Oligodendrocyte progenitor cell | |
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Details | |
System | Central nervous system |
Location | Brain, spinal cord |
Identifiers | |
Acronym(s) | OPC |
MeSH | D000073637 |
TH | H2.00.06.2.01007 |
Anatomical terms of microanatomy |
Oligodendrocyte progenitor cells (OPCs), also known as oligodendrocyte precursor cells, NG2-glia, O2A cells, or polydendrocytes, are a subtype of glia in the central nervous system named for their essential role as precursors to oligodendrocytes and myelin. [1] They are typically identified in the human by co-expression of PDGFRA and CSPG4.
OPCs play a critical role in developmental and adult myelinogenesis. They give rise to oligodendrocytes, which then wrap around axons and provide electrical insulation by forming a myelin sheath. This enables faster action potential propagation and high fidelity transmission without a need for an increase in axonal diameter. [2] The loss or lack of OPCs, and consequent lack of differentiated oligodendrocytes, is associated with a loss of myelination and subsequent impairment of neurological functions. [3] In addition, OPCs express receptors for various neurotransmitters and undergo membrane depolarization when they receive synaptic inputs from neurons.
OPCs are glial cells that are typically identified by co-expression of NG2 (a chondroitin sulfate proteoglycan encoded by CSPG4 in humans) and platelet-derived growth factor receptor alpha (encoded by PDGFRA ). [4] They are smaller than neurons, of comparable size to other glia, and can either have a bipolar or complex multipolar morphology with processes reaching up to ~50 μm. [5] OPCs comprise approximately 3–4% of cells in grey matter and 8–9% in white matter, making them the fourth largest group of glia after astrocytes, microglia and oligodendrocytes. [6]
OPCs are present throughout the brain, including the hippocampus and in all layers of the neocortex. [7] They distribute themselves and achieve a relatively even distribution through active self-repulsion. [5] [8] OPCs constantly survey their surroundings through actively extending and retracting processes that have been termed growth cone like processes. [9] Death or differentiation of an OPC is rapidly followed by migration or local proliferation of a neighboring cell to replace it.
In white matter, OPCs are found along unmyelinated axons [10] as well as along myelinated axons, engulfing nodes of Ranvier. [11] [12] Recently, OPCs have been shown to reside in close contact with NG2-expressing pericytes in cerebral white matter, as well. [13]
OPCs receive synaptic contacts onto their processes from both glutamatergic [14] and GABAergic neurons. [1] [15] OPCs receive preferred somatic contacts from fast-spiking GABAergic neurons, while non-fast spiking interneurons have a preference for contacting the processes. [16] These inhibitory connections (in mice) occur mainly during a specific period in development, from postnatal day 8 till postnatal day 13.
OPCs first appear during embryonic organogenesis. In the developing neural tube, Shh (Sonic hedgehog) signaling and expression of Nkx6.1/Nkx6.2 coordinate expression of Olig1 and Olig2 in neuroepithelial cells of the pMN and p3 domains of the ventral ventricular zone. [17] [18] [19] Together, Nkx2.2 and Olig1/Olig2 drive OPC specification. [20] [21]
In the forebrain, three regionally distinct sources have been shown to generate OPCs sequentially. OPCs first originate from Nkx2.1-expressing cells in the ventricular zone of the medial ganglionic eminence. [22] [23] [24] Some OPCs are also generated from multipotent progenitors in the subventricular zone (SVZ). These cells migrate into the olfactory bulb. [25] Depending on their origin in the SVZ, these progenitors give rise to either OPCs or astrocytes. Typically, cells originating from the posterior and dorsomedial SVZ produce more oligodendrocytes owing to increased exposure to posterior Shh signaling and dorsal Wnt signaling which favors OPC specification, in contrast to ventral Bmp signaling which inhibits it. [26] [27]
As development progresses, second and third waves of OPCs originate from Gsh2-expressing cells in the lateral and caudal ganglionic eminences and generate the majority of adult oligodendrocytes. [22] After the committed progenitor cells exit the germinal zones, they migrate and proliferate locally to eventually occupy the entire CNS parenchyma. OPCs are highly proliferative, migratory, and have bipolar morphology. [28]
OPCs continue to exist in both white and grey matter in the adult brain and maintain their population through self-renewal. [29] [30] White matter OPCs proliferate at higher rates and are best known for their contributions to adult myelinogenesis, while grey matter OPCs are slowly proliferative or quiescent and mostly remain in an immature state. [31] [32] Subpopulations of OPCs have different resting membrane potentials, ion channel expression, and ability to generate action potentials. [33]
Typically beginning in postnatal development, OPCs myelinate the entire central nervous system (CNS). [34] They differentiate into the less mobile premyelinating oligodendrocytes that further differentiate into oligodendrocytes, [35] a process characterized by the emergence of the expression of myelin basic protein (MBP), proteolipid protein (PLP), or myelin-associated glycoprotein (MAG). [28] Following terminal differentiation in vivo , mature oligodendrocytes wrap around and myelinate axons. In vitro , oligodendrocytes create an extensive network of myelin-like sheets. The process of differentiation can be observed both through morphological changes and cell surface markers specific to the discrete stage of differentiation, though the signals for differentiation are unknown. [36] The various waves of OPCs could myelinate distinct regions of the brain, which suggests that distinct functional subpopulations of OPCs perform different functions. [37]
Differentiation of OPCs into oligodendrocytes involves massive reorganization of cytoskeleton proteins ultimately resulting in increased cell branching and lamella extension, allowing oligodendrocytes to myelinate multiple axons. [28] Multiple pathways contribute to oligodendrocyte branching, but the exact molecular process by which oligodendrocytes extend and wrap around multiple axons remains incompletely understood. [28] Laminin, a component of the extracellular matrix, plays an important role in regulating oligodendrocyte production. Mice lacking laminin alpha2-subunit produced fewer OPCs in the subventricular zone (SVZ). [38] Deletion of Dicer1 disrupts normal brain myelination. However, miR-7a, and miRNA in OPCs, promotes OPC production during brain development. [39]
The possibility and in vivo relevance of OPC differentiation into astrocytes or neurons are highly debated. [1] Using Cre-Lox recombination-mediated genetic fate mapping, several labs have reported the fate of OPCs using different Cre driver and reporter mouse lines. [40] It is generally held that OPCs predominantly generate oligodendrocytes, and the rate at which they generate oligodendrocytes declines with age and is greater in white matter than in grey matter. Up to 30% of the oligodendrocytes that exist in the adult corpus callosum are generated de novo from OPCs over a period of 2 months. It is not known whether all OPCs eventually generate oligodendrocytes while self-renewing the population, or whether some remain as OPCs throughout the life of the animal and never differentiate into oligodendrocytes. [41]
OPCs may retain the ability to differentiate into astrocytes into adulthood. [42] [43] Using NG2-Cre mice, it was shown that OPCs in the prenatal and perinatal grey matter of the ventral forebrain and spinal cord generate protoplasmic type II astrocytes in addition to oligodendrocytes. However, contrary to the prediction from optic nerve cultures, OPCs in white matter do not generate astrocytes. When the oligodendrocyte transcription factor Olig2 is deleted specifically in OPCs, there is a region- and age-dependent switch in the fate of OPCs from oligodendrocytes to astrocytes. [44]
Whereas some studies suggested that OPCs can generate cortical neurons, [45] other studies rejected these findings. [46] The question is unresolved, as studies continue to find that certain populations of OPCs can form neurons. [47] In conclusion, these studies suggest that OPCs do not generate a significant number of neurons under normal conditions, and that they are distinct from neural stem cells that reside in the subventricular zone. [48]
As implied by their name, OPCs were long held to function purely as progenitors to oligodendrocytes. Their role as a progenitor cell type has since expanded to include both oligodendrocytes and some protoplasmic type II astrocytes in grey matter. [43] Later, additional functions were suggested.
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Spontaneous myelin repair was first observed in cat models. [49] It was later discovered to occur in the human CNS as well, specifically in cases of multiple sclerosis (MS). [50] Spontaneous myelin repair does not result in morphologically normal oligodendrocytes and is associated with thinner myelin compared to axonal diameter than normal myelin. [51] Despite morphological abnormalities, however, remyelination does restore normal conduction. [52] In addition, spontaneous remyelination does not appear to be rare, at least in the case of MS. Studies of MS lesions reported the average extent of remyelination as high as 47%. [53] Comparative studies of cortical lesions reported a greater proportion of remyelination in the cortex as opposed to white matter lesions. [50]
OPCs retain the ability to proliferate in adulthood and comprise 70–90% of the proliferating cell population in the mature CNS. [6] [54] Under conditions in the developing and mature CNS where a reduction in the normal number of oligodendrocytes or myelin occurs, OPCs react promptly by undergoing increased proliferation. Rodent OPCs proliferate in response to demyelination in acute or chronic lesions created by chemical agents such as lysolecithin, and newborn cells differentiate into remyelinating oligodendrocytes. [55] [56] A chelating agent cuprizone is also used in these demyelination studies in rats. [57] Similarly, OPC proliferation occurs in other types of injury that are accompanied by loss of myelin, such as spinal cord injury. [58]
Despite OPCs' potential to give rise to myelinating oligodendrocytes, complete myelin regeneration is rarely observed clinically or in chronic experimental models. Possible explanations for remyelination failure include depletion of OPCs over time, failure to recruit OPCs to the demyelinated lesion, and failure of recruited OPCs to differentiate into mature oligodendrocytes [58] (reviewed in [59] [60] [61] ). In fresh MS lesions, clusters of HNK-1+ oligodendrocytes have been observed, [62] which suggests that under favorable conditions OPCs expand around demyelinated lesions and generate new oligodendrocytes. In chronic MS lesions where remyelination is incomplete, there is evidence that there are oligodendrocytes with processes extending toward demyelinated axons, but they do not seem to be able to generate new myelin. [63] The mechanisms that regulate differentiation of OPCs into myelinating oligodendrocytes are an active area of research.
Another unanswered question is whether the OPC pool eventually becomes depleted after it is used to generate remyelinating cells. Clonal analysis of isolated OPCs in the normal mouse forebrain suggests that in the adult, most clones originating from single OPCs consist of either a heterogeneous population containing both oligodendrocytes and OPCs or a homogeneous population consisting exclusively of OPCs, suggesting that OPCs in the adult CNS are able to self-renew and are not depleted under normal conditions. [64] However, it is not known whether this dynamic is altered in response to demyelinating lesions.
Nodes of Ranvier are spaces between myelin sheathing. OPCs extend their processes to the nodes of Ranvier [11] and together with astrocyte processes make up the nodal glial complex. Since the nodes of Ranvier contain a high density of voltage-dependent sodium channels and allow regenerative action potentials to be generated, it is speculated that this location allows OPCs to sense and possibly respond to neuronal activity.
OPCs synthesize the neuromodulatory factors prostaglandin D2 synthase (PTGDS) and neuronal pentraxin 2 (NPTX2). [65] This is regulated by NG2, whose intracellular domain can be cleaved by γ-secretase [66] [67] and translocated to the nucleus. The NG2 ectodomain can also modulate AMPA and NMDA receptor-dependent LTP. Constitutive and activity-dependent cleavage of NG2 by ADAM10 releases the ectodomain, which contains two N-terminal LNS domains that act on neuronal synapses. [66] [67]
OPCs express numerous voltage-gated ion channels and neurotransmitter receptors. [68] Structural studies have shown that neurons form synapses with OPCs in both grey matter [14] and white matter. [11] [69] Electron microscopy revealed OPC membranes apposed to neuronal presynaptic terminals filled with synaptic vesicles. OPCs express AMPA receptors and GABAA receptors and undergo small membrane depolarizations in response to presynaptic vesicular glutamate or GABA release.
OPCs can undergo cell division while maintaining synaptic inputs from neurons. [70] These observations suggest that cells that receive neuronal synaptic inputs and those that differentiate into oligodendrocytes are not mutually exclusive cell populations but that the same population of OPCs can receive synaptic inputs and generate myelinating oligodendrocytes. However, OPCs appear to lose their ability to respond to synaptic inputs from neurons as they differentiate into mature oligodendrocytes. [71] [72] The functional significance of the neuron-OPC synapses remains to be elucidated.
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OPCs have been increasingly recognized for their pivotal role in modulating immune responses, particularly in autoimmune diseases such as multiple sclerosis. [73] [74] They may participate in both initiation and resolution of immune responses to disease or injury. [73] They are highly responsive to injury, undergo a morphological activation similar to that of astrocytes and microglia, and may contribute to glial scar formation. [75] Conversely, OPCs have been shown to downregulate microglia activation and protect against neuronal death. [76] They also express and secrete many immune-related molecules, such as chemokines, cytokines, interleukins, and other related ligands or receptors. [77] OPCs can internalize myelin debris via phagocytosis, a process mediated through the LRP1 pathway. [78] [79] Furthermore, recent works have illustrated that OPCs can act as antigen presenting cells via both MHC class I and class II and can modulate both CD4+ and CD8+ T cells. [80] [81] [82]
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Transplantation of OPCs has been considered as a possible treatment for neurological diseases which cause demyelination. However, it is difficult to generate a suitable number of quality cells for clinical use. Finding a source for these cells remains impractical as of 2016. Should adult cells be used for transplantation, a brain biopsy would be required for each patient, adding to the risk of immune rejection. Embryonically derived stem cells have been demonstrated to carry out remyelination under laboratory conditions, but some religious groups are opposed to their use.[ citation needed ] Adult central nervous system stem cells have also been shown to generate myelinating oligodendrocytes, but are not readily accessible. [83]
Even if a viable source of OPCs were found, identifying and monitoring the outcome of remyelination remains difficult, though multimodal measures of conduction velocity and emerging magnetic resonance imaging techniques offer improved sensitivity versus other imaging methods. [84] In addition, the interaction between transplanted cells and immune cells and the effect of inflammatory immune cells on remyelination have yet to be fully characterized. If the failure of endogenous remyelination is due to an unfavorable differentiation environment, then this will have to be addressed prior to transplantation.[ citation needed ]
It had been known since the early 1900s that astrocytes, oligodendrocytes, and microglia make up the major glial cell populations in the mammalian CNS. The presence of another glial cell population had escaped recognition because of the lack of a suitable marker to identify them in tissue sections. The notion that there exists a population of glial progenitor cells in the developing and mature CNS began to be entertained in the late 1980s by several independent groups. In one series of studies on the development and origin of oligodendrocytes in the rodent CNS, a population of immature cells that appeared to be precursors to oligodendrocytes was identified by the expression of the GD3 ganglioside. [85]
In a separate series of studies, cells from perinatal rat optic nerves that expressed the A2B5 ganglioside were shown to differentiate into oligodendrocytes in culture. [86] Subsequently, A2B5+ cells from other CNS regions and from adult CNS were also shown to generate oligodendrocytes. Based on the observation that these cells require PDGF for their proliferation and expansion, the expression of the alpha receptor for platelet-derived growth factor (Pdgfra) was used to search for the in vivo correlates of the A2B5+ cells, which led to the discovery of a unique population of Pdgfra+ cells in the CNS whose appearance and distribution were consistent with those of developing oligodendrocytes. [87]
Independently, Stallcup and colleagues generated an antiserum that recognized a group of rat brain tumor cell line, which exhibited properties that were intermediate between those of typical neurons and glial cells. Biochemical studies showed that the antiserum recognized a chondroitin sulfate proteoglycan with a core glycoprotein of 300 kDa, [88] and the antigen was named NG2 (nerve/glial antigen 2). [89] [90] NG2 was found to be expressed on A2B5+ oligodendrocyte precursor cells isolated from the perinatal rat CNS tissues and on process-bearing cells in the CNS in vivo. [88] [91] Comparison of NG2 and Pdgfra expression revealed that NG2 and PDGFRA are expressed on the same population of cells in the CNS. [4] These cells represent 2–9% of all the cells and remain proliferative in the mature CNS. [6]
Myelin is a lipid-rich material that surrounds nerve cell axons to insulate them and increase the rate at which electrical impulses pass along the axon. The myelinated axon can be likened to an electrical wire with insulating material (myelin) around it. However, unlike the plastic covering on an electrical wire, myelin does not form a single long sheath over the entire length of the axon. Rather, myelin ensheaths the axon segmentally: in general, each axon is encased in multiple long sheaths with short gaps between, called nodes of Ranvier. At the nodes of Ranvier, which are approximately one thousandth of a mm in length, the axon's membrane is bare of myelin.
Schwann cells or neurolemmocytes are the principal glia of the peripheral nervous system (PNS). Glial cells function to support neurons and in the PNS, also include satellite cells, olfactory ensheathing cells, enteric glia and glia that reside at sensory nerve endings, such as the Pacinian corpuscle. The two types of Schwann cells are myelinating and nonmyelinating. Myelinating Schwann cells wrap around axons of motor and sensory neurons to form the myelin sheath. The Schwann cell promoter is present in the downstream region of the human dystrophin gene that gives shortened transcript that are again synthesized in a tissue-specific manner.
Nervous tissue, also called neural tissue, is the main tissue component of the nervous system. The nervous system regulates and controls body functions and activity. It consists of two parts: the central nervous system (CNS) comprising the brain and spinal cord, and the peripheral nervous system (PNS) comprising the branching peripheral nerves. It is composed of neurons, also known as nerve cells, which receive and transmit impulses, and neuroglia, also known as glial cells or glia, which assist the propagation of the nerve impulse as well as provide nutrients to the neurons.
Oligodendrocytes, also known as oligodendroglia, are a type of neuroglia whose main functions are to provide support and insulation to axons within the central nervous system (CNS) of jawed vertebrates. Their function is similar to that of Schwann cells, which perform the same task in the peripheral nervous system (PNS). Oligodendrocytes accomplish this by forming the myelin sheath around axons. Unlike Schwann cells, a single oligodendrocyte can extend its processes to cover around 50 axons, with each axon being wrapped in approximately 1 μm of myelin sheath. Furthermore, an oligodendrocyte can provide myelin segments for multiple adjacent axons.
Glia, also called glial cells (gliocytes) or neuroglia, are non-neuronal cells in the central nervous system and the peripheral nervous system that do not produce electrical impulses. The neuroglia make up more than one half the volume of neural tissue in the human body. They maintain homeostasis, form myelin in the peripheral nervous system, and provide support and protection for neurons. In the central nervous system, glial cells include oligodendrocytes, astrocytes, ependymal cells and microglia, and in the peripheral nervous system they include Schwann cells and satellite cells.
In vertebrates, a neuroblast or primitive nerve cell is a postmitotic cell that does not divide further, and which will develop into a neuron after a migration phase. In invertebrates such as Drosophila, neuroblasts are neural progenitor cells which divide asymmetrically to produce a neuroblast, and a daughter cell of varying potency depending on the type of neuroblast. Vertebrate neuroblasts differentiate from radial glial cells and are committed to becoming neurons. Neural stem cells, which only divide symmetrically to produce more neural stem cells, transition gradually into radial glial cells. Radial glial cells, also called radial glial progenitor cells, divide asymmetrically to produce a neuroblast and another radial glial cell that will re-enter the cell cycle.
In neuroscience and anatomy, nodes of Ranvier, also known as myelin-sheath gaps, occur along a myelinated axon where the axolemma is exposed to the extracellular space. Nodes of Ranvier are uninsulated and highly enriched in ion channels, allowing them to participate in the exchange of ions required to regenerate the action potential. Nerve conduction in myelinated axons is referred to as saltatory conduction due to the manner in which the action potential seems to "jump" from one node to the next along the axon. This results in faster conduction of the action potential.
Astrocytes, also known collectively as astroglia, are characteristic star-shaped glial cells in the brain and spinal cord. They perform many functions, including biochemical control of endothelial cells that form the blood–brain barrier, provision of nutrients to the nervous tissue, maintenance of extracellular ion balance, regulation of cerebral blood flow, and a role in the repair and scarring process of the brain and spinal cord following infection and traumatic injuries. The proportion of astrocytes in the brain is not well defined; depending on the counting technique used, studies have found that the astrocyte proportion varies by region and ranges from 20% to around 40% of all glia. Another study reports that astrocytes are the most numerous cell type in the brain. Astrocytes are the major source of cholesterol in the central nervous system. Apolipoprotein E transports cholesterol from astrocytes to neurons and other glial cells, regulating cell signaling in the brain. Astrocytes in humans are more than twenty times larger than in rodent brains, and make contact with more than ten times the number of synapses.
Astrogliosis is an abnormal increase in the number of astrocytes due to the destruction of nearby neurons from central nervous system (CNS) trauma, infection, ischemia, stroke, autoimmune responses or neurodegenerative disease. In healthy neural tissue, astrocytes play critical roles in energy provision, regulation of blood flow, homeostasis of extracellular fluid, homeostasis of ions and transmitters, regulation of synapse function and synaptic remodeling. Astrogliosis changes the molecular expression and morphology of astrocytes, in response to infection for example, in severe cases causing glial scar formation that may inhibit axon regeneration.
Gliosis is a nonspecific reactive change of glial cells in response to damage to the central nervous system (CNS). In most cases, gliosis involves the proliferation or hypertrophy of several different types of glial cells, including astrocytes, microglia, and oligodendrocytes. In its most extreme form, the proliferation associated with gliosis leads to the formation of a glial scar.
Neural stem cells (NSCs) are self-renewing, multipotent cells that firstly generate the radial glial progenitor cells that generate the neurons and glia of the nervous system of all animals during embryonic development. Some neural progenitor stem cells persist in highly restricted regions in the adult vertebrate brain and continue to produce neurons throughout life. Differences in the size of the central nervous system are among the most important distinctions between the species and thus mutations in the genes that regulate the size of the neural stem cell compartment are among the most important drivers of vertebrate evolution.
Radial glial cells, or radial glial progenitor cells (RGPs), are bipolar-shaped progenitor cells that are responsible for producing all of the neurons in the cerebral cortex. RGPs also produce certain lineages of glia, including astrocytes and oligodendrocytes. Their cell bodies (somata) reside in the embryonic ventricular zone, which lies next to the developing ventricular system.
Remyelination is the process of propagating oligodendrocyte precursor cells to form oligodendrocytes to create new myelin sheaths on demyelinated axons in the Central nervous system (CNS). This is a process naturally regulated in the body and tends to be very efficient in a healthy CNS. The process creates a thinner myelin sheath than normal, but it helps to protect the axon from further damage, from overall degeneration, and proves to increase conductance once again. The processes underlying remyelination are under investigation in the hope of finding treatments for demyelinating diseases, such as multiple sclerosis.
Neuroregeneration involves the regrowth or repair of nervous tissues, cells or cell products. Neuroregenerative mechanisms may include generation of new neurons, glia, axons, myelin, or synapses. Neuroregeneration differs between the peripheral nervous system (PNS) and the central nervous system (CNS) by the functional mechanisms involved, especially in the extent and speed of repair. When an axon is damaged, the distal segment undergoes Wallerian degeneration, losing its myelin sheath. The proximal segment can either die by apoptosis or undergo the chromatolytic reaction, which is an attempt at repair. In the CNS, synaptic stripping occurs as glial foot processes invade the dead synapse.
Myelinogenesis is the formation and development of myelin sheaths in the nervous system, typically initiated in late prenatal neurodevelopment and continuing throughout postnatal development. Myelinogenesis continues throughout the lifespan to support learning and memory via neural circuit plasticity as well as remyelination following injury. Successful myelination of axons increases action potential speed by enabling saltatory conduction, which is essential for timely signal conduction between spatially separate brain regions, as well as provides metabolic support to neurons.
Endogenous regeneration in the brain is the ability of cells to engage in the repair and regeneration process. While the brain has a limited capacity for regeneration, endogenous neural stem cells, as well as numerous pro-regenerative molecules, can participate in replacing and repairing damaged or diseased neurons and glial cells. Another benefit that can be achieved by using endogenous regeneration could be avoiding an immune response from the host.
Myelin regulatory factor, also known as myelin gene regulatory factor (MRF), is a protein that in humans is encoded by the MYRF gene.
A neuronal lineage marker is an endogenous tag that is expressed in different cells along neurogenesis and differentiated cells such as neurons. It allows detection and identification of cells by using different techniques. A neuronal lineage marker can be either DNA, mRNA or RNA expressed in a cell of interest. It can also be a protein tag, as a partial protein, a protein or an epitope that discriminates between different cell types or different states of a common cell. An ideal marker is specific to a given cell type in normal conditions and/or during injury. Cell markers are very valuable tools for examining the function of cells in normal conditions as well as during disease. The discovery of various proteins specific to certain cells led to the production of cell-type-specific antibodies that have been used to identify cells.
Patrizia Casaccia is an Italian neuroscientist who is the Director of the Neuroscience Initiative of the Advanced Science Research Center at the CUNY Graduate Center, as well as a Professor of Neuroscience, Genetics & Genomics, and Neurology at the Icahn School of Medicine at Mount Sinai. Casaccia is a pioneer in the study of myelin. Her research focuses on understanding the neurobiological and neuroimmune mechanisms of multiple sclerosis and to translate findings into treatments. Casaccia co-founded the Center for Glial Biology at Mount Sinai and CUNY and is one of the Directors of the center.
A myelinoid or myelin organoid is a three dimensional in vitro cultured model derived from human pluripotent stem cells (hPSCs) that represents various brain regions, the spinal cord or the peripheral nervous system in early fetal human development. Myelinoids have the capacity to recapitulate aspects of brain developmental processes, microenvironments, cell to cell interaction, structural organization and cellular composition. The differentiating aspect dictating whether an organoid is deemed a cerebral organoid/brain organoid or myelinoid is the presence of myelination and compact myelin formation that is a defining feature of myelinoids. Due to the complex nature of the human brain, there is a need for model systems which can closely mimic complicated biological processes. Myelinoids provide a unique in vitro model through which myelin pathology, neurodegenerative diseases, developmental processes and therapeutic screening can be accomplished.