Physiologically Important Electrolytes as Regulators of TDP-43 Aggregation and Droplet-Phase Behavior

Area of Science:

• Biochemistry
• Neuroscience
• Molecular Biology

Background:

• Intraneuronal aggregation of TDP-43 protein is a hallmark of amyotrophic lateral sclerosis (ALS).
• The precise mechanism driving TDP-43 aggregation remains poorly understood.
• TDP-43 proteinopathies are a significant area of neurological research.

Purpose of the Study:

• To develop a simplified in vitro model for studying full-length TDP-43 aggregation.
• To investigate the role of physiological electrolytes in TDP-43 aggregation.
• To explore TDP-43 behavior within liquid-like protein droplets.

Main Methods:

• Refolding of YFP-tagged full-length TDP-43 (yTDP-43) into stable dimers in low-salt buffer.
• Induction of aggregation using physiological electrolytes (K+, Na+, Mg2+, Ca2+).
• Observation of yTDP-43 behavior in preformed Ddx4N1 droplets using microscopy.

Main Results:

• Soluble yTDP-43 dimers formed stable solutions.
• Physiological electrolytes induced reversible, non-amyloid aggregation into tufted particles (10-50 nm).
• Aggregation potency followed the order K+ < Na+ < Mg2+ < Ca2+, inversely related to the Hofmeister series.
• yTDP-43 partitioned into droplets, exhibiting liquid-liquid phase transition behavior before aggregating.
• Electrolyte-induced aggregation occurred rapidly, particularly at droplet peripheries.

Conclusions:

• TDP-43 aggregation is modulated by ion-specific effects at physiological concentrations.
• Local electrolyte concentrations may play a mechanistic role in the development of TDP-43 proteinopathies.
• The in vitro model provides insights into TDP-43 aggregation dynamics relevant to ALS pathogenesis.