Up-regulation of cytoskeletal proteins in activated microglia

Abstract

Objectives: This study investigates how the tumor necrosis factor (TNF-alpha) and interleukin-1beta (IL-1beta) affect the morphology, organization, and expression of actin, beta-actin and tubulin in microglia.

Materials and methods: Microglia cultures were prepared from neopallia of newborn mice. Immunofluorescence, immunoblotting, and ELISA studies were used.

Results: When microglia are treated with TNF-alpha, IL-1beta or a combination of both for 1-5 days, the majority change from an ameboid to a large, round and flat shape. F-actin and beta-actin isoform, which are diffusely arranged throughout the cytoplasm before stimulation, are reorganized into filamentous bundles underneath and parallel to the cell membrane, which projects into many ruffles. This organization is maintained even after withdrawal of the cytokines. The dense microtubule network of tubulin in nontreated microglia becomes less dense and extends to occupy the cytoplasm of the treated microglia. Immunoblotting shows that the amount of total actin, beta-actin isoform and tubulin increases in treated microglia. In addition, IL-1beta and a combination of both TNF-alpha and IL-1beta stimulate the release of IL-6 by microglia.

Conclusion: This study suggests that TNF-alpha and IL-1beta have an effect on the expression of cytoskeletal proteins similar to some extent to that of LPS. The up-regulation of actin, beta-actin and tubulin may play a key role in the motility and recruitment of microglia to the area of central nervous system inflammation.