Genome-wide association study revealed novel loci which aggravate asymptomatic hyperuricaemia into gout.

OBJECTIVE: The first ever genome-wide association study (GWAS) of clinically defined gout cases and asymptomatic hyperuricaemia (AHUA) controls was performed to identify novel gout loci that aggravate AHUA into gout. METHODS: We carried out a GWAS of 945 clinically defined gout cases and 1003 AHUA controls followed by 2 replication studies. In total, 2860 gout cases and 3149 AHUA controls (all Japanese men) were analysed. We also compared the ORs for each locus in the present GWAS (gout vs AHUA) with those in the previous GWAS (gout vs normouricaemia). RESULTS: This new approach enabled us to identify two novel gout loci (rs7927466 of CNTN5 and rs9952962 of MIR302F) and one suggestive locus (rs12980365 of ZNF724) at the genome-wide significance level (p<5.0×10-8). The present study also identified the loci of ABCG2, ALDH2 and SLC2A9. One of them, rs671 of ALDH2, was identified as a gout locus by GWAS for the first time. Comparing ORs for each locus in the present versus the previous GWAS revealed three 'gout vs AHUA GWAS'-specific loci (CNTN5, MIR302F and ZNF724) to be clearly associated with mechanisms of gout development which distinctly differ from the known gout risk loci that basically elevate serum uric acid level. CONCLUSIONS: This meta-analysis is the first to reveal the loci associated with crystal-induced inflammation, the last step in gout development that aggravates AHUA into gout. Our findings should help to elucidate the molecular mechanisms of gout development and assist the prevention of gout attacks in high-risk AHUA individuals.

GWAS of clinically defined gout and subtypes identifies multiple susceptibility loci that include urate transporter genes.

OBJECTIVE: A genome-wide association study (GWAS) of gout and its subtypes was performed to identify novel gout loci, including those that are subtype-specific. METHODS: Putative causal association signals from a GWAS of 945 clinically defined gout cases and 1213 controls from Japanese males were replicated with 1396 cases and 1268 controls using a custom chip of 1961 single nucleotide polymorphisms (SNPs). We also first conducted GWASs of gout subtypes. Replication with Caucasian and New Zealand Polynesian samples was done to further validate the loci identified in this study. RESULTS: In addition to the five loci we reported previously, further susceptibility loci were identified at a genome-wide significance level (p<5.0×10-8): urate transporter genes (SLC22A12 and SLC17A1) and HIST1H2BF-HIST1H4E for all gout cases, and NIPAL1 and FAM35A for the renal underexcretion gout subtype. While NIPAL1 encodes a magnesium transporter, functional analysis did not detect urate transport via NIPAL1, suggesting an indirect association with urate handling. Localisation analysis in the human kidney revealed expression of NIPAL1 and FAM35A mainly in the distal tubules, which suggests the involvement of the distal nephron in urate handling in humans. Clinically ascertained male patients with gout and controls of Caucasian and Polynesian ancestries were also genotyped, and FAM35A was associated with gout in all cases. A meta-analysis of the three populations revealed FAM35A to be associated with gout at a genome-wide level of significance (p meta =3.58×10-8). CONCLUSIONS: Our findings including novel gout risk loci provide further understanding of the molecular pathogenesis of gout and lead to a novel concept for the therapeutic target of gout/hyperuricaemia.

Increased expression of TRAIL receptor 3 on eosinophils in Churg-Strauss syndrome.

OBJECTIVE: Prolonged survival of eosinophils plays an important role in the pathogenesis of Churg-Strauss syndrome (CSS); however, its detailed molecular mechanism is still unclear. TRAIL and its receptors are expressed on a variety of cells, including eosinophils. In this study, we examined the expression of TRAIL receptors on eosinophils from patients with CSS. METHODS: TRAIL receptor expression was assessed on eosinophils from healthy volunteers, patients with CSS, patients with asthma, and patients with hypereosinophilia due to parasitic infection. TRAIL-induced apoptosis of eosinophils was compared between the patients with CSS and patients with asthma. RNA interference was used to assess the effects of suppression of TRAIL receptor 3. RESULTS: Expression of TRAIL receptor 3, a decoy receptor that acts as an antiapoptotic receptor, on eosinophils from patients with CSS was significantly higher than that in the other subjects. Moreover, in CSS, serum TRAIL receptor 3 levels showed a significant positive correlation with peripheral eosinophil counts, tissue-infiltrating eosinophils stained positive for this receptor, and peripheral T cells expressed TRAIL on their surface. Compared with asthma patients, eosinophils from CSS patients showed a significantly lower percentage of recombinant TRAIL, less autologous T cell-induced apoptosis, and decreased level of active caspase 3. Suppression of TRAIL receptor 3 through RNA interference significantly increased the recombinant TRAIL-induced apoptosis of eosinophils from CSS patients. CONCLUSION: Increased expression of TRAIL receptor 3 on eosinophils from patients with CSS was observed. These alterations in TRAIL receptor 3 expression might be involved in the molecular pathogenesis of CSS eosinophilia.

Discoidin domain receptor 1 contributes to eosinophil survival in an NF-kappaB-dependent manner in Churg-Strauss syndrome.

Churg-Strauss syndrome (CSS) is a systemic disease that shows marked eosinophilia along with eosinophil infiltration in the tissue. Prolonged eosinophil survival plays an important role in the pathogenesis of CSS; however, its detailed molecular mechanism remains unclear. Discoidin domain receptor 1 (DDR1) is a receptor tyrosine kinase, and its ligand is collagen. DDR1 was expressed in human leukocytes and fibroblasts, and it plays an important role in leukocyte cytokine production and fibroblast survival in an NF-kappaB-dependent manner. In this study, we examined in vitro and in vivo eosinophil DDR1 expression and its function in CSS patients. The expression level of DDR1 was significantly higher in the eosinophils of CSS patients, and the predominant isoform was DDR1b. Immunohistochemical findings revealed that the tissue-infiltrating eosinophils expressed endogenous DDR1. In CSS patients, DDR1 activation inhibited Fas agonistic antibody-induced apoptosis and up-regulated Fas agonistic antibody-induced cytokine production of eosinophils in an NF-kappaB-dependent manner. Suppression of DDR1 expression in the eosinophils by using RNA interference and addition of the DDR1-blocking protein abolished these effects. We propose that DDR1 contributes to the eosinophil survival in the tissue microenvironment of CSS and that it might be involved in the development of CSS.

Discoidin domain receptor 1 contributes to the survival of lung fibroblast in idiopathic pulmonary fibrosis.

Idiopathic pulmonary fibrosis (IPF), characterized by fibroblast proliferation and accumulation of extracellular matrix, including collagen, is a chronic progressive disorder that results in lung remodeling and fibrosis. However, the cellular mechanisms that may make fibroblasts resistant to apoptosis have not been completely elucidated. Discoidin domain receptor 1 (DDR1), a receptor tyrosine kinase whose ligand is collagen, is expressed in vivo and contributes in vitro to leukocyte differentiation and nuclear factor (NF)-kappaB activation, which may play an important role in fibroblast survival. In this study, we examined in vivo and in vitro DDR1 expression and its role in cell survival using fibroblasts obtained from IPF and non-IPF patients. Immunohistochemically, fibroblasts present in fibroblastic foci expressed endogenous DDR1. The DDR1 expression level was significantly higher in fibroblasts from IPF patients, and the predominant isoform was DDR1b. In IPF patients, DDR1 activation in fibroblasts inhibited Fas ligand-induced apoptosis and resulted in NF-kappaB nuclear translocation. Suppression of DDR1 expression in fibroblasts by siRNA abolished these effects, and an NF-kappaB inhibitor abrogated the anti-apoptotic effect of DDR1 activation. We propose that DDR1 contributes to fibroblast survival in the tissue microenvironment of IPF and that DDR1 up-regulation may occur in other fibroproliferative lung diseases as well.