Pleiotrophin mediates the neurotrophic effect of cyclic AMP on dopaminergic neurons: analysis of suppression-subtracted cDNA libraries and confirmation in vitro

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.

Interactions of Pleiotrophin with a Structurally Defined Heparin Hexasaccharide

Pleiotrophin (PTN) is a potent cytokine that plays an important role in neural generation, angiogenesis, inflammation, and cancers. Its interactions with the polysaccharide glycosaminoglycan (GAG) are crucial to PTN’s biological activities. In this study, we investigated the interaction of selectively protonated PTN with the heparin hexasaccharide ΔUA2S-(GlcNS6S-IdoA2S)₂-GlcNS6S using solution NMR. The use of a structurally defined oligosaccharide and selectively protonated PTN enabled us to obtain intermolecular contacts using unfiltered NOESY experiments, significantly increasing the amount of high-resolution structural information obtainable. Our data showed that PTN’s arginines, lysines, and tryptophans in the two structured domains have strong interactions with the 2-O-sulfated uronate protons in the heparin hexasaccharide. Consistent with the NMR data is the observation that 2-O-desulfation and N-desulfation/N-acetylation significantly decreased heparin hexasaccharides’ affinity for PTN, while 6-O-desulfation only modestly affected the interactions with PTN. These results allowed us to hypothesize that PTN has a preference for sulfate clusters centered on the GlcNS6S-IdoA2S disaccharide. Using these data and the fact that PTN domains mostly bind heparin hexasaccharides independently, models of the PTN-heparin complex were constructed.

Regulation of Pleiotrophin, Midkine, Receptor Protein Tyrosine Phosphatase β/ζ, and Their Intracellular Signaling Cascades in the Nucleus Accumbens During Opiate Administration

BACKGROUND

Most classes of addictive substances alter the function and structural plasticity of the brain reward circuitry. Midkine (MK) and pleiotrophin (PTN) are growth/differentiation cytokines which, similarly to neurotrophins, play an important role in repair, neurite outgrowth, and cell differentiation. PTN or MK signaling through receptor protein tyrosine phosphatase β/ζ (RPTPβ/ζ), leads to the activation of extracellular signal-regulated kinases and thymoma viral proto-oncogene. This activation induces morphological changes and modulates addictive behaviors. Besides, there is increasing evidence that during the development of drug addiction, astrocytes contribute to the synaptic plasticity by synthesizing and releasing substances such as cytokines.

METHODS

In the present work we studied the effect of acute morphine administration, chronic morphine administration, and morphine withdrawal on PTN, MK, and RPTPβ/ζ expression and on their signaling pathways in the nucleus accumbens.

RESULTS

Present results indicated that PTN, MK, and RPTPβ/ζ levels increased after acute morphine injection, returned to basal levels during chronic opioid treatment, and were up-regulated again during morphine withdrawal. We also observed an activation of astrocytes after acute morphine injection and during opiate dependence and withdrawal. In addition, immunofluorescence analysis revealed that PTN, but not MK, was overexpressed in astrocytes and that dopaminoceptive neurons expressed RPTPβ/ζ.

CONCLUSIONS

All these observations suggest that the neurotrophic and behavioral adaptations that occur during opiate addiction could be, at least partly, mediated by cytokines.

Glial activation and midkine and pleiotrophin transcription in the ventral tegmental area are modulated by morphine administration

Opiates cause persistent restructuring in the mesolimbic reward system. Although a possible role for midkine and pleiotrophin cytokines in the field of synaptic plasticity has been proposed, it has not been assessed whether morphine administration regulates astrogliosis and midkine and pleiotrophin transcription. We observed that single morphine injection and chronic morphine increased glial fibrillary acidic protein expression in the ventral tegmental area (VTA). Interestingly, single morphine injection and chronic morphine increased VTA midkine and pleiotrophin mRNA expression. Given these results, we hypothesize a role for these cytokines in mediating, at least in part, acute neuroprotective effects and chronic neurotrophic adaptations that contribute to drug dependence.

Pleiotrophin over-expression provides trophic support to dopaminergic neurons in parkinsonian rats

Background

Pleiotrophin is known to promote the survival and differentiation of dopaminergic neurons in vitro and is up-regulated in the substantia nigra of Parkinson's disease patients. To establish whether pleiotrophin has a trophic effect on nigrostriatal dopaminergic neurons in vivo, we injected a recombinant adenovirus expressing pleiotrophin in the substantia nigra of 6-hydroxydopamine lesioned rats.

Results

The viral vector induced pleiotrophin over-expression by astrocytes in the substantia nigra pars compacta, without modifying endogenous neuronal expression. The percentage of tyrosine hydroxylase-immunoreactive cells as well as the area of their projections in the lesioned striatum was higher in pleiotrophin-treated animals than in controls.

Conclusions

These results indicate that pleiotrophin over-expression partially rescues tyrosine hydroxylase-immunoreactive cell bodies and terminals of dopaminergic neurons undergoing 6-hydroxydopamine-induced degeneration.

PAd-shRNA-PTN reduces pleiotrophin of pancreatic cancer cells and inhibits neurite outgrowth of DRG

AIM: To investigate the silencing effects of pAd-shRNA-pleiotrophin (PTN) on PTN in pancreatic cancer cells, and to observe the inhibition of pAd-shRNA-PTN on neurite outgrowth from dorsal root ganglion (DRG) neurons in vitro.

METHODS: PAd-shRNA-PTN was used to infect pancreatic cancer BxPC-3 cells; assays were conducted for knockdown of the PTN gene on the 0th, 1st, 3rd, 5th, 7th and 9th d after infection using immunocytochemistry, real-time quantitative polymerase chain reaction (PCR), and Western blotting analysis. The morphologic changes of cultured DRG neurons were observed by mono-culture of DRG neurons and co-culture with BXPC-3 cells in vitro.

RESULTS: The real-time quantitative PCR showed that the inhibition rates of PTN mRNA expression in the BxPC-3 cells were 20%, 80%, 50% and 25% on the 1st, 3rd, 5th and 7th d after infection. Immunocytochemistry and Western blotting analysis also revealed the same tendency. In contrast to the control, the DRG neurons co-cultured with the infected BxPC-3 cells shrunk; the number and length of neurites were significantly decreased.

CONCLUSION: Efficient and specific knockdown of PTN in pancreatic cancer cells and the reduction in PTN expression resulted in the inhibition of neurite outgrowth from DRG neurons.

Adipocyte derived paracrine mediators of mammary ductal morphogenesis controlled by retinoic acid receptors

We generated a transgenic (Tg)-mouse model expressing a dominant negative-(DN)-RARα, (RARαG303E) under adipocytes-specific promoter to explore the paracrine role of adipocyte retinoic acid receptors (RARs) in mammary morphogenesis. Transgenic adipocytes had reduced level of RARα, β and γ, which coincided with a severely underdeveloped pubertal and mature ductal tree with profoundly decreased epithelial cell proliferation. Transplantation experiments of mammary epithelium and of whole mammary glands implicated a fat-pad dependent paracrine mechanism in the stunted phenotype of the epithelial ductal tree. Co-cultures of primary adipocytes, or in vitro differentiated adipocyte cell line, with mammary epithelium showed that when activated, adipocyte-RARs contribute to generation of secreted proliferative and pro-migratory factors. Gene expression microarrays revealed a large number of genes regulated by adipocyte-RARs. Among them, pleiotrophin (PTN) was identified as the paracrine effectors of epithelial cell migration. Its expression was found to be strongly inhibited by DN-RARα, an inhibition relieved by pharmacological doses of all-trans retinoic acid (atRA) in culture and in vivo. Moreover, adipocyte-PTHR, another atRA responsive gene, was found to be an up-stream regulator of PTN. Overall, these results support the existence of a novel paracrine loop controlled by adipocyte-RAR that regulates the mammary ductal tree morphogenesis.

Neuroprotective effects of the survival promoting peptide Y-P30

Y-P30 is a polypeptide survival promoting factor that has significant impact on the survival and differentiation of neurons in the developing brain. To address its potential role in brain injury we tested its neuroprotective effects in the oxygen-glucose deprivation (OGD) model with hippocampal slice cultures as an in vitro assay for ischemia. We could demonstrate that supplementation with Y-P30 leads to a significant neuroprotection at concentrations of 200 nM and 2 microM when it was added to the medium of hippocampal slice cultures 2 h before starting the deprivation of oxygen and glucose. A significant neuroprotective effect was found when the peptide was applied 2 h after injury. Y-P30 oligomerises in large complexes, which might hinder the passage through the culture membranes in our system. We therefore also applied Y-P30 directly on the hippocampal slices, which led to the most robust neuroprotection even at very low concentrations.

A novel purification method for CNS projection neurons leads to the identification of brain vascular cells as a source of trophic support for corticospinal motor neurons

One of the difficulties in studying cellular interactions in the CNS is the lack of effective methods to purify specific neuronal populations of interest. We report the development of a novel purification scheme, cholera toxin beta (CTB) immunopanning, in which a particular CNS neuron population is selectively labeled via retrograde axonal transport of the cell-surface epitope CTB, and then purified via immobilization with anti-CTB antibody. We have demonstrated the usefulness and versatility of this method by purifying both retinal ganglion cells and corticospinal motor neurons (CSMNs). Genomic expression analyses of purified CSMNs revealed that they express significant levels of many receptors for growth factors produced by brain endothelial cells; three of these factors, CXCL12, pleiotrophin, and IGF2 significantly enhanced purified CSMN survival, similar to previously characterized CSMN trophic factors BDNF and IGF1. In addition, endothelial cell conditioned medium significantly promoted CSMN neurite outgrowth. These findings demonstrate a useful method for the purification of several different types of CNS projection neurons, which in principle should work in many mammalian species, and provide evidence that endothelial-derived factors may represent an overlooked source of trophic support for neurons in the brain.

Heparin-binding protein pleiotrophin: an important player in the angiogenic process

Angiogenesis, the formation of new blood vessels from pre-existing ones, is a fundamental process in life, being also significantly important in several pathological situations. Pleiotrophin is a heparin-binding growth factor with pleiotrophic actions and significant role(s) in the formation of new blood vessels, being regulated by angiogenic stimuli and acting directly on endothelial cells. In this minireview, we summarize data on the regulation and mode of action of pleiotrophin and its involvement in physiological and tumor angiogenesis.

Activation of phospholipase C pathways by a synthetic chondroitin sulfate-E tetrasaccharide promotes neurite outgrowth of dopaminergic neurons

In dopaminergic neurons, chondroitin sulfate (CS) proteoglycans play important roles in neuronal development and regeneration. However, due to the complexity and heterogeneity of CS, the precise structure of CS with biological activity and the molecular mechanisms underlying its influence on dopaminergic neurons are poorly understood. In this study, we investigated the ability of synthetic CS oligosaccharides and natural polysaccharides to promote the neurite outgrowth of mesencephalic dopaminergic neurons and the signaling pathways activated by CS. CS-E polysaccharide, but not CS-A, -C or -D polysaccharide, facilitated the neurite outgrowth of dopaminergic neurons at CS concentrations within the physiological range. The stimulatory effect of CS-E polysaccharide on neurite outgrowth was completely abolished by its digestion into disaccharide units with chondroitinase ABC. Similarly to CS-E polysaccharide, a synthetic tetrasaccharide displaying only the CS-E sulfation motif stimulated the neurite outgrowth of dopaminergic neurons, whereas a CS-E disaccharide or unsulfated tetrasaccharide had no effect. Analysis of the molecular mechanisms revealed that the action of the CS-E tetrasaccharide was mediated through midkine-pleiotrophin/protein tyrosine phosphatase zeta and brain-derived neurotrophic factor/tyrosine kinase B receptor pathways, followed by activation of the two intracellular phospholipase C (PLC) signaling cascades: PLC/protein kinase C and PLC/inositol 1,4,5-triphosphate/inositol 1,4,5-triphosphate receptor signaling leading to intracellular Ca(2+) concentration-dependent activation of Ca(2+)/calmodulin-dependent kinase II and calcineurin. These results indicate that a specific sulfation motif, in particular the CS-E tetrasaccharide unit, represents a key structural determinant for activation of midkine, pleiotrophin and brain-derived neurotrophic factor-mediated signaling, and is required for the neuritogenic activity of CS in dopaminergic neurons.

Pleiotrophin is a neurotrophic factor for spinal motor neurons

Regeneration in the peripheral nervous system is poor after chronic denervation. Denervated Schwann cells act as a "transient target" by secreting growth factors to promote regeneration of axons but lose this ability with chronic denervation. We discovered that the mRNA for pleiotrophin (PTN) was highly up-regulated in acutely denervated distal sciatic nerves, but high levels of PTN mRNA were not maintained in chronically denervated nerves. PTN protected spinal motor neurons against chronic excitotoxic injury and caused increased outgrowth of motor axons out of the spinal cord explants and formation of "miniventral rootlets." In neonatal mice, PTN protected the facial motor neurons against cell death induced by deprivation from target-derived growth factors. Similarly, PTN significantly enhanced regeneration of myelinated axons across a graft in the transected sciatic nerve of adult rats. Our findings suggest a neurotrophic role for PTN that may lead to previously unrecognized treatment options for motor neuron disease and motor axonal regeneration.

Role of heparin binding growth factors in nigrostriatal dopamine system development and Parkinson's disease

The developmental biology of the dopamine (DA) system may hold important clues to its reconstruction. We hypothesized that factors highly expressed during nigrostriatal development and re-expressed after injury and disease may play a role in protection and reconstruction of the nigrostriatal system. Examination of gene expression in the developing striatum suggested an important role for the heparin binding growth factor family at time points relevant to establishment of dopaminergic innervation. Midkine, pleiotrophin (PTN), and their receptors syndecan-3 and receptor protein tyrosine phosphatase beta/zeta, were highly expressed in the striatum during development. Furthermore, PTN was up-regulated in the degenerating substantia nigra of Parkinson's patients. The addition of PTN to ventral mesencephalic cultures augmented DA neuron survival and neurite outgrowth. Thus, PTN was identified as a factor that plays a role in the nigrostriatal system during development and in response to disease, and may therefore be useful for neuroprotection or reconstruction of the DA system.

Involvement of Pleiotrophin in CNTF-mediated differentiation of the late retinal progenitor cells

Ciliary neurotrophic factor (CNTF) participates in retinal development by inhibiting rod differentiation and promoting bipolar and Müller cell differentiation. In order to identify genes which are regulated by CNTF in the developing retina, we carried out a subtractive hybridization study. By this approach, we identified the Pleiotrophin (Ptn) as an upregulated gene in postnatal day 0 (P0) retinal explants upon addition of CNTF. Correlation of overall expression patterns between different retinal cell markers and Ptn in situ hybridization suggest that Ptn transcripts are initially expressed in progenitor cells then in postmitotic precursors of the INL expressing the Chx10 gene, and later in some differentiated retinal Müller glial (RMG) cells and rod-bipolar cells. Overexpression of Ptn by in vitro electroporation of P0 rat retinal explants partially blocks rod differentiation and promotes bipolar cell production, similar to effects of exogenous CNTF and leukemia inhibitory factor (LIF). Furthermore, in P0 retinal explants from mice lacking Ptn, the inhibitory effect of CNTF and LIF on rod differentiation is partially reduced and the cytokine-induced bipolar cell differentiation is largely prevented. Together, these results demonstrate that influence of CNTF family of cytokines on the differentiation of late retinal progenitor cell population is partially mediated by the release of Ptn.

Immunodetection of heparin-binding growth associated molecule (pleiotrophin) in striatal interneurons

Pleiotrophin (PTN), a developmentally-regulated trophic factor, is over-expressed in the striatum of parkinsonian rats. Because striatal PTN can provide trophic support to dopamine neurons, we identified the cellular types containing PTN in the striatum of adult rats. By means of fluorescent double-immunolabeling, we found PTN to co-localize with a neuronal nuclei marker but not with glial fibrillary acidic protein. The number, distribution, and morphology of the PTN-immunolabeled cells suggested that they were interneurons. Further double-immunolabeling studies ruled out PTN localization to calretinin- and parvalbumin-containing interneurons. Instead, approximately 40% of the PTN-immunolabeled neurons contained nitric oxide synthase or somatostatin and approximately 60% expressed the vesicular acetylcholine transporter, supporting that they were GABAergic nitric oxide synthase/somatostatin-containing and cholinergic interneurons. Further work is necessary to determine if PTN from striatal interneurons can provide trophic support to dopamine neurons.