Intestinal nuclear receptor signaling in cystic fibrosis

Cystische fibrose (CF) is een complexe ziekte waarin de functionaliteit van het gastro-intestinale systeem, samen met het respiratoire systeem, een cruciale rol speelt in de prognose van de patiënt. De pathogenese van verschillende gastro-intestinale manifestaties van CF, zoals bacteriële overgroei in de dunne darm, dysbiose en een verhoogde fecale galzuur (GZ) uitscheiding, is nog niet volledig opgehelderd. Voor dit proefschrift was het doel om meer inzicht te krijgen in de pathofysiologie van de gastro-intestinale manifestaties van CF en op deze manier mogelijk ook nieuwe doelwitten voor therapie te ontdekken. Specifiek hebben wij ons gericht op signaaltransductie via intestinale nucleaire receptoren in CF, aangezien het bekend is dat deze ligand geactiveerde nucleaire receptoren belangrijke regulatoren zijn van het metabolisme. In hoofdstuk 2 evalueren we de functie van PPARδ in de darm aangezien er aanwijzingen zijn dat PPARδ een belangrijke rol speelt in CF gerelateerde bacteriële dysbiose. Verder onderzoeken we in hoofdstuk 3-5 de problemen van het GZ metabolisme bij CF en de rol van FXR signaaltransductie hierin. In hoofdstuk 6 wordt de rol van de enterohepatische kringloop van GZ in andere intestinale processen in meer detail bekeken. Concluderend, de studies beschreven in dit proefschrift laten zien dat de darm een belangrijk doelwit is voor behandelingen, zowel met betrekking tot CF als andere ziekten zoals hypercholesterolemie. We speculeren dat met name niet-absorbeerbare medicijnen aantrekkelijk zijn om dat ze lokaal in de darm activiteit kunnen uitoefenen met geringe systemische toxiciteit. We denken dat synthetische of natuurlijke liganden voor intestinale nucleaire receptoren grote potentie hebben om uit te groeien als effectieve behandelingen voor CF en het metabool syndroom

Intestinal nuclear receptor signaling in cystic fibrosis

Cystische fibrose (CF) is een complexe ziekte waarin de functionaliteit van het gastro-intestinale systeem, samen met het respiratoire systeem, een cruciale rol speelt in de prognose van de patiënt. De pathogenese van verschillende gastro-intestinale manifestaties van CF, zoals bacteriële overgroei in de dunne darm, dysbiose en een verhoogde fecale galzuur (GZ) uitscheiding, is nog niet volledig opgehelderd. Voor dit proefschrift was het doel om meer inzicht te krijgen in de pathofysiologie van de gastro-intestinale manifestaties van CF en op deze manier mogelijk ook nieuwe doelwitten voor therapie te ontdekken. Specifiek hebben wij ons gericht op signaaltransductie via intestinale nucleaire receptoren in CF, aangezien het bekend is dat deze ligand geactiveerde nucleaire receptoren belangrijke regulatoren zijn van het metabolisme. In hoofdstuk 2 evalueren we de functie van PPARδ in de darm aangezien er aanwijzingen zijn dat PPARδ een belangrijke rol speelt in CF gerelateerde bacteriële dysbiose. Verder onderzoeken we in hoofdstuk 3-5 de problemen van het GZ metabolisme bij CF en de rol van FXR signaaltransductie hierin. In hoofdstuk 6 wordt de rol van de enterohepatische kringloop van GZ in andere intestinale processen in meer detail bekeken. Concluderend, de studies beschreven in dit proefschrift laten zien dat de darm een belangrijk doelwit is voor behandelingen, zowel met betrekking tot CF als andere ziekten zoals hypercholesterolemie. We speculeren dat met name niet-absorbeerbare medicijnen aantrekkelijk zijn om dat ze lokaal in de darm activiteit kunnen uitoefenen met geringe systemische toxiciteit. We denken dat synthetische of natuurlijke liganden voor intestinale nucleaire receptoren grote potentie hebben om uit te groeien als effectieve behandelingen voor CF en het metabool syndroom

Impaired Intestinal Farnesoid X Receptor Signaling in Cystic Fibrosis Mice

BACKGROUND & AIMS: The bile acid (BA)-activated farnesoid X receptor (FXR) controls hepatic BA synthesis and cell proliferation via the intestinal hormone fibroblast growth factor 19. Because cystic fibrosis (CF) is associated with intestinal dysbiosis, anomalous BA handling, and biliary cirrhosis, we investigated FXR signaling in CF. METHODS: Intestinal and hepatic expression of FXR target genes and inflammation markers was assessed in Cftr null mice and controls. Localization of the apical sodium-dependent BA transporter was assessed, and BAs in gastrointestinal tissues were analyzed. The CF microbiota was characterized and FXR signaling was investigated in intestinal tissue and organoids. RESULTS: Ileal murine fibroblast growth factor 19 ortholog (Fgf15) expression was strongly reduced in CF mice, compared with controls. Luminal BA levels and localization of apical sodium-dependent BA transporter was not affected, and BAs induced Fgf15 up to normal levels in CF ileum, ex vivo, and CF organoids. CF mice showed a dysbiosis that was associated with a marked up-regulation of genes involved in host-microbe interactions, including those involved in mucin glycosylation, antimicrobial defense, and Toll-like receptor signaling. Antibiotic treatment reversed the up-regulation of inflammatory markers and restored intestinal FXR signaling in CF mice. Conversely, FXR-dependent gene induction in ileal tissue and organoids was repressed by bacterial lipopolysaccharide and proinflammatory cytokines, respectively. Loss of intestinal FXR activity was associated with a markedly blunted hepatic trophic response to oral BA supplementation, and with impaired repression of Cyp7a1, the gene encoding the rate-limiting enzyme in BA synthesis. CONCLUSIONS: In CF mice, the gut microbiota represses intestinal FXR activity, and, consequently, FXR-dependent hepatic cell proliferation and feedback control of BA synthesis

Defective FXR-FGF15 signaling and bile acid homeostasis in cystic fibrosis mice can be restored by the laxative polyethylene glycol

The gastrointestinal phenotype of cystic fibrosis (CF) features intestinal bile acid (BA) malabsorption, impaired intestinal farnesoid X receptor (FXR) activation, and consequently reduced fibroblast growth factor 19 (FGF19, FGF15 in mice) production. The osmotic laxative polyethylene glycol (PEG) has been shown to decrease intestinal mucus accumulation in CF mice and could, by doing so, improve BA reabsorption. Here we determined the effect of PEG on BA excretion and FXR-FGF15 signaling in CF mice. Male Cftr(-/-tm1Unc) (CF) and wild-type (WT) littermates were administered PEG 4000 in drinking water and fed either chow or a semisynthetic diet. PEG was withdrawn for 3 days before termination. Fecal BA excretion was measured at PEG dosages of 37 g/l (100%) and 0 g/l (0%). Ileal FXR activation was assessed by gene expression of its downstream targets Fgf15 and small heterodimer partner (Shp). In CF mice, PEG withdrawal increased fecal BA excretion on either diet compared with full PEG dosage (chow, 2-fold, P = 0.06; semisynthetic, 4.4-fold, P = 0.007). PEG withdrawal did not affect fecal BA excretion in WT mice on either diet. After PEG withdrawal, gene expression levels of intestinal FXR target genes Fgf15 and Shp were decreased in CF mice but unaffected in WT littermates. PEG did not affect the gene expression of the main intestinal BA transporter apical sodium-dependent bile acid transporter (ASBT). PEG treatment ameliorates intestinal BA malabsorption in CF mice and restores intestinal FXR-FGF15 signaling, independent from Asbt gene expression. These findings highlight the potential of PEG in the prevention and treatment of the gastrointestinal phenotype of CF.NEW &amp; NOTEWORTHY A gastrointestinal feature of cystic fibrosis is bile acid malabsorption and consequent impairment of farnesoid X receptor (FXR)-fibroblast growth factor 15 (FGF15) signaling. FXR-FGF15 signaling regulates various metabolic processes and could be implicated in metabolic and gastrointestinal complications of cystic fibrosis, such as diabetes and liver disease. In cystic fibrosis mice, treatment with the osmotic laxative polyethylene glycol is associated with decreased fecal bile acid loss and restoration of FXR-FGF15 signaling.</p

Novel role of a triglyceride-synthesizing enzyme:DGAT1 at the crossroad between triglyceride and cholesterol metabolism

AbstractAcyl-CoA:diacylglycerol acyltransferase 1 (DGAT1) is a key enzyme in triacylglycerol (TG) biosynthesis. Here we show that genetic deficiency and pharmacological inhibition of DGAT1 in mice alters cholesterol metabolism. Cholesterol absorption, as assessed by acute cholesterol uptake, was significantly decreased in the small intestine and liver upon DGAT1 deficiency/inhibition. Ablation of DGAT1 in the intestine (I-DGAT1−/−) alone is sufficient to cause these effects. Consequences of I-DGAT1 deficiency phenocopy findings in whole-body DGAT1−/− and DGAT1 inhibitor-treated mice. We show that deficiency/inhibition of DGAT1 affects cholesterol metabolism via reduced chylomicron size and increased trans-intestinal cholesterol excretion. These effects are independent of cholesterol uptake at the apical surface of enterocytes but mediated through altered dietary fatty acid metabolism. Our findings provide insight into a novel role of DGAT1 and identify a pathway by which intestinal DGAT1 deficiency affects whole-body cholesterol homeostasis in mice. Targeting intestinal DGAT1 may represent a novel approach for treating hypercholesterolemia

Impaired Intestinal Farnesoid X Receptor Signaling in Cystic Fibrosis Mice

Background & Aims: The bile acid (BA)-activated farnesoid X receptor (FXR) controls hepatic BA synthesis and cell proliferation via the intestinal hormone fibroblast growth factor 19. Because cystic fibrosis (CF) is associated with intestinal dysbiosis, anomalous BA handling, and biliary cirrhosis, we investigated FXR signaling in CF. Methods: Intestinal and hepatic expression of FXR target genes and inflammation markers was assessed in Cftr null mice and controls. Localization of the apical sodium-dependent BA transporter was assessed, and BAs in gastrointestinal tissues were analyzed. The CF microbiota was characterized and FXR signaling was investigated in intestinal tissue and organoids. Results: Ileal murine fibroblast growth factor 19 ortholog (Fgf15) expression was strongly reduced in CF mice, compared with controls. Luminal BA levels and localization of apical sodium-dependent BA transporter was not affected, and BAs induced Fgf15 up to normal levels in CF ileum, ex vivo, and CF organoids. CF mice showed a dysbiosis that was associated with a marked up-regulation of genes involved in host–microbe interactions, including those involved in mucin glycosylation, antimicrobial defense, and Toll-like receptor signaling. Antibiotic treatment reversed the up-regulation of inflammatory markers and restored intestinal FXR signaling in CF mice. Conversely, FXR-dependent gene induction in ileal tissue and organoids was repressed by bacterial lipopolysaccharide and proinflammatory cytokines, respectively. Loss of intestinal FXR activity was associated with a markedly blunted hepatic trophic response to oral BA supplementation, and with impaired repression of Cyp7a1, the gene encoding the rate-limiting enzyme in BA synthesis. Conclusions: In CF mice, the gut microbiota represses intestinal FXR activity, and, consequently, FXR-dependent hepatic cell proliferation and feedback control of BA synthesis

IVACAFTOR restores FGF19 regulated bile acid homeostasis in cystic fibrosis patients with an S1251N or a G551D gating mutation

Objective: Disruption of the enterohepatic circulation of bile acids (BAs) is part of the gastrointestinal phenotype of cystic fibrosis (CF). Ivacaftor (VX-770), a cystic fibrosis transmembrane conductance regulator (CFTR) potentiator, improves pulmonary function in CF patients with class III gating mutations. We studied the effect of ivacaftor on the enterohepatic circulation by assessing markers of BA homeostasis and their changes in CF patients. Methods: In CF patients with an S1251N mutation (N = 16; age 9–35 years S125N study/NTR4873) or a G551D mutation (N = 101; age 10–24 years; GOAL study/ NCT01521338) we analyzed plasma fibroblast growth factor 19 (FGF19) and 7α-hydroxy-4-cholesten-3-one (C4) levels, surrogate markers for intestinal BA absorption and hepatic synthesis, respectively, before and after treatment with ivacaftor. Results: At baseline, median FGF19 was lower (52% and 53%, P <.001) and median C4 higher (350% and 364%, P <.001), respectively, for the S1251 N and G551D mutation patient groups compared to healthy controls. Treatment with ivacaftor significantly increased FGF19 and reduced C4 levels towards normalization in both cohorts but this did not correlate with CFTR function in other organs, as measured by sweat chloride levels or pulmonary function. Conclusions: We demonstrate that patients with CFTR gating mutations display interruption of the enterohepatic circulation of BAs reflected by lower FGF19 and elevated C4 levels. Treatment with ivacaftor partially restored this disruption of BA homeostasis. The improvement did not correlate with established outcome measures of CF, suggesting involvement of modulating factors of CFTR correction in different organs

Altered intestinal bile salt biotransformation in a cystic fibrosis (Cftr(-/-)) mouse model with hepato-biliary pathology

Background: Cftr(-/-tm1UC) mice develop progressive hepato-biliary pathology. We hypothesize that this liver pathology is related to alterations' in biliary bile hydrophobicity and bile salt metabolism in Cftr(-/-tm1Unc) mice. Methods: We determined bile production, biliary and fecal bile salt- and lipid compositions and fecal bacterial composition of C57BL/6 J Cftr(-/-1Unc) and control mice. Results: We found no differences between the total biliary bile salt or lipid concentrations of Cfir(-/-) and controls. Compared to controls, Cftr(-/-) mice had a similar to 30% higher bile production and a low bile hydrophobicity, related to a similar to 7 fold higher concentration of the choleretic and hydrophilic bile salt ursocholate. These findings coexisted with a significantly smaller quantity of fecal Bacteroides bacteria. Conclusions: Liver pathology in Cftr(-/-tm1Unc) is not related to increased bile hydrophobicity. Cftr(-/-) mice do however display a biliary phenotype characterized by increased bile production and decreased biliary hydrophobicity. Our findings suggest Cftr dependent, alterations in intestinal bacterial biotransformation of bile salts. (C) 2014 Published by Elsevier B.V. on behalf of European Cystic Fibrosis Society