Assessing impacts of mitochondrial dysfunction on axonal microtubule bundles as potential mechanism in neurodegeneration

Mitochondrial dysfunction is an important cause for neurodegeneration, often associated with dyshomeostasis of reactive oxygen species, i.e. oxidative stress. However, apart from ATP production, mitochondria have many other functions the aberration of which may impact neurons in very different ways. Oxidative stress can cause the deterioration of axonal microtubule bundles, thus critically affecting the highways for life-sustaining transport and providing a potential path to neurodegeneration. We recently found that aberrant transport of mitochondria can have this effect by causing oxidative stress. We therefore asked which aberrations of mitochondrial physiology might impact microtubules, which of these might explain the observed consequences of aberrant mitochondrial transport, and whether mitochondria-induced microtubule phenotypes are always mediated by oxidative stress. Using one consistent Drosophila primary neuron system, we deleted 13 different mitochondrial factors known to be detrimental for neurons in vivo. Losses of five factors caused MT damage, all involving oxidative stress, hence supporting the path from mitochondria via oxidative stress to microtubule deterioration; we discuss Sod2 as potential candidate explaining effects of mitochondrial transport aberration. However, the loss of eight factors - seven of them important mitochondrial morphogenesis regulators - caused no microtubule damage, suggesting potential oxidative stress-independent pathways.