• We are sorry, but NCBI web applications do not support your browser and may not function properly. More information
Logo of pnasPNASInfo for AuthorsSubscriptionsAboutThis Article
Proc Natl Acad Sci U S A. Dec 13, 2005; 102(50): 18171–18176.
Published online Dec 5, 2005. doi:  10.1073/pnas.0508945102
PMCID: PMC1312406
Neuroscience

Human stem/progenitor cells from bone marrow promote neurogenesis of endogenous neural stem cells in the hippocampus of mice

Abstract

Stem/progenitor cells from bone marrow and other sources have been shown to repair injured tissues by differentiating into tissue-specific phenotypes, by secreting chemokines, and, in part, by cell fusion. Here we prepared the stem/progenitor cells from human bone marrow (MSCs) and implanted athem into the dentate gyrus of the hippocampus of immunodeficient mice. The implanted human MSCs markedly increased the proliferation of endogenous neural stem cells that expressed the stem cell marker Sox2. Labeling of the mice with BrdUrd demonstrated that, 7 days after implantation of the human MSCs, BrdUrd-labeled endogenous cells migrated throughout the dorsal hippocampus (positive for doublecortin) and expressed markers for astrocytes and for neural or oligodendrocyte progenitors. Subpopulations of BrdUrd-labeled cells exhibited short cytoplasmic processes immunoreactive for nerve growth factor and VEGF. By 30 days after implantation, the newly generated cells expressed markers for more mature neurons and astrocytes. Also, subpopulations of BrdUrd-labeled cells exhibited elaborate processes immunoreactive for ciliary neurotrophic factor, neurotrophin-4/5, nerve growth factor, or VEGF. Therefore, implantation of human MSCs stimulated proliferation, migration, and differentiation of the endogenous neural stem cells that survived as differentiated neural cells. The results provide a paradigm to explain recent observations in which MSCs or related stem/progenitor cells were found to produce improvements in disease models even though a limited number of the cells engrafted.

Numerous observations in the past decade have altered Cajal's “harsh decree” that the adult brain has a fixed number of neurons (see ref. 1). There is now a consensus that neural stem cells (NSCs) that can undergo neurogenesis are found in the adult brain within the subventricular zone lining the lateral ventricles and in the subgranular zone of the dentate gyrus (DG) (see ref. 2). Neurogenesis by NSCs and survival of newly differentiated cells can contribute to self-repair after neuronal loss (3). The process can be stimulated in response to CNS injury (4, 5) and by signaling from astroglia (6). However, neurogenesis by endogenous NSCs cannot fully compensate for the neural loss observed in CNS disorders and in aging. These observations have stimulated a search for agents that will increase neurogenesis or enhance neuroprotection. Several factors have recently been explored for their role in neurogenesis: nerve growth factor (NGF) (7), brain-derived neurotrophic factor (8), neurotrophin-4/5 (NT-4/5) (9), neurotrophin-3 (NT-3) (10, 11), ciliary neurotrophic factor (CNTF) (12), VEGF (13), fibroblast growth factor 2 (FGF-2), (14, 15), erythropoietin (EPO) (16), and the polycomb family transcriptional repressor BMI-1 (17, 18).

An alternate approach to restoring function following neuronal loss is implantation of stem/progenitor cells. The adult stem/progenitor cells for nonhematopoietic tissues from bone marrow, referred to as mesenchymal stem cells or marrow stromal cells (MSCs), and similar stem/progenitor cells from marrow or other tissues have been shown to home to damaged tissues and repair them by differentiating into the appropriate phenotypes, by producing chemokines, and perhaps by cell fusion followed by reductive division (see ref. 19). MSCs were first identified >30 years ago (2022), and they have been shown to differentiate into multiple cell phenotypes in culture, even when generated as clones of single-cell colonies. In rodents MSCs engraft into multiple tissues, including brain (23, 24). Shortly after MSCs were discovered, however, they attracted attention primarily because confluent cultures of the cells were found to serve as effective feeder layers (see ref. 25) for hematopoietic stem cells. The effectiveness of MSCs as feeder layers for hematopoietic stem cells has, in part, been explained by their production of a large number of growth stimulating factors (2629). For example, human MSCs have been shown to express neurotrophins not only in culture but also after implantation into the brains of rats (30) and immunodeficient mice (31).

We report here that implantation of human MSCs into the DG of the hippocampus of immunodeficient mice stimulated proliferation, migration, and differentiation of endogenous NSCs that survived as more mature neural cells. Implantation of the human MSCs also enhanced the expression of neurotrophins by endogenous cells.

Materials and Methods

Cell Culture. Human MSCs were obtained from the Tulane Center for the Preparation and Distribution of Adult Stem Cells. The cells were prepared as previously described (32, 33) with protocols approved by an Institutional Review Board. In brief, bone marrow aspirates were taken from the iliac crest of normal adult donors. Nucleated cells were isolated by using a density gradient (Ficoll-Paque, Amersham Pharmacia Biotech) and resuspended in complete human MSC medium: α-MEM (GIBCO/BRL, Grand Island, NY); 20% FBS (lot selected for rapid growth; Atlanta Biologicals, Norcross, GA); 100 units/ml penicillin (GIBCO/BRL); 100 μg/ml streptomycin (GIBCO/BRL); and 2 mM l-glutamine (GIBCO/BRL). Cells were then plated in 20 ml of medium in a 180-cm2 culture dish and incubated at 37°C with 5% humidified CO2. After 24 h, nonadherent cells were removed. Adherent cells were washed twice with PBS and incubated with fresh medium. After 5–7 days, the cells were harvested with 0.25% trypsin and 1 mM EDTA for 5 min at 37°C and then replated at ≈3–50 cells per cm2 (Cell Factory, Nunc). After ≈7 days, when the cultures had reached 70% confluence, the cells (passage 1) were harvested with trypsin/EDTA, resuspended at 1 × 106 cells per ml in 5% dimethyl sulfoxide and 30% FBS, frozen in 1-ml aliquots overnight at -80°C, and then stored in liquid nitrogen. For cell expansion, frozen vials of passage-1 human MSCs were thawed, plated in 25 ml of medium in a 180-cm2 culture plate (Nunc), and incubated at 37°C with 5% humidified CO2. After 24 h, the medium was removed, and adherent viable cells were washed twice with PBS, harvested with 0.25% trypsin and 1 mM EDTA, and replated at 100 cells per cm2. The cells were incubated until they were 70% confluent after ≈ 7 days, at which time they were harvested with trypsin/EDTA for analysis or transplantation.

Stereotaxic Surgery. Severe combined immunodeficient mice (n = 84; SCID-Beige, The Jackson Laboratory), 6–8 weeks old, were anesthetized with 0.07 ml of a mixture of ketamine (90.9 mg/ml) and xylazine (9.1 mg/ml). Stereotaxic surgery was used to deliver either 50,000 or 100,000 human MSCs in 2 or 4 μl, respectively, of PBS into the DG of the hippocampus at coordinates: A/P, -2.3 mm, M/L, ±1.3 mm, and D/V, -2.0 mm (34). The cell suspension was delivered at a rate of 500 nl/min. As controls, either 4 μl of PBS or 4 μl of PBS containing 100,000 nonviable MSCs was implanted. The MSCs were rendered nonviable by repeated freezing and thawing. The nonviability of the cells was confirmed by trypan blue staining and failure to observe growth after replating.

BrdUrd Administration. Mice (n = 24) received i.p. injections of 50 mg/kg BrdUrd (Sigma) in PBS with 0.007 M NaOH twice daily for 6 days beginning 24 h after implantation of MSCs. Mice were killed either on day 7 or on day 30 after implantation.

Real-Time RT-PCR for Proliferative Cell Nuclear Antigen (PCNA). Mice (n = 28) were killed, hippocampi were removed, and total RNA was isolated (Ambion, Austin, TX). All RNA samples were DNase-treated. Primer and probe sequences for PCNA were designed by using a software program (primerexpress, Applied Biosystems) and synthesized commercially (Integrated DNA Technologies, Coralville, IA). The primers were as follows: PCNA forward, 5′-GCG CAG AGG GTT GGT AGT TG-3′; PCNA reverse, 5′-CCC GAT TCA CGA TGC AGA A-3′. The TaqMan PCNA probe was 5′-/56-FAM/CGC TGT AGG CCT TCG CTG CCG/36-TAMNph/-3′. Assays with primers and probe for GAPDH mRNA (TaqMan Rodent GAPDH Control Reagents, Applied Biosystems) were used to normalize samples. RT-PCRs were incubated under the following conditions: 2-min uracil-N-glycosylase treatment at 50°C, 30-min reverse transcription at 60°C, and 5-min deactivation of uracil-N-glycosylase at 95°C. Amplification was carried out under the following conditions: 20-s denaturation at 94°C followed by 1-min annealing and extension at 62°C for 40 cycles. Assays were performed with an automated instrument (Model 7700, Applied Biosystems) and commercial reagents (TaqMan EZ RT-PCR Core Reagents, Applied Biosystems).

Real-Time PCR for Alu Sequences. Genomic DNA was extracted from isolated hippocampi of mice (n = 8; DNeasy, Qiagen, Valencia, CA). The sequence of the PCR primers and the probe used for detection of human Alu repetitive sequences (35) were as follows: Alu forward, 5′-CAT GGT GAA ACC CCG TCT CTA-3′; Alu reverse, 5′-GCC TCA GCC TCC CGA GTA G-3′; TaqMan probe, 5′-FAM-ATT AGC CGG GCG TGG TGG CG-TAMRA-3′ (Applied Biosystems). PCR assays for Alu sequences were performed in a volume of 50 μl that contained 25 μl of Universal PCR Master Mix (Applied Biosystems), 900 nM each of the forward and reverse primers, 250 nM TaqMan probe, and 50 ng of target template. Reactions were incubated at 50°C for 2 min for uracil-N-glycosylase activity and at 95°C for 10 min to activate the polymerase (AmpliTaq Gold, Applied Biosystems) followed by 40 cycles at 95°C for 15 s and 60°C for 1 min. Standard curves were generated by serially diluting human genomic DNA prepared from MSCs into samples containing genomic DNA from mouse brain for a total of 50 ng. Values were normalized by assays for GAPDH (Applied Biosystems).

Tissue Preparation. Mice were transcardially perfused with 20 ml of ice-cold PBS followed by 30 ml of 4% paraformaldehyde in PBS. Brains were removed, postfixed overnight at 4°C, and incubated in 30% sucrose at 4°C until equilibrated. Brains were frozen for 1 min at -50°C in dry-ice-cooled 2-methylbutane (Fisher Scientific) and stored at -80°C.

Immunostaining of Brain Sections. Coronal sections of 40 μm were cut by using a microtome and processed as free-floating sections. Sections were incubated in 3% H2O2/50% ice-cold methanol/PBS for 15 min followed by washes in PBS. Sections were then blocked in 5% normal serum from the species in which the secondary antibody was raised and 0.4% Triton-X-100 (Sigma) for 1 h at room temperature. Sections were subsequently incubated for 24 h with the primary antibodies at 4°C. We used anti-human nuclei antigen (anti-HNA; Chemicon; 1:100) to identify donor cells and anti-PCNA (Santa Cruz Biotechnology; 1:200) to identify proliferating cells. To identify secreted factors, we used anti-NGF (Santa Cruz Biotechnology; 1:1,000), anti-brain-derived neurotrophic factor (Santa Cruz Biotechnology; 1:1,000), anti-NT-4/5 (Santa Cruz Biotechnology; 1:1,000), anti-NT-3 (Chemicon; 1:200), anti-CNTF (Santa Cruz Biotechnology; 1:400), anti-VEGF (Santa Cruz Biotechnology; 1:400), anti-EPO (Santa Cruz Biotechnology; 1:100), and anti-BMI-1 (Santa Cruz Biotechnology; 1:100). We used anti-Sox2 (Stem-Cell Technologies; 1:100), anti-doublecortin (Santa Cruz Biotechnology; 1:400), and anti-nestin (Covance, Berkeley, CA; 1:400) to identify neural stem/progenitor cells; anti-Sternberger monoclonal incorporated-311 (anti-SMI-311; Sternberger Monoclonal Antibodies, Lutherville, MD; 1:5,000) and anti-neuronal nuclei (anti-NeuN, Chemicon; 1:400), to identify neurons; anti-NG-2 chondroitin sulfate proteoglycan (anti-NG-2, Chemicon; 1:500) to identify oligodendrocyte precursor cells; and anti-glial fibrillary acidic protein (anti-GFAP; Sigma; 1:400) to identify astrocytes. For BrdUrd processing, sections were incubated in 2 M HCl for 30 min at 37°C followed by 0.1 M borate buffer for 15 min at room temperature. Sections were then processed as described above. Rat anti-BrdUrd (Abcam, Cambridge, MA; 1:20) or mouse anti-BrdUrd (Sigma; 1:400) was used to identify newly generated cells. For visualization, the sections were incubated in secondary antiserum (Alexa Fluor 488, 1:500, or Alexa Fluor 594, 1:1,000; Invitrogen) for 1 h at room temperature followed by washes. Sections were then mounted on precoated slides (Superfrost Plus Microscope Slides, Fisher Scientific), coverslipped with a DNA counterstain (DAPI, Vector Laboratories), and stored at 4°C. Sections were analyzed by using an epifluorescence microscope (Eclipse E800, Nikon, Melville, NY) with spot-rt imaging software (Diagnostic Instruments, Sterling Heights, MI).

ELISAs. Mice (n = 6 per group) were killed, hippocampi were removed and pooled according to treatment condition, and protein was isolated (M-PER, Pierce, Rockford, IL). NGF and NT-4/5 were detected by using commercial ELISA kits (Emax ImmunoAssay System, Promega).

Statistical Analyses. All data were expressed as means and standard errors or standard deviations and analyzed by using ANOVA and Student's t tests. The level of significance for all analyses was p < 0.05.

Results

Implantation of Human MSCs Promoted Proliferation of Endogenous NSCs. Either 50,000 or 100,000 human MSCs were unilaterally implanted into the DG of the hippocampus of adult immunodeficient mice, and the hippocampi were assayed for survival of the human cells by real-time PCR assays of the human Alu sequences. The data were variable in that the levels were not detectable with the PCR assays of hippocampi in some samples, but up to 26% of the human cells survived in some mice at 3 days after implant (Table 1).

Table 1.
Survival of MSCs 3 days after implant

Real-time RT-PCR assays for mRNA for PCNA were used to determine whether implantation of the human MSCs increased proliferation of cells in the hippocampi. After 1 and 3 days, there was a significant increase in mRNA for PCNA in the implanted hippocampi compared with control vehicle-injected contralateral hippocampi (Fig. 1A). Also, there was no increase in proliferation compared with a second control consisting of injection of nonviable MSCs (Fig. 1B). Increased proliferation was no longer detected with the PCNA assay at 7 or 30 days.

Fig. 1.
Implantation of human MSCs promoted proliferation, migration, and survival of mouse NSCs. (A) Real-time RT-PCR assays for PCNA. Error bars indicate standard errors (n = 4). A significant increase (*, p < 0.05) over vehicle-injected controls was ...

To confirm proliferation and to determine which cells in the hippocampi were proliferating, sections were doubly stained with antibodies to PCNA to identify proliferating cells and antibodies to HNA to identify human cells. There was little evidence of proliferation of the implanted human MSCs (Fig. 1C). However, there was a marked increase in the proliferation of the endogenous mouse cells within the MSC-injected hippocampi.

To follow the fate of proliferating cells, BrdUrd was systemically administered after implantation of the human MSCs (Fig. 1D). In mice killed on day 1, 3, 7, or 30 after implantation of the human MSCs, there was a marked increase in newly generated BrdUrd-labeled cells in the implanted hippocampi compared with vehicle-injected or naive hippocampi (data not shown). Seven days after the implantation, the BrdUrd-labeled cells were immunoreactive for PCNA (Fig. 1E). A subpopulation of PCNA+ proliferating cells was immunoreactive for the stem cell marker Sox2 (Fig. 1E). By 30 days, BrdUrd-labeled cells were no longer immunoreactive for PCNA (Fig. 1E) or Sox2 (data not shown).

These data demonstrate that implanted MSCs stimulated the proliferation of endogenous NSCs within the hippocampus.

Migration of the Expanded Endogenous NSCs. Seven days after implantation of the MSCs, several newly generated BrdUrd-labeled NSCs expressed doublecortin, a marker for migrating neuronal cells (Fig. 1E). BrdUrd-labeled NSCs had migrated from the DG to the stratum radiatum, CA1 pyramidal cell layer, and the stratum oriens of the hippocampus. However, 30 days after implantation, the BrdUrd-labeled NSCs were no longer immunoreactive for doublecortin (data not shown), an observation that raised the possibility that the cells were no longer migrating.

Differentiation of Newly Generated NSCs into both Neural Precursors and Mature Neural Cells. Double fluorescence staining of sections from BrdUrd-labeled mice demonstrated that, at 7 days after implant, some of the expanded NSCs expressed nestin (Fig. 2A). At this stage, a subpopulation of BrdUrd-labeled cells were immunoreactive for NG-2 (Fig. 2 A), a phenotypic marker of oligodendrocyte progenitors. Of note was that, 30 days after implantation of the human MSCs, we no longer detected BrdUrd-labeled cells that were immunoreactive for nestin or NG-2. Although BrdUrd-labeled cells were no longer immunoreactive for NG-2, some endogenous cells stained for NG-2. Interestingly, some of the BrdUrd-labeled cells were in close proximity to and appeared to be contacted by oligodendrocyte progenitors. These results suggested that the proliferation had ceased and that BrdUrd-labeled cells had differentiated into more mature neural cells by 30 days after implantation.

Fig. 2.
Implantation of human MSCs promoted differentiation of mouse NSCs. (A) Subpopulations of newly generated BrdUrd-labeled cells expressed markers for neural progenitor cells (anti-nestin, green) or oligodendrocyte progenitor cells (anti-NG-2, green) at ...

Accordingly, we performed double fluorescence immunohistochemistry on sections from BrdUrd-labeled mice with antibodies to proteins expressed in mature neural cells. The results (Fig. 2B) demonstrated that, at 30 days after implantation, but not at 7 days, some of the newly generated cells were immunoreactive for NeuN and SMI-311, suggesting maturation of the newly generated cells into more mature neurons. The results also demonstrated that some of the newly generated cells expressed the astroglia marker anti-glial fibrillary acidic protein at both 7 and 30 days after implant, suggesting an astroglial response to the implanted MSCs. Interestingly, no detectable difference in astrogliosis was observed between MSC-injected or vehicle-injected hippocampi 30 days after implant, suggesting that newly generated astroglia survived and were incorporated into the host cytoarchitecture.

These data indicate that the implanted MSCs promoted the expansion of endogenous NSCs and that the expanded cells differentiated into more mature neural cells.

Newly Generated Cells Expressed Trophic Factors. To determine whether the expanded endogenous cells expressed neurotrophins, we performed further double-staining assays of the hippocampi. At 7 days after implantation, a subpopulation of BrdUrd-labeled cells exhibited short cytoplasmic processes that were immunoreactive for NGF and VEGF (Fig. 3); they were not immunoreactive for CNTF or NT-4/5. By 30 days after implantation, some BrdUrd-labeled cells exhibited elaborate processes that were immunoreactive not only for NGF and VEGF, but also for CNTF and NT-4/5. The results suggested that the BrdUrd-labeled cells had matured and integrated into the host cytoarchitecture.

Fig. 3.
Newly generated BrdUrd-labeled cells in the hippocampus expressed trophic factors. Newly generated cells exhibited short cytoplasmic processes at 7 days after implantation that were immunoreactive for NGF and VEGF, but not CNTF or NT-4/5. By 30 days after ...

Implanted Human MSCs Stimulated Synthesis of Neuronal Survival Factors. To determine whether the implanted human MSCs stimulated synthesis of neural survival factors, brain sections were doubly stained with antibodies to human-specific human nuclei antigen and to neurotrophins (Fig. 4). The results indicated that implantation of the human MSCs increased endogenous expression of NGF, VEGF, CNTF, FGF-2, and, to a lesser extent, BMI-1.

Fig. 4.
Implantation of human MSCs increased synthesis of trophic factors (green) in the hippocampus. NGF, CNTF, FGF-2, and, to a lesser extent, BMI-1 up-regulation was primarily localized to the dorsal hippocampus. VEGF up-regulation was primarily localized ...

NGF expression was localized primarily within the dorsal hippocampus and the DG of MSC-injected hippocampi, with little to no immunoreactivity in vehicle-injected hippocampi. VEGF expression was localized to the DG in close proximity to the human MSCs, with little to no immunoreactivity in vehicle-injected hippocampi. CNTF expression was localized mostly within the dorsal hippocampus and the DG, whereas expression in the vehicle-injected hippocampi was localized mainly to the subgranular zone of the DG. FGF-2 expression was localized mostly within the dorsal hippocampus and the DG of MSC-injected hemispheres, whereas expression in the vehicle-injected hippocampi was mainly localized to the subgranular zone of the DG. Also, BMI-1 expression was localized to the dorsal hippocampus and DG in the MSC-injected hemispheres, with similar but lower levels of expression in vehicle-injected hippocampi. In contrast, EPO expression was equally up-regulated in the hippocampus and DG of MSC-injected and vehicle-injected hippocampi.

The results were confirmed by ELISAs for neurotrophins on isolated hippocampi (Fig. 5). Seven days after implantation of the human MSCs, there was a marked increase in the levels of NGF and NT-4/5. The levels returned to control values 30 days after implantation of the human MSCs.

Fig. 5.
Implantation of human MSCs increased synthesis of trophic factors in the hippocampi. ELISAs for NGF and NT-4/5 are shown. (A) A marked increase in NGF concentration was observed in the implanted hippocampi compared with vehicle-injected controls at 7 ...

These data suggest that human MSCs regulate the proliferation and migration of newly generated endogenous NSCs in part by stimulating the synthesis by adjacent endogenous cells of factors that promote neurogenesis.

Discussion

The results presented here provide a paradigm for repair of tissues by MSCs. The MSCs implanted into the hippocampus did not proliferate, but they greatly increased proliferation of adjacent cells that expressed the stem cell marker Sox2. The increase in proliferation was detected at 1 and 3 days after implantation by real-time PCR assays and at 7 days by immunohistochemistry. Labeling of the mice with BrdUrd demonstrated that the newly generated cells expressed the migration marker doublecortin and migrated throughout the dorsal hippocampus. At 7 days after implantation, subpopulations of BrdUrd-labeled cells expressed markers for astrocytes and neural or oligodendrocyte progenitors; they also expressed the neurotrophins NGF and VEGF. At 30 days after the implantation, some of the newly generated cells expressed markers of more mature neurons and astrocytes. Also, they expressed CNTF and NT-4/5 in addition to NGF and VEGF. The results indicate that implantation of human MSCs in the mouse hippocampus stimulated proliferation, migration, and differentiation of the endogenous NSCs that survived as more differentiated neural cells.

The effects produced by the human MSCs are probably explained by their secretion of chemokines. After implantation, there was a generalized increase in expression in the hippocampus of NGF, VEGF, CNTF, and FGF-2 and, to a lesser extent, of BMI-1. These and some of the other chemokines expressed by MSCs probably accounted for the increase in neurogenesis. The chemokines secreted by MSCs may have acted directly on the NSCs. However, it is also possible that factors secreted by the MSCs activated nearby astrocytes and activation of the astrocytes produced the increase in neurogenesis, because astrocytes are located in close proximity to NSCs (6) in the hippocampus and express several factors that independently increase neurogenesis (36, 37).

The effects of MSCs on proliferation and differentiation of NSCs suggest that they may have similar effects on other stem/progenitor cells in other tissues. Such effects may well explain a number of recent reports in which administration of MSCs or related cells from bone marrow produced improvements in animal models and in clinical trials for heart disease and other disorders even though a limited number of cells engrafted (30, 3842).

Acknowledgments

We thank Dr. Bruce Bunnell for assistance in preparation of the manuscript. This work was supported in part by grants from National Institutes of Health (HL 073755, HL 073252, and P40 RR 17447), HCA Health Care Corporation, and the Louisiana Gene Therapy Research Consortium.

Notes

Author contributions: J.R.M., B.R.S., A.P.R., and J.L.S. performed research; and J.R.M., B.R.S., A.P.R., and D.J.P. wrote the paper.

Conflict of interest statement: No conflicts declared.

Abbreviations: MSC, stem/progenitor cell for nonhematopoietic tissues from bone marrow; NSC, neural stem cell; NGF, nerve growth factor; CNTF, ciliary neurotrophic factor; NT-4/5, neurotrophin-4/5; EPO, erythropoietin; DG, dentate gyrus; PCNA, proliferative cell nuclear antigen; HNA, human nuclei antigen.

References

1. Hallbergson, A. F., Gnatenco, C. & Peterson, D. A. (2003) J. Clin. Invest. 112, 1128-1133. [PMC free article] [PubMed]
2. Gage, F. H. (2000) Science 287, 1433-1438. [PubMed]
3. Arvidsson, A., Collin, T., Kirik, D., Kokaia, Z. & Lindvall, O. (2002) Nat. Med. 8, 963-970. [PubMed]
4. Aharoni, R., Arnon, R. & Eilam, R. (2005) J. Neurosci. 25, 8217-8228. [PubMed]
5. Emery, D. L., Fulp, C. T., Saatman, K. E., Schutz, C., Neugebauer, E. & McIntosh, T. K. (2005) J. Neurotrauma 22, 978-988. [PubMed]
6. Song, H., Stevens, C. F. & Gage, F. H. (2002) Nature 417, 39-44. [PubMed]
7. Fiore, M., Triaca, V., Amendola, T., Tirassa, P. & Aloe, L. (2002) Physiol. Behav. 77, 437-443. [PubMed]
8. Scharfman, H., Goodman, J., Macleod, A., Phani, S., Antonelli, C. & Croll, S. (2005) Exp. Neurol. 192, 348-356. [PubMed]
9. Scarisbrick, I. A., Asakura, K. & Rodriguez, M. (2000) Brain Res. Dev. Brain Res. 123, 87-90. [PubMed]
10. Collazo, D., Takahashi, H. & McKay, R. D. (1992) Neuron 9, 643-656. [PubMed]
11. Barnabe-Heider, F. & Miller, F. D. (2003) J. Neurosci. 23, 5149-5160. [PubMed]
12. Emsley, J. G. & Hagg, T. (2003) Exp. Neurol. 183, 298-310. [PubMed]
13. Schanzer, A., Wachs, F. P., Wilhelm, D., Acker, T., Cooper-Kuhn, C., Beck, H., Winkler, J., Aigner, L., Plate, K. H. & Kuhn, H. G. (2004) Brain Pathol. 14, 237-248. [PubMed]
14. Palmer, T. D., Ray, J. & Gage, F. H. (1995) Mol. Cell. Neurosci. 6, 474-486. [PubMed]
15. Jin, K., Sun, Y., Xie, L., Batteur, S., Mao, X. O., Smelick, C., Logvinova, A. & Greenberg, D. A. (2003) Aging Cell 2, 175-183. [PubMed]
16. Shingo, T., Sorokan, S. T., Shimazaki, T. & Weiss, S. (2001) J. Neurosci. 21, 9733-9743. [PubMed]
17. Molofsky, A. V., Pardal, R., Iwashita, T., Park, I. K., Clarke, M. F. & Morrison, S. J. (2003) Nature 425, 962-967. [PMC free article] [PubMed]
18. Molofsky, A. V., He, S., Bydon, M., Morrison, S. J. & Pardal, R. (2005) Genes Dev. 19, 1432-1437. [PMC free article] [PubMed]
19. Prockop, D. J., Gregory, C. A. & Spees, J. L. (2003) Proc. Natl. Acad. Sci. USA 100, 11917-11923. [PMC free article] [PubMed]
20. Owen, M. & Friedenstein, A. J. (1988) Ciba Found. Symp. 136, 42-60. [PubMed]
21. Caplan, A. I. (1995) Connect. Tissue Res. 31, S9-S14. [PubMed]
22. Prockop, D. J. (1997) Science 276, 71-74. [PubMed]
23. Pereira, R. F., O'Hara, M. D., Laptev, A. V., Halford, K. W., Pollard, M. D., Class, R., Simon, D., Livezey, K. & Prockop, D. J. (1998) Proc. Natl. Acad. Sci. USA 95, 1142-1147. [PMC free article] [PubMed]
24. Kopen, G. C., Prockop, D. J. & Phinney, D. G. (1999) Proc. Natl. Acad. Sci. USA 96, 10711-10716. [PMC free article] [PubMed]
25. Eaves, C., Miller, C., Conneally, E., Audet, J., Oostendorp, R., Cashman, J., Zandstra, P., Rose-John, S., Piret, J. & Eaves, A. (1999) Ann. N.Y. Acad. Sci. 872, 1-8. [PubMed]
26. Haynesworth, S. E., Barber, M. A. & Caplan, A. I. (1996) J. Cell Physiol. 166, 585-592. [PubMed]
27. Austin, T. W., Solar, G. P., Ziegler, F. C., Liem, L. & Matthews, W. (1997) Blood 89, 3624-3635. [PubMed]
28. Gregory, C. A., Singh, H., Perry, A. S. & Prockop, D. J. (2003) J. Biol. Chem. 278, 28067-28078. [PubMed]
29. Gregory, C. A., Perry, A. S., Reyes, E., Conley, A., Gunn, W. G. & Prockop, D. (2005) J. Biol. Chem. 280, 2309-2323. [PubMed]
30. Chen, X., Li, Y., Wang, L., Katakowski, M., Zhang, L., Chen, J., Xu, Y., Gautam, S. & Chopp, M. (2002) Neuropathology 22, 275-279. [PubMed]
31. Munoz, J. R., Reger, R. I., Spees, J., Gregory, C. & Prockop, D. J. (2003) Exp. Neurol. 181, 100.
32. Colter, D. C., Class, R., DiGirolamo, C. M. & Prockop, D. J. (2000) Proc. Natl. Acad. Sci. USA 97, 3213-3218. [PMC free article] [PubMed]
33. Sekiya, I., Larson, B. L., Smith, J. R., Pochampally, R., Cui, J. G. & Prockop, D. J. (2002) Stem Cells 20, 530-541. [PubMed]
34. Paxinos, G. & Franklin, K. (2001) The Mouse Brain in Stereotactic Coordinates (Academic, Chicago).
35. McBride, C., Gaupp, D. & Phinney, D. G. (2003) Cytotherapy 5, 7-13. [PubMed]
36. Rudge, J. S., Alderson, R. F., Pasnikowski, E., McClain, J., Ip, N. Y. & Lindsay, R. M. (1992) Eur. J. Neurosci. 4, 459-471. [PubMed]
37. Nakayama, T., Momoki-Soga, T. & Inoue, N. (2003) Neurosci. Res. 46, 241-249. [PubMed]
38. Chopp, M., Zhang, X. H., Li, Y., Wang, L., Chen, J., Lu, D., Lu, M. & Rosenblum, M. (2000) NeuroReport 11, 3001-3005. [PubMed]
39. Hofstetter, C. P., Schwarz, E. J., Hess, D., Widenfalk, J., El Manira, A., Prockop, D. J. & Olson, L. (2002) Proc. Natl. Acad. Sci. USA 99, 2199-2204. [PMC free article] [PubMed]
40. Pittenger, M. F. & Martin, B. J. (2004) Circ. Res. 95, 9-20. [PubMed]
41. Iihoshi, D., Honmou, O., Houkin, K., Hashi, K. & Kocsis, J. (2004) Brain Res. 1007, 1-9. [PubMed]
42. Gnecchi, M., He, H., Liang, O. D., Melo, L. G., Morello, F., Mu, H., Noiseux, N., Zhang, L., Pratt, R. E., Ingwall, J. S. & Dzau, V. J. (2005) Nat. Med. 11, 367-368. [PubMed]

Articles from Proceedings of the National Academy of Sciences of the United States of America are provided here courtesy of National Academy of Sciences
PubReader format: click here to try

Formats:

Related citations in PubMed

See reviews...See all...

Cited by other articles in PMC

See all...

Links

Recent Activity

Your browsing activity is empty.

Activity recording is turned off.

Turn recording back on

See more...