Gijs van der Zwet¹, Lauren Sluiter¹, Chang Li², Max Gentenaar³, Delaram Poormoghadam⁴, Jari Berkhout³, Andries Kalsbeek⁴, Boudewijn Lelieveldt², Lisa Koorneef¹

(1) Department of Anatomy & Embryology, Leiden University Medical Center, Leiden, the Netherlands.

(2) Department of Radiology, Leiden University Medical Center, Leiden, the Netherlands.

(3) Department of Internal Medicine, Division of Endocrinology, Leiden University Medical Center, Leiden, Netherlands.

(4) Laboratory of Endocrinology, Department of Laboratory Medicine, Amsterdam UMC, University of Amsterdam, Amsterdam, The Netherlands; Netherlands Institute for Neuroscience, Amsterdam, The Netherlands.

Glucocorticoids and their synthetic analogues frequently cause metabolic disturbances, osteoporosis and -particularly in children – growth retardation, but the involvement of dysregulated growth hormone (GH) secretion remains controversial. Recent single-cell transcriptome analyses identified two hypothalamic somatostatin (SST) neuronal subpopulations, Sst-Sfrp2 and Sst-Calb2, that likely inhibit pituitary GH secretion. Both populations express the glucocorticoid receptor (GR), suggesting glucocorticoid sensitivity, while the Sst-Sfrp2 neurons additionally express metabolic receptors Mc4r and Npy1r, indicating potential integration of metabolic cues.

Here we investigated how metabolic and glucocorticoid signaling interact to modulate the activity of these SST subpopulations. Female C57Bl/6 mice were treated for four days with the GR antagonist RU486 (60 mg/kg/day) or solvent, followed by the metabolic stressor of 16h fasting or ad libitum feeding before euthanasia (n=6/group). Multiplex immunohistochemistry revealed that fasting increased the total number of neuroendocrine SST neurons independently of RU486, but this was restricted to CALB2-negative SST neurons. Likewise, RU486 selectively increased the expression of neuronal activation marker C-FOS in CALB2-negative SST neurons – indicating subpopulation-specific glucocorticoid responsiveness. To explore mechanisms underlying this specificity, we analyzed spatial single-cell transcriptomic mouse brain data from the Allen Brain Cell atlas to map known GR signaling partners and glucocorticoid-metabolizing enzymes. Notably, Nr3c2, Trim24 and Arid3b were differentially expressed between SST subpopulations (|log2FC| >= 1), and these differences persisted when stratifying for sex and light/dark cycle.

We reveal selective responsiveness of SST subpopulations to fasting and GR antagonism and identified promising candidate genes that might explain cell type-specific GR responsivity. Ongoing work will determine how these mechanisms influence GH secretion and whether they can be utilized to guide the selection of selective GR modulators without GH-suppressive effects.