High K+ and IGF-1 protect cerebellar granule neurons via distinct signaling pathways.
In culture, cerebellar granule neurons die of apoptosis in serum-free media containing a physiologic level of K(+) but survive in a depolarizing concentration of K(+) or when insulin-like growth factor 1 (IGF-1) is added. Both Akt/PKB activation and caspase-3 inhibition were implicated as the underlying neuroprotective mechanisms. The duration of high K(+), however, induced survival effects that outlasted its transient activation of Akt, and granule neurons derived from caspase-3 knockout mice died to the same extent as did those from wild-type mice, suggesting that additional mechanisms are involved. To delineate these survival mechanisms, we compared the activities of two major survival pathways after high K(+)-induced depolarization or IGF-1 stimulation. Although IGF-1 promoted neuronal survival by activating its tyrosine kinase receptor, high K(+) depolarization provided the same effect by increasing the Ca(2+) influx through the L Ca(2+) channel. Moreover, high K(+)-induced depolarization resulted in sustained activation of MAP kinase, whereas IGF-1 activated Akt in 4 hr. Inhibition of MEK (MAP kinase kinase) by either PD98059 or UO126 abolished the protective effect of high K(+)-induced depolarization, but not that of IGF-1, suggesting that activation of the MAP kinase pathway is necessary for high K(+) neuroprotective effects. We demonstrated also that high K(+)-induced depolarization, but not IGF-1, increased phosphorylation of cAMP-response element-binding protein (CREB) and protein synthesis, both of which can be blocked by UO126. Overall, our findings suggested that high K(+)-induced depolarization, unlike IGF-1, promoted neuronal survival via activating MAP kinase, possibly by increasing CREB-dependent transcriptional activation of specific proteins that promote neuronal survival.
Zhong
Jin
J
Departments of Pediatrics and Anatomy and Cell Biology, Indiana University School of Medicine, Indianapolis, IN 46202, USA.
Deng
Jixian
J
Huang
Su
S
Yang
Xianlin
X
Lee
Wei-Hua
WH
D000818:Animals; D000831:Animals, Newborn; D017209:Apoptosis / Q000187:drug effects; D015153:Blotting, Western / Q000379:methods; D002118:Calcium / Q000378:metabolism; D020169:Caspases / Q000378:metabolism; D002470:Cell Survival / Q000187:drug effects; D002478:Cells, Cultured; D002531:Cerebellum / Q000166:cytology* / Q000187:drug effects; D016895:Culture Media, Serum-Free / Q000494:pharmacology; D017362:Cyclic AMP Response Element-Binding Protein / Q000378:metabolism; D004347:Drug Interactions; D004791:Enzyme Inhibitors / Q000494:pharmacology; D016257:Fura-2 / Q000378:metabolism; D007334:Insulin-Like Growth Factor I / Q000494:pharmacology*; D007770:L-Lactate Dehydrogenase / Q000378:metabolism; D008562:Membrane Glycoproteins / Q000378:metabolism; D051379:Mice; D020928:Mitogen-Activated Protein Kinases / Q000378:metabolism; D009474:Neurons / Q000187:drug effects* / Q000502:physiology; D018696:Neuroprotective Agents / Q000494:pharmacology*; D011188:Potassium / Q000494:pharmacology*; D017346:Protein Serine-Threonine Kinases; D011518:Proto-Oncogene Proteins / Q000378:metabolism; D051057:Proto-Oncogene Proteins c-akt; D015398:Signal Transduction / Q000502:physiology*; D013997:Time Factors
D016895:Culture Media, Serum-Free; D017362:Cyclic AMP Response Element-Binding Protein; D004791:Enzyme Inhibitors; D008562:Membrane Glycoproteins; D018696:Neuroprotective Agents; D011518:Proto-Oncogene Proteins; D007334:Insulin-Like Growth Factor I; D007770:L-Lactate Dehydrogenase; D017346:Protein Serine-Threonine Kinases; D051057:Proto-Oncogene Proteins c-akt; D020928:Mitogen-Activated Protein Kinases; D020169:Caspases; D011188:Potassium; D002118:Calcium; D016257:Fura-2