Glycogen synthase kinase 3 (GSK-3) is a serine/threonine protein kinase that has been implicated in the regulation of cell fate and in the Wnt signaling pathway. GSK-3 plays an important role in the PI3 kinase and Akt mediated cell survival pathways, and its activity can be inhibited by Akt-mediated phosphorylation at Ser21 of GSK-3α and Ser9 of GSK-3β. GSK-3 has also been implicated in alzheimer’s disease. Six Tau protein isoforms have been identified, all of which are phosphorylated by GSK-3.