Sex-specific placental differences as a contributor to sex-specific metabolic programming?

Abstract

Over the past decades, maternal nutritional intake has been proven to affect the prenatal and post-natal development of the foetus as well as its long-term health (see (Jimenez-Chillaron et al. 2012) and (Lillycrop & Burdge 2015) for recent overviews). In this journal, we have recently shown that maternal Western-style diet gives rise to long lasting programming of the liver in adult mouse offspring (Pruis et al. 2014), affecting mostly the males. Moreover, we demonstrated that several aspects of sex-specific programming are already present in 2-week-old offspring (Mischke et al. 2013), that is, well before puberty. The question arising now is whether this sexual dimorphism was already present during prenatal development, and which factors contributed to its manifestation. One major determinant of development and intrauterine growth is the placental supply of nutrients, which occurs primarily by a combination of diffusion and transporter-mediated transport (Sandovici et al. 2012). The surface area for exchange is a major determinant of these pathways. Despite the important role of the placenta, very few studies have investigated the relation of sex and placental development as a putative explanation of sex-specific programming. Therefore, we here present an overview of the foetal and placental findings in our previously described mouse model (Pruis et al. 2014). To determine the impact of maternal diet and sex on foetal development, C57BL/6J dams were fed either a low-fat diet (10 kcal% from fat, 18 mg cholesterol kg−1) or Western-style high-fat diet (45 kcal% from fat, 196.5 mg cholesterol kg−1) 2 weeks pre-mating and during pregnancy. At gestational day 18.5, dams were killed under isoflurane anaesthesia and foetuses and placentas were characterized. Interestingly, male foetuses exposed to the Western diet during development weighed significantly more than those exposed to low-fat diet, while there was no difference in body length (P = 0.085, not significant) (Fig. 1a,b). In addition, also the placentas of male offspring exposed to Western diet were of a slightly, but significantly larger weight than low-fat diet-fed male offspring (Fig. 1c). In female offspring of these dams, none of these differences due to maternal diet were observed (Fig. 1a–c). Due to the set-up of the experiments, we had only 5 male and 5 female placenta samples for histological examination. However, we observed a distinct difference in placental histology in terms of the ratio between the labyrinth layer and the spongiotrophoblast layer in male offspring (Fig. 1d,e). As mentioned previously, the major determinant of intrauterine growth is the placental supply of nutrients to the foetus. The labyrinthine zone is the main site for nutrient transfer in the mouse placenta during late gestation, and its absolute volume and volume fraction are known to increase progressively during the second half of pregnancy. The estimated depth of the labyrinth layer for the male mice was 872 ± 161 μm, while the measurement for the females was 340 ± 48 μm. As placental layering was affected, mRNA levels of selected transporter genes were measured on gestational day 18.5 by TaqMan real-time PCR. We determined the expression of genes responsible for glucose transport (Glut1 (Slc2a1), Glut4 (Slc2a2), Glut12 (Slc2a12), cholesterol uptake (Ldlr, Scarb1), and cholesterol excretion (Abca1, Abcg1). Neither maternal diet nor sex significantly affected the examined transcription levels (Fig. 1f). In summary, we observed an increase in weight of the male foetuses and their placentas under Western diet conditions. Moreover, there was a distinct difference between the male and female placentas: The larger labyrinth diameter in male placentas compared with the female placentas might lead to a higher transport capacity of nutrients, which let us speculate that the male placenta supports transport of excess maternal nutrients to the male foetus. On the contrary, the female placenta might act as a barrier which limits nutrient supply to the female foetus. As a result, the male foetus shows increased growth under these conditions of maternal surplus nutrients, whereas the female foetus is protected. Our findings are supported by other mouse studies which report that placental changes to prenatal stimuli differ between both sexes, supporting the idea that placentas of female foetuses protect against prenatal insults (Cuffe et al. 2012, 2014, O'Connell et al. 2013). Our findings might contribute to a better understanding of the sex differences observed in many animal studies in the field of long-term metabolic programming. The authors have no conflicts of interest to declare. This research was performed within the framework of CTMM, the Center for Translational Molecular Medicine (www.ctmm.nl), project PREDICCt (grant 01C-104), and supported by the Dutch Heart Foundation, Dutch Diabetes Research Foundation and Dutch Kidney Foundation. TP is supported by the Netherlands Organization for Health Research and Development (ZonMW TOP grant 91211053).