Parallel expression patterns of NR4A nuclear receptor family genes in the pituitary gland of proestrus rats

The NR4A nuclear receptor family (NR4As), encompassing NR4A1, NR4A2, and NR4A3, exerts pivotal roles in cellular processes through intricate expression patterns and interactions. Despite the influence of some NR4As on anterior pituitary functions regulated by the hypothalamus, their physiological expression patterns remain unclear. In our prior work, we demonstrated the specific upregulation of NR4A3 in the rat anterior pituitary gland during the proestrus afternoon, coinciding with a gonadotropin surge. In this study, we investigated changes in pituitary Nr4a gene expression throughout the estrous cycle in rats and a gonadotropin surge-induced model. Nr4a1 and Nr4a2 gene expression significantly increased during proestrus, aligning with previous observations for Nr4a3. Furthermore, prolactin gene expression increased sequentially with rising Nr4a gene expression, while thyroid-stimulating hormone beta gene expression remained stable. Immunohistochemistry revealed a widespread and differential distribution of NR4A proteins in the anterior pituitary, with NR4A1 and NR4A3 being particularly abundant in thyrotrophs, and NR4A2 in gonadotrophs. In estrogen-treated ovariectomized rats, elevated luteinizing hormone secretion corresponded to markedly upregulated expression of Nr4a1, Nr4a2, and Nr4a3. In gonadotroph and somatomammotroph cell lines, gonadotropin- and thyrotropin-releasing hormones transiently and dose-dependently increased the expression of Nr4a genes. These findings suggest that hypothalamic hormone secretion during proestrus may induce the parallel expression of pituitary Nr4a genes, potentially influencing the pituitary gene expression program related to endocrine functions before and after ovulation.