PROJECT SUMMARY: Effective regulation of fear is essential for optimal mental health. Fear dysregulation is a hallmark of post- traumatic stress disorder (PTSD), a debilitating condition afflicting 22% of combat veterans. Impaired prefrontal cortex (PFC) functioning contributes to fear dysregulation in PTSD. Not all trauma-exposed individuals develop PTSD suggesting pre-trauma risk factors. Elucidating the nature of such factors will help identify novel therapeutics. Recent evidence supports an association between chronic inflammation and PTSD risk. Accordingly, many inflammatory diseases are linked to increased PTSD. Growing evidence supports a strong association between severe asthma and PTSD, however the severe asthma associated factors and mechanisms that regulate PTSD relevant PFC deficits remain unknown. Our published and recent data using unique mouse paradigms of aeroallergen house dust mite (HDM)-induced driven inflammation, show compromised fear extinction only in mice with Th17/IL17A expansion, an effect dependent on IL17A receptor signaling and peripheral IL17A. Importantly, this is accompanied by 1) reduced neuronal activation in the PFC an extinction- regulatory area and 2) microglial/T cell/endothelial alterations within the subfornical organ (SFO), a BBB-devoid area projecting to the PFC. Collectively these observations inform our hypothesis: severe asthma relevant IL- 17A activates a complex, multi-cellular signaling cascade within the SFO which engages the PFC to regulate fear. This hypothesis will be tested in 3 aims. Aim 1 will determine if IL-17A signaling, and Th17 cell activity is necessary and sufficient for HDM-Th17/IL17A driven fear extinction deficits The ability of IL-17A blockade (neutralizing mAb) or Th17 antagonism (small molecule inhibitor) to reverse fear extinction deficits/neuroimmune alterations in mice with Th2/Th17 responses, or recombinant IL17A to induce fear extinction deficits/neuroimmune alterations in mice with Th2 responses will be assessed. Aim 2 will determine if SFO?IL projections are necessary and sufficient for HDM-Th17/IL17A driven fear extinction deficits Using a retroCre-dependent chemogenetic strategy we will inhibit or activate SFO?IL projections to assess effects on fear extinction in HDM treated mice with Th2 versus Th2/Th17A Aim 3 will identify transcriptomic profiles in the SFO and PFC associated with HDM-Th2/Th17 effects and fear Using single-cell RNAseq, the transcriptional profile of SFO and PFC derived cells will be generated with cell-specific signatures of immune cells, glia, endothelial cells and neurons to identify DEGs and signaling pathways uniquely activated in HDM TH2 vs Th2/Th17 mice. Validation and association with HDM-Th2/Th17 effects on fear will be performed using Aim 1/Aim 2 tissue. Impact: Our data reveals a unique core mechanism by which adaptive immune mediators associated with chronic lung inflammation regulate cortical deficits and fear, relevant to mental health. Completion of these studies will broaden our understanding of how peripheral inflammatory mediators modulate brain function and behavior and identify novel risk factors and therapeutic targets for fear-associated pathologies.

PROJECT NARRATIVE Abnormal fear regulation is observed in psychiatric disorders, particularly PTSD, a debilitating condition afflicting 8% of civilians and about 22% of combat veterans annually. Growing evidence supports an association of autoimmune conditions and severe asthma with PTSD prevalence and risk, however contributory mechanisms are not clear. Using immune-targeting, and cell-circuit approaches, this R01 investigates T cell-derived inflammatory mediators, unique forebrain circuits and cellular transcriptional signatures by which asthma related inflammation promotes fear dysregulation relevant to PTSD.