The ALS/FTLD associated protein C9orf72 associates with SMCR8 and WDR41 to regulate the autophagy-lysosome pathway

Abstract

Hexanucleotide repeat expansion in the C9orf72 gene is a leading cause of frontotemporal lobar degeneration (FTLD) with amyotrophic lateral sclerosis (ALS). Reduced expression of C9orf72 has been proposed as a possible disease mechanism. However, the cellular function of C9orf72 remains to be characterized. Here we report the identification of two binding partners of C9orf72: SMCR8 and WDR41. We show that WDR41 interacts with the C9orf72/SMCR8 heterodimer and WDR41 is tightly associated with the Golgi complex. We further demonstrate that C9orf72/SMCR8/WDR41 associates with the FIP200/Ulk1 complex, which is essential for autophagy initiation. C9orf72 deficient mice, generated using the CRISPR/Cas9 system, show severe inflammation in multiple organs, including lymph node, spleen and liver. Lymph node enlargement and severe splenomegaly are accompanied with macrophage infiltration. Increased levels of autophagy and lysosomal proteins and autophagy defects were detected in both the spleen and liver of C9orf72 deficient mice, supporting an in vivo role of C9orf72 in regulating the autophagy/lysosome pathway. In summary, our study elucidates potential physiological functions of C9orf72 and disease mechanisms of ALS/FTLD.Electronic supplementary materialThe online version of this article (doi:10.1186/s40478-016-0324-5) contains supplementary material, which is available to authorized users.

Loss of C9orf72 Enhances Autophagic Activity via Deregulated mTOR and TFEB Signaling

“…We observed a relative increase in LC3I levels upon loss of C9orf72 (S2 Fig), in consistence with a recent report for LC3 levels in C9orf72 KO mouse liver and spleen tissues [39], which we interpret as an increase in autophagosome turnover instead of a decrease in LC3II formation. In support of this model, we did not observe a decrease in LC3II levels after Bafilomycin treatment under full nutrient conditions, suggesting that the formation of LC3II is intact (S3 Fig).…”

“…There have been recent reports describing C9orf72’s functions in autophagy [39, 41–43], including a decrease in autophagy initiation as a result of knockdown of C9orf72 [41, 42]. These observations are not necessarily mutually exclusive to our present study.…”

Haploinsufficiency leads to neurodegeneration in C9ORF72 ALS/FTD human induced motor neurons

“…Although studies in mice have indicated that C9orf72 activity is important for myeloid cell function 14,18 , a report in mouse neurons and zebrafish suggests that C9orf72 isoform A may modulate poly-Q Ataxin-2 toxicity 20 , and studies have implicated C9ORF72 in regulating autophagy 20,31,32,38 , our study provides the first direct evidence showing that gain- and loss-of-function C9ORF72 mechanisms cooperate to cause the degeneration of human motor neurons. Recent studies have shown that C9ORF72 isoform A, but not isoform B, can form a functional complex with SMCR8 and WDR41 20 .…”

The role of lysosomes and autophagosomes in frontotemporal lobar degeneration

“…Progranulin (PGRN) is localized to lysosomes through at least two independent trafficking pathways . Although the role of C9orf72 protein is unclear, it is believed to be implicated in membrane trafficking and autophagy . Furthermore, while heterozygous loss of function mutations in GRN cause FTLD‐TDP , homozygous mutations in GRN cause a lysosomal storage disorder known as neuronal ceroid lipofuscinosis (NCL) .…”