A new zebrafish model for congenital adrenal hyperplasia

The gene, CYP21A2, is responsible for production of steroid 21-hydroxylase. As an enzyme, it is involved in cascades to produce the hormones - cortisol and aldosterone. The clinical consequences of CAH result from cortisol and aldosterone insufficiency and from sex steroid excess. Glucocorticoid replacement therapy diminishes the symptoms but long term, comorbidities are common.

To determine the underlying molecular pathogenesis of steroid 21-hydroxylase deficiency (21OHD), the MOST (Modelling steroidogenesis) project looked at the function of 21-hydroxylase and the whole organism response to its deficiency during development and in adult life in the zebrafish.

Research results focused on the effects of zebrafish Cyp21a2 (zCyp11a2) protein and include its effects at the start of cortisol production in the embryo. In the adult, production is limited to steroidogenic tissues. An alternative transcript of zCyp21a2 that is highly conserved among species was identified that is inherited through the maternal line and is expressed throughout early development.

The role of zCyp21a2 during development was established using a range of transient knockdown mutants. Stereomicroscopic observations and liquid chromatography/tandem mass spectrometry were used to study resulting phenotypes.

MOST scientists also designed pairs of transcription activator-like effector nucleases to edit the genomes by inserting and deleting sequences. Using sequencing, high resolution melting and enzymatic digestion studies they observed mutant fish embryos showing hyper-pigmented phenotype, characteristic of primary adrenal insufficiency in humans.

Studies to evaluate whole organism impact of 21-OHD are ongoing despite project end. The MOST project has made major headway in translational research of adrenal disease using the zebrafish as a cutting edge model. Data fuelled the publication of two abstracts for high-profile conferences. The work has also featured in Sex Dev and a book chapter "The hypothalamo-pituitary-adrenal axis and its regulation" in the book (in press) "Neuroendocrine Disorders in Children".

In collaboration with other expert labs, the researchers have developed a method to discriminate between different types of steroidogenic disorders. This promises to be of huge benefit in clinical practice for the prediction and early diagnosis of congenital adrenal disorders.