Subventricular zone microglia transcriptional networks

Establishment of a high-content compatible platform to assess effects of monocyte-derived factors on neural stem cell proliferation and differentiation

During neuroinflammation, monocytes that infiltrate the central nervous system (CNS) may contribute to regenerative processes depending on their activation status. However, the extent and mechanisms of monocyte-induced CNS repair in patients with neuroinflammatory diseases remain largely unknown, partly due to the lack of a fully human assay platform that can recapitulate monocyte-neural stem cell interactions within the CNS microenvironment. We therefore developed a human model system to assess the impact of monocytic factors on neural stem cells, establishing a high-content compatible assay for screening monocyte-induced neural stem cell proliferation and differentiation. The model combined monocytes isolated from healthy donors and human embryonic stem cell derived neural stem cells and integrated both cell-intrinsic and -extrinsic properties. We identified CNS-mimicking culture media options that induced a monocytic phenotype resembling CNS infiltrating monocytes, while allowing adequate monocyte survival. Monocyte-induced proliferation, gliogenic fate and neurogenic fate of neural stem cells were affected by the conditions of monocytic priming and basal neural stem cell culture as extrinsic factors as well as the neural stem cell passage number as an intrinsic neural stem cell property. We developed a high-content compatible human in vitro assay for the integrated analysis of monocyte-derived factors on CNS repair.

Adult Neoneurogenesis and Oligodendrogenesis in Multiple Sclerosis: A Systematic Review of Human and Animal Studies

Introduction: The subventricular zone promotes remyelination through activation differentiation of oligodendroglial precursor cells (OPCs) and neural stem cells (NSCs) into mature oligodendrocytes and thus in the adult brain. In multiple sclerosis (MS) this regenerative capability is halted resulting in neurodegeneration. We aimed to systematically search and synthesize evidence on mechanisms and phenomena associated with subventricular zone (SVZ) dysfunction in MS. Materials and Methods: Our systematic review was reported according to the PRISMA-ScR statement. MEDLINE, SCOPUS, ProQuest, and Google Scholar were searched using the terms "subventricular zone" and "multiple sclerosis," including English-written in vivo and postmortem studies. Results: Twenty studies were included. Thirteen studies on models of experimental autoimmune encephalomyelitis (EAE) reported among others strong stathmin immunoreactivity in the SVZ of EAE models, the role of MOG immunization in neurogenesis impairment, the effect of parenchymal OPCs and NSCs in myelin repair, and the importance of ependymal cells (E1/E2) and ciliated B1 cells in SVZ stem cell signaling. CXCR4 signaling and transcriptional profiles of SVZ microglia, Gli1 pathway, and galactin-3 were also explored. Studies in humans demonstrated microstructural SVZ damage in progressive MS and the persistence of black holes near the SVZ, whereas postmortem confirmed the generation of polysialic acid-neural cell adhesion molecule and NG2-positive progenitors through SVZ activation, SVZ stathmin immunoreactivity, Shh pathway, and Gal-3 upregulation. Discussion: Oligodendrogenesis defects translate to reduced remyelination, a hallmark of MS that determines its end-phenotype and disease course. Conclusion: The role of inflammation and subsequent SVZ microenvironment disruption is evident in MS pathology.

Stat1 is an inducible transcriptional repressor of neural stem cells self-renewal program during neuroinflammation

A central issue in regenerative medicine is understanding the mechanisms that regulate the self-renewal of endogenous stem cells in response to injury and disease. Interferons increase hematopoietic stem cells during infection by activating STAT1, but the mechanisms by which STAT1 regulates intrinsic programs in neural stem cells (NSCs) during neuroinflammation is less known. Here we explored the role of STAT1 on NSC self-renewal. We show that overexpressing Stat1 in NSCs derived from the subventricular zone (SVZ) decreases NSC self-renewal capacity while Stat1 deletion increases NSC self-renewal, neurogenesis, and oligodendrogenesis in isolated NSCs. Importantly, we find upregulation of STAT1 in NSCs in a mouse model of multiple sclerosis (MS) and an increase in pathological T cells expressing IFN-γ rather than interleukin 17 (IL-17) in the cerebrospinal fluid of affected mice. We find IFN-γ is superior to IL-17 in reducing proliferation and precipitating an abnormal NSC phenotype featuring increased STAT1 phosphorylation and Stat1 and p16ink4a gene expression. Notably, Stat1-/- NSCs were resistant to the effect of IFN-γ. Lastly, we identified a Stat1-dependent gene expression profile associated with an increase in the Sox9 transcription factor, a regulator of self-renewal. Stat1 binds and transcriptionally represses Sox9 in a transcriptional luciferase assay. We conclude that Stat1 serves as an inducible checkpoint for NSC self-renewal that is upregulated during chronic brain inflammation leading to decreased self-renewal. As such, Stat1 may be a potential target to modulate for next generation therapies to prevent progression and loss of repair function in NSCs/neural progenitors in MS.

The good, the bad, and the opportunities of the complement system in neurodegenerative disease

The complement cascade is a critical effector mechanism of the innate immune system that contributes to the rapid clearance of pathogens and dead or dying cells, as well as contributing to the extent and limit of the inflammatory immune response. In addition, some of the early components of this cascade have been clearly shown to play a beneficial role in synapse elimination during the development of the nervous system, although excessive complement-mediated synaptic pruning in the adult or injured brain may be detrimental in multiple neurogenerative disorders. While many of these later studies have been in mouse models, observations consistent with this notion have been reported in human postmortem examination of brain tissue. Increasing awareness of distinct roles of C1q, the initial recognition component of the classical complement pathway, that are independent of the rest of the complement cascade, as well as the relationship with other signaling pathways of inflammation (in the periphery as well as the central nervous system), highlights the need for a thorough understanding of these molecular entities and pathways to facilitate successful therapeutic design, including target identification, disease stage for treatment, and delivery in specific neurologic disorders. Here, we review the evidence for both beneficial and detrimental effects of complement components and activation products in multiple neurodegenerative disorders. Evidence for requisite co-factors for the diverse consequences are reviewed, as well as the recent studies that support the possibility of successful pharmacological approaches to suppress excessive and detrimental complement-mediated chronic inflammation, while preserving beneficial effects of complement components, to slow the progression of neurodegenerative disease.

Role of EGFR in the Nervous System

Epidermal growth factor receptor (EGFR) is the first discovered member of the receptor tyrosine kinase superfamily and plays a fundamental role during embryogenesis and in adult tissues, being involved in growth, differentiation, maintenance and repair of various tissues and organs. The role of EGFR in the regulation of tissue development and homeostasis has been thoroughly investigated and it has also been demonstrated that EGFR is a driver of tumorigenesis. In the nervous system, other growth factors, and thus other receptors, are important for growth, differentiation and repair of the tissue, namely neurotrophins and neurotrophins receptors. For this reason, for a long time, the role of EGFR in the nervous system has been underestimated and poorly investigated. However, EGFR is expressed both in the central and peripheral nervous systems and it has been demonstrated to have specific important neurotrophic functions, in particular in the central nervous system. This review discusses the role of EGFR in regulating differentiation and functions of neurons and neuroglia. Furthermore, its involvement in regeneration after injury and in the onset of neurodegenerative diseases is examined.

Convergence of human cellular models and genetics to study neural stem cell signaling to enhance central nervous system regeneration and repair

Human central nervous system (CNS) regeneration is considered the holy grail of neuroscience research, and is one of the most pressing and difficult questions in biology and science. Despite more than 20 years of work in the field of neural stem cells (NSCs), the area remains in its infancy as our understanding of the fundamental mechanisms that can be leveraged to improve CNS regeneration in neurological diseases is still growing. Here, we focus on the recent lessons from lower organism CNS regeneration genetics and how such findings are starting to illuminate our understanding of NSC signaling pathways in humans. These findings will allow us to improve upon our knowledge of endogenous NSC function, the utility of exogenous NSCs, and the limitations of NSCs as therapeutic vehicles for providing relief from devastating human neurological diseases. We also discuss the limitations of activating NSC signaling for CNS repair in humans, especially the potential for tumor formation. Finally, we will review the recent advances in new culture techniques, including patient-derived cells and cerebral organoids to model the genetic regulation of signaling pathways controlling the function of NSCs during injury and disease states.

Endogenous spinal cord stem cells in multiple sclerosis and its animal model

The adult mammalian spinal cord (SC) harbors neural stem cells (NSCs). The SC-NSCs are mostly quiescent during physiological conditions but are quickly activated in traumatic injury models. The SC-NSCs generate mostly glia, but are able to differentiate into neurons when affected by favourable conditions. An example is the inflammatory milieu in the SC of rat EAE, where the SC-NSCs migrate into demyelinated lesions and give rise to both glia and neurons. In MS, cells with progenitor phenotypes accumulate in inflammatory lesions both in brain and SC, but the extent to which these cells contribute to repair remains to be revealed.

Chi3l3 induces oligodendrogenesis in an experimental model of autoimmune neuroinflammation

In demyelinating diseases including multiple sclerosis (MS), neural stem cells (NSCs) can replace damaged oligodendrocytes if the local microenvironment supports the required differentiation process. Although chitinase-like proteins (CLPs) form part of this microenvironment, their function in this differentiation process is unknown. Here, we demonstrate that murine Chitinase 3-like-3 (Chi3l3/Ym1), human Chi3L1 and Chit1 induce oligodendrogenesis. In mice, Chi3l3 is highly expressed in the subventricular zone, a stem cell niche of the adult brain, and in inflammatory brain lesions during experimental autoimmune encephalomyelitis (EAE). We find that silencing Chi3l3 increases severity of EAE. We present evidence that in NSCs Chi3l3 activates the epidermal growth factor receptor (EGFR), thereby inducing Pyk2-and Erk1/2- dependent expression of a pro-oligodendrogenic transcription factor signature. Our results implicate CLP-EGFR-Pyk2-MEK-ERK as a key intrinsic pathway controlling oligodendrogenesis.

Microglia Responses in Acute and Chronic Neurological Diseases: What Microglia-Specific Transcriptomic Studies Taught (and did Not Teach) Us

Over the last decade, microglia have been acknowledged to be key players in central nervous system (CNS) under both physiological and pathological conditions. They constantly survey the CNS environment and as immune cells, in pathological contexts, they provide the first host defense and orchestrate the immune response. It is well recognized that under pathological conditions microglia have both sequential and simultaneous, beneficial and detrimental effects. Cell-specific transcriptomics recently became popular in Neuroscience field allowing concurrent monitoring of the expression of numerous genes in a given cell population. Moreover, by comparing two or more conditions, these approaches permit to unbiasedly identify deregulated genes and pathways. A growing number of studies have thus investigated microglial transcriptome remodeling over the course of neuropathological conditions and highlighted the molecular diversity of microglial response to different diseases. In the present work, we restrict our review to microglia obtained directly from in vivo samples and not cell culture, and to studies using whole-genome strategies. We first critically review the different methods developed to decipher microglia transcriptome. In particular, we compare advantages and drawbacks of flow cytometry and laser microdissection to isolate pure microglia population as well as identification of deregulated microglial genes obtained via RNA sequencing (RNA-Seq) vs. microarrays approaches. Second, we summarize insights obtained from microglia transcriptomes in traumatic brain and spinal cord injuries, pain and more chronic neurological conditions including Amyotrophic lateral sclerosis (ALS), Alzheimer disease (AD) and Multiple sclerosis (MS). Transcriptomic responses of microglia in other non-neurodegenerative CNS disorders such as gliomas and sepsis are also addressed. Third, we present a comparison of the most activated pathways in each neuropathological condition using Gene ontology (GO) classification and highlight the diversity of microglia response to insults focusing on their pro- and anti-inflammatory signatures. Finally, we discuss the potential of the latest technological advances, in particular, single cell RNA-Seq to unravel the individual microglial response diversity in neuropathological contexts.

RETRACTED: Neural Stem Cells Engineered to Express Three Therapeutic Factors Mediate Recovery from Chronic Stage CNS Autoimmunity

This article has been retracted: please see Elsevier Policy on Article Withdrawal (http://www.elsevier.com/locate/withdrawalpolicy). This article has been retracted at the request of the editor-in-chief. Similarities were found between images in this article and a previously published article in Scientific Reports (Zhang et al., 2015, Sci. Rep. 30, 17407, https://doi.org/10.1038/srep17407). Similarities were also found between images within this article. These concerns were initially reported in a PubPeer thread (https://pubpeer.com/publications/11D757FEEACDC81ACAF60BD0A32607). Image analysis performed by the editorial office confirmed findings of image reuse in Figures 2C and 5C of the Molecular Therapy article. In addition, some of the original data provided by the authors do not match the published article. This reuse (and in part misrepresentation) of data without appropriate attribution represents a severe abuse of the scientific publishing system. The authors disagree with this retraction and maintain that these mistakes do not alter the conclusions of the study.

Identification of a microglia phenotype supportive of remyelination

In multiple sclerosis, endogenous oligodendrocyte precursor cells (OPCs) attempt to remyelinate areas of myelin damage. During disease progression, however, these attempts fail. It has been suggested that modulating the inflammatory environment of the lesion might provide a promising therapeutic approach to promote endogenous remyelination. Microglia are known to play a central role in neuroinflammatory processes. To investigate the microglia phenotype that supports remyelination, we performed genome-wide gene expression analysis of microglia from the corpus callosum during demyelination and remyelination in the mouse cuprizone model, in which remyelination spontaneously occurs after an episode of toxin-induced primary demyelination. We provide evidence for the existence of a microglia phenotype that supports remyelination already at the onset of demyelination and persists throughout the remyelination process. Our data show that microglia are involved in the phagocytosis of myelin debris and apoptotic cells during demyelination. Furthermore, they express a cytokine and chemokine repertoire enabling them to activate and recruit endogenous OPCs to the lesion site and deliver trophic support during remyelination. This study not only provides a detailed transcriptomic analysis of the remyelination-supportive microglia phenotype but also reinforces the notion that the primary function of microglia is the maintenance of tissue homeostasis and the support of regeneration already at the earliest stages in the development of demyelinating lesions.