High-throughput screening for myelination promoting compounds using human stem cell-derived oligodendrocyte progenitor cells

Myelin dysfunction in aging and brain disorders: mechanisms and therapeutic opportunities

Myelin is a multilamellar membrane that surrounds axons in the vertebrate nervous system. Properly functioning myelin is essential for the rapid conduction of nerve impulses, and it metabolically supports axonal integrity. Emerging evidence indicates that myelin is also involved in various aspects of cognition, with adaptive myelination playing a critical role in memory consolidation and motor learning. However, these physiological processes can be disrupted in various diseases. Understanding the mechanisms underlying myelin pathology is therefore essential for the development of targeted therapies for associated medical conditions. This review provides a comprehensive overview of the role of myelin in neural function, with a particular focus on adaptive myelination in cognition. We also highlight myelin dysfunction and the underlying mechanisms in the aging brain, as well as in diverse brain disorders and neurological conditions, including neurodegenerative diseases, psychiatric conditions, brain injuries, chemotherapy-related cognitive impairment, and neurological symptoms associated with COVID-19. Furthermore, we discuss the therapeutic potential of recently identified pro-myelinating compounds in aging-associated cognitive decline and brain disorders, as well as the future of remyelination therapies. Current evidence suggests that restoring functional myelin may serve as a therapeutic strategy for various medical conditions associated with myelin dysfunction.

Novel Approaches to the Treatment of Preterm White Matter Injury through Targeting Remyelination

Preterm white matter injury (WMI) is a common cause of cerebral palsy and cognitive disability after premature birth. Preterm WMI is caused by a differentiation arrest in the oligodendrocyte (OL) lineage, and a failure of myelination. As there are no specific treatments, care is supportive and focused on rehabilitation. However, novel high-throughput screening methods have enabled the identification of "pro-myelinating" compounds that promote OL differentiation and myelination. Many of these compounds stimulate remyelination in animal models and patients with demyelinating disorders. The shared mechanisms of remyelination and developmental myelination suggest that pro-myelinating compounds may have potential utility in preterm WMI.

Mechanisms of action of repurposed Ebola virus antivirals - the roles of phospholipidosis and cholesterol homeostasis

Cell-based drug repurposing screens have been a common approach to identifying compounds with antiviral properties. For Ebola virus (EBOV), such screens yield unexpectedly high hit rates. We investigated two mechanisms underlying the anti-EBOV activities of repurposed compounds. Phospholipidosis (PLD) is excessive accumulation of cellular lipids that confounds screens for SARS-CoV-2. We performed a meta-analysis of published screens and supplemented these with our own using infectious EBOV at biosafety level-4. A list of nearly 400 hit compounds from seven anti-EBOV screens was compiled. Most (63 %) of these hits were predicted to induce PLD, and their anti-EBOV activities broadly correlated with PLD induction. PLD-inducing compounds did not inhibit infection by several other highly pathogenic viruses, suggesting that PLD was not a confounding factor for screens against Lassa, Crimean-Congo hemorrhagic fever, and Rift Valley fever viruses. Of four cells lines tested, HeLa cells were the least susceptible to PLD induction. In addition to PLD, many of the hit compounds identified disrupt cholesterol homeostasis. Previous research found inhibition of cholesterol synthesis by statins blocked EBOV infection. To understand if compounds inhibiting this mechanism could contribute to high hit rates, we further examined this pathway. We identified multiple additional inhibitors of cholesterol biosynthesis, that also blocked EBOV infection, albeit with varying potency and cytotoxicity across cell lines. EBOV inhibitors that acted through this mechanism were suppressed by the addition of exogenous cholesterol. Our findings help define the effects that contribute to anti-EBOV activities and hence facilitate the selection of lead molecules suitable for subsequent development.

A human iPSC-Derived myelination model for investigating fetal brain injuries

Cerebral white matter injuries, such as periventricular leukomalacia, are major contributors to neurodevelopmental impairments in preterm infants. Despite the clinical significance of these conditions, human-relevant models for studying fetal brain development and injury mechanisms remain limited. This study introduces a human iPSC-derived myelination model developed using a microfluidic device. The platform combines spinal cord-patterned neuronal and oligodendrocyte spheroids to recapitulate axon-glia interactions and myelination processes in vitro. The model successfully achieved axonal fascicle formation and compact myelin deposition, as validated by immunostaining and transmission electron microscopy. Functional calcium imaging confirmed neuronal activity within the system, underscoring its physiological relevance. While myelination efficiency was partial, with some axons remaining unmyelinated under the current conditions, this model represents a significant advancement in human myelin biology, offering a foundation for investigating fetal and perinatal brain injuries and related pathologies. Future refinements, such as improved myelination coverage and incorporating additional CNS cell types, will enhance its utility for studying disease mechanisms and enabling high-throughput drug screening.

Restoring the Multiple Sclerosis Associated Imbalance of Gut Indole Metabolites Promotes Remyelination and Suppresses Neuroinflammation

In multiple sclerosis (MS) the circulating metabolome is dysregulated, with indole lactate (ILA) being one of the most significantly reduced metabolites. We demonstrate that oral supplementation of ILA impacts key MS disease processes in two preclinical models. ILA reduces neuroinflammation by dampening immune cell activation as well as infiltration; and promotes remyelination and in vitro oligodendrocyte differentiation through the aryl hydrocarbon receptor (AhR). Supplementation of ILA, a reductive indole metabolite, restores the gut microbiome's oxidative/reductive metabolic balance by lowering circulating indole acetate (IAA), an oxidative indole metabolite, that blocks remyelination and oligodendrocyte maturation. The ILA-induced reduction in circulating IAA is linked to changes in IAA-producing gut microbiota taxa and pathways that are also dysregulated in MS. Notably, a lower ILA:IAA ratio correlates with worse MS outcomes. Overall, these findings identify ILA as a potential anti-inflammatory remyelinating agent and provide insights into the role of gut dysbiosis-related metabolic alterations in MS progression.

Glial Cells as Key Regulators in Neuroinflammatory Mechanisms Associated with Multiple Sclerosis

Even though several highly effective treatments have been developed for multiple sclerosis (MS), the underlying pathological mechanisms and drivers of the disease have not been fully elucidated. In recent years, there has been a growing interest in studying neuroinflammation in the context of glial cell involvement as there is increasing evidence of their central role in disease progression. Although glial cell communication and proper function underlies brain homeostasis and maintenance, their multiple effects in an MS brain remain complex and controversial. In this review, we aim to provide an overview of the contribution of glial cells, oligodendrocytes, astrocytes, and microglia in the pathology of MS during both the activation and orchestration of inflammatory mechanisms, as well as of their synergistic effects during the repair and restoration of function. Additionally, we discuss how the understanding of glial cell involvement in MS may provide new therapeutic targets either to limit disease progression or to facilitate repair.

Oligodendrocyte-derived laminin-γ1 regulates the blood-brain barrier and CNS myelination in mice

Although oligodendrocytes (OLs) synthesize laminin-γ1, the most widely used γ subunit, its functional significance in the CNS remains unknown. To answer this important question, we generated a conditional knockout mouse line with laminin-γ1 deficiency in OL lineage cells (γ1-OKO). γ1-OKO mice exhibit weakness/paralysis and die by post-natal day 33. Additionally, they develop blood-brain barrier (BBB) disruption in the cortex and striatum. Subsequent studies reveal decreased major facilitator superfamily domain containing 2a expression and increased endothelial caveolae vesicles, but unaltered tight junction protein expression and tight junction ultrastructure, indicating a transcellular, rather than a paracellular, mechanism of BBB breakdown. Furthermore, significantly reduced OL lineage cells, OL precursor cells (OPCs), proliferating OPCs, and mature OLs are observed in γ1-OKO brains in a region-specific manner. Consistent with this finding, various defects in myelination are detected in γ1-OKO brains at biochemical and ultrastructural levels. Overall, these results highlight important roles of OL-derived laminin-γ1 in BBB maintenance and OL biology (proliferation, differentiation, and myelination).

Identity and Maturity of iPSC-Derived Oligodendrocytes in 2D and Organoid Systems

Oligodendrocytes originating in the brain and spinal cord as well as in the ventral and dorsal domains of the neural tube are transcriptomically and functionally distinct. These distinctions are also reflected in the ultrastructure of the produced myelin, and the susceptibility to myelin-related disorders, which highlights the significance of the choice of patterning protocols in the differentiation of induced pluripotent stem cells (iPSCs) into oligodendrocytes. Thus, our first goal was to survey the different approaches applied to the generation of iPSC-derived oligodendrocytes in 2D culture and in organoids, as well as reflect on how these approaches pertain to the regional and spatial fate of the generated oligodendrocyte progenitors and myelinating oligodendrocytes. This knowledge is increasingly important to disease modeling and future therapeutic strategies. Our second goal was to recap the recent advances in the development of oligodendrocyte-enriched organoids, as we explore their relevance to a regional specification alongside their duration, complexity, and maturation stages of oligodendrocytes and myelin biology. Finally, we discuss the shortcomings of the existing protocols and potential future explorations.

Discovery and Optimization of Selective Brain-Penetrant EBP Inhibitors that Enhance Oligodendrocyte Formation

The inhibition of emopamil binding protein (EBP), a sterol isomerase within the cholesterol biosynthesis pathway, promotes oligodendrocyte formation, which has been proposed as a potential therapeutic approach for treating multiple sclerosis. Herein, we describe the discovery and optimization of brain-penetrant, orally bioavailable inhibitors of EBP. A structure-based drug design approach from literature compound 1 led to the discovery of a hydantoin-based scaffold, which provided balanced physicochemical properties and potency and an improved in vitro safety profile. The long half-lives of early hydantoin-based EBP inhibitors in rodents prompted an unconventional optimization strategy, focused on increasing metabolic turnover while maintaining potency and a brain-penetrant profile. The resulting EBP inhibitor 11 demonstrated strong in vivo target engagement in the brain, as illustrated by the accumulation of EBP substrate zymostenol after repeated dosing. Furthermore, compound 11 enhanced the formation of oligodendrocytes in human cortical organoids, providing additional support for our therapeutic hypothesis.

A novel approach to increase glial cell populations in brain microphysiological systems

Brain microphysiological systems (bMPS), which recapitulate human brain cellular architecture and functionality more closely than traditional monolayer cultures, have become a practical, non-invasive, and increasingly relevant platform for the study of neurological function in health and disease. These models include 3D spheroids and organoids as well as organ-on-chip models. Currently, however, existing 3D brain models vary in reflecting the relative populations of the different cell types present in the human brain. Most of the models consist mainly of neurons, while glial cells represent a smaller portion of the cell populations. Here, by means of a chemically defined glial-enriched medium (GEM), we present an improved method to expand the population of astrocytes and oligodendrocytes without compromising neuronal differentiation in bMPS. An important finding is that astrocytes not only increased in number but also changed in morphology when cultured in GEM, more closely recapitulating primary culture astrocytes. We demonstrate oligodendrocyte and astrocyte enrichment in GEM bMPS using a variety of complementary methods. We found that GEM bMPS are electro-chemically active and showed different patterns of Ca +2 staining and flux. Synaptic vesicles and terminals observed by electron microscopy were also present. No significant changes in neuronal differentiation were observed by gene expression, however, GEM enhanced neurite outgrowth and cell migration, and differentially modulated neuronal maturation in two different iPSC lines. Our results have the potential to significantly improve in vivo-like functionality of bMPS for the study of neurological diseases and drug discovery, contributing to the unmet need for safe human models.