Prolactin receptor‐mediated activation of pSTAT5 in the pregnant mouse brain

Abstract

Pregnancy represents a period of remarkable adaptive physiology throughout the body, with many of these important adaptations mediated by changes in gene transcription in the brain. A marked activation of the transcription factor signal transducer and activator of transcription 5 (STAT5) has been described in the brain during pregnancy and likely drives some of these changes. We aimed to investigate the physiological mechanism causing this increase in phosphorylated STAT5 (pSTAT5) during pregnancy. In various tissues, STAT5 is known to be activated by a number of different cytokines, including erythropoietin, growth hormone and prolactin. Because the lactogenic hormones that act through the prolactin receptor (PRLR), prolactin and its closely-related placental analogue placental lactogen, are significantly increased during pregnancy, we hypothesised that this receptor was primarily responsible for the pregnancy-induced increase in pSTAT5 in the brain. By examining temporal changes in plasma prolactin levels and the pattern of pSTAT5 immunoreactivity in the hypothalamus during early pregnancy, we found that the level of pSTAT5 was sensitive to circulating levels of endogenous prolactin. Using a transgenic model to conditionally delete PRLRs from forebrain neurones (Prlr lox/lox /CamK-Cre), we assessed the relative contribution of the PRLR to the up-regulation of pSTAT5 in the brain of pregnant mice. In the absence of PRLRs on most forebrain neurones, a significant reduction in pSTAT5 was observed throughout the hypothalamus and amygdala in late pregnancy, confirming that PRLR is key in mediating this response. The exception to this was the hypothalamic paraventricular nucleus, where only 17% of pSTAT5 immunoreactivity during pregnancy was in PRLR-expressing cells. Taken together, these data indicate that, although there are region-specific mechanisms involved, lactogenic activity through the PRLR is the primary signal activating STAT5 in the brain during pregnancy.

A reduction in voluntary physical activity in early pregnancy in mice is mediated by prolactin

“…In the MPOA, there was a significant reduction of Prlr from GABAergic neurons ( Figure 4—figure supplement 1B , Mann–Whitney non-parametric test, p=0.0091, U = 0). As previously shown, Prlr is not significantly reduced in the PVN in the Prlr lox/lox / Camk2a Cre mice ( Figure 4—figure supplement 1A , Mann–Whitney non-parametric test PVN: p=0.6065, U = 26; Gustafson et al, 2020 ).…”

“…During pregnancy, elevated levels of phosphorylation of the transcription factor signal transducer and activator of transcription 5 (pSTAT5) are detected throughout the brain. This is a well-characterized intracellular signaling molecule-activated downstream of the Prlr (and a range of other cytokines), but we have shown that the majority of pSTAT5 in the brain during pregnancy is caused by increased Prlr activation ( Gustafson et al, 2020 ), both by surges in prolactin early in pregnancy and by rising placental lactogen as pregnancy progresses ( Phillipps et al, 2020 ). During lactation, various regions within the brain show increased prolactin-induced pSTAT5 expression compared to mice in the diestrous phase of the estrous cycle, including the medial POA, BNST, PVN, and medial amygdala ( Brown et al, 2011 ).…”

“…Thus, in this mouse line, GFP is a useful marker of cells in which Cre-mediated recombination (and therefore Prlr deletion) has taken place. Similar to our previous work, here we show that while Prlr lox/lox / Camk2a Cre do not have a complete Prlr deletion in the forebrain, there are areas of extensive deletion (as measured by reduced prolactin-induced pSTAT5), such as the arcuate nucleus and VMN, and areas where Prlr is reduced by about 50% such as the medial POA (MPOA) ( Figure 4—figure supplement 1A , Mann–Whitney non-parametric test MPOA: p=0.0262, U = 7, Arc: p=0.0002, U = 0, VMN: p = 0.0071, U = 7; Brown et al, 2016 ; Gustafson et al, 2020 ). In the MPOA, there was a significant reduction of Prlr from GABAergic neurons ( Figure 4—figure supplement 1B , Mann–Whitney non-parametric test, p=0.0091, U = 0).…”

Prolactin-Induced Adaptation in Glucose Homeostasis in Mouse Pregnancy Is Mediated by the Pancreas and Not in the Forebrain

“…Prlr lox/lox /CamK-Cre mice showed positively-stained GFP cells throughout the hypothalamus, as previously reported (36), and had high GFP expression in the arcuate nucleus, indicative of deletion of the Prlr (Figure 2). Previously, we have reported attenuated prolactin-induced pSTAT5 in the arcuate nucleus of Prlr lox/lox / CamK-Cre demonstrating greatly reduced Prlr activity indicative of Prlr deletion (33,36,41). Since brain GFP expression in Prlr lox/lox / Pdx-Cre was significantly less than Prlr lox/lox /Rip-Cre mice (Figure 2), limited to just the arcuate nucleus, and the pregnant Prlr lox/lox /Rip-Cre mice glucose tolerance results were compromised by effects of the Rip-Cre transgene itself (Figures 1D, E), only Prlr lox/lox /Pdx-Cre mice were subsequently used for experiments to determine the contribution of prolactin action in the pancreas and brain in mediating pregnancy-induced adaptations in glucose homeostasis.…”

Growth hormone and prolactin: So much still to learn

“…A deeper understanding of the intracellular pathways mediating GH and prolactin actions may provide insights into tissue specific effects and the importance of temporal aspects of hormone action. Two papers describing actions of prolactin over differing timescales highlight the necessity of considering the canonical pathways activated by GH and prolactin through Stat5 activation 17 and potential novel pathways mediating rapid action 18 …”