George M. Slavich

From Stress to Inflammation and Major Depressive Disorder: A Social Signal Transduction Theory of Depression

Major life stressors, especially those involving interpersonal stress and social rejection, are among the strongest proximal risk factors for depression. In this review, we propose a biologically plausible, multilevel theory that describes neural, physiologic, molecular, and genomic mechanisms that link experiences of social-environmental stress with internal biological processes that drive depression pathogenesis. Central to this social signal transduction theory of depression is the hypothesis that experiences of social threat and adversity up-regulate components of the immune system involved in inflammation. The key mediators of this response, called proinflammatory cytokines, can in turn elicit profound changes in behavior, which include the initiation of depressive symptoms such as sad mood, anhedonia, fatigue, psychomotor retardation, and social-behavioral withdrawal. This highly conserved biological response to adversity is critical for survival during times of actual physical threat or injury. However, this response can also be activated by modern-day social, symbolic, or imagined threats, leading to an increasingly proinflammatory phenotype that may be a key phenomenon driving depression pathogenesis and recurrence, as well as the overlap of depression with several somatic conditions including asthma, rheumatoid arthritis, chronic pain, metabolic syndrome, cardiovascular disease, obesity, and neurodegeneration. Insights from this theory may thus shed light on several important questions including how depression develops, why it frequently recurs, why it is strongly predicted by early life stress, and why it often co-occurs with symptoms of anxiety and with certain physical disease conditions. This work may also suggest new opportunities for preventing and treating depression by targeting inflammation.

Neural sensitivity to social rejection is associated with inflammatory responses to social stress

Although stress-induced increases in inflammation have been implicated in several major disorders, including cardiovascular disease and depression, the neurocognitive pathways that underlie inflammatory responses to stress remain largely unknown. To examine these processes, we recruited 124 healthy young adult participants to complete a laboratory-based social stressor while markers of inflammatory activity were obtained from oral fluids. A subset of participants (n = 31) later completed an fMRI session in which their neural responses to social rejection were assessed. As predicted, exposure to the laboratory-based social stressor was associated with significant increases in two markers of inflammatory activity, namely a soluble receptor for tumor necrosis factor-α (sTNFαRII) and interleukin-6 (IL-6). In the neuroimaging subsample, greater increases in sTNFαRII (but not IL-6) were associated with greater activity in the dorsal anterior cingulate cortex and anterior insula, brain regions that have previously been associated with processing rejection-related distress and negative affect. These data thus elucidate a neurocognitive pathway that may be involved in potentiated inflammatory responses to acute social stress. As such, they have implications for understanding how social stressors may promote susceptibility to diseases with an inflammatory component.

The Emerging Field of Human Social Genomics

Although we generally experience our bodies as being biologically stable across time and situations, an emerging field of research is demonstrating that external social conditions, especially our subjective perceptions of those conditions, can influence our most basic internal biological processes—namely, the expression of our genes. This research on human social genomics has begun to identify the types of genes that are subject to social-environmental regulation, the neural and molecular mechanisms that mediate the effects of social processes on gene expression, and the genetic polymorphisms that moderate individual differences in genomic sensitivity to social context. The molecular models resulting from this research provide new opportunities for understanding how social and genetic factors interact to shape complex behavioral phenotypes and susceptibility to disease. This research also sheds new light on the evolution of the human genome and challenges the fundamental belief that our molecular makeup is relatively stable and impermeable to social-environmental influence.

Clinical anxiety, cortisol and interleukin-6: evidence for specificity in emotion-biology relationships.

Anxiety confers increased risk for inflammatory diseases, and elevated inflammatory activity in anxious individuals may contribute to this increased risk. One complication, however, is that anxiety could be associated with inflammatory activity either through a specific anxiety pathway or through a more general negative emotionality pathway. To investigate, we measured levels of the stress hormone cortisol, the pro-inflammatory cytokine interleukin-6 (IL-6), and the systemic inflammatory marker C-reactive protein (CRP), as well as depression and neuroticism, in clinically anxious and non-anxious adults. Compared with non-anxious participants, clinically anxious participants exhibited significantly lower levels of morning cortisol and significantly higher levels of IL-6, independent of age, sex, and depressive symptoms. These group differences were robust when controlling for neuroticism. Conversely, the groups had equivalent levels of CRP in all analyses. Results are indicative of anxiety-specific effects on inflammatory activity, and highlight a pathway by which anxiety may increase risk for inflammatory diseases.

Dysregulated diurnal cortisol pattern is associated with glucocorticoid resistance in women with major depressive disorder

Dysfunction of the hypothalamic-pituitary-adrenal (HPA) axis is believed to play a role in the pathophysiology of depression. To investigate mechanisms that may underlie this effect, we examined several indices of HPA axis function - specifically, diurnal cortisol slope, cortisol awakening response, and suppression of cortisol release following dexamethasone administration - in 26 pre-menopausal depressed women and 23 never depressed women who were matched for age and body mass index. Salivary cortisol samples were collected at waking, 30 min after waking, and at bedtime over three consecutive days. On the third day, immediately after the bedtime sample, participants ingested a 0.5mg dexamethasone tablet; they then collected cortisol samples at waking and 30 min after waking the following morning. As predicted, depressed women exhibited flatter diurnal cortisol rhythms and more impaired suppression of cortisol following dexamethasone administration than non-depressed women over the three sampling days. In addition, flatter diurnal cortisol slopes were associated with reduced cortisol response to dexamethasone treatment, both for all women and for depressed women when considered separately. Finally, greater self-reported depression severity was associated with flatter diurnal cortisol slopes and with less dexamethasone-related cortisol suppression for depressed women. Depression in women thus appears to be characterized by altered HPA axis functioning, as indexed by flatter diurnal cortisol slopes and an associated impaired sensitivity of cortisol to dexamethasone. Given that altered HPA axis functioning has been implicated in several somatic conditions, the present findings may be relevant for understanding the pathophysiology of both depression and depression-related physical disease.

Social Influences on Clinical Outcomes of Patients With Ovarian Cancer

PURPOSE Previous research has demonstrated relationships of social support with disease-related biomarkers in patients with ovarian cancer. However, the clinical relevance of these findings to patient outcomes has not been established. This prospective study examined how social support relates to long-term survival among consecutive patients with ovarian cancer. We focused on two types of social support: social attachment, a type of emotional social support reflecting connections with others, and instrumental social support reflecting the availability of tangible assistance. PATIENTS AND METHODS Patients were prospectively recruited during a presurgical clinic visit and completed surveys before surgery. One hundred sixty-eight patients with histologically confirmed epithelial ovarian cancer were observed from the date of surgery until death or December 2010. Clinical information was obtained from medical records. RESULTS In a Cox regression model, adjusting for disease stage, grade, histology, residual disease, and age, greater social attachment was associated with a lower likelihood of death (hazard ratio [HR], 0.87; 95% CI, 0.77 to 0.98; P = .018). The median survival time for patients with low social attachment categorized on a median split of 15 was 3.35 years (95% CI, 2.56 to 4.15 years). In contrast, by study completion, 59% of patients with high social attachment were still alive after 4.70 years. No significant association was found between instrumental social support and survival, even after adjustment for covariates. CONCLUSION Social attachment is associated with a survival advantage for patients with ovarian cancer. Clinical implications include the importance of screening for deficits in the social environment and consideration of support activities during adjuvant treatment.

Stressful life events, chronic difficulties, and the symptoms of clinical depression.

Major life events and chronic difficulties have been found to be associated with the onset of depression. Little is known, however, about how exposure to such stressors is related to the clinical presentation of this disorder. We addressed this issue by administering an interview-based measure of life stress, the Beck Depression Inventory, and the Global Assessment of Functioning scale to 100 adults diagnosed with major depressive disorder. Participants who experienced a preonset severe life event exhibited greater overall levels of depression severity, endorsed more cognitive and somatic symptoms of depression, and functioned at lower levels than did their counterparts without preonset severe life events. In contrast, exposure to a preonset severe difficulty was unrelated to participants’ severity of depression, cognitive and somatic symptoms, or level of global functioning. These findings highlight the potentially greater importance of acute stress compared with chronic stress for influencing these key clinical features of depression.

Major Life Events and Major Chronic Difficulties Are Differentially Associated With History of Major Depressive Episodes

Major life events have been found to precede onsets of a 1st lifetime episode of depression more commonly than subsequent recurrences. Despite general empirical support for this finding, few data directly address how the role of major life events may change over successive recurrences. Further, little research has examined major chronic difficulties in relation to a 1st lifetime episode versus a recurrence of depression. The present study tested the associations between major life events and major difficulties in relation to lifetime history of depressive episodes in a sample of 96 individuals diagnosed with major depression. Using investigator-based measures of life stress, the authors found that, whereas major life events were associated with fewer lifetime episodes, major chronic difficulties were related to more prior episodes. These findings are discussed in terms of underlying mechanisms that may account for the changing role of major life stress over successive recurrences of depression.

Gender Differences in Life Events Prior to Onset of Major Depressive Disorder: The Moderating Effect of Age

Theoretical models attempting to explain why approximately twice as many women as men suffer from depression often involve the role of stressful life events. However, detailed empirical evidence regarding gender differences in rates of life events that precede onset of depression is lacking, due in part to the common use of checklist assessments of stress that have been shown to possess poor validity. The present study reports on a combined sample of 375 individuals drawn from 4 studies in which all participants were diagnosed with major depressive disorder and assessed with the Life Events and Difficulties Schedule (Bifulco et al., 1989), a state-of-the-art contextual interview and life stress rating system. Women reported significantly more severe and nonsevere, independent and dependent, and other-focused and subject-focused life events prior to onset of depression than did men. Further, these relations were significantly moderated by age, such that gender differences in rates of most types of events were found primarily in young adulthood. These results are discussed in term of their implications for understanding the etiological role of stressful life events in depression.

Greater amygdala activity and dorsomedial prefrontal–amygdala coupling are associated with enhanced inflammatory responses to stress

Psychological stress is implicated in the etiology of many common chronic diseases and mental health disorders. Recent research suggests that inflammation may be a key biological mediator linking stress and health. Nevertheless, the neurocognitive pathways underlying stress-related increases in inflammatory activity are largely unknown. The present study thus examined associations between neural and inflammatory responses to an acute laboratory-based social stressor. Healthy female participants (n=31) were exposed to a brief episode of stress while they underwent an fMRI scan. Blood samples were taken before and after the stressor, and plasma was assayed for markers of inflammatory activity. Exposure to the stressor was associated with significant increases in feelings of social evaluation and rejection, and with increases in levels of inflammation. Analyses linking the neural and inflammatory data revealed that heightened neural activity in the amygdala in response to the stressor was associated with greater increases in inflammation. Functional connectivity analyses indicated that individuals who showed stronger coupling between the amygdala and the dorsomedial prefrontal cortex (DMPFC) also showed a heightened inflammatory response to the stressor. Interestingly, activity in a different set of neural regions was related to increases in feelings of social rejection. These data show that greater amygdala activity in response to a stressor, as well as tighter coupling between the amygdala and the DMPFC, are associated with greater increases in inflammatory activity. Results from this study begin to identify neural mechanisms that might link stress with increased risk for inflammation-related disorders such as cardiovascular disease and depression.