Efficacy of small‐molecule glycogen synthase kinase‐3 inhibitors in the postnatal rat model of tau hyperphosphorylation

Background and purpose: Glycogen synthase kinase‐3 (GSK‐3) affects neuropathological events associated with Alzheimeŕs disease (AD) such as hyperphosphorylation of the protein, tau. GSK‐3β expression, enzyme activity and tau phosphorylated at AD‐relevant epitopes are elevated in juvenile rodent brains. Here, we assess five GSK‐3β inhibitors and lithium in lowering phosphorylated tau (p‐tau) and GSK‐3β enzyme activity levels in 12‐day old postnatal rats. Experimental approach: Brain levels of inhibitors following treatment in vivo were optimized based on pharmacokinetic data. At optimal doses, p‐tau (Ser 396 ) levels in brain tissue was measured by immunoblotting and correlated with GSK‐3β enzyme activities in the same tissues. Effects of GSK inhibitors on p‐tau, GSK‐3β activities and cell death were measured in a human neuronal cell line (LUHMES). Key results: Lithium and CHIR98014 reduced tau phosphorylation (Ser 396 ) in the cortex and hippocampus of postnatal rats, while Alsterpaullone and SB216763 were effective only in hippocampus. AR‐A014418 and Indirubin‐3′‐monoxime were ineffective in either brain region. Inhibition of p‐tau in brain required several‐fold higher levels of GSK inhibitors than the IC 50 values obtained in recombinant or cell‐based GSK‐3β enzyme activity assays. The inhibitory effect on GSK‐3β activity ex vivo correlated with protection against cell death and decrease of p‐tau‐ in LUHMES cells, using low μ M inhibitor concentrations. Conclusions and Implications: Selective small‐molecule inhibitors of GSK‐3 reduce tau phosphorylation in vivo . These findings corroborate earlier suggestions that GSK‐3β may be an attractive target for disease‐modification in AD and related conditions where tau phosphorylation is believed to contribute to disease pathogenesis. British Journal of Pharmacology (2007) 152 , 959–979; doi: 10.1038/sj.bjp.0707471 ; published online 1 October 2007