Understanding the molecular pathophysiology of stress on the developing and adult brain

Stress is associated with significant morbidity including depression and anxiety. Activation of the hypothalamic-pituitary-adrenal (HPA) axis leads to synthesis of cortisol, which is a key mediator of the pathology of chronic stress. Our work has established the presence of the entire pathway to cortisol biosynthesis not only in the adrenal, but also in the brain. This expression appears to be crucial to stress responses and the production of both adaptive and maladaptive changes in the zebrafish brain. Importantly, whilst the brain responds to steroid that are synthesised peripherally, it also synthesises neurosteroids de novo. We therefore, hypothesise that steroidogenic enzymes in the brain are key components of the pathophysiological mechanisms responding to stress in the central nervous system. Therefore, we have generated several glucocorticoid-deficient zebrafish lines (cyp11a2, cyp11c1, cyp21a2, cyp17a2, fdx1b) and a mutant with defective glucocorticoid receptor that cannot mediate glucocorticoid signalling and confers glucocorticoid resistance. This project will employ our in vivo models to dissect the molecular pathophysiology of dysregulated stress responses in zebrafish larvae and adults. In addition, the project will create novel brain-specific mutants in which neurosteroid biosynthesis is impaired. Our ultimate goal is the discovery of pathways that can be targeted to modulate stress-associated disorders such as anxiety and depression.

This project will:
1. define the downstream consequences of genetically disrupted stress responses.
2. define the impact of stress on neural progenitors and neural activity in the CNS.
3. perform a chemical screen to identify drugs ameliorating the adverse impacts of dysregulated stress responses in the brain.

Novelty: The expression patterns of steroidogenic enzymes in the brain have been characterized in teleosts and mammals, but their functional roles in maintaining brain health and their potential drug-targetability for treating pathophysiological states induced by stress, have not been studied.

Experimental approach: Firstly, this project will explore the dynamic regulation of steroidogenic enzyme expression patterns in the brain in response to both environmental stressors and genetic disruption, by employing RNA-seq, bioinformatic analysis and quantitative PCR. Secondly, the impact of stress on proliferation of neural progenitors in the CNS will be explored using in situ hybridisation techniques, cell proliferation assays, apoptosis assays, as well as bright-field and fluorescence microscopy. The impact of stress on neural activity in wild-type larvae and mutant larvae (exhibiting persistent HPA axis activation in the brain) will be monitored using a neuron-specific transgene encoding the neural activity reporter NBT:GCaMP3. Finally, we will use a standard library of 2000 compounds to screen for substances ameliorating acute and chronic stress-related changes in gene expression in wild-type and mutant larvae in the CNS. Thus, this project will address exciting research questions and provide a wide range of transferable skills to the applicant.

The work will be conducted in a vibrant, interdisciplinary research setting at the Bateson Centre, which was ranked in the UK top five for biological research. The work will be co-supervised by a clinician scientist (Dr Nils Krone) and a biologist (Dr Vincent Cunliffe), both of whom have extensive experience in basic science and translational research.

Overall, this project combines cutting-edge technology with cross-cutting research questions to discover important novel pathophysiological pathways in the central-nervous system that are relevant to treatments of stress-linked affective disorders.