PADI4 polymorphisms and susceptibility to rheumatoid arthritis: a meta-analysis

Implications of Peptidyl Arginine Deiminase 4 gene transcription and polymorphisms in susceptibility to rheumatoid arthritis in an Iranian population

BACKGROUND

Peptidyl arginine deiminase 4 (PADI4) has been implicated in Rheumatoid arthritis (RA) pathogenesis. Here we aimed to evaluate the association of PADI4 gene rs11203367 and rs1748033 single nucleotide polymorphisms (SNPs) with RA proneness.

METHODS

The mRNA expression of PADI4 was determined in the whole blood samples. The genotyping of PADI4 polymorphisms was conducted using allelic discrimination TaqMan genotyping Real-time PCR.

RESULTS

The alleles and genotypes of rs11203367 polymorphism were not associated with susceptibility to RA risk. The T allele (OR = 1.58, 95%CI: 1.21-2.04, P = 0.0005), TT genotype (OR = 2.79, 95%CI: 1.53-5.06, P = 0.0007), TC genotype (OR = 1.52, 95%CI: 1.04-2.23, P = 0.0291), dominant (OR = 1.72, 95%CI: 1.19-2.47, P = 0.0034) and recessive (OR = 2.19, 95%CI: 1.25-3.82, P = 0.0057) models of rs1748033 SNP were associated with higher risk of RA. There was a significant upregulation of PADI4 mRNA in the RA patients compared to controls. mRNA expression of PADI4 had significantly positive correlation with anti-CCP level (r = 0.37, P = 0.041), RF level (r = 0.39, P = 0.037), and CRP level (r = 0.39, P = 0.024).

CONCLUSION

PADI4 gene rs1748033 SNP was associated with increased RA risk. This polymorphism might affect the RA pathogenesis regardless of impressing the levels of PADI-4 in serum.

Peptidylarginine deiminase 4 -104C/T polymorphism and risk of rheumatoid arthritis: A pooled analysis based on different populations

Background

Many studies have analyzed the association between peptidylarginine deiminase 4 (PADI4) -104C/T polymorphism and rheumatoid arthritis (RA). However, the results are inconsistent. This meta-analysis, based on different populations, updated and reevaluated the possible associations between PADI4 -104C/T polymorphism and the susceptibility to RA.

Methods

A literature search was performed on PubMed and related Chinese databases up to April 2017. The association between PADI4 -104C/T polymorphism and RA risk was evaluated by calculating pooled odds ratios (ORs) and 95% confidence intervals (CIs).

Results

A total of seventeen studies, including 5,756 RA cases and 4,987 controls, were screened out. In the overall population, PADI -104C/T polymorphism was significantly associated with an increased RA risk. In this meta-analysis stratified by ethnicity, a significant association between PADI -104C/T polymorphism and RA risk was established in China and Japan.

Conclusions

Our study indicated a significantly increased association between PADI -104C/T polymorphism and RA in Chinese and Japanese populations. Because most included populations in this meta-analysis were Asian, further studies are needed to elucidate whether the PADI4 -104C/T gene confers RA in other ethnic groups.

Hypoxia‑induced autophagy is inhibited by PADI4 knockdown, which promotes apoptosis of fibroblast‑like synoviocytes in rheumatoid arthritis

Impaired apoptosis of rheumatoid arthritis (RA)-fibroblast-like synoviocytes (FLS) is pivotal in the process of RA. Peptidyl arginine deiminase type IV (PADI4) is associated with autoantibody regulation via histone citrullination in RA. The present study aimed to investigate the role of PADI4 in the apoptosis of RA-FLS. FLS were isolated from patients with RA and a rat model. The effects of PADI4 on RA-FLS were investigated in vitro and in vivo. Hypoxia-induced autophagy was induced by 1% O₂ and was detected by immunohistochemical and immunofluorescence analysis; in addition, apoptosis was detected by flow cytometry. RA-FLS obtained from RA rat model exhibited significant proliferation under severe hypoxia conditions. Hypoxia also significantly induced autophagy and elevated the expression of PADI4. Subsequently, short hairpin RNA-mediated PADI4 knockdown was demonstrated to significantly inhibit hypoxia-induced autophagy and promote apoptosis in RA-FLS. The results of these in vitro and in vivo studies suggested that PADI4 may be closely associated with hypoxia-induced autophagy, and the inhibition of hypoxia-induced autophagy by PADI4 knockdown may contribute to an increase in the apoptosis of RA-FLS.

Increased autophagy in fibroblast-like synoviocytes leads to immune enhancement potential in rheumatoid arthritis

The incidence of rheumatoid arthritis (RA) has been reported to be correlated with a disorder of immunregulation. Rheumatoid arthritis fibroblast-like synoviocytes (RA-FLSs) play an important role in regulating the local immune microenvironment. However, the potential mechanism of RA-FLS in regulating the immnue response is not clearly understood. In this study, we demonstrated that the expression of HIF-1α was significantly up-regulated in rheumatoid arthritis tissue which indicated that the hypoxia condition in the microenvironment. We also observed that RA-FLSs demonstrated the potential to up-regulate immune activation. Meanwhile, the level of autophagy increased in RA-FLSs compared with control group. Besides that, the expression of IL-6 was up-regulated not only in RA-FLSs but also in the fibroblasts that treated with hypoxia condition. Accordingly, we found that autophagy inhibitiors could effectively inhibit the immune activation function of RA-FLSs medicated by IL-6. Taken together, the results we demonstrated above indicated that the hypoxia microenvironment could effectively induce the incidence of autophagy and then lead to the immune activation function of RA-FLSs medicated by IL-6.

Meta-analysis of the association between PADI4 -92C/G polymorphism and rheumatoid arthritis in the Chinese population

Many studies have evaluated the correlation between peptidylarginine deiminase 4 (PADI4) -92C/G polymorphism and rheumatoid arthritis (RA), but the results remain inconclusive. Therefore, we performed a meta-analysis in the Chinese population to provide comprehensive data on the association between PADI4 -92C/G polymorphism and RA. Eligible studies published before May 2016 were identified in PubMed and Chinese databases. The strengths of these associations were assessed by pooled odds ratios (OR) and 95% confidence interval (CI). Eight studies documenting a total of 1351 RA cases and 1585 controls were included in this meta-analysis. In the overall analysis, a significant association between the PADI4 -92C/G polymorphism and RA was found in the Chinese population (G vs C: OR=1.32, 95%CI=1.02-1.71; GG+CG vs CC: OR=1.75, 95%CI=1.20-2.53). The subgroup analyses stratified by geographic area(s) and source of controls revealed significant results in South China, in hospital-based studies and population-based studies. In summary, this meta-analysis suggested that PADI4 -92C/G polymorphism may be associated with the RA incidence in the Chinese population, especially for South China. Further studies conducted on other ethnic groups are required for definite conclusions.

Peptidylarginine deiminase 2 is required for tumor necrosis factor alpha-induced citrullination and arthritis, but not neutrophil extracellular trap formation

Citrullination, the post-translational conversion of arginines to citrullines, may contribute to rheumatoid arthritis development given the generation of anti-citrullinated protein antibodies (ACPAs). However, it is not known which peptidylarginine deiminase (PAD) catalyzes the citrullination seen in inflammation. PAD4 exacerbates inflammatory arthritis and is critical for neutrophil extracellular traps (NETs). NETs display citrullinated antigens targeted by ACPAs and thus may be a source of citrullinated protein. However, PAD4 is not required for citrullination in inflamed lungs. PAD2 is important for citrullination in healthy tissues and is present in NETs, but its role in citrullination in the inflamed joint, NETosis and inflammatory arthritis is unknown. Here we use mice with TNFα-induced inflammatory arthritis, a model of rheumatoid arthritis, to identify the roles of PAD2 and PAD4 in citrullination, NETosis, and arthritis. In mice with TNFα-induced arthritis, citrullination in the inflamed ankle was increased as determined by western blot. This increase was unchanged in the ankles of mice that lack PAD4. In contrast, citrullination was nearly absent in the ankles of PAD2-deficient mice. Interestingly, PAD2 was not required for NET formation as assessed by immunofluorescence or for killing of Candida albicans as determined by viability assay. Finally, plasma cell numbers as assessed by flow cytometry, IgG levels quantified by ELISA, and inflammatory arthritis as determined by clinical and pathological scoring were all reduced in the absence of PAD2. Thus, PAD2 contributes to TNFα-induced citrullination and arthritis, but is not required for NETosis. In contrast, PAD4, which is critical for NETosis, is dispensable for generalized citrullination supporting the possibility that NETs may not be a major source of citrullinated protein in arthritis.

A molecular signature of preclinical rheumatoid arthritis triggered by dysregulated PTPN22

A unique feature of rheumatoid arthritis (RA) is the presence of anti-citrullinated protein antibodies (ACPA). Several risk factors for RA are known to increase the expression or activity of peptidyl arginine deiminases (PADs), which catalyze citrullination and, when dysregulated, can result in hypercitrullination. However, the consequence of hypercitrullination is unknown and the function of each PAD has yet to be defined. Th cells of RA patients are hypoglycolytic and hyperproliferative due to impaired expression of PFKFB3 and ATM, respectively. Here, we report that these features are also observed in peripheral blood mononuclear cells (PBMCs) from healthy at-risk individuals (ARIs). PBMCs of ARIs are also hypercitrullinated and produce more IL-2 and Th17 cytokines but fewer Th2 cytokines. These abnormal features are due to impaired induction of PTPN22, a phosphatase that also suppresses citrullination independently of its phosphatase activity. Attenuated phosphatase activity of PTPN22 results in aberrant expression of IL-2, ATM, and PFKFB3, whereas diminished nonphosphatase activity of PTPN22 leads to hypercitrullination mediated by PADs. PAD2- or PAD4-mediated hypercitrullination reduces the expression of Th2 cytokines. By contrast, only PAD2-mediated hypercitrullination can increase the expression of Th17 cytokines. Taken together, our data depict a molecular signature of preclinical RA that is triggered by impaired induction of PTPN22.

Prevalence of soluble peptidylarginine deiminase 4 (PAD4) and anti-PAD4 antibodies in autoimmune diseases

The objectives of this study are to investigate the prevalence of PAD4 and anti-PAD4 antibodies (Abs) in autoimmune diseases and to clarify their association with anticitrullinated protein antibodies (ACPAs) and shared epitope (SE) in patients with rheumatoid arthritis (RA). Levels of human PAD4 and anti-PAD4 Abs in serum or plasma were measured using sandwich ELISA. Samples were obtained from patients with RA (n = 148), SLE (n = 36), or SS (n = 37) and from healthy controls (HCs; n = 40). Antibodies against cyclic citrullinated glucose-6-phosphate isomerase (GPI) (CCG)-2, CCG-7, anti-CEP-1, and anti-CCP Abs were also measured using ELISA. Patients with RA were genotyped for HLA-DRB1. The human PAD4 and anti-PAD4 Ab levels were compared with the ACPA and SE in patients with RA. The PAD4 levels were 111.9 U/ml in the RA, 30.4 U/ml in the SLE, 81.9 U/ml in the SS patients, and 46.6 U/ml in the HCs. The PAD4 levels were significantly higher in the RA than in the SLE patients or the HCs. Anti-PAD4 Abs were detected in 29.7 % of the patients with RA, but not in the patients with SLE or SS, nor in the HCs. In the RA patients, the PAD4 levels in the anti-PAD4 Ab-negative group were significantly higher than those in the anti-PAD4 Ab-positive group. Moreover, anti-CCG-2, CCG-7, CEP-1, and anti-CCP Ab levels were significantly higher in the anti-PAD4 Ab-positive group than in the anti-PAD4 Ab-negative group. In the RA patients, the PAD4 levels were not correlated with ACPAs. Neither PAD4 nor anti-PAD4 Abs were significantly correlated with the presence of SE alleles. The PAD4 levels were higher in RA than in SLE or HC. Anti-PAD4 Abs appeared specifically in patients with RA. Moreover, anti-PAD4 Abs were associated with ACPAs.

Associations Between PADI4 Gene Polymorphisms and Rheumatoid Arthritis: An Updated Meta-analysis

BACKGROUND AND AIMS

Studies investigating the association between the peptidylarginine deiminase 4 (PADI4) gene polymorphisms and rheumatoid arthritis (RA) reported conflicting results. The aim of this meta-analysis was to assess the association between PADI4 gene polymorphisms and RA.

METHODS

A systematic literature search was conducted to identify relevant studies. Pooled odds ratios (ORs) with 95% confidence intervals (CIs) were used to estimate the strength of the association.

RESULTS

A total of 34 studies from 28 articles involving 19859 patients with RA and 25771 healthy controls were included. Significant association of PADI4-94G/A polymorphism and RA was observed (OR = 0.891, 95% CI = 0.833-0.954, p = 0.001) in the overall study population and in the Asian populations (OR = 0.824, 95% CI = 0.759-0.894, p = 0.000) respectively. For the -92C/G polymorphism, a significant association was observed (OR = 1.481, 95% CI = 1.166-1.882, p = 0.001) in Africans. For the -90C/T polymorphism, a significant association was observed (OR = 0.576, 95% CI = 0.381-0.872, p = 0.009) in the Latin American population. The pooled estimates for the other polymorphisms were not statistically significantly associated with RA (PADI4-104C/T, -89A/G, -96T/C).

CONCLUSIONS

This meta-analysis demonstrates that PADI4-94G/A polymorphism is associated with susceptibility to RA in the overall population and in the Asian population. The PADI4 -92C/G polymorphism confers susceptibility to RA in Africans and the PADI4-90C/T polymorphism was associated with RA in the Latin American population.

Hydrochlorothiazide-induced hyperuricaemia in the pharmacogenomic evaluation of antihypertensive responses study

OBJECTIVE

Elevations in uric acid (UA) and the associated hyperuricaemia are commonly observed secondary to treatment with thiazide diuretics. We sought to identify novel single nucleotide polymorphisms (SNPs) associated with hydrochlorothiazide (HCTZ)-induced elevations in UA and hyperuricaemia.

METHODS

A genome-wide association study of HCTZ-induced changes in UA was performed in Caucasian and African American participants from the pharmacogenomic evaluation of antihypertensive responses (PEAR) study who were treated with HCTZ monotherapy. Suggestive SNPs were replicated in Caucasians and African Americans from the PEAR study who were treated with HCTZ add-on therapy. Replicated regions were followed up through expression and pathway analysis.

RESULTS

Five unique gene regions were identified in African Americans (LUC7L2, ANKRD17/COX18, FTO, PADI4 and PARD3B), and one region was identified in Caucasians (GRIN3A). Increases in UA of up to 1.8 mg dL(-1) were observed following HCTZ therapy in individuals homozygous for risk alleles, with heterozygotes displaying an intermediate phenotype. Several risk alleles were also associated with an increased risk of HCTZ-induced clinical hyperuricaemia. A composite risk score, constructed in African Americans using the 'top' SNP from each gene region, was strongly associated with HCTZ-induced UA elevations (P = 1.79 × 10(-7) ) and explained 11% of the variability in UA response. Expression studies in RNA from whole blood revealed significant differences in expression of FTO by rs4784333 genotype. Pathway analysis showed putative connections between many of the genes identified through common microRNAs.

CONCLUSION

Several novel gene regions were associated with HCTZ-induced UA elevations in African Americans (LUC7L2, COX18/ANKRD17, FTO, PADI4 and PARD3B), and one region was associated with these elevations in Caucasians (GRIN3A).