Fluorescence Lifetime-Based FRET Biosensors for Monitoring N Terminal Domain-Dependent Interactions of TDP-43 in Living Cells: A Novel Approach for ALS and FTD Drug Discovery.

Pathological aggregates of TDP-43 are implicated in Alzheimer's disease, frontotemporal dementia, and amyotrophic lateral sclerosis. While therapeutic efforts have traditionally focused on mitigating end-stage TDP-43 aggregation, recent evidence highlights an upstream and potentially targetable event: the loss of functional nuclear TDP-43 multimers due to disrupted N-terminal domain (NTD) interactions. To address this, we developed fluorescence lifetime (FLT)-based FRET biosensors to monitor TDP-43 multimerization in living cells that couple a full-length TDP-43 FLT-FRET biosensor screen with an NTD-deletion counter screen, forming the foundation of a novel high-throughput screening (HTS) platform. Screening the 2682 compound FDA-approved Selleck library, we identified the small molecule ketoconazole, which stabilizes functional nuclear TDP-43 multimers in an NTD-dependent manner with low micromolar potency. Ketoconazole rescues TDP-43 mislocalization and aggregation, restores SREBP2 mRNA levels under TDP-43 overexpression, improves neuronal health, and partially restores motor function in a TDP-43 model. These findings establish both the biosensors and the HTS platform as innovative tools for TDP-43 drug discovery and support an exciting translational approach for targeting TDP-43 proteinopathies.