Progenitor cell-based treatment of glial disease

Young glial progenitor cells competitively replace aged and diseased human glia in the adult chimeric mouse brain

Competition among adult brain cells has not been extensively researched. To investigate whether healthy glia can outcompete diseased human glia in the adult forebrain, we engrafted wild-type (WT) human glial progenitor cells (hGPCs) produced from human embryonic stem cells into the striata of adult mice that had been neonatally chimerized with mutant Huntingtin (mHTT)-expressing hGPCs. The WT hGPCs outcompeted and ultimately eliminated their human Huntington's disease (HD) counterparts, repopulating the host striata with healthy glia. Single-cell RNA sequencing revealed that WT hGPCs acquired a YAP1/MYC/E2F-defined dominant competitor phenotype upon interaction with the host HD glia. WT hGPCs also outcompeted older resident isogenic WT cells that had been transplanted neonatally, suggesting that competitive success depended primarily on the relative ages of competing populations, rather than on the presence of mHTT. These data indicate that aged and diseased human glia may be broadly replaced in adult brain by younger healthy hGPCs, suggesting a therapeutic strategy for the replacement of aged and diseased human glia.

Glial-restricted progenitor cells: a cure for diseased brain?

The central nervous system (CNS) is home to neuronal and glial cells. Traditionally, glia was disregarded as just the structural support across the brain and spinal cord, in striking contrast to neurons, always considered critical players in CNS functioning. In modern times this outdated dogma is continuously repelled by new evidence unravelling the importance of glia in neuronal maintenance and function. Therefore, glia replacement has been considered a potentially powerful therapeutic strategy. Glial progenitors are at the center of this hope, as they are the source of new glial cells. Indeed, sophisticated experimental therapies and exciting clinical trials shed light on the utility of exogenous glia in disease treatment. Therefore, this review article will elaborate on glial-restricted progenitor cells (GRPs), their origin and characteristics, available sources, and adaptation to current therapeutic approaches aimed at various CNS diseases, with particular attention paid to myelin-related disorders with a focus on recent progress and emerging concepts. The landscape of GRP clinical applications is also comprehensively presented, and future perspectives on promising, GRP-based therapeutic strategies for brain and spinal cord diseases are described in detail.

Astrocytic contributions to Huntington's disease pathophysiology

Huntington's disease (HD) is a fatal, monogenic, autosomal dominant neurodegenerative disease caused by a polyglutamine-encoding CAG expansion in the huntingtin (HTT) gene that results in mutant huntingtin proteins (mHTT) in cells throughout the body. Although large parts of the central nervous system (CNS) are affected, the striatum is especially vulnerable and undergoes marked atrophy. Astrocytes are abundant within the striatum and contain mHTT in HD, as well as in mouse models of the disease. We focus on striatal astrocytes and summarize how they participate in, and contribute to, molecular pathophysiology and disease-related phenotypes in HD model mice. Where possible, reference is made to pertinent astrocyte alterations in human HD. Astrocytic dysfunctions related to cellular morphology, extracellular ion and neurotransmitter homeostasis, and metabolic support all accompany the development and progression of HD, in both transgenic mouse and human cellular and chimeric models of HD. These findings reveal the potential for the therapeutic targeting of astrocytes so as to restore synaptic as well as tissue homeostasis in HD. Elucidation of the mechanisms by which astrocytes contribute to HD pathogenesis may inform a broader understanding of the role of glial pathology in neurodegenerative disorders and, by so doing, enable new strategies of glial-directed therapeutics.

Cell reprogramming for oligodendrocytes: A review of protocols and their applications to disease modeling and cell-based remyelination therapies

Oligodendrocytes are a type of glial cells that produce a lipid-rich membrane called myelin. Myelin assembles into a sheath and lines neuronal axons in the brain and spinal cord to insulate them. This not only increases the speed and efficiency of nerve signal transduction but also protects the axons from damage and degradation, which could trigger neuronal cell death. Demyelination, which is caused by a loss of myelin and oligodendrocytes, is a prominent feature of many neurological conditions, including Multiple sclerosis (MS), spinal cord injuries (SCI), and leukodystrophies. Demyelination is followed by a time of remyelination mediated by the recruitment of endogenous oligodendrocyte precursor cells, their migration to the injury site, and differentiation into myelin-producing oligodendrocytes. Unfortunately, endogenous remyelination is not sufficient to overcome demyelination, which explains why there are to date no regenerative-based treatments for MS, SCI, or leukodystrophies. To better understand the role of oligodendrocytes and develop cell-based remyelination therapies, human oligodendrocytes have been derived from somatic cells using cell reprogramming. This review will detail the different cell reprogramming methods that have been developed to generate human oligodendrocytes and their applications to disease modeling and cell-based remyelination therapies. Recent developments in the field have seen the derivation of brain organoids from pluripotent stem cells, and protocols have been devised to incorporate oligodendrocytes within the organoids, which will also be reviewed.

Modelling the Interplay Between Neuron-Glia Cell Dysfunction and Glial Therapy in Autism Spectrum Disorder

Autism spectrum disorder (ASD) is a complicated, interpersonally defined, static condition of the underdeveloped brain. Although the aetiology of autism remains unclear, disturbance of neuronglia interactions has lately been proposed as a significant event in the pathophysiology of ASD. In recent years, the contribution of glial cells to autism has been overlooked. In addition to neurons, glial cells play an essential role in mental activities, and a new strategy that emphasises neuron-glia interactions should be applied. Disturbance of neuron-glia connections has lately been proposed as a significant event in the pathophysiology of ASD because aberrant neuronal network formation and dysfunctional neurotransmission are fundamental to the pathology of the condition. In ASD, neuron and glial cell number changes cause brain circuits to malfunction and impact behaviour. A study revealed that reactive glial cells result in the loss of synaptic functioning and induce autism under inflammatory conditions. Recent discoveries also suggest that dysfunction or changes in the ability of microglia to carry out physiological and defensive functions (such as failure in synaptic elimination or aberrant microglial activation) may be crucial for developing brain diseases, especially autism. The cerebellum, white matter, and cortical regions of autistic patients showed significant microglial activation. Reactive glial cells result in the loss of synaptic functioning and induce autism under inflammatory conditions. Replacement of defective glial cells (Cell-replacement treatment), glial progenitor cell-based therapy, and medication therapy (inhibition of microglia activation) are all utilised to treat glial dysfunction. This review discusses the role of glial cells in ASD and the various potential approaches to treating glial cell dysfunction.

The Journey of iPSC-derived OPCs in Demyelinating Disorders: From In vitro Generation to In vivo Transplantation

Loss of myelination is common among neurological diseases. It causes significant disability, even death, if it is not treated instantly. Different mechanisms involve the pathophysiology of demyelinating diseases, such as genetic background, infectious, and autoimmune inflammation. Recently, regenerative medicine and stem cell therapy have shown to be promising for the treatment of demyelinating disorders. Stem cells, including embryonic stem cells (ESCs), induced pluripotent stem cells (iPSCs), and adult stem cells (ASCs), can differentiate into oligodendrocyte progenitor cells (OPCs), which may convert to oligodendrocytes (OLs) and recover myelination. IPSCs provide an endless source for OPCs generation. However, the restricted capacity of proliferation, differentiation, migration, and myelination of iPSC-derived OPCs is a notable gap for future studies. In this article, we have first reviewed stem cell therapy in demyelinating diseases. Secondly, methods of different protocols have been discussed among in vitro and in vivo studies on iPSC-derived OPCs to contrast OPCs' transplantation efficacy. Lastly, we have reviewed the results of iPSCs-derived OLs production in each demyelination model.

The regenerative potential of glial progenitor cells and reactive astrocytes in CNS injuries

Cell therapeutic approaches focusing on the regeneration of damaged tissue have been a popular topic among researchers in recent years. In particular, self-repair scarring from the central nervous system (CNS) can significantly complicate the treatment of an injured patient. In CNS regeneration schemes, either glial progenitor cells or reactive glial cells have key roles to play. In this review, the contribution and underlying mechanisms of these progenitor/reactive glial cells during CNS regeneration are discussed, as well as their role in CNS-related diseases.

Engrafted glial progenitor cells yield long-term integration and sensory improvement in aged mice

Aging causes astrocyte morphological degeneration and functional deficiency, which impairs neuronal functions. Until now, whether age-induced neuronal deficiency could be alleviated by engraftment of glial progenitor cell (GPC) derived astrocytes remained unknown. In the current study, GPCs were generated from embryonic cortical neural stem cells in vitro and transplanted into the brains of aged mice. Their integration and intervention effects in the aged brain were examined 12 months after transplantation. Results indicated that these in-vitro-generated GPC-derived astrocytes possessed normal functional properties. After transplantation they could migrate, differentiate, achieve long-term integration, and maintain much younger morphology in the aged brain. Additionally, these GPC-derived astrocytes established endfeet expressing aquaporin-4 (AQP4) and ameliorate AQP4 polarization in the aged neocortex. More importantly, age-dependent sensory response degeneration was reversed by GPC transplantation. This work demonstrates that rejuvenation of the astrocyte niche is a promising treatment to prevent age-induced degradation of neuronal and behavioral functions.

Oligodendrocyte Development and Implication in Perinatal White Matter Injury

Perinatal white matter injury (WMI) is the most common brain injury in premature infants and can lead to life-long neurological deficits such as cerebral palsy. Preterm birth is typically accompanied by inflammation and hypoxic-ischemic events. Such perinatal insults negatively impact maturation of oligodendrocytes (OLs) and cause myelination failure. At present, no treatment options are clinically available to prevent or cure WMI. Given that arrested OL maturation plays a central role in the etiology of perinatal WMI, an increased interest has emerged regarding the functional restoration of these cells as potential therapeutic strategy. Cell transplantation and promoting endogenous oligodendrocyte function are two potential options to address this major unmet need. In this review, we highlight the underlying pathophysiology of WMI with a specific focus on OL biology and their implication for the development of new therapeutic targets.

Human Glial Progenitor Cells Effectively Remyelinate the Demyelinated Adult Brain

Neonatally transplanted human glial progenitor cells (hGPCs) can myelinate the brains of myelin-deficient shiverer mice, rescuing their phenotype and survival. Yet, it has been unclear whether implanted hGPCs are similarly able to remyelinate the diffusely demyelinated adult CNS. We, therefore, ask if hGPCs could remyelinate both congenitally hypomyelinated adult shiverers and normal adult mice after cuprizone demyelination. In adult shiverers, hGPCs broadly disperse and differentiate as myelinating oligodendrocytes after subcortical injection, improving both host callosal conduction and ambulation. Implanted hGPCs similarly remyelinate denuded axons after cuprizone demyelination, whether delivered before or after demyelination. RNA sequencing (RNA-seq) of hGPCs back from cuprizone-demyelinated brains reveals their transcriptional activation of oligodendrocyte differentiation programs, while distinguishing them from hGPCs not previously exposed to demyelination. These data indicate the ability of transplanted hGPCs to disperse throughout the adult CNS, to broadly myelinate regions of dysmyelination, and also to be recruited as myelinogenic oligodendrocytes later in life, upon demyelination-associated demand.

POLR3-Related Leukodystrophy: Exploring Potential Therapeutic Approaches

Leukodystrophies are a class of rare inherited central nervous system (CNS) disorders that affect the white matter of the brain, typically leading to progressive neurodegeneration and early death. Hypomyelinating leukodystrophies are characterized by the abnormal formation of the myelin sheath during development. POLR3-related or 4H (hypomyelination, hypodontia, and hypogonadotropic hypogonadism) leukodystrophy is one of the most common types of hypomyelinating leukodystrophy for which no curative treatment or disease-modifying therapy is available. This review aims to describe potential therapies that could be further studied for effectiveness in pre-clinical studies, for an eventual translation to the clinic to treat the neurological manifestations associated with POLR3-related leukodystrophy. Here, we discuss the therapeutic approaches that have shown promise in other leukodystrophies, as well as other genetic diseases, and consider their use in treating POLR3-related leukodystrophy. More specifically, we explore the approaches of using stem cell transplantation, gene replacement therapy, and gene editing as potential treatment options, and discuss their possible benefits and limitations as future therapeutic directions.

Stem cell therapies as a therapeutic option to counter chemo brain: a negative effect of cancer treatment

Chemo brain, a constellation of cognitive deficiencies followed by chemotherapy drugs, used to treat different types of cancers and adversely impacts the quality of life of a cancer survivor. The underlying mechanism of chemo brain remains vague, thus delaying the advancement of efficient treatments. Unfortunately, there is no US FDA approved medicine for chemo brain and often medicines considered for chemo brain are already the ones approved for other diseases. Nevertheless, researches exploring stem cell transplantation in different neurodegenerative diseases demonstrate that cellular transplantation could reverse chemotherapy-induced chemo brain. This review talks about the mechanism behind the cognitive impairments instigated by different chemotherapy drugs used in cancer treatment, and how stem cell therapy could be advantageous to overcome this disease.

Particles Containing Cells as a Strategy to Promote Remyelination in Patients With Multiple Sclerosis

The repair of demyelinated lesions is a key objective in multiple sclerosis research. Remyelination fundamentally depends on oligodendrocyte progenitor cells (OPC) reaching the lesion; this is influenced by numerous factors including age, disease progression time, inflammatory activity, and the pool of OPCs available, whether they be NG2 cells or cells derived from neural stem cells. Administering OPCs has been proposed as a potential cell therapy; however, these cells can only be administered directly. This article discusses the potential administration of OPCs encapsulated within hydrogel particles composed of biocompatible biomaterials, via the nose-to-brain pathway. We also discuss conditions for the indication of this therapy, and such related issues as the influence on endogenous remyelination, migration of OPCs to demyelinated areas, and the immune response, given the autoimmune nature of multiple sclerosis. Chitosan and derivatives constitute the most promising biomaterial for this purpose, although these issues must be addressed. In conclusion, this line of research may yield an alternative to the remyelinating drugs currently being studied.

Human Glial Chimeric Mice to Define the Role of Glial Pathology in Human Disease

Human glial progenitor cells (hGPCs) can engraft, expand, and differentiate into functional oligodendrocytes and astrocytes when transplanted neonatally into murine hosts, in which they outcompete the host glial pool to ultimately colonize and dominate the recipient brains. When congenitally hypomyelinated mutants are used as hosts, the donor hGPCs generate myelinogenic oligodendrocytes as well as astrocytes, so that the recipient mice develop a largely humanized white matter, with entirely human-derived myelin. In addition, by neonatally engrafting hGPCs derived from patient- and disease-specific pluripotent stem cells, glial chimeric mice may be produced in which large proportions of all macroglial cells are not only human but also patient and disease specific. Human glial chimeric mice thus provide intriguing preparations by which to investigate the species-specific contributions of human glia to both cognition and human-selective neurodegenerative and neuropsychiatric diseases, as well as the potential for therapeutic glial cell replacement in these disorders. This review presents an overview of the uses, characteristics, and limitations of the human glial chimeric brain model, while providing a step-by-step protocol for the establishment of these mice.

The Thrombin Receptor Restricts Subventricular Zone Neural Stem Cell Expansion and Differentiation

Thrombin is frequently increased in the CNS after injury yet little is known regarding its effects on neural stem cells. Here we show that the subventricular zone (SVZ) of adult mice lacking the high affinity receptor for thrombin, proteinase activated receptor 1 (PAR1), show increased numbers of Sox2+ and Ki-67+ self-renewing neural stem cells (NSCs) and Olig2+ oligodendrocyte progenitors. SVZ NSCs derived from PAR1-knockout mice, or treated with a PAR1 small molecule inhibitor (SCH79797), exhibited enhanced capacity for self-renewal in vitro, including increases in neurosphere formation and BrdU incorporation. PAR1-knockout SVZ monolayer cultures contained more Nestin, NG2+ and Olig2+ cells indicative of enhancements in expansion and differentiation towards the oligodendrocyte lineage. Cultures of NSCs lacking PAR1 also expressed higher levels of myelin basic protein, proteolipid protein and glial fibrillary acidic protein upon differentiation. Complementing these findings, the corpus callosum and anterior commissure of adult PAR1-knockout mice contained greater numbers of Olig2+ progenitors and CC1+ mature oligodendrocytes. Together these findings highlight PAR1 inhibition as a means to expand adult SVZ NSCs and to promote an increased number of mature myelinating oligodendrocytes in vivo that may be of particular benefit in the context of neural injury where PAR1 agonists such as thrombin are deregulated.