Impaired glymphatic transport in hypoxic-ischemic encephalopathy

Hypoxic-ischemic encephalopathy (HIE) is a major cause of neonatal brain injury. The glymphatic system aids in waste clearance via perivascular pathways and is crucial in maintaining brain functions. While studies have shown that diseases such as stroke and traumatic brain injury disrupt glymphatic function, the impact of HIE on this system remains largely unexplored. We utilized an HIE mouse model with dynamic contrast-enhanced MRI (DCE-MRI) to conduct both qualitative and quantitative assessment of glymphatic transports dysfunction in different brain regions. Fluorescent cerebrospinal fluid (CSF) tracers were used to investigate the effects of HIE on glymphatic system development. Mice brain sections were subjected to Aquaporin-4 (AQP4) immunohistochemical staining, allowing for detailed morphological assessment of AQP4 polarization in affected brain regions. HIE mice exhibited delayed glymphatic transport dynamics, with prolonged time-to-peak tracer enhancement and increased retention in olfactory bulb, basal forebrain, and hypothalamus regions. Quantitative kinetic analysis showed significant reductions in Kf (CSF-to-perivascular space transfer constants) and Ks (perivascular-to-parenchyma transfer constants), alongside elevated Vf (perivascular volume fractions) across cortical and subcortical structures. Fluorescent CSF tracer analysis indicates that HIE impaired glymphatic system maturation in neonatal mice. This impairment progressed to persistent glymphatic dysfunction. Histologically validated via immunofluorescence, HIE-induced astrocytic AQP4 mis-polarization directly correlates with glymphatic transport dysfunction, underscoring AQP4's critical role in glymphatic system integrity. Our multimodal imaging study combining DCE-MRI and CSF tracer analysis indicates that HIE can cause regional impairments of glymphatic function and adversely affect brain development.