Metformin Regulates AMPK-STRT1-PGC1α Pathway To Improve Cognitive Function Of SAMP8 Mice

Objective: Alzheimer’s disease(AD) is the nervous system degenerative disease. Research on the pathogeny of Alzheimer’s disease is always a hot issue in brain field. Main hypothesis is amyloid(Aβ) deposition in neurons and neurofibrillary tangles(NFT). In recent years, some researches has pointed out that metformin can improve the spatial learning and memory ability of rodents, but also extend the life of rodents. Hence, this studies aimed to explore that metformin improve the ability of learning and memory molecular and epigenetic mechanisms in SAMP8 mice.Methods: In this study, firstly, using water maze test and novel object recognition test detected learning memory ability of 3 months SAMP8 mice and 8 months SAMP8 mice, compared with similar months SAMR1 mice. Applicating Western Bloting assay was to detect AMPK, AMPKp-172, PGC1α, SIRT1, BDNF, BACE1 and Aβ molecular change trends in the hippocampus brains area. Secondly, 7 months SAMP8 mice were injected metformin(200 mg/kg) for 38 days. The control group(7 months SAMP8 mice) was injected saline recording weight,which was detect every three days. The 39 days began to detect the learning and memory ability. After the sacrifice, the corresponding molecular changes were detected. Lastly, using chromatin immune coprecipitation technology(CHIP) explored that metformin treated epigenetic mechanism of alzheimer’s disease.Results: In the novel object test, 8 months SAMP8 mice identification index decreased(P < 0.05) compared with 8 months SAMR1 mice. In water maze test, 8 months SAMP8 mice showed that crossing the platform times and staying time in the target quadrant significantly reduced(P < 0.05). However,3 months SAMP8 mice and 3 months SAMR1 mice did not have significant differences(P> 0.05). Mice swimming speed did not significant change(P>0.05) during the test. Western Bloting found that AMPK-SIRT1-PGC1α signaling pathway activity decline(P<0.05) in the hippocampus regions of 8 months SAMP8 mice compared with 8 months SAMR1 mice; BACE1 and Aβ molecular level significantly rise(P<0.05); BDNF and PSD95 protein level significantly down-regulation(P < 0.05). However,3 months SAMP8 mice and 3 months SAMR1 mice did not have significant differences(P> 0.05). After intraperitoneal injection of metformin, 8 months SAMP8 mice evidently improved the ability of learning and memory. In novel object test, MET group mice exhibited higher new object recognition index contrasted with saline group mice(P<0.05). In water maze test, compared with saline group mice, MET group mice emerged that crossing the number of the target platform and spending time in the target quadrant significantly increased(P<0.05). Mice swimming speed did not significant change(P>0.05) during the test. Western Bloting experiments found that, compared with saline group mice, AMPK-SIRT1-PGC1α signaling pathways remarkable activated(P<0.05) in the hippocampus of MET group mice; BACE1 and Aβ protein level were significantly decreased(P<0.05). Besides, BDNF and PSD95 melocure level were distinct increase; CHIP experiments found that compared with saline group mice, BACE1 exons promoter region of the acetylation of histone H3 combination level were significantly reduced(P < 0.05) in the MET group mice; the BDNF gene exon IV and VI the promoter region of the acetylation of histone H3 combination levels increased significantly(P < 0.05) in the MET group mice.Conclusion: According to the above experimental results, we speculated that AMPK-SIRT1-PGC1α signaling pathway down-regulation was one of Alzheimer’s disease mechanism. Hence, it induced BACE1 the protein level increase and Aβ deposition. In addition, BDNF and PSD95 protein level were down-regulation in the hippocampus of 8 months SAMP8 mice. This study found that low dose metformin could active AMPK-SIRT1-PGC1α signaling pathways and inhibit BACE1 protein level and the expression of Aβ. At the same time, low dose metformin increased the activity of BDNF and PSD95 and then improved the synaptic plasticity of the central nervous system.Through chromatin immune co-precipitation technique, we found that the metformin activated AMPK-SIRT1-PGC1α signaling pathway. The pathway lowered BACE1 exons promoter region combination ability of the acetylation of histone H3 levels to regulate the expression of BACE1 and Aβ. Besides, the pathway increased the BDNF gene exon IV and VI the promoter region combination ability of the acetylation of histone H3 levels to promote expression of BDNF protein, and then improved the ability of learning and memory.Therefore, this study found that low doses of metformin could improve the cognitive function damage of SAMP8 mice. Western bloting experiments and chromatin immune coprecipitation technology shown that metformin alleviated cognitive impairment molecules and epigenetic mechanisms. It was provided a new theoretical basis that the perspective of genes explored the pathogenesis of Alzheimer’s disease in the furture.