Endocrine Abstracts

JOINT2386

Synthetic glucocorticoids are extensively prescribed. Although they improved the management of chronic inflammatory diseases, these treatments are also associated with numerous adverse effects, with an inter-individual variability that remains poorly understood. Glucocorticoids exert their effects via the glucocorticoid receptor (GR), encoded by the NR3C1 gene. Only few variants associated with glucocorticoid sensitivity have been described and the molecular mechanisms involved are not fully understood. The N363S variant, which encodes for substitution of an asparagine with a serine at amino acid 363, has been associated with increased glucocorticoid sensitivity, but has never been further characterized. Performing in vitro studies, we demonstrated that maximal transactivation activity (GR_WT 93,8%±5.1 vs GR_N363S 142.6%±9,0, n=38, P<0.0001) and target gene expression were higher in response to dexamethasone in HEK 293T cells expressing the variant. Next, we aim to assess the impact of the N363S variant in vivo using a novel mouse model expressing the variant. As the mutated amino acid is conserved across species, we introduced a point mutation into the coding sequence of the mouse Nr3c1 gene (c.1139 A>G), using the CRISPR/Cas9 system. The genotype (Wild type: WT; heterozygous: HET; homozygous: HOM) was assessed by PCR. First, we evaluated the impact of the variant on weight, glucose metabolism, and HPA axis activity without any glucocorticoid treatment. Next, we studied its impact on glucocorticoid-induced adverse effects after treatment with dexamethasone (1 mg/kg/d) for 28 days via osmotic pumps. The viability and fertility of the mice were not affected by the genotype. In absence of dexamethasone treatment, we observed no genotype-based differences in adrenal gland weight, corticosterone secretion levels after a single intraperitoneal administration of dexamethasone (WT 9.4 ng/ml [3.5;12.2]; HET 4.4 ng/ml [2.6;6.2]; HOM 9.6 ng/ml [4.8; 12.6], n=4), glucose metabolism (fasting glycemia, WT 117 mg/dL[90;145], HET 107 mg/dL [95;121], HOM 96 mg/dL [83;138], n=3) or behavioral outcomes. The impact of the N363S variant on the development of adverse effects, such as glucocorticoid-induced adrenal insufficiency, impaired glucose metabolism and depressive features, is currently being investigated after prolonged dexamethasone treatment. Overall, we developed a novel mouse model expressing the N363S variant of the Nr3c1 gene that will improve scientific knowledge on glucocorticoid sensitivity. Further, the N363S variant could be used as a predictive tool for personalized medicine.