PARAZITOLOGICKÝ ÚSTAV | Independent somatic distribution of heme and iron in ticks

Independent somatic distribution of heme and iron in ticks

Ticks are blood-feeding ectoparasites with distinct genomic reductions, inevitably linking them to a parasitic lifestyle. Ticks have lost the genomic coding and, thus, biochemical capacity to synthesize heme, an essential metabolic cofactor, de novo. Instead, they are equipped with acquisition and distribution pathways for reuse of host heme. Unlike insects or mammals, ticks and mites cannot cleave the porphyrin ring of heme to release iron. Bioavailable iron is thus acquired by ticks from the host serum transferrin. Somatic trafficking of iron, however, is independent of heme and is mediated by a secretory type of ferritin. Heme and iron systemic homeostasis in ticks represents, therefore, key adaptive traits enabling successful feeding and reproduction.

When blood is on the menu

Ticks are parasitic chelicerates that feed blood once per developmental stage, with each feeding being followed by molting or oviposition. Host blood represents a rich protein solution with hemoglobin being the predominant protein constituent. High levels of host hemoglobin in the tick midgut reflect its tendency to form crystals within the midgut lumen [1]. An adult tick female, weighing about 2 mg when unfed, typically engorges an amount of blood exceeding up to one hundred times its original bodyweight. In one blood meal, it receives roughly 150 mg of hemoglobin carrying about 6 mg of bound heme. Handling such extreme dietary conditions would not be possible without gradual evolutionary adaptations [2]. Particular adaptations that allow ticks to use host hemoglobin efficiently, while preventing cytotoxicity of heme, and how ticks go about iron uptake and distribution, considering the lack of heme oxygenase, will be addressed in this review. Pending questions related to specific traits in tick metallobiology are appended at its end.

Perner J., Hajdušek O., Kopáček P. 2022: Independent somatic distribution of heme and iron in ticks. Current Opinion in Insect Science 51: 100916. [IF=5.186] DOI: 10.1016/j.cois.2022.100916

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Independent somatic distribution of heme and iron in ticks

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