Mutations in hnRNP A1 drive neurodegeneration and alternative RNA splicing of neuronal gene targets

Abstract

RNA binding protein dysfunction is a pathogenic feature of multiple neurological diseases, including multiple sclerosis (MS). Neurodegeneration (the loss of, or damage to neurons and axons) is the primary driver of disease progression in MS. Herein, we utilized a novel, neuron-specific model of neurodegeneration by transducing primary mouse neurons with mutant forms of the RNA binding protein heterogeneous nuclear ribonucleoprotein A1 (hnRNP A1) identified from MS patients, including one within the M9-nuclear localization sequence of hnRNP A1 (A1(P275S)) and a second in the prion-like domain of hnRNP A1 (A1(F263S)) to test the hypothesis that neuronal hnRNP A1 dysfunction drives neurodegeneration in MS.

Examination of hnRNP A1 localization in neurons revealed an increase in nucleocytoplasmic mislocalization in neurons transduced with A1(P275S), but not A1(F263S). Yet, both A1(F263S) and A1(P275S) induced neurodegeneration evidenced by significant reductions in total neurite length and complexity and an increase in FluoroJade-C neuronal cell body staining. RNA sequencing and differential alternative splicing analysis of mutant-expressing neurons revealed dramatic changes in alternative RNA splicing of transcripts critical to neuronal function. Further, amyloid precursor protein (APP), a marker for neurodegeneration in MS, showed differential splicing in mutant-expressing neurons, which was confirmed in MS brains with hnRNP A1 dysfunction.

Overall, we have identified that hnRNP A1 plays a complex role in neuronal function and regulation by mediating the alternative splicing of neuron-specific transcripts. When neuronal hnRNP A1 function is impaired, as in disease, resultant dysfunction propagates through multiple pathways that may influence the progression of neurodegeneration in MS.