The recently identified P2Y-like receptor GPR17 is a sensor of brain damage and a new target for brain repair.
ABSTRACT: Deciphering the mechanisms regulating the generation of new neurons and new oligodendrocytes, the myelinating cells of the central nervous system, is of paramount importance to address new strategies to replace endogenous damaged cells in the adult brain and foster repair in neurodegenerative diseases. Upon brain injury, the extracellular concentrations of nucleotides and cysteinyl-leukotrienes (cysLTs), two families of endogenous signaling molecules, are markedly increased at the site of damage, suggesting that they may act as "danger signals" to alert responses to tissue damage and start repair. Here we show that, in brain telencephalon, GPR17, a recently deorphanized receptor for both uracil nucleotides and cysLTs (e.g., UDP-glucose and LTD(4)), is normally present on neurons and on a subset of parenchymal quiescent oligodendrocyte precursor cells. We also show that induction of brain injury using an established focal ischemia model in the rodent induces profound spatiotemporal-dependent changes of GPR17. In the lesioned area, we observed an early and transient up-regulation of GPR17 in neurons expressing the cellular stress marker heat shock protein 70. Magnetic Resonance Imaging in living mice showed that the in vivo pharmacological or biotechnological knock down of GPR17 markedly prevents brain infarct evolution, suggesting GPR17 as a mediator of neuronal death at this early ischemic stage. At later times after ischemia, GPR17 immuno-labeling appeared on microglia/macrophages infiltrating the lesioned area to indicate that GPR17 may also acts as a player in the remodeling of brain circuitries by microglia. At this later stage, parenchymal GPR17+ oligodendrocyte progenitors started proliferating in the peri-injured area, suggesting initiation of remyelination. To confirm a specific role for GPR17 in oligodendrocyte differentiation, the in vitro exposure of cortical pre-oligodendrocytes to the GPR17 endogenous ligands UDP-glucose and LTD(4) promoted the expression of myelin basic protein, confirming progression toward mature oligodendrocytes. Thus, GPR17 may act as a "sensor" that is activated upon brain injury on several embryonically distinct cell types, and may play a key role in both inducing neuronal death inside the ischemic core and in orchestrating the local remodeling/repair response. Specifically, we suggest GPR17 as a novel target for therapeutic manipulation to foster repair of demyelinating wounds, the types of lesions that also occur in patients with multiple sclerosis.
Project description:The basic helix-loop-helix transcription factor Olig1 promotes oligodendrocyte maturation and is required for myelin repair. We characterized an Olig1-regulated G protein-coupled receptor, GPR17, whose function is to oppose the action of Olig1. Gpr17 was restricted to oligodendrocyte lineage cells, but was downregulated during the peak period of myelination and in adulthood. Transgenic mice with sustained Gpr17 expression in oligodendrocytes exhibited stereotypic features of myelinating disorders in the CNS. Gpr17 overexpression inhibited oligodendrocyte differentiation and maturation both in vivo and in vitro. Conversely, Gpr17 knockout mice showed early onset of oligodendrocyte myelination. The opposing action of Gpr17 on oligodendrocyte maturation reflects, at least partially, upregulation and nuclear translocation of the potent oligodendrocyte differentiation inhibitors ID2/4. Collectively, these findings suggest that GPR17 orchestrates the transition between immature and myelinating oligodendrocytes via an ID protein-mediated negative regulation and may serve as a potential therapeutic target for CNS myelin repair.
Project description:Promoting remyelination is recognized as a novel strategy to foster repair in neurodegenerative demyelinating diseases, such as multiple sclerosis. In this respect, the receptor GPR17, recently emerged as a new target for remyelination, is expressed by early oligodendrocyte precursors (OPCs) and after a certain differentiation stage it has to be downregulated to allow progression to mature myelinating oligodendrocytes. Here, we took advantage of the first inducible GPR17 reporter mouse line (GPR17-iCreERT2 xCAG-eGFP mice) allowing to follow the final fate of GPR17+ cells by tamoxifen-induced GFP-labeling to unveil the destiny of these cells in two demyelination models: experimental autoimmune encephalomyelitis (EAE), characterized by marked immune cell activation and inflammation, and cuprizone induced demyelination, where myelin dysfunction is achieved by a toxic insult. In both models, demyelination induced a strong increase of fluorescent GFP+ cells at damaged areas. However, only in the cuprizone model reacting GFP+ cells terminally differentiated to mature oligodendrocytes, thus contributing to remyelination. In EAE, GFP+ cells were blocked at immature stages and never became myelinating oligodendrocytes. We suggest these strikingly distinct fates be due to different permissiveness of the local CNS environment. Based on previously reported GPR17 activation by emergency signals (e.g., Stromal Derived Factor-1), we propose that a marked inflammatory milieu, such as that reproduced in EAE, induces GPR17 overactivation resulting in impaired downregulation, untimely and prolonged permanence in OPCs, leading, in turn, to differentiation blockade. Combined treatments with remyelinating agents and anti-inflammatory drugs may represent new potential adequate strategies to halt neurodegeneration and foster recovery.
Project description:Unveiling the mechanisms participating in the damage and repair of traumatic brain injury (TBI) is fundamental to develop new therapies. The P2Y-like GPR17 receptor has recently emerged as a sensor of damage and a key actor in lesion remodeling/repair in the rodent brain, but its role in humans is totally unknown. Here, we characterized GPR17 expression in brain specimens from seven intensive care unit TBI patients undergoing neurosurgery for contusion removal and from 28 autoptic TBI cases (and 10 control subjects of matched age and gender) of two university hospitals. In both neurosurgery and autoptic samples, GPR17 expression was strong inside the contused core and progressively declined distally according to a spatio-temporal gradient. Inside and around the core, GPR17 labeled dying neurons, reactive astrocytes, and activated microglia/macrophages. In peri-contused parenchyma, GPR17 decorated oligodendrocyte precursor cells (OPCs) some of which had proliferated, indicating re-myelination attempts. In autoptic cases, GPR17 expression positively correlated with death for intracranial complications and negatively correlated with patients' post-traumatic survival. Data indicate lesion-specific sequential involvement of GPR17 in the (a) death of irreversibly damaged neurons, (b) activation of microglia/macrophages remodeling the lesion, and (c) activation/proliferation of multipotent parenchymal progenitors (both reactive astrocytes and OPCs) starting repair processes. Data validate GPR17 as a target for neurorepair and are particularly relevant to setting up new therapies for TBI patients.
Project description:Identification of additional uses for existing drugs is a hot topic in drug discovery and a viable alternative to de novo drug development. HAMI3379 is known as an antagonist of the cysteinyl-leukotriene CysLT2 receptor, and was initially developed to treat cardiovascular and inflammatory disorders. In our study we identified HAMI3379 as an antagonist of the orphan G protein-coupled receptor GPR17. HAMI3379 inhibits signaling of recombinant human, rat, and mouse GPR17 across various cellular backgrounds, and of endogenous GPR17 in primary rodent oligodendrocytes. GPR17 blockade by HAMI3379 enhanced maturation of primary rat and mouse oligodendrocytes, but was without effect in oligodendrocytes from GPR17 knockout mice. In human oligodendrocytes prepared from inducible pluripotent stem cells, GPR17 is expressed and its activation impaired oligodendrocyte differentiation. HAMI3379, conversely, efficiently favored human oligodendrocyte differentiation. We propose that HAMI3379 holds promise for pharmacological exploitation of orphan GPR17 to enhance regenerative strategies for the promotion of remyelination in patients.
Project description:The CNS plays a pivotal role in energy homeostasis, but whether oligodendrocytes are involved has been largely unexplored. Here, we show that signaling through GPR17, a G-protein-coupled receptor predominantly expressed in the oligodendrocyte lineage, regulates food intake by modulating hypothalamic neuronal activities. GPR17-null mice and mice with an oligodendrocyte-specific knockout of GPR17 have lean phenotypes on a high-fat diet, suggesting that GPR17 regulates body weight by way of oligodendrocytes. Downregulation of GPR17 results in activation of cAMP-protein kinase A (PKA) signaling in oligodendrocytes and upregulated expression of pyruvate dehydrogenase kinase 1 (PDK1), which promotes lactate production. Elevation of lactate activates AKT and STAT3 signaling in the hypothalamic neurons, leading to increased expression of Pomc and suppression of Agrp. Our findings uncover a critical role of oligodendrocytes in metabolic homeostasis, where GPR17 modulates the production of lactate, which, in turn, acts as a metabolic signal to regulate neuronal activity.
Project description:Oligodendrocytes are the myelin-producing cells of the central nervous system (CNS). A variety of brain disorders from "classical" demyelinating diseases, such as multiple sclerosis, stroke, schizophrenia, depression, Down syndrome and autism, are shown myelination defects. Oligodendrocyte myelination is regulated by a complex interplay of intrinsic, epigenetic and extrinsic factors. Gpr17 (G protein-coupled receptor 17) is a G protein-coupled receptor, and has been identified to be a regulator for oligodendrocyte development. Here, we demonstrate that the absence of Gpr17 enhances remyelination in vivo with a toxin-induced model whereby focal demyelinated lesions are generated in spinal cord white matter of adult mice by localized injection of LPC(L-a-lysophosphatidylcholine). The increased expression of the activated form of Erk1/2 (phospho-Erk1/2) in lesion areas suggested the potential role of Erk1/2 activity on the Gpr17-dependent modulation of myelination. The absence of Gpr17 enhances remyelination is correlate with the activated Erk1/2 (phospho-Erk1/2).Being a membrane receptor, Gpr17 represents an ideal druggable target to be exploited for innovative regenerative approaches to acute and chronic CNS diseases.
Project description:Nucleotides and cysteinyl-leukotrienes (CysLTs) are unrelated signaling molecules inducing multiple effects through separate G-protein-coupled receptors: the P2Y and the CysLT receptors. Here we show that GPR17, a Gi-coupled orphan receptor at intermediate phylogenetic position between P2Y and CysLT receptors, is specifically activated by both families of endogenous ligands, leading to both adenylyl cyclase inhibition and intracellular calcium increases. Agonist-response profile, as determined by [(35)S]GTPgammaS binding, was different from that of already known CysLT and P2Y receptors, with EC(50) values in the nanomolar and micromolar range, for CysLTs and uracil nucleotides, respectively. Both rat and human receptors are highly expressed in the organs typically undergoing ischemic damage, that is, brain, heart and kidney. In vivo inhibition of GPR17 by either CysLT/P2Y receptor antagonists or antisense technology dramatically reduced ischemic damage in a rat focal ischemia model, suggesting GPR17 as the common molecular target mediating brain damage by nucleotides and CysLTs. In conclusion, the deorphanization of GPR17 revealed a dualistic receptor for two endogenous unrelated ligand families. These findings may lead to dualistic drugs of previously unexplored therapeutic potential.
Project description:Replacement of the lost myelin sheath is a therapeutic goal for treating demyelinating diseases of the central nervous system (CNS), such as multiple sclerosis (MS). The G protein (heterotrimeric guanine nucleotide-binding protein)-coupled receptor (GPCR) GPR17, which is phylogenetically closely related to receptors of the "purinergic cluster," has emerged as a modulator of CNS myelination. However, whether GPR17-mediated signaling positively or negatively regulates this critical process is unresolved. We identified a small-molecule agonist, MDL29,951, that selectively activated GPR17 even in a complex environment of endogenous purinergic receptors in primary oligodendrocytes. MDL29,951-stimulated GPR17 engaged the entire set of intracellular adaptor proteins for GPCRs: G proteins of the G?(i), G?(s), and G?(q) subfamily, as well as ?-arrestins. This was visualized as alterations in the concentrations of cyclic adenosine monophosphate and inositol phosphate, increased Ca²? flux, phosphorylation of extracellular signal-regulated kinases 1 and 2 (ERK1/2), as well as multifeatured cell activation recorded with label-free dynamic mass redistribution and impedance biosensors. MDL29,951 inhibited the maturation of primary oligodendrocytes from heterozygous but not GPR17 knockout mice in culture, as well as in cerebellar slices from 4-day-old wild-type mice. Because GPCRs are attractive targets for therapeutic intervention, inhibiting GPR17 emerges as therapeutic strategy to relieve the oligodendrocyte maturation block and promote myelin repair in MS.
Project description:The G protein-coupled receptor 17 (GPR17), a Gi-coupled GPCR, acts as an intrinsic timer of oligodendrocyte differentiation and myelination. The expression of GPR17 is upregulated during differentiation of oligodendrocyte precursor cells (OPCs) into premyelinating oligodendrocytes (preoligodendrocytes), whereas it is markedly downregulated during terminal maturation of myelinating oligodendrocytes. Nasu-Hakola disease (NHD) is a rare autosomal recessive disorder caused by a loss-of-function mutation of either TYROBP (DAP12) or TREM2. Pathologically, the brains of NHD patients exhibit extensive demyelination designated leukoencephalopathy, astrogliosis, accumulation of axonal spheroids, and activation of microglia predominantly in the white matter of frontal and temporal lobes. Although GPR17 is a key regulator of oligodendrogenesis, a pathological role of GPR17 in NHD brains with relevance to development of leukoencephalopathy remains unknown. We studied the expression of GPR17 in five NHD brains and eight control brains by immunohistochemistry. We identified GPR17-immunoreactive preoligodendrocytes with a multipolar ramified morphology distributed in the white matter and the grey matter of all cases examined. However, we did not find statistically significant differences in the number of GPR17-expressing cells between NHD and control brains both in the white matter and the grey matter due to great variability from case to case. These observations do not support the view that GPR17-positive preoligodendrocytes play a central role in the development of leukoencephalopathy in NHD brains.
Project description:One of the most important goals in the treatment of demyelinating diseases such as multiple sclerosis (MS) is, in addition to immunomodulation, reconstruction of the lost myelin sheath. The modulator of the central nervous system myelination is the metabotropic receptor coupled to the G-protein: GPR17. GPR17 receptors are considered to be sensors of local damage to the myelin sheath, and play a role in the reconstruction and repair of demyelinating plaques caused by ongoing inflammatory processes. GPR17 receptors are present on nerve cells and precursor oligodendrocyte cells. Under physiological conditions, they are responsible for the differentiation and subsequent maturation of oligodendrocytes, while under pathological conditions (during damage to nerve cells), their expression increases to become mediators in the demyelinating processes. Moreover, they are essential not only in both the processes of inducing damage and the death of neurons, but also in the local repair of the damaged myelin sheath. Therefore, GPR17 receptors may be recognized as the potential goal in creating innovative therapies for the treatment of the neurodegenerative process in MS, based on the acceleration of the remyelination processes. This review examines the role of GRP17 in pathomechanisms of MS development.