Glial Processes Research Articles

Sparse Annotation is Sufficient for Bootstrapping Dense Segmentation.

Producing dense 3D reconstructions from biological imaging data is a challenging instance segmentation task that requires significant ground-truth training data for effective and accurate deep learning-based models. Generating training data requires intense human effort to annotate each instance of an object across serial section images. Our focus is on the especially complicated brain neuropil, comprising an extensive interdigitation of dendritic, axonal, and glial processes visualized through serial section electron microscopy. We developed a novel deep learning-based method to generate dense 3D segmentations rapidly from sparse 2D annotations of a few objects on single sections. Models trained on the rapidly generated segmentations achieved similar accuracy as those trained on expert dense ground-truth annotations. Human time to generate annotations was reduced by three orders of magnitude and could be produced by non-expert annotators. This capability will democratize generation of training data for large image volumes needed to achieve brain circuits and measures of circuit strengths.

The role of oligodendrocyte progenitor cells in the spatiotemporal vascularization of the human and mouse neocortex.

Brain vasculature formation begins with vessel invasion from the perineural vascular plexus, which expands through vessel sprouting and growth. Recent studies have indicated the existence of oligodendrocyte-vascular crosstalk during development. However, the relationship between oligodendrocyte progenitor cells (OPCs) and the ordered spatiotemporal vascularization of the neocortex has not been elucidated. Our findings suggest that OPCs play a complex role in the vessel density of the embryonic and postnatal neocortex. Analyses of normal human and mouse embryonic cerebral cortex show that vascularization and OPC distribution are tightly controlled in a spatially and temporally restricted manner, exhibiting a positive correlation. Loss of OPCs at both embryonic and postnatal stages led to a reduction in vascular density, suggesting that OPC populations play a role in vascular density. Nonetheless, dynamic observation on cultured brain slices and staining of tissue sections indicate that OPC migration is unassociated with the proximity to blood vessels, primarily occurring along radial glial cell processes. Additionally, in vitro experiments demonstrate that OPC secretions promote vascular endothelial cell (VEC) growth. Together, these observations suggest that vessel density is influenced by OPC secretions.

Microenvironment T-Type calcium channels regulate neuronal and glial processes to promote glioblastoma growth.

Background Glioblastoma (GBM) is the most common primary malignant brain tumor. The aim of this study was to elucidate the role of microenvironment and intrinsic T-type calcium channels (Cav3) in regulating tumor growth and progression. Methods We grafted syngeneic GBM cells into Cav3.2 knockout mice to assess the role of microenvironment T-Type calcium channels on GBM tumor growth. We performed single-cell RNA-seq (scRNA-seq) of tumors from WT and Cav3.2 KO mice to elucidate the regulation of tumors by the microenvironment. We used neurons from WT and Cav3.2 KO mice in co-culture with GBM stem cells (GSC) to assess the effects of Cav3.2 on neuron/GSC synaptic connections and tumor cell growth. Results Cav3.2 KO in the microenvironment led to significant reduction of GBM growth and prolongation of animal survival. scRNA-seq showed that microenvironment Cav3.2 regulates neuronal and glial biological processes. Microenvironment Cav3.2 downregulated numerous genes associated with regulating the OPC cell state in GBM tumors such as SOX10 and Olig2. Neuronal Cav3.2 promoted neuron/GSC synaptic connections and GSC growth. Treatment of GSCs with the Cav3 blocker mibefradil downregulated genes associated with neuronal processes. The Cav3 blocker drug mibefradil synergized with temozolomide (TMZ) and radiation to reduce in vivo tumor growth and prolong animal survival. Conclusions Together these data reveal a role for microenvironment Cav3 in promoting GBM tumor progression through regulating neuronal and glial processes particularly associated with the OPC-cell state. Targeting both intrinsic and microenvironment Cav3 with the inhibitor mibefradil significantly enhanced the anti-GBM effects of TMZ and radiation.

Single-Nucleus Landscape of Glial Cells and Neurons in Alzheimer's Disease.

Alzheimer's disease (AD) is a neurodegenerative disease with a projected significant increase in incidence. Therefore, this study analyzed single-nucleus AD data to provide a theoretical basis for the clinical development and treatment of AD. We downloaded AD-related monocyte data from the Gene Expression Omnibus database, annotated cells, compared cell abundance between groups, and investigated glial and neuronal cell biological processes and pathways through functional enrichment analysis. Furthermore, we constructed a global regulatory network for AD based on cell communication and ecological analyses. Our findings revealed increased abundance of Capping Protein Regulator And Myosin 1 linker 1 (CARMIL1)+ astrocytes (AST), Immunoglobulin Superfamily Member 21 (IGSF21)+ microglia (MIC), SRY-Box Transcription Factor 6 (SOX6)+ inhibitory neurons (InNeu), and laminin alpha-2 chain (LAMA2)+ oligodendrocytes (OLI) cell subgroups in tissues of patients with AD, while prostaglandin D2 synthase (PTGDS)+ AST, Src Family Tyrosine Kinase (FYN)+ MIC, and Proteolipid Protein 1 (PLP1)+ InNeu subgroups specifically decreased. We found that the cell phenotype of patients with AD shifted from a simpler to a more complex state compared to the control group. Cell communication analysis revealed strong communication between MIC and NEU. Furthermore, AST, MIC, NEU, and OLI were involved in oxidative stress- and inflammation-related pathways, potentially contributing to disease development. This study provides a theoretical basis for further exploring the specific mechanisms underlying AD.

Involvement of vimentin- and BLBP-positive glial cells and their MMP expression in axonal regeneration after spinal cord transection in goldfish.

In goldfish, spinal cord injury triggers the formation of a fibrous scar at the injury site. Regenerating axons are able to penetrate the scar tissue, resulting in the recovery of motor function. Previous findings suggested that regenerating axons enter the scar through tubular structures surrounded by glial elements with laminin-positive basement membranes and that glial processes expressing glial fibrillary acidic protein (GFAP) are associated with axonal regeneration. How glia contribute to promoting axonal regeneration, however, is unknown. Here, we revealed that glial processes expressing vimentin or brain lipid-binding protein (BLBP) also enter the fibrous scar after spinal cord injury in goldfish. Vimentin-positive glial processes were more numerous than GFAP- or BLBP-positive glial processes in the scar tissue. Regenerating axons in the scar tissue were more closely associated with vimentin-positive glial processes than GFAP-positive glial processes. Vimentin-positive glial processes co-expressed matrix metalloproteinase (MMP)-14. Our findings suggest that vimentin-positive glial processes closely associate with regenerating axons through tubular structures entering the scar after spinal cord injury in goldfish. In intact spinal cord, ependymo-radial glial cell bodies express BLBP and their radial processes express vimentin, suggesting that vimentin-positive glial processes derive from migrating ependymo-radial glial cells. MMP-14 expressed in vimentin-positive glial cells and their processes might provide a beneficial environment for axonal regeneration.

MRI signatures of cortical microstructure in human development align with oligodendrocyte cell-type expression.

Neuroanatomical changes to the cortex during adolescence have been well documented using MRI, revealing ongoing cortical thinning and volume loss with age. However, the underlying cellular mechanisms remain elusive with conventional neuroimaging. Recent advances in MRI hardware and new biophysical models of tissue informed by diffusion MRI data hold promise for identifying the cellular changes driving these morphological observations. This study used ultra-strong gradient MRI to obtain high-resolution, in vivo estimates of cortical neurite and soma microstructure in sample of typically developing children and adolescents. Cortical neurite signal fraction, attributed to neuronal and glial processes, increased with age (mean R2 fneurite=.53, p<3.3e-11, 11.91% increase over age), while apparent soma radius decreased (mean R2 Rsoma=.48, p<4.4e-10, 1% decrease over age) across domain-specific networks. To complement these findings, developmental patterns of cortical gene expression in two independent post-mortem databases were analysed. This revealed increased expression of genes expressed in oligodendrocytes, and excitatory neurons, alongside a relative decrease in expression of genes expressed in astrocyte, microglia and endothelial cell-types. Age-related genes were significantly enriched in cortical oligodendrocytes, oligodendrocyte progenitors and Layer 5-6 neurons (pFDR<.001) and prominently expressed in adolescence and young adulthood. The spatial and temporal alignment of oligodendrocyte cell-type gene expression with neurite and soma microstructural changes suggest that ongoing cortical myelination processes contribute to adolescent cortical development. These findings highlight the role of intra-cortical myelination in cortical maturation during adolescence and into adulthood.

Molecular overlaps of neurological manifestations of COVID-19 and schizophrenia from a proteomic perspective.

COVID-19, a complex multisystem disorder affecting the central nervous system, can also have psychiatric sequelae. In addition, clinical evidence indicates that a diagnosis of a schizophrenia spectrum disorder is a risk factor for mortality in patients with COVID-19. In this study, we aimed to explore brain-specific molecular aspects of COVID-19 by using a proteomic approach. We analyzed the brain proteome of fatal COVID-19 cases and compared it with differentially regulated proteins found in postmortem schizophrenia brains. The COVID-19 proteomic dataset revealed a strong enrichment of proteins expressed by glial and neuronal cells and processes related to diseases with a psychiatric and neurodegenerative component. Specifically, the COVID-19 brain proteome enriches processes that are hallmark features of schizophrenia. Furthermore, we identified shared and distinct molecular pathways affected in both conditions. We found that brain ageing processes are likely present in both COVID-19 and schizophrenia, albeit possibly driven by distinct processes. In addition, alterations in brain cell metabolism were observed, with schizophrenia primarily impacting amino acid metabolism and COVID-19 predominantly affecting carbohydrate metabolism. The enrichment of metabolic pathways associated with astrocytic components in both conditions suggests the involvement of this cell type in the pathogenesis. Both COVID-19 and schizophrenia influenced neurotransmitter systems, but with distinct impacts. Future studies exploring the underlying mechanisms linking brain ageing and metabolic dysregulation may provide valuable insights into the complex pathophysiology of these conditions and the increased vulnerability of schizophrenia patients to severe outcomes.

Extensive soma-soma plate-like contact sites (ephapses) connect suprachiasmatic nucleus neurons.

The hypothalamic suprachiasmatic nucleus (SCN) is the central pacemaker for mammalian circadian rhythms. As such, this ensemble of cell-autonomous neuronal oscillators with divergent periods must maintain coordinated oscillations. To investigate ultrastructural features enabling such synchronization, 805 coronal ultrathin sections of mouse SCN tissue were imaged with electron microscopy and aligned into a volumetric stack, from which selected neurons within the SCN core were reconstructed insilico. We found that clustered SCN core neurons were physically connected to each other via multiple large soma-to-soma plate-like contacts. In some cases, a sliver of a glial process was interleaved. These contacts were large, covering on average ∼21% of apposing neuronal somata. It is possible that contacts may be the electrophysiological substrate for synchronization between SCN neurons. Such plate-like contacts may explain why the synchronization of SCN neurons is maintained even when chemical synaptic transmission or electrical synaptic transmission via gap junctions is blocked. Such ephaptic contact-mediated synchronization among nearby neurons may therefore contribute to the wave-like oscillations of circadian core clock genes and calcium signals observed in the SCN.

Regulation of cell distancing in peri-plaque glial nets by Plexin-B1 affects glial activation and amyloid compaction in Alzheimer's disease.

Communication between glial cells has a profound impact on the pathophysiology of Alzheimer's disease (AD). We reveal here that reactive astrocytes control cell distancing in peri-plaque glial nets, which restricts microglial access to amyloid deposits. This process is governed by guidance receptor Plexin-B1 (PLXNB1), a network hub gene in individuals with late-onset AD that is upregulated in plaque-associated astrocytes. Plexin-B1 deletion in a mouse AD model led to reduced number of reactive astrocytes and microglia in peri-plaque glial nets, but higher coverage of plaques by glial processes, along with transcriptional changes signifying reduced neuroinflammation. Additionally, a reduced footprint of glial nets was associated with overall lower plaque burden, a shift toward dense-core-type plaques and reduced neuritic dystrophy. Altogether, our study demonstrates that Plexin-B1 regulates peri-plaque glial net activation in AD. Relaxing glial spacing by targeting guidance receptors may present an alternative strategy to increase plaque compaction and reduce neuroinflammation in AD.

Ultrastructural differences impact cilia shape and external exposure across cell classes in the visual cortex

A primary cilium is a membrane-bound extension from the cell surface that contains receptors for perceiving and transmitting signals that modulate cell state and activity. Primary cilia in the brain are less accessible than cilia on cultured cells or epithelial tissues because in the brain they protrude into a deep, dense network of glial and neuronal processes. Here, we investigated cilia frequency, internal structure, shape, and position in large, high-resolution transmission electron microscopy volumes of mouse primary visual cortex. Cilia extended from the cell bodies of nearly all excitatory and inhibitory neurons, astrocytes, and oligodendrocyte precursor cells (OPCs) but were absent from oligodendrocytes and microglia. Ultrastructural comparisons revealed that the base of the cilium and the microtubule organization differed between neurons and glia. Investigating cilia-proximal features revealed that many cilia were directly adjacent to synapses, suggesting that cilia are poised to encounter locally released signaling molecules. Our analysis indicated that synapse proximity is likely due to random encounters in the neuropil, with no evidence that cilia modulate synapse activity as would be expected in tetrapartite synapses. The observed cell class differences in proximity to synapses were largely due to differences in external cilia length. Many key structural features that differed between neuronal and glial cilia influenced both cilium placement and shape and, thus, exposure to processes and synapses outside the cilium. Together, the ultrastructure both within and around neuronal and glial cilia suggest differences in cilia formation and function across cell types in the brain.

Brain organoids engineered to give rise to glia and neural networks after 90 days in culture exhibit human-specific proteoforms.

Human brain organoids are emerging as translationally relevant models for the study of human brain health and disease. However, it remains to be shown whether human-specific protein processing is conserved in human brain organoids. Herein, we demonstrate that cell fate and composition of unguided brain organoids are dictated by culture conditions during embryoid body formation, and that culture conditions at this stage can be optimized to result in the presence of glia-associated proteins and neural network activity as early as three-months in vitro. Under these optimized conditions, unguided brain organoids generated from induced pluripotent stem cells (iPSCs) derived from male-female siblings are similar in growth rate, size, and total protein content, and exhibit minimal batch-to-batch variability in cell composition and metabolism. A comparison of neuronal, microglial, and macroglial (astrocyte and oligodendrocyte) markers reveals that profiles in these brain organoids are more similar to autopsied human cortical and cerebellar profiles than to those in mouse cortical samples, providing the first demonstration that human-specific protein processing is largely conserved in unguided brain organoids. Thus, our organoid protocol provides four major cell types that appear to process proteins in a manner very similar to the human brain, and they do so in half the time required by other protocols. This unique copy of the human brain and basic characteristics lay the foundation for future studies aiming to investigate human brain-specific protein patterning (e.g., isoforms, splice variants) as well as modulate glial and neuronal processes in an in situ-like environment.

Evidence for glia-mediated, age-dependent remodeling of myelin at the axon initial segment.

Due to its proximity to the axon initial segment (AIS), the paranode of the first myelin segment can influence the threshold for action potentials and how a neuron participates in a neuronal circuit. Using serial section electron microscopy, we examined its three-dimensional (3D) organization in the ventral horn of the mouse spinal cord. The myelin loops of postnatal day 18 mice resemble those at the node of Ranvier. However, in 3-month-old mice, 13 of 22 para-AIS showed 4 types of alteration: (A) A cytoplasmic foot process, with ultrastructural characteristics of an astrocyte, was interposed between the axolemma and the myelin loops. (B) A thin extension of the inner tongue was present between the foot process and axolemma. (C) The foot process was absent. The inner tongue extension was a broad lamella from which a thin extension reached beyond the loops and spiraled around axon. (D) One set of loops was adjacent to the axon, and another was further back and underlain by compact myelin. We suggest that (A)-(C) are steps in a progression toward (D). In this progression, a glial process displaces the original loops, the inner tongue reactivates and extends beneath the foot process, then wraps around the axon to form a new set of loops. This is the first study of the 3D organization of myelin at the AIS and provides evidence for glia-mediated age-dependent remodeling at this critical region.

Modulatory Processes in Craniofacial Pain States.

Pain is a common symptom associated with many disorders affecting the craniofacial tissues that include the teeth and their supporting structures, the jaw, face and tongue muscles, and the temporomandibular joint. Most acute craniofacial pain states are easily recognized and readily treated, but chronic craniofacial pain states (e.g., temporomandibular disorders [TMD], trigeminal neuropathies, and some headaches) may be especially challenging to manage successfully. This chapter provides an overview of the processes that underlie craniofacial pain, with a focus on the pain-modulatory mechanisms operating in craniofacial tissues and in the central nervous system (CNS), including the role of endogenous chemical processes such as those involving opioids. The chapter outlines in particular findings from preclinical studies that have provided substantial information about the neural as well as nonneural (e.g., glial) processes involved in the initiation, transmission, and modulation of nociceptive signals in the trigeminal system, and also draws attention to their clinical correlates. The increased understanding gained from these preclinical studies of how nociceptive signals can be modulated will contribute to improvements in presently available therapeutic approaches to manage craniofacial pain as well as to the development of novel analgesic approaches.

Unusual morphology of foveal Müller glia in an adult human born pre-term.

The fovea of the human retina, a specialization for acute and color vision, features a high concentration of cone photoreceptors. A pit on the inner retinal aspect is created by the centrifugal migration of post-receptoral neurons. Foveal cells are specified early in fetal life, but the fovea reaches its final configuration postnatally. Pre-term birth retards migration resulting in a small pit, a small avascular zone, and nearly continuous inner retinal layers. To explore the involvement of Müller glia, we used serial-section electron microscopic reconstructions to examine the morphology and neural contacts of Müller glia contacting a single foveal cone in a 28-year-old male organ donor born at 28 weeks of gestation. A small non-descript foveal avascular zone contained massed glial processes that included a novel class of 'inner' Müller glia. Similar to classic 'outer' Müller glia that span the retina, inner Müller glia have bodies in the inner nuclear layer (INL). These cells are densely packed with intermediate filaments and insert processes between neurons. Unlike 'outer' Müller glia, 'inner' Müller glia do not reach the external limiting membrane but instead terminate at the outer plexiform layer. One completely reconstructed inner cell ensheathed cone pedicles and a cone-driven circuit of midget bipolar and ganglion cells. Inner Müller glia outnumber foveal cones by 1.8-fold in the outer nuclear layer (221,448 vs. 123,026 cells/mm2). Cell bodies of inner Müller glia outnumber those of outer Müller glia by 1.7-fold in the INL (41,872 vs. 24,631 cells/ mm2). Müller glia account for 95 and 80% of the volume of the foveal floor and Henle fiber layer, respectively. Determining whether inner cells are anomalies solely resulting from retarded lateral migration of inner retinal neurons in pre-term birth requires further research.

Reduced Bergmann glial process terminations and lateral appendages in essential tremor.

Postmortem examination of the essential tremor cerebellum has revealed a variety of pathological changes centered in and around Purkinje cells. Studies have predominantly focused on cerebellar neuronal connections. Bergmann glial morphology has not yet been studied in essential tremor. Among their many roles, Bergmann glia in the cerebellar cortex ensheath Purkinje cell synapses and provide neuroprotection. Specifically, the complex radial processes and lateral appendages of Bergmann glia are structural domains that modulate Purkinje cell synaptic transmission. In this study, we investigate whether Bergmann glia morphology is altered in the essential tremor cerebellum. We applied the Golgi-Kopsch method and used computerized three-dimensional cell reconstruction to visualize Bergmann glia in the postmortem cerebellum of 34 cases and 17 controls. We quantified morphology of terminal structures (number of terminations and lateral appendage density) and morphology of radial processes (total process length, branch length, branch order, and branch volume) in each glial cell. We quantified number of branches and volume as well. Essential tremor cases had a 31.9% decrease in process terminations and a 35.7% decrease in lateral appendage density in Bergmann glia. Total process length and branch length did not differ between essential tremor cases and controls. We found also a reduction in number of secondary and tertiary branches and tertiary branches volume. These findings suggest that Bergmann glia in essential tremor cases have more alterations in their terminal structures, with a relative preservation of radial processes, and highlight a potential role for these astrocytes in the disease pathophysiology.

Astrocyte calcium dysregulation and cerebrovascular impairments in the 5XFAD mouse model of familial Alzheimer’s disease

AbstractBackgroundAmyloid deposits (Aβ) in the brain are a primary diagnostic marker of Alzheimer’s disease, and are associated with the degeneration of synapses and cognitive decline. However, recent advances in cell specific approaches have revealed that glial processes may also contribute to the progression of disease pathology. Astrocytes are a glial cell in the brain responsible for a plethora of essential functions in the brain, such as the removal of synaptic glutamate, and control over cerebrovascular function. Astrocyte Ca2+ signaling is closely coupled to these functions. These pathways are dysregulated with disease onset, and contribute to astrocyte reactivity. Our group showed previously in a diet model of VCID, that changes in astrocyte calcium signaling and network synchronicity were associated with deficits in cerebrovascular function. Here we examined the spatial and temporal relationship of astrocyte Ca2+ signals to neurovascular coupling in 5XFAD mice to determine the relationship between reactive astrocytes and cerebrovascular function.Method5XFAD and littermate controls aged to 6 months were injected with AAV2/5‐Gfa104‐jGCaMP8f into barrel cortex before cranial window installation. At 7 months, mice were briefly anaesthetized before retroorbital injection of 500kb rhodamine dextran. Mice were then imaged awake under a two‐photon microscope for functional hyperemia measures in response to timed air puff whisker stimulation. Spontaneous and evoked Ca2+ transients were measured by ∆F/F calculation of Ca2+ peaks extracted by custom MATLAB algorithms. Analysis of astrocyte endfoot Ca2+ was measured along vessels stimulated for neurovascular coupling to relate vasoactivity to Ca2+ signaling kinetics and intensity.Result5XFAD mice showed a significant reduction is astrocyte Ca2+ rise time kinetics compared to wild type controls, as well as parameters of functional hyperemia. Timing of neurovascular coupling in response to stimulation and the latency of astrocyte calcium kinetics was characterized for the 5XFAD model and shown to differ between soma and endfoot processes.ConclusionAmyloid induced pathology induces changes in astrocyte Ca2+ signaling. Dysregulation of astrocyte signaling may have a mechanistic role in the kinetics of neurovascular coupling and/or cerebrovascular dysfunction with disease progression. However, further analysis of astrocyte endfoot coverage and manipulation of astrocyte signaling during functional hyperemia is needed to further clarify mechanism.

RTID-05. SURGICAL WINDOW OF OPPORTUNITY TRIAL REVEALS MECHANISMS OF RESPONSE AND RESISTANCE TO NAVTEMADLIN (KRT-232) IN PATIENTS WITH RECURRENT GLIOBLASTOMA

Abstract Over half of glioblastoma multiforme (GBM) patients retain wild-type p53, resulting in potential susceptibility to MDM2 inhibitors. These molecules disrupt the interaction between p53 and its negative regulator MDM2, resulting in downstream pathway signaling and cell fate decisions such as growth inhibition and death from cellular stress. We have analyzed clinical samples from 21 patients with recurrent GBM treated with the MDM2 inhibitor KRT-232, all of which relapsed despite the biological promise of this small molecule. By analyzing on-treatment biopsy samples, we detected upregulation of p53 transcriptional targets, suggesting blood-brain barrier penetrance and drug pharmacodynamics. However, in patient-derived cell lines, treatment with KRT-232 at the clinically achieved concentration was only sufficient to stall but not reduce tumor growth. Cell death via apoptosis was achieved in these cell line models when MDM2 inhibition was combined with the chemotherapeutic agent temozolomide. These drugs have non-overlapping mechanisms of action and exhibit synergy in our cell line models. Normal human bone marrow cells underwent a reversible growth inhibition phenotype when treated with KRT-232 and TMZ, supporting the idea that a therapeutic window exists with this combination. We additionally observed that tumor progression occurred in the absence of p53 inactivating mutations, suggesting that other mechanisms of resistance to KRT-232 may modulate drug response and resistance in GBM. Indeed, drug treatment induced an adaptive response in human tumors, characterized by the upregulation of genes involved in glial cell differentiation processes. Ongoing work is focused on understanding how tumor heterogeneity and cell state modulate response and resistance of GBMs to MDM2 inhibition and other therapeutic strategies that reactivate p53 signaling. Our study highlights the utility of tissue sampling during clinical trials and represents the first clinical effort to detect adaptive changes in human tumor tissue associated with p53 reactivation.

Impact of Developmental Changes of GABAA Receptors on Interneuron-NG2 Glia Transmission in the Hippocampus.

NG2 glia receive synaptic input from neurons, but the functional impact of this glial innervation is not well understood. In the developing cerebellum and somatosensory cortex the GABAergic input might regulate NG2 glia differentiation and myelination, and a switch from synaptic to extrasynaptic neuron-glia signaling was reported in the latter region. Myelination in the hippocampus is sparse, and most NG2 glia retain their phenotype throughout adulthood, raising the question of the properties and function of neuron-NG2 glia synapses in that brain region. Here, we compared spontaneous and evoked GABAA receptor-mediated currents of NG2 glia in juvenile and adult hippocampi of mice of either sex and assessed the mode of interneuron-glial signaling changes during development. With patch-clamp and pharmacological analyses, we found a decrease in innervation of hippocampal NG2 glia between postnatal days 10 and 60. At the adult stage, enhanced activation of extrasynaptic receptors occurred, indicating a spillover of GABA. This switch from synaptic to extrasynaptic receptor activation was accompanied by downregulation of γ2 and upregulation of the α5 subunit. Molecular analyses and high-resolution expansion microscopy revealed mechanisms of glial GABAA receptor trafficking and clustering. We found that gephyrin and radixin are organized in separate clusters along glial processes. Surprisingly, the developmental loss of γ2 and postsynaptic receptors were not accompanied by altered glial expression of scaffolding proteins, auxiliary receptor subunits or postsynaptic interaction proteins. The GABAergic input to NG2 glia might contribute to the release of neurotrophic factors from these cells and influence neuronal synaptic plasticity.

Amyloid Precursor Protein (APP) Regulates Gliogenesis and Neurogenesis of Human Neural Stem Cells by Several Signaling Pathways.

Numerous studies have focused on the pathophysiological role of amyloid precursor protein (APP) because the proteolytic processing of APP to β-amyloid (Aβ) peptide is a central event in Alzheimer's disease (AD). However, many authors consider that alterations in the physiological functions of APP are likely to play a key role in AD. Previous studies in our laboratory revealed that APP plays an important role in the differentiation of human neural stem cells (hNSCs), favoring glial differentiation (gliogenesis) and preventing their differentiation toward a neuronal phenotype (neurogenesis). In the present study, we have evaluated the effects of APP overexpression in hNSCs at a global gene level by a transcriptomic analysis using the massive RNA sequencing (RNA-seq) technology. Specifically, we have focused on differentially expressed genes that are related to neuronal and glial differentiation processes, as well as on groups of differentially expressed genes associated with different signaling pathways, in order to find a possible interaction between them and APP. Our data indicate a differential expression in genes related to Notch, Wnt, PI3K-AKT, and JAK-STAT signaling, among others. Knowledge of APP biological functions, as well as the possible signaling pathways that could be related to this protein, are essential to advance our understanding of AD.

Potential roles of enteric glial cells in Crohn's disease: A critical review.

Enteric glial cells in the enteric nervous system are critical for the regulation of gastrointestinal homeostasis. Increasing evidence suggests two-way communication between enteric glial cells and both enteric neurons and immune cells. These interactions may be important in the pathogenesis of Crohn's disease (CD), a chronic relapsing disease characterized by a dysregulated immune response. Structural abnormalities in glial cells have been identified in CD. Furthermore, classical inflammatory pathways associated with CD (e.g., the nuclear factor kappa-B pathway) function in enteric glial cells. However, the specific mechanisms by which enteric glial cells contribute to CD have not been summarized in detail. In this review, we describe the possible roles of enteric glial cells in the pathogenesis of CD, including the roles of glia-immune interactions, neuronal modulation, neural plasticity, and barrier integrity. Additionally, the implications for the development of therapeutic strategies for CD based on enteric glial cell-mediated pathogenic processes are discussed.