Neurofilament sidearms modulate parallel and crossed-filament orientations inducing nematic to isotropic and re-entrant birefringent hydrogels

• Published in: Nature communications 2013-07, Vol.4 (1), p.2224-2224, Article 2224
• Main Authors: Deek, Joanna, Chung, Peter J., Kayser, Jona, Bausch, Andreas R., Safinya, Cyrus R.
• Format: Article
• Language: English
• Subjects: 639/301/923/1027; 639/766/747; Animals; Axons - chemistry; BIO, MATSCI; Birefringence; Cattle; Cytoskeleton - chemistry; Cytoskeleton - metabolism; Humanities and Social Sciences; Hydrogels - chemistry; Liquid Crystals - chemistry; multidisciplinary; Osmolar Concentration; Scattering, Small Angle; Science; Science (multidisciplinary); Spinal Cord - chemistry; Water - chemistry; X-Ray Diffraction
• ISSN: 2041-1723; 2041-1723
• DOI: 10.1038/ncomms3224

Neurofilaments are intermediate filaments assembled from the subunits neurofilament-low, neurofilament-medium and neurofilament-high. In axons, parallel neurofilaments form a nematic liquid-crystal hydrogel with network structure arising from interactions between the neurofilaments’ C-terminal sidearms. Here we report, using small-angle X-ray-scattering, polarized-microscopy and rheometry, that with decreasing ionic strength, neurofilament-low–high, neurofilament-low–medium and neurofilament-low–medium–high hydrogels transition from the nematic hydrogel to an isotropic hydrogel (with random, crossed-filament orientation) and to an unexpected new re-entrant liquid-crystal hydrogel with parallel filaments—the bluish-opaque hydrogel—with notable mechanical and water retention properties reminiscent of crosslinked hydrogels. Significantly, the isotropic gel phase stability is sidearm-dependent: neurofilament-low–high hydrogels exhibit a wide ionic strength range, neurofilament-low–medium hydrogels a narrow ionic strength range, whereas neurofilament-low hydrogels lack the isotropic gel phase. This suggests a dominant regulatory role for neurofilament-high sidearms in filament reorientation plasticity, facilitating organelle transport in axons. Neurofilament-inspired biomimetic hydrogels should therefore exhibit remarkable structure-dependent moduli and slow and fast water-release properties. Neurofilaments are intermediate filaments that form nematic liquid-crystal hydrogels in axons. Here, the authors show that upon decreasing ionic strength the hydrogels transform to isotropic and re-entrant birefringent hydrogels, with notable mechanical and water retention properties.