Neuron-oligodendrocyte potassium shuttling at nodes of Ranvier protects against inflammatory demyelination

Retigabine, a potassium channel opener, restores thalamocortical neuron functionality in a murine model of autoimmune encephalomyelitis

BACKGROUND

Multiple Sclerosis (MS) is an autoimmune neurodegenerative disease, whose primary hallmark is the occurrence of inflammatory lesions in white and grey matter structures. Increasing evidence in MS patients and respective murine models reported an impaired ionic homeostasis driven by inflammatory-demyelination, thereby profoundly affecting signal propagation. However, the impact of a focal inflammatory lesion on single-cell and network functionality has hitherto not been fully elucidated.

OBJECTIVES

In this study, we sought to determine the consequences of a localized cortical inflammatory lesion on the excitability and firing pattern of thalamic neurons in the auditory system. Moreover, we tested the neuroprotective effect of Retigabine (RTG), a specific Kv7 channel opener, on disease outcome.

METHODS

To resemble the human disease, we focally administered pro-inflammatory cytokines, TNF-α and IFN-γ, in the primary auditory cortex (A1) of MOG35-55 immunized mice. Thereafter, we investigated the impact of the induced inflammatory milieu on afferent thalamocortical (TC) neurons, by performing ex vivo recordings. Moreover, we explored the effect of Kv7 channel modulation with RTG on auditory information processing, using in vivo electrophysiological approaches.

RESULTS

Our results revealed that a cortical inflammatory lesion profoundly affected the excitability and firing pattern of neighboring TC neurons. Noteworthy, RTG restored control-like values and TC tonotopic mapping.

CONCLUSION

Our results suggest that RTG treatment might robustly mitigate inflammation-induced altered excitability and preserve ascending information processing.

Clemastine improves emotional and social deficits in adolescent social isolation mice by reversing demyelination

Adolescence is a critical period for social experience-dependent oligodendrocyte maturation and myelination. Adolescent stress predisposes to cause irreversible changes in brain structure and function with lasting effects on adulthood or beyond. However, the molecular mechanisms linking adolescent social isolation stress with emotional and social competence remain largely unknown. In our study, we found that social isolation during adolescence leads to anxiety-like behaviors, depression-like behaviors, impaired social memory and altered patterns of social ultrasonic vocalizations in mice. In addition, adolescent social isolation stress induces demyelination in the prefrontal cortex and hippocampus of mice, with decreased myelin-related gene expression and disrupted myelin structure. More importantly, clemastine was sufficient to rescue the impairment of emotional and social memory by promoting remyelination. These findings reveal the demyelination mechanism of emotional and social deficits caused by social isolation stress in adolescence, and provides potential therapeutic targets for treating stress-related mental disorders.

Contribution of inwardly rectifying potassium channel 4.1 in orofacial neuropathic pain: Regulation of pannexin 3 via the reactive oxygen species-activated P38 MAPK signal pathway

The involvement of inwardly rectifying potassium channel 4.1 (Kir4.1) in neuropathic pain has been established. However, there is limited understanding of the downstream mechanism through which Kir4.1 contributes to orofacial neuropathic pain. The objective of this study was to examine the regulation of Kir4.1 on the expression of pannexin 3 (Panx3) in the trigeminal ganglion (TG) and the underlying mechanism in the context of orofacial neuropathic pain caused by chronic constriction injury of the infraorbital nerve (CCI-ION). The study observed a significant increase in Panx3 expression in the TG of mice with CCI-ION. Inhibition of Panx3 in the TG of CCI-ION mice resulted in alleviation of orofacial mechanical allodynia. Furthermore, conditional knockdown (CKD) of Kir4.1 in the TG of both male and female mice led to mechanical allodynia and upregulation of Panx3 expression. Conversely, overexpression of Kir4.1 decreased Panx3 levels in the TG and relieved mechanical allodynia in CCI-ION mice. In addition, silencing Kir4.1 in satellite glial cells (SGCs) decreased Panx3 expression and increased the phosphorylation of P38 MAPK. Moreover, silencing Kir4.1 in SGCs increased the levels of reactive oxygen species (ROS). The elevated phosphorylation of P38 MAPK resulting from Kir4.1 silencing was inhibited by using a superoxide scavenger known as the tempol. Silencing Panx3 in the TG in vivo attenuated the mechanical allodynia caused by Kir4.1 CKD. In conclusion, these findings suggest that the reduction of Kir4.1 promotes the expression of Panx3 by activating the ROS-P38 MAPK signalling pathway, thus contributing to the development of orofacial neuropathic pain.

The neuropathobiology of multiple sclerosis

Chronic low-grade inflammation and neuronal deregulation are two components of a smoldering disease activity that drives the progression of disability in people with multiple sclerosis (MS). Although several therapies exist to dampen the acute inflammation that drives MS relapses, therapeutic options to halt chronic disability progression are a major unmet clinical need. The development of such therapies is hindered by our limited understanding of the neuron-intrinsic determinants of resilience or vulnerability to inflammation. In this Review, we provide a neuron-centric overview of recent advances in deciphering neuronal response patterns that drive the pathology of MS. We describe the inflammatory CNS environment that initiates neurotoxicity by imposing ion imbalance, excitotoxicity and oxidative stress, and by direct neuro-immune interactions, which collectively lead to mitochondrial dysfunction and epigenetic dysregulation. The neuronal demise is further amplified by breakdown of neuronal transport, accumulation of cytosolic proteins and activation of cell death pathways. Continuous neuronal damage perpetuates CNS inflammation by activating surrounding glia cells and by directly exerting toxicity on neighbouring neurons. Further, we explore strategies to overcome neuronal deregulation in MS and compile a selection of neuronal actuators shown to impact neurodegeneration in preclinical studies. We conclude by discussing the therapeutic potential of targeting such neuronal actuators in MS, including some that have already been tested in interventional clinical trials.

ICA-27243 improves neuromuscular function and preserves motoneurons in the transgenic SOD1G93A mice

Amyotrophic lateral sclerosis (ALS) is a progressive neurodegenerative disease characterized by the death of upper and lower motor neurons (MNs). Excessive neuronal excitability has been implicated in MN degeneration; thus, modulation of hyperexcitability appears as a promising therapeutic strategy. Potassium channels are attractive targets since they can be activated at subthreshold voltages and can regulate neuronal excitability. In this study, we assayed the effects of N-(6-Chloro-pyridin-3-yl)-3,4-difluorobenzamide compound, known as ICA-27243, as a potential treatment for ALS. ICA-27243 is a highly selective Kv7.2/7.3 opener used mainly in epilepsy models. In the in vitro model of spinal cord organotypic cultures (SCOCs) exposed to acute excitotoxicity, ICA-27243 prevented MN degeneration at a dose-of 10 ​μM. Administration of ICA-27243 to transgenic SOD1G93A ALS mice improved the decline of neuromuscular function, maintained locomotion and coordination in the rotarod, decreased spinal MN death and attenuated glial reactivity. In conclusion, we report here for the first time that ICA-27243 is an effective treatment for ALS, emphasizing the potential of targeting Kv channels to reduce neuronal hyperexcitability.

Acriflavine, a HIF-1 inhibitor, preserves vision in an experimental autoimmune encephalomyelitis model of optic neuritis

Introduction

Optic neuritis (ON) is often an early sign of multiple sclerosis (MS), and recent studies show a link between HIF-1 pathway activation and inflammation. This study aimed to determine if inhibition of the HIF-1 pathway using the HIF-1a antagonist acriflavine (ACF) can reduce clinical progression and rescue the ocular phenotype in an experimental autoimmune encephalomyelitis (EAE) ON model.

Methods

EAE-related ON was induced in 60 female C57BL/6J mice by immunization with MOG33-55, and 20 EAE mice received daily systemic injections of ACF at 5 mg/kg. Changes in the visual function and structure of ACF-treated EAE mice were compared to those of placebo-injected EAE mice and naïve control mice.

Results

ACF treatment improved motor-sensory impairment along with preserving visual acuity and optic nerve function. Analysis of retinal ganglion cell complex alsoshowed preserved thickness correlating with increased survival of retinal ganglion cells and their axons. Optic nerve cell infiltration and magnitude of demyelination were decreased in ACF-treated EAE mice. Subsequent in vitro studies revealed improvements not only attributed to the inhibition of HIF-1 butalso to previously unappreciated interaction with the eIF2a/ATF4 axis in the unfolded protein response pathway.

Discussion

This study suggests that ACF treatment is effective in an animal model of MS via its pleiotropic effects on the inhibition of HIF-1 and UPR signaling, and it may be a viable approach to promote rehabilitation in MS.

Mechanisms of axonal support by oligodendrocyte-derived extracellular vesicles

Extracellular vesicles (EVs) have recently emerged as versatile elements of cell communication in the nervous system, mediating tissue homeostasis. EVs influence the physiology of their target cells via horizontal transfer of molecular cargo between cells and by triggering signalling pathways. In this Review, we discuss recent work revealing that EVs mediate interactions between oligodendrocytes and neurons, which are relevant for maintaining the structural integrity of axons. In response to neuronal activity, myelinating oligodendrocytes release EVs, which are internalized by neurons and provide axons with key factors that improve axonal transport, stress resistance and energy homeostasis. Glia-to-neuron transfer of EVs is thus a crucial facet of axonal preservation. When glial support is impaired, axonal integrity is progressively lost, as observed in myelin-related disorders, other neurodegenerative diseases and with normal ageing. We highlight the mechanisms that oligodendroglial EVs use to sustain axonal integrity and function.

Seeking neuroprotection in multiple sclerosis: an ongoing challenge

Multiple sclerosis (MS) is an autoimmune disease of the CNS, featuring inflammation and demyelination with variable recovery. In this issue of the JCI, Kapell, Fazio, and authors address the potential for targeting neuron-oligodendrocyte potassium shuttling at the nodes of Ranvier as a neuroprotective strategy during inflammatory demyelination of the CNS in experimental MS. Their extensive and impressive study could serve as a template for defining the physiologic properties of a putative protective pathway. The authors examined MS features in existent disease models, investigated the impact of pharmacologic intervention, and evaluated its status in tissues from patients with MS. We await future studies that will tackle the challenge of translating these findings into a clinical therapy.