Neuroglia: Realising their true potential

The Neglected Sibling: NLRP2 Inflammasome in the Nervous System

While classical NOD-like receptor pyrin domain containing protein 1 (NLRP1) and NLRP3 inflammasomal proteins have been extensively investigated, the contribution of NLRP2 is still ill-defined in the nervous system. Given the putative significance of NLRP2 in orchestrating neuroinflammation, further inquiry is needed to gain a better understanding of its connectome, hence its specific targeting may hold a promising therapeutic implication. Therefore, bioinformatical approach for extracting information, specifically in the context of neuropathologies, is also undoubtedly preferred. To the best of our knowledge, there is no review study selectively targeting only NLRP2. Increasing, but still fragmentary evidence should encourage researchers to thoroughly investigate this inflammasome in various animal- and human models. Taken together, herein we aimed to review the current literature focusing on the role of NLRP2 inflammasome in the nervous system and more importantly, we provide an algorithm-based protein network of human NLRP2 for elucidating potentially valuable molecular partnerships that can be the beginning of a new discourse and future therapeutic considerations.

Role of transforming growth factor-β in peripheral nerve regeneration

Injuries caused by trauma and neurodegenerative diseases can damage the peripheral nervous system and cause functional deficits. Unlike in the central nervous system, damaged axons in peripheral nerves can be induced to regenerate in response to intrinsic cues after reprogramming or in a growth-promoting microenvironment created by Schwann cells. However, axon regeneration and repair do not automatically result in the restoration of function, which is the ultimate therapeutic goal but also a major clinical challenge. Transforming growth factor (TGF) is a multifunctional cytokine that regulates various biological processes including tissue repair, embryo development, and cell growth and differentiation. There is accumulating evidence that TGF-β family proteins participate in peripheral nerve repair through various factors and signaling pathways by regulating the growth and transformation of Schwann cells; recruiting specific immune cells; controlling the permeability of the blood-nerve barrier, thereby stimulating axon growth; and inhibiting remyelination of regenerated axons. TGF-β has been applied to the treatment of peripheral nerve injury in animal models. In this context, we review the functions of TGF-β in peripheral nerve regeneration and potential clinical applications.

The Role of Glial Cells in Different Phases of Migraine: Lessons from Preclinical Studies

Migraine is a complex and debilitating neurological disease that affects 15% of the population worldwide. It is defined by the presence of recurrent severe attacks of disabling headache accompanied by other debilitating neurological symptoms. Important advancements have linked the trigeminovascular system and the neuropeptide calcitonin gene-related peptide to migraine pathophysiology, but the mechanisms underlying its pathogenesis and chronification remain unknown. Glial cells are essential for the correct development and functioning of the nervous system and, due to its implication in neurological diseases, have been hypothesised to have a role in migraine. Here we provide a narrative review of the role of glia in different phases of migraine through the analysis of preclinical studies. Current evidence shows that astrocytes and microglia are involved in the initiation and propagation of cortical spreading depolarization, the neurophysiological correlate of migraine aura. Furthermore, satellite glial cells within the trigeminal ganglia are implicated in the initiation and maintenance of orofacial pain, suggesting a role in the headache phase of migraine. Moreover, microglia in the trigeminocervical complex are involved in central sensitization, suggesting a role in chronic migraine. Taken altogether, glial cells have emerged as key players in migraine pathogenesis and chronification and future therapeutic strategies could be focused on targeting them to reduce the burden of migraine.

Astrocytes and the Psychiatric Sequelae of COVID-19: What We Learned from the Pandemic

COVID-19, initially regarded as specific lung disease, exhibits an extremely broad spectrum of symptoms. Extrapulmonary manifestations of the disease also include important neuropsychiatric symptoms with atypical characteristics. Are these disturbances linked to stress accompanying every systemic infection, or are due to specific neurobiological changes associated with COVID-19? Evidence accumulated so far indicates that the pathophysiology of COVID-19 is characterized by systemic inflammation, hypoxia resulting from respiratory failure, and neuroinflammation (either due to viral neurotropism or in response to cytokine storm), all affecting the brain. It is reasonable to hypothesize that all these events may initiate or worsen psychiatric and cognitive disorders. Damage to the brain triggers a specific type of reactive response mounted by neuroglia cells, in particular by astrocytes which are the homeostatic cell par excellence. Astrocytes undergo complex morphological, biochemical, and functional remodeling aimed at mobilizing the regenerative potential of the central nervous system. If the brain is not directly damaged, resolution of systemic pathology usually results in restoration of the physiological homeostatic status of neuroglial cells. The completeness and dynamics of this process in pathological conditions remain largely unknown. In a subset of patients, glial cells could fail to recover after infection thus promoting the onset and progression of COVID-19-related neuropsychiatric diseases. There is evidence from post-mortem examinations of the brains of COVID-19 patients of alterations in both astrocytes and microglia. In conclusion, COVID-19 activates a huge reactive response of glial cells, that physiologically act as the main controller of the inflammatory, protective and regenerative events. However, in some patients the restoration of glial physiological state does not occur, thus compromising glial function and ultimately resulting in homeostatic failure underlying a set of specific neuropsychiatric symptoms related to COVID-19.

Role of Microglial Cells in the Pathophysiology of MS: Synergistic or Antagonistic?

Many studies indicate an important role of microglia and their cytokines in the pathophysiology of multiple sclerosis (MS). Microglia are the macrophages of the central nervous system (CNS). They have many functions, such as being "controllers" of the CNS homeostasis in pathological and healthy conditions, playing a key role in the active immune defense of the CNS. Macroglia exhibit a dual role, depending on the phenotype they adopt. First, they can exhibit neurotoxic effects, which are harmful in the case of MS. However, they also show neuroprotective and regenerative effects in this disease. Many of the effects of microglia are mediated through the cytokines they secrete, which have either positive or negative properties. Neurotoxic and pro-inflammatory effects can be mediated by microglia via lipopolysaccharide and gamma interferon. On the other hand, the mediators of anti-inflammatory and protective effects secreted by microglia can be, for example, interleukin-4 and -13. Further investigation into the role of microglia in MS pathophysiology may perhaps lead to the discovery of new therapies for MS, as recent research in this area has been very promising.

Cells of the Central Nervous System: An Overview of Their Structure and Function

The central nervous system is the last major organ system in the vertebrate body to yield its cellular structure, due to the complexity of its cells and their interactions. The fundamental unit of the nervous system is the neuron, which forms complex circuits that receive and integrate information and generate adaptive responses. Each neuron is composed of an input domain consisting of multiple dendrites along with the cell body, which is also responsible for the majority of macromolecule synthesis for the cell. The output domain is the axon which is a singular extension from the cell body that propagates the action potential to the synapse, where signals pass from one neuron to another. Facilitating these functions are cohorts of supporting cells consisting of astrocytes, oligodendrocytes and microglia along with NG2 cells and ependymal cells. Astrocytes have a dazzling array of functions including physical support, maintenance of homeostasis, development and integration of synaptic activity. Oligodendrocytes form the myelin sheath which surrounds axons and enables rapid conduction of the nerve impulse. Microglia are the resident immune cells, providing immune surveillance and remodeling of neuronal circuits during development and trauma. All these cells function in concert with each other, producing the remarkably diverse functions of the nervous system.

Melatonin and metformin counteract cognitive dysfunction equally in male rats with doxorubicin-induced chemobrain

Melatonin (Mel) and metformin (Met) show beneficial effects in various brain pathologies. However, the effects of Mel and Met on doxorubicin (DOX)-induced chemobrain remain in need of elucidation. We aimed to investigate whether Mel and Met provide neuroprotective effects on glial dysmorphologies, brain inflammation, oxidative stress, brain mitochondrial dysfunction, apoptosis, necroptosis, neurogenesis, hippocampal dysplasticity, and cognitive dysfunction in rats with DOX-induced chemobrain. Thirty-two male Wistar rats were divided into 2 groups and received normal saline (NSS, as control, n = 8) or DOX (3 mg/kg/day; n = 24) by intraperitoneal (i.p.) injection on days 0, 4, 8, 15, 22, and 29. The DOX-treated group was divided into 3 subgroups receiving either vehicle (NSS; n = 8), Mel (10 mg/kg/day; n = 8), or Met (250 mg/kg/day; n = 8) by gavage for 30 consecutive days. Following this, cognitive function was assessed in all rats. The number of glial cells and their fluorescence intensity had decreased, while the glial morphology in DOX-treated rats showed a lower process complexity. Brain mitochondrial dysfunction, an increase in brain inflammation, oxidative stress, apoptosis and necroptosis, a decrease in the number of hippocampal dendritic spines and neurogenesis, and cognitive decline were also observed in DOX-treated rats. Mel and Met equally improved those brain pathologies, resulting in cognitive improvement in DOX-treated rats. In conclusion, concomitant treatment with either Mel or Met counteract DOX-induced chemobrain by preservation of glial morphology, brain inflammation, brain oxidative stress, brain mitochondrial function, hippocampal plasticity, and brain apoptosis. This study highlighted the role of the glia as key mediators in DOX-induced chemobrain.

Glial Cells Response in Stroke

As the second-leading cause of death, stroke faces several challenges in terms of treatment because of the limited therapeutic interventions available. Previous studies primarily focused on metabolic and blood flow properties as a target for treating stroke, including recombinant tissue plasminogen activator and mechanical thrombectomy, which are the only USFDA approved therapies. These interventions have the limitation of a narrow therapeutic time window, the possibility of hemorrhagic complications, and the expertise required for performing these interventions. Thus, it is important to identify the contributing factors that exacerbate the ischemic outcome and to develop therapies targeting them for regulating cellular homeostasis, mainly neuronal survival and regeneration. Glial cells, primarily microglia, astrocytes, and oligodendrocytes, have been shown to have a crucial role in the prognosis of ischemic brain injury, contributing to inflammatory responses. They play a dual role in both the onset as well as resolution of the inflammatory responses. Understanding the different mechanisms driving these effects can aid in the development of therapeutic targets and further mitigate the damage caused. In this review, we summarize the functions of various glial cells and their contribution to stroke pathology. The review highlights the therapeutic options currently being explored and developed that primarily target glial cells and can be used as neuroprotective agents for the treatment of ischemic stroke.

The implication of a diversity of non-neuronal cells in disorders affecting brain networks

In the central nervous system (CNS) neurons are classically considered the functional unit of the brain. Analysis of the physical connections and co-activation of neurons, referred to as structural and functional connectivity, respectively, is a metric used to understand their interplay at a higher level. A myriad of glial cell types throughout the brain composed of microglia, astrocytes and oligodendrocytes are key players in the maintenance and regulation of neuronal network dynamics. Microglia are the central immune cells of the CNS, able to affect neuronal populations in number and connectivity, allowing for maturation and plasticity of the CNS. Microglia and astrocytes are part of the neurovascular unit, and together they are essential to protect and supply nutrients to the CNS. Oligodendrocytes are known for their canonical role in axonal myelination, but also contribute, with microglia and astrocytes, to CNS energy metabolism. Glial cells can achieve this variety of roles because of their heterogeneous populations comprised of different states. The neuroglial relationship can be compromised in various manners in case of pathologies affecting development and plasticity of the CNS, but also consciousness and mood. This review covers structural and functional connectivity alterations in schizophrenia, major depressive disorder, and disorder of consciousness, as well as their correlation with vascular connectivity. These networks are further explored at the cellular scale by integrating the role of glial cell diversity across the CNS to explain how these networks are affected in pathology.

Recent advances in the use of CRISPR/Cas for understanding the early development of molecular gaps in glial cells

Glial cells are non-neuronal elements of the nervous system (NS) and play a central role in its development, maturation, and homeostasis. Glial cell interest has increased, leading to the discovery of novel study fields. The CRISPR/Cas system has been widely employed for NS understanding. Its use to study glial cells gives crucial information about their mechanisms and role in the central nervous system (CNS) and neurodegenerative disorders. Furthermore, the increasingly accelerated discovery of genes associated with the multiple implications of glial cells could be studied and complemented with the novel screening methods of high-content and single-cell screens at the genome-scale as Perturb-Seq, CRISP-seq, and CROPseq. Besides, the emerging methods, GESTALT, and LINNAEUS, employed to generate large-scale cell lineage maps have yielded invaluable information about processes involved in neurogenesis. These advances offer new therapeutic approaches to finding critical unanswered questions about glial cells and their fundamental role in the nervous system. Furthermore, they help to better understanding the significance of glial cells and their role in developmental biology.

Induced Pluripotent Stem Cells for Treatment of Alzheimer’s and Parkinson’s Diseases

Neurodegenerative diseases are a group of debilitating pathologies in which neuronal tissue dies due to the buildup of neurotoxic plaques, resulting in detrimental effects on cognitive ability, motor control, and everyday function. Stem cell technology offers promise in addressing this problem on multiple fronts, but the conventional sourcing of pluripotent stem cells involves harvesting from aborted embryonic tissue, which comes with strong ethical and practical concerns. The keystone discovery of induced pluripotent stem cell (iPSC) technology provides an alternative and endless source, circumventing the unfavorable issues with embryonic stem cells, and yielding fundamental advantages. This review highlights iPSC technology, the pathophysiology of two major neurodegenerative diseases, Alzheimer’s and Parkinson’s, and then illustrates current state-of-the-art approaches towards the treatment of the diseases using iPSCs. The technologies discussed in the review emphasize in vitro therapeutic neural cell and organoid development for disease treatment, pathological modeling of neurodegenerative diseases, and 3D bioprinting as it applies to both.

Glial Purinergic Signals and Psychiatric Disorders

Emotion-related neural networks are regulated in part by the activity of glial cells, and glial dysfunction can be directly related to emotional diseases such as depression. Here, we discuss three different therapeutic strategies involving astrocytes that are effective for treating depression. First, the antidepressant, fluoxetine, acts on astrocytes and increases exocytosis of ATP. This has therapeutic effects via brain-derived neurotrophic factor-dependent mechanisms. Second, electroconvulsive therapy is a well-known treatment for drug-resistant depression. Electroconvulsive therapy releases ATP from astrocytes to induce leukemia inhibitory factors and fibroblast growth factor 2, which leads to antidepressive actions. Finally, sleep deprivation therapy is well-known to cause antidepressive effects. Sleep deprivation also increases release of ATP, whose metabolite, adenosine, has antidepressive effects. These independent treatments share the same mechanism, i.e., ATP release from astrocytes, indicating an essential role of glial purinergic signals in the pathogenesis of depression.

Astrocytes as essential time-keepers of the central pacemaker

Since the early observations made by Santiago Ramon y Cajal more than a century ago till now, astrocytes have gradually gained protagonism as essential partners of neurons in building brain circuits that regulate complex behavior. In mammals, processes such as sleep-wake cycle, locomotor activity, cognition and memory consolidation, homeostatic and hedonic appetite and stress response (among others), are synchronized in 24-h rhythms by the circadian system. In such a way, physiology efficiently anticipates and adapts to daily recurring changes in the environment. The hypothalamic suprachiasmatic nucleus (SCN) is considered the central pacemaker, it has been traditionally described as a nucleus of around 10,000 neurons nearly all GABAergic able to be entrained by light and to convey time information through multiple neuronal and hormonal pathways. Only recently, this neuro-centered view was challenged by breakthrough discoveries implicating astrocytes as essential time-keepers. In the present review, we will describe the current view on the SCN circuit and discuss whether astrocytic functions described in other brain regions and state-of-the-art experimental approaches, could help explaining better those well- and not so well-known features of the central pacemaker.

Biomaterials for Neural Tissue Engineering

The therapy of neural nerve injuries that involve the disruption of axonal pathways or axonal tracts has taken a new dimension with the development of tissue engineering techniques. When peripheral nerve injury (PNI), spinal cord injury (SCI), traumatic brain injury (TBI), or neurodegenerative disease occur, the intricate architecture undergoes alterations leading to growth inhibition and loss of guidance through large distance. To improve the limitations of purely cell-based therapies, the neural tissue engineering philosophy has emerged. Efforts are being made to produce an ideal scaffold based on synthetic and natural polymers that match the exact biological and mechanical properties of the tissue. Furthermore, through combining several components (biomaterials, cells, molecules), axonal regrowth is facilitated to obtain a functional recovery of the neural nerve diseases. The main objective of this review is to investigate the recent approaches and applications of neural tissue engineering approaches.

[New technologies to unveil the role of brain glial cells]

Brain function relies on complex interactions between neurons and different types of glial cells, such as astrocytes, microglia and oligodendrocytes. The relatively young field of "gliobiology" is thriving. Thanks to various technical innovations, it is now possible to address challenging biological questions on glial cells and unravel their multiple roles in brain function and dysfunction.

Decoding the role of zebrafish neuroglia in CNS disease modeling

Neuroglia, including microglia and astrocytes, is a critical component of the central nervous system (CNS) that interacts with neurons to modulate brain activity, development, metabolism and signaling pathways. Thus, a better understanding of the role of neuroglia in the brain is critical. Complementing clinical and rodent data, the zebrafish (Danio rerio) is rapidly becoming an important model organism to probe the role of neuroglia in brain disorders. With high genetic and physiological similarity to humans and rodents, zebrafish possess some common (shared), as well as some specific molecular biomarkers and features of neuroglia development and functioning. Studying these common and zebrafish-specific aspects of neuroglia may generate important insights into key brain mechanisms, including neurodevelopmental, neurodegenerative, neuroregenerative and neurological processes. Here, we discuss the biology of neuroglia in humans, rodents and fish, its role in various CNS functions, and further directions of translational research into the role of neuroglia in CNS disorders using zebrafish models.

The role of neuroglia in autism spectrum disorders

Neuroglia are a large class of neural cells of ectodermal (astroglia, oligodendroglia, and peripheral glial cells) and mesodermal (microglia) origin. Neuroglial cells provide homeostatic support, protection, and defense to the nervous tissue. Pathological potential of neuroglia has been acknowledged since their discovery. Research of the recent decade has shown the key role of all classes of glial cells in autism spectrum disorders (ASD), although molecular mechanisms defining glial contribution to ASD are yet to be fully characterized. This narrative conceptualizes recent findings of the broader roles of glial cells, including their active participation in the control of cerebral environment and regulation of synaptic development and scaling, highlighting their putative involvement in the etiopathogenesis of ASD.