GSK3-ARC/Arg3.1 and GSK3-Wnt Signaling Axes Trigger Amyloid-β Accumulation and Neuroinflammation in Middle-aged Shugoshin 1 Mice

The cerebral amyloid-β accumulation that begins in middle age is considered the critical triggering event in the pathogenesis of late-onset Alzheimer's disease (LOAD). However, the molecular mechanism remains elusive. The Shugoshin 1 (Sgo1 ) mouse model, a model for mitotic cohesinopathy-genomic instability that is observed in human AD at a higher rate, showed spontaneous accumulation of amyloid-β in the brain at old age. With the model, novel insights into the molecular mechanism of LOAD development are anticipated. In this study, the initial appearance of cerebral amyloid-β accumulation was determined as 15-18 months of age (late middle age) in the Sgo1 model. The amyloid-β accumulation was associated with unexpected GSK3α/β inactivation, Wnt signaling activation, and ARC/Arg3.1 accumulation, suggesting involvement of both the GSK3-Arc/Arg3.1 axis and the GSK3-Wnt axis. As observed in human AD brains, neuroinflammation with IFN-γ expression occurred with amyloid-β accumulation and was pronounced in the aged (24-month-old) Sgo1 model mice. AD-relevant protein panels (oxidative stress defense, mitochondrial energy metabolism, and β-oxidation and peroxisome) analysis indicated (a) early increases in Pdk1 and Phb in middle-aged Sgo1 brains, and (b) misregulations in 32 proteins among 130 proteins tested in old age. Thus, initial amyloid-β accumulation in the Sgo1 model is suggested to be triggered by GSK3 inactivation and the resulting Wnt activation and ARC/Arg3.1 accumulation. The model displayed characteristics and affected pathways similar to those of human LOAD including neuroinflammation, demonstrating its potential as a study tool for the LOAD development mechanism and for preclinical AD drug research and development.