Oxidative Stress-Related Signaling Pathways Predict Oocytes' Fertilization In Vitro and Embryo Quality.

Oocyte development and fertilization are largely influenced by the microenvironment of the follicular fluid (FF), and the exploration of its molecular/metabolic composition may help in improving in vitro fertilization (IVF) outcomes. Here, the concentrations of molecules related to oxidative stress/inflammation were measured in FF from follicles at oocyte retrieval during IVF. Here, the FF antioxidant potential was correlated with the number of retrieved/mature oocytes and the number of fertilized ones. FF collected from the follicles of normal fertilized oocytes presented an elevated antioxidant capability, lower levels of pro-inflammatory molecules (i.e., IL-6, IL-8, IL-12, TGF-ß, and HIF-1α), and a higher IL-10 concentration. FF samples from follicles at oocyte retrieval that resulted in top-quality embryos displayed a peculiar antioxidant capability and a further decrease in proinflammatory molecules when compared with FF, giving rise to poor-quality embryos. Finally, pro-inflammatory molecules were lower and accompanied by a high antioxidant capability in samples giving rise to successful embryo implantation. The antioxidant capability and IL-10 displayed a good predictive ability for fertilization and embryo quality. Overall, our data showed the great influence of oxidative stress on the oocytes' fertilization, and shed light on the importance of controlling the inflammatory and oxidative status of FF to obtain good-quality embryos with significant implantation potential.

The Role of Amyloid-ß, Tau, and α-Synuclein Proteins as Putative Blood Biomarkers in Patients with Cerebral Amyloid Angiopathy.

BACKGROUND: Cerebral amyloid angiopathy (CAA) is a cerebrovascular disorder characterized by the deposition of amyloid-ß protein (Aß) within brain blood vessels that develops in elderly people and Alzheimer's disease (AD) patients. Therefore, the investigation of biomarkers able to differentiate CAA patients from AD patients and healthy controls (HC) is of great interest, in particular in peripheral fluids. OBJECTIVE: The current study aimed to detect the neurodegenerative disease (ND)-related protein (i.e., Aß1-40, Aß1-42, tau, and α-synuclein) levels in both red blood cells (RBCs) and plasma of CAA patients and HC, evaluating their role as putative peripheral biomarkers for CAA. METHODS: For this purpose, the proteins' concentration was quantified in RBCs and plasma by homemade immunoenzymatic assays in an exploratory cohort of 20 CAA patients and 20 HC. RESULTS: The results highlighted a significant increase of Aß1-40 and α-synuclein concentrations in both RBCs and plasma of CAA patients, while higher Aß1-42 and t-tau levels were detected only in RBCs of CAA individuals compared to HC. Moreover, Aß1-42/Aß1-40 ratio increased in RBCs and decreased in plasma of CAA patients. The role of these proteins as candidate peripheral biomarkers easily measurable with a blood sample in CAA needs to be confirmed in larger studies. CONCLUSION: In conclusion, we provide evidence concerning the possible use of blood biomarkers for contributing to CAA diagnosis and differentiation from other NDs.

Discovery of MDM2-p53 and MDM4-p53 protein-protein interactions small molecule dual inhibitors.

MDM2 and MDM4 are key negative regulators of p53, an important protein involved in several cell processes (e.g. cell cycle and apoptosis). Not surprisingly, the p53 tumor suppressor function is inactivated in tumors overexpressing these two proteins. Therefore, both MDM2 and MDM4 are considered important therapeutic targets for an effective reactivation of the p53 function. Herein, we present our studies on the development of spiropyrazoline oxindole small molecules able to inhibit MDM2/4-p53 protein-protein interactions (PPIs). Twenty-seven potential spiropyrazoline oxindole dual inhibitors were prepared based on in silico structural optimization studies of a hit compound with MDM2 and MDM4 proteins. The antiproliferative activity of the target compounds was evaluated in cancer cell lines harboring wild-type p53 and overexpressing MDM2 and/or MDM4. The most active compounds in SJSA-1 cells, 2q and 3b, induce cell death via apoptosis and control cell growth by targeting the G0/G1 cell cycle checkpoint in a concentration-dependent manner. The ability of the five most active spiropyrazoline oxindoles in dissociating p53 from MDM2 and MDM4 was analyzed by an immunoenzymatic assay. Three compounds inhibited MDM2/4-p53 PPIs with IC50 values in the nM range, while one compound inhibited more selectively the MDM2-p53 PPI over the MDM4-p53 PPI. Collectively, these results show: i) 3b may serve as a valuable lead for obtaining selective MDM2-p53 PPI inhibitors and more efficient anti-osteosarcoma agents; ii) 2a, 2q and 3f may serve as valuable leads for obtaining dual MDM2/4 inhibitors and more effective p53 activators.

α-Glyceryl-phosphoryl-ethanolamine protects human hippocampal neurons from ageing-induced cellular alterations.

Brain ageing has been related to a decrease in cellular metabolism, to an accumulation of misfolded proteins and to an alteration of the lipid membrane composition. These alterations act as contributive aspects of age-related memory decline by reducing membrane excitability and neurotransmitter release. In this sense, precursors of phospholipids (PLs) can restore the physiological composition of cellular membranes and ameliorate the cellular defects associated with brain ageing. In particular, phosphatidylcholine (PC) and phosphatidylethanolamine (PE) have been shown to restore mitochondrial function, reduce the accumulation of amyloid beta (Aß) and, at the same time, provide the amount of acetylcholine needed to reduce memory deficit. Among PL precursors, alpha-glycerylphosphorylethanolamine (GPE) has shown to protect astrocytes from Aß injuries and to slow-down ageing of human neural stem cells. GPE has been evaluated in aged human hippocampal neurons, which are implicated in learning and memory, and constitute a good in vitro model to investigate the beneficial properties of GPE. In order to mimic cellular ageing, the cells have been maintained 21 days in vitro and challenged with GPE. Results of the present paper showed GPE ability to increase PE and PC content, glucose uptake and the activity of the chain respiratory complex I and of the GSK-3ß pathway. Moreover, the nootropic compound showed an increase in the transcriptional/protein levels of neurotrophic and well-being related genes. Finally, GPE counteracted the accumulation of ageing-related misfolded proteins (a-synuclein and tau). Overall, our data underline promising effects of GPE in counteracting cellular alterations related to brain ageing and cognitive decline.

Endometrial Dysbiosis Is Related to Inflammatory Factors in Women with Repeated Implantation Failure: A Pilot Study.

An abnormal endometrial microbiota has been suggested to impair the process of embryo implantation, thus leading to repeated implantation failure (RIF) in women undergoing in vitro fertilization (IVF). However, the molecular mechanisms linking uterine microbiota and IVF out-comes are still an open question. The aim of this cohort study was to outline the relationship between endometrial microbiota, inflammation and IVF outcomes. To this purpose, endometrial microbiota and selected components of the "cytokine network" were analyzed in women presenting RIF and divided between eubiosis and dysbiosis groups, according to the percentage of endometrial lactobacilli (≥90% or <90%, respectively). The Dysbiosis group presented significantly higher tissue concentrations of the inflammatory markers (IL-6, IL-1ß, HIF-1α and COX-2) and significantly lower levels of the anti-inflammatory/well-being factors, IL-10 and IGF-1, with respect to women with eubiosis. Moreover, the Lactobacillus percentage was negatively related to the concentrations of the inflammatory molecules and positively related to IL-10/IGF-1. Interestingly, the number of IVF attempts was directly related to the levels of the inflammatory factors COX-2, IL-1ß and HIF-1α in the eubiosis group. Overall, endometrial dysbiosis was demonstrated to be associated with inflammation-related endometrial changes affecting the process of embryo implantation, underlining the importance of assessing uterine microbiota in patients undergoing IVF.

The Mediterranean Diet Positively Affects Resting Metabolic Rate and Salivary Microbiota in Human Subjects: A Comparison with the Vegan Regimen.

Salivary microbiota, comprising bacteria shed from oral surfaces, has been shown to be individualized, temporally stable, and influenced by macronutrient intake and lifestyle. Nevertheless, the effect of long-term dietary patterns on oral microbiota composition and the relationship between oral microbiota composition and metabolic rate remains to be examined. Herein, salivary microbiota composition and metabolic profile were analyzed in human subjects with vegan (VEG) or Mediterranean (MED) long-term dietary patterns. MED subjects presented significantly higher percentages of Subflava and Prevotella species as compared to VEG ones. Moreover, MED subjects showed a lower carbohydrate and a higher lipid consumption than VEG subjects, and, accordingly, a significantly higher basal metabolic rate (BMR) and a lower respiratory quotient (RQ). Prevotella abundance was demonstrated to be inversely related to RQ and carbohydrate consumption, whereas Subflava percentages were demonstrated to be positively correlated to BMR. Lactobacillus abundance, which was inversely related to Subflava presence in MED subjects, was associated with decreased BMR (Harris-Benedict) values. Overall, our data evidence the influence of macronutrient intake on metabolic profile and oral microbiota and confirm the positive effects of the Mediterranean diet on BMR and on the abundance of microbial species associated with a better macronutrient metabolism.

Exploring Epithelial-Mesenchymal Transition Signals in Endometriosis Diagnosis and In Vitro Fertilization Outcomes.

Endometriosis (EMS) pathogenesis has been related to the release of inflammatory mediators in peritoneal fluid, creating an altered microenvironment that leads to low-grade oocyte/embryos and to the reduction of implantation rates. The Epithelial-Mesenchymal Transition (EMT), an inflammation-related process, can be a further contributing factor to EMS. This study aimed to investigate, among various cytokines and EMT markers (Cadherins, TGF-ß, HIF-1α), diagnostic markers of EMS and prognostic factors of in vitro fertilization (IVF) outcomes. Herein, EMS patients manifested higher serum levels of the inflammatory molecules IL-6, IL-8, and IL-12 and a decrease in the concentrations of the anti-inflammatory IL-10. Moreover, biochemical markers associated with the EMT process were more elevated in serum and follicular fluid (FF) of EMS patients than in controls. At the end, the number of good-quality embryos was inversely related to serum IL-6 and EMT markers. Interestingly, serum IL-6 and FF IL-10 concentrations differentiated EMS patients from controls. Finally, serum IL-8 and E-Cadherin levels, as well as FF IL-10, predicted positive IVF outcome with great accuracy. Our data confirm the pivotal role of inflammatory mediators (i.e., IL-6 and IL-10) in EMS pathogenesis and suggest that EMT-related markers are elevated in EMS patients and can be predictive of IVF outcome.

Two mixed valence diruthenium(II,III) isomeric complexes show different anticancer properties.

In this paper it is demonstrated that the nature of the ligands of two Ru2(ii,iii) paddlewheel complexes dramatically affects the overall anticancer properties in cells. Herein, the complex [Ru2(EB776)4Cl] was found to be more active against a glioblastoma model with respect to its isomer [Ru2(EB106)4Cl]. These different effects depend on the steric hindrance, on the allowed conformations of the complexes and on the presence of hydrophilic regions in [Ru2(EB776)4Cl], which overall lead to a lower "steric protection".

Locking PDK1 in DFG-out conformation through 2-oxo-indole containing molecules: Another tools to fight glioblastoma.

The phosphoinositide-dependent kinase-1 (PDK1) is one of the main components of the PI3K/Akt pathway. Also named the "master kinase" of the AGC family, PDK1 plays a critical role in tumorigenesis, by enhancing cell proliferation and inhibiting apoptosis, as well as in cell invasion and metastasis formation. Although there have been done huge efforts in discovering specific compounds targeting PDK1, nowadays no PDK1 inhibitor has yet entered the clinic. With the aim to pick out novel and potent PDK1 inhibitors, herein we report the design and synthesis of a new class of molecules obtained by merging the 2-oxo-indole nucleus with the 2-oxo-pyridonyl fragment, two moieties with high affinity for the PDK1 hinge region and its DFG-out binding site, respectively. To this purpose, a small series of compounds were synthesised and a tandem application of docking and Molecular Dynamic (MD) was employed to get insight into their mode of binding. The OXID-pyridonyl hybrid 8, possessing the lower IC50 (IC50 = 112 nM), was also tested against recombinant kinases involved in the PI3K/PDK1/Akt pathway and was subjected to vitro studies to evaluate the cytotoxicity and the inhibition of tumour cell migration. All together the results let us to consider 8, as a lead compound of a new generation of PDK1 inhibitors and encourage us to further studies in this direction.

Long lasting MDM2/Translocator protein modulator: a new strategy for irreversible apoptosis of human glioblastoma cells.

The development of multi-target drugs and irreversible modulators of deregulated signalling proteins is the major challenge for improving glioblastoma multiforme (GBM) treatment. Reversible single-target drugs are not sufficient to sustain a therapeutic effect over time and may favour the activation of alternative signalling pathways and the onset of resistance phenomena. Thus, a multi-target compound that has a long-lasting mechanism of action might have a greater and longer life span of anti-proliferative activity. Recently, a dual-target indol-3ylglyoxyldipeptide derivative, designed to bind to the Translocator Protein (TSPO) and reactivate p53 function via dissociation from its physiological inhibitor, murine double minute 2 (MDM2), has been developed as a potent GBM pro-apoptotic agent. In this study, this derivative was chemically modified to irreversibly bind MDM2 and TSPO. The new compound elicited a TSPO-mediated mitochondrial membrane dissipation and restored p53 activity, triggering a long-lasting apoptosis of GBM cells. These effects were sustained over time, involved a stable activation of extracellular signal regulated kinases and were specifically observed in cancer cells, in which these protein kinases are deregulated. Dual-targeting and irreversible binding properties combined in the same molecule may represent a useful strategy to overcome the time-limited effects elicited by classical chemotherapies.

Trazodone regulates neurotrophic/growth factors, mitogen-activated protein kinases and lactate release in human primary astrocytes.

BACKGROUND: In the central nervous system, glial cells provide metabolic and trophic support to neurons and respond to protracted stress and insults by up-regulating inflammatory processes. Reactive astrocytes and microglia are associated with the pathophysiology of neuronal injury, neurodegenerative diseases and major depression, in both animal models and human brains. Several studies have reported clear anti-inflammatory effects of anti-depressant treatment on astrocytes, especially in models of neurological disorders. Trazodone (TDZ) is a triazolopyridine derivative that is structurally unrelated to other major classes of antidepressants. Although the molecular mechanisms of TDZ in neurons have been investigated, it is unclear whether astrocytes are also a TDZ target. METHODS: The effects of TDZ on human astrocytes were investigated in physiological conditions and following inflammatory insult with lipopolysaccharide (LPS) and tumour necrosis factor-α (TNF-α). Astrocytes were assessed for their responses to pro-inflammatory mediators and cytokines, and the receptors and signalling pathways involved in TDZ-mediated effects were evaluated. RESULTS: TDZ had no effect on cell proliferation, but it decreased pro-inflammatory mediator release and modulated trophic and transcription factor mRNA expression. Following TDZ treatment, the AKT pathway was activated, whereas extracellular signal-regulated kinase and c-Jun NH2-terminal kinase were inhibited. Most importantly, a 72-h TDZ pre-treatment before inflammatory insult completely reversed the anti-proliferative effects induced by LPS-TNF-α. The expression or the activity of inflammatory mediators, including interleukin-6, c-Jun NH2-terminal kinase and nuclear factor κB, were also reduced. Furthermore, TDZ affected astrocyte metabolic support to neurons by counteracting the inflammation-mediated lactate decrease. Finally, TDZ protected neuronal-like cells against neurotoxicity mediated by activated astrocytes. These effects mainly involved an activation of 5-HT1A and an antagonism at 5-HT2A/C serotonin receptors. Fluoxetine, used in parallel, showed similar final effects nevertheless it activates different receptors/intracellular pathways. CONCLUSIONS: Altogether, our results demonstrated that TDZ directly acts on astrocytes by regulating intracellular signalling pathways and increasing specific astrocyte-derived neurotrophic factor expression and lactate release. TDZ may contribute to neuronal support by normalizing trophic and metabolic support during neuroinflammation, which is associated with neurological diseases, including major depression.

Lactate dehydrogenase-A inhibition induces human glioblastoma multiforme stem cell differentiation and death.

Therapies that target the signal transduction and metabolic pathways of cancer stem cells (CSCs) are innovative strategies to effectively reduce the recurrence and significantly improve the outcome of glioblastoma multiforme (GBM). CSCs exhibit an increased rate of glycolysis, thus rendering them intrinsically more sensitive to prospective therapeutic strategies based on the inhibition of the glycolytic pathway. The enzyme lactate dehydrogenase-A (LDH-A), which catalyses the interconversion of pyruvate and lactate, is up-regulated in human cancers, including GBM. Although several papers have explored the benefits of targeting cancer metabolism in GBM, the effects of direct LDH-A inhibition in glial tumours have not yet been investigated, particularly in the stem cell subpopulation. Here, two representative LDH-A inhibitors (NHI-1 and NHI-2) were studied in GBM-derived CSCs and compared to differentiated tumour cells. LDH-A inhibition was particularly effective in CSCs isolated from different GBM cell lines, where the two compounds blocked CSC formation and elicited long-lasting effects by triggering both apoptosis and cellular differentiation. These data demonstrate that GBM, particularly the stem cell subpopulation, is sensitive to glycolytic inhibition and shed light on the therapeutic potential of LDH-A inhibitors in this tumour type.

The ubiquitin ligase Mdm2 controls oligodendrocyte maturation by intertwining mTOR with G protein-coupled receptor kinase 2 in the regulation of GPR17 receptor desensitization.

During oligodendrocyte precursor cell (OPC) differentiation, defective control of the membrane receptor GPR17 has been suggested to block cell maturation and impair remyelination under demyelinating conditions. After the immature oligodendrocyte stage, to enable cells to complete maturation, GPR17 is physiologically down-regulated via phosphorylation/desensitization by G protein-coupled receptor kinases (GRKs); conversely, GRKs are regulated by the "mammalian target of rapamycin" mTOR. However, how GRKs and mTOR are connected to each other in modulating GPR17 function and oligodendrogenesis has remained elusive. Here we show, for the first time, a role for Murine double minute 2 (Mdm2), a ligase previously involved in ubiquitination/degradation of the onco-suppressor p53 protein. In maturing OPCs, both rapamycin and Nutlin-3, a small molecule inhibitor of Mdm2-p53 interactions, increased GRK2 sequestration by Mdm2, leading to impaired GPR17 down-regulation and OPC maturation block. Thus, Mdm2 intertwines mTOR with GRK2 in regulating GPR17 and oligodendrogenesis and represents a novel actor in myelination.

Trazodone treatment protects neuronal-like cells from inflammatory insult by inhibiting NF-κB, p38 and JNK.

Growing evidence suggests that alterations of the inflammatory/immune system contribute to the pathogenesis of major depression and that inflammatory processes may influence the antidepressant treatment response. Depressed patients exhibit increased levels of inflammatory markers in both the periphery and brain, and high co-morbidity exists between depression and diseases associated with inflammatory alterations. Trazodone (TDZ) is a triazolopyridine derivative that belongs to the class of serotonin receptor antagonists and reuptake inhibitors. Although the trophic and protective properties of classic antidepressants have extensively been exploited, the effects of TDZ remain to be fully elucidated. In this study, the pharmacological activities of TDZ on human neuronal-like cells were investigated under both physiological and inflammatory conditions. An in vitro inflammatory model was established using lipopolysaccharide (LPS) and tumour necrosis factor-α (TNF-α), which efficiently mimic the stress-related changes in neurotrophic and pro-inflammatory genes. Our results showed that TDZ significantly increased the mRNA expression of both brain-derived nerve factor (BDNF) and cAMP response element-binding protein (CREB) and decreased the cellular release of the pro-inflammatory cytokine interferon gamma (IFN-γ) in neuronal-like cells. In contrast, neuronal cell treatment with LPS and TNF-α decreased the expression of CREB and BDNF and increased the expression of nuclear factor kappa B (NF-κB), a primary transcription factor that functions in inflammatory response initiation. Moreover, the two agents induced the release of pro-inflammatory cytokines (i.e., interleukin-6 and IFN-γ) and decreased the production of the anti-inflammatory cytokine interleukin-10. TDZ pre-treatment completely reversed the decrease in cell viability and counteracted the decrease in BDNF and CREB expression mediated by LPS-TNF-α. In addition, the production of inflammatory mediators was inhibited, and the release of interleukin-10 was restored to control levels. Furthermore, the intracellular signalling mechanism regulating TDZ-elicited effects was specifically investigated. TDZ induced extracellular signal-regulated kinase (ERK) phosphorylation and inhibited constitutive p38 activation. Moreover, TDZ counteracted the activation of p38 and c-Jun NH2-terminal kinase (JNK) elicited by LPS-TNF-α, suggesting that the neuro-protective role of TDZ could be mediated by p38 and JNK. Overall, our results demonstrated that the protective effects of TDZ under inflammation in neuronal-like cells function by decreasing pro-inflammatory signalling and by enhancing anti-inflammatory signalling.

Combined inhibition of AKT/mTOR and MDM2 enhances Glioblastoma Multiforme cell apoptosis and differentiation of cancer stem cells.

The poor prognosis of Glioblastoma Multiforme (GBM) is due to a high resistance to conventional treatments and to the presence of a subpopulation of glioma stem cells (GSCs). Combination therapies targeting survival/self-renewal signals of GBM and GSCs are emerging as useful tools to improve GBM treatment. In this context, the hyperactivated AKT/mammalian target of the rapamycin (AKT/mTOR) and the inhibited wild-type p53 appear to be good candidates. Herein, the interaction between these pathways was investigated, using the novel AKT/mTOR inhibitor FC85 and ISA27, which re-activates p53 functionality by blocking its endogenous inhibitor murine double minute 2 homologue (MDM2). In GBM cells, FC85 efficiently inhibited AKT/mTOR signalling and reactivated p53 functionality, triggering cellular apoptosis. The combined therapy with ISA27 produced a synergic effect on the inhibition of cell viability and on the reactivation of p53 pathway. Most importantly, FC85 and ISA27 blocked proliferation and promoted the differentiation of GSCs. The simultaneous use of these compounds significantly enhanced GSC differentiation/apoptosis. These findings suggest that FC85 actively enhances the downstream p53 signalling and that a combination strategy aimed at inhibiting the AKT/mTOR pathway and re-activating p53 signalling is potentially effective in GBM and in GSCs.

Oxysterols act as promiscuous ligands of class-A GPCRs: in silico molecular modeling and in vitro validation.

According to classical pharmacology, each neurotransmitter/hormonal receptor, including GPCRs, is exclusively activated by highly specific ligands. However, recent evidence challenges this dogma. Oxysterols are produced at inflammatory sites and can surprisingly potently activate the Epstein Barr virus induced gene receptor-2 (EBI2), a GPCR involved in adaptive immune responses. Similarly, oxysterols promiscuously operate CXCR2, a chemokine receptor participating to immune reactions and cancer development. Both EBI2 and CXCR2 are phylogenetically related to GPR17, another GPCR implicated in inflammatory/immune neurodegenerative events. Here, we used an integrated approach combining comparative modeling, molecular docking and in vitro experiments to investigate their potential interactions with oxysterols. All three receptors share the binding site to allocate oxysterols with different local arrangements, higher sensitivity to specific oxysterols and different activation thresholds. Such differences may dictate the diverse biological effects induced by oxysterols, depending on production site, concentration, specific spatiotemporal features and receptor expression on targeted cells. Thus, EBI2, CXCR2 and GPR17 are promiscuously operated by oxysterols making this class of ligands a 'fil rouge' linking oxidative stress, inflammation and neurodegeneration. Such a transversal role may represent a conserved, "unspecific" (but selective) signaling mode, by which emergency molecules activate multiple receptors involved in inflammatory/immune responses.

A rapid and efficient immunoenzymatic assay to detect receptor protein interactions: G protein-coupled receptors.

G protein-coupled receptors (GPCRs) represent one of the largest families of cell surface receptors, and are the target of at least one-third of the current therapeutic drugs on the market. Along their life cycle, GPCRs are accompanied by a range of specialized GPCR-interacting proteins (GIPs), which take part in receptor proper folding, targeting to the appropriate subcellular compartments and in receptor signaling tasks, and also in receptor regulation processes, such as desensitization and internalization. The direction of protein-protein interactions and multi-protein complexes formation is crucial in understanding protein function and their implication in pathological events. Although several methods have been already developed to assay protein complexes, some of them are quite laborious, expensive, and, more important, they do not generate fully quantitative results. Herein, we show a rapid immunoenzymatic assay to quantify GPCR interactionswith its signaling proteins. The recently de-orphanized GPCR, GPR17, was chosen as a GPCR prototype to optimize the assay. In a GPR17 transfected cell line and primary oligodendrocyte precursor cells, GPR17 interaction with proteins involved in the typical GPCR regulation, such as desensitization and internalization machinery, was investigated. The obtained results were validated by co-immunoprecipitation experiments, confirming this new method as a rapid and quantitative assay to study protein-protein interactions.

Does GRK-ß arrestin machinery work as a "switch on" for GPR17-mediated activation of intracellular signaling pathways?

During oligodendrocyte-precursor cell (OPC) differentiation program, an impairment in the regulatory mechanisms controlling GPR17 spatio-temporal expression and functional activity has been suggested to contribute to defective OPC maturation, a crucial event in the pathogenesis of multiple sclerosis. GRK-ß arrestin machinery is the primary actor in the control of G-protein coupled receptor (GPCR) functional responses and changes in these regulatory protein activities have been demonstrated in several immune/inflammatory diseases. Herein, in order to shed light on the molecular mechanisms controlling GPR17 regulatory events during cell differentiation, the role of GRK/ß-arrestin machinery in receptor desensitization and signal transduction was investigated, in transfected cells and primary OPC. Following cell treatment with the two classes of purinergic and cysteinyl-leukotriene (cysLT) ligands, different GRK isoforms were recruited to regulate GPR17 functional responses. CysLT-mediated receptor desensitization mainly involved GRK2; this kinase, via a G protein-dependent mechanism, promoted a transient binding of the receptor to ß-arrestins, rapid ERK phosphorylation and sustained nuclear CREB activation. Furthermore, GRK2, whose expression parallels that of the receptor during differentiation process, appeared to be crucial to induce cysLT-mediated maturation of OPCs. On the other hand, purinergic ligand exclusively recruited the GRK5 subtype, and induced, via a G protein-independent/ß-arrestin-dependent mechanism, a receptor/ß-arrestin stable association, slower and sustained ERK stimulation and marginal CREB activation. These results show that purinergic and cysLT ligands, through the recruitment of specific GRK isoforms, address distinct intracellular pathways, most likely reinforcing the same final response. The identification of these mechanisms and players controlling GPR17 responses during OPC differentiation could be useful to identify new targets in demyelination diseases and to develop new therapeutical strategies.