Research reportHemoglobin-induced neuronal degeneration in the hippocampus after neonatal intraventricular hemorrhage

- Intraventricular injection of hemoglobin induces neuronal death in the hippocampus.
- Hippocampal volume is decreased bilaterally after neonatal intraventricular hemorrhage.
- Intraventricular injection of hemoglobin increases JNK activation in the hippocampus.
- Activated JNK is co-localized to hemoglobin receptor CD163 in the hippocampus.
- CD163 is expressed in neurons in the neonatal hippocampus after intraventricular hemoglobin injection.

Neuronal degeneration following neonatal intraventricular hemorrhage (IVH) is incompletely understood. Understanding the mechanisms of degeneration and cell loss may point toward specific treatments to limit injury. We evaluated the role of hemoglobin (Hb) in cell death after intraventricular injection in neonatal rats. Hb was injected into the right lateral ventricle of post-natal day 7 rats. Rats exposed to anesthesia were used for controls. The CA-1 region of the hippocampus was analyzed via immunohistochemistry, hematoxylin and eosin (H&E) staining, Fluoro-Jade C staining, Western blots, and double-labeling stains. Compared to controls, intraventricular injection of Hb decreased hippocampal volume (27% decrease; p<0.05), induced neuronal loss (31% loss; p<0.01), and increased neuronal degeneration (2.7 fold increase; p<0.01), which were all significantly reduced with the iron chelator, deferoxamine. Hb upregulated p-JNK (1.8 fold increase; p<0.05) and increased expression of the Hb/haptoglobin endocytotic receptor CD163 in neurons in vivo and in vitro (cultured cortical neurons). Hb induced expression of the CD163 receptor, which co-localized with p-JNK in hippocampal neurons, suggesting a potential pathway by which Hb enters the neuron to result in cell death. There were no differences in neuronal loss or degenerating neurons in Hb-injected animals that developed hydrocephalus versus those that did not. Intraventricular injection of Hb causes hippocampal neuronal degeneration and cell loss and increases brain p-JNK levels. p-JNK co-localized with the Hb/haptoglobin receptor CD163, suggesting a novel pathway by which Hb enters the neuron after IVH to result in cell death.