A mosquito juvenile hormone binding protein (mJHBP) regulates the activation of innate immune defenses and hemocyte development
Abstract
Insects rely on the innate immune system for defense against pathogens, some aspects of which are under hormonal control. Here we provide direct experimental evidence showing that the juvenile hormone-binding protein (mJHBP) of Aedes aegypti is required for the regulation of innate immune responses and the development of mosquito blood cells (hemocytes). Using an mJHBP-deficient mosquito line generated by means of CRISPR-Cas9 gene editing technology we uncovered a mutant phenotype characterized by immunosuppression at the humoral and cellular levels, which profoundly affected susceptibility to bacterial infection. Bacteria-challenged mosquitoes exhibited significantly higher levels of septicemia and mortality relative to the wild type (WT) strain, delayed expression of antimicrobial peptides (AMPs), severe developmental dysregulation of embryonic and larval hemocytes (reduction in the total number of hemocytes) and increased differentiation of the granulocyte lineage. Interestingly, injection of recombinant wild type mJHBP protein into adult females three-days before infection was sufficient to restore normal immune function. Similarly, injection of mJHBP into fourth-instar larvae fully restored normal larval/pupal hemocyte populations in emerging adults. More importantly, the recovery of normal immuno-activation and hemocyte development requires the capability of mJHBP to bind JH III. These results strongly suggest that JH III functions in mosquito immunity and hemocyte development in a manner that is perhaps independent of canonical JH signaling, given the lack of developmental and reproductive abnormalities. Because of the prominent role of hemocytes as regulators of mosquito immunity, this novel discovery may have broader implications for the understanding of vector endocrinology, hemocyte development, vector competence and disease transmission.
Author summary
There are many unanswered questions concerning the nature of immune responses of mosquitoes to bacteria, viruses and parasites. This is important because a variety of human pathogens are transmitted by mosquitoes during the process of consuming blood. Much of mosquito physiology is under the control of hormones and we aim to understand a potential role for an important hormone known as juvenile hormone in anti-bacterial immunity. We have produced a strain of the mosquito, Aedes aegypti, that is deficient in the production of a protein that circulates in the blood while carrying juvenile hormone. This strain is shown to have less ability to control bacterial infection, to have lower levels of proteins involved in immunity and to have smaller numbers of blood cells that are known to be important in the mosquito immune response. If the protein is administered to the deficient strain by injection, the immune response and blood cell numbers return to near-normal levels. Other results suggest that the association of the protein with juvenile hormone is important for its ability to function in the immune system. Overall, this study describes an important new protein regulator of mosquito immunity and a potential role of juvenile hormone in this process.
Kim I.H., Castillo J.C., Aryan A., Martin-Martin I., Nouzova M., Noriega F.G., Barletta A.B.F., Calvo E., Adelman Z.N., Ribeiro J.M.C., Andersen J.F. 2020: A mosquito juvenile hormone binding protein (mJHBP) regulates the activation of innate immune defenses and hemocyte development. PLOS Pathogens (in press). [IF = 6.463]
