Joseph A. Odin

Variants at IRF5-TNPO3, 17q12-21 and MMEL1 are associated with primary biliary cirrhosis

We genotyped individuals with primary biliary cirrhosis and unaffected controls for suggestive risk loci (genome-wide association P < 1 × 10−4) identified in a previous genome-wide association study. Combined analysis of the genome-wide association and replication datasets identified IRF5-TNPO3 (combined P = 8.66 × 10−13), 17q12-21 (combined P = 3.50 × 10−13) and MMEL1 (combined P = 3.15 × 10−8) as new primary biliary cirrhosis susceptibility loci. Fine-mapping studies showed that a single variant accounts for the IRF5-TNPO3 association. As these loci are implicated in other autoimmune conditions, these findings confirm genetic overlap among such diseases.

Increased prevalence of primary biliary cirrhosis near superfund toxic waste sites

Primary biliary cirrhosis (PBC) and primary sclerosing cholangitis (PSC) are uncommon liver diseases of unknown etiology. Reported clustering of PBC cases may be due to environmental factors. Individuals with PBC have a high prevalence of thyroid disease and thyroid disease is reportedly more prevalent near Superfund toxic waste sites (SFS). The objective of this study was to examine the prevalence and potential clustering of individuals with PBC and PSC near SFS. De‐identified clinical and demographic data were used to determine the observed prevalence for each New York City zip code (n = 174) and borough (n = 5) of patients with PBC (PBC‐OLT) or PSC (PSC‐OLT) who were listed for liver transplantation. The expected prevalence was calculated using Organ Procurement and Transfer Network (OPTN) and U.S. Census data. Both PBC‐OLT patients and patients not listed for liver transplantation (PBC‐MSSM) were included in the cluster analysis. Prevalence ratios of PBC‐OLT and PSC‐OLT cases were compared for each zip code and for each borough with regard to the proximity or density of SFS, respectively. SaTScan software was used to identify clusters of PBC‐OLT cases and PBC‐MSSM cases. Prevalence ratio of PBC‐OLT, not PSC‐OLT, was significantly higher in zip codes containing or adjacent to SFS (1.225 vs. 0.670, respectively, P = .025). The borough of Staten Island had the highest prevalence ratio of PBC‐OLT cases and density of SFS. Significant clusters of both PBC‐OLT and PBC‐MSSM were identified surrounding SFS. In conclusion, toxin exposure may be a risk factor influencing the clustering of PBC cases. (HEPATOLOGY 2006;43:525–531.)

Cyclin-dependent kinase inhibition by the KLF6 tumor suppressor protein through interaction with cyclin D1

Kruppel-like factor 6 (KLF6) is a tumor suppressor gene inactivated in prostate and colon cancers, as well as in astrocytic gliomas. Here, we establish that KLF6 mediates growth inhibition through an interaction with cyclin D1, leading to reduced phosphorylation of the retinoblastoma protein (Rb) at Ser795. Furthermore, introduction of KLF6 disrupts cyclin D1-cyclin-dependent kinase (cdk) 4 complexes and forces the redistribution of p21Cip/Kip onto cdk2, which promotes G1 cell cycle arrest. Our data suggest that KLF6 converges with the Rb pathway to inhibit cyclin D1/cdk4 activity, resulting in growth suppression.

Immunochip analyses identify a novel risk locus for primary biliary cirrhosis at 13q14, multiple independent associations at four established risk loci and epistasis between 1p31 and 7q32 risk variants

To further characterize the genetic basis of primary biliary cirrhosis (PBC), we genotyped 2426 PBC patients and 5731 unaffected controls from three independent cohorts using a single nucleotide polymorphism (SNP) array (Immunochip) enriched for autoimmune disease risk loci. Meta-analysis of the genotype data sets identified a novel disease-associated locus near the TNFSF11 gene at 13q14, provided evidence for association at six additional immune-related loci not previously implicated in PBC and confirmed associations at 19 of 22 established risk loci. Results of conditional analyses also provided evidence for multiple independent association signals at four risk loci, with haplotype analyses suggesting independent SNP effects at the 2q32 and 16p13 loci, but complex haplotype driven effects at the 3q25 and 6p21 loci. By imputing classical HLA alleles from this data set, four class II alleles independently contributing to the association signal from this region were identified. Imputation of genotypes at the non-HLA loci also provided additional associations, but none with stronger effects than the genotyped variants. An epistatic interaction between the IL12RB2 risk locus at 1p31and the IRF5 risk locus at 7q32 was also identified and suggests a complementary effect of these loci in predisposing to disease. These data expand the repertoire of genes with potential roles in PBC pathogenesis that need to be explored by follow-up biological studies.

Caspase induction by IgA antimitochondrial antibody: IgA-mediated biliary injury in primary biliary cirrhosis

Anti‐mitochondrial antibodies (AMAs) have long been recognized as a serological hallmark of primary biliary cirrhosis (PBC). Although high titers of immunoglobulin (Ig)A AMAs are found in bile, saliva, and urine of patients, a pathogenic role for this antibody has remained elusive. Functional studies of this IgA in general have been impeded by low quantities of antibody and the inability to recover antigen‐specific IgA in dimeric form. Using a newly defined synthetic group A. Streptococcus derived peptide, we purified large quantities of dimeric and monomeric IgA from patient sera. The purified IgA was incubated with Madine‐Darby canine kidney (MDCK) cells transfected with the human polymeric Ig receptor (pIgR) and the cells studied by flow cytometric analysis for binding of carboxyfluorescein conjugated VAD‐fmk peptide to activated caspase enzymes. A total of 87% of PBC patients that were anti‐PDC‐E2 positive had serum IgA that increased caspase activation in MDCK‐pIgR+ cells compared to serum‐derived IgA from controls with a maximum reaction 48 hours after addition of IgA. The titer of anti‐PDC‐E2 IgA among the PBC patients strongly correlated with caspase activation (cc = 0.88). Pre‐absorption of the IgA using recombinant 2‐oxo‐acid dehydrogenase complex significantly diminished this activation. IgG from the same PBC patients did not induce caspase activation. These data suggest that during transcytosis through pIgR‐positive cells, exposure to PDC‐E2‐specific dimeric IgA results in the initiation of caspase activation. In conclusion, we propose that due to an even greater concentration of dimeric IgA in biliary and mucosal secretions, constant transcytosis would render the exposed cells more susceptible to apoptosis resulting in subsequent bile duct damage. (HEPATOLOGY 2004;39:1415–1422.)

Association of primary biliary cirrhosis with variants in the CLEC16A, SOCS1, SPIB and SIAE immunomodulatory genes

We fine mapped two primary biliary cirrhosis (PBC) risk loci, CLEC16A (C-type lectin domain family 16 member A)–suppressor of cytokine signaling 1 (SOCS1) and Spi-B protein (SPIB) and sequenced a locus, sialic acid acetylesterase (SIAE), proposed to harbor autoimmunity-associated mutations. In all, 1450 PBC cases and 2957 healthy controls were genotyped for 84 single-nucleotide polymorphisms (SNPs) across the CLEC16A-SOCS1 and SPIB loci. All 10 exons of the SIAE gene were resequenced in 381 cases and point substitutions of unknown significance assayed for activity and secretion. Fine mapping identified 26 SNPs across the CLEC16A-SOCS1 and 11 SNPs across the SPIB locus with significant association to PBC, the strongest signals at the CLEC16A-SOCS1 locus emanating from a SOCS1 intergenic SNP (rs243325; P=9.91 × 10−9) and at the SPIB locus from a SPIB intronic SNP (rs34944112; P=3.65 × 10−9). Among the associated SNPs at the CLEC16A-SOCS1 locus, two within the CLEC16A gene as well as one SOCS1 SNP (rs243325) remained significant after conditional logistic regression and contributed independently to risk. Sequencing of the SIAE gene and functional assays of newly identified variants revealed six patients with functional non-synonymous SIAE mutations (Fishers P=9 × 10−4 vs controls) We demonstrate independent effects on risk of PBC for CLEC16A, SOCS1 and SPIB variants, while identifying functionally defective SIAE variants as potential factors in risk for PBC.

Kupffer cell activation by ambient air particulate matter exposure may exacerbate non-alcoholic fatty liver disease

Owing to increased obesity, non-alcoholic fatty liver disease (NAFLD) is now the most prevalent liver disease in the United States. NAFLD is considered a component of metabolic syndrome, a cluster of disorders that also includes diabetes mellitus, dyslipidemia, arteriosclerosis, and hypertension. Exposure to ambient air particulate matter with aerodynamic diameters < 2.5 μm (PM2.5) is a risk factor for arteriosclerosis and lung disease, but its effect on NAFLD is unknown. PM2.5 induces pulmonary dysfunction via Toll-like receptor (TLR) activation on alveolar macrophages. TLR activation of Kupffer cells, resident hepatic macrophages, and subsequent pro-inflammatory cytokine production have been shown to play a key role in NAFLD progression. We hypothesized that PM2.5 exposure is a significant risk factor for the progression of NAFLD. Thus, following exposure of male C57BL/6 mice fed high fat chow (HFC) to concentrated air particulate matter (CAPs) or filtered air for 6 weeks, progression of NAFLD was evaluated by standardized histological assessment of hepatic inflammation and fibrosis. In mice fed HFC, the hepatic inflammatory grade (3.00 ± 0.00 vs. 1.50 ± 0.71, P < 0.001) and fibrosis stage (1.00 ± 0.00 vs. 0.60 ± 0.52, P = 0.023) were both significantly higher in mice exposed to CAPs versus filtered air, respectively. Increased numbers of Kupffer cells contained PM in CAPs-exposed mice scores of (2.00 ± 0.94 vs. 0.20 ± 0.42, respectively, P < 0.001). PM exposure increased IL-6 secretion up to seven-fold in a dose-dependent manner by isolated wild-type but not TLR4−/− Kupffer cells (P < 0.050). In conclusion, ambient PM2.5 exposure may be a significant risk factor for NAFLD progression.

Apoptosis and the liver: relation to autoimmunity and related conditions.

Apoptosis is a normal physiologic form of cell death that follows activation of either an intrinsic or extrinsic pathway. In the intrinsic, various stimuli, such as oxidative stress, lead to mitochondrial dysfunction and the release of pro-apoptotic factors. Ligand binding to cell surface death receptors, such as Fas, activates the extrinsic pathway. Due to the rapid clearance of apoptotic cells, detection and quantification of apoptotic cells is prone to underestimation. In the liver, the importance of apoptosis is evident both during development and homeostasis of the biliary tree. Apoptosis also plays a prominent role in liver pathogenesis. Induction of the extrinsic apoptotic pathway by cytotoxic lymphocytes predominates in autoimmune liver diseases, viral hepatitis, and liver allograft rejection. Biliary cell apoptosis is highly regulated by bcl-2 family members. Both the extrinsic and intrinsic pathways are active in alcohol-related liver disease. Overexpression of anti-apoptotic proteins and FasL allow liver tumor cells to evade tumor specific cytotoxic lymphocytes. Agents that modulate apoptosis may be of future therapeutic benefit in a number of liver diseases.

Evaluation of fatigue in U.S. patients with primary biliary cirrhosis

OBJECTIVES:Fatigue, which may have a significant impact on quality of life, is the most common reported symptom in primary biliary cirrhosis (PBC). Multiple instruments to quantify fatigue and quality of life in liver disease have been validated, but have not been broadly applied to U.S. PBC patients. This study examines the extent of fatigue and its effect on quality of life in U.S. PBC patients.METHODS:Seventy patients with PBC were administered two validated questionnaires about quality of life (the Mayo version of the NIDDK-QA) and fatigue (the Fisk Fatigue Impact Score) and a proposed physical measure of fatigue in PBC (the grip strength test) on the day of routine physician visit. Nonparametric methods were employed.RESULTS:The fatigue and quality of life domain scores (physical functioning, liver symptoms, health satisfaction, Karnofsky index) discriminated between patients with and without self-reported fatigue (p < 0.05), as opposed to the grip strength results. Fatigue and quality of life domains correlated strongly with each other (r between 0.33 and 0.74, p ≤ 0.006) and not with the grip strength results. Neither quality of life nor fatigue scores correlated with age.CONCLUSIONS:The correlation between fatigue and quality of life scores suggests fatigue has an impact on quality of life in U.S. primary biliary cirrhosis patients. However, our fatigue scores suggest U.S. PBC patients have less fatigue than non-U.S. PBC patients. The grip strength is an insensitive measure of fatigue in U.S. PBC patients.

Toll-like receptors and liver disease

Toll‐like receptors (TLRs) are pattern recognition receptors that play an important role in host defence by recognizing pathogen‐associated molecular patterns (PAMP). Recent studies indicate that TLR signalling plays an important role in progression of chronic liver diseases. Ongoing clinical trials suggest that therapeutic manipulation of TLR pathways may offer novel means of reversing chronic liver diseases. Upon activation by their respective ligands, TLRs initiate an intracellular pro‐inflammatory/anti‐inflammatory signalling cascade via recruitment of various adaptor proteins. TLR associated signalling pathways are tightly regulated to keep a check on inappropriate production of pro‐inflammatory cytokines and interferons thereby preventing various autoimmune and inflammatory processes. Herein, we review the current state of knowledge of hepatic distribution, signalling pathways and therapeutic modulation of TLRs in chronic liver diseases.