FMRP-Mediated Proteasome Regulation: A Novel Mechanism in ALS Pathology

Amyotrophic Lateral Sclerosis (ALS) is a rare and fatal neurodegenerative disease characterized by the hallmark cytoplasmic accumulation and aggregation of TAR DNA binding protein 43 (TDP-43), which impairs proteasome activity through its interaction with Tankyrase (TNKS). Using molecular and imaging techniques, we have identified a novel role for the Fragile X Mental Retardation Protein (FMRP) in regulating the TNKS/PI31-mediated proteasome activation mechanism in co-operation with TDP-43. Our results demonstrate that depletion of FMRP causes nuclear translocation of TDP-43, reducing cytoplasmic TNKS/TDP-43 co-localization, thereby releasing TNKS in the cytoplasm. Free TNKS gets associated with proteasome inhibitor of 31 kDa (PI31), reversing PI31-mediated inhibition of proteasome assembly, trafficking, and activity. Thus, FMRP regulates proteasome activity by modulating the subcellular distribution of TDP-43. Interestingly, FMRP expression is elevated in specific brain regions and spinal cords of TDP-43^A315T transgenic ALS mice that helps more TDP-43 to stay in cytoplasm to sequester more TNKS with it, resulting in proteasome dysfunction in ALS disease system. We have demonstrated for the first time that FMRP can act as a disease modifier for ALS. ALS patients with high FMRP expression in the brain and spinal cord may exhibit more severe protein aggregation due to proteasome dysfunction.