Effects of Vimentin Intermediate Filaments on the Structure and Dynamics of In Vitro Multicomponent Interpenetrating Cytoskeletal Networks

We investigate the rheological properties of interpenetrating networks reconstituted from the main cytoskeletal components: filamentous actin, microtubules, and vimentin intermediate filaments. The elastic modulus is determined largely by actin, with little contribution from either microtubules or vimentin. However, vimentin dramatically impacts the relaxation, with even small amounts significantly increasing the relaxation time of the interpenetrating network. This highly unusual decoupling between dissipation and elasticity may reflect weak attractive interactions between vimentin and actin networks.

Figure 1

(a) TEM image of a cytoskeletal network, containing F-actin (red), microtubules (yellow), and VIFs (green). (b) Confocal image of a network composed of $1\mathrm{mg}/\mathrm{mL}$ F-actin (red), $1\mathrm{mg}/\mathrm{mL}$ microtubules (green), and $0.5\mathrm{mg}/\mathrm{mL}$ VIFs (unlabeled). (c) SEM image of the three-component cytoskeletal network. VIFs are colored green.

Figure 2

(a)–(f) Two-dimensional heat maps of probability distributions of particle positions in various networks, showing the means (lines) and standard deviations $\overline{\sigma }$ (circles). Scale bar: 200 nm. Letters in legends represent network components. A: $1\mathrm{mg}/\mathrm{mL}$ F-actin; M: $1\mathrm{mg}/\mathrm{mL}$ microtubules; V: $0.5\mathrm{mg}/\mathrm{mL}$ VIFs. (g) Time and ensemble-averaged mean-squared displacements of probe particles.

Figure 3

(a)-(d) Frequency-dependent elastic moduli $G^{\prime }(f)$ (solid symbols) and loss moduli $G^{\prime \prime }(f)$ (open symbols) of three-component cytoskeletal networks. Concentrations labeled in mg/mL in lower right, A: F-actin; M: microtubules; V: VIFs. Blue lines in (a)–(d) indicate plateau elastic moduli, which barely change with $c_V$. Network crossover frequency (red lines) decreases as $c_V$ increases. (e)–(h) Frequency-dependent rheological properties of VIF-F-actin networks. Relaxation time (yellow lines) decreases as $c_A$ increases, while plateau elastic modulus (green lines) increases with $c_A$. Concentrations are labeled in mg/mL in lower right.

Figure 4

(a) Plateau elastic modulus $G_0$ and (b) relaxation time ${\tau }_r$ variation with VIF concentration $c_V$ for the network containing $1\mathrm{mg}/\mathrm{mL}$ F-actin and $1\mathrm{mg}/\mathrm{mL}$ microtubules. (c) $G_0$ and (d) ${\tau }_r$ variation with $c_A$ in VIF-F-actin networks, with $c_V$ fixed at $0.5\mathrm{mg}/\mathrm{mL}$. Yellow line in (d) is a B-spline fit. The insert in (d) depicts the reptation tube (gray) of an actin filament. Red: F-actin. Green: VIFs.