sb-415286 and Potassium-Deficiency

Although numerous studies have demonstrated a neuroprotective and anti-apoptotic role of lithium in neuronal cell cultures, the precise mechanism by which this occurs, remains to be elucidated. In this study, we evaluated the lithium-mediated neuroprotection against colchicine-induced apoptosis in cultured cerebellar granule neurons. Previously, it has been demonstrated that colchicine mediates apoptosis in cerebellar granule neurons through cytoskeletal alteration and activation of an intrinsic pro-apoptotic pathway. Recently we also demonstrated a potential role of cyclin-dependent kinase 5 (cdk5) in this pathway. Here we report that colchicine induces dephosphorylation in Ser-9 and phosphorylation in Tyr-216, and thus activation, of glycogen synthase kinase-3beta in cerebellar granule neurons, and that this modification is inhibited by the presence of 5 mM lithium. However, the selective glycogen synthase kinase-3beta inhibitors SB-415286 and SB-216763 were unable to prevent colchicine-induced apoptosis in these cells, suggesting that the anti-apoptotic activity of lithium is not mediated by glycogen synthase kinase-3beta under these conditions. On the other hand, 5 mM lithium prevented the colchicine-induced increase in cdk5 expression and breakdown of cdk5/p35 to cdk5/p25. In addition, we show that up-regulation of cdk5/p25 is unrelated to inhibition of the activity of myocyte enhancer factor 2, a pro-survival transcription factor. These data suggest a previously undescribed neuroprotective mechanism of lithium associated with the modulation of cdk5/p35 or cdk5/p25 expression.

Topics: Aminophenols; Analysis of Variance; Animals; Animals, Newborn; Apoptosis; Blotting, Western; Caspases; Cell Survival; Cells, Cultured; Cerebellum; Colchicine; Culture Media, Serum-Free; Cyclin-Dependent Kinase 5; Cyclin-Dependent Kinases; DNA-Binding Proteins; Dose-Response Relationship, Drug; Enzyme Inhibitors; Flow Cytometry; Glycogen Synthase Kinase 3; Glycogen Synthase Kinase 3 beta; Indoles; Lithium; Maleimides; MEF2 Transcription Factors; Microscopy, Electron, Transmission; Myogenic Regulatory Factors; Neurons; Neuroprotective Agents; Potassium Deficiency; Rats; Rats, Sprague-Dawley; Serine; Threonine; Time Factors; Transcription Factors