Human and mouse cortical astrocytes: a comparative view from development to morphological and functional characterization

Role of glial cells in motor neuron degeneration in hereditary spastic paraplegias

This review provides a comprehensive overview of hereditary spastic paraplegias (HSPs) and summarizes the recent progress on the role of glial cells in the pathogenesis of HSPs. HSPs are a heterogeneous group of neurogenetic diseases characterized by axonal degeneration of cortical motor neurons, leading to muscle weakness and atrophy. Though the contribution of glial cells, especially astrocytes, to the progression of other motor neuron diseases like amyotrophic lateral sclerosis (ALS) is well documented, the role of glial cells and the interaction between neurons and astrocytes in HSP remained unknown until recently. Using human pluripotent stem cell-based models of HSPs, a study reported impaired lipid metabolisms and reduced size of lipid droplets in HSP astrocytes. Moreover, targeting lipid dysfunction in astrocytes rescues axonal degeneration of HSP cortical neurons, demonstrating a non-cell-autonomous mechanism in axonal deficits of HSP neurons. In addition to astrocytes, recent studies revealed dysfunctions in HSP patient pluripotent stem cell-derived microglial cells. Increased microgliosis and pro-inflammation factors were also observed in HSP patients' samples, pointing to an exciting role of innate immunity and microglia in HSP. Building upon these recent studies, further investigation of the detailed molecular mechanism and the interplay between glial cell dysfunction and neuronal degeneration in HSP by combining human stem cell models, animal models, and patient samples will open avenues for identifying new therapeutic targets and strategies for HSP.

The Triad of Blood-Brain Barrier Integrity: Endothelial Cells, Astrocytes, and Pericytes in Perinatal Stroke Pathophysiology

Pediatric stroke, a significant cause of long-term neurological deficits in children, often arises from disruptions within neurovascular unit (NVU) components. The NVU, a dynamic ensemble of astrocytes, endothelial cells, pericytes, and microglia, is vital for maintaining cerebral homeostasis and regulating vascular brain development. Its structural integrity, particularly at the blood-brain barrier (BBB), depends on intercellular junctions and the basement membrane, which together restrict paracellular transport and shield the brain from systemic insults. Dysfunction in this intricate system is increasingly linked to pediatric stroke and related cerebrovascular conditions. Mutations disrupting endothelial cell adhesion or pericyte-endothelial interactions can compromise BBB stability, leading to pathological outcomes such as intraventricular hemorrhage in the germinal matrix, a hallmark of vascular brain immaturity. Additionally, inflammation, ferroptosis, necroptosis, and autophagy are key cellular processes influencing brain damage and repair. Excessive activation of these mechanisms can exacerbate NVU injury, whereas targeted therapeutic modulation offers potential pathways to mitigate damage and support recovery. This review explores the cellular and molecular mechanisms underlying NVU dysfunction, BBB disruption, and subsequent brain injury in pediatric stroke. Understanding the interplay between genetic mutations, environmental stressors, and NVU dynamics provides new insights into stroke pathogenesis. The susceptibility of the germinal matrix to vascular rupture further emphasizes the critical role of NVU integrity in early brain development. Targeting inflammatory pathways and cell death mechanisms presents promising strategies to preserve NVU function and improve outcomes for affected neonates.

The Rise of Pluripotent Stem Cell-Derived Glia Models of Neuroinflammation

Neuroinflammation is a blanket term that describes the body's complex inflammatory response in the central nervous system (CNS). It encompasses a phenotype shift to a proinflammatory state, the release of cytokines, the recruitment of peripheral immune cells, and a wide variety of other processes. Neuroinflammation has been implicated in nearly every major CNS disease ranging from Alzheimer's disease to brain cancer. Understanding and modeling neuroinflammation is critical for the identification of novel therapeutic targets in the treatment of CNS diseases. Unfortunately, the translation of findings from non-human models has left much to be desired. This review systematically discusses the role of human pluripotent stem cell (hPSC)-derived glia and supporting cells within the CNS, including astrocytes, microglia, oligodendrocyte precursor cells, pericytes, and endothelial cells, to describe the state of the field and hope for future discoveries. hPSC-derived cells offer an expanded potential to study the pathobiology of neuroinflammation and immunomodulatory cascades that impact disease progression. While much progress has been made in the development of models, there is much left to explore in the application of these models to understand the complex inflammatory response in the CNS.

From Physiology to Pathology of Astrocytes: Highlighting Their Potential as Therapeutic Targets for CNS Injury

In the mammalian central nervous system (CNS), astrocytes are the ubiquitous glial cells that have complex morphological and molecular characteristics. These fascinating cells play essential neurosupportive and homeostatic roles in the healthy CNS and undergo morphological, molecular, and functional changes to adopt so-called 'reactive' states in response to CNS injury or disease. In recent years, interest in astrocyte research has increased dramatically and some new biological features and roles of astrocytes in physiological and pathological conditions have been discovered thanks to technological advances. Here, we will review and discuss the well-established and emerging astroglial biology and functions, with emphasis on their potential as therapeutic targets for CNS injury, including traumatic and ischemic injury. This review article will highlight the importance of astrocytes in the neuropathological process and repair of CNS injury.

Astrocytes in Primary Familial Brain Calcification (PFBC): Emphasis on the Importance of Induced Pluripotent Stem Cell-Derived Human Astrocyte Models

Primary familial brain calcification (PFBC) is a rare, progressive central nervous system (CNS) disorder without a cure, and the current treatment methodologies primarily aim to relieve neurological and psychiatric symptoms of the patients. The disease is characterized by abnormal bilateral calcifications in the brain, however, our mechanistic understanding of the biology of the disease is still limited. Determining the roles of the specific cell types and molecular mechanisms involved in the pathophysiological processes of the disease is of great importance for the development of novel and effective treatment methodologies. There is a growing interest in the involvement of astrocytes in PFBC, as recent studies have suggested that astrocytes play a central role in the disease and that functional defects in these cells are critical for the development and progression of the disease. This review aims to discuss recent findings on the roles of astrocytes in PFBC pathophysiology, with a focus on known expression and roles of PFBC genes in astrocytes. Additionally, we discuss the importance of human astrocytes for PFBC disease modeling, and astrocytes as a potential therapeutic target in PFBC. Utilization of species-specific and physiologically relevant PFBC model systems can open new avenues for basic research, drug development, and regenerative medicine.

Capillary basal lamina in human brain and spinal cord has fibrillar collagen type I and type III: Ignorance may not be bliss

The capillary basal lamina (BL) located between the endothelial cell, pericyte and perivascular astrocyte plays important roles in normal and diseased central nervous system (CNS). Using immunohistochemistry (IHC), electron microscopy (EM) and post-embedding immunogold EM (IEM), we studied capillary BL in biopsy and autopsy tissues of human CNS from cases with and without significant brain pathology and aged from 4 days to 49 years. In all cases, IHC showed, in the BL of microvessels, immunoreactivity for collagen types I, III, IV, VI and fibronectin. EM revealed fusion of the BL of capillary endothelial cells or pericyte with perivascular astrocyte BL, which was focally split, resulting in expanded spaces bordered by BL and containing striated fibrils. There was no significant thickening of fused or split BL. IEM showed localization of collagen I and III to banded fibrils, and of collagen IV to split and fused BL. These characteristic ultrastructural findings in human capillary BL were not found in normal or transgenic mice. Our observations of fibrillar collagen in young individuals complement previous observations of similar findings in older individuals. This raises the possibility that fibrillar collagen in human vascular BL plays a significant role in CNS capillary physiology and pathophysiology. The species-specific differences in capillary morphology between humans and mice might have relevance to poor correlations between benefits of immunotherapy and drug treatment in mice compared with human.

Impact of perfusion on neuronal development in human derived neuronal networks

Advanced in vitro models of the brain have evolved in recent years from traditional two-dimensional (2D) ones, based on rodent derived cells, to three-dimensional (3D) ones, based on human neurons derived from induced pluripotent stem cells. To address the dynamic changes of the tissue microenvironment, bioreactors are used to control the in vitro microenvironment for viability, repeatability, and standardization. However, in neuronal tissue engineering, bioreactors have primarily been used for cell expansion purposes, while microfluidic systems have mainly been employed for culturing organoids. In this study, we explored the use of a commercial perfusion bioreactor to control the culture microenvironment of neuronal cells in both 2D and 3D cultures. Namely, neurons differentiated from human induced pluripotent stem cells (iNeurons) were cultured in 2D under different constant flow rates for 72 h. The impact of different flow rates on early-stage neuronal development and synaptogenesis was assessed by morphometric characterization and synaptic analysis. Based on these results, two involving variable flow rates were developed and applied again in 2D culture. The most effective protocol, in terms of positive impact on neuronal development, was then used for a preliminary study on the application of dynamic culturing conditions to neuronal cells in 3D. To this purpose, both iNeurons, co-cultured with astrocytes, and the human neuroblastoma cells SH-SY5Y were embedded into a hydrogel and maintained under perfusion for up to 28 days. A qualitative evaluation by immunocytochemistry and confocal microscopy was carried out to assess cell morphology and the formation of a 3D neuronal network.

Reactive astrocytes generated from human iPSC are pro-inflammatory and display altered metabolism

Astrocytes are the most abundant type of glial cell in the central nervous system and they play pivotal roles in both normal health and disease. Their dysfunction is detrimental to many brain related pathologies. Under pathological conditions, such as Alzheimer's disease, astrocytes adopt an activated reactive phenotype which can contribute to disease progression. A prominent risk factor for many neurodegenerative diseases is neuroinflammation which is the purview of glial cells, such as astrocytes and microglia. Human in vitro models have the potential to reveal relevant disease specific mechanisms, through the study of individual cell types such as astrocytes or the addition of specific factors, such as those secreted by microglia. The aim of this study was to generate human cortical astrocytes, in order to assess their protein and gene expression, examine their reactivity profile in response to exposure to the microglial secreted factors IL-1α, TNFα and C1q and assess their functionality in terms of calcium signalling and metabolism. The successfully differentiated and stimulated reactive astrocytes display increased IL-6, RANTES and GM-CSF secretion, and increased expression of genes associated with reactivity including, IL-6, ICAM1, LCN2, C3 and SERPINA3. Functional assessment of these reactive astrocytes showed a delayed and sustained calcium response to ATP and a concomitant decrease in the expression of connexin-43. Furthermore, it was demonstrated these astrocytes had an increased glycolytic capacity with no effect on oxidative phosphorylation. These findings not only increase our understanding of astrocyte reactivity but also provides a functional platform for drug discovery.

Animal Models of Febrile Seizures: Limitations and Recent Advances in the Field

Febrile seizures (FSs) are defined as seizures occurring in children aged 6 months to 5 years with a background of elevated body temperature. It is one of the most common neurological disorders of childhood, emphasizing the importance of understanding the causes of FSs and their impact on the developing nervous system. However, there are significant limitations to the technologies currently available for studying the etiology and pathophysiology of seizures in humans. It is currently not possible to adequately capture the subtle molecular and structural rearrangements of the nervous system that can occur after seizures in humans. The use of animal models can be invaluable for these purposes. The most commonly used models in modern research are hyperthermic models in rats and mice aged 10-12 days. While these models can reproduce many of the characteristics of FSs, they have certain limitations. This review outlines the key considerations when working with models of FSs, provides an overview of current approaches to producing seizures in different model subjects, and presents a summary of key findings regarding morphological and functional changes in the brain and behavioral alterations that have been identified in studies using animal models of FSs.

Specific cleavage of IGFBP-4 by papp-a in nervous tissue

Astrocytes are subtypes of glial cells involved in metabolic, structural, homeostatic, and neuroprotective processes that help neurons maintain viability. Insulin-like growth factors IGF-1 and IGF-2 are known to have neuroprotective effects on neurons and glial cells through interaction with specific receptors. IGF forms a complex with IGF-binding proteins (IGFBP) in nervous tissue and is released from the complex via IGFBP proteolysis by specific proteases. It has been reported that IGFBP-2, 5 and 6 are cleaved by specific proteases in the central nervous system (CNS), followed by IGF release; however, it was unknown whether IGFBP-4 was exposed to a particular proteolysis in nervous tissue. Using neurons and astrocytes derived from human induced pluripotent stem cell lines (hiPSC), as well as rat brain-sourced primary neuron-glia cultures, we demonstrated that IGFBP-4 is specifically cleaved in nervous tissue by the Pregnancy Associated Plasma Protein A (PAPP-A) protease and that this cleavage is IGF-dependent. Our results indicate that astrocyte rather than neuron PAPP-A cleaves IGFBP-4 in nervous tissue suggesting that this may be one of the fundamental mechanisms for IGF interchange between these two types of cells.

The predominance of "astrocytic" intranuclear inclusions in neuronal intranuclear inclusion disease manifesting encephalopathy-like symptoms: A case series with brain biopsy

Neuronal intranuclear inclusion disease (NIID) is a neurodegenerative disorder represented by eosinophilic intranuclear inclusions (EIIs) and GGC/CGG repeat expansion in the NOTCH2NLC gene. We report here two adult cases of NIID, genetically confirmed, with manifestation of encephalopathy-like symptoms and address the histopathologic findings obtained by brain biopsies, with a focus on "astrocytic" intranuclear inclusions (AIIs). Case 1 presented with paroxysmal restlessness, vertigo, or fever and was later involved in severe dementia and tetraparesis. Case 2 presented with forgetfulness and then with paroxysmal fever and headache. In both cases, delimited areas with gadolinium enhancement on magnetic resonance imaging and corresponding hyperperfusion were detected, leading to brain biopsies of the cortex. On histology, Case 1 showed an abnormal lamination, where the thickness of layers was different from usual. Both neurons and astrocytes showed some dysmorphologic features. Notably, astrocytes rather than neurons harbored EIIs. Case 2 showed a cortex, where neurons tended to be arrayed in a columnar fashion. Astrocytes showed some dysmorphologic features. Notably, much more astrocytes than neurons harbored EIIs. By a double-labeling immunofluorescence study for p62/NeuN and p62/glial fibrillary acidic protein, the predominance of AIIs was confirmed in both cases. Considering the physiological functions of astrocytes for the development and maintenance of the cortex, the encephalopathy-like symptoms, dynamic change of cerebral blood flow, and cortical dysmorphology can reasonably be explained by the dysfunction of EII-bearing astrocytes rather than EII-bearing neurons. This study suggests the presence of a subtype of NIID where AIIs rather than "neuronal" intranuclear inclusions are likely a key player in the pathogenesis of NIID, particularly in cases with encephalopathy-like symptoms. The importance of AIIs ("gliopathy") should be more appreciated in future studies of NIID.

The challenges to detect, quantify, and characterize viral reservoirs in the current antiretroviral era

A major barrier to cure HIV is the early generation of viral reservoirs in tissues. These viral reservoirs can contain intact or defective proviruses, but both generates low levels of viral proteins contribute to chronic bystander damage even in the ART era. Most viral reservoir detection techniques are limited to blood-based, reactivation, and sequencing assays that lack spatial properties to examine the contribution of the host's microenvironment to latency and cure efforts. Currently, little is known about the contribution of the microenvironment to viral reservoir survival, residual viral expression, and associated inflammation. Only a few spatiotemporal techniques are available, and fewer integrate spatial genomics, transcriptomics, and proteomics into the analysis of the viral reservoir microenvironment-all essential components to cure HIV. During the development of these spatial techniques, many considerations need to be included in the analysis to avoid misinterpretation. This manuscript tries to clarify some critical concepts in viral reservoir detection by spatial techniques and the upcoming opportunities for cure efforts.

Brain stars take the lead during critical periods of early postnatal brain development: relevance of astrocytes in health and mental disorders

In the brain, astrocytes regulate shape and functions of the synaptic and vascular compartments through a variety of released factors and membrane-bound proteins. An imbalanced astrocyte activity can therefore have drastic negative impacts on brain development, leading to the onset of severe pathologies. Clinical and pre-clinical studies show alterations in astrocyte cell number, morphology, molecular makeup and astrocyte-dependent processes in different affected brain regions in neurodevelopmental (ND) and neuropsychiatric (NP) disorders. Astrocytes proliferate, differentiate and mature during the critical period of early postnatal brain development, a time window of elevated glia-dependent regulation of a proper balance between synapse formation/elimination, which is pivotal in refining synaptic connectivity. Therefore, any intrinsic and/or extrinsic factors altering these processes during the critical period may result in an aberrant synaptic remodeling and onset of mental disorders. The peculiar bridging position of astrocytes between synaptic and vascular compartments further allows them to "compute" the brain state and consequently secrete factors in the bloodstream, which may serve as diagnostic biomarkers of distinct healthy or disease conditions. Here, we collect recent advancements regarding astrogenesis and astrocyte-mediated regulation of neuronal network remodeling during early postnatal critical periods of brain development, focusing on synapse elimination. We then propose alternative hypotheses for an involvement of aberrancies in these processes in the onset of ND and NP disorders. In light of the well-known differential prevalence of certain brain disorders between males and females, we also discuss putative sex-dependent influences on these neurodevelopmental events. From a translational perspective, understanding age- and sex-dependent astrocyte-specific molecular and functional changes may help to identify biomarkers of distinct cellular (dys)functions in health and disease, favouring the development of diagnostic tools or the selection of tailored treatment options for male/female patients.

Investigations of Astrocyte Calcium Signaling and Imaging with Classical and Nonclassical Light

The application of light in studying and influencing cellular behavior with improved temporal and spatial resolution remains a key objective in fields such as chemistry, physics, medicine, and engineering. In the brain, nonexcitable cells called astrocytes play essential roles in regulating homeostasis and cognitive function through complex calcium signaling pathways. Understanding these pathways is vital for deciphering brain physiology and neurological disorders like Parkinson's and Alzheimer's. Despite challenges in selectively targeting astrocyte signaling pathways due to shared molecular equipment with neurons, recent advancements in laser technology offer promising avenues. However, the effort to use laser light properties to study astroglial cell function is still limited. This work aims to exploit an in-depth pharmacological analysis of astrocyte calcium channels to determine the physiological mechanism induced by exposure to classical nanosecond-pulsed light. We herein report molecular clues supporting the use of visible-nanosecond laser pulses as a promising approach to excite primary rat neocortical astrocytes and unprecedentedly report on the implementation of entangled two-photon microscopy to image them.

Dissecting reactive astrocyte responses: lineage tracing and morphology-based clustering

Brain damage triggers diverse cellular and molecular events, with astrocytes playing a crucial role in activating local neuroprotective and reparative signaling within damaged neuronal circuits. Here, we investigated reactive astrocytes using a multidimensional approach to categorize their responses into different subtypes based on morphology. This approach utilized the StarTrack lineage tracer, single-cell imaging reconstruction and multivariate data analysis. Our findings identified three profiles of reactive astrocyte responses, categorized by their effects on cell size- and shape- related morphological parameters: "moderate", "strong," and "very strong". We also examined the heterogeneity of astrocyte reactivity, focusing on spatial and clonal distribution. Our research revealed a notable enrichment of protoplasmic and fibrous astrocytes within the "strong" and "very strong" response subtypes. Overall, our study contributes to a better understanding of astrocyte heterogeneity in response to an injury. By characterizing the diverse reactive responses among astrocyte subpopulations, we provide insights that could guide future research aimed at identifying novel therapeutic targets to mitigate brain damage and promote neural repair.

Astrocytes adopt a progenitor-like migratory strategy for regeneration in adult brain

Mature astrocytes become activated upon non-specific tissue damage and contribute to glial scar formation. Proliferation and migration of adult reactive astrocytes after injury is considered very limited. However, the regenerative behavior of individual astrocytes following selective astroglial loss, as seen in astrocytopathies, such as neuromyelitis optica spectrum disorder, remains unexplored. Here, we performed longitudinal in vivo imaging of cortical astrocytes after focal astrocyte ablation in mice. We discovered that perilesional astrocytes develop a remarkable plasticity for efficient lesion repopulation. A subset of mature astrocytes transforms into reactive progenitor-like (REPL) astrocytes that not only undergo multiple asymmetric divisions but also remain in a multinucleated interstage. This regenerative response facilitates efficient migration of newly formed daughter cell nuclei towards unoccupied astrocyte territories. Our findings define the cellular principles of astrocyte plasticity upon focal lesion, unravelling the REPL phenotype as a fundamental regenerative strategy of mature astrocytes to restore astrocytic networks in the adult mammalian brain. Promoting this regenerative phenotype bears therapeutic potential for neurological conditions involving glial dysfunction.

Identification of the abnormalities in astrocytic functions as potential drug targets for neurodegenerative disease

INTRODUCTION

Historically, astrocytes were seen primarily as a supportive cell population within the brain; with neurodegenerative disease research focusing exclusively on malfunctioning neurons. However, astrocytes perform numerous tasks that are essential for maintenance of the central nervous system`s complex processes. Disruption of these functions can have negative consequences; hence, it is unsurprising to observe a growing amount of evidence for the essential role of astrocytes in the development and progression of neurodegenerative diseases. Targeting astrocytic functions may serve as a potential disease-modifying drug therapy in the future.

AREAS COVERED

The present review emphasizes the key astrocytic functions associated with neurodegenerative diseases and explores the possibility of pharmaceutical interventions to modify these processes. In addition, the authors provide an overview of current advancement in this field by including studies of possible drug candidates.

EXPERT OPINION

Glial research has experienced a significant renaissance in the last quarter-century. Understanding how disease pathologies modify or are caused by astrocyte functions is crucial when developing treatments for brain diseases. Future research will focus on building advanced models that can more precisely correlate to the state in the human brain, with the goal of routinely testing therapies in these models.

Human stem cell transplantation models of Alzheimer's disease

Alzheimer's disease (AD) is the most frequent form of dementia. It is characterized by pronounced neuronal degeneration with formation of neurofibrillary tangles and deposition of amyloid β throughout the central nervous system. Animal models have provided important insights into the pathogenesis of AD and they have shown that different brain cell types including neurons, astrocytes and microglia have important functions in the pathogenesis of AD. However, there are difficulties in translating promising therapeutic observations in mice into clinical application in patients. Alternative models using human cells such as human induced pluripotent stem cells (iPSCs) may provide significant advantages, since they have successfully been used to model disease mechanisms in neurons and in glial cells in neurodegenerative diseases in vitro and in vivo. In this review, we summarize recent studies that describe the transplantation of human iPSC-derived neurons, astrocytes and microglial cells into the forebrain of mice to generate chimeric transplantation models of AD. We also discuss opportunities, challenges and limitations in using differentiated human iPSCs for in vivo disease modeling and their application for biomedical research.

Neuron-Astrocyte Interactions: A Human Perspective

This chapter explores the intricate interactions between neurons and astrocytes within the nervous system with a particular emphasis on studies conducted in human tissue or with human cells. We specifically explore how neuron-astrocyte interactions relate to processes of cellular development, morphology, migration, synapse formation, and metabolism. These findings enrich our understanding of basic neurobiology and how disruptions in these processes are relevant to human diseases.The study of human neuron-astrocyte interactions is made possible because of transformative in vitro advancements that have facilitated the generation and sustained culture of human neural cells. In addition, the rise of techniques like sequencing at single-cell resolution has enabled the exploration of numerous human cell atlases and their comparisons to other animal model systems. Thus, the innovations outlined in this chapter illuminate the convergence and divergence of neuron-astrocyte interactions across species. As technologies progress, continually more sophisticated in vitro systems will increasingly reflect in vivo environments and deepen our command of neuron-glial interactions in human biology.

Blockade of mGluR5 in astrocytes derived from human iPSCs modulates astrocytic function and increases phagocytosis

TNF-α is essential for induction and maintenance of inflammatory responses and its dysregulation is associated with susceptibility to various pathogens that infect the central nervous system. Activation of both microglia and astrocytes leads to TNF-α production, which in turn triggers further activation of these cells. Astrocytes have been implicated in the pathophysiology of a wide range of neurodegenerative diseases with either harmful or protective roles, as these cells are capable of secreting several inflammatory factors and also promote synapse elimination and remodeling. These responses are possible because they sense their surroundings via several receptors, including the metabotropic glutamate receptor 5 (mGluR5). Under neuroinflammatory conditions, mGluR5 activation in astrocytes can be neuroprotective or have the opposite effect. In the current study, we investigated the role of mGluR5 in hiPSC-derived astrocytes subjected to pro-inflammatory stimulation by recombinant TNF-α (rTNF-α). Our results show that mGluR5 blockade by CTEP decreases the secreted levels of pro-inflammatory cytokines (IL-6 and IL-8) following short rTNF-α stimulation, although this effect subsides with time. Additionally, CTEP enhances synaptoneurosome phagocytosis by astrocytes in both non-stimulated and rTNF-α-stimulated conditions, indicating that mGluR5 blockade alone is enough to drive synaptic material engulfment. Finally, mGluR5 antagonism as well as rTNF-α stimulation augment the expression of the reactivity marker SERPINA3 and reduces the expression of synaptogenic molecules. Altogether, these data suggest a complex role for mGluR5 in human astrocytes, since its blockade may have beneficial and detrimental effects under inflammatory conditions.

Distinctive biophysical features of human cell-types: insights from studies of neurosurgically resected brain tissue

Electrophysiological characterization of live human tissue from epilepsy patients has been performed for many decades. Although initially these studies sought to understand the biophysical and synaptic changes associated with human epilepsy, recently, it has become the mainstay for exploring the distinctive biophysical and synaptic features of human cell-types. Both epochs of these human cellular electrophysiological explorations have faced criticism. Early studies revealed that cortical pyramidal neurons obtained from individuals with epilepsy appeared to function "normally" in comparison to neurons from non-epilepsy controls or neurons from other species and thus there was little to gain from the study of human neurons from epilepsy patients. On the other hand, contemporary studies are often questioned for the "normalcy" of the recorded neurons since they are derived from epilepsy patients. In this review, we discuss our current understanding of the distinct biophysical features of human cortical neurons and glia obtained from tissue removed from patients with epilepsy and tumors. We then explore the concept of within cell-type diversity and its loss (i.e., "neural homogenization"). We introduce neural homogenization to help reconcile the epileptogenicity of seemingly "normal" human cortical cells and circuits. We propose that there should be continued efforts to study cortical tissue from epilepsy patients in the quest to understand what makes human cell-types "human".

Deepening the role of excitation/inhibition balance in human iPSCs-derived neuronal networks coupled to MEAs during long-term development

Objective.The purpose of this study is to investigate whether and how the balance between excitation and inhibition ('E/I balance') influences the spontaneous development of human-derived neuronal networksin vitro. To achieve that goal, we performed a long-term (98 d) characterization of both homogeneous (only excitatory or inhibitory neurons) and heterogeneous (mixed neuronal types) cultures with controlled E/I ratios (i.e. E:I 0:100, 25:75, 50:50, 75:25, 100:0) by recording their electrophysiological activity using micro-electrode arrays.Approach.Excitatory and inhibitory neurons were derived from human induced pluripotent stem cells (hiPSCs). We realized five different configurations by systematically varying the glutamatergic and GABAergic percentages.Main results.We successfully built both homogeneous and heterogeneous neuronal cultures from hiPSCs finely controlling the E/I ratios; we were able to maintain them for up to 3 months. Homogeneity differentially impacted purely inhibitory (no bursts) and purely excitatory (few bursts) networks, deviating from the typical traits of heterogeneous cultures (burst dominated). Increased inhibition in heterogeneous cultures strongly affected the duration and organization of bursting and network bursting activity. Spike-based functional connectivity and image-based deep learning analysis further confirmed all the above.Significance.Healthy neuronal activity is controlled by a well-defined E/I balance whose alteration could lead to the onset of neurodevelopmental disorders like schizophrenia or epilepsy. Most of the commonly usedin vitromodels are animal-derived or too simplified and thus far from thein vivohuman condition. In this work, by performing a long-term study of hiPSCs-derived neuronal networks obtained from healthy human subjects, we demonstrated the feasibility of a robustin vitromodel which can be further exploited for investigating pathological conditions where the E/I balance is impaired.