nr3c1 null mutant zebrafish are viable and reveal DNA-binding-independent activities of the glucocorticoid receptor

Abstract

Glucocorticoids (GCs) play important roles in developmental and physiological processes through the transcriptional activity of their cognate receptor (Gr). Using CRISPR/Cas9 technology, we established a zebrafish null Gr mutant line and compared its phenotypes with wild type and a zebrafish line with partially silenced gr (grs357/s357). Homozygous gr−/− larvae are morphologically inconspicuous and, in contrast to GR−/− knockout mice, viable through adulthood, although with reduced fitness and early life survival. Mutants gr−/− are fertile, but their reproductive capabilities fall at around 10 months of age, when, together with cardiac and intestinal abnormalities already visible at earlier stages, increased fat deposits are also observed. Mutants show higher levels of whole-body cortisol associated with overstimulated basal levels of crh and pomca transcripts along the HPI axis, which is unresponsive to a mechanical stressor. Transcriptional activity linked to immune response is also hampered in the gr−/− line: after intestinal damage by dextran sodium sulphate exposure, there are neither inflammatory nor anti-inflammatory cytokine gene responses, substantiating the hypothesis of a dual-action of the GC-GR complex on the immune system. Hence, the zebrafish gr mutant line appears as a useful tool to investigate Gr functions in an integrated in vivo model.

Postnatal triglyceride accumulation is regulated by mineralocorticoid receptor activation under basal and stress conditions

“…It is already known that a lack of GR in zebrafish promotes lipid accumulation (Facchinello et al . ; Faught & Vijayan, ), but whether MR plays a role in this phenotype remains to be determined.…”

“…There is some evidence that MR complements the role of GR in the larval zebrafish stress response and mediates stress-related behaviour (Faught & Vijayan, 2018). There is no evidence that MR plays any role in adipogenesis in lower vertebrates; however, in GRKO fish there was an increase in both total lipid and subcutaneous fat, despite the fish being hypercortisolemic (Facchinello et al 2017;Faught & Vijayan, 2019). Here we identify that not only does MR play a role in TG biosynthesis during zebrafish development, but it may also modulate the transcriptional function of GR.…”

“…Beyond childhood, it is also necessary to examine the impact that these early perturbations in TG and cholesterol biosynthesis may have on adults. It is already known that a lack of GR in zebrafish promotes lipid accumulation (Facchinello et al 2017;Faught & Vijayan, 2019), but whether MR plays a role in this phenotype remains to be determined.…”

“…A role for MR in lipid metabolism in zebrafish ( Danio rerio ) was also evident from the higher lipid accumulation observed in ubiquitous GR knockout zebrafish (Facchinello et al . ; Faught & Vijayan, ), which lacks aldosterone, suggesting a conserved role for GCs. However, results contradictory to the above were also reported.…”

“…Also, high levels of MR mRNA were detected in the adipose tissue of obese mice (ob/ob), and treatment with eplerenone, a MR antagonist, attenuated obesity-related insulin resistance (Hirata et al 2009(Hirata et al , 2012. A role for MR in lipid metabolism in zebrafish (Danio rerio) was also evident from the higher lipid accumulation observed in ubiquitous GR knockout zebrafish (Facchinello et al 2017;Faught & Vijayan, 2019), which lacks aldosterone, suggesting a conserved role for GCs. However, results contradictory to the above were also reported.…”