Neurite growth is regulated by NADPH Oxidase (NOX1 and 2) and in this study, we investigate whether neuritic abnormalities observed in stem cell models of Huntington's disease relates to altered NOX function during NGF-driven differentiation of PC12 neuronal cells. NOX1 and 2 were contained in separate vesicular compartments, and by overexpression inhibited or promoted neurite extension, respectively. Expression of mutant Htt (mHtt; exon 1 fragment) accelerated neuronal induction causing longer neurites in the first phase of differentiation, but fewer and shorter mature neurites. Htt/mHtt increased NOX2 protein levels but did not change global oxidant production; However, Htt/mHtt prominently redistributed NOX activity to neurites. Oxidant production was concentrated in intraluminal vesicles in multivesicular bodies, and mHtt specifically increased secretion of NOX1 in exosomes, which demonstrated oxidant production capacity, while rerouting NOX2 to lysosomal degradation. Knockdown of TSG101, required for intraluminal vesicle formation, increased cellular levels of NOX2/p22phox and neurite growth.

Our study provides new insights on the disposition of NOX enzymes in nerve cells, indicating that deficient neurites in HD may be a correlate of altered trafficking, distribution, and activity of NOX.