Project Four: Clinical studies of PACAP-CRF systems in human PTSD

The goal of Project 4 is to determine whether variation in CRF and PACAP system signaling tracks with hyperarousal intermediate phenotypes in women and men with PTSD.

Although Post-Traumatic Stress Disorder (PTSD) was once conceptualized as a direct consequence of extreme stress, the influence of constitutional factors on illness liability is now recognized. Prominent among these factors are genetic risk and biological sex: PTSD is 30-40% heritable and twice as common in women. Neurobiological mechanisms have been difficult to identify, leading to efforts to identify dimensional symptom measures and intermediate phenotypes that are sensitive to disease-promoting influences. Altered function of CRF (corticotropin-releasing factor) and PACAP (pituitary adenylate cyclase-activating polypeptide) systems are candidate mechanisms of sex-dependent moderation of risk for PTSD and other DSM-defined conditions, including Major Depressive Disorder (MDD). In women with PTSD, higher blood PACAP levels and allelic variation in the PAC1 receptor (PAC1R) predict greater anxious arousal symptoms and total symptoms, and greater physiological arousal during anxiety-related paradigms. Variation in CRF and its type-I receptor (CRFR1) are associated with PTSD and MDD, and contribute to sex differences in physiological arousal following severe stress. CRF and PACAP systems overlap with brain areas implicated in alterations in RDoC domains (fear, anxiety, arousal) seen in PTSD, including extended amygdala (extAMG) and medial prefrontal cortex (mPFC). Our premise is that studying dimensions of hyperarousal across multiple levels of analysis will identify intermediate phenotypes of PTSD. In 230 patients with DSM-defined PTSD (115 women and 115 men), we will examine relationships of CRF/PACAP biomarkers with neuroimaging measures of the amygdala (AMG) and bed nucleus of the stria terminalis (BNST), due to evidence of their roles in fear and anxiety, and of their relevance to PTSD. We also will examine the mPFC, which affects arousal responses to threat via reciprocal connections with the AMG and BNST.

We propose an innovative combination of CRF/PACAP, physiology, and brain measures: (1) blood levels of PACAP and hypothalamic pituitary adrenal axis (HPA) hormones (ACTH and cortisol, to serve as indices of CRF activity); (2) genetic, epigenetic, and mRNA variation in CRFR1 and PAC1R; (3) functional connectivity using resting state functional magnetic resonance imaging (rsfMRI); (4) structural connectivity using diffusion tensor imaging (DTI); (5) glutamate metabolism and neuron integrity using magnetic resonance spectroscopy (MRS); (6) physiological indices of arousal during fear conditioning and dark enhanced startle paradigms; (7) clinical symptoms (anxious arousal, dysphoric arousal, sleep dysregulation).

Our overarching hypothesis is that we will identify CRF-, PACAP-, and CRF+PACAPpredominant intermediate phenotypes, and sex-dependent relationships.