Lifelong molecular consequences of high Glucocorticoids exposure during development

Abstract

Chronic or severe stress exposure during development primes an individual for altered stress sensitivity in adulthood and increases psychiatric disease susceptibility. However, the identity and function of genes affected by developmental stress exposure are poorly understood. Here, we used an optogenetic zebrafish model to identify brain-wide molecular alterations caused by chronic Glucocorticoid (GC) exposure during development and following subsequent exposure to an acute stressor in adulthood. We show that developmental GC-exposed fish display wide-ranging behavioral changes affecting social behavior, food consumption, and associative learning. The brain transcriptome of GC-exposed fish showed alteration of genes associated with DNA metabolism, axon development, and social behavior-related genes such as oxytocin across the life course. Strikingly, when GC-exposed fish were subjected to a stress challenge in adulthood, they showed exaggerated endocrine responses and a great number of brain-wide transcriptional changes, including gene sets associated with axon development, neuronal signaling, and epigenetic modulators. These altered gene sets showed an overrepresentation of genes linked to human psychiatric disorders. In short, our study provides a unique resource of long-term, time-dependent gene expression changes induced by developmental GC-exposure and identifies novel GC-primed genes which may shape adult responses of early life stress-exposed individuals.

Elevated glucocorticoid alters the developmental dynamics of hypothalamic neurogenesis

“…We conclude that the phenotypes observed in our optogenetic model are the result of exposure to elevated GC produced in the interrenal, rather than to other interrenal steroid hormones, since cortisol is the primary output of the interrenal gland in zebrafish 25,56,57 . It is likely that the GC-induced alteration of the hypothalamic development trajectory observed in our model is mediated by GRregulated gene transcription and potentially epigenetic mechanisms.…”

“…Our lab previously generated an optogenetic zebrafish model, Tg(star:bPAC-2A-tdTomato) uex300 , in which the endogenous cortisol level can be increased specifically in response to acute blue light exposure using an optogenetic protein beggiatoa Photoactivated Adenylate Cylase (bPAC) (Fig.1a) 23,24,25 . In order to determine the effects of elevated GC on the brain across development, we raised transgenic fish under standard aquarium lighting conditions, where the blue light component of the white light is sufficient to activate bPAC, which led to significantly elevated cortisol levels in Tg(star:bPAC-2A-tdTomato) uex300 compared with wild types from hatching through until late juvenile/early adult stage (Fig.1b) 25 . Tg(star:bPAC-2A-tdTomato) uex300 raised under standard light condition will be referred to throughout as star:bPAC+ or bPAC+.…”

“…Size of the dot indicates the ratio of differentially expressed genes from each GO term, whilst the colour shows the adjusted p-value. a-b taken from Choi et al ., 25 .…”

“…To investigate the effects of elevated GC on brain development we performed bulk RNA-sequencing (RNA-seq) of whole brain samples from star:bPAC+ and wild-type fish at different developmental stages 25 . Gene Ontology (GO) analysis of differentially expressed genes (DEGs) that were down-regulated in star:bPAC+ brains compared with wild types were enriched for a number of biological processes, including Neurogenesis at all developmental stages (GO:0022008, adjusted p-value 2.47E-20 at 6 days post fertilization (dpf), 5.45E-08 at 13 dpf, 1.11E-17 at 120 dpf).…”

“…In order to determine the effects of elevated GC on the brain across development, we raised transgenic fish under standard aquarium lighting conditions, where the blue light component of the white light is sufficient to activate bPAC, which led to significantly elevated cortisol levels in Tg(star:bPAC-2A-tdTomato) uex300 compared with wild types from hatching through until late juvenile/early adult stage (Fig. 1b) 25 . Tg(star:bPAC-2A-tdTomato) uex300 raised under standard light condition will be referred to throughout as star:bPAC+ or bPAC+.…”