Brain injury activates microglia that induce neural stem cell proliferation ex vivo and promote differentiation of neurosphere-derived cells into neurons and oligodendrocytes

doi:10.1016/j.neuroscience.2010.09.045

Neuroscience

Volume 171, Issue 4, 29 December 2010, Pages 1386-1396

https://doi.org/10.1016/j.neuroscience.2010.09.045 Get rights and content

Abstract

Brain damage, such as ischemic stroke, enhances proliferation of neural stem/progenitor cells (NSPCs) in the subventricular zone (SVZ). To date, no reliable in vitro systems, which can be used to unravel the potential mechanisms underlying this lesion-induced effect, have been established. Here, we developed an ex vivo method to investigate how the proliferation of NSPCs changes over time after experimental stroke or excitotoxic striatal lesion in the adult rat brain by studying the effects of microglial cells derived from an injured brain on NSPCs. We isolated NSPCs from the SVZ of brains with lesions and analyzed their growth and differentiation when cultured as neurospheres. We found that NSPCs isolated from the brains 1–2 weeks following injury consistently generated more and larger neurospheres than those harvested from naive brains. We attributed these effects to the presence of microglial cells in NSPC cultures that originated from injured brains. We suggest that the effects are due to released factors because we observed increased proliferation of NSPCs isolated from non-injured brains when they were exposed to conditioned medium from cultures containing microglial cells derived from injured brains. Furthermore, we found that NSPCs derived from injured brains were more likely to differentiate into neurons and oligodendrocytes than astrocytes. Our ex vivo system reliably mimics what is observed in vivo following brain injury. It constitutes a powerful tool that could be used to identify factors that promote NSPC proliferation and differentiation in response to injury-induced activation of microglial cells, by using tools such as proteomics and gene array technology.

Research Highlights

▶Neurospheres are larger and more numerous when derived and cultured from an injured brain, SVZ, (ischemic stroke and excitotoxic brain injury). ▶A proliferative population of microglial cells are retrieved from injured neurosphere cultures that exert a robust proliferative effect on neurospheres. ▶Microglial cultures from injured brains can be used as an ex vivo system to study proliferation of neural stem/progenitor cells.

Section snippets

Animals

We used male Sprague–Dawley rats (B&K Stockholm, Sweden), aged 10–12 weeks at the start of the experiment. All experiments were approved by the Malmö-Lund Ethical Committee. Animals had free access to food and water and were housed under a 12-h light/12-h dark cycle. We used a minimal number of animals and efforts were done to avoid suffering.

Experimental model of stroke

We induced experimental stroke, focal brain ischemia, by transient middle cerebral artery occlusion (tMCAO) using an established protocol (Memezawa et

Distinct microgliosis in the striatum of rats at one and four weeks following brain injury

To develop an ex vivo system to study the effect of microglial cells on NSPCs, we activated microglial cells by inducing experimental stroke (tMCAO) and excitotoxic brain injury in rats. We first examined striatal microgliosis following brain injury using immunohistochemistry for the microglial marker CD11b at 1 and 4 weeks post-injury. At both time points, the microglial hyperplasia appeared identical at the cellular level with hypertrophic microglial cells that exhibited characteristic bushy

Discussion

We have developed an ex vivo model to study activated microglia-induced proliferation of NSPCs following brain injury in vivo. We found that microglia activated because of brain injury influenced NSPC proliferation. Specifically, we demonstrated an increase in cell proliferation in neurospheres generated from NSPCs isolated from the ipsilateral SVZ tissue following both ischemic stroke and excitotoxin-induced lesion. Enhanced neurogenesis has been suggested to occur in stroke patients (Jin et

Conclusion

We have generated an ex vivo model to study the response of NSPCs to microglial cells obtained from injured brains. Our data imply that microglial cells present in acutely damaged SVZ/striatum release factors that initially promote proliferation. We also show that NSPCs derived from an injured brain differentiate to a higher extent into neurons and oligodendrocytes. These results suggest that a microglial change might underlie the increased cell proliferation observed in the SVZ and the

Acknowledgments

This work was supported by the Swedish Research Council (including NeuroFortis, Strong Research Environment on Neurodegeneration and Brain Repair), EU 6th framework program PROMEMORIA, Crafoord Foundation, Gyllenstiernska Krapperup foundation, Royal Physiographic Society, Swedish Stroke Association, Bergvall Foundation, Kock Foundation, Lars Hierta Foundation, Tore Nilsson Foundation and Segerfalk Foundation. We also thank C. Sjölund and B. Haraldsson for providing technical assistance and

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Regeneration, Repair, and Developmental NeuroscienceResearch PaperBrain injury activates microglia that induce neural stem cell proliferation ex vivo and promote differentiation of neurosphere-derived cells into neurons and oligodendrocytes

Abstract

Research Highlights

Section snippets

Animals

Experimental model of stroke

Distinct microgliosis in the striatum of rats at one and four weeks following brain injury

Discussion

Conclusion

Acknowledgments

Brain Res

Neurobiol Dis

Mol Cell Neurosci

Neuron

Prog Neurobiol

Exp Neurol

J Neurol Sci

Exp Neurol

Trends Neurosci

J Neurosci Methods

Neuroscience

Exp Neurol

The endocannabinoid system drives neural progenitor proliferation

FASEB J

Neuronal replacement from endogenous precursors in the adult brain after stroke

Nat Med

Stem cells for ischemic brain injury: a critical review

J Comp Neurol

In vitro neuronal and glial differentiation from embryonic or adult neural precursor cells are differently affected by chronic or acute activation of microglia

Glia

Forebrain ependymal cells are notch-dependent and generate neuroblasts and astrocytes after stroke

Nat Neurosci

Cultured rat microglial cells synthesize the endocannabinoid 2-arachidonylglycerol, which increases proliferation via a CB2 receptor-dependent mechanism

Mol Pharmacol

Human neuroblasts migrate to the olfactory bulb via a lateral ventricular extension

Science

Class III beta-tubulin is constitutively coexpressed with glial fibrillary acidic protein and nestin in midgestational human fetal astrocytes: implications for phenotypic identity

J Neuropathol Exp Neurol

Quinolinic acid-induced inflammation in the striatum does not impair the survival of neural allografts in the rat

Eur J Neurosci

Neurogenesis in the adult human hippocampus

Nat Med

Involvement of microglia-neuron interactions in the tumor necrosis factor-alpha release, microglial activation, and neurodegeneration induced by trimethyltin

J Neurosci Res

Differential activation of microglia in neurogenic versus non-neurogenic regions of the forebrain

Glia

Focal cerebral ischemia induces increased myelin basic protein and growth-associated protein-43 gene transcription in peri-infarct areas in the rat brain

Exp Brain Res

Microglia as a source and target of cytokines

Glia

Microglia: active sensor and versatile effector cells in the normal and pathologic brain

Nat Neurosci

Regeneration, Repair, and Developmental Neuroscience
Research Paper
Brain injury activates microglia that induce neural stem cell proliferation ex vivo and promote differentiation of neurosphere-derived cells into neurons and oligodendrocytes