Liver X receptors regulate adrenal cholesterol balance

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Abstract
Cholesterol is the obligate precursor to adrenal steroids but is cytotoxic at high concentrations. Here, we show the role of the liver X receptors (LXRα and LXRβ) in preventing accumulation of free cholesterol in mouse adrenal glands by controlling expression of genes involved in all aspects of cholesterol utilization, including the steroidogenic acute regulatory protein, StAR, a novel LXR target. Under chronic dietary stress, adrenal glands from Lxrαβ–/– mice accumulated free cholesterol. In contrast, wild-type animals maintained cholesterol homeostasis through basal expression of genes involved in cholesterol efflux and storage (ABC transporter A1 [ABCA1], apoE, SREBP-1c) while preventing steroidogenic gene (StAR) expression. Upon treatment with an LXR agonist that mimics activation by oxysterols, expression of these target genes was increased. Basally, Lxrαβ–/– mice exhibited a marked decrease in ABCA1 and a derepression of StAR expression, causing a net decrease in cholesterol efflux and an increase in steroidogenesis. These changes occurred under conditions that prevented the acute stress response and resulted in a phenotype more specific to the loss of LXRα, including hypercorticosteronemia, cholesterol ester accumulation, and adrenomegaly. These results imply LXRα provides a safety valve to limit free cholesterol levels as a basal protective mechanism in the adrenal gland, where cholesterol is under constant flux.