Functional Activity of TDP-43: A Direct Biomarker for ALS.

Area of Science:

• Neuroscience
• Biochemistry
• Biomarker Discovery

Background:

• TDP-43 protein dysfunction is a key hallmark of amyotrophic lateral sclerosis (ALS).
• Current diagnostic methods lack a direct measure of TDP-43 functional activity in biofluids.
• There is a need for reliable biomarkers to assess disease progression and patient stratification in ALS.

Purpose of the Study:

• To develop and validate a novel serum-based assay for quantifying TDP-43 RNA-binding activity.
• To assess the utility of this assay in discriminating ALS patients from controls.
• To explore the correlation of TDP-43 activity with ALS genotypes and disease progression.

Main Methods:

• Development of a homogeneous time-resolved FRET (hTR-FRET) assay using synthetic UU-rich RNA probes.
• Analysis of 1,080 serum samples from controls, sporadic ALS, and genetic ALS subgroups (C9orf72, SOD1) from multiple biorepositories.
• Cross-sectional and longitudinal analyses to evaluate assay performance and correlation with clinical data.

Main Results:

• The hTR-FRET assay detected elevated TDP-43 RNA-binding activity in ALS patients compared to controls (AUC = 0.79).
• Distinct TDP-43 activity levels were observed across different ALS genotypes, with a threshold achieving 95% specificity against controls.
• Longitudinal analysis showed a modest inverse correlation between TDP-43 activity and ALSFRS-R in one cohort.

Conclusions:

• The developed hTR-FRET assay provides a direct functional measurement of TDP-43 biology relevant to ALS.
• This assay demonstrates potential as a diagnostic biomarker for ALS, aiding in patient stratification and monitoring.
• Further prospective studies are warranted to fully establish the clinical utility of this novel TDP-43 activity assay.