Anti-amnesic Effect And Mechanism Of Cocaine-and Amphetamine-regulated Transcript (CART) In APP/PS1Mice

Backgroud:Alzheimer’s disease (AD) is presently considered the most devastating progressive neurodegenerative disorder. The key pathological feature of AD is described as the accumulation and deposition of Amyloid β protein (Aβ)(neuritic plaques) in the brain. Synaptic deficiency in AD is associated with reduced mRNA expression of several immediate early genes (IEGs) and AP-induced mitochondrial dysfunction.Objectives:The aims of this study are:1) to determine the expression patterns of CART in APP/PS1transgenic mouse brains;2) to investigate the effects of CART on synaptic impairment induced by Aβ;3) to explore the mechanism underlying of CART on Aβ-induced synaptic toxicity.Methods:The expression patterns of CART and Aβ in WT, APP/PS1mice and AD patients were determined by immunostaining. APP/PS1transgenic mice (10months old, n=30/group) were injected with CART or vehicle (2.5μg/kg, intra-vena caudalis). The blood-to-brain unidirectional influx of131I-CART was tested by radioactive labeling procedure. Learning and memory impairment was tested by Morris water maze, and the induction of synaptic plasticity was assessed electrophysiologically. The structure and number of synapses were determined by transmission electron microscope (TEM) and western blot in vivo. The expression of synaptic-related proteins, mitochondrial fission and fusion proteins were measured by real-time PCR and western blot, and the expression of IEGs were determined by a reporter gene assay. Mitochondrial depolarization and reactive oxygen species (ROS) production were measured by fluorescence microscopy and FACS analysis. The levels of 8-hydroxy-2-de-axyguanine (8-OHdG), Neurotrophin-3(3-NT),4-Hydroxynonenal (4-HNE) and ATP were measured by the ELISA. Statistical analyses were performed using ANOVA and post hoc Fisher’s PLSD tests, with P<0.05considered statistically significant.Results:In non-AD controls, CART was mainly distributed in cell body and neuritis in hypothalamus and cortex. In APP/PS1mice, CART was observed in amyloid plaques and neuritis, especially in pyriform cortex. Similar to APP/PS1mice, AD patients had CART immunoreactive in amyloid plaques, cells, and neuritis. The uptake of CART by the brain was high in thalamus, cortex, and hippocampus. CART administration significantly protected against learning and memory impairments in APP/PS1mice (P<0.05, n=30/group), and partially improved long-term potentiation (LTP) induction and synaptic efficiency. CART treatment induced several IEGs, including Nur77, Arc and Homerla, and regulated the expression of Nur77by increasing promoter activity. CART could suppress A(3induced intracellular ROS production and attenuated mitochondrial potentials reduction. Furthermore, mitochondrial functions were significantly improved in CART-treated animals compared to vehicle treatment.Conclusion:Our findings suggest that CART distributes in amyloid plaques and neuritis. CART significantly improves synaptic plasticity in AD models. The improvement in synaptic plasticity is also associated with the upregulation of IEGs expression and the reversion of mitochondrial dysfunction. Thus, CART may serve as a novel therapeutic target for AD.