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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.

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.

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.

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.

To better understand the phenotype of pleiotrophin (PTN the protein, Ptn the gene) genetically deficient mice (Ptn -/-), we compared the transcriptional profiles of aortae obtained from Ptn -/- and wild type (WT, Ptn +/+) mice using a 14,400 gene microarray chip (Affymetrix) and confirmed the analysis of relevant genes by real time RT-PCR. We found striking alterations in expression levels of different genes of the renin-angiotensin system of Ptn -/- mice relative to WT (Ptn +/+) mice. The mRNA levels of the angiotensin converting enzyme (ACE) were significantly decreased in Ptn -/- mice whereas the mRNA levels of the angiotensin II type 1 (AT1) and angiotensin II type 2 (AT2) receptors were significantly increased in Ptn -/- mice when they were compared with mRNA levels in WT (Ptn +/+) mice aortae. These data demonstrate for the first time that the levels of expression of the Ptn gene markedly influence expression levels of the genes encoding the key proteins of the renin-angiotensin system in mouse aorta and suggest the tentative conclusion that levels of Ptn gene expression have the potential to critically regulate the downstream activities of angiotensin II, through the regulation of its synthesis by ACE and its receptor mediated functions through regulation of both the AT1 and AT2 receptors.

To better understand the phenotype of pleiotrophin (PTN the protein, Ptn the gene) genetically deficient mice (Ptn -/-), we compared the transcriptional profiles of aortae obtained from Ptn -/- and wild type (WT, Ptn +/+) mice using a 14,400 gene microarray chip (Affymetrix) and confirmed the analysis of relevant genes by real time RT-PCR. We identified a dramatic upregulation of expression of tyrosine hydroxylase (TH), DOPA decarboxylase, and dopamine beta-hydroxylase in aortae of Ptn -/- mice in comparison with WT (Ptn +/+) mice. In contrast, transcripts of phenylethanolamine-N-methyltransferase, the enzyme catalyzing the conversion of norepinephrine into epinephrine, were not detected in aortae in either mouse strain. These findings suggest that Ptn gene expression has a critical role in determining the levels of expression of the enzymes of catecholamine biosynthesis in aorta and through this mechanism, PTN may regulate levels of endogenous catecholamine synthesis and potentially the vascular tone of aorta., (Copyright 2004 Elsevier Inc.)

Pleiotrophin (PTN the protein, Ptn the gene) is a 136 amino acid secreted heparin-binding cytokine that signals diverse functions, including lineage-specific differentiation of glial progenitor cells, neurite outgrowth, and angiogenesis. Pleiotrophin gene expression is found in cells in early differentiation during different development periods and upregulated in cells with an early differentiation phenotype in wound repair. The Ptn gene is a protooncogene. It is strongly expressed in different human tumor cells and expression of the Ptn gene in tumor cells in vivo accelerates growth and stimulates tumor angiogenesis. Separate independent domains have been identified in PTN to signal transformation and tumor angiogenesis. Pleiotrophin is the first ligand of any of the known transmembrane tyrosine phosphatases. Pleiotrophin inactivates the receptor protein tyrosine phosphatase (RPTP) beta/zeta. The interaction of PTN and RPTP beta/zeta increases steady-state tyrosine phosphorylation of beta-catenin. Pleiotrophin thus regulates both normal cell functions and different pathological conditions at many levels. It signals these functions through a transmembrane tyrosine phosphatase., ((c)2002 Elsevier Science.)

Trophic factors are being increasingly recognized as important contributors to growth, differentiation, and maintenance of viability within the mammalian nervous system during development. Pleiotrophin (PTN) is a secreted 18-kDa heparin binding protein that stimulates mitogenesis and angiogenesis and neurite and glial process outgrowth guidance activities in vitro. We localized the sites and time course of expression of the Ptn gene and its protein product in developing and adult mouse nervous system. Expression of the Ptn gene was first observed at embryo day 8.5 (E8.5). At E12.5, transcripts of the Ptn gene were localized in developing neuroepithelium at sites of active cell division in the spinal cord and brain. At E15.5, transcripts were found in the somata of some but not all neurons and glia whereas in the adult its pattern of expression was nearly exclusively restricted to the brain. The PTN protein was found almost entirely in association with the axonal tracts during development and in adults. Furthermore, as opposed to the finding of PTN in both central and peripheral nervous systems during development, PTN was not expressed beyond the exit where axonal tracts become the peripheral nervous system in adults. At all sites and times examined, the somata that contained Ptn transcripts corresponded with the axonal tracts that contained the PTN protein. The results establish that Ptn is expressed in early development at sites of active mitogenesis in developing neuroepithelium and later in both glial cells and neurons at sites of neuronal and glial process formation in developing axonal tracts. The findings establish a correspondence in the localization of PTN within the nervous system at sites of normal developmental processes that correlate with the functional activities of PTN previously described in vitro.