Transplantation of Schwann Cells Inside PVDF-TrFE Conduits to Bridge Transected Rat Spinal Cord Stumps to Promote Axon Regeneration Across the Gap

Novel Tissue-Engineered Multimodular Hyaluronic Acid-Polylactic Acid Conduits for the Regeneration of Sciatic Nerve Defect

The gold standard for the treatment of peripheral nerve injuries, the autograft, presents several drawbacks, and engineered constructs are currently suitable only for short gaps or small diameter nerves. Here, we study a novel tissue-engineered multimodular nerve guidance conduit for the treatment of large nerve damages based in a polylactic acid (PLA) microfibrillar structure inserted inside several co-linear hyaluronic acid (HA) conduits. The highly aligned PLA microfibers provide a topographical cue that guides axonal growth, and the HA conduits play the role of an epineurium and retain the pre-seeded auxiliary cells. The multimodular design increases the flexibility of the device. Its performance for the regeneration of a critical-size (15 mm) rabbit sciatic nerve defect was studied and, after six months, very good nerve regeneration was observed. The multimodular approach contributed to a better vascularization through the micrometrical gaps between HA conduits, and the pre-seeded Schwann cells increased axonal growth. Six months after surgery, a cross-sectional available area occupied by myelinated nerve fibers above 65% at the central and distal portions was obtained when the multimodular device with pre-seeded Schwann cells was employed. The results validate the multi-module approach for the regeneration of large nerve defects and open new possibilities for surgical solutions in this field.

Repair of the Injured Spinal Cord by Schwann Cell Transplantation

Spinal cord injury (SCI) can result in sensorimotor impairments or disability. Studies of the cellular response to SCI have increased our understanding of nerve regenerative failure following spinal cord trauma. Biological, engineering and rehabilitation strategies for repairing the injured spinal cord have shown impressive results in SCI models of both rodents and non-human primates. Cell transplantation, in particular, is becoming a highly promising approach due to the cells’ capacity to provide multiple benefits at the molecular, cellular, and circuit levels. While various cell types have been investigated, we focus on the use of Schwann cells (SCs) to promote SCI repair in this review. Transplantation of SCs promotes functional recovery in animal models and is safe for use in humans with subacute SCI. The rationales for the therapeutic use of SCs for SCI include enhancement of axon regeneration, remyelination of newborn or sparing axons, regulation of the inflammatory response, and maintenance of the survival of damaged tissue. However, little is known about the molecular mechanisms by which transplanted SCs exert a reparative effect on SCI. Moreover, SC-based therapeutic strategies face considerable challenges in preclinical studies. These issues must be clarified to make SC transplantation a feasible clinical option. In this review, we summarize the recent advances in SC transplantation for SCI, and highlight proposed mechanisms and challenges of SC-mediated therapy. The sparse information available on SC clinical application in patients with SCI is also discussed.

Engineered axon tracts within tubular biohybrid scaffolds

Injuries to the nervous system that involve the disruption of axonal pathways are devastating to the individual and require specific tissue engineering strategies. Here we analyse a cells-biomaterials strategy to overcome the obstacles limiting axon regenerationin vivo, based on the combination of a hyaluronic acid (HA) single-channel tubular conduit filled with poly-L-lactide acid (PLA) fibres in its lumen, with pre-cultured Schwann cells (SCs) as cells supportive of axon extension. The HA conduit and PLA fibres sustain the proliferation of SC, which enhance axon growth acting as a feeder layer and growth factor pumps. The parallel unidirectional ensemble formed by PLA fibres and SC tries to recapitulate the directional features of axonal pathways in the nervous system. A dorsal root ganglion (DRG) explant is planted on one of the conduit's ends to follow axon outgrowth from the DRG. After a 21 d co-culture of the DRG + SC-seeded conduit ensemble, we analyse the axonal extension throughout the conduit by scanning, transmission electronic and confocal microscopy, in order to study the features of SC and the grown axons and their association. The separate effects of SC and PLA fibres on the axon growth are also experimentally addressed. The biohybrid thus produced may be considered a synthetic axonal pathway, and the results could be of use in strategies for the regeneration of axonal tracts.

Designer, injectable gels to prevent transplanted Schwann cell loss during spinal cord injury therapy

Transplantation of patient-derived Schwann cells is a promising regenerative medicine therapy for spinal cord injuries; however, therapeutic efficacy is compromised by inefficient cell delivery. We present a materials-based strategy that addresses three common causes of transplanted cell death: (i) membrane damage during injection, (ii) cell leakage from the injection site, and (iii) apoptosis due to loss of endogenous matrix. Using protein engineering and peptide-based assembly, we designed injectable hydrogels with modular cell-adhesive and mechanical properties. In a cervical contusion model, our hydrogel matrix resulted in a greater than 700% improvement in successful Schwann cell transplantation. The combination therapy of cells and gel significantly improved the spatial distribution of transplanted cells within the endogenous tissue. A reduction in cystic cavitation and neuronal loss were also observed with substantial increases in forelimb strength and coordination. Using an injectable hydrogel matrix, therefore, can markedly improve the outcomes of cellular transplantation therapies.

On the Viability and Potential Value of Stem Cells for Repair and Treatment of Central Neurotrauma: Overview and Speculations

Central neurotrauma, such as spinal cord injury or traumatic brain injury, can damage critical axonal pathways and neurons and lead to partial to complete loss of neural function that is difficult to address in the mature central nervous system. Improvement and innovation in the development, manufacture, and delivery of stem-cell based therapies, as well as the continued exploration of newer forms of stem cells, have allowed the professional and public spheres to resolve technical and ethical questions that previously hindered stem cell research for central nervous system injury. Recent in vitro and in vivo models have demonstrated the potential that reprogrammed autologous stem cells, in particular, have to restore functionality and induce regeneration-while potentially mitigating technical issues of immunogenicity, rejection, and ethical issues of embryonic derivation. These newer stem-cell based approaches are not, however, without concerns and problems of safety, efficacy, use and distribution. This review is an assessment of the current state of the science, the potential solutions that have been and are currently being explored, and the problems and questions that arise from what appears to be a promising way forward (i.e., autologous stem cell-based therapies)-for the purpose of advancing the research for much-needed therapeutic interventions for central neurotrauma.

Aligned fibrous PVDF-TrFE scaffolds with Schwann cells support neurite extension and myelination in vitro

OBJECTIVE

Polyvinylidene fluoride-trifluoroethylene (PVDF-TrFE), which is a piezoelectric, biocompatible polymer, holds promise as a scaffold in combination with Schwann cells (SCs) for spinal cord repair. Piezoelectric materials can generate electrical activity in response to mechanical deformation, which could potentially stimulate spinal cord axon regeneration. Our goal in this study was to investigate PVDF-TrFE scaffolds consisting of aligned fibers in supporting SC growth and SC-supported neurite extension and myelination in vitro.

APPROACH

Aligned fibers of PVDF-TrFE were fabricated using the electrospinning technique. SCs and dorsal root ganglion (DRG) explants were co-cultured to evaluate SC-supported neurite extension and myelination on PVDF-TrFE scaffolds.

MAIN RESULTS

PVDF-TrFE scaffolds supported SC growth and neurite extension, which was further enhanced by coating the scaffolds with Matrigel. SCs were oriented and neurites extended along the length of the aligned fibers. SCs in co-culture with DRGs on PVDF-TrFE scaffolds promoted longer neurite extension as compared to scaffolds without SCs. In addition to promoting neurite extension, SCs also formed myelin around DRG neurites on PVDF-TrFE scaffolds.

SIGNIFICANCE

This study demonstrated PVDF-TrFE scaffolds containing aligned fibers supported SC-neurite extension and myelination. The combination of SCs and PVDF-TrFE scaffolds may be a promising tissue engineering strategy for spinal cord repair.

Microencapsulated Schwann cell transplantation inhibits P2X3 receptor expression in dorsal root ganglia and neuropathic pain

Schwann cell transplantation is a promising method to promote neural repair, and can be used for peripheral nerve protection and myelination. Microcapsule technology largely mitigates immune rejection of transplanted cells. We previously showed that microencapsulated olfactory ensheathing cells can reduce neuropathic pain and we hypothesized that microencapsulated Schwann cells can also inhibit neuropathic pain. Rat Schwann cells were cultured by subculture and then microencapsulated and were tested using a rat chronic constriction injury (CCI) neuropathic pain model. CCI rats were treated with Schwann cells or microencapsulated Schwann cells and were compared with sham and CCI groups. Mechanical withdrawal threshold and thermal withdrawal latency were assessed preoperatively and at 1, 3, 5, 7, 9, 11 and 14 days postoperatively. The expression of P2X3 receptors in L4-5 dorsal root ganglia of the different groups was detected by double-label immunofluorescence on day 14 after surgery. Compared with the chronic constriction injury group, mechanical withdrawal threshold and thermal withdrawal latency were higher, but the expression of P2X3 receptors was remarkably decreased in rats treated with Schwann cells and microencapsulated Schwann cells, especially in the rats transplanted with microencapsulated Schwann cells. The above data show that microencapsulated Schwann cell transplantation inhibits P2X3 receptor expression in L4-5 dorsal root ganglia and neuropathic pain.