Lutzomyia longipalpis Antimicrobial Peptides: Differential Expression during Development and Potential Involvement in Vector Interaction with Microbiota and Leishmania

Abstract

Antimicrobial peptides (AMPs) are produced to control bacteria, fungi, protozoa, and other infectious agents. Sand fly larvae develop and feed on a microbe-rich substrate, and the hematophagous females are exposed to additional pathogens. We focused on understanding the role of the AMPs attacin (Att), cecropin (Cec), and four defensins (Def1, Def2, Def3, and Def4) in Lutzomyia longipalpis, the main vector of visceral leishmaniasis in the Americas. Larvae and adults were collected under different feeding regimens, in addition to females artificially infected by Leishmania infantum. AMPs’ gene expression was assessed by qPCR, and gene function of Att and Def2 was investigated by gene silencing. The gene knockdown effect on bacteria and parasite abundance was evaluated by qPCR, and parasite development was verified by light microscopy. We demonstrate that L. longipalpis larvae and adults trigger AMPs expression during feeding, which corresponds to an abundant presence of bacteria. Att and Def2 expression were significantly increased in Leishmania-infected females, while Att suppression favored bacteria growth. In conclusion, L. longipalpis AMPs’ expression is tuned in response to bacteria and parasites but does not seem to interfere with the Leishmania cycle.

Phlebotomus papatasi Antimicrobial Peptides in Larvae and Females and a Gut-Specific Defensin Upregulated by Leishmania major Infection

“…The modulation of defensin genes also occurred in L. longipalpis, where both of them were reported to be modulated after the parasitic infection. LlDef1 was reduced after L. mexicana [65], and LlDef2 was increased after L. infantum infection [19]. In addition, the P. duboscqi defensin, which is more similar to LlDef2, was increased by L. major infection [18].…”

“…The insect defensins motif six conserved cysteines responsible for intra-chain disulfide bonds [46]. It was also previously reported that the sand fly defensin group was divided into two branches, one containing the L. longipalpis defensin 1, 3, and 4, (LlDef1, LlDef3, and LlDef4) and another containing the LlDef2 and N. neivai defensin 2 [19]. Interestingly, the P. duboscqi defensin was previously shown to be closely related to the black soldier fly Hermetia illucens [47], and in our current analysis, it grouped with the L. longipalpis defensin 2.…”

“…The attacin family signature domain contains a prolinerich propeptide (N-terminus) and two glycine-rich domains (C-terminus) [44]. In a previous study, the P. papatasi attacin sequence was shown to be closely related to L. longipalpis and Nyssomyia neivai [19]. In addition, the dipteran attacin group formed separately from the coleopteran and lepidopteran groups [45].…”

“…This may have occurred as a counterbalance between effector molecules or due to changes in bacterial diversity within the larvae gut. Similarly, L. longipalpis larvae adjust their AMPs expression throughout their developmental stages with a more evident increase in attacin and two defensin genes (LlDef2 and LlDef4) in L3 larvae compared to the non-feeding larval stage [19]. In addition, AMPs expression in L. longipalpis L3 larvae was also adjusted according to the microbial challenge offered through artificial feeding.…”

“…For example, a recombinant defensin peptide encoded by the Phlebotomus duboscqi defensin gene has effective activity against L. major promastigotes [18]. Moreover, the suppression of a defensin gene in L. longipalpis, mediated by RNAi, slightly increased L. infantum detection [19]. These results suggest that sand flies express defensins potentially driven toward the parasites.…”