Abstract
ATP-gated P2X7 receptor (P2RX7) channel is a key component for purinergic signaling and plays important roles in the innate immune response in mammals. However, the expression, molecular properties and immune significances of P2RX7 in lower vertebrates are still very limited. Here we identified and characterized a novel bony fish P2RX7 homologue cDNA, termed poP2RX7, in Japanese flounder (Paralichthys olivaceus). PoP2RX7 protein shares about 60–88% sequence similarity and 45–78% sequence identity with known vertebrate P2RX7 proteins. Phylogenetic analysis placed poP2RX7 and other P2RX7 proteins within their own cluster apart from other P2RX members. While the functional poP2RX7 channel shares structural features in common with known P2RX7 homologs, electrophysiological studies revealed that BzATP, the more potent agonist for known mammalian and fish P2RX7s, shows similar potency to ATP in poP2RX7 activation. poP2RX7 mRNA constitutively expressed in all examined tissues from unstimulated healthy Japanese flounder with dominant expression in hepatopancreas and the lowest expression in head kidney, trunk kidney, spleen and gill. poP2RX7 mRNA expression, however, was significantly induced in Japanese flounder head kidney primary cells by Poly(I:C) and bacterial endotoxin LPS stimulations. In vivo experiments further revealed that poP2RX7 gene expression was substantially up-regulated by immune challenge with infectious bacteria Edwardsiella tarda and Vibrio anguillarum. Moreover, activation of poP2RX7 results in an increased gene expression of multifunctional cytokines IL-1β and IL-6 in the head kidney primary cells. Collectively, we identified and characterized a novel fish P2RX7 homolog which is engaged in Japanese flounder innate immune response probably through modulation of pro-inflammatory cytokines expression.
Highlights
The purinergic P2X receptors (P2RXs) composed of seven members in vertebrates, termed P2RX1-7, are a family of ligandgated membrane ion channels that open in response to the binding of extracellular ATP [1]
In line with the observation that P2RX7 predominantly expresses in the immune cells/organs, activated P2RX7 by extracellular ATP following tissue injury or infection has been evidenced to play a central role in mammalian innate immune responses through the secretion of pro-inflammatory cytokines IL-18 and IL-1b [4], induction of apoptosis [11], generation of reactive oxygen and nitrogen intermediates [12] and stimulation of phagosome– lysosome fusion [13]
To test whether poP2RX7 remains the conserved role in fish, we examined the influence of poP2RX7 channel activation on the gene expression of predominant pro-inflammatory cytokines IL-1b and IL-6 in P. olivaceus head kidney primary cells by qRT-PCR
Summary
The purinergic P2X receptors (P2RXs) composed of seven members in vertebrates, termed P2RX1-7, are a family of ligandgated membrane ion channels that open in response to the binding of extracellular ATP [1]. P2RX subunits exhibit overall similar topological structures: two membrane-spanning domains, separated by a large extracellular loop with both N and C termini in cytosol [2] and these subunits may assemble as homo- or heterotrimers to form functional receptors. In line with the observation that P2RX7 predominantly expresses in the immune cells/organs, activated P2RX7 by extracellular ATP following tissue injury or infection has been evidenced to play a central role in mammalian innate immune responses through the secretion of pro-inflammatory cytokines IL-18 and IL-1b [4], induction of apoptosis [11], generation of reactive oxygen and nitrogen intermediates [12] and stimulation of phagosome– lysosome fusion [13]. P2RX7 has received much more research interests than other P2RXs because of these distinctive properties
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
