Cytosolic Phospholipase A Facilitates Oligomeric Amyloid-β Peptide Association with Microglia via Regulation of Membrane-Cytoskeleton Connectivity.

Cytosolic phospholipase A (cPLA) mediates oligomeric amyloid-β peptide (oAβ)-induced oxidative and inflammatory responses in glial cells. Increased activity of cPLA has been implicated in the neuropathology of Alzheimer's disease (AD), suggesting that cPLA regulation of oAβ-induced microglial activation may play a role in the AD pathology. We demonstrate that LPS, IFNγ, and oAβ increased phosphorylated cPLA (p-cPLA) in immortalized mouse microglia (BV2). Aβ association with primary rat microglia and BV2 cells, possibly via membrane-binding and/or intracellular deposition, presumably indicative of microglia-mediated clearance of the peptide, was reduced by inhibition of cPLA. However, cPLA inhibition did not affect the depletion of this associated Aβ when cells were washed and incubated in a fresh medium after oAβ treatment. Since the depletion was abrogated by NHCl, a lysosomal inhibitor, these results suggested that cPLA was not involved in the degradation of the associated Aβ. To further dissect the effects of cPLA on microglia cell membranes, atomic force microscopy (AFM) was used to determine endocytic activity. The force for membrane tether formation (F) is a measure of membrane-cytoskeleton connectivity and represents a mechanical barrier to endocytic vesicle formation. Inhibition of cPLA increased F in both unstimulated BV2 cells and cells stimulated with LPS + IFNγ. Thus, increasing p-cPLA would decrease F, thereby increasing endocytosis. These results suggest a role of cPLA activation in facilitating oAβ endocytosis by microglial cells through regulation of the membrane-cytoskeleton connectivity.