Early-life perturbations in glucocorticoid activity impacts on the structure, function and molecular composition of the adult zebrafish (Danio rerio) heart

Abstract

BackgroundTransient early-life perturbations in glucocorticoids (GC) are linked with cardiovascular disease risk in later life. Here the impact of early life manipulations of GC on adult heart structure, function and gene expression were assessed.Methods and resultsZebrafish embryos were incubated in dexamethasone (Dex) or injected with targeted glucocorticoid receptor (GR) morpholino knockdown (GR Mo) over the first 120 h post fertilisation (hpf); surviving embryos (>90%) were maintained until adulthood under normal conditions. Cardiac function, heart histology and cardiac genes were assessed in embryonic (120 hpf) and adult (120 days post fertilisation (dpf)) hearts.GR Mo embryos (120 hpf) had smaller hearts with fewer cardiomyocytes, less mature striation pattern, reduced cardiac function and reduced levels of vmhc and igf mRNA compared with controls. GR Mo adult hearts were smaller with diminished trabecular network pattern, reduced expression of vmhc and altered echocardiographic Doppler flow compared to controls. Dex embryos had larger hearts at 120 hpf (Dex 107.2 ± 3.1 vs. controls 90.2 ± 1.1 μm, p < 0.001) with a more mature trabecular network and larger cardiomyocytes (1.62 ± 0.13 cells/μm vs control 2.18 ± 0.13 cells/μm, p < 0.05) and enhanced cardiac performance compared to controls. Adult hearts were larger (1.02 ± 0.07 μg/mg vs controls 0.63 ± 0.06 μg/mg, p = 0.0007), had increased vmhc and gr mRNA levels.ConclusionPerturbations in GR activity during embryonic development results in short and long-term alterations in the heart.

Cardiac GR and MR: From Development to Pathology

“…Clearly though, the expressed GR could be precociously activated by excessively high maternal or exogenous glucocorticoid, prior to E15.5. Dexamethasone treatment of zebrafish embryos from shortly after fertilisation promoted the maturation of the trabecular network and underlying myofibril structure, and improved cardiac performance (assessed by echocardiography) [40]. Conversely, diminished glucocorticoid action (by morpholino--mediated reduction in GR levels) impaired cardiac maturation, adversely affecting the structure and function of the embryonic heart [40].…”

“…Dexamethasone treatment of zebrafish embryos from shortly after fertilisation promoted the maturation of the trabecular network and underlying myofibril structure, and improved cardiac performance (assessed by echocardiography) [40]. Conversely, diminished glucocorticoid action (by morpholino--mediated reduction in GR levels) impaired cardiac maturation, adversely affecting the structure and function of the embryonic heart [40]. Whether these effects were direct within the heart or secondary to effects of GR knock--down elsewhere was not tested.…”

The First Fifteen Years of Steroid Receptor Research in Zebrafish; Characterization and Functional Analysis of the Receptors

“…These effects were shown to be specific for the gr knockdown, since gr mRNA rescued the phenotypes of the morpholino-treated embryos [67,68]. In addition, morpholino-treated embryos had smaller hearts and reduced cardiac function [69]. The strong effect of the translation-blocking morpholino was explained by its ability to target maternally deposited mRNA, whereas a splice-blocking morpholino only interferes with mRNA which is transcribed de novo, so it is only effective after zygotic transcription has started [67].…”

Glucocorticoid Regulation of Ependymal Glia and Regenerative Potential after Spinal Cord Injury

“…Solutions were replaced every 48 h. Based on published data (58,59,60), we performed a dose range study of 1-100 µM to establish 10 µM as ideal concentration (minimal sufficient to inhibit functional recovery following cord transection). This dose did not affect behavioral responses, gross morphology, or survival in non-injured fish exposed for 120 h.…”