| BackgroundSpinal cord injury(SCI)is a disease with high disability rates,numerous complications and poor prognosis with traditional treatments.Due to its expensive treatment costs,it causes a heavy burden on both families and countries every year.According to clinical trial results,human umbilical cord mesenchymal stem cell transplantation is a long-term safe and reliable treatment technology,which usually stimulates endogenous repair through paracrine.However,its therapeutic effect on SCI is still limited,which may be related to its hardly long-term survival at the injury site.Biomedical engineering technology is expected to solve this problem.Hyaluronic acid hydrogel is a type of biodegradable and water-soluble gel scaffold that simulates the natural extracellular matrix of the central nervous system.It can fill damaged tissue and provide effective physical and biochemical support for regenerated neurons and transplanted cells.Previous studies have shown that dopamine nanoparticles can reduce reactive oxygen species in the environment,facilitate the survival of transplanted stem cells at the injury site;inhibit the activation of microglia,reduce inflammation,which will promote functional recovery after SCI.This study aimed to construct a multifunctional "carrier"(HA-P-M hydrogel)that can carry human umbilical cord mesenchymal stem cells,repair the injured microenvironment of the spinal cord and promote endogenous stem cell regeneration and repair,which will provide a potential therapeutic strategy for the treatment of SCI.ObjectiveTo investigate whether the dopamine nanoparticle-modified hydrogel scaffold which carry human umbilical cord mesenchymal stem cells can repair spinal cord injury and its cellular mechanism.Methods and resultsIn this study,we used the hyaluronic acid hydrogel modified by dopamine monomer(HA-DA).The dopamine group could neutralize the strong oxidation of sodium periodate as a crosslinking agent and also enhance the biological adhesion of hyaluronic acid hydrogel,so that it could be effectively connected to the cranial and caudal of lesion site.The characterization of HA-DA was verified by Fourier-transform infrared spectroscope and proton nuclear magnetic resonance.The results showed that the dopamine group had been successfully grafted onto the hyaluronic acid.The results of transmission electron microscopy showed that PDA NP was successfully prepared and the average diameter was between 140 nm and 400 nm.20 μg/ml PDANP had the highest biocompatibility with human umbilical cord mesenchymal stem cells,so 20μg/ml was selected for premixed with hyaluronic acid hydrogel.At the same time,the experimental results also demonstrated that PDA NP can effectively reduce ROS in microglia cells,thereby reducing microglia’s secretion of inflammatory factors,such as IL-1β and IL-6,which will reduce the inflammatory response after spinal cord injury.qPCR results showed that HA-P-M hydrogel could increase the expression of Tujl and MAP2 by 3 times and reduce the expression of GFAP by 0.5 times.In this study,the transverse spinal cord injury model was used.In vivo,the results showed that the HAP-M group had an obvious movement in hind limb.In order to study the mechanism of repairing spinal cord injury with HA-P-M hydrogel,the potential cellular and molecular mechanism was analyzed and predicted by RNA-seq technology.The analyzed results showed that the HA-P-M hydrogel could reduce the inflammatory and immune responses at the injured area,and increase the number of new neurons in the injured area.The experiments to verify the results was performed,and the results showed that after spinal cord injury,the expression of pro-inflammatory factors was down-regulated,the expression of anti-inflammatory factors was up-regulated,and the number of neurons was increased.NestincreERT2::Rosa26LSL-tdTomato transgenic mouse was used to track endogenous stem cells and investigate the effect of the biological scaffold on endogenous neural stem cells.The results showed that the biological scaffold could effectively promote the recruitment of endogenous neural stem cells and effectively supplement new neurons at the site of injury.ConclusionPolydopamine-modified hydrogel scaffold loaded with human umbilical cord mesenchymal stem cells can repair spinal cord injury by reducing reactive oxygen species in microglia,alleviating inflammation at the injury site,promoting proliferation of endogenous neural stem cells and their differentiation into neurons,which will promote functional recovery after spinal cord injury. |
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