Small molecule JRMS modulating importin-β1 chaperone activity as a therapeutic strategy reducing TDP-43 pathology

Neuronal cytoplasmic aggregation and nuclear depletion of the TAR DNA-binding protein 43 (TDP-43) is the most characteristic pathology of amyotrophic lateral sclerosis (ALS) and frontotemporal dementia (FTD), causing toxicity through cytoplasmic gain and nuclear loss of function mechanisms. In addition to its canonical role in nuclear cytoplasmic transport (NCT), the nuclear import receptor, importin-β1 (KPNB1) also acts as a molecular chaperone capable of preventing and reversing aberrant protein aggregation. Previous studies have demonstrated that increased expression of KPNB1 solubilizes TDP-43 aggregates and restores its nuclear localization. Here, we identify JRMS, a small molecule that enhances the chaperone activity of KPNB1 by increasing its cytoplasmic availability. JRMS treatment reduced cytoplasmic aggregation and promoted nuclear localization of full-length and pathological truncated TDP-43 variants across multiple experimental systems, including cell lines, primary neurons, iPSC-derived cortical neurons, organotypic brain slices and in vivo model. The effects of JRMS were KPNB1 dependent and occurred without inducing cytotoxicity or perturbing basal NCT. These findings identify JRMS as a promising therapeutic strategy for targeting TDP-43 pathology in ALS/FTD and other related TDP-43 proteinopathies.