Knockdown I2PP2A attenuates tau hyperphosphorylation and the underlying mechanisms

Abstract

In Alzheimer's disease, increased inhibitor-2 of protein phosphatase-2A (I2PP-2A) level has been associated with decreased protein phosphatase-2A activity and hyperphosphorylation tau. Thus, reduction of I2PP-2A level could be important in the treatment of Alzheimer's disease. pSUPER-siI2PP-2A was constructed and transfected into HEK293/tau cells with administered wortmannin or okadaic acid. Western blots was used to detected the levels of hyperphosphrylated tau, GSK-3β and phospho-GSK-3β (Ser9). PP-2A activity was assayed using a serine/threonine phosphatse assay system (Promega, MA) according to the manufacturer's protocol. We found that I2PP-2A could only interact with the catalytic subunit of PP-2A and had no interaction with the regulatory subunit. Increased activity of PP-2A was for the associational level of I2PP-2A was decreased while transfection with pSUPER-siI2PP-2A. We also found that hyperphosphorylation tau levels induced by okadaic acid or wortmannin were decreased while transfection with DNA plasmid pSUPER-siI2PP-2A expressing siRNA targeting I2PP-2A. Knockdown I2PP-2A decreased the activity of GSK-3β, for it decreased the total levels of GSK-3β protein and mRNA, however increased the level of phospho-GSK-3β (Ser9), which was phosphorylated by PKA. All of these suggest that I2PP-2A may be a promising target for AD therapy.