To investigate the effect of pramlintide, a pancreatic amyloid peptide analog, on learning and memory of Alzheimer’s disease (AD) mice through antioxidant stress, and to determine the expression of phosphatidylinositol 3-kinase/protein kinase B (PI3K/Akt) signaling pathway.

The APP/PS1 mice were divided into a pramlintide treatment group(intraperitoneal injection of 0.5 μmol/L per day for 10 weeks) and an AD group (same dose of PBS), with 5 mice in each group. The learning and memory abilities were detected with water maze test, the pathological changes of the hippocampus were observed with HE staining and immunohistochemistry, the morphological characteristics of dendritic spines in hippocampus were observed after Golgi staining, and the ultrastructure of hippocampal neurons was observed through transmission electron microscopy (TEM). The content of malondialdehyde (MDA) and the level of superoxide dismutase (SOD) in the hippocampal tissue were detected by biochemical assay, and the levels of inflammatory factors IL-6, TNF-α and IL-1β were determined with ELISA. Western blotting was applied to measure the expression of PI3K/Akt signaling pathway related proteins in the hippocampus. In the cell experiment, SH-SY5Y cells were added with Aβ 1-42 to establish a cell model of AD. After the cells were treated with pramlintide, the levels of oxidative stress and inflammatory response were detected, and cell apoptosis was detected by immunofluorescence.

The animal experiments showed that pramlintide treatment resulted in significantly shortened escape latency (P<0.01), increased platform crossings (P<0.01), and prolonged time to exploring hidden platform(P<0.01). In the hippocampal tissue of the pramlintide treatment group, HE staining displayed hippocampal neurons in high density and neat arrangement (P<0.05), immunohistochemical results showed significantly reduced Aβ protein (P<0.01), Golgi staining results demonstrated more dendritic spines (P<0.05), TEM revealed almost intact neuronal mitochondrial structure, with reduced vacuolization and clear and identifiable morphology. When compared with the AD group, the levels of oxidative stress and inflammatory response were decreased (P<0.01), and the relative expression of p-PI3K/PI3K and p-Akt/Akt proteins was increased (P<0.01) in the treatment group. In cell experiments, the levels of oxidative stress and inflammatory response were decreased in AD cell model after pramlintide treatment (P<0.01), and the results of immunofluorescence showed that cell apoptosis was declined (P<0.01).

Pramlintide can improve the cognitive function, reduce the hippocampal deposition of Aβ, reduce oxidative stress and inflammatory response, alleviate the pathological changes of neuronal ultrastructure, and enhance the expression of PI3K/Akt signaling pathway in AD mice.

To investigate the effects of amylin, also known as islet amyloid polypeptide (IAPP), on learning and memory abilities and the phosphatidylinositol 3-kinase/protein kinase B (PI3K/Akt) signaling pathway in APP/PS1 mice.

A total of 20 APP/PS1 mice were randomly divided into Alzheimer's disease (AD) group and IAPP group, with 10 mice in each group. The mice in the latter group were given an intraperitoneal injection of 0.5 μmol/L IAPP, and those of the former group received same dose of PBS. Both interventions were given once per day, for 10 weeks. Morris water maze test was used to measure the learning and memory abilities; HE staining was employed to observe the pathological changes in the hippocampus; Transmission electron microscopy was utilized to observe the ultrastructure of hippocampal neurons; Biochemical assay were conducted to detect the contents of glutathione peroxidase (GSH-Px), malondialdehyde (MDA) and superoxide dismutase (SOD) in hippocampal tissues; ELISA was applied to measure the levels of inflammatory factors such as IL-1β, IL-6, and TNF-α as well as content of Aβ42 in hippocampal tissues; And Western blotting was conducted to detect the expression of PI3K/Akt proteins.

Compared with the AD group, significantly shorter platform latency (P<0.01), increased number of traversing the platform and longer time to explore the hidden platform (P<0.01) were observed in the IAPP group, but no such difference was seen in the swimming speed of the mice. HE staining displayed that the IAPP group had more and well-arranged nerve cells in the hippocampal tissue when compared with the AD group (P<0.05). Lower Aβ protein expression (P<0.01), reduced oxidative stress and decreased contents of inflammatory factors (P<0.01) in hippocampal tissue were observed in the IAPP group than the AD group. The IAPP group showed clearer structure of neuronal mitochondria, reduced vacuolization, and better arranged microtubules and microfilaments, and elevated expression of p-PI3K/PI3K and p-Akt/Akt proteins when compared with the AD group (P<0.01).

Amylin can reduce oxidative stress and inflammatory responses, improve learning and memory abilities in AD mice, and promote the activity of PI3K/Akt signaling pathway.

To investigate the effects of intraperitoneal injection of islet amyloid polypeptide（IAPP）on the expression profiles of circular RNAs（circRNAs）and messenger RNAs（mRNAs）in the brain tissue of Alzheimer's disease（AD）mice and wild-type（WT）mice.

Six 10-month-old male APP/PS1 transgenic AD model and C57 WT mice（20~30 g）were employed in this study. They were randomly divided into 2 groups, and further assigned into AD+IAPP（AD mice with IAPP intraperitoneal injection）, WT+IAPP（WT mice with IAPP intraperitoneal injection）, AD+PBS（AD mice injected with same dose of PBS intraperitoneally）and WT+PBS（WT mice with intraperitoneal injection of PBS）groups（n=3）. After the intervention, total RNA was extracted from the brain tissue of 4 groups of mice, and gene chip sequencing was performed to screen differentially expressed circRNAs and mRNAs between AD+IAPP and WT+IAPP mice and between AD+PBS and WT+PBS mice. Among the differentially expressed circRNAs between AD+IAPP and WT+IAPP mice, 6 circRNAs were selected and subjected to real-time quantitative polymerase chain reaction（qRT-PCR）to verify the reliability of the microarray results. Gene ontology（GO）enrichment analysis and Kyoto Encyclopedia of Genes and Genomics（KEGG）pathway enrichment analysis were performed on the differentially expressed mRNAs. Subsequently, a competitive endogenous RNA（ceRNA）network was constructed for significantly differentially expressed circRNA_45921.

There were 237 circRNAs significantly differentially expressed between AD+IAPP and WT+IAPP mice, of which 157 were up-regulated and 80 were down-regulated. Totally 663 significantly differentially expressed mRNAs were found, including 348 up-regulated and 315 down-regulated. The results of qRT-PCR showed that the differential expression of 6 circRNAs was consistent with the results of gene chip, indicating that the results of gene chip sequencing were reliable. GO enrichment analysis revealed that differentially up-regulated mRNAs were significantly enriched in nucleoside phosphate binding, organelles and metabolism processes of phosphate containing compounds. The differentially down-regulated mRNAs were significantly enriched in transmembrane signal receptor activity, supramolecular fibers and tissue development. KEGG enrichment analysis indicated that differentially upregulated mRNAs were mainly enriched in signal pathways such as insulin secretion, oxidative phosphorylation, and Parkinson's disease, while those down-regulated ones in signal pathways such as neuroactive ligand receptor interactions, calcium signaling pathways, tyrosine metabolism and phenylalanine metabolism. CeRNA network displayed that the circRNA_45921/miR-34c-5p/Eef2k regulatory network may play a role in the functioning of IAPP.

Intraperitoneal injection of IAPP alters the expression profiles of circRNA and mRNA in the brain tissues of AD mice and WT mice. Differentially expressed Paip2, Cdon, Ttr, and circRNA_45921/miR-34c-5p/Eef2k regulatory network may have regulatory roles in IAPP regulating the development of AD.