Placental PHLDA2 expression was significantly 2.3 fold higher in RFM pregnancies resulting in delivery of a growth restricted compared with a normal birth weight infant (Fig. 1a). Results remained statistically significant when comparing normalisation to a single housekeeping gene YWHAZ with the geometric mean of YWHAZ and L19 expression in a subset of samples (Additional file 1: Figure S1).
Placental PHLDA2 expression in RFM pregnancies. Placental PHLDA2 expression was significantly increased in RFM pregnancies resulting in delivery of a growth restricted infant (a) Fetal growth restriction was defined as delivery of a term infant with a custom birth weight centile 10th. Placental PHLDA2 was not significantly altered in RFM pregnancies where infants were born preterm (b) or admitted to NICU at delivery (c) There was a significant inverse association between placental PHLDA2 expression and maternal serum hPL levels (d) RFM?=?reduced fetal movements. Error bars represent SEM. ** P??0.01
When participants were further classified according to severity of growth restriction, PHLDA2 expression was significantly 1.7 fold higher in cases with custom birth weight centile 10th (p?=?0.01, ?=?12. v. 82) and 3.2 fold higher in cases with custom birth weight centile 3rd (p??0.001, ?=?8 v. 82). Placental PHLDA2 expression was also significantly inversely associated with birth weight (r?=??0.24, p?=?0.01, ?=?109), custom birth weight centiles (r?=??0.25, p?=?0.01, ?=?109) and, in this study, also placental weight (r?=??0.39, p?=?0.03, ?=?31).
We subsequently analysed placental PHLDA2 expression in relation to preterm delivery and NICU admission at birth, which are other common poor perinatal outcomes associated with RFM. There was no significant correlation between placental PHLDA2 expression and gestational age (r?=??1.41, p?=?0.14, ?=?109) and was no significant difference in expression between preterm and term deliveries (Fig. 1b). Placental PHLDA2 expression was not significantly altered in infants admitted to NICU at delivery (for perinatal asphyxia) (Fig. 1c) and there was no significant correlation between placental PHLDA2 and other measures of infant wellbeing at delivery including Apgar scores at 1 min (r?=?0.01, p?=?0.93, ?=?106) and 5 min (r?=??0.11, p?=?0.27, ?=?105) or with arterial cord blood pH (r?=?? 0.7, p?=?0.52, ?=?76).
Imprinted genes have been demonstrated to regulate the endocrine lineage of the mouse placenta, in particular expression of placental lactogens [18]. In this study there was a significant inverse association between placental PHLDA2 expression and maternal serum hPL levels (Fig. 1d) suggesting that PHLDA2 may regulate the production of placental hormones in human pregnancies. In further multiple linear regression analysis controlling for infant birth weight, offspring gender and gestational age (F(4,69)?=?5.34, p?=?0.001, R
2?=?0.24), the association between placental PHLDA2 expression and serum hPL levels failed to reach statistical significance (p?=?0.07), with only infant birth weight significantly associated with maternal serum hPL levels (p?=?0.01). This is perhaps not surprising since, in the mouse model, elevated Phlda2 drives both growth restriction and reduced expression of placental lactogens [19, 21]. Data from the animal model supports a causal association between placental PHLDA2 expression and maternal serum hPL levels.