A Substitution in the Ligand Binding Domain of the Porcine Glucocorticoid Receptor Affects Activity of the Adrenal Gland

Glucocorticoids produced in the adrenal cortex under the control of the hypothalamic-pituitary axis play a vital role in the maintenance of basal and stress-related homeostasis and influence health and well-being. To identify loci affecting regulation of the hypothalamic-pituitary-adrenal (HPA) axis in the pig we performed a genome-wide association study for two parameters of acute and long-term adrenal activity: plasma cortisol level and adrenal weight. We detected a major quantitative trait locus at the position of the glucocorticoid receptor gene (NR3C1) – a key regulator of HPA axis activity. To determine the causal variant(s), we resequenced the coding region of NR3C1 and found three missense single nucleotide polymorphisms (SNPs). SNP c.1829C.T, leading to a p.Ala610Val substitution in the ligand binding domain, showed large (about 0.66 and 1.26 phenotypic standard deviations for cortisol level and adrenal weight, respectively), and highly significant (2.1E-39#log10(1/p)#1.7E+0) negative effects on both traits. We were able to replicate the association in three commercial pig populations with different breed origins. We analyzed effects of the p.Ala610Val substitution on glucocorticoid-induced transcriptional activity of porcine glucocorticoid receptor (GR) in vitro and determined that the substitution introduced by SNP c.1829C.T increased sensitivity of GR by about two-fold. Finally, we found that non-coding polymorphisms in linkage disequilibrium with SNP c.1829C.T have only a minor effect on the expression of NR3C1 in tissues related to the HPA axis. Our findings provide compelling evidence that SNP c.1829C.T in porcine NR3C1 is a gain-of