Introduction: Encephalopathy of prematurity (EP) is a broad designation that encompasses the neurological pathologies that are common after preterm birth and are associated with neurological deficits in survivors. A common feature of EP is cerebral microhemorrhages. In adults, cerebral microhemorrhages are recognized to play important roles in neurodegenerative diseases but in neonates, the consequences of microhemorrhages are not fully understood. Here, we sought to understand the contributors to and consequences of cerebral microhemorrhages in the neonatal period and how mode of birth, vaginal or abdominal (Caesarian (C)-section), affected their incidence/severity. We report on a novel rat model of EP in which exposure to two pro-angiogenic stimuli in-utero predisposes to cerebral microhemorrhages during birth and are associated with long-term neurological deficit.
Methods: Pregnant Wistar rats were subjected to intrauterine ischemia (IUI) and maternal lipopolysaccharide (mLPS) at embryonic day (E) 19. Pups were born vaginally or abdominally at E21-22. Brains were evaluated for angiogenic markers, microhemorrhages, myelination, and axonal development. Neurological function (social, motor, and cognitive behavior) was assessed until 6 weeks.
Results: Intrauterine ischemia and inflammation (IUI+mLPS) weakened cerebral blood vessels by inducing angiogenesis. This response was characterized by altered mRNA (Vegf, Cd31, Mmp2, Mmp9, Timp1, Timp2) and protein (CD31, MMP2, MMP9) levels of angiogenic markers, increased in situ proteolytic activity of metalloproteinases, and reduced collagen IV immunoreactivity. This led to prominent hemorrhages, white matter damage, axonopathy, and accompanying behavioral deficits in injured pups after vaginal delivery. In pups exposed to the same prenatal insults of IUI+mLPS but delivered via C-section, hemorrhages were minimal, neurological function was similar to controls, and myelination and axonal development were significantly better persevered.
Conclusions: Intrauterine pro-angiogenic stimuli (IUI+mLPS) predisposed to vascular fragility, led to cerebral microhemorrhages, and were associated with long-term deficit. Strikingly, these outcomes were avoided if injured pups were delivered via C-section.
Patient Care: This work demonstrates the devastating role that brain microhemorrhages play in the overall pathology of neonatal brain function. This work has shown experimentally that the grave aftereffects of the combined prenatal insults can be significantly ameliorated if microhemorrhages are avoided, for example, by C-section.
Learning Objectives: At the conclusion of this activity, participants should be able:
To describe the long-term consequences of cerebral microhemorrhages in the neonatal period.
To recognize that reducing hemorrhage incidence and severity might lead to better neurological outcome in premature infants.