REGULATION OF Aβ- OR ROS-MEDIATED NEURITE DEGENERATION BY AK5

Abstract

Adenylate kinases (AKs) play a key role in nucleotide metabolism via nucleotide phosphoryl exchange. A new member of this family, Ak5, has recently been identified, but its function remains unknown. In this study, we find that neuronal Ak5 mediates amyloid-beta (Ab) or ROS-mediated neurite degeneration and neurotoxicity. Cell-based functional screening was performed using cell-based tau aggregation assay and cDNA expression library. Primary cortical or hippocampal neurons from mouse embryos (E16 or E18) were prepared and seeded on poly-L-lysine-coated glass cover slips. For Immunocytochemistry, Cells were double-stained with Ak5 and beta-tubulin and washed with PBS before the incubation with FITC-conjugated or TRITC-conjugated secondary antibodies. In vitro microtubule assay was performed using purified AK5 and tubulins. We found that Ak5 is mainly expressed in the hippocampus and cortex of the mouse brains. Compared to AK1, purified Ak5 protein shows little kinase activity in vitro. From pull-down and LC/MS/MS analysis, we found the microtubules as an interaction partner of Ak5 in the mouse brains. Ak5 expression is significantly up-regulated in the neuronal cells exposed to Ab and hydrogen peroxides (H2O2). Also ectopic expression of Ak5 lead to neurite degeneration and neuronal death. Interestingly, Ak5 antagonizes the interaction of tau with microtubules in vitro and in cells. Furthermore, expression of Ak5 is increased in the brains of AD model mice and patients. We conclude that Ak5 plays a novel role in Ab- or ROS-mediated neurite degeneration via its competitive binding with tau to microtubules, providing insight into a mechanism for tau-mediated neurodegeneration in AD. Reference: Park H, Kam TI, Kim Y, Choi H, Gwon Y, Kim C, Koh JY, Jung YK (2012) Neuropathogenic role of adenylate kinase-1 in Aβ-mediated tau phosphorylation via AMPK and GSK3β. Hum Mol Genet 21: 2725–2737. Solaroli N, Panayiotou C, Johansson M, Karlsson A (2009) Identification of two active functional domains of human adenylate kinase 5. FEBS Lett 583: 2872–2876.