# Reversal of Postnatal Brain Astrocytes and Ependymal Cells towards a Progenitor Phenotype in Culture

## TL;DR

This study shows that brain astrocytes and ependymal cells can be reversed to a progenitor-like state in culture, offering a platform to study the molecular mechanisms behind this reversal.

## Contribution

The study establishes a controlled platform to investigate the reversal of mature brain cells to progenitor-like states.

## Key findings

- Inhibiting GSK3 and TGFβ pathways enables astrocytes to become Sox2-expressing, mitotic cells that generate oligodendrocytes.
- Ependymal cells can be induced to enter mitosis through stress or growth factors like FGF2 and EGF.
- The reversal of astrocytes does not fully restore a true neural stem cell identity, as indicated by a lack of neurogenic activity.

## Abstract

Astrocytes and ependymal cells have been reported to be able to switch from a mature cell identity towards that of a neural stem/progenitor cell. Astrocytes are widely scattered in the brain where they exert multiple functions and are routinely targeted for in vitro and in vivo reprogramming. Ependymal cells serve more specialized functions, lining the ventricles and the central canal, and are multiciliated, epithelial-like cells that, in the spinal cord, act as bi-potent progenitors in response to injury. Here, we isolate or generate ependymal cells and post-mitotic astrocytes, respectively, from the lateral ventricles of the mouse brain and we investigate their capacity to reverse towards a progenitor-like identity in culture. Inhibition of the GSK3 and TGFβ pathways facilitates the switch of mature astrocytes to Sox2-expressing, mitotic cells that generate oligodendrocytes. Although this medium allows for the expansion of quiescent NSCs, isolated from live rats by “milking of the brain”, it does not fully reverse astrocytes towards the bona fide NSC identity; this is a failure correlated with a concomitant lack of neurogenic activity. Ependymal cells could be induced to enter mitosis either via exposure to neuraminidase-dependent stress or by culturing them in the presence of FGF2 and EGF. Overall, our data confirm that astrocytes and ependymal cells retain a high capacity to reverse to a progenitor identity and set up a simple and highly controlled platform for the elucidation of the molecular mechanisms that regulate this reversal.