Novel monoclonal antibodies targeting the RRM2 domain of human TDP-43 protein

Transactive response DNA-binding protein of 43 kilodaltons (TDP-43) is a 414 amino acid protein that under physiologic conditions localizes to the nucleus and participates in the regulation of RNA metabolism through two RNA recognition motifs (RRM1 and RRM2). In neurodegenerative diseases, TDP-43 may become hyperphosphorylated, ubiquitinated, and aggregate into cytoplasmic inclusions. TDP-43 is now well-characterized as a pathologic protein of amyotrophic lateral sclerosis (ALS) and frontotemporal lobar degeneration with TDP-43 proteinopathy (FTLD-TDP). Additionally, a common TDP-43 proteinopathy arising outside of the context of ALS and FTLD-TDP has been recently described, termed "limbic predominant age-related TDP-43 encephalopathy (LATE)." In the current study, two novel mouse-derived monoclonal antibodies, 2G11 and 2H1, raised against an epitope within the RRM2 domain of TDP-43 (residues 198-216), were characterized for specificity and immunohistochemical application in human brain from cases of Alzheimer's disease (AD), Lewy Body Disease (LBD), amyotrophic lateral sclerosis (ALS), and frontotemporal lobe degeneration with TDP-43 inclusions (FTLD-TDP). Immunoblot analysis of these antibodies in HEK293T cells revealed efficient detection of intact human TDP-43 protein, and in N2A cells showed no reactivity for mouse TDP-43. Immunohistochemically applied to formalin-fixed paraffin-embedded tissues, 2G11 and 2H1 robustly identified the classic inclusions of ALS and FTLD-TDP, and efficaciously provided a diagnosis of LATE in cases of AD and LBD. These novel antibodies label aberrant intracytoplasmic protein inclusions without relying on hyperphosphorylated epitopes, and provide elegant discrimination between TDP-43 and tau neurofibrillary tangles within neurodegenerative comorbidity.