Controlling FKBP51 for the treatment of PTSD

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U.S. Veterans are at increased risk for developing psychiatric symptoms and disorders compared to the civilian population. The hypothalamic-pituitary-adrenal (HPA) axis has long been linked to stress-induced psychiatric disorders. The 51kDa FK506-binding protein, FKBP51, together with the 90kDa heat shock protein (Hsp90), regulates the activity of steroid hormone complexes in the HPA axis and other cascades. The FKBP51-chaperone complex slows the response of the HPA axis to circulating stress hormones. Recently, it has been discovered that there are naturally occurring genetic variants in the form of single nucleotide polymorphisms (SNPs) in the gene encoding FKBP51, FKBP5, that cause DNA demethylation and increased expression of FKBP5. FKBP5 levels have been shown to increase during stress and aging by a similar mechanism. The SNPs that promote demethylation are also associated with increased risk for stress-induced psychopathologies such as post-traumatic stress disorder (PTSD) and major depressive disorder (MDD). Importantly, mice lacking Fkbp5 are protected from behavioral phenotypes associated with mood disorders. We have now generated a novel transgenic mouse model that overexpresses FKBP5 in the forebrain. We have also generated a novel cell line which overexpresses fluorescently labelled FKBP51, which can be easily tracked in real time. With these tools, we will test the hypothesis that mechanisms which decrease the levels of FKBP51 in mice will improve resiliency to stress-induced behavioral deficits. This proposal will focus on 1) increasing the rate of FKBP51 protein turnover through chaperone regulation and decreasing FKBP5 levels by disrupting protein translation through use of antisense oligonucleotides (ASOs) and 2) improving our understanding of how FKBP51 contributes to stress-induced behavioral deficits. First, we will increase FKBP51 degradation through chaperone protein modulation. Since we know that chaperone proteins, like Hsp90, are vital for protein triage and we know that FKBP51 works with Hsp90 to regulate steroid hormone complexes, we hypothesize that there is a larger chaperone protein repertoire which regulates FKBP51 turnover. Using cells expressing fluorescently tagged FKBP51, we will modulate protein chaperones using shRNA. We will identify novel protein chaperone-FKBP51 interactions by measuring changes in FKBP51 half-life. We will also determine the rate and route of FKBP51 turnover as well as assess the impact of various cellular stressors on FKBP51 stability. Next, we will test our lead Fkbp5-specific ASOs for their efficacy in reducing Fkbp5 in the brain of wild-type mice exposed to stress. Protection from stress-induced behavioral deficits will be evaluated. Lastly, in an effort to evaluate the impact of FKBP51 on the most common PTSD symptom reported by Veterans, we will determine the role of FKBP51 in the regulation of sleep disruption, which is caused by circadian desynchrony. We will determine whether mice lacking or overexpressing FKBP51 have altered circadian synchrony basally or in response to stress. The results from these studies may reveal that FKBP51-targeted therapies could be beneficial for reversing the circadian disruption that is commonly found in PTSD as well as in other psychiatric disorders and aging. If this is in fact the case, then circadian rhythmicity could be measured as a robust readout for the effectiveness of any FKBP51-targeted therapies that are developed.