TRAF6 and p62 inhibit amyloid β-induced neuronal death through p75 neurotrophin receptor

Small molecule modulation of p75NTR engages the autophagy-lysosomal pathway and reduces huntingtin aggregates in cellular and mouse models of Huntington's disease

Huntington's disease (HD) is a neurodegenerative disorder caused by a CAG repeat expansion in the HTT gene encoding a mutant huntingtin (mHtt) protein. mHtt aggregates within neurons causing degeneration primarily in the striatum. There is currently a need for disease-modifying treatments for HD. Many therapeutic studies have focused on lowering mHtt levels by reducing its production or enhancing its clearance. One way to clear mHtt aggregates is to promote autophagy, which is disrupted in HD. Our previous studies showed that the small molecule p75 neurotrophin receptor (p75NTR) ligand, LM11A-31, prevented HD-related neuropathologies and behavioral deficits in multiple HD mouse models. This study investigated whether modulating p75NTR with LM11A-31, would reduce mHtt aggregates via autophagic/lysosomal mechanisms in HD models. LM11A-31 decreased mHtt aggregates in human neuroblastoma SH-SY5Y cells expressing mHtt (exon 1 with 74 CAG repeats) and in the striatum of R6/2 and zQ175dn mouse models of HD. The LM11A-31 associated decrease in mHtt aggregates in vitro was accompanied by increased autophagic/lysosomal activity as indicated by altered levels of relevant markers including p62/SQSTM1 and the lysosomal protease, mature cathepsin D, and increased autophagy flux. In R6/2 and/or zQ175dn striatum, LM11A-31 increased AMPK activation, normalized p62/SQSTM1 and LC3II levels, and enhanced LAMP1 and decreased LC3B association with mHtt. Thus, LM11A-31 reduces mHtt aggregates and may do so via engaging autophagy/lysosomal systems. LM11A-31 has successfully completed a Phase 2a clinical trial for mild-to-moderate Alzheimer's disease and our results here strengthen its potential as a candidate for HD clinical testing.

The dependence of basal forebrain cholinergic neurons on NGF: The case in Alzheimer pathology

This chapter discusses the dependency of basal forebrain cholinergic neurons (BFCNs) on endogenous nerve growth factor (NGF) for the structural and physiologic maintenance of the neuronal cell somata, axonal projections, and terminal synapses. It covers the discovery of NGF and the occurrence of a CNS neurotrophin family and their cognate receptors and their signaling mechanisms. It concludes with a description of the NGF metabolic pathway and its dysregulation in Alzheimer disease (AD) and Down syndrome pathology, explaining the progressive atrophy of BFCNs, which starts at preclinical stages and is reflected in body fluid biomarkers.

Gastrodin regulates the TLR4/TRAF6/NF-κB pathway to reduce neuroinflammation and microglial activation in an AD model

BACKGROUND

Gastrodia elata (Orchidaceae) is a medicinal plant used in traditional Chinese medicine. The rhizomes contain numerous active components, of which Gastrodin (p-hydroxymethylphenyl-B-D-glucopyranoside) forms the basis of the traditional medicine Gastrodiae Rhizoma. Gastrodin is also found in other medicinal plants and has neuroprotective, antioxidant, and anti-inflammatory effects. Neuroinflammation plays a crucial role in neurodegeneration. Research indicates that consuming meals and drinks containing Gastrodiaelata can enhance cognitive functioning and memory in elderly patients. The mechanisms relevant to the problem have not been completely understood.

PURPOSE

The aim was to examine the in vivo and in vitro anti-neuroinflammatory effects of Gastrodin.

STUDY DESIGN

The neuroprotective effects of Gastrodin on the TLR4/TRAF6/NF-κB pathway and Stat3 phosphorylation in LPS-treated C57BL/6 mice and BV-2 cells were investigated.

METHODS

1. C57BL/6 mice were assigned to model, gastrodin, donepezil, and control groups (n = 10 per group). The Gastrodin group received 100 mg/kg/d for five days, and the Dopenezil group 1.3 mg/kg/d. A neuroinflammation model was established by administering intraperitoneal injections of 2 mg/kg LPS to all groups, excluding the control. To induce microglial activation in Gastrodin-treated mouse microglial BV-2 cells, 1 µg/ml LPS was introduced for 24 h Morris water mazes were utilized to evaluate learning and spatial memory. Expression and subcellular localization of TLR4/TRAF6/NF-κB axis-related proteins and p-Stat3, Iba-1, GFAP, iNOS, and CD206 were assessed by immunofluorescence, western blots, and ELISA. qRT-PCR was performed to determine and measure IL-1β, TNF-α, cell migration, and phagocytosis. Overexpression of TRAF6 was induced by transfection, and the effect of Gastrodin on IL-1β and p-NF-κB p65 levels was assessed.

RESULTS

1. In mice, gastrodin treatment mitigated LPS-induced deficits in learning and spatial memory, as well as reducing neuroinflammation in the hippocampus, expression of TLR4/TRAF6/NF-κB pathway proteins, activation of microglia and astrocytes, and phosphorylation of Stat3. 2. Gastrodin pretreatment improved LPS-induced inflammation in vitro, reducing expression of TLR4/TRAF6/NF-κB-associated proteins and p-Stat3, inducing microglial transformation from M1 to M2, and inhibiting migration and phagocytosis. Overexpression of TRAF6 inhibited the Gastrodin-induced effects.

CONCLUSION

Gastrodin suppresses neuroinflammation and microglial activation by modifying the TLR4/TRAF6/NF-κB pathway and Stat3 phosphorylation.

NGF and Its Role in Immunoendocrine Communication during Metabolic Syndrome

Nerve growth factor (NGF) was the first neurotrophin described. This neurotrophin contributes to organogenesis by promoting sensory innervation and angiogenesis in the endocrine and immune systems. Neuronal and non-neuronal cells produce and secrete NGF, and several cell types throughout the body express the high-affinity neurotrophin receptor TrkA and the low-affinity receptor p75NTR. NGF is essential for glucose-stimulated insulin secretion and the complete development of pancreatic islets. Plus, this factor is involved in regulating lipolysis and thermogenesis in adipose tissue. Immune cells produce and respond to NGF, modulating their inflammatory phenotype and the secretion of cytokines, contributing to insulin resistance and metabolic homeostasis. This neurotrophin regulates the synthesis of gonadal steroid hormones, which ultimately participate in the metabolic homeostasis of other tissues. Therefore, we propose that this neurotrophin's imbalance in concentrations and signaling during metabolic syndrome contribute to its pathophysiology. In the present work, we describe the multiple roles of NGF in immunoendocrine organs that are important in metabolic homeostasis and related to the pathophysiology of metabolic syndrome.

p75NTR enhances cognitive dysfunction in a mouse Alzheimer's disease model by inhibiting microRNA-210-3p-mediated PCYT2 through activation of NF-κB

Alzheimer's disease (AD) is a main cause of dementia and exhibits abnormality in cognitive behaviors. Here, we probed into the role of p75 neurotrophin receptor (p75NTR) in cognitive dysfunction in AD. Primarily, C57BL/6 mouse and neuroblastoma cells were treated by amyloid-beta1-42 (Aβ_1-42), respectively, to establish the in vivo and in vitro models of AD. The downstream genes of p75NTR were predicted by RNA-sequencing and bioinformatics analysis. Then the interaction among p75NTR, nuclear factor kappa B (NF-κB), microRNA-210-3p (miR-210-3p) and phosphoethanolamine cytidylyltransferase 2 (PYCT2) was verified, followed by analysis of their effects on cognitive behaviors and biological characteristics of hippocampal neurons of mouse with AD-like symptoms. p75NTR knockout alleviated cognitive dysfunction in mice with AD-like symptoms and reduced Aβ_1-42-induced hippocampal neuron damage and apoptosis. p75NTR up-regulated miR-210-3p expression by activating NF-κB, thereby limiting PCYT2 expression. PCYT2 silencing in p75NTR^-/- mice promoted neuronal apoptosis and aggravated cognitive dysfunction in AD mouse models. In summary, p75NTR is capable of accelerating cognitive dysfunction in AD by mediating the NF-κB/miR-210-3p/PCYT2 axis.

Nrf2 Regulates Oxidative Stress and Its Role in Cerebral Ischemic Stroke

Cerebral ischemic stroke is characterized by acute ischemia in a certain part of the brain, which leads to brain cells necrosis, apoptosis, ferroptosis, pyroptosis, etc. At present, there are limited effective clinical treatments for cerebral ischemic stroke, and the recovery of cerebral blood circulation will lead to cerebral ischemia-reperfusion injury (CIRI). Cerebral ischemic stroke involves many pathological processes such as oxidative stress, inflammation, and mitochondrial dysfunction. Nuclear factor erythroid 2-related factor 2 (Nrf2), as one of the most critical antioxidant transcription factors in cells, can coordinate various cytoprotective factors to inhibit oxidative stress. Targeting Nrf2 is considered as a potential strategy to prevent and treat cerebral ischemia injury. During cerebral ischemia, Nrf2 participates in signaling pathways such as Keap1, PI3K/AKT, MAPK, NF-κB, and HO-1, and then alleviates cerebral ischemia injury or CIRI by inhibiting oxidative stress, anti-inflammation, maintaining mitochondrial homeostasis, protecting the blood-brain barrier, and inhibiting ferroptosis. In this review, we have discussed the structure of Nrf2, the mechanisms of Nrf2 in cerebral ischemic stroke, the related research on the treatment of cerebral ischemia through the Nrf2 signaling pathway in recent years, and expounded the important role and future potential of the Nrf2 pathway in cerebral ischemic stroke.

Amyloidogenesis and Neurotrophic Dysfunction in Alzheimer’s Disease: Do They have a Common Regulating Pathway?

The amyloid cascade hypothesis has predominately been used to describe the pathogenesis of Alzheimer’s disease (AD) for decades, as Aβ oligomers are thought to be the prime cause of AD. Meanwhile, the neurotrophic factor hypothesis has also been proposed for decades. Accumulating evidence states that the amyloidogenic process and neurotrophic dysfunction are mutually influenced and may coincidently cause the onset and progress of AD. Meanwhile, there are intracellular regulators participating both in the amyloidogenic process and neurotrophic pathways, which might be the common original causes of amyloidogenesis and neurotrophic dysfunction. In this review, the current understanding regarding the role of neurotrophic dysfunction and the amyloidogenic process in AD pathology is briefly summarized. The mutual influence of these two pathogenesis pathways and their potential common causal pathway are further discussed. Therapeutic strategies targeting the common pathways to simultaneously prevent amyloidogenesis and neurotrophic dysfunction might be anticipated for the disease-modifying treatment of AD.

Exploration of Aberrant E3 Ligases Implicated in Alzheimer's Disease and Development of Chemical Tools to Modulate Their Function

The Ubiquitin Proteasome System (UPS) is responsible for the degradation of misfolded or aggregated proteins via a multistep ATP-dependent proteolytic mechanism. This process involves a cascade of ubiquitin (Ub) transfer steps from E1 to E2 to E3 ligase. The E3 ligase transfers Ub to a targeted protein that is brought to the proteasome for degradation. The inability of the UPS to remove misfolded or aggregated proteins due to UPS dysfunction is commonly observed in neurodegenerative diseases, such as Alzheimer's disease (AD). UPS dysfunction in AD drives disease pathology and is associated with the common hallmarks such as amyloid-β (Aβ) accumulation and tau hyperphosphorylation, among others. E3 ligases are key members of the UPS machinery and dysfunction or changes in their expression can propagate other aberrant processes that accelerate AD pathology. The upregulation or downregulation of expression or activity of E3 ligases responsible for these processes results in changes in protein levels of E3 ligase substrates, many of which represent key proteins that propagate AD. A powerful way to better characterize UPS dysfunction in AD and the role of individual E3 ligases is via the use of high-quality chemical tools that bind and modulate specific E3 ligases. Furthermore, through combining gene editing with recent advances in 3D cell culture, in vitro modeling of AD in a dish has become more relevant and possible. These cell-based models of AD allow for study of specific pathways and mechanisms as well as characterization of the role E3 ligases play in driving AD. In this review, we outline the key mechanisms of UPS dysregulation linked to E3 ligases in AD and highlight the currently available chemical modulators. We present several key approaches for E3 ligase ligand discovery being employed with respect to distinct classes of E3 ligases. Where possible, specific examples of the use of cultured neurons to delineate E3 ligase biology have been captured. Finally, utilizing the available ligands for E3 ligases in the design of proteolysis targeting chimeras (PROTACs) to degrade aberrant proteins is a novel strategy for AD, and we explore the prospects of PROTACs as AD therapeutics.

Neurotrophins as Key Regulators of Cell Metabolism: Implications for Cholesterol Homeostasis

Neurotrophins constitute a family of growth factors initially characterized as predominant mediators of nervous system development, neuronal survival, regeneration and plasticity. Their biological activity is promoted by the binding of two different types of receptors, leading to the generation of multiple and variegated signaling cascades in the target cells. Increasing evidence indicates that neurotrophins are also emerging as crucial regulators of metabolic processes in both neuronal and non-neuronal cells. In this context, it has been reported that neurotrophins affect redox balance, autophagy, glucose homeostasis and energy expenditure. Additionally, the trophic support provided by these secreted factors may involve the regulation of cholesterol metabolism. In this review, we examine the neurotrophins' signaling pathways and their effects on metabolism by critically discussing the most up-to-date information. In particular, we gather experimental evidence demonstrating the impact of these growth factors on cholesterol metabolism.

Anticancer activity of gold nanobioconjugates synthesized from Elephantopus scaber (linn.) leaf extract

Introduction

Medicinal plants are the major natural resources for the treatment of human ailments including cancer therapy. The current cancer treatments such as surgery, radiation, and chemotherapy affect normal cells too. Thus, treatments like synthesized nanoscale particles using plant extracts have proven to be potential anticancer agent.

Aim of the Study

We hypothesize that the gold nanoparticles (AuNPs) synthesized using Elephantopus scaber hydro-methanolic extract may have anti-cancer activity along with their synergistic counterparts with adriamycin (ADR) on human breast cancer MCF-7: human breast cancer (A-549), human oral cancer (squamous cell carcinoma [SCC]-40), and COLO-205: human colon cancer cell lines.

Materials and Methods

The phytosynthesized AuNPs were characterized for ultraviolet-visible (UV-Vis) spectroscopy, nanoparticle tracking analysis (NTA), X-ray diffraction, scanning electron microscopy, transmission electron microscopy (TEM), and Fourier transform infrared (FTIR) analysis. The anticancer ability of the AuNPs against human MCF-7, A-549, SCC-40, and COLO-205 through sulforhodamine B assay has been studied.

Results

The synthesis of AuNPs was confirmed with the UV-Vis spectrophotometer with a peak at 540 nm. The FTIR analysis showed polyphenolic groups were major found to be the reduction and capping agent for AuNPs. According to the results obtained, AuNPs showed good anti-proliferative activity with GI50 <10 μg/ml on MCF-7 cancer cell line. The synergistic effect of AuNPs + ADR was even better for all the four cell lines than that of the AuNPs alone.

Conclusion

The green synthesis of AuNPs is a simple, eco-friendly, and cost-effective method with dominantly spherical morphology ranging from 20 to 40 nm confirmed by NTA and TEM analysis. The study reveals the potent therapeutic value of the AuNPs.

A Systems Biology Approach for Hypothesizing the Effect of Genetic Variants on Neuroimaging Features in Alzheimer's Disease

BACKGROUND

Neuroimaging markers provide quantitative insight into brain structure and function in neurodegenerative diseases, such as Alzheimer's disease, where we lack mechanistic insights to explain pathophysiology. These mechanisms are often mediated by genes and genetic variations and are often studied through the lens of genome-wide association studies. Linking these two disparate layers (i.e., imaging and genetic variation) through causal relationships between biological entities involved in the disease's etiology would pave the way to large-scale mechanistic reasoning and interpretation.

OBJECTIVE

We explore how genetic variants may lead to functional alterations of intermediate molecular traits, which can further impact neuroimaging hallmarks over a series of biological processes across multiple scales.

METHODS

We present an approach in which knowledge pertaining to single nucleotide polymorphisms and imaging readouts is extracted from the literature, encoded in Biological Expression Language, and used in a novel workflow to assist in the functional interpretation of SNPs in a clinical context.

RESULTS

We demonstrate our approach in a case scenario which proposes KANSL1 as a candidate gene that accounts for the clinically reported correlation between the incidence of the genetic variants and hippocampal atrophy. We find that the workflow prioritizes multiple mechanisms reported in the literature through which KANSL1 may have an impact on hippocampal atrophy such as through the dysregulation of cell proliferation, synaptic plasticity, and metabolic processes.

CONCLUSION

We have presented an approach that enables pinpointing relevant genetic variants as well as investigating their functional role in biological processes spanning across several, diverse biological scales.

Ubiquitin biology in neurodegenerative disorders: From impairment to therapeutic strategies

The abnormal accumulation of neurotoxic proteins is the typical hallmark of various age-related neurodegenerative disorders (NDDs), including Alzheimer's disease, Parkinson's disease, Huntington's disease, Amyotrophic lateral sclerosis and Multiple sclerosis. The anomalous proteins, such as Aβ, Tau in Alzheimer's disease and α-synuclein in Parkinson's disease, perturb the neuronal physiology and cellular homeostasis in the brain thereby affecting the millions of human lives across the globe. Here, ubiquitin proteasome system (UPS) plays a decisive role in clearing the toxic metabolites in cells, where any aberrancy is widely reported to exaggerate the neurodegenerative pathologies. In spite of well-advancement in the ubiquitination research, their molecular markers and mechanisms for target-specific protein ubiquitination and clearance remained elusive. Therefore, this review substantiates the role of UPS in the brain signaling and neuronal physiology with their mechanistic role in the NDD's specific pathogenic protein clearance. Moreover, current and future promising therapies are discussed to target UPS-mediated neurodegeneration for better public health.

p62: Friend or Foe? Evidences for OncoJanus and NeuroJanus Roles

p62 is a versatile protein involved in the delicate balance between cell death and survival, which is fundamental for cell fate decision in the context of both cancer and neurodegenerative diseases. As an autophagy adaptor, p62 recognizes polyubiquitin chains and interacts with LC3, thereby targeting the selected cargo to the autophagosome with consequent autophagic degradation. Beside this function, p62 behaves as an interactive hub in multiple signalling including those mediated by Nrf2, NF-κB, caspase-8, and mTORC1. The protein is thus crucial for the control of oxidative stress, inflammation and cell survival, apoptosis, and metabolic reprogramming, respectively. As a multifunctional protein, p62 falls into the category of those factors that can exert opposite roles in the cells. Chronic p62 accumulation was found in many types of tumors as well as in stress granules present in different forms of neurodegenerative diseases. However, the protein seems to have a Janus behaviour since it may also serve protective functions against tumorigenesis or neurodegeneration. This review describes the diversified roles of p62 through its multiple domains and interactors and specifically focuses on its oncoJanus and neuroJanus roles.

The Ubiquitin System in Alzheimer's Disease

Alzheimer's disease (AD) is the most common form of dementia, most prevalent in the elderly population and has a significant impact on individuals and their family as well as the health care system and the economy. While the number of patients affected by various forms of dementia including AD is on the increase, there is currently no cure. Although genome-wide association studies have identified genetic markers for familial AD, the molecular mechanisms underlying the initiation and development of both familial and sporadic AD remain poorly understood. Most neurodegenerative diseases and in particular those associated with dementia have been defined as proteinopathies due to the presence of intra- and/or extracellular protein aggregates in the brain of affected individuals. Although loss of proteostasis in AD has been known for decades, it is only in recent years that we have come to appreciate the role of ubiquitin-dependent mechanisms in brain homeostasis and in brain diseases. Ubiquitin is a highly versatile post-translational modification which regulates many aspects of protein fate and function, including protein degradation by the Ubiquitin-Proteasome System (UPS), autophagy-mediated removal of damaged organelles and proteins, lysosomal turnover of membrane proteins and of extracellular molecules brought inside the cell through endocytosis. Amyloid-β (Aβ) fragments as well as hyperphosphorylation of Tau are hallmarks of AD, and these are found in extracellular plaques and intracellular fibrils in the brain of individuals with AD, respectively. Yet, whether it is the oligomeric or the soluble species of Aβ and Tau that mediate toxicity is still unclear. These proteins impact on mitochondrial energy metabolism, inflammation, as well as a number of housekeeping processes including protein degradation through the UPS and autophagy. In this chapter, we will discuss the role of ubiquitin in neuronal homeostasis as well as in AD; summarise crosstalks between the enzymes that regulate protein ubiquitination and the toxic proteins Tau and Aβ; highlight emerging molecular mechanisms in AD as well as future strategies which aim to exploit the ubiquitin system as a source for next-generation therapeutics.

Candidate Genes and MiRNAs Linked to the Inverse Relationship Between Cancer and Alzheimer's Disease: Insights From Data Mining and Enrichment Analysis

The incidence of cancer and Alzheimer’s disease (AD) increases exponentially with age. A growing body of epidemiological evidence and molecular investigations inspired the hypothesis of an inverse relationship between these two pathologies. It has been proposed that the two diseases might utilize the same proteins and pathways that are, however, modulated differently and sometimes in opposite directions. Investigation of the common processes underlying these diseases may enhance the understanding of their pathogenesis and may also guide novel therapeutic strategies. Starting from a text-mining approach, our in silico study integrated the dispersed biological evidence by combining data mining, gene set enrichment, and protein-protein interaction (PPI) analyses while searching for common biological hallmarks linked to AD and cancer. We retrieved 138 genes (ALZCAN gene set), computed a significant number of enriched gene ontology clusters, and identified four PPI modules. The investigation confirmed the relevance of autophagy, ubiquitin proteasome system, and cell death as common biological hallmarks shared by cancer and AD. Then, from a closer investigation of the PPI modules and of the miRNAs enrichment data, several genes (SQSTM1, UCHL1, STUB1, BECN1, CDKN2A, TP53, EGFR, GSK3B, and HSPA9) and miRNAs (miR-146a-5p, MiR-34a-5p, miR-21-5p, miR-9-5p, and miR-16-5p) emerged as promising candidates. The integrative approach uncovered novel miRNA-gene networks (e.g., miR-146 and miR-34 regulating p62 and Beclin1 in autophagy) that might give new insights into the complex regulatory mechanisms of gene expression in AD and cancer.

SQSTM1/p62: A Potential Target for Neurodegenerative Disease

Neurodegenerative diseases, characterized by a progressive loss of brain function, affect the lives of millions of individuals worldwide. The complexity of the brain poses a challenge for scientists trying to map the biochemical and physiological pathways to identify areas of pathological errors. Brain samples of patients with neurodegenerative diseases have been shown to contain large amounts of misfolded and abnormally aggregated proteins, resulting in dysfunction in certain brain centers. Removal of these abnormal molecules is essential in maintaining protein homeostasis and overall neuronal health. Macroautophagy is a major route by which cells achieve this. Administration of certain autophagy-enhancing compounds has been shown to provide therapeutic effects for individuals with neurodegenerative conditions. SQSTM1/p62 is a scaffold protein closely involved in the macroautophagy process. p62 functions to anchor the ubiquitinated proteins to the autophagosome membrane, promoting degradation of unwanted molecules. Modulators targeting p62 to induce autophagy and promote its protective pathways for aggregate protein clearance have high potential in the treatment of these conditions. Additionally, causal relationships have been found between errors in regulation of SQSTM1/p62 and the development of a variety of neurodegenerative disorders, including Alzheimer's, Parkinson's, Huntington's, amyotrophic lateral sclerosis, and frontotemporal lobar degeneration. Furthermore, SQSTM1/p62 also serves as a signaling hub for multiple pathways associated with neurodegeneration, providing a potential therapeutic target in the treatment of neurodegenerative diseases. However, rational design of a p62-oriented autophagy modulator that can balance the negative and positive functions of multiple domains in p62 requires further efforts in the exploration of the protein structure and pathological basis.

Suppression of MIF-induced neuronal apoptosis may underlie the therapeutic effects of effective components of Fufang Danshen in the treatment of Alzheimer's disease

Fufang Danshen (FFDS or Compound Danshen) consists of three Chinese herbs Danshen (Salviae miltiorrhizae radix et rhizome), Sanqi (Notoginseng radix et rhizome) and Tianranbingpian (Borneolum, or D-borneol), which has been show to significantly improve the function of the nervous system and brain metabolism. In this study we explored the possible mechanisms underlying the therapeutic effects of the combination of the effective components of FFDS (Tan IIA, NG-R1 and Borneol) in the treatment of Alzheimer's disease (AD) based on network pharmacology. We firstly constructed AD-related FFDS component protein interaction networks, and revealed that macrophage migration inhibitory factor (MIF) might regulate neuronal apoptosis through Bad in the progression of AD. Then we investigated the apoptosis-inducing effects of MIF and the impact of the effective components of FFDS in human neuroblastoma SH-SY5Y cells. We observed the characteristics of a "Pendular state" of MIF, where MIF (8 ng/mL) increased the ratio of p-Bad/Bad by activating Akt and the IKKα/β signaling pathway to assure cell survival, whereas MIF (50 ng/mL) up-regulated the expression of Bad to trigger apoptosis of SH-SY5Y cells. MIF displayed neurotoxicity similar to Aβ_1-42, which was associated with the MIF-induced increased expression of Bad. Application of the FFDS composite solution significantly decreased the expression levels of Bad, suppressed MIF-induced apoptosis in SH-SY5Y cells. In a D-galactose- and AlCl₃-induced AD mouse model, administration of the FFDS composite solution significantly improved the learning and memory, as well as neuronal morphology, and decreased the serum levels of INF-γ. Therefore, the FFDS composite solution exerts neuroprotective effects through down-regulating the level of Bad stimulated by MIF.

A zebrafish model for C9orf72 ALS reveals RNA toxicity as a pathogenic mechanism

The exact mechanism underlying amyotrophic lateral sclerosis (ALS) and frontotemporal dementia (FTD) associated with the GGGGCC repeat expansion in C9orf72 is still unclear. Two gain-of-function mechanisms are possible: repeat RNA toxicity and dipeptide repeat protein (DPR) toxicity. We here dissected both possibilities using a zebrafish model for ALS. Expression of two DPRs, glycine-arginine and proline-arginine, induced a motor axonopathy. Similarly, expanded sense and antisense repeat RNA also induced a motor axonopathy and formed mainly cytoplasmic RNA foci. However, DPRs were not detected in these conditions. Moreover, stop codon-interrupted repeat RNA still induced a motor axonopathy and a synergistic role of low levels of DPRs was excluded. Altogether, these results show that repeat RNA toxicity is independent of DPR formation. This RNA toxicity, but not the DPR toxicity, was attenuated by the RNA-binding protein Pur-alpha and the autophagy-related protein p62. Our findings demonstrate that RNA toxicity, independent of DPR toxicity, can contribute to the pathogenesis of C9orf72-associated ALS/FTD.

A Review on Ubiquitination of Neurotrophin Receptors: Facts and Perspectives

Ubiquitination is a reversible post-translational modification involved in a plethora of different physiological functions. Among the substrates that are ubiquitinated, neurotrophin receptors (TrkA, TrkB, TrkC, and p75^NTR) have been studied recently. TrkA is the most studied receptor in terms of its ubiquitination, and different E3 ubiquitin ligases and deubiquitinases have been implicated in its ubiquitination, whereas not much is known about the other neurotrophin receptors aside from their ubiquitination. Additional studies are needed that focus on the ubiquitination of TrkB, TrkC, and p75^NTR in order to further understand the role of ubiquitination in their physiological and pathological functions. Here we review what is currently known regarding the ubiquitination of neurotrophin receptors and its physiological and pathological relevance.

Oxidative stress-mediated NFκB phosphorylation upregulates p62/SQSTM1 and promotes retinal pigmented epithelial cell survival through increased autophagy

p62 is a scaffolding adaptor implicated in the clearance of protein aggregates by autophagy. Reactive oxygen species (ROS) can either stimulate or inhibit NFκB-mediated gene expression influencing cellular fate. We studied the effect of hydrogen peroxide (H2O2)-mediated oxidative stress and NFκB signaling on p62 expression in the retinal pigment epithelium (RPE) and investigated its role in regulation of autophagy and RPE survival against oxidative damage. Cultured human RPE cell line ARPE-19 and primary human adult and fetal RPE cells were exposed to H2O2-induced oxidative stress. The human apolipoprotein E4 targeted-replacement (APOE4) mouse model of AMD was used to study expression of p62 and other autophagy proteins in the retina. p62, NFκB p65 (total, phosphorylated, nuclear and cytoplasmic) and ATG10 expression was assessed by mRNA and protein analyses. Cellular ROS and mitochondrial superoxide were measured by CM-H2DCFDA and MitoSOX staining respectively. Mitochondrial viability was determined using MTT activity. qPCR-array system was used to investigate autophagic genes affected by p62. Nuclear and cytoplasmic levels of NFκB p65 were evaluated after cellular fractionation by Western blotting. We report that p62 is up-regulated in RPE cells under H2O2-induced oxidative stress and promotes autophagic activity. Depletion of endogenous p62 reduces autophagy by downregulation of ATG10 rendering RPE more susceptible to oxidative damage. NFκB p65 phosphorylation at Ser-536 was found to be critical for p62 upregulation in response to oxidative stress. Proteasome inhibition by H2O2 causes p62-NFκB signaling as antioxidant pre-treatment reversed p62 expression and p65 phosphorylation when RPE was challenged by H2O2 but not when by Lactacystin. p62 protein but not RNA levels are elevated in APOE4-HFC AMD mouse model, suggesting reduction of autophagic flux in disease conditions. Our findings suggest that p62 is necessary for RPE cytoprotection under oxidative stress and functions, in part, by modulating ATG10 expression. NFκB p65 activity may be a critical upstream initiator of p62 expression in RPE cells under oxidative stress.

Hippocampal endosomal, lysosomal, and autophagic dysregulation in mild cognitive impairment: correlation with aβ and tau pathology

Endosomal-lysosomal and autophagic dysregulation occurs in the hippocampus in prodromal Alzheimer disease (AD), but its relationship with β-amyloid (Aβ) and tau pathology remains unclear. To investigate this issue, we performed immunoblot analysis of hippocampal homogenates from cases with an antemortem clinical diagnosis of no cognitive impairment, mild cognitive impairment (MCI), and AD. Western blot analysis revealed significant increases in the acid hydrolase cathepsin D and early endosome marker rabaptin5 in the MCI group compared with AD, whereas levels of phosphorylated mammalian target of rapamycin proteins (pmTOR), total mammalian target of rapamycin (mTOR), p62, traf6, and LilrB2 were comparable across clinical groups. Hippocampal Aβ1-40 and Aβ1-42 concentrations and AT8-immunopositive neurofibrillary tangle density were not significantly different across the clinical groups. Greater cathepsin D expression was associated with global cognitive score and episodic memory score but not with mini mental state examination or advanced neuropathology criteria. These results indicate that alterations in hippocampal endosomal-lysosomal proteins in MCI are independent of tau or Aβ pathology.

BAG2 Is Repressed by NF-κB Signaling, and Its Overexpression Is Sufficient to Shift Aβ1-42 from Neurotrophic to Neurotoxic in Undifferentiated SH-SY5Y Neuroblastoma

Amyloid-beta (Aβ) binds to various neuronal receptors and elicits a context- and dose-dependent toxic or trophic response from neurons. The molecular mechanisms for this phenomenon are presently unknown. The cochaperone BAG2 has been shown to mediate important cellular responses to stress, including cell cycle arrest and apoptosis. Here, we use SH-SY5Y neuroblastoma cells to characterize BAG2 expression and regulation and investigate the involvement of BAG2 in Aβ1-42-mediated neurotrophism or neurotoxicity in the context of differentiation. We report that BAG2 is upregulated on differentiation of SH-SY5Y cells into neuron-like cells. This increase in BAG2 expression is accompanied by a change in response to treatment with Aβ1-42 from neurotrophic to neurotoxic. Further, overexpression of BAG2 in undifferentiated SH-SY5Y cells was sufficient to induce the change from neurotrophic to neurotoxic response. Of several transcription factors queried, the putative BAG2 promoter had a higher-than-expected occurrence of response elements (RE) for nuclear factor kappa-light-chain-enhancer of activated B cells (NF-κB). Treatment with JSH-23, a potent inhibitor of NF-κB, caused a marked increase in BAG2 mRNA expression, suggesting that NF-κB is a repressor of BAG2 transcription in undifferentiated SH-SY5Y cells. Together, these data suggest that NF-κB-mediated modulation of BAG2 expression constitutes a "switch" that regulates the shift between the neurotrophic and neurotoxic effects of Aβ1-42.

Failure of ubiquitin proteasome system: risk for neurodegenerative diseases

The ubiquitin proteasome system (UPS) is the primary proteolytic quality control system in cells and has an essential function in the nervous system. UPS dysfunction has been linked to neurodegenerative conditions, including Alzheimer's, Parkinson's and Huntington's diseases. The pathology of neurodegenerative diseases is characterized by the abnormal accumulation of insoluble protein aggregates or inclusion bodies within neurons. The failure or dysregulation of the UPS prevents the degradation of misfolded/aberrant proteins, leading to deficient synaptic function that eventually affects the nervous system. In this review, we discuss the UPS and its physiological roles in the nervous system, its influence on neuronal function, and how UPS dysfunction contributes to the development of neurodegenerative diseases.

TRAF6 upregulation in spinal astrocytes maintains neuropathic pain by integrating TNF-α and IL-1β signaling

The proinflammatory cytokines tumor necrosis factor (TNF) α and interleukin (IL) 1β have been strongly implicated in the pathogenesis of neuropathic pain, but the intracellular signaling of these cytokines in glial cells is not fully understood. TNF receptor-associated factor 6 (TRAF6) plays a key role in signal transduction in the TNF receptor superfamily and the IL-1 receptor superfamily. In this study, we investigated the role of TRAF6 in neuropathic pain in mice after spinal nerve ligation (SNL). SNL induced persistent TRAF6 upregulation in the spinal cord. Interestingly, TRAF6 was mainly colocalized with the astrocytic marker glial fibrillary acidic protein on SNL day 10 and partially expressed in microglia on SNL day 3. In cultured astrocytes, TRAF6 was upregulated after exposure to TNF-α or IL-1β. TNF-α or IL-1β also increased CCL2 expression, which was suppressed by both siRNA and shRNA targeting TRAF6. TRAF6 siRNA treatment also inhibited the phosphorylation of c-Jun N-terminal kinase (JNK) in astrocytes induced by TNF-α or IL-1β. JNK inhibitor D-NKI-1 dose-dependently decreased IL-1β-induced CCL2 expression. Moreover, spinal injection of TRAF6 siRNA decreased intrathecal TNF-α- or IL-1β-induced allodynia and hyperalgesia. Spinal TRAF6 inhibition via TRAF6 siRNA, shRNA lentivirus, or antisense oligodeoxynucleotides partially reversed SNL-induced neuropathic pain and spinal CCL2 expression. Finally, intrathecal injection of TNF-α-activated astrocytes induced mechanical allodynia, which was attenuated by pretreatment of astrocytes with TRAF6 siRNA. Taken together, the results suggest that TRAF6, upregulated in spinal cord astrocytes in the late phase after nerve injury, maintains neuropathic pain by integrating TNF-α and IL-1β signaling and activating the JNK/CCL2 pathway in astrocytes.

Role of p75 neurotrophin receptor in stem cell biology: more than just a marker

p75(NTR), the common receptor for both neurotrophins and proneurotrophins, has been widely studied because of its role in many tissues, including the nervous system. More recently, a close relationship between p75(NTR) expression and pluripotency has been described. p75(NTR) was shown to be expressed in various types of stem cells and has been used to prospectively isolate stem cells with different degrees of potency. Here, we give an overview of the current knowledge on p75(NTR) in stem cells, ranging from embryonic to adult stem cells, and cancer stem cells. In an attempt to address its potential role in the control of stem cell biology, the molecular mechanisms underlying p75(NTR) signaling in different models are also highlighted. p75(NTR)-mediated functions include survival, apoptosis, migration, and differentiation, and depend on cell type, (pro)neurotrophin binding, interacting transmembrane co-receptors expression, intracellular adaptor molecule availability, and post-translational modifications, such as regulated proteolytic processing. It is therefore conceivable that p75(NTR) can modulate cell-fate decisions through its highly ramified signaling pathways. Thus, elucidating the potential implications of p75(NTR) activity as well as the underlying molecular mechanisms of p75(NTR) will shed new light on the biology of both normal and cancer stem cells.

TRAF molecules in cell signaling and in human diseases

The tumor necrosis factor receptor (TNF-R)-associated factor (TRAF) family of intracellular proteins were originally identified as signaling adaptors that bind directly to the cytoplasmic regions of receptors of the TNF-R superfamily. The past decade has witnessed rapid expansion of receptor families identified to employ TRAFs for signaling. These include Toll-like receptors (TLRs), NOD-like receptors (NLRs), RIG-I-like receptors (RLRs), T cell receptor, IL-1 receptor family, IL-17 receptors, IFN receptors and TGFβ receptors. In addition to their role as adaptor proteins, most TRAFs also act as E3 ubiquitin ligases to activate downstream signaling events. TRAF-dependent signaling pathways typically lead to the activation of nuclear factor-κBs (NF-κBs), mitogen-activated protein kinases (MAPKs), or interferon-regulatory factors (IRFs). Compelling evidence obtained from germ-line and cell-specific TRAF-deficient mice demonstrates that each TRAF plays indispensable and non-redundant physiological roles, regulating innate and adaptive immunity, embryonic development, tissue homeostasis, stress response, and bone metabolism. Notably, mounting evidence implicates TRAFs in the pathogenesis of human diseases such as cancers and autoimmune diseases, which has sparked new appreciation and interest in TRAF research. This review presents an overview of the current knowledge of TRAFs, with an emphasis on recent findings concerning TRAF molecules in signaling and in human diseases.