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Osmotic Pump-based Drug-delivery for <em>In Vivo</em> Remyelination Research on the Central Nervous System

Demyelination has been identified in not only multiple sclerosis (MS), but also other central nervous system diseases such as Alzheimer's disease and ...

Third Military Medical University

As the most abundant gap junction protein in the central nervous system (CNS), astrocytic connexin 43 (Cx43) maintains astrocyte network homeostasis, affects oligodendroglial development and participates in CNS pathologies as well as injury progression. However, its role in remyelination is not yet fully understood. To address this issue, we used astrocyte-specific Cx43 conditional knockout (Cx43 cKO) mice generated through the use of a hGFAP-cre promoter, in combination with mice carrying a floxed Cx43 allele that were subjected to lysolecithin so as to induce demyelination. We found no significant difference in the demyelination of the corpus callosum between Cx43 cKO mice and their non-cre littermate controls, while the remyelination process in Cx43 cKO mice was accelerated. Moreover, an increased number of mature oligodendrocytes and an unaltered number of oligodendroglial lineage cells were found in Cx43 cKO mouse lesions. This indicates that oligodendrocyte precursor cell (OPC) differentiation was facilitated by astroglial Cx43 depletion as remyelination progressed. Underlying the latter, there was a down-regulated glial activation and modulated local inflammation as well as a reduction of myelin debris in Cx43 cKO mice. Importantly, 2 weeks of orally administrating boldine, a natural alkaloid that blocks Cx hemichannel activity in astrocytes without affecting gap junctional communication, obviously modulated local inflammation and promoted remyelination. Together, the data suggest that the astrocytic Cx43 hemichannel is negatively involved in the remyelination process by favoring local inflammation. Consequently, inhibiting Cx43 hemichannel functionality may be a potential therapeutic approach for demyelinating diseases in the CNS.

Connexin 43 deletion in astrocytes promotes CNS remyelination by modulating local inflammation.

Epigenetic alterations and impaired oligodendroglial myelination in the prefrontal cortex have been shown to correlate with behavioral and cognitive dysfunctions in social deprivation. Our previous study demonstrated that quetiapine, an atypical antipsychotic, could promote oligodendroglial differentiation and myelination. However, whether and how quetiapine could be beneficial in modulating aberrant epigenetic alterations in oligodendroglial cells and relieving behavioral alterations from social isolation is unknown. In this study, quetiapine was orally administered in adolescent mice undergoing mild stress of social isolation. We firstly confirmed that social isolation during a novel adolescent period could impair sociability, but not locomotive behaviors in mice. Moreover, quetiapine alleviated myelin deficits, and increased levels of histone methylation (H3K9me3) in mature oligodendroglia in the prefrontal cortex of socially isolated mice. Strikingly, quetiapine treatment significantly increased locomotive activity, and successfully reversed social avoidance behavior of the socially isolated mice. Taken together, our data suggest that quetiapine may rescue behavioral changes from social isolation through modulating epigenetic status toward the beneficial direction for oligodendroglial maturation, providing new insights into the pharmacological mechanism of quetiapine for mental illnesses.

Quetiapine Modulates Histone Methylation Status in Oligodendroglia and Rescues Adolescent Behavioral Alterations of Socially Isolated Mice.

Oligodendroglial lineage cells go through a series of morphological changes before myelination. Prior to myelination, cell processes and membrane structures enlarge by approximately 7,000 times, which is required to support axonal wrapping and myelin segment formation. Failure of these processes leads to maldevelopment and impaired myelination. Quetiapine, an atypical antipsychotic drug, was proved to promote oligodendroglial differentiation and (re)myelination, pending detailed effects and regulatory mechanism. In this study, we showed that quetiapine promotes morphological maturation of oligodendroglial lineage cells and myelin segment formation, and a short-term quetiapine treatment is sufficient to induce these changes. To uncover the underlying mechanism, we examined the effect of quetiapine on the Oligodendrocyte transcription factor 1 (Olig1). We found that quetiapine upregulates Olig1 expression level and promotes nuclear Olig1 translocation to the cytosol, where it functions not as a transcription modulator, but in a way that highly correlates with oligodendrocyte morphological transformation. In addition, quetiapine treatment reverses the negative regulatory effect of the Olig1-regulated G protein-coupled receptor 17 (GPR17) on oligodendroglial morphological maturation. Our results demonstrate that quetiapine enhances oligodendroglial differentiation and myelination by promoting cell morphological transformation. This would shed light on the orchestration of oligodendroglia developmental mechanisms, and provides new targets for further therapeutic research.

Quetiapine promotes oligodendroglial process outgrowth and membrane expansion by orchestrating the effects of Olig1.

Astrocyte maldevelopment is implicated in various neuropsychiatric diseases associated with early life stress. However, the underlying astrocytopathy mechanism, which can result in the psychiatric symptoms, remains unclear. In this study, it is shown that a reduced oligodendrocyte precursor cell (OPC) population accompanies hindered hippocampal astrocytic development in an improved parental isolation mouse model, and that the loss of OPCs suppresses astrocytic network formation and activity. It is further demonstrated that OPC-derived Wnt ligands, in particular Wnt7b, are required for Wnt/β-catenin pathway-mediated astrocytic development and subsequent effects related to neuronal function. In addition, focal replenishment of Wnt7a/b is sufficient to rescue astrocytic maldevelopment. These results elucidate a Wnt-paracrine-dependent but myelin-independent role of OPCs in regulating astrocytic development, which provides a unique insight into the astrocytopathy mechanism in early life stress, and can be implicated in the pathogenesis of human early life stress-related neuropsychiatric disorders.

Reduced Oligodendrocyte Precursor Cell Impairs Astrocytic Development in Early Life Stress.

Oligodendrocyte (OL) maturation arrest in human white matter injury contributes significantly to the failure of endogenous remyelination in multiple sclerosis (MS) and newborn brain injuries such as hypoxic ischemic encephalopathy (HIE) that cause cerebral palsy. In this study, we identify an oligodendroglial-intrinsic factor that controls OL maturation specifically in the setting of injury. We find a requirement for the ring finger protein Rnf43 not in normal development but in neonatal hypoxic injury and remyelination in the adult mammalian CNS. Rnf43, but not the related Znrf3, is potently activated by Wnt signaling in OL progenitor cells (OPCs) and marks activated OPCs in human MS and HIE. Rnf43 is required in an injury-specific context, and it promotes OPC differentiation through negative regulation of Wnt signal strength in OPCs at the level of Fzd1 receptor presentation on the cell surface. Inhibition of Fzd1 using UM206 promotes remyelination following ex vivo and in vivo demyelinating injury.

Xiaorui Wang

Third Military Medical University

Osmotic Pump-based Drug-delivery for In Vivo Remyelination Research on the Central Nervous System