Expression of the heparin-binding cytokines, midkine (MK) and HB-GAM (pleiotrophin) is associated with epithelial-mesenchymal interactions during fetal development and organogenesis

Midkine prevented hypoxic injury of mouse embryonic stem cells through activation of Akt and HIF-1α via low-density lipoprotein receptor-related protein-1

Stem cell functions are dramatically altered by oxygen in tissue culture, which means the antioxidant/oxidant balance is critical for protection as well as toxicity. This study examined the effect of the heparin-binding growth factor midkine (MK) on hypoxia-induced apoptosis and related signal pathways in mouse embryonic stem cells (mESCs). Hypoxia (60 h) increased lactate dehydrogenase release and apoptosis, and reduced cell viability and proliferation. These effects were reversed by MK (100 ng/ml). MK also reversed hypoxia-induced increases of intracellular reactive oxygen species, c-Jun N-terminal kinase (JNK), and p38 mitogen-activated protein kinase (MAPK) phosphorylation. Blockage of JNK and p38 MAPK using small interference (si)RNAs produced a decrease in apoptosis. A loss of mitochondrial membrane potential, increases of cytochrome c release from mitochondria to cytosol, and cleaved caspase-3 expression, as well as decreases in cIAP-2 and Bcl-2 were also reversed by MK. Hypoxia alone and hypoxia with MK increased low-density lipoprotein receptor-related protein-1 (LRP-1) mRNA and protein expression. Hypoxia with MK rapidly increased serine/threonine protein kinase (Akt) phosphorylation which reversed by LRP-1 Ab (0.1 µg/ml) and prolonged heme oxygenase-1 (HO-1) expression. In addition, hypoxia with MK increased the expression of hypoxia-inducible factor-1α (HIF-1α). Moreover, inhibition of Akt, HO-1, and HIF-1α signaling pathways abolished the MK-induced blockage of apoptosis. In conclusion, MK partially prevented hypoxic injury of mESCs through activation of Akt, HO-1, and HIF-1α via LRP-1.

A closer look at the nitrogen next door: 1H-15N NMR methods for glycosaminoglycan structural characterization

Recently, experimental conditions were presented for the detection of the N-sulfoglucosamine (GlcNS) NHSO(3)(-) or sulfamate (1)H and (15)N NMR resonances of the pharmaceutically and biologically important glycosaminoglycan (GAG) heparin in aqueous solution. In the present work, we explore further the applicability of nitrogen-bound proton detection to provide structural information for GAGs. Compared to the detection of (15)N chemical shifts of aminosugars through long-range couplings using the IMPACT-HNMBC pulse sequence, the more sensitive two-dimensional (1)H-(15)N HSQC-TOCSY experiments provided additional structural data. The IMPACT-HNMBC experiment remains a powerful tool as demonstrated by the spectrum measured for the unsubstituted amine of 3-O-sulfoglucosamine (GlcN(3S)), which cannot be observed with the (1)H-(15)N HSQC-TOCSY experiment due to the fast exchange of the amino group protons with solvent. The (1)H-(15)N HSQC-TOCSY NMR spectrum reported for the mixture of model compounds GlcNS and N-acetylglucosamine (GlcNAc) demonstrate the broad utility of this approach. Measurements for the synthetic pentasaccharide drug Arixtra® (Fondaparinux sodium) in aqueous solution illustrate the power of this NMR pulse sequence for structural characterization of highly similar N-sulfoglucosamine residues in GAG-derived oligosaccharides.

Pleiotrophin expression during odontogenesis

Pleiotrophin (PTN) is an extracellular matrix-associated growth factor and chemokine expressed in mesodermal and ectodermal cells. It plays an important role in osteoblast recruitment and differentiation. There is limited information currently available about PTN expression during odontoblast differentiation and tooth formation, and thus the authors aimed to establish the spatiotemporal expression pattern of PTN during mouse odontogenesis. Immortalized mouse dental pulp (MD10-D3, MD10-A11) and odontoblast-like (M06-G3) and ameloblast-like (EOE-3M) cell lines were grown and samples prepared for immunocytochemistry, Western blot, and conventional and quantitative PCR analysis. Effects of BMP2, BMP4, and BMP7 treatment on PTN expression in odontoblast-like M06-G3 cells were tested by quantitative PCR. Finally, immunohistochemistry of sectioned mice mandibles and maxillaries at developmental stages E16, E18, P1, P6, P10, and P28 was performed. The experiments showed that PTN, at both the mRNA and protein level, was expressed in all tested epithelial and mesenchymal dental cell lines and that the level of PTN mRNA was influenced differentially by the bone morphogenetic proteins. The authors observed initial expression of PTN in the inner enamel epithelium with prolonged expression in the ameloblasts and odontoblasts throughout their stages of maturation and strong expression in the terminally differentiated and enamel matrix-secreting ameloblasts and odontoblasts of the adult mouse incisors and molars.

In vitro studies on odontogenic tumors

Ameloblastomas are uncommon benign neoplasms of the jaws. They originate from dental epithelial cells, but they are not capable of mineralizing or forming enamel. The study of these tumors is limited to live tissue collected from patients during scheduled surgery. Ameloblastomas grow slowly in vivo and this property is translated to their behavior in vitro. Here, we describe the methods to culture ameloblastomas in organotypic cultures, as well as to isolate stem/progenitor cells from these tumors.

Midkine in inflammation

The 13 kDa heparin-binding growth factor midkine (MK) was originally identified as a molecule involved in the orchestration of embryonic development. Recent studies provided evidence for a new role of MK in acute and chronic inflammatory processes. Accordingly, several inflammatory diseases including nephritis, arthritis, atherosclerosis, colitis, and autoimmune encephalitis have been shown to be alleviated in the absence of MK in animal models. Reduced leukocyte recruitment to the sites of inflammation was found to be one important mechanism attenuating chronic inflammation when MK was absent. Furthermore, MK was found to modulate expression of proinflammatory cytokines and the expansion of regulatory T-cells. Here, we review the current understanding of the role of MK in different inflammatory disorders and summarize the knowledge of MK biology.

Midkine and Alk signaling in sympathetic neuron proliferation and neuroblastoma predisposition

Neuroblastoma (NB) is the most common extracranial solid tumor in childhood and arises from cells of the developing sympathoadrenergic lineage. Activating mutations in the gene encoding the ALK tyrosine kinase receptor predispose for NB. Here, we focus on the normal function of Alk signaling in the control of sympathetic neuron proliferation, as well as on the effects of mutant ALK. Forced expression of wild-type ALK and NB-related constitutively active ALK mutants in cultures of proliferating immature sympathetic neurons results in a strong proliferation increase, whereas Alk knockdown and pharmacological inhibition of Alk activity decrease proliferation. Alk activation upregulates NMyc and trkB and maintains Alk expression by an autoregulatory mechanism involving Hand2. The Alk-ligand Midkine (Mk) is expressed in immature sympathetic neurons and in vivo inhibition of Alk signaling by virus-mediated shRNA knockdown of Alk and Mk leads to strongly reduced sympathetic neuron proliferation. Taken together, these results demonstrate that the extent and timing of sympathetic neurogenesis is controlled by Mk/Alk signaling. The predisposition for NB caused by activating ALK mutations may thus be explained by aberrations of normal neurogenesis, i.e. elevated and sustained Alk signaling and increased NMyc expression.

Notch signalling pathway in tooth development and adult dental cells

Notch signalling is a highly conserved intercellular signal transfer mechanism that includes canonical and non-canonical pathways. It regulates differentiation and proliferation of stem/progenitor cells by means of para-inducing effects. Expression and activation of Notch signalling factors (receptors and ligands) are critical not only for development of the dental germ but also for regeneration of injured tissue associated with mature teeth. Notch signalling plays key roles in differentiation of odontoblasts and osteoblasts, calcification of tooth hard tissue, formation of cusp patterns and generation of tooth roots. After tooth eruption, Notch signalling can also be triggered in dental stem cells of the pulp, where it induces them to differentiate into odontoblasts, thus generating fresh dentine tissue. Other signalling pathways, such as TGFβ, NF-κB, Wnt, Fgf and Shh also interact with Notch signalling during tooth development.

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.

Heparin characterization: challenges and solutions

Although heparin is an important and widely prescribed pharmaceutical anticoagulant, its high degree of sequence microheterogeneity and size polydispersity make molecular-level characterization challenging. Unlike nucleic acids and proteins that are biosynthesized through template-driven assembly processes, heparin and the related glycosaminoglycan heparan sulfate are actively remodeled during biosynthesis through a series of enzymatic reactions that lead to variable levels of O- and N-sulfonation and uronic acid epimers. As summarized in this review, heparin sequence information is determined through a bottom-up approach that relies on depolymerization reactions, size- and charge-based separations, and sensitive mass spectrometric and nuclear magnetic resonance experiments to determine the structural identity of component oligosaccharides. The structure-elucidation process, along with its challenges and opportunities for future analytical improvements, is reviewed and illustrated for a heparin-derived hexasaccharide.

The role of pleiotrophin and beta-catenin in fetal lung development

Mammalian lung development is a complex biological process, which is temporally and spatially regulated by growth factors, hormones, and extracellular matrix proteins. Abnormal changes of these molecules often lead to impaired lung development, and thus pulmonary diseases. Epithelial-mesenchymal interactions are crucial for fetal lung development. This paper reviews two interconnected pathways, pleiotrophin and Wnt/β-catenin, which are involved in fibroblast and epithelial cell communication during fetal lung development.

Midkine: a novel prognostic biomarker for cancer

Since diagnosis at an early stage still remains a key issue for modern oncology and is crucial for successful cancer therapy, development of sensitive, specific, and non-invasive tumor markers, especially, in serum, is urgently needed. Midkine (MK), a plasma secreted protein, was initially identified in embryonal carcinoma cells at early stages of retinoic acid-induced differentiation. Multiple studies have reported that MK plays important roles in tumor progression, and is highly expressed in various malignant tumors. Because increased serum MK concentrations also have been reported in patients with various tumors, serum MK may have the potential to become a very useful tumor marker. Here, we review and discuss the possibility and usefulness of MK as a novel tumor marker.

Biology of human hair: know your hair to control it

Hair can be engineered at different levels--its structure and surface--through modification of its constituent molecules, in particular proteins, but also the hair follicle (HF) can be genetically altered, in particular with the advent of siRNA-based applications. General aspects of hair biology are reviewed, as well as the most recent contributions to understanding hair pigmentation and the regulation of hair development. Focus will also be placed on the techniques developed specifically for delivering compounds of varying chemical nature to the HF, indicating methods for genetic/biochemical modulation of HF components for the treatment of hair diseases. Finally, hair fiber structure and chemical characteristics will be discussed as targets for keratin surface functionalization.

Midkine expression is regulated by the circadian clock in the retina of the zebrafish

The retina displays numerous processes that follow a circadian rhythm. These processes are coordinated through the direct action of light on photoreceptive molecules and, in the absence of light, through autocrine/paracrine actions of extracellular neuromodulators. We previously described the expression of the genes encoding the secreted heparin-binding growth factors, midkine-a (mdka) and midkine-b (mdkb), in the retina of the zebrafish. Here, we provide evidence that the expression of mdka and mdkb follows a daily rhythm, which is independent of the presence or absence of light, and we propose that the expression of mdka is regulated by the circadian clock. Both qualitative and quantitative measures show that for mdka, the levels of mRNA and protein decrease during the night and increase during the subjective day. Qualitative measures show that the expression of mdkb increases during the second half of the subjective night and decreases during the second half of the subjective day. Within horizontal cells, the two midkine paralogs show asynchronous circadian regulation. Though intensely studied in the contexts of physiology and disease, this is the first study to provide evidence for the circadian regulation of midkines in the vertebrate nervous system.

Pleiotrophin induces neurite outgrowth and up-regulates growth-associated protein (GAP)-43 mRNA through the ALK/GSK3beta/beta-catenin signaling in developing mouse neurons

Pleiotrophin (PTN) is highly expressed in the nervous system during embryogenesis; however, little is known about its functional role in neural development. By using whole mount in situ hybridization, we observed that the expression pattern of PTN was similar to that of Wnt3a; PTN mRNA was abundant in the nervous tissue along the dorsal midline and in the forelimb and hindlimb buds of embryonic mice (E8.5-E12.5). Treatment with recombinant PTN (100ng/ml) induced phosphorylation of glycogen synthase kinase 3beta (GSK3beta), nuclear localization of beta-catenin and up-regulation of growth-associated protein (GAP)-43 mRNA in cultured embryonic mouse (E14.5) neurons. Furthermore, recombinant PTN enhanced neurite outgrowth from cortical explants embedded in Matrigel. These PTN-induced biochemical changes and neurite outgrowth were attenuated by the co-treatment with anti-anaplastic lymphoma kinase (ALK) antibodies, but not with anti-protein tyrosine phosphatase (PTP)zeta antibodies. These findings imply that ALK is involved in the PTN signaling on neural development.

The angiogenic factor midkine is regulated by dexamethasone and retinoic acid during alveolarization and in alveolar epithelial cells

Background

A precise balance exists between the actions of endogenous glucocorticoids (GC) and retinoids to promote normal lung development, in particular during alveolarization. The mechanisms controlling this balance are largely unknown, but recent evidence suggests that midkine (MK), a retinoic acid-regulated, pro-angiogenic growth factor, may function as a critical regulator. The purpose of this study was to examine regulation of MK by GC and RA during postnatal alveolar formation in rats.

Methods

Newborn rats were treated with dexamethasone (DEX) and/or all-trans-retinoic acid (RA) during the first two weeks of life. Lung morphology was assessed by light microscopy and radial alveolar counts. MK mRNA and protein expression in response to different treatment were determined by Northern and Western blots. In addition, MK protein expression in cultured human alveolar type 2-like cells treated with DEX and RA was also determined.

Results

Lung histology confirmed that DEX treatment inhibited and RA treatment stimulated alveolar formation, whereas concurrent administration of RA with DEX prevented the DEX effects. During normal development, MK expression was maximal during the period of alveolarization from postnatal day 5 (PN5) to PN15. DEX treatment of rat pups decreased, and RA treatment increased lung MK expression, whereas concurrent DEX+RA treatment prevented the DEX-induced decrease in MK expression. Using human alveolar type 2 (AT2)-like cells differentiated in culture, we confirmed that DEX and cAMP decreased, and RA increased MK expression.

Conclusion

We conclude that MK is expressed by AT2 cells, and is differentially regulated by corticosteroid and retinoid treatment in a manner consistent with hormonal effects on alveolarization during postnatal lung development.

Pleiotrophin is expressed in avian somites and tendon anlagen

Pleiotrophin (Ptn) is a secreted, developmentally regulated growth factor associated with the extracellular matrix. During mammalian embryogenesis, Ptn has been suggested to play a role in the development of various embryonic structures including nervous system and skeleton. In the avian embryo, Ptn has been proposed to be involved in limb cartilage development, but embryonic Ptn expression has not been comprehensively studied. We isolated a cDNA fragment containing the full-length coding sequence of chick Ptn and studied the expression of Ptn in detail until embryonic day 10. We, furthermore, isolated a 6,385-bp phage clone containing the Ptn cDNA of 2,551 bp and additional 3,787 bp downstream of the published Ptn cDNA sequence classifying a yet Ptn-unrelated chEST clone as the 3' untranslated region of Ptn. Our studies revealed novel expression domains in developing somites and during limb formation. We found prominent expression in the somitocoel cells of epithelial somites, and in a sclerotomal subcompartment, the syndetome, which gives rise to the axial tendons in the vertebral motion segment. In the limbs, Ptn was markedly expressed in tendon anlagen and in phalangeal joints. Our results introduce Ptn as a novel marker gene in avian somite and tendon development.

Anaplastic lymphoma kinase: signalling in development and disease

RTKs (receptor tyrosine kinases) play important roles in cellular proliferation and differentiation. In addition, RTKs reveal oncogenic potential when their kinase activities are constitutively enhanced by point mutation, amplification or rearrangement of the corresponding genes. The ALK (anaplastic lymphoma kinase) RTK was originally identified as a member of the insulin receptor subfamily of RTKs that acquires transforming capability when truncated and fused to NPM (nucleophosmin) in the t(2;5) chromosomal rearrangement associated with ALCL (anaplastic large cell lymphoma). To date, many chromosomal rearrangements leading to enhanced ALK activity have been described and are implicated in a number of cancer types. Recent reports of the EML4 (echinoderm microtubule-associated protein like 4)–ALK oncoprotein in NSCLC (non-small cell lung cancer), together with the identification of activating point mutations in neuroblastoma, have highlighted ALK as a significant player and target for drug development in cancer. In the present review we address the role of ALK in development and disease and discuss implications for the future.

Cellular expression of midkine-a and midkine-b during retinal development and photoreceptor regeneration in zebrafish

In the retina of adult teleosts, stem cells are sustained in two specialized niches: the ciliary marginal zone (CMZ) and the microenvironment surrounding adult Müller glia. Recently, Müller glia were identified as the regenerative stem cells in the teleost retina. Secreted signaling molecules that regulate neuronal regeneration in the retina are largely unknown. In a microarray screen to discover such factors, we identified midkine-b (mdkb). Midkine is a highly conserved heparin-binding growth factor with numerous biological functions. The zebrafish genome encodes two distinct midkine genes: mdka and mdkb. Here we describe the cellular expression of mdka and mdkb during retinal development and the initial, proliferative phase of photoreceptor regeneration. The results show that in the embryonic and larval retina mdka and mdkb are expressed in stem cells, retinal progenitors, and neurons in distinct patterns that suggest different functions for the two molecules. Following the selective death of photoreceptors in the adult, mdka and mdkb are coexpressed in horizontal cells and proliferating Müller glia and their neurogenic progeny. These data reveal that Mdka and Mdkb are signaling factors present in the retinal stem cell niches in both embryonic and mature retinas, and that their cellular expression is actively modulated during retinal development and regeneration.

Enamel-free teeth: Tbx1 deletion affects amelogenesis in rodent incisors

TBX1 is a principal candidate gene for DiGeorge syndrome, a developmental anomaly that affects the heart, thymus, parathyroid, face, and teeth. A mouse model carrying a deletion in a functional region of the Tbx1 gene has been extensively used to study anomalies related to this syndrome. We have used the Tbx1 null mouse to understand the tooth phenotype reported in patients afflicted by DiGeorge syndrome. Because of the early lethality of the Tbx1-/- mice, we used long-term culture techniques that allow the unharmed growth of incisors until their full maturity. All cultured incisors of Tbx1-/- mice were hypoplastic and lacked enamel, while thorough histological examinations demonstrated the complete absence of ameloblasts. The absence of enamel is preceded by a decrease in proliferation of the ameloblast precursor cells and a reduction in amelogenin gene expression. The cervical loop area of the incisor, which contains the niche for the epithelial stem cells, was either severely reduced or completely missing in mutant incisors. In contrast, ectopic expression of Tbx1 was observed in incisors from mice with upregulated Fibroblast Growth Factor signalling and was closely linked to ectopic enamel formation and deposition in these incisors. These results demonstrate that Tbx1 is essential for the maintenance of ameloblast progenitor cells in rodent incisors and that its deletion results in the absence of enamel formation.

Expression and purification of bioactive high-purity human midkine in Escherichia coli

Midkine is a heparin-binding growth factor, which plays important roles in the regulation of cell growth and differentiation. The non-tagged recombinant human midkine (rhMK) is therefore required to facilitate its functional studies of this important growth factor. In the present work, rhMK was expressed in Escherichia coli (E. coli) BL21 (DE3). The expression of midkine was efficiently induced by isopropyl-beta-D-thiogalactopyranoside (IPTG). After sonication, midkine was recovered in an insoluble form, and was dissolved in guanidine hydrochloride buffer. Renaturation of the denatured protein was carried out in the defined protein refolding buffer, and the refolded protein was purified using S-Sepharose ion-exchange chromatography. The final preparation of the rhMK was greater than 98% pure as measured by sodium dodecylsulfate-polyacrylamid gel electrophoresis (SDS-PAGE) and reverse phase high performance liquid chromatography (RP-HPLC). The purified rhMK enhanced the proliferation of NIH3T3 cells.

Human adipose tissue-derived mesenchymal stem cells as a novel feeder layer for epithelial cells

We examined a novel human feeder cell layer of mesenchymal stem cells harvested from human adipose tissues. Gene expression analyses and colony-forming assay with human primary epithelial cells showed that the adipose tissue-derived mesenchymal stem cells produced various factors to support epithelial stem/progenitor maintenance and cell growth. Using the mesenchymal stem cells as novel feeder layers, transplantable epithelial cell sheets could be effectively generated ex vivo on temperature-responsive cell-culture surfaces.

The large functional spectrum of the heparin-binding cytokines MK and HB-GAM in continuously growing organs: the rodent incisor as a model

The heparin binding molecules MK and HB-GAM are involved in the regulation of growth and differentiation of many tissues and organs. Here we analyzed the expression of MK and HB-GAM in the developing mouse incisors, which are continuously growing organs with a stem cell compartment. Overlapping but distinct expression patterns for MK and HB-GAM were observed during all stages of incisor development (initiation, morphogenesis, cytodifferentiation). Both proteins were detected in the enamel knot, a transient epithelial signaling structure that is important for tooth morphogenesis, and the cervical loop where the stem cell niche is located. The functions of MK and HB-GAM were studied in dental explants and organotypic cultures in vitro. In mesenchymal explants, MK stimulated HB-GAM expression and, vice-versa, HB-GAM upregulated MK expression, thus indicating a regulatory loop between these proteins. BMP and FGF molecules also activated expression of both cytokines in mesenchyme. The proliferative effects of MK and HB-GAM varied according to the mesenchymal or epithelial origin of the tissue. Growth, cytodifferentiation and mineralization were inhibited in incisor germs cultured in the presence of MK neutralizing antibodies. These results demonstrate that MK and HB-GAM are involved in stem cells maintenance, cytodifferentiation and mineralization processes during mouse incisor development.

Therapeutic effect of midkine on cardiac remodeling in infarcted rat hearts

BACKGROUND

Midkine is expressed in the developing fetus and in adult organs stressed by ischemia, but its physiologic role in ischemic organs is poorly understood. Here we investigated the effect of midkine on cardiac remodeling after ischemia caused by myocardial infarction.

METHODS

The expression pattern of the endogenous midkine gene in rat heart was evaluated by real-time polymerase chain reaction for 2 weeks after myocardial infarction. To investigate its effect, recombinant midkine was injected into hearts 2 weeks after myocardial infarction, and cardiac functions were monitored by echocardiography. Six weeks later, the hearts were removed, and the areas of infarcted and viable tissue and the extent of cardiomyocyte hypertrophy were determined histologically.

RESULTS

The midkine gene was strongly upregulated in the infarcted myocardium, but this upregulation lasted less than 2 weeks. Cardiac remodeling was significantly and dose-dependently attenuated by midkine treatment. The midkine treatment also increased collagen accumulation and facilitated angiogenesis in the infarcted area, and the viable muscle area after myocardial infarction dose-dependently increased. Despite this increase of viable muscle area, the midkine-treated hearts showed significantly less cardiomyocyte hypertrophy than vehicle-treated hearts, suggesting midkine had prevented chronically ischemic cells from dying and dropping out by angiogenesis.

CONCLUSIONS

Our results indicate midkine can attenuate cardiac remodeling after myocardial infarction, and suggest midkine has therapeutic potential for subacute myocardial infarction.

The ligand Jelly Belly (Jeb) activates the Drosophila Alk RTK to drive PC12 cell differentiation, but is unable to activate the mouse ALK RTK

The Drosophila Alk receptor tyrosine kinase (RTK) drives founder cell specification in the developing visceral mesoderm and is crucial for the formation of the fly gut. Activation of Alk occurs in response to the secreted ligand Jelly Belly. No homologues of Jelly Belly are described in vertebrates, therefore we have approached the question of the evolutionary conservation of the Jeb-Alk interaction by asking whether vertebrate ALK is able to function in Drosophila. Here we show that the mouse ALK RTK is unable to rescue a Drosophila Alk mutant, indicating that mouse ALK is unable to recognise and respond to the Drosophila Jeb molecule. Furthermore, the overexpression of a dominant-negative Drosophila Alk transgene is able to block the visceral muscle fusion event, which an identically designed dominant-negative construct for the mouse ALK is not. Using PC12 cells as a model for neurite outgrowth, we show here for the first time that activation of dAlk by Jeb results in neurite extension. However, the mouse Alk receptor is unable to respond in any way to the Drosophila Jeb protein in the PC12 system. In conclusion, we find that the mammalian ALK receptor is unable to respond to the Jeb ligand in vivo or in vitro. These results suggest that either (i) mouse ALK and "mouse Jeb" have co-evolved to the extent that mALK can no longer recognise the Drosophila Jeb ligand or (ii) that the mALK RTK has evolved such that it is no longer activated by a Jeb-like molecule in vertebrates.

Expression of the heparin-binding growth factor midkine in the cerebrospinal fluid of patients with neurological disorders

OBJECTIVE

This study was to clarify the roles of midkine (MK) in the brain.

METHODS

We determined cerebrospinal fluid MK levels in patients with neurological disorders by enzyme-linked immunoassay and immunostained autopsied brain samples in patients with meningitis.

RESULTS

MK levels were 0.37+/-0.21 ng/ml in controls (n=46, mean +/- S.D.), 0.67+/-0.19 ng/ml in patients with cerebral infarction (n=8), 1.78+/-1.32 ng/ml in patients with meningitis (n=25; ANOVA and post-hoc Fisher's PLSD test, p<0.0001), 0.31+/-0.25 ng/ml in patients with human T-lymphotrophic virus type I-associated myelopathy/tropical spastic paraparesis (n=29), and 0.42+/-0.17 ng/ml in patients with amyotrophic lateral sclerosis (n=8). The regression equations were Y=0.005X+0.498 (Y, CSF MK level; X, cell number) and Y=0.007X+0.326 (Y, MK level; X, protein level) for all CSF samples. Autopsy brain samples from patients with meningitis expressed MK weakly in mononuclear cells on immunohistochemical examination. Western blot and polymerase chain reaction analyses showed that leukocytes were MK positive. CSF MK levels were not high in patients with cerebral infarction but were increased in patients with meningitis. CSF MK levels were high in normal controls, compared to those of other cytokines. MK was expressed in choroid plexus of normal brain and released there.

CONCLUSION

Our findings suggested that MK may maintain normal adult brain as a neurotrophic factor, and that MK may be released from leucocytes in brain of patients with meningitis as an immunological mediator.

Genetische Störungen der Zahnentwicklung und Dentition

Die Zähne sind Organe, die aus ektodermalen epithelialen Aussackungen im Bereich des 1. Kiemenbogens entstehen, gesteuert von epitheliomesenchymalen Interaktionen. Dabei spielen zahlreiche Signalmoleküle speziell der 4 großen Familien TGF-β, FGF, Hedgehog und WNT sowie diverse Transkriptionsfaktoren eine Rolle. Eine Beteiligung der Retinoide an der Odontogenese ist durch umfangreiche Befunde belegt, auch wenn die Inaktivierung relevanter Gene in Mausmodellen meist keine Zahnanomalien verursacht. Die Zahnentwicklung wird klassischerweise in verschiedene Stadien eingeteilt: Entstehung der Zahnleiste, der Zahnknospe, der Schmelzkappe, der Schmelzglocke, die Wurzelbildung und der Zahndurchbruch. Anomalien der Zahnentwicklung können isoliert oder gemeinsam mit anderen Symptomen im Zusammenhang mit Syndromen auftreten. Sie können genetisch bedingt sein oder unter Einwirkung teratogener Stoffe während der Bildung und Mineralisierung der Zahnkeime zustande kommen. Dentibukkale Entwicklungsanomalien treten im Kontext seltener Erkrankungen auf und finden zunehmend Beachtung, da sie bei bestimmten Erkrankungen in der Diagnostik und als prädikative Faktoren wichtige Anhaltspunkte geben können. Allerdings ist hierfür eine interdisziplinäre und internationale Kooperation notwendig, die bislang erst in Ansätzen verwirklicht wurde.

Female infertility in mice deficient in midkine and pleiotrophin, which form a distinct family of growth factors

Midkine and pleiotrophin form a family of growth factors. Mice deficient in one of the genes show few abnormalities on reproduction and development. To understand their roles in these processes, we produced mice deficient in both genes; the double deficient mice were born in only one third the number expected by Mendelian segregation and 4 weeks after birth weighed about half as much as wild-type mice. Most of the female double deficient mice were infertile. In these mice, the numbers of mature follicles and of ova at ovulation were reduced compared to numbers in wild-type mice. Both midkine and pleiotrophin were expressed in the follicular epithelium and granulosa cells of the ovary. The expression of these factors in the uterus was dramatically altered during the estrous cycle. The diestrus and proestrus periods were long and the estrus period was short in the double deficient mice, indicating the role of the factors in the estrous cycle. Furthermore, vaginal abnormality was found in about half of the double deficient mice. These abnormalities in combination resulted in female infertility. Therefore, midkine and pleiotrophin, together with their signaling receptors, play important roles in the female reproductive system.

Midkine, a heparin-binding growth factor, is expressed in neural precursor cells and promotes their growth

Midkine, a heparin-binding growth factor, was found to be expressed in neural precursor cells, which consist of neural stem cells and the progenitor cells. When embryonic brain cells were allowed to form neurospheres enriched in neural precursor cells, numbers were significantly smaller from the midkine-deficient brain than from the wild-type brain. Dissociated neurosphere cells yielded nestin-positive neural precursor cells and differentiated neuronal cells upon culture on a substratum. Neural precursor cells from the midkine-deficient brain spread poorly and grew less effectively on a substratum coated with poly-l-lysine than the cells on midkine-coated substratum. Neural precursor cells from the wild-type brain spread and grew well on both the substrata. Differentiation to neurons and glia cells was not affected by the absence of midkine. Heparitinase digestion of dissociated neurosphere cells resulted in poor growth of neural precursor cells, while chondroitinase digestion had no effect. These results indicate that midkine is involved in the growth of neural precursor cells and suggest that the interaction with heparan sulfate proteoglycans is important in midkine action to these cells.

Anaplastic lymphoma kinase is a dependence receptor whose proapoptotic functions are activated by caspase cleavage

Anaplastic lymphoma kinase (ALK) is a receptor tyrosine kinase, initially discovered as part of the NPM-ALK fusion protein, resulting from the t(2;5) translocation that is frequently associated with anaplastic large-cell lymphomas. The native ALK protein is normally expressed in the developing and, at a weaker level, adult nervous system. We recently demonstrated that the oncogenic, constitutively kinase-activated NPM-ALK protein was antiapoptotic when expressed in Jurkat lymphoblastic cells treated with cytotoxic drugs. In contrast, we now show that Jurkat cells overexpressing the wild-type ALK receptor are more sensitive to doxorubicin-induced apoptosis than parental cells. Moreover, the ALK protein is cleaved during apoptosis in a caspase-dependent manner. Mutation of aspartic residues to asparagine allowed us to map the caspase cleavage site in the juxtamembrane region of ALK. In order to assess the role of ALK in neural cell-derived tissue, we transiently expressed ALK in the 13.S.1.24 rat neuroblast immortalized cell line. ALK expression led to apoptotic cell death of the neuroblasts. ALK ligation by specific activating antibodies decreased ALK-facilitated apoptosis in both lymphoid and neuronal cell lines. Moreover, ALK transfection reduced the survival of primary cultures of cortical neurons. Thus, ALK has a proapoptotic activity in the absence of ligand, whereas it is antiapoptotic in the presence of its ligand and when the kinase is intrinsically activated. These properties place ALK in the growing family of dependence receptors.

Mice doubly deficient in the midkine and pleiotrophin genes exhibit deficits in the expression of beta-tectorin gene and in auditory response

alpha-Tectorin and beta-tectorin are major noncollagenous proteins of the tectorial membrane, which plays a crucial role in the reception of sonic signals in the cochlea. Midkine and pleiotrophin are closely related proteins that serve as growth factors and cytokines. In mice doubly deficient in the midkine gene and pleiotrophin gene, expression of beta-tectorin mRNA was nearly abolished in the cochlea on day 1 and 7 after birth. Expression of alpha-tectorin mRNA was unaffected in the double knockout mice, and expression of beta-tectorin mRNA was not altered in mice deficient in only the midkine or pleiotrophin gene. In newborn wild-type mice, both midkine and pleiotrophin were expressed in the greater epithelial ridge of the cochlea, in which beta-tectorin mRNA was strongly expressed. These results indicate that either midkine or pleiotrophin is required for significant expression of beta-tectorin. In agreement with the view that beta-tectorin is essential for normal auditory function, mice doubly deficient in both midkine and pleiotrophin genes exhibited very severe auditory deficits. We observed that mice deficient in either midkine or pleiotrophin gene were also impaired in their auditory response, but the level of the deficit was generally low or moderate. The present finding illustrates the importance of growth factor expression in the cochlea for auditory function.

Waking-up the sleeping beauty: recovery of the ancestral bird odontogenic program

Recent advances in molecular and developmental genetics have provided tools for understanding evolutionary changes in the nature of the epithelial-mesenchymal interactions regulating the patterned outgrowth of the tooth primordia. Tissue recombination experiments in mice have identified the oral epithelium as providing the instructive information for the initiation of tooth development. Teeth were lost in birds for more than 80 million years ago, but despite their disappearance, a number of gene products and the requisite tissue interactions needed for tooth formation are found in the avian oral region. It is believed that the avian ectomesenchyme has lost the odontogenic capacity, whilst the oral epithelium retains the molecular signaling required to induce odontogenesis. In order to investigate the odontogenic capacity of the neural crest-derived mesenchyme and its potential activation of the avian oral epithelium, we have realized mouse neural tube transplantations to chick embryos to replace the neural crest cells of chick with those of mouse. Teeth are formed in the mouse/chick chimeras, indicating that timing is critical for the acquisition of the odontogenic potential by the epithelium and, furthermore, suggesting that odontogenesis is initially directed by species-specific mesenchymal signals interplaying with common epithelial signals.

Midkine, a heparin-binding growth factor, produced by the host enhances metastasis of Lewis lung carcinoma cells

Midkine is a heparin-binding growth factor and is expressed by a number of tumor cells, contributing to their growth both in vitro and in vivo. Spontaneous lung metastasis of Lewis lung carcinoma cells, which did not significantly express MK, was significantly less extensive in mice deficient in the midkine gene than in wild-type mice, when the tumor was subcutaneously grown above the thigh. Midkine strongly enhanced migration of Lewis lung carcinoma cells in vitro. Therefore, midkine is also a host factor enhancing tumor metastasis. Anti-midkine therapy for malignancy may act on midkine produced by both the tumor and host.

Midkine is a potent regulator of the catecholamine biosynthesis pathway in mouse aorta

To discover regulatory pathways dependent on midkine (Mk the gene, MK the protein) signaling, we compared the transcriptional profiles of aortae obtained from Mk -/- and wild type (WT, +/+) mice; the comparison demonstrated an extraordinary high level expression of tyrosine hydroxylase (12-fold), the rate-limiting enzyme in catecholamine biosynthesis, DOPA decarboxylase (73-fold), and dopamine beta-hydroxylase (75-fold) in aortae of Mk -/- mice compared with aortae of WT (+/+) mice. Phenylethanolamine-N-methyltransferase, the enzyme catalyzing the conversion of norepinephrine into epinephrine, was not detected in either Mk -/- and WT (+/+) mouse aorta. The protein levels of tyrosine hydroxylase, DOPA decarboxylase and dopamine beta-hydroxylase confirmed the analysis of the transcriptional profiles. Surprisingly, MK failed to regulate the enzymes of the catecholamine biosynthesis pathway in 10 other tissues studied. Furthermore, the expression levels of the enzymes of catecholamine biosynthesis in aortae of Mk -/- mice were effectively the same as those in aortae of Pleiotrophin (Ptn the gene, PTN the protein) genetically deficient (Ptn -/-) mice when compared with WT (+/+) mice. The remarkable increases in levels of expression of tyrosine hydroxylase, DOPA decarboxylase and dopamine beta-hydroxylase suggest that MK together with PTN are very important regulators of the catecholamine pathway in mouse aorta and may critically regulate catecholamine biosynthesis and function in inflammatory and the other pathological conditions in which Mk or Ptn are upregulated. The data also establish that norepinephrine is effectively the only catecholamine synthesized in mouse aorta.

Upregulation of pleiotrophin expression in rat hepatic stellate cells by PDGF and hypoxia: Implications for its role in experimental biliary liver fibrogenesis

Pleiotrophin (PTN) is a secretory heparin binding protein with various biological activities including mitogenesis, angiogenesis, and tissue repair after injury. Recent studies have shown that PTN is a strong mitogen of hepatocytes and involved in liver regeneration. In adult liver cells Ptn gene is mainly expressed by quiescent hepatic stellate cells (HSCs). Although we have been able to demonstrate mRNA and protein expression of the anaplastic lymphoma kinase-the receptor tyrosine kinase for PTN-on HSCs, PTN did not act as a mitogen of HSCs in contrast to hepatocytes. PTN immunoreactivity was markedly increased in experimental fibrogenesis by common bile duct ligation and observed in sinusoidal HSCs. In primary HSC cultures, Ptn transcription was significantly increased by PDGF-BB, and under hypoxic atmosphere. Mechanistically, hypoxia and PDGF mediated induction of PTN expression in sinusoidal HSCs may provide a strong mitogenic signal for hepatocytes to limit the damage to the parenchymal cells in biliary-type liver fibrogenesis.

Miple1 and miple2 encode a family of MK/PTN homologues in Drosophila melanogaster

Midkine (MK) and Pleiotrophin (PTN) are small heparin-binding cytokines with closely related structures. To date, this family of proteins has been implicated in multiple processes, such as growth, survival, and migration of various cells, and has roles in neurogenesis and epithelial-mesenchymal interaction during organogenesis. In this report, we have characterized two members of the MK/PTN family of proteins in Drosophila, named Miple1 and Miple2, from Midkine and Pleiotrophin. Drosophila miple1 and miple2 encode secreted proteins which are expressed in spatially restricted, nonoverlapping patterns during embryogenesis. Expression of miple1 can be found at high levels in the central nervous system, while miple2 is strongly expressed in the developing midgut endoderm. The identification of homologues of the MK/PTN family in this genetically tractable model organism should allow an analysis of their function during complex developmental processes.

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.

Xylosyltransferase I acceptor properties of fibroblast growth factor and its fragment bFGF (1-24)

Human basic fibroblast growth factor (bFGF) is a heparin-binding growth factor containing a G-S-G-motif which is a potential recognition sequence of xylosyltransferase I (XT-I). Here, we show that the recombinant human bFGF was xylosylated in vitro by human XT-I and that the fragment bFGF (1-24) is a good XT-I acceptor (K(m) = 20.8 microM for native XT-I and K(m) = 22.3 microM for recombinant XT-I). MALDI and MALDI-PSD time-of-flight mass spectrometric analyses of the xylosylated bFGF protein demonstrate the transfer of xylose to the serine residue of the G-S-G-motif in the amino terminal end of bFGF. The peptide bFGF (1-24) is well suitable as an acceptor substrate for XT-I and can be used in a radiochemical assay to measure the XT-I activity in cell culture supernatant and human body fluids, respectively. Furthermore, we could demonstrate that the XT-I interacts strongly with heparin and that this glycosaminoglycan is a predominantly non-competitive inhibitor of the enzyme using the fragment bFGF (1-24) as xylose acceptor.

Midkine, a newly discovered regulator of the renin–angiotensin pathway in mouse aorta: Significance of the pleiotrophin/midkine developmental gene family in angiotensin II signaling

We previously demonstrated that pleiotrophin (PTN the protein, Ptn the gene) highly regulates the levels of expression of the genes encoding the proteins of the renin-angiotensin pathway in mouse aorta. We now demonstrate that the levels of expression of these same genes are significantly regulated in mouse aorta by the PTN family member midkine (MK the protein, Mk the gene); a 3-fold increase in expression of renin, an 82-fold increase in angiotensinogen, a 6-fold decrease in the angiotensin converting enzyme, and a 6.5-fold increase in the angiotensin II type 1 and a 9-fold increase in the angiotensin II type 2 receptor mRNAs were found in Mk-/- mouse aorta in comparison with the wild type (WT, +/+). The results in Mk-/- mice are remarkably similar to those previously reported in Ptn-/- mouse aorta, with the single exception of that the levels of the angiotensinogen gene expression in Ptn-/- mice are equal to those in WT+/+ mouse aorta, and thus, in contrast to Mk gene expression unaffected by levels of Ptn gene expression. The data indicate that MK and PTN share striking but not complete functional redundancy. These data support potentially high levels importance of MK and the MK/PTN developmental gene family in downstream signals initiated by angiotensin II either in development or in the many pathological conditions in which MK expression levels are increased, such as atherosclerosis and many human neoplasms that acquire constitutive endogenous Mk gene expression by mutation during tumor progression and potentially provide a target through the renin-angiotensin pathway to treat advanced malignancies.

Conformational determinants of the intracellular localization of midkine

Midkine (MK) is a multifunctional growth factor and has been discovered to play important roles in carcinogenesis. MK has been reported to localize to the nucleus and nucleolus, however, the data are not consistent and the signals responsible for the localization are unknown. Here we reported that human MK exclusively localized to the nucleus and nucleolus in HepG2 cells by using GFP as a tracking molecule. In order to identify the motifs required for the nuclear localization and nucleolar accumulation, point- and deletion-mutations were introduced and the corresponding subcellular localizations were analyzed. Data revealed that (i) K79R81, K86K87, and the C-terminal tail of MK constitute the nuclear localization determinant of MK, and (ii) the C-terminal tail is the key element controlling MK nucleolar accumulation though the N-terminal tail, K79R81, and K86K87 also contribute to this process. Taken together, our results provide the first documentation about the determinants required for MK nuclear and nucleolar localization.

Overexpression of heparin-binding growth-associated molecule in malignant glioma cells

The highly invasive and angiogenic characteristics of malignant gliomas depend on the production of growth factors and angiogenic factors. Heparin-binding growth-associated molecule (HB-GAM) is a secreted growth factor that is mitogenic for endothelial cells. To examine the expression profile of HB-GAM in malignant glioma cells, messenger ribonucleic acid (mRNA) expression was analyzed in 10 malignant glioma cell lines, two glioblastoma tissue specimens, and two normal brain tissue specimens by the reverse transcription-polymerase chain reaction. HB-GAM mRNA was expressed in all specimens including normal brain tissue specimens. Western blot analysis revealed that HB-GAM protein contents in glioma cell lines and glioblastoma tissues were 1.8 to 6.3 times higher than those in normal brain tissues. The effect of neutralizing anti-platelet-derived growth factor (PDGF) antibody was also examined on the production of HB-GAM in malignant glioma cells, since malignant glioma cells secrete PDGF that upregulates HB-GAM expression. Treatment of U251 and T98G glioblastoma cells with the anti-PDGF antibody did not affect the HB-GAM production. These results suggest that HB-GAM is overexpressed in malignant glioma cells and is involved in tumor growth.

Microarray analysis of retinoid-dependent gene activity during rat embryogenesis: increased collagen fibril production in a model of retinoid insufficiency

Retinoic acid (RA) is an essential mediator of embryogenesis. Some, but not all, of its targets have been identified. We previously developed a rat model of gestational retinoid deficiency (RAD; Power et al. [1999] Dev. Dyn. 216:469-480) and generated embryos with developmental impairments that closely resemble genetic and dietary models of retinoid insufficiency. Here, we used microarray analysis and expression profiling to identify 88 transcripts whose abundance was altered under conditions of retinoid insufficiency, as compared with normal embryos. Among these, the induction by RAD of genes involved in collagen I synthesis (COL1A1, IA2 and VA2, prolyl-4-hydroxylase-alpha1) and protein galactosylation (galactokinase, ABO galactosyltransferase, UDP-galactose transporter-related protein) was especially noteworthy because extracellular matrix regulates many developmental events. We also identified several genes involved with stress responses (cathepsin H, UBC2E, IGFBP3, smoothelin). Real-time polymerase chain reaction analysis of selected candidates revealed excellent agreement with the array findings. Further validation came from the demonstration that these genes were similarly dysregulated in two genetic models of retinoid insufficiency, the retinol binding protein null-mutant embryo and the Raldh2 null-mutant embryo. In situ hybridization of RAD embryos found increased collagen IA1 and IGFBP3 mRNA within the connective mesenchyme and vasculature, respectively, and a failure to repress the growth factor midkine within the RAD neural tube. Many of the identified genes were not known previously to respond to retinoid status and will provide new insights to retinoid roles and to the consequences of retinoid insufficiency.

The angiogenic peptide pleiotrophin (PTN/HB-GAM) is expressed in fracture healing: an immunohistochemical study in rats

INTRODUCTION

Formation of new blood vessels is essential for the process of fracture healing.

MATERIALS AND METHODS

We investigated the expression of the angiogenic factor pleiotrophin/HB-GAM in a closed fracture model in rats by immunohistochemical methods.

RESULTS

Histologically, 5 days after fracture the callus was predominantly composed of fibrous tissue. On day 10 a prominent chondral callus connected both ends of the fractured tibia. There was a continuous transition from the chondral callus to the newly formed bone adjacent to the corticalis of the tibia. On day 15 the amount of woven bone had increased, and in 3 of 5 animals the proximal and distal tibiae were connected by a bridge of woven bone. Pleiotrophin could be immunostained in fibroblasts and endothelial cells of the fibrous tissue between the fractured tibia ends. The chondral callus remained largely pleiotrophin-negative. Only single chondrocytes adjacent to the newly formed bone were pleiotrophin-positive. On days 10 and 15 strong immunoreactivity for pleiotrophin in the well vascularized, newly formed, woven bone was detectable. Osteoblasts, endothelial cells and fibroblasts were strongly pleiotrophin-positive.

CONCLUSIONS

These results show the presence of the angiogenic peptide pleiotrophin during fracture healing.

Distinctive expression of midkine in the repair period of rat brain during neurogenesis: immunohistochemical and immunoelectron microscopic observations

Distinctive expression of midkine (MK) was observed during the repair period of fetal brain neuroepithelium. MK is a heparin-binding growth factor that occurs as a product of a retinoic acid-inducible gene, and has a molecular mass of 13 kDa. MK expression was examined immunohistochemically and by immunoelectron microscopy during a period of repair in developing rat brain at the neurogenesis stage. Injury was induced in rat fetuses by transplacental administration of ethylnitrosourea (ENU) on embryonic Day (E) 16, and histological changes were examined up to 48 hr thereafter (i.e., up to E 18). In normal rat fetuses, MK immunostaining was observed in the cytoplasm and radial and horizontal processes of all cells in the neuroepithelium (NE), subventricular zone (SV), and intermediate zone (IMZ). In ENU-administered brains, cells in the NE, SV, and IMZ were damaged severely, especially 16-24 hr after ENU administration. The remaining neuroepithelial cells, with the exception of those in M-phase and the tips of processes at the ventricular surface, were negative for MK immunohistochemistry 16-24 hr after the administration of ENU. Forty-eight hours after the administration, the cytoplasm and processes of cells in the NE, SV, and IMZ were MK immunopositive. Our previous data reported that the cell cycle of most NE cells is synchronized to the S-phase 16 hr after ENU administration and to the M-phase at 24 hr, and many NE cells were recovered 48 hr after ENU administration. The previous results taken together with the present results indicate that: (1) MK expression does not increase during the repair period of the NE, being different from adults; (2) MK expression is likely to be suppressed at S-phase according to the condition of the NE; and (3) MK expression is not essential for every cell cycle phase of NE cells; but (4) is necessary to maintain the M-phase of NE cells.

Chondroitin sulfate chains on syndecan-1 and syndecan-4 from normal murine mammary gland epithelial cells are structurally and functionally distinct and cooperate with heparan sulfate chains to bind growth factors. A novel function to control binding of midkine, pleiotrophin, and basic fibroblast growth factor

A comparative analysis was carried out of heparan sulfate (HS) and chondroitin sulfate (CS) chains of the ectodomains of hybrid type transmembrane proteoglycans, syndecan-1 and -4, synthesized simultaneously by normal murine mammary gland epithelial cells. Although the HS chains were structurally indistinguishable, intriguingly the CS chains were structurally and functionally distinct, probably reflecting the differential regulation of sulfotransferases involved in the synthesis of HS and CS. The CS chains of the two syndecans comprised nonsulfated, 4-O-, 6-O-, and 4,6-O-disulfated N-acetylgalactosamine-containing disaccharide units and were significantly different, with a higher degree of sulfation for syndecan-4. Functional analysis using a BIAcore system showed that basic fibroblast growth factor (bFGF) specifically bound only to the HS chains of both syndecans, whereas midkine (MK) and pleiotrophin (PTN) bound not only to the HS but also to the CS chains. Stronger binding of MK and PTN to the CS chains of syndecan-4 than those of syndecan-1 was revealed, supporting the structural and functional differences. Intriguingly, removal of the CS chains decreased the association and dissociation rate constants of MK, PTN, and bFGF for both syndecans, suggesting the simultaneous binding of these growth factors to both types of chains, producing a ternary complex that transfers the growth factors to the corresponding cell surface receptors more efficiently compared with the HS chains alone. The involvement of the core protein was also shown in the binding of MK and PTN to syndecan-1, suggesting the possibility of cooperation with the HS and/or CS chains in the binding of these growth factors and their delivery to the cell surface receptors.

Midkine is regulated by hypoxia and causes pulmonary vascular remodeling

Midkine (MK) is expressed in a precise temporal-spatial pattern during lung morphogenesis; however, its role in pulmonary homeostasis is unknown. Increased MK staining and mRNA expression were observed in the lungs of hypoxia-susceptible CAST/eiJ mice during hypoxia. MK expression was induced by hypoxia in cell lines in vitro. Because the transcription factor hypoxiainducible factor-1alpha (HIF-1alpha) modulates cellular responses to hypoxia, we tested whether increased expression of MK in the lung was mediated by HIF-1alpha. HIF-1alpha enhanced the transcription of MK, acting on HIF-1alpha regulatory elements located in the MK gene promoter. Site-directed mutagenesis of the 3' HIF response element in the MK promoter blocked the stimulatory effects of HIF-1alpha. To directly assess the role of MK on lung morphogenesis, transgenic mice were generated in which MK was expressed in the respiratory epithelial cells of the developing lung. MK increased muscularization of small pulmonary arteries, increasing alpha-smooth muscle actin and caldesmon staining and the expression of myocardin. MK directly enhanced the expression of myocardin and the smooth muscle-specific genes alpha-smooth muscle actin, calponin, and SM-22 in vascular smooth muscle precursor cells. Expression of MK in the respiratory epithelium is regulated by hypoxia and HIF-1alpha. These data provide a model wherein the respiratory epithelium responds to hypoxia via HIF-1alpha-dependent regulation of MK, enhancing myocardin expression to influence pulmonary vascular gene expression.

Midkine, a heparin-binding cytokine, plays key roles in intraperitoneal adhesions

Midkine is a heparin-binding cytokine or growth factor and promotes the migration of inflammatory leukocytes. Upon partial hepatectomy, adhesion of the intestine was less severe in midkine-deficient mice than in wild-type mice. In a newly developed assay, in which the omentum adhered to the injured peritoneal wall, the incidence of adhesion in the deficient mice was reduced to 20% of that in the wild-type mice. Administration of midkine to the deficient mice increased the frequency of adhesion. The area of adhesion was also reduced to 8.3% in the deficient mice. The extent of migration of macrophages and neutrophils in the omentum around the adhesive region was reduced in the deficient mice. Therefore, midkine was concluded to play important roles in the formation of intraperitoneal adhesions, at least partly by promoting the migration of macrophages and neutrophils to the omentum.