CYB5A polymorphism increases androgens and reduces risk of rheumatoid arthritis in women.

INTRODUCTION: Rheumatoid arthritis (RA) is characterized by decreased androgen levels, which was the first hormonal abnormality described. Several studies indicated that steroidogenesis is directed towards endogenous glucocorticoids at the expense of androgens. The decisive step governing androgen synthesis is the 17,20-lyase activity of the CYP17A1 gene-encoded enzyme cytochrome P450 17A1. Here, we focused on the role in RA of the critical cofactor for 17,20-lyase activity, cytochrome b5, encoded by the CYB5A gene. METHODS: Data sets of two genome wide RA association studies (GWAS) were screened for single nucleotide polymorphisms (SNP) in the CYB5A gene. Candidate SNPs in CYB5A were studied in a case-control study population of Slovakia. Expression analyses were done in synovial fibroblasts from RA patients by quantitative real-time polymerase chain reaction, and cytochrome b5-expression was detected by immunohistochemistry. Real-life androgen production after steroid conversion was measured using radiolabeled substrates. RESULTS: The study identified the RA-associated intronic SNP rs1790834 in the CYB5A gene in one GWAS and confirmed the same SNP in our study. The minor allele reduced RA risk selectively in women (P=4.1*10(-3); OR=0.63, 95% CI [0.46-0.86]). The protective effect was confined to rheumatoid factor-positive (OR=0.53, [0.37-0.75]) and anti-cyclic citrullinated peptide-positive (OR=0.58, [0.41-0.83]) cases, respectively. The protective allele doubles CYB5A mRNA-expression resulting in 2-3fold activation of steroid 17,20-lyase activity, and protective allele was accompanied by a higher density of cytochrome b5-positive cells in synovial tissue. CONCLUSIONS: CYB5A is the first RA susceptibility gene involved in androgen synthesis. Our functional analysis of SNP rs1790834 indicates that it contributes to the sex bias observed in RA.

N-cadherin promoter polymorphisms and risk of osteoarthritis.

Osteoarthritis (OA) is the most common form of arthritis. It is characterized by cartilage destruction and bone remodeling, mediated in part by synovial fibroblasts (SFs). Given the functional significance of cadherins in these cells, we aimed at determining the role of genetic variants of N-cadherin (CDH2) in OA of the knee and hip. Six single-nucleotide polymorphisms in the genomic region of the CDH2 gene were genotyped in 312 patients with OA and 259 healthy control subjects. Gene expression of CDH2 was analyzed by qRT-PCR. Liquid chromatography-mass spectrometry was used to identify a transcription factor isolated by DNA pulldown. Its potential for binding to gene variants was examined by electrophoretic mobility shift assay, enzyme-linked immunosorbent assay, and chromatin immunoprecipitation. Genetic analysis identified a polymorphism located in the CDH2 promoter region to be associated with risk of OA. The minor allele of rs11564299 had a protective effect against OA. Compared to carriers of the major allele, carriers of the minor allele of rs11564299 displayed increased N-cadherin levels in SFs. Based on in silico analysis, the minor allele was predicted to generate a novel transcription factor binding site, Direct-binding assays and mass spectrometric analysis identified hnRNP K as binding selectively to the minor allele. In summary, a CDH2 promoter polymorphism influences the risk of OA, and hnRNP K was found to be involved in the regulation of elevated N-cadherin expression in patients with OA carrying the minor allele of rs11564299.

Genetics in neuroendocrine immunology: implications for rheumatoid arthritis and osteoarthritis.

Both genetic and environmental factors contribute to rheumatoid arthritis (RA) as well as osteoarthritis (OA). For RA, most of the known genetic markers are linked with genes from immunological pathways. Recent genome-wide association studies (GWAS) on RA identified known and novel susceptibility genes like HLA-DRB1, PTPN22, STAT4, TRAF1/C5, OLIG3/TNFAIP3, CD40, CCL21, MMEL1-TNFRSF14, CDK6, PRKCQ, IL2RB, and KIF5A-PIP4K2C. These association signals explain more than 50% of the genetic influence on RA. In contrast, less GWAS data for OA exist. Most OA susceptibility genes arose from classical candidate gene analyses and were not replicated in all study samples. Neuroendocrine factors are hypothesized to play an important role both in RA and OA etiology. Here, we discuss these findings and present an outlook for genetic association studies after GWAS.

Association of common polymorphisms in known susceptibility genes with rheumatoid arthritis in a Slovak population using osteoarthritis patients as controls.

INTRODUCTION: Both genetic and environmental factors contribute to rheumatoid arthritis (RA), a common and complex autoimmune disease. As well as the major susceptibility gene HLA-DRB1, recent genome-wide and candidate-gene studies reported additional evidence for association of single nucleotide polymorphism (SNP) markers in the PTPN22, STAT4, OLIG3/TNFAIP3 and TRAF1/C5 loci with RA. This study was initiated to investigate the association between defined genetic markers and RA in a Slovak population. In contrast to recent studies, we included intensively-characterized osteoarthritis (OA) patients as controls. METHODS: We used material of 520 RA and 303 OA samples in a case-control setting. Six SNPs were genotyped using TaqMan assays. HLA-DRB1 alleles were determined by employing site-specific polymerase chain reaction (PCR) amplification. RESULTS: No statistically significant association of TRAF1/C5 SNPs rs3761847 and rs10818488 with RA was detected. However, we were able to replicate the association signals between RA and HLA-DRB1 alleles, STAT4 (rs7574865), PTPN22 (rs2476601) and OLIG3/TNFAIP3 (rs10499194 and rs6920220). The strongest signal was detected for HLA-DRB1*04 with an allelic P = 1.2*10-13 (OR = 2.92, 95% confidence interval (CI) = 2.18 - 3.91). Additionally, SNPs rs7574865STAT4 (P = 9.2*10-6; OR = 1.71, 95% CI = 1.35 - 2.18) and rs2476601PTPN22 (P = 9.5*10-4; OR = 1.67, 95% CI = 1.23 - 2.26) were associated with susceptibility to RA, whereas after permutation testing OLIG3/TNFAIP3 SNPs rs10499194 and rs6920220 missed our criteria for significance (Pcorr = 0.114 and Pcorr = 0.180, respectively). CONCLUSIONS: In our Slovak population, HLA-DRB1 alleles as well as SNPs in STAT4 and PTPN22 genes showed a strong association with RA.