Neural stem cells persist after embryonic development in the subventricular zone (SVZ) niche and produce new neural cells during postnatal life; ependymal cells are a key component associated with this neurogenic niche. In the animal model of human hydrocephalus, the hyh mouse, the ependyma of the lateral ventricles is progressively lost during late embryonic and early postnatal life and disappears from most of the ventricular surface throughout its life span. To determine the potential consequences of this loss on the SVZ, we characterized the abnormalities in this neurogenic niche in hyh mice. There was overall disorganization and a marked reduction of proliferative cells in the SVZ of both newborn and adult hyh hydrocephalic mice in vivo; neuroblasts were displaced to the ventricular surface, and their migration through the rostral migratory stream was reduced. The numbers of resident neural progenitor cells in hyh mice were also markedly reduced, but they were capable of proliferating, forming neurospheres, and differentiating into neurons and glia in vitro in a manner indistinguishable from that of wild-type progenitor cells. These findings suggest that the reduction of proliferative activity observed in vivo is not caused by a cell autonomous defect of SVZ progenitors but is a consequence of a reduced number of these cells. Furthermore, the overall tissue disorganization of the SVZ and displacement of neuroblasts imply alterations in the neurogenic niche of postnatal hyh mice.
A heterogeneous population of ependymal cells lines the brain ventricles. The evidence about the origin and birth dates of these cell populations is scarce. Furthermore, the possibility that mature ependymal cells are born (ependymogenesis) or self-renewed (ependymal proliferation) postnatally is controversial. The present study was designed to investigate both phenomena in wild-type (wt) and hydrocephalic α-SNAP mutant (hyh) mice at different postnatal stages. In wt mice, proliferating cells in the ventricular zone (VZ) were only found in two distinct regions: the dorsal walls of the third ventricle and Sylvian aqueduct (SA). Most proliferating cells were monociliated and nestin+, likely corresponding to radial glial cells. Postnatal cumulative BrdU-labeling showed that most daughter cells remained in the VZ of both regions and they lost nestin-immunoreactivity. Furthermore, some labeled cells became multiciliated and GLUT-1+, indicating they were ependymal cells born postnatally. Postnatal pulse BrdU-labeling and Ki-67 immunostaining further demonstrated the presence of cycling multiciliated ependymal cells. In hydrocephalic mutants, the dorsal walls of the third ventricle and SA expanded enormously and showed neither ependymal disruption nor ventriculostomies. This phenomenon was sustained by an increased ependymogenesis. Consequently, in addition to the physical and geometrical mechanisms traditionally explaining ventricular enlargement in fetal-onset hydrocephalus, we propose that postnatal ependymogenesis could also play a role. Furthermore, as generation of new ependymal cells during postnatal stages was observed in distinct regions of the ventricular walls, such as the roof of the third ventricle, it may be a key mechanism involved in the development of human type 1 interhemispheric cysts.
Germinal matrix hemorrhages (GMH) and the consequent posthemorrhagic hydrocephalus (PHH) are among the most common and severe neurological complications of preterm birth that require lifelong complex neurosurgical care. GMH and PHH provoke disruption of neuroepithelium/ependyma development, a key structure implicated in brain development and homeostasis. Neuroepithelial/ependymal damage causes lifelong cognitive and motor deficits; however, no therapy is directed to recover the damaged ependyma. This study is aimed to test the possibilities of ependymal repair in GMH/PHH using neural stem cells (NSCs) or ependymal progenitors (EpPs). Thus, it sets the basis for a therapeutic approach to treating ependymal damage and preventing brain developmental deficits. GMH/PHH was induced in 4-day-old mice using different experimental procedures involving collagenase, blood, or blood serum injections. PHH severity was characterized using magnetic resonance, immunofluorescence, and protein expression quantification with mass spectrometry. Additionally, a newexvivoapproach using ventricular walls from mice developing moderate and severe GMH/PHH was generated to study ependymal restoration and wall regeneration after stem cell treatments. NSCs or EpPs obtained from newborn mice were transplanted in the explants, and pretreatment with mesenchymal stem cells (MSCs) was tested. Ependymal differentiation and the effect of MSC-conditioned microenvironment were investigated in both explants and primary cultures. In the animals, PHH severity was correlated with the extension of GMH, ependymal disruption, astroglial/microglial reactions, and ventriculomegaly. In the explants, the severity and extension of GMH hindered the survival rates of the transplanted NSCs/EpPs. In the explants affected with GMH, new multiciliated ependymal cells could be generated from transplanted NSCs and, more efficiently, from EpPs. Blood and TNFα negatively affected ciliogenesis in cells expressing Foxj1. Pretreatment with mesenchymal stem cells (MSC) improved the survival rates of EpPs and ependymal differentiation while reducing the edematous and inflammatory conditions in the explants. In conclusion, in GMH/PHH, the ependyma can be restored from either NSC or EpP transplantation, being EpPs in an MSC-conditioned microenvironment more efficient for this purpose. Modifying the neuroinflammatory microenvironment by MSC pretreatment positively influenced the success of the ependymal restoration.
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