Endocrine Abstracts

Maturation of the definitive adrenal cortex occurs between 3 and 6 weeks post-partum and involves onset of CYP11B2 expression and establishment of the laminin-encased 3D structure of glomeruli that contain rosettes of 10 to 15 zona glomerulosa (zG) cells that work in coordination to produce optimal amounts of aldosterone. Although this process is dependent on canonical WNT/b-catenin signaling, cellular sources of WNT ligands remain elusive and the mechanisms involved in the extensive extra-cellular matrix remodeling associated with rosette/glomeruli morphogenesis are unknown. Beyond their role in innate immunity, macrophages are involved in extra-cellular matrix remodeling under a wide variety of pathophysiological conditions and have the capacity to produce WNT ligands. This, together with the presence of macrophages within the zG cells, strongly suggest that macrophages may play a role in zG morphogenesis and differentiation. Supporting this idea, a recent publication has shown that intra-tissular aldosterone concentration was reduced in the absence of macrophages under stress conditions. However, whether macrophages play a direct role in controlling aldosterone secretion or an indirect role by remodelling the postnatal zG is unknown. The presence of tissue resident macrophages in a specific zone is dependent on the production of trophic factors such as IL34, CSF1, CSF2 or CX3CL1 by nearby, tissue resident ‘niche’ cells. In return, macrophages are thought to provide positive ‘feedback’ signals to their niche, generating mutually beneficial circuits between the niche and its macrophages. To gain insight into the role of macrophages in zG morphogenesis and homeostasis, we used single cell sequencing and RNAscope analyses to show expression of CX3CL1 in the zG and of CX3CR1 in macrophages. Interestingly, CX3CL1 expression in the zG was downstream of WNT signalling, suggesting existence of a bi-directional interaction between macrophages and zG. To further study the role of macrophages during the maturation of the zG, we pharmacologically depleted macrophages by the small molecule inhibitor Pexidartinib at different time points between 3- and 12-weeks post-partum, when maturation of the zG occurs. Short-term depletion of macrophages resulted in a more disorganized and elongated zG, suggesting a delay in maturation. However, long-term depletion of macrophages resulted in exacerbated maturation of the rosettes, suggesting that the short-term zG defect was followed by establishment of a compensatory mechanism to allow formation of rosettes even in the absence of macrophages. Whether these perturbations of the zG are correlated with an altered production of aldosterone is still under study.