Dopamine receptor (DAR) is required for the antibacterial immune responses in hemocytes of Procambarus clarkii

Dopamine receptors (DARs) are a type of evolutionarily conserved G-protein-coupled receptors, which are capable of coordinating the interactions between neuroendocrine and immune systems. However, their roles in the systemic antibacterial immune of invertebrates remains unclear. This study aimed to elucidate the immunomodulatory functions and the underlying mechanisms of Dopamine receptor D1-like receptor (DAR) in the process of bacterial infection in P. clarkii. In this study, it was found that the expression levels were significantly up-regulated in hemocytes, hepatopancreas, intestines, and gills post V. harveyi stimulation. Pc-DAR regulated the expression of antimicrobial peptides (AMPs) genes by promoting the expression of Relish to maintain the homeostasis of the hemolymph microbiota. Moreover, Pc-DAR regulated the melanization process to clear bacteria through the phenoloxidase system. Mechanistically, the inhibition of DAR could regulate the concentrations of downstream cAMP and PKA, thereby influencing intracellular genes expression and enzymes activities. Subsequently, our results revealed that Pc-dar were involved in the cellular immune process. It executed this function by upregulating the expression of the scavenger receptor protein gene (Pc-SRB) and two small GTPases (Pc-rab 7 and Pc-rab 11), which were related to the transportation of phagosomes to lysosomes in the cytoplasm. By detecting changes in the content of antioxidant enzymes, we speculated that Pc-DAR might regulate the reactive oxygen species (ROS) balance in the body by modulating antioxidant enzymes (SOD, CAT, GST). Overall, our results revealed that Pc-DAR plays an important immunomodulatory role in crayfish. We speculated that Pc-DAR is necessary for the effective maintaining of antibacterial immune responses during bacterial infection. And its function is associated with the cAMP-PKA signaling pathway.