UC Irvine

Huntington’s disease (HD) is a late-onset autosomal neurodegenerative disease caused by the abnormal expansion of polyglutamine (polyQ) in the Huntington gene with the mitochondrial dysfunction as an early pathological mechanism. Individuals carrying 7-35 glutamine repeats are considered normal while above 41 repetitions will always lead to HD. Compelling evidence shows that the cell-cell transfer of the mutant Huntingtin (mHTT) protein aggregates may play an essential role in the pathogenesis of HD. Most recently in our lab, we showed that energy metabolism is altered in polyQ expressing cells. Yet many questions remain: 1) Does the transfer of the polyQ aggregates occur between cells? 2) If so, do the Huntingtin proteins of normal length increase protein aggregation in normal length Huntingtin expressing cells? 3) Is there any influence in energy metabolism as a consequence of the transfer of the pathogenic polyQ aggregate from infected cells? In this research, mHTT aggregates transfer intermediated NADH fluorescence lifetime change was measured using fluorescence lifetime imaging microscopy (FLIM) coupled with phasor analysis. Results obtained here suggest a metabolic shift from oxidative phosphorylation (OXPHOS) to more glycolytic state caused by the internalization of mHTT aggregates in HEK293 cells, which may lead to oxidative stress and cell death. Nuclear FLIM analysis shows a lifetime shift towards a lower fraction of bound NADH, which indicates a possible transcriptional dysregulation for infected cells. In addition, we performed Number and Brightness (N&B) analysis to map the oligomerization in live cells induced by mHTT aggregates. As seen in the results, there is a significant accumulation of endogenous HTT proteins after the internalization of extracellular mHTT aggregates. Altogether, the FLIM and N&B analysis used here provide a better understanding of the metabolic dysfunction and protein aggregation mediated by mHTT aggregate, which can be useful for further research in the field of neurodegenerative disease.