SNP (1513A > C AND 489C > T) OF P2X7 RECEPTOR IN SYSTEMIC LUPUS ERYTHEMATOSUS WITH SEROSITIS

Background: Our preliminary data demonstrated that expression and activity of P2X7R was impaired in Systemic Lupus Erythematosus (SLE) and associated with a reduced production of IL-1β . Serositis is a typical manifestation of SLE characterized by a marked inflammation, which has been suggested to be an “inflammasome driven” manifestation. Objectives: to investigate the role of 1513A>C (rs3751143) and 489C>T (rs208294) Single Nucleotide Polymorphisms (SNPs) which are differently associated with loss or gain of function, respectively, of P2X7R, a potent activator of the NLRP3 inflammasome and IL-1β release, in patients with SLE and with a history of serositis (SLE-S). Methods: DNA was extracted from whole blood and used for evaluation of 2 P2X7R SNPs (1513A>C and 489C>T). Considering the combined action of these two SNPs, the overall activity of P2X7R was divided, into three groups: GOF (gain of function), normal function (NF), and LOF (loss of function). In addition, peripheral blood mononuclear cells (PBMCs) were isolated from venous blood and employed to evaluate P2X7R and NLRP3 expression by RT-PCR, assess P2X7R activity as Benzoyl ATP (BzATP)-induced intracellular Calcium ([Ca2+]i) increments and evaluate in vitro IL-1β and IL-6 release following stimulation with lipopolysaccharide (LPS) and BzATP, either separately or in combination. Results: 33 SLE patients (pts), 11 with (SLE-S) and 22 without serositis (SLE-NS) were enrolled. Mean age was 40.9±10.9 years and disease duration was 135.3± 108.6 months. No significant difference in disease activity and clinical characteristic was found between the two groups (table 1). Evaluating 1513A>C SNP, 20 pts were positive for A/A and 13 for A/C phenotype respectively, while in case of 489C>T SNP, 7 pts presented C/C, 12 C/T and 14 T/T phenotype with a comparable distribution between SLE-NS and SLE-S (table 1). After combination of different phenotypes, 9 pts presented normal function (NF), 22 gain of function (GOF) and 2 loss of function (LOF) with no significant difference between SLE-S and SLE-NS (table 1). P2X7R activity, (evaluated as IL-1 β production and [Ca2+]i increments,) and expression (evaluated with RT-PCR) were comparable between SLE-S and SLE-NS. No significant difference was found between expression and activity of P2X7R and NLRP3 and the two SNPs evaluated Conclusions: our data indicate that the 1513A>C and 489C>T SNPs do not seem linked with reduced activity and expression of P2X7R that we previously observed in our cohort of lupus patients. Furthermore, no significant association was found between expression of these SNPs and development of serositis.