Anti-apoptotic wild-type Alzheimer amyloid precursor protein signaling involves the p38 mitogen-activated protein kinase/MEF2 pathway.

Alzheimer amyloid precursor protein (APP) effectively protects against apoptosis in neuronal cells under stress, but the mechanisms of this anti-apoptotic effect remain largely unknown. Transcription factors act as critical molecular switches in promoting neuronal survival. The myocyte enhancer factor-2 (MEF2) is a transcription factor, and is known to be necessary for neurogenesis and activity-dependent neuronal survival. This study examined the possible role of MEF2 in the anti-apoptotic signaling pathways activated by APP. We report that expression of wild-type human APP (hAPPwt) but not familial Alzheimer's disease mutant APP (FAD-hAPPmut) in APP-deficient rat B103 cells led to a significant increase in the level of phosphorylated MEF2. This differential phosphorylation was dependent on enhanced activation of p38 mitogen-activated protein kinase (p38 MAPK). Also, expression of hAPPwt mediated an increase in MEF2 DNA binding affinity that correlated with p38 MAPK-dependent trans-activation of a MEF2-responsive reporter gene. Furthermore, over-expression of dominant negative MEF2 in hAPPwt-expressing cells enhanced staurosporine-induced apoptosis, in contrast MEF2wt enhanced the capacity of hAPPwt to confer resistance to apoptosis. Thus, MEF2 plays a critical role in APP-mediated signaling pathways that inhibit neuronal apoptosis. A model of anti-apoptotic APP signaling is proposed where APP mediates p38 MAPK-dependent phosphorylation and activation of MEF2. Once activated MEF2 regulates neuronal survival by stimulation of MEF2-dependent gene transcriptions. Alteration of this function by mutations in APP and aberrant APP processing could contribute to neuronal degeneration seen in AD.