Chronic stress decreases availability of heat shock proteins to glucocorticoid receptor in response to novel acute stress in Wistar rat hypothalamus

Single-cell molecular profiling of all three components of the HPA axis reveals adrenal ABCB1 as a regulator of stress adaptation

Chronic activation and dysregulation of the neuroendocrine stress response have severe physiological and psychological consequences, including the development of metabolic and stress-related psychiatric disorders. We provide the first unbiased, cell type-specific, molecular characterization of all three components of the hypothalamic-pituitary-adrenal axis, under baseline and chronic stress conditions. Among others, we identified a previously unreported subpopulation of Abcb1b+ cells involved in stress adaptation in the adrenal gland. We validated our findings in a mouse stress model, adrenal tissues from patients with Cushing's syndrome, adrenocortical cell lines, and peripheral cortisol and genotyping data from depressed patients. This extensive dataset provides a valuable resource for researchers and clinicians interested in the organism's nervous and endocrine responses to stress and the interplay between these tissues. Our findings raise the possibility that modulating ABCB1 function may be important in the development of treatment strategies for patients suffering from metabolic and stress-related psychiatric disorders.

Toll-like receptor 4: innate immune regulator of neuroimmune and neuroendocrine interactions in stress and major depressive disorder

Major depressive disorder (MDD) poses one of the highest disease burdens worldwide. Yet, current treatments targeting serotonergic and noradrenaline reuptake systems are insufficient to provide long-term relief from depressive symptoms in most patients, indicating the need for new treatment targets. Having the ability to influence behavior similar to depressive symptoms, as well as communicate with neuronal and neuroendocrine systems, the innate immune system is a strong candidate for MDD treatments. Given the complex nature of immune signaling, the main question becomes: What is the role of the innate immune system in MDD? The current review presents evidence that toll-like receptor 4 (TLR4), via driving both peripheral and central immune responses, can interact with serotonergic neurotransmission and cause neuroendocrine disturbances, thus integrating with widely observed hallmarks of MDD. Additionally, through describing the multi-directional communication between immune, neural and endocrine systems in stress, TLR4—related mechanisms can mediate stress-induced adaptations, which are necessary for the development of MDD. Therefore, apart from exogenous pathogenic mechanisms, TLR4 is involved in immune changes as a result of endogenous stress signals, playing an integral part in the pathophysiology, and could be a potential target for pharmacological treatments to improve current interventions for MDD.

Serum amyloid A inhibits dendritic cell apoptosis to induce glucocorticoid resistance in CD4(+) T cells

Mediators produced by the airway epithelium control the activation, recruitment, and survival of pulmonary dendritic cells (DC) that present antigen to CD4(+) T cells during the genesis and exacerbation of allergic asthma. The epithelial-derived acute phase protein, serum amyloid A (SAA), induces DC maturation and TH17 polarization. TH17 responses are associated with severe forms of allergic asthma that are poorly controlled by corticosteroids. We sought to determine whether SAA would enhance the survival of DC during serum starvation and could then contribute to the development of a glucocorticoid-resistant phenotype in CD4(+) T cells. Bone marrow-derived dendritic cells (BMDC) that were serum starved in the presence of SAA were protected from activation of caspase-3 and released less lactate dehydrogenase. In comparison with untreated serum-starved BMDC, treatment with SAA downregulated mRNA expression of the pro-apoptotic molecule Bim, increased production of the pro-survival heat shock protein 70 (HSP70), and induced secretion of pro-inflammatory cytokines. SAA-treated BMDC that were serum starved for 48 h remained capable of presenting antigen and induced OTII CD4(+) T cells to secrete IL-17A, IL-17F, IL-21, IL-22, and IFNγ in the presence of ovalbumin. IL-17A, IL-17F, IL-21, and IFNγ production occurred even when the CD4(+) T cells were treated with dexamethasone (Dex), whereas glucocorticoid treatment abolished cytokine secretion by T cells cocultured with untreated serum-starved BMDC. Measurement of Dex-responsive gene expression demonstrated CD4(+) T cells as the target of glucocorticoid hyperresponsiveness manifest as a consequence of BMDC stimulation by SAA. Finally, allergic airway disease induced by SAA and antigen inhalation was unresponsive to Dex treatment. Our results indicate that apo-SAA affects DC to both prolong their viability and increase their inflammatory potential under apoptosis-inducing conditions. These findings reveal mechanisms through which SAA enhances the CD4(+) T-cell-stimulating capacity of antigen-presenting cells that may actively participate in the pathogenicity of glucocorticoid-resistant lung disease.