A potential role for insulin treatment during pregnancy in reducing postpartum psychological distress in maternal obesity: an administrative population health study

A locus control region generates distinct active placental lactogen and inactive growth hormone gene domains in term placenta that are disrupted with obesity

INTRODUCTION

Placental villi include an outer syncytiotrophoblast (STB) layer and an inner layer of cytotrophoblasts (CTBs) that fuse to generate the STB layer in pregnancy. While activation of the locus containing the human (h) placental lactogen (hPL) genes (hPL-A/CSH1 and hPL-B/CSH2) begins in the CTBs, their expression in the STB requires epigenetic modifications and interactions between locus control region (LCR) and gene regulatory sequences. No factor that limits or facilitates hPL LCR/gene interactions for locus activation is reported. The paternally-expressed gene 3 (PEG3/PW1) transcription factor was pursued as a candidate. PEG3 is expressed by villous CTBs but not the STB and putative binding sites were identified in hPL-related sequences.

METHODS

PEG3 expression was assessed in multiple cell types including in CTB-like JEG-3 cells. PEG3 binding was also assessed in JEG-3 cells and term placenta samples from women with or without maternal obesity, where chromosomal architecture of the hPL gene locus was also examined.

RESULTS

In JEG-3 cells, PEG3 was found to bind to hypersensitive site (HS III-V) sequences within the LCR. Knockdown of PEG3 in these cells resulted in increased hPL gene expression. In term placenta, PEG3 binding at placenta-specific HS IV was increased with maternal obesity, where a decrease in hPL RNA levels is seen, while PEG3 binding was reduced in women with obesity who develop insulin-treated gestational diabetes mellitus (O/GDM + Ins), where increased hPL gene expression is observed. Chromatin conformation capture revealed distinct hPL gene domain interactions that are modified with maternal obesity but largely reversed in O/GDM + Ins, correlating with PEG3 binding.

DISCUSSION

Decreased PEG3 binding may be required for hPL domain generation and expression during CTB to STB transition.

Effect of high fat diet on maternal behavior, brain-derived neurotrophic factor and neural stem cell proliferation in mice expressing human placental lactogen during pregnancy

Maternal obesity is a serious health concern because it increases risks of neurological disorders, including anxiety and peripartum depression. In mice, a high fat diet (HFD) in pregnancy can negatively affect placental structure and function as well as maternal behavior reflected by impaired nest building and pup-retrieval. In humans, maternal obesity in pregnancy is associated with reduced placental lactogen (PL) gene expression, which has been linked to a higher risk of depression. PL acting predominantly through the prolactin receptor maintains energy homeostasis and is a marker of placenta villous trophoblast differentiation during pregnancy. Impaired neurogenesis and low serum levels of brain-derived neurotrophic factor (BDNF) have also been implicated in depression. Augmented neurogenesis in brain during pregnancy was reported in the subventricular zone (SVZ) of mice at gestation day 7 and linked to increased prolactin receptor signaling. Here, we used transgenic CD-1 mice that express human (h) PL during pregnancy to investigate whether the negative effects of diet on maternal behavior are mitigated in these (CD-1[hGH/PL]) mice. Specifically, we examined the effect of a HFD on nest building prepartum and pup retrieval postpartum, as well as on brain BDNF levels and neurogenesis. In contrast to wild-type CD-1[WT]mice, CD-1[hGH/PL] mice displayed significantly less anxiety-like behavior, and showed no impairment in prepartum nest building or postpartum pup-retrieval when fed a HFD. Furthermore, the HFD decreased prepartum and increased postpartum BDNF levels in CD-1[WT] but not CD-1[hGH/PL] mice. Finally, neurogenesis in the SVZ as well as phosphorylated mitogen-activated protein kinase, indicative of lactogenic signaling, appeared unaffected by pregnancy and diet at gestation day 7 in CD-1[hGH/PL] mice. These observations indicate that CD-1[hGH/PL] mice are resistant to the negative effects of HFD reported for CD-1[WT] mice, including effects on maternal behaviors and BDNF levels, and potentially, neurogenesis. This difference probably reflects a direct or indirect effect of the products of the hGH/PL transgene.

The Prolactin Family of Hormones as Regulators of Maternal Mood and Behavior

Transition into motherhood involves profound physiological and behavioral adaptations that ensure the healthy development of offspring while maintaining maternal health. Dynamic fluctuations in key hormones during pregnancy and lactation induce these maternal adaptations by acting on neural circuits in the brain. Amongst these hormonal changes, lactogenic hormones (e.g., prolactin and its pregnancy-specific homolog, placental lactogen) are important regulators of these processes, and their receptors are located in key brain regions controlling emotional behaviors and maternal responses. With pregnancy and lactation also being associated with a marked elevation in the risk of developing mood disorders, it is important to understand how hormones are normally regulating mood and behavior during this time. It seems likely that pathological changes in mood could result from aberrant expression of these hormone-induced behavioral responses. Maternal mental health problems during pregnancy and the postpartum period represent a major barrier in developing healthy mother-infant interactions which are crucial for the child's development. In this review, we will examine the role lactogenic hormones play in driving a range of specific maternal behaviors, including motivation, protectiveness, and mother-pup interactions. Understanding how these hormones collectively act in a mother's brain to promote nurturing behaviors toward offspring will ultimately assist in treatment development and contribute to safeguarding a successful pregnancy.