Characterization of bursicon homodimers’ role in innate immune responses in Aedes aegypti

Bursicon is a neuropeptide hormone consisting of two cystine-knot proteins (bursicon and partner of bursicon), and the heterodimeric bursicon is responsible for cuticle tanning and wing expansion. Recent studies show that each of bursicon subunits could also form homodimers to induce the innate immune response in D. Melanogaster. Whether this is true in other insect species remains unclear. In this study, we expressed the Aedes aegypti recombinant bursicon proteins in HEK 293T cells and used the recombinant proteins to test homodimer’s roles in innate immune system of Ae. aegypti. Results showed that bursicon homodimers could up-regulate several anti-microbial peptide (AMP) genes in mosquito larvae and adults. When mosquito larval fat bodies were incubated with bursicon homodimers, the homodimers could stimulate AMP expression, leading to inhibition of bacterial growth in bacterial growth inhibition assay. These results suggested bursicon homodimers play an important role in innate immunity of mosquitoes. Combined with the work in Drosophila, it is speculated that this role is conserved among insects, at least in Diptera. Future work will be focus on the signaling pathways through which bursicon regulates the innate immunity in Ae. Aegypti.