Live cell imaging and CLEM reveals effects of Mutant Huntingtin Aggregation Process

Huntingtons disease is a neurodegenerative disease caused by expansion of CAG repeats in exon-1 of Huntingtin (HTT) gene leading to production of mutant Huntingtin (mHtt) protein. Htt protein is known to play crucial roles in regulation of cytoskeletal dynamics and vesicular transport in physiological conditions. By combining in vitro time-lapse imaging and correlative light and electron microscopy (CLEM), we investigated the subcellular dynamics of mHtt during the process aggregate formation. Here we show that distribution of F-actin is affected by mHtt aggregation. F-actin tends to relocate from the peripheral to perinuclear area in cells with mHtt aggregates, possibly caused by sequestration of F-actin from cell membrane to aggregation zones. In accordance with this, mHtt in hippocampal neurons were aggregated into axonal varicosities together with F-actin as they have higher F-actin expression in their neurites compared to their soma. Additionally, correlative light and electron microscopy (CLEM) revealed increased mitochondrial accumulation at the periphery of mHtt aggregates which is surrounded by a F-actin mesh. Mitochondria targeted HyPerRed, a genetically encoded hydrogen peroxide sensor, revealed that oxidative stress in mHtt expressing cells increased. Thus, our findings give new insights about the pathology caused by mHtt through interplay of aggregates with F-actin cytoskeleton and mitochondrial oxidative stress.