Growing evidence suggests dysregulated autophagy contributes toward several neurodegenerative diseases, including ALS and FTD. In the session 7A – genetics and genomics, Professor John Hardy from University College London highlighted that many ALS causing mutations occur in genes that regulate autophagy. In addition, accumulation of misfolded protein in motor neurons is a pathological hallmark of the disease, and is suggestive of autophagy incapable of clearing protein aggregates.
First in session 4A, Shinji Hadano presented data comparing a Sqstm-/-SOD1H46R ALS mouse and SOD1H46R ALS mouse. Sqstm/p62 is involved in autophagy, and he showed that the Sqstm/p62 knock out reduced lifespan, impaired growth and increased motor dysfunction in the SOD1H46R ALS mice. The Sqstm/p62 knock out in the SOD1H46R ALS mouse also caused axonal degeneration in the spinal cord. Furthermore, inactivating Alsin (which regulates endocytic trafficking and autophagy) in addition to the p62/SQSTM knock out, accelerated disease in the SOD1H46R ALS mice. This shows that impaired autophagy increases the SOD1H46R protein toxicity, but rationally, this also suggests that activating autophagy could be neuro-protective against misfolded SOD1 protein and a potential therapeutic pathway.
The next talk was given by Chris Webster from Sheffield, who implicated C9ORF72 protein in autophagy initiation. First, he showed that knocking down C9ORF72 in HeLa cells by siRNA prevented autophagy induction – measured by LC3-I to LC3-II conversion via immunoblot, and an mCherry-EGFP-LC3 autophagy reporter via immunofluorescence. Conversely, overexpression of C9ORF72 induced autophagy. Secondly, he showed that C9ORF72 binds FIP200 and ULK1 – both proteins are components of the autophagy initiation complex. If C9ORF72 protein is indeed involved in autophagy, and C9ORF72 protein levels are reduced in C9ORF72-ALS patients, then reduced C9ORF72 levels could cause impaired autophagy. Interestingly, p62 positive inclusions found in the cerebellum and hippocampus explicitly in C9ORF72-ALS patients suggest this could be true.
Pannilage Nirma Perera presented work using an m-TOR independent autophagy activating drug – rilmenidine – in SOD1G93A mice. Autophagy is the main pathway for removing misfolded proteins and damaged organelles in neurons. Activating autophagy is a potential way of ameliorating toxicity caused by misfolded SOD1 or other misfolded proteins thought to cause neurodegeneration. In the study, rilmenidine increased LC3-II levels, and decreased VDAC1 levels in the spinal cords of SOD1G93A mice, indicating increased autophagy. In addition, soluble mutant SOD1 levels in the spinal cord were also diminished. Unexpectedly however, rilmenidine did not affect disease onset but actually accelerated disease progression in SOD1G93A mice.
Finally, Soo presented work looking at the effect of mutant FUS on autophagy, ER stress and ER-golgi transport. Transfected mutant FUS causes ER stress, impairs autophagosome formation and disrupts ER-golgi transport in Neuro2a cells. Rab1 is involved in membrane trafficking and autophagosome formation. Rab1 overexpression decreased ER stress, rescued the autophagy defects, and rescued ER-golgi transport caused by mFUS. This work further supports the autophagy pathway as a potential therapeutic target in ALS with FUS mutations.
In summary, impaired autophagy seems likely to play an important role in ALS pathogenesis. It also seems that autophagy could be a potential therapeutic pathway, and a worthy area of ALS research.