RBM45 Modulates the Antioxidant Response in Amyotrophic Lateral Sclerosis through Interactions with KEAP1

Abstract

Amyotrophic lateral sclerosis (ALS) is a fatal neurodegenerative disease characterized by the selective loss of motor neurons. Various factors contribute to the disease, including RNA binding protein dysregulation and oxidative stress, but their exact role in pathogenic mechanisms remains unclear. We have recently linked another RNA binding protein, RBM45, to ALS via increased levels of protein in the cerebrospinal fluid of ALS patients and its localization to cytoplasmic inclusions in ALS motor neurons. Here we show RBM45 nuclear exit in ALS spinal cord motor neurons compared to controls, a phenotype recapitulated in vitro in motor neurons treated with oxidative stressors. We find that RBM45 binds and stabilizes KEAP1, the inhibitor of the antioxidant response transcription factor NRF2. ALS lumbar spinal cord lysates similarly show increased cytoplasmic binding of KEAP1 and RBM45. Binding of RBM45 to KEAP1 impedes the protective antioxidant response, thus contributing to oxidative stress-induced cellular toxicity. Our findings thus describe a novel link between a mislocalized RNA binding protein implicated in ALS (RBM45) and dysregulation of the neuroprotective antioxidant response seen in the disease.

ACKNOWLEDGMENTS

We thank D. Zhang (University of Arizona) and Y. Xiong (University of North Carolina at Chapel Hill) for plasmids as well as M. Collins (Barrow Neurological Institute) for help with the Huygens software.

This work was supported by National Institutes of Health/National Institutes of Neurological Disorders and Stroke grants NS061867 and NS068179 to R.B.

R.B. is a founder of Iron Horse Diagnostics, Inc., a biotechnology company focused on diagnostic and prognostic biomarkers for ALS and other neurologic disorders.

N.B. and R.B. designed research. A.K. performed immunoprecipitations, T.K. prepared primary rat neuronal cultures, and Y.L. helped with DNA cloning. N.B. and R.B. wrote the manuscript, with critical evaluation from all authors. All authors read and approved the final manuscript.