Potassium ion channels as a molecular target to reduce virus infection and mortality of honey bee colonies

Mode of toxicity of the β-triketone leptospermone to Aedes aegypti mosquitoes

Leptospermone, a natural β-triketone and major constituent of manuka oil (Leptospermum scoparium), is an established inhibitor of plant HPPD and was identified to induce rapid knockdown and induce high toxicity to Aedes aegypti adults via topical and tarsal contact exposure with LD50 values of 150 ng/mg of mosquito and 357 ng/cm2, respectively. Although toxic to mosquitoes, leptospermone was non-toxic to ticks, the honey bee, or the fruit fly indicating a high degree of insect specificity. Importantly, leptospermone was equally toxic to non-blood fed and blood-fed mosquitoes suggesting the mode of action is not via HPPD inhibition. Molecular modeling suggested high structural similarities between leptospermone and mammalian sulfonamide carbonic anhydrase (CA) inhibitors. In vitro potency assays with mosquito midgut homogenate or purified CA verify leptospermone inhibits Ae. aegypti CA, but not mammalian CAs. CAs are metalloenzymes that regulate the pH of tissues and ubiquitously expressed throughout insect tissues but are abundantly expressed in the mosquito midgut and, thus, we tested leptospermone to alter pH regulation in the mosquito midgut. Indeed, leptospermone significantly reduced the pH of Ae. aegypti midguts when compared to control mosquitoes which further supports the notion that leptospermone mode of action in insects is via inhibition of CA. These data verify leptospermone is an effective mosquitocide that induces rapid knockdown and toxicity to Ae. aegypti at doses that approach natural pyrethrins against pyrethroid-resistant mosquito strains. Further, the data indicate leptospermone mode of action is CA inhibition, which is a novel mosquitocide target and is different when compared to the mode of action in plants.

Fire ants exhibit self-medication but lack preventive behavioral immunity against a viral pathogen

Behavioral immunity in ants encompasses collective behaviors that help defend against pathogens and parasites by reducing infection risks and limiting disease spread. However, much of the research has focused on fungal pathogens, leaving the behavioral immunity responses to viral pathogens largely unexplored. This study represents the first attempt to characterize behavioral immunity in ants against viral pathogens using the red imported fire ant, Solenopsis invicta and one of its common viruses, Solenopsis invicta virus 3 (SINV-3), as the model system. Given that SINV-3 infection has been shown to cause adverse effects on fire ants, we hypothesized that fire ants may mount behavioral immunity defenses against SINV-3 infection, specifically through avoidance behavior, organizational segregation worker discrimination, and self-medication. Surprisingly, none of the preventive behavioral immunity behaviors we tested were observed, suggesting fire ants' inability to detect or mount collective defenses against SINV-3 infection. However, SINV-3-infected fire ants exhibited increased consumption of reactive oxygen species (ROS)-containing food, providing evidence of therapeutic self-medication. These findings suggest that while no evidence suggest fire ants employing preventive behavioral immunity against SINV-3, they may mitigate the effects of infection through self-medication, highlighting a different adaptive strategy in response to viral pathogens. This study opens new avenues for understanding the adaptive strategies of ants to cope with viral pathogens.

Deformed wing virus coopts the host arginine kinase to enhance its fitness in honey bees (Apis mellifera)

BACKGROUND

Deformed wing virus (DWV) is a major honey bee pathogen that is actively transmitted by the parasitic mite Varroa destructor and plays a primary role in Apis mellifera winter colony losses. Despite intense investigation on this pollinator, which has a unique environmental and economic importance, the mechanisms underlying the molecular interactions between DWV and honey bees are still poorly understood. Here, we report on a group of honey bee proteins, identified by mass spectrometry, that specifically co-immunoprecipitate with DWV virus particles.

RESULTS

Most of the proteins identified are involved in fundamental metabolic pathways. Among the co-immunoprecipitated proteins, one of the most interesting was arginine kinase (ArgK), a conserved protein playing multiple roles both in physiological and pathological processes and stress response in general. Here, we investigated in more detail the relationship between DWV and this protein. We found that argK RNA level positively correlates with DWV load in field-collected honey bee larvae and adults and significantly increases in adults upon DWV injection in controlled laboratory conditions, indicating that the argK gene was upregulated by DWV infection. Silencing argK gene expression in vitro, using RNAi, resulted in reduced DWV viral load, thus confirming that argK upregulation facilitates DWV infection, likely through interfering with the delicate balance between metabolism and immunity.

CONCLUSIONS

In summary, these data indicate that DWV modulates the host ArgK through transcriptional regulation and cooptation to enhance its fitness in honey bees. Our findings open novel perspectives on possible new therapies for DWV control by targeting specific host proteins.

Comparative transcriptome analysis of whiteflies raised on cotton leaf curl Multan virus-infected cotton plants

Cotton leaf curl Multan virus (CLCuMuV), a serious viral disease causative agent in cotton plants in South Asia, is transmitted by the Bemisia tabaci cryptic species complex in a persistent circulative manner. A previous study indicated that Asia II-7 whiteflies could transmit CLCuMuV, while Mediterranean (MED) whiteflies failed to transmit CLCuMuV. However, little is known about the genes involved in this process. In this study, Asia II-7 and MED B. tabaci were utilized to determine transcriptomic responses after 48 h of acquisition access periods (AAPs). Result of Illumina sequencing revealed that, 14,213 and 8,986 differentially expressed genes (DEGs) were identified. Furthermore, DEGs related to the immune system and metabolism of Asia II-7 and MED in response to CLCuMuV-infected plants were identified and analyzed using Gene Ontologies (GO) and the Kyoto Encyclopedia of Genes and Genomes (KEGG), and the number of related DEGs in MED was lower than that of Asia II-7. The most abundant groups of DEGs between both viruliferous and aviruliferous whitefly species were the zf-C2H2 family of transcription factors (TFs). Notably, in comparison to viruliferous MED, Asia II-7 exhibited more DEGs related to cathepsin biosynthesis. Overall, this study provides the basic information for investigating the molecular mechanism of how begomoviruses affect B. tabaci metabolism and immune response either as vector cryptic species or non-vector species.

Contribution of inwardly rectifying potassium channel 4.1 in orofacial neuropathic pain: Regulation of pannexin 3 via the reactive oxygen species-activated P38 MAPK signal pathway

The involvement of inwardly rectifying potassium channel 4.1 (Kir4.1) in neuropathic pain has been established. However, there is limited understanding of the downstream mechanism through which Kir4.1 contributes to orofacial neuropathic pain. The objective of this study was to examine the regulation of Kir4.1 on the expression of pannexin 3 (Panx3) in the trigeminal ganglion (TG) and the underlying mechanism in the context of orofacial neuropathic pain caused by chronic constriction injury of the infraorbital nerve (CCI-ION). The study observed a significant increase in Panx3 expression in the TG of mice with CCI-ION. Inhibition of Panx3 in the TG of CCI-ION mice resulted in alleviation of orofacial mechanical allodynia. Furthermore, conditional knockdown (CKD) of Kir4.1 in the TG of both male and female mice led to mechanical allodynia and upregulation of Panx3 expression. Conversely, overexpression of Kir4.1 decreased Panx3 levels in the TG and relieved mechanical allodynia in CCI-ION mice. In addition, silencing Kir4.1 in satellite glial cells (SGCs) decreased Panx3 expression and increased the phosphorylation of P38 MAPK. Moreover, silencing Kir4.1 in SGCs increased the levels of reactive oxygen species (ROS). The elevated phosphorylation of P38 MAPK resulting from Kir4.1 silencing was inhibited by using a superoxide scavenger known as the tempol. Silencing Panx3 in the TG in vivo attenuated the mechanical allodynia caused by Kir4.1 CKD. In conclusion, these findings suggest that the reduction of Kir4.1 promotes the expression of Panx3 by activating the ROS-P38 MAPK signalling pathway, thus contributing to the development of orofacial neuropathic pain.

Cloning, functional expression, and pharmacological characterization of inwardly rectifying potassium channels (Kir) from Apis mellifera

Potassium channels belong to the super family of ion channels and play a fundamental role in cell excitability. Kir channels are potassium channels with an inwardly rectifying property. They play a role in setting the resting membrane potential of many excitable cells including neurons. Although putative Kir channel family genes can be found in the Apis mellifera genome, their functional expression, biophysical properties, and sensitivity to small molecules with insecticidal activity remain to be investigated. We cloned six Kir channel isoforms from Apis mellifera that derive from two Kir genes, AmKir1 and AmKir2, which are present in the Apis mellifera genome. We studied the tissue distribution, the electrophysiological and pharmacological characteristics of three isoforms that expressed functional currents (AmKir1.1, AmKir2.2, and AmKir2.3). AmKir1.1, AmKir2.2, and AmKir2.3 isoforms exhibited distinct characteristics when expressed in Xenopus oocytes. AmKir1.1 exhibited the largest potassium currents and was impermeable to cesium whereas AmKir2.2 and AmKir2.3 exhibited smaller currents but allowed cesium to permeate. AmKir1 exhibited faster opening kinetics than AmKir2. Pharmacological experiments revealed that both AmKir1.1 and AmKir2.2 are blocked by the divalent ion barium, with IC50 values of 10-5 and 10-6 M, respectively. The concentrations of VU041, a small molecule with insecticidal properties required to achieve a 50% current blockade for all three channels were higher than those needed to block Kir channels in other arthropods, such as the aphid Aphis gossypii and the mosquito Aedes aegypti. From this, we conclude that Apis mellifera AmKir channels exhibit lower sensitivity to VU041.