Source: Zhongshan School of Medicine
Edited by: Tan Rongyu, Wang Dongmei

Traumatic spinal cord injury can lead to spinal cord tissue defects. The harsh microenvironment in the injury area brings great challenges to the regeneration of spinal cord tissue and the survival of transplanted cells. Since the transplantation of embryonic spinal cord tissue in the injury site of spinal cord has been nearly 30 years, the idea of replacing the missing spinal cord neurons with embryonic spinal neurons and forming neuronal relay in the injury/graft site has been gradually formed and verified. However, the transplantation of embryonic spinal cord tissue is limited by ethical restrictions and the graft is obtained difficultly, which does not meet the requirements of clinical translation. The key for researchers to overcome the difficulties is how to effectively apply new tissue engineering techniques such as cytokines, biomaterials, stem cells and tissue culture time in vitro to construct neural network tissue similar to embryonic spinal cord. Recently, Professor Zeng Yuan-shan’s team of Sun Yat-sen University revealed that neurotrophin-3 (NT-3), a key molecule, was screened based on the bioinformatics of embryonic spinal cord development and the neural stem cells (NSCs) expressing NT-3 receptor (tyrosine kinase receptor C, TrkC) were induced to self-organize into a neural network tissue in three-dimensional (3D) scaffold materials by using NT-3 controlled release technique. The tissue-engineered neural network tissue can integrate functionally with the host spinal neural circuit after transplantation into rat spinal cord injury with complete transection. This therapeutic strategy provides a novel idea for the construction of a microenvironment optimized NSC-derived tissue engineering neural network tissue for repairing central nerve injury.

On April 8, 2021, the research results of Professor Zeng Yuan-shan’s team were published online in the international TOP publication Bioactive Materials (CAS Q1): “An NT-3-releasing bioscaffold supports the formation of TrkC-modified neural stem cell-derived neural network tissue with efficacy in repairing spinal cord injury”. The first author is Dr. Li Ge (Associate Researcher of Zhongshan School of Medicine, Sun Yat-sen University and Guangdong Provincial People’s Hospital); Professor Zeng Yuan-shan and Dr. Zeng Xiang (Researcher) are corresponding authors (Zhongshan School of Medicine, Sun Yat-sen University).

The mechanism underlying neurogenesis during embryonic spinal cord development involves a specific ligand/receptor interaction, which may be to help guide the construction of tissue-engineered neural network tissue for transplantation to repair the structure and function of spinal cord injury with complete transection. The present study analyzed embryonic spinal cord single cell atlases and found that NT-3 and its receptor TrkC played an important role in the development and maturation of spinal cord neurons. Then, a method of ligand/receptor interaction was designed to promote the self-organization of neural network tissue. The TrkC over-expressing NSCs were seeded into NT-3-releasing 3D scaffolds to differentiate into neurons with mature phenotype and electrophysiological function in the NT-3-enriched microenvironment. Most importantly, over time in culture, exogenous NT-3 created a unique ecological niche, together with growth factors and extracellular matrix (such as laminin) derived from autocrine stem cells. The dynamic integration of the neurotrophin, growth factor-derived from autocrine stem cells and extracellular matrix deposited on the scaffold promoted tissue-like assembly, and finally, it formed the neural network tissue that is composed of neurons with transmitting excitatory information, oligodendrocytes with myelinating potential, astrocytes, a few stem cells and extracellular matrix. After the neural network tissue was transplanted into the 2 mm gap of rat spinal cord transection, it was observed that the neural network tissue containing the ecological niche could survive for a longer time in the injury/graft area, maintain the differentiated phenotype of related cells, and form the structures of synapse and myelin sheath. In addition, host nerve fibers regenerated into the injury/graft area of spinal cord and they formed synaptic structures with transplanted NSC-derived neurons, which promoted the improvement of motor function of paralyzed hindlimbs in rats.

For focusing on improving the microenvironment in the spinal cord injury area and reconstructing the spinal cord neural circuit, this study takes the lead in simulating the mechanism of induced neuronogenesis between ligands and receptors during embryonic development. Tissue engineering design is carried out on the four elements of seed cells, bioactive factors, biological scaffold materials and tissue culture time. By optimizing biological materials and gene-modified stem cells, accurate engineering induction is realized to meet the needs of efficient tissue engineering for the construction of biological tissues.


Figure note: The sustained-release NT-3 three-dimensional microenvironment supports the self-organization of the NSCs into a neural network tissue with the function of repairing transected spinal cord injury. A: Single-cell data of embryonic spinal cord development revealed that, during the differentiation from neural progenitor cells to neurons, the neurotrophin-3 (NTF3, NT-3) was specifically expressed in motor neurons, while its receptor NTRK3 (TrkC) was not only expressed in the progenitor cells, but also widely expressed in various types of neurons. B: Immunoelectron microscopy showed NT-3 protein labeled with nanogold on the surface of the scaffolds. C: Showing cylindrical sustained-release scaffolds with the shape of biomimetic spinal cord. D: Displaying action potential of neurons in self-organizing neural network tissue in vitro. E: Spontaneous excitatory postsynaptic current was detected in the neuron. F: Immunoelectron microscopy showed that an oligodendrocyte formed myelin sheath to wrap nerve fiber in transplanted neural network tissue. G: Immunoelectron microscopy displayed that TrkC over-expressing neuron formed a synaptic structure in transplanted neural network tissue. H: Schematic diagram revealed that NT-3 sustained-release biological complex induces the formation of TrkC-modified NSC-derived neural network tissue. When the neural network tissue is transplanted into the injury/graft site of rat spinal cord, it can act as a tissue engineering neuronal relay and integrate functionally with host spinal cord tissue.

The present study was supported by grants from the major project of National Natural Science Foundation of China, the National Key R&D Program of China, the Foundation of Guangdong Province and the Start-up Foundation of Guangdong Province.

Link to the article: https://authors.elsevier.com/sd/article/S2452-199X(21)00147-X