A novel role for the Receptor for Advanced Glycation End-products in neural progenitor cells derived from adult SubVentricular Zone

High mobility group box 1 in the central nervous system: regeneration hidden beneath inflammation

High-mobility group box 1 was first discovered in the calf thymus as a DNA-binding nuclear protein and has been widely studied in diverse fields, including neurology and neuroscience. High-mobility group box 1 in the extracellular space functions as a pro-inflammatory damage-associated molecular pattern, which has been proven to play an important role in a wide variety of central nervous system disorders such as ischemic stroke, Alzheimer's disease, frontotemporal dementia, Parkinson's disease, multiple sclerosis, epilepsy, and traumatic brain injury. Several drugs that inhibit high-mobility group box 1 as a damage-associated molecular pattern, such as glycyrrhizin, ethyl pyruvate, and neutralizing anti-high-mobility group box 1 antibodies, are commonly used to target high-mobility group box 1 activity in central nervous system disorders. Although it is commonly known for its detrimental inflammatory effect, high-mobility group box 1 has also been shown to have beneficial pro-regenerative roles in central nervous system disorders. In this narrative review, we provide a brief summary of the history of high-mobility group box 1 research and its characterization as a damage-associated molecular pattern, its downstream receptors, and intracellular signaling pathways, how high-mobility group box 1 exerts the repair-favoring roles in general and in the central nervous system, and clues on how to differentiate the pro-regenerative from the pro-inflammatory role. Research targeting high-mobility group box 1 in the central nervous system may benefit from differentiating between the two functions rather than overall suppression of high-mobility group box 1.

Is it all the RAGE? Defining the role of the receptor for advanced glycation end products in Parkinson's disease

The receptor for advanced glycation end products (RAGE) is a transmembrane receptor that belongs to the immunoglobulin superfamily and is extensively associated with chronic inflammation in non-transmissible diseases. As chronic inflammation is consistently present in neurodegenerative diseases, it was largely assumed that RAGE could act as a critical modulator of neuroinflammation in Parkinson's disease (PD), similar to what was reported for Alzheimer's disease (AD), where RAGE is postulated to mediate pro-inflammatory signaling in microglia by binding to amyloid-β peptide. However, accumulating evidence from studies of RAGE in PD models suggests a less obvious scenario. Here, we review physiological aspects of RAGE and address the current questions about the potential involvement of this receptor in the cellular events that may be critical for the development and progression of PD, exploring possible mechanisms beyond the classical view of the microglial activation/neuroinflammation/neurodegeneration axis that is widely assumed to be the general mechanism of RAGE action in the adult brain.

Mammalian Diaphanous1 signalling in neurovascular complications of diabetes

Over the past few decades, diabetes gradually has become one of the top non-communicable disorders, affecting 476.0 million in 2017 and is predicted to reach 570.9 million people in 2025. It is estimated that 70 to 100% of all diabetic patients will develop some if not all, diabetic complications over the course of the disease. Despite different symptoms, mechanisms underlying the development of diabetic complications are similar, likely stemming from deficits in both neuronal and vascular components supplying hyperglycaemia-susceptible tissues and organs. Diaph1, protein diaphanous homolog 1, although mainly known for its regulatory role in structural modification of actin and related cytoskeleton proteins, in recent years attracted research attention as a cytoplasmic partner of the receptor of advanced glycation end-products (RAGE) a signal transduction receptor, whose activation triggers an increase in proinflammatory molecules, oxidative stressors and cytokines in diabetes and its related complications. Both Diaph1 and RAGE are also a part of the RhoA signalling cascade, playing a significant role in the development of neurovascular disturbances underlying diabetes-related complications. In this review, based on the existing knowledge as well as compelling findings from our past and present studies, we address the role of Diaph1 signalling in metabolic stress and neurovascular degeneration in diabetic complications. In light of the most recent developments in biochemical, genomic and transcriptomic research, we describe current theories on the aetiology of diabetes complications, highlighting the function of the Diaph1 signalling system and its role in diabetes pathophysiology.

Receptors for Advanced Glycation End Products (RAGE): Promising Targets Aiming at the Treatment of Neurodegenerative Conditions

Advanced glycation end products (AGEs) are compounds formed after the non-enzymatic addition of reducing sugars to lipids, proteins, and nucleic acids. They are associated with the development of various clinical complications observed in diabetes and cardiovascular diseases, such as retinopathy, nephropathy, diabetic neuropathy, and others. In addition, compelling evidence indicates that these molecules participate in the progression of neurodegenerative diseases, such as Alzheimer's disease, Parkinson's disease, and amyotrophic lateral sclerosis. Multiple cellular and molecular alterations triggered by AGEs that could alter homeostasis have been identified. One of the main targets for AGE signaling is the receptor for advanced glycation end-products (RAGE). Importantly, this receptor is the target of not only AGEs, but also amyloid β peptides, HMGB1 (high-mobility group box-1), members of the S100 protein family, and glycosaminoglycans. The activation of this receptor induces intracellular signaling cascades that are involved in pathological processes and cell death. Therefore, RAGE represents a key target for pharmacological interventions in neurodegenerative diseases. This review will discuss the various effects of AGEs and RAGE activation in the pathophysiology of neurodegenerative diseases, as well as the currently available pharmacological tools and promising drug candidates.

Role of RAGE in the Pathogenesis of Neurological Disorders

This review reflects upon our own as well as other investigators' studies on the role of receptor for advanced glycation end-products (RAGE), bringing up the latest information on RAGE in physiology and pathology of the nervous system. Over the last ten years, major progress has been made in uncovering many of RAGE-ligand interactions and signaling pathways in nervous tissue; however, the translation of these discoveries into clinical practice has not come to fruition yet. This is likely, in part to be the result of our incomplete understanding of this crucial signaling pathway. Clinical trials examining the therapeutic efficacy of blocking RAGE-external ligand interactions by genetically engineered soluble RAGE or an endogenous RAGE antagonist, has not stood up to its promise; however, other trials with different blocking agents are being considered with hope for therapeutic success in diseases of the nervous system.

Longterm Increased S100B Enhances Hippocampal Progenitor Cell Proliferation in a Transgenic Mouse Model

(1) The neurotrophic protein S100B is a marker of brain injury and has been associated with neuroregeneration. In S100Btg mice rendering 12 copies of the murine S100B gene we evaluated whether S100B may serve as a treatment option. (2) In juvenile, adult, and one-year-old S100Btg mice (female and male; n = 8 per group), progenitor cell proliferation was quantified in the subgranular zone (SGZ) and the granular cell layer (GCL) of the dentate gyrus with the proliferative marker Ki67 and BrdU (50 mg/kg). Concomitant signaling was quantified utilizing glial fibrillary acidic protein (GFAP), apolipoprotein E (ApoE), brain-derived neurotrophic factor (BDNF), and the receptor for advanced glycation end products (RAGE) immunohistochemistry. (3) Progenitor cell proliferation in the SGZ and migration to the GCL was enhanced. Hippocampal GFAP was reduced in one-year-old S100Btg mice. ApoE in the hippocampus and frontal cortex of male and BDNF in the frontal cortex of female S100Btg mice was reduced. RAGE was not affected. (4) Enhanced hippocampal neurogenesis in S100Btg mice was not accompanied by reactive astrogliosis. Sex- and brain region-specific variations of ApoE and BDNF require further elucidations. Our data reinforce the importance of this S100Btg model in evaluating the role of S100B in neuroregenerative medicine.

Glial PAMPering and DAMPening of Adult Hippocampal Neurogenesis

Adult neurogenesis represents a mature brain's capacity to integrate newly generated neurons into functional circuits. Impairment of neurogenesis contributes to the pathophysiology of various mood and cognitive disorders such as depression and Alzheimer's Disease. The hippocampal neurogenic niche hosts neural progenitors, glia, and vasculature, which all respond to intrinsic and environmental cues, helping determine their current state and ultimate fate. In this article we focus on the major immune communication pathways and mechanisms through which glial cells sense, interact with, and modulate the neurogenic niche. We pay particular attention to those related to the sensing of and response to innate immune danger signals. Receptors for danger signals were first discovered as a critical component of the innate immune system response to pathogens but are now also recognized to play a crucial role in modulating non-pathogenic sterile inflammation. In the neurogenic niche, viable, stressed, apoptotic, and dying cells can activate danger responses in neuroimmune cells, resulting in neuroprotection or neurotoxicity. Through these mechanisms glial cells can influence hippocampal stem cell fate, survival, neuronal maturation, and integration. Depending on the context, such responses may be appropriate and on-target, as in the case of learning-associated synaptic pruning, or excessive and off-target, as in neurodegenerative disorders.

HMGB1-RAGE Pathway Contributes to the Abnormal Migration of Endogenous Subventricular Zone Neural Progenitors in an Experimental Model of Focal Microgyria

Abnormal migration of subventricular zone (SVZ)-derived neural progenitor cells (SDNPs) is involved in the pathological and epileptic processes of focal cortical dysplasias (FCDs), but the underlying mechanisms are not clear. Recent studies indicated that high mobility group box 1 (HMGB1)/receptor for advanced glycation end products (RAGE) are widely expressed in epileptic specimens of FCDs, which suggests that the HMGB1-RAGE pathway is involved in the pathological and/or epileptic processes of FCDs. The present study used Nestin-GFP^tg/+ transgenic mice, and we established a model of freezing lesion (FL), as described in our previous report. A "migrating stream" composed of GFP-Nestin⁺ SDNPs was derived from the SVZ region and migrated to the cortical FL area. We found that translocated HMGB1 and RAGE were expressed in cortical lesion in a clustered distribution pattern, which was especially obvious in the early stage of FL compared to the sham group. Notably, the number of GFP-Nestin⁺ SDNPs within the "migrating stream" was significantly decreased when the HMGB1-RAGE pathway was blocked by a RAGE antagonist or deletion of the RAGE gene. The absence of RAGE also decreased the activity of pentylenetetrazol-induced cortical epileptiform discharge. In summary, this study provided experimental evidence that the levels of extranuclear HMGB1 and its receptor RAGE were increased in cortical lesion in the early stage of the FL model. Activation of the HMGB1-RAGE pathway may contribute to the abnormal migration of SDNPs and the hyperexcitability of cortical lesion in the FL model.

Abnormal Rat Cortical Development Induced by Ventricular Injection of rHMGB1 Mimics the Pathophysiology of Human Cortical Dysplasia

Cortical dysplasia (CD) is a common cause of drug-resistant epilepsy. Increasing studies have implicated innate immunity in CD with epilepsy. However, it is unclear whether innate immune factors induce epileptogenic CD. Here, we injected recombinant human high mobility group box 1 (rHMGB1) into embryonic rat ventricles to determine whether rHMGB1 can induce epileptogenic CD with pathophysiological characteristics similar to those of human CD. Compared with controls and 0.1 μg rHMGB1-treated rats, the cortical organization was severely disrupted in the 0.2 μg rHMGB1-treated rats, and microgyria and heterotopia also emerged; additionally, disoriented and deformed neurons were observed in the cortical lesions and heterotopias. Subcortical heterotopia appeared in the white matter and the gray–white junction of the 0.2 μg rHMGB1-treated rats. Moreover, there was decreased number of neurons in layer V–VI and an increased number of astrocytes in layer I and V of the cortical lesions. And the HMGB1 antagonist dexmedetomidine alleviated the changes induced by rHMGB1. Further, we found that TLR4 and NF-κB were increased after rHMGB1 administration. In addition, the excitatory receptors, N-methyl-D-aspartate receptor 1 (NR1), 2A (NR2A), and 2B (NR2B) immunoreactivity were increased, and immunoreactivity of excitatory amino acid transporter 1 (EAAT1) and 2 (EAAT2) were reduced in 0.2 μg rHMGB1-treated rats compared with controls. While there were no differences in the glutamic acid decarboxylase 65/67 (GAD65/67) immunoreactivity between the two groups. These results indicate that the excitation of cortical lesions was significantly increased. Furthermore, electroencephalogram (EEG) showed a shorter latency of seizure onset and a higher incidence of status epilepticus in the 0.2 μg rHMGB1-treated rats; the frequency and amplitude of EEG were higher in the treated rats than controls. Intriguingly, spontaneous electrographic seizure discharges were detected in the 0.2 μg rHMGB1-treated rats after 5 months of age, and spike-wave discharges of approximately 8 Hz were the most significantly increased synchronous propagated waves throughout the general brain cortex. Taken together, these findings indicate that rHMGB1 exposure during pregnancy could contribute to the development of epileptogenic CD, which mimicked some pathophysiological characteristics of human CD.

β2 and α2 adrenergic receptors mediate the proneurogenic in vitro effects of norquetiapine

Positive modulation of adult hippocampal neurogenesis may contribute to the therapeutic effects of clinically relevant antidepressant drugs, including atypical antipsychotics. Quetiapine, an antipsychotic which represents a therapeutic option in patients who are resistant to classical antidepressants, promotes adult hippocampal neurogenesis in preclinical studies. Norquetiapine, the key active metabolite of quetiapine in humans, has a distinctive receptor profile than the parent compound. The drug is indeed a high affinity norepinephrine transporter inhibitor and such activity has been proposed to contribute to its antidepressant effect. At present, no information is available on the effects of norquetiapine on adult neurogenesis. We extensively investigated the activity of quetiapine and norquetiapine on adult murine neural stem/progenitor cells and their progeny. Additionally, selective antagonists for β₂/α₂ adrenergic receptors allowed us to evaluate if these receptors could mediate quetiapine and norquetiapine effects. We demonstrated that both drugs elicit in vitro proneurogenic effects but also that norquetiapine had distinctive properties which may depend on its ability to inhibit norepinephrine transporter and involve β₂/α₂ adrenergic receptors. Animal care and experimental procedures were approved by the Institutional Animal Care and Use Committees (IACUC) at University of Piemonte Orientale, Italy (approval No. 1033/2015PR) on September 29, 2015.

The Impact of Advanced Glycation End-Products (AGEs) on Proliferation and Apoptosis of Primary Stem Cells: A Systematic Review

Stem cell-based regenerative therapies hold great promises to treat a wide spectrum of diseases. However, stem cell engraftment and survival are still challenging due to an unfavorable transplantation environment. Advanced glycation end-products (AGEs) can contribute to the generation of these harmful conditions. AGEs are a heterogeneous group of glycated products, nonenzymatically formed when proteins and/or lipids become glycated and oxidized. Our typical Western diet as well as cigarettes contain high AGEs content. AGEs are also endogenously formed in our body and accumulate with senescence and in pathological situations. Whether AGEs have an impact on stem cell viability in regenerative medicine remains unclear, and research on the effect of AGEs on stem cell proliferation and apoptosis is still ongoing. Therefore, this systematic review provides a clear overview of the effects of glycated proteins on cell viability in various types of primary isolated stem cells used in regenerative medicine.

Advanced glycation end products in musculoskeletal system and disorders

The human population is ageing globally, and the number of old people is increasing yearly. Diabetes is common in the elderly, and the number of diabetic patients is also increasing. Elderly and diabetic patients often have musculoskeletal disorder, which are associated with advanced glycation end products (AGEs). AGEs are heterogeneous molecules derived from non-enzymatic products of the reaction of glucose or other sugar derivatives with proteins or lipids, and many different types of AGEs have been identified. AGEs are a biomarker for ageing and for evaluating disease conditions. Fluorescence, spectroscopy, mass spectrometry, chromatography, and immunological methods are commonly used to measure AGEs, but there is no standardized evaluation method because of the heterogeneity of AGEs. The formation of AGEs is irreversible, and they accumulate in tissue, eventually causing damage. AGE accumulation has been confirmed in neuromusculoskeletal tissues, including bones, cartilage, muscles, tendons, ligaments, and nerves, where they adversely affect biomechanical properties by causing charge changes and forming cross-linkages. AGEs also bind to receptors, such as the receptor for AGEs (RAGE), and induce inflammation by intracellular signal transduction. These mechanisms cause many varied aging and diabetes-related pathological conditions, such as osteoporosis, osteoarthritis, sarcopenia, tendinopathy, and neuropathy. Understanding of AGEs related pathomechanism may lead to develop novel methods for the prevention and therapy of such disorders which affect patients' quality of life. Herein, we critically review the current methodology used for detecting AGEs, and present potential mechanisms by which AGEs cause or exacerbate musculoskeletal disorders.

The receptor for advanced glycation end-products enhances lung epithelial wound repair: An in vitro study

Re-epithelialization of the alveolar surface is a key process of lung alveolar epithelial barrier repair after acute lung injury. The receptor for advanced glycation end-products (RAGE) pathway plays key roles in lung homeostasis, and its involvement in wound repair has been already reported in human bronchial epithelial cells. However, its effects on lung alveolar epithelial repair after injury remain unknown. We investigated whether RAGE stimulation with its ligands high-mobility group box 1 protein (HMGB1) or advanced glycation end-products (AGEs), alone or associated with RAGE inhibition using RAGE antagonist peptide, affects in vitro wound healing in human alveolar epithelial A549 cells. We further asked whether these effects could be associated with changes in cell proliferation and migration. We found that treatment of A549 cells with HMGB1 or AGEs promotes RAGE-dependent wound healing after a scratch assay. In addition, both RAGE ligands increased cell proliferation in a RAGE-dependent manner. Treatment with HMGB1 increased migration of alveolar epithelial cells at 12 h, independently of RAGE, whereas AGEs stimulated migration as measured 48 h after injury in a RAGE-dependent manner. Taken together, these results suggest that RAGE pathway is involved in lung alveolar epithelial wound repair, possibly through enhanced cell migration and proliferation.

Astrocyte-Derived Paracrine Signals: Relevance for Neurogenic Niche Regulation and Blood-Brain Barrier Integrity

Astrocytes are essential for proper regulation of the central nervous system (CNS). Importantly, these cells are highly secretory in nature. Indeed they can release hundreds of molecules which play pivotal physiological roles in nervous tissues and whose abnormal regulation has been associated with several CNS disorders. In agreement with these findings, recent studies have provided exciting insights into the key contribution of astrocyte-derived signals in the pleiotropic functions of these cells in brain health and diseases. In the future, deeper analysis of the astrocyte secretome is likely to further increase our current knowledge on the full potential of these cells and their secreted molecules not only as active participants in pathophysiological events, but as pharmacological targets or even as therapeutics for neurological and psychiatric diseases. Herein we will highlight recent findings in our and other laboratories on selected molecules that are actively secreted by astrocytes and contribute in two distinct functions with pathophysiological relevance for the astroglial population: i) regulation of neural stem cells (NSCs) and their progeny within adult neurogenic niches; ii) modulation of the blood–brain barrier (BBB) integrity and function.

Salmeterol, a β2 Adrenergic Agonist, Promotes Adult Hippocampal Neurogenesis in a Region-Specific Manner

Neurogenesis persists in the subgranular zone of the hippocampal formation in the adult mammalian brain. In this area, neural progenitor cells (NPCs) receive both permissive and instructive signals, including neurotransmitters, that allow them to generate adult-born neurons which can be functionally integrated in the preexisting circuit. Deregulation of adult hippocampal neurogenesis (ahNG) occurs in several neuropsychiatric and neurodegenerative diseases, including major depression, and represents a potential therapeutic target. Of interest, several studies suggested that, both in rodents and in humans, ahNG is increased by chronic administration of classical monoaminergic antidepressant drugs, suggesting that modulation of this process may participate to their therapeutic effects. Since the established observation that noradrenergic innervations from locus coeruleus make contact with NPC in the dentate gyrus, we investigated the role of beta adrenergic receptor (β-AR) on ahNG both in vitro and in vivo. Here we report that, in vitro, activation of β₂-AR by norepinephrine and β₂-AR agonists promotes the formation of NPC-derived mature neurons, without affecting NPC survival or differentiation toward glial lineages. Additionally, we show that a selective β₂-AR agonist able to cross the blood-brain barrier, salmeterol, positively modulates hippocampal neuroplasticity when chronically administered in adult naïve mice. Indeed, salmeterol significantly increased number, maturation, and dendritic complexity of DCX⁺ neuroblasts. The increased number of DCX⁺ cells was not accompanied by a parallel increase in the percentage of BrdU⁺/DCX⁺ cells suggesting a potential prosurvival effect of the drug on neuroblasts. More importantly, compared to vehicle, salmeterol promoted ahNG, as demonstrated by an increase in the actual number of BrdU⁺/NeuN⁺ cells and in the percentage of BrdU⁺/NeuN⁺ cells over the total number of newly generated cells. Interestingly, salmeterol proneurogenic effects were restricted to the ventral hippocampus, an area related to emotional behavior and mood regulation. Since salmeterol is commonly used for asthma therapy in the clinical setting, its novel pharmacological property deserves to be further exploited with a particular focus on drug potential to counteract stress-induced deregulation of ahNG and depressive-like behavior.

Changes in Neuroimmune and Neuronal Death Markers after Adolescent Alcohol Exposure in Rats are Reversed by Donepezil

Adolescent intermittent ethanol (AIE) exposure diminishes neurogenesis and dendritic spine density in the dentate gyrus. The cholinesterase inhibitor, donepezil (Aricept), reverses AIE effects on dendritic spines, possibly by interacting with inflammatory and/or epigenetic mediators after AIE exposure. This study tests the hypothesis that donepezil reverses AIE-induced neuroimmune, and epigenetic changes in the adult dentate gyrus. Adolescent Sprague-Dawley male rats (PD30-43) were given 10 intermittent, intragastric doses of ethanol (5.0 g/kg) or isovolumetric water (AIW). Twenty-one days later half of the animals from each group were treated with either donepezil or isovolumetric water (i.g.) once daily for four days. Two hours after the last donepezil or water dose animals were sacrificed and brains prepared for immunohistochemical analyses. AIE reduced immunoreactivity for doublecortin (DCX) and increased immunoreactivity for activated caspase-3 and death receptor-3 in adulthood, suggesting an enduring attenuation of neurogenesis and an increase in progenitor death. These effects were reversed by donepezil treatment in adulthood. AIE also increased immunoreactivity for the inflammatory signaling molecules HMGB1 and RAGE, as well as the activated phosphorylated transcription factor pNFκB p65, and the gene silencing marker dimethylated histone H3K9. All of these AIE effects were also reversed by donepezil, with the exception of HMGB1.

Protection against RAGE-mediated neuronal cell death by sRAGE-secreting human mesenchymal stem cells in 5xFAD transgenic mouse model

Alzheimer's disease (AD), which is the most commonly encountered neurodegenerative disease, causes synaptic dysfunction and neuronal loss due to various pathological processes that include tau abnormality and amyloid beta (Aβ) accumulation. Aβ stimulates the secretion and the synthesis of Receptor for Advanced Glycation End products (RAGE) ligand by activating microglial cells, and has been reported to cause neuronal cell death in Aβ_1-42 treated rats and in mice with neurotoxin-induced Parkinson's disease. The soluble form of RAGE (sRAGE) is known to reduce inflammation, and to decrease microglial cell activation and Aβ deposition, and thus, it protects from neuronal cell death in AD. However, sRAGE protein has too a short half-life for therapeutic purposes. We developed sRAGE-secreting umbilical cord derived mesenchymal stem cells (sRAGE-MSCs) to enhance the inhibitory effects of sRAGE on Aβ deposition and to reduce the secretion and synthesis of RAGE ligands in 5xFAD mice. In addition, these cells improved the viability of injected MSCs, and enhanced the protective effects of sRAGE by inhibiting the binding of RAGE and RAGE ligands in 5xFAD mice. These findings suggest sRAGE protein from sRAGE-MSCs has better protection against neuronal cell death than sRAGE protein or single MSC treatment by inhibiting the RAGE cell death cascade and RAGE-induce inflammation.

Proneurogenic Effects of Trazodone in Murine and Human Neural Progenitor Cells

Several antidepressants increase adult hippocampal neurogenesis (ahNG) in rodents, primates, and, potentially, humans. This effect may at least partially account for their therapeutic activity. The availability of antidepressants whose mechanism of action involves different neurotransmitter receptors represents an opportunity for increasing our knowledge on their distinctive peculiarities and for dissecting the contribution of receptor subtypes in ahNG modulation. The aim of this study was to evaluate, in vitro, the effects of the antidepressant trazodone (TZD) on ahNG by using primary cultures of murine adult hippocampal neural progenitor cells (ahNPCs) and human induced pluripotent stem cell (iPSC)-derived NPCs. We demonstrated that TZD enhances neuronal differentiation of murine as well as human NPCs. TZD is a multimodal antidepressant, which binds with high affinity to 5-HT_2a, α₁, and 5-HT_1a and with lower affinity to 5-HT_2c, α₂ and 5-HTT. We demonstrated that TZD proneurogenic effects were mediated by 5-HT_2a antagonism both in murine and in human NPCs and by 5-HT_2c antagonism in murine cells. Moreover NF-κB p50 nuclear translocation appeared to be required for TZD-mediated proneurogenic effects. Interestingly, TZD had no proneurogenic effects in 5-HT depleted ahNPCs. The TDZ bell-shaped dose-response curve suggested additional effects. However, in our model 5-HT_1a and α₁/α₂ receptors had no role in neurogenesis. Overall, our data also demonstrated that serotoninergic neurotransmission may exert both positive and negative effects on neuronal differentiation of ahNPCs in vitro.

HMGB1/Advanced Glycation End Products (RAGE) does not aggravate inflammation but promote endogenous neural stem cells differentiation in spinal cord injury

Receptor for advanced glycation end products (RAGE) signaling is involved in a series of cell functions after spinal cord injury (SCI). Our study aimed to elucidate the effects of RAGE signaling on the neuronal recovery after SCI. In vivo, rats were subjected to SCI with or without anti-RAGE antibodies micro-injected into the lesion epicenter. We detected Nestin/RAGE, SOX-2/RAGE and Nestin/MAP-2 after SCI by Western blot or immunofluorescence (IF). We found that neural stem cells (NSCs) co-expressed with RAGE were significantly activated after SCI, while stem cell markers Nestin and SOX-2 were reduced by RAGE blockade. We found that RAGE inhibition reduced nestin-positive NSCs expressing MAP-2, a mature neuron marker. RAGE blockade does not improve neurobehavior Basso, Beattie and Bresnahan (BBB) scores; however, it damaged survival of ventral neurons via Nissl staining. Through in vitro study, we found that recombinant HMGB1 administration does not lead to increased cytokines of TNF-α and IL-1β, while anti-RAGE treatment reduced cytokines of TNF-α and IL-1β induced by LPS via ELISA. Meanwhile, HMGB1 increased MAP-2 expression, which was blocked after anti-RAGE treatment. Hence, HMGB1/RAGE does not exacerbate neuronal inflammation but plays a role in promoting NSCs differentiating into mature neurons in the pathological process of SCI.

Factors Released from Endothelial Cells Exposed to Flow Impact Adhesion, Proliferation, and Fate Choice in the Adult Neural Stem Cell Lineage

The microvasculature within the neural stem cell (NSC) niche promotes self-renewal and regulates lineage progression. Previous work identified endothelial-produced soluble factors as key regulators of neural progenitor cell (NPC) fate and proliferation; however, endothelial cells (ECs) are sensitive to local hemodynamics, and the effect of this key physiological process has not been defined. In this study, we evaluated adult mouse NPC response to soluble factors isolated from static or dynamic (flow) EC cultures. Endothelial factors generated under dynamic conditions significantly increased neuronal differentiation, while those released under static conditions stimulated oligodendrocyte differentiation. Flow increases EC release of neurogenic factors and of heparin sulfate glycosaminoglycans that increase their bioactivity, likely underlying the enhanced neuronal differentiation. Additionally, endothelial factors, especially from static conditions, promoted adherent growth. Together, our data suggest that blood flow may impact proliferation, adhesion, and the neuron-glial fate choice of adult NPCs, with implications for diseases and aging that reduce flow.

Novel insights into the role of NF-κB p50 in astrocyte-mediated fate specification of adult neural progenitor cells

Within the CNS nuclear factor-kappa B (NF-κB) transcription factors are involved in a wide range of functions both in homeostasis and in pathology. Over the years, our and other groups produced a vast array of information on the complex involvement of NF-κB proteins in different aspects of postnatal neurogenesis. In particular, several extracellular signals and membrane receptors have been identified as being able to affect neural progenitor cells (NPC) and their progeny via NF-κB activation. A crucial role in the regulation of neuronal fate specification in adult hippocampal NPC is played by the NF-κB p50 subunit. NF-κB p50KO mice display a remarkable reduction in adult hippocampal neurogenesis which correlates with a selective defect in hippocampal-dependent short-term memory. Moreover absence of NF-κB p50 can profoundly affect the in vitro proneurogenic response of adult hippocampal NPC (ahNPC) to several endogenous signals and drugs. Herein we briefly review the current knowledge on the pivotal role of NF-κB p50 in the regulation of adult hippocampal neurogenesis. In addition we discuss more recent data that further extend the relevance of NF-κB p50 to novel astroglia-derived signals which can influence neuronal specification of ahNPC and to astrocyte-NPC cross-talk.

Cell autonomous and noncell-autonomous role of NF-κB p50 in astrocyte-mediated fate specification of adult neural progenitor cells

In previous work, we demonstrated that NF-κB p50 acts as crucial regulator of adult hippocampal neural progenitor cells (ahNPC). Indeed, NF-κB p50 knockout (KO) mice are characterized by remarkably reduced hippocampal neurogenesis. As a follow up to that work, herein we show that when cultured in vitro, ahNPC from wild type (WT) and p50KO mice are not significantly different in their neurogenic potential. This observation prompted us to investigate cell-autonomous and noncell-autonomous consequences of p50 absence on neuronal fate specification of ahNPC. In particular, we focused our attention on astrocytes, known to provide soluble proneurogenic signals, and investigated the influence of WT and p50KO astrocyte conditioned media (ACM) on WT and p50KO ahNPC differentiation. Interestingly, while WT ACM promoted both neuronal and astroglial differentiations, p50KO ACM only supported astroglial differentiation of WT ahNPC. By using a LC-MS/MS approach, we identified some proteins, which are significantly upregulated in p50KO compared with WT astrocytes. Among them, lipocalin-2 (LCN-2) was recognized as a novel astroglial-derived signal regulating neuronal fate specification of ahNPC. Interestingly, LCN-2 proneurogenic effect was greatly reduced in p50KO NPC, where LCN-2 receptor gene expression appeared downregulated. In addition to that, we demonstrated p50KO NPC unresponsiveness to both neuronal and astroglial fate specification signals from WT and p50KO ACM, and we identified a reduced expression of α2δ1, a thrombospondin-1 receptor, as another phenotypic change occurring in ahNPC in the absence of p50. Altogether, our data suggest that dysregulated NPC-astrocyte communication may contribute to a reduced hippocampal neurogenesis in p50KO mice in vivo. GLIA 2016 GLIA 2017;65:169-181.

RAGE Expression and ROS Generation in Neurons: Differentiation versus Damage

RAGE is a multiligand receptor able to bind advanced glycation end-products (AGEs), amphoterin, calgranulins, and amyloid-beta peptides, identified in many tissues and cells, including neurons. RAGE stimulation induces the generation of reactive oxygen species (ROS) mainly through the activity of NADPH oxidases. In neuronal cells, RAGE-induced ROS generation is able to favor cell survival and differentiation or to induce death through the imbalance of redox state. The dual nature of RAGE signaling in neurons depends not only on the intensity of RAGE activation but also on the ability of RAGE-bearing cells to adapt to ROS generation. In this review we highlight these aspects of RAGE signaling regulation in neuronal cells.

Reduced soluble RAGE is associated with disease severity of axonal Guillain-Barré syndrome

Soluble receptor for advanced glycation end products (sRAGE) is an anti-inflammatory factor that mitigates the proinflammatory effects of high mobility group box 1 (HMGB1). The aim of this study was to investigate whether Guillain-Barré syndrome (GBS)-related inflammation are mediated by sRAGE and HMGB1. We measured serum sRAGE, HMGB1, IL-6, and TNF-α levels in 86 patients with GBS and analysed associations between sRAGE or HMGB1 and clinical variables in these subjects. In addition, we determined cerebrospinal fluid sRAGE and HMGB1 levels in a cross-sectional study of 50 patients with GBS who had matched serum samples. We found serum sRAGE levels in patients with the acute motor axonal neuropathy (AMAN) subtype of GBS, but not other subtypes, were significantly lower than those in healthy controls, and were significantly correlated with GBS disability score and Erasmus GBS outcome score, while serum HMGB1, IL-6, and TNF-α levels in all subtypes of GBS were significantly higher than those in healthy controls. Moreover, increased sRAGE levels and decreased HMGB1 levels after treatment were observed. Our results showed that serum sRAGE may be a useful biomarker for inflammation in the AMAN GBS subtype, while HMGB1 may be related to the inflammatory process across all types of GBS.

Receptor for advanced glycation end products (RAGE) and its ligands: focus on spinal cord injury

Spinal cord injury (SCI) results in neuronal and glial death and the loss of axons at the injury site. Inflammation after SCI leads to the inhibition of tissue regeneration and reduced neuronal survival. In addition, the loss of axons after SCI results in functional loss below the site of injury accompanied by neuronal cell body’s damage. Consequently, reducing inflammation and promoting axonal regeneration after SCI is a worthy therapeutic goal. The receptor for advanced glycation end products (RAGE) is a transmembrane protein and receptor of the immunoglobulin superfamily. RAGE is implicated in inflammation and neurodegeneration. Several recent studies demonstrated an association between RAGE and central nervous system disorders through various mechanisms. However, the relationship between RAGE and SCI has not been shown. It is imperative to elucidate the association between RAGE and SCI, considering that RAGE relates to inflammation and axonal degeneration following SCI. Hence, the present review highlights recent research regarding RAGE as a compelling target for the treatment of SCI.

High-mobility group box 1 released from astrocytes promotes the proliferation of cultured neural stem/progenitor cells

Astrocytes are major components of the adult neurogenic niche and play a crucial role in regulating neural stem cell proliferation and differentiation. Following brain injury, astrocytes become reactive and release high-mobility group box 1 (HMGB1), which plays a crucial role in the inflammatory process. However, although it has been reported that HMGB1 promotes neural stem/progenitor cell (NS/PC) proliferation in the developing brain, whether HMGB1 released by reactive astrocytes regulates NS/PC proliferation remains unknown. In this study, we aimed to investigate whether HMGB1 released from reactive astrocytes enhances NS/PC proliferation and to elucidate the possible mechanisms involved in this process. To evaluate the effects of HMGB1 on NS/PC proliferation, NS/PCs were cultured in HMGB1 culture medium and astrocyte-conditioned medium with or without reactive astrocyte-derived HMGB1 by RNA interference (RNAi). To explore the possible mechanisms, the HMGB1 receptor for advanced glycation endproducts (RAGE) in the NS/PCs was blocked with anti-RAGE antibody, and c-Jun N-terminal protein kinase (JNK) in the NS/PCs was inhibited using the potent JNK inhibitor, SP600125. Our results suggested that HMGB1 released from reactive astrocytes promoted NS/PC proliferation in vitro, and the blockade of RAGE or the inhibition of the JNK signaling pathway in the NS/PCs prevented the HMGB1-induced NS/PC proliferation. Our findings demonstrated that HMGB1 released by reactive astrocytes promoted NS/PC proliferation by binding RAGE and enhancing the phosphorylation of the JNK signaling pathway. These findings support a previously described mechanism of a crosstalk between astrocytes and NS/PCs, and suggest that reactive astrocyte-derived HMGB1 plays an important role in the repair of the central nervous system following brain injury.

Mechanisms of therapeutic resistance in cancer (stem) cells with emphasis on thyroid cancer cells

The two main reasons for death of cancer patients, tumor recurrence and metastasis, are multi-stage cellular processes that involve increased cell plasticity and coincide with elevated resistance to anti-cancer treatments. Epithelial-to-mesenchymal transition (EMT) is a key contributor to metastasis in many cancer types, including thyroid cancer and is known to confer stem cell-like properties onto cancer cells. This review provides an overview of molecular mechanisms and factors known to contribute to cancer cell plasticity and capable of enhancing cancer cell resistance to radio- and chemotherapy. We elucidate the role of DNA repair mechanisms in contributing to therapeutic resistance, with a special emphasis on thyroid cancer. Next, we explore the emerging roles of autophagy and damage-associated molecular pattern responses in EMT and chemoresistance in tumor cells. Finally, we demonstrate how cancer cells, including thyroid cancer cells, can highjack the oncofetal nucleoprotein high-mobility group A2 to gain increased transformative cell plasticity, prevent apoptosis, and enhance metastasis of chemoresistant tumor cells.

NF-κB mediated regulation of adult hippocampal neurogenesis: relevance to mood disorders and antidepressant activity

Adult hippocampal neurogenesis is a peculiar form of process of neuroplasticity that in recent years has gained great attention for its potential implication in cognition and in emotional behavior in physiological conditions. Moreover, a vast array of experimental studies suggested that adult hippocampal neurogenesis may be altered in various neuropsychiatric disorders, including major depression, where its disregulation may contribute to cognitive impairment and/or emotional aspects associated with those diseases. An intriguing area of interest is the potential influence of drugs on adult neurogenesis. In particular, several psychoactive drugs, including antidepressants, were shown to positively modulate adult hippocampal neurogenesis. Among molecules which could regulate adult hippocampal neurogenesis the NF-κB family of transcription factors has been receiving particular attention from our and other laboratories. Herein we review recent data supporting the involvement of NF-κB signaling pathways in the regulation of adult neurogenesis and in the effects of drugs that are endowed with proneurogenic and antidepressant activity. The potential implications of these findings on our current understanding of the process of adult neurogenesis in physiological and pathological conditions and on the search for novel antidepressants are also discussed.

Upregulation of mGlu2 receptors via NF-κB p65 acetylation is involved in the Proneurogenic and antidepressant effects of acetyl-L-carnitine

Acetyl-L-carnitine (ALC) is a naturally occurring molecule with an important role in cellular bioenergetics and as donor of acetyl groups to proteins, including NF-κB p65. In humans, exogenously administered ALC has been shown to be effective in mood disturbances, with a good tolerability profile. No current information is available on the antidepressant effect of ALC in animal models of depression and on the putative mechanism involved in such effect. Here we report that ALC is a proneurogenic molecule, whose effect on neuronal differentiation of adult hippocampal neural progenitors is independent of its neuroprotective activity. The in vitro proneurogenic effects of ALC appear to be mediated by activation of the NF-κB pathway, and in particular by p65 acetylation, and subsequent NF-κB-mediated upregulation of metabotropic glutamate receptor 2 (mGlu2) expression. When tested in vivo, chronic ALC treatment could revert depressive-like behavior caused by unpredictable chronic mild stress, a rodent model of depression with high face validity and predictivity, and its behavioral effect correlated with upregulated expression of mGlu2 receptor in hippocampi of stressed mice. Moreover, chronic, but not acute or subchronic, drug treatment significantly increased adult born neurons in hippocampi of stressed and unstressed mice. We now propose that this mechanism could be potentially involved in the antidepressant effect of ALC in humans. These results are potentially relevant from a clinical perspective, as for its high tolerability profile ALC may be ideally employed in patient subpopulations who are sensitive to the side effects associated with classical antidepressants.

High-mobility group box-1 protein and β-amyloid oligomers promote neuronal differentiation of adult hippocampal neural progenitors via receptor for advanced glycation end products/nuclear factor-κB axis: relevance for Alzheimer's disease

Dysregulated hippocampal neurogenesis has been associated with neurodegenerative disorders, including Alzheimer's disease (AD), in which it may potentially represent an auto-reparatory mechanism that could counteract neuronal loss and cognitive impairment. We evaluated hippocampal neurogenesis in TgCRND8 mice and reported that, at 32 weeks of age, corresponding to an advanced AD-like neuropathology stage, increased numbers of proliferating cells, doublecortin-expressing progenitors/neuroblasts, and early postmitotic calretinin-expressing neurons were present compared with wild-type (WT) littermates. When hippocampal neural progenitor cells (NPCs) were isolated from TgCRND8 mice, we demonstrated that (1) their neurogenic potential was higher compared with WT NPCs; (2) medium conditioned by TgCRND8 NPC promoted neuronal differentiation of WT NPCs; and (3) the proneurogenic effect of TgCRND8-conditioned medium was counteracted by blockade of the receptor for advanced glycation end products (RAGE)/nuclear factor-κB (NF-κB) axis. Furthermore, we showed that β-amyloid 1-42 (Aβ(1-42)) oligomers, but not monomers and fibrils, and the alarmin high-mobility group box-1 protein (HMGB-1) could promote neuronal differentiation of NPCs via activation of the RAGE/NF-κB axis. Altogether, these data suggest that, in AD brain, an endogenous proneurogenic response could be potentially triggered and involve signals (Aβ(1-42) oligomers and HMGB-1) and pathways (RAGE/NF-κB activation) that also contribute to neuroinflammation/neurotoxicity. A more detailed analysis confirmed no significant increase of new mature neurons in hippocampi of TgCRND8 compared with WT mice, suggesting reduced survival and/or integration of newborn neurons. Therapeutic strategies in AD should ideally combine the ability of sustaining hippocampal neurogenesis as well as of counteracting an hostile brain microenvironment so to promote survival of vulnerable cell populations, including adult generated neurons.

Receptor for Advanced Glycation Endproducts is upregulated in temporal lobe epilepsy and contributes to experimental seizures

Toll-like receptor 4 (TLR4) activation in neuron and astrocytes by High Mobility Group Box 1 (HMGB1) protein is a key mechanism of seizure generation. HMGB1 also activates the Receptor for Advanced Glycation Endproducts (RAGE), but it was unknown whether RAGE activation contributes to seizures or to HMGB1 proictogenic effects. We found that acute EEG seizures induced by 7ng intrahippocampal kainic acid (KA) were significantly reduced in Rage-/- mice relative to wild type (Wt) mice. The proictogenic effect of HMGB1 was decreased in Rage-/- mice, but less so, than in Tlr4-/- mice. In a mouse mesial temporal lobe epilepsy (mTLE) model, status epilepticus induced by 200ng intrahippocampal KA and the onset of the spontaneous epileptic activity were similar in Rage-/-, Tlr4-/- and Wt mice. However, the number of hippocampal paroxysmal episodes and their duration were both decreased in epileptic Rage-/- and Tlr4-/- mice vs Wt mice. All strains of epileptic mice displayed similar cognitive deficits in the novel object recognition test vs the corresponding control mice. CA1 neuronal cell loss was increased in epileptic Rage-/- vs epileptic Wt mice, while granule cell dispersion and doublecortin (DCX)-positive neurons were similarly affected. Notably, DCX neurons were preserved in epileptic Tlr4-/- mice. We did not find compensatory changes in HMGB1-related inflammatory signaling nor in glutamate receptor subunits in Rage-/- and Tlr4-/- naïve mice, except for ~20% NR2B subunit reduction in Rage-/- mice. RAGE was induced in neurons, astrocytes and microvessels in human and experimental mTLE hippocampi. We conclude that RAGE contributes to hyperexcitability underlying acute and chronic seizures, as well as to the proictogenic effects of HMGB1. RAGE and TLR4 play different roles in the neuropathologic sequelae developing after status epilepticus. These findings reveal new molecular mechanisms underlying seizures, cell loss and neurogenesis which involve inflammatory pathways upregulated in human epilepsy.

S100B protein in tissue development, repair and regeneration

The Ca²⁺-binding protein of the EF-hand type, S100B, exerts both intracellular and extracellular regulatory activities. As an intracellular regulator, S100B is involved in the regulation of energy metabolism, transcription, protein phosphorylation, cell proliferation, survival, differentiation and motility, and Ca²⁺ homeostasis, by interacting with a wide array of proteins (i.e., enzymes, enzyme substrates, cytoskeletal subunits, scaffold/adaptor proteins, transcription factors, ubiquitin E3 ligases, ion channels) in a restricted number of cell types. As an extracellular signal, S100B engages the pattern recognition receptor, receptor for advanced glycation end-products (RAGE), on immune cells as well as on neuronal, astrocytic and microglial cells, vascular smooth muscle cells, skeletal myoblasts and cardiomyocytes. However, RAGE may not be the sole receptor activated by S100B, the protein being able to enhance bFGF-FGFR1 signaling by interacting with FGFR1-bound bFGF in particular cell types. Moreover, extracellular effects of S100B vary depending on its local concentration. Increasing evidence suggests that at the concentration found in extracellular fluids in normal physiological conditions and locally upon acute tissue injury, which is up to a few nM levels, S100B exerts trophic effects in the central and peripheral nervous system and in skeletal muscle tissue thus participating in tissue homeostasis. The present commentary summarizes results implicating intracellular and extracellular S100B in tissue development, repair and regeneration.

Nuclear factor kappa B signaling initiates early differentiation of neural stem cells

Inflammatory mediators, many of which activate the signaling of nuclear factor kappa B (NFκB), have received increasing attention in the field of neurogenesis. NFκB signaling regulates neurite outgrowth and neural plasticity as well as the proliferation/apoptosis and terminal differentiation of neural stem cells (NSCs). Early neurogenesis from NSCs produces identical progeny through symmetric division and committed daughter cells through asymmetric division. Here, we show that NFκB signaling is required for NSC initial differentiation. The canonical IKKβ/IκBα/p65 pathway is activated during the initial stages of neural differentiation induced by treatment with TNFα or withdrawal of epidermal growth factor/basic fibroblast growth factor. NSC-specific inhibition of NFκB in transgenic mice causes an accumulation of Nestin(+) /Sox2(+) /glial fibrillary acidic protein(+) NSCs. Inhibition of NFκB signaling in vitro blocks differentiation and asymmetric division and maintains NSCs in an undifferentiated state. The induction of initial differentiation and asymmetry by NFκB signaling occurs through the inhibition of C/EBPβ expression. Our data reveal a novel function of NFκB signaling in early neurogenesis and provide insight into the molecular mechanisms underlying neurodevelopmental disorders and neurodegenerative diseases.

NFκB signaling regulates embryonic and adult neurogenesis

Both embryonic and adult neurogenesis involves the self-renewal/proliferation, survival, migration and lineage differentiation of neural stem/progenitor cells. Such dynamic process is tightly regulated by intrinsic and extrinsic factors and complex signaling pathways. Misregulated neurogenesis contributes much to a large range of neurodevelopmental defects and neurodegenerative diseases. The signaling of NFκB regulates many genes important in inflammation, immunity, cell survival and neural plasticity. During neurogenesis, NFκB signaling mediates the effect of numerous niche factors such as cytokines, chemokines, growth factors, extracellular matrix molecules, but also crosstalks with other signaling pathways such as Notch, Shh, Wnt/β-catenin. This review summarizes current progress on the NFκB signaling in all aspects of neurogenesis, focusing on the novel role of NFκB signaling in initiating early neural differentiation of neural stem cells and embryonic stem cells.

The role of receptor for advanced glycation end products (RAGE) in neuronal differentiation

The receptor for advanced glycation end products (RAGE) is a multiligand receptor protein thought to play an important role in neuronal differentiation. RAGE can bind a number of ligands and activate a variety of signalling pathways that lead to diverse downstream effects. Amphoterin and S100B are endogenous ligands, the interaction of which with RAGE is known to be involved in defined physiological processes. The present study investigated the spatiotemporal pattern of the expression for RAGE and its ligands, amphoterin and S100B, during neuronal differentiation of NT2/D1 cells. In this study, all three proteins were shown to increase with progression of neuronal differentiation as determined by Western blotting, raising the possibility that both amphoterin and S100B may interact with RAGE and have important functions during the process of cell differentiation. Moreover, blocking the activation of RAGE with neutralizing antibody in the presence of retinoic acid disrupted the progression of normal neuronal differentiation. Immunocytochemistry (ICC) studies showed that amphoterin partially colocalized with RAGE within differentiating NT2 cells, whereas S100B showed a high degree of colocalization. This result suggests that S100B is more likely to be the principal ligand for RAGE during the differentiation process and that RAGE and amphoterin might have both independent and combined roles. Moreover, RAGE was expressed only in cells that were committed to a neuronal phenotype, suggesting direct involvement of RAGE in mediating cellular changes within differentiating neuronal cells. Further detailed studies are now required to characterize fully the role of RAGE during the neuronal differentiation period.

Regulation of neural process growth, elaboration and structural plasticity by NF-κB

The nuclear factor-kappa B (NF-κB) family of transcription factors has recently emerged as a major regulator of the growth and elaboration of neural processes. NF-κB signaling has been implicated in controlling axon initiation, elongation, guidance and branching and in regulating dendrite arbor size and complexity during development and dendritic spine density in the adult. NF-κB is activated by a variety of extracellular signals, and either promotes or inhibits growth depending on the phosphorylation status of the p65 NF-κB subunit. These novel roles for NF-κB, together with recent evidence implicating NF-κB in the regulation of neurogenesis in the embryo and adult, have important implications for neural development and for learning and memory in the mature nervous system.