Abstract
Congenital adrenal hyperplasia is a group of common inherited disorders leading to glucocorticoid deficiency. Most cases are caused by 21-hydroxylase deficiency (21OHD). The systemic consequences of imbalanced steroid hormone biosynthesis due to severe 21OHD remains poorly understood. Therefore, we developed a zebrafish model for 21OHD, which focuses on the impairment of glucocorticoid biosynthesis. A single 21-hydroxylase gene (cyp21a2) is annotated in the zebrafish genome based on sequence homology. Our in silico analysis of the 21-hydroxylase (Cyp21a2) protein sequence suggests a sufficient degree of similarity for the usage of zebrafish cyp21a2 to model aspects of human 21OHD in vivo. We determined the spatiotemporal expression patterns of cyp21a2 by whole-mount in situ hybridization and reverse transcription polymerase chain reaction throughout early development. Early cyp21a2 expression is restricted to the interrenal gland (zebrafish adrenal counterpart) and the brain. To further explore the in vivo consequences of 21OHD we created several cyp21a2 null-allele zebrafish lines by using a transcription activator–like effector nuclease genomic engineering strategy. Homozygous mutant zebrafish larvae showed an upregulation of the hypothalamic–pituitary–interrenal (HPI) axis and interrenal hyperplasia. Furthermore, Cyp21a2-deficient larvae had a typical steroid profile, with reduced concentrations of cortisol and increased concentrations of 17-hydroxyprogesterone and 21-deoxycortisol. Affected larvae showed an upregulation of the HPI axis and interrenal hyperplasia. Downregulation of the glucocorticoid-responsive genes pck1 and fkbp5 indicated systemic glucocorticoid deficiency. Our work demonstrates the crucial role of Cyp21a2 in glucocorticoid biosynthesis in zebrafish larvae and establishes an in vivo model allowing studies of systemic consequences of altered steroid hormone synthesis.
Highlights
Steroid hormones are key regulators of sex development, behavior, body homeostasis and metabolism
Our work demonstrates the crucial role of Cyp21a2 in glucocorticoid biosynthesis in zebrafish larvae and establishes a novel in vivo model allowing for studies of systemic consequences of altered steroid hormone synthesis
congenital adrenal hyperplasia (CAH) ranks amongst the most common inherited metabolic endocrine disorders occurring in about 1 in 10,000 to 1 in 15,000 affected individuals (1,2). It is associated with significant morbidity and mortality (3,4) and represents a classic example of conditions with severe systemic consequences due to altered steroid hormone synthesis
Summary
Steroid hormones are key regulators of sex development, behavior, body homeostasis and metabolism. Deficiencies of steroid hormone synthesis and action are common causes of disorders of sex development (DSD) including congenital adrenal hyperplasia (CAH). CAH ranks amongst the most common inherited metabolic endocrine disorders occurring in about 1 in 10,000 to 1 in 15,000 affected individuals (1,2) It is associated with significant morbidity and mortality (3,4) and represents a classic example of conditions with severe systemic consequences due to altered steroid hormone synthesis. CYP21A2 is a cytochrome P450 enzyme located in the endoplasmic reticulum, which in humans catalyzes the conversion of 17-hydroxyprogesterone to 11deoxycortisol, a cortisol precursor, and the conversion of progesterone to 11deoxycorticosterone, a precursor of aldosterone in humans (2) Disruption of this pathway renders patients unable to synthesize cortisol efficiently and results in the overproduction of ACTH by the pituitary due to diminished negative feedback.
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