P2X7 receptor gene polymorphism analysis in rheumatoid arthritis A. Al-Shukaili*, J. Al-Kaabi†, B. Hassan†, T. Al-Araimi†, M. Al-Tobi‡, M. Al-Kindi‡, A. Al-Maniri§, A. Al-Gheilani– & A. Al-Ansari– Summary The P2X7 receptor, a member of the P2X family of nucleotide-gated channels, is predominantly expressed by monocytic cells. The activation of this receptor has been associated with downstream-signalling cascades, resulting in the release of a number of inflammatory mediators. There are more than 815 single nucleotide polymorphisms (SNPs) that have been described in the human P2X7R gene, but only few have been function- ally characterized. The main aim of this study is to determine whether P2X7R gene polymorphisms confer susceptibility to rheumatoid arthritis (RA). A total of 125 patients with RA and 158 healthy volunteers were enrolled in this study. DNA fragment was PCR ampli- fied and sequenced on the AB 3130 Genetic Analyzer. No significant difference in allele frequencies of 489 C fi T, 1096 C fi G and 1513 A fi C polymorphisms, among sporadic cases of RA and healthy controls was found. However, the 1513A ⁄ C genotype was signifi- cantly associated with the presence of rheumatoid factor and anti-MCV autoantibody in RA patients. Interest- ingly, the genotype frequency of 1068 A ⁄ A was 0.19 in the RA group and 0.09 in control group (P = 0.025). Consequently, this polymorphism (AA) is two folds greater in the RA group compared to controls. More- over, this polymorphism was significantly associated with mean concentration of C-reactive protein in RA patients. In contrast, 946G fi A and 1729 T fi A were not detected in both groups. As a result, these two polymorphisms are uncommon in Omani Arab popula- tion. Polymorphism at position 1068 and 1513 in the P2X7R gene might contribute to the pathogenesis of RA. Moreover, the loss-of-function SNP at position 1096 C fi G or the gain-of-function SNP at position 489 C fi T of the P2X7 gene does not appear to be a susceptibility gene locus for the development of RA. Further studies are required to confirm this finding. Introduction The biological effects of extracellular ATP and other nucleotide are mediated via stimulation of two pri- mary classes of purinergic receptor, P1 and P2. P1 receptors respond to adenosine, whereas, P2 receptors are activated by ATP, ADP, UTP and other forms of nucleotides. There are 15 cloned and characterized mammalian P2 receptors; including: 8 P2Y and 7 P2X (P2X1-7). However, P2X7 receptor (P2X7R) has exten- sive interest because of its unique structure and physi- ological functions (Chen & Brosnan, 2006; Ferrari et al., 2006; Lister et al., 2007). The P2X7R is a protein of 595 amino acid long, with two transmembrane domains, an extracellular residue and intracellular N and C termini (North, 2002; Ferrari et al., 2006). This receptor is expressed primarily (though not exclusively) on cells of haemo- poietic origin (Collo et al., 1997). The stimulation of the P2X7R by ATP or its stable analogue 2¢,3¢-O-(ben- zoyl-4-benzoyl)-ATP (BzATP) results in the opening of a nonselective cationic channel and influxes of Na + , K + and Ca + , promoting several responses among which one is cell proliferation (Nuttle & Dubyak, 1994; Baricordi et al., 1999). However, upon prolonged activation, the P2X7R forms an aqueous pore that allows the passage of hydrophilic molecules of up to 900 Da that can ultimately lead to cell death (Smart et al., 2003). Moreover, the activation of this receptor has been associated with downstream-signalling cas- cades resulting in the release of a number of inflamma- tory mediators, such as IL-1b and IL-18, and in turn IL-6, IL-8 and tumour necrosis factor alpha (TNF-a) (Lister et al., 2007). These proinflammatory cytokines play a crucial role in the pathogenesis of many inflam- matory diseases including rheumatoid arthritis (RA). Moreover, it has been shown that P2X7R activation, in both mouse bone marrow-derived macrophages (BMDMs) and human lung alveolar macrophages, releases sufficient amounts of lysosomal cathepsins into the extracellular medium independent of proin- flammatory cytokines. This production of lysosomal * Department of Microbiology & Immunology, College of Medicine and Health Sciences, Sultan Qaboos University (SQU), Muscat, Oman, † Rheumatology Unit, Department of Medicine, SQU, Mus- cat, Oman, ‡ Department of Biochemistry, College of Medicine and Health Sciences, SQU, Muscat, Oman, § Department of Family Medicine and Public Health, SQU, Muscat, Oman and – Department of Biology, College of Science, SQU, Muscat, Oman Received 12 January 2011; revised 4 April 2011; accepted 9 May 2011 Correspondence: Ahmed Al-Shukaili, Department of Microbiology & Immunology, College of Medicine and Health Sciences, Sultan Qaboos University (SQU), P.O. Box 35, PC 123, Muscat, Sultanate of Oman. Tel: +968 99 36 25 24; Fax: +968 244 13 419; E-mail: shukaily@squ.edu.om ª 2011 Blackwell Publishing Ltd, International Journal of Immunogenetics 38, 389–396 389 doi: 10.1111/j.1744-313X.2011.01019.x