Age-dependent effects of Armc5 haploinsufficiency on adrenocortical function

Inactivating mutations in the Armadillo repeat-containing 5 (ARMC5) gene have recently been discovered in primary macronodular adrenal hyperplasia (PMAH), a cause of Cushing syndrome. Biallelic ARMC5 inactivation in PMAH suggested that ARMC5 may have tumor suppressor functions in the adrenal cortex. We generated and characterized a new mouse model of Armc5 deficiency. Almost all Armc5 knockout mice died during early embryonic development, around 6.5 and 8.5 days. Knockout embryos did not undergo gastrulation, as demonstrated by the absence of mesoderm development at E7.5. Armc5 heterozygote mice (Armc5+/-) developed normally but at the age of 1 year, their corticosterone levels decreased; this was associated with a decrease of protein kinase A (PKA) catalytic subunit α (Cα) expression both at the RNA and protein levels that were also seen in human patients with PMAH and ARMC5 defects. However, this was transient, as corticosterone levels normalized later, followed by the development of hypercorticosteronemia in one-third of the mice at 18 months of age, which was associated with increases in PKA and Cα expression. Adrenocortical tissue analysis from Armc5+/- mice at 18 months showed an abnormal activation of the Wnt/β-catenin signaling pathway in a subset of zona fasciculata cells. These data confirm that Armc5 plays an important role in early mouse embryonic development. Our new mouse line can be used to study tissue-specific effects of Armc5. Finally, Armc5 haploinsufficiency leads to Cushing syndrome in mice, but only later in life, and this involves PKA, its catalytic subunit Cα, and the Wnt/β-catenin pathway.