The phasor FLIM method reveals a link between a change in energy metabolism and mHtt protein spread in healthy Mammalian cells when co-cultured with Huntington diseased cells.

Huntington Disease (HD) is a late-onset autosomal neurodegenerative disease characterized by the aggregations of mutant Huntingtin proteins (mHTT). A glutamine stretch (PolyQ) at the N-terminal of the Huntingtin protein is generated by the abnormal expansion of CAG trinucleotide repeats in exon 1 of the HTT gene. While the resulting polyQ aggregates are the predominate feature of HD, the intercellular spread of the expanded protein and the effect upon this transfer inside healthy cells have not yet fully understood. Here, we have employed the phasor Fluorescence Lifetime Imaging Microscopy (FLIM) method to measure NADH fluorescence lifetime change after the internalization of the PolyQ protein. Based on our analysis, we have found a significant decrease in the fraction of bound NADH in both cytoplasmic and nucleus regions when cells are co-cultured or when healthy cells uptake the supernatant containing polyQ proteins and aggregates. Overall, our FLIM study combined with confocal fluorescence imaging visualizes the absorption of the mutant Htt protein aggregates which results in a distinct NADH fluorescence lifetime between control cells and acceptor cells. These studies show, for the first time, the influence of how neighboring cells expressing the expanded Htt protein can regulate energy metabolism in healthy cells.