Distinct sub-cellular autophagy impairments occur independently of protein aggregation in aged induced neurons from patients with Huntington’s disease

Huntington’s disease (HD) is an inherited neurodegenerative disorder caused by CAG expansions in the huntingtin (HTT) gene. Modelling HD in the lab has proven challenging as rodent models poorly reproduce the disease process and cellular models fail to include age-dependent processes crucial to the disease. Here we generated induced neurons (iNs) that retained age-dependent epigenetic characteristics of the donors through direct reprogramming of skin fibroblasts. HD-iNs displayed a transcriptionally regulated, distinct neurite specific alteration in autophagy, characterized by reduced transport of late autophagic structures and subsequent cargo degradation. In addition, HD-iNs displayed shorter, smaller and fewer neurites. CRISPRi-mediated silencing of both HTT alleles did not rescue the morphology nor the autophagic defect in HD-iNs. Strikingly, it resulted in additional autophagy alterations when done using ctrl-iNs, highlighting the importance of wt HTT in neuronal autophagy. In summary, our results have identified a distinct subcellular autophagy impairment in aged patient derived HD-neurons. In addition, we have shown a role for normal wt HTT in autophagy. Together this work provides a new rational for future development of autophagy activation therapies while also highlighting problems that may arise using non allele specific HTT silencing approaches, some of which are now in clinical trials. Examination of DNA methylation of directly reprogrammed induced neurons from healthy donors and Huntington’s disease patients.