The N1575Y mutation in the sodium channel of Anopheles gambiae synergizes the effect of L1014F/S mutations on pyrethroid resistance

Pyrethroid insecticides possess high insecticidal activities and low mammalian toxicity and represent one of the most powerful weapons in the global fight against malaria and other arthropod-borne human diseases. However, pyrethroid resistance has become a serious obstacle in effective use of pyrethroids in controlling these human disease vectors. One major mechanism of pyrethroid resistance, known as knockdown resistance (kdr), is caused by mutations in the sodium channel, which is the site of pyrethroid action. In the African malaria vector Anopheles gambiae, two kdr mutations, L1014F/S, are found in many pyrethroid resistant populations globally. Recently, a new sodium channel mutation N1575Y was found to be concurrent with the L1014F mutation in several pyrethroid resistant populations of An. gambiae. To examine the role of this new sodium channel mutation in pyrethroid resistance, we introduced the N1575Y mutation into an Aedes aegypti sodium channel, AaNa_v1-1, alone or in combination with the L1014F mutation and examined the gating properties of the mutant channels expressed in Xenopus oocytes. Our analyses show that the N1575Y mutation, by itself, did not alter AaNa_v sensitivity to two pyrethroid insecticides: permethrin and deltamethrin. However, when mutated together with L1014F, the N1575Y mutation made L1014F channels 10-fold and 4-fold more resistant to permethrin and deltamethrin, respectively. The N1575Y mutation also synergized the effect of another kdr mutation, L1014S, which is widely distributed in pyrethroid-resistant An. mosquitoes. None of the mutations tested significantly affected channel gating. Our findings demonstrate that N1575Y functions as an enhancer of the L1014F/S-mediated pyrethroid resistance and provide a molecular explanation for the emerging co-occurrence of N1575Y and L1014F in pyrethroid-resistant populations.