Periodic Reporting for period 1 - QuinADAR1 (Protection from malaria in the Fulani ethnic group of West Africa involves reduced levels of A-to-I RNA editing by ADAR1)
Período documentado: 2019-06-01 hasta 2021-05-31
Every year, there are an estimated over 200 million cases of malaria worldwide. Malaria is caused by infection with the protozoan parasite Plasmodium, which are spread by the bite of a malaria-infected Anopheles mosquito. Despite a concerted international effort to combat the disease, malaria still causes approximately half a million deaths every year, the vast majority of which are young children with Plasmodium falciparum infection in sub-Saharan Africa. An acknowledged hurdle in the development of new strategies for the treatment and prevention of malaria is our limited understanding of the biology of Plasmodium infection and its complex interaction with the human host.
We have previously investigated what mediates an effective human immune response to infection with P.falciparum malaria. Specifically, through studying the Fulani ethnic group of West Africa, who are relatively resistant to malaria infection. Since the first report of the different response of Fulani to P.falciparum in 1996, populations of Fulani from Mali to as far east as Sudan have consistently been reported to have fewer symptomatic cases of malaria, lower P.falciparum infection rates, and lower P.falciparum density in infected individuals. The basis of the Fulani protection from malaria has never been established. However, we performed a pilot study which suggested that reduced levels of adenosine-to-inosine (A-to-I) editing of RNA following P.falciparum infection can drive a more effective innate immune response in the Fulani.
A key role of A-to-I editing of RNA is the regulation of innate immunity via the RIG-I like receptor (RLR) antiviral response pathway. The conversion of adenosine (A) to inosine (I) by hydrolytic deamination is the most common RNA base modification in humans. A-to-I modification is catalysed by two adenosine deaminases acting on RNAs (ADARs), ADAR1 and ADAR2, which act upon double stranded RNAs as substrates. A-to-I edited sites are widespread, with millions of editing sites identified in the human transcriptome. During infection, RLR family receptors Retinoic acid-inducible gene I (RIG-I) and Melanoma differentiation-associated gene 5 (MDA5) detect viral RNA and signal via MAVS to activate the antiviral immune response, including activation of type I and type III interferons (IFNs) and pro-inflammatory cytokines. The activation of the RLR pathway by viral or other ‘non-self’ RNAs, but not RNA of the human cell (‘self’ RNA) can be regulated by A-to-I editing of 'self' RNA by ADAR1. In the absence of ADAR1, unedited ‘self’ RNA can be recognised as 'non-self' and activate the RLR pathway, upregulating innate immune responses.
The objective of this project was to investigate whether levels of A-to-I editing of RNA are transiently reduced as part of the innate immune response to P.falciparum infection. A relatively stronger reduction of levels of A-to-I editing of RNA may enable individuals to mount a more effective immune response and contribute to their relative protection from the disease. Further, we will investigate whether targeting of ADAR1 and/or reduction in levels of A-to-I editing of RNA may present a novel strategy to boost immune response to malaria.
We have previously investigated what mediates an effective human immune response to infection with P.falciparum malaria. Specifically, through studying the Fulani ethnic group of West Africa, who are relatively resistant to malaria infection. Since the first report of the different response of Fulani to P.falciparum in 1996, populations of Fulani from Mali to as far east as Sudan have consistently been reported to have fewer symptomatic cases of malaria, lower P.falciparum infection rates, and lower P.falciparum density in infected individuals. The basis of the Fulani protection from malaria has never been established. However, we performed a pilot study which suggested that reduced levels of adenosine-to-inosine (A-to-I) editing of RNA following P.falciparum infection can drive a more effective innate immune response in the Fulani.
A key role of A-to-I editing of RNA is the regulation of innate immunity via the RIG-I like receptor (RLR) antiviral response pathway. The conversion of adenosine (A) to inosine (I) by hydrolytic deamination is the most common RNA base modification in humans. A-to-I modification is catalysed by two adenosine deaminases acting on RNAs (ADARs), ADAR1 and ADAR2, which act upon double stranded RNAs as substrates. A-to-I edited sites are widespread, with millions of editing sites identified in the human transcriptome. During infection, RLR family receptors Retinoic acid-inducible gene I (RIG-I) and Melanoma differentiation-associated gene 5 (MDA5) detect viral RNA and signal via MAVS to activate the antiviral immune response, including activation of type I and type III interferons (IFNs) and pro-inflammatory cytokines. The activation of the RLR pathway by viral or other ‘non-self’ RNAs, but not RNA of the human cell (‘self’ RNA) can be regulated by A-to-I editing of 'self' RNA by ADAR1. In the absence of ADAR1, unedited ‘self’ RNA can be recognised as 'non-self' and activate the RLR pathway, upregulating innate immune responses.
The objective of this project was to investigate whether levels of A-to-I editing of RNA are transiently reduced as part of the innate immune response to P.falciparum infection. A relatively stronger reduction of levels of A-to-I editing of RNA may enable individuals to mount a more effective immune response and contribute to their relative protection from the disease. Further, we will investigate whether targeting of ADAR1 and/or reduction in levels of A-to-I editing of RNA may present a novel strategy to boost immune response to malaria.
To determine whether levels of A-to-I editing of RNA are transiently reduced as part of the innate immune response to P.falciparum infection, we analysed RNA-sequencing data for levels of A-to-I editing, in different models of protection from malaria infection. We found that across many different models of infection, including a) protected Fulani individuals, compared to control Mossi individuals, b) individuals participating in P.falciparum vaccination studies (compared to unvaccinated individuals), c) individuals with repeated prior infection by P.falciparum (compared to people who have never been exposed to malaria before), and d) young individuals as they transition from susceptibility to resistance to malaria after repeated natural exposures to P.falciparum (with non-symptomatic individuals compared to symptomatic individuals in the same community), there were reduced levels of editing in protected individuals, and conversely increased levels of editing in unprotected individuals. This analysis shows that levels of A-to-I editing change in individuals following P.falciparum infection, and specifically supports our hypothesis that A-to-I editing levels are reduced in individuals protected from malaria.
We also looked at specific cell types involved in the changes of A-to-I editing. By treating immune cells isolated from the blood of healthy blood donors with P.falciparum grown in culture, we could see that innate immune cells such as monocytes, macrophages, and dendritic cells had reduced levels of ADAR1 expression and reduced A-to-I RNA editing shortly after exposure to stimuli found in malaria, within just a few hours.
Finally, to see if reduced levels of ADAR1 and/or A-to-I editing levels are enough to give protection against malaria, we used a rodent malaria (P.yoelii) to infect normal (wild-type) mice, and mice with only one working copy of the Adar1 gene (Adar1 +/- heterozygous mice). In normal mice, the malaria infection last about 30 days, before there is no more P.yoelli parasite detected in their blood. In Adar1+/- mice, there is significantly less P.yoelii parasite detected in their blood, over the whole 30 days of the infection. This strongly supports our hypothesis that reduced levels of ADAR1 and A-to-I RNA editing can drive a protective immune response against malaria.
We also looked at specific cell types involved in the changes of A-to-I editing. By treating immune cells isolated from the blood of healthy blood donors with P.falciparum grown in culture, we could see that innate immune cells such as monocytes, macrophages, and dendritic cells had reduced levels of ADAR1 expression and reduced A-to-I RNA editing shortly after exposure to stimuli found in malaria, within just a few hours.
Finally, to see if reduced levels of ADAR1 and/or A-to-I editing levels are enough to give protection against malaria, we used a rodent malaria (P.yoelii) to infect normal (wild-type) mice, and mice with only one working copy of the Adar1 gene (Adar1 +/- heterozygous mice). In normal mice, the malaria infection last about 30 days, before there is no more P.yoelli parasite detected in their blood. In Adar1+/- mice, there is significantly less P.yoelii parasite detected in their blood, over the whole 30 days of the infection. This strongly supports our hypothesis that reduced levels of ADAR1 and A-to-I RNA editing can drive a protective immune response against malaria.
We have identified a novel pathway that can confer protection against malaria. Reduction in A-to-I RNA editing by ADAR1 during infection with the Plasmodium is associated with protection from malaria, and targeting ADAR1 can reduce levels of parasitemia in mouse models during malaria infection. Currently, we and others are searching for small molecule inhibitors of ADAR1, which could be developed as drugs used to boost immune responses, during infections but also in other diseases such as cancer. In the future, targeting ADAR1 may provide as with an exciting new tool to prevent or treat malaria infections.