Genetic deletion or tyrosine phosphatase inhibition of PTPRZ1 activates c-Met to up-regulate angiogenesis and lung adenocarcinoma growth.

Protein tyrosine phosphatase receptor zeta 1 (PTPRZ1) is a transmembrane tyrosine phosphatase (TP) expressed in endothelial cells and required for stimulation of cell migration by vascular endothelial growth factor A165 (VEGFA165 ) and pleiotrophin (PTN). It is also over or under-expressed in various tumor types. In this study, we used genetically engineered Ptprz1-/- and Ptprz1+/+ mice to study mechanistic aspects of PTPRZ1 involvement in angiogenesis and investigate its role in lung adenocarcinoma (LUAD) growth. Ptprz1-/- lung microvascular endothelial cells (LMVEC) have increased angiogenic features compared with Ptprz1+/+ LMVEC, in line with the increased lung angiogenesis and the enhanced chemically induced LUAD growth in Ptprz1-/- compared with Ptprz1+/+ mice. In LUAD cells isolated from the lungs of urethane-treated mice, PTPRZ1 TP inhibition also enhanced proliferation and migration. Expression of beta 3 (ß3 ) integrin is decreased in Ptprz1-/- LMVEC, linked to enhanced VEGF receptor 2 (VEGFR2), c-Met tyrosine kinase (TK) and Akt kinase activities. However, only c-Met and Akt seem responsible for the enhanced endothelial cell activation in vitro and LUAD growth and angiogenesis in vivo in Ptprz1-/- mice. A selective PTPRZ1 TP inhibitor, VEGFA165 and PTN also activate c-Met and Akt in a PTPRZ1-dependent manner in endothelial cells, and their stimulatory effects are abolished by the c-Met TK inhibitor (TKI) crizotinib. Altogether, our data suggest that low PTPRZ1 expression is linked to worse LUAD prognosis and response to c-Met TKIs and uncover for the first time the role of PTPRZ1 in mediating c-Met activation by VEGFA and PTN.

Role of Receptor Protein Tyrosine Phosphatase ß/ζ in Neuron-Microglia Communication in a Cellular Model of Parkinson's Disease.

Pleiotrophin (PTN) is a neurotrophic factor that regulates glial responses in animal models of different types of central nervous system (CNS) injuries. PTN is upregulated in the brain in different pathologies characterized by exacerbated neuroinflammation, including Parkinson's disease. PTN is an endogenous inhibitor of Receptor Protein Tyrosine Phosphatase (RPTP) ß/ζ, which is abundantly expressed in the CNS. Using a specific inhibitor of RPTPß/ζ (MY10), we aimed to assess whether the PTN/RPTPß/ζ axis is involved in neuronal and glial injury induced by the toxin MPP+. Treatment with the RPTPß/ζ inhibitor MY10 alone decreased the viability of both SH-SY5Y neuroblastoma cells and BV2 microglial cultures, suggesting that normal RPTPß/ζ function is involved in neuronal and microglial viability. We observed that PTN partially decreased the cytotoxicity induced by MPP+ in SH-SY5Y cells underpinning the neuroprotective function of PTN. However, MY10 did not seem to modulate the SH-SY5Y cell loss induced by MPP+. Interestingly, we observed that media from SH-SY5Y cells treated with MPP+ and MY10 decreases microglial viability but may elicit a neuroprotective response of microglia by upregulating Ptn expression. The data suggest a neurotrophic role of microglia in response to neuronal injury through upregulation of Ptn levels.

Pleiotrophin deletion alters glucose homeostasis, energy metabolism and brown fat thermogenic function in mice.

AIMS/HYPOTHESIS: Pleiotrophin, a developmentally regulated and highly conserved cytokine, exerts different functions including regulation of cell growth and survival. Here, we hypothesise that this cytokine can play a regulatory role in glucose and lipid homeostasis. METHODS: To test this hypothesis, we performed a longitudinal study characterising the metabolic profile (circulating variables and tissue mRNA expression) of gene-targeted Ptn-deficient female mice and their corresponding wild-type counterparts at different ages from young adulthood (3 months) to older age (15 months). Metabolic cages were used to investigate the respiratory exchange ratio and energy expenditure, at both 24°C and 30°C. Undifferentiated immortalised mouse brown adipocytes (mBAs) were treated with 0.1 µg/ml pleiotrophin until day 6 of differentiation, and markers of mBA differentiation were analysed by quantitative real-time PCR (qPCR). RESULTS: Ptn deletion was associated with a reduction in total body fat (20.2% in Ptn+/+ vs 13.9% in Ptn-/- mice) and an enhanced lipolytic response to isoprenaline in isolated adipocytes from 15-month-old mice (189% in Ptn+/+ vs 273% in Ptn-/- mice). We found that Ptn-/- mice exhibited a significantly lower QUICKI value and an altered lipid profile; plasma triacylglycerols and NEFA did not increase with age, as happens in Ptn+/+ mice. Furthermore, the contribution of cold-induced thermogenesis to energy expenditure was greater in Ptn-/- than Ptn+/+ mice (42.6% and 33.6%, respectively). Body temperature and the activity and expression of deiodinase, T3 and mitochondrial uncoupling protein-1 in the brown adipose tissue of Ptn-/- mice were higher than in wild-type controls. Finally, supplementing brown pre-adipocytes with pleiotrophin decreased the expression of the brown adipocyte markers Cidea (20% reduction), Prdm16 (21% reduction), and Pgc1-α (also known as Ppargc1a, 11% reduction). CONCLUSIONS/INTERPRETATION: Our results reveal for the first time that pleiotrophin is a key player in preserving insulin sensitivity, driving the dynamics of adipose tissue lipid turnover and plasticity, and regulating energy metabolism and thermogenesis. These findings open therapeutic avenues for the treatment of metabolic disorders by targeting pleiotrophin in the crosstalk between white and brown adipose tissue.

Pleiotrophin regulates microglia-mediated neuroinflammation.

BACKGROUND: Pleiotrophin (PTN) is a cytokine found highly upregulated in the brain in different disorders characterized by overt neuroinflammation such as neurodegenerative diseases, drug addiction, traumatic injury, and ischemia. In the present work, we have explored whether PTN modulates neuroinflammation and if Toll-like receptor 4 (TLR4), crucial in the initiation of an immune response, is involved. METHODS: In immunohistochemistry assays, we studied lipopolysaccharide (LPS, 7.5 mg/kg i.p.)-induced changes in glial fibrillary acidic protein (GFAP, astrocyte marker) and ionized calcium-binding adaptor molecule 1 (Iba1, microglia marker) expression in the prefrontal cortex (PFC) and striatum of mice with transgenic PTN overexpression in the brain (PTN-Tg) and in wild-type (WT) mice. Cytokine protein levels were assessed in the PFC by X-MAP technology. The influence of TLR4 signaling in LPS effects in both genotypes was assessed by pretreatment with the TLR4 antagonist (TAK-242, 3.0 mg/kg i.p.). Murine BV2 microglial cells were treated with PTN (0.5 µg/ml) and LPS (1.0 µg/ml) and assessed for the release of nitric oxide (NO). RESULTS: We found that LPS-induced microglial activation is significantly increased in the PFC of PTN-Tg mice compared to that of WT mice. The levels of TNF-α, IL-6, and MCP-1 in response to LPS were significantly increased in the PFC of PTN-Tg mice compared to that of WT mice. Pretreatment with TAK-242 efficiently blocked increases in cytokine contents in a similar manner in both genotypes. Concomitant incubation of BV2 cells with LPS and PTN significantly potentiated the production of NO compared to cells only treated with LPS. CONCLUSIONS: Our findings identify for the first time that PTN is a novel and potent regulator of neuroinflammation. Pleiotrophin potentiates LPS-stimulated microglia activation. Our results suggest that regulation of the PTN signaling pathways may constitute new therapeutic opportunities particularly in those neurological disorders characterized by increased PTN cerebral levels and neuroinflammation.

Midkine Is a Novel Regulator of Amphetamine-Induced Striatal Gliosis and Cognitive Impairment: Evidence for a Stimulus-Dependent Regulation of Neuroinflammation by Midkine.

Midkine (MK) is a cytokine that modulates amphetamine-induced striatal astrogliosis, suggesting a possible role of MK in neuroinflammation induced by amphetamine. To test this hypothesis, we studied astrogliosis and microglial response induced by amphetamine (10 mg/kg i.p. four times, every 2 h) in different brain areas of MK-/- mice and wild type (WT) mice. We found that amphetamine-induced microgliosis and astrocytosis are enhanced in the striatum of MK-/- mice in a region-specific manner. Surprisingly, LPS-induced astrogliosis in the striatum was blocked in MK-/- mice. Since striatal neuroinflammation induced by amphetamine-type stimulants correlates with the cognitive deficits induced by these drugs, we also tested the long-term effects of periadolescent amphetamine treatment (3 mg/kg i.p. daily for 10 days) in a memory task in MK-/- and WT mice. Significant deficits in the Y-maze test were only observed in amphetamine-pretreated MK-/- mice. The data demonstrate for the first time that MK is a novel modulator of neuroinflammation depending on the inflammatory stimulus and the brain area considered. The data indicate that MK limits amphetamine-induced striatal neuroinflammation. In addition, our data demonstrate that periadolescent amphetamine treatment in mice results in transient disruption of learning and memory processes in absence of endogenous MK.

Adolescent intermittent ethanol exposure decreases perineuronal nets in the hippocampus in a sex dependent manner: Modulation through pharmacological inhibition of RPTPß/ζ.

Adolescence is a critical period for brain maturation in which this organ undergoes critical plasticity mechanisms that increase its vulnerability to the effects of alcohol. Significantly, ethanol-induced disruption of hippocampal neurogenesis has been related to cognitive decline in adulthood. During adolescence, the maturation of perineuronal nets (PNNs), extracellular matrix structures highly affected by ethanol consumption, plays a fundamental role in neurogenesis and plasticity in the hippocampus. Receptor Protein Tyrosine Phosphatase (RPTP) ß/ζ is a critical anchor point for PNNs on the cell surface. Using the adolescent intermittent access to ethanol (IAE) model, we previously showed that MY10, a small-molecule inhibitor of RPTPß/ζ, reduces chronic ethanol consumption in adolescent male mice but not in females and prevents IAE-induced neurogenic loss in the male hippocampus. We have now tested if these effects of MY10 are related to sex-dependent modulatory actions on ethanol-induced effects in PNNs. Our findings suggest a complex interplay between alcohol exposure, neural structures, and sex-related differences in the modulation of PNNs and parvalbumin (PV)-positive cells in the hippocampus. In general, IAE increased the number of PV + cells in the female hippocampus and reduced PNNs intensity in different hippocampal regions, particularly in male mice. Notably, we found that pharmacological inhibition of RPTPß/ζ with MY10 regulates ethanol-induced alterations of PNNs intensity, which correlates with the protection of hippocampal neurogenesis from ethanol neurotoxic effects and may be related to the capacity of MY10 to increase the gene expression of key components of PNNs.

Periadolescent amphetamine treatment causes transient cognitive disruptions and long-term changes in hippocampal LTP depending on the endogenous expression of pleiotrophin.

Amphetamine treatment during adolescence causes long-term cognitive deficits in rats. Pleiotrophin (PTN) is a cytokine with important roles in the modulation of synaptic plasticity, whose levels of expression are significantly regulated by amphetamine administration. To test the possibility that the long-term consequences of periadolescent amphetamine treatment cross species and, furthermore, to test the hypothesis that PTN could be one of the factors involved in the adult cognitive deficits observed after periadolescent amphetamine administrations, we comparatively studied the long-term consequences of periadolescent amphetamine treatment (3 mg/kg intraperitoneal, daily during 10 days) in normal wild-type (PTN+/+) and in PTN genetically deficient (PTN-/-) mice. Within the first week after cessation of treatment, significant deficits in the passive avoidance and Y-maze tests were only observed in amphetamine-pretreated PTN-/- mice. However, 13 and 26 days after the last administration, we did not find significant differences in Y-maze between amphetamine- and saline-pretreated PTN-/- mice. In addition, we did not find any genotype- or treatment-related anxiogenic- or depressive-like behaviour in adult mice. Furthermore, we observed a significantly enhanced long-term potentiation (LTP) in CA1 hippocampal slices from saline-pretreated PTN-/- mice compared with saline-pretreated PTN+/+ mice. Interestingly, amphetamine pre-treatment during adolescence significantly enhanced LTP in adult PTN+/+ mice but did not cause any effect in PTN-/- mice, suggesting LTP mechanisms saturation in naïve PTN-/- mice. The data demonstrate that periadolescent amphetamine treatment causes transient cognitive deficits and long-term alterations of hippocampal LTP depending on the endogenous expression of PTN.

Inhibition of RPTPß/ζ reduces chronic ethanol intake in adolescent mice and modulates ethanol effects on hippocampal neurogenesis and glial responses in a sex-dependent manner.

Pleiotrophin (PTN) is a cytokine that modulates ethanol drinking and reward and regulates glial responses in different contexts. PTN is an inhibitor of Receptor Protein Tyrosine Phosphatase (RPTP) ß/ζ. Inhibition of RPTPß/ζ reduces binge-like drinking in adult male mice. Whether inhibition of RPTPß/ζ is effective in reducing ethanol consumption during adolescence and in both sexes remained to be studied. In this work, male and female adolescent mice underwent an intermittent access to ethanol (IAE) 2-bottle choice protocol. Treatment with MY10 (60 mg/kg, i.g.), a small-molecule RPTPß/ζ inhibitor, reduced chronic 3-week ethanol consumption only in male mice. We detected an ethanol-induced overall decrease in hippocampal GFAPir and Iba1ir, independently of the treatment received, suggesting that RPTPß/ζ is not key in the regulation of IAE-induced glial responses. However, we found a significant negative correlation between the size of microglial cells and the number of hippocampal neuronal progenitors only in male mice after IAE. This correlation was disrupted by treatment with MY10 before each drinking session, which may be related to the ability of MY10 to regulate the intensity of the perineuronal nets (PNNs) in the hippocampus in a sex-dependent manner. The data show for the first time that inhibition of RPTPß/ζ reduces chronic voluntary ethanol consumption in adolescent mice in a sex-dependent manner. In addition, we show evidence for sex-specific differences in the effects of IAE on glial responses and hippocampal neurogenesis, which may be related to different actions of the RPTPß/ζ signalling pathway in the brains of male and female mice.

Receptor protein tyrosine phosphatase ß/ζ regulates loss of neurogenesis in the mouse hippocampus following adolescent acute ethanol exposure.

Adolescence is a critical period for brain maturation in which this organ is more vulnerable to the damaging effects of ethanol. Administration of ethanol in mice induces a rapid cerebral upregulation of pleiotrophin (PTN), a cytokine that regulates the neuroinflammatory processes induced by different insults and the behavioral effects of ethanol. PTN binds Receptor Protein Tyrosine Phosphatase (RPTP) ß/ζ and inhibits its phosphatase activity, suggesting that RPTPß/ζ may be involved in the regulation of ethanol effects. To test this hypothesis, we have treated adolescent mice with the RPTPß/ζ inhibitor MY10 (60 mg/kg) before an acute ethanol (6 g/kg) administration. Treatment with MY10 completely prevented the ethanol-induced neurogenic loss in the hippocampus of both male and female mice. In flow cytometry studies, ethanol tended to increase the number of NeuN+/activated Caspase-3+ cells particularly in female mice, but no significant effects were found. Ethanol increased Iba1+ cell area and the total marked area in the hippocampus of female mice, suggesting sex differences in ethanol-induced microgliosis. In addition, ethanol reduced the circulating levels of IL-6 and IL-10 in both sexes, although this reduction was only found significant in males and not affected by MY10 treatment. Interestingly, MY10 alone increased the total marked area and the number of Iba1+ cells only in the female hippocampus, but tended to reduce the circulating levels of TNF-α only in male mice. In summary, the data identify a novel modulatory role of RPTPß/ζ on ethanol-induced loss of hippocampal neurogenesis, which seems unrelated to glial and inflammatory responses. The data also suggest sex differences in RPTPß/ζ function that may be relevant to immune responses and ethanol-induced microglial responses.

Implication of the PTN/RPTPß/ζ Signaling Pathway in Acute Ethanol Neuroinflammation in Both Sexes: A Comparative Study with LPS.

Binge drinking during adolescence increases the risk of alcohol use disorder, possibly by involving alterations of neuroimmune responses. Pleiotrophin (PTN) is a cytokine that inhibits Receptor Protein Tyrosine Phosphatase (RPTP) ß/ζ. PTN and MY10, an RPTPß/ζ pharmacological inhibitor, modulate ethanol behavioral and microglial responses in adult mice. Now, to study the contribution of endogenous PTN and the implication of its receptor RPTPß/ζ in the neuroinflammatory response in the prefrontal cortex (PFC) after acute ethanol exposure in adolescence, we used MY10 (60 mg/kg) treatment and mice with transgenic PTN overexpression in the brain. Cytokine levels by X-MAP technology and gene expression of neuroinflammatory markers were determined 18 h after ethanol administration (6 g/kg) and compared with determinations performed 18 h after LPS administration (5 g/kg). Our data indicate that Ccl2, Il6, and Tnfa play important roles as mediators of PTN modulatory actions on the effects of ethanol in the adolescent PFC. The data suggest PTN and RPTPß/ζ as targets to differentially modulate neuroinflammation in different contexts. In this regard, we identified for the first time important sex differences that affect the ability of the PTN/RPTPß/ζ signaling pathway to modulate ethanol and LPS actions in the adolescent mouse brain.

Metabolomics and biochemical alterations caused by pleiotrophin in the 6-hydroxydopamine mouse model of Parkinson's disease.

Pleiotrophin (PTN) is a cytokine involved in nerve tissue repair processes, neuroinflammation and neuronal survival. PTN expression levels are upregulated in the nigrostriatal pathway of Parkinson's Disease (PD) patients. We aimed to characterize the dopaminergic injury and glial responses in the nigrostriatal pathway of mice with transgenic Ptn overexpression in the brain (Ptn-Tg) after intrastriatal injection of the catecholaminergic toxic 6-hydroxydopamine (6-OHDA) at a low dose (5 µg). Ten days after surgery, the injection of 6-OHDA induced a significant decrease of the number of tyrosine hydroxylase (TH)-positive neurons in the substantia nigra and of the striatal TH contents in Wild type (Wt) mice. In contrast, these effects of 6-OHDA were absent in Ptn-Tg mice. When the striatal Iba1 and GFAP immunoreactivity was studied, no statistical differences were found between vehicle-injected Wt and Ptn-Tg mice. Furthermore, 6-OHDA did not cause robust glial responses neither on Wt or Ptn-Tg mice 10 days after injections. In metabolomics studies, we detected interesting metabolites that significantly discriminate the more injured 6-OHDA-injected Wt striatum and the more protected 6-OHDA-injected Ptn-Tg striatum. Particularly, we detected groups of metabolites, mostly corresponding to phospholipids, whose trends were opposite in both groups. In summary, the data confirm lower 6-OHDA-induced decreases of TH contents in the nigrostriatal pathway of Ptn-Tg mice, suggesting a neuroprotective effect of brain PTN overexpression in this mouse model of PD. New lipid-related PD drug candidates emerge from this study and the data presented here support the increasingly recognized "lipid cascade" in PD.

Genetic inactivation of midkine, not pleiotrophin, facilitates extinction of alcohol-induced conditioned place preference.

Pleiotrophin (PTN) and midkine (MK) are growth factors that modulate alcohol consumption and reward. Since both PTN and MK limit the rewarding effects of alcohol, pharmacological potentiation of the PTN and MK signaling pathways has been proposed for the treatment of alcohol use disorders (AUD). Although the use of this therapy in the prevention of alcohol relapse is important, the potential role of these cytokines in extinguishing alcohol-induced seeking behavior is a key question that remains unanswered. To fill this gap, we have now studied the extinction of the conditioned place preference (CPP) induced by different doses of alcohol in Ptn knockout (Ptn-/-) and Mk knockout (Mk-/-) mice. The data confirm a higher sensitivity of Ptn-/- mice to the conditioning effects of a low dose (1 g/kg) and a rewarding dose (2 g/kg) of alcohol, while Mk-/- mice are only more susceptible to the conditioning effects of the low dose of this drug. More importantly, the percentage of Mk-/- mice, not Ptn-/- mice, that efficiently extinguished alcohol-induced CPP was significantly higher than that of Wt mice. Taken together, the data presented here confirm that Ptn and Mk are genetic factors that determine the conditioning effects of alcohol in mice and that Mk is a novel factor that plays an important role in the extinction of alcohol-induced CPP.

The neurotrophic factor pleiotrophin modulates amphetamine-seeking behaviour and amphetamine-induced neurotoxic effects: evidence from pleiotrophin knockout mice.

Pleiotrophin (PTN), a neurotrophic factor with important roles in survival and differentiation of dopaminergic neurons, is up-regulated in the nucleus accumbens after amphetamine administration suggesting that PTN could modulate amphetamine-induced pharmacological or neuroadaptative effects. To test this hypothesis, we have studied the effects of amphetamine administration in PTN genetically deficient (PTN -/-) and wild type (WT, +/+) mice. In conditioning studies, we found that amphetamine induces conditioned place preference in both PTN -/- and WT (+/+) mice. When these mice were re-evaluated after a 5-day period without amphetamine administration, we found that WT (+/+) mice did not exhibit amphetamine-seeking behaviour, whereas, PTN -/- mice still showed a robust drug-seeking behaviour. In immunohystochemistry studies, we found that amphetamine (10 mg/kg, four times, every 2 hours) causes a significant increase of glial fibrillary acidic protein positive cells in the striatum of amphetamine-treated PTN -/- mice compared with WT mice 4 days after last administration of the drug, suggesting an enhanced amphetamine-induced astrocytosis in the absence of endogenous PTN. Interestingly, we found in concomitant in vitro studies that PTN (3 µM) limits amphetamine (1 mM)-induced loss of viability of PC12 cell cultures, effect that could be related to the ability of PTN to induce the phosphorylation of Akt and ERK1/2. To test this possibility, we used specific Akt and ERK1/2 inhibitors uncovering for the first time that PTN-induced protective effects against amphetamine-induced toxicity in PC12 cells are mediated by the ERK1/2 signalling pathway. The data suggest an important role of PTN to limit amphetamine-induced neurotoxic and rewarding effects.

Role of RPTPß/ζ in neuroinflammation and microglia-neuron communication.

Pleiotrophin (PTN) is a cytokine that is upregulated in different neuroinflammatory disorders. Using mice with transgenic PTN overexpression in the brain (Ptn-Tg), we have found a positive correlation between iNos and Tnfα mRNA and Ptn mRNA levels in the prefrontal cortex (PFC) of LPS-treated mice. PTN is an inhibitor of Receptor Protein Tyrosine Phosphatase (RPTP) ß/ζ, which is mainly expressed in the central nervous system. We aimed to test if RPTPß/ζ is involved in the modulation of neuroinflammatory responses using specific inhibitors of RPTPß/ζ (MY10 and MY33-3). Treatment with MY10 potentiated LPS-induced microglial responses in the mouse PFC. Surprisingly, MY10 caused a decrease in LPS-induced NF-κB p65 expression, suggesting that RPTPß/ζ may be involved in a novel mechanism of potentiation of microglial activation independent of the NF-κB p65 pathway. MY33-3 and MY10 limited LPS-induced nitrites production and iNos increases in BV2 microglial cells. SH-SY5Y neuronal cells were treated with the conditioned media from MY10/LPS-treated BV2 cells. Conditioned media from non-stimulated and from LPS-stimulated BV2 cells increased the viability of SH-SY5Y cultures. RPTPß/ζ inhibition in microglial cells disrupted this neurotrophic effect of microglia, suggesting that RPTPß/ζ plays a role in the neurotrophic phenotype of microglia and in microglia-neuron communication.

Pleiotrophin inhibits hippocampal long-term potentiation: a role of pleiotrophin in learning and memory.

Pleiotrophin (PTN) is a growth factor that has been shown to be involved in hippocampal synaptic plasticity and learning. To further understand the involvement of PTN in memory processes, we performed in vitro electrophysiological studies in PTN-stimulated CA1 from rat hippocampal slices combined with the behavioural testing of PTN deficient (PTN - / - ) mice. We found that PTN inhibited hippocampal long-term potentiation (LTP) induced by high-frequency stimulation (HFS) consisted in three trains of 100 Hz separated by 20 s. To test the possibility that PTN might be involved in behavioural memory processes, we tested the learning behaviour of PTN - / - mice using the Y-maze test. We did not observe significant differences in recognition memory between PTN - / - and Wild Type (WT) mice when a 30 min-interval intertrial (ITI) was used in the Y-maze test. However, whereas WT mice showed disruption of recognition memory using a 60 min-ITI, PTN - / - mice maintained the recognition memory. The data demonstrate that PTN inhibits hippocampal LTP in vitro and might play a role in memory processes in vivo.

Targeting the pleiotrophin/receptor protein tyrosine phosphatase beta/zeta signaling pathway to limit neurotoxicity induced by drug abuse.

This review compiles the scientific basis to propose the pleiotrophin/receptor protein tyrosine phosphatase beta/zeta signaling pathway as a new therapeutic target to prevent drug of abuse-induced toxicity. In addition, potential guidelines are provided for the development of new therapeutic compounds derived from that knowledge. This approach may be relevant since efficient therapeutic strategies are currently lacking in this field, even when drug-induced neurotoxicity seems to underlie the neurodegenerative disorders diagnosed in drug addicts.

Connecting Metainflammation and Neuroinflammation Through the PTN-MK-RPTPß/ζ Axis: Relevance in Therapeutic Development.

Inflammation is a common factor of pathologies such as obesity, type 2 diabetes or neurodegenerative diseases. Chronic inflammation is considered part of the pathogenic mechanisms of different disorders associated with aging. Interestingly, peripheral inflammation and the associated metabolic alterations not only facilitate insulin resistance and diabetes but also neurodegenerative disorders. Therefore, the identification of novel pathways, common to the development of these diseases, which modulate the immune response and signaling is key. It will provide highly relevant information to advance our knowledge of the multifactorial process of aging, and to establish new biomarkers and/or therapeutic targets to counteract the underlying chronic inflammatory processes. One novel pathway that regulates peripheral and central immune responses is triggered by the cytokines pleiotrophin (PTN) and midkine (MK), which bind its receptor, Receptor Protein Tyrosine Phosphatase (RPTP) ß/ζ, and inactivate its phosphatase activity. In this review, we compile a growing body of knowledge suggesting that PTN and MK modulate the immune response and/or inflammation in different pathologies characterized by peripheral inflammation associated with insulin resistance, such as aging, and in central disorders characterized by overt neuroinflammation, such as neurodegenerative diseases and endotoxemia. Evidence strongly suggests that regulation of the PTN and MK signaling pathways may provide new therapeutic opportunities particularly in those neurological disorders characterized by increased PTN and/or MK cerebral levels and neuroinflammation. Importantly, we discuss existing therapeutics, and others being developed, that modulate these signaling pathways, and their potential use in pathologies characterized by overt neuroinflammation.

Inhibition of RPTPß/ζ blocks ethanol-induced conditioned place preference in pleiotrophin knockout mice.

Pleiotrophin (PTN) and Midkine (MK) are neurotrophic factors that are upregulated in the prefrontal cortex after alcohol administration and have been shown to reduce ethanol drinking and reward. PTN and MK are endogenous inhibitors of Receptor Protein Tyrosine Phosphatase (RPTP) ß/ζ. Interestingly, pharmacological inhibition of RPTPß/ζ reduces ethanol consumption and blocks ethanol-induced conditioned place preference (CPP) in wild type mice. Since PTN-knockout (Ptn-/-) mice are more sensitive to the conditioning effects of alcohol, we aimed to test the effects of MY10, a small-molecule inhibitor of RPTPß/ζ, on ethanol-induced CPP in Ptn-/- mice. The data presented here demonstrate for the first time that a regular dose of MY10, known to block ethanol consumption and reward in wild type mice, also blocks the rewarding effects of ethanol in the more vulnerable individuals lacking PTN, the endogenous inhibitor of RPTPß/ζ. In addition, since MY10 readily penetrates the blood brain barrier (BBB), we tested its effects in a series of behavioural tests in Ptn+/+ and Ptn-/- mice. The data indicate that MY10 does not cause gross behavioural effects in wild type mice. However, MY10 tended to induce anxiolytic effects in Ptn-/- mice in the elevated plus maze paradigm. Overall, the data indicate that MY10 rescues Ptn-/- mice from their increased susceptibility to the conditioning effects of ethanol and may induce anxiolytic effects in individuals with reduced or absent PTN functions. Further studies are needed to confirm the potential of pharmacological inhibition of RPTPß/ζ as a new therapeutic strategy in the treatment of anxiety-related disorders.

Pleiotrophin prevents cocaine-induced toxicity in vitro.

Pleiotrophin is a cytokine involved in differentiation, survival and repair processes in the central nervous system. Pleiotrophin is upregulated in the brain after administration of different drugs of abuse, thus suggesting a protective role of this cytokine on drug-induced toxicity. We have tested this hypothesis in vitro using NG108-15 cells, a line widely used for neurotoxicity studies. It was found that pleiotrophin (3 and 6 microM) significantly prevents cocaine (5 mM)-induced cytotoxicity as measured by the neutral red test. Similar results were obtained in PC12 cells, which were found to endogenously express both pleiotrophin and its main target, receptor protein tyrosine phosphatase (RPTP) beta/zeta. Blockade of pleiotrophin signaling using anti-pleiotrophin antibodies (2 microg/ml) did not potentiate cocaine-induced toxicity; interestingly, incubation of PC12 cells only with anti-pleiotrophin antibodies significantly reduced cellular viability, thus suggesting an important role of endogenous pleiotrophin signaling in cell survival. The data suggest that pleiotrophin overexpression in response to drugs of abuse may be relevant to prevent drug-induced toxicity.

Comparative study of alpha2-adrenoceptors in Fischer 344 and Lewis rats. Evidence for clonidine-induced place aversion.

Fischer 344 (F344) and Lewis rat strains have been shown to exhibit different vulnerability to development or maintenance of opioid seeking behaviours probably due to differences in the endogenous opioid system. Since opioid and alpha(2)-adrenergic mechanisms closely interact in nociception and substance abuse, strain differences may be expected to affect alpha(2)-adrenoceptor-mediated events. The sensitivity of these two strains to alpha(2)-adrenoceptor-mediated antinociception has been reported to be markedly different. In this work we have further studied the function of alpha(2)-adrenoceptors in F344 and Lewis rats by means of several in vivo and in vitro procedures. Comparative studies of [(3)H]RX821002 and [(35)S]GTPgammaS binding revealed that alpha(2)-adrenoceptors could be slightly more responsive to agonist stimulation in the brain cortex of F344 rats, which is in agreement with previous antinociception studies. However, these differences were modest, not observed in the spinal cord and did not translate into functional differences concerning the effects of clonidine on vas deferens contractility and body temperature. Conditioning experiments showed that a moderate dose of clonidine, which is relevant in antinociceptive and opioid antiwithdrawal studies, induces a robust place aversion which is also equivalent in F344 and Lewis rats. This finding underlies the consistency of the effect and its independency of genetic differences between both rat strains. It seems therefore that the pharmacological properties of alpha(2)-adrenoceptors are similar in F344 and Lewis rats, and thus the previously reported differences in clonidine-induced antinociception could be attributed to other factors such as dissimilar endogenous function of specific noradrenergic pathways.