Treatment of Syringomyelia Characterized by Focal Dilatation of the Central Canal Using Mesenchymal Stem Cells and Neural Stem Cells

Abstract

BACKGROUND:

Syringomyelia is a progressive chronic disease that leads to nerve pain, sensory dissociation, and dyskinesia. Symptoms often do not improve after surgery. Stem cells have been widely explored for the treatment of nervous system diseases due to their immunoregulatory and neural replacement abilities.

METHODS:

In this study, we used a rat model of syringomyelia characterized by focal dilatation of the central canal to explore an effective transplantation scheme and evaluate the effect of mesenchymal stem cells and induced neural stem cells for the treatment of syringomyelia.

RESULTS:

The results showed that cell transplantation could not only promote syrinx shrinkage but also stimulate the proliferation of ependymal cells, and the effect of this result was related to the transplantation location. These reactions appeared only when the cells were transplanted into the cavity. Additionally, we discovered that cell transplantation transformed activated microglia into the M2 phenotype. IGF1-expressing M2 microglia may play a significant role in the repair of nerve pain.

CONCLUSION:

Cell transplantation can promote cavity shrinkage and regulate the local inflammatory environment. Moreover, the proliferation of ependymal cells may indicate the activation of endogenous stem cells, which is important for the regeneration and repair of spinal cord injury.

Supplementary Information

The online version contains supplementary material available at 10.1007/s13770-024-00637-1.

Introduction

Syringomyelia refers to a longitudinally oriented fluid-filled cavity within the spinal cord [1]. The pathogenesis of syringomyelia is mainly caused by Chiari malformation, but it can also result from spinal cord injury, tumors, myelitis, arachnoiditis, tethered cord, and other factors. Acquired syringomyelia is believed to be caused by a disruption in normal cerebrospinal fluid (CSF) circulation. However, the pathogenesis of acquired syringomyelia is still disputed [2–4].

Syringomyelia is a chronic, progressive disease. It can cause progressive loss of function or even mobility and often requires surgical intervention. Although the progression of functional impairment can be stabilized after intervention, the symptoms usually persist. In particular, a debilitating central pain syndrome may prove to be quite therapy-resistant, despite adequate surgical therapy and collapse of the syrinx on imaging [4].

Several studies have demonstrated the benefits of cell therapy, which has emerged as a prominent treatment for spinal cord injury and trauma-induced syringomyelia [5–10]. Mesenchymal stem cells (MSCs) are widely employed due to their immunomodulatory capabilities, as well as their ability to bypass ethical barriers associated with stem cell transplantation [11]. Induced neural stem cells (iNSCs) are a predominant cell type in current research on neural stem cell therapy for spinal cord injury [12, 13] because NSCs may differentiate into neurons in the spinal cord to replace dead neurons. However, few studies have been performed on cell therapy for focal dilatation of central canal (FDCC)-syringomyelia [14, 15]. In 2022, a case report reported that MSCs were effective in treating this kind of syringomyelia, but direct evidence between cells and syringomyelia was lacking [14]. Regarding the application of neural stem cells, there have been no reports on the application of neural stem cells to such syringomyelic models. In addition, there is no systematic research on cell transplantation methods. In this study, we first used iNSCs to confirm an effective transplantation method and then compared the effects of iNSCs and MSCs on syringomyelia. We utilized iNSCs and MSCs for cell intervention experiments on an FDCC-syringomyelia rat model developed in our laboratory, which involved extradural compression to block CSF flow [16]. This study will provide research evidence for the possibility of cell therapy for FDCC-syringomyelia. We believe that cell therapy has a potential effect on cavity contraction and alleviates neuropathic pain, offering hope for the effective treatment of syringomyelia.

Materials and methods

Animals

A total of 20 adult female Sprague–Dawley rats weighing 220–250 g (WeiTong LiHua, Beijing, China) were used to establish the syringomyelia model. Fifteen rats met the inclusion criteria and were included in the experimental group. These 15 rats exhibited central canal dilatation in MRI results, with a maximum diameter of central canal dilatation > 0.5 mm. The experiment consisted of four transplantation groups: iNSCs transplanted in the syrinx (iNSC-syrinx group, three animals), iNSCs transplanted in the parenchyma of the spinal cord (iNSC-parenchyma group, three animals), MSCs transplanted in the syrinx (MSC-syrinx group, three animals), and vehicle transplanted in the syrinx (vehicle group, six animals) groups. All rats were housed under standard housing conditions at the Animal Experiment Center of Xuanwu Hospital. The animal experiments were approved by the Animal Ethics Committee of Xuanwu Hospital (XW-20210723-1) and adhered to the China Animal Management Regulations.

Animal surgery and syringomyelia model establishment

The detailed surgical procedures are described in our previous study [16]. Briefly, under anesthesia, a 3 cm incision was made in the middle of the rat’s back. Using a microscope, the paravertebral muscles and tissues of the intervertebral space between T12 and T13 were dissected to expose the T12/T13 intervertebral space and ligament flavum. The ligamentum flavum was then carefully cut using coronal scissors. Cotton wool strips were twisted into long, thin pieces and inserted into the extradural space below the T13 lamina. After flushing the surgical area with saline solution, the muscles and skin were sutured. Intraperitoneal injection of penicillin was administered to prevent postoperative infections.

In vivo MRI

The detailed procedures for the in vivo MRI are described in our previous study [16]. Briefly, a 7.0 A Tesla MRI scanner (PharmaScan 7 T, Bruker Corp., Karlsruhe, Germany) with 400 mT/m gradients was used for the MRI test. The rats were positioned on a table and secured with two restraining belts to immobilize the trunk. Following rapid whole-body localization scans, sagittal and axial T2-weighted images were acquired using a fat-saturated RARE sequence, with the operation site as the center. A rat volume coil with an 89 mm diameter was employed for transmission and data collection. Data analysis was conducted using RadiAnt DICOM Viewer software (Version 4.6.9, Medixant, Poznan, Poland).

Cell preparation

MSCs were extracted from the bone marrow of 4-week-old male young SD rats and cultured until the P1 generation. They were then frozen and stored in a laboratory refrigerator at − 80 °C until future use. The P1 generation of MSCs was resuscitated before the experiment, and lentivirus with FUGW (containing EGFP gene fragment, Addgene) was transfected when the cell proliferation reached 80%. The cells were labeled with GFP and cultured to the P3 generation for transplantation. The GFP knock-in induced neural stem cell (iNSC) cell line has been described in our previous work [17, 18]. The suspension of MSCs included 5 × 10⁴ cells/µL and iNSCs 1 × 10⁵ cells/µL.

Decompression operation and cell transplantation

Six weeks after the surgery, rats with syrinx underwent decompression following the method described in our previous study [16]. Briefly, the rats were anesthetized with enflurane, and the lamina and strip were removed. Cotton was carefully stripped from the compression site without causing damage to the spinal cord. The cell transplantation method was as follows: MRI was performed to locate the syrinx, and the transplantation site was located according to the location of the syrinx, which is shown in Fig. 1A and B. The compressed anterior edge (rostral) and the midpoint of the spinal cord were used as origin points (X = 0). The distance from the syrinx to the origin point was Y, and the depth was Z. A microsyringe (Agilent, 10 µL) under a stereoscope (RWD) was used to determine the transplantation site. The total volume of transplanted cell suspension was 10 µL per rat. All rats were immunosuppressed with once daily subcutaneous administration of 10 mg/kg cyclosporin (Sandimmun, Novartis) starting 24 h before transplantation.

Fig. 1.

The site of transplantation impacts the outcome. A, B Transplant sites (X = 0); C–E MRI images of rat spinal cord in three groups before and after cell transplantation; F The percent of syrinx shrank ratio in the three groups. (n = 3; *p < 0.05; **p < 0.01; ***p < 0.001)

Immunohistochemical analysis

Two weeks after cell transplantation, all rats were transcardially perfused with 0.9% NaCl solution, followed by 4% paraformaldehyde (PFA). The spinal cord was postfixed, soaked in 30% sucrose solution at 4 °C for 48 h, and then embedded in OCT compound. The spinal cord segments containing cavities were either frozen and stored at − 80 °C or sectioned at 20 µm thickness using a low-temperature microtome and placed on slides. For immunofluorescence, the following primary antibodies were used: mouse anti-green fluorescent protein (GFP, 1:500, eBiosciense), goat anti-ionized calcium binding adaptor molecule-1 (Iba1, 1:500, Abcam), mouse-anti GFAP (1:500, Santa Cruz), rabbit-anti GFAP (1:200, Zhong Shan Jin Qiao), mouse anti-SOX2 (1:400, Santa Cruz), rabbit-anti SOX2 (1:400, CST), mouse-anti nestin (1:400, Millipore), mouse-anti human nuclei (Hu-Nu, 1:500, Millipore), rabbit-anti KI67 (1:500, Millipore), rabbit-anti CD206 (1:400, ABclonal), and rabbit-anti TNF-α (1:400, ABclonal). Primary antibodies were diluted in 0.01 M phosphate buffer with 0.3% Triton X-100 (PBST). Secondary antibodies were conjugated to Alexa Fluor 488 (1:200, Jackson), Cy3 (1:200, Jackson), or Alexa Fluor 647 (1:200, Jackson). All sections were preincubated in PBST with 3% donkey serum albumin for 30 min, incubated with primary antibodies overnight at 4 °C, rinsed, and then incubated with secondary antibodies for 1 h at room temperature. Finally, all sections were counterstained with the nuclear marker DAPI (1 µg/mL, Yeasen). The images were captured using a Leica SCN400 Slide Scanner confocal microscope (Leica Microsystems).

Measurement standard of the syrinx

The diameter of all the syrinx observed in the MRI results was measured as depicted in Fig. 1C–E, and the sum of the diameters was the size of the syrinx. The percent of syrinx shrinkage was the ratio of the cavity shrinkage value post-transplantation to the cavity size pre-transplantation.

Statistical analysis

Quantitative assessments following cell transplantation were conducted at the spinal segment coinciding with the syrinx location. Average optical density measurements utilized Photoshop and ImageJ software. Cell viability statistics determined the proportion of viable cells within the region containing the transplanted cells. The results are expressed as the mean ± SEM (standard error of the mean, SEM). Statistical analysis was performed using SPSS Statistics 20 software. The Gaussian distribution of the datasets was assessed using a one-sample Kolmogorov–Smirnov test. One-way ANOVA was used to determine the differences between multiple groups. A value of p < 0.05 was considered statistically significant.

Results

The restoration of the syrinx is related to the location of the transplant cells

INSCs were transplanted into the syrinx and parenchyma of the spinal cord to determine which method was effective for syringomyelia. The iNSC suspension and vehicle were transplanted separately into the largest cavity of the spinal cord, and another group was transplanted with iNSCs into the parenchyma of the spinal cord. The transplanted site location is depicted in Fig. 1A and B, which was determined by MRI. Through MRI, we found that the cavity of the central canal shrank when iNSCs were transplanted into the syrinx rather than transplanted into the parenchyma (Fig. 1C and D), and the contraction of the syrinx was not complete in the control group (Fig. 1E). The syrinx exhibited a reduction of 87.4% ± 21.82% in the iNSCs transplanted in the syrinx group, 11.6% ± 9.8% in the iNSCs transplanted in the parenchyma group, and 36.68% ± 27.71% in the vehicle group (Fig. 1F). These findings were consistent with tissue staining, which revealed a significant reduction in the dilated central canal following iNSC transplantation into the syrinx compared to the other two groups (Fig. 2). Although decompression alone could lead to a contraction in the syrinx size in the absence of cellular intervention, this effect was inferior to that of cell transplantation in the syrinx. In conclusion, cell transplantation plays a crucial role in syrinx contraction and is dependent on the location of transplantation.

Fig. 2.

Cell transplantation in the syrinx promotes cavity recovery. A Control group transplanted buffer solution; B INSC were transplanted far away from the cavity; C INSC were transplanted into the syrinx. The syrinx is reduced, and iNSCs can be seen in the syrinx. (red arrowhead indicates the cell transplant site; Bar = 0.5 mm)

Both MSCs and iNSCs can promote syrinx shrinkage

We observed a reduction in the syrinx size after iNSCs were transplanted into the syrinx. We then transplanted MSCs into the syrinx to compare the effect of the two cells on syringomyelia. A total of six rats were used, including three transplanted with MSCs and three transplanted with vehicle. The syrinx shrank obviously when MSCs and iNSCs were transplanted into the syrinx versus the vehicle group, as shown by MRI, and immunofluorescence staining also showed a reduction in the syrinx size in the MSC- and iNSC-transplanted groups (Fig. 3A–C). There was no significant difference in the effect of MSCs and iNSCs on syrinx shrinkage by statistical analysis (Fig. 3D). A small number of GFP-labeled iNSCs expressing anti-human nuclear protein were found in the central canal (Fig. 3c1–c3). Neural stem cells exhibited a survival rate of approximately 12%, whereas mesenchymal stem cells (MSCs) demonstrated a survival rate of approximately 77% (Fig. S1). The results showed that both kinds of cells could cause cavity shrinkage, but the effect was not different.

Fig. 3.

The cavity contracted after MSCs and iNSCs were transplanted into the syrinx. A MRI image of rat spinal cord pre- and posttransplantation in the control group and immunofluorescence staining of corresponding rat spinal cord sections. It exhibited a persistently large syrinx; B MSCs transplanted into the syrinx. MRI image and immunofluorescence results indicate that the syrinx shrank in the same rat. C We could see iNSCs in the syrinx, and the syrinx shrank. c1–c3 Enlarged view of iNSCs at corresponding positions in successive slices (Hu-Nu, human nuclear antigen is red and GFP is green). D The percent of syrinx shrank ratio in the three groups. Bar = 200 µm (in A–C); Bar = 100 µm (in c1-c3) (n = 3; *p < 0.05; **p < 0.01; ***p < 0.001)

Ependymal cell proliferation after cells are transplanted into the central canal

Sox2 + ependymal cells indicated the location of the central canal (Fig. 4A–D). We found thickening of ependymal cells after cell transplantation in the syrinx, indicating their proliferation. Comparing the expression of SOX2 + cells under the different conditions, we found a higher number of Sox2-positive ependymal cells after MSC and iNSC transplantation into the syrinx compared to the condition without cells in the syrinx (Fig. 4E). Rats without iNSC transplantation exhibited a persistently large syrinx with no noticeable proliferation of ependymal cells (Fig. 4B and E). Meletis identified endogenous NSCs as ependymal cells through genetic profiling [19]. The increased proliferation of ependymal cells suggests that the transplantation of cells may activate endogenous stem cells. To confirm this, we stained for the stem cell marker nestin. Two weeks after transplantation, we observed an increase in nestin-positive cells in both the MSC and iNSC transplantation groups compared to the vehicle and naïve groups, where no differences were observed between the MSC and iNSC transplantation groups (Fig. 5). These results suggest that cell transplantation into the syrinx may promote the activation of endogenous stem cells.

Fig. 4.

Effect of cell transplantation on ependymal cells. A–D The morphology of the central canal in the vehicle, MSC and iNSC transplantation groups. Sox2-positive cells were central ependymal cells. E Integrated optical density of sox2-positive ependymal cells per unit length (n = 6; *p < 0.05; **p < 0.01; ***p < 0.001; Bar = 200 µm)

Fig. 5.

Expression of Nestin + cells after cell transplantation. A Expression of nestin in the central canal of rats in different groups; Nestin-positive cells increased in the vehicle-, iNSC- and MSC-transplanted groups. B Comparison of nestin + cells under four different conditions. Bar = 50 µm (n = 3; *p < 0.05; **p < 0.01; ***p < 0.001)

Additionally, no Ki67-positive cells were detected in the proliferated ependymal cells, suggesting that these cells did not continue to proliferate at this time, thereby reducing the risk of tumorigenesis (results not shown).

Activated microglial polarization into the M2 phenotype after cell transplantation

Under homeostatic conditions, microglia exhibit a ramified morphology and are distributed outside ependymal cells [20]. However, when the syrinx was formed, microglia were activated, leading to enlarged cell bodies and a change in morphology to spherical or rod-shaped appearances (Fig. 6A) [21]. Due to dilation of the central canal, the tight connection between ependymal cells was disrupted, resulting in increased spacing between cells and invasion of microglia into the ependymal cell layer. Although the syrinx recovered and ependymal cells proliferated after cell transplantation, microglia were still present, and their numbers increased. The expression of microglia was higher in the MSC and iNSC transplantation groups, primarily concentrated at the cell transplantation site or around the ependymal cells 2 weeks after transplantation (Fig. 6B).

Fig. 6.

Activation of Iba1-positive microglia cells around the syrinx. A Compared with naïve rats, microglia invaded ependymal cells after transplantation and became activated. B Quantitative analysis of microglia under different conditions and microglial proliferation after iNSC and MSC transplantation (area within 0.5 mm around the syrinx) (n = 6; Bar = 200 μm; *p < 0.05; **p < 0.01; ***p < 0.001)

Microglia have two major phenotypes, known as M1 and M2 [22]. M1-type microglia are associated with tissue injury and inflammation, and they recruit inflammatory cells by expressing cytokines such as tumor necrosis factor (TNF)-α and interleukin (IL)-1β. Conversely, M2-type microglia regulate tissue repair and have anti-inflammatory effects. M2-type microglia express IL-4, IL-10, CD206 and growth factors such as insulin-like growth factor 1 (IGF1) and transforming growth factor (TGF)-β [23]. In our results, we found that few microglia expressed TNF-α and CD206 (Fig. 7). Further analysis revealed that the activated microglia predominantly expressed IGF1 (Fig. 8A), indicating their polarization into the M2 phenotype, which promotes nerve repair and exhibits anti-inflammatory properties [22, 23]. IGF1 was significantly increased after cell transplantation, especially in the MSC-transplanted group (Fig. 8B). Previous studies have highlighted the critical role of microglia in regulating spontaneous recovery and protecting neural tissues after spinal cord injury (SCI) [24, 25]. Keita Kohno et al. noted that IGF1-expressing microglia were a key factor in remitting and relapsing neuropathic pain [26]. Therefore, cell transplantation may have an advantageous effect on the recovery of nerve pain after syringomyelia, especially under the action of MSCs.

Fig. 7.

CD206 and TNF-α were not primarily expressed by microglia. A and B CD206 and TNFα were expressed after MSC and iNSC transplantation, but they were rarely expressed by microglia. C No microglia expressed CD206 and TNF-α in the vehicle groups. (Yellow arrowhead indicates microglia expressing TNFα or CD206)

Fig. 8.

Predominance of M2-type microglia A activated microglia mainly expressed IGF1 in the iNSC and MSC transplantation groups (yellow arrowhead indicates microglia expressing IGF1). B Quantitative analysis of IGF1 under different conditions. The expression of IGF1 was increased after iNSC and MSC transplantation (n = 6; *p < 0.05; **p < 0.01; ***p < 0.001)

Discussion

In this study, cell therapy was carried out based on a novel FDCC-syringomyelia model. Unexpectedly, we found that it could not only cause cavity recovery but also promote the proliferation of ependymal cells after MSCs and iNSCs were transplanted, and this phenomenon can only be caused when cells are transplanted into the cavity. These results have important implications for the activation of endogenous stem cells and nerve regeneration after syringomyelia. More work should be done to identify the role of endogenous stem cells in future research.

The underlying clinical pathogenesis of nerve pain and sensory disturbances in syringomyelia remains unclear. Even after syrinx reduction surgery, symptoms may not be alleviated, possibly due to nerve injury or the chronic inflammatory environment associated with syringomyelia. First, some studies have shown that the basic pathology in syringomyelia is a progressively expanding cavity in the central spinal canal. This expanding CSF-filled “syrinx” compresses the spinothalamic tract neurons decussating in the anterior white commissure. However, the posterior columns are spared, as they are located distally. This results in loss of pain and temperature sensation with preserved touch and vibratory sense (segmental dissociated sensory loss) [27]. Therefore, spinal cord injury caused by the pressure of the enlarged cavity is one of the causes of the disease symptoms. Removing the pressure caused by the syrinx by reducing the syrinx is significant for symptom recovery. Second, the unfavorable environment also leads to further nerve damage and hinders nerve regeneration and repair. Cell therapy has the potential to improve the local inflammatory environment and promote nerve regeneration.

MSCs, known for their paracrine signaling, have been shown to play a crucial role in tissue repair and microenvironment regulation in spinal cord injury treatment [11, 28, 29]. Neural stem cells are also involved in cell-mediated regeneration and plasticity following spinal cord injury [30]. The primary rationale for employing neural stem cells involves leveraging their neuron replacement capability, which may aid in the restoration of damaged sensory neurons around the cavity. However, no nerve cells derived from induced neural stem cells (iNSCs) were detected 2 weeks post-transplantation. This absence might be attributable to the cell survival rate and the timing of the experimental endpoint. Enhancing the cell survival rate and extending observation durations are essential for future research.

Doses for cell transplantation have undergone validation by researchers. Optimal results were observed with higher doses of neural stem cells (> 3 × 10⁶ cell/kg) [31]. Nonetheless, the cell suspension must not exert excessive pressure on the spinal cord. Typical neural stem cell transplantation employs a concentration of 1 × 10⁵/μL. Considering the weight of the rat, a 10 μL suspension was utilized as the total transplantation volume, equating to 1 × 10⁶ cells in total. For intramedullary transplantation, studies have evaluated various doses of mesenchymal stem cells (MSCs). The findings indicate that higher doses may enhance neuroprotective effects[32]. However, given the cell volume, the maximum number of cells that can be suspended in a given liquid volume is limited. Additionally, higher cell concentrations presented complications during transplantation due to the cell density, challenging the maintenance of a stable suspension in the syringe and necessitating resuspension between injections. Therefore, a concentration of 50,000 cells/μL was selected for this study, with a total volume of 10 μL and a total cell count of 5 × 10⁵.

The purpose of this study was to treat syringomyelia with these two types of cells from the perspective of improving the environment and nerve regeneration. However, due to the limitations of the model, the sensation test results in live rats cannot be verified. The reason is that the model is based on spinal cord compression, resulting in syringomyelic formation. Although previous modeling experiments have indicated that the spinal cord is not damaged after compression is removed, compression can still cause irreversible damage to the spinal cord in some animals, which affects the authenticity of animal sensory evaluation, so this part of the data was not shown. In fact, sensory assessment methods in rats do not simulate a clinical situation. We can only use temperature and pain perception to test the sensory changes of rats’ hind limbs, which requires a large number of model animals as a basis. The data that can be included in the statistics are those rats with undamaged spinal cords and successful cell transplants. This will be carried out in the next experiment.

This result suggested that the persistence of primary symptoms is the key factor that can interfere with the recovery of syringomyelia. It is not enough to reduce the enlarged cavity, and a surgical operation that can remove the original symptom is necessary. The results of this study indicate that stem cell transplantation can significantly reduce the cavity and improve the microenvironment, highly suggesting that cell therapy can improve the sensory disturbance caused by the cavity. If stem cell therapy can be used at the same time through surgery, it may be an effective way to relieve symptoms caused by sensory pathways.

The localization and function of ependymal cells within the CNS ventricular system make them important cellular barriers that regulate the transport and exchange of molecules between the brain and the body [33]. Some articles point out that the blood-CSF barrier and the CSF-brain barrier are derived from ependymal cells and primarily function to regulate CSF homeostasis and dynamics [34]. Syringomyelia results in central canal dilation, which breaks the arrangement and tight junctions between individual ependymal cells, severely disrupting barrier function and contributing to aspects of neurodegeneration [33]. After cell transplantation, the ependymal cell layer thickens, which may promote the proliferation of endogenous stem cells. This thickening may play a crucial role in establishing a robust barrier function, preventing further expansion of the cavity and subsequent nerve injury. Further research is needed to determine whether ependymal cell recovery or replenishment can be achieved following injury or dysfunction.

The microenvironment surrounding endogenous neural stem cells has been recognized as a crucial factor in stem cell-mediated neural repair [35]. Studies have demonstrated that bFGF-MSCs can enhance the proliferation of endogenous stem cells [36]. Lineage tracing experiments have shown that endogenous neural stem cells can be activated, migrate to the site of injury, and differentiate into glial cells [37, 38]. The glial scar, often considered inhibitory, also plays a beneficial role in containing secondary damage caused by prolonged inflammation at the injury site [39, 40]. The proliferation of endogenous stem cells is necessary to prevent further expansion of the injury, provide neurotrophic support [41], and affects immune regulation and myelin regeneration [42]. Therefore, the proliferation of ependymal cells and increased expression of nestin-positive cells indicate an enhanced potential for the activation of endogenous stem cells, which may contribute to the improvement of the inflammatory environment at the syrinx site. This, in turn, is beneficial for tissue repair, nerve regeneration, and the treatment of sensory disorders associated with syringomyelia. This study emphasizes the importance of precise localization of cell transplantation to mobilize stem cells and avoid occupying normal tissue. Future studies aim to optimize the transplantation protocol and achieve precise localization.

Microglia were activated and proliferated following decompression and cell transplantation. This activation may be attributed to the presence of exogenous grafts and the stress response after decompression. Several studies have indicated that microglia are highly dynamic and undergo extensive proliferation during the initial 2 weeks, accumulating around the lesion [24]. However, the transplanted cells influenced the transformation of activated microglia into M2 cells, initiating neuroprotective functions. At this stage, the microglia present in the syrinx and surrounding the transplanted cells may play a significant role in regulating the local microenvironment of the syrinx, promoting the recovery of syringomyelia and relieving nerve pain.

In clinical cases, sensory disturbances resulting from syringomyelia often persist post-decompression surgery despite a reduction in the cavity size. This persistence may be attributed to sensory neuron damage induced by the cavity. Stem cells could be pivotal in ameliorating the cavity’s inflammatory environment and facilitating nerve regeneration. In this study, the transplanted cells markedly reduced the cavity size and enhanced the proliferation of anti-inflammatory microglia, thereby creating conducive conditions for nerve regeneration. This research offers a novel treatment approach for syringomyelia.

Supplementary Information

Below is the link to the electronic supplementary material.

Author contributions

The authors would like to thank XW and BQ for their contribution to the model-building and cell transplantation experiments. We also thank SC for the tissue sectioning and staining, TZ for preparing cells, and YG, LM, SL, QL, ZC, and FJ for their contribution to the design.

Data availability

The datasets generated during and/or analysed during the current study are available from the corresponding author on reasonable request.

Declarations

Conflict of interest

The authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest.

Ethical statement

The animal studies were performed after receiving approval from the Institutional Animal Care and Use Committee (IACUC) of Xuanwu Hospital Capital Medical University (IACUC approval No. XW-20210723-1).