The J Domain of Sacsin Disrupts Intermediate Filament Assembly

Area of Science:

• Neuroscience
• Cell Biology
• Genetics

Background:

• Autosomal Recessive Spastic Ataxia of the Charlevoix Saguenay (ARSACS) results from SACS gene mutations, leading to sacsin protein dysfunction.
• A hallmark of ARSACS is the aberrant accumulation of neurofilament (NF) bundles in neurons and vimentin intermediate filaments (IF) in fibroblasts.
• This suggests sacsin plays a crucial role in maintaining intermediate filament (IF) homeostasis within cells.

Purpose of the Study:

• To investigate the mechanism by which sacsin regulates neurofilaments (NF) and vimentin intermediate filaments (IF).
• To determine if the J domain of sacsin (SacsJ) can therapeutically resolve NF bundles in ARSACS models.

Main Methods:

• Studied NF assembly in vitro using purified NF proteins.
• Utilized a cell-penetrating peptide derived from the SacsJ domain (SacsJ-myc-TAT).
• Assessed the effects of SacsJ-myc-TAT on NF and vimentin IF networks in cultured Sacs-/- neurons and Sacs+/+ fibroblasts and motor neurons.

Main Results:

• The SacsJ domain was found to interact with NF proteins, disassembling NFL filaments and inhibiting their initial assembly in vitro.
• SacsJ-myc-TAT effectively disassembled NF bundles in cultured Sacs-/- motor neurons, restoring the NF network.
• However, the peptide caused some loss of vimentin IF and NF in cultured Sacs+/+ cells, indicating potential off-target effects.

Conclusions:

• Sacsin, via its SacsJ domain, acts as a key regulator of both neurofilament (NF) and vimentin intermediate filament (IF) networks.
• The SacsJ domain holds potential for therapeutic intervention in ARSACS by targeting aberrant NF accumulations.
• Further research is needed to optimize the specificity of SacsJ-derived peptides to minimize unintended effects on normal IF networks.