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Endocrinology
Endocrinology
endo
Endocrinology
0013-7227
1945-7170
Oxford University Press US

10.1210/endocr/bqae091
bqae091
Letter to the Editor Response
AcademicSubjects/MED00250
Response to Letter to the Editor From Hoekstra: “Adrenal Abcg1 Controls Cholesterol Flux and Steroidogenesis”
Breault David T Department of Pediatrics, Harvard Medical School, Boston Children's Hospital, Boston, MA 02115, USA
Harvard Stem Cell Institute, Cambridge, MA 02138, USA

Flück Christa E Division of Pediatric Endocrinology, Diabetology and Metabolism, Department of Pediatrics, Inselspital, Bern University Hospital, 3010 Bern, Switzerland
Department for BioMedical Research, University Hospital Inselspital, University of Bern, 3010 Bern, Switzerland

https://orcid.org/0000-0002-5372-5692
Pignatti Emanuele Division of Pediatric Endocrinology, Diabetology and Metabolism, Department of Pediatrics, Inselspital, Bern University Hospital, 3010 Bern, Switzerland
Department for BioMedical Research, University Hospital Inselspital, University of Bern, 3010 Bern, Switzerland

Correspondence: Emanuele Pignatti, PhD, Pädiatrische Endokrinologie/Diabetologie/Metabolik, Medizinische Universitätskinderklink Bern, Inselspital, Freiburgstrasse 15/C843, 3010 Bern, Switzerland. Email: emanuele.pignatti@unibe.ch.
10 2024
23 7 2024
23 7 2024
165 10 bqae09112 6 2024
17 6 2024
05 9 2024
© The Author(s) 2024. Published by Oxford University Press on behalf of the Endocrine Society.
2024
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pmcWe are writing in response to Dr. Menno Hoekstra's recent letter (1) concerning our work “Adrenal Abcg1 Controls Cholesterol Flux and Steroidogenesis” published in Endocrinology last February (2).

In 2019, Dr. Hoekstra's team published findings on a mouse model demonstrating mild glucocorticoid insufficiency and a reduction in adrenal cholesteryl esters following systemic deletion of the transporter Abcg1 (3). Our research, however, showed that adrenal-specific inactivation of Abcg1 results in mild hypersecretion of corticosterone without altering adrenal fat composition (2).

We believe that these contrasting results provide an opportunity for further exploration and understanding. In our discussion, we proposed 3 potential reasons for these discrepancies:

Systemic vs adrenal-specific deletion: We suggested that global deletion of Abcg1 might influence corticotropin-releasing hormone and/or adrenocorticotropin hormone (ACTH). Dr. Hoekstra highlighted that their protocol included ACTH stimulation 3 hours before sample collection, which addresses acute exposure. However, the possibility of prolonged low ACTH levels contributing to adrenal hypofunction remains plausible, as documented in both human and mouse models of secondary adrenal insufficiency following corticosteroid treatment (4). Further research could clarify the impact of systemic Abcg1 deletion on ACTH levels and/or other factors related to the hypophyseal-pituitary-adrenal axis.

Adrenal cortex function/development: We hypothesized that global Abcg1 inactivation could impair adrenal cortex function or cause dysgenesis. Dr. Hoekstra's letter did not address this possibility, suggesting an area for additional investigation to determine the broader effects of Abcg1 deletion on adrenal cortex development.

Degree of Abcg1 recombination: Dr. Hoekstra noted residual Abcg1 transcripts in the zona Fasciculata in Fig. 1C of our paper and argued that the remaining transcripts may account for phenotype discrepancies (2). Of note, we observed a significant reduction in signal dots compared to controls, and whole-adrenal quantitative PCR showed a marked decrease in Abcg1 transcripts. Together, this indicates substantial Abcg1 reduction across the cortex following tissue-specific recombination. Nevertheless, even residual levels of Abcg1 transcripts are unlikely to explain the phenotypic gain-of-function (ie, higher corticosterone levels) observed in our model of adrenal-specific Abcg1 deletion.

In addition, Dr. Hoekstra raised concerns about the suitability of the aldosterone synthase (AS, Cyp11b2)-regulated Cre system for recombination in the zona fasciculata, where AS is not expressed. We refer to numerous lineage-tracing studies over the past decade, which confirm that AS-expressing cells in the zona glomerulosa transdifferentiate into zona fasciculata cells (5, 6). Consistent with these findings, the specific Cre-expressing mouse strain we used achieves nearly complete renewal of the steroidogenic cortex from AS-expressing cell descendants by 11 to 12 weeks of age (7). Thus, our experiments were appropriately conducted at this developmental stage. Moreover, we are pleased to share that additional lineage-tracing experiments using an mTmG allele (8) in Abcg1 conditional knock-out and control mice at 12 weeks of age showed no impact of Abcg1 deletion on transdifferentiation of zona glomerulosa cells into zona fasciculata cells (data not shown).

We thank Dr. Hoekstra for prompting this discussion and for the opportunity to clarify our findings. We hope these points contribute to a deeper understanding of Abcg1's role in adrenal physiology and encourage further collaborative research in this area.

Disclosures

The authors have nothing to disclose.

Abbreviations

ACTH adrenocorticotropic hormone

AS aldosterone synthase
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References

1 Hoekstra  M . Letter to the editor from Hoekstra: ‘Adrenal Abcg1 controls cholesterol flux and steroidogenesis'. Endocrinology. 2024;165(9):bqae097. Doi: 10.1210/endocr/bqae097.
2 Liimatta  J, Curschellas  E, Altinkilic  EM, et al  Adrenal Abcg1 controls cholesterol flux and steroidogenesis. Endocrinology. 2024;165 (3 ):bqae014.38301271
3 Hoekstra  M, Ouweneel  AB, Nahon  JE, et al  ATP-binding cassette transporter G1 deficiency is associated with mild glucocorticoid insufficiency in mice. Biochim Biophys Acta Mol Cell Biol Lipids. 2019;1864 (4 ):443‐451.30633988
4 Finco  I, Lerario  AM, Hammer  GD. Sonic hedgehog and WNT signaling promote adrenal gland regeneration in male mice. Endocrinology. 2018;159 (2 ):579‐596.29211850
5 Freedman  BD, Kempna  PB, Carlone  DL, et al  Adrenocortical zonation results from lineage conversion of differentiated zona Glomerulosa cells. Dev Cell. 2013;26 (6 ):666‐673.24035414
6 Grabek  A, Dolfi  B, Klein  B, Jian-Motamedi  F, Chaboissier  M-C, Schedl  A. The adult adrenal cortex undergoes rapid tissue renewal in a sex-specific manner. Cell Stem Cell. 2019;25 (2 ):290‐296.e2.31104943
7 Pignatti  E, Leng  S, Carlone  DL, Breault  DT. Regulation of zonation and homeostasis in the adrenal cortex. Mol Cell Endocrinol. 2017;441 :146‐155.27619404
8 Muzumdar  MD, Tasic  B, Miyamichi  K, Li  L, Luo  L. A global double-fluorescent cre reporter mouse. Genesis. 2007;45 (9 ):593‐605.17868096
