Neural precursors and neuronal production in the adult mammalian forebrain

Regionally specified human neural progenitor cells derived from the mesencephalon and forebrain undergo increased neurogenesis following overexpression of ASCL1

Human neural progenitor cells (hNPC) derived from the developing brain can be expanded in culture and subsequently differentiated into neurons and glia. They provide an interesting source of tissue for both modeling brain development and developing future cellular replacement therapies. It is becoming clear that hNPC are regionally and temporally specified depending on which brain region they were isolated from and its developmental stage. We show here that hNPC derived from the developing cortex (hNPC(CTX)) and ventral midbrain (hNPC(VM)) have similar morphological characteristics and express the progenitor cell marker nestin. However, hNPC(CTX) cultures were highly proliferative and produced large numbers of neurons, whereas hNPC(VM) divided slowly and produced fewer neurons but more astrocytes. Microarray analysis revealed a similar expression pattern for some stemness markers between the two growing cultures, overlaid with a regionally specific profile that identified some important differentially expressed neurogenic transcription factors. By overexpressing one of these, the transcription factor ASCL1, we were able to regain neurogenesis from hNPC(VM) cultures, which produced larger neurons with more neurites than hNPC(CTX) but no fully mature dopamine neurons. Thus, hNPC are regionally specified and can be induced to undergo neurogenesis following genetic manipulation. Although this restores neuronal production with a region-specific phenotype, it does not restore full neurochemical maturation, which may require additional factors.

Golli myelin basic proteins regulate oligodendroglial progenitor cell migration through voltage-gated Ca2+ influx

Migration of oligodendrocyte progenitor cells (OPCs) from proliferative zones to their final location in the brain is an essential step in nervous system development. Golli proteins, products of the myelin basic protein gene, can modulate voltage-gated Ca(2+) uptake in OPCs during process extension and retraction. Given the importance of process extension/retraction on movement, the consequences of golli expression on OPC migration were examined in vivo and in vitro using time-lapse imaging of isolated OPCs and acute brain slice preparations from golli KO and golli J37 overexpressing mice (JOE). The results indicated that golli stimulated migration, and this enhanced motility was associated with increases in the activity of voltage operated Ca(2+) channels (VOCCs). Activation of VOCCs by high K(+) resulted in a significant increase in the migration speed of JOE OPCs versus control cells and golli-mediated modulation of OPC migration disappeared in the presence of VOCC antagonists. During migration, OPCs generated Ca(2+) oscillations that were dependent on voltage-calcium influx and both the amplitude and frequency of these Ca(2+) transients correlated positively with the rate of cell movement under a variety of pharmacological treatments. The Ca(2+) transient amplitude and the rate of cell movement were significantly lower in KO cells and significantly higher in JOE cells suggesting that the presence of golli promotes OPC migration by increasing the size of voltage-mediated Ca(2+) oscillations. These data define a new molecule that regulates Ca(2+) homeostasis in OPCs, and are the first to demonstrate that voltage-gated Ca(2+) channels can regulate an OPC function, such as migration.

Role of Endogenous Neural Stem Cells in Neurological Disease and Brain Repair

These examples show that stem-cell-based therapy of neuro-psychiatric disorders will not follow a single scheme, but rather include widely different approaches. This is in accordance with the notion that the impact of stem cell biology on neurology will be fundamental, providing a shift in perspective, rather than introducing just one novel therapeutic tool. Stem cell biology, much like genomics and proteomics, offers a "view from within" with an emphasis on a theoretical or real potential and thereby the inherent openness, which is central to the concept of stem cells. Thus, stem cell biology influences many other, more traditional therapeutic approaches, rather than introducing one distinct novel form of therapy. Substantial advances have been made i n neural stemcell research during the years. With the identification of stem and progenitor cells in the adult brain and the complex interaction of different stem cell compartments in the CNS--both, under physiological and pathological conditions--new questions arise: What is the lineage relationship between t he different progenitor cells in the CNS and how much lineage plasticity exists? What are the signals controlling proliferation and differentiation of neural stem cells and can these be utilized to allow repair of the CNS? Insights in these questions will help to better understand the role of stem cells during development and aging and the possible relation of impaired or disrupted stem cell function and their impact on both the development and treatment of neurological disease. A number o f studies have indicated a limited neuronal and glial regeneration certain pathological conditions. These fundamental observations have already changed our view on understanding neurological disease and the brain's capacity for endogenous repair. The following years will have to show how we can influence andmodulate endogenous repair nisms by increasing the cellular plasticity in the young and aged CNS.

Development of a tissue-engineered composite implant for treating traumatic paraplegia in rats

This study was designed to assess a new composite implant to induce regeneration of injured spinal cord in paraplegic rats following complete cord transection. Neuronal xenogeneic cells from biopsies of adult nasal olfactory mucosa (NOM) of human origin, or spinal cords of human embryos, were cultured in two consecutive stages: stationary cultures in a viscous semi-solid gel (NVR-N-Gel) and in suspension on positively charged microcarriers (MCs). A tissue-engineered tubular scaffold, containing bundles of parallel nanofibers, was developed. Both the tube and the nanofibers were made of a biodegradable dextran sulphate-gelatin co-precipitate. The suturable scaffold anchored the implant at the site of injury and provided guidance for the regenerating axons. Implants of adult human NOM cells were implanted into eight rats, from which a 4 mm segment of the spinal cord had been completely removed. Another four rats whose spinal cords had also been transected were implanted with a composite implant of cultured human embryonic spinal cord cells. Eight other cord-transected rats served as a control group. Physiological and behavioral analysis, performed 3 months after implantation, revealed partial recovery of function in one or two limbs in three out of eight animals of the NOM implanted group and in all the four rats that were implanted with cultured human embryonic spinal cord cells. Animals of the control group remained completely paralyzed and did not show transmission of stimuli to the brain. The utilization of an innovative composite implant to bridge a gap resulting from the transection and removal of a 4 mm spinal cord segment shows promise, suggesting the feasibility of this approach for partial reconstruction of spinal cord lesions. Such an implant may serve as a vital bridging station in acute and chronic cases of paraplegia.

BrdU-, neuroD (nrd)- and Hu-studies reveal unusual non-ventricular neurogenesis in the postembryonic zebrafish forebrain

In the postembryonic zebrafish forebrain, subpial locations of neurogenesis do exist in the early cerebellar external granular layer, and--unusually among vertebrates--in the primordial pretectal (M1) and preglomerular (M2) Anlagen as shown here with 5-bromo-2'-deoxyuridine (BrdU)/Hu-immunocytochemistry and in situ hybridization of neuroD. An intermediate BrdU incubation time of 12-16 h reveals in addition to proliferative ventricularly located cells those in M1 and M2. This BrdU saturation-labeling shows--in conjunction with a Hu-assay demonstrating earliest neuronal differentiation--that proliferating cells in M1 and M2 represent neuronal progenitors. This is demonstrated by single BrdU-labeled and double BrdU-/Hu-labeled cells in these aggregates. Further, expression of NeuroD--a marker for freshly determined neuronal cells--confirms this unusual subpial postembryonic forebrain neurogenesis.

Adenoviral brain-derived neurotrophic factor induces both neostriatal and olfactory neuronal recruitment from endogenous progenitor cells in the adult forebrain

Neural progenitor cells persist throughout the adult forebrain subependyma, and neurons generated from them respond to brain-derived neurotrophic factor (BDNF) with enhanced maturation and survival. To induce neurogenesis from endogenous progenitors, we overexpressed BDNF in the adult ventricular zone by transducing the forebrain ependyma to constitutively express BDNF. We constructed a bicistronic adenovirus bearing BDNF under cytomegalovirus (CMV) control, and humanized green fluorescent protein (hGFP) under internal ribosomal entry site (IRES) control. This AdCMV:BDNF:IRES:hGFP (AdBDNF) was injected into the lateral ventricles of adult rats, who were treated for 18 d thereafter with the mitotic marker bromodeoxyuridine (BrdU). Three weeks after injection, BDNF averaged 1 microg/gm in the CSF of AdBDNF-injected animals but was undetectable in control CSF. In situ hybridization demonstrated BDNF and GFP mRNA expression restricted to the ventricular wall. In AdBDNF-injected rats, the olfactory bulb exhibited a >2.4-fold increase in the number of BrdU(+)-betaIII-tubulin(+) neurons, confirmed by confocal imaging, relative to AdNull (AdCMV:hGFP) controls. Importantly, AdBDNF-associated neuronal recruitment to the neostriatum was also noted, with the treatment-induced addition of BrdU(+)-NeuN(+)-betaIII-tubulin(+) neurons to the caudate putamen. Many of these cells also expressed glutamic acid decarboxylase, cabindin-D28, and DARPP-32 (dopamine and cAMP-regulated phosphoprotein of 32 kDa), markers of medium spiny neurons of the neostriatum. These newly generated neurons survived at least 5-8 weeks after viral induction. Thus, a single injection of adenoviral BDNF substantially augmented the recruitment of new neurons into both neurogenic and non-neurogenic sites in the adult rat brain. The intraventricular delivery of, and ependymal infection by, viral vectors encoding neurotrophic agents may be a feasible strategy for inducing neurogenesis from resident progenitor cells in the adult brain.

Identification, isolation, and promoter-defined separation of mitotic oligodendrocyte progenitor cells from the adult human subcortical white matter

Previous studies have suggested the persistence of oligodendrocyte progenitor cells in the adult mammalian subcortical white matter. To identify oligodendrocyte progenitors in the adult human subcortical white matter, we transfected dissociates of capsular white matter with plasmid DNA bearing the gene for green fluorescence protein (hGFP), placed under the control of the human early promoter (P2) for the oligodendrocytic protein cyclic nucleotide phosphodiesterase (P/hCNP2). Within 4 d after transfection with P/hCNP2:hGFP, a discrete population of small, bipolar cells were noted to express GFP. These cells were A2B5-positive (A2B5(+)), incorporated bromodeoxyuridine in vitro, and constituted <0.5% of all cells. Using fluorescence-activated cell sorting (FACS), the P/hCNP2-driven GFP(+) cells were then isolated and enriched to near-purity. In the weeks after FACS, most P/hCNP2:hGFP-sorted cells matured as morphologically and antigenically characteristic oligodendrocytes. Thus, the human subcortical white matter harbors mitotically competent progenitor cells, which give rise primarily to oligodendrocytes in vitro. By using fluorescent transgenes of GFP expressed under the control of an early oligodendrocytic promoter, these oligodendrocyte progenitor cells may be extracted and purified from adult human white matter in sufficient numbers for implantation and cell-based therapy.