Prostaglandin E2 synthase in the blacklegged tick, Ixodes scapularis

Ticks are obligatory ectoparasites that feed exclusively on the blood of vertebrates and often transmit a number of pathogens, including viruses, bacteria, and protozoa.  Tick-borne diseases result in substantial economic loss in the animal industry and present risks to human health.  The blacklegged tick, Ixodes scapularis, is known to transmit the most important tick-borne pathogen, Borrelia burgdorferi, the causative agent of Lyme Disease.  Tick salivary glands, and their secretions, contain various bioactive components that aid in the manipulation of hosts' defenses.  Ticks secrete large amounts of prosaglandin E₂ (PGE₂) into the host, where it impacts the host’s haemostatic response and facilitates blood feeding.  PGE₂ is also known to have an autocrine or paracrine function in the tick salivary glands, likely through a PGE₂ receptor, leading to the secretion (exocytosis) of other salivary proteins.  We were interested in the biosynthetic pathway of PGE₂ in the tick salivary glands.  We have identified and cloned a gene encoding a PGE synthase (PGES) ortholog in I. scapularis.  The expression pattern, examined by quantitative reverse transcription PCR and immunohistochemistry, supports that this gene is expressed in the tick salivary glands constitutively throughout tick feeding.  RNA interference suppressing the expression of the PGES gene resulted in the ticks’ inability to successfully complete their feeding.  The identification and functional study of PGES, along with the description of its expression patterns, provides critical information into the biosynthetic pathway of PGE₂ in the tick salivary glands, and opens the door to future studies into the disruption of tick feeding.