Expression of HB-GAM (heparin-binding growth-associated molecules) in the pathways of developing axonal processes in vivo and neurite outgrowth in vitro induced by HB-GAM

The roles of pleiotrophin in brain injuries: a narrative review of the literature

BACKGROUND

Pleiotrophin (PTN), a secreted multifunctional growth factor, is highly expressed in the developing brain. Recently, many studies have indicated that PTN participates in the development of brain and plays a neuroprotection after brain injury, especially promoting neuronal survival and neurite outgrowth, stimulating oligodendrocyte maturation and myelination, modulating neuroinflammation, and so on.

OBJECTIVE

However, no reviews comprehensively summarize the roles of PTN in brain injuries. Considering this, this review focuses on the roles and related regulatory pathways of PTN in brain injuries, what is known to date.

METHODS

PubMed and Embase databases have been searched, and related studies are compiled and summarized.

RESULTS

Our review has found PTN participates in the repairment of brain injuries, including hypoxic-ischemic brain injury, preterm white matter injury, traumatic brain injury, and neurodegenerative diseases, mainly based on animal data and small sample size studies. Besides, PTN interacts with receptors, such as, Z-type protein tyrosine phosphatase receptor and syndecan-3, regulating related pathways in these events.

CONCLUSION

It suggests PTN as a promising candidate for the treatment of brain injuries clinically. However, the evidence is early in its development. Further multi-center and large-sample studies are warranted to support our findings and determine the clinical value of PTN for treating brain injuries.

Pleiotrophin and the Expression of Its Receptors during Development of the Human Cerebellar Cortex

During embryonic and fetal development, the cerebellum undergoes several histological changes that require a specific microenvironment. Pleiotrophin (PTN) has been related to cerebral and cerebellar cortex ontogenesis in different species. PTN signaling includes PTPRZ1, ALK, and NRP-1 receptors, which are implicated in cell differentiation, migration, and proliferation. However, its involvement in human cerebellar development has not been described so far. Therefore, we investigated whether PTN and its receptors were expressed in the human cerebellar cortex during fetal and early neonatal development. The expression profile of PTN and its receptors was analyzed using an immunohistochemical method. PTN, PTPRZ1, and NRP-1 were expressed from week 17 to the postnatal stage, with variable expression among granule cell precursors, glial cells, and Purkinje cells. ALK was only expressed during week 31. These results suggest that, in the fetal and neonatal human cerebellum, PTN is involved in cell communication through granule cell precursors, Bergmann glia, and Purkinje cells via PTPRZ1, NRP-1, and ALK signaling. This communication could be involved in cell proliferation and cellular migration. Overall, the present study represents the first characterization of PTN, PTPRZ1, ALK, and NRP-1 expression in human tissues, suggesting their involvement in cerebellar cortex development.

Heparin-Binding Growth-Associated Molecule (Pleiotrophin) Affects Sensory Signaling and Selected Motor Functions in Mouse Model of Anatomically Incomplete Cervical Spinal Cord Injury

Heparin-binding growth-associated molecule (pleiotrophin) is a neurite outgrowth-promoting secretory protein that lines developing fiber tracts in juvenile CNS (central nervous system). Previously, we have shown that heparin-binding growth-associated molecule (HB-GAM) reverses the CSPG (chondroitin sulfate proteoglycan) inhibition on neurite outgrowth in the culture medium of primary CNS neurons and enhances axon growth through the injured spinal cord in mice demonstrated by two-photon imaging. In this study, we have started studies on the possible role of HB-GAM in enhancing functional recovery after incomplete spinal cord injury (SCI) using cervical lateral hemisection and hemicontusion mouse models. In vivo imaging of blood-oxygen-level-dependent (BOLD) signals associated with functional activity in the somatosensory cortex was used to assess the sensory functions during vibrotactile hind paw stimulation. The signal displays an exaggerated response in animals with lateral hemisection that recovers to the level seen in the sham-operated mice by injection of HB-GAM to the trauma site. The effect of HB-GAM treatment on sensory-motor functions was assessed by performance in demanding behavioral tests requiring integration of afferent and efferent signaling with central coordination. Administration of HB-GAM either by direct injection into the trauma site or by intrathecal injection improves the climbing abilities in animals with cervical hemisection and in addition enhances the grip strength in animals with lateral hemicontusion without affecting the spontaneous locomotor activity. Recovery of sensory signaling in the sensorimotor cortex by HB-GAM to the level of sham-operated mice may contribute to the improvement of skilled locomotion requiring integration of spatiotemporal signals in the somatosensory cortex.

Pleiotrophin: Activity and mechanism

Pleiotrophin (PTN) is a potent mitogenic cytokine with a high affinity for the polysaccharide glycosaminoglycan (GAG). Although it is most strongly associated with neural development during embryogenesis and the neonatal period, its expression has also been linked to a plethora of other physiological events including cancer metastasis, angiogenesis, bone development, and inflammation. A considerable amount of research has been carried out to understand the mechanisms by which PTN regulates these events. In particular, PTN has now been shown to bind a diverse collection of receptors including many GAG-containing proteoglycans. These interactions lead to the activation of many intracellular kinases and, ultimately, activation and transformation of cells. Structural studies of PTN in complex with both GAG and domains from its non-proteoglycan receptors reveal a binding mechanism that relies on electrostatic interactions and points to PTN-induced receptor oligomerization as one of the possible ways PTN uses to control cellular functions.

Pleiotrophin increases neurite length and number of spiral ganglion neurons in vitro

Acoustic trauma, aging, genetic defects or ototoxic drugs are causes for sensorineural hearing loss involving sensory hair cell death and secondary degeneration of spiral ganglion neurons. Auditory implants are the only available therapy for severe to profound sensorineural hearing loss when hearing aids do not provide a sufficient speech discrimination anymore. Neurotrophic factors represent potential therapeutic candidates to improve the performance of cochlear implants (CIs) by the support of spiral ganglion neurons (SGNs). Here, we investigated the effect of pleiotrophin (PTN), a well-described neurotrophic factor for different types of neurons that is expressed in the postnatal mouse cochlea. PTN knockout mice exhibit severe deficits in auditory brainstem responses, which indicates the importance of PTN in inner ear development and function and makes it a promising candidate to support SGNs. Using organotypic explants and dissociated SGN cultures, we investigated the influence of PTN on the number of neurons, neurite number and neurite length. PTN significantly increased the number and neurite length of dissociated SGNs. We further verified the expression of important PTN-associated receptors in the SG. mRNA of anaplastic lymphoma kinase, α_v integrin, β₃ integrin, receptor protein tyrosine phosphatase β/ζ, neuroglycan C, low-density lipoprotein receptor-related protein 1 and syndecan 3 was detected in the inner ear. These results suggest that PTN may be a novel candidate to improve sensorineural hearing loss treatment in the future.

Introduction and validation of a new semi-automated method to determine sympathetic fiber density in target tissues

In recent years, the role of sympathetic nervous fibers in chronic inflammation has become increasingly evident. At the onset of inflammation, sympathetic activity is increased in the affected tissue. However, sympathetic fibers are largely absent from chronically inflamed tissue. Apparently, there is a very dynamic relationship between sympathetic innervation and the immune system in areas of inflammation, and hence a rapid and easy method for quantification of nerve fiber density of target organs is of great value to answer potential research questions. Currently, nervous fiber densities are either determined by tedious manual counting, which is not suitable for high throughput approaches, or by expensive automated processes relying on specialized software and high-end microscopy equipment. Usually, tyrosine hydroxylase (TH) is used as the marker for sympathetic fibers. In order to overcome the current quantification bottleneck with a cost-efficient alternative, an automated process was established and compared to the classic manual approach of counting TH-positive sympathetic fibers. Since TH is not exclusively expressed on sympathetic fibers, but also in a number of catecholamine-producing cells, a prerequisite for automated determination of fiber densities is to reliably distinct between cells and fibers. Therefore, an additional staining using peripherin exclusively expressed in nervous fibers as a secondary marker was established. Using this novel approach, we studied the spleens from a syndecan-3 knockout (SDC3KO) mouse line, and demonstrated equal results on SNS fiber density for both manual and automated counts (Manual counts: wildtype: 22.57 +/- 11.72 fibers per mm²; ko: 31.95 +/- 18.85 fibers per mm²; p = 0.05; Automated counts: wildtype: 31.6 +/- 18.98 fibers per mm²; ko: 45.49 +/- 19.65 fibers per mm²; p = 0.02). In conclusion, this new and simple method can be used as a high-throughput approach to reliably and quickly estimate SNS nerve fiber density in target tissues.

8q22.1 Microduplication Syndrome: Why the Brain Should Be Spared? A Literature Review and a Case Report

Microduplication of chromosome 8q22.1 is mainly associated to Leri's pleonosteosis syndrome phenotype, an extremely rare autosomal dominant disease encompassing the GDF6 and SDC2 genes. To date, most of the authors focus their attention only on skeletal symptoms of the disease, and they do not systematically research or describe the co-occurrence of psychiatric illnesses or mental disorders with these muscular-skeletal diseases. In this report, we provide a description of an 8-year-old girl, with a positive family history for both skeletal malformations and bipolar disorders (BD). We suggest a possible association between Leri's pleonosteosis features and psychiatric symptoms. Furthermore, our report could be added to the large amount of reports that describe the correlation between genetic regions and disease risk for both psychiatric and rheumatological disorders.

Inhibition and enhancement of neural regeneration by chondroitin sulfate proteoglycans

The current dogma in neural regeneration research implies that chondroitin sulfate proteoglycans (CSPGs) inhibit plasticity and regeneration in the adult central nervous system (CNS). We argue that the role of the CSPGs can be reversed from inhibition to activation by developmentally expressed CSPG-binding factors. Heparin-binding growth-associated molecule (HB-GAM; also designated as pleiotrophin) has been studied as a candidate molecule that might modulate the role of CSPG matrices in plasticity and regeneration. Studies in vitro show that in the presence of soluble HB-GAM chondroitin sulfate (CS) chains of CSPGs display an enhancing effect on neurite outgrowth. Based on the in vitro studies, we suggest a model according to which the HB-GAM/CS complex binds to the neuron surface receptor glypican-2, which induces neurite growth. Furthermore, HB-GAM masks the CS binding sites of the neurite outgrowth inhibiting receptor protein tyrosine phosphatase sigma (PTPσ), which may contribute to the HB-GAM-induced regenerative effect. In vivo studies using two-photon imaging after local HB-GAM injection into prick-injury of the cerebral cortex reveal regeneration of dendrites that has not been previously demonstrated after injuries of the mammalian nervous system. In the spinal cord, two-photon imaging displays HB-GAM-induced axonal regeneration. Studies on the HB-GAM/CS mechanism in vitro and in vivo are expected to pave the way for drug development for injuries of brain and spinal cord.

HB-GAM (pleiotrophin) reverses inhibition of neural regeneration by the CNS extracellular matrix

Chondroitin sulfate (CS) glycosaminoglycans inhibit regeneration in the adult central nervous system (CNS). We report here that HB-GAM (heparin-binding growth-associated molecule; also known as pleiotrophin), a CS-binding protein expressed at high levels in the developing CNS, reverses the role of the CS chains in neurite growth of CNS neurons in vitro from inhibition to activation. The CS-bound HB-GAM promotes neurite growth through binding to the cell surface proteoglycan glypican-2; furthermore, HB-GAM abrogates the CS ligand binding to the inhibitory receptor PTPσ (protein tyrosine phosphatase sigma). Our in vivo studies using two-photon imaging of CNS injuries support the in vitro studies and show that HB-GAM increases dendrite regeneration in the adult cerebral cortex and axonal regeneration in the adult spinal cord. Our findings may enable the development of novel therapies for CNS injuries.

Sugar glues for broken neurons

Proteoglycans (PGs) regulate diverse functions in the central nervous system (CNS) by interacting with a number of growth factors, matrix proteins, and cell surface molecules. Heparan sulfate (HS) and chondroitin sulfate (CS) are two major glycosaminoglycans present in the PGs of the CNS. The functionality of these PGs is to a large extent dictated by the fine sulfation patterns present on their glycosaminoglycan (GAG) chains. In the past 15 years, there has been a significant expansion in our knowledge on the role of HS and CS chains in various neurological processes, such as neuronal growth, regeneration, plasticity, and pathfinding. However, defining the relation between distinct sulfation patterns of the GAGs and their functionality has thus far been difficult. With the emergence of novel tools for the synthesis of defined GAG structures, and techniques for their characterization, we are now in a better position to explore the structure-function relation of GAGs in the context of their sulfation patterns. In this review, we discuss the importance of GAGs on CNS development, injury, and disorders with an emphasis on their sulfation patterns. Finally, we outline several GAG-based therapeutic strategies to exploit GAG chains for ameliorating various CNS disorders.

In situ hybridization analysis of the temporospatial expression of the midkine/pleiotrophin family in rat embryonic pituitary gland

Pituitary gland development is controlled by numerous signaling molecules, which are produced in the oral ectoderm and diencephalon. A newly described family of heparin-binding growth factors, namely midkine (MK)/pleiotrophin (PTN), is involved in regulating the growth and differentiation of many tissues and organs. Using in situ hybridization with digoxigenin-labeled cRNA probes, we detected cells expressing MK and PTN in the developing rat pituitary gland. At embryonic day 12.5 (E12.5), MK expression was localized in Rathke's pouch (derived from the oral ectoderm) and in the neurohypophyseal bud (derived from the diencephalon). From E12.5 to E19.5, MK mRNA was expressed in the developing neurohypophysis, and expression gradually decreased in the developing adenohypophysis. To characterize MK-expressing cells, we performed double-staining of MK mRNA and anterior pituitary hormones. At E19.5, no MK-expressing cells were stained with any hormone. In contrast, PTN was expressed only in the neurohypophysis primordium during all embryonic stages. In situ hybridization clearly showed that MK was expressed in primitive (immature/undifferentiated) adenohypophyseal cells and neurohypophyseal cells, whereas PTN was expressed only in neurohypophyseal cells. Thus, MK and PTN might play roles as signaling molecules during pituitary development.

The survival promoting peptide Y-P30 promotes cellular migration

Y-P30, the 30 amino acid N-terminal peptide of the dermcidin gene, has been found to promote neuronal survival and differentiation. Its early presence in development and import to the fetal brain led to the hypothesis that Y-P30 has an influence on proliferation, differentiation and migration. Neurospheres derived from neural stem cells isolated from E13 mouse cortex and striatal ganglionic eminences were treated with Y-P30, however, the proportion of progenitors, neurons and astrocytes generated in differentiation assays was not altered. A short Y-P30 treatment of undifferentiated striatal and cortical neurospheres failed to alter the proportion of BrdU-positive cells. A longer treatment reduced the percentage of BrdU-positive cells and GABA-immunoreactive neurons only in striatal spheres. The presence of Y-P30 enhanced migration of T24 human bladder carcinoma cells in a wound-healing assay in vitro. Further, Y-P30 enhanced migration of T24 cells, rat primary cortical astrocytes and PC12 cells in chemotactic Boyden chamber assays. Together, these findings suggest that a major function of Y-P30 is to promote migration of neural and non-neural cell types.

Expression of pleiotrophin in the prostate is androgen regulated and it functions as an autocrine regulator of mesenchyme and cancer associated fibroblasts and as a paracrine regulator of epithelia

BACKGROUND

Androgens and paracrine signaling from mesenchyme/stroma regulate development and disease of the prostate, and gene profiling studies of inductive prostate mesenchyme have identified candidate molecules such as pleiotrophin (Ptn).

METHODS

Ptn transcripts and protein were localized by in situ and immunohistochemistry and Ptn mRNA was quantitated by Northern blot and qRT-PCR. Ptn function was examined by addition of hPTN protein to rat ventral prostate organ cultures, primary human fetal prostate fibroblasts, prostate cancer associated fibroblasts, and BPH1 epithelia.

RESULTS

During development, Ptn transcripts and protein were expressed in ventral mesenchymal pad (VMP) and prostatic mesenchyme. Ptn was localized to mesenchyme surrounding ductal epithelial tips undergoing branching morphogenesis, and was located on the surface of epithelia. hPTN protein stimulated branching morphogenesis and stromal and epithelial proliferation, when added to rat VP cultures, and also stimulated growth of fetal human prostate fibroblasts, prostate cancer associated fibroblasts, and BPH1 epithelia. PTN mRNA was enriched in patient-matched normal prostate fibroblasts versus prostate cancer associated fibroblasts. PTN also showed male enriched expression in fetal human male urethra versus female, and between wt male and ARKO male mice. Transcripts for PTN were upregulated by testosterone in fetal human prostate fibroblasts and organ cultures of female rat VMP. Ptn protein was increased by testosterone in organ cultures of female rat VMP and in rat male urethra compared to female.

CONCLUSIONS

Our data suggest that in the prostate Ptn functions as a regulator of both mesenchymal and epithelial proliferation, and that androgens regulate Ptn levels.

Increased trabecular bone formation in mice lacking the growth factor midkine

Midkine (Mdk) and pleiotrophin (Ptn) comprise a family of heparin-binding growth factors known primarily for their effects on neuronal cells. Since transgenic mice overexpressing Ptn have been reported to display increased bone density, we have previously analyzed Ptn-deficient mice but failed to detect any abnormality of skeletal development and remodeling. Together with the finding that Mdk expression increases in the course of primary osteoblast differentiation, we reasoned that Mdk, rather than Ptn, could play a physiologic role in bone formation. Here, we show that Mdk-deficient mice display an increased trabecular bone volume at 12 and 18 months of age, accompanied by cortical porosity. Histomorphometric quantification demonstrated an increased bone-formation rate compared with wild-type littermates, whereas bone resorption was differentially affected in trabecular and cortical bone of Mdk-deficient mice. To understand the effect of Mdk on bone formation at the molecular level, we performed a genome-wide expression analysis of primary osteoblasts and identified Ank and Enpp1 as Mdk-induced genes whose decreased expression in Mdk-deficient osteoblasts may explain, at least in part, the observed skeletal phenotype. Finally, we performed ovariectomy and observed bone loss only in wild-type but not in Mdk-deficient animals. Taken together, our data demonstrate that Mdk deficiency, at least in mice, results in an increased trabecular bone formation, thereby raising the possibility that Mdk-specific antagonists might prove beneficial in osteoporosis therapy.

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.

Neuritogenic activity of chondroitin/dermatan sulfate hybrid chains of embryonic pig brain and their mimicry from shark liver. Involvement of the pleiotrophin and hepatocyte growth factor signaling pathways

Accumulating evidence suggests the involvement of chondroitin sulfate (CS) and dermatan sulfate (DS) hybrid chains in the brain's development and critical roles for oversulfated disaccharides and IdoUA residues in the growth factor-binding and neuritogenic activities of these chains. In the pursuit of sources of CS/DS with unique structures, neuritogenic activity, and therapeutic potential, two novel CS/DS preparations were isolated from shark liver by anion exchange chromatography. The major (80%) low sulfated and minor (20%) highly sulfated fractions had an average molecular mass of 3.8-38.9 and 75.7 kDa, respectively. Digestion with various chondroitinases (CSases) revealed a large panel of disaccharides with either GlcUA or IdoUA scattered along the polysaccharide chains in both of the fractions. The higher M(r) fraction, richer in IdoUA(2-O-sulfate)alpha1-3GalNAc(4-O-sulfate) and GlcUAbeta/IdoUAalpha1-3GalNAc(4,6-O-disulfate) units, exerted greater neurite outgrowth-promoting (NOP) activity and better promoted the binding of various heparin-binding growth factors, including pleiotrophin (PTN), midkine, recombinant human heparin-binding epidermal growth factor-like growth factor, VEGF(165), fibroblast growth factor-2, fibroblast growth factor-7, and hepatocyte growth factor (HGF). These activities were largely abolished by digestion with CSase ABC or B but only moderately affected by a mixture of CSases AC-I and AC-II. In addition, the NOP activity of the larger fraction was markedly reduced by desulfation with alkali, suggesting a role for the 2-O-sulfate of IdoUA(2-O-sulfate)alpha1-3GalNAc(4-O-sulfate). The NOP activity of the higher molecular weight fraction and that of the embryonic pig brain-derived CS/DS fraction were also sup pressed to a large extent by antibodies against HGF, PTN, and their individual receptors cMet and anaplastic lymphoma kinase, revealing the involvement of the HGF and PTN signaling pathways in the activity.

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.

Exogenous Pleiotrophin Applied to Lesioned Nerve Impairs Muscle Reinnervation

Pleiotrophin (PTN) is a heparin-binding growth factor involved in nerve regeneration after peripheral nerve injury. After crush injury, PTN is found in distal nerve segments in several non-neural cell types, including Schwann cells, macrophages, and endothelial cells, but not in axons. To further clarify the role for PTN in nerve regeneration, we investigated the effects of PTN applied to lesioned peripheral nerve in vivo. PTN in a dose of 1 mg/kg impaired muscle reinnervation. Thus, gastrocnemius muscle failed to recover its contractile properties as assessed by in situ maximal isometric tetanic force. PTN also decreased non-neural cell densities and delayed macrophage recruitment in the distal crushed nerve. These results are discussed in the light of recent evidence that PTN is a multifunctional polypeptide.

You can't go home again: transcriptionally driven alteration of cell signaling by NGF

Here we review findings indicating that neurotrophins such as NGF promote changes in gene transcription that in turn influence the ways that cells subsequently respond to trophic factors. As a result, initial responses of "naïve" cells to NGF and other trophic agents differ from those of cells with prior NGF exposure. We discuss specific examples based on reports in the literature as well as on data derived from a serial analysis of gene expression (SAGE) study of NGF-promoted transcriptional changes in PC12 pheochromocytoma cells.

Midkine regulates pleiotrophin organ-specific gene expression: evidence for transcriptional regulation and functional redundancy within the pleiotrophin/midkine developmental gene family

Midkine (MK) and the highly related cytokine pleiotrophin (PTN) constitute the PTN/MK developmental gene family. The Mk and Ptn genes are essential for normal development of the catecholamine and renin-angiotensin pathways and the synthesis of different collagens. It is not known whether the Ptn and Mk genes regulate each other or whether PTN and MK are functionally redundant in development. We have now compared the levels of expression of Ptn and Mk in genetically deficient Mk -/- and Ptn -/- mice and found highly significant increases in Ptn gene expression in spinal cord, dorsal root ganglia, eye, heart, aorta, bladder, and urethra, but not in brain, bone marrow, testis, and lung of Mk -/- mice compared with wild type mice; a remarkable approximately 230-fold increase in Ptn expression levels was found in heart of Mk -/- mice and highly significant but lesser increases were found in six other organs. Differences in levels of Mk gene expression in Ptn -/- mice could not be detected in any of the organs tested. The data demonstrate that MK regulates Ptn gene expression with a high degree of organ specificity, suggesting that Ptn gene expression follows Mk gene expression in development, that the increase in Ptn gene expression is compensatory for the absence of MK in Mk -/- mice, that PTN and MK share a high degree of functional redundancy, and that MK may be very important in the development of heart in mouse.

Pleiotrophin cellular localization in nerve regeneration after peripheral nerve injury

Pleiotrophin (PTN) is a member of the family of heparin-binding growth factors that displays mitogenic activities and promotes neurite outgrowth in vitro. In vivo, PTN is widely expressed along pathways of developing axons during the late embryonic and early postnatal period. Although the level of PTN gene expression is very low during adulthood, activation of the gene may occur during recovery from injury and seems to play an important role in tissue regeneration processes. In this study, we investigated whether PTN was involved in the regenerative process of injured peripheral nerves. To refer localization of the fluorescent markers to myelinated axons, we developed a specific computer tool for colocalization of fluorescence images with phase contrast images. Immunohistochemical analysis showed PTN in different types of nonneural cells in distal nerve segments, including Schwann cells, macrophages, and endothelial cells, but not in axons. Schwann cells exhibited PTN immunoreactivity as early as 2 days after injury, whereas PTN-positive macrophages were found 1 week later. Strong PTN immunoreactivity was noted in endothelial cells at all time points. These findings support the idea that PTN participates in the adaptive response to peripheral nerve injury. A better understanding of its contribution may suggest new strategies for enhancing peripheral nerve regeneration.

The two thrombospondin type I repeat domains of the heparin-binding growth-associated molecule bind to heparin/heparan sulfate and regulate neurite extension and plasticity in hippocampal neurons

HB-GAM (heparin-binding growth-associated molecule, also designated as pleiotrophin) and midkine form a two-member family of extracellular matrix proteins that bind tightly to sulfated carbohydrate structures such as heparan sulfate. These proteins are used by developing neurons as extracellular cues in axonal growth and guidance. HB-GAM was recently reported to enhance differentiation of neural stem cells. Based on the solution structure of HB-GAM, we have recently shown that HB-GAM consists of two beta-sheet domains flanked by flexible lysine-rich N- and C-terminal tails with no apparent structure. These domains are homologous to thrombospondin type I repeats present in numerous extracellular proteins that interact with the cell surface. Our findings showed that the two beta-sheet domains fold independently. We showed that the domains (but not the lysine-rich tails) in HB-GAM are required and sufficient for interaction with hippocampal neurons. The individual domains bind heparan sulfate weakly and fail to produce significant biological effects in neurite outgrowth and long term potentiation assays. The amino acids in the linker region joining the two domains may be replaced with glycines with no effect on protein function. These results suggest a co-operative action of the two beta-sheet domains in the biologically relevant interaction with neuron surface heparan sulfate.

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

To better understand the particular vulnerability of mesencephalic dopaminergic neurons to toxins or gene mutations causing parkinsonism, we have taken advantage of a primary cell culture system in which these neurons die selectively. Antimitotic agents, such as cytosine arabinoside or cAMP, prevent the death of the neurons by arresting astrocyte proliferation. To identify factors implicated in either the death of the dopaminergic neurons or in the neuroprotective effect of cAMP, we constructed cDNA libraries enriched by subtractive hybridization and suppressive PCR in transcripts that are preferentially expressed in either control or cAMP-treated cultures. Differentially expressed transcripts were identified by hybridization of the enriched cDNAs with a commercially available cDNA expression array. The proteoglycan receptors syndecan-3 and the receptor protein tyrosine phosphatase zeta/beta were found among the transcripts preferentially expressed under control conditions, and their ligand, the cytokine pleiotrophin, was highly represented in the cDNA libraries for both conditions. Since pleiotrophin is expressed during embryonic and perinatal neural development and following lesions in the adult brain, we investigated its role in our cell culture model. Pleiotrophin was not responsible for the death of dopaminergic neurons under control conditions, or for their survival in cAMP-treated cultures. It was, however, implicated in the initial and cAMP-dependent enhancement of the differentiation of the dopaminergic neurons in our cultures. In addition, our experiments have provided evidence for a cAMP-dependent regulatory pathway leading to protease activation, and the identification of pleiotrophin as a target of this pathway.

Gene expression changes in the course of neural progenitor cell differentiation

The molecular changes underlying neural progenitor differentiation are essentially unknown. We applied cDNA microarrays with 13,627 clones to measure dynamic gene expression changes during the in vitro differentiation of neural progenitor cells that were isolated from the subventricular zone of postnatal day 7 mice and grown in vitro as neurospheres. In two experimental series in which we withdrew epidermal growth factor and added the neurotrophins Neurotrophin-4 or BDNF, four time points were investigated: undifferentiated cells grown as neurospheres, and cells 24, 48, and 96 hr after differentiation. Expression changes of selected genes were confirmed by semiquantitative RT-PCR. Ten different groups of gene expression dynamics obtained by cluster analysis are described. To correlate selected gene expression changes to the localization of respective proteins, we performed immunostainings of cultured neurospheres and of brain sections from adult mice. Our results provide new insights into the genetic program of neural progenitor differentiation and give strong hints to as yet unknown cellular communications within the adult subventricular zone stem cell niche.

alpha4beta1- and alpha6beta1-integrins are functional receptors for midkine, a heparin-binding growth factor

Midkine is a heparin-binding growth factor that promotes the growth, survival, migration and differentiation of various target cells. So far, receptor-type protein tyrosine phosphatase zeta, low-density-lipoprotein-receptor-related protein and anaplastic lymphoma kinase have been identified as receptors for midkine. We found beta1 integrin in midkine-binding proteins from 13-day-old mouse embryos. beta1-Integrin bound to a midkine-agarose column and was eluted mostly with EDTA. Further study revealed that the alpha-subunits capable of binding to midkine were alpha4 and alpha6. Purified alpha4beta1- and alpha6beta1-integrins bound midkine. Anti-alpha4 antibody inhibited the midkine-dependent migration of osteoblastic cells, and anti-alpha6 antibody inhibited the midkine-dependent neurite outgrowth of embryonic neurons. After midkine treatment, tyrosine phosphorylation of paxillin, an integrin-associated molecule, was transiently increased in osteoblastic cells. Therefore, we concluded that alpha4beta1- and alpha6beta1-integrins are functional receptors for midkine. We observed that the low-density-lipoprotein-receptor-related-protein-6 ectodomain was immunoprecipitated with alpha6beta1-integrin and alpha4beta1-integrin. The low-density-lipoprotein-receptor-related-protein-6 ectodomain was also immunoprecipitated with receptor-type protein tyrosine phosphatase zeta. alpha4beta1- and alpha6beta1-Integrins are expected to co-operate with other midkine receptors, possibly in a multimolecular complex that contains other midkine receptors.

Midkine and pleiotrophin in neural development and cancer

The midkine (MK) family consists of only two members, namely heparin-binding growth factors MK and pleiotrophin (PTN). During embryogenesis, MK is highly expressed in the mid-gestational period, whereas PTN expression reaches the maximum level around birth. Both proteins are localized in the radial glial processes of the embryonic brain, along which neural stem cells migrate and differentiate. Zebrafish and Xenopus MK can induce neural tissues. In addition, deposits of MK and/or PTN are found in neurodegenerative diseases, such as Alzheimer's disease and multiple system atrophy. Both molecules are induced in reactive astrocytes by ischemic insults. In this context, it is interesting that LDL receptor-related protein is a receptor for MK and PTN, and this receptor has been implicated in the pathogenesis of Alzheimer's disease. MK and PTN share receptors, and show similar biological activities that include fibrinolytic, anti-apoptotic, mitogenic, transforming, angiogenic, and chemotactic ones. These activities explain how these molecules are involved in carcinogenesis. MK is detected in human carcinoma specimens from pre-cancerous stages to advanced stages. Strong expression of PTN is also detected in several carcinomas, although, in general, MK is expressed more intensely and in a wide range of carcinomas than PTN. The blood MK level is frequently elevated in advanced human carcinomas, decreases after surgical removal of the tumors, and is correlated with prognostic factors. Thus, it is a good market for evaluating the progress of carcinomas. Furthermore, antisense oligonucleotides for MK and ribozymes for PTN show anti-tumor activity. Therefore, MK and PTN are candidate molecular targets for therapy for human carcinomas.

HB-GAM inhibits proliferation and enhances differentiation of neural stem cells

Proliferation of neural stem cells in the embryonic cerebral cortex is regulated by many growth factors and their receptors. Among the key molecules stimulating stem cell proliferation are FGF-2 and the FGF receptor-1. This ligand-receptor system is highly dependent on the surrounding heparan sulfates. We have found that heparin-binding growth-associated molecule (HB-GAM, also designated as pleiotrophin) regulates neural stem cell proliferation in vivo and in vitro. Deficiency of HB-GAM results in a pronounced, up to 50% increase in neuronal density in the adult mouse cerebral cortex. This phenotype arises during cortical neurogenesis, when HB-GAM knockout embryos display an enhanced proliferation rate as compared to wild-type embryos. Further, our in vitro studies show that exogenously added HB-GAM inhibits formation and growth of FGF-2, but not EGF, stimulated neurospheres, restricts the number of nestin-positive neural stem cells, and inhibits FGF receptor phosphorylation. We propose that HB-GAM functions as an endogenous inhibitor of FGF-2 in stem cell proliferation in the developing cortex.

Receptor-like protein tyrosine phosphatase zeta/RPTP beta is expressed on tangentially aligned neurons in early mouse neocortex

Protein tyrosine phosphatase zeta (PTPzeta)/RPTPbeta is a chondroitin sulfate proteoglycan predominantly expressed in the brain. In this study, we examined immunohistochemical localisation of PTPzeta in the mouse telencephalon from embryonic day 9.5 (E9.5) to E15.5. During E10.5-E12.5, immunoreactivities for PTPzeta are specifically observed on the tangentially aligned neurons at the preplate (PP) of the neocortex, as well as on the neurons at the mantle layer (ML) of the ganglionic eminences (GEs). Likewise, neurons immunoreactive for CR50, a marker for Cajal-Retzius neurons, are aligned from the ML of the ganglionic eminences to the PP of the neocortex and co-express PTPzeta. During E13.5-E15.5, PTPzeta-positive neurons are present at the subplate (SP) as well as at the marginal zone (MZ) of the neocortex. These results indicate that PTPzeta is a useful marker for early-generated neocortical neurons in mice: Cajal-Retzius neurons as well as the subplate neurons.

The role of ECM molecules in activity-dependent synaptic development and plasticity

Growth and guidance of neurites (axons and dendrites) during development is the prerequisite for the establishment of functional neural networks in the adult organism. In the adult, mechanisms similar to those used during development may regulate plastic changes that underlie important nervous system functions, such as memory and learning. There is now ever-increasing evidence that extracellular matrix (ECM)-associated factors are critically involved in the formation of neuronal connections during development, and their plastic changes in the adult. Here, we review the current literature on the role of ECM components in activity-dependent synaptic development and plasticity, with the major focus on the thrombospondin type I repeat (TSR) domain-containing proteins. We propose that ECM components may modulate neuronal development and plasticity by: 1) regulating cellular motility and morphology, thus contributing to structural alterations that are associated with the expression of synaptic plasticity, 2) coordinating transsynaptic signaling during plasticity via their cell surface receptors, and 3) defining the physical parameters of the extracellular space, thereby regulating diffusion of soluble signaling molecules in the extracellular space (ECS).

Expression and Function of the Receptor Protein Tyrosine Phosphatase ζ and Its Ligand Pleiotrophin in Human Astrocytomas

Using subtractive cloning combined with cDNA array analysis, we previously identified the genes encoding for the protein tyrosine phosphatase zeta/receptor-type protein tyrosine phosphatase beta (PTPzeta/RPTPbeta) and its ligand pleiotrophin (PTN) as overexpressed in human glioblastomas compared to normal brain. Both molecules have been implicated in neuronal migration during central nervous system development, and PTN is known to be involved in tumor growth and angiogenesis. We confirm overexpression of both molecules at the protein level in astrocytic gliomas of different malignancy grades. PTPzeta/RPTPbeta immunoreactivity was associated with increasing malignancy grade and localized predominantly to the tumor cells. PTN immunoreactivity as determined by ELISA and immunohistochemistry analysis was increased in low-grade astrocytomas compared to normal brain. Further increase in malignant gliomas was marginal, and thus no correlation with malignancy grade or microvessel density was present. However, PTN levels were significantly associated with those of fibroblast growth factor-2, suggesting co-regulation of both factors. Functionally, PTN induced weak chemotactic and strong haptotactic migration of glioblastoma and cerebral microvascular endothelial cells. Haptotaxis of glioblastoma cells towards PTN was specifically inhibited by an anti-PTPzeta/RPTPbeta antibody. Our findings suggest that upregulated expression of PTN and PTPzeta/RPTPbeta in human astrocytic tumor cells can create an autocrine loop that is important for glioma cell migration. Although PTN is a secreted growth factor, it appears to exert its mitogenic effects mostly in a matrix-immobilized form, serving as a substrate for migrating tumor cells.

HB-GAM/Pleiotrophin and Midkine are differently expressed and distributed during retinoic acid-induced neural differentiation of P19 cells

HB-GAM/Pleiotrophin and Midkine (MK) are developmentally-regulated proteins with putative functions during cell growth and differentiation. Using the P19 cell which is a model to study the events associated with early development, we examined the expression and cellular localization of HB-GAM and MK during neural differentiation of P19 cells induced by retinoic acid (RA). The temporal expressions of HB-GAM and MK transcripts and both the levels and cellular localizations of the corresponding proteins appeared dramatically different. MK mRNA, already expressed in untreated P19 cells, was transiently increased by exposure to RA and then largely down regulated. More interestingly, HB-GAM which was not detected in untreated P19 cells was strongly expressed after 2 days of RA treatment and this expression persists throughout the duration of the culture suggesting that it could be involved in different aspects of this differentiation process.

Molecular mechanism of ureteric bud development

The urinary collecting system is derived from an epithelial protrusion arising from the Wolffian duct called the ureteric bud (UB) by the signal from its inductive tissue, metanephric mesenchyme (MM). Targeted gene mutation studies have shown that several transcription factors and MM-secreted glial cell line-derived neurotrophic factor (GDNF) are critical for initiation of the UB. After initiation, the UB undergoes branching morphogenesis. Results obtained from in vitro culture systems, including an isolated UB culture, together with gene mutation studies suggest that interplay of multiple positive and negative soluble factors as well as extracellular matrix (ECM) and matrix-degrading proteinases regulate branching morphogenesis.

Identification of numerous genes differentially expressed in rat brain during postnatal development by suppression subtractive hybridization and expression analysis of the novel rat gene rMMS2

During postnatal development the potential for axonal growth and regeneration in the central nervous system (CNS) becomes very restricted. This decline of axon growth and regeneration might be due to developmental alterations in the expression level of genes which are strongly expressed in differentiating neurons during formation of axons, but which are downregulated later in development. In order to identify genes which are downregulated in rat brain with the completion of neuronal differentiation, we performed suppression subtractive hybridization (SSH) with rat cerebellum at two developmental stages. Several differentially expressed genes were identified. We present the detailed expression analysis of one of these, rMMS2, which is the rat homologue of mouse ubiquitin-conjugating enzyme-like protein MMS2 and belongs to a family of ubiquitin-conjugating enzyme variants (UEVs) that are highly similar to ubiquitin-conjugating enzymes E2 (Ubcs) but lack the essential amino acid residue in the active site. UEVs play a role in DNA repair and are possibly involved in ubiquitination, which may be important for the assembly and function of neuronal circuits. In the present study, we examined the temporal and spatial expression of rMMS2 transcript and show a strong developmental downregulation in rat brain by Northern blot analysis and in situ hybridization. The mRNA of rMMS2 is widely distributed in rat brain at late embryonic development but is differentially regulated during postnatal development; its expression is strongly reduced during maturation of the CNS. Our results show that SSH is a suitable method for identifying genes which are regulated during postnatal development and suggest that the newly identified rat UEV rMMS2 may play a role in neuronal development and differentiation.

Induction of human osteoprogenitor chemotaxis, proliferation, differentiation, and bone formation by osteoblast stimulating factor-1/pleiotrophin: osteoconductive biomimetic scaffolds for tissue engineering

The process of bone growth, regeneration, and remodeling is mediated, in part, by the immediate cell-matrix environment. Osteoblast stimulating factor-1 (OSF-1), more commonly known as pleiotrophin (PTN), is an extracellular matrix-associated protein, present in matrices, which act as targets for the deposition of new bone. However, the actions of PTN on human bone progenitor cells remain unknown. We examined the effects of PTN on primary human bone marrow stromal cells chemotaxis, differentiation, and colony formation (colony forming unit-fibroblastic) in vitro, and in particular, growth and differentiation on three-dimensional biodegradable porous scaffolds adsorbed with PTN in vivo. Primary human bone marrow cells were cultured on tissue culture plastic or poly(DL-lactic acid-co-glycolic acid) (PLGA; 75:25) porous scaffolds with or without addition of recombinant human PTN (1 pg-50 ng/ml) in basal and osteogenic conditions. Negligible cellular growth was observed on PLGA scaffold alone, generated using a super-critical fluid mixing method. PTN (50 microg/ml) was chemotactic to human osteoprogenitors and stimulated total colony formation, alkaline phosphatase-positive colony formation, and alkaline phosphatase-specific activity at concentrations as low as 10 pg/ml compared with control cultures. The effects were time-dependent. On three-dimensional scaffolds adsorbed with PTN, alkaline phosphatase activity, type I collagen formation, and synthesis of cbfa-1, osteocalcin, and PTN were observed by immunocytochemistry and PTN expression by in situ hybridization. PTN-adsorbed constructs showed morphologic evidence of new bone matrix and cartilage formation after subcutaneous implantation as well as within diffusion chambers implanted into athymic mice. In summary, PTN has the ability to promote adhesion, migration, expansion, and differentiation of human osteoprogenitor cells, and these results indicate the potential to develop protocols for de novo bone formation for skeletal repair that exploit cell-matrix interactions.

Pleiotrophin/Osteoblast-stimulating factor 1: dissecting its diverse functions in bone formation

OSF-1, more commonly known as pleiotrophin (PTN) or heparin-binding growth-associated molecule (HB-GAM), belongs to a new family of secreted HB proteins, which are structurally unrelated to any other growth factor family. The aims of this study were to dissect the diverse functions of PTN in bone formation. The study showed that PTN was synthesized by osteoblasts at an early stage of osteogenic differentiation and was present at sites of new bone formation, where PTN was stored in the new bone matrix. Low concentrations (10 pg/ml) of PTN stimulated osteogenic differentiation of mouse bone marrow cells and had a modest effect on their proliferation, whereas higher concentrations (ng/ml) had no effect. However, PTN did not have the osteoinductive potential of bone morphogenetic proteins (BMPs) because it failed to convert C2C12 cells, a premyoblastic cell line, to the osteogenic phenotype, whereas recombinant human BMP-2 (rhBMP-2) was able to do so. When PTN was present together with rhBMP-2 during the osteoinductive phase, PTN inhibited the BMP-mediated osteoinduction in C2C12 cells at concentrations between 0.05 pg/ml and 100 ng/ml. However, when added after osteoinduction had been achieved, PTN enhanced further osteogenic differentiation. An unusual effect of PTN (50 ng/ml) was the induction of type I collagen synthesis by chondrocytes in organ cultures of chick nasal cartilage and rat growth plates. Thus, PTN had multiple effects on bone formation and the effects were dependent on the concentration of PTN and the timing of its presence. To explain these multiple effects, we propose that PTN is an accessory signaling molecule, which is involved in a variety of processes in bone formation. PTN enhances or inhibits primary responses depending on the prevailing concentrations, the primary stimulus, and the availability of appropriate receptors.

Identification of pleiotrophin as a mesenchymal factor involved in ureteric bud branching morphogenesis

Branching morphogenesis is central to epithelial organogenesis. In the developing kidney, the epithelial ureteric bud invades the metanephric mesenchyme, which directs the ureteric bud to undergo repeated branching. A soluble factor(s) in the conditioned medium of a metanephric mesenchyme cell line is essential for multiple branching morphogenesis of the isolated ureteric bud. The identity of this factor had proved elusive, but it appeared distinct from factors such as HGF and EGF receptor ligands that have been previously implicated in branching morphogenesis of mature epithelial cell lines. Using sequential column chromatography, we have now purified to apparent homogeneity an 18 kDa protein, pleiotrophin, from the conditioned medium of a metanephric mesenchyme cell line that induces isolated ureteric bud branching morphogenesis in the presence of glial cell-derived neurotrophic factor. Pleiotrophin alone was also found to induce the formation of branching tubules in an immortalized ureteric bud cell line cultured three-dimensionally in an extracellular matrix gel. Consistent with an important role in ureteric bud morphogenesis during kidney development, pleiotrophin was found to localize to the basement membrane of the developing ureteric bud in the embryonic kidney. We suggest that pleiotrophin could act as a key mesenchymally derived factor regulating branching morphogenesis of the ureteric bud and perhaps other embryonic epithelial structures.

Heparan sulfate proteoglycan expression in the optic chiasm of mouse embryos

Previous studies have demonstrated that heparan sulfate (HS) proteoglycans (PGs) regulate neurite outgrowth through binding to a variety of cell surface molecules, extracellular matrix proteins, and growth factors. The present study investigated the possible involvement of HS-PGs in retinal axon growth by examining its expression in the retinofugal pathway of mouse embryos by using a monoclonal antibody against the HS epitope. Immunoreactive HS was first detected in all regions of the retina at embryonic day (E) 11. The staining was gradually lost in the central regions and restricted to the retinal periphery at later developmental stages (E12--E16). Prominent staining for HS was consistently found in the retinal fiber layer and at the optic disk, indicating a possible supportive role of HS-PGs in axon growth in the retina. At the ventral diencephalon, immunostaining for HS was first detected at E12, before arrival of any retinal axons. The staining matched closely the neurons that are immunopositive for the stage-specific embryonic antigen 1 (SSEA-1). At E13 to E16, when axons are actively exploring their paths across the chiasm, immunoreactivity for HS was particularly intense at the midline. This characteristic expression pattern suggests a role for HS-PGs in defining the path of early axons in the chiasm and in regulating development of axon divergence at the midline. Furthermore, HS immunoreactivity is substantially reduced at regions flanking both sides of the midline, which coincides spatially to the position of actin-rich growth cones from subpial surface to the deep regions of the optic axon layer at the chiasm. Moreover, at the threshold of the optic tract, immunoreactive HS was localized to deep parts of the fiber layer. These findings indicate that changes in age-related fiber order in the optic chiasm and optic tract of mouse embryos are possibly regulated by a spatially restricted expression of HS-PGs.

Enhanced hippocampal long-term potentiation in mice lacking heparin-binding growth-associated molecule

Heparin-binding growth-associated molecule (HB-GAM) (pleiotrophin) is a highly conserved extracellular matrix-associated protein implicated in a diverse range of developmental processes, including the formation and plasticity of neuronal connections. Using gene targeting, we have in the present study created HB-GAM-deficient mice that are viable and fertile and show no gross anatomical abnormalities. The hippocampal structure as well as basal excitatory synaptic transmission in the area CA1 appear normal in the mice lacking HB-GAM. However, hippocampal slices from HB-GAM-deficient mice display a lowered threshold for induction of long-term potentiation (LTP), which reverts back to the wild-type level by application of HB-GAM. HB-GAM expression in hippocampus is activity-dependent and upregulated in several neuropathological conditions. Thus, we suggest that HB-GAM acts as an inducible signal to inhibit LTP in hippocampus.

Pleiotrophin induces angiogenesis: involvement of the phosphoinositide-3 kinase but not the nitric oxide synthase pathways

Pleiotrophin (PTN) is a developmentally regulated protein that has been shown to be involved in tumor growth and metastasis presumably by activating tumor angiogenesis. To clarify the potential angiogenic activity of PTN and to analyze the signaling pathways involved in this process, we used an in vitro model of Human Umbilical Vein Endothelial Cells (HUVEC). We show that PTN was mitogenic toward a variety of endothelial cells including HUVEC, stimulated HUVEC migration across a reconstituted basement membrane and induced the formation of capillary-like structures by HUVEC grown as 3D-cultures in Matrigel or collagen. The signaling pathways triggered following endothelial cell stimulation by PTN were studied by using pharmacological inhibitors of the Phosphoinositide-3 kinase (PI3K) and endothelial Nitric Oxide Synthase (eNOS), two enzymes that have been shown to be crucial in the angiogenic response to Vascular Endothelial Growth Factor (VEGF). Whereas wortmannin (a PI3K inhibitor) and L-NAME (an eNOS inhibitor) dramatically reduced HUVEC growth induced by VEGF, only the former inhibitor reduced the growth induced by PTN and to a lesser extent that stimulated by basic Fibroblast Growth Factor. Thus, our results indicate that PTN induces angiogenesis and utilizes PI3K- but not eNOS-dependent pathways for its angiogenic activity.

A role for Pax6 in the normal development of dorsal thalamus and its cortical connections

The transcription factor Pax6 is widely expressed throughout the developing nervous system, including most alar regions of the newly formed murine diencephalon. Later in embryogenesis its diencephalic expression becomes more restricted. It persists in the developing anterior thalamus (conventionally termed “ventral” thalamus) and pretectum but is downregulated in the body of the posterior (dorsal) thalamus. At the time of this downregulation, the dorsal thalamus forms its major axonal efferent pathway via the ventral telencephalon to the cerebral cortex. This pathway is absent in mice lacking functional Pax6 (small eye homozygotes: Sey/Sey). We tested whether the mechanism underlying this defect includes abnormalities of the dorsal thalamus itself. We exploited a new transgenic mouse ubiquitously expressing green fluorescent protein tagged with tau, in which axonal tracts are clearly visible, and co-cultured dorsal thalamic explants from Pax6(+/+)or Pax6(Sey/Sey)embryos carrying the transgene with wild-type tissues from other regions of the forebrain. Whereas Pax6(+/+)thalamic explants produced strong innervation of wild-type ventral telencephalic explants in a pattern that mimicked the thalamocortical tract in vivo, Pax6(Sey)(/Sey) explants did not, indicating a defect in the ability of mutant dorsal thalamic cells to respond to signals normally present in ventral telencephalon. Pax6(Sey)(/Sey) embryos also showed early alterations in the expression of regulatory genes in the region destined to become dorsal thalamus. Whereas in normal mice Nkx2.2 and Lim1/Lhx1 are expressed ventral to this region, in the mutants their expression domains are throughout it, suggesting that a primary action of Pax6 is to generate correct dorsoventral patterning in the diencephalon. Our results suggest that normal thalamocortical development requires the actions of Pax6 within the dorsal thalamus itself.

Interaction of fimbriae of Haemophilus influenzae type B with heparin-binding extracellular matrix proteins

The interaction of the fimbriae of Haemophilus influenzae type b (Hib) with two heparin-binding extracellular matrix proteins, human fibronectin (Fn) and heparin-binding growth-associated molecule (HB-GAM) from mouse, were studied. The fimbriated Hib strain 770235 fim+, as well as the recombinant strain E. coli HB101(pMH140), which expressed Hib fimbriae, adhered strongly to Fn and HB-GAM immobilized on glass. Purified Hib fimbriae bound to Fn and HB-GAM, and within the Fn molecule, the binding was localized to the N-terminal 30,000-molecular-weight (30K) and 40K fragments, which contain heparin-binding domains I and II, respectively. Fimbrial binding to Fn, HB-GAM, and the 30K and the 40K fragments was inhibited by high concentrations of heparin. The results show that fimbriae of Hib interact with heparin-binding extracellular matrix proteins. The nonfimbriated Hib strain 770235 fim- exhibited a low level of adherence to Fn but did not react with HB-GAM, indicating that Hib strains also possess a fimbria-independent mechanism to interact with Fn.

Proteoglycans in the developing brain: new conceptual insights for old proteins

Proteoglycans are a heterogeneous class of proteins bearing sulfated glycosaminoglycans. Some of the proteoglycans have distinct core protein structures, and others display similarities and thus may be grouped into families such as the syndecans, the glypicans, or the hyalectans (or lecticans). Proteoglycans can be found in almost all tissues being present in the extracellular matrix, on cellular surfaces, or in intracellular granules. In recent years, brain proteoglycans have attracted growing interest due to their highly regulated spatiotemporal expression during nervous system development and maturation. There is increasing evidence that different proteoglycans act as regulators of cell migration, axonal pathfinding, synaptogenesis, and structural plasticity. This review summarizes the most recent data on structures and functions of brain proteoglycans and focuses on new physiological concepts for their potential roles in the developing central nervous system.

Heparin-binding proteins HB-GAM (pleiotrophin) and amphoterin in the regulation of cell motility

Fractionation of proteins from perinatal rat brain was monitored using a neurite outgrowth assay. Two neurite-promoting proteins, HB-GAM (heparin-binding growth-associated molecule; also known as pleiotrophin) and amphoterin, were isolated, cloned and produced by baculovirus expression for structural and functional studies. HB-GAM is highly expressed in embryonic and early post-natal fiber pathways of the nervous system, and it enhances axonal growth/guidance by binding to N-syndecan (syndecan-3) at the neuron surface. N-syndecan in turn communicates with the cytoskeleton through the cortactin/src-kinase pathway to enhance neurite extension. In addition to N-syndecan, the chondroitin sulfate proteoglycan RPTP beta/zeta (receptor-type tyrosine phosphatase beta/zeta) is implicated in the receptor mechanism of HB-GAM. HB-GAM is also prominently expressed in developing and regenerating bone as a matrix-bound cue for migration of osteoblasts/osteoblast precursors to the site of bone deposition. HB-GAM is suggested to regulate motility in osteoblasts through a similar mechanism as in neurons. Structural studies using heteronuclear NMR reveal two similar protein domains in HB-GAM, both consisting of three anti-parallel beta-strands. Search of sequence databases shows that the beta structures of HB-GAM and of the similar domains of MK (midkine) correspond to the thrombospondin type I (TSR) sequence motif. We suggest that the TSR sequence motif, found in several neurite outgrowth-promoting and other cell surface and matrix-binding proteins, defines a beta structure similar to those found in HB-GAM and MK. In general, amphoterin is highly expressed in immature and transformed cells. We suggest a model, according to which amphoterin is an autocrine/paracrine regulator of invasive migration. Amphoterin binds to RAGE (receptor of advanced glycation end products), an immunoglubulin superfamily member related to N-CAM (neural cell adhesion molecule), that communicates with the GTPases Cdc42 and Rac to regulate cell motility. In addition, ligation of RAGE by amphoterin activates NF-kappaB to regulate transcription.

Heparin-binding growth-associated molecule contains two heparin-binding beta -sheet domains that are homologous to the thrombospondin type I repeat

Heparin-binding growth-associated molecule (HB-GAM) is an extracellular matrix-associated protein implicated in the development and plasticity of neuronal connections of brain. Binding to cell surface heparan sulfate is indispensable for the biological activity of HB-GAM. In the present paper we have studied the structure of recombinant HB-GAM using heteronuclear NMR. These studies show that HB-GAM contains two beta-sheet domains connected by a flexible linker. Both of these domains contain three antiparallel beta-strands. In addition to this domain structure, HB-GAM contains the N- and C-terminal lysine-rich sequences that lack a detectable structure and appear to form random coils. Studies using CD and NMR spectroscopy suggest that HB-GAM undergoes a conformational change upon binding to heparin, and that the binding occurs primarily to the beta-sheet domains of the protein. Search of sequence data bases shows that the beta-sheet domains of HB-GAM are homologous to the thrombospondin type I repeat (TSR). Sequence comparisions show that the beta-sheet structures found previously in midkine, a protein homologous with HB-GAM, also correspond to the TSR motif. We suggest that the TSR sequence motif found in various extracellular proteins defines a beta-sheet structure similar to that found in HB-GAM and midkine. In addition to the apparent structural similarity, a similarity in biological functions is suggested by the occurrence of the TSR sequence motif in a wide variety of proteins that mediate cell-to-extracellular matrix and cell-to-cell interactions, in which the TSR domain mediates specific cell surface binding.

Distinct expression of midkine and pleiotrophin in the spinal cord and placental tissues during early mouse development

Midkine and pleiotrophin comprise a family of heparin-binding growth factors, and are expressed in overlapping tissues during the mid- to late-gestation periods of mouse development. Their distinct expression during early mouse development, as revealed by in situ hybridization, was reported. Midkine was expressed in the embryonic ectoderm from as early as embryonic day (E5.5). In the neural tube midkine was expressed specifically in the neuroepithelium, that is, in the whole area of the neural tube at E9.5, and in the ventricular zone from E10.5-13.5. At E15.5, when the neuroepithelium disappeared, midkine concomitantly became undetectable. In contrast, pleiotrophin expression started exclusively in the neural plate at E8.5, and in the lateral plate of the neural tube at E9.5. It then became restricted to a dorsal ventricular zone from E11.5-13.5, and finally to the central gray neurons at E15.5. Moreover, pleiotrophin was expressed in the ventral horns. Among placental tissues, midkine was detected in the chorion, the fetal component of the placenta, whereas pleiotrophin was found in the decidua basalis, the maternal component of the placenta. The distinct expression of midkine and pleiotrophin suggests their differential role in early development.

Regulation of signaling by protein-tyrosine phosphatases: potential roles in the nervous system

During neuronal development, cells respond to a variety of environmental cues through cell surface receptors that are coupled to a signaling transduction machinery based on protein tyrosine phosphorylation and dephosphorylation. Receptor and non-receptor tyrosine kinases have received a great deal of attention; however, in the last few years, receptor (plasma membrane associated) and non-receptor protein-tyrosine phosphatases (PTPs) have also been shown to play important roles in development of the nervous system. In many cases PTPs have provocative distribution patterns or have been shown to be associated with specific cell adhesion and growth factor receptors. Additionally, altering PTP expression levels or activity impairs neuronal behavior. In this review we outline what is currently known about the role of PTPs in development, differentiation and neuronal physiology.

Incorporation of heparin-binding peptides into fibrin gels enhances neurite extension: an example of designer matrices in tissue engineering

The goal of this work was to improve the potential of fibrin to promote nerve regeneration by enzymatically incorporating exogenous neurite-promoting heparin-binding peptides. The effects on neurite extension of four different heparin-binding peptides, derived from the heparin-binding domains of antithrombin III, neural cell adhesion molecule and platelet factor 4, were determined. These exogenous peptides were synthesized as bi-domain peptide chimeras, with the second domain being a substrate for factor XIIIa. This coagulation transglutaminase covalently bound the peptides within the fibrin gel during coagulation. The heparin-binding peptides enhanced the degree of neurite extension from embryonic chick dorsal root ganglia through 3-dimensional fibrin gels, and the extent of enhancement was found to correlate positively with the heparin-binding affinity of the individual domains. The enhancement could be inhibited by competition with soluble heparin, by degradation of cell-surface proteoglycans, and by inhibition of the covalent immobilization of the peptide. These results demonstrate an important potential role for proteoglycan-binding components of the extracellular matrix in neurite extension and suggest that fibrin gels modified with covalently bound heparin-binding peptides could serve as a therapeutic agent to enhance peripheral nerve regeneration through nerve guide tubes. More generally, the results demonstrate that the biological responses to fibrin, the body's natural wound healing matrix, can be dramatically improved by the addition of exogenous bioactive peptides in a manner such that they become immobilized during coagulation.-Sakiyama, S. E., Schense, J. C., Hubbell, J. A. Incorporation of heparin-binding peptides into fibrin gels enhances neurite extension: an example of designer matrices in tissue engineering.