Heparin binding epidermal growth factor-like growth factor (HB-EGF) is an angiogenic factor mediating radial migration of the developing forebrain, while vascular endothelial growth factor (VEGF) is known to influence rostral migratory stream in rodents. Cell migratory defects have been identified in animal models of hydrocephalus; however, the relationship between HB-EGF and hydrocephalus is unclear. We show that mice overexpressing human HB-EGF with β-galactosidase reporter exhibit an elevated VEGF, localization of β-galactosidase outside the subventricular zone (SVZ), subarachnoid hemorrhage, and ventriculomegaly. In Wistar polycystic kidney rats with hydrocephalus, alteration of migratory trajectory is detected. Furthermore, VEGF infusions into the rats result in ventriculomegaly with an increase of SVZ neuroblast in rostral migratory stream, whereas VEGF ligand inhibition prevents it. Our results support the idea that excess HB-EGF leads to a significant elevation of VEGF and ventricular dilatation. These data suggest a potential pathophysiological mechanism that elevated HB-EGF can elicit VEGF induction and hydrocephalus.

Hydrocephalus, characterized by dilatation of the cerebral ventricles due to excessive accumulation of cerebrospinal fluid (CSF), is classified into congenital and acquired hydrocephalus1. It can develop as a complication of subarachnoid hemorrhage (SAH)2, which is often reported as post-hemorrhagic hydrocephalus (PHH)3. The PHH has several types, namely, hydrocephalus following SAH, intraventricular hemorrhage (IVH), and germinal matrix hemorrhage (GMH)3,4. Ages of patients with hydrocephalus encompass a wide spectrum: fetal to adult onset. Neural and non-neural cells including vascular endothelial cells are affected by hydrocephalus, especially, with elevated intracranial pressure5.

Heparin binding epidermal growth factor-like growth factor (HB-EGF) is an angiogenic growth factor of two distinct forms: membrane-bound and soluble HB-EGF. HB-EGF is localized in the ventricular zone (E13) and cortical layers (E16) during development6. In pathological conditions, vascular endothelial cell7, wound fluid8 and blood cell such as monocyte, macrophage, and platelet are known to release HB-EGF. In cerebral blood vessels prior to vasoconstriction, active HB-EGF is produced through phosphorylation of its receptor, epidermal growth factor receptor (EGFR) via enzymatic cleavage of the membrane-bound precursor HB-EGF9. The soluble HB-EGF is shown to mediate vasospastic response in parenchymal vessels. In SAH associated with intracranial aneurysm, rupture of the aneurysm evokes blood into the subarachnoid space. Coagulation of such subarachnoid blood activates platelets, which release growth factors in the wall of the vessels10. While HB-EGF plays a causal role in vasoconstriction of an animal model with SAH9, whether excess HB-EGF is involved in the pathogenesis of hydrocephalus is unknown.

HB-EGF has been implicated in migration of the forebrain cells. During neural development, cell migration allows precursors to move towards the destined location11,12. Radial migration, a mechanism that young neurons use during corticogenesis ceases after birth12. The rostral migratory stream (RMS), a specialized route of cell movement reported in adult rodents is tangential migration from subventricular zone (SVZ) to the olfactory bulb and continues during adulthood13,14. The SVZ, also called as subependyma is the germinal region in the adult brain with a heterogeneous cytoarchitecture contacting cerebrospinal fluid (CSF)15,16. The subependyma accounts for neurogenesis and migration of neuroblast13,14. In the prenatal forebrain, it has been suggested that developmental changes in HB-EGF regulate the cell migration by a chemoattractive mechanism6. Cells of ventricular explants expressing EGFR have been shown to migrate towards the soluble HB-EGF6. HB-EGF is also shown to induce vascular endothelial growth factor (VEGF)18. Consistent with this, an anti-HB-EGF monoclonal antibody, Y-142, is exhibited to inhibit VEGF protein production in the supernatant of cell culture more effectively than a VEGF inhibitor, bevacizumab19. Using VEGFR1 knockout mice, it has been proposed that the proper cell migration of the postnatal forebrain depends on endogenous VEGF signaling20. In prenatal impairments of radial migration, hydrocephalus is reported postnatally17 but it is yet unclear whether hydrocephalus is caused by the defective postnatal migration of neuroblasts or by other factors. While involvement of growth factors in neural migration of the forebrain is known, HB-EGF mediated hydrocephalus, particularly, in the adult brain has not been reported.

Here we hypothesize that HB-EGF affects VEGF signaling and the fluid circulation in the cerebral ventricles. In testing this hypothesis we demonstrate whether exogenous HB-EGF induces VEGF. Using mice expressing human HB-EGF, we determine the localization of HB-EGF in the postnatal brain with and without hydrocephalus. By infusing VEGF, VEGFR2 blocker, and co-infusion with VEGF ligand inhibitor in rats, we demonstrate whether VEGF receptor or ligand inhibition changes neural progenitors of the SVZ and ventriculomegaly in rats. Using a ciliopathy model with hydrocephalus independent of HB-EGF, we further test whether cell migration in either tangential or radial orientation is altered in hydrocephalus. We predict that the regulation of ventricular size and neuroblast migration in this setting and others is potentially mediated by the actions of HB-EGF to impact the signal transduction network that regulates relocation of the SVZ cells in hydrocephalus.