Lack of astrocytes hinders parenchymal oligodendrocyte precursor cells from reaching a myelinating state in osmolyte-induced demyelination

Star power: harnessing the reactive astrocyte response to promote remyelination in multiple sclerosis

Astrocytes are indispensable for central nervous system development and homeostasis. In response to injury and disease, astrocytes are integral to the immunological- and the, albeit limited, repair response. In this review, we will examine some of the functions reactive astrocytes play in the context of multiple sclerosis and related animal models. We will consider the heterogeneity or plasticity of astrocytes and the mechanisms by which they promote or mitigate demyelination. Finally, we will discuss a set of biomedical strategies that can stimulate astrocytes in their promyelinating response.

Astrocyte signaling and interactions in Multiple Sclerosis

Multiple Sclerosis (MS) is a common cause of impairment in working-aged adults. MS is characterized by neuroinflammation and infiltration of peripheral immune cells to the brain, which cause myelin loss and death of oligodendrocytes and neurons. Many studies on MS have focused on the peripheral immune sources of demyelination and repair. However, recent studies revealed that a glial cell type, the astrocytes, undergo robust morphological and transcriptomic changes that contribute significantly to demyelination and myelin repair. Here, we discuss recent findings elucidating signaling modalities that astrocytes acquire or lose in MS and how these changes alter the interactions of astrocytes with other nervous system cell types.

Thalamic Neuron Resilience during Osmotic Demyelination Syndrome (ODS) Is Revealed by Primary Cilium Outgrowth and ADP-ribosylation factor-like protein 13B Labeling in Axon Initial Segment

A murine osmotic demyelinating syndrome (ODS) model was developed through chronic hyponatremia, induced by desmopressin subcutaneous implants, followed by precipitous sodium restoration. The thalamic ventral posterolateral (VPL) and ventral posteromedial (VPM) relay nuclei were the most demyelinated regions where neuroglial damage could be evidenced without immune response. This report showed that following chronic hyponatremia, 12 h and 48 h time lapses after rebalancing osmolarity, amid the ODS-degraded outskirts, some resilient neuronal cell bodies built up primary cilium and axon hillock regions that extended into axon initial segments (AIS) where ADP-ribosylation factor-like protein 13B (ARL13B)-immunolabeled rod-like shape content was revealed. These AIS-labeled shaft lengths appeared proportional with the distance of neuronal cell bodies away from the ODS damaged epicenter and time lapses after correction of hyponatremia. Fine structure examination verified these neuron abundant transcriptions and translation regions marked by the ARL13B labeling associated with cell neurotubules and their complex cytoskeletal macromolecular architecture. This necessitated energetic transport to organize and restore those AIS away from the damaged ODS core demyelinated zone in the murine model. These labeled structures could substantiate how thalamic neuron resilience occurred as possible steps of a healing course out of ODS.

Fructose: A New Variable to Consider in SIADH and the Hyponatremia Associated With Long-Distance Running?

Fructose has recently been proposed to stimulate vasopressin secretion in humans. Fructose-induced vasopressin secretion is not only postulated to result from ingestion of fructose-containing drinks but may also occur from endogenous fructose production via activation of the polyol pathway. This raises the question of whether fructose might be involved in some cases of vasopressin-induced hyponatremia, especially in situations where the cause is not fully known such as in the syndrome of inappropriate secretion of diuretic hormone (SIADH) and exercise-associated hyponatremia, which has been observed in marathon runners. Here we discuss the new science of fructose and vasopressin, and how it may play a role in some of these conditions, as well as in the complications associated with rapid treatment (such as the osmotic demyelination syndrome). Studies to test the role of fructose could provide new pathophysiologic insights as well as novel potential treatment strategies for these common conditions.

The NG2-glia is a potential target to maintain the integrity of neurovascular unit after acute ischemic stroke

The neurovascular unit (NVU) plays a critical role in health and disease. In the current review, we discuss the critical role of a class of neural/glial antigen 2 (NG2)-expressing glial cells (NG2-glia) in regulating NVU after acute ischemic stroke (AIS). We first introduce the role of NG2-glia in the formation of NVU during development as well as aging-induced damage to NVU and accompanying NG2-glia change. We then discuss the reciprocal interactions between NG2-glia and the other component cells of NVU, emphasizing the factors that could influence NG2-glia. Damage to the NVU integrity is the pathological basis of edema and hemorrhagic transformation, the most dreaded complication after AIS. The role of NG2-glia in AIS-induced NVU damage and the effect of NG2-glia transplantation on AIS-induced NVU damage are summarized. We next discuss the role of NG2-glia and the effect of NG2-glia transplantation in oligodendrogenesis and white matter repair as well as angiogenesis which is associated with the outcome of the patients after AIS. Finally, we review the current strategies to promote NG2-glia proliferation and differentiation and propose to use the dental pulp stem cells (DPSC)-derived exosome as a promising strategy to reduce AIS-induced injury and promote repair through maintaining the integrity of NVU by regulating endogenous NG2-glia proliferation and differentiation.

Central Pontine Myelinolysis With Carbamazepine-Induced Syndrome of Inappropriate Antidiuretic Hormone and Its Management: A Case Report and Literature Review

Aggressive treatment of hyper or hypoosmolar conditions can trigger osmotic demyelination syndrome. We describe the case of a 53-year-old male who began using carbamazepine to treat bipolar affective disorder and was later diagnosed with carbamazepine-induced syndrome of inappropriate antidiuretic hormone secretion. The patient's mental state gradually improved once the hyponatremia was corrected using 3% normal saline and supportive therapy. The patient presented to the outpatient clinic with confusion and altered sensorium. Brain computed tomography showed diffuse cerebral atrophy and periventricular ischemia demyelination alterations, and magnetic resonance imaging showed an enhanced section in the brainstem that included the pons, suggesting osmotic demyelination alterations. Ventilatory support and supportive therapy were initiated, and hyponatremia was rectified. Although the patient did well with the treatment, his prognosis was still dismal, so he was sent home with instructions to follow up.

Adaptation of the Brain to Hyponatremia and Its Clinical Implications

Hyponatremia is the most common electrolyte disorder, occurring in up to 25% of hospitalized patients. Hypo-osmotic hyponatremia when severe and left untreated invariably results in cell swelling, which can lead to fatal consequences, especially in the central nervous system. The brain is particularly vulnerable to the consequences of decreased extracellular osmolarity; because of being encased in the rigid skull, it cannot withstand persistent swelling. Moreover, serum sodium is the major determinant of extracellular ionic balance, which in turn governs crucial brain functions such as the excitability of neurons. For these reasons, the human brain has developed specific ways to adapt to hyponatremia and prevent brain edema. On the other hand, it is well known that rapid correction of chronic and severe hyponatremia can lead to brain demyelination, a condition known as osmotic demyelination syndrome. In this paper, we will discuss the mechanisms of brain adaptation to acute and chronic hyponatremia and the neurological symptoms of these conditions as well as the pathophysiology and prevention of osmotic demyelination syndrome.

Differential transcriptomic changes in the central nervous system and urinary bladders of mice infected with a coronavirus

Multiple sclerosis (MS) often leads to the development of neurogenic lower urinary tract symptoms (LUTS). We previously characterized neurogenic bladder dysfunction in a mouse model of MS induced by a coronavirus, mouse hepatitis virus (MHV). The aim of the study was to identify genes and pathways linking neuroinflammation in the central nervous system with urinary bladder (UB) dysfunction to enhance our understanding of the mechanisms underlying LUTS in demyelinating diseases. Adult C57BL/6 male mice (N = 12) received either an intracranial injection of MHV (coronavirus-induced encephalomyelitis, CIE group), or sterile saline (control group). Spinal cord (SC) and urinary bladders (UB) were collected from CIE mice at 1 wk and 4 wks, followed by RNA isolation and NanoString nCounter Neuroinflammation assay. Transcriptome analysis of SC identified a significantly changed expression of >150 genes in CIE mice known to regulate astrocyte, microglia and oligodendrocyte functions, neuroinflammation and immune responses. Two genes were significantly upregulated (Ttr and Ms4a4a), and two were downregulated (Asb2 and Myct1) only in the UB of CIE mice. Siglec1 and Zbp1 were the only genes significantly upregulated in both tissues, suggesting a common transcriptomic link between neuroinflammation in the CNS and neurogenic changes in the UB of CIE mice.

Myelin repair is fostered by the corticosteroid medrysone specifically acting on astroglial subpopulations

Background

Multiple sclerosis is characterised by inflammation, oligodendrocyte loss and axonal demyelination and shows an additional impact on astrocytes, and their polarization. Although a certain degree of spontaneous myelin repair can be observed, disease progression, and aging impair regeneration efforts highlighting the need to better understand glial cell dynamics to establish specific regenerative treatments.

Methods

Applying a chronic demyelination model, we here analysed demyelination and remyelination related effects on astrocytes and stem cell niches and studied the consequences of medrysone application on myelin repair, and astrocyte polarization.

Findings

Medrysone induced recovery of mature oligodendrocytes, myelin expression and node formation. In addition, C3d/S100a10 co-expression in astrocytes was enhanced. Moreover, Timp1 expression in C3d positive astrocytes revealed another astrocytic phenotype with a myelination promoting character.

Interpretation

Based on these findings, specific astrocyte subpopulations are suggested to act in a myelin regenerative way and manner the regulation of which can be positively modulated by this corticosteroid.

Funding

This work was supported by the Jürgen Manchot Stiftung, the Research Commission of the medical faculty of the Heinrich-Heine-University of Düsseldorf, the Christiane and Claudia Hempel Foundation for clinical stem cell research and the James and Elisabeth Cloppenburg, Peek and Cloppenburg Düsseldorf Stiftung.

A Novel Splice Variant of BCAS1 Inhibits β-Arrestin 2 to Promote the Proliferation and Migration of Glioblastoma Cells, and This Effect Was Blocked by Maackiain

Brain-enriched myelin-associated protein 1 (BCAS1) is frequently highly expressed in human cancer, but its detailed function is unclear. Here, we identified a novel splice variant of the BCAS1 gene in glioblastoma multiforme (GBM) named BCAS1-SV1. The expression of BCAS1-SV1 was weak in heathy brain cells but high in GBM cell lines. The overexpression of BCAS1-SV1 significantly increased the proliferation and migration of GBM cells, whereas the RNA-interference-mediated knockdown of BCAS1-SV1 reduced proliferation and migration. Moreover, using a yeast-two hybrid assay, immunoprecipitation, and immunofluorescence staining, we confirmed that β-arrestin 2 is an interaction partner of BCAS1-SV1 but not BCAS1. The downregulation of β-arrestin 2 directly enhanced the malignancy of GBM and abrogated the effects of BCAS1-SV1 on GBM cells. Finally, we used a yeast two-hybrid-based growth assay to identify that maackiain (MK) is a potential inhibitor of the interaction between BCAS1-SV1 and β-arrestin 2. MK treatment lessened the proliferation and migration of GBM cells and prolonged the lifespan of tumor-bearing mice in subcutaneous xenograft and intracranial U87-luc xenograft models. This study provides the first evidence that the gain-of-function BCAS1-SV1 splice variant promotes the development of GBM by suppressing the β-arrestin 2 pathway and opens up a new therapeutic perspective in GBM.

Reactive Astrocytes Derived From Human Induced Pluripotent Stem Cells Suppress Oligodendrocyte Precursor Cell Differentiation

Astrocytes are instrumental in maintaining central nervous system (CNS) homeostasis and responding to injury. A major limitation of studying neurodegenerative diseases like multiple sclerosis (MS) is lack of human pathological specimens obtained during the acute stages, thereby relegating research to post-mortem specimens obtained years after the initiation of pathology. Rodent reactive astrocytes have been shown to be cytotoxic to neurons and oligodendrocytes but may differ from human cells, especially in diseases with genetic susceptibility. Herein, we purified human CD49f⁺ astrocytes from induced pluripotent stem cells derived from individual patient and control peripheral leukocytes. We compared TNF and IL1α stimulated human reactive astrocytes from seven persons with MS and six non-MS controls and show their transcriptomes are remarkably similar to those described in rodents. The functional effect of astrocyte conditioned media (ACM) was examined in a human oligodendrocyte precursor cell (OPC) line differentiation assay. ACM was not cytotoxic to the OPCs but robustly inhibited the myelin basic protein (MBP) reporter. No differences were seen between MS and control stimulated astrocytes at either the transcript level or in ACM mediated OPC suppression assays. We next used RNAseq to interrogate differentially expressed genes in the OPC lines that had suppressed differentiation from the human ACM. Remarkably, not only was OPC differentiation and myelin gene expression suppressed, but we observed induction of several immune pathways in OPCs exposed to the ACM. These data support the notion that reactive astrocytes can inhibit OPC differentiation thereby limiting their remyelination capacity, and that OPCs take on an immune profile in the context of inflammatory cues.

Effects and mechanisms of probucol on aging-related hippocampus-dependent cognitive impairment

BACKGROUND

In the present study, we aimed to investigate the effects of probucol on aging-related hippocampus-dependent cognitive impairment and explore the potential mechanisms.

METHODS

D-galactose (100 mg/kg, once daily for 6 weeks) was subcutaneously injected to induce aging in mice. Then the mice were administered with probucol or vehicle once a day for 2 weeks. The hippocampus-related cognition was evaluated with Morris water maze test, novel object recognition test, and contextual fear conditioning test. Moreover, synaptic plasticity was assessed, and RNA-sequencing was applied to further explore the molecular mechanisms.

RESULTS

Aging mice induced by D-galactose showed conspicuous learning and memory impairment, which was significantly ameliorated by probucol. Meanwhile, probucol enhanced the spine density and dendritic branches, improved long-term potentiation, and increased the expression of PSD95 of aging mice. Probucol regulated 70 differentially expressed genes compared to D-galactose group, of which 38 genes were upregulated and 32 genes were downregulated. At last, RNA-sequencing results were verified by quantitative reverse transcription-polymerase chain reaction.

CONCLUSIONS

Probucol improved learning and memory in aging mice through enhancing synaptic plasticity and regulating gene expression, indicating the potential application of probucol to prevent and treat aging-related disorders.

A primary cilium in oligodendrocytes: a fine structure signal of repairs in thalamic Osmotic Demyelination Syndrome (ODS)

A murine osmotic demyelination syndrome (ODS) model of the central nervous system included the relay thalamic ventral posterolateral (VPL) and ventral posteromedial (VPM) nuclei. Morphologic comparisons between treatments have revealed oligodendrocyte changes and, already 12 hours following the osmolality restoration, some heavily contrasted oligodendrocytes formed a unique intracellular primary cilium. This unique structure, found in vivo, in mature CNS oligodendrocytes, could account for a local awakening of some of the developmental proteome as it can be expressed in oligodendrocyte precursor cells. This resilience accompanied the emergence of arl13b protein expression along with restoration of nerve cell body axon hillocks shown in a previous issue of this journal. Additionally, the return of several thalamic oligodendrocyte fine features (nucleus, organelles) was shown 36 h later, including some mitosis. Those cell restorations and recognized translational activities comforted that local repairs could again take place, due to oligodendrocyte resilience after ODS instead or added to a postulated immigration of oligodendrocyte precursor cells distant from the sites of myelinolysis.