The neurogenic basic helix–loop–helix transcription factor NeuroD6 confers tolerance to oxidative stress by triggering an antioxidant response and sustaining the mitochondrial biomass

Preserving mitochondrial mass, bioenergetic functions and ROS (reactive oxygen species) homoeostasis is key to neuronal differentiation and survival, as mitochondria produce most of the energy in the form of ATP to execute and maintain these cellular processes. In view of our previous studies showing that NeuroD6 promotes neuronal differentiation and survival on trophic factor withdrawal, combined with its ability to stimulate the mitochondrial biomass and to trigger comprehensive antiapoptotic and molecular chaperone responses, we investigated whether NeuroD6 could concomitantly modulate the mitochondrial biomass and ROS homoeostasis on oxidative stress mediated by serum deprivation. In the present study, we report a novel role of NeuroD6 as a regulator of ROS homoeostasis, resulting in enhanced tolerance to oxidative stress. Using a combination of flow cytometry, confocal fluorescence microscopy and mitochondrial fractionation, we found that NeuroD6 sustains mitochondrial mass, intracellular ATP levels and expression of specific subunits of respiratory complexes upon oxidative stress triggered by withdrawal of trophic factors. NeuroD6 also maintains the expression of nuclear-encoded transcription factors, known to regulate mitochondrial biogenesis, such as PGC-1α (peroxisome-proliferator-activated receptor γ co-activator-1α), Tfam (transcription factor A, mitochondrial) and NRF-1 (nuclear respiratory factor-1). Finally, NeuroD6 triggers a comprehensive antioxidant response to endow PC12-ND6 cells with intracellular ROS scavenging capacity. The NeuroD6 effect is not limited to the classic induction of the ROS-scavenging enzymes, such as SOD2 (superoxide dismutase 2), GPx1 (glutathione peroxidase 1) and PRDX5 (peroxiredoxin 5), but also to the recently identified powerful ROS suppressors PGC-1α, PINK1 (phosphatase and tensin homologue-induced kinase 1) and SIRT1. Thus our collective results support the concept that the NeuroD6–PGC-1α–SIRT1 neuroprotective axis may be critical in co-ordinating the mitochondrial biomass with the antioxidant reserve to confer tolerance to oxidative stress

Neuronal caspase 2 activity and function requires RAIDD, but not PIDD

Caspase 2 was initially identified as a neuronally expressed developmentally down-regulated gene (HUGO gene nomenclature CASP2) and has been shown to be required for neuronal death induced by several stimuli, including NGF (nerve growth factor) deprivation and Aβ (β-amyloid). In non-neuronal cells the PIDDosome, composed of caspase 2 and two death adaptor proteins, PIDD (p53-inducible protein with a death domain) and RAIDD {RIP (receptor-interacting protein)-associated ICH-1 [ICE (interleukin-1β-converting enzyme)/CED-3 (cell-death determining 3) homologue 1] protein with a death domain}, has been proposed as the caspase 2 activation complex, although the absolute requirement for the PIDDosome is not clear. To investigate the requirement for the PIDDosome in caspase-2-dependent neuronal death, we have examined the necessity for each component in induction of active caspase 2 and in execution of caspase-2-dependent neuronal death. We find that both NGF deprivation and Aβ treatment of neurons induce active caspase 2 and that induction of this activity depends on expression of RAIDD, but is independent of PIDD expression. We show that treatment of wild-type or PIDD-null neurons with Aβ or NGF deprivation induces formation of a complex of caspase 2 and RAIDD. We also show that caspase-2-dependent execution of neurons requires RAIDD, not PIDD. Caspase 2 activity can be induced in neurons from PIDD-null mice, and NGF deprivation or Aβ use caspase 2 and RAIDD to execute death of these neurons

Studying Quantum Dot Blinking through the Addition of an Engineered Inorganic Hole Trap

An all-inorganic compound colloidal quantum dot incorporating a highly emissive CdSe core, which is linked by a CdS tunneling barrier to an engineered charge carrier trap composed of PbS, is designed, and its optical properties are studied in detail at the single-particle level. Study of this structure enables a deeper understanding of the link between photoinduced charging and surface trapping of charge carriers and the phenomenon of quantum dot blinking. In the presence of the hole trap, a “gray” emissive state appears, associated with charging of the core. Rapid switching is observed between the “on” and the “gray” state, although the switching dynamics in and out of the dark “off” state remain unaffected. This result completes the links in the causality chain connecting charge carrier trapping, charging of QDs, and the appearance of a “gray” emission state