Characterisation of P2X3 receptors in spotted sea bass (Lateolabrax maculatus): P2X3a and P2X3b mediate pro-inflammatory innate immune response.

The purinergic receptor P2X3 plays a crucial role in regulating inflammation and immunity upon activation by extracellular adenosine triphosphate (ATP). In this study, two P2X3 subtypes, LmP2X3a and LmP2X3b, were identified in spotted sea bass (Lateolabrax maculatus). Both LmP2X3a and LmP2X3b exhibited similar topological structures, conserved genomic organization, and gene synteny with their counterparts. The two genes were constitutively expressed in all tested tissues except the liver and were significantly upregulated in the head kidney, spleen, intestine, and gill after stimulation with Edwardsiella tarda, LPS, and poly (I:C), indicating their roles in the immune response. Further analysis revealed that activation of P2X3a and P2X3b upregulated IL-1β expression, while inhibiting IL-10 expression. Additionally, activated LmP2X3a and LmP2X3b promoted NF-κB promoter activity and the expression of NF-κB signaling pathway-related genes (p50 or p52). These findings suggests that LmP2X3a and LmP2X3b may play a pro-inflammatory role by modulating the NF-κB signaling pathway. Furthermore, ATP- stimulated LmP2X3a and LmP2X3b upregulated the expression of TNF-α, p53, caspase3, caspase6 and caspase7, indicating their involvement in apoptosis. Notably, ATP-activated LmP2X3a directly triggered apoptosis, whereas no such effect was observed in LmP2X3b. Taken together, our results demonstrate that P2X3a and P2X3b play critical roles in pro-inflammatory innate immunity in spotted sea bass. To the best of our knowledge, this is the first report on the immune function of P2X3a and P2X3b in fish.