Transferrin affects food intake and reproduction in the hard tick Haemaphysalis longicornis

Transferrin (Tsf) is an extracellular protein with a high affinity for iron in vertebrates, but its function and mechanism in ticks are poorly understood. This study investigated Tsf in the hard tick Haemaphysalis longicornis Neumann (Ixodida: Ixodidae) for the first time. The results showed that Tsf was expressed in three developmental stages (larva, nymph, and female) and in various tissues (salivary glands, ovary, midgut, and Malpighian tubules), with higher expression levels observed after a blood meal. Using the Escherichia coli expression system, it was revealed that the hard tick Tsf protein exhibited iron chelation, radical-scavenging, antibacterial, and hemolytic activities in vitro. Silencing Tsf using RNA interference (RNAi) had adverse effects on the feeding ability and reproduction of H. longicornis, resulting in decreased engorgement weight, ovary weight, egg mass weight, egg hatching rate as well as a prolonged incubation period of eggs from oviposition to larvae hatching. Additionally, proteomics was used to investigate the mechanisms underlying the effects of Tsf on food intake and reproduction in H. longicornis females. The results revealed that Tsf may affect these processes through various pathways, including the ubiquitin–proteasome pathway, lipid metabolic pathways, carbohydrate metabolic pathways, oxidative stress, abnormal mRNA degradation, endocytosis, vesicle transport, and cell cycle regulation. These results contribute to a better understanding of the function and mechanism of Tsf in ticks. Furthermore, this study provides a novel antigen for anti-tick vaccine from the perspective of inhibiting tick iron metabolism.