Prolactin Regulation of Gene Expression in the Arcuate Nucleus during Lactation

Important physiological changes occur during lactation to allow for nourishment of the offspring. Specific neuronal groups within the arcuate nucleus of the hypothalamus influence prolactin (PRL) secretion, metabolism and fertility during lactation. Our overall goal was to identify gene expression changes in the arcuate nucleus during lactation and examine the roles of PRL and ovarian hormones in regulating expression of select genes. We evaluated transcriptome changes in the arcuate nucleus during lactation using RNA-sequencing. Thirty-seven differentially expressed genes, including neuropeptides, signaling molecules, receptors and enzymes, were identified between suckled and pup-deprived groups. Selected genes were evaluated by qRT-PCR in ovary-intact and ovariectomized lactating models, which included non-lactating, suckled and 24hr pup-deprived lactating groups. The mRNA expression of tyrosine hydroxylase (Th), kisspeptin (Kiss1), and neurokinin B (Tac3) was decreased, whereas mRNA expression of proenkephalin (Penk), parathyroid hormone 2 receptor (Pth2r), insulin-like growth factor binding protein 3 (Igfbp3), membrane progesterone receptor beta (Paqr8), suppressor of cytokine signaling 2 (Socs2) and cytokine-inducible SH2 domain-containing protein (Cish) was increased in suckled lactating rats. In 24hr pup-deprived dams, mRNA expression of Pth2r, Igfbp3, Paqr8, Socs2 and Cish was decreased and Th was increased, as compared to suckled rats. The mRNA expression of Kiss1 and Tac3 was increased and Penk was decreased after 72hr, but not 24hr, pup deprivation suggesting gene expression of these neuropeptides is slow to return to non-lactating levels after removing the suckling stimulus. Tyrosine hydroxylase (TH) protein and enkephalin (ENK) peptide expression was examined by immunohistochemistry. Lactating rats had increased ENK in the median eminence and decreased TH in the median eminence and arcuate nucleus as compared to virgin ovariectomized rats. ENK co-localization with TH in the arcuate nucleus was more predominant in lactating rats. Penk, Igfbp3, Pth2r, Cish, and Socs2 mRNA expression was decreased after 72hr bromocriptine treatment in suckled rats, suggesting that these genes are PRL-regulated. In contrast, gene expression of Th, Tac3 and Kiss1 were increased and Paqr8 was decreased with 72hr pup-deprivation, but expression of these genes, were not altered with bromocriptine treatment, indicating that these genes are regulated by a non-PRL component of the suckling stimulus. The mRNA expression of Kiss1, Socs2 and Igfbp3 was increased and Penk was decreased in ovariectomized as compared to ovary intact lactating rats, suggesting that ovarian hormones influence the expression of these genes during lactation. Our data show gene expression changes in the arcuate nucleus that may contribute to increased PRL secretion (Th, Penk and Pth2r), decreased PRL receptor signaling (Cis and Socs2), reduced fertility (Kiss1 and Tac3), increased metabolism (Igfbp3) and support a role for progesterone membrane actions (Paqr8). The expression of some genes appeared to be selectively regulated by ovarian hormone input and/or PRL feedback