Cushing's Syndrome and Fetal Features Resurgence in Adrenal Cortex–Specific Prkar1a Knockout Mice

Abstract

Carney complex (CNC) is an inherited neoplasia syndrome with endocrine overactivity. Its most frequent endocrine manifestation is primary pigmented nodular adrenocortical disease (PPNAD), a bilateral adrenocortical hyperplasia causing pituitary-independent Cushing's syndrome. Inactivating mutations in PRKAR1A, a gene encoding the type 1 α-regulatory subunit (R1α) of the cAMP–dependent protein kinase (PKA) have been found in 80% of CNC patients with Cushing's syndrome. To demonstrate the implication of R1α loss in the initiation and development of PPNAD, we generated mice lacking Prkar1a specifically in the adrenal cortex (AdKO). AdKO mice develop pituitary-independent Cushing's syndrome with increased PKA activity. This leads to autonomous steroidogenic genes expression and deregulated adreno-cortical cells differentiation, increased proliferation and resistance to apoptosis. Unexpectedly, R1α loss results in improper maintenance and centrifugal expansion of cortisol-producing fetal adrenocortical cells with concomitant regression of adult cortex. Our data provide the first in vivo evidence that loss of R1α is sufficient to induce autonomous adrenal hyper-activity and bilateral hyperplasia, both observed in human PPNAD. Furthermore, this model demonstrates that deregulated PKA activity favors the emergence of a new cell population potentially arising from the fetal adrenal, giving new insight into the mechanisms leading to PPNAD.

PKA signaling drives reticularis differentiation and sexually dimorphic adrenal cortex renewal

“…We previously showed that adrenal-specific ablation of Prkar1a using the Akr1b7-Cre driver in mice (AdKO mice) resulted in ACTH-independent Cushing's syndrome and centrifugal expansion of large fetal-like cells from the innermost cortex (19). Because the Akr1b7-Cre driver targets recombination to both the definitive (adult) and transient (fetal or X-zone) cortices (24), the origin of these cells has remained elusive.…”

“…Gain-and loss-of-function models have shown that the RSPO/WNT/β-catenin pathway is a driver of zG identity, a repressor of zF identity, and has tumorigenic activity when constitutively activated (14)(15)(16)(17). Reciprocally, constitutive activation of cAMP/PKA signaling was shown to inhibit zG fate, trigger zF identity, and counteract β-catenin-induced tumorigenesis (18,19). Decreased PKA signaling, resulting from mutations in the ACTH receptor MC2R, or in its coreceptor MRAP, are associated with cortical atrophy, altered zF differentiation, and, yet, intact zG (20)(21)(22).…”

“…In contrast, patients with unbuffered PKA activity, resulting from mutations in PRKAR1A (the regulatory subunit of cAMP-dependent PKA), develop micronodular hyperplasia and glucocorticoid excess (ACTH-independent Cushing's syndrome) (23). Strikingly, mice bearing adrenal-specific loss of Prkar1a (AdKO model) also develop Cushing's syndrome and show zonation defects consisting of expansion of a third zone, with features typical of both zF and transient fetal X-zone (19). However, whether these cells originated from the fetal or definitive cortex was unclear.…”

MECHANISMS IN ENDOCRINOLOGY: Autocrine/paracrine regulatory mechanisms in adrenocortical neoplasms responsible for primary adrenal hypercorticism

“…The hyperplastic adrenal cortex in the vicinity of the pheochromocytoma, contrasting with atrophy of the residual cortex, is in favor of paracrine regulation of adrenocortical hyperplasia cells by pheochromocyte secretory products. Similarly, the preferential localization of adrenocortical micronodules close to the corticomedullary junction observed in adrenal from patients with primary pigmented nodular adrenocortical disease (PPNAD) with inactivating mutation of PRKAR1A or in mouse models of PPNAD (54,55) is consistent with cortical-medullary interactions. Intercellular communication between chromaffin and steroidogenic cells is supposed to be more intense in corticomedullary mixed tumors, as these well-circumscribed tumors are composed of an intimately admixed population of adrenocortical cells and pheochromocytes (56,57,58,59).…”

“…In the adrenocortical cell line H295R, PRKAR1A inactivation inhibits TGFb-induced apoptosis through a decrease in SMAD3 expression, which plays a major role in TGFb signaling (229). This mechanism may be involved in adrenocortical hyperplasia and resistance of adrenocortical cells to apoptosis observed in PPNAD (55).…”