Tethered growth factors on biocompatible scaffolds improve stemness of cultured rat and human neural stem cells and growth of oligodendrocyte progenitors.

Currently, there is no widely accepted technique to efficiently and reproducibly grow stem and progenitor cells in vitro. Stem cells require contact with extracellular matrices as well as signals from growth factors to proliferate and to retain their stemness. We have shown a novel tissue culture platform (StemTrix cultureware) that transforms standard tissue culture plasticware into a multi-functional chitosan-based scaffold that supports the expansion of neural stem cells. The StemTrix scaffold is comprised of chitosan with immobilized heparin which in turn tethers heparin-binding growth factors. The scaffold is also coated with an adhesive ECM protein. Here we demonstrate that fibronectin or the RGD peptide contained in fibronectin are equally effective in promoting the adhesion, viability and growth of rat and human neural stem cells. When FGF-2 and heparin-binding EGF are tethered to the StemTrix cultureware neural stem cells grow ∼3 times faster and remain in a more primitive state as determined by both Western Blot and gene expression analyses. Another important feature of this new culture platform is that the NSCs remain in a primitive and proliferative state for 4days without refreshing the culture medium or providing new growth factors, which represents a 20-fold extension of FGF-2's biological activity vs when it is freely soluble in the medium. To test the utility of this scaffold for propagating other types of stem cells and progenitors we tethered platelet-derived growth factor (PDGF) and FGF-2 alone and in combination to the scaffold and tested the efficacy of this platform to maintain primary oligodendrocyte progenitors or the CG-4 cell line in a primitive state. Oligodendrocyte progenitors plated onto this multifunctional film proliferated for at least 3days without providing soluble growth factors while inhibiting the expression of the differentiation marker myelin-basic protein. Oligodendrocyte progenitors proliferated 3 times more rapidly than cells maintained on fibronectin-coated culture substrates in culture medium supplemented with soluble FGF-2 and PDGF. Finally, we show that StemTrix cultureware can be produced using clinical grade components, providing users with a fully defined platform suitable for clinical use that maintains stem cells or progenitors in a more uniform and primitive state.

Subacute Transplantation of Native and Genetically Engineered Neural Progenitors Seeded on Microsphere Scaffolds Promote Repair and Functional Recovery After Traumatic Brain Injury.

There is intense interest and effort toward regenerating the brain after severe injury. Stem cell transplantation after insult to the central nervous system has been regarded as the most promising approach for repair; however, engrafting cells alone might not be sufficient for effective regeneration. In this study, we have compared neural progenitors (NPs) from the fetal ventricular zone (VZ), the postnatal subventricular zone, and an immortalized radial glia (RG) cell line engineered to conditionally secrete the trophic factor insulin-like growth factor 1 (IGF-1). Upon differentiation in vitro, the VZ cells were able to generate a greater number of neurons than subventricular zone cells. Furthermore, differentiated VZ cells generated pyramidal neurons . In vitro, doxycycline-driven secretion of IGF-1 strongly promoted neuronal differentiation of cells with hippocampal, interneuron and cortical specificity. Accordingly, VZ and engineered RG-IGF-1-hemagglutinin (HA) cells were selected for subsequent in vivo experiments. To increase cell survival, we delivered the NPs attached to a multifunctional chitosan-based scaffold. The microspheres containing adherent NPs were injected subacutely into the lesion cavity of adult rat brains that had sustained controlled cortical impact injury. At 2 weeks posttransplantation, the exogenously introduced cells showed a reduction in stem cell or progenitor markers and acquired mature neuronal and glial markers. In beam walking tests assessing sensorimotor recovery, transplanted RG cells secreting IGF-1 contributed significantly to functional improvement while native VZ or RG cells did not promote significant recovery. Altogether, these results support the therapeutic potential of chitosan-based multifunctional microsphere scaffolds seeded with genetically modified NPs expressing IGF-1 to promote repair and functional recovery after traumatic brain injuries.

Optimizing a multifunctional microsphere scaffold to improve neural precursor cell transplantation for traumatic brain injury repair.

Tissue engineering using stem cells is widely used to repair damaged tissues in diverse biological systems; however, this approach has met with less success in regenerating the central nervous system (CNS). In this study we optimized and characterized the surface chemistry of chitosan-based scaffolds for CNS repair. To maintain radial glial cell (RGC) character of primitive neural precursors, fibronectin was adsorbed to chitosan. The chitosan was further modified by covalently linking heparin using genipin, which then served as a linker to immobilize fibroblast growth factor-2 (FGF-2), creating a multifunctional film. Fetal rat neural precursors plated onto this multifunctional film proliferated and remained multipotent for at least 3 days without providing soluble FGF-2. Moreover, they remained less mature and more highly proliferative than cells maintained on fibronectin-coated substrates in culture medium supplemented with soluble FGF-2. To create a vehicle for cell transplantation, a 3% chitosan solution was electrosprayed into a coagulation bath to generate microspheres (range 30-100 µm, mean 64 µm) that were subsequently modified. Radial glial cells seeded onto these multifunctional microspheres proliferated for at least 7 days in culture and the microspheres containing cells were small enough to be injected, using 23 Gauge Hamilton syringes, into the brains of adult rats that had previously sustained cortical contusion injuries. When analysed 3 days later, the transplanted RGCs were positive for the stem cell/progenitor marker Nestin. These results demonstrate that this multifunctional scaffold can be used as a cellular and growth factor delivery vehicle for the use in developing cell transplantation therapies for traumatic brain injuries. Copyright © 2013 John Wiley & Sons, Ltd.

Improvements in biomaterial matrices for neural precursor cell transplantation.

Progress is being made in developing neuroprotective strategies for traumatic brain injuries; however, there will never be a therapy that will fully preserve neurons that are injured from moderate to severe head injuries. Therefore, to restore neurological function, regenerative strategies will be required. Given the limited regenerative capacity of the resident neural precursors of the CNS, many investigators have evaluated the regenerative potential of transplanted precursors. Unfortunately, these precursors do not thrive when engrafted without a biomaterial scaffold. In this article we review the types of natural and synthetic materials that are being used in brain tissue engineering applications for traumatic brain injury and stroke. We also analyze modifications of the scaffolds including immobilizing drugs, growth factors and extracellular matrix molecules to improve CNS regeneration and functional recovery. We conclude with a discussion of some of the challenges that remain to be solved towards repairing and regenerating the brain.

Heparin crosslinked chitosan microspheres for the delivery of neural stem cells and growth factors for central nervous system repair.

An effective paradigm for transplanting large numbers of neural stem cells after central nervous system (CNS) injury has yet to be established. Biomaterial scaffolds have shown promise in cell transplantation and in regenerative medicine, but improved scaffolds are needed. In this study we designed and optimized multifunctional and biocompatible chitosan-based films and microspheres for the delivery of neural stem cells and growth factors for CNS injuries. The chitosan microspheres were fabricated by coaxial airflow techniques, with the sphere size controlled by varying the syringe needle gauge and the airflow rate. When applying a coaxial airflow at 30 standard cubic feet per hour, ∼300µm diameter spheres were reproducibly generated that were physically stable yet susceptible to enzymatic degradation. Heparin was covalently crosslinked to the chitosan scaffolds using genipin, which bound fibroblast growth factor-2 (FGF-2) with high affinity while retaining its biological activity. At 1µgml(-1) approximately 80% of the FGF-2 bound to the scaffold. A neural stem cell line, GFP+RG3.6 derived from embryonic rat cortex, was used to evaluate cytocompatibility, attachment and survival on the crosslinked chitosan-heparin complex surfaces. The MTT assay and microscopic analysis revealed that the scaffold containing tethered FGF-2 was superior in sustaining survival and growth of neural stem cells compared to standard culture conditions. Altogether, our results demonstrate that this multifunctional scaffold possesses good cytocompatibility and can be used as a growth factor delivery vehicle while supporting neural stem cell attachment and survival.