L-MYC Expression Maintains Self-Renewal and Prolongs Multipotency of Primary Human Neural Stem Cells

Abstract

Pre-clinical studies indicate that neural stem cells (NSCs) can limit or reverse CNS damage through direct cell replacement, promotion of regeneration, or delivery of therapeutic agents. Immortalized NSC lines are in growing demand due to the inherent limitations of adult patient-derived NSCs, including availability, expandability, potential for genetic modifications, and costs. Here, we describe the generation and characterization of a new human fetal NSC line, immortalized by transduction with L-MYC (LM-NSC008) that in vitro displays both self-renewal and multipotent differentiation into neurons, oligodendrocytes, and astrocytes. These LM-NSC008 cells were non-tumorigenic in vivo, and migrated to orthotopic glioma xenografts in immunodeficient mice. When administered intranasally, LM-NSC008 distributed specifically to sites of traumatic brain injury (TBI). These data support the therapeutic development of immortalized LM-NSC008 cells for allogeneic use in TBI and other CNS diseases.

Figure 1

Visualization of Primary NSCs in Culture (A) Primary NSCs (NSC008) were isolated from the brain of a 10-week-old fetus and cultured in flasks (passage 5). Primary NSCs grew as neurospheres in suspension. Scale bar, 100 μm. (B) Primary NSCs were transduced with a retroviral virus expressing the L-MYC gene. NSC.Lmyc cells (LM-NSC008) were cultured under the same conditions as untransduced primary NSCs. LM-NSC008 cells preferentially grew as a monolayer. Scale bar, 100 μm. (C) PCR analysis of genomic DNA derived from LM-NSC008 cells. The experiment was repeated three times. (D and E) Karyotype analysis of the LM-NSC008 cell line at passage 2 (D) and passage 10 (E).

Figure 2

Growth Kinetics and Migration of Primary NSC008 and LM-NSC008 Cells in Culture (A) Proliferation of primary NSC008 and LM-NSC008 cells (passage 6) grown for 10 days in culture media (serum-free media containing FGF and EGF). Mean values ± SD of two independent experiments in triplicate measurements are shown. (B) Flow cytometry analysis of NSC008 and LM-NSC008 expressing stem cell markers. Mean values ± SD of four independent experiments in triplicates are shown. (C) Tropism of NSC008 and LM-NSC008 cells to conditioned media from U87 human glioma cells as assessed by Boyden chamber migration assay. Mean values ± SD of three independent experiments in triplicate measurements are shown. (D) Dose response of U251 human glioma cells to CPT-11 and to CPT-11 in the presence of hCE1m6 expressed by LM-NSC008 cells. Mean values ± SD of two independent experiments in quadruplicates are shown. RLU, relative light unit. (E–H) Immunocytochemical staining of LM-NSC008 cells grown for 10 days in differentiation media. Cells were stained for neuronal class III β-TUBULIN (E), the astrocyte markers SOX9 (F) and GFAP (G) (inset Stem123), and oligodendrocyte marker O4 (H). Scale bars, 100 μm.

Figure 3

Tumor-Specific Migration of LM-NSC008 Cells from Contralateral Hemisphere In Vivo (A, B, D, E) U251 human glioma xenografts were established in adult NSG mice. Consecutive horizontal brain sections from a tumor-bearing mouse that received an intracranial (contralateral to the tumor) injection of LM-NSC008 cells (2 × 10⁵) labeled with feraheme. (A) Immunohistochemical staining of adjacent brain sections with EGFP antibodies to visualize tumor xenografts (scale bar, 1000 μm). (D) Enlargement of tumor area shown as inset in (A) (scale bar, 100 μm). (B) Prussian blue staining of axial brain sections, feraheme-labeled NSCs (blue) (scale bar, 1000 μm). (E) Higher-magnification of tumor site shown as inset in (B) with blue LM-NSC008 cells (scale bar, 100 μm). (C and F) Three-dimensional reconstruction of tumors (green) and LM-NSC008 cells (red) (n = 6). (F) 3D enlargement of tumor area shown as inset in (C). (G) A summary of 3D reconstructions of tumors and LM-NSC008 cells at the tumor site. Scale bars 1,000 μm (A–C) and 100 μm (D–F). Asterisk indicates a mouse number.

Figure 4

Distribution of LM-NSC008 Cells to TBI Sites (A) Prussian blue staining of brain section with TBI, demonstrating iron-labeled LM-NSC008 cells (blue) distributed throughout injury site. Scale bar, 500 μm. (B) Magnified area of TBI described in (A). Scale bar, 100 μm. (C) 3D reconstruction of LM-NSC008 cells distributed in the vicinity of TBI site. Scale bar, 150 μm. (D) Prussian blue staining of sham-injured brain section demonstrating rare (10–20) LM-NSC008 cells occasionally visualized around sham surgery sites. Scale bar, 500 μm. (E) Magnified area of injury site described in (D) Scale bar, 100 μm. (F) 3D reconstruction of LM-NSC008 cell distribution in sham-injured brain. Scale bar, 150 μm. (G) Quantification of average numbers of HB1.F3.CD and LM-NSC008 cells at TBI and sham injury sites (n = 5). The arrows in (B, C, E, F) indicate LM-NSC008 cells in the vicinity of TBI or sham injury site. Statistical analysis of the treated and control groups was performed using one-way ANOVA. Tukey's adjusted p values are reported for pairwise comparisons of migration of hNSCs to TBI and sham injury sites.

Figure 5

LM-NSC008 Cell Fate in Non-Tumor-Bearing Brain NSG mice were injected intracerebrally with LM-NSC008 cells (5 × 10⁵, right frontal lobe) and euthanized 1 week (A, D, G), 4 weeks (B, E, H), and 12 weeks (C, F, I) (n = 6) after injection. (A–C) Immunohistochemical (IHC) detection of apoptotic NSCs by using TUNEL staining. (D–F) IHC detection of the human-specific cell proliferation marker Ki-67. (G–I) IHC of mouse brain tissue using human-specific NESTIN antibodies. (J–L) z-Axis projection of all Ki-67- and hNESTIN-stained sections. NESTIN staining pseudocolored green and Ki-67 stained red. (M) Quantification of the percentile of Ki-67-positive cells compared with the total injected dose of LM-NSC008 cells. Scale bars, 100 μm.

Figure 6

Summary of Up- and Downregulated Genes within Samples Analyzed (A) Untransduced NSC008 at passage 2 were compared with NSC008 at passage 9, L-MYC transduced cells (LM-NSC008) were compared at passages 2 versus 12, and NSC008 and LM-NSC008 cells were compared with differentiated LM-NSC008 cells. (B) Heatmap showing upregulated (red) and downregulated (green) genes.