Deciphering Human Adrenocortical Functional Zonation and Its Integration into the Endocrine Axis In Vivo

About This Grant

The adrenal cortex is a vital endocrine organ that produces steroid hormones essential for the body's homeostasis. Its organization into three concentric zones enables spatially regulated production of distinct adrenal hormones, a process known as functional zonation. Structural or functional defects in the adult cortex cause primary adrenal insufficiency (PAI), a life-threatening condition affecting millions with no permanent cure, while developmental disruptions in adrenal formation or zonation can lead to congenital adrenal disorders and tumors. In rodents, zonation is established perinatally via centripetal migration and stepwise “transdifferentiation” of subcapsular progenitors within the definitive zone (DZ), regulated by opposing actions of WNT-activating signals from outer capsule (Cap) cells and adrenocorticotropic hormone (ACTH). However, species-specific differences in adrenal organogenesis and steroidogenesis limit the translational value of rodent models for human PAI. To bridge this gap, we developed the first human adrenal organoid model from induced pluripotent stem cells (iPSCs) that recapitulates adrenal development both in vitro and in vivo. This proposal aims to exploit this platform to define and assess the therapeutic relevance of cellular and endocrine/paracrine signaling mechanisms regulating adrenocortical development, with the goal of transforming treatment of life-threatening adrenal diseases. In humans, adrenal cortical zonation begins prenatally, forming three zones: the DZ, the glucocorticoid (cortisol)-producing transitional zone (TZ), and the androgen-producing fetal zone (FZ), which correspond to the functional zones of the adult adrenal cortex. Notably, our organoids can be reliably directed to produce CD10/MME⁺ DZ-like cell (DZLC) progenitors that exhibit striking similarity to in vivo human DZ cells. DZLCs can be further differentiated into TZ-like cells (TZLCs) through combined stimulation with RSPO3 (a Wnt- ligand dependent potentiator of Wnt signaling) and ACTH, and subsequently into FZ-like cells (FZLCs) with ACTH alone. Exogenous RSPO3 is dispensable when DZLCs are co-encapsulated with iPSC-derived RSPO3- secreting Cap-like cells (CapLCs), which mimic the native capsule and enable ACTH-driven transdifferentiation of DZLCs into TZLCs. This contrasts with rodents, where ACTH promotes and WNT suppresses TZ fate. Thus, our in vitro directed transdifferentiation data support the central hypothesis that prenatal human adrenocortical homeostasis is orchestrated by DZ progenitors within a capsular niche that, through self-renewal and transdifferentiation, give rise to both TZ and FZ under coordinated control of WNT and ACTH signaling. Supporting this, our preliminary data show that encapsulation of DZLCs with CapLCs restores functional zonation after transplantation into a hemi-adrenalectomized immunodeficient mouse model, resulting in a long-lived adrenal cortex producing both cortisol and androgens in an ACTH responsive manner. Leveraging our adrenal organoid platform, we will determine whether these progenitor-derived populations can integrate into the host endocrine axis to fully restore adrenal function in vivo.