During an immune challenge, a host will adapt its behavior in a manner that enhances its ability to overcome that challenge. In mammals, this adaptive behavior is often manifested as increased sleep. The complex relationship between sleep and the immune response is not well understood at either the functional or the molecular level. In an effort to understand this relationship, this project exploits the Drosophila genetic model. The fruit fly Drosophila is a powerful model system that exhibits all of the behavioral features associated with sleep. The innate immune response in this species is also well characterized and has many features that are shared with that in mammals. Central to this reciprocal relationship between sleep and immune function is a family of transcription factor genes, NFκB. The first aim will test the hypothesis that, in the absence of infection, NFκB activity progressively increases during wakefulness and promotes sleep after reaching a threshold. Sleep then leads to decreased NFκB levels. Real time daily activity levels of NFκB in living flies will be measured using a reporter assay that was developed in the PI's laboratory. Flies that lack one or more NFκB genes are also expected to have severely reduced sleep. Second, following bacterial infection there is a large burst in NFκB that peaks 6-12 hours after the infection and promotes sleep. Manipulations of sleep using mechanical or genetic methods will be used to disrupt this burst of NFκB activity and to affect immune function. Specifically, manipulations that enhance peak NFκB activity after the infection as well as the ensuing recovery sleep will improve immune function as measured by rates of survival. Conversely, sustaining high levels of NFκB by blocking a recovery sleep will decrease immune function. Results of this work will provide important mechanistic insight into how sleep as an adaptive behavior influences immune function.
Understanding molecular mechanisms of adaptive behavior during an immune response in insects has important agricultural implications as well as for mammalian biology. This project will provide educational opportunities for a post-doctoral trainee, undergraduate, and high school students. The PI is committed to participating in educational programs that benefit individuals from groups which are traditionally underrepresented in the sciences.
The overall goal of the project was to evaluate a functional role of sleep in the innate immune response. When we get sick, the natural response is to get more sleep. However, there is surprisingly little experimental evidence that supports a role of sleep in the recovery process. To gain a better understanding of this process, we exploited the Drosophila genetic model system to address questions regarding the reciprocal relationship between sleep and the immune system. Fruit flies exhibit all of the behavioral features associated with sleep. The innate immune response in this species is also well characterized and has many features that are shared with that in mammals. Central to the relationship between sleep and the immune response are NFκB genes, Relish, Dorsal and Dif. We have previously found that Relish is necessary for infection-induced sleep. Results from the current project showed that Dorsal and Dif also have roles in daily sleep. To test a role of sleep in immune function, both mechanical and genetic approaches were used to keep flies awake before or after a bacterial infection. Genetic and pharmacological approaches were also used to increase sleep in flies. The results showed that enhancing sleep increased the flies’ ability to clear a bacterial infection and improved survival. Conversely, we found surprising effects of sleep deprivation before and after a bacterial infection. Sleep deprivation (SD) before inoculation increased the infection-induced recovery sleep and improved survival. SD after infection delayed the recovery sleep period, which was nonetheless still enhanced as compared to non-deprived controls. SD after infection also increased survival, but the survival rate did not improve until after flies had experienced sleep. SD increased transcriptional activity of NFκB in flies, indicating that this transcription factor causes the enhanced infection-induced sleep by prior SD. In support of this hypothesis, the effect of SD on infection-induced sleep and survival was abolished in mutant flies that lacked both the Relish and Dif genes. This finding suggests that Relish and Dif have redundant roles in this process: when one of these genes is absent, the other increases with SD and thereby promotes sleep during infection. We conclude from these findings that infection-induced sleep is an adaptive response that promotes survival. This project represents the first long-term effort to identify the genetic pathways involved in the complex interactions between the innate immune system and sleep. Understanding molecular mechanisms of adaptive behavior during an immune response in insects has important agricultural implications. This project provided educational opportunities for undergraduate and high school students as well as for post-doctoral trainees.
