Evidence of metabolic compartmentation in the bovine placenta and significance for the regulation of placental function and fetal growth in pregnancies bearing in vivo- or in vitro-produced embryos

Abstract

The concept of metabolic zonation in the liver proposes that opposing or complementary metabolic pathways are carried out within distinct regions of the liver lobule to maintain optimal metabolic homeostasis. As bovine placentomes differ in mass and shapes within the reproductive tract, which is even more pronounced in cloned-derived concepti, the aims of this study were to investigate the occurrence of metabolic zonation in the bovine placenta by placentome shape and size, and to compare placental functions between control and cloned concepti, which may relate to the abnormal conceptus growth after cloning. Bovine pregnancies established after superovulation/AI (n=4), in vitro fertilization (n=4) or cloning by nuclear transfer (n=6) were slaughtered on Day 225 of gestation. Placentomes were excised, weighed, measured, and classified by shape as types A, B, C, or D; cDNA from each placentome type/group was used for RT-qPCR analyses of 24 target gene products related to carbohydrate and lipid metabolism, placental function, IGF system and apoptosis. No differences in gene expression were detected between clones and controls. However, the gene expression pattern revealed differences in metabolic profile only between placentome types, with an increase in expression in type C in relation to type A placentomes, in special for IGF2 (5.8-fold) and IGF2r (1.6-fold), glucose transporters (1.2-fold), and fructogenesis (2.0- to 2.3-fold), suggesting a potential metabolic zonation in the bovine placenta. Morphological changes in the placenta of clones may influence placental function and metabolic compartmentalization, likely disturbing placental control on fetal growth and programming towards the end of pregnancy.