Abstract
Ixodid ticks are notorious blood-sucking ectoparasites and are completely dependent on blood-meals from hosts. In addition to the direct severe effects on health and productivity, ixodid ticks transmit various deadly diseases to humans and animals. Unlike rapidly feeding vessel-feeder hematophagous insects, the hard ticks feed on hosts for a long time (5−10 days or more), making a large blood pool beneath the skin. Tick's salivary glands produce a vast array of bio-molecules that modulate their complex and persistent feeding processes. However, the specific molecule that functions in the development and maintenance of a blood pool is yet to be identified. Recently, we have reported on longistatin, a 17.8-kDa protein with two functional EF-hand Ca++-binding domains, from the salivary glands of the disease vector, Haemaphysalis longicornis, that has been shown to be linked to blood-feeding processes. Here, we show that longistatin plays vital roles in the formation of a blood pool and in the acquisition of blood-meals. Data clearly revealed that post-transcriptional silencing of the longistatin-specific gene disrupted ticks' unique ability to create a blood pool, and they consequently failed to feed and replete on blood-meals from hosts. Longistatin completely hydrolyzed α, β and γ chains of fibrinogen and delayed fibrin clot formation. Longistatin was able to bind with fibrin meshwork, and activated fibrin clot-bound plasminogen into its active form plasmin, as comparable to that of tissue-type plasminogen activator (t-PA), and induced lysis of fibrin clot and platelet-rich thrombi. Plasminogen activation potentiality of longistatin was increased up to 4 times by soluble fibrin. Taken together, our results suggest that longistatin may exert potent functions both as a plasminogen activator and as an anticoagulant in the complex scenario of blood pool formation; the latter is critical to the feeding success and survival of ixodid ticks.
Highlights
Blood coagulation is a very complex but well-synchronized biochemical process by which blood forms a clot and the damaged blood vessel is sealed by a platelet-rich fibrin plug leading to hemostasis
Despite the fact that mammalian hosts are armored with strong blood clotting machineries, ticks manage to keep the blood in a fluid state and to maintain a blood pool until a full blood-meal is secured
We show that longistatin, a salivary gland protein identified from the tick Haemaphysalis longicornis, can efficiently manipulate the host’s blood clotting machineries, such as fibrinogen, fibrin and plasminogen, and can help prevent cascade of blood clotting
Summary
Blood coagulation is a very complex but well-synchronized biochemical process by which blood forms a clot and the damaged blood vessel is sealed by a platelet-rich fibrin plug leading to hemostasis. The process leads to the generation of thrombin, which converts fibrinogen to fibrin, the building block of a hemostatic plug [1,2,3,4,5]. Homeostasis in blood fluidity is vital for humans and for hematophagous animals, which have to counteract their hosts’ hemostatic mechanisms and/or facilitate the fibrinolytic process to keep the blood in a fluid state during acquisition and digestion of blood-meals. It is believed that blood sucking-animals require an extensive spectrum of anticoagulant and/or fibrinolytic mechanisms to maximize their feeding as part of their diverse survival strategies. Hematophagous animals are thought to possess anticoagulant and/or fibrinolytic proteins that have been acquired during their evolution [1,10,11]
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