Whole-blood incubation method to study neutrophil cytoskeletal dynamics

Inhibition of actin polymerization by peroxynitrite modulates neutrophil functional responses

Peroxynitrite, a potent oxidant generated in inflammatory tissues, can nitrate tyrosine residues on a variety of proteins. Based on previous studies suggesting that actin might be a potential target for peroxynitrite-mediated nitration in neutrophils, we investigated the effects of peroxynitrite on actin function. We show here that peroxynitrite and the peroxynitrite generator (SIN-1) modified actin in a concentration-dependent manner, resulting in an inhibition of globular-actin polymerization and filamentous-actin depolymerization in vitro. The effects of peroxynitrite were inhibited by the pyrrolopyrimidine antioxidant PNU-101033E, which has been shown previously to specifically block peroxynitrite-mediated tyrosine nitration. Furthermore, spectrophotometric and immunoblot analysis of peroxynitrite-treated actin demonstrated a concentration-dependent increase in nitrotyrosine, which was also blocked by PNU-101033E. Activation of neutrophils in the presence of a nitric oxide donor (S-nitroso-N-acetylpenicillamine) resulted in nitration of exogenously added actin. Nitrated actin was also found in peroxynitrite-treated neutrophils, suggesting that actin may be an important intracellular target during inflammation. To investigate this issue, we analyzed the effect of peroxynitrite treatment on a number of actin-dependent neutrophil processes. Indeed, neutrophil actin polymerization, migration, phagocytosis, and respiratory burst activity were all inhibited by SIN-1 treatment in a concentration-dependent manner. Therefore, the ability of peroxynitrite to inhibit actin dynamics has a significant effect on actin-dependent, cellular processes in phagocytic cells and may modulate their host defense function.

Function of the cytoskeleton in human neutrophils and methods for evaluation

The cytoskeleton plays a critical role in the determination of cell shape and serves as a scaffold for critical cellular enzymes and adhesion molecules. It provides structural integrity for the cell and regulates the function of many biochemical events that are critical to cellular function. The microfilamentous cytoskeleton participates in force generation necessary for shape change and motion. In neutrophils and other motile cells, polymerization of actin likely drives extension of the lamellae and participates in force generation through interaction with myosin, by polymerization alone and by osmotic mechanisms. Here, we will focus on the microfilamentous cytoskeleton in the neutrophil and briefly review its function as well as some direct and indirect methods that have been used to asses its role in neutrophil function. The discussion will address general approaches and leaves the details of the methods to the references.