Thrombopoietin gene expression in the developing human central nervous system

Thrombopoietin exerts a neuroprotective effect by inhibiting the suppression of neuronal proliferation and axonal outgrowth in intrauterine growth restriction rats

Chronic hypoxia in utero causes intrauterine growth restriction (IUGR) of the fetus. IUGR infants are known to be at higher risk for neurodevelopmental disorders, but the mechanism is unclear. In this study, we analyzed the structure of the cerebral cortex using IUGR model rats generated through a reduced uterine perfusion pressure operation. IUGR rats exhibited thinner cerebral white matter and enlarged lateral ventricles compared with control rats. Expression of neuron cell markers, Satb2, microtubule-associated protein (MAP)-2, α-tubulin, and nestin was reduced in IUGR rats, indicating that neurons were diminished at various developmental stages in IUGR rats, from neural stem cells to mature neurons. However, there was no increase in apoptosis in IUGR rats. Cells positive for Ki67, a marker of cell proliferation, were reduced in neurons and all glial cells of IUGR rats. In primary neuron cultures, axonal elongation was impaired under hypoxic culture conditions mimicking the intrauterine environment of IUGR infants. Thus, in IUGR rats, chronic hypoxia in utero suppresses the proliferation of neurons and glial cells as well as axonal elongation, resulting in cortical thinning and enlarged lateral ventricles. Thrombopoietin (TPO), a platelet growth factor, inhibited the decrease in neuron number and promoted axon elongation in primary neurons under hypoxic conditions. Intraperitoneal administration of TPO to IUGR rats resulted in increases in the number of NeuN-positive cells and the area coverage of Satb2. In conclusion, suppression of neuronal proliferation and axonal outgrowth in IUGR rats resulted in cortical thinning and enlargement of lateral ventricles. TPO administration might be a novel therapeutic strategy for treating brain dysmaturation in IUGR infants.

The cytokine receptor CRLF3 is a human neuroprotective EV-3 (Epo) receptor

The evolutionary conserved orphan cytokine receptor-like factor 3 (CRLF3) has been implicated in human disease, vertebrate hematopoiesis and insect neuroprotection. While its specific functions are elusive, experimental evidence points toward a general role in cell homeostasis. Erythropoietin (Epo) is a major regulator of vertebrate hematopoiesis and a general cytoprotective cytokine. Erythropoietic functions mediated by classical Epo receptor are understood in great detail whereas Epo-mediated cytoprotective mechanisms are more complex due to involvement of additional Epo receptors and a non-erythropoietic splice variant with selectivity for certain receptors. In the present study, we show that the human CRLF3 mediates neuroprotection upon activation with the natural Epo splice variant EV-3. We generated CRLF3 knock-out iPSC lines and differentiated them toward the neuronal lineage. While apoptotic death of rotenone-challenged wild type iPSC-derived neurons was prevented by EV-3, EV-3-mediated neuroprotection was absent in CRLF3 knock-out neurons. Rotenone-induced apoptosis and EV-3-mediated neuroprotection were associated with differential expression of pro-and anti-apoptotic genes. Our data characterize human CRLF3 as a receptor involved in Epo-mediated neuroprotection and identify CRLF3 as the first known receptor for EV-3.

CAMT-MPL: congenital amegakaryocytic thrombocytopenia caused by MPL mutations - heterogeneity of a monogenic disorder - a comprehensive analysis of 56 patients

Congenital amegakaryocytic thrombocytopenia caused by deleterious homozygous or compound heterozygous mutations in MPL (CAMT-MPL) is a rare inherited bone marrow failure syndrome presenting as an isolated thrombocytopenia at birth progressing to pancytopenia due to exhaustion of hematopoietic progenitors. The analysis of samples and clinical data from a large cohort of 56 patients with CAMT-MPL resulted in a detailed description of the clinical picture and reliable genotype-phenotype correlations for this rare disease. We extended the spectrum of CAMT causing MPL mutations regarding number (17 novel mutations) and impact. Clinical courses showed great variability with respect to the severity of thrombocytopenia, the development of pancytopenia and the consequences from bleedings. The most severe clinical problems were (i) intracranial bleedings pre- and perinatally and the resulting long-term consequences, and (ii) the development of aplastic anemia in the later course of the disease. An important and new finding was that thrombocytopenia was not detected at birth in a quarter of the patients. The rate of non-hematological abnormalities in CAMT-MPL was higher than described so far. Most of the anomalies were related to the head region (brain anomalies, ocular and orbital anomalies) and consequences of intracranial bleedings. The present study demonstrates a higher variability of clinical courses than described so far and has important implications on diagnosis and therapy. The diagnosis CAMT-MPL has to be considered even for those patients who are inconspicuous in the first months of life or show somatic anomalies typical for other inherited bone marrow failure syndromes.

Congenital amegakaryocytic thrombocytopenia - Not a single disease

Congenital amegakaryocytic thrombocytopenia (CAMT) is a rare inherited bone marrow failure syndrome (IBMFS) that is characterized by severe thrombocytopenia at birth due to ineffective megakaryopoiesis and development towards aplastic anemia during the first years of life. CAMT is not a single monogenetic disorder; rather, many descriptions of CAMT include different entities with different etiologies. CAMT in a narrow sense, which is primarily restricted to the hematopoietic system, is caused mainly by mutations in the gene for the thrombopoietin receptor (MPL), sometimes in the gene for its ligand (THPO). CAMT in association with radio-ulnar synostosis, which is not always clinically apparent, is mostly caused by mutations in MECOM, rarely in HOXA11. Patients affected by other IBMFS - especially Fanconi anemia or dyskeratosis congenita - may be misdiagnosed as having CAMT when they lack typical disease features of these syndromes or have only mild symptoms. This article reviews scientific and clinical aspects of the various disorders associated with the term "CAMT" with a main focus on the disease caused by mutations in the MPL gene.

The last intron of the human thrombopoietin gene enhances expression in milk of transgenic mice

Introns can enhance gene expression levels. This effect is known as intron-mediated enhancement, which is different from that of enhancers or promoters. In our previous study, under the control of the cytomegalovirus or goat β-casein promoter, the vector containing intron V-TPOcDNA expressed the highest thrombopoietin (TPO) level, whereas the vector containing TPOgDNA expressed the lowest level. In order to verify whether intron V also improves TPO expression in the milk of transgenic mice, rat whey acidic protein promoter was used as regulatory element to construct mammary gland expression vectors including pTPOWA (containing TPOcDNA), pTPOWB (containing intron V-TPOcDNA), and pTPOWC (containing TPOgDNA). These vectors were transfected into HC-11 cells and the supernatants were analyzed at 48 h. The highest TPO level was found in pTPOWB (795 pg/mL) and the lowest level in pTPOWC (193 pg/mL). Then, corresponding vectors were microinjected into fertilized mice zygotes. Transgenic mice were identified by polymerase chain reaction and Southern blot. Enzyme-linked immunosorbent assay was performed to measure TPO levels in the milk of lactating transgenic mice. The highest and lowest TPO levels were found in transgenic mice carrying intron V-TPOcDNA (2,307 pg/mL) and in transgenic mice carrying TPOgDNA (242 pg/mL), respectively. Thus, intron V remarkably improved TPO expression in transgenic mice.

Exome sequencing reveals a thrombopoietin ligand mutation in a Micronesian family with autosomal recessive aplastic anemia

We recently identified 2 siblings afflicted with idiopathic, autosomal recessive aplastic anemia. Whole-exome sequencing identified a novel homozygous missense mutation in thrombopoietin (THPO, c.112C>T) in both affected siblings. This mutation encodes an arginine to cysteine substitution at residue 38 or residue 17 excluding the 21-amino acid signal peptide of THPO receptor binding domain (RBD). THPO has 4 conserved cysteines in its RBD that form 2 disulfide bonds. Our in silico modeling predicts that introduction of a fifth cysteine may disrupt normal disulfide bonding to cause poor receptor binding. In functional assays, the mutant-THPO-containing media shows two- to threefold reduced ability to sustain UT7-TPO cells, which require THPO for proliferation. Both parents and a sibling with heterozygous R17C change have reduced platelet counts, whereas a sibling with wild-type sequence has normal platelet count. Thus, the R17C partial loss-of-function allele results in aplastic anemia in the homozygous state and mild thrombocytopenia in the heterozygous state in our family. Together with the recent identification of THPO receptor (MPL) mutations and the effects of THPO agonists in aplastic anemia, our results have clinical implications in the diagnosis and treatment of patients with aplastic anemia and highlight a role for the THPO-MPL pathway in hematopoiesis in vivo.

Role of pseudoexons and pseudointrons in human cancer

In all eukaryotic organisms, pre-mRNA splicing and alternative splicing processes play an essential role in regulating the flow of information required to drive complex developmental and metabolic pathways. As a result, eukaryotic cells have developed a very efficient macromolecular machinery, called the spliceosome, to correctly recognize the pre-mRNA sequences that need to be inserted in a mature mRNA (exons) from those that should be removed (introns). In healthy individuals, alternative and constitutive splicing processes function with a high degree of precision and fidelity in order to ensure the correct working of this machinery. In recent years, however, medical research has shown that alterations at the splicing level play an increasingly important role in many human hereditary diseases, neurodegenerative processes, and especially in cancer origin and progression. In this minireview, we will focus on several genes whose association with cancer has been well established in previous studies, such as ATM, BRCA1/A2, and NF1. In particular, our objective will be to provide an overview of the known mechanisms underlying activation/repression of pseudoexons and pseudointrons; the possible utilization of these events as biomarkers of tumor staging/grading; and finally, the treatment options for reversing pathologic splicing events.

Analysis of protein isoforms: can we do it better?

Protein isoforms/splice variants can play important roles in various biological processes and can potentially be used as biomarkers or therapeutic targets/mediators. Thus, there is a need for efficient and, importantly, accurate methods to distinguish and quantify specific protein isoforms. Since protein isoforms can share a high percentage of amino acid sequence homology and dramatically differ in their cellular concentration, the task for accuracy and efficiency in methodology and instrumentation is challenging. The analysis of intact proteins has been perceived to provide a more accurate and complete result for isoform identification/quantification in comparison to analysis of the corresponding peptides that arise from protein enzymatic digestion. Recently, novel approaches have been explored and developed that can possess the accuracy and reliability important for protein isoform differentiation and isoform-specific peptide targeting. In this review, we discuss the recent development in methodology and instrumentation for enhanced detection of protein isoforms as well as the examples of their biological importance.

Flt3 ligand synergizes with granulocyte-colony-stimulating factor in bone marrow mobilization to improve functional outcome after spinal cord injury in the rat

BACKGROUND AIMS

The effect of granulocyte-colony-stimulating factor (G-CSF) and/or the cytokine fms-like thyrosin kinase 3 (Flt3) ligand on functional outcome and tissue regeneration was studied in a rat model of spinal cord injury (SCI).

METHODS

Rats with a balloon-induced compression lesion were injected with G-CSF and/or Flt3 ligand to mobilize bone marrow cells. Behavioral tests (Basso-Beattie-Bresnahan and plantar test), blood counts, morphometric evaluation of the white and gray matter, and histology were performed 5 weeks after SCI.

RESULTS

The mobilization of bone marrow cells by G-CSF, Flt3 ligand and their combination improved the motor and sensory performance of rats with SCI, reduced glial scarring, increased axonal sprouting and spared white and gray matter in the lesion. The best results were obtained with a combination of G-CSF and Flt3. G-CSF alone or in combination with Flt3 ligand significantly increased the number of white blood cells, but not red blood cells or hemoglobin content, during and after the time-course of bone marrow stimulation. The combination of factors led to infiltration of the lesion by CD11b(+) cells.

CONCLUSIONS

The observed improvement in behavioral and morphologic parameters and tissue regeneration in animals with SCI treated with a combination of both factors could be associated with a prolonged time-course of mobilization of bone marrow cells. The intravenous administration of G-CSF and/or Flt3 ligand represents a safe and effective treatment modality for SCI.

Inflammation stimulates thrombopoietin (Tpo) expression in rat brain-derived microvascular endothelial cells, but suppresses Tpo in astrocytes and microglia

Thrombopoietin (Tpo) and its receptor (c-Mpl; TpoR), which primary regulate megakaryopoiesis and platelet production, are also expressed in the central nervous system (CNS). Increased Tpo concentrations are present in the cerebrospinal fluid (CSF) of some patients with bacterial or viral meningitis. Since previous data implicated a proapoptotic role of Tpo on newly generated neuronal cells, we herein elucidated the regulation of Tpo in primary rat neurons (e17), astrocytes, and microglia (p0-p3), as well as in brain-derived vascular endothelial cells of 3-week-old rats after exposure to bacterial lipopolysaccharide (LPS). LPS inhibited Tpo gene expression in astrocytes and microglia, but not in neurons, most likely due to absence of Toll-like receptor 4 in neurons. While Tpo mRNA expression recovered in astrocytes after 24 h, it remained suppressed in microglia. Furthermore, we detected Tpo mRNA expression in primary brain-derived vascular endothelial cells, which also express the TpoR. In these cells, LPS significantly up-regulated Tpo mRNA expression. TpoR mRNA and protein expression remained constitutive in all cell types. Thus, our data provide evidence for a cell-type-specific modulation of Tpo mRNA expression by inflammation in brain-derived cells. Transient down-regulation of Tpo expression in astrocytes and microglia may limit Tpo-induced neuronal cell death in inflammatory brain disorders.

Neonatal thrombocytopenia and megakaryocytopoiesis

Thrombocytopenia is common among sick neonates, affecting 20% to 35% of all patients admitted to the neonatal intensive care unit (NICU). While most cases of neonatal thrombocytopenia are mild or moderate and resolve within 7 to 14 days with appropriate therapy, 2.5% to 5% of NICU patients develop severe thrombocytopenia, sometimes lasting for several weeks and requiring >20 platelet transfusions. The availability of thrombopoietic agents offers the possibility of decreasing the number of platelet transfusions and potentially improving the outcomes of these infants. However, adding thrombopoietin (TPO) mimetics to the therapeutic armamentarium of neonatologists will require careful attention to the substantial developmental differences between neonates and adults in the process of megakaryocytopoiesis and in their responses to TPO. Taken together, the available data suggest that TPO mimetics will stimulate platelet production in neonates, but might do so through different mechanisms and at different doses than those established for adults. In addition, the specific groups of thrombocytopenic neonates most likely to benefit from therapy with TPO mimetics need to be defined, and the potential nonhematological effects of these agents on the developing organism need to be considered. This review summarizes our current understanding of neonatal megakaryocytopoiesis, and examines in detail the developmental factors relevant to the potential use of TPO mimetics in neonates.

Thrombopoietin contributes to neuronal damage in experimental bacterial meningitis

Thrombopoietin (Tpo), which primarily regulates megakaryopoiesis, and its receptor (c-Mpl) are expressed in the brain, where Tpo exhibits proapototic effects on neurons. In the present study, we investigated the implication of Tpo in experimental pneumococcal meningitis. Following intrathecal infection with the encapsulated Streptococcus pneumoniae strain D39, we observed upregulation of Tpo mRNA expression at 12 h and 24 h in brain homogenates of wild-type C57BL/6 mice. c-Mpl mRNA expression was upregulated at 12 h and returned to baseline at 24 h. Compared to wild-type mice, mutants with homozygous Tpo receptor ablation (c-Mpl(-/-)) displayed reduced microglial activation and neuronal apoptosis in the dentate gyrus. Concentrations of bacteria in blood or cerebrospinal fluid (CSF), as well as CSF pleocytosis, were not significantly different between wild-type and c-Mpl(-/-) mice. In human postmortem brain, Tpo protein was colocalized to macrophages during encephalitis. In murine primary microglia and RAW264.7 macrophages, upregulation of Tpo mRNA was induced by D39-conditioned medium but not by bacterial lipopeptide or by medium conditioned by pneumococcal mutants defective in hydrogen peroxide formation (ΔspxB) or pneumolysin (Δpln). We conclude that Tpo acts as a mediator of neuronal damage in bacterial meningitis.

Increasing platelets without transfusion: is it time to introduce novel thrombopoietic agents in neonatal care?

The Food and Drug Administration recently approved two novel thrombopoiesis-stimulating agents, Romiplostim (AMG-531, Nplate) and Eltrombopag (Promacta), for the treatment of adults with immune thrombocytopenic purpura. For physicians taking care of critically ill neonates, this offers the opportunity of decreasing platelet transfusions and potentially improving the outcomes of neonates with severe and prolonged thrombocytopenia. However, several developmental factors need to be taken into consideration. First, the population of thrombocytopenic neonates likely to benefit from these agents needs to be carefully selected. Second, the mechanisms underlying neonatal and adult thrombocytopenia differ from each other and are incompletely understood, and pre-clinical evidence suggests that the response of neonates to thrombopoietic factors might be different from that of adults. Finally, the potential non-hematopoietic effects of thrombopoietin have not been well established. Here, we will discuss these issues in detail, and will highlight the critical developmental differences between neonates and adults that need to be considered as we think about introducing these agents into neonatal care.

Expression pattern of the thrombopoietin receptor (Mpl) in the murine central nervous system

BACKGROUND

Thrombopoietin (Thpo) and its receptor (Mpl), which regulate megakaryopoiesis, are expressed in the central nervous system (CNS), where Thpo is thought to exert pro-apoptotic effects on newly generated neurons. Mpl expression has been analysed in brain tissue on transcript level and in cultured primary rat neurons and astrocytes on protein level. Herein, we analysed Mpl expression in the developing and adult murine CNS by immunohistochemistry and investigated the brain of mice with homozygous Mpl deficiency (Mpl-/-) by MRI.

RESULTS

Mpl was not detectable at developmental stages E12 to E15 in any resident cells of the CNS. From E18 onwards, robust Mpl expression was found in various brain areas, including cerebral cortex, olfactory bulb, thalamus, hypothalamus, medulla, pons, and the grey matter of spinal cord. However, major developmental changes became obvious: In the subventricular zone of the cerebral cortex Mpl expression occurred only during late gestation, while in the hippocampus Mpl expression was detectable for first time at stage P4. In the white matter of the cerebellum Mpl expression was restricted to the perinatal period. In the adult cerebellum, Mpl expression switched to Purkinje cell. The majority of other Mpl-positive cells were NeuN-positive neurons. None of the cells could be double-labelled with astrocyte marker GFAP. Mpl-/- mice showed no gross abnormalities of the brain.

CONCLUSIONS

Our data locate Mpl expression to neurons at different subdivisions of the spinal cord, rhombencephalon, midbrain and prosencephalon. Besides neuronal cells Mpl protein is also expressed in Purkinje cells of the adult cerebellum.

Pathogenesis of chronic immune thrombocytopenia: increased platelet destruction and/or decreased platelet production

Chronic immune thrombocytopenia (ITP) is a haematological disorder in which patients predominantly develop skin and mucosal bleeding. Early studies suggested ITP was primarily due to immune-mediated peripheral platelet destruction. However, increasing evidence indicates that an additional component of this disorder is immune-mediated decreased platelet production that cannot keep pace with platelet destruction. Evidence for increased platelet destruction is thrombocytopenia following ITP plasma infusions in normal subjects, in vitro platelet phagocytosis, and decreased platelet survivals in ITP patients that respond to therapies that prevent in vivo platelet phagocytosis; e.g., intravenous immunoglobulin G, anti-D, corticosteroids, and splenectomy. The cause of platelet destruction in most ITP patients appears to be autoantibody-mediated. However, cytotoxic T lymphocyte-mediated platelet (and possibly megakaryocyte) lysis, may also be important. Studies supporting suppressed platelet production include: reduced platelet turnover in over 80% of ITP patients, morphological evidence of megakaryocyte damage, autoantibody-induced suppression of in vitro megakaryocytopoiesis, and increased platelet counts in most ITP patients following treatment with thrombopoietin receptor agonists. This review summarizes data that indicates that the pathogenesis of chronic ITP may be due to both immune-mediated platelet destruction and/or suppressed platelet production. The relative importance of these two mechanisms undoubtedly varies among patients.

Advances in the understanding of congenital amegakaryocytic thrombocytopenia

Congenital amegakaryocytic thrombocytopenia (MIM #604498) is an extremely rare inherited bone marrow failure syndrome, usually presenting as a severe thrombocytopenia at birth due to ineffective megakaryocytopoiesis and no characteristic physical anomalies. Usually the isolated thrombocytopenia progresses to pancytopenia during the first years of life. The only curative therapy to date is haematopoietic stem cell transplantation. Most of the cases of congenital amegakaryocytic thrombocytopenia are caused by defective expression or function of the thrombopoietin receptor due to homozygous or compound heterozygous mutations in the gene MPL. The essential roles of thrombopoietin as a lineage specific regulator of platelet production and as a regulator of haematopoietic stem cell function are reflected in the haematological defects seen in affected individuals.

Thrombopoietin and its splicing variants: structure and functions in thrombopoiesis and beyond

Since its cloning in 1994, several studies have reported that thrombopoietin (THPO) presents several alternative splicing products that differ from the full-length protein in its 5' UTR, N- or C-terminal regions. Most of these splice variants are evolutionarily conserved and have been detected in different tissues as well as in cell lines. Although the possible functions of the THPO isoforms are still elusive, different clues link them to the peculiar mechanism that regulates THPO production. Moreover, novel fields to explore possible roles of the THPO variants are opened by observations that this hormone can influence the formation of hematopoietic progenitors and its expression occurs in some tumors as well as in tissues not directly related to the thrombopoiesis. In this review, we summarize the structure and functions of THPO through the published evidence on its splicing isoforms and discuss about their involvement with physiopathologic phenomena.

Thrombopoietin inhibits nerve growth factor-induced neuronal differentiation and ERK signalling

Thrombopoietin (TPO), a hematopoietic growth factor regulating platelet production, and its receptor (TPOR) were recently shown to be expressed in the brain where they exert proapoptotic activity. Here we used PC12 cells, an established model of neuronal differentiation, to investigate the effects of TPO on neuronal survival and differentiation. These cells expressed TPOR mRNA. TPO increased cell death in neuronally differentiated PC12 cells but had no effect in undifferentiated cells. Surprisingly, TPO inhibited nerve growth factor (NGF)-induced differentiation of PC12 cells in a dose- and time-dependent manner. This inhibition was dependent on the activity of Janus kinase-2 (JAK2). Using phospho-kinase arrays and Western blot we found downregulation of the NGF-stimulated phosphorylation of the extracellular signal-regulated kinase p42ERK by TPO with no effect on phosphorylation of Akt or stress kinases. NGF-induced phosphorylation of ERK-activating kinases, MEK1/2 and C-RAF was also reduced by TPO while NGF-induced RAS activation was not attenuated by TPO treatment. In contrast to its inhibitory effects on NGF signalling, TPO had no effect on epidermal growth factor (EGF)-stimulated ERK phosphorylation or proliferation of PC12 cells. Our data indicate that TPO via activation of its receptor-bound JAK2 delays the NGF-dependent acquisition of neuronal phenotype and decreases neuronal survival by suppressing NGF-induced ERK activity.

Autologous bone marrow transplantation in patients with subacute and chronic spinal cord injury

Stem cell transplants into spinal cord lesions may help to improve regeneration and spinal cord function. Clinical studies are necessary for transferring preclinical findings from animal experiments to humans. We investigated the transplantation of unmanipulated autologous bone marrow in patients with transversal spinal cord injury (SCI) with respect to safety, therapeutic time window, implantation strategy, method of administration, and functional improvement. We report data from 20 patients with complete SCI who received transplants 10 to 467 days postinjury. The follow-up examinations were done at 3, 6, and 12 months after implantation by two independent neurologists using standard neurological classification of SCI, including the ASIA protocol, the Frankel score, the recording of motor and somatosensory evoked potentials, and MRI evaluation of lesion size. We compared intra-arterial (via catheterization of a. vertebralis) versus intravenous administration of all mononuclear cells in groups of acute (10-30 days post-SCI, n=7) and chronic patients (2-17 months postinjury, n=13). Improvement in motor and/or sensory functions was observed within 3 months in 5 of 6 patients with intra-arterial application, in 5 of 7 acute, and in 1 of 13 chronic patients. Our case study shows that the implantation of autologous bone marrow cells appears to be safe, as there have been no complications following implantation to date (11 patients followed up for more than 2 years), but longer follow-ups are required to determine that implantation is definitively safe. Also, we cannot yet confirm that the observed beneficial effects were due to the cell therapy. However, the outcomes following transplantation in acute patients, and in one chronic patient who was in stable condition for several months prior to cell implantation, are promising. It is evident that transplantation within a therapeutic window of 3-4 weeks following injury will play an important role in any type of stem cell SCI treatment. Trials involving a larger population of patients and different cell types are needed before further conclusions can be drawn.

High Thrombopoietin Concentrations in The Cerebrospinal Fluid of Neonates with Sepsis And Intraventricular Hemorrhage May Contribute to Brain Damage

Thrombopoietin (TPO) and its receptor (TPOR) are expressed in the central nervous system (CNS). Although TPO shares significant homology with various neurotrophins, recent data indicate a proapoptotic function of TPO in the CNS. In this study, TPO concentrations were analyzed in the cerebrospinal fluid (CSF) of neonates. Human neuroblastoma-derived SH-SY5Y cells were established to elucidate the effects of inflammation and hypoxia on neuronal Tpo expression. TPO was detectable in the CSF of 6 of 15 neonates with bacterial infection/sepsis (median 140, range 2-613 pg/mL), 5 of 9 neonates with posthemorrhagic hydrocephalus (median 31, range 1.4-469 pg/mL), 3 of 4 neonates with posthemorrhagic hydrocephalus plus bacterial infection/sepsis or meningitis (median 97, range 6-397 pg/mL), but not in controls ( n = 3). Neither the presence of detectable TPO nor its level in the CSF significantly correlated with any clinical or laboratory parameter. In SH-SY5Y cells, TPO and TPOR expression was detected by RT-PCR and Western blot analysis. In vitro, interleukin-6 (IL-6) did not significantly change Tpo gene expression. In contrast, Tpo mRNA expression significantly decreased under hypoxia, whereas erythropoietin (EPO) mRNA expression increased. In conclusion, our data provide evidence that in neuronal cells, TPO production is regulated by different mechanisms than in hepatocytes.

Transplantation of bone marrow stem cells as well as mobilization by granulocyte-colony stimulating factor promotes recovery after spinal cord injury in rats

Emerging clinical studies of treating brain and spinal cord injury (SCI) with autologous adult stem cells led us to compare the effect of an intravenous injection of mesenchymal stem cells (MSCs), an injection of a freshly prepared mononuclear fraction of bone marrow cells (BMCs) or bone marrow cell mobilization induced by granulocyte colony stimulating factor (G-CSF) in rats with a balloon- induced spinal cord compression lesion. MSCs were isolated from rat bone marrow by their adherence to plastic, labeled with iron-oxide nanoparticles and expanded in vitro. Seven days after injury, rats received an intravenous injection of MSCs or BMCs or a subcutaneous injection of GCSF (from day 7 to 11 post-injury). Functional status was assessed weekly for 5 weeks after SCI, using the Basso-Beattie-Bresnehan (BBB) locomotor rating score and the plantar test. Animals with SCI treated with MSCs, BMCs, or G-CSF had higher BBB scores and better recovery of hind limb sensitivity than controls injected with saline. Morphometric measurements showed an increase in the spared white matter. MR images of the spinal cords were taken ex vivo 5 weeks after SCI using a Bruker 4.7-T spectrometer. The lesions populated by grafted MSCs appeared as dark hypointense areas. Histology confirmed a large number of iron-containing and PKH 26-positive cells in the lesion site. We conclude that treatment with three different bone marrow cell populations had a positive effect on behavioral outcome and histopathological assessment after SCI, which was most pronounced after MSC injection.

Cell type specific signalling by hematopoietic growth factors in neural cells

Correct timing and spatial location of growth factor expression is critical for undisturbed brain development and functioning. In terminally differentiated cells distinct biological responses to growth factors may depend on cell type specific activation of signalling cascades. We show that the hematopoietic growth factors thrombopoietin (TPO) and granulocyte colony-stimulating factor (GCSF) exert cell type specific effects on survival, proliferation and the degree of phosphorylation of Akt1, ERK1/2 and STAT3 in rat hippocampal neurons and cortical astrocytes. In neurons, TPO induced cell death and selectively activated ERK1/2. GCSF protected neurons from TPO- and hypoxia-induced cell death via selective activation of Akt1. In astrocytes, neither TPO nor GCSF had any effect on cell viability but inhibited proliferation. This effect was accompanied by activation of ERK1/2 and inhibition of STAT3 activity. A balance between growth factors, their receptors and signalling proteins may play an important role in regulation of neural cell survival.

Bone marrow stem cells and polymer hydrogels--two strategies for spinal cord injury repair

1. Emerging clinical studies of treating brain and spinal cord injury (SCI) led us to examine the effect of autologous adult stem cell transplantation as well as the use of polymer scaffolds in spinal cord regeneration. We compared an intravenous injection of mesenchymal stem cells (MSCs) or the injection of a freshly prepared mononuclear fraction of bone marrow cells (BMCs) on the treatment of an acute or chronic balloon-induced spinal cord compression lesion in rats. Based on our experimental studies, autologous BMC implantation has been used in a Phase I/II clinical trial in patients (n=20) with a transversal spinal cord lesion. 2. MSCs were isolated from rat bone marrow by their adherence to plastic, labeled with iron-oxide nanoparticles and expanded in vitro. Macroporous hydrogels based on derivatives of 2-hydroxyethyl methacrylate (HEMA) or 2-hydroxypropyl methacrylamide (HPMA) were prepared, then modified by their copolymerization with a hydrolytically degradable crosslinker, N,O-dimethacryloylhydroxylamine, or by different surface electric charges. Hydrogels or hydrogels seeded with MSCs were implanted into rats with hemisected spinal cords. 3. Lesioned animals grafted with MSCs or BMCs had smaller lesions 35 days postgrafting and higher scores in BBB testing than did control animals and also showed a faster recovery of sensitivity in their hind limbs using the plantar test. The functional improvement was more pronounced in MSC-treated rats. In MR images, the lesion populated by grafted cells appeared as a dark hypointense area and was considerably smaller than in control animals. Morphometric measurements showed an increase in the volume of spared white matter in cell-treated animals. In the clinical trial, we compared intraarterial (via a. vertebralis, n=6) versus intravenous administration of BMCs (n=14) in a group of subacute (10-33 days post-SCI, n=8) and chronic patients (2-18 months, n=12). For patient follow-up we used MEP, SEP, MRI, and the ASIA score. Our clinical study revealed that the implantation of BMCs into patients is safe, as there were no complications following cell administration. Partial improvement in the ASIA score and partial recovery of MEP or SEP have been observed in all subacute patients who received cells via a. vertebralis (n=4) and in one out of four subacute patients who received cells intravenously. Improvement was also found in one chronic patient who received cells via a. vertebralis. A much larger population of patients is needed before any conclusions can be drawn. The implantation of hydrogels into hemisected rat spinal cords showed that cellular ingrowth was most pronounced in copolymers of HEMA with a positive surface electric charge. Although most of the cells had the morphological properties of connective tissue elements, we found NF-160-positive axons invading all the implanted hydrogels from both the proximal and distal stumps. The biodegradable hydrogels degraded from the border that was in direct contact with the spinal cord tissue. They were resorbed by macrophages and replaced by newly formed tissue containing connective tissue elements, blood vessels, GFAP-positive astrocytic processes, and NF-160-positive neurofilaments. Additionally, we implanted hydrogels seeded with nanoparticle-labeled MSCs into hemisected rat spinal cords. Hydrogels seeded with MSCs were visible on MR images as hypointense areas, and subsequent Prussian blue histological staining confirmed positively stained cells within the hydrogels. 4. We conclude that treatment with different bone marrow cell populations had a positive effect on behavioral outcome and histopathological assessment after SCI in rats; this positive effect was most pronounced following MSC treatment. Our clinical study suggests a possible positive effect in patients with SCI. Bridging the lesion cavity can be an approach for further improving regeneration. Our preclinical studies showed that macroporous polymer hydrogels based on derivatives of HEMA or HPMA are suitable materials for bridging cavities after SCI; their chemical and physical properties can be modified to a specific use, and 3D implants seeded with different cell types may facilitate the ingrowth of axons.

Treatment of complete spinal cord injury patients by autologous bone marrow cell transplantation and administration of granulocyte-macrophage colony stimulating factor

Transplantation of bone marrow cells into the injured spinal cord has been found to improve neurologic functions in experimental animal studies. However, it is unclear whether bone marrow cells can similarly improve the neurologic functions of complete spinal cord injury (SCI) in human patients. To address this issue, we evaluated the therapeutic effects of autologous bone marrow cell transplantation (BMT) in conjunction with the administration of granulocyte macrophage-colony stimulating factor (GM-CSF) in six complete SCI patients. BMT in the injury site (1.1 x 10(6) cells/microL in a total of 1.8 mL) and subcutaneous GM-CSF administration were performed on five patients. One patient was treated with GM-CSF only. The follow-up periods were from 6 to 18 months, depending on the patients. Sensory improvements were noted immediately after the operations. Sensory recovery in the sacral segment was noted mainly 3 weeks to 7 months postoperatively. Significant motor improvements were noted 3 to 7 months postoperatively. Four patients showed neurologic improvements in their American Spiral Injury Association Impairment Scale (AIS) grades (from A to C). One patient improved to AIS grade B from A and the last patient remained in AIS grade A. No immediate worsening of neurologic symptoms was found. Side effects of GMCSF treatment such as a fever (>38 degrees C) and myalgia were noted. Serious complications increasing mortality and morbidity were not found. The follow-up study with magnetic resonance imaging 4-6 months after injury showed slight enhancement within the zone of BMT. Syrinx formation was not definitely found. BMT and GM-CSF administration represent a safe protocol to efficiently manage SCI patients, especially those with acute complete injury. To demonstrate the full therapeutic value of this protocol, long-term and more comprehensive case-control clinical studies are required.

Congenital amegakaryocytic thrombocytopenia: a retrospective clinical analysis of 20 patients

Congenital amegakaryocytic thrombocytopenia (CAMT) is a rare bone marrow failure syndrome characterised by isolated thrombocytopenia because of ineffective megakaryocytopoiesis at birth. In the last 10 years, we collected data from 20 patients diagnosed with CAMT based on a severe thrombocytopenia since birth and absent or markedly decreased numbers of megakaryocytes in the bone marrow. Fanconi's anaemia and thrombocytopenia absent radii syndrome were ruled out for all patients. We retrospectively compared the clinical courses, laboratory findings and treatment outcome. Development of pancytopenia was observed in 14 of the patients, only one patient presented with an isolated thrombocytopenia over a period of over 14 years. One boy died from bleeding complications. We defined two groups of patients according to the course of platelet counts during the first year of life, which also differed in the course of development of pancytopenia. Physical anomalies in addition to haematopoiesis were found in a number of patients: two children presented with cardiac defects, six with growth abnormalities, and four with retardation of psychomotor development. Fifteen patients were treated with haematopoietic stem cell transplantation, four of whom died of transplantation-related events.

Patterns of protein expression in infectious meningitis: a cerebrospinal fluid protein array analysis

Seventy-nine cytokines, chemokines, and growth factors were measured by protein array analysis in the cerebrospinal fluid of patients with meningitis and controls. Several factors were found to be regulated, which have not been studied in the CNS before, e.g., macrophage inflammatory protein-1delta (CCL15) and neutrophil-activating peptide-2 (CXCL7). In pneumococcal meningitis, other new observations were an increase of macrophage migration inhibitory factor, monocyte chemoattractant protein-2 (CCL8), pulmonary and activation-regulated chemokine (CCL18), and macrophage inflammatory protein-3alpha (CCL20), and a sustained upregulation of several growth factors. In viral meningitis, new findings were an elevation of CCL8, thrombopoietin, and vascular endothelial growth factor.

Thrombopoietin in the Cerebrospinal Fluid of Patients with Aseptic and Bacterial Meningitis

Despite the recent evidence of the localization of thrombopoietin (TPO) and its receptor in the central nervous system (CNS), TPO protein concentrations in the cerebrospinal fluid (CSF) remained to be clarified. We previously reported that serum TPO is increased in children with meningitis. To determine changes in TPO concentrations in the CSF by meningitis and to explore the relationship between serum and CSF TPO concentrations, we measured TPO concentrations in 110 CSF samples and 33 serum/CSF pairs from 11 bacterial meningitis, 49 aseptic meningitis, and 50 nonmeningitis children. In only 12% (13 of 110) of CSF samples (0 bacterial meningitis, 8 aseptic meningitis, and 5 controls), TPO concentrations could be determined (24.1 +/- 29.0 pg/ml). CSF TPO concentrations did not significantly differ among the three groups and did not correlate with age. TPO concentrations in all serum samples were detectable, and mean concentrations in bacterial meningitis (510.6 +/- 237.0 pg/ml) were significantly higher than those in aseptic meningitis (136.6 +/- 71.6, p < 0.01) and controls (181.3 +/- 88.3, p < 0.01). These findings suggest that TPO is not produced in the CNS of patients with meningitis and that TPO did not cross the blood-brain barrier even during meningeal infection.

A hematopoietic growth factor, thrombopoietin, has a proapoptotic role in the brain

Central nervous and hematopoietic systems share developmental features. We report that thrombopoietin (TPO), a stimulator of platelet formation, acts in the brain as a counterpart of erythropoietin (EPO), a hematopoietic growth factor with neuroprotective properties. TPO is most prominent in postnatal brain, whereas EPO is abundant in embryonic brain and decreases postnatally. Upon hypoxia, EPO and its receptor are rapidly reexpressed, whereas neuronal TPO and its receptor are down-regulated. Unexpectedly, TPO is strongly proapoptotic in the brain, causing death of newly generated neurons through the Ras-extracellular signal-regulated kinase 1/2 pathway. This effect is not only inhibited by EPO but also by neurotrophins. We suggest that the proapoptotic function of TPO helps to select for neurons that have acquired target-derived neurotrophic support.