Endoplasmic Reticulum Stress Induces the Early Appearance of Pro-apoptotic and Anti-apoptotic Proteins in Neurons of Five Familial Alzheimer's Disease Mice

Background: Amyloid beta (A beta) deposits and the endoplasmic reticulum stress (ERS) are both well established in the development and progression of Alzheimer's disease (AD). However, the mechanism and role of A beta-induced ERS in AD-associated pathological progression remain to be elucidated. Methods: The five familial AD (5xFAD) mice and wild-type (WT) mice aged 2, 7, and 12 months were used in the present study. Morris water maze test was used to evaluate their cognitive performance. Immunofluorescence and Western blot analyses were used to examine the dynamic changes of pro-apoptotic (CCAAT/enhancer-binding protein homologous protein [CHOP] and cleaved caspase-12) and anti-apoptotic factors (chaperone glucose-regulated protein [GRP] 78 and endoplasmic reticulum-associated protein degradation-associated ubiquitin ligase synovial apoptosis inhibitor 1 [SYVN1]) in the ERS-associated unfolded protein response (UPR) pathway. Results: Compared with age-matched WT mice, 5xFAD mice showed higher cleaved caspase-3, lower neuron-positive staining at the age of 12 months, but earlier cognitive deficit at the age of 7 months (all P < 0.05). Interestingly, for 2-month-old 5xFAD mice, the related proteins involved in the ERS-associated UPR pathway, including CHOP, cleaved caspase-12, GRP 78, and SYVN1, were significantly increased when compared with those in age-matched WT mice (all P < 0.05). Moreover, ERS occurred mainly in neurons, not in astrocytes. Conclusions: These findings suggest that compared with those of age-matched WT mice, ERS-associated pro-apoptotic and anti-apoptotic proteins are upregulated in 2-month-old 5xFAD mice, consistent with intracellular A beta aggregation in neurons.