The presence of P2RX7 single nuclear polymorphism is associated with a gain of function in P2X7 receptor and inflammasome activation in SLE complicated with pericarditis.

OBJECTIVES: A case control study was conducted to evaluate the possible influence of P2RX7 single nuclear polymorphism and P2X7 receptor activity in the susceptibility of SLE with pericarditis in Chinese Han population. METHODS: We studied a cohort of SLE patients with (SLE+PCS) or without (SLE-PCS) history of pericarditis and demographic, therapeutic and clinical data were retrospectively collected. P2RX7 489 C>T (His155Tyr) genotype of each subject was analysed and classified as CC or C>T (CT and TT) variant. After isolation of peripheral blood mononuclear cells and macrophages from whole blood by centrifugation on Ficoll gradient, in vitro macrophage releases of IL-1ß and IL-18 primed by LPS were evaluated by cytometric bead array. NLRP3 expression were evaluated by western blot after normalisation of house-keeping gene α-Tubulin. Finally, P2X7 receptor activity was analysed after stimulation with agonist ATP, by measuring permeability changes using ethidium bromide (EB) uptake fluorescent probe. The Hardy-Weinberg Equilibrium (HWE) analysis was used to detect the association of P2RX7 489C>T SNP with SLE complicated with pericarditis. Spearman linear regression analysis was performed to evaluate the association of macrophages uptake of EB and NLRP3 expression. RESULTS: In total 68 SLE+PCS patients and 72 SLE-PCS patients from the cohort were enrolled. No significant differences in demographic, disease activity and serological features were found between the two subgroups. The HWE analysis detected a significant positive association between SLE+PCS and the 489 C>T SNP (OR=0.65, 95%CI (0.46-0.92), p=0.03). No association was found in SLE-PCS patients carrying either genotype CC or C>T. It was shown that in vitro inflammasome-dependent IL-1ß/IL-18 release from macrophages was higher in SLE+PCS patients compared to SLE-PCS, especially in those bearing the C>T variant genotype, and consequently the WB analysis ofNLRP3 expression in SLE+PCS patients bearing C>T genotype was significantly higher compared to the other genotype carriers (F=13.1, p<0.01). We also detected that macrophages of SLE+PCS patients carrying SNP 489C>T showed a higher EB uptake in response to ATP than subjects carrying wild type (CC). The Spearman linear regression analysis showed a significant association of macrophages EB uptake and NLRP3 expression as well as its dependent IL-1ß and IL-18 in SLE+PCS subjects carrying SNP 489 C>T. CONCLUSIONS: Our results suggest that 489 C>T polymorphism of the P2RX7 gene is associated with activation of inflammasome NLRP3 and an increased release of IL-1ß and IL-18. The EB uptake increase in macrophages of LE+PCS subjects carrying 489C>T displays the functional upregulation of P2RX7, which may be involved in the pathogenesis of SLE complicated with pericarditis in the presence of P2RX7 SNP 489C>T.