Andrea J. Mothe

Advances in stem cell therapy for spinal cord injury

Spinal cord injury (SCI) is a devastating condition producing great personal and societal costs and for which there is no effective treatment. Stem cell transplantation is a promising therapeutic strategy, though much preclinical and clinical research work remains. Here, we briefly describe SCI epidemiology, pathophysiology, and experimental and clinical stem cell strategies. Research in stem cell biology and cell reprogramming is rapidly advancing, with the hope of moving stem cell therapy closer to helping people with SCI. We examine issues important for clinical translation and provide a commentary on recent developments, including termination of the first human embryonic stem cell transplantation trial in human SCI.

Repair of the injured spinal cord by transplantation of neural stem cells in a hyaluronan-based hydrogel

Traumatic injury to the spinal cord causes cell death, demyelination, axonal degeneration, and cavitation resulting in functional motor and sensory loss. Stem cell therapy is a promising approach for spinal cord injury (SCI); however, this strategy is currently limited by the poor survival and uncontrolled differentiation of transplanted stem cells. In an attempt to achieve greater survival and integration with the host tissue, we examined the survival and efficacy of adult brain-derived neural stem/progenitor cells (NSPCs) injected within a hydrogel blend of hyaluronan and methyl cellulose (HAMC) into a subacute, clinically relevant model of rat SCI. Prior to use, HAMC was covalently modified with recombinant rat platelet-derived growth factor-A (rPDGF-A) to promote oligodendrocytic differentiation. SCI rats transplanted with NSPCs in HAMC-rPDGF-A showed improved behavioral recovery compared to rats transplanted with NSPCs in media. Rats with NSPC/HAMC-rPDGF-A transplants had a significant reduction in cavitation, improved graft survival, increased oligodendrocytic differentiation, and sparing of perilesional host oligodendrocytes and neurons. These data suggest that HAMC-rPDGF-A is a promising vehicle for cell delivery to the injured spinal cord.

An In Vivo Characterization of Trophic Factor Production Following Neural Precursor Cell or Bone Marrow Stromal Cell Transplantation for Spinal Cord Injury

Cellular transplantation strategies for repairing the injured spinal cord have shown consistent benefit in preclinical models, and human clinical trials have begun. Interactions between transplanted cells and host tissue remain poorly understood. Trophic factor secretion is postulated a primary or supplementary mechanism of action for many transplanted cells, however, there is little direct evidence to support trophin production by transplanted cells in situ. In the present study, trophic factor expression was characterized in uninjured, injured-untreated, injured-treated with transplanted cells, and corresponding control tissue from the adult rat spinal cord. Candidate trophic factors were identified in a literature search, and primers were designed for these genes. We examined in vivo trophin expression in 3 paradigms involving transplantation of either brain or spinal cord-derived neural precursor cells (NPCs) or bone marrow stromal cells (BMSCs). Injury without further treatment led to a significant elevation of nerve growth factor (NGF), leukemia inhibitory factor (LIF), insulin-like growth factor-1 (IGF-1), and transforming growth factor-β1 (TGF-β1), and lower expression of vascular endothelial growth factor isoform A (VEGF-A) and platelet-derived growth factor-A (PDGF-A). Transplantation of NPCs led to modest changes in trophin expression, and the co-administration of intrathecal trophins resulted in significant elevation of the neurotrophins, glial-derived neurotrophic factor (GDNF), LIF, and basic fibroblast growth factor (bFGF). BMSCs transplantation upregulated NGF, LIF, and IGF-1. NPCs isolated after transplantation into the injured spinal cord expressed the neurotrophins, ciliary neurotrophic factor (CNTF), epidermal growth factor (EGF), and bFGF at higher levels than host cord. These data show that trophin expression in the spinal cord is influenced by injury and cell transplantation, particularly when combined with intrathecal trophin infusion. Trophins may contribute to the benefits associated with cell-based repair strategies for spinal cord injury.

Review of transplantation of neural stem/progenitor cells for spinal cord injury

Spinal cord injury (SCI) is a debilitating condition often resulting in paralysis, yet currently there is no effective treatment. Stem cell transplantation is a promising therapeutic strategy for promoting tissue repair after SCI. Stem cells offer a renewable source of cells with inherent plasticity for tissue regeneration. Neural stem/progenitor cells (NSPCs) are multipotent cells that self‐renew and are committed to the neural lineage, and thus, they are especially suited to SCI repair. NSPCs may differentiate into neural cells after transplantation into the injured spinal cord, replacing lost or damaged cells, providing trophic support, restoring connectivity, and facilitating regeneration. Here, we review experimental studies and considerations for clinical translation of NSPC transplantation for SCI.

Transplanted neural stem/progenitor cells generate myelinating oligodendrocytes and Schwann cells in spinal cord demyelination and dysmyelination.

Stem cell therapy is a promising approach for remyelination strategies in demyelinating and traumatic disorders of the spinal cord. Self-renewing neural stem/progenitor cells (NSPCs) reside in the adult mammalian brain and spinal cord. We transplanted NSPCs derived from the adult spinal cord of transgenic rats into two models of focal demyelination and congenital dysmyelination. Focal demyelination was induced by X-irradiation and ethidium bromide injection (X-EB); and dysmyelination was in adult shiverer mutant mice, which lack compact CNS myelin. We examined the differentiation potential and myelinogenic capacity of NSPCs transplanted into the spinal cord. In X-EB lesions, the transplanted cells primarily differentiated along an oligodendrocyte lineage but only some of the oligodendrocytic progeny remyelinated host axons. In this glial-free lesion, NSPCs also differentiated into cells with Schwann-like features based on ultrastructure, expression of Schwann cell markers, and generation of peripheral myelin. In contrast, after transplantation into the spinal cord of adult shiverer mice, the majority of the NSPCs expressed an oligodendrocytic phenotype which myelinated the dysmyelinated CNS axons forming compact myelin, and none had Schwann cell-like features. This is the first study to examine the differentiation and myelinogenic capacity of adult spinal cord stem/progenitors in focal demyelination and dysmyelination of the adult rodent spinal cord. Our findings demonstrate that these NSPCs have the inherent plasticity to differentiate into oligodendrocytes or Schwann-like cells depending on the host environment, and that both cell types are capable of myelinating axons in the demyelinated and dysmyelinated adult spinal cord.

Oligodendrocytes and Radial Glia Derived From Adult Rat Spinal Cord Progenitors: Morphological and Immunocytochemical Characterization

Self-renewing, multipotent neural progenitor cells (NPCs) reside in the adult mammalian spinal cord ependymal region. The current study characterized, in vitro, the native differentiation potential of spinal cord NPCs isolated from adult enhanced green fluorescence protein rats. Neurospheres were differentiated, immunocytochemistry (ICC) was performed, and the positive cells were counted as a percentage of Hoescht+ nuclei in 10 random fields. Oligodendrocytes constituted most of the NPC progeny (58.0% of differentiated cells; 23.4% in undifferentiated spheres). ICC and electron microscopy (EM) showed intense myelin production by neurospheres and progeny. The number of differentiated astrocytes was 18.0%, but only 2.8% in undifferentiated spheres. The number of differentiated neurons was 7.4%, but only 0.85% in undifferentiated spheres. The number of differentiated radial glia (RG) was 73.0% and in undifferentiated spheres 80.9%. EM showed an in vitro phagocytic capability of NPCs. The number of undifferentiated NPCs was 32.8% under differentiation conditions and 78.9% in undifferentiated spheres. Compared with ependymal region spheres, the spheres derived from the peripheral white matter of the spinal cord produced glial-restricted precursors. These findings indicate that adult rat spinal cord ependymal NPCs differentiate preferentially into oligodendrocytes and RG, which may support axonal regeneration in future trials of transplant therapy for spinal cord injury.

Neural Stem/Progenitor Cells from the Adult Human Spinal Cord Are Multipotent and Self-Renewing and Differentiate after Transplantation

Neural stem/progenitor cell (NSPC) transplantation is a promising therapy for spinal cord injury (SCI). However, little is known about NSPC from the adult human spinal cord as a donor source. We demonstrate for the first time that multipotent and self-renewing NSPC can be cultured, passaged and transplanted from the adult human spinal cord of organ transplant donors. Adult human spinal cord NSPC require an adherent substrate for selection and expansion in EGF (epidermal growth factor) and FGF2 (fibroblast growth factor) enriched medium. NSPC as an adherent monolayer can be passaged for at least 9 months and form neurospheres when plated in suspension culture. In EGF/FGF2 culture, NSPC proliferate and primarily express nestin and Sox2, and low levels of markers for differentiating cells. Leukemia inhibitory factor (LIF) promotes NSPC proliferation and significantly enhances GFAP expression in hypoxia. In differentiating conditions in the presence of serum, these NSPC show multipotentiality, expressing markers of neurons, astrocytes, and oligodendrocytes. Dibutyryl cyclic AMP (dbcAMP) significantly enhances neuronal differentiation. We transplanted the multipotent NSPC into SCI rats and show that the xenografts survive, are post-mitotic, and retain the capacity to differentiate into neurons and glia. Together, these findings reveal that multipotent self-renewing NSPC cultured and passaged from adult human spinal cords of organ transplant donors, respond to exogenous factors that promote selective differentiation, and survive and differentiate after transplantation into the injured spinal cord.

Analysis of Green Fluorescent Protein Expression in Transgenic Rats for Tracking Transplanted Neural Stem/Progenitor Cells:

Green fluorescent protein (GFP) expression was evaluated in tissues of different transgenic rodents—Sprague-Dawley (SD) rat strain [SD-Tg(GFP)Bal], W rat strain [Wistar-TgN(CAG-GFP)184ys], and M mouse strain [Tg(GFPU)5Nagy/J]—by direct fluorescence of native GFP expression and by immunohistochemistry. The constitutively expressing GFP transgenic strains showed tissue-specific differences in GFP expression, and GFP immunohistochemistry amplified the fluorescent signal. The fluorescence of stem/progenitor cells cultured as neurospheres from the ependymal region of the adult spinal cord from the GFP SD and W rat strains was assessed in vitro. After transplantation of the cells into wildtype spinal cord, the ability to track the grafted cells was evaluated in vivo. Cultured stem/progenitor cells from the SD strain required GFP immunostaining to be visualized. Likewise, after transplantation of SD cells into the spinal cord, immunohistochemical amplification of the GFP signal was required for detection. In contrast, GFP expression of stem/progenitor cells generated from the W strain was readily detected by direct fluorescence both in vitro and in vivo without the need for immunohistochemical amplification. The cultured stem/progenitor cells transplanted into the spinal cord survived for at least 49 days after transplantation, and continued to express GFP, demonstrating stable expression of the GFP transgene in vivo.

Chitosan Channels Containing Spinal Cord-Derived Stem/Progenitor Cells for Repair of Subacute Spinal Cord Injury in the Rat

OBJECTIVE: We evaluated the survival and differentiation capacity of neural stem/progenitor cells (NSPCs) derived from the adult rat spinal cord and seeded on intramedullary chitosan channels that were implanted in a subacute rat spinal cord injury model. METHODS: We implanted into the injured spinal cord a chitosan channel filled with NSPCs harvested from the spinal cord of adult transgenic rats expressing green fluorescent protein 3 weeks after extradural 35g clip compression injury at T8. The NSPC-chitosan channel group was compared with 2 control groups not receiving channels: 1 receiving a direct intramedullary injection of NSPCs into the lesion cavity and 1 receiving trauma alone. The survival and differentiation of NSPCs were evaluated with immunohistochemical and histopathological techniques, and functional improvement was assessed for 6 weeks with the Basso, Beattie, and Bresnahan locomotor score. RESULTS: The NSPC-chitosan channel group showed enhanced survival of NSPCs compared with NSPCs transplanted directly into the lesion cavity, although there was no significant difference in functional recovery between the treatment and control groups. In addition, the intramedullary implantation of the chitosan channel did not worsen the functional deficit after the 35g clip injury. CONCLUSIONS: Chitosan channels enhanced the survival of transplanted NSPCs in the subacutely injured spinal cord. Functional deficits were not exacerbated by the intramedullary transplantation of chitosan channels into the site of injury.

In Vitro Characterization of Trophic Factor Expression in Neural Precursor Cells

In cellular transplantation strategies for repairing the injured central nervous system, interactions between transplanted neural precursor cells (NPCs) and host tissue remain incompletely understood. Although trophins may contribute to the benefits observed, little research has explored this possibility. Candidate trophic factors were identified, and primers were designed for these genes. Template RNA was isolated from 3 NPC sources, and also from bone marrow stromal cells (BMSCs) and embryonic fibroblasts as comparative controls. Quantitative polymerase chain reaction was performed to determine the effect of cell source, passaging, cellular differentiation, and environmental changes on trophin factor expression in NPCs. Results were analyzed with multivariate statistical analyses. NPCs, BMSCs, and fibroblasts each expressed trophic factors in unique patterns. Trophic factor expression was similar among NPCs whether harvested from rat or mouse, brain or spinal cord, or their time in culture. The expression of neurotrophin NT-3, NT-4/5, glial-derived neurotrophic factor, and insulin-like growth factor-1 decreased with time in culture. Induced differentiation of NPCs led to a marked and statistically significant increase in the expression of trophic factors. Culture conditions and environmental changes were also associated with significant changes in trophin expression. These results suggest that trophins could contribute to the benefits associated with transplantation of NPCs as well as BMSCs. Trophic factor expression changes with NPC differentiation and environmental conditions, which could have important implications with regard to their behavior after in vivo transplantation.