TBK1 haploinsufficiency results in changes in the K63-ubiquitination profiles in brain and fibroblasts from affected and presymptomatic mutation carriers

BACKGROUND: Frontotemporal dementia (FTD) is a neurodegenerative disease, resulting in progressive problems in language and/or behaviour and is often diagnosed before 65 years of age. Ubiquitin positive protein aggregates in the brain are among the key pathologic hallmarks of frontotemporal lobar degeneration (FTLD) postmortem. The TANK-binding kinase 1 gene (TBK1) is on the list of genes that can contribute to the development of FTD as well as the related neurodegenerative disease amyotrophic lateral sclerosis (ALS). METHODS: In this study, using an array of clinical and neuropathological data combined with biochemical and proteomics assays, we analyze the TBK1 splice-mutation (c.1340 + 1G > A) in a Swedish family with a history of FTD and ALS. We also explore the K63 ubiquitination landscape in post-mortem brain tissue and fibroblast cultures. RESULTS: The intronic (c.1340 + 1G > A) mutation in TBK1 results in haploinsufficiency and affects the activity of the protein in symptomatic and pre-symptomatic mutation carriers. CONCLUSION: Our results suggest that the mutation leads to a significant reduction of TBK1 activity and induce alterations in K63 ubiquitination profile of the cell already in the presymptomatic stages. SUPPLEMENTARY INFORMATION: The online version contains supplementary material available at 10.1007/s00415-021-10887-x.