Activation of astrocytes: involvement of NADPH oxidase and cytosolic phospholipase A2
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[ACCESS RESTRICTED TO THE UNIVERSITY OF MISSOURI AT AUTHOR'S REQUEST.] Reactive oxygen species (ROS) are produced in cells by enzymic and non-enzymic mechanisms and play important roles in the pathogenesis of neurodegenerative diseases. However, mechanisms for the increase in ROS and their effects leading to altered cell metabolism have not been studied in detail in the central nervous system. In the first series of studies, we examined ROS production in primary rat astrocytes and their downstream effects on changes in signaling cascades and morphology using menadione. ROS production induced by menadione was completely inhibited by NADPH oxidase inhibitors including apocynin and gp91ds-tat. Menadione also stimulated phosphorylation of p38 and ERK, and caused actin polymerization and which can be inhibited by inhibitors for NAPDH oxidase and MAPK. In the second part, we tested the role of cytosolic phospholipase A2 in astrocytes in response to oxidative stress. Menadione increased the immunoreactivity of phospho-cPLA2 and caused plasma membranes to become more gel-like, which were abrogated by down regulating cPLA2 with siRNA. In summary, our study demonstrated the important role of NAPDH oxidase in production of ROS and their link to activation of MAPK pathways and cPLA2 in astrocytes. We further demonstrated that excess production of ROS, such as that mediated by menadione, can alter cell membrane properties, morphology, and cytoskeletal arrangement and in turn cell death mechanism.
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