Cell Proliferation, Movement and Differentiation during Maintenance of the Adult Mouse Adrenal Cortex

Su-Ping Chang,John D West,Christopher J Kenyon,Steven D Morley,Frida Nilsson,Hamish D Morrison,Harpal Singh Randeva

doi:10.1371/journal.pone.0081865

Abstract

Appropriate maintenance and regeneration of adult endocrine organs is important in both normal physiology and disease. We investigated cell proliferation, movement and differentiation in the adult mouse adrenal cortex, using different 5-bromo-2'-deoxyuridine (BrdU) labelling regimens and immunostaining for phenotypic steroidogenic cell markers. Pulse-labelling showed that cell division was largely confined to the outer cortex, with most cells moving inwards towards the medulla at around 13-20 µm per day, though a distinct labelled cell population remained in the outer 10% of the cortex. Pulse-chase-labelling coupled with phenotypic immunostaining showed that, unlike cells in the inner cortex, most BrdU-positive outer cortical cells did not express steroidogenic markers, while co-staining for BrdU and Ki67 revealed that some outer cortical BrdU-positive cells were induced to proliferate following acute adrenocorticotropic hormone (ACTH) treatment. Extended pulse-chase-labelling identified cells in the outer cortex which retained BrdU label for up to 18-23 weeks. Together, these observations are consistent with the location of both slow-cycling stem/progenitor and transiently amplifying cell populations in the outer cortex. Understanding the relationships between these distinct adrenocortical cell populations will be crucial to clarify mechanisms underpinning adrenocortical maintenance and long-term adaptation to pathophysiological states.

Highlights

The adult adrenal cortex consists of three principal concentric morphological zones, surrounding a central medulla, distinguished by their cellular organisation and steroid hormone products
The principal aims of this study were to combine BrdU pulse-chase labelling with immunostaining for phenotypic steroidogenic enzyme markers (i) to identify cell division patterns and the rate and direction of adult adrenocortical cell movement; (ii) to assess different stages of cell differentiation in the adrenocortical zones; (iii) to distinguish slow-cycling and terminally differentiated BrdU-labelled adrenocortical cell populations by assessing whether or not they are able to proliferate following acute trophic stimulus and (iv) to determine if long-term LRCs are present in the adult mouse adrenal cortex
Single BrdU injection showed that cell proliferation occurred primarily in the outer 40% of the adrenal cortex, with the main proliferative area concentrated at 5% to 25% from the capsule, encompassing the boundary between the zona glomerulosa (ZG) and zona fasciculata (ZF)

Summary

Introduction

The adult adrenal cortex consists of three principal concentric morphological zones, surrounding a central medulla, distinguished by their cellular organisation and steroid hormone products (reviewed in 1). In rats and some other species, an additional morphologically-distinct zone, the zona intermedia (ZI), has been described at the boundary between the ZG and ZF ([2] and references therein). In the rat, this has subsequently been termed the ‘undifferentiated zone’ (ZU) because, cells in this region express some steroidogenic enzymes (e.g. steroid 21-hydroxylase; 21-OH; approved symbol Cyp21a1), they do not express either the ZGspecific aldosterone synthase (AS; approved symbol Cyp11b2) or the ZF-specific 11β-hydroxylase (11β-OH; approved symbol Cyp11b1) [2]. That these ZI/ZU cells are part of the ZG, which comprises a mixture of both terminally differentiated steroidogenic cells and cells with a less differentiated, more plastic phenotype [3]

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Conclusion