Nuclear and mitochondrial control of the apoptosis machinery regulates neural stem cell fate

Abstract

Mounting evidence supports the idea that conserved elements of apoptosis are also integral components of cell differentiation. Our studies were driven by the ambition to further characterize the molecular pathways underlying the role of the apoptosis machinery in neural stem cell (NSC) fate decision in vitro, and to identify potential checkpoints to improve neural fate as an alternative to cell death. We began by showing that under neural differentiation conditions, the proapoptotic protein p53 interacts with the histone H3 lysine 27-specific demethylase JMJD3, a master regulator of neurogenesis. JMJD3 was shown to stabilize p53, in an ADP ribosylation factor (ARF)-dependent manner. We also demonstrated that, throughout neurogenesis, JMJD3 directly demethylates p53 and induces its nuclear translocation, subsequently increasing neural fate. We next investigated whether mitochondrial apoptosis-associated events could also influence neural differentiation. Curiously, we showed that increased reactive oxigen species (ROS) production, mitochondrial membrane permeabilization, cytochrome c release, and mitophagy occured at early stages of NSC differentiation, without involving cell death per se. More importantly, we revealed that at early-stage NSC differentiation, p53 is translocated to mitochondria, to prevent differentiationinduced mitochondrial stress and enhance neuronal differentiation, through a mechanism partially dependent on manganese superoxide dismutase (MnSOD) stabilization. Finally, we evaluated whether the endogenous bile acid tauroursodeoxycholic acid (TUDCA), a well-known regulator of mitochondrial apoptosis, could also modulate NSC proliferation and differentiation potential. Interestingly, treatment of NSCs with TUDCA increased the NSC pool and astroglia-to-neuron conversion, by preventing differentiation-mediated mitochondrial damage and regulating mitochondrial levels of reactive oxigen species (ROS) and adenosine triphosphate (ATP). In conclusion, these studies contribute to an integrated view of the possible interplay between classic executioners of neural cell death and NSC fate decision, and identify new molecular targets that could prove useful in improving neuroreplacement therapies.