c-Fos Expression Differentially Acts in the Healthy Brain Compared with Alzheimer’s Disease

The proto-oncogene c-Fos is known as a reliable marker of cell activation, which is immediately induced after a new stimulus in specific brain regions, depending on the nature of the stimulus applied. However, the expression of c-Fos is increased in Alzheimer’s disease (AD) and contributes to amyloid β-peptide-induced neurotoxicity. This review attempted to focus on the role of c-Fos in learning and memory in both healthy brain and AD, emphasizing on possible mechanisms. Comparing the available findings, regarding learning and memory, c-Fos expression leads to memory formation through ERK (extracellular signal-regulated kinase)/CREB (cAMP response element-binding protein) and long-term potentiation, while it is down regulated after the repetition and habituation of stimuli. However, its overexpression in neurons and glia of AD, contributes to cognitive deficits and neuronal loss, which represents a defect in its ability to habituate to repeated stimuli. Also, expression pattern in glial is associated with constitutive CREB activation following increasing amyloid beta (Aβ), activation transcription factor (ATF3), and cytochrome c in apoptosis pathways. Thus, two contradictory roles of c-Fos in the healthy brain and AD, reveal more complexity in c-Fos up and down stream signaling pathways, bioavailability, and sensitivity. Future studies focusing on c-Fos modulation, might offer promising strategies to mitigate cognitive decline in AD.