Cross-linked Actin Networks Research Articles

Shear field mapping in actin networks by using magnetic tweezers.

An improved magnetic bead microrheometer based on phase contrast microscopy allowing high resolution measurements of local deformations within macromolecular network is applied to study local viscoelastic properties of cross-linked actin networks. By embedding nonmagnetic colloidal beads as probes into the networks, the spatial variation of the strain field within cross-linked actin networks can be mapped. Moreover, the Poisson ratio and shear modulus can be measured locally.

Cytoskeletal Changes in Cultured Human Glaucoma Trabecular Meshwork Cells

Glucocorticoid treatment of cultured human trabecular meshwork (TM) cells has been shown to reorganize actin microfilaments into cross-linked actin networks (CLANs) and to alter TM cell function. The purpose of the present study is to determine whether similar microfilament structural changes occur in TM cells derived from glaucoma patients. The microfilament structures of nine different TM cell cultures, derived from four glaucoma patients and from five normal subjects, was examined by epifluorescent microscopy and by whole-mount transmission electron microscopy. The cells were cultured in the absence and presence of dexamethasone (DEX) for 7-14 days. The normal TM cell lines and glaucoma cell line TM13 had relatively low levels of cross-linked actin networks in the absence of exogenously added glucocorticoids. In contrast, the glaucoma cell lines TM23, TM36C, and TM48D had high levels of CLANs without the addition of dexamethasone. The addition of 10 M DEX to the culture medium significantly increased CLAN expression in all normal as well as glaucoma TM cell lines. CLAN formation in glaucoma TM cells or in TM cells exposed to glucocorticoids may be a factor contributing to the generation of ocular hypertension.

Dexamethasone induced ultrastructural changes in cultured human trabecular meshwork cells.

Glucocorticoid-induced ocular hypertension has been demonstrated in both animals and humans. It is possible that glucocorticoid-induced changes in trabecular meshwork (TM) cells are responsible for this hypertension. In order to elaborate further the effect of glucocorticoids on the trabecular meshwork, the ultrastructural consequences of dexamethasone (DEX) treatment were examined in three different human TM cell lines. Confluent TM cells were treated with 0.1 microM of DEX for 14 days, and then processed for light, epifluorescent microscopy or transmission electron microscopy (TEM). The effect of DEX treatment on TM cell and nuclear size was quantified using computer assisted morphometrics. Morphometric analysis showed a significant increase in both TM cell and nuclear size after 14 days of DEX treatment. Epifluorescent microscopy of rhodamine-phalloidin stained, control TM cells showed the normal arrangement of stress fibers. In contrast, DEX-treated TM cells showed unusual geodesic dome-like cross-linked actin networks. Control TM cells had the normal complement and arrangement of organelles as well as electron dense inclusions and large vacuoles. DEX-treated TM cells showed stacked arrangements of smooth and rough endoplasmic reticulum, proliferation of the Golgi apparatus, pleomorphic nuclei and increased amounts of extracellular matrix material. The DEX-induced alterations observed in the present study may be an indication of the processes that are occurring in the in vivo disease process.

Viscoelastic moduli of sterically and chemically cross-linked actin networks in the dilute to semidilute regime: measurements by oscillating disk rheometer

The frequency dependencies of the dynamic viscoelastic moduli were measured as a function of (i) the monomer (G-actin) concentration (ii) the temperature and (iii) the actin chain length. Scaling laws relating the terminal relaxation time to the chain length and the plateau value of the storage modulus to the actin monomer concentration were established. Viscoelastic moduli of chemically crosslinked actin networks were measured as a function of the actin to crosslinker ratio and of the temperature