, P < 0.01). In advanced NASH, for each 4 μg/L increase in adiponectin there was an odds ratio OR of 2.0 (95% confidence interval [CI]: 1.3‐3.0, P < 0.01) for a 5% reduction in hepatic fat. Adiponectin was highly and significantly associated with almost complete hepatic fat loss or burnt‐out NASH (12.1 versus 7.4 μg/L, P = 0.001) on multivariate analysis. A relationship between adiponectin, bile acids, and adipocyte fexaramine activation was demonstrated in vivo and in vitro, suggestive of hepatocyte‐adipocyte crosstalk. Conclusion: Serum adiponectin levels in advanced NASH are independently associated with hepatic fat loss. Adiponectin may in part be responsible for the paradox of burnt‐out NASH. (HEPATOLOGY 2012)

Critical illness evokes elevated circulating bile acids related to altered hepatic transporter and nuclear receptor expression.

Hyperbilirubinemia is common during critical illness and is associated with adverse outcome. Whether hyperbilirubinemia reflects intensive care unit (ICU) cholestasis is unclear. Therefore, the aim of this study was to analyze hyperbilirubinemia in conjunction with serum bile acids (BAs) and the key steps in BA synthesis, transport, and regulation by nuclear receptors (NRs). Serum BA and bilirubin levels were determined in 130 ICU and 20 control patients. In liver biopsies messenger RNA (mRNA) expression of BA synthesis enzymes, BA transporters, and NRs was assessed. In a subset (40 ICU / 10 controls) immunohistochemical staining of the transporters and receptors together with a histological evaluation of cholestasis was performed. BA levels were much more elevated than bilirubin in ICU patients. Conjugated cholic acid (CA) and chenodeoxycholic acid (CDCA) were elevated, with an increased CA/CDCA ratio. Unconjugated BA did not differ between controls and patients. Despite elevated serum BA levels, CYP7A1 protein, the rate‐limiting enzyme in BA synthesis, was not lowered in ICU patients. Also, protein expression of the apical bile salt export pump (BSEP) was decreased, whereas multidrug resistance‐associated protein (MRP) 3 was strongly increased at the basolateral side. This reversal of BA transport toward the sinusoidal blood compartment is in line with the increased serum conjugated BA levels. Immunostaining showed marked down‐regulation of nuclear farnesoid X receptor, retinoid X receptor alpha, constitutive androstane receptor, and pregnane X receptor nuclear protein levels. Conclusion: Failure to inhibit BA synthesis, up‐regulate canalicular BA export, and localize pivotal NR in the hepatocytic nuclei may indicate dysfunctional feedback regulation by increased BA levels. Alternatively, critical illness may result in maintained BA synthesis (CYP7A1), reversal of normal BA transport (BSEP/MRP3), and inhibition of the BA sensor (FXR/RXRα) to increase serum BA levels. (HEPATOLOGY 2011;)

Dose Escalation of Tamoxifen in Patients with Low Endoxifen Level: Evidence for Therapeutic Drug Monitoring—The TADE Study

Purpose: Endoxifen is the major mediator of tamoxifen effect and endoxifen levels <15 nmol/L may be associated with increased risk of breast cancer recurrence. We increased tamoxifen dose in breast cancer patients with low endoxifen levels and assessed the influence of various parameters on reaching 15 nmol/L and 30 nmol/L endoxifen levels. Experimental Design: Tamoxifen dose was increased in those with endoxifen levels below 30 nmol/L. Toxicity, including hot flash score, was measured. CYP2D6 metabolizer status was classified as ultra-rapid (UM), extensive (EM), intermediate (IM), or poor (PM) based genotype of somatic DNA. Results: Dosage was escalated in 68 of 122 participants. On 20 mg tamoxifen, 24% had endoxifen levels below 15 nmol/L and this reduced to 6% following dose escalation. In over 50% of cases, there was no identified cause for low endoxifen. Low baseline endoxifen level, and not CYP2D6 metabolizer status, independently predicted reaching threshold targets for both the 15 nmol/L and 30 nmol/L targets (P = 0.04 and 0.003 respectively). The 15 nmol/L target was reached in all UM/EM and IM patients, 63% of PM patients, and 58% of those with baseline endoxifen of <10 nmol/L. There was no correlation between hot flash score and genotype or any tamoxifen metabolite level including endoxifen (R = 0.07). Conclusions: Low endoxifen on standard dose tamoxifen was the only independent predictor of failure to achieve potentially therapeutic levels. Trials examining tamoxifen dose escalation and breast cancer outcome should be guided by endoxifen levels alone, without reference to CYP2D6 genotype or presence of hot flashes. Clin Cancer Res; 22(13); 3164–71. ©2016 AACR. See related commentary by Hertz and Rae, p. 3121

Metformin-Mediated Bambi Expression in Hepatic Stellate Cells Induces Prosurvival Wnt/β-Catenin Signaling

AMP-activated protein kinase (AMPK) regulates lipid, cholesterol, and glucose metabolism in specialized metabolic tissues, such as muscle, liver, and adipose tissue. Agents that activate AMPK, such as metformin and 5-aminoimidazole-4-carboxamide-1-beta-4-ribofuranoside (AICAR), have beneficial effects on liver glucose and lipid metabolism. In addition, AMPK activation in proliferating hepatic stellate cells (HSC) induces growth arrest and inhibits hepatic fibrosis. As metformin and AICAR act in different ways to achieve their effects, our aim was to examine the effects of AMPK activation in quiescent HSCs with these two agents on HSC function. We found that phospho-AMPK levels were markedly upregulated by both AICAR and metformin in quiescent HSCs. However, although AICAR treatment induced cell death, cells treated with metformin did not differ from untreated controls. AICAR-mediated HSC cell death was paralleled by loss of expression of the TGF-β decoy receptor Bambi, whereas metformin increased Bambi expression. Transfection of siRNA-Bambi into HSCs also induced cell death, mimicking the effects of AICAR, whereas overexpression of Bambi partially rescued AICAR-treated cells. As Bambi has previously been shown to promote cell survival through Wnt/β-catenin signaling, a reporter incorporating binding sites for a downstream target of this pathway was transfected into HSCs and was induced. We conclude that although AICAR and metformin both activate AMPK in quiescent HSCs, AICAR rapidly induced cell death, whereas metformin-treated cells remained viable. The finding that metformin increases Bambi expression and activates Wnt/β-catenin signaling provides a possible mechanistic explanation for this observation. These results suggest that AICAR and metformin may confer disease-specific therapeutic benefits. Cancer Prev Res; 5(4); 553–61. ©2012 AACR.

Withholding parenteral nutrition during critical illness increases plasma bilirubin but lowers the incidence of biliary sludge

Cholestatic liver dysfunction (CLD) and biliary sludge often occur during critical illness and are allegedly aggravated by parenteral nutrition (PN). Delaying initiation of PN beyond day 7 in the intensive care unit (ICU) (late PN) accelerated recovery as compared with early initiation of PN (early PN). However, the impact of nutritional strategy on biliary sludge and CLD has not been fully characterized. This was a preplanned subanalysis of a large randomized controlled trial of early PN versus late PN (n = 4,640). In all patients plasma bilirubin (daily) and liver enzymes (alanine aminotransferase [ALT], aspartate aminotransferase [AST], gamma‐glutamyl transpeptidase [GGT], alkaline phosphatase [ALP], twice weekly; n = 3,216) were quantified. In a random predefined subset of patients, plasma bile acids (BAs) were also quantified at baseline and on days 3, 5, and last ICU‐day (n = 280). Biliary sludge was ultrasonographically evaluated on ICU‐day 5 (n = 776). From day 1 after randomization until the end of the 7‐day intervention window, bilirubin was higher in the late PN than in the early PN group (P < 0.001). In the late PN group, as soon as PN was started on day 8 bilirubin fell and the two groups became comparable. Maximum levels of GGT, ALP, and ALT were lower in the late PN group (P < 0.01). Glycine/taurine‐conjugated primary BAs increased over time in ICU (P < 0.01), similarly for the two groups. Fewer patients in the late PN than in the early PN group developed biliary sludge on day 5 (37% versus 45%; P = 0.04). Conclusion: Tolerating substantial caloric deficit by withholding PN until day 8 of critical illness increased plasma bilirubin but reduced the occurrence of biliary sludge and lowered GGT, ALP, and ALT. These results suggest that hyperbilirubinemia during critical illness does not necessarily reflect cholestasis and instead may be an adaptive response that is suppressed by early PN. (Hepatology 2014;60:202–210)

Modulation of the intestinal bile acid/farnesoid X receptor/fibroblast growth factor 15 axis improves alcoholic liver disease in mice

Alcoholic liver disease (ALD) is associated with changes in the intestinal microbiota. Functional consequences of alcohol‐associated dysbiosis are largely unknown. The aim of this study was to identify a mechanism of how changes in the intestinal microbiota contribute to ALD. Metagenomic sequencing of intestinal contents demonstrated that chronic ethanol feeding in mice is associated with an over‐representation of bacterial genomic DNA encoding choloylglycine hydrolase, which deconjugates bile acids in the intestine. Bile acid analysis confirmed an increased amount of unconjugated bile acids in the small intestine after ethanol administration. Mediated by a lower farnesoid X receptor (FXR) activity in enterocytes, lower fibroblast growth factor (FGF)‐15 protein secretion was associated with increased hepatic cytochrome P450 enzyme (Cyp)‐7a1 protein expression and circulating bile acid levels. Depletion of the commensal microbiota with nonabsorbable antibiotics attenuated hepatic Cyp7a1 expression and reduced ALD in mice, suggesting that increased bile acid synthesis is dependent on gut bacteria. To restore intestinal FXR activity, we used a pharmacological intervention with the intestine‐restricted FXR agonist fexaramine, which protected mice from ethanol‐induced liver injury. Whereas bile acid metabolism was only minimally altered, fexaramine treatment stabilized the gut barrier and significantly modulated hepatic genes involved in lipid metabolism. To link the beneficial metabolic effect to FGF15, a nontumorigenic FGF19 variant—a human FGF15 ortholog—was overexpressed in mice using adeno‐associated viruses. FGF19 treatment showed similarly beneficial metabolic effects and ameliorated alcoholic steatohepatitis. Conclusion: Taken together, alcohol‐associated metagenomic changes result in alterations of bile acid profiles. Targeted interventions improve bile acid–FXR–FGF15 signaling by modulation of hepatic Cyp7a1 and lipid metabolism, and reduce ethanol‐induced liver disease in mice. (Hepatology 2018;67:2150‐2166).

Cistromic and genetic evidence that the vitamin D receptor mediates susceptibility to latitude-dependent autoimmune diseases

The vitamin D receptor (VDR) is a ligand-activated transcription factor that regulates gene expression in many cell types, including immune cells. It requires binding of 1,25 dihydroxy vitamin D3 (1,25D3) for activation. Many autoimmune diseases show latitude-dependent prevalence and/or association with vitamin D deficiency, and vitamin D supplementation is commonly used in their clinical management. 1,25D3 is regulated by genes associated with the risk of autoimmune diseases and predominantly expressed in myeloid cells. We determined the VDR cistrome in monocytes and monocyte-derived inflammatory (DC1) and tolerogenic dendritic cells (DC2). VDR motifs were highly overrepresented in ChIP-Seq peaks in stimulated monocyte (40%), DC1 (21%) and DC2 (47%), P<E−100 for all. Of the nearly 11 000 VDR-binding peaks identified across the genome in DC1s, 1317 were shared with DC2s (91% of DC2 sites) and 1579 with monocytes (83% of monocyte sites). Latitude-dependent autoimmune disease risk polymorphisms were highly overrepresented within 5 kb of the peaks. Several transcription factor recognition motifs were highly overrepresented in the peaks, including those for the autoimmune risk gene, BATF. This evidence indicates that VDR regulates hundreds of myeloid cell genes and that the molecular pathways controlled by VDR in these cells are important in maintaining tolerance.