Two haplotypes of the P2X₇receptor containing the Ala‐348 to Thr polymorphism exhibit a gain‐of‐function effect and enhanced interleukin‐1β secretion

Abstract

The P2X(7) receptor is an ATP-gated cation channel expressed in immune cells and plays a role in proinflammatory cytokine release from monocytes and macrophages. This study investigated the coinheritance of 12 functionally relevant single nucleotide polymorphisms (SNPs) in the human P2X(7) gene (P2RX7), and the functional effect of each singly and in combination was assessed by measurements of ATP-induced currents and ethidium(+) uptake. Genotyping of 3430 Caucasian subjects identified 4 common haplotypes in addition to the common (wild-type) P2X(7)-1. Two haplotypes (denoted P2X(7)-2 and P2X(7)-4) contained various combinations of gain-of-function SNPs. P2X(7)-4 was identified uniquely by the Gln-460 to Arg polymorphism (rs2230912). When expressed in HEK-293 cells, recombinant P2X(7)-2, and P2X(7)-4 haplotypes displayed a 3-fold and 5-fold increase, respectively, in receptor function compared to the wild-type P2X(7)-1. Both P2X(7) haplotypes contained the Ala-348>Thr polymorphism (rs1718119), and this mutation was critical for the gain-of-function effect. Peripheral blood monocytes and erythrocytes from subjects homozygous for gain-of-function P2X(7) haplotypes exhibited increased ATP-induced ethidium(+) uptake and (86)Rb(+) efflux, respectively, and this correlated with increased IL-1beta secretion from LPS-primed monocytes. Inheritance of these P2X(7) haplotypes predisposing to increased proinflammatory cytokine secretion may be important in genetic association studies of inflammatory, infectious, and psychiatric disorders.

Non-synonymous polymorphisms in the P2RX 4 are related to bone mineral density and osteoporosis risk in a cohort of Dutch fracture patients

“…The allele frequencies for the Tyr315Cys and Ser242Gly polymorphism in our population were almost identical to the previously published data Stokes et al [26]. Both SNPs were shown to be in HWE, indicating a valid population for current study.…”

Single-nucleotide polymorphisms in the P2X7 receptor gene are associated with post-menopausal bone loss and vertebral fractures

“…Haplotype analysis of P2X7 genotypes identified 17 haplotypes with population frequencies 41.0 % (Table 4). Grouping the haplotypes based on the haplotype blocks containing the 1068, 1096, 1405 and 1513 polymorphisms as described by Stokes et al 30 showed similar haplotype frequencies between the Australian cohort and the DOPS cohort. Aggregating patients into a group of haplotypes carrying 'high-risk' loss-of-function variants showed the same accelerated BMD loss as for the Group A defined above on the basis of SNPs (data not shown).…”

“…Both P2X7-2 and P2X7-4 contain the Ala348Thr polymorphism and this variant is critical for the gain-of-function effect. 30 Analysis showed a lesser fracture rate for subjects with one or two of this gain-of-function allele.…”

“…30 Thus, the variant allele of Gln460Arg is therefore likely to be co-inherited with other gain-offunction polymorphisms in the P2X7 receptor, which subsequently are associated with low risk of bone loss. Recently, it was shown that the P2X4 receptor can be co-expressed together with the P2X7 receptor and that P2X4 and P2X7 subunits can form heteromeric channels.…”

“…However, while the inheritance of the Gln460Arg minor allele in isolation causes insignificant loss-of-function, the 460-Arg is nearly always co-inherited with 155Tyr and 348Thr and thus is a marker of the major gainof-function haplotype of P2RX7 in Caucasians. 30 In this study, we performed an association analysis of non-synonymous variants in P2RX7 and changes in bone mineral density (BMD) and fracture rates over 10 years in post-menopausal women. A risk model based on the functional effects of the individual variants on receptor function showed a clear association to the regulation of bone mass.…”