Phosphatidylinositol and PI-4-monophosphate recover amyloid β protein-induced inhibition of Cl −-ATPase activity

Abstract

The neuronal Cl −-ATPase/pump is a candidate for an outwardly directed active Cl − transport system, which requires phosphatidylinositol-4-monophosphate (PI4P) for its optimal activity. We previously reported that low concentrations (1–10 nM) of amyloid β proteins (Aβs, Aβ1-42, Aβ25–35), the neurotoxic peptides in Alzheimer's disease, reduced Cl −-ATPase activity in cultured rat hippocampal neurons without any changes in the activities of Na +/K +-ATPase or anion-insensitive Mg 2+-ATPase, and decreased PI, PIP, and PIP2 levels in neuronal plasma membranes (Journal of Neurochemistry 2001, 78, 569–579). In this study, we examined the effects of exogenously applied PI and PI4P on the Aβ25-35-induced changes in Cl −-ATPase activity, the intracellular concentration of Cl − ([Cl −] i), and glutamate neurotoxicity using primary cultured rat hippocampal neurons. The Aβ decreased Cl −-ATPase activity to 47% of control and increased [Cl −] i in hippocampal pyramidal cell-like neurons to a level 3 times higher than the control. The addition of PI (50–750 nM) or PI4P (50–150 nM) dose-dependently blocked the inhibitory effects of Aβ on Cl −-ATPase activity. High doses of PI (750 nM) and PI4P (100–150 nM) reduced Na +/K +-ATPase activity to 41% and 35% of control, respectively, but this inhibition was attenuated by the co-application of phosphatidylserine (PS, 1 μM). PI or PI4P (75 nM each) reversed the Aβ-induced increase in [Cl −] i. In the Aβ-exposed culture, stimulation by glutamate (10 μM, 10 min) resulted in an increase in DNA fragmentation and decreases in cell viability. Addition of PI or PI4P prevented the Aβ-induced aggravation of glutamate neurotoxicity. Thus, PI and PI4P were demonstrated to prevent Aβ-induced decreases in Cl −-ATPase activity and increases in neuronal [Cl −] i in parallel with the attenuation of Aβ-induced aggravation of glutamate neurotoxicity.