Single nucleotide polymorphisms that were identified in affective mood disorders affect ATP-activated P2X7 receptor functions

Abstract

Genetic linkage studies have previously identified many single non-synonymous nucleotide polymorphisms (SNPs) in the human P2RX7 gene in individuals with affective mood disorders. The P2RX7 gene encodes the P2X(7) receptor (P2X(7)R) that operates as an ATP-activated Ca(2+)-permeable cationic channel and induces formation of a large pore, the two functional properties that are critical for the physiological and pathological roles of the receptor. The current knowledge regarding the effects of SNPs on the P2X(7)R functional properties, which is indispensable to help elucidate the disease mechanism, is limited. In this study, we introduced by site-directed mutagenesis twelve SNP mutations in the human P2X(7) receptor that were previously identified in or associated with affective mood disorders, expressed the resultant mutants in human embryonic kidney cells, and characterized their functional properties by electrophysiology. All mutations except Q460R gave rise to profound effects on the P2X(7)R function. G150R, E186K and I568N conferred complete loss of function. V76A, R117W, L191P, T357S and E496A resulted in strong impairment of, whereas H155Y and A348T caused significant increase in, both ATP-activated ion channel function and pore formation. Q521H reduced the receptor's sensitivity to extracellular Ca(2+) inhibition. An atomic structure model of the human P2X(7)R, based on the crystal structure of the zebrafish P2X(4) receptor, suggests that the SNP mutational effects may result from changes in subunit interaction, agonist binding and/or channel gating. These results provide essential knowledge for a better understanding of the relationships between human P2RX7 SNPs and associated pathologies as well as the receptor structure-function relationships.