Znrf3 exon 2 deletion mice do not recapitulate congenital adrenal hypoplasia.

Abstract

Wnt/β-catenin signaling is essential for adrenocortical development. Zinc and ring finger 3 (ZNRF3), an E3 ubiquitin ligase that attenuates Wnt/β-catenin signaling, is negatively regulated by R-spondin via an extracellular domain that is partially encoded by exon 2 of ZNRF3. We recently identified ZNRF3 exon 2 deletions in three individuals with congenital adrenal hypoplasia. ZNRF3 exon 2 deletion impairs R-spondin binding, thereby attenuating β-catenin expression, eventually developing congenital adrenal hypoplasia. To elucidate the influence of ZNRF3/Znrf3 exon 2 deletion on adrenocortical development, we generated homozygous Znrf3 exon 2 deletion (Znrf3Δ2/Δ2) mice. The adrenal glands of Znrf3Δ2/Δ2 mice did not show gross morphological changes at birth but became enlarged with age. Moderate hyperplasia of the zona fasciculata (ZF), dispersed medulla arrangement, and a radially spreading zone comprised of cells with large nuclei between the ZF and medulla were observed at 6 weeks of age. Immunohistochemistry revealed low levels of 20α-hydroxysteroid dehydrogenase, a marker of the adrenal X-zone, in Znrf3Δ2/Δ2 mice. Plasma ACTH and serum corticosterone levels in Znrf3Δ2/Δ2 mice did not differ significantly from those in wild-type mice. Transcriptome analyses of the adrenal glands revealed substantial downregulation of X-zone markers but no significant changes in the expression of genes involved in the Wnt/β-catenin signaling pathway. These results show that a species-specific difference in the effects of ZNRF3/Znrf3 exon 2 deletions in humans and mice; Znrf3Δ2/Δ2 mice do not develop congenital adrenal hypoplasia but instead exhibit moderate ZF hyperplasia, dispersed medulla arrangement, and X-zone dysplasia.