Gerald U Denk

University of Technology Munich, München, Bavaria, Germany

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Publications (32)105.48 Total impact

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    ABSTRACT: The transcription factor T-bet regulates the production of interferon-γ and cytotoxic molecules in effector CD8 T cells, and its expression correlates with improved control of chronic viral infections. However, the role of T-bet in infections with differential outcome remains poorly defined. Here, we report that high expression of T-bet in virus-specific CD8 T cells during acute hepatitis B virus (HBV) and hepatitis C virus (HCV) infection was associated with spontaneous resolution, whereas T-bet deficiency was more characteristic of chronic evolving infection. T-bet strongly correlated with interferon-γ production and proliferation of virus-specific CD8 T cells, and its induction by antigen and IL-2 stimulation partially restored functionality in previously dysfunctional T-bet-deficient CD8 T cells. However, restoration of a strong interferon-γ response required additional stimulation with IL-12, which selectively induced the phosphorylation of STAT4 in T-bet(+) CD8 T cells. The observation that T-bet expression rendered CD8 T cells responsive to IL-12 suggests a stepwise mechanism of T cell activation in which T-bet facilitates the recruitment of additional transcription factors in the presence of key cytokines. These findings support a critical role of T-bet for viral clearance and suggest T-bet deficiency as an important mechanism behind chronic infection.
    The Journal of experimental medicine. 09/2014;
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    ABSTRACT: Hepatic apoptosis is involved in the pathogenesis of immune-mediated liver diseases such as autoimmune hepatitis (AIH), primary biliary cirrhosis (PBC), and primary sclerosing cholangitis (PSC). The aim of our study was to quantify distinct markers of apoptosis in sera of patients with AIH, PBC, and PSC, and to evaluate correlation with markers of disease activity and prognosis. Sera of patients with AIH, PBC, and PSC, and of healthy controls were collected and distinct cell death markers were quantified using a bead-based multiplex enzyme linked immunosorbent assay (sICAM, MIF, sFas, PAI-1) or single enzyme linked immunosorbent assays (DNAse, M30, M65). In comparison with healthy controls the apoptotic markers sFas, sICAM (only in PSC patients), M30, and the cell death marker M65 were substantially elevated in sera of patients with immune-mediated liver diseases, whereas DNAse activity was reduced. Interestingly, patients with advanced PSC presented with higher levels of sICAM, M30, and M65 than patients with mild PSC. Regression analysis revealed correlations between serum levels of sICAM, M30, and M65 with the Mayo Risk Score for PSC, and of M65 with the Mayo Risk Score for PBC. Concentrations of the serum markers of apoptosis sFas and M30 and of the marker of total cell death M65 are elevated in patients with immune-mediated liver diseases, whereas activity of DNAse is reduced. In patients with PSC sICAM, M30, and M65 may serve as indicators for disease activity and prognosis.
    Hepatology Research 01/2014; · 2.07 Impact Factor
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    ABSTRACT: T-cell exhaustion seems to play a critical role in CD8+ T-cell dysfunction during chronic viral infections. However, up to now little is known about the mechanisms underlying CD4+ T-cell dysfunction during chronic hepatitis B virus (CHB) infection and the role of inhibitory molecules such as programmed death 1 (PD-1) for CD4+ T-cell failure.
    PLoS ONE 01/2014; 9(8):e105703. · 3.53 Impact Factor
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    ABSTRACT: Hydrophobic bile salts such as glycochenodeoxycholate (GCDC) accumulate in cholestatic liver disease and induce hepatocellular apoptosis, promoting pro-fibrotic signalling. The tissue microenvironment is an integral player in cellular pathophysiology, but it is not routinely incorporated into laboratory studies. Tissue oxygen partial pressure (pO2 ) may be an underestimated component of the microenvironment: in the liver, a pO2 of 30-45mmHg (approximately 6%O2 ) is physiologic, due to predominantly portal blood supply. It was the aim of this project to investigate the impact of physiologic hypoxia (i.e., 6%O2 ) on hepatocellular function, namely, bile salt-induced apoptosis. Human hepatoma cells (HepG2-Ntcp) and primary rat hepatocytes were cultured at standard laboratory (hyperoxic) conditions (21%O2 ) and at physiologic hypoxia (6%O2 ) in parallel for 1-8 days to study hepatocellular apoptosis and activation of signalling pathways. Standard laboratory analyses were applied for bile salt uptake, caspase-3/-7 activity, western blotting and gene-array analysis. Culturing at physiologic hypoxia protected both human and rat hepatocytes against GCDC-induced apoptosis: caspase-3/-7 activation was diminished by 3.1±0.5-fold in human HepG2-Ntcp and completely abolished in primary rat hepatocytes. Bile salt uptake was unaffected. Induction of hypoxia-inducible factor-1α indicated adaption to physiologic hypoxia. The MEK/ERK cascade was activated and anti-apoptotic mediators were induced: N-Myc down-regulated gene, gelsolin and carbonic anhydrase IX were upregulated 12.4-, 6.5- and 5.2-fold, respectively. We conclude from these data that (i) physiologic hypoxia protects hepatocytes from bile salt-induced apoptosis, (ii) tissue pO2 is a crucial, underestimated component of the microenvironment and should (iii) be considered when studying hepatocellular physiology in vitro. This article is protected by copyright. All rights reserved.
    Liver international: official journal of the International Association for the Study of the Liver 10/2013; · 3.87 Impact Factor
  • Hepatology Research 12/2012; 42(12):1252-4. · 2.07 Impact Factor
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    ABSTRACT: β-Muricholic acid (βMCA) is a trihydroxylated bile acid that constitutes the major bile acid in rat and mouse. βMCA is more hydrophilic than ursodeoxycholic acid and has been evaluated for dissolution of cholesterol gallstones. Since it is unknown if βMCA has beneficial effects on hepatocyte cell death we determined the effect of tauro-βMCA (TβMCA) on apoptosis in vitro. Human Ntcp-transfected HepG2 cells and primary hepatocytes from rat and mouse were incubated with the proapoptotic glycochenodeoxycholic acid (GCDCA) as well as the free fatty acid palmitate in the absence and presence of TβMCA. Apoptosis was quantified using caspase 3/7-assays and after Hoechst 33342 staining. The mitochondrial membrane potential (MMP) was measured fluorometrically using JC-1 (5,5',6,6'-tetrachloro-1,1',3,3'-tetraethyl-benzimidazol-carbocyaniniodide). Immunoblotting was performed against the proapoptotic Bcl-2-protein Bax. In Ntcp-HepG2 cells, GCDCA markedly increased apoptosis after 4h. Co-incubation with TβMCA reduced apoptosis to 49% (p<0.01 vs. GCDCA, each; n=6). While GCDCA (100μmol/L) reduced the MMP to 34% after 6h, combination treatment with TβMCA restored the MMP to control levels at all time points (n=4). TβMCA also restored breakdown of the MMP induced by palmitate. GCDCA induced a translocation of Bax from the cytosol to mitochondria that was inhibited by simultaneous treatment with TβMCA in eqimolar concentrations. TβMCA restricts hepatocellular apoptosis induced by low micromolar concentrations of GCDCA or palmitate via inhibition of Bax translocation to mitochondria and preservation of the MMP. Thus, further studies are warranted to evaluate a potential use of TβMCA in ameliorating liver injury in cholestasis.
    Biochemical and Biophysical Research Communications 07/2012; 424(4):758-64. · 2.28 Impact Factor
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    ABSTRACT: The chromosome 4q27 region harboring IL2 and IL21 is an established risk locus for ulcerative colitis (UC) and various other autoimmune diseases. Considering the strong coincidence of primary sclerosing cholangitis (PSC) with UC and the increased frequency of other autoimmune disorders in patients with primary biliary cirrhosis (PBC), we investigated whether genetic variation in the IL2/IL21 region may also modulate the susceptibility to these two rare cholestatic liver diseases. Four strongly UC-associated single nucleotide polymorphisms (SNPs) within the KIAA1109/TENR/IL2/IL21 linkage disequilibrium block were genotyped in 124 PBC and 41 PSC patients. Control allele frequencies from 1,487 healthy, unrelated Caucasians were available from a previous UC association study. The minor alleles of all four markers were associated with a decreased susceptibility to PSC (rs13151961: p = 0.013, odds ratio (OR) 0.34; rs13119723: p = 0.023, OR 0.40; rs6822844: p = 0.031, OR 0.41; rs6840978: p = 0.043, OR 0.46). Moreover, a haplotype consisting of the four minor alleles also had a protective effect on PSC susceptibility (p = 0.0084, OR 0.28). A haplotype of the four major alleles was independently associated with PSC when excluding the patients with concomitant inflammatory bowel disease (p = 0.033, OR 4.18). The IL2/IL21 region may be one of the highly suggestive but so far rarely identified shared susceptibility loci for PSC and UC.
    Digestion 02/2011; 84(1):29-35. · 1.94 Impact Factor
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    ABSTRACT: Bei jungen Patienten mit rezidivierenden Gallenkoliken trotz Cholezystektomie und begleitender Leberwerterhöhung stellt das „low phospholipid associated cholelithiasis“ (LPAC-) Syndrom eine wichtige Differenzialdiagnose dar. Hinweisend für ein LPAC-Syndrom ist ein Symptomenkomplex aus Beschwerderekurrenz nach Cholezystektomie, echoreichen intrahepatischen Foki in der Abdomensonographie, Auftreten einer intrahepatischen Schwangerschaftscholestase bzw. das Auftreten einer Cholestase unter hormoneller Antikonzeption sowie familiär gehäuften Gallensteinen. Bei rechtzeitiger Diagnose ist die Erkrankung mit Ursodeoxycholsäure gut zu therapieren. “Low phospholipid associated cholelithiasis” (LPAC) syndrome is an important differential diagnosis in younger patients with biliary symptoms after cholecystectomy and concomitant elevated serum liver tests. Typical symptoms include recurrence of biliary colics after cholecystectomy, echogenic material in the intrahepatic bile ducts, intrahepatic cholestasis of pregnancy or cholestasis under hormonal contraception and a family history of gallstone disease. Patients with LPAC syndrome can be successfully treated with ursodeoxycholic acid. SchlüsselwörterGenetik–Hepatopathie–Intrahepatische Konkremente–LPAC-Syndrom–Ursodeoxycholsäure KeywordsGenetics–Hepatopathy–Intrahepatic cholelithiasis–LPAC syndrome–Ursodeoxycholic acid
    Der Internist 01/2011; 52(10):1234-1237. · 0.33 Impact Factor
  • Journal of Hepatology - J HEPATOL. 01/2011; 54.
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    ABSTRACT: The ATP-binding cassette transporter A1 (ABCA1) is a membrane-bound protein that is abundant in macrophages and is essential for the first step of reverse cholesterol transport and maintenance of homeostasis of high-density lipoprotein (HDL)-bound cholesterol. Low serum HDL levels are associated with increased risk for cardiovascular disease. Homozygous and heterozygous mutations in the ABCA1 gene may be associated with increased atherosclerosis. Here we report about two heterozygous mutations c.5398A>C and c.2369G>A in the ABCA1 gene associated with HDL cholesterol deficiency in serum.
    Experimental and Clinical Endocrinology & Diabetes 01/2011; 119(1):53-5. · 1.56 Impact Factor
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    ABSTRACT: "Low phospholipid associated cholelithiasis" (LPAC) syndrome is an important differential diagnosis in younger patients with biliary symptoms after cholecystectomy and concomitant elevated serum liver tests. Typical symptoms include recurrence of biliary colics after cholecystectomy, echogenic material in the intrahepatic bile ducts, intrahepatic cholestasis of pregnancy or cholestasis under hormonal contraception and a family history of gallstone disease. Patients with LPAC syndrome can be successfully treated with ursodeoxycholic acid.
    Der Internist 12/2010; 52(10):1234-7. · 0.33 Impact Factor
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    ABSTRACT: NorUDCA (24-norursodeoxycholic acid), the C₂₃-homolog of ursodeoxycholic acid (UDCA), showed remarkable therapeutic effects in cholestatic Mdr2 (Abcb4) (multidrug resistance protein 2/ATP-binding cassette b4) knockout mice with sclerosing/fibrosing cholangitis. In contrast to UDCA, norUDCA is inefficiently conjugated in human and rodent liver, and conjugation has been discussed as a key step for the anticholestatic action of UDCA in cholestasis. We compared the choleretic, anticholestatic, and antiapoptotic properties of unconjugated and taurine-conjugated UDCA (C₂₄) and norUDCA (C₂₃) in isolated perfused rat liver (IPRL) and in natrium/taurocholate cotransporting polypeptide (Ntcp)-transfected human hepatoma (HepG2) cells. Taurolithocholic acid (TLCA) was used to induce a predominantly hepatocellular cholestasis in IPRL. Bile flow was determined gravimetrically; bile acids determined by gas chromatography and liquid chromatography/tandem mass spectrometry; the Mrp2 model substrate, 2,4-dinitrophenyl-S-glutathione (GS-DNP) was determined spectrophotometrically; and apoptosis was determined immunocytochemically. The choleretic effect of C₂₃-bile acids was comparable to their C₂₄-homologs in IPRL. In contrast, TnorUDCA, but not norUDCA antagonized the cholestatic effect of TLCA. Bile flow (percent of controls) was 8% with TLCA-induced cholestasis, and unchanged by coinfusion of norUDCA (14%). However, it was increased by TnorUDCA (83%), UDCA (73%) and TUDCA (136%). Secretion of GS-DNP was markedly reduced by TLCA (5%), unimproved by norUDCA (4%) or UDCA (17%), but was improved modestly by TnorUDCA (26%) or TUDCA (58%). No apoptosis was observed in IPRL exposed to low micromolar TLCA, but equivalent antiapoptotic effects of TUDCA and TnorUDCA were observed in Ntcp-HepG2 cells exposed to TLCA. CONCLUSION: Conjugation is essential for the anticholestatic effect of norUDCA in a model of hepatocellular cholestasis. Combined therapy with UDCA and norUDCA may be superior to UDCA or norUDCA monotherapy in biliary disorders in which hepatocyte as well as cholangiocyte dysfunction contribute to disease progression.
    Hepatology 11/2010; 52(5):1758-68. · 12.00 Impact Factor
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    ABSTRACT: Gallstones are very common. However, there is a small group of patients with low phospholipid-associated cholelithiasis (LPAC) that is characterized by symptomatic cholelithiasis at a young age (<40 years), recurrence of biliary symptoms despite cholecystectomy and concrements or sludge in the intra- and extrahepatic biliary system. The LPAC syndrome is associated with mutations of the adenosine triphosphate-binding cassette, subfamily B, member 4 (ABCB4) gene encoding the hepatobiliary phospholipid translocator multidrug resistance protein 3 (MDR3). Impairment of MDR3 leads to a reduction of biliary phosphatidyl choline levels resulting in a lithogenic and toxic bile. This causes recurrent cholelithiasis, continuous irritations of the biliary tract with cholangitis, chronic cholestasis and even biliary cirrhosis. Here we report on a family with ABCB4 deficiency and LPAC syndrome associated with a novel mutation (c.3203T>A) in the ABCB4 gene.
    Hepatology Research 09/2010; 40(9):937-41. · 2.07 Impact Factor
  • Zeitschrift Fur Gastroenterologie - Z GASTROENTEROL. 01/2010; 48(08).
  • Zeitschrift Fur Gastroenterologie - Z GASTROENTEROL. 01/2010; 48(08).
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    ABSTRACT: Inactivation of the Fanconi anemia (FA) pathway through defects in one of 13 FA genes occurs at low frequency in various solid cancer entities among the general population. As FA pathway inactivation confers a distinct hypersensitivity towards DNA interstrand-crosslinking (ICL)-agents, FA defects represent rational targets for individualized therapeutic strategies. Except for pancreatic cancer, however, the prevalence of FA defects in gastrointestinal (GI) tumors has not yet been systematically explored. A panel of GI cancer cell lines was screened for FA pathway inactivation applying FANCD2 monoubiquitination and FANCD2/RAD51 nuclear focus formation and a newly identified FA pathway-deficient cell line was functionally characterized. The hepatocellular carcinoma (HCC) line HuH-7 was defective in FANCD2 monoubiquitination and FANCD2 nuclear focus formation but proficient in RAD51 focus formation. Gene complementation studies revealed that this proximal FA pathway inactivation was attributable to defective FANCC function in HuH-7 cells. Accordingly, a homozygous inactivating FANCC nonsense mutation (c.553C > T, p.R185X) was identified in HuH-7, resulting in partial transcriptional skipping of exon 6 and leading to the classic cellular FA hypersensitivity phenotype; HuH-7 cells exhibited a strongly reduced proliferation rate and a pronounced G2 cell cycle arrest at distinctly lower concentrations of ICL-agents than a panel of non-isogenic, FA pathway-proficient HCC cell lines. Upon retroviral transduction of HuH-7 cells with FANCC cDNA, FA pathway functions were restored and ICL-hypersensitivity abrogated. Analyses of 18 surgical HCC specimens yielded no further examples for genetic or epigenetic inactivation of FANCC, FANCF, or FANCG in HCC, suggesting a low prevalence of proximal FA pathway inactivation in this tumor type. As the majority of HCC are chemoresistant, assessment of FA pathway function in HCC could identify small subpopulations of patients expected to predictably benefit from individualized treatment protocols using ICL-agents.
    Molecular Cancer 01/2010; 9:127. · 5.13 Impact Factor
  • Digestion 01/2010; 82(4):262-4. · 1.94 Impact Factor
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    ABSTRACT: Aim: Ursodeoxycholic acid exerts anticholestatic effects in various cholestatic disorders and experimental models of cholestasis. Its taurine conjugate (TUDCA) stimulates bile salt secretion in isolated perfused rat livers (IPRL) under physiological, non-cholestatic conditions, in part by mitogen-activated protein kinase (MAPK)-dependent mechanisms. The role of MAPK in the anticholestatic effect of TUDCA, however, is unclear. Therefore, we studied the role of MAPK in the anticholestatic effect of TUDCA in IPRL and isolated rat hepatocytes (IRH) in taurolithocholic acid (TLCA)-induced cholestasis. Methods: Bile flow, biliary levels of 2,4-dinitrophenyl-S-glutathione (GS-DNP) as a marker of hepatobiliary organic anion secretion and activity of lactate dehydrogenase (LDH) in hepatovenous effluate as a marker of hepatocellular damage in IPRL perfused with TUDCA and/or TLCA were determined in the presence or absence of MAPK inhibitors. In addition, phosphorylation of Erk 1/2 and p38(MAPK) induced by TUDCA and/or TLCA was studied by Western immunoblot in IPRL and IRH. Results: TUDCA-induced bile flow was impaired by the Erk 1/2 inhibitor PD98059 in normal livers (-28%), but not in livers made cholestatic by TLCA. GS-DNP secretion was unaffected by PD98059 under both conditions. TUDCA-induced bile formation and organic anion secretion both in the presence and absence of TLCA were unaffected by the p38(MAPK) inhibitor SB202190. Erk 1/2 phosphorylation in liver tissue was unchanged after bile salt exposure for 70 min, but was transiently enhanced by TUDCA in IRH. Conclusion: MAPK do not mediate the anticholestatic effects of TUDCA in TLCA-induced cholestasis.
    Hepatology Research 08/2008; 38(7):717-26. · 2.07 Impact Factor
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    ABSTRACT: Ursodeoxycholic acid (UDCA) exerts anticholestatic effects in part by protein kinase C (PKC)-dependent mechanisms. Its taurine conjugate, TUDCA, is a cPKC alpha agonist. We tested whether protein kinase A (PKA) might contribute to the anticholestatic action of TUDCA via cooperative cPKC alpha-/PKA-dependent mechanisms in taurolithocholic acid (TLCA)-induced cholestasis. In perfused rat liver, bile flow was determined gravimetrically, organic anion secretion spectrophotometrically, lactate dehydrogenase (LDH) release enzymatically, cAMP response-element binding protein (CREB) phosphorylation by immunoblotting, and cAMP by immunoassay. PKC/PKA inhibitors were tested radiochemically. In vitro phosphorylation of the conjugate export pump, Mrp2/Abcc2, was studied in rat hepatocytes and human Hep-G2 hepatoma cells. In livers treated with TLCA (10 micromol/l)+TUDCA (25 micromol/l), combined inhibition of cPKC by the cPKC-selective inhibitor Gö6976 (100 nmol/l) or the non-selective PKC inhibitor staurosporine (10 nmol/l) and of PKA by H89 (100 nmol/l) reduced bile flow by 36% (p<0.05) and 48% (p<0.01), and secretion of the Mrp2/Abcc2 substrate, 2,4-dinitrophenyl-S-glutathione, by 31% (p<0.05) and 41% (p<0.01), respectively; bile flow was unaffected in control livers or livers treated with TUDCA only or TLCA+taurocholic acid. Inhibition of cPKC or PKA alone did not affect the anticholestatic action of TUDCA. Hepatic cAMP levels and CREB phosphorylation as readout of PKA activity were unaffected by the bile acids tested, suggesting a permissive effect of PKA for the anticholestatic action of TUDCA. Rat and human hepatocellular Mrp2 were phosphorylated by phorbol ester pretreatment and recombinant cPKC alpha, nPKC epsilon, and PKA, respectively, in a staurosporine-sensitive manner. UDCA conjugates exert their anticholestatic action in bile acid-induced cholestasis in part via cooperative post-translational cPKC alpha-/PKA-dependent mechanisms. Hepatocellular Mrp2 may be one target of bile acid-induced kinase activation.
    Gut 06/2008; 57(10):1448-54. · 10.73 Impact Factor
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    ABSTRACT: Ursodeoxycholic acid (UDCA) is used in the therapy of cholestatic liver diseases. Apoptosis induced by toxic bile acids plays an important role in the pathogenesis of liver injury during cholestasis and appears to be mediated by the human transcription factor AP-1. We aimed to study if TUDCA can decrease taurolitholic acid (TLCA)-induced apoptosis by modulating AP-1. TLCA (20 microM) upregulated AP-1 proteins cFos (26-fold) and JunB (11-fold) as determined by quantitative real-time PCR in HepG2-Ntcp hepatoma cells. AP-1 transcriptional activity increased by 300% after exposure to TLCA. cFos and JunB expression as well as AP-1 transcriptional activity were unaffected by TUDCA (75 microM). However, TUDCA significantly decreased TLCA-induced upregulation of cFos and JunB. Furthermore, TUDCA inhibited TLCA-induced AP-1 transcriptional activity and reduced TLCA-induced apoptosis. These data suggest that reversal of bile acid-induced AP-1 activation may be relevant for the antiapoptotic effect of TUDCA in liver cells.
    Biochemical and Biophysical Research Communications 03/2008; 367(1):208-12. · 2.28 Impact Factor

Publication Stats

247 Citations
105.48 Total Impact Points

Institutions

  • 2007–2008
    • University of Technology Munich
      • Medizinische Klinik und Poliklinik III - Hämatologie/Onkologie
      München, Bavaria, Germany
  • 2003–2007
    • Ludwig-Maximilians-University of Munich
      München, Bavaria, Germany
  • 2004–2006
    • Yale-New Haven Hospital
      New Haven, Connecticut, United States
    • Yale University
      • Yale Liver Center
      New Haven, CT, United States