| Neural cell death plays a critical role in normal nervous system development and dysregulated neural stem cell death contributes to brain malformation, tumorgenesis, and possibly, neurodegenerative disease.;The two major forms of cell death in the nervous system are apoptotic and autophagic. Altered clearance of proteins may lead to neuronal dysfunction and neuron loss via apoptotic and/or autophagic pathways. The research presented here examined the molecular regulation of the autophagic and apoptotic pathways in vivo and in vitro by using models of lysosome dysfunction and hypoxia.;In vivo investigation of lysosome dysfunction-induced death utilized the cathepsin D (CD)-deficient mouse model. CD is a major lysosomal aspartate protease and mice deficient for this gene show increased accumulation of autophagic vacuoles (AVs) and neurodegeneration (Koike et al. 2003;Koike et al. 2000). This study showed CD deficiency resulted in AV accumulation followed by an age-dependent decrease in Akt signaling.;To test the hypothesis that altered lysosome function would lead to neural precursor cell (NPC) death via an interaction between autophagy- and apoptosis-associated proteins, we treated NPCs with potent inducers of autophagy, such as the lysosomotropic agent chloroquine (CQ), and the vacuolar ATPase inhibitor bafilomycin A1 (Baf A1), or starvation. NPCs deficient for bax or p53 exhibited decreased caspase activation and NPC death in response to these agents. Lysosome dysfunction triggered an Atg7-dependent up-regulation of phospho-p53, caspase-3, and LC3-II, indicating that Atg7 lies upstream in this cell death pathway.;To study hypoxia-induced NPC death in vitro, NPCs were treated with hypoxia mimetics desferroxamine (DFO) or cobalt chloride (CoCl 2), or oxygen glucose deprivation (OGD). Hypoxia exposure resulted in increased hypoxia inducible factor alpha (HIF1alpha) and bcl-2/adenovirus E1B 19 kDa interacting protein-3 (BNIP3) expression. BNIP3 shRNA knockdown failed to affect hypoxia-induced caspase-3 activation but was able to attenuate cell death and nuclear translocation of apoptosis inducing factor (AIF). These findings indicate that multiple Bcl-2 family members critically regulate hypoxia through a caspase-independent and -dependent NPC death pathway.;In total, these studies provide new insights into the molecular pathways regulating neural stem cell death and suggest possible molecular targets for the development of neuroprotective agents. |
