Abstract
Early life stress (ELS) is considered a major risk factor for developing psychopathology. Increasing evidence points towards sex-dependent dysregulation of the hypothalamic-pituitary-adrenal (HPA) axis as a contributing mechanism. Additionally, clinical studies suggest that the mineralocorticoid receptor (MR) may further confer genetic vulnerability/resilience on a background of ELS. The link between ELS, sex and the HPA axis and how this interacts with MR genotype is understudied, yet important to understand vulnerability/resilience to stress. We used the early life-limited nesting and bedding model to test the effect of ELS on HPA properties in adult female and male mice carrying a forebrain-specific heterozygous knockout for MR. Basal HPA axis activity was measured by circadian peak and nadir corticosterone levels, in addition to body weight and weight of stress-sensitive tissues. HPA axis reactivity was assessed by mapping corticosterone levels after 10 min immobilization. Additionally, we measured the effects of ELS on steroid receptor [MR and glucocorticoid receptor (GR)] levels in the dorsal hippocampus and medial prefrontal cortex (mPFC) with western blot. Finally, behavioral reactivity towards a novel environment was measured as a proxy for anxiety-like behavior. Results show that HPA axis activity under rest conditions was not affected by ELS. HPA axis reactivity after immobilization was decreased by ELS in females and increased, at trend-level in males. This effect in females was further exacerbated by low expression of the MR. We also observed a sex*ELS interaction regarding MR and GR expression in the dorsal hippocampus, with a significant upregulation of MR in males only. The sex-dependent interaction with ELS was not reflected in the behavioral response to novel environment and time spent in a sheltered compartment. We did find increased locomotor activity in all groups after a history of ELS, which attenuated after 4 h in males but not females regardless of condition. Our findings support that ELS alters HPA axis functioning sex-dependently. Genetic predisposition to low MR function may render females more susceptible to the harmful effect of ELS whereas in males low MR function promotes resilience. We propose that this model may be a useful tool to investigate the underlying mechanisms of sex-dependent and genetic vulnerability/resilience to stress-related psychopathology.
Highlights
Life is a sensitive developmental period, during which stress experienced early in life, may induce long-lasting consequences for the ability to deal with challenging situations later in life (Heim et al, 2008; Strüber et al, 2014)
A recent meta-analysis revealed that the association between stress-induced cortisol responses and stress-related psychopathology is sex-dependent: women with depression or anxiety disorders overall showed a blunted response to psychosocial stress, whereas men showed the opposite (Zorn et al, 2017)
Adult mineralocorticoid receptor (MR) and glucocorticoid receptor (GR) Expression We evaluated the effect of early life stress (ELS) and/or MR genotype on MR and GR expression in the dorsal hippocampus and medial prefrontal cortex (mPFC) given their prominent role in the stress circuitry (Jankord and Herman, 2008)
Summary
Life is a sensitive developmental period, during which stress experienced early in life (early life stress, ELS), may induce long-lasting consequences for the ability to deal with challenging situations later in life (Heim et al, 2008; Strüber et al, 2014). Ample evidence associates changes in HPA axis function with depression or anxiety disorders, both with respect to circadian rhythmicity, response to the dexamethasone-CRH test or cortisol responses evoked by psychosocial stress (Künzel et al, 2003; Pariante and Lightman, 2008; Keller et al, 2017; Zorn et al, 2017) This body of literature includes observations in high-risk proband of women with depression, who do not (yet) show any symptoms of depression themselves (Modell et al, 2005), suggesting a causative role of HPA axis disturbances in the precipitation of depressive symptoms. This suggests that ELS in a sex-dependent manner may dysregulate HPA axis reactivity, which adds to the vulnerability to depression
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