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Targeting Zika Virus at the Source
The development of therapeutics to treat infectious diseases is often focused around targeting the microbes inside of the human host. However, some scientists are instead focusing on stopping vector-borne pathogens at their intermediate host–the mosquito.
The authors of this paper aimed to use this approach to identify potential therapeutic targets for Zika virus, which is primarily transmitted by the Aedes aegypti mosquito. Targeting this virus was of great interest, since there is currently no treatment for Zika virus that is used in the clinic.
The main focus of this paper was to determine if adiponectin was important for Zika virus survival in its insect host. In humans, adiponectin is often used as a biomarker for certain diseases, such as diabetes. Interestingly, the adiponectin pathway has been associated with infectious pathogens in other mosquito species. However, the protein’s role in A. aegypti is unclear.
Break it, and see what happens!
To determine the role of the adiponectin receptor in A. aegypti (AaARLP), the authors used a reverse genetics technique. Reverse genetics is a common approach used to identify the function of a gene of interest. In this approach, scientists will often use genetic methods to make the gene non-functional, and will compare the phenotypes of the broken gene to the wild type gene.
In this case, the authors used RNA interference to silence the AaARLP receptor. RNA interference is a molecular genetics method in which researchers can target the degradation of a specific RNA that encodes a protein of interest. In this case, the researchers targeted the degradation of the RNA that makes the AaRLP receptor in a group of A. aegypti and let them feed off mice that were infected with Zika virus. They then measured the levels of Zika virus in the initial location of the virus (the midgut) and the location of virus progression throughout the mosquito (the body).
In the silenced AaARLP group, Zika virus expression was lower in the midgut at 2 and 7 days post infection (see image-1). There was also lower Zika virus expression in the body of the mosquitoes at 7 days post infection. Since the reduction of virus was not as dramatic between the wild type and silenced group at 7 days post infection, the authors reasoned that AaARLP was important for slowing down the Zika virus’ movement from the midgut to the body of the mosquito.
Image 1: Levels of Zika virus in a mouse model using AaARLP silenced strains (pink) compared to wild type (black). Image source: Figure 2E-G of Chen, et. al 2024.
To further investigate the role of AaARLP during Zika infection, the authors performed RNA sequencing on the wild type versus the silenced AaARLP mosquitos during infection. This experiment would provide information on what other genes are upregulated or downregulated in the absence of the adiponectin receptor. At two days post infection, no genes were significantly upregulated or downregulated between the two groups, which suggests that AaARLP most likely doesn’t play a large role in early infection.
Investigating a new protein’s role in Zika infection
Despite the fact that no genes were differentially regulated during early Zika infection in the AaARLP silenced strains, the authors decided to repeat the RNA sequencing at a later infection time point. At seven days post-infection, the authors observed an upregulation of various genes in the AaARLP silenced strain compared to the wild type. These included four different genes that encode the enzyme trypsin, which is important for the degradation of proteins in the gut. Since trypsin was highly expressed during infection, the authors hypothesized that this protein may be playing a role in Zika virus infection.
To determine the effect of trypsin on Zika infection itself, the authors silenced the four different trypsin genes in the mosquitos and let them feed off of mice with Zika virus, as they did previously. Interestingly, silencing all four of the genes resulted in a decrease in Zika virus in the midgut of the mosquitoes at two days post infection, but a higher level of Zika virus in the midgut at seven days post infection. This result suggested that the trypsin genes are most likely delaying the progression of Zika virus infection to the midgut of the mosquitoes.
Image 2: Model of the role of AaARLP and trypsin in Zika virus progression through the mosquito. Image source: Figure 6 from Chen, et. al 2024.
What are the next steps?
This paper showed that the adiponectin receptor AaRLP and the enzyme trypsin were both important in the progression of Zika virus in the mosquito host (see image-2). Understanding the major players in Zika virus infections in the mosquito could help to identify targets for future therapeutics. If we can eliminate the virus in the mosquito, perhaps we can prevent the spread of Zika virus to humans.
Overall, more work is needed to determine if AaRLP and trypsin are good candidates for pathogen inhibition in the mosquito. Despite more research being needed, this work provides a great foundation for our ability to stop Zika virus at the source.
Link to the original post: Chen T, Marín-López A, Raduwan H, Fikrig E.0.Aedes aegypti adiponectin receptor-like protein signaling facilitates Zika virus infection. mBio0:e02433-24.https://doi.org/10.1128/mbio.02433-24
Featured image: created by author with BioRender
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