Interaction of genetic variation at ADH1B and MLXIPL with alcohol consumption for elevated serum urate level and gout among people of European ethnicity.

BACKGROUND: Alcohol consumption is a risk factor for hyperuricaemia and gout. Multiple single-nucleotide polymorphisms (SNPs) have been identified as associated with both alcohol consumption and serum urate or gout in separate genome-wide association studies (GWAS). This study aimed to identify and characterise interactions between these shared signals of genetic association and alcohol consumption for serum urate level, hyperuricaemia, and gout. METHODS: This research was conducted using the UK Biobank resource. The association of alcohol consumption with serum urate and gout was tested among 458,405 European participants. Candidate SNPs were identified by comparing serum urate, gout, and alcohol consumption GWAS for shared signals of association. Multivariable-adjusted linear and logistic regression analyses were conducted with the inclusion of interaction terms to identify SNP-alcohol consumption interactions for association with serum urate level, hyperuricaemia, and gout. The nature of these interactions was characterised using genotype-stratified association analyses. RESULTS: Alcohol consumption was associated with elevated serum urate and gout. For serum urate level, non-additive interactions were identified between alcohol consumption and rs1229984 at the ADH1B locus (P = 3.0 × 10-44) and rs6460047 at the MLXIPL locus (P = 1.4 × 10-4). ADH1B also demonstrated interaction with alcohol consumption for hyperuricaemia (P = 7.9 × 10-13) and gout (P = 8.2 × 10-9). Beer intake had the most significant interaction with ADH1B for association with serum urate and gout among men, while wine intake had the most significant interaction among women. In the genotype-stratified association analyses, ADH1B and MLXIPL were associated with serum urate level and ADH1B was associated with hyperuricaemia and gout among consumers of alcohol but not non-consumers. CONCLUSIONS: In this large study of European participants, novel interactions with alcohol consumption were identified at ADH1B and MLXIPL for association with serum urate level and at ADH1B for association with hyperuricaemia and gout. The association of ADH1B with serum urate and gout may occur through the modulation of alcohol metabolism rate among consumers of alcohol.

Comparative genomics of clinical Stenotrophomonas maltophilia isolates reveals genetic diversity which correlates with colonization and persistence in vivo.

Stenotrophomonas maltophilia is a Gram-negative emerging opportunistic pathogen often present in people with respiratory diseases such as cystic fibrosis (CF). People with CF (pwCF) experience lifelong polymicrobial infections of the respiratory mucosa. Our prior work showed that Pseudomonas aeruginosa promotes persistence of S. maltophilia in mouse respiratory infections. As is typical for environmental opportunistic pathogens, S. maltophilia has a large genome and a high degree of genetic diversity. In this study, we evaluated the genomic content of S. maltophilia, combining short and long read sequencing to construct nearly complete genomes of 10 clinical isolates. The genomes of these isolates were then compared with all publicly available S. maltophilia genome assemblies, and each isolate was then evaluated for colonization/persistence in vivo, both alone and in coinfection with P. aeruginosa. We found that while the overall genome size and GC content were fairly consistent between strains, there was considerable variability in both genome structure and gene content. Similarly, there was significant variability in S. maltophilia colonization and persistence in experimental mouse respiratory infections in the presence or absence of P. aeruginosa. Ultimately, this study gives us a greater understanding of the genomic diversity of clinical S. maltophilia isolates, and how this genomic diversity relates to both interactions with other pulmonary pathogens and to host disease progression. Identifying the molecular determinants of infection with S. maltophilia can facilitate development of novel antimicrobial strategies for a highly drug-resistant pathogen.

Comparative genomics of clinical Stenotrophomonas maltophilia isolates reveals regions of diversity which correlate with colonization and persistence in vivo.

Stenotrophomonas maltophilia is a Gram-negative emerging opportunistic pathogen often found in respiratory diseases such as cystic fibrosis (CF). Patients with CF experience lifelong polymicrobial infections of the respiratory mucosa. Our prior work showed that P. aeruginosa promotes persistence of S. maltophilia mouse respiratory infections. As is typical for environmental opportunistic pathogens, S. maltophilia has a large genome and a high degree of genetic diversity. In this study, we evaluated the genomic content of S. maltophilia, combining short and long read sequencing to construct complete genomes of 10 clinical isolates which were then compared with the larger phylogeny of S. maltophilia genomic sequence data, and compared colonization/persistence in vivo, alone and in coinfection with P. aeruginosa. We found that while the overall genome size and GC content were fairly consistent, there was considerable variability in arrangement and gene content. Similarly, there was significant variability in S. maltophilia colonization and persistence in vivo in experimental mouse respiratory infection. Ultimately, this study gives us a greater understanding of the genomic diversity of S. maltophilia isolated from patients, and how this genomic diversity relates to interactions with other pulmonary pathogens, and to host disease progression. Identifying the molecular determinants of infection with S. maltophilia can facilitate development of novel antimicrobial strategies for a highly drug-resistant pathogen.

Genetic and Physiological Effects of Insulin-Like Growth Factor-1 (IGF-1) on Human Urate Homeostasis.

SIGNIFICANCE STATEMENT: Hyperinsulinemia induces hyperuricemia by activating net renal urate reabsorption in the renal proximal tubule. The basolateral reabsorptive urate transporter GLUT9a appears to be the dominant target for insulin. By contrast, IGF-1 infusion reduces serum urate (SU), through mechanisms unknown. Genetic variants of IGF1R associated with reduced SU have increased IGF-1R expression and interact with genes encoding the GLUT9 and ABCG2 urate transporters, in a sex-specific fashion, which controls the SU level. Activation of IGF-1/IGF-1R signaling in Xenopus oocytes modestly activates GLUT9a and inhibits insulin's stimulatory effect on the transporter, which also activates multiple secretory urate transporters-ABCG2, ABCC4, OAT1, and OAT3. The results collectively suggest that IGF-1 reduces SU by activating secretory urate transporters and inhibiting insulin's action on GLUT9a. BACKGROUND: Metabolic syndrome and hyperinsulinemia are associated with hyperuricemia. Insulin infusion in healthy volunteers elevates serum urate (SU) by activating net urate reabsorption in the renal proximal tubule, whereas IGF-1 infusion reduces SU by mechanisms unknown. Variation within the IGF1R gene also affects SU levels. METHODS: Colocalization analyses of a SU genome-wide association studies signal at IGF1R and expression quantitative trait loci signals in cis using COLOC2, RT-PCR, Western blotting, and urate transport assays in transfected HEK 293T cells and in Xenopus laevis oocytes. RESULTS: Genetic association at IGF1R with SU is stronger in women and is mediated by control of IGF1R expression. Inheritance of the urate-lowering homozygous genotype at the SLC2A9 locus is associated with a differential effect of IGF1R genotype between men and women. IGF-1, through IGF-1R, stimulated urate uptake in human renal proximal tubule epithelial cells and transfected HEK 293T cells, through activation of IRS1, PI3/Akt, MEK/ERK, and p38 MAPK; urate uptake was inhibited in the presence of uricosuric drugs, specific inhibitors of protein tyrosine kinase, PI3 kinase (PI3K), ERK, and p38 MAPK. In X. laevis oocytes expressing ten individual urate transporters, IGF-1 through endogenous IGF-1R stimulated urate transport mediated by GLUT9, OAT1, OAT3, ABCG2, and ABCC4 and inhibited insulin's stimulatory action on GLUT9a and OAT3. IGF-1 significantly activated Akt and ERK. Specific inhibitors of PI3K, ERK, and PKC significantly affected IGF-1 stimulation of urate transport in oocytes. CONCLUSIONS: The combined results of infusion, genetics, and transport experiments suggest that IGF-1 reduces SU by activating urate secretory transporters and inhibiting insulin's action.

Association of Gout Polygenic Risk Score With Age at Disease Onset and Tophaceous Disease in European and Polynesian Men With Gout.

OBJECTIVE: To determine whether a gout polygenic risk score (PRS) is associated with age at gout onset and tophaceous disease in European, East Polynesian, and West Polynesian men and women with gout. METHODS: A 19-variant gout PRS was produced in 7 European gout cohorts (N = 4,016), 2 East Polynesian gout cohorts (N = 682), and 1 West Polynesian gout cohort (N = 490). Sex-stratified regression models were used to estimate the relationship between the PRS and age at gout onset and tophaceous disease. RESULTS: The PRS was associated with earlier age at gout onset in men (ß = -3.61 in years per unit PRS [95% confidence interval (95% CI) -4.32, -2.90] in European men; ß = -6.35 [95% CI -8.91, -3.80] in East Polynesian men; ß = -3.51 [95% CI -5.46, -1.57] in West Polynesian men) but not in women (ß = 0.07 [95% CI -2.32, 2.45] in European women; ß = 0.20 [95% CI -7.21, 7.62] in East Polynesian women; ß -3.33 [95% CI -9.28, 2.62] in West Polynesian women). The PRS showed a positive association with tophaceous disease in men (odds ratio [OR] for the association 1.15 [95% CI 1.00, 1.31] in European men; OR 2.60 [95% CI 1.66, 4.06] in East Polynesian men; OR 1.53 [95% CI 1.07, 2.19] in West Polynesian men) but not in women (OR for the association 0.68 [95% CI 0.42, 1.10] in European women; OR 1.45 [95% CI 0.39, 5.36] in East Polynesian women). The PRS association with age at gout onset was robust to the removal of ABCG2 variants from the PRS in European and East Polynesian men (ß = -2.42 [95% CI -3.37, -1.46] and ß = -6.80 [95% CI -10.06, -3.55], respectively) but not in West Polynesian men (ß = -1.79 [95% CI -4.74, 1.16]). CONCLUSION: Genetic risk variants for gout also harbor risk for earlier age at gout onset and tophaceous disease in European and Polynesian men. Our findings suggest that earlier gout onset involves the accumulation of gout risk alleles in men but perhaps not in women, and that this genetic risk is shared across multiple ancestral groups.

Pseudomonas aeruginosa Promotes Persistence of Stenotrophomonas maltophilia via Increased Adherence to Depolarized Respiratory Epithelium.

Stenotrophomonas maltophilia is an emerging opportunistic respiratory pathogen in people with cystic fibrosis (CF). S. maltophilia is frequently observed in polymicrobial infections, and we have previously shown that Pseudomonas aeruginosa promotes colonization and persistence of S. maltophilia in mouse respiratory infections. In this study, we used host and bacterial RNA sequencing to further understand the molecular underpinnings of this interaction. To evaluate S. maltophilia transcript profiles, we used a recently described method for selective capture of bacterial mRNA transcripts with strain-specific RNA probes. We found that factors associated with the type IV pilus, including the histidine kinase subunit of a chemotactic two-component signaling system (chpA), had increased transcript levels during dual-species infection. Using immortalized CF respiratory epithelial cells, we found that infection with P. aeruginosa increases adherence of S. maltophilia, at least in part due to disruption of epithelial tight junctions. In contrast, an isogenic S. maltophilia chpA mutant strain lacked cooperative adherence to CF epithelia and decreased bacterial burden in vivo in dual-species infections with P. aeruginosa. Similarly, P. aeruginosa lacking elastase (lasB) failed to promote S. maltophilia adherence or bacterial colonization and persistence in vivo. Based on these results, we propose that disruption of lung tissue integrity by P. aeruginosa facilitates adherence of S. maltophilia to the lung epithelia, likely in a type IV pilus-dependent manner. These data lend insight into S. maltophilia colonization and persistence in people in later stages of CF disease and may have implications for interactions with other bacterial opportunists. IMPORTANCE Despite advances in treatment options for people with CF, complications of bacterial infections remain the greatest driver of morbidity and mortality in this patient population. These infections often involve more than one bacterial pathogen, and our understanding of how interspecies interactions impact disease progression is lacking. Previous work in our lab found that two CF pathogens, Stenotrophomonas maltophilia and Pseudomonas aeruginosa, can work together in the lung to cause more severe infection. In the present study, we found that infection with P. aeruginosa promotes persistence of S. maltophilia by interfering with epithelial barrier integrity. Depolarization of the epithelial cell layer by P. aeruginosa-secreted elastase increased S. maltophilia adherence, likely in a type IV pilus-dependent manner. Ultimately, this work sheds light on the molecular mechanisms governing an important multispecies interaction seen in pulmonary diseases such as CF.

Local genetic covariance between serum urate and kidney function estimated with Bayesian multitrait models.

Hyperuricemia (serum urate >6.8 mg/dl) is associated with several cardiometabolic and renal diseases, such as gout and chronic kidney disease. Previous studies have examined the shared genetic basis of chronic kidney disease and hyperuricemia in humans either using single-variant tests or estimating whole-genome genetic correlations between the traits. Individual variants typically explain a small fraction of the genetic correlation between traits, thus the ability to map pleiotropic loci is lacking power for available sample sizes. Alternatively, whole-genome estimates of genetic correlation indicate a moderate correlation between these traits. While useful to explain the comorbidity of these traits, whole-genome genetic correlation estimates do not shed light on what regions may be implicated in the shared genetic basis of traits. Therefore, to fill the gap between these two approaches, we used local Bayesian multitrait models to estimate the genetic covariance between a marker for chronic kidney disease (estimated glomerular filtration rate) and serum urate in specific genomic regions. We identified 134 overlapping linkage disequilibrium windows with statistically significant covariance estimates, 49 of which had positive directionalities, and 85 negative directionalities, the latter being consistent with that of the overall genetic covariance. The 134 significant windows condensed to 64 genetically distinct shared loci which validate 17 previously identified shared loci with consistent directionality and revealed 22 novel pleiotropic genes. Finally, to examine potential biological mechanisms for these shared loci, we have identified a subset of the genomic windows that are associated with gene expression using colocalization analyses. The regions identified by our local Bayesian multitrait model approach may help explain the association between chronic kidney disease and hyperuricemia.

Genetic correlations between traits associated with hyperuricemia, gout, and comorbidities.

Hypertension, obesity, chronic kidney disease and type 2 diabetes are comorbidities that have very high prevalence among persons with hyperuricemia (serum urate > 6.8 mg/dL) and gout. Here we use multivariate genetic models to test the hypothesis that the co-association of traits representing hyperuricemia and its comorbidities is genetically based. Using Bayesian whole-genome regression models, we estimated the genetic marker-based variance and the covariance between serum urate, serum creatinine, systolic blood pressure (SBP), blood glucose and body mass index (BMI) from two independent family-based studies: The Framingham Heart Study-FHS and the Hypertension Genetic Epidemiology Network study-HyperGEN. The main genetic findings that replicated in both FHS and HyperGEN, were (1) creatinine was genetically correlated only with urate and (2) BMI was genetically correlated with urate, SBP, and glucose. The environmental covariance among the traits was generally highest for trait pairs involving BMI. The genetic overlap of traits representing the comorbidities of hyperuricemia and gout appears to cluster in two separate axes of genetic covariance. Because creatinine is genetically correlated with urate but not with metabolic traits, this suggests there is one genetic module of shared loci associated with hyperuricemia and chronic kidney disease. Another module of shared loci may account for the association of hyperuricemia and metabolic syndrome. This study provides a clear quantitative genetic basis for the clustering of comorbidities with hyperuricemia.

The Shared Genetic Basis of Hyperuricemia, Gout, and Kidney Function.

Increased urate levels and gout correlate with chronic kidney disease with consensus that the primary driver of this relationship is reduced kidney function. However, a comparison of results of genome-wide association studies in serum urate levels and kidney function indicate a more complex situation. Approximately 20% of loci are shared-comprised of those in which the urate-raising allele associates with reduced kidney function, the vice versa situation, and those in which the signals/alleles are different. Although there is very little known regarding the molecular basis of the shared genetic relationship, it is clear that there is no major role for urate transporters and associated transportasome machinery. Some loci, however, do provide clues. The ATXN2 locus, with a shared signal, is one of only a small number of master regulators of expression by chromatin interaction, regulating expression of genes relevant for cholesterol and blood pressure. This suggests a role for systemic metabolic alteration. At HNF4A there is genetic heterogeneity with different genetic variants conferring risk to hyperuricemia and chronic kidney disease, suggesting different pathways. Interestingly, the shared loci congregate in the olfactory receptor pathway. The genome-wide association studies have generated a range of experimentally testable hypotheses that should provide insights into the shared pathogenesis of hyperuricemia/gout and chronic kidney disease.

Comorbidities in gout and hyperuricemia: causality or epiphenomena?

PURPOSE OF REVIEW: To review advances in the understanding of potentially causal relationships between gout, hyperuricemia and comorbidities. RECENT FINDINGS: Observational studies reveal 4-5 comorbidity clusters in gout patients. There tend to be gout alone, gout with chronic kidney disease and gout with other metabolic comorbidities. However, heterogeneous study populations and confounding make inference difficult for causal relationships. Mendelian randomization leverages genetic information as an instrumental variable to indicate putatively causal relationships between traits of epidemiological interest. Thus far, Mendelian randomization has not indicated widespread causal relationships of serum urate for comorbid traits. However, BMI has a small causal effect on serum urate, which may partially explain the increased prevalence of metabolic syndrome and cardiovascular disease among those with gout and hyperuricemia. There is a lack of robust and sufficiently powered Mendelian randomization studies for many serum urate-associated traits, such as hypertension. No adequately powered studies have been completed for gout and its comorbidities. SUMMARY: Although observational studies indicate putative causal effects of serum urate on comorbidities, Mendelian randomization studies suggest that serum urate does not have a causal role on the various tested comorbidities. There remains work to be done in clarifying the causal role of gout per se on the same traits.