Calcifying Nanoparticles As Novel Etiologic Agents Of Idiopathic Preterm Birth And Preterm Premature Rupture Of The Membranes

Preterm birth (PTB) is a leading cause of neonatal morbidity and mortality. In many cases, preterm birth is preceded by preterm premature rupture of the membranes (PPROM) without any identifiable cause. Pathological calcification, i.e. the deposition of hydroxyapatite (HA) in non-skeletal tissue, has been implicated in degenerative diseases of soft tissue, such as atherosclerosis. Multiple pathogenic mechanisms have been described, including the aberrant aggregation of HA into calcifying nanoparticles (CNPs) and the HA-induced differentiation of mesenchymal cells into osteoblasts in a process called ectopic osteogenesis. The objective of this thesis was to explore the possibility that CNPs form in human amniotic fluid (AF), deposit in fetal membranes, and are mechanistically linked to pathogenic pathways leading to PPROM and PTB. In a cross sectional study of reproductive tissues collected from women with singleton preterm deliveries, we demonstrate that CNP deposition is more frequently observed in women with PTB and PPROM compared to intact membranes at clinical presentation. Immunohistochemical analysis revealed markers of ectopic osteogenesis in fetal membranes affected by HA deposition. In a prospective study of AF from women presenting with preterm labor or PPROM who underwent amniocentesis to rule-out infection, we discovered decreased levels of fetuin-A, an endogenous inhibitor of biomineralization, as well as other essential AF proteins, in women with PPROM in the absence of infection. In a long-term culture experiment, we observed aggregation of CNPs in the AF of women with PTB. Furthermore, these AF-derived CNPs induced pathological structural and functional effects on term amniochorion explants. In conclusion, the results of this thesis demonstrate that disruption of the protein-mineral balance of AF leads to CNP formation and deposition in fetal membranes, which may play a pathogenic role in PPROM and idiopathic preterm birth