Response of human oligodendrocyte progenitors to growth factors and axon signals

Pathology and Treatments of Alzheimer's Disease Based on Considering Changes in Brain Energy Metabolism Due to Type 2 Diabetes

Alzheimer's disease (AD) is a progressive neurodegenerative disorder with cognitive dysfunction, memory decline, and behavioral disturbance, and it is pathologically characterized by the accumulation of amyloid plaques and neurofibrillary tangles in the brain. Although various hypotheses have been proposed to explain the pathogenesis of AD, including the amyloid beta hypothesis, oxidative stress hypothesis, and abnormal phosphorylation of tau proteins, the exact pathogenic mechanisms underlying AD remain largely undefined. Furthermore, effective curative treatments are very limited. Epidemiologic studies provide convincing evidence for a significant association between type 2 diabetes and AD. Here, we showed energy metabolism using glucose, lactate, ketone bodies, and lipids as energy substrates in a normal brain, and changes in such energy metabolism due to type 2 diabetes. We also showed the influences of such altered energy metabolism due to type 2 diabetes on the pathology of AD. Furthermore, we comprehensively searched for risk factors related with type 2 diabetes for AD and showed possible therapeutic interventions based on considering risk factors and altered brain energy metabolism due to type 2 diabetes for the development of AD.

A Novel Approach to Increase Glial Cell Populations in Brain Microphysiological Systems

Brain microphysiological systems (bMPS) recapitulate human brain cellular architecture and functionality more closely than traditional monolayer cultures and have become increasingly relevant for the study of neurological function in health and disease. Existing 3D brain models vary in reflecting the relative populations of different cell types present in the human brain. Most models consist mainly of neurons, while glial cells represent a smaller portion of the cell populations. Here, by means of a chemically defined glial-enriched medium (GEM), an improved method to expand the population of astrocytes and oligodendrocytes without compromising neuronal differentiation in bMPS, is presented. An important finding is that astrocytes also change in morphology when cultured in GEM, more closely recapitulating primary culture astrocytes. GEM bMPS are electro-chemically active and show different patterns of calcium staining and flux. Synaptic vesicles and terminals observed by electron microscopy are also present. No significant changes in neuronal differentiation are observed by gene expression, however, GEM enhanced neurite outgrowth and cell migration, and differentially modulated neuronal maturation in two different cell lines. These results have the potential to significantly improve functionality of bMPS for the study of neurological diseases and drug discovery, contributing to the unmet need for safe human models.

The interaction between insulin resistance and Alzheimer's disease: a review article

Insulin serves multiple functions as a growth-promoting hormone in peripheral tissues. It manages glucose metabolism by promoting glucose uptake into cells and curbing the production of glucose in the liver. Beyond this, insulin fosters cell growth, drives differentiation, aids protein synthesis, and deters degradative processes like glycolysis, lipolysis, and proteolysis. Receptors for insulin and insulin-like growth factor-1 are widely expressed in the central nervous system. Their widespread presence in the brain underscores the varied and critical functions of insulin signaling there. Insulin aids in bolstering cognition, promoting neuron extension, adjusting the release and absorption of catecholamines, and controlling the expression and positioning of gamma-aminobutyric acid (GABA). Importantly, insulin can effortlessly traverse the blood-brain barrier. Furthermore, insulin resistance (IR)-induced alterations in insulin signaling might hasten brain aging, impacting its plasticity and potentially leading to neurodegeneration. Two primary pathways are responsible for insulin signal transmission: the phosphoinositide 3-kinase (PI3K)/protein kinase B (AKT) pathway, which oversees metabolic responses, and the mitogen-activated protein kinase (MAPK) pathway, which guides cell growth, survival, and gene transcription. This review aimed to explore the potential shared metabolic traits between Alzheimer's disease (AD) and IR disorders. It delves into the relationship between AD and IR disorders, their overlapping genetic markers, and shared metabolic indicators. Additionally, it addresses existing therapeutic interventions targeting these intersecting pathways.

Cracking the Code of Neuronal Cell Fate

Transcriptional regulation is fundamental to most biological processes and reverse-engineering programs can be used to decipher the underlying programs. In this review, we describe how genomics is offering a systems biology-based perspective of the intricate and temporally coordinated transcriptional programs that control neuronal apoptosis and survival. In addition to providing a new standpoint in human pathology focused on the regulatory program, cracking the code of neuronal cell fate may offer innovative therapeutic approaches focused on downstream targets and regulatory networks. Similar to computers, where faults often arise from a software bug, neuronal fate may critically depend on its transcription program. Thus, cracking the code of neuronal life or death may help finding a patch for neurodegeneration and cancer.

How Can Insulin Resistance Cause Alzheimer's Disease?

Alzheimer's disease (AD) is a neurodegenerative disorder associated with cognitive decline. Despite worldwide efforts to find a cure, no proper treatment has been developed yet, and the only effective countermeasure is to prevent the disease progression by early diagnosis. The reason why new drug candidates fail to show therapeutic effects in clinical studies may be due to misunderstanding the cause of AD. Regarding the cause of AD, the most widely known is the amyloid cascade hypothesis, in which the deposition of amyloid beta and hyperphosphorylated tau is the cause. However, many new hypotheses were suggested. Among them, based on preclinical and clinical evidence supporting a connection between AD and diabetes, insulin resistance has been pointed out as an important factor in the development of AD. Therefore, by reviewing the pathophysiological background of brain metabolic insufficiency and insulin insufficiency leading to AD pathology, we will discuss how can insulin resistance cause AD.

A Pathophysiological Intersection of Diabetes and Alzheimer's Disease

Diabetes is among the most prevalent diseases of the modern world and is strongly linked to an increased risk of numerous neurodegenerative disorders, although the exact pathophysiological mechanisms are not clear yet. Insulin resistance is a serious pathological condition, connecting type 2 diabetes, metabolic syndrome, and obesity. Recently, insulin resistance has been proven to be connected also to cognitive decline and dementias, including the most prevalent form, Alzheimer's disease. The relationship between diabetes and Alzheimer's disease regarding pathophysiology is so significant that it has been proposed that some presentations of the condition could be termed type 3 diabetes.

OCT4-induced oligodendrocyte progenitor cells promote remyelination and ameliorate disease

The generation of human oligodendrocyte progenitor cells (OPCs) may be therapeutically valuable for human demyelinating diseases such as multiple sclerosis. Here, we report the direct reprogramming of human somatic cells into expandable induced OPCs (iOPCs) using a combination of OCT4 and a small molecule cocktail. This method enables generation of A2B5⁺ (an early marker for OPCs) iOPCs within 2 weeks retaining the ability to differentiate into MBP-positive mature oligodendrocytes. RNA-seq analysis revealed that the transcriptome of O4⁺ iOPCs was similar to that of O4⁺ OPCs and ChIP-seq analysis revealed that putative OCT4-binding regions were detected in the regulatory elements of CNS development-related genes. Notably, engrafted iOPCs remyelinated the brains of adult shiverer mice and experimental autoimmune encephalomyelitis mice with MOG-induced 14 weeks after transplantation. In conclusion, our study may contribute to the development of therapeutic approaches for neurological disorders, as well as facilitate the understanding of the molecular mechanisms underlying glial development.

Multiple Sclerosis and Aging: The Dynamics of Demyelination and Remyelination

Multiple sclerosis (MS) is a chronic inflammatory disease of the central nervous system (CNS) leading to demyelination and neurodegeneration. Life expectancy and age of onset in MS patients have been rising over the last decades, and previous studies have shown that age affects disease progression. Therefore, age appears as one of the most important factors in accumulating disability in MS patients. Indeed, the degeneration of oligodendrocytes (OGDs) and OGD precursors (OPCs) increases with age, in association with increased inflammatory activity of astrocytes and microglia. Similarly, age-related neuronal changes such as mitochondrial alterations, an increase in oxidative stress, and disrupted paranodal junctions can impact myelin integrity. Conversely, once myelination is complete, the long-term integrity of axons depends on OGD supply of energy. These alterations determine pathological myelin changes consisting of myelin outfolding, splitting, and accumulation of multilamellar fragments. Overall, these data demonstrate that old mature OGDs lose their ability to produce and maintain healthy myelin over time, to induce de novo myelination, and to remodel pre-existing myelinated axons that contribute to neural plasticity in the CNS. Furthermore, as observed in other tissues, aging induces a general decline in regenerative processes and, not surprisingly, progressively hinders remyelination in MS. In this context, this review will provide an overview of the current knowledge of age-related changes occurring in cells of the oligodendroglial lineage and how they impact myelin synthesis, axonal degeneration, and remyelination efficiency.

Transcriptional Profiles of Cell Fate Transitions Reveal Early Drivers of Neuronal Apoptosis and Survival

Neuronal apoptosis and survival are regulated at the transcriptional level. To identify key genes and upstream regulators primarily responsible for these processes, we overlayed the temporal transcriptome of cerebellar granule neurons following induction of apoptosis and their rescue by three different neurotrophic factors. We identified a core set of 175 genes showing opposite expression trends at the intersection of apoptosis and survival. Their functional annotations and expression signatures significantly correlated to neurological, psychiatric and oncological disorders. Transcription regulatory network analysis revealed the action of nine upstream transcription factors, converging pro-apoptosis and pro-survival-inducing signals in a highly interconnected functionally and temporally ordered manner. Five of these transcription factors are potential drug targets. Transcriptome-based computational drug repurposing produced a list of drug candidates that may revert the apoptotic core set signature. Besides elucidating early drivers of neuronal apoptosis and survival, our systems biology-based perspective paves the way to innovative pharmacology focused on upstream targets and regulatory networks.

Insulin and Insulin Resistance in Alzheimer's Disease

Insulin plays a range of roles as an anabolic hormone in peripheral tissues. It regulates glucose metabolism, stimulates glucose transport into cells and suppresses hepatic glucose production. Insulin influences cell growth, differentiation and protein synthesis, and inhibits catabolic processes such as glycolysis, lipolysis and proteolysis. Insulin and insulin-like growth factor-1 receptors are expressed on all cell types in the central nervous system. Widespread distribution in the brain confirms that insulin signaling plays important and diverse roles in this organ. Insulin is known to regulate glucose metabolism, support cognition, enhance the outgrowth of neurons, modulate the release and uptake of catecholamine, and regulate the expression and localization of gamma-aminobutyric acid (GABA). Insulin is also able to freely cross the blood–brain barrier from the circulation. In addition, changes in insulin signaling, caused inter alia insulin resistance, may accelerate brain aging, and affect plasticity and possibly neurodegeneration. There are two significant insulin signal transduction pathways: the PBK/AKT pathway which is responsible for metabolic effects, and the MAPK pathway which influences cell growth, survival and gene expression. The aim of this study is to describe the role played by insulin in the CNS, in both healthy people and those with pathologies such as insulin resistance and Alzheimer’s disease.

Nutritional regulation of oligodendrocyte differentiation regulates perineuronal net remodeling in the median eminence

The mediobasal hypothalamus (MBH; arcuate nucleus of the hypothalamus [ARH] and median eminence [ME]) is a key nutrient sensing site for the production of the complex homeostatic feedback responses required for the maintenance of energy balance. Here, we show that refeeding after an overnight fast rapidly triggers proliferation and differentiation of oligodendrocyte progenitors, leading to the production of new oligodendrocytes in the ME specifically. During this nutritional paradigm, ME perineuronal nets (PNNs), emerging regulators of ARH metabolic functions, are rapidly remodeled, and this process requires myelin regulatory factor (Myrf) in oligodendrocyte progenitors. In genetically obese ob/ob mice, nutritional regulations of ME oligodendrocyte differentiation and PNN remodeling are blunted, and enzymatic digestion of local PNN increases food intake and weight gain. We conclude that MBH PNNs are required for the maintenance of energy balance in lean mice and are remodeled in the adult ME by the nutritional control of oligodendrocyte differentiation.

Identification of novel myelin repair drugs by modulation of oligodendroglial differentiation competence

BACKGROUND

In multiple sclerosis loss of myelin and oligodendrocytes impairs saltatory signal transduction and leads to neuronal loss and functional deficits. Limited capacity of oligodendroglial precursor cells to differentiate into mature cells is the main reason for inefficient myelin repair in the central nervous system. Drug repurposing constitutes a powerful approach for identification of pharmacological compounds promoting this process.

METHODS

A phenotypic compound screening using the subcellular distribution of a potent inhibitor of oligodendroglial cell differentiation, namely p57kip2, as differentiation competence marker was conducted. Hit compounds were validated in terms of their impact on developmental cell differentiation and myelination using both rat and human primary cell cultures and organotypic cerebellar slice cultures, respectively. Their effect on spontaneous remyelination was then investigated following cuprizone-mediated demyelination of the corpus callosum.

FINDINGS

A number of novel small molecules able to promote oligodendroglial cell differentiation were identified and a subset was found to foster human oligodendrogenesis as well as myelination ex vivo. Among them the steroid danazol and the anthelminthic parbendazole were found to increase myelin repair.

INTERPRETATION

We provide evidence that early cellular processes involved in differentiation decisions are applicable for the identification of regeneration promoting drugs and we suggest danazol and parbendazole as potent therapeutic candidates for demyelinating diseases.

FUNDING

This work was supported by the Jürgen Manchot Foundation, Düsseldorf; Research Commission of the Medical Faculty of Heinrich-Heine-University Düsseldorf; Christiane and Claudia Hempel Foundation; Stifterverband/Novartisstiftung; James and Elisabeth Cloppenburg, Peek and Cloppenburg Düsseldorf Stiftung and International Progressive MS Alliance (BRAVEinMS).

Insulin resistance and bioenergetic manifestations: Targets and approaches in Alzheimer's disease

AIM

Insulin has a well-established role in cognition, neuronal detoxification and synaptic plasticity. Insulin transduction affect neurotransmitter functions, influence bioenergetics and regulate neuronal survival through regulating glucose energy metabolism and downward pathways.

METHODS

A systematic literature review of PubMed, Medline, Bentham, Scopus and EMBASE (Elsevier) databases was carried out with the help of the keywords like "Alzheimer's disease; Hypometabolism; Oxidative stress; energy failure in AD, Insulin; Insulin resistance; Bioenergetics" till June 2020. The review was conducted using the above keywords to collect the latest articles and to understand the nature of the extensive work carried out on insulin resistance and bioenergetic manifestations in Alzheimer's disease.

KEY FINDINGS

The article sheds light on insulin resistance mediated hypometabolic state on pathological progression of AD. The disrupted insulin signaling has pathological outcome in form of disturbed glucose homeostasis, altered bioenergetic state which increases build-up of senile plaques (Aβ), neurofibrillary tangles (τ), decline in transportation of glucose and activation of inflammatory pathways. The mechanistic link of insulin resistant state with therapeutically explorable potential transduction pathways is the focus of the reviewed work.

SIGNIFICANCE

The present work opines that the mechanism by which the insulin resistance mediates dysregulation of bioenergetics and progresses to neurodegenerative state holds the tangible potential to succeed in the development of novel dementia therapies. Further, hypometabolic complications and altered insulin signaling may be explored as a mechanistic relation between bioenergetic deficits and AD.

MiRNA-145-5p prevents differentiation of oligodendrocyte progenitor cells by regulating expression of myelin gene regulatory factor

The roles of specific microRNAs (miRNA) in oligodendrocyte (OL) differentiation have been studied in depth. However, miRNAs in OL precursors and oligodendrocyte progenitor cells (OPCs) have been less extensively investigated. MiR-145-5p is highly expressed in OPCs relative to differentiating OLs, suggesting this miRNA may serve a function specifically in OPCs. Knockdown of miR-145-5p in primary OPCs led to spontaneous differentiation, as evidenced by an increased proportion of MAG⁺ cells, increased cell ramification, and upregulation of multiple myelin genes including MYRF, TPPP, and MAG, and OL cell cycle exit marker Cdkn1c. Supporting this transition to a differentiating state, proliferation was reduced in miR-145-5p knockdown OPCs. Further, knockdown of miR-145-5p in differentiating OLs showed enhanced differentiation, with increased branching, myelin membrane production, and myelin gene expression. We identified several OL-specific genes targeted by miR-145-5p that exhibited upregulation with miR-145-5p knockdown, including myelin gene regulatory factor (MYRF), that could be regulating the prodifferentiation phenotype in both miR-145 knockdown OPCs and OLs. Indeed, spontaneous differentiation with knockdown of miR-145-5p was fully rescued by concurrent knockdown of MYRF. However, proliferation rate was only partially rescued with MYRF knockdown, and overexpression of miR-145-5p in OPCs increased proliferation rate without affecting expression of already lowly expressed differentiation genes. Taken together, these data suggest that in OPCs miR-145-5p both prevents differentiation at least in part by preventing expression of MYRF and promotes proliferation via as-yet-unidentified mechanisms. These findings clarify the need for differential regulation of miR-145-5p between OPCs and OLs and may have further implications in demyelinating diseases such as multiple sclerosis where miR-145-5p is dysregulated.

Co-culture of Human Stem Cell Derived Neurons and Oligodendrocyte Progenitor Cells

Crosstalk between neurons and oligodendrocytes is important for proper brain functioning. Multiple co-culture methods have been developed to study oligodendrocyte maturation, myelination or the effect of oligodendrocytes on neurons. However, most of these methods contain cells derived from animal models. In the current protocol, we co-culture human neurons with human oligodendrocytes. Neurons and oligodendrocyte precursor cells (OPCs) were differentiated separately from pluripotent stem cells according to previously published protocols. To study neuron-glia cross-talk, neurons and OPCs were plated in co-culture mode in optimized conditions for additional 28 days, and prepared for OPC maturation and neuronal morphology analysis. To our knowledge, this is one of the first neuron-OPC protocols containing all human cells. Specific neuronal abnormalities not observed in mono-cultures of Tuberous Sclerosis Complex (TSC) neurons, became apparent when TSC neurons were co-cultured with TSC OPCs. These results show that this co-culture system can be used to study human neuron-OPC interactive mechanisms involved in health and disease.

Helper CD4 T cells expressing granzyme B cause glial fibrillary acidic protein fragmentation in astrocytes in an MHCII-independent manner

During inflammatory processes of the central nervous system, helper T cells have the capacity to cross the blood-brain barrier and injure or kill neural cells through cytotoxic mechanisms. Glial fibrillary acidic protein (GFAP) is an intermediate filament protein that is part of the astrocyte cytoskeleton that can become fragmented in neuroinflammatory conditions. The mechanism of action by which helper T cells with cytotoxic properties injure astrocytes is not completely understood. Primary human astrocytes were obtained from fetal brain tissue. Human helper (CD4⁺ ) T cells were isolated from peripheral blood mononuclear cells and activated with the superantigen staphylococcal enterotoxin E (SEE). Granzyme B was detected by enzyme linked immunosorbent assay and intracellular flow cytometry. GFAP fragmentation was monitored by western blotting. Cell death was monitored by lactic acid dehydrogenase release and terminal biotin-dUTP nick labeling (TUNEL). Astrocyte migration was monitored by scratch assay. Adult human oligodendrocytes were cultured with sublethally injured astrocytes to determine support function. Helper T cells activated with SEE expressed granzyme B but not perforin. Helper T cells released granzyme B upon contact with astrocytes and caused GFAP fragmentation in a caspase-dependent, MHCII-independent manner. Sublethally injured astrocytes were not apoptotic; however, their processes were thin and elongated, their migration was attenuated, and their ability to support oligodendrocytes was reduced in vitro. Helper T cells can release granzyme B causing sublethal injury to astrocytes, which compromises the supportive functions of astrocytes. Blocking these pathways may lead to improved resolution of neuroinflammatory lesions.

Brain insulin resistance in type 2 diabetes and Alzheimer disease: concepts and conundrums

Considerable overlap has been identified in the risk factors, comorbidities and putative pathophysiological mechanisms of Alzheimer disease and related dementias (ADRDs) and type 2 diabetes mellitus (T2DM), two of the most pressing epidemics of our time. Much is known about the biology of each condition, but whether T2DM and ADRDs are parallel phenomena arising from coincidental roots in ageing or synergistic diseases linked by vicious pathophysiological cycles remains unclear. Insulin resistance is a core feature of T2DM and is emerging as a potentially important feature of ADRDs. Here, we review key observations and experimental data on insulin signalling in the brain, highlighting its actions in neurons and glia. In addition, we define the concept of 'brain insulin resistance' and review the growing, although still inconsistent, literature concerning cognitive impairment and neuropathological abnormalities in T2DM, obesity and insulin resistance. Lastly, we review evidence of intrinsic brain insulin resistance in ADRDs. By expanding our understanding of the overlapping mechanisms of these conditions, we hope to accelerate the rational development of preventive, disease-modifying and symptomatic treatments for cognitive dysfunction in T2DM and ADRDs alike.

BDNF Val66Met polymorphism modulates the effect of loneliness on white matter microstructure in young adults

Loneliness is a common experience. Susceptibility to loneliness is a stable trait and is heritable. Previous studies have suggested that loneliness may impact regional gray matter density and brain activation to social stimuli, but its relation to white matter structure and how it may interact with genetic factors remains unclear. In this study, we investigated whether and how a common polymorphism (Val66Met) in the brain-derived neurotrophic factor gene modulated the association between loneliness and white matter microstructure in 162 young adults. The tract-based spatial statistics analyses revealed that the relationships between loneliness and white matter microstructures were significantly different between Val/Met heterozygotes and Val/Val homozygotes. Specifically, loneliness was significantly correlated with reduced fractional anisotropy and increased radial diffusivity in widespread white matter fibers within Val/Met heterozygotes. It was also significantly correlated with increased radial diffusivity in Met/Met genotypes but showed no significant association with white matter measures in Val/Val genotypes. Furthermore, the associations between loneliness and fractional anisotropy (or radial diffusivity) in Val/Met heterozygotes turned out to be global effects. These results provide evidence that loneliness may interact with the BDNF Val66Met polymorphism to shape the microstructures of white matter, and the Val/Met heterozygotes may be more susceptible to social environment.

Rapid and efficient generation of oligodendrocytes from human induced pluripotent stem cells using transcription factors

Rapid and efficient protocols to generate oligodendrocytes (OL) from human induced pluripotent stem cells (iPSC) are currently lacking, but may be a key technology to understand the biology of myelin diseases and to develop treatments for such disorders. Here, we demonstrate that the induction of three transcription factors (SOX10, OLIG2, NKX6.2) in iPSC-derived neural progenitor cells is sufficient to rapidly generate O4⁺ OL with an efficiency of up to 70% in 28 d and a global gene-expression profile comparable to primary human OL. We further demonstrate that iPSC-derived OL disperse and myelinate the CNS of Mbp^shi/shiRag^-/- mice during development and after demyelination, are suitable for in vitro myelination assays, disease modeling, and screening of pharmacological compounds potentially promoting oligodendroglial differentiation. Thus, the strategy presented here to generate OL from iPSC may facilitate the studying of human myelin diseases and the development of high-throughput screening platforms for drug discovery.

Targeting human oligodendrocyte progenitors for myelin repair

Oligodendrocyte development has been studied for several decades, and has served as a model system for both neurodevelopmental and stem/progenitor cell biology. Until recently, the vast majority of studies have been conducted in lower species, especially those focused on rodent development and remyelination. In humans, the process of myelination requires the generation of vastly more myelinating glia, occurring over a period of years rather than weeks. Furthermore, as evidenced by the presence of chronic demyelination in a variety of human neurologic diseases, it appears likely that the mechanisms that regulate development and become dysfunctional in disease may be, in key ways, divergent across species. Improvements in isolation techniques, applied to primary human neural and oligodendrocyte progenitors from both fetal and adult brain, as well as advancements in the derivation of defined progenitors from human pluripotent stem cells, have begun to reveal the extent of both species-conserved signaling pathways and potential key differences at cellular and molecular levels. In this article, we will review the commonalities and differences in myelin development between rodents and man, describing the approaches used to study human oligodendrocyte differentiation and myelination, as well as heterogeneity within targetable progenitor pools, and discuss the advances made in determining which conserved pathways may be both modeled in rodents and translate into viable therapeutic strategies to promote myelin repair.

CXCR7 Is Involved in Human Oligodendroglial Precursor Cell Maturation

Differentiation of oligodendroglial precursor cells (OPCs), a crucial prerequisite for central nervous system (CNS) remyelination in diseases such as Multiple Sclerosis (MS), is modulated by a multitude of extrinsic and intrinsic factors. In a previous study we revealed that the chemokine CXCL12 stimulates rodent OPC differentiation via activation of its receptor CXCR7. We could now demonstrate that CXCR7 is also expressed on NogoA- and Nkx2.2-positive oligodendroglial cells in human MS brains and that stimulation of cultured primary fetal human OPCs with CXCL12 promotes their differentiation as measured by surface marker expression and morphologic complexity. Pharmacological inhibition of CXCR7 effectively blocks these CXCL12-dependent effects. Our findings therefore suggest that a specific activation of CXCR7 could provide a means to promote oligodendroglial differentiation facilitating endogenous remyelination activities.

Delayed nerve stimulation promotes axon-protective neurofilament phosphorylation, accelerates immune cell clearance and enhances remyelination in vivo in focally demyelinated nerves

Rapid and efficient axon remyelination aids in restoring strong electrochemical communication with end organs and in preventing axonal degeneration often observed in demyelinating neuropathies. The signals from axons that can trigger more effective remyelination in vivo are still being elucidated. Here we report the remarkable effect of delayed brief electrical nerve stimulation (ES; 1 hour @ 20 Hz 5 days post-demyelination) on ensuing reparative events in a focally demyelinated adult rat peripheral nerve. ES impacted many parameters underlying successful remyelination. It effected increased neurofilament expression and phosphorylation, both implicated in axon protection. ES increased expression of myelin basic protein (MBP) and promoted node of Ranvier re-organization, both of which coincided with the early reappearance of remyelinated axons, effects not observed at the same time points in non-stimulated demyelinated nerves. The improved ES-associated remyelination was accompanied by enhanced clearance of ED-1 positive macrophages and attenuation of glial fibrillary acidic protein expression in accompanying Schwann cells, suggesting a more rapid clearance of myelin debris and return of Schwann cells to a nonreactive myelinating state. These benefits of ES correlated with increased levels of brain derived neurotrophic factor (BDNF) in the acute demyelination zone, a key molecule in the initiation of the myelination program. In conclusion, the tremendous impact of delayed brief nerve stimulation on enhancement of the innate capacity of a focally demyelinated nerve to successfully remyelinate identifies manipulation of this axis as a novel therapeutic target for demyelinating pathologies.

Role of p38MAPK in S1P receptor-mediated differentiation of human oligodendrocyte progenitors

FTY720 is a sphingosine 1-phosphate receptor (S1PR) modulator used as a daily therapy to reduce disease activity in the relapsing form of multiple sclerosis (MS). FTY720 readily accesses the CNS. Previous studies have shown that phosphorylated FTY720 (FTY720-p) enhances oligodendrocyte progenitor cell (OPC) survival, differentiation, and remyelination following experimentally induced demyelination in rodents. To elucidate the underlying mechanism, human fetal OPCs alone or in co-culture with rat dorsal root ganglia neurons (DRGN) were treated daily with FTY720-p, a condition that desensitizes cellular responses to S1P, the natural ligand of S1PR. In co-cultures, FTY720-p and S1P given daily or every three days increased the number of O1/MBP double positive cells and axonal ensheathment. In cultures composed of PDGFRα-antibody selected cells alone, daily application of FTY720-p also increased the number of O4/GC double positive cells. At an early time point (day 2), FTY720-p activated ERK1/2, CREB and p38MAPK in O4-positive cells, as well as in β-III Tubulin positive neurons and GFAP positive astrocytes. In later cultures (day 6), FTY720-p activated p38MAPK in O4 positive cells, p38MAPK and ERK1/2 in neurons, and p38MAPK, ERK1/2 and CREB in astrocytes. A MEK inhibitor (U0126) prevented the differentiation of OPCs into O4-positive cells, while a p38MAPK inhibitor (PD169316) blocked progression into O4-positive and into GC-positive stages of differentiation. Our results demonstrate that FTY720-p, under conditions that model daily clinical use, can act directly on OPCs to impact differentiation, and also indirectly via neurons and astrocytes by activating ERK1/2 and p38MAPK.

Heterogeneity of oligodendrocyte progenitor cells in adult human brain

Objective

Remyelination in multiple sclerosis has been attributed to the presence of oligodendrocyte progenitor cells (OPCs) in brain parenchyma. However, the precise identity of these progenitors is poorly defined. Here, we characterized populations of OPCs in the adult human brain and examined their myelination capacity and profile of miRNAs. Comparisons were made with fetal OPCs and mature oligodendrocytes.

Methods

We isolated human adult and fetal (early-to-mid second trimester) OPCs from surgically resected brain tissues using O4-, A2B5-, and MOG-directed fluorescence activated cell sorting and transplanted them into dysmyelinated shiverer slices to examine their myelination capacity. We used qRT-PCR to analyze expression of selective miRNAs implicated in OPC biology.

Results

Three subsets of putative OPCs were identified in adult brains: (1) A2B5(+), (2) O4^low, and (3) A2B5(+)O4^highMOG(+) progenitors. In comparison, fetal brains contained (1) A2B5(+), (2) O4(+), and (3) A2B5(+)O4(+) progenitors, but no MOG(+) cells. We demonstrate that like fetal OPCs, adult OPCs have the capacity to ensheathe cerebellar axons. However, adult OPCs exhibit low to undetectable expression of miRNAs that were highly expressed in O4-expressing fetal OPCs. Adult OPCs also express different miRNAs compared to mature oligodendrocytes.

Interpretation

We conclude that phenotypically distinct subsets of OPCs are present in adult human brain and these OPCs show differential miRNA expression compared to fetal OPCs and mature oligodendrocytes. These suggest that remyelination in adult brain may involve multiple populations of progenitors within the brain and that OPC differentiation in adulthood may be differentially regulated compared to development.

Gas6 enhances axonal ensheathment by MBP+ membranous processes in human DRG/OL promyelinating co-cultures

The molecular requirements for human myelination are incompletely defined, and further study is needed to fully understand the cellular mechanisms involved during development and in demyelinating diseases. We have established a human co-culture model to study myelination. Our earlier observations showed that addition of human γ-carboxylated growth-arrest-specific protein 6 (Gas6) to human oligodendrocyte progenitor cell (OPC) cultures enhanced their survival and maturation. Therefore, we explored the effect of Gas6 in co-cultures of enriched OPCs plated on axons of human fetal dorsal root ganglia explant. Gas6 significantly enhanced the number of myelin basic protein-positive (MBP⁺) oligodendrocytes with membranous processes parallel with and ensheathing axons relative to co-cultures maintained in defined medium only for 14 days. Gas6 did not increase the overall number of MBP⁺ oligodendrocytes/culture; however, it significantly increased the length of MBP⁺ oligodendrocyte processes in contact with and wrapping axons. Multiple oligodendrocytes were in contact with a single axon, and several processes from one oligodendrocyte made contact with one or multiple axons. Electron microscopy supported confocal Z-series microscopy demonstrating axonal ensheathment by MBP⁺ oligodendrocyte membranous processes in Gas6-treated co-cultures. Contacts between the axonal and oligodendrocyte membranes were evident and multiple wraps of oligodendrocyte membrane around the axon were visible supporting a model system in which to study events in human myelination and aspects of non-compact myelin formation.

Oligodendrocyte progenitor cell susceptibility to injury in multiple sclerosis

Remyelination in multiple sclerosis (MS) is often incomplete. In experimental models, oligodendrocyte progenitor cells (OPCs) rather than previously myelinating oligodendrocytes (OLs) are responsible for remyelination. This study compares the relative susceptibility of adult human OPCs and mature OLs to injury in actively demyelinating MS lesions and under in vitro stress conditions. In all lesions (n = 20), the number of OLs (Olig2 weak/NogoA positive) was reduced compared to control white matter (mean 38 ± 4% of control value). In 11 cases, OPC numbers (Olig2 strong; NogoA negative) were also decreased; in eight of these, the reduction was greater for OPCs than for OLs. In the other nine samples, OPC numbers were greater than control white matter, indicating ongoing OPC migration and/or proliferation. Analysis of co-cultures with rat dorsal root ganglia neurons confirmed that OPCs were more capable of contacting and ensheathing axons than OLs. In isolated culture under stress conditions (withdrawal of serum/glucose and/or antioxidants), OPCs showed increased cell death and reduced process extension compared to OLs. Under all culture conditions, OPCs up-regulated expression of genes in the extrinsic proapoptotic pathway, and had increased susceptibility to tumor necrosis factor-induced cell death as compared to OLs. Our data suggest that susceptibility of OPCs to injury within the MS lesion environment contributes to the limited remyelination in MS.

CD133/CD140a-based isolation of distinct human multipotent neural progenitor cells and oligodendrocyte progenitor cells

The mechanisms underlying the specification of oligodendrocyte fate from multipotent neural progenitor cells (NPCs) in developing human brain are unknown. In this study, we sought to identify antigens sufficient to distinguish NPCs free from oligodendrocyte progenitor cells (OPCs). We investigated the potential overlap of NPC and OPC antigens using multicolor fluorescence-activated cell sorting (FACS) for CD133/PROM1, A2B5, and CD140a/PDGFαR antigens. Surprisingly, we found that CD133, but not A2B5, was capable of enriching for OLIG2 expression, Sox10 enhancer activity, and oligodendrocyte potential. As a subpopulation of CD133-positive cells expressed CD140a, we asked whether CD133 enriched bone fide NPCs regardless of CD140a expression. We found that CD133(+)CD140a(-) cells were highly enriched for neurosphere initiating cells and were multipotent. Importantly, when analyzed immediately following isolation, CD133(+)CD140a(-) NPCs lacked the capacity to generate oligodendrocytes. In contrast, CD133(+)CD140a(+) cells were OLIG2-expressing OPCs capable of oligodendrocyte differentiation, but formed neurospheres with lower efficiency and were largely restricted to glial fate. Gene expression analysis further confirmed the stem cell nature of CD133(+)CD140a(-) cells. As human CD133(+) cells comprised both NPCs and OPCs, CD133 expression alone cannot be considered a specific marker of the stem cell phenotype, but rather comprises a heterogeneous mix of glial restricted as well as multipotent neural precursors. In contrast, CD133/CD140a-based FACS permits the separation of defined progenitor populations and the study of neural stem and oligodendrocyte fate specification in the human brain.

Sox10-MCS5 enhancer dynamically tracks human oligodendrocyte progenitor fate

In this study, we sought to establish a novel method to prospectively and dynamically identify live human oligodendrocyte precursor cells (OPCs) and oligodendrocyte lineage cells from brain dissociates and pluripotent stem cell culture. We selected a highly conserved enhancer element of the Sox10 gene, known as MCS5, which directs reporter expression to oligodendrocyte lineage cells in mouse and zebrafish. We demonstrate that lentiviral Sox10-MCS5 induced expression of GFP at high levels in a subpopulation of human CD140a/PDGFαR-sorted OPCs as well as their immature oligodendrocyte progeny. Furthermore, we show that almost all Sox10-MCS5:GFP(high) cells expressed OPC antigen CD140a and human OPCs expressing SOX10, OLIG2, and PDGFRA mRNAs could be prospectively identified using GFP based fluorescence activated cells sorting alone. Additionally, we established a human induced pluripotent cell (iPSC) line transduced with the Sox10-MCS5:GFP reporter using a Rex-Neo cassette. Similar to human primary cells, GFP expression was restricted to embryoid bodies containing both oligodendrocyte progenitor and oligodendrocyte cells and co-localized with NG2 and O4-positive cells respectively. As such, we have developed a novel reporter system that can track oligodendrocyte commitment in human cells, establishing a valuable tool to improve our understanding and efficiency of human oligodendrocyte derivation.

Effects of the BDNF Val66Met polymorphism on white matter microstructure in healthy adults

The BDNF Val(66)Met polymorphism, a possible risk variant for mental disorders, is a potent modulator of neural plasticity in humans and has been linked to deficits in gray matter structure, function, and cognition. The impact of the variant on brain white matter structure, however, is controversial and remains poorly understood. Here, we used diffusion tensor imaging to examine the effects of BDNF Val(66)Met genotype on white matter microstructure in a sample of 85 healthy Caucasian adults. We demonstrate decreases of fractional anisotropy and widespread increases in radial diffusivity in Val/Val homozygotes compared with Met-allele carriers, particularly in prefrontal and occipital pathways. These data provide an independent confirmation of prior imaging genetics work, are consistent with complex effects of the BDNF Val(66)Met polymorphism on human brain structure, and may serve to generate hypotheses about variation in white matter microstructure in mental disorders associated with this variant.

Isolating, culturing, and polarizing primary human adult and fetal microglia

Microglia are an important component of the innate immune system within the central nervous system (CNS). Isolation and in vitro culturing of microglia can provide insight towards the basic biology of these cells as well as their interactions with neurons, astrocytes, and oligodendrocytes. While studies of rodent microglia and microglial cell lines have provided a basis for our understanding of these cells, human adult microglia exhibit distinct properties when compared to rodent cells. Furthermore, the study of human fetal microglia provides a window into the developing CNS. This chapter describes the protocols used to isolate, purify, and culture both human adult and fetal microglia. Under basal culture conditions, human microglia survive for extended periods in the absence of growth factors, thus allowing their properties to be investigated under resting conditions. In addition, both human adult and fetal microglia can be used to study how they respond to different polarization conditions. As is the case with macrophages, it is also possible to polarize microglia towards the pro-inflammatory "M1" and the anti-inflammatory "M2" phenotypes, as described in this chapter.

Regulation of miRNA 219 and miRNA Clusters 338 and 17-92 in Oligodendrocytes

MicroRNAs (miRs) regulate diverse molecular and cellular processes including oligodendrocyte (OL) precursor cell (OPC) proliferation and differentiation in rodents. However, the role of miRs in human OPCs is poorly understood. To identify miRs that may regulate these processes in humans, we isolated OL lineage cells from human white matter and analyzed their miR profile. Using endpoint RT-PCR assays and quantitative real-time PCR, we demonstrate that miR-219, miR-338, and miR-17-92 are enriched in human white matter and expressed in acutely isolated human OLs. In addition, we report the expression of closely related miRs (miR-219-1-3p, miR-219-2-3p, miR-1250, miR-657, miR-3065-5p, miR-3065-3p) in both rodent and human OLs. Our findings demonstrate that miRs implicated in rodent OPC proliferation and differentiation are regulated in human OLs and may regulate myelination program in humans. Thus, these miRs should be recognized as potential therapeutic targets in demyelinating disorders.

The tryptophan metabolite 3-hydroxyanthranilic acid plays anti-inflammatory and neuroprotective roles during inflammation: role of hemeoxygenase-1

Tryptophan metabolism by the kynurenine pathway (KP) is important to the pathogenesis of inflammatory, infectious, and degenerative diseases. The 3-hydroxykynurenine (3-HK) branch of the KP is activated in macrophages and microglia, leading to the generation of 3-HK, 3-hydroxyanthranilic acid (3-HAA), and quinolinic acid, which are considered neurotoxic owing to their free radical-generating and N-methyl-d-aspartic acid receptor agonist activities. We investigated the role of 3-HAA in inflammatory and antioxidant gene expression and neurotoxicity in primary human fetal central nervous system cultures treated with cytokines (IL-1 with or without interferon-γ) or with Toll-like receptor ligands mimicking the proinflammatory central nervous system environment. Results were analyzed by microarray, Western blot, immunostain, enzyme-linked immunosorbent assay, and neurotoxicity assays. 3-HAA suppressed glial cytokine and chemokine expression and reduced cytokine-induced neuronal death. 3-HK also suppressed cytokine-induced neuronal death. Unexpectedly, 3-HAA was highly effective in inducing in astrocytes the expression of hemeoxygenase-1 (HO-1), an antioxidant enzyme with anti-inflammatory and cytoprotective properties. Optimal induction of HO-1 required 3-HAA and cytokines. In human microglia, 3-HAA weakly induced HO-1 and lipopolysaccharide suppressed microglial HO-1 expression. 3-HAA-mediated HO-1 expression was confirmed in cultured adult human astrocytes and in vivo after 3-HAA injection to mouse brains. Together, our results demonstrate the novel neuroprotective activity of the tryptophan metabolite 3-HAA and have implications for future therapeutic approaches for neuroinflammatory disorders.

Immunopharmacology 2011: an updated report of clinical achievements and perspectives

On 26-30 June 2011 the Cuban Society of Pharmacology organized the Second International Congress on Immunopharmacology (Immunopharmacology 2011), held at the beautiful Convention Centre 'Plaza América' and the Meliá Varadero Hotel, in Varadero beach, Cuba. The main topics of the congress were immunopharmacology (including inflammation, cancer immunotherapy and immunomodulation), neuroimmunology, and the pharmacology of cytochrome P450 and transporters, among other relevant and updated related topics. Immunopharmacology 2011 offered an outstanding scientific program with the active contribution of 90 speakers from 23 foreign countries, as well as more than 170 Cuban researchers from the most important local institutions devoted to the development of immunology and pharmacology sciences.

Myelin genes are downregulated in canine fucosidosis

The processes regulating the complex neurodegenerative cascade of vacuolation, neuroinflammation, neuronal loss and myelin deficits in fucosidosis, a neurological lysosomal storage disorder, remain unclear. To elucidate these processes the gene expression profile of the cerebral cortex from untreated and intrathecal enzyme replacement therapy treated fucosidosis pups and age-matched unaffected controls were examined. Neuroinflammation and cell death processes were identified to have a major role in fucosidosis pathophysiology with 37% of differentially expressed (DE) genes involved in these processes. Critical, specific, early decreases in expression levels of key genes in myelin assembly were identified by gene expression profiling, including myelin-associated glycoprotein (MAG), myelin and lymphocyte protein (MAL), and oligodendrocyte myelin paranodal and inner loop protein (OPALIN). These gene expression changes may be indicative of early neuronal loss causing reduced electrical impulses required for oligodendrocyte maturation.