cytochalasin-d and Wiskott-Aldrich-Syndrome

Alzheimer's disease (AD) is characterized by the accumulation of extracellular amyloid-beta (A beta) fibrils with microglia. Recently, there has been great interest in the microglial phagocytosis of A beta, because the microglial pathway is considered to be one of the A beta clearance pathways in the brain parenchyma. However, the mechanism of microglial phagocytosis of A beta is not fully understood and, thus, was investigated in this study. At one minute after exposure to A beta(1-42) (A beta 42), A beta immunoreactivity was detected at the cell surface of microglia. After 1 h, marked immunoreactivity was observed in the cytosolic vesicles. At 12 h, delayed phagocytosis of fibrillar A beta 42 was also observed with the formation of a large phagocytic cup. The microglial cell shape rapidly changed to an ameboid form during the process of phagocytosis. Although neither neural Wiskott-Aldrich syndrome protein (N-WASP) nor WASP interacting SH3 protein (WISH) immunoreactivity was co-localized with filamentous actin (F-actin) distribution, both WASP family verprolin-homologous protein (WAVE) and Rac1 immunoreactivity was co-localized with F-actin in the lamellipodia of phogocytic microglia. These results suggest that WAVE and Rac1 participate in the phagocytosis of A beta 42 by microglia.

Topics: Amyloid beta-Peptides; Animals; Cells, Cultured; Cytochalasin D; Microfilament Proteins; Microglia; Peptide Fragments; Phagocytosis; rac1 GTP-Binding Protein; Rats; Rats, Wistar; Saccharomyces cerevisiae Proteins; Wiskott-Aldrich Syndrome; Wiskott-Aldrich Syndrome Protein Family

The Wiskott-Aldrich syndrome (WAS) is a primary immunodeficiency disorder caused by a mutation in WAS protein (WASp) that results in defective actin polymerization. Although the function of many hematopoietic cells requires WASp, the specific expression and function of this molecule in natural killer (NK) cells is unknown. Here, we report that WAS patients have increased percentages of peripheral blood NK cells and that fresh enriched NK cells from two patients with a WASp mutation have defective cytolytic function. In normal NK cells, WASp was expressed and localized to the activating immunologic synapse (IS) with filamentous actin (F-actin). Perforin also localized to the NK cell-activating IS but at a lesser frequency than F-actin and WASp. The accumulation of F-actin and WASp at the activating IS was decreased significantly in NK cells that had been treated with the inhibitor of actin polymerization, cytochalasin D. NK cells from WAS patients lacked expression of WASp and accumulated F-actin at the activating IS infrequently. Thus, WASp has an important function in NK cells. In patients with WASp mutations, the resulting NK cell defects are likely to contribute to their disease.

Topics: Actins; Child; Child, Preschool; Cytochalasin D; Cytotoxicity, Immunologic; Humans; Infant; Killer Cells, Natural; Male; Microscopy, Confocal; Otitis Media; Proteins; Reference Values; Synapses; Thrombocytopenia; Wiskott-Aldrich Syndrome; Wiskott-Aldrich Syndrome Protein