ABSTRACT
Alzheimer's disease (AD) is a progressively neurodegenerative disorder, which seriously affects human health but is still irreversible up to now. Recent studies indicate that type 2 diabetes mellitus (T2DM) is an important risk factor for AD, and the drugs used for treatment of T2DM have shown some neuroprotective effects in the treatment of AD. Glucagon-like peptide-1 (GLP-1)/ glucose-dependent insulinotropic polypeptide (GIP)/glucagon (Gcg) receptor Triagonist is a new monomeric polypeptide equally activating the GLP-1/GIP/Gcg receptors, which is built on the basis of GLP-1/Gcg receptor coagonist core sequence, and incorporated with partial amino acids of GIP. Recently, the Triagonist has been reported to be effective in alleviating diabetic complications in rodent models of obesity. The present study observed for the first time the cognitive improvement effects of the Triagonist in the triple-transgenic AD mice (3xTg-AD) by using multiple behavioral techniques, and explored its probable molecular mechanisms using ELISA and Western blot. The results showed that the chronic treatment with the Triagonist (i.p.) significantly reversed the impairments in working memory of 3xTg-AD mice, with an obvious increase in the percentage of correct spontaneous alternation in the Y maze; the Triagonist treatment also improved long-term spatial memory and re-learning ability of 3xTg-AD mice in classical Morris water maze and reverse water maze tests, with decreased escape latency in under water platform tests and increased swimming time in probe tests. ELISA and Western blot experiments showed that the Triagonist up-regulated the levels of cAMP, PKA and p-CREB in the hippocampus of 3xTg-AD mice. These results indicate that GLP-1/GIP/Gcg receptor Triagonist can improve the cognitive behaviors in 3xTg-AD mice, and the up-regulation of hippocampal cAMP/PKA/CREB signal pathway may mediate the neuroprotection of the Triagonist, suggesting that the GLP-1/GIP/Gcg receptor Triagonist may be a novel therapeutic strategy for the treatment of AD.
ABSTRACT
The deposition of amyloid-β protein (Aβ) in the brain is the most important pathological feature of Alzheimer's disease (AD). The mechanism of Aβ neurotoxicity may be closely related to the disturbance of intracellular Cahomeostasis. Non-invasive micro-test technique (NMT) is a novel technique developed in recent years, which can be used to directly record transmembrane ion influx and efflux in a non-contact way by detecting the diffusion potentials outside of the membrane. The present study examined the effects of Aβpretreatment on glutamate (Glu)-induced Cainflux and low [Ca] solution-induced Caefflux in the hippocampal slices of C57BL/6 mice using NMT. The results showed that: (1) acute administration of Glu (2.5, 5, 10 mmol/L) evoked a persistent transmembrane Cainflux in hippocampal CA1 neurons, with a rapid onset and subsequent decay; (2) pretreatment with Aβ dose-dependently increased the average rate of Cainflux induced by Glu during the initial 5 min, which was blocked by NMDA receptor antagonist D-APV; (3) perfusion with low [Ca] artificial cerebrospinal fluid (aCSF) induced a continuous Caefflux, which was mostly blocked by KB-R7943, a specific antagonist of Na/Caexchanger; (4) Aβpretreatment partially inhibited the low [Ca] aCSF-induced Caefflux. These results indicate that Aβ not only facilitates Cainflux but also inhibits Caefflux, which jointly contribute to the Aβ-induced intracellular Caoverload; the potentiation of Aβ on Glu excitotoxicity is mainly mediated by NMDA receptors, while the target for Aβ to affect Caefflux was mainly Na/Caexchanger. NMT showed multiple advantages in detecting transmembrane Caflux in brain slices, such as non-invasiveness to target cells, fast, convenient and real-time acquisition of Caflux. Therefore, this study provided new experimental evidence for Aβ-induced Caoverload, as well as a novel application for NMT in measuring transmembrane Caflux of neurons in the brain.