Neurofilament networks: Salt-responsive hydrogels with sidearm-dependent phase behavior

Area of Science:

• Biophysics
• Neuroscience
• Materials Science

Background:

• Neurofilaments (NFs) are neuron-specific intermediate filaments crucial for neuronal structure.
• NFs assemble from NF-Low (NF-L), NF-Medium (NF-M), and NF-High (NF-H) monomers.
• Previous studies indicated NF subunit composition affects hydrogel network properties.

Purpose of the Study:

• To investigate the salt-dependent phase behavior of reconstituted bovine NF networks.
• To determine how varying binary and ternary subunit ratios influence NF network properties.

Main Methods:

• Utilized polarized optical microscopy and Small-Angle X-ray Scattering (SAXS).
• Examined reconstituted bovine NF networks across a range of salt concentrations.
• Analyzed various binary (NF-L/NF-M, NF-L/NF-H) and ternary (NF-L/NF-M/NF-H) subunit ratios.

Main Results:

• Observed three distinct salt-induced liquid crystalline phases: liquid-ordered B(G) and N(G), and disordered I(G).
• Identified specific roles for NF sidearms: NF-H drives parallel-to-cross filament transitions, while NF-M suppresses the disordered I(G) phase.
• Demonstrated that NF-H shifts the I(G) to N(G) transition in NF-LH copolymers towards physiological salt concentrations compared to NF-M in NF-LM copolymers.

Conclusions:

• In ternary mixtures, NF-H's role is modulated by NF-M concentration, influencing transitions to disordered or increased spacing.
• Understanding subunit-specific roles in NF network regulation is key to deciphering mechanisms of NF dysfunction in disease states.
• Findings provide insights into the structural basis of neurofilament assembly and its implications for neurological disorders.