Placental phenotyping for a better approach to clinical therapies

BACKGROUND. Pregnancy pathologies with abnormal placental phenotype, namely Intrauterine Growth Restriction (IUGR) and Preeclampsia (PE), are well recognized to have a greater risk of neonatal mortality and morbidity and of cardiovascular and metabolic diseases in later life. Intrauterine growth, which mainly depends on placental functionality, leads to the delivery (both at term and pre-term) of infants with sizes that may be normal or small for the infant genetic potential, leading to individuals with different neonatal nutritional and pharmacological needs. Nevertheless, the distinction between these two infant phenotypes is still difficult. A well-defined placental phenotype may help to optimize neonatal protocols. Abnormalities of placental morphology have been reported in IUGR and severe PE, as well as defects in the oxygenation of the feto-placental unit. Moreover, several in vitro and in vivo studies also conducted by our group clearly showed changes in placental nutrient and micronutrient transport capacity. We also recently demonstrated an increased mitochondrial (mt) DNA content in both IUGR placentas and maternal blood at delivery vs controls. We are currently investigating mt functionality in IUGR and PE placentas, for better understanding if possible mt abnormalities may represent specific oxidative markers of these pathologies. Here we report our recent results on placental cells oxygen (O2) consumption and Respiratory Chain Complexes (RCC) gene expression in pregnancies complicated by IUGR or PE compared to normal pregnancies, to assess the respiratory phenotype of the placenta related to the pregnancy outcome. METHODS. Cytotrophoblast cells were isolated from 16 placentas (8 IUGR, 3 PE alone, 5 Controls -C-) of non-smoking women at elective caesarean section, and characterized by cytofluorimetry using cytokeratin-7 and anti-vimentin antibodies. mRNA levels of NDUFA9 (CI), ETFDH (CII), UQCRC1 (CIII) and COX4I1 (CIV) were quantified by Real Time (RT) PCR. O2 consumption, accounting for the mt functionality, was evaluated by High Resolution Respirometry (HRR), by administration of substrates and inhibitors of different RCC, thus allowing the measure of the global cell and of single complexes activity. Data were normalized by mtDNA content. RESULTS IUGR presented significantly lower CIII and CIV mRNA levels vs C. On the contrary, both raw and normalized data in IUGR with or without PE (but not in PE without IUGR) showed significantly higher O2 consumption levels of RCC (altogether and singularly) vs C, particularly for CIV, suggesting a compensatory mechanism to their lower expression. These results shed new light into placental oxygenation in IUGR, suggesting that increased placental oxygen utilization may represent a limiting step in fetal growth restriction. In conclusion, a detailed placental phenotyping may aid clinicians in the identification of babies at risk of short- and long-term consequences. This may help neonatologist in adopting early and more specific neonatal nutrition treatments or therapies by diversifying infants with small for gestational age size to infants with small size which did not reach their growth potential.