Validating UBC9 as a Molecular Target to Develop a Therapy for All Forms of ALS
Abstract
Our goal is to develop novel disease-modifying small-molecule drugs that block neurodegeneration in ALS to slow disease progression. Most efforts by others that have been made to develop therapeutics to treat ALS have employed strategies designed to block the pathogenic actions of individual mutant genes and proteins that cause very rare forms of familial ALS (fALS). However, accumulated evidence has indicated that dysfunction of multiple molecular and cellular pathways may cause sporadic ALS (sALS), the form of the disease most ALS patients have. As a consequence, developing therapeutics that target one disease-causing protein may not block neurodegeneration mediated by other disease-causing proteins and cellular mechanisms in the vast majority of ALS patients. This may explain why no therapy has been developed that blocks disease progression of ALS. We are using a different approach to develop therapeutics to treat ALS that is designed to block common mechanisms that cause neurodegeneration in all ALS patients. Using an RNAi screening technology, we identified a protein, UBC9, that may be involved in neurodegeneration induced by multiple proteins that cause pathogenesis in ALS. We showed that reducing the expression of UBC9 in neurons blocks neurodegeneration induced by mutant forms of the cytoskeleton proteins TUBA4A and PFN1 and the RNA-processing protein TDP43 that cause fALS. UBC9 is a novel molecular target and has not been the focus of drug discovery in ALS in the past. It catalyzes the conjugation of SUMO molecules on target proteins. SUMOs are small ubiquitin-like modifiers that modulate protein localization, conformation, and stability. UBC9 and the SUMO pathway are essential for maintaining nuclear structure and for nucleocytoplasmic shuttling (NCS). NCS is necessary for FUS and TDP43 to translocate from the cytoplasm to the nucleus where they regulate RNA processing and mutations in FUS and TDP43 that cause fALS impair the transport of these proteins to the nucleus. Wild-type TDP43 has also been implicated in pathogenesis of sALS, and defects in NCS caused by aberrant UBC9 activity and SUMOylation may impair transport of wild-type TDP43 to the nucleus in sALS to cause pathogenesis. In fact, aberrant SUMOylation has been implicated in ALS pathogenesis by others, and NCS defects have been observed in C9ORF72, and SOD1 ALS models, and human sALS patients, and modulation of nuclear export appears beneficial in ALS. Our studies showed an interrelationship and crossover of different disease pathways in ALS and a role of aberrant NCS and SUMOylation linked to dysfunction of those pathways. We also showed that mutant forms of the cytoskeleton proteins TUBA4A and PFN1 that cause fALS and impair cytoskeleton dynamics also impair NCS of wild-type FUS and TDP43 needed for appropriate RNA processing. Knocking down the SUMOylating enzyme UBC9 rescues defects in NCS in cells expressing mutant TUBA4A and increases wild-type TDP43 levels in the nucleus, suggesting that excessive SUMOylation by UBC9 may impair nuclear localization of TDP43. Our results suggest that UBC9 is a master regulator of multiple disease pathways in ALS and indicate that inhibitors of UBC9 activity will be beneficial in slowing disease pathogenesis in all ALS patients. To further establish the role of UBC9 in ALS, we propose to test the efficacy of inhibiting expression of UBC9 using siRNA in blocking neurodegeneration in human iPSC-derived neuronal models of ALS from patients with a range of different forms of fALS and new neuronal models from patients with sALS. Our results may have clinical applications and contribute to the advancement of therapeutics for ALS because UBC9 is an enzyme that is druggable, and validating UBC9 s role in neurodegeneration in a range of models of ALS may provide the basis for developing an entirely new family of small-molecule drugs to treat ALS. We also propose studies to determine the efficacy of inhibiting UB
Document Details
- Document Type
- DoD Grant Award
- Publication Date
- Oct 29, 2018
- Source ID
- W81XWH1810696
Entities
People
- Steven Finkbeiner
Organizations
- The J. David Gladstone Institutes
- United States Army