| Objectives: Alzheimer’s disease is a common neurodegeneration disorder characterized by progressive memory loss and cognitive decline as well as behavioral and personality changes. Extracelluar β-amyloid deposition and intracellular neurofibrillary tangles are the hallmark lesion of AD, the exact pathogenesis of AD is unclear yet. Amyloid-β(Aβ) is peptide is a main component of senile plaque, but also its main pathogenic molecule. Emerging evidence has indicated that large amounts of soluble Aβ in the brain of AD patients, which produced from amyloid-β precursor protein(AβPP) considered as early pathogenic events in AD development. In addition, related studies of soluable Aβimpairs long-term potention and promotes synaptic damages, the synaptic loss is largely relevant to the decline of memory cognitive function. It is highlighted the significant impact of Aβ deposition on synaptic degeneration and cognitive deficits in AD.Senescence-accelerated mouse prone 8 is a model for the study of aging and anti-aging, and it has a lot of typical pathology feature of AD, such as Aβdeposited, synaptic degeneration, neurofibrillary tangle, mitochondrial structure and dysfunction, accompanied by life cycles shorten, learning and memory impairment and other behavioral changes. Therefore it is known as a better ideal model for AD. SS31 peptide is a new type mitochondrial targeting peptide, which can penetrate the blood-brain barrier and mitochondrial membrane, gathered at a high concentration in the mitochondrial inner membrane. SS31 has anti-inflammatory, anti-oxidative stress and lower Aβlevels, protects mitochondrial and synaptic structural integrity. However, there is rarely comprehensive research on the protective effect of SS31 on the structure and functional alteration in mitochondrial and synapses using brain tissue from SAMP8 mice. The aim of our study was to investigate whetherSS31 could protect synaptic function from Aβ-induced toxicity and improve cognitive performance in SAMP8 mice. This may provide some theoretical and experimental evidence for the pathogenesis of AD, but also provide new ideas for the treatment of AD.Methods: The mice were purchased from Tianjin University of Traditional Chinese Medicine and were clean animal. The experiment was carried out in the Clininal Research Center of Hebei General Hospital. The mouse was fed by the feeder of the animal centre, which are fed with standard mouse grain and clean water. Eight-mouth-old male SAMR1(n=10, 24-35 g)and SAMP8(n=30, 24-35 g) mice were randomly divided into normal control groups(SAMR1 group), SAMP8 model groups(SAMP8 group), SAMP8saline-treated groups(Vehicle group), and SAMP8 SS31-treated groups(SS31group). SS31 was diluted with saline before use, and 5 mg/kg daily by intraperitoneal injections for a total of 8 weeks, with the vehicle group treated with saline by the same approach. Morris water maze was carried out at the 7th week of the drug/vehicle treatments, and all animals were sacrificed at the end of experiment, with brains harvested for anatomical and biochemical analyses.The transmission electron microscope was used to test the synaptic morphological changes, the Western blot were used to test the protein expression of Aβ, GAP43, PSD95 and SYN in the hippocampus of different groups.Results:1 SS31 treatment rescued cognitive impairment in SAMP8 mice The Morris water maze was used to delect the spatial learning and memory ability:1.1 Place navigation test: All groups exerted a significant progressive decline in the escape latency during 5 days of training(P<0.01), indicating that all mice developed a memory of the hidden platform(Fig.1A).1.1.1 Escape latency : Mice in the SAMP8 group showed a remarkable prolonged escape latency as compared to the SAMR1 group(P<0.01). The behavioral deficit in SAMP8 mice was ameliorated by treatment with SS31(Vehicle group vs SS31 group, P<0.01 in days 2, 3, 4, and P<0.05 in day 5).There was no significant difference in the escape latency during 5 days of training between SAMP8 group and Vehicle group(P>0.05)(Fig.1A).1.1.2 Swimming distance: the same trend of results was noted as with the eacape latency(Fig.1B, Fig.2).1.2 Space exploration experiments:Time spent in target quadrant(%): In the probe trial without the platform, the SAMP8 group spent significantly less time in the target quadrant than the SAMR1 group(P<0.01), and presented no significant difference from the Vehicle mice(P>0.05). SS31 treatment significantly modified the performance(Vehicle group vs SS31 group,P<0.05), showing that SS31 improved memory impairment in SAMP8 mice(Fig. 1C, Fig.3).1.3 In order to determine whether the group difference in escape latency was caused by swimming ability, the swimming speed in probe trial was calculated for each group. However, the results showed no difference in swimming speed between any two groups(P>0.05)(Fig.1D).2 SS31 treatment protected mitochondrial and synaptic ultrastructure in SAMP8 mouse hippocamous The ultrastructural changes of synaptic between different groups were observed by transmission electron microscope(Fig.4): The thickness of PSD and the curvature of the synaptic interface in SAMR1 mice were50.483±0.897 and 1.057±0.006 nm, respectively. The two parameters in the untreated SAMP8 mice were 30.665±0.796 and 1.029±0.006 nm, respectively.SAMR1 mice showed greater levels of the thickness of PSD relative to untreated SAMP8 mice(P<0.01). There is no significant difference in the curvature of the synaptic interface between two groups(P>0.05). In the SS31 treated animals there was a significant increase in the thickness of PSD(34.129±0.879 nm) relative the vehicle control(29.689±0.782 nm)(P<0.05).However, the results of the curvature of the synaptic interface showed no significant difference between the SS31 treated mice(1.048±0.005) and vehicle controls(1.027±0.004)(P>0.05). No differences in the two parameterswere found between the untreated and saline-treated SAMP8 mice(P>0.05).3 SS31 treatment lower Aβ42 levels in SAMP8 mouse hippocampus.Western blot was used to quantify the levels of Aβ42 in the hippocampal lysates for all animal groups(Fig.5, Table 3). Compared with SAMR1 mice,Aβ42 levels were significantly elevated in untreated SAMP8 mice(P<0.01).Compared with saline-treated SAMP8 mice, Aβ42 concentration was significantly lower in the SS31-treated SAMP8 mice(P<0.01). There was no significant difference(P>0.05) in Aβ42 levels between the untreated SAMP8 and saline-treated SAMP8 groups.4 SS31 treatment restored synaptic protein alteration in SAMP8 mouse hippocampus The expression of representative presynaptic and postsynaptic proteins,including the growth-associated protein 43(GAP43), postsynaptic density protein 95(PSD95) and synaptophysin(SYN), were assessed using hippocampal lysates for all groups(Fig.6, Table 2, Table 3). Levels of GAP43,PSD95 and SYN were significantly lower in the untreated SAMP8 mice than in SAMR1 mice(P<0.01). The levels of the three proteins were increased in the SS31 treated relative to untreated or saline-treated SAMP8 groups(P<0.01), while no significant difference existed between untreated SAMP8 and saline-treated SAMP8 mice(P>0.05).Conclusion: Aβ deposition,synaptic structure changes and dysfunction in the hippocampus of SAMP8 mice. The new type mitochondrial targeting antioxidant peptide SS31 may be of potential utility for AD therapy, with its pharmacological efficacy involves lowering of central Aβ levels and protection of mitochondrial homeostasis and synaptic integrity, which may help slow down cognitive decline. |
PDF Full Text Request