Effect Of S14G-Humanin And Its Mechanism On Prevention Of Alzheimer’s Disease In Transgenic Mice

Background and ObjectivesAlzheimer’s disease (AD), the most common cause of dementia amongolder people, is a progressive neurodegenerative disorder characterized bypathological amyloid plaques, neurofibrillary tangles, granulovacuolardegeneration of hippocampal pyramidal cells and neuron loss. Alzheimer’sdisease, in most cases, sneaks in and is sinister in its ability to hide. Thesymptoms of it include progressive deterioration in memory and personalitychanges. Although the pathogenesis of AD still remains unclear, increasingevidence has shown that aggregation, fibrillization, and deposition ofamyloid-beta protein (Aβ) as well as formation of senile plaques and theneurotoxicity of Aβ to synapse and neuron around it play a crucial role in thedevelopment of AD.S14G-Humanin (HNG), a synthetic derivative of Humanin(HN), has been shown to have strong neuroprotective ability against AD-relatedinsults in vitro and prevent cognitive impairments in Aβ-infused animal models.However, whether HNG treatment has the disease-modifying efficacy on ADwith pre-existing well-established amyloid plaque pathology remains unclear. The investigation of the effect of HNG treatment on AD with pre-existingwell-established amyloid plaque pathology may help to exploring new therapiesfor AD. In this study, we employed9-month-old APPswe/PS1dE9mice toinvestigate the effects of3-month HNG treatment on AD with pre-existing robustamyloid plaque pathology through behavioral analyses and the analyses of thechanges of various Aβ, gliocyte and inflammatory cells in the brains of theanimal models.MethodsThe9-month-old female APPswe/PS1dE9mice and their matchednon-transgenic wild-type (WT) littermates used in the study were randomlyassigned into the following four groups (n=8, each group): HNG-treatedAPPswe/PS1dE9mice, vehicle-treated APPswe/PS1dE9mice, HNG-treated WTmice, and vehicle-treated WT mice. Different groups were received differenttreatments for3month. Their spatial learning and memory, the changes ofvarious Aβ, gliocyte and inflammatory cells in their brains were evaluated by allkinds of tests such as Morris water maze tests, passive avoidance training,immunohistochemical and histological staining, and sandwich ELISA. Theresults of the tests were evaluated by relevant statistical analysis.Results1. The results of Morris water navigation task revealed that vehicle-treatedAPPswe/PS1dE9mice had significantly longer escape latencies relative tovehicle-and HNG-treated WT mice (p <0.001, respectively). Whereas, HNGtreatment in APPswe/PS1dE9mice resulted in a significant decrease in escapelatency compared with vehicle-treated APPswe/PS1dE9mice (p <0.01). Theresults of a probe trial showed that vehicle-treated APPswe/PS1dE9mice spentsignificantly less time in the target quadrant relative to vehicle-and HNG-treated WT mice (p <0.001, respectively). However, HNG-treated APPswe/PS1dE9mice spent significantly more time in the target quadrant compared to thevehicle-treated APPswe/PS1dE9mice (p <0.001).2. The total Aβ plaques in the brains of vehicle-treated APPswe/PS1dE9miceand HNG-treated APPswe/PS1dE9mice was detected by usingImmunohistochemical and histological staining and the fibrillar plaques by usingThioflavin S staining. The results indicated that both the total Aβ plaque load andthe fibrillar Aβ plaque load in HNG-treated APPswe/PS1dE9mice weresignificantly decreased in cerebral cortex (p <0.001) compared to vehicle-treatedcontrol mice. Similarly, the plaques were also reduced in hippocampus (p <0.001)in HNG-treated APPswe/PS1dE9mice.3. The levels of soluble and insoluble Aβ in brain from APPswe/PS1dE9mice treated with HNG or vehicle were examined by sandwich ELISA.Compared with vehicle controls, HNG treatment significantly lowered the levelsof insoluble total Aβ1-x (p <0.001), insoluble Aβ1-40(p <0.01), and insolubleAβ1-42(p <0.001) in the cerebral cortex and hippocampus, respectively.However, there were no significant differences in the levels of soluble Aβ (totalAβ1-x, Aβ1-40, Aβ1-42) between the two groups (p>0.05).4. APP βCTF levels in brain from APPswe/PS1dE9mice treated with HNGor vehicle were examined by ELISA. No significant difference was found in theAPP βCTF levels in hippocampus and cerebral cortex between HNG-andvehicle-treated APPswe/PS1dE9mice (p>0.05).5. The levels of reactive astrocytes and activated microglia in cerebral cortexand hippocampus from the four groups were examined by immunohistochemicalstaining. The results showed that vehicle-treated APPswe/PS1dE9mice had asignificant increase in the amount of activated microglia in cerebral cortex and hippocampus compared with vehicle-and HNG-treated WT mice (p <0.001,respectively), while HNG treatment in APPswe/PS1dE9mice resulted in asignificant decrease in the amount of activated microglia in cerebral cortex andhippocampus compared with vehicle-treated APPswe/PS1dE9mice (p <0.001,respectively).6. The levels of inflammatory cytokines (IL-1β, IL-6, and TNFa levels) incerebral cortex from the four groups were quantitatively measured by ELISA.The results indicated that a significant increase in the levels of IL-1β (p <0.001,respectively), IL-6(p <0.01, respectively), and TNFα (p <0.001, respectively) invehicle-treated APPswe/PS1dE9mice compared with vehicle-and HNG-treatedWT mice, while HNG treatment in APPswe/PS1dE9mice significantly decreasedthese elevated levels of IL-1β (p <0.001), IL-6(p <0.01), and TNFα (p <0.001)compared with vehicle-treated APPswe/PS1dE9mice.ConclusionIn summary, the present results provide evidence that1. Intraperitoneal injection of HNG is effective in improving cognitive deficits inthe middle-aged APPswe/PS1dE9mice with pre-existing abundant Aβ pathology.2. HNG treatment is effective in reducing cerebral plaque deposition (the total Aβplaques load and the fibrillar plaques load) in the middle-aged APPswe/PS1dE9mice.3. HNG treatment is effective in lowering the levels of insoluble total Aβ1-x,insoluble Aβ1-40, and insoluble Aβ1-42in the cerebral cortex and hippocampusof the middle-aged APPswe/PS1dE9mice.4. HNG treatment is effective in decreasing the amount of activated microgliaand reactive astrocyte in in the cerebral cortex and hippocampus of themiddle-aged APPswe/PS1dE9mice. 5. HNG treatment is effective in lowering the levels of inflammatory cytokines(IL-1β, IL-6, and TNFa levels) in cerebral cortex of the middle-agedAPPswe/PS1dE9mice.