MR/GR Signaling in the Brain during the Stress Response

This contribution is about mineralocorticoid receptors (MRs) in their capacity as mediators of glucocorticoid action in the brain. This paradox has evolved because MRs are promiscuous and bind with high-affinity cortisol and corticosterone as well as aldosterone, deoxycorticosterone, and progesterone. The MRs “see,” however, predominantly glucocorticoids, because of their 100–1000-fold excess over aldosterone; bioavailability is further enhanced because of local regeneration of glucocorticoids by 11βOH-steroid dehydrogenase (HSD-1). In contrast to these glucocorticoid-preferring MR, the evolutionary later appearance of aldosterone-selective MR in epithelial cells depends on co-localization with the oxidase 11β-hydroxysteroid-dehydrogenase type 2 (HSD-2) in a few hundred neurons in the nucleus tractus solitarii (NTS), which innervate frontal brain regions to regulate cognitive, emotional, and motivational aspects of salt appetite. The glucocorticoid-MRs and classical glucocorticoid receptors (GRs) mediate in a complementary manner the glucocorticoid coordination of circadian events and mediate the regulation of stress coping and adaptation. If an individual is exposed to a threat, MRs are crucial for the selection of a particular coping style, which is via GR activation subsequently stored in the memory for future use. Our contribution is concluded with the notion that an imbalance in MR- and GR-mediated actions increases susceptibility to stress-related disorders

Temporal associations between salivary cortisol and emotions in clinically depressed individuals and matched controls:A dynamic time warp analysis

Depression can be understood as a complex dynamic system where depressive symptoms interact with one another. Cortisol is suggested to play a major role in the pathophysiology of depression, but knowledge on the temporal interplay between cortisol and depressive symptoms is scarce. We aimed to analyze the temporal connectivity between salivary cortisol and momentary affective states in depressed individuals and controls. Thirty pair-matched depressed and non-depressed participants completed questionnaires on momentary positive (PA) and negative (NA) affect and collected saliva three times a day for 30 days. The association between cortisol and affect was analyzed by dynamic time warp (DTW) analyses. These analyses involved lag-1 backward to lag-1 forward undirected analyses and lag-0 and lag-1 forward directed analyses. Large inter- and intra-individual variability in the networks were found. At the group level, with undirected analysis PA and NA were connected in the networks in depressed individuals and in controls. Directed analyses indicated that increases in cortisol preceded specific NA items in controls, but tended to follow upon specific affect items increase in depressed individuals. To conclude, at group level, changes in cortisol levels in individuals diagnosed with a depression may be a result of changes in affect, rather than a cause.</p

Role of SGK in mineralocorticoid-regulated sodium transport

Role of SGK in mineralocorticoid-regulated sodium transport. Mineralocorticoids stimulate electrogenic Na+ transport in tight epithelia by altering the transcription of specific genes. Although the earliest mineralocorticoid effect is to increase the activity of the epithelial sodium channel (ENaC), ENaC mRNA and protein levels do not change. Instead, physiologic observations suggest that a mineralocorticoid target gene(s) encodes an ENaC regulator(s). To begin to identify and characterize mineralocorticoid-regulated target genes, we used suppression-subtractive hybridization to generate a cDNA library from A6 cells, a stable cell line of Xenopus laevis of distal nephron origin. A serine-threonine kinase, SGK, was identified from this screen. Sequence comparison revealed that frog, rat, and human SGK are 92% identical and 96% similar at the amino acid level. SGK mRNA was confirmed by Northern blot to be strongly and rapidly corticosteroid stimulated in A6 cells. In situ hybridization revealed that SGK was strongly stimulated by aldosterone in rat collecting duct but not proximal tubule cells. Low levels of SGK were present in rat glomeruli, but SGK was unregulated in this structure. Finally, SGK stimulated ENaC activity approximately sevenfold when coexpressed in Xenopus laevis oocytes. These data suggest that SGK is an important mediator of aldosterone effects on Na+ transport in tight epithelia. In view of the existence of SGK homologues in invertebrates, it is interesting to speculate that SGK is an ancient kinase that was adapted to the control of epithelial Na+ transport by early vertebrates as they made the transition from a marine to a freshwater environment

Antisense-Mediated RNA Targeting: Versatile and Expedient Genetic Manipulation in the Brain

A limiting factor in brain research still is the difficulty to evaluate in vivo the role of the increasing number of proteins implicated in neuronal processes. We discuss here the potential of antisense-mediated RNA targeting approaches. We mainly focus on those that manipulate splicing (exon skipping and exon inclusion), but will also briefly discuss mRNA targeting. Classic knockdown of expression by mRNA targeting is only one possible application of antisense oligonucleotides (AON) in the control of gene function. Exon skipping and inclusion are based on the interference of AONs with splicing of pre-mRNAs. These are powerful, specific and particularly versatile techniques, which can be used to circumvent pathogenic mutations, shift splice variant expression, knock down proteins, or to create molecular models using in-frame deletions. Pre-mRNA targeting is currently used both as a research tool, e.g., in models for motor neuron disease, and in clinical trials for Duchenne muscular dystrophy and amyotrophic lateral sclerosis. AONs are particularly promising in relation to brain research, as the modified AONs are taken up extremely fast in neurons and glial cells with a long residence, and without the need for viral vectors or other delivery tools, once inside the blood brain barrier. In this review we cover (1). The principles of antisense-mediated techniques, chemistry, and efficacy. (2) The pros and cons of AON approaches in the brain compared to other techniques of interfering with gene function, such as transgenesis and short hairpin RNAs, in terms of specificity of the manipulation, spatial, and temporal control over gene expression, toxicity, and delivery issues. (3) The potential applications for Neuroscience. We conclude that there is good evidence from animal studies that the central nervous system can be successfully targeted, but the potential of the diverse AON-based approaches appears to be under-recognized

Paired Hormone Response Elements Predict Caveolin-1 as a Glucocorticoid Target Gene

Glucocorticoids act in part via glucocortocoid receptor binding to hormone response elements (HREs), but their direct target genes in vivo are still largely unknown. We developed the criterion that genomic occurrence of paired HREs at an inter-HRE distance less than 200 bp predicts hormone responsiveness, based on synergy of multiple HREs, and HRE information from known target genes. This criterion predicts a substantial number of novel responsive genes, when applied to genomic regions 10 kb upstream of genes. Multiple-tissue in situ hybridization showed that mRNA expression of 6 out of 10 selected genes was induced in a tissue-specific manner in mice treated with a single dose of corticosterone, with the spleen being the most responsive organ. Caveolin-1 was strongly responsive in several organs, and the HRE pair in its upstream region showed increased occupancy by glucocorticoid receptor in response to corticosterone. Our approach allowed for discovery of novel tissue specific glucocorticoid target genes, which may exemplify responses underlying the permissive actions of glucocorticoids

Application of a pharmacological transcriptome filter identifies a shortlist of mouse glucocorticoid receptor target genes associated with memory consolidation

Glucocorticoids regulate memory consolidation, facilitating long-term storage of relevant information to adequately respond to future stressors in similar conditions. This effect of glucocorticoids is well-established and is observed in multiple types of behaviour that depend on various brain regions. By and large, higher glucocorticoid levels strengthen event-related memory, while inhibition of glucocorticoid signalling impairs consolidation. The mechanism underlying this glucocorticoid effect remains unclear, but it likely involves the transcriptional effects of the glucocorticoid receptor (GR). We here used a powerful paradigm to investigate the transcriptional effects of GR in the dorsal hippocampus of mice after training in an auditory fear conditioning task, aiming to identify a shortlist of GR target genes associated to memory consolidation. Therefore, we utilized in an explorative study the properties of selective GR modulators (CORT108297 and CORT118335), alongside the endogenous agonist corticosterone and the classical GR antagonist RU486, to pinpoint GR-dependent transcriptional changes. First, we confirmed that glucocorticoids can modulate memory strength via GR activation. Subsequently, by assessing the specific effects of the available GR-ligands on memory strength, we established a pharmacological filter which we imposed on the hippocampal transcriptome data. This identified a manageable shortlist of eight genes by which glucocorticoids may modulate memory consolidation, warranting in-depth follow-up. Overall, we showcase the strength of the concept of pharmacological transcriptome filtering, which can be readily applied to other research topics with an established role of glucocorticoids

Coordination of Axial Trunk Rotations During Gait in Low Back Pain. A Narrative Review

Chronic low back pain patients have been observed to show a reduced shift of thorax-pelvis relative phase towards out-of-phase movement with increasing speed compared to healthy controls. Here, we review the literature on this phase shift in patients with low back pain and we analyze the results presented in literature in view of the theoretical motivations to assess this phenomenon. Initially, based on the dynamical systems approach to movement coordination, the shift in thorax-pelvis relative phase with speed was studied as a self-organizing transition. However, the phase shift is gradual, which does not match a self-organizing transition. Subsequent emphasis in the literature therefore shifted to a motivation based on biomechanics. The change in relative phase with low back pain was specifically linked to expected changes in trunk stiffness due to ‘guarded behavior’. We found that thorax-pelvis relative phase is affected by several interacting factors, including active drive of thorax rotation through trunk muscle activity, stride frequency and the magnitude of pelvis rotations. Large pelvis rotations and high stride frequency observed in low back pain patients may contribute to the difference between patients and controls. This makes thorax-pelvis relative phase a poor proxy of trunk stiffness. In conclusion, thorax-pelvis relative phase cannot be considered as a collective variable reflecting the orderly behaviour of a complex underlying system, nor is it a marker of specific changes in trunk biomechanics. The fact that it is affected by multiple factors may explain the considerable between-subject variance of this measure in low back pain patients and healthy controls alike

Restricted effects of androgens on glucocorticoid signaling in the mouse prefrontal cortex and midbrain

Glucocorticoids are key executors of the physiological response to stress. Previous studies in mice showed that the androgen receptor (AR) influenced the transcriptional outcome of glucocorticoid treatment in white and brown adipocytes and in the liver. In the brain, we observed that chronic hypercorticism induced changes in gene expression that tended to be more pronounced in male mice. In the present study, we investigated if glucocorticoid signaling in the brain could be modulated by androgen. After chronic treatment with corticosterone, dihydrotestosterone, a combination of both, and corticosterone in combination with the AR antagonist enzalutamide, we compared the expression of glucocorticoid receptor (NR3C1, also abbreviated GR) target genes in brain regions where AR and GR are co-expressed, namely: prefrontal cortex, hypothalamus, hippocampus, ventral tegmental area and substantia nigra. We observed that androgen affected glucocorticoid signaling only in the prefrontal cortex and the substantia nigra. Dihydrotestosterone and corticosterone independently and inversely regulated expression of Sgk1 and Tsc22d3 in prefrontal cortex. AR antagonism with enzalutamide attenuated corticosterone-induced expression of Fkbp5 in the prefrontal cortex and of Fkbp5 and Sgk1 in the substantia nigra. Additionally, in the substantia nigra, AR antagonism increased expression of Th and Slc18a1, two genes coding for key components of the dopaminergic system. Our data indicate that androgen influence over glucocorticoid stimulation in the brain is not a dominant phenomenon in the context of high corticosterone levels, but can occur in the prefrontal cortex and substantia nigra