Co-culture of exogenous oligodendrocytes with unmyelinated cerebella: Revisiting ex vivo models and new tools to study myelination

Positive effect of evobrutinib in CNS remyelination models and lack of synergy with clemastine-A dose response study

Background

To recover normal functions, remyelination in multiple sclerosis is crucial. Although endogenous remyelination occurs, it is often insufficient, and finding molecules promoting repair of demyelinated lesions is needed.

Objectives

To compare the remyelination potential of evobrutinib, an inhibitor of Bruton's tyrosine kinase and clemastine, an antagonist of M1 muscarinic acetylcholine receptor.

Methods

Remyelination was investigated in lysolecithin demyelinated organotypic mouse cerebellar slices and a transgenic Xenopus model of inducible-demyelination.

Results

Evobrutinib (100 nM) and clemastine (200 nM) potentiated remyelination of mouse cerebellar slices by a factor of 2.9 and 1.76, respectively. In conditionally demyelinated Xenopus, evobrutinib and clemastine increased remyelination by a factor of 1.61 and 1.92, respectively. Evobrutinib targets Bruton's tyrosine kinase expressed by microglia, and we showed that the increase in number of myeloid cells following demyelination is due to an extravasation from nearby vessels of macrophages migrating toward the optic nerve. In contrast, clemastine is expected to antagonize muscarinic receptor 1 expressing cells of the oligodendroglial lineage. We investigated a possible synergistic effect on remyelination by adding simultaneously both molecules. In both experimental models tested no significative improvement on remyelination of co-treatment with evobrutinib plus clemastine was observed.

Discussion

While evobrutinib increased 1.59 fold the number of microglia/macrophages, in the presence of clemastine the number of innate immune cells was decreased by 0.39 fold, therefore counteracting the beneficial effect of microglia/macrophages on remyelination.

Temporal dynamics of neutrophil functions in multiple sclerosis

Early neuroinflammatory injury plays a crucial role in initiating and progressing multiple sclerosis (MS). Neutrophils are forerunners to neural lesions in MS, yet the temporal alterations of their functions in MS remains unclear. This study demonstrated a positive correlation between circulatory neutrophil counts and disease activity and severity in treatment-naïve MS patients. In experimental autoimmune encephalomyelitis (EAE), we documented the recruitment of neutrophils to spinal cord during the preclinical phase, with these cells contributing to the disruption of the blood-spinal cord barrier (BSCB) during the onset of the disease. Furthermore, during the peak phase, infiltrated neutrophils promoted demyelination through formation of neutrophil extracellular traps (NETs), cytokine secretion and antigen presentation. Notably, the inhibition of neutrophil infiltration using a CXCR2 inhibitor effectively mitigated white matter damage and physical disability, underscoring their potential as therapeutic targets. In conclusion, neutrophils represent promising candidates for both disease treatment and prognosis evaluation in MS. By elucidating their temporal roles and mechanisms of action, we can potentially harness their modulation to improve patient outcomes and disease management.

Pharmacogenomic screening identifies and repurposes leucovorin and dyclonine as pro-oligodendrogenic compounds in brain repair

Oligodendrocytes are critical for CNS myelin formation and are involved in preterm-birth brain injury (PBI) and multiple sclerosis (MS), both of which lack effective treatments. We present a pharmacogenomic approach that identifies compounds with potent pro-oligodendrogenic activity, selected through a scoring strategy (OligoScore) based on their modulation of oligodendrogenic and (re)myelination-related transcriptional programs. Through in vitro neural and oligodendrocyte progenitor cell (OPC) cultures, ex vivo cerebellar explants, and in vivo mouse models of PBI and MS, we identify FDA-approved leucovorin and dyclonine as promising candidates. In a neonatal chronic hypoxia mouse model mimicking PBI, both compounds promote neural progenitor cell proliferation and oligodendroglial fate acquisition, with leucovorin further enhancing differentiation. In an adult MS model of focal de/remyelination, they improve lesion repair by promoting OPC differentiation while preserving the OPC pool. Additionally, they shift microglia from a pro-inflammatory to a pro-regenerative profile and enhance myelin debris clearance. These findings support the repurposing of leucovorin and dyclonine for clinical trials targeting myelin disorders, offering potential therapeutic avenues for PBI and MS.

Complementary strategies to be used in conjunction with animal models for multiple sclerosis drug discovery: adapting preclinical validation of drug candidates to the need of remyelinating strategies

INTRODUCTION

The quest for novel MS therapies focuses on promoting remyelination and neuroprotection, necessitating innovative drug design paradigms and robust preclinical validation methods to ensure efficient clinical translation. The complexity of new drugs action mechanisms is strengthening the need for solid biological validation attempting to address all possible pitfalls and biases precluding access to efficient and safe drugs.

AREAS COVERED

In this review, the authors describe the different in vitro and in vivo models that should be used to create an integrated approach for preclinical validation of novel drugs, including the evaluation of the action mechanism. This encompasses 2D, 3D in vitro models and animal models presented in such a way to define the appropriate use in a global process of drug screening and hit validation.

EXPERT OPINION

None of the current available tests allow the concomitant evaluation of anti-inflammatory, immune regulators or remyelinating agents with sufficient reliability. Consequently, the collaborative efforts of academia, industry, and regulatory agencies are essential for establishing standardized protocols, validating novel methodologies, and translating preclinical findings into clinically meaningful outcomes.

Antagonistic actions of PAK1 and NF2/Merlin drive myelin membrane expansion in oligodendrocytes

In the central nervous system, the formation of myelin by oligodendrocytes (OLs) relies on the switch from the polymerization of the actin cytoskeleton to its depolymerization. The molecular mechanisms that trigger this switch have yet to be elucidated. Here, we identified P21-activated kinase 1 (PAK1) as a major regulator of actin depolymerization in OLs. Our results demonstrate that PAK1 accumulates in OLs in a kinase-inhibited form, triggering actin disassembly and, consequently, myelin membrane expansion. Remarkably, proteomic analysis of PAK1 binding partners enabled the identification of NF2/Merlin as its endogenous inhibitor. Our findings indicate that Nf2 knockdown in OLs results in PAK1 activation, actin polymerization, and a reduction in OL myelin membrane expansion. This effect is rescued by treatment with a PAK1 inhibitor. We also provide evidence that the specific Pak1 loss-of-function in oligodendroglia stimulates the thickening of myelin sheaths in vivo. Overall, our data indicate that the antagonistic actions of PAK1 and NF2/Merlin on the actin cytoskeleton of the OLs are critical for proper myelin formation. These findings have broad mechanistic and therapeutic implications in demyelinating diseases and neurodevelopmental disorders.

From 2D to 3D Co-Culture Systems: A Review of Co-Culture Models to Study the Neural Cells Interaction

The central nervous system (CNS) controls and regulates the functional activities of the organ systems and maintains the unity between the body and the external environment. The advent of co-culture systems has made it possible to elucidate the interactions between neural cells in vitro and to reproduce complex neural circuits. Here, we classified the co-culture system as a two-dimensional (2D) co-culture system, a cell-based three-dimensional (3D) co-culture system, a tissue slice-based 3D co-culture system, an organoid-based 3D co-culture system, and a microfluidic platform-based 3D co-culture system. We provide an overview of these different co-culture models and their applications in the study of neural cell interaction. The application of co-culture systems in virus-infected CNS disease models is also discussed here. Finally, the direction of the co-culture system in future research is prospected.

Microglia-neuron interaction at nodes of Ranvier depends on neuronal activity through potassium release and contributes to remyelination

Microglia, the resident immune cells of the central nervous system, are key players in healthy brain homeostasis and plasticity. In neurological diseases, such as Multiple Sclerosis, activated microglia either promote tissue damage or favor neuroprotection and myelin regeneration. The mechanisms for microglia-neuron communication remain largely unkown. Here, we identify nodes of Ranvier as a direct site of interaction between microglia and axons, in both mouse and human tissues. Using dynamic imaging, we highlight the preferential interaction of microglial processes with nodes of Ranvier along myelinated fibers. We show that microglia-node interaction is modulated by neuronal activity and associated potassium release, with THIK-1 ensuring their microglial read-out. Altered axonal K⁺ flux following demyelination impairs the switch towards a pro-regenerative microglia phenotype and decreases remyelination rate. Taken together, these findings identify the node of Ranvier as a major site for microglia-neuron interaction, that may participate in microglia-neuron communication mediating pro-remyelinating effect of microglia after myelin injury.

Microglia are important for brain homeostasis and plasticity. The mechanisms underlying microglia-neuron interactions are still unclear. Here, the authors show that microglia preferentially interact with the nodes of Ranvier along axons. This interaction is modulated by neuronal activity and contributes to remyelination in mice.