Loss of TDP-43 oligomerization or RNA binding elicits distinct aggregation patterns.

Area of Science:

• Neuroscience
• Molecular Biology
• Biochemistry

Background:

• TAR DNA-binding protein 43 (TDP-43) aggregation is central to neurodegenerative diseases such as amyotrophic lateral sclerosis (ALS) and frontotemporal lobar degeneration (FTLD).
• Physiologically, TDP-43 resides in the nucleus, forms oligomers, and participates in liquid-liquid phase separation (LLPS) condensates.
• Pathologically, TDP-43 forms inclusions in the cytoplasm or nucleus, but the transition mechanism is unclear.

Purpose of the Study:

• To investigate how TDP-43 oligomerization and RNA binding influence its stability, function, phase separation, and localization.
• To elucidate the distinct pathways leading to TDP-43 aggregation under conditions mimicking neurodegenerative diseases.

Main Methods:

• Utilized cellular systems, including human neurons and cell lines, to express structure-based TDP-43 variants at near-physiological levels.
• Investigated the impact of RNA binding and impaired proteasomal activity on TDP-43 behavior.
• Analyzed the localization and formation mechanisms of TDP-43 aggregates.

Main Results:

• TDP-43 oligomerization and RNA binding are critical regulators of its stability, splicing activity, LLPS, and subcellular localization.
• RNA binding modulates TDP-43 oligomerization.
• Impaired proteasomal activity induced cytoplasmic inclusions of monomeric TDP-43 and nuclear inclusions of RNA-binding deficient TDP-43.
• Aggregates formed through distinct pathways: LLPS-driven in the nucleus and aggresome-dependent in the cytoplasm.

Conclusions:

• Oligomerization and RNA binding are key determinants of TDP-43's physiological and pathological states.
• Distinct cellular mechanisms, LLPS and aggresome pathways, underlie the formation of heterogeneous TDP-43 pathological species observed in patients.
• This study provides insights into the origins of TDP-43 proteinopathies.