Greater inflammatory activity and blunted glucocorticoid signaling in monocytes of chronically stressed caregivers

Abstract

Chronic stress is associated with morbidity and mortality from numerous conditions, many of whose pathogenesis involves persistent inflammation. Here, we examine how chronic stress influences signaling pathways that regulate inflammation in monocytes. The sample consisted of 33 adults caring for a family member with glioblastoma and 47 controls whose lives were free of major stressors. The subjects were assessed four times over eight months. Relative to controls, caregivers' monocytes showed increased expression of genes bearing response elements for nuclear-factor kappa B, a key pro-inflammatory transcription factor. Simultaneously, caregivers showed reduced expression of genes with response elements for the glucocorticoid receptor, a transcription factor that conveys cortisol's anti-inflammatory signals to monocytes. Transcript origin analyses revealed that CD14+/CD16- cells, a population of immature monocytes, were the predominate source of inflammatory gene expression among caregivers. We considered hormonal, molecular, and functional explanations for caregivers' decreased glucocorticoid-mediated transcription. Across twelve days, the groups displayed similar diurnal cortisol profiles, suggesting that differential adrenocortical activity was not involved. Moreover, the groups' monocytes expressed similar amounts of glucocorticoid receptor protein, suggesting that differential receptor availability was not involved. In ex vivo studies, subjects' monocytes were stimulated with lipopolysaccharide, and caregivers showed greater production of the inflammatory cytokine interleukin-6 relative to controls. However, no group differences in functional glucocorticoid sensitivity were apparent; hydrocortisone was equally effective at inhibiting cytokine production in caregivers and controls. These findings may help shed light on the mechanisms through which caregiving increases vulnerability to inflammation-related diseases.

Keywords: Cytokines; Depression; Genomics; Glucocorticoids; Inflammation; Stress.

Fig. 1

Psychological sequelae of caregiving. Self-reports of perceived stress and depressive symptoms were collected from 33 adults caring for a family member with glioblastoma, and 47 control subjects without major stressors in their lives. Averaged across assessments, caregivers’ levels of (a) perceived stress (p = .0001) and (b) depressive symptoms (p = .0001) were nearly twice that of controls.

Fig. 2

Monocyte transcriptional activity. Genome-wide expression profiling was performed on immunomagnetically isolated CD14+ monocytes techniques. TELiS bioinformatics analyses quantified response element prevalence in promoters of differentially expressed genes; the results were averaged across assessments. Relative to controls, monocytes of caregivers showed (a) increased expression of genes bearing response elements for the pro-inflammatory transcription factor nuclear factor kappa B (p = .0017), and (b) decreased expression of genes bearing response elements for the glucocorticoid receptor (p = .04). Caregivers’ monocytes also showed upregulation of genes with response elements for (c) Cyclic AMP Response Element Binding Protein (p = .007) and (d) Early Growth Response Protein 1 (p = .04).

Fig. 3

Cellular sources of transcriptional disparity. Transcript origin analyses were performed to identify the cellular origins of differentially expressed genes. Data from Ingersoll et al., 2010 were used to calculate diagnosticity scores, indicating whether transcripts are expressed predominately by a specific cell type. Averaged across assessments, results indicated that upregulated genes in caregivers were predominately expressed by CD14+/16− cells, a population of immature, inflammatory monocytes (p < .001). Down-regulated genes were not selectively associated with either subset.

Fig. 4

Diurnal cortisol output and glucocorticoid receptor expression. (a) Salivary cortisol was assessed at six points over the diurnal cycle, on a total of twelve days across the study. Averaged across assessments, caregivers and controls displayed similar patterns of diurnal cortisol output (p’s > .25). (b) Flow cytometry was used to quantify glucocorticoid receptor protein expression. Averaged across assessments, the groups’ monocytes had similar GR abundance (p = .41).

Fig. 5

Functional glucocorticoid sensitivity. Whole blood was cultured for 6 h with the bacterial product lipoploysaccharide (50 ng/mL) and varying dosages of hydrocortisone. Production of the inflammatory cytokine interleukin-6 was measured by flow cytometric analysis of mean fluorescence intensity in CD14+ cells, and averaged across assessments. Relative to control subjects, the caregivers’ monocytes produced higher levels of IL-6 when stimulated with LPS, and this disparity persisted when the cells were co-incubated with hydrocortisone at doses from 10⁻⁵ to 10⁻⁷ mol/L (p’s from .01– to .04).