Neuroprotective Effect And Mechanism Of S14G-Humanin Against Beta-amyloid-induced Synaptic Plasticity Impairment And Dysfunction In Progression Of Alzheimer's Disease

Background and objective:Growing evidence has shown that both soluble and fibrillar amyloid-beta peptide (Aβ) play a critical role in the pathogenesis of Alzheimer's disease (AD). It is now considered to be a key problem that how to inhibit the neurotoxcity of Aβin clinical therapy for the disease. Although the novel neuroprotective agents Humanin and its derivative S14G-Humanin (HNG), have brought new hope for AD therapy, the effect and precise mechanism of HNG on neuroprotection against Aβ-indued dysfunction still remain to be elucidated. In order to better understand the therapeutic potential of Humanin and its derivative for AD, we investigated for the first the neuroprotective effect and mechanism of HNG against Aβ-induced impairment on synaptic plasicity in mouse hippocampal slices, and on congnitive function and Aβexpression in APP/PS-1 transgenic mice.Methods:1. By using multi-channel extra-cellular recording system (MED system), immunohistochemistry and Western blot, we investigated the neuroprotective effect and mechanism of HNG against soluble Aβ-induced impairment on synaptic plasticity in mouse hippocampal slices in vitro.2. By using multiple ethological tests, immunohistochemistry and Thioflavin-S staining, we investigated neuroprotective effect and mechanism of HNG on ethology and Aβexpression in APP/PS-1 transgenic mice in vivo.Results:1. Among normal control group, Aβ25-35 group, HNG group and different concentration HNG+Aβ25-35 groups, amplitude and slope of excitatory postsynaptic potential (EPSP) gradually increased with application of increasing stimulus intensity, and no significant changes were found between each group at the same stimulus intensity (P>0.05).2. Compared with normal control group, both early-phase long-term potentiation (E-LTP) and late-phase long-term potentiation (L-LTP) in hippocampal CA1 region were significantly inhibited by Aβ25-35 (P<0.001), and HNG had no direct influence on the E-LTP and L-LTP induction (P>0.05).3. Compared with Aβ25-35 group, co-application of 100nM HNG appeared to be a tendency of reducing Aβ25-35-induced E-LTP and L-LTP inhibition, but it did not reach statistic significance (P>0.05). Moreover, co-application of 200nM HNG greatly ameliorated Aβ25-35-induced E-LTP and L-LTP inhibition (P<0.05), and co-application of 400nM HNG completely blocked Aβ25-35-induced E-LTP and L-LTP inhibition (P<0.001).4. Among normal control group, HNG group, Aβ25-35 group and Aβ25-35+HNG group, no significant differences were found in the level of p-CREB(Ser133) between groups during E-LTP induction (P>0.05). However, when compared with normal control and HNG group, Aβ25-35 induced a significant reduction of p-CREB(Ser133) during L-LTP induction (P<0.001), while the decreased p-CREB(Ser133) was restored by HNG treatment (P<0.001).5. Morris water maze tests revealed that APP/PS-1+HNG group has significantly shorter escape laterncy in the hidden platform-swimming trails, and significantly more time in the target quadrant in probe trail compared with APP/PS-1+vehicle group (P<0.05). Furthermore, step-through tests showed that APP/PS-1+HNG group has significantly longer laterncy for entering dark chamber after electric shock compared with APP/PS-1+vehicle group (P<0.05), and shuttle-box tests disclosed that APP/PS-1+HNG group has significantly more active avoidance number in acquisition and retention tests as compared with APP/PS-1+vehicle group (P<0.05).6. As compared with APP/PS-1+vehicle group, APP/PS-1+HNG group appeared to be no significant difference in Aβplaque area in hippocampus and cortex (P>0.05), while significant reduction of fibrilliar Aβplaque area was seen in hippocampus and cortex (P<0.001).Conclusions:1. Low-concentration soluble Aβmay cause synaptic plasticity impairment by inhibiting E-LTP and L-LTP induction in hippocampal CA1 region.2. HNG has a protective role on Aβ-induced synaptic plasticity impairment by reversing the soluble Aβ-induced E-LTP and L-LTP inhibition in hippocampal CA1 region in a dose-dependent manner.3. p-CREB(Ser133) could not involve in soluble Aβ-induced E-LTP inhibition, or HNG-induced E-LTP protection against Aβin hippocampal CA1 region.4. Soluble Aβinhibited L-LTP induction through reducing p-CREB(Ser133) level in hippocampal CA1 region, while HNG efficacy for L-LTP protection through restoring p-CREB(Ser133) expression in CA1 region.5. HNG may ameliorate the dysfunction of spatial learning and memory, insulting stimulus-induced memory, reflexsive learning and memory in APP/PS-1 transgenic mouse.6. HNG could not reduce the production of Aβ, but could inhibit the formation and deposition of fibrilliar Aβplaque in hippocampus and cortex in APP/PS-1 transgenic mice.