Lith genes control mucin accumulation, cholesterol crystallization, and gallstone formation in A/J and AKR/J inbred mice

Research progress on the immune microenvironment of the gallbladder in patients with cholesterol gallstones

Cholesterol gallstones are very common in hepatobiliary surgery and have been studied to a certain extent by doctors worldwide for decades. However, the mechanism of cholesterol gallstone formation is not fully understood, so there is currently no completely effective drug for the treatment and prevention of cholesterol gallstones. The formation and development of cholesterol gallstones are caused by a variety of genetic and environmental factors, among which genetic susceptibility, intestinal microflora disorders, impaired gallbladder motility, and immune disorders are important in the pathogenesis of cholesterol gallstones. This review focuses on recent advances in these mechanisms. We also discuss some new targets that may be effective in the treatment and prevention of cholesterol gallstones, which may be hot areas in the future.

Risk Factors for Early Recurrence of Gallstones in Patients Undergoing Laparoscopy Combined With Choledochoscopic Lithotomy: A Single-Center Prospective Study

Objective: For patients with gallstones, laparoscopy combined with choledochoscopic lithotomy is a therapeutic surgical option for preservation rather than the removal of the gallbladder. However, postoperative recurrence of gallstones is a key concern for both patients and surgeons. This prospective study was performed to investigate the risk factors for early postoperative recurrence of gallstones.

Methods: The clinical data of 466 patients were collected. Each patient was followed up for up to 2 years. The first follow-up visit occurred 4 months after the operation, and a follow-up visit was carried out every 6 months thereafter. The main goal of each visit was to confirm the presence or absence of gallbladder stones. The factors associated with gallstone recurrence were analyzed by univariate analysis and Cox regression.

Results: In total, 466 eligible patients were included in the study, and 438 patients (180 men and 258 women) completed the 2-year postoperative follow-up. The follow-up rate was 94.0%. Recurrence of gallstones was detected in 5.71% (25/438) of the patients. Univariate analysis revealed five risk factors for the recurrence of gallstones. Multivariate Cox regression analysis showed that multiple gallstones, a gallbladder wall thickness of ≥4 mm, and a family history of gallbladder stones were the three predictive factors for postoperative recurrence of gallstones (P < 0.05).

Conclusion: The overall 2-year recurrence rate of gallstones after the operation was 5.71%. Multiple gallstones, a gallbladder wall thickness of ≥4 mm, and a family history of gallstones were the three risk factors associated with early postoperative recurrence of gallstones.

Physical Activity Modulating Lipid Metabolism in Gallbladder Diseases

Physical activity encompasses a series of overall benefits on cardiovascular health and metabolic disorders. Research has recently focused on the hepatobiliary tract, as an additional target of the health-related outcomes of different types of physical exercise. Here, we focus on the global features of physical activity with respect to exercise modality and intensity, and on studies linking physical activity to lipid metabolism, gallbladder diseases (gallstones, symptoms, complications and health-related quality of life), gallbladder motor-function, enterohepatic circulation of bile acids, and systemic metabolic inflammation. Additional studies need to unravel the pathophysiological mechanisms involved in both beneficial and harmful effects of physical activity in populations with different metabolic conditions.

Systems genetics of liver fibrosis: identification of fibrogenic and expression quantitative trait loci in the BXD murine reference population

The progression of liver fibrosis in response to chronic injury varies considerably among individual patients. The underlying genetics is highly complex due to large numbers of potential genes, environmental factors and cell types involved. Here, we provide the first toxicogenomic analysis of liver fibrosis induced by carbon tetrachloride in the murine ‘genetic reference panel’ of recombinant inbred BXD lines. Our aim was to define the core of risk genes and gene interaction networks that control fibrosis progression. Liver fibrosis phenotypes and gene expression profiles were determined in 35 BXD lines. Quantitative trait locus (QTL) analysis identified seven genomic loci influencing fibrosis phenotypes (pQTLs) with genome-wide significance on chromosomes 4, 5, 7, 12, and 17. Stepwise refinement was based on expression QTL mapping with stringent selection criteria, reducing the number of 1,351 candidate genes located in the pQTLs to a final list of 11 cis-regulated genes. Our findings demonstrate that the BXD reference population represents a powerful experimental resource for shortlisting the genes within a regulatory network that determine the liver's vulnerability to chronic injury.

Systems genetics of hepatocellular damage in vivo and in vitro: identification of a critical network on chromosome 11 in mouse

Quantitative trait locus (QTL) mapping is a powerful method to find modifier loci that influence disease risk and progression without prior knowledge of underlying genetic mechanisms. The aim of this study is to identify gene loci that contribute to individual differences in liver fibrosis following chronic liver damage. For this purpose, we carried out a mapping study across a panel of 21 BXD recombinant inbred strains using primary hepatocytes challenged with transforming growth factor (TGF)-β for 48 h. We identified a 6 Mb interval on chromosome 11 that is a major modifier of TGF-β-induced hepatocyte injury. Corresponding in vivo genetic analysis of fibrosis after chronic hepatotoxic injury by carbon tetrachloride (CCl4 ip for 6 wk) highlighted the same locus. Expression QTL (eQTL) analysis in liver tissues in the BXD family identified six polymorphisms in this region that are associated with strong cis eQTLs and that correlate well with gene expression in liver after both 6 wk CCl4 treatment and acute ethanol damage of the liver. Within this interval we rank two genes containing coding sequence variants as strong candidates that may modulate the severity of liver fibrosis: 1) the extracellular proteinase inhibitor gene Expi (also known as Wdnm1 or Wfdc18) and 2) musashi RNA-binding protein 2 (Msi2). The powerful combination of experimental, genetics, and bioinformatics methods, as well as combined in vitro and in vivo approaches can be used to define QTLs, genes, and even candidate sequence variants linked to hepatotoxicity and fibrosis.

Single nucleotide polymorphism rs3732860 in the 3'-untranslated region of CYP8B1 gene is associated with gallstone disease in Han Chinese

BACKGROUND AND AIMS

Gallstone disease (GD) is a common disease of multigenetic origin; however, the major susceptibility loci for GD in human populations remain unidentified. This study aimed to identify the genetic factors contributing to gallstone development in Chinese.

METHODS

A genome-wide scan was conducted in 12 Han Chinese GD families to identify linkage loci. The linkage region showing the highest logarithm of odds score encompasses the sterol 12α-hydroxylase gene (CYP8B1). Replication analysis with an independent sample of 192 GD patients and 192 unrelated, matched controls was carried out to verify the associations between CYP8B1 polymorphisms and GD.

RESULTS

Three loci (D3S1266, D4S406, and D9S1682) showed suggestive or nominal evidence of linkage in all 12 GD families. The logarithm of odds score of D3S1266 reached 2.71 in the families with late-onset patients. The single nucleotide polymorphism rs3732860 in the 3'-untranslated region of CYP8B1 showed significant association to GD (P = 0.022), and carriers of the A allele had lower risk of GD (odds ratio = 1.46, 95% confidence interval: 1.055-2.034) compared with carriers of the G allele.

CONCLUSIONS

The single nucleotide polymorphism rs3732860 in the 3'-untranslated region of the CYP8B1 gene is associated with risk of GD in Chinese Han and appears to be responsible for the observed linkage with D3S1266.

Recurrence of gallstones after cholecystectomy is associated with ABCG5/8 genotype

BACKGROUND

Gallstone disease is a frequent and economically highly relevant disorder, with cholecystectomy representing one of the most frequently performed operations world-wide. Gallstone recurrence after cholecystectomy is associated with complications such as biliary sepsis and pancreatitis. As yet, variant ABCG8-D19H is the most widely recognized genetic risk factor for gallstone disease. The aim of the study is to investigate whether ABCG8-D19H is associated with gallstone recurrence after cholecystectomy.

METHODS

Two thousand three hundred and eight patients from an earlier study of gallstone risk factors were re-contacted by mail, leading to 1,915 patients with available clinical and genetic information. Symptomatic gallstone recurrence was established if it occurred more than six months after surgery. Median follow-up time after cholecystectomy was eight years.

RESULTS

Gallstones recurred in 37 patients (1.9%). ABCG-D19H was found to be significantly associated with gallstone recurrence (p = 0.034). The allelic odds ratio was 1.97 (95% CI 1.12-∞). In a multivariate logistic regression analysis adjusted for age, sex, BMI and type of surgery, ABCG8-D19H remained a significant predictor, both in the total cohort (p = 0.024) and in the subgroup for whom information on type and scheduling of surgery was available (N = 1,650, p = 0.020).

CONCLUSIONS

ABCG8-D19H is a predictor of gallstone recurrence, a major long term postoperative biliary complication. Moreover, the observed association also reemphasizes the importance of the sterolin transporter for stone formation.

Polysaccharides and mucin 5AC (MUC5AC) expression in gallbladder mucosa of young patients with gallstones as evaluated by spatial visualization and quantification

The study aimed at examination of tissue expression of polysaccharides and secretory mucin 5AC (MUC5AC) in young patients (up to 25 years of age) with a symptomatic gallstones. For comparison, patients most frequently subjected to cholecystectomy were studied, i.e. patients of approximately 50 years of age with the same diagnosis. In quantitative studies on tissue expression of both mucus components, the modern technique of spatial visualization was applied for the first time. Application of the technique permitted to demonstrate significant positive relationships between expression of glycoproteins (immunocytochemical ABC technique for detection of MUC5AC) and expression of sugar components in mucus (PAS technique) and to confirm suitability of the technique for quantitative appraisal of both histochemical and immunocytochemical reactions. An even higher expression of polysaccharides in the entire mucosa and of MUC5AC was detected in gallbladder epithelium of 50-year-old patients, as compared to young patients with symptomatic gallstones. In the young patients, expression of polysaccharides correlated with inflammatory activity (grading), width of gallbladder wall and PLT level in peripheral blood. A significantly higher expression of polysaccharides in gallbladder epithelium was demonstrated in young patients admitted in the emergency mode to the hospital. These correlations in young patients may suggest a role of both mucus components in pathogenesis of cholelithiasis in this age group. A quantitative appraisal of mucus component expression in the two parts of gallbladder mucosa (epithelium vs. entire mucosa) using spatial visualization technique permitted to more accurately compare production of glycoproteins and of polysaccharides in patients with cholelithiasis and to demonstrate additional correlations of a potential clinical significance.

Loci from a genome-wide analysis of bilirubin levels are associated with gallstone risk and composition

BACKGROUND & AIMS

Genome-wide association studies have mapped loci that are associated with serum levels of bilirubin. Bilirubin is a major component of gallstones so we investigated whether these variants predict gallstone bilirubin content and overall risk for gallstones.

METHODS

Loci that were identified in a meta-analysis to attain a genome-wide significance level of a P value less than 1.0×10(-7) (UGT1A1, SLCO1B1, LST-3TM12, SLCO1A2) were analyzed in 1018 individuals with known gallstone composition. Gallstone risk was analyzed in 2606 German choleystecomized individuals and 1121 controls and was replicated in 210 cases and 496 controls from South America.

RESULTS

By using the presence of bilirubin as a phenotype, variants rs6742078 (UGT1A1; P = .003), rs4149056 (SLCO1B1; P = .003), and rs4149000 (SLCO1A2; P = .015) were associated with gallstone composition. In regression analyses, only UGT1A1 and SLCO1B1 were independently retained in the model. UGT1A1 (rs6742078; P = .018) was associated with overall gallstone risk. In a sex-stratified analysis, only male carriers of rs6742078 had an increased risk for gallstone disease (P = 2.1×10(-7); odds ratio(recessive), 2.34; P(women) = .47). The sex-specific association of rs6742078 was confirmed in samples from South America (P(men) = .046; odds ratio(recessive), 2.19; P(women) = .96).

CONCLUSIONS

The UGT1A1 Gilbert syndrome variant rs6742078 is associated with gallstone disease in men; further studies are required regarding the sex-specific physiology of bilirubin and bile acid metabolism. Variants of ABCG8 and UGT1A1 are the 2 major risk factors for overall gallstone disease, they contribute a population attributable risk of 21.2% among men.

Gallstone disease in Swedish twins: risk is associated with ABCG8 D19H genotype

OBJECTIVE

Recently, variants of the hepatocanalicular cholesterol hemitransporters ABCG5/8 were linked to gallstone disease; ABCG8 D19H in Caucasians and ABCG5 Q604E in Chinese. We investigated these polymorphisms in Swedish twins by merging the Swedish Twin Registry with the Hospital Discharge and Causes of Death Registries for gallstone disease-related diagnoses.

DESIGN

All monozygotic (MZ) twins with gallstone disease alive in the Stockholm area were invited to participate. Gallstone disease was defined by entry in all above mentioned registries, questionnaire or abdominal ultrasound.

SUBJECTS

ABCG5 Q604E and ABCG8 D19H genotyping was performed in 24 unique MZ and eight dizygotic (DZ) twins from concordant pairs. Screening of the TwinGene database for gallstone disease resulted in an additional 20 concordant MZ and 54 twins from concordant DZ pairs. We included 109 concordantly stone-free MZ and 126 stone-free independent DZ twins as controls.

RESULTS

Amongst the 341 twins, 20.8% carried at least one D19H allele as compared to 9.4% of stone-free controls. The association analysis showed that D19H positivity significantly increased the risk of gallstone disease [odds ratio (OR), 2.54; 95% confidence interval (CI), 1.33-4.82; P = 0.004]. We also found a trend for a positive association between gallstone disease and the Q604E variant (OR, 1.47; 95% CI, 1.00-2.16; P = 0.052).

CONCLUSION

Twins carrying a heterozygous or homozygous ABCG8 D19H genotype have a significantly increased risk of gallstone disease. Our study confirms the ABCG8 D19H genotype as a major risk factor for gallstone disease.

Pathogenesis of gallstones

Cholesterol gallstone formation is a complex process and involves phase separation of cholesterol crystals from supersaturated bile. In most cases, cholesterol hypersecretion is considered the primary event in gallstone formation. The sterol is transported through the hepatocytic canalicular membrane by ABCG5-G8. Expression of this transport protein is regulated by transcription factor Liver X Receptor-alpha, which may be responsible for biliary hypersecretion. Hydrophobic bile salt pool, bile concentration, excess pronucleating mucin, and impaired gallbladder and intestinal motility are secondary phenomena in most cases but nevertheless may contribute to gallstone formation.

Roles of infection, inflammation, and the immune system in cholesterol gallstone formation

Cholesterol gallstone formation is a complex process mediated by genetic and environmental factors. Until recently, the role of the immune system in the pathogenesis of cholesterol gallstones was not considered a valid topic of research interest. This review collates and interprets an extensive body of basic literature, some of which is not customarily considered to be related to cholelithogenesis, describing the multiple facets of the immune system that appear to be involved in cholesterol cholelithogenesis. A thorough understanding of the immune interactions with biliary lipids and cholecystocytes should modify current views of the pathogenesis of cholesterol gallstones, promote further research on the pathways involved, and lead to novel diagnostic tools, treatments, and preventive measures.

Megalin and cubilin in the human gallbladder epithelium

Although the role of cholesterol absorption by the gallbladder epithelium in gallstone formation is well established, the exact process is poorly understood. Potential candidates for regulation of transepithelial cholesterol transport are suggested to be two large membrane multiple ligand receptors, megalin and cubilin. We studied the expression of these two proteins in both acalculous and calculous human gallbladder epithelia. Adult human gallbladder tissues were received from 21 patients (9 men, 12 women) who had undergone cholecystectomy. The patients were divided into two groups: group A (calculous gallbladder group; 5 men, 6 women; mean age 64.4 +/- 11.1 years) with cholelithiasis, and group B (acalculous gallbladder group; 4 men, 6 women; mean age 55.3 +/- 16.1 years). In the gallbladder tissues megalin and cubilin expression was studied by immunohistochemistry and conventional RT-PCR, and gene expression levels were estimated by real-time RT-PCR. Both megalin and cubilin gene transcripts were found in total RNA preparations from acalculous gallbladder. In contrast, in preparations from calculous gallbladder, none or only one of the proteins was detected. Immunoreactive proteins were detected in the simple columnar acalculous gallbladder epithelium but not in the calculous gallbladder epithelium. Our results show different expression patterns of the two proteins in calculous gallbladders and acalculous gallbladders. In the latter both proteins are expressed, suggesting an association with gallstone formation and implying a putative role of the two proteins in cholesterol endocytosis. In other words, the presence of both proteins may be essential for the prevention of stone formation.

Investigation of the Lith6 candidate genes APOBEC1 and PPARG in human gallstone disease

BACKGROUND

Genetic susceptibility contributes to the aetiology of gallbladder diseases as shown by multiple epidemiological studies. A major gallstone susceptibility locus (Lith6) was identified in 2003 by quantitative trait locus mapping in mice. Two attractive positional and functional candidate genes in apolipoprotein B mRNA-editing protein (APOBEC1) and peroxisome proliferator-activated receptor gamma (PPARG) are located in this interval.

AIMS

To investigate APOBEC1 and PPARG as candidate genes for common symptomatic gallstone disease in humans.

PATIENTS AND METHODS

Eight hundred and ten patients who underwent cholecystectomy for symptomatic gallstone disease (median age of onset 50) were compared with 718 sex-matched control individuals. An independent additional sample included 368 gallstone patients and 368 controls. Control individuals were sonographically free of gallstones. Haplotype tagging and all known coding single nucleotide polymorphisms were genotyped for PPARG (N=32) and APOBEC1 (N=11).

RESULTS

The investigated high-risk patient sample provides a power of greater than 80% for the detection of odds ratios down to 1.45. No evidence of association of the two genes in the single-point tagging markers, coding variants and in the sliding window haplotype analysis was detected (all nominal single point P-values >0.04). A logistic regression analysis including age, sex and BMI as covariates was also negative (nominal P-values > or =0.08).

CONCLUSIONS

In the investigated German samples, no evidence of association of APOBEC1 and PPARG with gallstone susceptibility was detected. Systematic fine mapping of the complete Lith6 region is required to identify the causative genetic variants for gallstone in mice and humans.

A genome-wide association scan identifies the hepatic cholesterol transporter ABCG8 as a susceptibility factor for human gallstone disease

With an overall prevalence of 10-20%, gallstone disease (cholelithiasis) represents one of the most frequent and economically relevant health problems of industrialized countries. We performed an association scan of >500,000 SNPs in 280 individuals with gallstones and 360 controls. A follow-up study of the 235 most significant SNPs in 1,105 affected individuals and 873 controls replicated the disease association of SNP A-1791411 in ABCG8 (allelic P value P(CCA) = 4.1 x 10(-9)), which was subsequently attributed to coding variant rs11887534 (D19H). Additional replication was achieved in 728 German (P = 2.8 x 10(-7)) and 167 Chilean subjects (P = 0.02). The overall odds ratio for D19H carriership was 2.2 (95% confidence interval: 1.8-2.6, P = 1.4 x 10(-14)) in the full German sample. Association was stronger in subjects with cholesterol gallstones (odds ratio = 3.3), suggesting that His19 might be associated with a more efficient transport of cholesterol into the bile.

Gallstone disease

Gallstone disease is one of the most prevalent gastrointestinal diseases with a substantial burden to health care systems that is supposed to increase in ageing populations at risk. Aetiology and pathogenesis of cholesterol gallstones still are not well defined, and strategies for prevention and efficient nonsurgical therapies are missing. This review summarizes current concepts on the pathogenesis of cholesterol gallstones with focus on the uptake and secretion of biliary lipids and special emphasis on recent studies into the genetic background.

Are plasma lipid levels related to ABCG5/ABCG8 polymorphisms? A preliminary study in siblings with gallstones

BACKGROUND

The role of ABCG5 and ABCG8 genes in the determination of plasma lipid levels is currently under intensive investigation. The aim of this study was to evaluate plasma lipid levels in sibling pairs with gallstones and to assess their correlation with common gene polymorphisms in the ABCG5/ABCG8 genes.

METHODS

Plasma levels of cholesterol, HDL-cholesterol, and triglycerides were measured in 68 patients belonging to 34 sibling pairs with gallstones (affected sibling pairs, mean age 56.3 years) and in 68 gallstone carriers with stone-free siblings (age/gender-matched controls in a ratio of 2:1 with the index patients of the study group). Four and one non-synonymous sequence variants in ABCG8 and ABCG5 genes, respectively, were determined in the affected sibling pairs, employing allelic discrimination with 5' nuclease assays.

RESULTS

Plasma triglyceride levels were higher and HDL-cholesterol levels lower in the index patients than in controls. Plasma lipid levels were correlated in the members of the affected sibling pairs. Triglyceride levels were higher in carriers of the common alleles for ABCG5 Q604E and ABCG8 D19H sequence variants, and HDL-cholesterol was lower in carriers of the common alleles for ABCG5 Q604E than in carriers of the rare alleles.

CONCLUSIONS

The significantly different plasma lipid levels in siblings with gallstones versus controls, as well as the correlation of plasma lipids in affected sibling pairs, confirm the genetic influence in gallstone disease. Polymorphisms in ABCG5/ABCG8 genes might contribute to the genetic variation in plasma lipid levels and in cholesterol saturation of the bile.

Investigation of the Lith1 candidate genes ABCB11 and LXRA in human gallstone disease

Genetic susceptibility in the causation of gallbladder diseases was recognized as early as 1937. A major gallstone susceptibility locus (Lith1) was identified in 1995 by quantitative trait locus mapping in mice. Two attractive positional and functional candidate genes in LXRA and ABCB11 are located in this interval. ABCB11 is associated with progressive familial cholestasis. This study was undertaken to investigate LXRA and ABCB11 as candidate genes for gallstone disease in humans. Eight hundred and ten patients who underwent cholecystectomy for symptomatic gallstone disease (median age of onset, 50 years) were compared with 718 sex-matched control individuals. Control individuals were sonographically free of gallstones. Haplotype tagging and all known coding single nucleotide polymorphisms (SNPs) were genotyped for ABCB11 (n=29) and LXRA (n=10). The investigated high-risk patient sample provides a power of greater than 80% for the detection of odds ratios down to 1.55. No evidence of association of the two genes in the single point tagging markers, coding variants or in the sliding window haplotype analysis was detected (all nominal single-point P values>or=.08). In conclusion, in the investigated German sample, no evidence of association of ABCB11 and LXRA to gallstone susceptibility was detected. The gallstone trait is not allelic to progressive familial cholestasis at the ABCB11 locus. Systematic fine mapping of the Lith1 region is required to identify the causative genetic variants for gallstone in mice and humans.

A genomewide search finds major susceptibility loci for gallbladder disease on chromosome 1 in Mexican Americans

Gallbladder disease (GBD) is one of the major digestive diseases. Its risk factors include age, sex, obesity, type 2 diabetes, and metabolic syndrome (MS). The prevalence of GBD is high in minority populations, such as Native and Mexican Americans. Ethnic differences, familial aggregation of GBD, and the identification of susceptibility loci for gallstone disease by use of animal models suggest genetic influences on GBD. However, the major susceptibility loci for GBD in human populations have not been identified. Using ultrasound-based information on GBD occurrence and a 10-cM gene map, we performed multipoint variance-components analysis to localize susceptibility loci for GBD. Phenotypic and genotypic data from 715 individuals in 39 low-income Mexican American families participating in the San Antonio Family Diabetes/Gallbladder Study were used. Two GBD phenotypes were defined for the analyses: (1) clinical or symptomatic GBD, the cases of cholecystectomies due to stones confirmed by ultrasound, and (2) total GBD, the clinical GBD cases plus the stone carriers newly diagnosed by ultrasound. With use of the National Cholesterol Education Program/Adult Treatment Panel III criteria, five MS risk factors were defined: increased waist circumference, hypertriglyceredemia, low high-density lipoprotein cholesterol, hypertension, and high fasting glucose. The MS risk-factor score (range 0-5) for a given individual was used as a single, composite covariate in the genetic analyses. After accounting for the effects of age, sex, and MS risk-factor score, we found stronger linkage signals for the symptomatic GBD phenotype. The highest LOD scores (3.7 and 3.5) occurred on chromosome 1p between markers D1S1597 and D1S407 (1p36.21) and near marker D1S255 (1p34.3), respectively. Other genetic locations (chromosomes 2p, 3q, 4p, 8p, 9p, 10p, and 16q) across the genome exhibited some evidence of linkage (LOD >or=1.2) to symptomatic GBD. Some of these chromosomal regions corresponded with the genetic locations of Lith loci, which influence gallstone formation in mouse models. In conclusion, we found significant evidence of major genetic determinants of symptomatic GBD on chromosome 1p in Mexican Americans.

Prevalence of gallstone disease in first-degree relatives of patients with cholelithiasis

AIM: To evaluate the influence of familiality on the prevalence of gallstone disease (GD) in Italy.

METHODS: Families of 79 subjects with gallstones (cases) and of 79 subjects without gallstones (controls) were investigated for the presence of gallstones by ultrasonography. Index cases and index controls were matched for age, sex, and operative unit. Sixty-three and sixty-two husbands and wives of index cases and index controls, respectively, were also studied.

RESULTS: Overall,the prevalence of GD was significantly higher ( χ²=14.52, P<0.001) in the 202 first-degree relatives of subjects with gallstones than that in the 201 first-degree relatives of subjects without gallstones (28.6% vs 12.4%, relative risk (RR) 1.80, 95% confidence interval (CI) 1.29-2.63). In particular, prevalence of GD was significantly higher in mothers, fathers, and sisters of index cases than that in the respective family members of index controls. The highest RR was observed in mothers (RR=2.35, 95%CI 1.38-4.3). Prevalence of GD was not obviously different in brothers and also in husbands and wives of index cases and index controls. Family members of index cases did not differ from family members of control cases with respect to the most important risk factors for gallstones (age, diabetes, BMI, and number of pregnancies) with an exception of a higher prevalence of diabetes in fathers of index controls than in fathers of index cases.

CONCLUSION: This study confirms that familiality plays a very important role in the pathogenesis of gallstones.

Quantitative trait loci for baseline white blood cell count, platelet count, and mean platelet volume

A substantial genetic contribution to baseline peripheral blood counts has been established. We performed quantitative trait locus/loci (QTL) analyses to identify chromosome (Chr) regions harboring genes influencing the baseline white blood cell (WBC) count, platelet (Plt) count, and mean platelet volume (MPV) in F(2) intercrosses between NZW/LacJ, SM/J, and C57BLKS/J inbred mice. We identified six significant WBC QTL: Wbcq1 (peak LOD score at 38 cM, Chr 1), Wbcq2 (42 cM, Chr 3), Wbcq3 (0 cM, Chr 15), Wbcq4 (58 cM, Chr 1), Wbcq5 (82 cM, Chr 1), and Wbcq6 (8 cM, Chr 14). Three significant Plt QTL were identified: Pltq1 (24 cM, Chr 2), Pltq2 (36 cM, Chr 7), and Pltq3 (10 cM, Chr 12). Two significant MPV QTL were identified, Mpvq1 (62 cM, Chr 15) and Mpvq2 (44 cM, Chr 8). In total, the WBC QTL accounted for up to 31% of the total variance in baseline WBC count, while the Plt and MPV QTL accounted for up to 30% and 49% of the total variance, respectively. These analyses underscore the genetic complexity underlying these traits in normal populations and provide the basis for future studies to identify novel genes involved in the regulation of mammalian hematopoiesis.

Single and interacting QTLs for cholesterol gallstones revealed in an intercross between mouse strains NZB and SM

Quantitative trait locus (QTL) mapping was employed to investigate the genetic determinants of cholesterol gallstone formation in a large intercross between mouse strains SM/J (resistant) and NZB/B1NJ (susceptible). Animals consumed a gallstone-promoting diet for 18 weeks. QTL analyses were performed using gallstone weight and gallstone absence/presence as phenotypes; various models were explored for genome scans. We detected seven single QTLs: three new, significant QTLs were named Lith17 [chromosome (Chr) 5, peak=60 cM, LOD=5.4], Lith18 (Chr 5, 76 cM, LOD=4.3), and Lith19 (Chr 8, 0 cM, LOD=5.3); two confirmed QTLs identified previously and were named Lith20 (Chr 9, 44 cM, LOD=2.7) and Lith21 (Chr 10, 24 cM, LOD=2.9); one new, suggestive QTL (Chr 17) remains unnamed. Upon searching for epistatic interactions that contributed to gallstone susceptibility, the final suggestive QTL on Chr 7 was determined to interact significantly with Lith18 and, therefore, was named Lith22 (65 cM). A second interaction was identified between Lith19 and a locus on Chr 11; this QTL was named Lith23 (13 cM). mRNA expression analyses and amino acid haplotype analyses likely eliminated Slc10a2 as a candidate gene for Lith19. The QTLs identified herein largely contributed to gallstone formation rather than gallstone severity. Cloning the genes underlying these murine QTLs should facilitate prediction and cloning of the orthologous human genes.

Association of a lithogenic Abcg5/Abcg8 allele on Chromosome 17 (Lith9) with cholesterol gallstone formation in PERA/EiJ mice

To examine further the genetic determinants of cholesterol gallstone susceptibility in inbred mice, we performed quantitative trait locus (QTL) analysis of an intercross of gallstone-susceptible PERA/EiJ and gallstone-resistant DBA/2J inbred mice. Three hundred twenty-four F2 offspring were phenotyped for cholelithiasis during consumption of a lithogenic diet and genotyped using microsatellite markers. Linkage analysis was performed by interval mapping. In addition, we analyzed the combined datasets from this cross and from an independent cross of strain PERA and gallstone-resistant I/Ln mice. QTL mapping detected one significant new gallstone susceptibility (Lith) locus on Chromosome 13 (Lith15). A second significant QTL on Chr 6 (Lith16) confirmed a previous QTL. Furthermore, suggestive QTLs confirmed Lith loci from previous crosses on Chromosomes 1, 2, 5, 16 and X. QTL analysis of the dataset derived from the combined crosses increased the detection power and narrowed confidence intervals of Lith loci on Chromosomes 2, 6, 13, and 16. Moreover, the analysis of combined datasets revealed a shared QTL between both crosses on Chromosome 17 (Lith9). Significantly higher mRNA expression of Abcg5 and Abcg8 in strain PERA compared with strains I/Ln and DBA/2 further substantiated that the PERA allele of Abcg5/Abcg8 was responsible for lithogenicity underlying Lith9.

Identification of cholelithogenic enterohepatic helicobacter species and their role in murine cholesterol gallstone formation

BACKGROUND & AIMS

Helicobacter spp are common inhabitants of the hepatobiliary and gastrointestinal tracts of humans and animals and cause a variety of well-described diseases. Recent epidemiologic results suggest a possible association between enterohepatic Helicobacter spp and cholesterol cholelithiasis, chronic cholecystitis, and gallbladder cancer. To test this, we prospectively investigated the effects of Helicobacter spp infection in cholesterol gallstone pathogenesis in the highly susceptible C57L/J mouse model.

METHODS

Helicobacter spp-free adult male C57L mice were infected with several different enterohepatic Helicobacter spp or left uninfected and fed either a lithogenic diet or standard mouse chow for 8 and 18 weeks. At the conclusion of the study, bile was examined microscopically and diagnostic culture and polymerase chain reaction were performed.

RESULTS

Mice infected with Helicobacter bilis or coinfected with Helicobacter hepaticus and Helicobacter rodentium and fed a lithogenic diet developed cholesterol gallstones at 80% prevalence by 8 weeks compared with approximately 10% in uninfected controls. Monoinfections with H hepaticus , Helicobacter cinaedi , and H rodentium gave a cholesterol gallstone prevalence of 40%, 30%, and 20%, respectively; the latter 2 groups did not differ significantly from uninfected animals. Neither infected nor uninfected mice fed a chow diet developed cholesterol gallstones.

CONCLUSIONS

These findings, along with prior epidemiologic studies, suggest that Helicobacter spp play a major role in the pathophysiology of cholesterol gallstone formation in mice and perhaps humans.

Megalin and cubilin expression in gallbladder epithelium and regulation by bile acids

Cholesterol crystal formation in the gallbladder is a key step in gallstone pathogenesis. Gallbladder epithelial cells might prevent luminal gallstone formation through a poorly understood cholesterol absorption process. Genetic studies in mice have highlighted potential gallstone susceptibility alleles, Lith genes, which include the gene for megalin. Megalin, in conjunction with the large peripheral membrane protein cubilin, mediates the endocytosis of numerous ligands, including HDL/apolipoprotein A-I (apoA-I). Although the bile contains apoA-I and several cholesterol-binding megalin ligands, the expression of megalin and cubilin in the gallbladder has not been investigated. Here, we show that both proteins are expressed by human and mouse gallbladder epithelia. In vitro studies using a megalin-expressing cell line showed that lithocholic acid strongly inhibits and cholic and chenodeoxycholic acids increase megalin expression. The effects of bile acids (BAs) were also demonstrated in vivo, analyzing gallbladder levels of megalin and cubilin from mice fed with different BAs. The BA effects could be mediated by the farnesoid X receptor, expressed in the gallbladder. Megalin protein was also strongly increased after feeding a lithogenic diet. These results indicate a physiological role for megalin and cubilin in the gallbladder and provide support for a role for megalin in gallstone pathogenesis.

Use of a dense single nucleotide polymorphism map for in silico mapping in the mouse

Rapid expansion of available data, both phenotypic and genotypic, for multiple strains of mice has enabled the development of new methods to interrogate the mouse genome for functional genetic perturbations. In silico mapping provides an expedient way to associate the natural diversity of phenotypic traits with ancestrally inherited polymorphisms for the purpose of dissecting genetic traits. In mouse, the current single nucleotide polymorphism (SNP) data have lacked the density across the genome and coverage of enough strains to properly achieve this goal. To remedy this, 470,407 allele calls were produced for 10,990 evenly spaced SNP loci across 48 inbred mouse strains. Use of the SNP set with statistical models that considered unique patterns within blocks of three SNPs as an inferred haplotype could successfully map known single gene traits and a cloned quantitative trait gene. Application of this method to high-density lipoprotein and gallstone phenotypes reproduced previously characterized quantitative trait loci (QTL). The inferred haplotype data also facilitates the refinement of QTL regions such that candidate genes can be more easily identified and characterized as shown for adenylate cyclase 7.

Genetic analysis of cholesterol gallstone formation: searching for Lith (gallstone) genes

The genetics of cholesterol cholelithiasis is complex because a number of interacting genes regulate biliary cholesterol homeostasis. Quantitative trait locus (QTL) analysis is a powerful method for identifying primary rate-limiting genetic defects and discriminating them from secondary downstream lithogenic effects caused by mutations of the primary genes. The subsequent positional cloning of such genes responsible for QTLs may lead to the discovery of pathophysiologic functions of Lith (gallstone) genes. In this review, we present a map of candidate genes for Lith genes that may determine gallstone susceptibility in mice. The physical-chemical, pathophysiologic, and genetic studies of Lith genes in bile, liver, gallbladder, and intestine will be crucial for elucidating the genetic mechanisms of cholesterol gallstone disease in mice and in humans. Because exceptionally close homology exists between mouse and human genomes, the orthologous human LITH genes can often be recognized after mouse genes are identified.

Hepatic overexpression of murine Abcb11 increases hepatobiliary lipid secretion and reduces hepatic steatosis

Abcb11 encodes for the liver bile salt export pump, which is rate-limiting for hepatobiliary bile salt secretion. We employed transthyretin-Abcb11 and BAC-Abcb11 transgenes to develop mice overexpressing the bile salt export pump in the liver. The mice manifest increases in bile flow and biliary secretion of bile salts, phosphatidylcholine, and cholesterol. Hepatic gene expression of cholesterol 7alpha-hydroxylase and ileal expression of the apical sodium bile salt transporter are markedly reduced, whereas gene expression of targets of the nuclear bile salt receptor FXR (ileal lipid-binding protein, short heterodimer partner (SHP) is increased. Because these changes in gene expression are associated with an increased overall hydrophobicity of the bile salt pool and a 4-fold increase of the FXR ligand taurodeoxycholate, they reflect bile salt-mediated regulation of FXR and SHP target genes. Despite the increased biliary secretion of bile salts, fecal bile salt excretion is unchanged, suggestive of an enhanced enterohepatic cycling of bile salts. Abcb11 transgenic mice fed a lithogenic (high cholesterol/fat/cholic acid) diet display markedly reduced hepatic steatosis compared with wild-type controls. We conclude that mice overexpressing Abcb11 display an increase in biliary bile salt secretion and taurodeoxycholate content, which is associated with FXR/SHP-mediated changes in hepatic and ileal gene expression. Because these mice are resistant to hepatic lipid accumulation, regulation of Abcb11 may be important for the pathogenesis and treatment of steatohepatitis.

FXR and ABCG5/ABCG8 as determinants of cholesterol gallstone formation from quantitative trait locus mapping in mice

BACKGROUND & AIMS

Cholesterol gallstone formation is a complex genetic trait. To identify additional cholesterol gallstone susceptibility loci, we performed a quantitative trait locus analysis using an intercross of PERA/Ei and I/LnJ inbred strains of mice.

METHODS

Mice of both sexes were examined for gallstone weight and evaluated according to a scoring system for the physical chemistry of cholelithiasis during feeding of a lithogenic diet. Intercross offspring were genotyped, and linkage analysis was performed by interval mapping. Differences in messenger RNA expression of positional candidate genes were determined using reverse-transcription and real-time polymerase chain reaction.

RESULTS

We identified significant loci associated with gallstone weight on chromosomes 10 and 4, named Lith7 and Lith8, respectively (both susceptibility alleles conferred by strain I/LnJ). Positional candidate genes with higher expression in I/LnJ mice are Fxr (official symbol, Nr1h4), encoding the nuclear bile salt receptor, on chromosome 10 and Shp1 (official symbol, Nr0b2), encoding the small heterodimer partner 1, on chromosome 4. A significant locus associated with gallstone score on chromosome 17, named Lith9 (susceptibility allele conferred by strain PERA/Ei), colocalizes with the genes Abcg5 and Abcg8 that encode the canalicular cholesterol transporter. Higher hepatic messenger RNA expression of Abcg5 and Abcg8 in strain PERA/Ei correlates positively with higher biliary cholesterol levels.

CONCLUSIONS

Our findings suggest a primary role of the nuclear bile salt receptor FXR and the canalicular cholesterol transporter ABCG5/ABCG8 in the genetic susceptibility and pathogenesis of cholesterol cholelithiasis in these strains of inbred mice.

Lith6: a new QTL for cholesterol gallstones from an intercross of CAST/Ei and DBA/2J inbred mouse strains

A complex genetic basis determines the individual predisposition to develop cholesterol gallstones in response to environmental factors. We employed quantitative trait locus/loci (QTL) analyses of an intercross between inbred strains CAST/Ei (susceptible) and DBA/2J (resistant) to determine the subset of gallstone susceptibility (Lith) genes these strains possess. Parental and first filial generation mice of both genders and male intercross offspring were evaluated for gallstone formation after feeding a lithogenic diet. Linkage analysis was performed using a form of multiple interval mapping. One significant QTL colocalized with Lith1 [chromosome (chr) 2, 50 cM], a locus identified previously. Significantly, new QTL were detected and named Lith10 (chr 6, 4 cM), Lith6 (chr 6, 54 cM), and Lith11 (chr 8, 58 cM). Statistical and genetic analyses suggest that Lith6 comprises two QTL in close proximity. Our molecular and genetic data support the candidacy of peroxisome proliferator-activated receptor gamma (Pparg) and Slc21a1, encoding Pparg, and the basolateral bile acid transporter SLC21A1 (Slc21a1/Oatp1), respectively, as genes underlying Lith6.

New quantitative trait loci that contribute to cholesterol gallstone formation detected in an intercross of CAST/Ei and 129S1/SvImJ inbred mice

Cholesterol gallstone formation is a response to interactions between multiple genes and environmental stimuli. To determine the subset of cholesterol gallstone susceptibility (Lith) genes possessed by strains CAST/Ei (susceptible) and 129S1/SvImJ (resistant), we conducted quantitative trait locus (QTL) analyses of an intercross between these strains. Parental strains and F(1) mice of both genders were evaluated for gallstone formation after consumption of a lithogenic diet for 8 wk. Gallstone susceptibility of strain CAST was predominantly due to cholesterol hypersecretion. Male intercross offspring were genotyped and phenotyped for cholesterol gallstone formation after consumption of the lithogenic diet for 10 wk. Linkage analysis was performed using PSEUDOMARKER software. One significant, new QTL was detected and named Lith13 [chromosome (Chr) 5, 30 cM]. Statistical analyses and QTL fine mapping suggest this QTL may comprise two closely linked loci. We confirmed the presence of Lith6 (Chr 6). Suggestive QTL were detected on Chrs 1, 2, 5, 14, and 16. The QTL on Chrs 2 and 16 confirmed previously identified, suggestive QTL. Therefore, they were named Lith12 (101 cM) and Lith14 (42 cM), respectively. We identified candidate genes based on known function and location and performed mRNA expression analyses using both parental strains and intercross progeny for preliminary evaluation of their contributions to gallstone formation. Cebpb (Lith12), Pparg (Lith6), and Slc21a1 (Lith6) displayed expression differences. Our work continues to demonstrate the genetic complexity and to elucidate the pathophysiology of cholesterol gallstone formation. It should facilitate the development of new approaches for treating this common human disorder.

Mapping cholesterol gallstone susceptibility (Lith) genes in inbred mice

The individual risk for developing cholesterol gallstones in response to specific environmental factors is determined by complex genetics involving multiple genes. In this review, we introduce inbred mice as a model to localise and identify the murine genes that harbour cholesterol gallstone susceptibility alleles (Lith genes). These genes are associated with increased risk of gallstone formation when mice are fed a lithogenic diet containing cholesterol and cholic acid. We summarise the steps involved in localising the chromosomal regions that harbour Lith genes, focusing particularly on the initial step known as quantitative trait locus mapping, which employs breeding crosses of gallstone-susceptible and gallstone-resistant inbred mouse strains. Subsequent steps to narrow the chromosomal regions of the quantitative trait loci and identify the underlying Lith genes are outlined, with particular reference to the examples of Lith1 and Lith2, the first discovered quantitative trait loci associated with murine cholesterol cholelithiasis. We have now reported five quantitative trait loci for murine cholelithogenesis, which are officially named Lith1 through Lith5. Once the genes underlying these quantitative trait loci and other chromosomal loci from ongoing mouse crosses are identified and confirmed, the 'road-map' for discovery of orthologous human LITH genes will be available and, thereafter, their putative roles in cholesterol gallstone formation can be tested in selected human populations.