Adult-Onset Deficiency of Mitochondrial Complex III in a Mouse Model of Alzheimer's Disease Decreases Amyloid Beta Plaque Formation

For decades, mitochondrial dysfunctions and the generation of reactive oxygen species have been proposed to promote the development and progression of the amyloid pathology in Alzheimer's disease, but this association is still debated. It is unclear whether different mitochondrial dysfunctions, such as oxidative phosphorylation deficiency and oxidative stress, are triggers or rather consequences of the formation of amyloid aggregates. Likewise, the role of the different mitochondrial oxidative phosphorylation complexes in Alzheimer's patients' brain remains poorly understood. Previous studies showed that genetic ablation of oxidative phosphorylation enzymes from early age decreased amyloid pathology, which were unexpected results. To better model oxidative phosphorylation defects in aging, we induced the ablation of mitochondrial Complex III (CIIIKO) in forebrain neurons of adult mice with amyloid pathology. We found that mitochondrial Complex III dysfunction in adult neurons induced mild oxidative stress but did not increase amyloid beta accumulation. On the contrary, CIIIKO-AD mice showed decreased plaque number, decreased Aβ42 toxic fragment, and altered amyloid precursor protein clearance pathway. Our results support the hypothesis that mitochondrial dysfunctions alone, caused by oxidative phosphorylation deficiency, is not the cause of amyloid accumulation.

The oligosaccharide portion of ganglioside GM1 regulates mitochondrial function in neuroblastoma cells

The crucial role of ganglioside GM1 in the regulation of neural homeostasis has been assessed by several studies. Recently we shed new light on the molecular basis underlying GM1 effects demonstrating that GM1 oligosaccharide directly binds TrkA receptor and triggers MAPK pathway activation leading to neuronal differentiation and protection. Following its exogenous administration, proteomic analysis revealed an increased expression of proteins involved in several biochemical mechanisms, including mitochondrial bioenergetics. Based on these data, we investigated the possible effect of GM1 oligosaccharide administration on mitochondrial function. We show that wild-type Neuro2a cells exposed to GM1 oligosaccharide displayed an increased mitochondrial density and an enhanced mitochondrial activity together with reduced reactive oxygen species levels. Interestingly, using a Neuro2a model of mitochondrial dysfunction, we found an increased mitochondrial oxygen consumption rate as well as increased complex I and II activities upon GM1 oligosaccharide administration. Taken together, our data identify GM1 oligosaccharide as a mitochondrial regulator that by acting at the plasma membrane level triggers biochemical signaling pathway inducing mitochondriogenesis and increasing mitochondrial activity. Although further studies are necessary, the capability to enhance the function of impaired mitochondria points to the therapeutic potential of the GM1 oligosaccharide for the treatment of pathologies where these organelles are compromised, including Parkinson's disease.