Functional genomic approaches to delineate preterm birth and its regulation of placental transporter proteins

Abstract

Preterm birth (PTB) affects 12.7% of all pregnancies in the US and causes significant fetal and neonatal morbidity and mortality. Greater than 85% of PTBs (< 28 weeks gestation) have evidence of localized inflammation. Current efforts to prevent prematurity have met with little success and progress to identify effective new therapeutic agents has been modest. This dissertation is aimed at improving the current understanding of the molecular pathways underlying PTB and the effects of PTB and inflammation on drug transport and metabolism. Chapter 1 describes concepts and current understanding of preterm birth and the pharmacological challenges to its prevention. The first part of this chapter includes a discussion of the clinical issues and mechanistic research in PTB and genomic approaches to understand its pathophysiology. The second part focuses on placental transporters and their regulation during pregnancy and disease. A difficult challenge in identifying the mechanisms that control labor has been developing tools for examining whole-genome expression profiles in the context of known biology. Chapter 2 presents a novel methodology in gene array profiling used to extract relevant information from gene networks to elucidate the mechanisms of myometrial quiescence and activation. In Chapter 3, this approach was exercised in human myometrial tissue from term and preterm pregnancies. Results indicate that labor is characterized by muscle contraction, cell adhesion and remodeling gene sets. The initiation of term labor involves proteins mapped to inflammatory-related processes while preterm labor is triggered by multiple regulatory pathways. Chapter 4 addresses the involvement of key drug transporters in pregnancy- and inflammation-mediated changes in drug disposition and fetal susceptibility. Changes in transporter expression were analyzed by real-time PCR and immunoblotting techniques on placentas of women with term, preterm and inflammation-associated preterm pregnancies. MDR1 and BCRP were up-regulated in early gestation and amplified with inflammation but these changes were not mediated by nuclear hormone receptors, regulatory cytokines, or gram-negative bacterial components. In conclusion, inflammatory responses initiate preterm labor and result in an inherent up-regulation of MDR1 and BCRP to protect the fetus from endogenous stress factors. Finally, in Chapter 5, future directions to extend this research are presented.