Investigating the role of TDP-43 citrullination in ALS pathogenesis

MASSI/XU – ABSTRACT Pathological molecular alteration and the associated aggregation of the TAR-DNA-binding protein-43 (TDP-43), a protein involved in RNA processing, are hallmarks of the neurodegenerative diseases amyotrophic lateral sclerosis (ALS) and frontotemporal lobar degeneration (FTLD). They are also observed in a variety of other devastating neurodegenerative diseases, including traumatic brain injury (TBI), Alzheimer's disease (AD), Parkinson's disease (PD), and limbic-predominant age-related TDP-43 encephalopathy (LATE). Recently, we and others have observed that, in patient protein aggregates, TDP-43 is citrullinated at two specific sites. Protein citrullination (PC) is a common post-translational modification known to modulate protein function. Interestingly, altered PC has been observed in various neurodegenerative diseases including ALS, PD, AD, Creutzfeldt-Jakob disease (CJD) and multiple sclerosis (MS). The goal of this proposal is to interrogate the hypothesis that citrullination of TDP-43 impacts its RNA-binding activity and stability, resulting in cytoplasmic mislocalization and aggregation. We aim to elucidate the structural basis underlying the effect of PC on both the structure, stability and liquid-liquid phase separation (LLPS) of TDP-43 (Aim 1). We also aim to determine how citrullination impacts TDP-43 RNA-binding activity and splicing regulation (Aim 2). Finally, we will characterize the effect of citrullination on the nuclear versus cytoplasmic localization of TDP-43 to determine if mislocalization of TDP-43 to the cytoplasm leads to its aggregation (Aim 3). Collectively, the outcomes from these aims will provide novel insights into the role of PC in neurodegeneration in general and ALS in particular. The long-term goal of this research is to utilize these molecular insights to develop TDP-43-based therapeutic strategies to treat a broad class of devastating neurodegenerative diseases.