Postdoctoral Fellow, University of California San Diego
Background and hypothesis: Posttraumatic stress disorder (PTSD) affects 8% of the American population while rates are higher in military veterans. The catechol-O-methyltransferase (COMT) enzyme is implicated in the catabolism of dopamine and the val158met single nucleotide polymorphism (SNP) in the COMT gene has been associated with a greater risk of PTSD. We have previously shown, in a “humanized” COMTval158met SNP mouse line, that Val/Val carriers, compared to Met/Met carriers, exhibited altered inflammatory responses and greater enduring anxiety-like responses up to 14 days after predator stress. Recent evidence has implicated inflammation as a potential mechanism of PTSD risk and symptom maintenance. Because catecholamines play a key role in immune signaling we hypothesized that the COMTval158met SNP association with PTSD risk may be via alteration in the inflammatory state. Methods: We investigated the effect of lipopolysaccharide (LPS, 1 mg/kg, IP), a toll-like receptor 4 (TLR4) agonist that triggers a strong inflammatory response, in the “humanized” COMTval158met mouse line. Avoidance behaviors were assessed in the open field (exploratory behavior) and light-dark box (anxiety behavior) one week after injection. Results: In males, LPS increased avoidance behaviors in both genotypes, with the highest response in Val/Val mice. Female LPS-treated mice exhibited lower avoidance behaviors in both genotypes, with a greater effect in Val/Val mice. Conclusions: These results suggest (1) that the COMTval158met SNP modulates the response to LPS; and (2) that sex-dependent immune pathways might play a role in the COMTval158met SNP-modulated response to trauma. These findings also support that targeting the immune signaling pathways might be a novel therapeutic alternative for PTSD patients. catechol-O-methyltransferase (COMT) enzyme is implicated in the catabolism of catecholamines and plays a key role in cortical signaling. The val158met single nucleotide polymorphism (SNP) in the COMT gene has been associated with a greater risk for posttraumatic stress disorder (PTSD).
Abstract: Post-traumatic stress disorder (PTSD) is a highly debilitating stress and anxiety-related disorder that occurs in response to specific trauma or abuse. Genetic risk factors may account for up to 30-40% of the heritability of PTSD. Understanding the gene pathways that are associated with PTSD, and how those genes interact with the fear and stress circuitry to mediate risk and resilience for PTSD will enable the development of targeted therapies to prevent the occurrence of or decrease the severity of this complex multi-gene disorder. This review will summarize recent research on genetic approaches to understanding PTSD risk and resilience in human populations, including candidate genes and their epigenetic modifications, genome-wide association studies and neural imaging genetics approaches. Despite challenges faced within this field of study such as inconsistent results and replications, genetic approaches still offer exciting opportunities for the identification and development of novel therapeutic targets and therapies in the future.
Pub.: 01 Mar '17, Pinned: 01 Jul '17
Abstract: This study had two purposes. First: to compare predator and water submersion stress cFos activation in medial prefrontal cortices (mPFC) and the medial amygdala (MeA). Second: to identify markers of vulnerability to stressors within these areas. Rats were either predator or submersion stressed and tested 1.75 h later for anxiety. Immediately thereafter, rats were sacrificed and cFos expression was examined. Predator and submersion stress equally increased anxiety-like behavior in the elevated plus maze (EPM) and hole board. To examine vulnerability, rats which were less anxious (LA) and more (highly) anxious (MA) in the EPM were selected from among handled control and stressed animals. LA stressed rats were considered stress non-responsive while MA stressed rats were considered stress responsive. Predator stress, but not submersion stress, activated MeA cFos. CFos expression of mPFC cells was elevated in LA rats and reduced in MA rats in predator stressed animals only, correlating negatively with anxiety. These findings are consistent with data implicating greater mPFC excitability in protection against the effects on affect of traumatic stress. The findings also suggest that this conclusion is stressor specific, applying to predator stress but not submersion stress. Both stressors have been suggested to model hyperarousal and comorbid anxiety aspects of PTSD in humans. Hence the use of these paradigms to identify brain bases of vulnerability and resilience to traumatic stress in PTSD has translation potential. On the other hand, our evidence of stressor specificity of vulnerability/resilience markers raises a caution. The data suggest that preclinical markers of vulnerability/resilience in a given stress paradigm are at best suggestive, and translational value must ultimately be confirmed in humans.
Pub.: 06 Oct '11, Pinned: 01 Jul '17
Abstract: Posttraumatic stress disorder (PTSD) is a serious and debilitating condition with a prevalence rate of approximately 8% in the United States. Given the number of veterans returning from conflicts around the globe with PTSD, and the substantial number of civilians experiencing traumas, new perspectives on the biology of PTSD are needed. Based on the concept that PTSD is a disorder of stress response systems, numerous studies have suggested changes in hypothalamic-pituitary-adrenal (HPA) axis and sympathetic-adrenal-medullary (SAM) system function in patients with PTSD. Given that both glucocorticoids and catecholamines exert powerful effects on the immune system, it is surprising that relatively few studies have examined immune changes in patients with PTSD. Moreover, patients with PTSD are known to have increased rates of comorbidity with somatic disorders that involve immune and inflammatory processes. Patients with PTSD have been found to exhibit a number of immune changes including increased circulating inflammatory markers, increased reactivity to antigen skin tests, lower natural killer cell activity, and lower total T lymphocyte counts. Studies with humans and rodents suggest that certain proinflammatory cytokines are able to induce neurochemical and behavioral changes that resemble some key features of PTSD. This short article reviews immune alterations in PTSD, and considers possible mechanisms by which such changes may be related to neuroendocrine alterations and medical comorbidities of PTSD.
Pub.: 12 Oct '10, Pinned: 01 Jul '17
Abstract: Dopaminergic and serotonergic systems have been implicated in PTSD. The present study evaluated the association of four catechol-O-methyltransferase (COMT) gene loci, and the joint effect of COMT and tryptophan hydroxylase 2 (TPH2) genes on PTSD symptoms.Subjects included 200 Caucasian Armenian adults exposed to the 1988 Spitak earthquake from 12 multigenerational (3-5 generations) families. Instruments used included the UCLA PTSD Reaction Index based on DSM-5 criteria, and the Beck Depression Inventory.The adjusted heritabilitiy of vulnerability to DSM-5 based PTSD symptoms was 0.60 (p<10(-4)). There was a significant association of the COMT allele rs4633C with total PTSD (p<0.03), and D category (p<0.04) (negative alterations in cognitions and mood) severity scores, but not with C category (avoidance) scores. There was no genetic correlation between C and D category severity scores. COMT allele rs4633C and the TPH-2 allele rs11178997T together accounted for 7% of the variance in PTSD severity scores (p<0.001). None of the COMT alleles were associated with depression.The ratings of earthquake exposure and prior trauma may have been subject to recall bias. The findings may not be generalizable to other ethnic/racial populations.COMT allele rs4633C may be causally related and/or is in linkage disequilibrium with gene(s) that are causally related to PTSD symptoms. Carriers of these COMT and the TPH-2 alleles may be at increased risk for PTSD. The findings provide biological support for dividing DSM-IV category C symptoms into DSM-5 categories C and D.
Pub.: 03 Dec '14, Pinned: 21 Jun '17
Abstract: Posttraumatic stress disorder (PTSD) has been associated in cross-sectional studies with peripheral inflammation. It is not known whether this observed association is the result of PTSD predisposing to inflammation (as sometimes postulated) or to inflammation predisposing to PTSD.To determine whether plasma concentration of the inflammatory marker C-reactive protein (CRP) helps predict PTSD symptoms.The Marine Resiliency Study, a prospective study of approximately 2600 war zone-deployed Marines, evaluated PTSD symptoms and various physiological and psychological parameters before deployment and at approximately 3 and 6 months following a 7-month deployment. Participants were recruited from 4 all-male infantry battalions imminently deploying to a war zone. Participation was requested of 2978 individuals; 2610 people (87.6%) consented and 2555 (85.8%) were included in the present analysis. Postdeployment data on combat-related trauma were included for 2208 participants (86.4% of the 2555 included) and on PTSD symptoms at 3 and 6 months after deployment for 1861 (72.8%) and 1617 (63.3%) participants, respectively.Severity of PTSD symptoms 3 months after deployment assessed by the Clinician-Administered PTSD Scale (CAPS).We determined the effects of baseline plasma CRP concentration on postdeployment CAPS using zero-inflated negative binomial regression (ZINBR), a procedure designed for distributions, such as CAPS in this study, that have an excess of zeroes in addition to being positively skewed. Adjusting for the baseline CAPS score, trauma exposure, and other relevant covariates, we found baseline plasma CRP concentration to be a highly significant overall predictor of postdeployment CAPS scores (P = .002): each 10-fold increment in CRP concentration was associated with an odds ratio of nonzero outcome (presence vs absence of any PTSD symptoms) of 1.51 (95% CI, 1.15-1.97; P = .003) and a fold increase in outcome with a nonzero value (extent of symptoms when present) of 1.06 (95% CI, 0.99-1.14; P = .09).AND RELEVANCE A marker of peripheral inflammation, plasma CRP may be prospectively associated with PTSD symptom emergence, suggesting that inflammation may predispose to PTSD.
Pub.: 01 Mar '14, Pinned: 21 Jun '17
Abstract: The prevalence of posttraumatic stress disorder (PTSD) is high in the armed services, with a rate up to 20%. Multiple studies have associated markers of inflammatory signaling prior to trauma with increased risk of PTSD, suggesting a potential role of the immune system in the development of this psychiatric disorder. One question that arises is if "priming" the immune system before acute trauma alters the stress response and increases enduring effects of trauma. We investigated the time course of inflammatory response to predator stress, a robust stressor that induces enduring PTSD-like behaviors, and the modulation of these effects via prior immune activation with the bacterial endotoxin, lipopolysaccharide (LPS), a Toll-like receptor 4 (TLR4) agonist. Mice exposed to predator stress exhibited decreased pro-/anti-inflammatory balance in the brain 6h after stress, suggesting that predator exposure acutely suppressed the immune system by increasing anti-inflammatory cytokines levels. Acute immune activation with LPS before a single predator stress did not alter the enduring avoidance behavior in stressed mice. Our findings suggest that acute inflammation, at least via TLR4 activation, is not sufficient to increase susceptibility for PTSD-like behaviors in this model. Future studies will examine if chronic inflammation is required to induce similar immune changes to those observed in PTSD patients in this model.
Pub.: 06 Feb '17, Pinned: 21 Jun '17