J Neurol Surg A Cent Eur Neurosurg 2015; 76 - P058
DOI: 10.1055/s-0035-1564550

Phenotypical Characterization of Microglia in the Subventricular Zone after Neonatal Hypoxia-ischemia in Rat

U. Fisch 1, 2, C. Brégère 2, L. Chicha 2, R. Guzman 1, 2
  • 1Departement of Neurosurgery, University Hospital Basel, Basel, Switzerland
  • 2Brain Ischemia and Regeneration, Department of Biomedicine, University Basel, Basel, Switzerland

Aims: Currently, the role of microglia in the context of central nervous system (CNS) regeneration is not fully elucidated, mainly because microglia display extensive heterogeneity of phenotype after CNS damage.1 Recent studies in rat indicate that microglia accumulate in the subventricular zone (SVZ) and support neurogenesis in healthy newborn and after adult ischemia.2 3 We aim to characterize the temporal profile of SVZ microglial phenotype after hypoxic-ischemic (HI) brain injury in rat neonates. We hypothesize that SVZ microglia adopt a pro-neurogenic phenotype, which might contribute to CNS regeneration following HI. Methods: Postnatal day (P) 7 Sprague Dawley rats were subjected to right-sided HI and sacrificed at P10, P20 or P40. Sham-operated animals served as controls. Brain sections of 3 animals per group and time-point were stained for microglia (Iba1, CD68), neuroblast (DCX) and proliferating cells (BrdU) followed by cell number quantification. In parallel, rtPCR of inflammatory pathways in SVZ microglia were performed following laser-capture microdissection (LCM). Results: In HI animals the right-sided HI SVZ demonstrated a robust increase in size from P10 to P40 (mean 0.36 vs. 3. 6mm2), whereas the contralateral SVZ decreased similar to sham animals. In sham animals, the SVZ decreased from P10 to P40 (0.4 vs. 0.24 mm2). The total number of Iba1 cells in the HI SVZ increased while it decreased in the contralateral SVZ and in sham animals (mean at P40: 291 vs. 123 vs. 140) . However, if adjusted to the SVZ area, Iba1 cell density in the HI SVZ decreased from P10 to P40 (1,254/mm2 vs. 219/mm2, p = 0.0004). The CD68/Iba1 ratio at P10 was equal in the HI, contralateral and sham SVZ. Thereafter it remained high in HI SVZ while it decreased in the other groups (mean ratio at P40: 0.2 vs. 0.06 vs 0.06). Conclusions: Our data are in accordance with the current knowledge of reactive neurogenesis in the SVZ after an injury. Our data support the potentially important role of microglia within the HI SVZ with an increase in total cell number and elevated CD68/Iba1 ratio in contrast to the contralateral and control SVZ. Further stainings are ongoing to confirm these observations. In addition, the gene expression profile of SVZ microglia should lead to further conclusions on differences in cellular function.

References

References

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2 Shigemoto-Mogami Y, Hoshikawa K, Goldman JE, Sekino Y, Sato K. Microglia enhance neurogenesis and oligodendrogenesis in the early postnatal subventricular zone. J Neurosci 2014;34(6):2231–2243

3 Thored P, Heldmann U, Gomes-Leal W, et al. Long-term accumulation of microglia with proneurogenic phenotype concomitant with persistent neurogenesis in adult subventricular zone after stroke. Glia 2009;57(8):835–849