Monocarboxylate transporter 1 and the vulnerability of oligodendrocyte lineage cells to metabolic stresses

Pyruvate maintains and enhances the pro-inflammatory response of microglia caused by glucose deficiency in early stroke

Pro-inflammatory microglia mainly rely on glycolysis to maintain cytokine production during ischemia, accompanied by an increase in inducible nitric oxide synthase (iNOS) and monocarboxylate transporter 1 (MCT1). The role of energy metabolism in the pro-inflammatory response of microglia is currently unclear. In this study, we tested the response of microglia in mice after cerebral ischemia and simulated an energy environment in vitro using low glucose culture medium. The research results indicate that the expression levels of iNOS and arginase 1 (ARG1) increase in the ischemic mouse brain, but the upregulation of MCT1 expression is mainly present in iNOS positive microglia. In microglia exposed to low glucose conditions, iNOS and MCT1 levels increased, while ARG1 levels decreased. Under the same conditions, knocking down MCT1 in microglia leads to a decrease in iNOS levels, while overexpression of MCT1 leads to the opposite result. The use of NF-κB inhibitors reduced the expression levels of iNOS and MCT1 in microglia. In summary, our data indicate that pyruvate maintains and enhances the NF-κB regulated pro-inflammatory response of microglia induced by low glucose.

Oligodendroglia Confer Neuroprotection to NSC-34 Motor Neuronal Cells Against the Toxic Insults of Cerebrospinal Fluid from Sporadic Amyotrophic Lateral Sclerosis Patients

Amyotrophic lateral sclerosis (ALS) is a complex neurodegenerative disorder with multifactorial pathomechanisms affecting not only motor neurons but also glia. Both astrocytes and microglia get activated and contribute significantly to neurodegeneration. The role of oligodendroglia in such a situation remains obscure, especially in the sporadic form of ALS (SALS), which contributes to 90% of cases. Here, we have investigated the role of oligodendroglia in SALS pathophysiology using a human oligodendroglial cell line, MO3.13, by exposing the cells to cerebrospinal fluid from SALS patients (ALS-CSF; 10% v/v for 48 h). ALS-CSF significantly reduced the viability of MO3.13 cells and down-regulated the expression of oligodendroglia-specific proteins, namely, CNPase and Olig2. Furthermore, to investigate the effect of the observed oligodendroglial changes on motor neurons, NSC-34 motor neuronal cells were co-cultured/supplemented with conditioned/spent medium of MO3.13 cells upon exposure to ALS-CSF. Live cell imaging experiments revealed protection to NSC-34 cells against ALS-CSF toxicity upon co-culture with MO3.13 cells. This was evidenced by the absence of neuronal cytoplasmic vacuolation and beading of neurites, which instead resulted in better neuronal differentiation. Enhanced lactate levels and increased expression of its transporter, MCT-1, with sustained expression of trophic factors, namely, GDNF and BDNF, by MO3.13 cells hint towards metabolic and trophic support provided by the surviving oligodendroglia. Similar metabolic changes were seen in the lumbar spinal cord oligodendroglia of rat neonates intrathecally injected with ALS-CSF. The findings indicate that oligodendroglia are indeed rescuer to the degenerating motor neurons when the astrocytes and microglia turn topsy-turvy.

Cerebral Ischemic Preconditioning Aggravates Death of Oligodendrocytes

Neurodegeneration can benefit from ischemic preconditioning, a natural adaptive reaction to sublethal noxious stimuli. Although there is growing interest in advancing preconditioning to preserve brain function, preconditioning is not yet considered readily achievable in clinical settings. One of the most challenging issues is that there is no fine line between preconditioning stimuli and lethal stimuli. Here, we show deleterious effect of preconditioning on oligodendrocyte precursor cells (OPCs). We identified Bcl-2/adenovirus E1B 19-kDa interacting protein 3 (BNIP3), a mitochondrial BH3-only protein specifically involved in OPCs loss after preconditioning. Repeated ischemia stabilized BNIP3 and increased the vulnerability of OPCs to subsequent ischemic events. BNIP3 became mitochondrial-bound and was concurrent with the dysfunction of monocarboxylate transporter 1 (MCT1). Inhibition of BNIP3 by RNAi or necrostatin-1 (Nec-1) and knocking out of BNIP3 almost completely prevented OPCs loss and preserved white matter integrity. Together, our results suggest that the unfavorable effect of BNIP3 on OPCs should be noted for safe development of ischemic tolerance. BNIP3 inhibition appears to be a complementary approach to improve the efficacy of preconditioning for ischemic stroke.

Interactions Between Astrocytes and Oligodendroglia in Myelin Development and Related Brain Diseases

Astrocytes (ASTs) and oligodendroglial lineage cells (OLGs) are major macroglial cells in the central nervous system. ASTs communicate with each other through connexin (Cx) and Cx-based network structures, both of which allow for quick transport of nutrients and signals. Moreover, ASTs interact with OLGs through connexin (Cx)-mediated networks to modulate various physiological processes in the brain. In this article, following a brief description of the infrastructural basis of the glial networks and exocrine factors by which ASTs and OLGs may crosstalk, we focus on recapitulating how the interactions between these two types of glial cells modulate myelination, and how the AST-OLG interactions are involved in protecting the integrity of the blood-brain barrier (BBB) and regulating synaptogenesis and neural activity. Recent studies further suggest that AST-OLG interactions are associated with myelin-related diseases, such as multiple sclerosis. A better understanding of the regulatory mechanisms underlying AST-OLG interactions may inspire the development of novel therapeutic strategies for related brain diseases.

Monocarboxylate Transporter 1 May Benefit Cerebral Ischemia via Facilitating Lactate Transport From Glial Cells to Neurons

Monocarboxylate transporter 1 (MCT1) is expressed in glial cells and some populations of neurons. MCT1 facilitates astrocytes or oligodendrocytes (OLs) in the energy supplement of neurons, which is crucial for maintaining the neuronal activity and axonal function. It is suggested that MCT1 upregulation in cerebral ischemia is protective to ischemia/reperfusion (I/R) injury. Otherwise, its underlying mechanism has not been clearly discussed. In this review, it provides a novel insight that MCT1 may protect brain from I/R injury via facilitating lactate transport from glial cells (such as, astrocytes and OLs) to neurons. It extensively discusses (1) the structure and localization of MCT1; (2) the regulation of MCT1 in lactate transport among astrocytes, OLs, and neurons; and (3) the regulation of MCT1 in the cellular response of lactate accumulation under ischemic attack. At last, this review concludes that MCT1, in cerebral ischemia, may improve lactate transport from glial cells to neurons, which subsequently alleviates cellular damage induced by lactate accumulation (mostly in glial cells), and meets the energy metabolism of neurons.

Neuron-glia (mis)interactions in brain energy metabolism during aging

Life expectancy in humans is increasing, resulting in a growing aging population, that is accompanied by an increased disposition to develop cognitive deterioration. Hypometabolism is one of the multiple factors related to inefficient brain function during aging. This review emphasizes the metabolic interactions between glial cells (astrocytes, oligodendrocytes, and microglia) and neurons, particularly, during aging. Glial cells provide support and protection to neurons allowing adequate synaptic activity. We address metabolic coupling from the expression of transporters, availability of substrates, metabolic pathways, and mitochondrial activity. In aging, the main metabolic exchange machinery is altered with inefficient levels of nutrients and detrimental mitochondrial activity that results in high reactive oxygen species levels and reduced ATP production, generating a highly inflammatory environment that favors deregulated cell death. Here, we provide an overview of the glial-to-neuron mechanisms, from the molecular components to the cell types, emphasizing aging as the crucial risk factor for developing neurodegenerative/neuroinflammatory diseases.

Glucose metabolic crosstalk and regulation in brain function and diseases

Brain glucose metabolism, including glycolysis, the pentose phosphate pathway, and glycogen turnover, produces ATP for energetic support and provides the precursors for the synthesis of biological macromolecules. Although glucose metabolism in neurons and astrocytes has been extensively studied, the glucose metabolism of microglia and oligodendrocytes, and their interactions with neurons and astrocytes, remain critical to understand brain function. Brain regions with heterogeneous cell composition and cell-type-specific profiles of glucose metabolism suggest that metabolic networks within the brain are complex. Signal transduction proteins including those in the Wnt, GSK-3β, PI3K-AKT, and AMPK pathways are involved in regulating these networks. Additionally, glycolytic enzymes and metabolites, such as hexokinase 2, acetyl-CoA, and enolase 2, are implicated in the modulation of cellular function, microglial activation, glycation, and acetylation of biomolecules. Given these extensive networks, glucose metabolism dysfunction in the whole brain or specific cell types is strongly associated with neurologic pathology including ischemic brain injury and neurodegenerative disorders. This review characterizes the glucose metabolism networks of the brain based on molecular signaling and cellular and regional interactions, and elucidates glucose metabolism-based mechanisms of neurological diseases and therapeutic approaches that may ameliorate metabolic abnormalities in those diseases.

Mitochondria in Myelinating Oligodendrocytes: Slow and Out of Breath?

Myelin is a lipid-rich membrane that wraps around axons and facilitates rapid action potential propagation. In the brain, myelin is synthesized and maintained by oligodendrocytes. These cells have a high metabolic demand that requires mitochondrial ATP production during the process of myelination, but they rely less on mitochondrial respiration after myelination is complete. Mitochondria change in morphology and distribution during oligodendrocyte development. Furthermore, the morphology and dynamic properties of mitochondria in mature oligodendrocytes seem different from any other brain cell. Here, we first give a brief introduction to oligodendrocyte biology and function. We then review the current knowledge on oligodendrocyte metabolism and discuss how the available data on mitochondrial morphology and mobility as well as transcriptome and proteome studies can shed light on the metabolic properties of oligodendrocytes.

Oligodendroglial Energy Metabolism and (re)Myelination

Central nervous system (CNS) myelin has a crucial role in accelerating the propagation of action potentials and providing trophic support to the axons. Defective myelination and lack of myelin regeneration following demyelination can both lead to axonal pathology and neurodegeneration. Energy deficit has been evoked as an important contributor to various CNS disorders, including multiple sclerosis (MS). Thus, dysregulation of energy homeostasis in oligodendroglia may be an important contributor to myelin dysfunction and lack of repair observed in the disease. This article will focus on energy metabolism pathways in oligodendroglial cells and highlight differences dependent on the maturation stage of the cell. In addition, it will emphasize that the use of alternative energy sources by oligodendroglia may be required to save glucose for functions that cannot be fulfilled by other metabolites, thus ensuring sufficient energy input for both myelin synthesis and trophic support to the axons. Finally, it will point out that neuropathological findings in a subtype of MS lesions likely reflect defective oligodendroglial energy homeostasis in the disease.

Impaired Oligodendrocyte Development Following Preterm Birth: Promoting GABAergic Action to Improve Outcomes

Preterm birth is associated with poor long-term neurodevelopmental and behavioral outcomes, even in the absence of obvious brain injury at the time of birth. In particular, behavioral disorders characterized by inattention, social difficulties and anxiety are common among children and adolescents who were born moderately to late preterm (32-37 weeks' gestation). Diffuse deficits in white matter microstructure are thought to play a role in these poor outcomes with evidence suggesting that a failure of oligodendrocytes to mature and myelinate axons is responsible. However, there remains a major knowledge gap over the mechanisms by which preterm birth interrupts normal oligodendrocyte development. In utero neurodevelopment occurs in an inhibitory-dominant environment due to the action of placentally derived neurosteroids on the GABA_A receptor, thus promoting GABAergic inhibitory activity and maintaining the fetal behavioral state. Following preterm birth, and the subsequent premature exposure to the ex utero environment, this action of neurosteroids on GABA_A receptors is greatly reduced. Coinciding with a reduction in GABAergic inhibition, the preterm neonatal brain is also exposed to ex utero environmental insults such as periods of hypoxia and excessive glucocorticoid concentrations. Together, these insults may increase levels of the excitatory neurotransmitter glutamate in the developing brain and result in a shift in the balance of inhibitory: excitatory activity toward excitatory. This review will outline the normal development of oligodendrocytes, how it is disrupted under excitation-dominated conditions and highlight how shifting the balance back toward an inhibitory-dominated environment may improve outcomes.

Claudin-1 and Claudin-3 as Molecular Regulators of Myelination in Leukoaraiosis Patients

OBJECTIVES

Leukoaraiosis is described as white matter lesions that are associated with cognitive dysfunction, neurodegenerative disorders, etc. Myelin depletion is a salient pathological feature of, and the loss of oligodendrocytes is one of the most robust alterations evident in, white matter degeneration. Recent studies have revealed that claudin proteins are aberrantly expressed in leukoaraiosis and regulate oligodendrocyte activity. However, the roles of claudin-1 and claudin-3 in oligodendrocytes and leukoaraiosis are still not well-defined.

METHODS

Quantitative polymerase chain reaction was used to measure the expression of claudin-1 (CLDN1), claudin-3 (CLDN3), and myelinogenesis-related genes such as myelin basic protein (MBP), proteolipid protein (PLP), oligodendrocyte transcription factor 2 (OLIG2), and SRY-box transcription factor 10 (SOX10) in leukoaraiosis patients (n=122) and healthy controls (n=122). The expression of claudin-1 and claudin-3 was either ectopically silenced or augmented in Oli-neu oligodendrocytes, and colony formation, apoptosis, and migration assays were performed. Finally, the expression of myelin proteins was evaluated by western blotting.

RESULTS

Our results revealed that in addition to SOX10, the expression levels of claudin-1, claudin-3, and myelinogenesis-related proteins were prominently downregulated in leukoaraiosis patients, compared to those in healthy controls. Furthermore, the growth and migration of Oli-neu cells were downregulated upon silencing claudin-1 or claudin-3. However, the overexpression of claudin-1 or claudin-3 resulted in the reduction of the degree of apoptosis in Oli-neu cells. In addition, claudin-1 and claudin-3 promoted the expression of MBP, OLIG2, PLP, and SOX10 at the translational level.

CONCLUSION

Our data has demonstrated that the abnormal expression of claudin-1 and claudin-3 regulates the pathological progression of leukoaraiosis by governing the viability and myelination of oligodendrocytes. These findings provide novel insights into the regulatory mechanisms underlying the roles of claudin-1 and claudin-3 in leukoaraiosis.

Demyelinating processes in aging and stroke in the central nervous system and the prospect of treatment strategy

Demyelination occurs in response to brain injury and is observed in many neurodegenerative diseases. Myelin is synthesized from oligodendrocytes in the central nervous system, and oligodendrocyte death‐induced demyelination is one of the mechanisms involved in white matter damage after stroke and neurodegeneration. Oligodendrocyte precursor cells (OPCs) exist in the brain of normal adults, and their differentiation into mature oligodendrocytes play a central role in remyelination. Although the differentiation and maturity of OPCs drive endogenous efforts for remyelination, the failure of axons to remyelinate is still the biggest obstacle to brain repair after injury or diseases. In recent years, studies have made attempts to promote remyelination after brain injury and disease, but its cellular or molecular mechanism is not yet fully understood. In this review, we discuss recent studies examining the demyelination process and potential therapeutic strategies for remyelination in aging and stroke. Based on our current understanding of the cellular and molecular mechanisms underlying remyelination, we hypothesize that myelin and oligodendrocytes are viable therapeutic targets to mitigate brain injury and to treat demyelinating‐related neurodegeneration diseases.

Brain energy metabolism and multiple sclerosis: progress and prospects

Multiple sclerosis (MS) is an autoimmune disease accompanied with nerve pain and paralysis. Although various pathogenic causes of MS have been suggested, including genetic and environmental factors, how MS occurs remains unclear. Moreover, MS should be diagnosed based on clinical experiences because of no disease-specific biomarker and currently available treatments for MS just can reduce relapsing frequency or severity with little effects on disease disability. Therefore, more efforts are required to identify pathophysiology of MS and diagnosis markers. Recent evidence indicates another aspect of MS pathogenesis, energy failure in the central nervous system (CNS). For instance, inflammation that is a characteristic MS symptom and occurs frequently in the CNS of MS patients can result into energy failure in mitochondria and cytosol. Indeed, metabolomics studies for MS have reported energy failure in oxidative phosphorylation and alteration of aerobic glycolysis. Therefore, studies on the metabolism in the CNS may provide another insight for understanding complexity of MS and pathogenesis, which would facilitate the discovery of promising strategies for developing therapeutics to treat MS. This review will provide an overview on recent progress of metabolomic studies for MS, with a focus on the fluctuation of energy metabolism in MS.

Compromised Lactate Efflux Renders Vulnerability of Oligodendrocyte Precursor Cells to Metabolic Stresses

Among the brain cells, oligodendrocyte progenitor cells (OPCs) are the most vulnerable in response to hypoxic and ischemic insults, of which the mechanism remains unknown. Brain cells are known to import or export lactate via differentially expressed monocarboxylate transporters (MCTs) to maintain energy metabolism and pH homeostasis. The present study aims to determine the role of MCT1 in the high vulnerability of OPCs. Here we show that a mild ischemic condition equivalent to ischemic preconditioning caused detectable loss of OPCs. MCT1, which is primarily expressed in oligodendrocyte lineage cells including OPCs, was up-regulated immediately under oxygen-glucose deprivation (OGD) conditions. However, persistent hypoxia, but not hypoglycemia, inhibited the function of MCT1, leading to an intracellular lactate accumulation and acidosis in OPCs. Neurons, which express primarily MCT2, were able to export lactate and maintain an intracellular pH homeostasis under similar conditions. The results support that compromised lactate efflux resulting from hypoxia-induced dysfunction of MCT1 contributes to the high vulnerability of OPCs.

Metabolic Regulation of Glial Phenotypes: Implications in Neuron-Glia Interactions and Neurological Disorders

Glial cells are multifunctional, non-neuronal components of the central nervous system with diverse phenotypes that have gained much attention for their close involvement in neuroinflammation and neurodegenerative diseases. Glial phenotypes are primarily characterized by their structural and functional changes in response to various stimuli, which can be either neuroprotective or neurotoxic. The reliance of neurons on glial cells is essential to fulfill the energy demands of the brain for its proper functioning. Moreover, the glial cells perform distinct functions to regulate their own metabolic activities, as well as work in close conjunction with neurons through various secreted signaling or guidance molecules, thereby constituting a complex network of neuron-glial interactions in health and disease. The emerging evidence suggests that, in disease conditions, the metabolic alterations in the glial cells can induce structural and functional changes together with neuronal dysfunction indicating the importance of neuron-glia interactions in the pathophysiology of neurological disorders. This review covers the recent developments that implicate the regulation of glial phenotypic changes and its consequences on neuron-glia interactions in neurological disorders. Finally, we discuss the possibilities and challenges of targeting glial metabolism as a strategy to treat neurological disorders.

Selective Susceptibility of Oligodendrocytes to Carbon Monoxide Poisoning: Implication for Delayed Neurologic Sequelae (DNS)

Delayed neurologic sequelae (DNS) are recurrent-transient neuropsychiatric consequences of carbon monoxide (CO) intoxication. Pathologically DNS features damages to the brain white matter. Here we test a hypothesis that direct cytotoxicity of CO to oligodendrocytes plays a role in the development of DNS. In an in vitro model of CO poisoning with the carbon monoxide releasing molecule-2 (CORM-2) as a CO donor, we show that CORM-2 at concentrations higher than 200 µM significantly inhibited viability and caused significant death of PC12 cells. Similar minimum toxicity concentration was observed on primary brain cells including neurons, astrocytes, and microglia. Interestingly, oligodendrocytes showed cytotoxicity to CORM-2 at a much lower concentration (100 µM). We further found that CORM-2 at 100 µM inhibited proteolipid protein (PLP) production and reduced myelin coverage on axons in an in vitro model of myelination. Our results show that direct cytotoxicity is a mechanism of CO poisoning and DNS may result from a high susceptibility of oligodendrocytes to CO poisoning.

Monocarboxylate Transporter 1 in Brain Diseases and Cancers

Background:

Monocarboxylate Transporter 1 (MCT1), an important membrane transport protein, mediates the translocation of monocarboxylates together with protons across biological membranes. Due to its pathological significance, MCT1 plays an important role in the progression of some diseases, such as brain diseases and cancers.

Methods:

We summarize the general description of MCT1 and provide a comprehensive understanding of the role of MCT1 in brain diseases and cancers. Furthermore, this review discusses the opportunities and challenges of MCT1- targeting drug-delivery systems in the treatment of brain diseases and cancers.

Results:

In the brain, loss of MCT1 function is associated with pathologies of degeneration and injury of the nervous system. In tumors, MCT1 regulates the activity of signaling pathways and controls the exchange of monocarboxylates in aerobic glycolysis to affect tumor metabolism, proliferation and invasion. Meanwhile, MCT1 also acts as a good biomarker for the prediction and diagnosis of cancer progressions.

Conclusion:

MCT1 is an attractive transporter in brain diseases and cancers. Moreover, the development of MCT1- based small molecule drugs and MCT1 inhibitors in the clinic is promising. This review systematically summarizes the basic characteristics of MCT1 and its role in brain diseases and cancers, laying the foundation for further research on MCT1.

Myelin Damage in Diffuse Axonal Injury

Diffuse axonal injury (DAI) is characterized by delayed axonal disconnection. Although the effect of DAI on axonal pathology has been well documented, there is limited information regarding the role of myelin in the pathogenesis of DAI. We used a modified Marmarou method to create a moderate DAI model in adult rat and examined the corpus callosum and brain stem for myelin pathology and dynamic glial responses to DAI. During the first week following DAI, Luxol Fast Blue staining and western blot analysis for MBP showed significant loss of myelin in the corpus callosum and the brain stem. Increased apoptosis of mature oligodendrocyte, as depicted by its marker CC-1, was observed. Conversely, there was an increased number of Olig2-positive cells accompanied by hypertrophic microglia/macrophage and mild reactive astrocytes. Electron microscopy revealed degenerating axons in the corpus callosum and marked myelin abnormalities in the brain stem in the early stage of DAI. Brain stem regions exhibited myelin intrusions or external protrusions with widespread delamination and myelin collapse, leading to degeneration of accompanying axons. Our results show distinct pathologic processes involving axon and myelin between the corpus callosum and the brain stem in DAI. Oligodendrocyte selective vulnerability and subsequent demyelination may contribute to axonal degeneration in the brain stem. Defining the cause of ongoing oligodendrocyte death and promoting myelin regeneration may provide important targets for therapeutic interventions of DAI.

Hypoxic preconditioning improves long-term functional outcomes after neonatal hypoxia-ischemic injury by restoring white matter integrity and brain development

Aims

Neonatal hypoxia–ischemia (H/I) results in gray and white matter injury, characterized by neuronal loss, failure of neural network formation, retarded myelin formation, and abnormal accumulation of oligodendrocyte progenitor cells (OPCs). These changes lead to severe neurological deficits and mortality. Sublethal hypoxic preconditioning (HPC) can protect the developing brain against H/I. However, limited evidence is available concerning its effect on white matter injury.

Methods

In this study, P6 neonatal Sprague‐Dawley rats were subjected to normoxic (21% O₂) or HPC (7.8% O₂) for 3 hours followed 24 hours later by H/I brain injury. Neurological deficits were assessed by gait, righting reflex, foot fault, and Morris water maze tests. Compound action potential of the corpus callosum was recorded 35 days after surgery, and the correlation between axon myelination and neurological function was determined.

Results

Hypoxic preconditioning significantly attenuated H/I brain injury at 7 days and remarkably improved both sensorimotor and cognitive functional performances up to 35 days after H/I. HPC‐afforded improvement in long‐term neurological outcomes was attributable, at least in part, to restoration of the differentiation and maturation capacity in oligodendrocyte progenitor cells, amelioration of microglia/macrophage activation and neuroinflammation, and continuation of brain development after H/I.

Conclusions

Hypoxic preconditioning restores white matter repair, development, and functional integrity in developing brain after H/I brain injury.

Oligodendrocyte Bioenergetics in Health and Disease

The human brain weighs approximately 2% of the body; however, it consumes about 20% of a person’s total energy intake. Cellular bioenergetics in the central nervous system involves a delicate balance between biochemical processes engaged in energy conversion and those responsible for respiration. Neurons have high energy demands, which rely on metabolic coupling with glia, such as with oligodendrocytes and astrocytes. It has been well established that astrocytes recycle and transport glutamine to neurons to make the essential neurotransmitters, glutamate and GABA, as well as shuttle lactate to support energy synthesis in neurons. However, the metabolic role of oligodendrocytes in the central nervous system is less clear. In this review, we discuss the energetic demands of oligodendrocytes in their survival and maturation, the impact of altered oligodendrocyte energetics on disease pathology, and the role of energetic metabolites, taurine, creatine, N-acetylaspartate, and biotin, in regulating oligodendrocyte function.

Monocarboxylate transporter 1 and the vulnerability of oligodendrocyte lineage cells to metabolic stresses

AIMS

Oligodendrocytes, especially oligodendrocyte precursor cells, are known to be sensitive to hypoxic and metabolic stresses. Vulnerability of oligodendrocytes is considered a contributing factor to white matter dysfunction. However, little is known about the energy processing characteristics of oligodendrocyte lineage cells under basal and metabolic stress conditions. The aim of this study was to identify the energy requirements and cellular responses of oligodendrocytes at different developmental stages.

METHODS

We compared the metabolic stress responses between myelinating oligodendrocytes (OLs) and oligodendrocyte precursor cells (OPCs). Differential regulation of cellular response was also investigated.

RESULTS

We found that, following cerebral ischemia, monocarboxylate transporter 1 (MCT1) expression was upregulated in the peri-infarct striatum but not in the cortex of the brain. In vitro ischemia models were used to induce oligodendrocyte stress as well. An increase in MCT1 expression was detected in OPCs after a mild oxygen-glucose deprivation. Double-labeled immunohistochemical analysis revealed that OPCs and OLs responded differently to metabolic stresses and that the susceptibility to metabolic stresses of OPCs and OLs was associated with their distinct expression profiles of MCT1.

CONCLUSION

Taken together, this study shows that MCT1 plays a role in the responses of OPCs and OLs to metabolic and ischemic stresses and suggests that redistribution of energy substrates is a determinant in white matter injury.