Neurobiol Dis. 2015 Feb;74:229-39. doi: 10.1016/j.nbd.2014.11.016.

Neurogenesis is enhanced by stroke in multiple new stem cell niches along the ventricular system at sites of high BBB permeability.

Ruihe Lin 1, Jingli Cai 1, Cody Nathan 1, Xiaotao Wei 1, Stephanie Schleidt 1, Robert Rosenwasser 2, Lorraine Iacovitti 1,

1 The Joseph and Marie Field Cerebrovascular Research Laboratory at Jefferson, Farber Institute of Neurosciences, Department of Neuroscience, Jefferson Medical College, Thomas Jefferson University, Philadelphia, PA 19107, USA

2 The Joseph and Marie Field Cerebrovascular Research Laboratory at Jefferson, Department of Neurological Surgery, Jefferson Medical College, Thomas Jefferson University, Philadelphia, PA 19107, USA

 

Abstract

Objectives: Neural stem cells (NSCs) critical for the continued production of new neurons and glia are sequestered in distinct stem cell niches of the adult brain. Until recently, only the subventricular zone (SVZ) of the anterolateral ventricle and the subgranular zone (SGZ) of the hippocampus have been recognized as adult stem cell niches (15). Work from our laboratory further indicated that midline ventricular structures known as circumventricular organs (CVOs) also serve as adult neural stem cell (NSC) niches (6, 7). Therefore, in this study, we examined stem cell niches along the entire extent of the ventricular system in the adult rat brain to investigate whether ischemic stroke injury (MCAO) or sustained intraventricular infusion of the mitogen bFGF would trigger an up-regulation in NSC proliferation, neurogenesis and gliogenesis.

Methods: Adult Rats and mice were subjected either to focal ischemic stroke (MCAO) or intraventricular bFGF infusion in the experiments. BrdU administrations were carried out simultaneously. Brain tissue was collected on day 4 and 14 post-surgery, and then processed for immunostaining of multiple markers. Sodium-fluorescein uptake assay was also performed to assess the blood brain barrier (BBB) integrity after MCAO.

Results: In these studies, we found that by 4 days following MCAO, most CVO niches exhibited a significant increase in the number of BrdU-labeled cells as compared to controls. This proliferative effect was sustained and enhanced over time (14 days after stroke). Similar results were observed when rats were intraventricularly infused with the stem cell mitogen bFGF for 14 days. We also observed cell proliferation at novel sites along the third and fourth ventricle walls. As in the SVZ and SGZ, many BrdU+ cells in the CVOs and other ventricular niches co-expressed the NSC markers GFAP, nestin and Sox2. Moreover, BrdU-labeled NSCs in all of these sites differentiated to express glial and neuronal markers. Importantly, after stroke, we further observed increased BBB leakage in all brain stem cell niches. These data indicate a positive correlation between stem cell proliferation and the degree of BBB leakiness in the adult brain, both of which are amplified after ischemic injury.

Conclusions: We conclude that CVOs, 3V and 4V are novel stem cell niches which have the capacity to respond to cues from various sources (blood, CSF) to enhance neurogenesis and gliogenesis. We further suggest that because of their leaky BBB, stem cell niches are well-positioned to respond to circulating injury-related cues which may be important for stem-cell mediated brain repair.

KEYWORDS: Blood brain barrier; CVO; Neural stem cell; Neurogenesis; Stroke

PMID: 25484283

 

Supplementary

Previous studies have established the subventricular (SVZ) and subgranular (SGZ) zones as sites of neurogenesis in the adult forebrain(15). Several years ago, our laboratory further showed that an additional series of adult stem cell niches called the CVOs exist along the ventricular midline (6, 7).

 

R fig1-2

 

In this study, we examined neurogenesis/gliogenesis in the SVZ and CVO sites. We found ischemic injury and bFGF infusion induces a sustained proliferation of NSCs in SVZ and CVO niches (Fig.1 & 2).

Our study further revealed the third and fourth ventricles are potential stem cell niches (Fig.3 & 4). These findings suggest that stem cell niches are present at multiple sites along the entire ventricular system, not only in the forebrain as once thought, and that stem cells in these niches are increased dramatically following injury or bFGF.

 

R fig3-4

Significantly, in all of stem cell niches, we found BrdU+ labeled Dcx+ neurons, Olig2+ oligodendrocytes and GFAP+nestin- astrocyte progenitors 14 days after MCAO injury and bFGF infusion(Fig.5 & 6).

 

R fig-6

Moreover, further disruption of BBB integrity and function following stroke resulted in greater spread of fluorescein at these sites (Fig.7), indicating a positive correlation between stem cell proliferation and the degree of BBB leakiness in the adult brain.

 

R fig7

Importance of the study: Our data indicate that stem cell niches are more extensive than once believed and exist at multiple sites along the entire ventricular system, consistent with the potential for widespread neurogenesis and gliogenesis in the adult brain, particularly after injury. These findings also raise the possibility that injury-induced factors in the circulating blood may leak through the porous BBB at all niche sites in the brain to regulate endogenous neurogenesis after stroke.

 

References:

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  7. L. B. Bennett, J. Cai, G. Enikolopov, L. Iacovitti, Heterotopically transplanted CVO neural stem cells generate neurons and migrate with SVZ cells in the adult mouse brain. Neurosci. Lett. 475, 1–6 (2010).

 

Acknowledgements: We gratefully acknowledge the generous support of NSF 1026669 to LI and the Joseph and Marie Field Foundation to Dr. Robert Rosenwasser and LI.

 

Contact:

Lorraine Iacovitti, PhD

Professor

The Joseph and Marie Field Cerebrovascular Research Laboratory at Jefferson

Department of Neuroscience

Farber Institute of Neurosciences

Jefferson Medical College

Thomas Jefferson University

Philadelphia, PA 19107, USA

Lorraine.iacovitti@jefferson.edu

 

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