Apoptotic neurons induce proliferative responses of progenitor cells in the postnatal neocortex

• Published in: Experimental neurology 2015-11, Vol.273, p.126-137
• Main Authors: Petrenko, Volodymyr, Mihhailova, Jevgenia, Salmon, Patrick, Kiss, Jozsef Z.
• Format: Article
• Language: English
• Subjects: Animals; Animals, Newborn; Apoptosis; Apoptosis - drug effects; Apoptosis - genetics; Apoptosis - physiology; Brain Injuries - pathology; Brain Injuries - physiopathology; Caspase 3 - metabolism; Cell Proliferation - drug effects; Cell Proliferation - physiology; Cerebral Cortex - cytology; Cerebral Cortex - growth & development; Developing brain; Diphtheria toxin; Diphtheria Toxin - pharmacology; Eye Proteins - genetics; Eye Proteins - metabolism; Heparin-binding EGF-like Growth Factor - genetics; Heparin-binding EGF-like Growth Factor - metabolism; Homeobox Protein SIX3; Homeodomain Proteins - genetics; Homeodomain Proteins - metabolism; In Vitro Techniques; Mice; Mice, Inbred C57BL; Mice, Transgenic; Nerve Net - drug effects; Nerve Net - physiology; Nerve Tissue Proteins - genetics; Nerve Tissue Proteins - metabolism; Neural progenitors; Neural Stem Cells - physiology; Neurogenesis; Neuroglia - drug effects; Neuroglia - physiology; Neurons - physiology; Neurons - ultrastructure; Rats; Rats, Wistar; Time Factors
• ISSN: 0014-4886; 1090-2430
• DOI: 10.1016/j.expneurol.2015.08.010

Apoptotic cell death is the leading cause of neuronal loss after neonatal brain injury. Little is known about the intrinsic capacity of the immature cerebral cortex for replacing dead cells. Here we test the hypothesis that neuronal apoptosis is able to trigger compensatory proliferation in surrounding cells. In order to establish a “pure” apoptotic cell death model and to avoid the confounding effects of broken blood–brain barrier and inflammatory reactions, we used a diphtheria toxin (DT) and diphtheria toxin receptor (DTR) system to induce ablation of layer IV neurons in the rodent somatosensory cortex during the early postnatal period. We found that DT-triggered apoptosis is a slowly progressing event lasting about for 7days. While dying cells expressed the morphological features of apoptosis, we could not detect immunoreactivity for activated caspase-3 in these cells. Microglia activation and proliferation represented the earliest cellular responses to apoptotic cell death. In addition, we found that induced apoptosis triggered a massive proliferation of undifferentiated progenitor cell pool including Sox2 as well as NG2 cells. The default differentiation pattern of proliferating progenitors appears to be the glial phenotype; we could not find evidence for newly generated neurons in response to apoptotic neuronal death. These results suggest that mitotically active progenitor populations are intrinsically capable to contribute to the repair process of injured cortical tissue and may represent a potential target for neuronal replacement strategies. [Display omitted] •New, highly reproducible models of perinatal neuronal ablation are developed.•Apoptotic neurons induce early glial responses in the developing brain.•Induced apoptosis triggers proliferation of Sox2 and NG2 progenitor populations.•Lack of compensatory neurogenesis after neuronal injury in the developing cortex