RabGEF1/Rabex-5 Regulates TrkA-Mediated Neurite Outgrowth and NMDA-Induced Signaling Activation in NGF-Differentiated PC12 Cells

Electroacupuncture regulates Rab5a-mediating NGF transduction to improve learning and memory ability in the early stage of AD mice

AIMS

Nerve growth factor (NGF) loss is a potential factor for the degeneration of basal forebrain cholinergic neurons (BFCNs) in Alzheimer's disease (AD), and Rab5a is a key regulatory molecule of NGF signaling transduction. Here, we investigated the changes of Rab5a in 5 × FAD mice and further explored the mechanism of Electroacupuncture (EA) treatment in improving cognition in the early stage of AD.

METHODS

The total Rab5a and Rab5a-GTP in 5-month-old 5 × FAD mice and wild-type mice were detected using WB and IP technologies. 5 × FAD mice were treated with EA at the Bai hui (DU20) and Shen ting (DU24) acupoints for 4 weeks and CRE/LOXP technology was used to confirm the role of Rab5a in AD mediated by EA stimulation. The Novel Object Recognition and Morris water maze tests were used to evaluate the cognitive function of 5 × FAD mice. The Nissl, immunohistochemistry, and Thioflavin S staining were used to observe pathological morphological changes in the basal forebrain circuit. The Golgi staining was used to investigate the synaptic plasticity of the basal forebrain circuit and WB technology was used to detect the expression levels of cholinergic-related and NGF signal-related proteins.

RESULTS

The total Rab5a was unaltered, but Rab5a-GTP increased and the rab5a-positive early endosomes appeared enlarged in the hippocampus of 5 × FAD mice. Notably, EA reduced Rab5a-GTP in the hippocampus in the early stage of 5 × FAD mice. EA could improve object recognition memory and spatial learning memory by reducing Rab5a activity in the early stage of 5 × FAD mice. Moreover, EA could reduce Rab5a activity to increase NGF transduction and increase the levels of phosphorylated TrkA, AKT, and ERK in the basal forebrain and hippocampus, and increase the expression of cholinergic-related proteins, such as ChAT, vAchT, ChT1, m1AchR, and m2AchR in the basal forebrain and ChAT, m1AchR, and m2AchR in the hippocampus, improving synaptic plasticity in the basal forebrain hippocampal circuit in the early stage of 5 × FAD mice.

CONCLUSIONS

Rab5a hyperactivation is an early pathological manifestation of 5 × FAD mice. EA could suppress Rab5a-GTP to promote the transduction of NGF signaling, and enhance the synaptic plasticity of the basal forebrain hippocampal circuit improving cognitive impairment in the early stage of 5 × FAD mice.

Cyanidin Ameliorates Bisphenol A-Induced Alzheimer's Disease Pathology by Restoring Wnt/β-Catenin Signaling Cascade: an In Vitro Study

Alzheimer's disease (AD) is a progressive neurodegenerative disorder causing memory loss and cognitive decline, linked to amyloid-beta (Aβ) plaques and hyperphosphorylated tau protein accumulation in the brain. Environmental pollutant bisphenol A (BPA) has been implicated in AD pathology due to its neurotoxic effects. This study aims to evaluate cyanidin from flower bracts of Musa acuminata Colla (red variety; AAA group) for its neuroprotective properties against BPA-induced AD pathology. The extraction of cyanidin was optimized using 70% ethanol in acidified water, showing promising anti-acetylcholinesterase activity. Cyanidin was effectively purified from the resultant extract and characterized using spectroscopic techniques. Two gradient doses of cyanidin (90 and 10 µg/ml) were determined based on cell viability assay. The role of cyanidin in promoting nerve growth and differentiation was assessed in PC12 cells for up to 72 h. A discernible and statistically significant difference was assessed in neurite extension at both doses at 72 h, followed by pre-treatment with cyanidin. BPA stimulation significantly increased the p-tau expression compared to the control (p < 0.0001). Pre-treatment with cyanidin reduced the tau expression; however, a significant difference was observed compared to control cells (p = 0.0003). Cyanidin significantly enhanced the mRNA expression of Wnt3a (p < 0.0001), β-catenin (p = 0.0004), and NeuroD1 (p = 0.0289), and decreased the expression of WIF1(p = 0.0040) and DKK1 (p < 0.0001), which are Wnt antagonist when compared to cells stimulated with BPA. Conclusively, our finding suggests that cyanidin could agonize nerve growth factor and promote neuronal differentiation, reduce tau-hyperphosphorylation by restoring the Wnt/β-catenin signaling cascade, and thereby render its neuroprotective potential against BPA-induced AD pathology.

Proteomic analysis across patient iPSC-based models and human post-mortem hippocampal tissue reveals early cellular dysfunction and progression of Alzheimer's disease pathogenesis

The hippocampus is a primary region affected in Alzheimer's disease (AD). Because AD postmortem brain tissue is not available prior to symptomatic stage, we lack understanding of early cellular pathogenic mechanisms. To address this issue, we examined the cellular origin and progression of AD pathogenesis by comparing patient-based model systems including iPSC-derived brain cells transplanted into the mouse brain hippocampus. Proteomic analysis of the graft enabled the identification of pathways and network dysfunction in AD patient brain cells, associated with increased levels of Aβ-42 and β-sheet structures. Interestingly, the host cells surrounding the AD graft also presented alterations in cellular biological pathways. Furthermore, proteomic analysis across human iPSC-based models and human post-mortem hippocampal tissue projected coherent longitudinal cellular changes indicative of early to end stage AD cellular pathogenesis. Our data showcase patient-based models to study the cell autonomous origin and progression of AD pathogenesis.

Nerve growth factor in metabolic complications and Alzheimer's disease: Physiology and therapeutic potential

As the population ages, obesity and metabolic complications as well as neurological disorders are becoming more prevalent, with huge economic burdens on both societies and families. New therapeutics are urgently needed. Nerve growth factor (NGF), first discovered in 1950s, is a neurotrophic factor involved in regulating cell proliferation, growth, survival, and apoptosis in both central and peripheral nervous systems. NGF and its precursor, proNGF, bind to TrkA and p75 receptors and initiate protein phosphorylation cascades, resulting in changes of cellular functions, and are associated with obesity, diabetes and its complications, and Alzheimer's disease. In this article, we summarize changes in NGF levels in metabolic and neuronal disorders, the signal transduction initiated by NGF and proNGF, the physiological and pathophysiological relevance, and therapeutic potential in treating chronic metabolic diseases and cognitive decline.

Endolysosomal Targeting of Mitochondria Is Integral to BAX-Mediated Mitochondrial Permeabilization during Apoptosis Signaling

Mitochondrial outer membrane permeabilization (MOMP) is a core event in apoptosis signaling. However, the underlying mechanism of BAX and BAK pore formation remains incompletely understood. We demonstrate that mitochondria are globally and dynamically targeted by endolysosomes (ELs) during MOMP. In response to pro-apoptotic BH3-only protein signaling and pharmacological MOMP induction, ELs increasingly form transient contacts with mitochondria. Subsequently, ELs rapidly accumulate within the entire mitochondrial compartment. This switch-like accumulation period temporally coincides with mitochondrial BAX clustering and cytochrome c release. Remarkably, interactions of ELs with mitochondria control BAX recruitment and pore formation. Knockdown of Rab5A, Rab5C, or USP15 interferes with EL targeting of mitochondria and functionally uncouples BAX clustering from cytochrome c release, while knockdown of the Rab5 exchange factor Rabex-5 impairs both BAX clustering and cytochrome c release. Together, these data reveal that EL-mitochondrial inter-organelle communication is an integral regulatory component of functional MOMP execution during cellular apoptosis signaling.

Cucurbitacin B induces neurogenesis in PC12 cells and protects memory in APP/PS1 mice

Cucurbitacin B (CuB) isolated from Cucumis melo by using a PC12 cell bioassay system exhibited significant nerve growth factor (NGF)‐mimic or NGF‐enhancing activity in PC12 and primary neuron cells. It was also demonstrated pro‐neurogenesis effects in ICR and APP/PS1 mice and improved memory deficit of APP/PS1 mice. Its possible mechanism includes significant induction of the phosphorylation of glucocorticoid receptor (GR), protein kinase C (PKC), phospholipase C (PLC) and inhibition of cofilin. ChemProteoBase profiling, binding assay and cellular thermal shift assay (CETSA) were used to determine the target protein. Results revealed that CuB could affect actin dynamics as an actin inhibitor but did not bind with GR. The protein level of cofilin in PC12 cells after treating 0.3 μM and different temperatures was significantly higher than that of control group. Other neurotrophic signalling pathways, such as TrkA/TrkB, were analysed with specific inhibitors and Western blot. The inhibitors of TrkA, PLC, PKC, Ras, Raf and ERK1/2 significantly decreased the percentage of PC12 cells with neurite outgrowth and shortened the length of neurite outgrowth induced by CuB. CuB significantly induced the phosphorylation of TrkA, ERK and CREB. The phosphorylation of these proteins was obviously decreased by their specific inhibitors. These results suggest that cofilin is a candidate target protein of CuB in PC12 cells and that the GR/PLC/PKC and TrkA/Ras/Raf/ERK signalling pathways play important roles in the neuroprotective effect of CuB.

Long-term prenatal exposure to paracetamol is associated with DNA methylation differences in children diagnosed with ADHD

BACKGROUND

Epidemiological studies have shown that long-term exposure to paracetamol during pregnancy is associated with attention-deficit/hyperactivity disorder (ADHD). The mechanism by which paracetamol may modulate the increased risk of developing ADHD is currently unknown. We have conducted an epigenome-wide association study (n = 384 cord blood samples) and investigated whether prenatal exposure to paracetamol is associated with DNA methylation in children diagnosed with ADHD.

RESULTS

Analyses identified significant differences in DNA methylation (n = 6211 CpGs) associated with prenatal exposure to paracetamol for more than 20 days in children diagnosed with ADHD compared to controls. In addition, these samples were differentially methylated compared to samples with ADHD exposed to paracetamol for less than 20 days (n = 2089 CpGs) and not exposed to paracetamol (n = 193 CpGs). Interestingly, several of the top genes ranked according to significance and effect size have been linked to ADHD, neural development, and neurotransmission. Gene ontology analysis revealed enrichment of pathways involved in oxidative stress, neurological processes, and the olfactory sensory system, which have previously been implicated in the etiology of ADHD.

CONCLUSIONS

These initial findings suggest that in individuals susceptible to ADHD, prenatal long-term exposure to paracetamol is associated with DNA methylation differences compared to controls.

Rab GTPase signaling in neurite outgrowth and axon specification

Neurons are highly polarized cells that contain specialized subcellular domains involved in information transmission in the nervous system. Specifically, the somatodendritic compartment receives neuronal inputs while the axons convey information through the synapse. The establishment of asymmetric domains requires a specific delivery of components, including organelles, proteins, and membrane. The Rab family of small GTPases plays an essential role in membrane trafficking. Signaling cascades triggered by extrinsic and intrinsic factors tightly regulate Rab functions in cells, with Rab protein activation depending on GDP/GTP binding to establish a binary mode of action. This review summarizes the contributions of several Rab family members involved in trans-Golgi, early/late endosomes, and recycling endosomes during neurite development and axonal outgrowth. The regulation of some Rabs by guanine exchanging factors and GTPase activating proteins will also be addressed. Finally, discussion will be provided on how specific effector-mediated Rab activation modifies several molecules essential to neuronal differentiation. © 2016 Wiley Periodicals, Inc.