Na,K-ATPase Acts as a Beta-Amyloid Receptor Triggering Src Kinase Activation.

Beta-amyloid (Aß) has a dual role, both as an important factor in the pathology of Alzheimer's disease and as a regulator in brain physiology. The inhibitory effect of Aß42 oligomers on Na,K-ATPase contributes to neuronal dysfunction in Alzheimer's disease. Still, the physiological role of the monomeric form of Aß42 interaction with Na,K-ATPase remains unclear. We report that Na,K-ATPase serves as a receptor for Aß42 monomer, triggering Src kinase activation. The co-localization of Aß42 with α1- and ß1-subunits of Na,K-ATPase, and Na,K-ATPase with Src kinase in SH-SY5Y neuroblastoma cells, was observed. Treatment of cells with 100 nM Aß42 causes Src kinase activation, but does not alter Na,K-ATPase transport activity. The interaction of Aß42 with α1ß1 Na,K-ATPase isozyme leads to activation of Src kinase associated with the enzyme. Notably, prevention of Na,K-ATPase:Src kinase interaction by a specific inhibitor pNaKtide disrupts the Aß-induced Src kinase activation. Stimulatory effect of Aß42 on Src kinase was lost under hypoxic conditions, which was similar to the effect of specific Na,K-ATPase ligands, the cardiotonic steroids. Our findings identify Na,K-ATPase as a Aß42 receptor, thus opening a prospect on exploring the physiological and pathological Src kinase activation caused by Aß42 in the nervous system.

Distinct Effects of Beta-Amyloid, Its Isomerized and Phosphorylated Forms on the Redox Status and Mitochondrial Functioning of the Blood-Brain Barrier Endothelium.

The Alzheimer's disease (AD)-associated breakdown of the blood-brain barrier (BBB) promotes the accumulation of beta-amyloid peptide (Aß) in the brain as the BBB cells provide Aß transport from the brain parenchyma to the blood, and vice versa. The breakdown of the BBB during AD may be caused by the emergence of blood-borne Aß pathogenic forms, such as structurally and chemically modified Aß species; their effect on the BBB cells has not yet been studied. Here, we report that the effects of Aß42, Aß42, containing isomerized Asp7 residue (iso-Aß42) or phosphorylated Ser8 residue (p-Aß42) on the mitochondrial potential and respiration are closely related to the redox status changes in the mouse brain endothelial cells bEnd.3. Aß42 and iso-Aß42 cause a significant increase in nitric oxide, reactive oxygen species, glutathione, cytosolic calcium and the mitochondrial potential after 4 h of incubation. P-Aß42 either does not affect or its effect develops after 24 h of incubation. Aß42 and iso-Aß42 activate mitochondrial respiration compared to p-Aß42. The isomerized form promotes a greater cytotoxicity and mitochondrial dysfunction, causing maximum oxidative stress. Thus, Aß42, p-Aß42 and iso-Aß42 isoforms differently affect the BBBs' cell redox parameters, significantly modulating the functioning of the mitochondria. The changes in the level of modified Aß forms can contribute to the BBBs' breakdown during AD.