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

Potential dual role of nuclear factor-kappa B in experimental subarachnoid hemorrhage-induced early brain injury in rabbits

OBJECTIVE AND DESIGN

Nuclear factor-kappa B (NF-κB) has multiple physiological and pathological functions. The role of NF-κB can be protective or destructive. We aim to investigate the biphasic activation of NF-κB in brain after subarachnoid hemorrhage (SAH).

MATERIAL OR SUBJECTS

Eighty male New Zealand rabbits are assigned to control, SAH, vehicle, and pyrrolidine dithiocarbamate (PDTC) groups.

TREATMENT

PDTC (3 mg/kg, dissolved in saline) was injected into cisterna magna.

METHODS

Immunofluorescence and electrophoretic mobility shift assay experiments were performed to assess the activation of NF-κB. The levels of inflammatory and apoptosis mediators were detected by ELISA and real-time polymerase chain reaction. Nissl and immunofluorescent stain was performed to evaluate neuron injury.

RESULTS

NF-κB activity in the brain cortex showed two peaks after SAH. Inflammatory mediators exhibited similar time course. PDTC could significantly inhibit the NF-κB activity and inflammatory mediators. Suppressing the early NF-κB activity significantly decreased neuron injury, while inhibiting the late one could statistically increase neuron injury.

CONCLUSIONS

The biphasic NF-κB activation in the brain cortex after SAH played a decisive role on neuronal fate through the inflammatory signaling pathway. The early NF-κB activity contributed to neuron damage after SAH. Nevertheless, the late activated NF-κB may serve as a protector.

TRIM32 ubiquitin E3 ligase, one enzyme for several pathologies: From muscular dystrophy to tumours

TRIM32 is a member of the TRIpartite Motif family characterised by the presence of an N-terminal three-domain-module that includes a RING domain, which confers E3 ubiquitin ligase activity, one or two B-box domains and a Coiled-Coil region that mediates oligomerisation. Several TRIM32 substrates were identified including muscular proteins and proteins involved in cell cycle regulation and cell motility. As ubiquitination is a versatile post-translational modification that can affect target turnover, sub-cellular localisation or activity, it is likely that diverse substrates may be differentially affected by TRIM32-mediated ubiquitination, reflecting its multi-faceted roles in muscle physiology, cancer and immunity. With particular relevance for muscle physiology, mutations in TRIM32 are associated with autosomal recessive Limb-Girdle Muscular Dystrophy 2H, a muscle-wasting disease with variable clinical spectrum ranging from almost asymptomatic to wheelchair-bound patients. In this review, we will focus on the ability of TRIM32 to mark specific substrates for proteasomal degradation discussing how the TRIM32-proteasome axis may (i) be important for muscle homeostasis and for the pathogenesis of muscular dystrophy; and (ii) define either an oncogenic or tumour suppressive role for TRIM32 in the context of different types of cancer.

Targeting IκB kinase β in Adipocyte Lineage Cells for Treatment of Obesity and Metabolic Dysfunctions

IκB kinase β (IKKβ), a central coordinator of inflammation through activation of nuclear factor-κB, has been identified as a potential therapeutic target for the treatment of obesity-associated metabolic dysfunctions. In this study, we evaluated an antisense oligonucleotide (ASO) inhibitor of IKKβ and found that IKKβ ASO ameliorated diet-induced metabolic dysfunctions in mice. Interestingly, IKKβ ASO also inhibited adipocyte differentiation and reduced adiposity in high-fat (HF)-fed mice, indicating an important role of IKKβ signaling in the regulation of adipocyte differentiation. Indeed, CRISPR/Cas9-mediated genomic deletion of IKKβ in 3T3-L1 preadipocytes blocked these cells differentiating into adipocytes. To further elucidate the role of adipose progenitor IKKβ signaling in diet-induced obesity, we generated mice that selectively lack IKKβ in the white adipose lineage and confirmed the essential role of IKKβ in mediating adipocyte differentiation in vivo. Deficiency of IKKβ decreased HF-elicited adipogenesis in addition to reducing inflammation and protected mice from diet-induced obesity and insulin resistance. Further, pharmacological inhibition of IKKβ also blocked human adipose stem cell differentiation. Our findings establish IKKβ as a pivotal regulator of adipogenesis and suggest that overnutrition-mediated IKKβ activation serves as an initial signal that triggers adipose progenitor cell differentiation in response to HF feeding. Inhibition of IKKβ with antisense therapy may represent as a novel therapeutic approach to combat obesity and metabolic dysfunctions. Stem Cells 2016;34:1883-1895.

Dynamic Trk and G Protein Signalings Regulate Dopaminergic Neurodifferentiation in Human Trophoblast Stem Cells

Understanding the mechanisms in the generation of neural stem cells from pluripotent stem cells is a fundamental step towards successful management of neurodegenerative diseases in translational medicine. Albeit all-trans retinoic acid (RA) has been associated with axon outgrowth and nerve regeneration, the maintenance of differentiated neurons, the association with degenerative disease like Parkinson's disease, and its regulatory molecular mechanism from pluripotent stem cells to neural stem cells remain fragmented. We have previously reported that RA is capable of differentiation of human trophoblast stem cells to dopamine (DA) committed progenitor cells. Intracranial implantation of such neural progenitor cells into the 6-OHDA-lesioned substantia nigra pars compacta successfully regenerates dopaminergic neurons and integrity of the nigrostriatal pathway, ameliorating the behavioral deficits in the Parkinson’s disease rat model. Here, we demonstrated a dynamic molecular network in systematic analysis by addressing spatiotemporal molecular expression, intracellular protein-protein interaction and inhibition, imaging study, and genetic expression to explore the regulatory mechanisms of RA induction in the differentiation of human trophoblast stem cells to DA committed progenitor cells. We focused on the tyrosine receptor kinase (Trk), G proteins, canonical Wnt2B/β-catenin, genomic and non-genomic RA signaling transductions with Tyrosine hydroxylase (TH) gene expression as the differentiation endpoint. We found that at the early stage, integration of TrkA and G protein signalings aims for axonogenesis and morphogenesis, involving the novel RXRα/Gα_q/11 and RARβ/Gβ signaling pathways. While at the later stage, five distinct signaling pathways together with epigenetic histone modifications emerged to regulate expression of TH, a precursor of dopamine. RA induction generated DA committed progenitor cells in one day. Our results provided substantial mechanistic evidence that human trophoblast stem cell-derived neural stem cells can potentially be used for neurobiological study, drug discovery, and as an alternative source of cell-based therapy in neurodegenerative diseases like Parkinson’s disease.

NF-KappaB in Long-Term Memory and Structural Plasticity in the Adult Mammalian Brain

The transcription factor nuclear factor kappaB (NF-κB) is a well-known regulator of inflammation, stress, and immune responses as well as cell survival. In the nervous system, NF-κB is one of the crucial components in the molecular switch that converts short- to long-term memory-a process that requires de novo gene expression. Here, the researches published on NF-κB and downstream target genes in mammals will be reviewed, which are necessary for structural plasticity and long-term memory, both under normal and pathological conditions in the brain. Genetic evidence has revealed that NF-κB regulates neuroprotection, neuronal transmission, and long-term memory. In addition, after genetic ablation of all NF-κB subunits, a severe defect in hippocampal adult neurogenesis was observed during aging. Proliferation of neural precursors is increased; however, axon outgrowth, synaptogenesis, and tissue homeostasis of the dentate gyrus are hampered. In this process, the NF-κB target gene PKAcat and other downstream target genes such as Igf2 are critically involved. Therefore, NF-κB activity seems to be crucial in regulating structural plasticity and replenishment of granule cells within the hippocampus throughout the life. In addition to the function of NF-κB in neurons, we will discuss on a neuroinflammatory role of the transcription factor in glia. Finally, a model for NF-κB homeostasis on the molecular level is presented, in order to explain seemingly the contradictory, the friend or foe, role of NF-κB in the nervous system.

Dynamic aberrant NF-κB spurs tumorigenesis: a new model encompassing the microenvironment

Recently it was discovered that a transient activation of transcription factor NF-κB can give cells properties essential for invasiveness and cancer initiating potential. In contrast, most oncogenes to date were characterized on the basis of mutations or by their constitutive overexpression. Study of NF-κB actually leads to a far more dynamic perspective on cancer: tumors caused by diverse oncogenes apparently evolve into cancer after loss of feedback regulation for NF-κB. This event alters the cellular phenotype and the expression of hormonal mediators, modifying signals between diverse cell types in a tissue. The result is a disruption of stem cell hierarchy in the tissue, and pervasive changes in the microenvironment and immune response to the malignant cells.

C/EBPβ and C/EBPδ transcription factors: Basic biology and roles in the CNS

CCAAT/enhancer binding protein (C/EBP) β and C/EBPδ are transcription factors of the basic-leucine zipper class which share phylogenetic, structural and functional features. In this review we first describe in depth their basic molecular biology which includes fascinating aspects such as the regulated use of alternative initiation codons in the C/EBPβ mRNA. The physical interactions with multiple transcription factors which greatly opens the number of potentially regulated genes or the presence of at least five different types of post-translational modifications are also remarkable molecular mechanisms that modulate C/EBPβ and C/EBPδ function. In the second part, we review the present knowledge on the localization, expression changes and physiological roles of C/EBPβ and C/EBPδ in neurons, astrocytes and microglia. We conclude that C/EBPβ and C/EBPδ share two unique features related to their role in the CNS: whereas in neurons they participate in memory formation and synaptic plasticity, in glial cells they regulate the pro-inflammatory program. Because of their role in neuroinflammation, C/EBPβ and C/EBPδ in microglia are potential targets for treatment of neurodegenerative disorders. Any strategy to reduce C/EBPβ and C/EBPδ activity in neuroinflammation needs to take into account its potential side-effects in neurons. Therefore, cell-specific treatments will be required for the successful application of this strategy.

TRIM32 Senses and Restricts Influenza A Virus by Ubiquitination of PB1 Polymerase

Polymerase basic protein 1 (PB1) is the catalytic core of the influenza A virus (IAV) RNA polymerase complex essential for viral transcription and replication. Understanding the intrinsic mechanisms which block PB1 function could stimulate development of new anti-influenza therapeutics. Affinity purification coupled with mass spectrometry (AP-MS) was used to identify host factors interacting with PB1. Among PB1 interactors, the E3 ubiquitin ligase TRIM32 interacts with PB1 proteins derived from multiple IAV strains. TRIM32 senses IAV infection by interacting with PB1 and translocates with PB1 to the nucleus following influenza infection. Ectopic TRIM32 expression attenuates IAV infection. Conversely, RNAi depletion and knockout of TRIM32 increase susceptibility of tracheal and lung epithelial cells to IAV infection. Reconstitution of trim32^-/- mouse embryonic fibroblasts with TRIM32, but not a catalytically inactive mutant, restores viral restriction. Furthermore, TRIM32 directly ubiquitinates PB1, leading to PB1 protein degradation and subsequent reduction of polymerase activity. Thus, TRIM32 is an intrinsic IAV restriction factor which senses and targets the PB1 polymerase for ubiquitination and protein degradation. TRIM32 represents a model of intrinsic immunity, in which a host protein directly senses and counters viral infection in a species specific fashion by directly limiting viral replication.

Influenza A virus presents a continued threat to global health with considerable economic and social impact. Vaccinations against influenza are not always effective, and many influenza strains have developed resistance to current antiviral drugs. Thus, it is imperative to find new strategies for the prevention and treatment of influenza. Influenza RNA-dependent RNA polymerase is a multifunctional protein essential for both transcription and replication of the viral genome. However, we have little understanding of the mechanisms regulating viral RNA polymerase activity or the innate cellular defenses against this critical viral enzyme. We describe how the E3 ubiquitin ligase, TRIM32, inhibits the activity of the influenza RNA polymerase and defends respiratory epithelial cells against infection with influenza A viruses. TRIM32 directly senses the PB1 subunit of the influenza virus RNA polymerase complex and targets it for ubiquitination and proteasomal degradation, thereby reducing viral polymerase activity.

Modification of Helicobacter pylori Peptidoglycan Enhances NOD1 Activation and Promotes Cancer of the Stomach

Helicobacter pylori (H. pylori) is the strongest known risk factor for gastric carcinogenesis. One cancer-linked locus is the cag pathogenicity island, which translocates components of peptidoglycan into host cells. NOD1 is an intracellular immune receptor that senses peptidoglycan from Gram-negative bacteria and responds by inducing autophagy and activating NF-κB, leading to inflammation-mediated bacterial clearance; however chronic pathogens can evade NOD1-mediated clearance by altering peptidoglycan structure. We previously demonstrated that the H. pylori cag(+) strain 7.13 rapidly induces gastric cancer in Mongolian gerbils. Using 2D-DIGE and mass spectrometry, we identified a novel mutation within the gene encoding the peptidoglycan deacetylase PgdA; therefore, we sought to define the role of H. pylori PgdA in NOD1-dependent activation of NF-κB, inflammation, and cancer. Coculture of H. pylori strain 7.13 or its pgdA(-) isogenic mutant with AGS gastric epithelial cells or HEK293 epithelial cells expressing a NF-κB reporter revealed that pgdA inactivation significantly decreased NOD1-dependent NF-κB activation and autophagy. Infection of Mongolian gerbils with an H. pylori pgdA(-) mutant strain led to significantly decreased levels of inflammation and malignant lesions in the stomach; however, preactivation of NOD1 before bacterial challenge reciprocally suppressed inflammation and cancer in response to wild-type H. pylori. Expression of NOD1 differs in human gastric cancer specimens compared with noncancer samples harvested from the same patients. These results indicate that peptidoglycan deacetylation plays an important role in modulating host inflammatory responses to H. pylori, allowing the bacteria to persist and induce carcinogenic consequences in the gastric niche.

LPS promote the odontoblastic differentiation of human dental pulp stem cells via MAPK signaling pathway

Human dental pulp stem cells (hDPSCs) show significant potential for exploitation in novel regeneration strategies, although lack of understanding of their responses to bacterial challenge constrains their application. The present study aimed to investigate whether lipopolysaccharide (LPS), the major pathogenic factor of Gram-negative bacteria, regulates the differentiation of hDPSCs and which intracellular signaling pathways may be involved. LPS treatment significantly promoted the differentiation of hDPSCs demonstrable by increased mineralized nodule formation and mRNA expression of several odontoblastic markers in a dose-dependent manner. While inhibition of TLR4, p38, and ERK signaling markedly antagonized LPS-mediated differentiation of hDPSCs. The inhibition of JNK and NF-κB signaling had no detectable effect on LPS activation of hDPSCs. LPS stimulation resulted in phosphorylation of NF-κB p65, IκB-α, extracellular signal-regulated kinase (ERK), c-Jun N-terminal kinase (JNK), and p38 mitogen-activated protein kinase (MAPK) in DPSCs in a time-dependent manner, which was markedly suppressed by their specific inhibitors, respectively. Data demonstrated that LPS promoted odontoblastic differentiation of hDPSCs via TLR4, ERK, and P38 MAPK signaling pathways, but not NF-κB signaling.

The role of inflammatory cytokines as key modulators of neurogenesis

Neurogenesis is an important process in the regulation of brain function and behaviour, highly active in early development and continuing throughout life. Recent studies have shown that neurogenesis is modulated by inflammatory cytokines in response to an activated immune system. To disentangle the effects of the different cytokines on neurogenesis, here we summarise and discuss in vitro studies on individual cytokines. We show that inflammatory cytokines have both a positive and negative role on proliferation and neuronal differentiation. Hence, this strengthens the notion that inflammation is involved in molecular and cellular mechanisms associated with complex cognitive processes and, therefore, that alterations in brain-immune communication are relevant to the development of neuropsychiatric disorders.

The effects of harvesting media on biological characteristics and repair potential of neural stem cells after traumatic brain injury

Various solutions are utilized widely for the isolation, harvesting, sorting, testing and transplantation of neural stem cells (NSCs), whereas the effects of harvesting media on the biological characteristics and repair potential of NSCs remain unclear. To examine some of these effects, NSCs were isolated from cortex of E14.5 mice and exposed to the conventional harvesting media [0.9% saline (Saline), phosphate-buffered saline (PBS) or artificial cerebrospinal fluid (ACSF)] or the proliferation culture medium (PCM) for different durations at 4°C. Treated NSCs were grafted by in situ injection into the lesion sites of traumatic brain injury (TBI) mice. In vitro, harvesting media-exposed NSCs displayed time-dependent reduction of viability and proliferation. S phase entry decreased in harvesting media-exposed cells, which was associated with upregulation of p53 protein and downregulation of cyclin E1 protein. Moreover, harvesting media exposure induced the necrosis and apoptosis of NSCs. The levels of Fas-L, cleaved caspase 3 and 8 were increased, which suggests that the death receptor signaling pathway is involved in the apoptosis of NSCs. In addition, exposure to Saline did not facilitate the neuronal differentiation of NSCs, suggesting that Saline exposure may be disadvantageous for neurogenesis. In vivo, NSC-mediated functional recovery in harvesting media-exposed NSC groups was notably attenuated in comparison with the PCM-exposed NSC group. In conclusion, harvesting media exposure modulates the biological characteristics and repair potential of NSCs after TBI. Our results suggest that insight of the effects of harvesting media exposure on NSCs is critical for developing strategies to assure the successful long-term engraftment of NSCs.

TLR7-expressing cells comprise an interfollicular epidermal stem cell population in murine epidermis

Normal interfollicular epidermis (IFE) homeostasis is maintained throughout the entire life by its own stem cells that self-renew and generate progeny that undergo terminal differentiation. However, the fine markers of the stem cells in interfollicular epidermis are not well defined yet. Here we found that TLR7 identified the existence of progenitors and interfollicular epidermal stem cells in murine skin. In vitro, TLR7-expressing cells comprised of two subpopulations that were competent to proliferate and exhibited distinct differentiation potentials. Three-dimensional (3D) organotypic culture and skin reconstitution assays showed that TLR7-expressing cells were able to reconstruct the interfollicular epidermis. Finally, TLR7-expressing cells maintained the intact interfollicular epidermal structures revealed in serial transplantation assays in vivo in mice. Taken together, our results suggest that TLR7-expressing cells comprise an interfollicular epidermal stem cell population.

Myelin-specific T helper 17 cells promote adult hippocampal neurogenesis through indirect mechanisms

CD4 ⁺ T cells provide a neuro-immunological link in the regulation of adult hippocampal neurogenesis, but the exact mechanisms underlying enhanced neural precursor cell proliferation and the relative contribution of different T helper (Th) cell subsets have remained unclear. Here, we explored the pro-proliferative potential of interleukin 17-producing T helper (Th17) cells, a developmentally and functionally distinct Th cell subset that is a key mediator of autoimmune neurodegeneration. We found that base-line proliferation of hippocampal precursor cells in a T cell-deficient mouse model of impaired hippocampal neurogenesis can be restored upon adoptive transfer with homogeneous Th17 populations enriched for myelin-reactive T cell receptors (TCR). In these experiments, enhanced proliferation was independent of direct interactions of infiltrating Th17 cells with precursor cells or neighboring cells in the hippocampal neurogenic niche. Complementary studies in immunocompetent mice identified several receptors for Th17 cell-derived cytokines with mRNA expression in hippocampal precursor cells and dentate gyrus tissue, suggesting that Th17 cell activity in peripheral lymphoid tissues might promote hippocampal neurogenesis through secreted cytokines.

Myelin-specific T helper 17 cells promote adult hippocampal neurogenesis through indirect mechanisms

CD4 ⁺ T cells provide a neuro-immunological link in the regulation of adult hippocampal neurogenesis, but the exact mechanisms underlying enhanced neural precursor cell proliferation and the relative contribution of different T helper (Th) cell subsets have remained unclear. Here, we explored the pro-proliferative potential of interleukin 17-producing T helper (Th17) cells, a developmentally and functionally distinct Th cell subset that is a key mediator of autoimmune neurodegeneration. We found that base-line proliferation of hippocampal precursor cells in a T cell-deficient mouse model of impaired hippocampal neurogenesis can be restored upon adoptive transfer with homogeneous Th17 populations enriched for myelin-reactive T cell receptors (TCR). In these experiments, enhanced proliferation was independent of direct interactions of infiltrating Th17 cells with precursor cells or neighboring cells in the hippocampal neurogenic niche. Complementary studies in immunocompetent mice identified several receptors for Th17 cell-derived cytokines with mRNA expression in hippocampal precursor cells and dentate gyrus tissue, suggesting that Th17 cell activity in peripheral lymphoid tissues might promote hippocampal neurogenesis through secreted cytokines.

IKKβ links vascular inflammation to obesity and atherosclerosis

IKKβ functions in smooth muscle cells to regulate vascular inflammatory responses and atherosclerosis development.

IκB kinase β (IKKβ), a central coordinator of inflammatory responses through activation of NF-κB, has been implicated in vascular pathologies, but its role in atherogenesis remains elusive. Here, we demonstrate that IKKβ functions in smooth muscle cells (SMCs) to regulate vascular inflammatory responses and atherosclerosis development. IKKβ deficiency in SMCs driven by a SM22Cre-IKKβ-flox system rendered low density lipoprotein receptor-null mice resistant to vascular inflammation and atherosclerosis induced by high-fat feeding. Unexpectedly, IKKβ-deficient mice were also resistant to diet-induced obesity and metabolic disorders. Cell lineage analysis revealed that SM22Cre is active in primary adipose stromal vascular cells and deficiency of IKKβ diminished the ability of these cells to differentiate, leading to accumulation of adipocyte precursor cells in adipose tissue. Mechanistically, reduction of IKKβ expression or pharmacological inhibition of IKKβ inhibited proteasome-mediated β-catenin ubiquitination and degradation in murine preadipocytes, resulting in elevated β-catenin levels and impaired adipocyte differentiation. Further, chronic treatment of mice with a potent IKKβ inhibitor decreased adipogenesis and ameliorated diet-induced obesity. Our findings demonstrate a pivotal role of IKKβ in linking vascular inflammation to atherosclerosis and adipose tissue development, and provide evidence for using appropriate IKKβ inhibitors in the treatment of obesity and metabolic disorders.

Preeclampsia enhances neuroglial marker expression in umbilical cord Wharton's jelly-derived mesenchymal stem cells

OBJECTIVE

The aim of the study was to compare the neuroglial phenotype of Wharton's jelly-derived mesenchymal stem cells (WJ-MSC) from pregnancies complicated with preeclampsia and gestational age (GA)-matched controls.

METHODS

WJ-MSC were isolated from umbilical cords from both groups and analyzed for the cell surface expression of MSC markers and the gene and protein expression of neuroglial markers.

RESULTS

All WJ cells were highly positive for the MSC markers CD105, CD90 and CD73, but negative for markers specific for hematopoietic (CD34) and immunological cells (CD45, CD14, CD19 and HLA-DR). WJ-MSC from both groups expressed neuroglial markers (MAP-2, GFAP, MBP, Musashi-1 and Nestin) at the mRNA and protein level. The protein expressions of neuronal (MAP-2) and oligodendrocytic (MBP) markers were significantly increased in WJ-MSC from preeclampsia versus GA-matched controls.

CONCLUSIONS

WJ-MSC from preeclamptic patients are possibly more committed to neuroglial differentiation through the activation of pathways involved both in the pathophysiology of the disease and in neurogenesis.

An epigenetic signature of developmental potential in neural stem cells and early neurons

A cardinal property of neural stem cells (NSCs) is their ability to adopt multiple fates upon differentiation. The epigenome is widely seen as a read-out of cellular potential and a manifestation of this can be seen in embryonic stem cells (ESCs), where promoters of many lineage-specific regulators are marked by a bivalent epigenetic signature comprising trimethylation of both lysine 4 and lysine 27 of histone H3 (H3K4me3 and H3K27me3, respectively). Bivalency has subsequently emerged as a powerful epigenetic indicator of stem cell potential. Here, we have interrogated the epigenome during differentiation of ESC-derived NSCs to immature GABAergic interneurons. We show that developmental transitions are accompanied by loss of bivalency at many promoters in line with their increasing developmental restriction from pluripotent ESC through multipotent NSC to committed GABAergic interneuron. At the NSC stage, the promoters of genes encoding many transcriptional regulators required for differentiation of multiple neuronal subtypes and neural crest appear to be bivalent, consistent with the broad developmental potential of NSCs. Upon differentiation to GABAergic neurons, all non-GABAergic promoters resolve to H3K27me3 monovalency, whereas GABAergic promoters resolve to H3K4me3 monovalency or retain bivalency. Importantly, many of these epigenetic changes occur before any corresponding changes in gene expression. Intriguingly, another group of gene promoters gain bivalency as NSCs differentiate toward neurons, the majority of which are associated with functions connected with maturation and establishment and maintenance of connectivity. These data show that bivalency provides a dynamic epigenetic signature of developmental potential in both NSCs and in early neurons.

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.

Expression and function of NIK- and IKK2-binding protein (NIBP) in mouse enteric nervous system

BACKGROUND

NIK- and IKK2-binding protein (NIBP)/TRAPPC9 is expressed in brain neurons, and human NIBP mutations are associated with neurodevelopmental disorders. The cellular distribution and function of NIBP in the enteric nervous system (ENS) remain unknown.

METHODS

Western blot and reverse transcription-polymerase chain reaction analysis were used respectively to identify the protein and mRNA expression of NIBP and other neuronal markers. Multi-labeled immunofluorescent microscopy and confocal image analysis were used to examine the cellular distribution of NIBP-like immunoreactivity (IR) in whole mount intestine. Enteric neuronal cell line (ENC) was infected with lentivirus carrying NIBP or its shRNA expression vectors and treated with vehicle or tumor necrosis factor (TNF)α.

KEY RESULTS

NIBP is expressed at both mRNA and protein levels in different regions and layers of the mouse intestine. NIBP-like-IR was co-localized with various neuronal markers, but not with glial, smooth muscular, or interstitial cells of Cajal markers. A small population of NIBP-expressing cells and fibers in extra-ganglionic and intra-ganglionic area were negative for pan-neuronal markers HuD or Peripherin. Relatively high NIBP-like-IR was found in 35-44% of myenteric neurons and 9-10% of submucosal neurons. Approximately 98%, 87%, and 43% of these relatively high NIBP-expressing neurons were positive for choline acetyltransferase, neuronal nitric oxide synthase and Calretinin, respectively. NIBP shRNA knockdown in ENC inhibited TNFα-induced NFκB activation and neuronal differentiation, whereas NIBP overexpression promoted it.

CONCLUSIONS & INFERENCES

NIBP is extensively expressed in the ENS with relatively high level in a subpopulation of enteric neurons. Various NIBP expression levels in different neurons may represent dynamic trafficking or posttranslational modification of NIBP in some functionally active neurons and ultimately regulate ENS plasticity.

Derivation of neural stem cells from human adult peripheral CD34+ cells for an autologous model of neuroinflammation

Proinflammatory factors from activated T cells inhibit neurogenesis in adult animal brain and cultured human fetal neural stem cells (NSC). However, the role of inhibition of neurogenesis in human neuroinflammatory diseases is still uncertain because of the difficulty in obtaining adult NSC from patients. Recent developments in cell reprogramming suggest that NSC may be derived directly from adult fibroblasts. We generated NSC from adult human peripheral CD34+ cells by transfecting the cells with Sendai virus constructs containing Sox2, Oct3/4, c-Myc and Klf4. The derived NSC could be differentiated to glial cells and action potential firing neurons. Co-culturing NSC with activated autologous T cells or treatment with recombinant granzyme B caused inhibition of neurogenesis as indicated by decreased NSC proliferation and neuronal differentiation. Thus, we have established a unique autologous in vitro model to study the pathophysiology of neuroinflammatory diseases that has potential for usage in personalized medicine.

Novel functions of GABA signaling in adult neurogenesis

Neurotransmitter gamma-aminobutiric acid (GABA) through ionotropic GABA_A and metabotropic GABA_B receptors plays key roles in modulating the development, plasticity and function of neuronal networks. GABA is inhibitory in mature neurons but excitatory in immature neurons, neuroblasts and neural stem/progenitor cells (NSCs/NPCs). The switch from excitatory to inhibitory occurs following the development of glutamatergic synaptic input and results from the dynamic changes in the expression of Na⁺/K⁺/2Cl^- co-transporter NKCC1 driving Cl^- influx and neuron-specific K⁺/Cl^- co-transporter KCC2 driving Cl^- efflux. The developmental transition of KCC2 expression is regulated by Disrupted-in-Schizophrenia 1 (DISC1) and brain-derived neurotrophic factor (BDNF) signaling. The excitatory GABA signaling during early neurogenesis is important to the activity/experience-induced regulation of NSC quiescence, NPC proliferation, neuroblast migration and newborn neuronal maturation/functional integration. The inhibitory GABA signaling allows for the sparse and static functional networking essential for learning/memory development and maintenance.

Transgenic analysis of GFAP promoter elements

Transcriptional regulation of the glial fibrillary acidic protein gene (GFAP) is of interest because of its astrocyte specificity and its upregulation in response to CNS injuries. We have used a transgenic approach instead of cell transfection to identify promoter elements of the human GFAP gene, since previous observations show that GFAP transcription is regulated differently in transfected cultured cells from in the mouse. We previously showed that block mutation of enhancer regions spanning from bp -1488 to -1434 (the C1.1 segment) and -1443 to -1399 (C1.2) resulted in altered patterns of expression and loss of astrocyte specificity, respectively. This analysis has now been extended upstream to bp -1612 to -1489 (the B region), which previously has been shown especially important for expression. Block mutation of each of four contiguous sequences, which together span the B region, each decreased the level of transgene activity by at least 50%, indicating that multiple sites contribute to the transcriptional activity in a cooperative manner. Several of the block mutations also altered the brain region pattern of expression, astrocyte specificity and/or the developmental time course. Transgenes were then analyzed in which mutations were limited to specific transcription factor binding sites in each of the 4 B block segments as well as in C1.1 and C1.2. Whereas mutation of the conserved consensus AP-1 site unexpectedly had little effect on transgene expression; NFI, SP1, STAT3, and NF-κB were identified as having important roles in regulating the strength of GFAP promoter activity and/or its astrocyte specificity.

NF-κB: emerging roles in hippocampal development and function

The nuclear factor kappa-B family of transcription factors have been extensively studied in the immune system where they function to orchestrate the molecular response to immune challenge. However in recent years, members of this family have also been shown to play physiological roles in the development and function of the nervous system. The two best studied members of the nuclear factor kappa-B family are the p65 and the p50 proteins. In this review, we outline recent developments regarding the functions of these proteins in regulating hippocampal neurogenesis, neuronal growth and learning and memory and discuss the implications of their dysregulation during the development of the nervous system.

Stacking the DEK: from chromatin topology to cancer stem cells

Stem cells are essential for development and tissue maintenance and display molecular markers and functions distinct from those of differentiated cell types in a given tissue. Malignant cells that exhibit stem cell-like activities have been detected in many types of cancers and have been implicated in cancer recurrence and drug resistance. Normal stem cells and cancer stem cells have striking commonalities, including shared cell surface markers and signal transduction pathways responsible for regulating quiescence vs. proliferation, self-renewal, pluripotency and differentiation. As the search continues for markers that distinguish between stem cells, progenitor cells and cancer stem cells, growing evidence suggests that a unique chromatin-associated protein called DEK may confer stem cell-like qualities. Here, we briefly describe current knowledge regarding stem and progenitor cells. We then focus on new findings that implicate DEK as a regulator of stem and progenitor cell qualities, potentially through its unusual functions in the regulation of local or global chromatin organization.

Death receptors and mitochondria: two prime triggers of neural apoptosis and differentiation

BACKGROUND

Stem cell therapy is a strategy far from being satisfactory and applied in the clinic. Poor survival and differentiation levels of stem cells after transplantation or neural injury have been major problems. Recently, it has been recognized that cell death-relevant proteins, notably those that operate in the core of the executioner apoptosis machinery are functionally involved in differentiation of a wide range of cell types, including neural cells.

SCOPE OF REVIEW

This article will review recent studies on the mechanisms underlying the non-apoptotic function of mitochondrial and death receptor signaling pathways during neural differentiation. In addition, we will discuss how these major apoptosis-regulatory pathways control the decision between differentiation, self-renewal and cell death in neural stem cells and how levels of activity are restrained to prevent cell loss as final outcome.

MAJOR CONCLUSIONS

Emerging evidence suggests that, much like p53, caspases and Bcl-2 family members, the two prime triggers of cell death pathways, death receptors and mitochondria, may influence proliferation and differentiation potential of stem cells, neuronal plasticity, and astrocytic versus neuronal stem cell fate decision.

GENERAL SIGNIFICANCE

A better understanding of the molecular mechanisms underlying key checkpoints responsible for neural differentiation as an alternative to cell death will surely contribute to improve neuro-replacement strategies.

Biphasic activation of nuclear factor-kappa B in experimental models of subarachnoid hemorrhage in vivo and in vitro

It has been proven that nuclear factor-kappa B (NF-κB) is activated as a well-known transcription factor after subarachnoid hemorrhage (SAH). However, the panoramic view of NF-κB activity after SAH remained obscure. Cultured neurons were signed into control group and six hemoglobin- (Hb-) incubated groups. One-hemorrhage rabbit SAH model was produced, and the rabbits were divided randomly into one control group and five SAH groups. NF-κB activity was detected by electrophoretic mobility shift assay (EMSA) and immunohistochemistry. Real-time polymerase chain reaction (PCR) was performed to assess the downstream genes of NF-κB. NeuN immunofluorescence and lactate dehydrogenase (LDH) quantification were used to estimate the neuron injury. Double drastically elevated NF-κB activity peaks were detected in rabbit brains and cultured neurons. The downstream gene expressions showed an accordant phase peaks. NeuN-positive cells decreased significantly in day 3 and day 10 groups. LDH leakage exhibited a significant increase in Hb-incubated groups, but no significant difference was found between the Hb incubated groups. These results suggested that biphasic increasing of NF-κB activity was induced after SAH, and the early NF-κB activity peak indicated the injury role on neurons; however, the late peak might not be involved in the deteriorated effect on neurons.

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 genetic and epigenetic journey of embryonic stem cells into mature neural cells

Epigenetic changes occur throughout life from embryonic development into adulthood. This results in the timely expression of developmentally important genes, determining the morphology and identity of different cell types and tissues within the body. Epigenetics regulate gene expression and cellular morphology through multiple mechanisms without alteration in the underlying DNA sequences. Different epigenetic mechanisms include chromatin condensation, post-translational modification of histone proteins, DNA cytosine marks, and the activity of non-coding RNA molecules. Epigenetics play key roles in development, stem cell differentiation, and have high impact in human disease. In this review, we will discuss our current knowledge about these epigenetic mechanisms, with a focus on histone and DNA marks. We will then talk about the genetics and epigenetics of embryonic stem cell self-renewal and differentiation into neural stem cells, and further into specific neuronal cell types.