Non-viral delivery of the gene for glial cell line-derived neurotrophic factor to mesenchymal stem cells in vitro via a collagen scaffold

Liposomes in tissue engineering and regenerative medicine

Liposomes are vesicular structures made of lipids that are formed in aqueous solutions. Structurally, they resemble the lipid membrane of living cells. Therefore, they have been widely investigated, since the 1960s, as models to study the cell membrane, and as carriers for protection and/or delivery of bioactive agents. They have been used in different areas of research including vaccines, imaging, applications in cosmetics and tissue engineering. Tissue engineering is defined as a strategy for promoting the regeneration of tissues for the human body. This strategy may involve the coordinated application of defined cell types with structured biomaterial scaffolds to produce living structures. To create a new tissue, based on this strategy, a controlled stimulation of cultured cells is needed, through a systematic combination of bioactive agents and mechanical signals. In this review, we highlight the potential role of liposomes as a platform for the sustained and local delivery of bioactive agents for tissue engineering and regenerative medicine approaches.

Glial cell line-derived neurotrophic factor gene delivery via a polyethylene imine grafted chitosan carrier

Parkinson’s disease is known to result from the loss of dopaminergic neurons. Direct intracerebral injections of high doses of recombinant glial cell line-derived neurotrophic factor (GDNF) have been shown to protect adult nigral dopaminergic neurons. Because GDNF does not cross the blood–brain barrier, intracerebral gene transfer is an ideal option. Chitosan (CHI) is a naturally derived material that has been used for gene transfer. However, the low water solubility often leads to decreased transfection efficiency. Grafting of highly water-soluble polyethylene imines (PEI) and polyethylene glycol onto polymers can increase their solubility. The purpose of this study was to design a non-viral gene carrier with improved water solubility as well as enhanced transfection efficiency for treating Parkinsonism. Two molecular weights (Mw =600 and 1,800 g/mol) of PEI were grafted onto CHI (PEI600-g-CHI and PEI1800-g-CHI, respectively) by opening the epoxide ring of ethylene glycol diglycidyl ether (EX-810). This modification resulted in a non-viral gene carrier with less cytotoxicity. The transfection efficiency of PEI600-g-CHI/deoxyribonucleic acid (DNA) polyplexes was significantly higher than either PEI1800-g-CHI/DNA or CHI/DNA polyplexes. The maximal GDNF expression of PEI600-g-CHI/DNA was at the polymer:DNA weight ratio of 10:1, which was 1.7-fold higher than the maximal GDNF expression of PEI1800-g-CHI/DNA. The low toxicity and high transfection efficiency of PEI600-g-CHI make it ideal for application to GDNF gene therapy, which has potential for the treatment of Parkinson’s disease.

Neural ECM mimetics

The consequence of numerous neurological disorders is the significant loss of neural cells, which further results in multilevel dysfunction or severe functional deficits. The extracellular matrix (ECM) is of tremendous importance for neural regeneration mediating ambivalent functions: ECM serves as a growth-promoting substrate for neurons but, on the other hand, is a major constituent of the inhibitory scar, which results from traumatic injuries of the central nervous system. Therefore, cell and tissue replacement strategies on the basis of ECM mimetics are very promising therapeutic interventions. Numerous synthetic and natural materials have proven effective both in vitro and in vivo. The closer a material's physicochemical and molecular properties are to the original extracellular matrix, the more promising its effectiveness may be. Relevant factors that need to be taken into account when designing such materials for neural repair relate to receptor-mediated cell-matrix interactions, which are dependent on chemical and mechanical sensing. This chapter outlines important characteristics of natural and synthetic ECM materials (scaffolds) and provides an overview of recent advances in design and application of ECM materials for neural regeneration, both in therapeutic applications and in basic biological research.

Scaffolds to promote spinal cord regeneration

Substantial research effort in the spinal cord injury (SCI) field is directed towards reduction of secondary injury changes and enhancement of tissue sparing. However, pathway repair after complete transections, large lesions, or after chronic injury may require the implantation of some form of oriented bridging structure to restore tissue continuity across a trauma zone. These matrices or scaffolds should be biocompatible and create an environment that facilitates tissue growth and vascularization, and allow axons to regenerate through and beyond the implant in order to reconnect with "normal" tissue distal to the injury. The myelination of regrown axons is another important requirement. In this chapter, we describe recent advances in biomaterial technology designed to provide a terrain for regenerating axons to grow across the site of injury and/or create an environment for endogenous repair. Many different types of scaffold are under investigation; they can be biodegradable or nondegradable, natural or synthetic. Scaffolds can be designed to incorporate immobilized signaling molecules and/or used as devices for controlled release of therapeutic agents, including growth factors. These bridging structures can also be infiltrated with specific cell types deemed suitable for spinal cord repair.

Advanced Strategies for Articular Cartilage Defect Repair

Articular cartilage is a unique tissue owing to its ability to withstand repetitive compressive stress throughout an individual's lifetime. However, its major limitation is the inability to heal even the most minor injuries. There still remains an inherent lack of strategies that stimulate hyaline-like articular cartilage growth with appropriate functional properties. Recent scientific advances in tissue engineering have made significant steps towards development of constructs for articular cartilage repair. In particular, research has shown the potential of biomaterial physico-chemical properties significantly influencing the proliferation, differentiation and matrix deposition by progenitor cells. Accordingly, this highlights the potential of using such properties to direct the lineage towards which such cells follow. Moreover, the use of soluble growth factors to enhance the bioactivity and regenerative capacity of biomaterials has recently been adopted by researchers in the field of tissue engineering. In addition, gene therapy is a growing area that has found noteworthy use in tissue engineering partly due to the potential to overcome some drawbacks associated with current growth factor delivery systems. In this context, such advanced strategies in biomaterial science, cell-based and growth factor-based therapies that have been employed in the restoration and repair of damaged articular cartilage will be the focus of this review article.

Physical non-viral gene delivery methods for tissue engineering

The integration of gene therapy into tissue engineering to control differentiation and direct tissue formation is not a new concept; however, successful delivery of nucleic acids into primary cells, progenitor cells, and stem cells has proven exceptionally challenging. Viral vectors are generally highly effective at delivering nucleic acids to a variety of cell populations, both dividing and non-dividing, yet these viral vectors are marred by significant safety concerns. Non-viral vectors are preferred for gene therapy, despite lower transfection efficiencies, and possess many customizable attributes that are desirable for tissue engineering applications. However, there is no single non-viral gene delivery strategy that "fits-all" cell types and tissues. Thus, there is a compelling opportunity to examine different non-viral vectors, especially physical vectors, and compare their relative degrees of success. This review examines the advantages and disadvantages of physical non-viral methods (i.e., microinjection, ballistic gene delivery, electroporation, sonoporation, laser irradiation, magnetofection, and electric field-induced molecular vibration), with particular attention given to electroporation because of its versatility, with further special emphasis on Nucleofection™. In addition, attributes of cellular character that can be used to improve differentiation strategies are examined for tissue engineering applications. Ultimately, electroporation exhibits a high transfection efficiency in many cell types, which is highly desirable for tissue engineering applications, but electroporation and other physical non-viral gene delivery methods are still limited by poor cell viability. Overcoming the challenge of poor cell viability in highly efficient physical non-viral techniques is the key to using gene delivery to enhance tissue engineering applications.

Treatment of penetrating brain injury in a rat model using collagen scaffolds incorporating soluble Nogo receptor

Injuries and diseases of the central nervous system (CNS) have the potential to cause permanent loss of brain parenchyma, with severe neurological consequences. Cavitary defects in the brain may afford the possibility of treatment with biomaterials that fill the lesion site while delivering therapeutic agents. This study examined the treatment of penetrating brain injury (PBI) in a rat model with collagen biomaterials and a soluble Nogo receptor (sNgR) molecule. sNgR was aimed at neutralizing myelin proteins that hinder axon regeneration by inducing growth cone collapse. Scaffolds containing sNgR were implanted in the brains of adult rats 1 week after injury and analysed 4 weeks or 8 weeks later. Histological analysis revealed that the scaffolds filled the lesion sites, remained intact with open pores and were infiltrated with cells and extracellular matrix. Immunohistochemical staining demonstrated the composition of the cellular infiltrate to include macrophages, astrocytes and vascular endothelial cells. Isolated regions of the scaffold borders showed integration with surrounding viable brain tissue that included neurons and oligodendrocytes. While axon regeneration was not detected in the scaffolds, the cellular infiltration and vascularization of the lesion site demonstrated a modification of the injury environment with implications for regenerative strategies.

Implantation of a collagen scaffold seeded with adult rat hippocampal progenitors in a rat model of penetrating brain injury

Penetrating brain injury (PBI) is a complex central nervous system injury in which mechanical damage to brain parenchyma results in hemorrhage, ischemia, broad areas of necrosis, and eventually cavitation. The permanent loss of brain tissue affords the possibility of treatment using a biomaterial scaffold to fill the lesion site and potentially deliver pharmacological or cellular therapeutic agents. The administration of cellular therapy may be of benefit in both mitigating the secondary injury process and promoting regeneration through replacement of certain cell populations. This study investigated the survival and differentiation of adult rat hippocampal neural progenitor cells delivered by a collagen scaffold in a rat model of PBI. The cell-scaffold construct was implanted 1 week after injury and was observed to remain intact with open pores upon analysis 4 weeks later. Implanted neural progenitors were found to have survived within the scaffold, and also to have migrated into the surrounding brain. Differentiated phenotypes included astrocytes, oligodendrocytes, vascular endothelial cells, and possibly macrophages. The demonstrated multipotency of this cell population in vivo in the context of traumatic brain injury has implications for regenerative therapies, but additional stimulation appears necessary to promote neuronal differentiation outside normally neurogenic regions.

Environmental parameters influence non-viral transfection of human mesenchymal stem cells for tissue engineering applications

Non-viral transfection is a promising technique that could be used to increase the therapeutic potential of stem cells. The purpose of this study was to explore practical culture parameters of relevance in potential human mesenchymal stem cell (hMSC) clinical and tissue engineering applications, including type of polycationic transfection reagent, N/P ratio and dose of polycation/pDNA polyplexes, cell passage number, cell density and cell proliferation. The non-viral transfection efficiency was significantly influenced by N/P ratio, polyplex dose, cell density and cell passage number. hMSC culture conditions that inhibited cell division also decreased transfection efficiency, suggesting that strategies to promote hMSC proliferation may be useful to enhance transfection efficiency in future tissue engineering studies. Non-viral transfection treatments influenced hMSC phenotype, including the expression level of the hMSC marker CD105 and the ability of hMSCs to differentiate down the osteogenic and adipogenic lineages. The parameters found here to promote hMSC transfection efficiency, minimize toxicity and influence hMSC phenotype may be instructive in future non-viral transfection studies and tissue engineering applications.

The reparative response to cross-linked collagen-based scaffolds in a rat spinal cord gap model

Prior work demonstrated the improvement of peripheral nerve regeneration in gaps implanted with collagen scaffold-filled collagen tubes, compared with nerve autografts, and the promise of such implants for treating gaps in spinal cord injury (SCI) in rats. The objective of this study was to investigate collagen implants alone and incorporating select therapeutic agents in a 5-mm full-resection gap model in the rat spinal cord. Two studies were performed, one with a 6-week time point and one with a 2-week time point. For the 6-week study the groups included: (1) untreated control, (2) dehydrothermally (DHT)-cross-linked collagen scaffold, (3) DHT-cross-linked collagen scaffold seeded with adult rat neural stem cells (NSCs), and (4) DHT-cross-linked collagen scaffold incorporating plasmid encoding glial cell line-derived neurotropic factor (pGDNF). The 2-week study groups were: (1) nontreated control, (2) DHT-cross-linked collagen scaffold; (3) DHT-cross-linked collagen scaffold containing laminin; and (4) carbodiimide-cross-linked collagen scaffold containing laminin. The tissue filling the defect of all groups at 6 weeks was largely composed of fibrous scar; however, the tissue was generally more favorably aligned with the long axis of the spinal cord in all of the treatment groups, but not in the control group. Quantification of the percentage of animals per group containing cystic cavities in the defect showed a trend toward fewer rats with cysts in the groups in which the scaffolds were implanted compared to control. All of the collagen implants were clearly visible and mostly intact after 2 weeks. A band of fibrous tissue filling the control gaps was not seen in the collagen implant groups. In all of the groups there was a narrowing of the spinal canal within the gap as a result of surrounding soft tissue collapse into the defect. The narrowing of the spinal canal occurred to a greater extent in the control and DHT scaffold alone groups compared to the DHT scaffold/laminin and EDAC scaffold/laminin groups. Collagen biomaterials can be useful in the treatment of SCI to: favorably align the reparative tissue with the long axis of the spinal cord; potentially reduce the formation of fluid-filled cysts; serve as a delivery vehicle for NSCs and the gene for GDNF; and impede the collapse of musculature and connective tissue into the defect.

Advances in progenitor cell therapy using scaffolding constructs for central nervous system injury

Traumatic brain injury (TBI) is a major cause of morbidity and mortality in the United States. Current clinical therapy is focused on optimization of the acute/subacute intracerebral milieu, minimizing continued cell death, and subsequent intense rehabilitation to ameliorate the prolonged physical, cognitive, and psychosocial deficits that result from TBI. Adult progenitor (stem) cell therapies have shown promise in pre-clinical studies and remain a focus of intense scientific investigation. One of the fundamental challenges to successful translation of the large body of pre-clinical work is the delivery of progenitor cells to the target location/organ. Classically used vehicles such as intravenous and intra arterial infusion have shown low engraftment rates and risk of distal emboli. Novel delivery methods such as nanofiber scaffold implantation could provide the structural and nutritive support required for progenitor cell proliferation, engraftment, and differentiation. The focus of this review is to explore the current state of the art as it relates to current and novel progenitor cell delivery methods.

Cell-controlled and spatially arrayed gene delivery from fibrin hydrogels

We investigated fibrin-mediated gene transfer by embedding pDNA within the hydrogel during polymerization and using two modes of gene transfection with cells placed either on the surface (2D transfection) or within the hydrogel (3D transfection). Using this model, we found that cell transfection depended strongly on the local cell-pDNA microenvironment as defined by the 2D vs. 3D context, target cell type and density, as well as fibrinogen and pDNA concentrations. When cells were embedded within the fibrin matrix lipofectamine-induced cell death decreased significantly, especially at low target cell density. Addition of fibrinolytic inhibitors decreased gene transfer in a dose-dependent manner, suggesting that fibrin degradation may be necessary for efficient gene transfer. We also provided proof-of-concept that fibrin-mediated gene transfer can be used for spatially localized gene delivery, which is required in cell-transfection microarrays. When lipoplex-containing hydrogels were spotted in an array format gene transfer was strictly confined to pDNA-containing fibrin spots with no cross-contamination between neighboring sites. Collectively, our data suggest that fibrin may be used as a biomaterial to deliver genes in an efficient, cell-controlled and spatially localized manner for potential applications in vitro or in vivo.