Analysis On The Activity Of Calpain And Expression Of PSD-95 In Brain Of Transgenic Murine Model Of Alzheimer’s Disease

Alzheimer’s disease is characterized by cognitive dysfunction and memory loss. The most obvious neuropathological features include amyloid plaques, neurofibrillary tangles and synaptic loss. Calpain and PSD-95 are synapse-associated proteins. Aβ peptide can increase intracellar Ca2+concentration, activate calpain and hyperphosphorylate tau. The level of PSD-95 in AD patients is negatively correlated to Ap. In current study, using 3×Tg-AD model mice, the expression of calpain and PSD-95 in pathogenesis of AD were investigated to look for the time point when injured synaptic appeared and clarify the relationship between synaptic damage and AD pathogenesis.1. Compared with the control group, there was no significant difference in calpain activity and expression of PSD-95 at the age of 1 month and 3 month in AD group (P> 0.05). In AD group, calpain activity was significantly increased while the expression of PSD-95 was significantly reduced at the age of 6 month,9 month and 12 month (P< 0.05). Calpain activity was significantly increased while the expression of PSD-95 significantly reduced at the age of 16 month and 20 month in AD group (P< 0.01). These findings indicated that synaptic damage maybe occured at the sixth month in AD model mice.2. The calpain activity was increased slowly and expression of PSD-95 was reduced but not significantly in control group along with age (P> 0.05). However, calpain activity was significantly increased at the age of 6 month (P< 0.05), and extremely significant increased at the age of 16 month (P< 0.01), calpain activity was increased further by 368.9% at the age of 20 month (P< 0.01). Meanwhile, expression of PSD-95 was significantly reduced at the age of 6 month (P< 0.05), and extremely significantly decreased at the age of 16 month (P< 0.01), expression of PSD-95 was decreased further by 69.8% at the age of 20 month (P< 0.001). Above data demonstrated that calpain activity and expression of PSD-95 significantly changed at the sixth and sixteenth month in AD model mice.3. To investigate the effect of active immunotherapy,3×Tg-AD mice was treated with chimeric antigen 6Aβ15-TF and 6Aβ15-THc-C at 6 months of age. In AD mice treated with drug, the levels of humoral and cellular immunity were enhanced. The toxic proteins, Aβ and tau, dissipated and reached acceptable levels, and the pathological features significantly improved (P< 0.01), and the learning and memory ability significantly improved from the morris water maze test (P< 0.01). These results showed that the vaccine had a significant therapeutic effect for the AD model mice.4. In AD mice treated with drug, expression of dynaminl, synaptophysin, synapsin I, GluR1 and other synapse-associated protein were significantly increased (P< 0.05), which indicated that the mice neurons had been protected after immunotherapy. Although the mRNA expression of calpain and PSD-95 did not significantly change, calpain activity was significantly reduced and the protein expression of PSD-95 significantly increased (P< 0.01). These results showed that calpain activity and expression of PSD-95 are associated with AD vaccines and change of other synapse-associated proteins.In summary, the couse of 3xTg-AD was positively related to calpain activity while negatively to expression of PSD-95. The pathological features, learning and memory ability were improved after treatment. Our results suggested that PSD-95 may be contributed to a potential indicator evaluating the pharmacodynamic effects of AD vaccine.