The intracellular domain of sortilin interacts with Amyloid precursor protein and regulates its lysosomal and lipid raft trafficking

The processing of Amyloid precursor protein (APP) is multifaceted, comprising of protein transport, internalization and sequential proteolysis. However, the exact mechanism of APP intracellular trafficking and distribution remains unclear. To determine the interaction between sortilin and APP and the effect of sortilin on APP trafficking and processing, we studied the binding site and its function by mapping experiments, colocalization, coimmunoprecipitation and sucrose gradient fractionation. We identified for the first time that sortilin interacts with APP at both N- and C-terminal regions. The sortilin-FLVHRY (residues 787-792) and APP-NPTYKFFE (residues 759-766) motifs are crucial for the C-terminal interaction. We also found that lack of the FLVHRY motif reduces APP lysosomal targeting and increases APP distribution in lipid rafts in co-transfected HEK293 cells. These results are consistent with our in vivo data where sortilin knockout mice showed a decrease of APP lysosomal distribution and an increase of APP in lipid rafts. We further confirmed that overexpression of sortilin-FLVHRY mutants failed to rescue the lysosomal degradation of APP. Thus, our data suggests that sortilin is implicated in APP lysosomal and lipid raft targeting via its carboxyl-terminal F/YXXXXF/Y motif. Our study provides new molecular insights into APP trafficking and processing.Miao Yang, Balaji Virassamy, Swarna Lekha Vijayaraj, Yoon Lim, Khalil Saadipour, Yan- Jiang Wang, Yan-Chuang Han, Jin-Hua Zhong, Carlos R. Morales, Xin-Fu Zho

p75NTR ectodomain is a physiological neuroprotective molecule against amyloid-beta toxicity in the brain of Alzheimer's disease

In Alzheimer's disease (AD), neurodegenerative signals such as amyloid-beta (Aβ) and the precursors of neurotrophins, outbalance neurotrophic signals, causing synaptic dysfunction and neurodegeneration. The neurotrophin receptor p75 (p75NTR) is a receptor of Aβ and mediates Aβ-induced neurodegenerative signals. The shedding of its ectodomain from the cell surface is physiologically regulated; however, the function of the diffusible p75NTR ectodomain (p75ECD) after shedding remains largely not known. Here, we show that p75ECD levels in cerebrospinal fluid and in the brains of Alzheimer's patients and amyloid-beta precursor protein (APP)/PS1 transgenic mice were significantly reduced, due to inhibition of the sheddase-tumor necrosis factor-alpha-converting enzyme by Aβ. Restoration of p75ECD to the normal level by brain delivery of the gene encoding human p75ECD before or after Aβ deposition in the brain of APP/PS1 mice reversed the behavioral deficits and AD-type pathologies, such as Aβ deposit, apoptotic events, neuroinflammation, Tau phosphorylation and loss of dendritic spine, neuronal structures and synaptic proteins. Furthermore, p75ECD can also reduce amyloidogenesis by suppressing β-secretase expression and activities. Our data demonstrate that p75ECD is a physiologically neuroprotective molecule against Aβ toxicity and would be a novel therapeutic target and biomarker for AD.X-Q Yao, S-S Jiao, K Saadipour, F Zeng, Q-H Wang, C Zhu, L-L Shen, G-H Zeng, C-R Liang, J Wang, Y-H Liu, H-Y Hou, X Xu, Y-P Su, X-T Fan, H-L Xiao, L-F Lue, Y-Q Zeng, B Giunta, J-H Zhong, DG Walker, H-D Zhou, J Tan, X-F Zhou, and Y-J Wan

Effects of Ascorbic Acid on the Amplitude of Ventral Tegmental Area Field Action Potential in Morphine-Exposed Rats (An Electrophysiology Study)

Introduction & Objective: Evidences have indicated that the Ventral Tegmental Area (VTA) is the major source of dopamine (DA) neurons projecting to cortical and limbic regions involved in cognitive and motivational aspects of addiction. Also, studies have indicated that the Ascorbic acid (vitamin C) can reduce the dependency symptoms of opioids such as morphine via effect of activity on dopaminergic neuron in VTA. For this reason, the aim of this study was to assess the effects of ascorbic acid on the amplitude of Ventral Tegmental Area field action potential in morphine-exposed rats. Materials & Methods: Forty male Wistar’s rats were used in this experimental study conducted at Yasuj University of Medical Sciences in 2010. Animals were randomly divided into four groups after electrode implantation and recovery period: 1. No- Vit C and No-Addicted group (nVitC.nA) 2. Vit C and No-Addicted group (VitC.nA) 3. No- Vit C and Addicted group (nVitCA) 4.Vit C and Addicted (VitC.A), The Vit C groups received 500 mg/kg of Vit C during 20 days. For addicted groups morphine was administrated once daily for 20 days. In the 20th day, the field potential recording was accomplished. Two-way ANOVA was used for data analysis followed by the Tukey test for post hoc analysis. Results were considered significant at P < 0.05. Results: This study shows the exposure to morphine declined the power of Delta and Beta bands (p<0.05) and Vit C solely enhance power of Theta and Beta (p<0.05, p<0.001) in VTA nuclei. Furthermore, Vit C could alter power of some bands which were affected by morphine. Therefore it seems that Vit C has an increasing effects on them (p<0.05). Conclusion: Although the effect of Vit C on power of the VTA bands is not well known, but it is supposed that this phenomenon can be related to alteration in activity of dopaminergic neuron in the brain

Cellular trafficking of amyloid precursor protein in amyloidogenesis physiological and pathological significance

The accumulation of excess intracellular or extracellular amyloid beta (Aβ) is one of the key pathological events in Alzheimer's disease (AD). Aβ is generated from the cleavage of amyloid precursor protein (APP) by beta secretase-1 (BACE1) and gamma secretase (γ-secretase) within the cells. The endocytic trafficking of APP facilitates amyloidogenesis while at the cell surface, APP is predominantly processed in a non-amyloidogenic manner. Several adaptor proteins bind to both APP and BACE1, regulating their trafficking and recycling along the secretory and endocytic pathways. The phosphorylation of APP at Thr668 and BACE1 at Ser498, also influence their trafficking. Neurotrophins and proneurotrophins also influence APP trafficking through their receptors. In this review, we describe the molecular trafficking pathways of APP and BACE1 that lead to Aβ generation, the involvement of different signaling molecules or adaptor proteins regulating APP and BACE1 subcellular localization. We have also discussed how neurotrophins could modulate amyloidogenesis through their receptors.Noralyn Basco Mañucat-Tan, Khalil Saadipour, Yan-Jiang Wang, Larisa Bobrovskaya and Zhou Xin-F

Sortilin inhibits amyloid pathology by regulating non-specific degradation of APP

Amyloid plaque is one of the hallmarks of Alzheimer's disease (AD). The key component beta-amyloid (Aβ) is generated via proteolytic processing of amyloid precursor protein (APP). Sortilin (encoded by the gene Sort1) is a vacuolar protein sorting 10 protein domain-containing receptor, which is up-regulated in the brain of AD, colocalizes with amyloid plaques and interacts with APP. However, its role in amyloidogenesis remains unclear. In this study, we first found that the protein level of sortilin was up-regulated in the neocortex of aged (7 and 9months old) but not young (2 and 5months old) AD mice (APP/PS1). 9months old APP/PS1 transgenic mice with Sort1 gene knockout showed increased amyloid pathology in the brain; and this phenotype was rescued by intrahippocampal injection of AAV-hSORT1. Moreover, the 9months old APP/PS1 mice without Sort1 also displayed a decreased number of neurons and increased astrocyte activation in the hippocampus. In addition, the present study showed that the intracellular domain of sortilin was involved in the regulation of the non-specific degradation of APP. Together, our findings indicate that sortilin is a beneficial protein for the reduction of amyloid pathology in APP/PS1 mice by promoting APP degradation.Chun-Sheng Ruan, Jia Liu, Miao Yang, Khalil Saadipour, Yue-Qin Zeng, Hong Liao, Yan-Jiang Wang, Larisa Bobrovskaya, Xin-Fu Zho

Amyloid beta(1)--(42) (Abeta(42)) up-regulates the expression of sortilin via the p75NTR/RhoA signaling pathway

Sortilin, a Golgi sorting protein and a member of the VPS10P family, is the co-receptor for proneurotrophins, regulates protein trafficking, targets proteins to lysosomes, and regulates low density lipoprotein metabolism. The aim of this study was to investigate the expression and regulation of sortilin in Alzheimer's disease (AD). A significantly increased level of sortilin was found in human AD brain and in the brains of 6-month-old swedish-amyloid precursor protein/PS1dE9 transgenic mice. Aβ₄₂ enhanced the protein and mRNA expression levels of sortilin in a dose- and time-dependent manner in SH-SY5Y cells, but had no effect on sorLA. In addition, proBDNF also significantly increased the protein and mRNA expression of sortilin in these cells. The recombinant extracellular domain of p75NTR (P75ECD-FC), or the antibody against the extracellular domain of p75NTR, blocked the up-regulation of sortilin induced by Amyloid-β protein (Aβ), suggesting that Aβ₄₂ increased the expression level of sortilin and mRNA in SH-SY5Y via the p75NTR receptor. Inhibition of ROCK, but not Jun N-terminal kinase, suppressed constitutive and Aβ₄₂-induced expression of sortilin. In conclusion, this study shows that sortilin expression is increased in the AD brain in human and mice and that Aβ₄₂ oligomer increases sortilin gene and protein expression through p75NTR and RhoA signaling pathways, suggesting a potential physiological interaction of Aβ₄₂ and sortilin in Alzheimer's disease.Khalil Saadipour, Maio Yang, Yoon Lim, Kristen Georgiou, Ying Sun, Damien Keating, Jia Liu, Ye-Ran Wang, Wei-ping Gai, Jin-hua Zhong, Yan-Jiang Wang and Xin-fu Zho

p75NTR ectodomain is a physiological neuroprotective molecule against amyloid-beta toxicity in the brain of Alzheimer’s disease

In Alzheimer's disease (AD), neurodegenerative signals such as amyloid-beta (Aβ) and the precursors of neurotrophins, outbalance neurotrophic signals, causing synaptic dysfunction and neurodegeneration. The neurotrophin receptor p75 (p75NTR) is a receptor of Aβ and mediates Aβ-induced neurodegenerative signals. The shedding of its ectodomain from the cell surface is physiologically regulated; however, the function of the diffusible p75NTR ectodomain (p75ECD) after shedding remains largely not known. Here, we show that p75ECD levels in cerebrospinal fluid and in the brains of Alzheimer's patients and amyloid-beta precursor protein (APP)/PS1 transgenic mice were significantly reduced, due to inhibition of the sheddase-tumor necrosis factor-alpha-converting enzyme by Aβ. Restoration of p75ECD to the normal level by brain delivery of the gene encoding human p75ECD before or after Aβ deposition in the brain of APP/PS1 mice reversed the behavioral deficits and AD-type pathologies, such as Aβ deposit, apoptotic events, neuroinflammation, Tau phosphorylation and loss of dendritic spine, neuronal structures and synaptic proteins. Furthermore, p75ECD can also reduce amyloidogenesis by suppressing β-secretase expression and activities. Our data demonstrate that p75ECD is a physiologically neuroprotective molecule against Aβ toxicity and would be a novel therapeutic target and biomarker for AD