FosB Is Essential for the Enhancement of Stress Tolerance and Antagonizes Locomotor Sensitization by ΔFosB

BackgroundMolecular mechanisms underlying stress tolerance and vulnerability are incompletely understood. The fosB gene is an attractive candidate for regulating stress responses, because ΔFosB, an alternative splice product of the fosB gene, accumulates after repeated stress or antidepressant treatments. On the other hand, FosB, the other alternative splice product of the fosB gene, expresses more transiently than ΔFosB but exerts higher transcriptional activity. However, the functional differences of these two fosB products remain unclear.MethodsWe established various mouse lines carrying three different types of fosB allele, wild-type (fosB+), fosB-null (fosBG), and fosBd allele, which encodes ΔFosB but not FosB, and analyzed them in stress-related behavioral tests.ResultsBecause fosB+/d mice show enhanced ΔFosB levels in the presence of FosB and fosBd/d mice show more enhanced ΔFosB levels in the absence of FosB, the function of FosB can be inferred from differences observed between these lines. The fosB+/d and fosBd/d mice showed increased locomotor activity and elevated Akt phosphorylation, whereas only fosB+/d mice showed antidepressive-like behaviors and increased E-cadherin expression in striatum compared with wild-type mice. In contrast, fosB-null mice showed increased depression-like behavior and lower E-cadherin expression.ConclusionsThese findings indicate that FosB is essential for stress tolerance mediated by ΔFosB. These data suggest that fosB gene products have a potential to regulate mood disorder-related behaviors.