Phosphatidyl-Serine-Positive Cells with High Sensitivity to the Alzheimer's Disease Aβ Peptides Display Distinctive Mitochondrial Characteristics

Abstract

The Alzheimer's Aβ peptides exhibit cell-selective toxic effects in cultured cells and in neurons of Alzheimer's disease (AD) brains. As we previously showed ex vivo neuronal cells and cell lines consisted of subpopulations of cells characterized by differential levels of a common surface membrane target for the phosphatidyl-serine (PtdSer) specific binder annexin V and for the Alzheimer's Aβ peptidesbinding. These findings enable us to efficiently separate by flow cytometry sorting PtdSer positive cells on a variety of neuronal cell lines and ex vivo neurons and analyze their Aβ-binding affinity. We collected compelling data confirming the involvement of PtdSer as one of the surface membrane signal molecules for Aβ. This investigation used the persistent presence of PtdSer on the outer leaflet of the plasma membrane of PC12 cells to identify, sort and further culture the subpopulation of cells that are PtdSer positive (PtdSer+) and have high affinity to bind Aβ, and consequently are more likely to be harmed by Aβ. Various viability tests showed that the group of cells sorted as PtdSer+ was the most sensitive to Aβ toxic effects. The caspase3/7 activation level of the PtdSer+ subpopulation of cells was similar to one of the PtdSer negative (PtdSer-) subpopulation and the control cells. Therefore we assume, PtdSer+ cells are not undergoing apoptosis. Additionally, PtdSer+ cells have persistent higher levels of PtdSer on the outer leaflet of the plasma membrane, significantly lower levels of cytosolic ATP, lower mitochondrial mass and mitochondrial membrane potential, and slightly higher production of reactive oxidative species compared to PtdSer- and control cells. We hypothesize that all of these distinctive cellular and mitochondrial conditions are the basis for the high sensitivity to Aβ displayed by some selective cell lines and neurons.