Mature astrocytes regain stem cell potential and give rise to neurons

Abstract

Mature astrocytes and neural stem cells share several phenotypic and functional features. From their resemblance, the idea was born that mature astrocytes might in return act as stem cells giving rise to neurons. Mature astrocytes have been shown to re-enter the cell cycle when exposed to defined stimuli. Astrocytes are also able to generate neurons, at least after genetic reprogramming. Moreover, astrocytic cells isolated from injured brains generated multipotent and self-renewing neurospheres. However, the sequential processes leading to the conversion of astrocytes to stem cells are highly complex and difficult to study at single cell resolution. Therefore a clean cell system would be desirable to show the direct generation of neurons from astrocyte-derived stem cells without genetic reprogramming.We provide an in vitro model for the de-differentiation of astrocytes to neural stem cells by the exposure to defined growth factors. Astrocytes were generated from embryonic stem cell derived neural stem cells. They expressed markers of mature astrocytes like GFAP, Aqp4, and GLT-1 and reacted to inflammatory stimulation, a function which is typically found only in fully differentiated cells. By the addition of growth factors, they re-entered the cell cycle, upregulated markers of neural stem cells like nestin and RC2, and lost their responsiveness to inflammatory cytokines. The dedifferentiated cells were bipotent, giving rise to astrocytes and neurons.Thus, we found a de-differentiation of astrocytes without genetic reprogramming in a clean in vitro system and showed that these de-differentiated cells are neurogenic stem cells. The homogeneity of the cell populations in this system strongly facilitates the search for mechanisms and signaling pathways involved in de-differentiation.