TDP-43 oligomers detected as initial intermediate species during aggregate formation

Abstract

KEYWORDS: amyotrophic lateral sclerosis (ALS) (Lou Gehrig disease), TAR DNA-binding protein 43 (TDP-43) (TARDBP), RNA binding protein, protein aggregation, liquid droplet, frontotemporal dementia (FTD) (FTLD), aggregate propagation, ALS mutations, liquid-liquid phase separation. ABSTRACTAggregates of the RNA binding protein TDP-43 are a hallmark of amyotrophic lateral sclerosis (ALS) and frontotemporal dementia (FTD), which are neurodegenerative disorders with overlapping clinical, genetic and pathological features. Mutations in the TDP-43 gene are causative of ALS, supporting its central role in pathogenesis. The process of TDP-43 aggregation remains poorly understood and whether this includes formation of intermediate complexes is unknown. We characterized aggregates derived from purified TDP-43 as a function of time and analyzed them under semi-denaturing conditions. Our assays identified oligomeric complexes at the initial time points prior to the formation of large aggregates, suggesting that ordered oligomerization is an intermediate step of TDP-43 aggregation. In addition, we analyzed liquid-liquid phase separation of TDP-43 and detected similar oligomeric assembly upon the maturation of liquid droplets into solid-like fibrils. These results strongly suggest that the oligomers form during the early steps of TDP-43 misfolding. Importantly, ALSlinked mutations A315T and M337V significantly accelerate aggregation, rapidly decreasing the monomeric population and shortening the oligomeric phase. We also show that the aggregates generated from purified protein seed intracellular aggregation, which is detected by established markers of TDP-43 pathology. Remarkably, cytoplasmic aggregate propagation is detected earlier with A315T and M337V and is 50% more widespread than with wild-type aggregates. Our findings provide evidence for a controlled process of TDP-43 self-assembly into intermediate structures that provide a scaffold for aggregation. This process is altered by ALSlinked mutations, underscoring the role of perturbations in TDP-43 homeostasis in protein aggregation and ALS-FTD pathogenesis.

TDP-43 oligomerization and RNA binding are codependent but their loss elicits distinct pathologies

“…RNA-bound TDP-43 oligomers enact its physiological functions, maintain its localization and antagonize the formation of pathological aggregates (15 and this study), while RNAless TDP-43 oligomers, that may or may not have functional roles, undergo aberrant phase separation leading to nuclear aggregation (37 and this study). These observations clarify the apparently controversial role of the NTD in aggregate formation, which has been found both synergistic (35,(68)(69)(70) and antagonistic (15). Based on our observations, we propose that NTD-mediated TDP-43 self-interaction is a double-edged sword: in the presence of RNA, it is essential for TDP-43 to perform its functions and undergo physiological LLPS, while in the absence of RNA binding it promotes aberrant LLPS that leads to aggregation.…”

Femtomolar Biodetection by a Compact Core–Shell 3D Chiral Metamaterial

“…This results in a large shift of the CD features to refractive index changes, and, consequently, to biodetection sensitivity in the femtomolar concentration range. We applied our engineered sensing device against variable concentration of the transactive response (TAR) DNA-binding protein 43 (TDP-43), a distinctive protein of amyotrophic lateral sclerosis (ALS) and frontotemporal lobar degeneration (FTLD) [26,27] . Currently, the diagnosis of these neurodegenerative diseases is still clinically based and no biomarkers have yet been routinely incorporated into the clinical practice or clinical trials.…”