Mutations in ubiquilin2 (UBQLN2) have been linked to abnormal protein aggregation in amyotrophic lateral sclerosis (ALS). The mechanisms underlying UBQLN2-related neurodegenerative diseases remain unclear. Using a tetracycline-regulated gene expression system, the ALS-linked UBQLN2P497H mutant was selectively expressed in either the spinal motor neurons or astrocytes in rats. We found that selectively expressing mutant UBQLN2P497H in the spinal motor neurons caused several core features of ALS, including the progressive degeneration of motor neurons, the denervation atrophy of skeletal muscles, and the abnormal protein accumulation. Furthermore, mutant UBQLN2P497H accumulation was associated with an age-dependent decrease in several core autophagy-related proteins. ALS-like phenotypes were not observed when mutant UBQLN2P497H was overexpressed in the astrocytes, however, even though the expression of the mutant UBQLN2P497H protein was higher in these rats. Our results suggest that selectively expressing mutant UBQLN2P497H in motor neurons is sufficient to trigger the development of ALS in rats. Our results further indicate that the compromised autophagy-lysosomal pathway plays a critical role in the pathogenesis of UBQLN2-related neurodegenerative diseases.Electronic supplementary materialThe online version of this article (10.1186/s40478-018-0627-9) contains supplementary material, which is available to authorized users.

Mutations of Ubiquilin 2 (UBQLN2) or TANK-binding kinase 1 (TBK1) are associated with amyotrophic lateral sclerosis and frontotemporal degeneration (ALS/FTD). However, the mechanisms whereby UBQLN2 or TBK1 mutations lead to ALS and FTD remain unclear. Here, we explored the effect of UBQLN2 on TBK1 in HEK-293T cells or in CRISPR–Cas9-mediated IRF3 and IRF7 knockout (KO) cells. We found an interaction between TBK1 and UBQLN2, which was affected by ALS/FTD-linked mutations in TBK1 or UBQLN2. Co-expression of UBQLN2 with TBK1 elevated the protein level of TBK1 as well as the phosphorylation of TBK1 and IRF3 in a UBQLN2 dose-dependent manner, and this phosphorylation was reduced by mutant UBQLN2. In addition, the cellular production of IFN1 and related pro-inflammatory cytokines was substantially elevated when UBQLN2 and TBK1 were co-expressed, which was also decreased by mutant UBQLN2. Functional assay revealed that mutant UBQLN2 significantly reduced the binding affinity of TBK1 for its partners, including IRF3, (SQSTM1)/p62 and optineurin (OPTN). Moreover, complete loss of IRF3 abolished the induction of IFN1 and related pro-inflammatory cytokines enhanced by UBQLN2 in HEK-293T cells, whereas no significant change in IRF7 knockout cells was observed. Thus, our findings suggest that UBQLN2 promotes IRF3 phosphorylation via TBK1, leading to enhanced IFN1 induction, and also imply that the dysregulated TBK1-IRF3 pathway may play a role in UBQLN2-related neurodegeneration.