Feasibility of Human Neural Stem Cell Transplantation for the Treatment of Acute Subdural Hematoma in a Rat Model: A Pilot Study

Human neural stem cells (hNSCs) transplantation in several brain injury models has established their therapeutic potential. However, the feasibility of hNSCs transplantation is still not clear for acute subdural hematoma (ASDH) brain injury that needs external decompression. Thus, the aim of this pilot study was to test feasibility using a rat ASDH decompression model with two clinically relevant transplantation methods. Two different methods, in situ stereotactic injection and hNSC-embedded matrix seating on the brain surface, were attempted. Athymic rats were randomized to uninjured or ASDH groups (F344/NJcl-rnu/rnu, n = 7-10/group). Animals in injury group were subjected to ASDH, and received decompressive craniectomy and 1-week after decompression surgery were transplanted with green fluorescent protein (GFP)-transduced hNSCs using one of two approaches. Histopathological examinations at 4 and 8 weeks showed that the GFP-positive hNSCs survived in injured brain tissue, extended neurite-like projections resembling neural dendrites. The in situ transplantation group had greater engraftment of hNSCs than matrix embedding approach. Immunohistochemistry with doublecortin, NeuN, and GFAP at 8 weeks after transplantation showed that transplanted hNSCs remained as immature neurons and did not differentiate toward to glial cell lines. Motor function was assessed with rotarod, compared to control group (n = 10). The latency to fall from the rotarod in hNSC in situ transplanted rats was significantly higher than in control rats (median, 113 s in hNSC vs. 69 s in control, P = 0.02). This study first demonstrates the robust engraftment of in situ transplanted hNSCs in a clinically-relevant ASDH decompression rat model. Further preclinical studies with longer study duration are warranted to verify the effectiveness of hNSC transplantation in amelioration of TBI induced deficits.

Sequential actions of BMP receptors control neural precursor cell production and fate

Bone morphogenetic proteins (BMPs) have diverse and sometimes paradoxical effects during embryonic development. To determine the mechanisms underlying BMP actions, we analyzed the expression and function of two BMP receptors, BMPR-IA and BMPR-IB, in neural precursor cells in vitro and in vivo. Neural precursor cells always express Bmpr-1a, but Bmpr-1b is not expressed until embryonic day 9 and is restricted to the dorsal neural tube surrounding the source of BMP ligands. BMPR-IA activation induces (and Sonic hedgehog prevents) expression of Bmpr-1b along with dorsal identity genes in precursor cells and promotes their proliferation. When BMPR-IB is activated, it limits precursor cell numbers by causing mitotic arrest. This results in apoptosis in early gestation embryos and terminal differentiation in mid-gestation embryos. Thus, BMP actions are first inducing (through BMPR-IA) and then terminating (through BMPR-IB), based on the accumulation of BMPR-IB relative to BMPR-IA. We describe a feed-forward mechanism to explain how the sequential actions of these receptors control the production and fate of dorsal precursor cells from neural stem cells.

Regulation of neurogenesis by growth factors and neurotransmitters

The generation of neurons and glia in the developing nervous system is likely to be regulated by extrinsic factors, including growth factors and neurotransmitters. Evidence from in vivo and/or in vitro systems indicates that basic fibroblast growth factor, transforming growth factor (TGF)-alpha, insulin-like growth factor-1, and the monoamine neurotransmitters act to increase proliferation of neural precursors. Conversely, glutamate, gamma-aminobutyric acid, and opioid peptides are likely to play a role in down-regulating proliferation in the developing nervous system. Several other factors, including the neuropeptides vasoactive intestinal peptide and pituitary adenylate cyclase-activating peptide, as well as the growth factors platelet-derived growth factor, ciliary neurotrophic factor, and members of the TGF-beta family, have different effects on proliferation and differentiation depending on the system examined. Expression of many of these factors and their receptors in germinal regions of the central nervous system suggests that they can act directly on precursor populations to control their proliferation. Together, the findings discussed here indicate that proliferation and cell fate determination in the developing brain are regulated extrinsically by complex interactions between a relatively large number of growth factors and neurotransmitters.

Single factors direct the differentiation of stem cells from the fetal and adult central nervous system

Identifying the signals that regulate stem cell differentiation is fundamental to understanding cellular diversity in the brain. In this paper we identify factors that act in an instructive fashion to direct the differentiation of multipotential stem cells derived from the embryonic central nervous system (CNS). CNS stem cell clones differentiate to multiple fates: neurons, astrocytes, and oligodendrocytes. The differentiation of cells in a clone is influenced by extracellular signals: Platelet-derived growth factor (PDGF-AA, -AB, and -BB) supports neuronal differentiation. In contrast, ciliary neurotrophic factor and thyroid hormone T3 act instructively on stem cells to generate clones of astrocytes and oligodendrocytes, respectively. Adult stem cells had remarkably similar responses to these growth factors. These results support a simple model in which transient exposure to extrinsic factors acting through known pathways initiates fate decisions by multipotential CNS stem cells.

Functions of basic fibroblast growth factor and neurotrophins in the differentiation of hippocampal neurons

Restrictions in neuronal fate occur during the transition from a multipotential to a postmitotic cell. This and later steps in neuronal differentiation are determined by extracellular signals. We report that basic fibroblast growth factor is mitogenic for stem cells and is a differentiation factor for calbindin-expressing hippocampal neurons. The neurotrophin NT-3 is a differentiation factor for the same neurons but does not affect proliferation. NT-3 and brain-derived neurotrophic factor promote the maturation of neurons derived from stem cells that have been grown in vitro. These results define functions for basic fibroblast growth factor and neurotrophins in the differentiation processes that direct a multipotential stem cell to a specific neuronal fate.

Functional domains and phosphorylation of the orphan receptor Nur77

Nur77 represents a unique class within the steroid receptor superfamily since its synthesis is tightly regulated by extracellular signals and it is capable of potent transactivation activity in the absence of an exogenously added ligand. In this study, we sought to dissect the functional domains regulating the activities of Nur77 by deletion mapping. We demonstrate that whereas the transactivation activity of Nur77 resides in the amino-terminal domain, the carboxy-terminal domain regulates this activity. A short deletion from the carboxy terminus eliminates transactivation activity while a further deletion restores the activity. Deletion of the domain immediately carboxyl to the zinc fingers motif eliminates both DNA binding activity and nuclear localization, thus abolishing transactivation. Nur77 is posttranslationally modified predominantly by phosphorylation, which occurs primarily at the N-terminal domain. The growth-related kinase pp90rsk, but neither the pp44mapk nor the pp70s6k, can phosphorylate recombinant Nur77 in vitro. Furthermore, we have identified a site within the region required for sequence-specific DNA binding, Ser-354, that is phosphorylated by pp90rsk in vitro; this site is also phosphorylated in vivo. The possibility that phosphorylation might affect DNA binding is discussed.

RNR-1, a nuclear receptor in the NGFI-B/Nur77 family that is rapidly induced in regenerating liver

Liver regeneration following partial hepatectomy provides one of the few systems for analysis of mitogenesis in the fully developed, intact animal. Immediate-early growth response genes, induced in the absence of prior protein synthesis, play an important regulatory role in the regenerative process. During screening of a subtracted cDNA library of immediate-early genes induced during liver regeneration, a novel member of the thyroid/steroid receptor superfamily, RNR-1 (regenerating liver nuclear receptor), was identified. This gene is not expressed in quiescent liver but is rapidly induced following partial hepatectomy and is specific to hepatic growth as it is not induced in other mitogen-treated cells. RNR-1 is also expressed in brain. A full-length cDNA clone of RNR-1 encodes a 66-kDa, 597-amino acid protein as verified by in vitro translation in reticulocyte lysate. RNR-1 is highly homologous to r-NGFI-B/m-Nur77 particularly in the DNA binding (94%) and putative ligand binding (59%) domains. Using a mobility shift assay, we have shown that RNR-1 specifically binds to the NGFI-B DNA half-site and forms a complex very similar in size to the Nur77 complex, suggesting that RNR-1 also may bind as a monomer. Consistent with this finding, the A box region important in mediating half-site binding is 100% conserved between r-NGFI-B/m-Nur77. Both RNR-1 and Nur77 strongly transactivate a reporter driven by a consensus r-NGFI-B/Nur77 binding site, and their effect together is additive. As both the RNR-1 and r-NGFI/m-nur77 genes are induced during liver regeneration, it is very possible that RNR-1 acts concomitantly with r-NGFI/m-Nur77 in regulating the expression of delayed-early genes during liver regeneration.

Transcriptional activation by Nur77, a growth factor-inducible member of the steroid hormone receptor superfamily

nur77 is a growth factor-inducible immediate early gene that encodes a protein with extensive sequence homology to members of the steroid/thyroid hormone receptor superfamily. By analogy to steroid receptors, the Nur77 protein is thought to act as a ligand-dependent transcription factor that regulates the genomic response to growth factors. Using chimeric gene constructs, we show that Nur77 can indeed function as a transcription activator. Furthermore, Nur77 chimeras can activate transcription in the absence of an exogenously added ligand.

Nur77 is differentially modified in PC12 cells upon membrane depolarization and growth factor treatment

The rat pheochromocytoma cell line PC12 can be induced by growth factors to undergo proliferation and neuronal differentiation. These cells also have excitable membranes that can be depolarized by neurotransmitters or elevated levels of extracellular KCl. Treatment of PC12 cells with growth factors or membrane-depolarizing agents rapidly activates the expression of specific genes whose products are thought to mediate the subsequent biological responses. One such gene, nur77, is a member of the steroid and thyroid hormone receptor gene superfamily. We have identified the Nur77 protein and shown that it is synthesized rapidly and transiently in PC12 cells following stimulation, has a short half-life of 30 to 40 min, and is located in both the nucleus and the cytoplasm. Nur77 is posttranslationally modified, primarily by phosphorylation on serine residues. Phosphopeptide analysis reveals that Nur77 is modified differently upon membrane depolarization than after treatment with growth factors. We hypothesize that the activity of Nur77 is regulated by both differential gene expression and posttranslational modification and that these modes of regulation contribute to distinct downstream responses specific to membrane depolarization and growth factor treatment.

A gene inducible by serum growth factors encodes a member of the steroid and thyroid hormone receptor superfamily

We previously identified, by cDNA cloning, a set of genes that are expressed during the G0/G1 transition (cell cycle reentry) in mouse fibroblasts. These immediate early genes are transcriptionally activated within minutes of addition of serum or purified growth factors, and their mRNAs are superinduced in the presence of protein-synthesis inhibitors. We report here that one of these genes, represented by nur/77 cDNA (originally called 3CH77), encodes a member of the superfamily of ligand-binding transcription factors that includes the steroid and thyroid hormone receptors. The nur/77 cDNA sequence encodes a protein of 601 amino acids containing two regions of sequence similarity to members of this nuclear receptor superfamily, corresponding to their DNA-binding and ligand-binding domains. These results suggest that the growth factor-inducible immediate early gene nur/77 encodes a ligand-binding protein that regulates the genomic response to growth factors.