Localisation and characterisation of uncoupling protein-2 (UCP2) in the human preterm placenta

The increase in oxidative stress during pregnancy is associated with increased placental antioxidant enzyme activity and may additionally be limited by the uncoupling proteins (UCPs). There is little data on the expression and localisation of UCP2 in the human preterm placenta or on its role in the regulation of placental oxidative stress. Placentae were collected from women with singleton pregnancies who delivered between 24 and 36 weeks gestation (n = 54) and from a term reference group who delivered following uncomplicated pregnancy (n = 11). UCP2 expression and localisation was determined by quantitative real-time RTPCR using Taqman gene expression assays and immunohistochemistry. Placental lipid hydroperoxide and nitrotyrosine content was determined by ELISA. UCP2 mRNA expression increased from 24 to 41 weeks gestation (p < 0.001) and was positively correlated with placental weight (p = 0.004). While UCP2 expression was lower in small for gestational age infants (p = 0.045) it did not differ with respect to timing of antenatal betamethasone exposure nor with placental lipid hydroperoxide or nitrotyrosine content. UCP2 staining was identified in the cytotrophoblast in 34% of samples and in the syncytiotrophoblast in 63% of samples. Cytotrophoblast staining was more frequent in later gestations (p = 0.03) with syncytiotrophoblast UCP2 staining was not altered by gestation. In the preterm group, no association was observed with time since antenatal betamethasone exposure or placental lipid hydroperoxide or nitrotyrosine content. The current data supports gestation dependant alterations in UCP2 mRNA expression and immunohistochemical localisation in the human placenta but no evidence for an important role for UCP2 in protection against placental oxidative damage.