Range of Movement for Impingement and Dislocation Avoidance in Total Hip Replacement Predicted by Finite Element Model.

Dislocation is a serious complication in total hip replacement (THR). An inadequate range of movement (ROM) can lead to impingement of the prosthesis neck on the acetabular cup; furthermore, the initiation of subluxation and dislocation may occur. The objective of this study was to generate a parametric three-dimensional finite element (FE) model capable of predicting the dislocation stability for various positions of the prosthetic head, neck, and cup under various activities. Three femoral head sizes (28, 32, and 36 mm) were simulated. Nine acetabular placement positions (abduction angles of 25°, 40° and 60° combined with anteversion angles of 0°, 15° and 25°) were analyzed. The ROM and maximum resisting moment (RM) until dislocation were evaluated based on the stress distribution in the acetabulum component. The analysis allowed for the definition of a "safe zone" of movement for impingement and dislocation avoidance in THR: an abduction angle of 40°-60° and anteversion angle of 15°-25°. It is especially critical that the anteversion angle does not fall to 10°-15°. The sequence of the RM is a valid parameter for describing dislocation stability in FE studies.

Uncovering new pharmacological targets to treat neuropathic pain by understanding how the organism reacts to nerve injury.

The neuropathic pain syndrome is complex. Current drugs to treat neuropathic pain, including anticonvulsivants and antidepressants, fail in up to 40-50% of the patients, while in the rest of them total alleviation is not normally achieved. Increased research advances in the neurobiology of neuropathic pain have not translated in more successful pharmacological treatments by the moment, but recent progress in the experimental methods available for this purpose could result in significant advances in the short term. One rational possibility for the pharmaceutical development of new drugs, including target identification, drug design and evaluation studies, could be to focus on mimicking what organism does to limit nerve damage or to enhance the regeneration of injured axons. Following this strategy, neurotrophic factors such as nerve growth factor (NGF) and brain-derived neurotrophic factor (BDNF) have been postulated as potential pharmacological targets to treat neuropathic pain. In addition, during the last few years, strong scientific evidences point to novel neurotrophic factors, such as pleiotrophin (PTN), as important factors to limit neuropathic pain development because of their remodeling and angiogenic actions in the injured area. This review focuses on recent research advances identifying new pharmacological targets in the treatment of the cause, not only the symptoms, of neuropathic pain.

Oral iron treatment has a positive effect on iron metabolism in elite soccer players.

The purpose of this study was to assess the effects of oral iron supplementation on hematological and iron metabolism in elite soccer players. Thirty-five members of the Real Zaragoza SAD soccer team took part in this study: group A (GA, n = 24; Spanish Premier League) took an oral iron supplement of 80 mg day(-1) for 3 weeks, and group B (GB, n = 11; Spanish Third Division League) did not receive any supplementation. In GA, the parameters were measured before and after giving the iron supplements, while in GB, measurements were only made at the time of collecting the second set of data from GA. After supplementation, GA showed an increase in serum iron (SI) (P < 0.05), serum ferritin (Ftn) (P < 0.01), and transferrin saturation (Sat) (P < 0.01) with respect to the basal values. In addition, GA showed higher values of hematocrit (P < 0.01), mean corpuscular volume (P < 0.01), Ftn (P < 0.01), and Sat (P < 0.01) than GB. No significant differences were found in any other parameters. More specifically, a higher percentage of players had Ftn levels above upper limits in GA vs. GB (P < 0.05), and GB had a higher incidence of Ftn below lower limits with respect to subjects in GA (P < 0.01). Further, after treatment, 58.3% of GA had >800 mg of SI, while all players in GB presented levels below the lower limits. In conclusion, iron supplementation with 80 mg·day(-1) for 3 weeks, before the start of the soccer season, can be recommended for elite soccer players.

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

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

Blocking receptor protein tyrosine phosphatase beta/zeta: a potential therapeutic strategy for Parkinson's disease.

striatum of rodents in experimental models of Parkinson's disease. Interestingly, immunohistochemical studies have shown increased levels of PTN expression in the substantia nigra of patients with Parkinson's disease. Since, in other contexts, PTN has been shown to be critical in repair processes in the injured nervous system, the antecedents suggest that PTN could exhibit protective effects in Parkinson's disease. This hypothesis was confirmed when PTN was shown to support survival of dopaminergic neurons and to promote the differentiation of neural stem cells to dopaminergic neurons. These findings suggest a new therapeutic approach in the treatment of Parkinson's disease based on the molecular mechanism of action of PTN. Pleiotrophin receptor, receptor protein tyrosine phosphatase (RPTP) beta/zeta, is found active in monomeric form in neurons and glia within the central nervous system. Pleiotrophin induces dimerization of RPTPbeta/zeta inactivating its phosphatase activity, thus increasing the phosphorylation levels of its substrates such as beta-catenin, Fyn and beta-adducin. These substrates have been shown to be critical for the proliferation of dopaminergic progenitors and the survival and differentiation of dopaminergic neurons. This review summarizes the strong scientific basis to consider blocking RPTPbeta/zeta as a potentially novel therapeutic strategy in the treatment of Parkinson's disease and discusses various starting points to design antagonists of this receptor.

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

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

Noradrenergic and opioidergic alterations in neuropathy in different rat strains.

The Fischer 344 (F344) rat strain differs from the Lewis strain in the response to neuropathic pain. Recently, we found that F344 rats totally recover from mechanical allodynia induced by chronic constriction injury (CCI) of the sciatic nerve 28 days after surgery whereas Lewis rats are initiating their recovery at this time point. Thus, the use of this neuropathic pain model in these different rat strains constitutes a good strategy to identify possible target genes involved in the development of neuropathic pain. Since differences between Lewis and F344 rats in their response to pain stimuli in acute pain models have been related to differences in the endogenous opioid and noradrenergic systems, we aimed to determine the levels of expression of key genes of both systems in the spinal cord and dorsal root ganglia (DRG) of both strains 28 days after CCI surgery. Real time RT-PCR revealed minimal changes in gene expression in the spinal cord after CCI despite the strain considered, but marked changes in DRG were observed. A significant upregulation of prodynorphin gene expression occurred only in injured DRG of F344 rats, the most resistant strain to neuropathic pain. In addition, we found a significant downregulation of tyrosine hydroxylase and proenkephalin gene expression levels in both strains whereas delta-opioid receptor was found to be significantly downregulated only in injured DRG of Lewis rats although the same trend was observed in F344 rats. The data strongly suggest that dynorphins could be involved in strain differences concerning CCI resistance.

Different pattern of pleiotrophin and midkine expression in neuropathic pain: correlation between changes in pleiotrophin gene expression and rat strain differences in neuropathic pain.

Pleiotrophin (PTN) and midkine (MK) are two growth factors highly redundant in function that exhibit neurotrophic actions and are upregulated at sites of nerve injury, both properties being compatible with a potential involvement in the pathophysiological events that follow nerve damage (i.e. neuropathic pain). We have tested this hypothesis by comparatively studying PTN and MK gene expression in the spinal cord and dorsal root ganglia (DRG) of three rat strains known to differ in their behavioural responses to chronic constriction injury (CCI) of the sciatic nerve: Lewis, Fischer 344 (F344) and Sprague-Dawley (SD). Real time RT-PCR revealed minimal changes in PTN/MK gene expression in the spinal cord after CCI despite the strain considered, but marked changes were detected in DRG. A significant upregulation of PTN gene expression occurred in injured DRG of the F344 strain, the only strain that recovers from CCI-induced mechanical allodynia 28 days after surgery. In contrast, PTN was found to be downregulated in injured DRG of SD rats, the most sensitive strain in behavioural studies. These changes in PTN were not paralleled by concomitant modifications of MK gene expression. The results demonstrate previously unidentified differences between PTN and MK patterns of expression. Furthermore, the data suggest that upregulation of PTN, but not MK, could play an important role in the recovery from CCI.

Changes in BDNF gene expression correlate with rat strain differences in neuropathic pain.

The Fischer 344 (F344) rat inbred strain differs from the inbred Lewis and the outbred Sprague-Dawley (SD) in the response to different pain stimuli, which has been partially attributed to differences in the endogenous opioid and noradrenergic systems. Since brain-derived neutrophic factor (BDNF) modulates both the endogenous opioid and noradrenergic systems, we have now studied specific changes in BDNF gene expression related to the maintenance of neuropathic pain in the three rat strains. F344 rats were found to be the only strain that completely recovered from neuropathic pain (mechanical allodynia) 28 days after chronic constriction injury (CCI) of the sciatic nerve. Real time RT-PCR studies revealed minimal changes in the expression of BDNF in the spinal cord after CCI despite the strain considered, but marked changes in dorsal root ganglia (DRG) were observed. A significant upregulation of BDNF gene expression was found only in injured DRG of F344 rats, thus correlating with higher resistance to neuropathic pain. The data suggest that BDNF could be involved in strain differences concerning CCI resistance.

Morphine and yohimbine regulate midkine gene expression in the rat hippocampus.

Pleiotrophin and midkine are two recently discovered growth factors that promote survival and differentiation of catecholaminergic neurons. Chronic opioid stimulation has been reported to induce marked alterations of the locus coeruleus-hippocampus noradrenergic pathway, an effect that is prevented when opioids are coadministered with the alpha2-adrenoceptor antagonist yohimbine. The present work tries to examine a possible link between yohimbine reversal of morphine effects and pleiotrophin/midkine activation in the rat hippocampus by studying the levels of expression of pleiotrophin and midkine in response to acute and chronic administration of morphine, yohimbine and combinations of both drugs. Pleiotrophin gene expression was not altered by any treatment; however midkine mRNA levels were increased after chronic treatment with morphine. Chronic administration of yohimbine alone also increased midkine expression levels, whereas yohimbine and morphine administered together exhibited summatory effects on the upregulation of midkine expression levels. The data suggest that midkine could play a role in the prevention of opioid-induced neuroadaptations in hippocampus by yohimbine.

Yohimbine prevents morphine-induced changes of glial fibrillary acidic protein in brainstem and alpha2-adrenoceptor gene expression in hippocampus.

The alpha(2)-adrenoceptor antagonist yohimbine is known to oppose to several pharmacological effects of opioid drugs, but the consequences and the mechanisms involved remain to be clearly established. In the present study we have checked the effects of yohimbine on morphine-induced alterations of the expression of key proteins (glial fibrillary acidic protein, GFAP) and genes (alpha(2)-adrenoceptors) in rat brain areas known to be relevant in opioid dependence, addiction and individual vulnerability to drug abuse. Rats were treated with morphine in the presence or absence of yohimbine. The effects of the treatments on GFAP expression were studied by immunohistochemical staining in Locus Coeruleus (LC) and Nucleus of the Solitary Tract (NST), two important noradrenergic nuclei. In addition, drug effects on alpha(2)-adrenoceptor gene expression were determined by real time RT-PCR in the hippocampus, a brain area that receives noradrenergic input from the brainstem. Morphine administration increased GFAP expression both in LC and NST as it was previously reported in other brain areas. Yohimbine was found to efficiently prevent morphine-induced GFAP upregulation. Chronic (but not acute) morphine downregulated mRNA levels of alpha(2A)- and alpha(2C)-adrenoceptors in the hippocampus, while simultaneously increased the expression of the alpha(2B)-adrenoceptor gene. Again, yohimbine was able to prevent morphine-induced changes in the levels of expression of the three alpha(2)-adrenoceptor genes. These results correlate the well-established reduction of opioid dependence and addiction by yohimbine and suggest that this drug could interfere with the neural plasticity induced by chronic morphine in central noradrenergic pathways.

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.

Identification of the angiogenesis signaling domain in pleiotrophin defines a mechanism of the angiogenic switch.

Neoplasms progress through genetic and epigenetic mutations that deregulate pathways in the malignant cell that stimulate more aggressive growth of the malignant cell itself and/or remodel the tumor microenvironment to support the developing tumor mass. The appearance of new blood vessels in malignant tumors is known as the "angiogenic switch." The angiogenic switch triggers a stage of rapid tumor growth supported by extensive tumor angiogenesis and a more aggressive tumor phenotype and its onset is a poor prognostic indicator for host survival. Identification of the factors that stimulate the angiogenic switch thus is of high importance. Pleiotrophin (PTN the protein, Ptn the gene) is an angiogenic factor and the Ptn gene has been found to be constitutively expressed in many human tumors of different cell types. These studies use a nude mouse model to test if Ptn constitutively expressed in premalignant cells is sufficient to trigger an angiogenic switch in vivo. We introduced an ectopic Ptn gene into "premalignant" SW-13 cells and analyzed the phenotype of SW-13 Ptn cell tumor implants in the flanks of nude mice. SW-13 Ptn cell subcutaneous tumor implants grew very rapidly and had a striking increase in the density of new blood vessels compared to the SW-13 cell tumor implants, suggesting that constitutive PTN signaling in the premalignant SW-13 cell implants in the nude mouse recapitulates fully the angiogenic switch. It was found also that ectopic expression of the C-terminal domain of PTN in SW-13 cell implants was equally effective in initiating an angiogenic switch as the full-length PTN whereas implants of SW-13 cells in nude mice that express the N-terminal domain of PTN grew rapidly but failed to develop tumor angiogenesis. The data suggest the possibility that mutations that activate Ptn in premalignant cells are sufficient to stimulate an angiogenic switch in vivo and, since these mutations are frequently found in human malignancies, that constitutive PTN signaling may be an important contributor to progression of human tumors. The data also suggest that the C-terminal and the N-terminal domains of PTN equally initiate switches in premalignant cells to cells of a more aggressive tumor phenotype but the separate domains of PTN signal different mechanisms and perhaps signal through activation of a separate receptor-like protein.

Lewis and Fischer 344 strain differences in alpha2-adrenoceptors and tyrosine hydroxylase expression.

Lewis and Fischer 344 (F344) rats differ in their pharmacological responses to a variety of drugs such as opioids, which has been partially attributed to differences in the endogenous opioid tone. Since opioid and alpha2-adrenergic mechanisms closely interact in nociception and substance abuse, a comparative study of the endogenous alpha2-adrenergic system in both inbred strains is of interest. Alpha-2 adrenoceptor subtypes and tyrosine hydroxylase, the rate-limiting enzyme of the catecholamine biosynthesis, were studied by Taqman RT-PCR analysis of gene expression in four brain areas of F344 and Lewis rats: hypothalamus, hippocampus, striatum and cortex. No differences were found in the mRNA levels of alpha2A- and alpha2C-adrenoceptors in any of the areas examined, however F344 rats exhibited lower levels of alpha2B-adrenoceptor transcripts in the hippocampus and higher levels in the hypothalamus. Tyrosine hydroxylase gene expression was found to be higher in hippocampus and striatum of F344 rats compared to Lewis, and a consistent 2-fold increase of the protein levels was detected by Western blots only in the case of the hippocampus. These results together with previous studies strongly suggest that the hippocampal noradrenergic activity of Lewis and F344 rats could be involved in their different responses to pain, stress and drug addiction.

Pleiotrophin stimulates tyrosine phosphorylation of beta-adducin through inactivation of the transmembrane receptor protein tyrosine phosphatase beta/zeta.

Pleiotrophin (PTN the protein, Ptn the gene) signals through a unique mechanism; it inactivates the tyrosine phosphatase activity of its receptor, the transmembrane receptor protein tyrosine phosphatase (RPTP)beta/zeta, and increases tyrosine phosphorylation of the substrates of RPTPbeta/zeta through the continued activity of a yet to be described protein tyrosine kinase(s) in PTN-stimulated cells. We have now found that the cytoskeletal protein beta-adducin interacts with the intracellular domain of RPTPbeta/zeta in a yeast two-hybrid system, that beta-adducin is a substrate of RPTPbeta/zeta, that beta-adducin is phosphorylated in tyrosine in cells not stimulated by PTN, and that tyrosine phosphorylation of beta-adducin is sharply increased in PTN-stimulated cells, suggesting that beta-adducin is a downstream target of and regulated by the PTN/RPTPbeta/zeta signaling pathway. beta-Catenin was the first downstream target of the PTN/RPTPbeta/zeta signaling pathway to be identified; these data thus also suggest that PTN coordinately regulates steady state levels of tyrosine phosphorylation of the important cytoskeletal proteins beta-adducin and beta-catenin and, through PTN-stimulated tyrosine phosphorylation, beta-adducin may contribute to the disruption of cytoskeletal structure, increased plasticity, and loss of homophilic cell-cell adhesion that are the consequences of PTN stimulation of cells and a characteristic feature of different malignant cells with mutations that activate constitutive expression of the endogenous Ptn gene.

Pleiotrophin regulates serine phosphorylation and the cellular distribution of beta-adducin through activation of protein kinase C.

Pleiotrophin (PTN) was found to regulate tyrosine phosphorylation of beta-adducin through the PTN/receptor protein tyrosine phosphatase (RPTP)beta/zeta signaling pathway. We now demonstrate that PTN stimulates the phosphorylation of serines 713 and 726 in the myristoylated alanine-rich protein kinase (PK) C substrate domain of beta-adducin through activation of either PKC alpha or beta. We also demonstrate that PTN stimulates translocation of phosphoserine 713 and 726 beta-adducin either to nuclei, where it associates with nuclear chromatin and with centrioles of dividing cells, or to a membrane-associated site, depending on the phase of cell growth. Furthermore, we demonstrate that PTN stimulates the degradation of beta-adducin in PTN-stimulated cells. Phosphorylation of serines 713 and 726 in beta-adducin is known to markedly reduce the affinity of beta-adducin for spectrin and actin and to uncouple actin/spectrin/beta-adducin multimeric complexes needed for cytoskeletal stability. The data thus suggest that the PTN-stimulated phosphorylation of serines 713 and 726 in beta-adducin disrupts cytoskeletal protein complexes and integrity, features demonstrated in both PTN-stimulated cells and of highly malignant cells that constitutively express the endogenous Ptn gene. The data also support the important conclusion that PTN determines the cellular location of beta-adducin phosphorylated in serines 713 and 726 and raise the possibility that beta-adducin functions in support of structure of heterochromatin and centrioles during mitosis.

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.

Fyn is a downstream target of the pleiotrophin/receptor protein tyrosine phosphatase beta/zeta-signaling pathway: regulation of tyrosine phosphorylation of Fyn by pleiotrophin.

Pleiotrophin (PTN the protein, Ptn the gene) signals downstream targets through inactivation of its receptor, the transmembrane receptor protein tyrosine phosphatase (RPTP)beta/zeta, disrupting the balanced activity of RPTPbeta/zeta and the activity of a constitutively active tyrosine kinase. As a consequence of the inactivation of RPTPbeta/zeta, PTN stimulates a sharp increase in the levels of tyrosine phosphorylation of the substrates of RPTPbeta/zeta in PTN-stimulated cells. We now report that the Src family member Fyn interacts with the intracellular domain of RPTPbeta/zeta in a yeast two-hybrid system. We further demonstrate that Fyn is a substrate of RPTPbeta/zeta, and that tyrosine phosphorylation of Fyn is sharply increased in PTN-stimulated cells. In previous studies, we demonstrated that beta-catenin and beta-adducin are targets of the PTN/RPTPbeta/zeta-signaling pathway and defined the mechanisms through which tyrosine phosphorylation of beta-catenin and beta-adducin disrupts cytoskeletal protein complexes. We conclude that Fyn is a downstream target of the PTN/RPTPbeta/zeta-signaling pathway and suggest that PTN coordinately regulates tyrosine phosphorylation of beta-catenin, beta-adducin, and Fyn through the PTN/RPTPbeta/zeta-signaling pathway and that together Fyn, beta-adducin, and beta-catenin may be effectors of the previously described PTN-stimulated disruption of cytoskeletal stability, increased cell plasticity, and loss of cell-cell adhesion that are characteristic of PTN-stimulated cells and a feature of many human malignant cells in which mutations have established constitutive expression of the Ptn gene.

Pleiotrophin induces formation of functional neovasculature in vivo.

Pleiotrophin (PTN) is a heparin-binding growth/differentiation inducing cytokine that shares 50% amino acid sequence identity and striking domain homology with Midkine (MK), the only other member of the Ptn/Mk developmental gene family. The Ptn gene is expressed in sites of early vascular development in embryos and in healing wounds and its constitutive expression in many human tumors is associated with an angiogenic phenotype, suggesting that PTN has an important role in angiogenesis during development and in wound repair and advanced malignancies. To directly test whether PTN is angiogenic in vivo, we injected a plasmid to express PTN into ischemic myocardium in rats. Pleiotrophin stimulated statistically significant increases in both normal appearing new capillaries and arterioles each of which had readily detectable levels of the arteriole marker, smooth muscle cell alpha-actin. Furthermore, the newly formed blood vessels were shown to interconnect with the existent coronary vascular system. The results of these studies demonstrate directly that PTN is an effective angiogenic agent in vivo able to initiate new vessel formation that is both normal in appearance and function. The data suggest that PTN signals the more "complete" new blood vessel formation through its ability to stimulate different functions in different cell types not limited to the endothelial cell.

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.