Selective small‐molecule inhibitors of glycogen synthase kinase‐3 activity protect primary neurones from death

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Abstract
The phosphatidylinositol 3‐kinase (PI 3‐kinase)/protein kinase B (PKB; also known as Akt) signalling pathway is recognized as playing a central role in the survival of diverse cell types. Glycogen synthase kinase‐3 (GSK‐3) is a ubiquitously expressed serine/threonine protein kinase that is one of several known substrates of PKB. PKB phosphorylates GSK‐3 in response to insulin and growth factors, which inhibits GSK‐3 activity and leads to the modulation of multiple GSK‐3 regulated cellular processes. We show that the novel potent and selective small‐molecule inhibitors of GSK‐3; SB‐415286 and SB‐216763, protect both central and peripheral nervous system neurones in culture from death induced by reduced PI 3‐kinase pathway activity. The inhibition of neuronal death mediated by these compounds correlated with inhibition of GSK‐3 activity and modulation of GSK‐3 substrates tau and β‐catenin. Thus, in addition to the previously assigned roles of GSK‐3, our data provide clear pharmacological and biochemical evidence that selective inhibition of the endogenous pool of GSK‐3 activity in primary neurones is sufficient to prevent death, implicating GSK‐3 as a physiologically relevant principal regulatory target of the PI 3‐kinase/PKB neuronal survival pathway.