Daniel Gotthardt

Genome-Wide Association Analysis in Primary Sclerosing Cholangitis

BACKGROUND & AIMS We aimed to characterize the genetic susceptibility to primary sclerosing cholangitis (PSC) by means of a genome-wide association analysis of single nucleotide polymorphism (SNP) markers. METHODS A total of 443,816 SNPs on the Affymetrix SNP Array 5.0 (Affymetrix, Santa Clara, CA) were genotyped in 285 Norwegian PSC patients and 298 healthy controls. Associations detected in this discovery panel were re-examined in independent case-control panels from Scandinavia (137 PSC cases and 368 controls), Belgium/The Netherlands (229 PSC cases and 735 controls), and Germany (400 cases and 1832 controls). RESULTS The strongest associations were detected near HLA-B at chromosome 6p21 (rs3099844: odds ratio [OR], 4.8; 95% confidence interval [CI], 3.6-6.5; P = 2.6 x 10(-26); and rs2844559: OR, 4.7; 95% CI, 3.5-6.4; P = 4.2 x 10(-26) in the discovery panel). Outside the HLA complex, rs9524260 at chromosome 13q31 showed significant associations in 3 of 4 study panels. Lentiviral silencing of glypican 6, encoded at this locus, led to the up-regulation of proinflammatory markers in a cholangiocyte cell line. Of 15 established ulcerative colitis susceptibility loci, significant replication was obtained at chromosomes 2q35 and 3p21 (rs12612347: OR, 1.26; 95% CI, 1.06-1.50; and rs3197999: OR, 1.22; 95% CI, 1.02-1.47, respectively), with circumstantial evidence supporting the G-protein-coupled bile acid receptor 1 and macrophage-stimulating 1, respectively, as the likely disease genes. CONCLUSIONS Strong HLA associations and a subset of genes involved in bile homeostasis and other inflammatory conditions constitute key components of the genetic architecture of PSC.

Genome-wide association analysis in primary sclerosing cholangitis identifies two non-HLA susceptibility loci.

Primary sclerosing cholangitis (PSC) is a chronic bile duct disease affecting 2.4–7.5% of individuals with inflammatory bowel disease. We performed a genome-wide association analysis of 2,466,182 SNPs in 715 individuals with PSC and 2,962 controls, followed by replication in 1,025 PSC cases and 2,174 controls. We detected non-HLA associations at rs3197999 in MST1 and rs6720394 near BCL2L11 (combined P = 1.1 × 10−16 and P = 4.1 × 10−8, respectively).

Cellular uptake of fatty acids driven by the ER-localized acyl-CoA synthetase FATP4.

Long-chain fatty acids are important metabolites for the generation of energy and the biosynthesis of lipids. The molecular mechanism of their cellular uptake has remained controversial. The fatty acid transport protein (FATP) family has been named according to its proposed function in mediating this process at the plasma membrane. Here, we show that FATP4 is in fact localized to the endoplasmic reticulum and not the plasma membrane as reported previously. Quantitative analysis confirms the positive correlation between expression of FATP4 and uptake of fatty acids. However, this is dependent on the enzymatic activity of FATP4, catalyzing the esterification of fatty acids with CoA. Monitoring fatty acid uptake at the single-cell level demonstrates that the ER localization of FATP4 is sufficient to drive transport of fatty acids. Expression of a mitochondrial acyl-CoA synthetase also enhances fatty acid uptake, suggesting a general relevance for this mechanism. Our results imply that cellular uptake of fatty acids can be regulated by intracellular acyl-CoA synthetases. We propose that the enzyme FATP4 drives fatty acid uptake indirectly by esterification. It is not a transporter protein involved in fatty acid translocation at the plasma membrane.

Extended analysis of a genome-wide association study in primary sclerosing cholangitis detects multiple novel risk loci

BACKGROUND & AIMS A limited number of genetic risk factors have been reported in primary sclerosing cholangitis (PSC). To discover further genetic susceptibility factors for PSC, we followed up on a second tier of single nucleotide polymorphisms (SNPs) from a genome-wide association study (GWAS). METHODS We analyzed 45 SNPs in 1221 PSC cases and 3508 controls. The association results from the replication analysis and the original GWAS (715 PSC cases and 2962 controls) were combined in a meta-analysis comprising 1936 PSC cases and 6470 controls. We performed an analysis of bile microbial community composition in 39 PSC patients by 16S rRNA sequencing. RESULTS Seventeen SNPs representing 12 distinct genetic loci achieved nominal significance (p(replication) <0.05) in the replication. The most robust novel association was detected at chromosome 1p36 (rs3748816; p(combined)=2.1 × 10(-8)) where the MMEL1 and TNFRSF14 genes represent potential disease genes. Eight additional novel loci showed suggestive evidence of association (p(repl) <0.05). FUT2 at chromosome 19q13 (rs602662; p(comb)=1.9 × 10(-6), rs281377; p(comb)=2.1 × 10(-6) and rs601338; p(comb)=2.7 × 10(-6)) is notable due to its implication in altered susceptibility to infectious agents. We found that FUT2 secretor status and genotype defined by rs601338 significantly influence biliary microbial community composition in PSC patients. CONCLUSIONS We identify multiple new PSC risk loci by extended analysis of a PSC GWAS. FUT2 genotype needs to be taken into account when assessing the influence of microbiota on biliary pathology in PSC.

Electrochemical cues regulate assembly of the Frizzled/Dishevelled complex at the plasma membrane during planar epithelial polarization.

Dishevelled (Dsh) is a cytoplasmic multidomain protein that is required for all known branches of the Wnt signalling pathway. The Frizzled/planar cell polarity (Fz/PCP) signalling branch requires an asymmetric cortical localization of Dsh, but this process remains poorly understood. Using a genome-wide RNA interference (RNAi) screen in Drosophila melanogaster cells, we show that Dsh membrane localization is dependent on the Na+/H+ exchange activity of the plasma membrane exchanger Nhe2. Manipulating Nhe2 expression levels in the eye causes PCP defects, and Nhe2 interacts genetically with Fz. Our data show that the binding and surface recruitment of Dsh by Fz is pH- and charge-dependent. We identify a polybasic stretch within the Dsh DEP domain that binds to negatively charged phospholipids and appears to be mechanistically important. Dsh recruitment by Fz can be abolished by converting these basic amino-acid residues into acidic ones, as in the mutant, DshKR/E. In vivo, the DshKR/E(2×) mutant with two substituted residues fails to associate with the membrane during active PCP signalling but rescues canonical Wnt signalling defects in a dsh-background. These results suggest that direct interaction between Fz and Dsh is stabilized by a pH and charge-dependent interaction of the DEP domain with phospholipids. This stabilization is particularly important for the PCP signalling branch and, thus, promotes specific pathway selection in Wnt signalling.

Zinc Monotherapy Is Not as Effective as Chelating Agents in Treatment of Wilson Disease

BACKGROUND & AIMS Wilson disease is a genetic disorder that affects copper storage, leading to liver failure and neurologic deterioration. Patients are treated with copper chelators and zinc salts, but it is not clear what approach is optimal because there have been few studies of large cohorts. We assessed long-term outcomes of different treatments. METHODS Patients in tertiary care centers were retrospectively analyzed (n = 288; median follow-up time, 17.1 years) for adherence to therapy, survival, treatment failure, and adverse events from different treatment regimens (chelators, zinc, or a combination). Hepatic treatment failure was defined as an increase in activity of liver enzymes (aspartate aminotransferase, alanine aminotransferase, and γ-glutamyltransferase) >2-fold the upper limit of normal or >100% of baseline with an increase in urinary copper excretion. RESULTS The median age at onset of Wilson disease was 17.5 years. Hepatic and neuropsychiatric symptoms occurred in 196 (68.1%) and 99 (34.4%) patients, respectively. Hepatic treatment failure occurred more often from zinc therapy (14/88 treatments) than from chelator therapy (4/313 treatments; P < .001). Actuarial survival, without transplantation, showed an advantage for chelating agents (P < .001 vs zinc). Changes in treatment resulted mostly from adverse events, but the frequency did not differ between groups. Patients who did not respond to zinc therapy showed hepatic improvement after reintroduction of a chelating agent. CONCLUSIONS Treatments with chelating agents or zinc salt are effective in most patients with Wilson disease; chelating agents are better at preventing hepatic deterioration. It is important to identify patients who do not respond to zinc therapy and have increased activities of liver enzymes, indicating that a chelating agent should be added to the therapeutic regimen.

Alterations of phospholipid concentration and species composition of the intestinal mucus barrier in ulcerative colitis: a clue to pathogenesis.

Background: Phospholipids are essential for the normal function of the intestinal mucus barrier. The objective of this study was to systematically investigate phospholipids in the intestinal mucus of humans suffering from inflammatory bowel diseases, where a barrier defect is strongly supposed to be pathogenetic. Methods: Optimal mucus recovery was first validated in healthy mice and the method was then transferred to the endoscopic acquisition of ileal and colonic mucus from 21 patients with ulcerative colitis (UC), 10 patients with Crohns disease (CD), and 29 healthy controls. Nano‐electrospray ionization tandem mass spectrometry (ESI‐MS/MS) was used to determine phosphatidylcholine (PC), lysophosphatidylcholine (LPC), and sphingomyelin (SM) in lipid extracts of mucus specimens. Results: Human and rodent mucus contained very similar phospholipid species. In the ileal and colonic mucus from patients suffering from UC, the concentration of PC was highly significantly lower (607 ± 147 pmol/100 &mgr;g protein and 745 ± 148 pmol/100 &mgr;g protein) compared to that of patients with CD (3223 ± 1519 pmol/100 &mgr;g protein and 2450 ± 431 pmol/100 &mgr;g protein) and to controls (3870 ± 760 pmol/100 &mgr;g protein and 2790 ± 354 pmol/100 &mgr;g protein); overall, P = 0.0002 for ileal specimens and P < 0.0001 for colonic specimens. Independent of disease activity, patients suffering from UC showed an increased saturation grade of PC fatty acid residues and a higher LPC‐to‐PC ratio. Conclusions: The intestinal mucus barrier of patients with UC is significantly altered concerning its phospholipid concentration and species composition. These alterations may be very important for the pathogenesis of this disease and underline new therapeutic strategies. Inflamm Bowel Dis 2009

Influence of dominant bile duct stenoses and biliary infections on outcome in primary sclerosing cholangitis

BACKGROUND/AIMS In primary sclerosing cholangitis (PSC) dominant stenoses are frequently associated with bacterial, and in part, also fungal infections of the bile ducts. In the present study, the influence of dominant stenoses and of biliary infections on the long-term outcome was studied. METHODS In a prospective study, 171 patients were followed up for 20 years. All patients were treated with ursodeoxycholic acid. Dominant stenoses were treated endoscopically and during endoscopic procedures, bile was obtained for microbiologic analysis. RESULTS Of the 171 patients, 97 had or developed major bile duct stenoses and 96/97 were treated endoscopically. In the 55/97 patients with dominant stenosis, bile samples were obtained and of these, 41/55 had bacteria, five had also Candida and 2/55 had only Candida in their bile. Survival free of liver transplantation in patients without dominant stenosis at 18 years was 73.1% and of patients with dominant stenosis was 25.0% (p=0.011). Bacteria in bile had no effect on survival whereas Candida in bile was associated with reduced survival (p=0.025). CONCLUSIONS In patients with dominant stenosis, survival free of liver transplantation is reduced. Bacteria in bile do not worsen the outcome if dominant stenoses are opened endoscopically and infection is adequately treated with antibiotics. Candida in bile is associated with a poor prognosis and these patients need liver transplantation relatively soon.

Endoscopic dilation of dominant stenoses in primary sclerosing cholangitis: outcome after long-term treatment

BACKGROUND Primary sclerosing cholangitis is characterized by progressive fibrotic inflammation and obliteration of intra- and/or extrahepatic bile ducts. Total or subtotal stenoses of major bile ducts are associated with reduced survival. OBJECTIVE To evaluate the outcome after long-term endoscopic treatment. DESIGN Prospective, single-center study. SETTING Tertiary care academic medical center. PATIENTS A total of 171 patients treated with ursodeoxycholic acid were followed for as long as 20 years. At entry, 20 patients had dominant stenoses, and during a median follow-up period of 7.1 years, dominant stenosis developed in another 77. INTERVENTIONS Ninety-six patients with dominant stenoses were treated by repeated balloon dilation; 5 patients with complete obstruction with bacterial cholangitis were stented. MAIN OUTCOME MEASUREMENTS Survival free of liver transplantation, number of procedures, complications. RESULTS In total, 500 balloon dilations were performed and 5 stents were placed. Complications were pancreatitis (2.2%), bacterial cholangitis (1.4%), and bile duct perforation (0.2%); there were no deaths. Repeated endoscopic interventions allowed the preservation of a functioning common bile duct and of at least 1 hepatic duct up to 2 cm above the bifurcation in all patients. Progression of intrahepatic bile duct and liver disease led to the need for liver transplantation in 22 of 96 patients. Five years after the first dilation of a dominant stenosis, the survival free of liver transplantation rate was 81%, and after 10 years, it was 52%. LIMITATIONS Single-center study, no control group, primary end-stage liver disease excluded. CONCLUSION Repeated endoscopic balloon dilations of dominant stenoses allow the preservation of a functioning common bile duct for many years.

Genome-Wide Association Analysis in Primary Sclerosing Cholangitis and Ulcerative Colitis Identifies Risk Loci at GPR35 and TCF4

Approximately 60%‐80% of patients with primary sclerosing cholangitis (PSC) have concurrent ulcerative colitis (UC). Previous genome‐wide association studies (GWAS) in PSC have detected a number of susceptibility loci that also show associations in UC and other immune‐mediated diseases. We aimed to systematically compare genetic associations in PSC with genotype data in UC patients with the aim of detecting new susceptibility loci for PSC. We performed combined analyses of GWAS for PSC and UC comprising 392 PSC cases, 987 UC cases, and 2,977 controls and followed up top association signals in an additional 1,012 PSC cases, 4,444 UC cases, and 11,659 controls. We discovered novel genome‐wide significant associations with PSC at 2q37 [rs3749171 at G‐protein‐coupled receptor 35 (GPR35); P = 3.0 × 10−9 in the overall study population, combined odds ratio [OR] and 95% confidence interval [CI] of 1.39 (1.24‐1.55)] and at 18q21 [rs1452787 at transcription factor 4 (TCF4); P = 2.61 × 10−8, OR (95% CI) = 0.75 (0.68‐0.83)]. In addition, several suggestive PSC associations were detected. The GPR35 rs3749171 is a missense single nucleotide polymorphism resulting in a shift from threonine to methionine. Structural modeling showed that rs3749171 is located in the third transmembrane helix of GPR35 and could possibly alter efficiency of signaling through the GPR35 receptor. Conclusion: By refining the analysis of a PSC GWAS by parallel assessments in a UC GWAS, we were able to detect two novel risk loci at genome‐wide significance levels. GPR35 shows associations in both UC and PSC, whereas TCF4 represents a PSC risk locus not associated with UC. Both loci may represent previously unexplored aspects of PSC pathogenesis. (HEPATOLOGY 2013;58:1074–1083)