van den Bos, R. | Search bioRxiv

bioRxiv2019

Effects of early life glucocorticoid exposure on metabolism in zebrafish (Danio rerio) larvae

In this study we assessed the effects of increased cortisol levels during early embryonic development (0-6 hours post-fertilisation (hpf)), thereby mimicking maternal stress, on metabolism in zebrafish (Danio rerio) larvae. In two series of experiments fertilized eggs were exposed to a cortisol-containing, a dexamethasone-containing (to stimulate the glucocorticoid receptor (GR) specifically) or a control medium for 6 hours post-fertilisation (0-6 hpf). In the first series we measured oxygen consumption as a proxy for metabolism, in the second series gene-expression of genes related to gluconeogenesis and glucose transport. Previously we have found that at 5 days post-fertilisation (dpf) baseline cortisol levels are increased following cortisol pre-treatment but not following dexamethasone pre-treatment, suggesting a higher hypothalamus-pituitary-interrenal cells (HPI-axis) activity. Hence, we hypothesized that oxygen consumption and gene-expression were stronger in cortisol-treated than in dexamethasone-treated and control-treated subjects at 5 dpf. Indeed, we observed increased oxygen consumption in cortisol-treated subjects compared to dexamethasone-treated or control-treated subjects. However, gene-expression levels were not different between treatments, which may have been due to a developmental delay in this second series. We also reasoned that both cortisol-treated and dexamethasone-treated subjects would show a higher metabolism at 1 dpf than control-treated subjects as the HPI-axis is not functional as yet and more general processes are being stimulated by cortisol through GR stimulation. Indeed, we observed increased oxygen consumption and increased expression of genes related to gluconeogenesis and glucose transport in cortisol-treated and dexamethasone-treated subjects than control-treated subjects. These data show that early-life exposure to cortisol, mimicking thereby maternal stress, increased metabolism at different life stages, i.e. 1 and 5 dpf, involving the GR.

physiology↗

bioRxiv2019

Early life glucocorticoid exposure modulates immune function in zebrafish (Danio rerio) larvae

In this study we have assessed the effects of increased cortisol levels during early embryonic development on immune function in zebrafish (Danio rerio) larvae. Fertilized eggs were exposed to either a cortisol-containing, a dexamethasone-containing (to stimulate the glucocorticoid receptor selectively) or a control medium for 6 hours post-fertilisation (0-6 hpf). First, we measured baseline expression of a number of immune-related genes (socs3a, mpeg1.1, mpeg1.2 and irg1l) 5 days post-fertilisation (dpf) in larvae of the AB and TL strain to assess the effectiveness of our exposure procedure and potential strain differences. Cortisol and dexamethasone strongly up-regulated baseline expression of these genes independent of strain. The next series of experiments were therefore carried out in larvae of the AB strain only. We measured neutrophil/macrophage recruitment following tail fin amputation (performed at 3 dpf) and phenotypical changes as well as survival following LPS-induced sepsis (150 g/ml; 4-5 dpf). Dexamethasone, but not cortisol, exposure at 0-6 hpf enhanced neutrophil recruitment 4 hours post tail fin amputation. Cortisol and dexamethasone exposure at 0-6 hpf led to a milder phenotype (e.g. less tail fin damage) and enhanced survival following LPS challenge compared to control exposure. Gene-expression analysis showed accompanying differences in transcript abundance of tlr4bb, cxcr4a, myd88, il1{beta} and il10. These data show that early-life exposure to cortisol, which may be considered to be a model or proxy of maternal stress, induces an adaptive response to immune challenges, which seems mediated via the glucocorticoid receptor.

immunology↗