Physically painful memories are a major component of many fear-based anxiety disorders, including Post-Traumatic Stress Disorder (PTSD). While the need to remember painful stimuli is evolutionary advantageous, the ability to consolidate and extinguish these memories when no longer needed is also advantageous. But life-threatening painful memories are often the hardest to extinguish, which begs the question of whether there are additional molecular factors that play a role in specifically painful memory formation. One hypothesis is that painful stimuli may result in cellular stress which can act as an additional mediator of painful event memories. In this proposal we directly test this hypothesis using Drosophila melanogaster. Our previous work demonstrated the differential expression of cellular stress genes following aversive (electric shock) learning in the fruit fly. Here we focus on such genes thought to be involved in secretion (or secreted themselves) during times of cellular stress. We also will look further in depth at a protein known as NinaA which is involved in protein folding in the ER as well as may be involved in suppressing immune system functioning based on its human homolog (PPIB). Fruit flies that lack the NinaA protein fail to remember electric shock and fail to avoid painful stimuli. In this proposal we will ask whether NinaA and other cellular stress genes play a role in painful aversive stimuli integration and memory. To do this, animals with reduced expression of each gene will be run through a series of assays to assess their behavioral response to painful stimuli and a non-painful but still aversive stimuli. In order to look more broadly at the role of specific gene networks, in this case genes implicated in cellular stress, RNAseq datasets will be collected from the brains of animals who have experienced electric shock, painful heat, and painful mechanical stimulation. This will be compared to publicly available mammalian datasets looking at electric shock in aversive learning paradigms. We then hope to go on to map where these genes are acting and characterize their role in painful memory formation. The goal of this proposal is to implement a process for functionally validating gene networks from RNAseq data that may be non-intuitive to the associated phenotype. If we hope to develop novel treatments and drug targets for PTSD then we need to look in an unbiased way at what is happening at the molecular level in the brain during the acquisition of fear memories. RNAseq allows us this opportunity and reveals for us novel gene networks that can be functionally validated through a series of well-utilized behavioral assays.
Existing research has highlighted the need to better understand the role cellular stress plays in the formation of painful memories. Here we hope to elucidate the role a subset of cellular stress genes, recently shown to be differentially expressed following memory formation, play in the formation of memory of painful stimuli. We also ask whether cellular stress genes more broadly impact, or are involved in, different modalities of painful and non-painful stimuli learning.
