Neuron-oligodendroglial interactions during central nervous system development

It is well established that a variety of growth factors influence the differentiation of oligodendroglial lineage cells in culture, although little information is available concerning the role and source of these factors in vivo. Developing oligodendroglia are almost constantly in a neuronal environment and would be expected to respond to a variety of signals from neurons that affect their survival, migration, division, maturation and myelin production. However, very little is known about the specific interactions that occur between these two cell types. Here we review the experimental evidence for the influence of neurons on oligodendroglial differentiation, including studies on the effects of both soluble factors and contact dependent events. We also propose a scheme for the control of myelinogenesis via both internal and external signals. © 1993 Wiley-Liss, Inc.     

T cells and erythroid burst forming units in chronic lymphocytic leukemia

Substantial evidence exists indicating T cell abnormalities in chronic lymphocytic leukemia (CLL). There is also evidence that the T cell is an important source of burst promoting activity (BPA) for the peripheral blood (PB) erythroid burst forming unit (BFU-e). We studied the BPA of T cells and response of BFU-e in normals and untreated early stage B cell CLL patients in a methylcellulose colony assay. Normal null cell cultures grew significantly more BFU-e than CLL null cell cultures. Addition of autologous T cells to normal or CLL null cells significantly increased BFU-e only in normals. Allogeneic coculture of T cells from CLL patients with null cells from normals yielded normal responses of BFU-e in five of six cases. In contrast, allogeneic coculture of normal T cells with CLL null cells yielded a normal response in only one of six studies. Furthermore, adding increasing quantities of autologous or normal allogeneic T cells to CLL null cells did not augment the BFU-e response. Accounting for the expanded lymphocyte pool in CLL, BFU-e are decreased in concentration but the absolute number is normal or increased. The decrease in concentration could be secondary to expansion of the null cell fraction in CLL by pre-B cells. CLL T cells appeared to augment normal allogeneic PB BFU-e in a normal fashion, whereas, in several cases, CLL BFU-e were hyporesponsive to autologous or normal allogeneic T cells. It is therefore apparent that in untreated early stage B cell CLL, erythroid progenitor cells are present in the peripheral blood but are diluted in an expanded null cell compartment and may, in some cases, be hyporesponsive to T cell BPA. T cell BPA of CLL T cells in this early stage of disease is preserved.     

Effects of dexamethasone on fetal hemoglobin synthesis in peripheral blood erythroid burst-forming units

Colonies derived from erythroid burst-forming units (BFU-E) synthesize fetal hemoglobin (HbF) in amounts that far exceed in vivo levels. There is some evidence that HbF synthesis is controlled at the level of a primitive erythroid precursor cell. Dexamethasone may potentiate the development of BFU-E. Since a means of augmenting HbF production in sickle cell anemia or severe β-thalassemia would be of great therapeutic value, we studied the effects of dexamethasone on HbF and γ-globin chain synthesis in BFU-E from patients with sickle cell anemia and controls. HbF was measured by radioimmunoassay of BFU-E lysate and γ-chain synthesis by the incorporation of ³H-leucine into globin, which was then purified by gel filtration and column chromatography. Dexamethasone (10^?9 M) produced an increase in the number of BFU-E in 16 of 19 subjects when compared with numbers of BFU-E cultured with only erythropoietin. The individual BFU-E were larger and contained more subcolonies. Dexamethasone did not increase HbF or γ-chain synthesis, and there was no relationship between increased proliferation of BFU-E and augmented HbF production. Thus, although dexamethasone augmented the development of erythroid bursts, there was no increment in HbF.     

Isozyme patterns in erythrocytes from human fetuses

Starch gel electrophoretic patterns of 26 enzymes (corresponding to 36 gene loci) were examined in hemolysates of erythrocytes from 11 first-trimester and midtrimester human fetuses (65-138 gestation days). The zymograms of 16 enzymes were identical in fetal and control adult red cells. Six enzymes (enolase, guanylate kinase, lactate dehydrogenase, nucleoside Phosphorylase, phosphofructokinase, hexokinase) showed differences in the staining intensity of certain isozyme zones as compared with the controls. Also, the fetal red cell zymograms, in contrast to those of adults, contained the mitochondrial forms of isocitric dehydrogenase and glutamic oxaloacetic transaminase as well as more definite zones of phosphoglucomutase-3. Finally, some of the isozymes of uridine diphosphate kinase in the fetal cells had slightly retarded mobility. These observed differences between fetal and adult red cells could reflect the expression of a different program of protein synthesis in red cells of the fetuses or the epigenetic modifications of isozymes in immature red cells.     

Oxidative damage and defective DNA repair is linked to apoptosis of migrating neurons and progenitors during cerebral cortex development in Ku70-deficient mice

DNA repair plays a critical, but imprecisely defined role in neuronal survival during cortical neurogenesis. We examined cortical development in mice deficient for the DNA end-joining protein, Ku70. At gestational day 14.5, corresponding to the peak of neurogenesis, the Ku70(-/-) embryonic cerebral cortex displayed 25- to 30-fold more cell death than heterozygous littermates, as judged by DNA breaks, pyknosis and active caspase-3. In Ku70(-/-) embryos only, large clusters of dying neurons were found in the intermediate zone. Cell death declined until P4, when the number of dying cells became comparable to that in heterozygous mice. Two groups of dying cells were evident: a GLAST(+) neural progenitor population in the subventricular and ventricular zones, and a doublecortin(+) immature neuron population in the intermediate zone, the latter exhibiting strong staining for oxidative DNA damage. Antioxidants and lower oxygen tension reduced the high levels of neuronal death in primary cortical cultures derived from Ku70(-/-) mice, but not the low levels of cell death in wildtype cortical cultures. Results indicate migrating cortical neurons undergo oxidative DNA damage, which is normally repaired by non-homologous end joining. Failure to repair oxidative damage triggers a form of apoptosis involving caspase-3 activation.     

Repopulation of oligodendrocyte progenitor cell depleted tissue in a model of chronic demyelination

Some, but not all chronically demyelinated MS lesions are depleted of oligodendrocyte progenitor cells (OPCs) suggesting that OPCs are destroyed during the process of demyelination and some factor impedes OPC repopulation of the depleted tissue. The chronically demyelinated axons in MS lie in an astrocytic environment and it has been proposed that this might impede entry of OPCs into such regions. By depleting a short length of spinal cord of its OPCs using 40 Gy of X-irradiation in both normal rats and rats with progressive myelin loss accompanied by an astrocytosis (taiep rats), we investigated whether such changes affect the ability of OPCs to repopulate OPC-depleted tissue. In both taiep and normal rats, the rate of repopulation decreases with age, but no difference was detected in the rate at which OPCs repopulated normally myelinated and chronically demyelinated and astrocytosed tissue. This indicates that, if the astrocytic environment of the taiep CNS is comparable to that found in MS lesions, then the presence of chronically demyelinated axons and astrocytosis in chronic MS lesions does not represent a barrier to repopulation of the tissue by OPCs. However, similar to the situation in the normal adult rodent CNS, the rate of repopulation by endogenous OPCs in aged taiep rats is very slow, approximately 0.2 mm per week.     

Regeneration of granule neurons after lesioning of hippocampal dentate gyrus: evaluation using adult mice treated with trimethyltin chloride as a model

The hippocampal dentate gyrus in adult animals is known to contain neural progenitors that proliferate and differentiate into neurons in response to brain injury. Little has been observed, however, on regeneration of the granule cell layer of the dentate gyrus that has been directly injured. Using trimethyltin (TMT)-treated mice as an in vivo model, we evaluated the ability of this layer to regenerate after injury. The administration of TMT induced neuronal death in the dentate gyrus selectively 2 days later, with recovery of granule neurons on day 14 and thereafter. At an early stage (days 2-5) after the damage by TMT treatment, 5-bromo-2'-deoxyuridine (BrdU) incorporation into at least two different types of cells was facilitated in the dentate gyrus: BrdU-positive/neuronal nuclear antigen (NeuN)-negative cells were found predominantly in the subgranular zone and granule cell layer, whereas BrdU-positive/NeuN-positive cells were numerous in the dentate molecular layer and hilus. In addition, expression of proliferating cell nuclear antigen, nestin, NeuroD3, and doublecortin, which are markers for proliferating cells and neural progenitors/neuronal precursors, was extremely enhanced in the dentate gyrus at the early stage after treatment. Double staining revealed that BrdU was colocalized with nestin and doublecortin in the subgranular zone. Behavioral analysis revealed that TMT-induced cognition impairment was ameliorated by day 14 after the treatment. Taken together, our data indicate that the hippocampal dentate gyrus itself is capable of regenerating the neuronal cell layer through rapid enhancement of neurogenesis after injury.     

Hormonal and sensory inputs regulate distinct neuroblast cell cycle properties in adult cricket brain

From invertebrates to humans, it has been demonstrated that new neurons are added to specific brain structures throughout adult life. In the house cricket, adult neurogenesis occurs in the mushroom bodies, the main sensory integrative center of the brain, often considered an analogue of vertebrate hippocampus. We have previously shown that this neurogenesis can be modulated by hormones through the polyamine pathway and by environmental conditions through sensory inputs and the nitric oxide pathway. Environment-induced neurogenesis is independent of juvenile hormone levels, so we addressed the roles of sensory inputs and hormones in the control of neuroblast proliferation. Here, by using double labelling of cells specifically in S phase (5-bromo-2'-deoxyuridine) together with labelling of mitotically active cells in any phase (proliferating cell nuclear antigen), we show that juvenile hormone acts on progenitor cell proliferation by inducing quiescent neuroblasts to enter the cell cycle, whereas sensory inputs act by shortening the cell cycle. Thus, in the adult house cricket, regulation of neuroblast proliferation by hormonal and environmental cues occurs through two independent modes of action.     

Human adult olfactory neural progenitors rescue axotomized rodent rubrospinal neurons and promote functional recovery

Previously, our lab reported the isolation of patient-specific neurosphere-forming progenitor lines from human adult olfactory epithelium from cadavers as well as patients undergoing nasal sinus surgery. RT-PCR and ELISA demonstrated that the neurosphere-forming cells (NSFCs) produced BDNF. Since rubrospinal tract (RST) neurons have been shown to respond to exogenous BNDF, it was hypothesized that if the NSFCs remained viable following engraftment into traumatized spinal cord, they would rescue axotomized RS neurons from retrograde cell atrophy and promote functional recovery. One week after a partial cervical hemisection, GFP-labeled NSFCs suspended in Matrigel matrix or Matrigel matrix alone was injected into the lesion site. GFP-labeled cells survived up to 12 weeks in the lesion cavity or migrated within the ipsilateral white matter; the apparent number and mean somal area of fluorogold (FG)-labeled axotomized RST neurons were greater in the NSFC-engrafted rats than in lesion controls. Twelve weeks after engraftment, retrograde tracing with FG revealed that some RST neurons regenerated axons 4-5 segments caudal to the engraftment site; anterograde tracing with biotinylated dextran amine confirmed regeneration of RST axons through the transplants within the white matter for 3-6 segments caudal to the grafts. A few RST axons terminated in gray matter close to motoneurons. Matrix alone did not elicit regeneration. Behavioral analysis revealed that NSFC-engrafted rats displayed better performance during spontaneous vertical exploration and horizontal rope walking than lesion Matrigel only controls 11 weeks post transplantation. These results emphasize the unique potential of human olfactory neuroepithelial-derived progenitors as an autologous source of stem cells for spinal cord repair.     

Endogenous erythroid colony assay in patients with polycythemia vera and its clinical significance

Background Polycythemia vera (PV) is a malignant disorder of hemaopoietic stem cells which is characterized by clonal hyperproliferation and a low rate of apoptosis. This study was to assess endogenous erythroid colony (EEC) formation in the bone marrow of PV patients and determine its clinical significance.Methods The bone marrow mononuclear cells of 26 patients with PV, 2 patients with secondary erythrocytosis (SE), and 19 normal controls were cultured by Marsh‘ s method for EEC evaluation,and the clinical significance was evaluated.Results EECs appeared in 25 patients with PV but not in 2 patients with SE and 19 normal controls.The number of EECs and the EEC ratio [ EEC/erythropoietin ( EPO)-dependent colony forming uniterythroid (CFU-E)] in PV patients positively correlated with hemoglobin (Hb) levels. Their EEC number did not correlate with white blood cell (WBC) counts, platelet (PLT) counts, or leukocyte alkaline phosphatase (LAP) scores. Their EEC did not correlate with serum EPO levels. Fifteen patients with PV were treated with hydroxyurea ( Hu ) and/or interferon-alpha (IFN-α). Their EEC ratio before treatment positively correlated with the treatment time required for complete remission (CR) and negatively correlated with the time before relapse. The EEC numbers of 7 PV patients treated with Hu/IFN-α decreased after the blood cell counts dropped to normal levels. There was a positive correlation between the EEC ratio and the incidence of attacks of vascular thrombosis in PV patients. The numbers of apoptosised bone marrow mononuclear cells in PV patients were lower than those in normal controls. The EEC numbers of PV patients negatively correlated with the rate of apoptosis of bone marrow mononuclear cells.Conclusions EEC formation is characteristic in PV patients. EEC number in PV patients positively correlates with Hb levels, the time required for CR, and the incidence of attacks of vascular thrombosis. EEC number negatively correlates with the time before relapse. Bone marrow suppressive treatment might decrease EEC number. Thus, EEC number is a sensitive and specific parameter reflecting the abnormal hematopoietic clone burden induced by polycythemia vera. EEC number is an important diagnostic parameter for PV patients.