Effects Of S14G-Humanin And Its Mechanisms Against Dementia Model Induced By β-amyloid Peptide 31-35 In Rat

Background:Alzheimer's disease(AD)is the most common cause of dementia in the elderly population, characterized by progressive cognitive dysfunction. The etiology and pathogenesis of AD are complex so far, but the leading cause may be excessive deposition ofβ-amyloid protein (Aβ) in brain tissue and its neurotoxic effects. Therefore, it is important to effectively prevent or reduce the neurotoxic of Aβin prevention and treatment of AD. Full length of Aβ(Aβ1-40, Aβ1-42) and its fragment Aβ25-35 have shown toxic effects on neurons in various experimental models, while Aβ31-35, as a smaller Aβpeptides, also has the similar toxic effects compared with full length of Aβand Aβ25- 35. Therefore, it can be explored and studied as the shortest fragment with neruotoxicity of Aβ. Humanin (HN) and its derivative, S14G-Humanin (HNG), is recently discoveried as a new neuroprotective factor best known for its ability to markedly suppress neuronal injury caused by Aβ(Aβ1-40,Aβ1-42)and AD-related toxitic, however its exact mechanism has not been clarified. In our previous experiments, we also know that HN can superss apoptosis in cultured cortical neurons induced by Aβ31-35 in vitro.In present study, we further explore and analysis the effect and mechanism of HNG in vivo by building a AD model of intracerebroventricular injection.PARTⅠ:Effects of S14G-Humanin on Aβ31-35-induced dysfunction of behavior and apoptosis in ratObjective: To observe the effects of HNG on Aβ31-35-induced dysfunction of behavior and apoptosis in vivo.Methods: AD model was established by intracerebroventricular injection with aggregation of Aβ31-35, at the same time different concentrations of HNG were injected by intracerebroventri- cular. Morris water maze test was done to observe the rat's ability of learning and memory, then neuronal apoptosis was analyzed by TUNEL and caspase- 3 staining .Results:1. Learning and memory ability detected by Water maze: Compared with the control group, ability of leaning and memory is declined in Aβ31-35 group (P<0.05). Compared with the Aβ31-35 group, ability of leaning and memory is improved in Aβ31-35+HNG groups(1, 0.1 mmol /L,P<0.05). There is no remarkably difference between Aβ31-35 group and Aβ31-35+HNG group ( 0.01 mmol/L, P<0.05).2. Apoptosis detected by TUNEL: Compared with the control group, apoptotic index of hippocampal neurons are remarkably increased in Aβ31-35 group(P<0.05). Compared with the Aβ31-35 group, apoptotic index of hippocampal neurons are remarkably decreased in HNG groups(1, 0.1, 0.01 mmol/L, P<0.05). With the increasing of HNG concentration, apoptotic index are decreased.3. Caspase-3 detected by immunohistochemistry: Compared with the control group, positive cells of caspase-3 in hippocampal neurons are remarkably increased in Aβ31-35 group(P<0.05). Compared with the Aβ31-35 group, positive cells of caspase-3 in hippocampal neurons are remarkably decreased in HNG groups(1, 0.1, 0.01 mmol/L, P<0.05). With the increasing of HNG concentration, positive cells of caspase-3 are decreased.PARTⅡ:Mechanisms underlying of S14G-Humanin against Aβ31-35-induced neurotoxityObjective:To explore the effects of inflammatory on neuroprotective of HNG by observing shape and function of small glial cells.Methods: AD model was established by intracerebroventricular injection with aggregation of Aβ31-35, at the same time different concentrations of HNG were injected by intracerebroventricular. By observing shape and function of small glial cells, numbers of actived microgila and levels of IL-6 in hippocampus and cortex were detected by immunohistochemistry and ELISA kit.Results:1. Actived microglia detected by immunohistochemistry : Compared with the control group, actived microglias are remarkably elevated in Aβ31-35 group(P<0.05). Compared with the Aβ31-35 group, actived microglias in cortex and hippocampal are remarkably declined in HNG groups(1, 0.1, 0.01 mmol/L, P<0.05).With the increasing of HNG concentration, actived microglias in cortex and hippocampal are declined.2. IL-6 detected by ELISA: Compared with the control group, levels of IL-6 in cortex and hippocampal are remarkably incerased in Aβ31-35 group(P<0.05). Compared with the Aβ31-35 group, levels of IL-6 in cortex and hippocampal are remarkably decreased in HNG groups(1, 0.1, 0.01 mmol/L, P<0.05). With the increasing of HNG concentration, levels of IL-6 in cortex and hippocampal are decreased.Conclusion:1. HNG can remarkably improve rats'spatial learning and memory disorder and neuronal apoptosis induced by Aβ31-35. 2. One of the impossible neuroprotective mechanisms of HNG. is to inhibit activiated microglia which can induce inflammation.