Gain of Function Mutation in the Mineralocorticoid Receptor of the Brown Norway Rat

Abstract

The aim of this research was to identify the molecular bases of differences in sensitivity to corticosteroid hormones between Brown Norway and Fischer 344 rats. We previously showed an apparent insensitivity to adrenalectomy in Brown Norway rats. Based on our first hypothesis of a different activity/reactivity of the mineralocorticoid signaling pathway between the two rat strains, we sequenced Brown Norway and Fischer 344 mineralocorticoid receptor cDNA and identified a tyrosine to cysteine substitution (Y73C) in the N-terminal part of the Brown Norway mineralocorticoid receptor. As a first step, this substitution gave us a means to distinguish the Brown Norway allele from the Fischer 344 at the mineralocorticoid receptor locus in an F2 population. We showed a strong genetic linkage between the mineralocorticoid receptor genotype and sensitivity to adrenalectomy. A subsequent genome-wide linkage analysis confirmed the involvement of the mineralocorticoid receptor locus and implicated other loci, including one on chromosome 4, which collectively explain a large part of the strain differences in corticosteroid receptor responses. In vitro studies further revealed that the Y73C substitution induces greater transactivation of the mineralocorticoid receptor by aldosterone, and surprisingly by progesterone as well, which could substitute for aldosterone after adrenalectomy in Brown Norway rats. We challenged this hypothesis in vivo and showed that plasma progesterone is higher in Brown Norway male rats and partially compensates for aldosterone after adrenalectomy. This work illustrates the interest of a pluristrategic approach to explore the mineralocorticoid receptor signaling pathway and its implication in the regulation of hydroelectrolytic homeostasis and blood pressure.Adrenal steroids act through two receptor subtypes: the mineralocorticoid receptor (MR), 1 which exhibits a high affinity for aldosterone, deoxycorticosterone (DOC), and endogenous glucocorticoids (K d ϭ 0.5-1.0 nM), and the glucocorticoid receptor (GR), which binds cortisol and corticosterone with a lower affinity (K d ϭ 2.5-5.0 nM) than synthetic agonists like dexamethasone or RU28362 (K d ϭ 0.5-1.0 nM). Like other nuclear receptors, MR and GR bind to cis-acting DNA elements in the regulatory regions of target genes (1). The MR is located predominately in sodium-transporting epithelia and in the limbic system. It is involved in the maintenance of blood pressure (2) and brain function (3). The GR has a widespread distribution and is involved in almost all organic functions, including carbohydrate and lipid metabolism, modulation of immune responses, and behavior (4 -6). Both receptor types are also involved in the control of hypothalamic-pituitary-adrenal axis activity and reactivity to stress (7). Numerous diseases, such as hypertension, autoimmunity, obesity, mood, and behavioral disorders, are associated with disturbed corticosteroid secretion or action (8 -10). Vulnerability to such dysfunctions shows high interindividual variation, and the in...

Strain differences in hypothalamic–pituitary–adrenocortical axis function and adipogenic effects of corticosterone in rats

“…F344 and LEW rats exhibited the classical weight loss after ADX, partly related to a decrease in their food intake. On the contrary, as described previously in Brown Norway rats (Marissal-Arvy et al 2004), LOU rats showed an apparent insensitivity to ADX, suggesting the involvement of compensatory mechanisms for the lack of MR activation in these rats. The lowest doses of corticosterone (MR effect) restored the weight gain of F344 and LEW rats to sham values.…”

“…For instance, they could involve the greater norepinephrinergic tone (i.e., lipolysis) suggested in abdominal versus peripheral fat by Bartness & Bamshad (1998), associated or not with a high central MR activation stimulating SNS tone in LOU rats (Zhang et al 2006). Previously, we performed a genetic study on a Brown Norway!F344 F2 population that revealed a gain of function mutation in the Brown Norway MR, which was involved in the insensitivity of Brown Norway rats to ADX (Marissal-Arvy et al 2004). An MR harboring a gain of function could potentiate GR-related catabolic and feedback effects, notably by heterodimerization (Derfoul et al 2000).…”

Stress neuroendocrine profiles in five pig breeding lines and the relationship with carcass composition

“…Indeed large genetic variations of receptor efficiency and their metabolic implications have been described, e.g. in humans (DeRijk et al, 2002) and rats (Marissal-Arvy et al, 2004). The functionality of corticosteroid receptors will have to be explored in similar Pié train-line pigs to confirm this hypothesis.…”

Breeding for robustness: the role of cortisol

“…We also need more information about the systems genetics of the HPA axis for a more integrated understanding of its functioning and effects. Indeed, several sources of genetic variability are usually found in the same model (Marissal-Arvy et al, 2004), but very little is known about the interactions among various sources of variability within the axis, and how they eventually compensate for or potentiate each other. Some data indicate that the effect of a single mutation (Carter et al, 2009), or the consequence of GR hormone removal (de Jong et al, 2007), is strongly dependent on genetic background.…”