Onset, timing, and exposure therapy of stress disorders: mechanistic insight from a mathematical model of oscillating neuroendocrine dynamics

The hypothalamic-pituitary-adrenal (HPA) axis is a neuroendocrine system that regulates numerous physiological processes. Disruptions in the activity of the HPA axis are correlated with many stress-related diseases such as post-traumatic stress disorder (PTSD) and major depressive disorder. In this paper, we characterize "normal" and "diseased" states of the HPA axis as basins of attraction of a dynamical system describing the inhibition of peptide hormones such as corticotropin-releasing hormone (CRH) and adrenocorticotropic hormone (ACTH) by circulating glucocorticoids such as cortisol (CORT). In addition to including key physiological features such as ultradian oscillations in cortisol levels and self-upregulation of CRH neuron activity, our model distinguishes the relatively slow process of cortisol-mediated CRH biosynthesis from rapid trans-synaptic effects that regulate the CRH secretion process. Crucially, we find that the slow regulation mechanism mediates external stress-driven transitions between the stable states in novel, intensity, duration, and timing-dependent ways. These results indicate that the timing of traumatic events may be an important factor in determining if and how patients will exhibit hallmarks of stress disorders. Our model also suggests a mechanism whereby exposure therapy of stress disorders such as PTSD may act to normalize downstream dysregulation of the HPA axis.Comment: 30 pages, 16 figures, submitted to BMC Biology Direc

Pathway and biomarker discovery in a posttraumatic stress disorder mouse model

Posttraumatic stress disorder (PTSD), a prevalent psychiatric disorder, is caused by exposure to a traumatic event. Individuals diagnosed for PTSD not only experience significant functional impairments but also have higher rates of physical morbidity and mortality. Despite intense research efforts, the neurobiological pathways affecting fear circuit brain regions in PTSD remain obscure and most of the previous studies were limited to characterization of specific markers in periphery or defined brain regions. In my PhD study, I employed proteomics, metabolomics and transcriptomcis technologies interrogating a foot shock induced PTSD mouse model. In addition, I studied the effects of early intervention of chronic fluoxetine treatment. By in silico analyses, altered cellular pathways associated with PTSD were identified in stress-vulnerable brain regions, including prelimbic cortex (PrL), anterior cingulate cortex (ACC), basolateral amygdala (BLA), central nucleus of amygdala(CeA), nucleus accumbens (NAc) and CA1 of the dorsal hippocampus. With RNA sequencing, I compared the brain transcriptome between shocked and control mice, with and without fluoxetine treatment. Differentially expressed genes were identified and clustered, and I observed increased inflammation in ACC and decreased neurotransmitter signaling in both ACC and CA1. I applied in vivo 15N metabolic labeling combined with mass spectrometry to study alterations at proteome level in the brain. By integrating proteomics and metabolomics profiling analyses, I found decreased Citric Acid Cycle pathway in both NAc and ACC, and dysregulated cytoskeleton assembly and myelination pathways in BLA, CeA and CA1. In addition, chronic fluoxetine treatment 12 hours after foot shock prevented altered inflammatory gene expression in ACC, and Citric Acid Cycle in NAc and ACC, and ameliorated conditioned fear response in shocked mice. These results shed light on the role of immune response and energy metabolism in PTSD pathogenesis. Furthermore, I performed microdialysis in medial prefrontal cortex and hippocampus to measure the changes in extracellular norepinephrine and free corticosterone (CORT) in the shocked mouse and related them to PTSD-like symptoms, including hyperaroual and contextual fear response. I found that increased free CORT was related to immediate stress response, whereas norepinephrine level, in a brain region specific manner, predicted arousal and contextual fear response one month after trauma. I also applied metabolomics analysis to investigate molecular changes in prefrontal microdialysates of shocked mice. Citric Acid Cycle, Glyoxylate and Dicarboxylate metabolism and Alanine, Aspartate and Glutamate metabolism pathways were found to be involved in foot shock induced hyperarousal. Taken together, my study provides novel insights into PTSD pathogenesis and suggests potential therapeutic applications targeting dysregulated pathways

Serotonin and the CNS

Serotonin is an ancient neurotransmitter system involved in various systems and functions in the body and plays an important role in health and disease. The present volume illustrates the broadness of the involvement of serotonergic activity in many processes, focusing particularly on disorders of the brain, including depression, stress and fear, Alzheimer’s disease, aggression, sexual behavior, and neuro-immune disorders. Chapters illustrate techniques and methods used to study the complex role of the serotonergic system in all kinds of processes, present new hypotheses for several brain disorders like sleep and depression, and use mathematical modeling as a tool to advance knowledge of the extremely complex brain and body processes

Pathway and biomarker discovery in a posttraumatic stress disorder mouse model

Posttraumatic stress disorder (PTSD), a prevalent psychiatric disorder, is caused by exposure to a traumatic event. Individuals diagnosed for PTSD not only experience significant functional impairments but also have higher rates of physical morbidity and mortality. Despite intense research efforts, the neurobiological pathways affecting fear circuit brain regions in PTSD remain obscure and most of the previous studies were limited to characterization of specific markers in periphery or defined brain regions. In my PhD study, I employed proteomics, metabolomics and transcriptomcis technologies interrogating a foot shock induced PTSD mouse model. In addition, I studied the effects of early intervention of chronic fluoxetine treatment. By in silico analyses, altered cellular pathways associated with PTSD were identified in stress-vulnerable brain regions, including prelimbic cortex (PrL), anterior cingulate cortex (ACC), basolateral amygdala (BLA), central nucleus of amygdala(CeA), nucleus accumbens (NAc) and CA1 of the dorsal hippocampus. With RNA sequencing, I compared the brain transcriptome between shocked and control mice, with and without fluoxetine treatment. Differentially expressed genes were identified and clustered, and I observed increased inflammation in ACC and decreased neurotransmitter signaling in both ACC and CA1. I applied in vivo 15N metabolic labeling combined with mass spectrometry to study alterations at proteome level in the brain. By integrating proteomics and metabolomics profiling analyses, I found decreased Citric Acid Cycle pathway in both NAc and ACC, and dysregulated cytoskeleton assembly and myelination pathways in BLA, CeA and CA1. In addition, chronic fluoxetine treatment 12 hours after foot shock prevented altered inflammatory gene expression in ACC, and Citric Acid Cycle in NAc and ACC, and ameliorated conditioned fear response in shocked mice. These results shed light on the role of immune response and energy metabolism in PTSD pathogenesis. Furthermore, I performed microdialysis in medial prefrontal cortex and hippocampus to measure the changes in extracellular norepinephrine and free corticosterone (CORT) in the shocked mouse and related them to PTSD-like symptoms, including hyperaroual and contextual fear response. I found that increased free CORT was related to immediate stress response, whereas norepinephrine level, in a brain region specific manner, predicted arousal and contextual fear response one month after trauma. I also applied metabolomics analysis to investigate molecular changes in prefrontal microdialysates of shocked mice. Citric Acid Cycle, Glyoxylate and Dicarboxylate metabolism and Alanine, Aspartate and Glutamate metabolism pathways were found to be involved in foot shock induced hyperarousal. Taken together, my study provides novel insights into PTSD pathogenesis and suggests potential therapeutic applications targeting dysregulated pathways

Translational Biomarker Research for Militarily Relevant Populations in Neurocognitive Diseases

In recent decades more soldiers are being mobilized to conflict areas, such as the over 2 million service members, who have been deployed to Iraq and Afghanistan since October 2001, which includes but is not limited to Operation Enduring Freedom (OEF) and Operation Iraqi Freedom (OIF); or the 700,000 service veterans deployed to the Persian Gulf War in 1990-91 in the US. The UK mobilized over 46,000 military personnel to Iraq, 9,500 British troops to Afghanistan and 50,000 troops to the Gulf War. Soldiers are being exposed to traumatic events such as physical and psychological trauma, as well as chemical exposure and therefore service members are at risk of postdeployment health-related issues, associated commonly with post-traumatic stress disorder (PTSD) and traumatic brain injury (TBI) among OEF/OIF veterans, as well as Gulf War Illness (GWI) among the Persian Gulf War Veteran population. Although progress has been made in identifying underlying pathology for TBI and PTSD and acute as well as sub-acute biomarkers have been identified, with commercially available tests on the horizon, the work presented here addresses a critical but underinvestigated issue, the need for chronic biomarkers for these conditions, as they can go undetected for an extended period of time. Additionally, more evidence has surfaced that discusses how symptoms related to mild TBI (mTBI) can last for years after the insult, emphasizing the importance of investigatjng biomarkers at a late timepoint after injury as, owing to the mild nature of the injury, the condition was often undiagnosed at the time. PTSD itself still lacks an objective measure that can capture its complexity, whereas co-morbidity of PTSD with TBI further complicates the issue. The other mentioned militarily relevant condition, termed GWI, faces similar issues. Veterans deployed to the Persian Gulf War in 1991 suffer from a disease that has shown to exhibit persistent multisymptom complexity. No biomarker has been identified for this particular population thus making objective diagnosis difficult. Besides the identification of clinical biomarkers, much research has been done in preclinical models, yet there is still a need to verify and validate such animal models in order to demonstrate their utility. Once the validity of a preclinical model has been confirmed, investigation of pathogenic mechanisms in those models has the potential to reveal therapeutic targets of relevance to the human condition. Chapter 1 will discuss epidemiology, current clinical diagnosis and pathophysiology of TBI, PTSD and GWI as well as the status of biomarker research in each of these three areas. The thesis then focuses on the identification of plasma biomarkers in human patient populations, specifically in military populations suffering from TBI, PTSD or both at chronic time points post traumatic exposure (Chapters 2 & 3). In Chapter 4, we then explore whether or not such changes are present in our established animal model of TBI. In Chapter 5 we investigate peripheral biomarkers in plasma samples from Gulf War veterans and in two animal models of GWI. Given the complexity of TBI, PTSD and GWI clinical presentation and pathogenesis and their heterogeneity in human populations, it is anticipated that a valid biomarker for broad application will in fact require assessment of many markers to create a panel that can support diagnosis. The lipidomic and proteomic analyses I employed in this work are approaches with the required breadth and lack of bias to be successful in such an undertaking, and I hope that the work described in this thesis provides a foundation for future development of such biomarker panels

Comparative assessment of neurological vs metabolic allostasis as reflected in human skin fibroblasts

Physiological Science