Mosquitoes stop feeding on blood before satiety — Peptide in the blood a signal to stop feeding

A research group led by Senior Scientist Chisako Sakuma of the Laboratory for Nutritional Biology, RIKEN Center for Biosystems Dynamics Research, and Professor Hirotaka Kanuka of the Department of Tropical Medicine at Jikei University has announced their research results showing that "fibrinopeptide A (FPA)" present in mammalian blood signals yellow fever mosquitos to stop blood feeding before satiety. The findings are expected to contribute to the clarification of the blood-feeding mechanism of mosquitoes and the development of methods to artificially inhibit blood feeding. The results were published in the June 20 issue of the international journal Cell Reports.

Blood feeding by mosquitoes not only causes itchiness in their victims but also facilitates the transmission of many pathogens, such as the Japanese encephalitis virus, malarial plasmodia and dengue virus, posing a worldwide public health threat. Mechanistic clarification of blood-feeding behaviors and its inhibition are expected to contribute to curbing the spread of diseases caused by these pathogens.

Only females in the oogenesis stage engage in blood feeding, and they detect hosts, including humans, by body temperature and exhalation. It is known that mosquitoes probe blood vessels by inserting and withdrawing a needle-like structure (proboscis) into the skin, using the taste of blood to determine its suitability for feeding. Each blood feeding takes about 2-3 minutes, during which the body weight can increase by more than 2.5 times.

In 1959, a signal promoting blood feeding was identified as adenosine triphosphate (ATP) in host blood, and ATP has been reported to initiate and promote blood feeding in mosquitoes. Meanwhile, the detailed control mechanism of the signaling that arrests blood-feeding remained unknown, despite reports of a physical control mechanism involving abdominal distention.

It is known that mosquitoes sometimes stop blood feeding before their abdomens are fully distended. Based on the fact that ATP is a stimulant for blood feeding in mosquitoes, the research group in 2021 developed a technique to quantify blood intake easily. This method involves mixing a food dye with an ATP solution in an artificial blood feeding setup. In the artificial blood feeding method, an ATP solution is maintained at 42℃ and presented to mosquitoes through a Parafilm membrane to induce blood-feeding behavior.

In this study, the research group observed blood-feeding behavior using this method and noted that the intake of the ATP solution was greater than the intake of blood by mosquitoes from anesthetized mice. They explored the possibility that the host's blood contained a blood-feeding regulator. Mosquitoes are known to taste serum (devoid of ATP) without ingesting it, whereas they ingest red blood cells (containing ATP) obtained by centrifuging blood. Therefore, the research group tested the ATP solution supplemented with mouse serum and found that the number of mosquitoes ingesting the solution to satiety decreased drastically, whereas the number of mosquitoes ingesting small amounts increased.

Next, the research group separated serum components under various conditions, and each separated fraction was added to the ATP solution to identify the serum fraction containing a factor that reduces mosquito intake. They found that the intake was markedly reduced when a certain fraction was added. LC-MS/MS analysis of the fraction components revealed that the blood-feeding inhibitor was FPA. FPA is a fragment removed from the precursor fibrinogen during the production of fibrin for blood coagulation and does not play a critical physiological function in the host. Meanwhile, FPA sequences are conserved in mammals.

To investigate whether the levels of FPA in mosquitoes change during their blood-feeding behavior, the researchers collected mosquitoes during and immediately after blood feeding and analyzed them using LC-MS. The results showed that FPA was barely detectable in mosquitoes with slight weight gain during blood feeding, but it was detected in mosquitoes with obvious weight gain immediately after blood feeding. Furthermore, when synthetic FPA was added to the ATP solution, the number of mosquitoes ingesting the solution to satiety decreased at a certain FPA concentration. When mosquitoes were given mouse blood treated with a blood coagulation inhibitor (heparin), the number of mosquitoes ingesting blood to satiety increased at a certain dose. They also confirmed that the number of fully fed mosquitoes decreased when mice blood was supplemented with batroxobin, which cleaves FPA alone, and the FPA levels in those mosquitoes increased.

The findings suggest that mosquitoes undergo blood-feeding arrest in response to the detection of FPA in the ingested blood at concentrations common to many hosts, avoiding the risk of being noticed by the host. Moving forward, the group will conduct research to identify the FPA receptor, which is predicted to be present in the midgut where blood is delivered after blood feeding.

Sakuma said, "We speculate that mosquitoes use FPA to measure the duration of blood feeding. If they encounter difficulty ingesting blood smoothly and require more time than usual, they might stop feeding based on the concentration of FPA. If we can identify the receptor for FPA, we can explore its ligands, which may have applications in artificially inducing blood-feeding arrest."

Journal Information
Publication: Cell Reports
Title: Fibrinopeptide A-induced blood-feeding arrest in the yellow fever mosquito Aedes aegypti
DOI: 10.1016/j.celrep.2024.114354