Nuclear factor kappa-B cell (NF-κB), interferon regulatory Factor, and glucocorticoid receptor pathway activation in major depressive Disorder: The role of cytomegalovirus infection

Altered activity of major immunoregulatory pathways has been reported in major depressive disorder (MDD) and is thought to underlie the elevations in circulating inflammatory mediators present in a subgroup of patients. However, the drivers of these changes in gene expression remain unclear. One potential modulator of immune function is viral infection. Here we examined the relationship between cytomegalovirus (CMV), a common herpesvirus, that has been shown to be a pathological cofactor in inflammatory disorders, and activity of key coordinators of the innate inflammatory response in MDD. We used RNAseq to characterize gene expression differences in in 79 unmedicated individuals with MDD and 80 healthy controls (HCs). A well-established bioinformatic strategy was used to quantify transcription control pathway activity based on the relative prevalence of pre-specified transcription factor-binding motifs in the promoters of differentially expressed genes. The main aim was to characterize diagnostic differences in immunoregulatory pathway activity and determine if these were related to CMV serostatus or antibody titer (viral reactivation). Significantly increased activity of interferon regulatory factor 1 (IRF1) and nuclear factor kappa-B cell (NF-κB) pathways was observed in the MDD group compared with HCs. Transcript Origin Analyses using cell-specific reference transcriptomes indicated that the MDD-associated transcriptome changes derived primarily from myeloid lineage immune cells (classical and non-classical monocytes). A more modest MDD-associated upregulation of glucocorticoid receptor (GR) pathway activity was also present. CMV infection/activity across the combined MDD and HC groups was weakly related to GR pathway activation but not to IRF1 and NF-κB activity; the most salient signature of CMV was activation and/or expansion of the CD8+ T-cell population. The elevated MDD-associated NF-κB (but not IRF1) activity was markedly attenuated after controlling for CMV antibody titer or for CD8+ T-cell prevalence. At least some of the NF-κB signal in MDD may be attributable to the cellular immune response to CMV, suggesting that CMV infection may be one of several pathways contributing to inflammation in depression. The pronounced activation of the antiviral IRF-1 pathway in MDD suggests the contribution of viral processes although this specific antiviral effect was not specific to CMV. CMV may indirectly drive interferon responses by impairing T-cell control of other viral infections.