A rare P2X7 variant Arg307Gln with absent pore formation function protects against neuroinflammation in multiple sclerosis

Abstract

Multiple sclerosis (MS) is a chronic relapsing-remitting inflammatory disease of the central nervous system characterized by oligodendrocyte damage, demyelination and neuronal death. Genetic association studies have shown a 2-fold or greater prevalence of the HLA-DRB1*1501 allele in the MS population compared with normal Caucasians. In discovery cohorts of Australasian patients with MS (total 2941 patients and 3008 controls), we examined the associations of 12 functional polymorphisms of P2X7, a microglial/macrophage receptor with proinflammatory effects when activated by extracellular adenosine triphosphate (ATP). In discovery cohorts, rs28360457, coding for Arg307Gln was associated with MS and combined analysis showed a 2-fold lower minor allele frequency compared with controls (1.11% for MS and 2.15% for controls, P = 0.0000071). Replication analysis of four independent European MS case-control cohorts (total 2140 cases and 2634 controls) confirmed this association [odds ratio (OR) = 0.69, P = 0.026]. A meta-analysis of all Australasian and European cohorts indicated that Arg307Gln confers a 1.8-fold protective effect on MS risk (OR = 0.57, P = 0.0000024). Fresh human monocytes heterozygous for Arg307Gln have >85% loss of 'pore' function of the P2X7 receptor measured by ATP-induced ethidium uptake. Analysis shows Arg307Gln always occurred with 270His suggesting a single 307Gln-270His haplotype that confers dominant negative effects on P2X7 function and protection against MS. Modeling based on the homologous zP2X4 receptor showed Arg307 is located in a region rich in basic residues located only 12 Å from the ligand binding site. Our data show the protective effect against MS of a rare genetic variant of P2RX7 with heterozygotes showing near absent proinflammatory 'pore' function.

Purinergic receptorsP2RX4andP2RX7in familial multiple sclerosis

“…ATP‐induced ethidium uptake assays were performed on HEK293 cells transfected with 4 μg P2X7‐AcGFP plasmid DNA and/or 0.5 μg P2X4‐AcGFP plasmid DNA. The pAcGFP‐N1 vector (0.2 μg) was used as the mock‐transfected control, using linear polyethylenimine as described previously (Gu et al., ). Cell suspensions (1.0 ml) in HEPES‐buffered KCl medium (150 mM KCl, 10 mM HEPES, pH 7.5, plus 5 mM d ‐glucose, 0.1% BSA) were added to the cuvette of a Time Zero module and gently stirred with temperature maintained at 37°C.…”

“…The etiology of MS is complex with both genetic and environmental factors implicated in disease susceptibility, with the human leucocyte antigen‐DRB1 region providing the highest known attributable risk (Traboulsee et al., ). Recently, functional variants in genes for the purinergic receptors P2RX7 (MIM# 602566) and P2RX4 (MIM# 600846) have been shown to modulate MS susceptibility (Gu et al., ). P2RX7 variants resulting in loss‐of‐function were found to be protective against MS, particularly rs28360457:G>A (p.R307Q), which has a dominant negative effect on risk of MS, whereas a P2RX7 rs1718119:G>A (p.A348T) gain‐of‐function variant increased the risk of disease.…”

“…P2RX7 variants resulting in loss‐of‐function were found to be protective against MS, particularly rs28360457:G>A (p.R307Q), which has a dominant negative effect on risk of MS, whereas a P2RX7 rs1718119:G>A (p.A348T) gain‐of‐function variant increased the risk of disease. In addition, a rare P2RX4 rs28360472:A>G (p.Y315C) loss‐of‐function mutation showed a trend toward association, suggesting it increases the risk of MS (Gu et al., ; Stokes et al., ; Wiley et al., ).…”

The link of inflammation and neurodegeneration in progressive multiple sclerosis

“…Like glutamate, ATP, when in excess, is a potent endogenous toxin that can directly kill oligodendrocytes via activation of purinergic P2X7 receptors whose blockade during the chronic phase of EAE attenuates the symptoms and tissue damage [47]. Interestingly, P2X7 variants are associated with a reduced or increased risk to suffer from MS [48,49]. All in all, these studies in MS animal models and in the disease proper offer new ideas to develop novel therapies to treat PMS.…”

Therapeutic Targeting of the Cancer-Specific Cell Surface Biomarker nfP2X7

“…The C-terminal domain is critical for supplying the measured pore-forming properties of the homotrimeric membrane channel [19][20]. Prolonged exposure of the assembled channel to ATP in which all three sites are occupied close to the neighbouring residues K193 and K311 juxtaposed from adjacent monomers, found critical for function [21], results in additional pore dilation [20,22,23]. Saturation ATP binding to the three binding sites formed by the correct packing of the monomers in the trimer results in a rapid increase in the influx of calcium that results in turn in the activation of caspases [24], leading to apoptosis of the affected cell [25].…”