Cell transplantation and secretome based approaches in spinal cord injury regenerative medicine

The Effect of Tissue Inhibitor of Metalloproteinases on Scar Formation after Spinal Cord Injury

Spinal cord injury (SCI) often results in permanent loss of motor and sensory function. After SCI, the blood-spinal cord barrier (BSCB) is disrupted, causing the infiltration of neutrophils and macrophages, which secrete several kinds of cytokines, as well as matrix metalloproteinases (MMPs). MMPs are proteases capable of degrading various extracellular matrix (ECM) proteins, as well as many non-matrix substrates. The tissue inhibitor of MMPs (TIMP)-1 is significantly upregulated post-SCI and operates via MMP-dependent and MMP-independent pathways. Through the MMP-dependent pathway, TIMP-1 directly reduces inflammation and destruction of the ECM by binding and blocking the catalytic domains of MMPs. Thus, TIMP-1 helps preserve the BSCB and reduces immune cell infiltration. The MMP-independent pathway involves TIMP-1's cytokine-like functions, in which it binds specific TIMP surface receptors. Through receptor binding, TIMP-1 can stimulate the proliferation of several types of cells, including keratinocytes, aortic smooth muscle cells, skin epithelial cells, corneal epithelial cells, and astrocytes. TIMP-1 induces astrocyte proliferation, modulates microglia activation, and increases myelination and neurite extension in the central nervous system (CNS). In addition, TIMP-1 also regulates apoptosis and promotes cell survival through direct signaling. This review provides a comprehensive assessment of TIMP-1, specifically regarding its contribution to inflammation, ECM remodeling, and scar formation after SCI.

Transplantation of miR-145a-5p modified M2 type microglia promotes the tissue repair of spinal cord injury in mice

BACKGROUND

The traumatic spinal cord injury (SCI) can cause immediate multi-faceted function loss or paralysis. Microglia, as one of tissue resident macrophages, has been reported to play a critical role in regulating inflammation response during SCI processes. And transplantation with M2 microglia into SCI mice promotes recovery of motor function. However, the M2 microglia can be easily re-educated and changed their phenotype due to the stimuli of tissue microenvironment. This study aimed to find a way to maintain the function of M2 microglia, which could exert an anti-inflammatory and pro-repair role, and further promote the repair of spinal cord injury.

METHODS

To establish a standard murine spinal cord clip compression model using Dumont tying forceps. Using FACS, to sort microglia from C57BL/6 mice or CX3CR1GFP mice, and further culture them in vitro with different macrophage polarized medium. Also, to isolate primary microglia using density gradient centrifugation with the neonatal mice. To transfect miR-145a-5p into M2 microglia by Lipofectamine2000, and inject miR-145a-5p modified M2 microglia into the lesion sites of spinal cord for cell transplanted therapy. To evaluate the recovery of motor function in SCI mice through behavior analysis, immunofluorescence or histochemistry staining, Western blot and qRT-PCR detection. Application of reporter assay and molecular biology experiments to reveal the mechanism of miR-145a-5p modified M2 microglia therapy on SCI mice.

RESULTS

With in vitro experiments, we found that miR-145a-5p was highly expressed in M2 microglia, and miR-145a-5p overexpression could suppress M1 while promote M2 microglia polarization. And then delivery of miR-145a-5p overexpressed M2 microglia into the injured spinal cord area significantly accelerated locomotive recovery as well as prevented glia scar formation and neuron damage in mice, which was even better than M2 microglia transplantation. Further mechanisms showed that overexpressed miR-145a-5p in microglia inhibited the inflammatory response and maintained M2 macrophage phenotype by targeting TLR4/NF-κB signaling.

CONCLUSIONS

These findings indicate that transplantation of miR-145a-5p modified M2 microglia has more therapeutic potential for SCI than M2 microglia transplantation from epigenetic perspective.

Transplantation of olfactory mucosa mesenchymal stromal cells repairs spinal cord injury by inducing microglial polarization

STUDY DESIGN

Animal studies OBJECTIVES: To evaluate the therapeutic effect of olfactory mucosa mesenchymal stem cell (OM-MSCs) transplantation in mice with spinal cord injury (SCI) and to explore the mechanism by which OM-MSCs inhibit neuroinflammation and improve SCI.

SETTING

Xiangya Hospital, Central South University; Affiliated Hospital of Guangdong Medical University.

METHODS

Mice (C57BL/6, female, 6-week-old) were randomly divided into sham, SCI, and SCI + OM-MSC groups. The SCI mouse model was generated using Allen's method. OM-MSCs were immediately delivered to the lateral ventricle after SCI using stereotaxic brain injections. One day prior to injury and on days 1, 5, 7, 14, 21, and 28 post-injury, the Basso Mouse Scale and Rivlin inclined plate tests were performed. Inflammation and microglial polarization were evaluated using histological staining, immunofluorescence, and qRT-PCR.

RESULTS

OM-MSCs originating from the neuroectoderm have great potential in the management of SCI owing to their immunomodulatory effects. OM-MSCs administration improved motor function, alleviated inflammation, promoted the transformation of the M1 phenotype of microglia into the M2 phenotype, facilitated axonal regeneration, and relieved spinal cord injury in SCI mice.

CONCLUSIONS

OM-MSCs reduced the level of inflammation in the spinal cord tissue, protected neurons, and repaired spinal cord injury by regulating the M1/M2 polarization of microglia.

Application and challenges of olfactory ensheathing cells in clinical trials of spinal cord injury

Spinal cord injury (SCI) can lead to severe motor, sensory and autonomic nervous dysfunction, cause serious psychosomatic injury to patients. There is no effective treatment for SCI at present. In recent years, exciting evidence has been obtained in the application of cell-based therapy in basic research. These studies have revealed the fact that cells transplanted into the host can exert the pharmacological properties of treating and repairing SCI. Olfactory ensheathing cells (OECs) are a kind of special glial cells. The application value of OECs in the study of SCI lies in their unique biological characteristics, that is, they can survive and renew for life, give full play to neuroprotection, immune regulation, promoting axonal regeneration and myelination formation. The function of producing secretory group and improving microenvironment. This provides an irreplaceable treatment strategy for the repair of SCI. At present, some researchers have explored the possibility of treatment of OECs in clinical trials of SCI. Although OECs transplantation shows excellent safety and effectiveness in animal models, there is still lack of sufficient evidence to prove the effectiveness of their clinical application in clinical trials. There has been an obvious stagnation in the transformation of OECs transplantation into routine clinical practice, and clinical trials of cell therapy in this field are still facing major challenges and many problems that need to be solved. Therefore, this paper summarized and analyzed the clinical trials of OECs transplantation in the treatment of SCI, and discussed the problems and challenges of OECs transplantation in clinical trials.

The bone mesenchymal stem cell-derived exosomal miR-146a-5p promotes diabetic wound healing in mice via macrophage M1/M2 polarization

A diabetic wound is a refractory disease that afflicts patients globally. MicroRNA-146a-5p (miR-146a-5p) is reported to represent a potential therapeutic target for diabetic wounds. However, microRNA easily degrades in the wound microenvironment. This study extracted bone marrow mesenchymal stem cell (BMSC)-derived exosomes (EXO). Electroporation technology was used to load miR-146a-5p into EXO (labeled as EXO-miR-146a). The endothelial cells (human umbilical vein endothelial cells [HUVECs]) and macrophages were cocultured in transwell chambers in the presence of high glucose. Cell proliferation, migration, and angiogenesis were measured with cell counting kit 8, scratch, and tube forming assays, respectively. Flow cytometry was introduced to validate the biomarker of macrophages and BMSCs. The expression level of macrophage polarization-related proteins and tumor necrosis factor receptor-associated factor 6 (TRAF6) was assessed with western blotting analysis. The full-thickness skin wound model was developed to verify the in vitro results. EXO-miR-146a promoted the proliferation, migration, and angiogenesis of HUVECs in the hyperglycemic state by suppressing the TRAF6 expression in vitro. Additionally, EXO-miR-146a treatment facilitated M2 but inhibited M1 macrophage polarization. Furthermore, EXO-miR-146a enhances reepithelialization, angiogenesis, and M2 macrophage polarization, thereby accelerating diabetic wound healing in vivo. The EXO-miR-146a facilitated M2 macrophage polarization, proliferation, migration, and angiogenesis of HUVECs through TRAF6, thereby ameliorating intractable diabetic wound healing. These results established the basis for using EXO to deliver drugs and revealed mediators for diabetic wound treatment.

Spinal cord injury: Olfactory ensheathing cell-based therapeutic strategies

Spinal cord injury (SCI) is a highly disabling neurological disorder that is difficult to treat due to its complex pathophysiology and nerve regeneration difficulties. Hence, effective SCI treatments are necessary. Olfactory ensheathing cells (OECs), glial cells derived from the olfactory bulb or mucosa, are ideal candidates for SCI treatment because of their neuroprotective and regenerative properties, ample supply, and convenience. In vitro, animal model, and human trial studies have reported discoveries on OEC transplantation; however, shortcomings have also been demonstrated. Recent studies have optimized various OEC transplantation strategies, including drug integration, biomaterials, and gene editing. This review aims to introduce OECs mechanisms in repairing SCI, summarize the research progress of OEC transplantation-optimized strategies, and provide novel research ideas for SCI treatment.

Exosome-based regenerative rehabilitation: A novel ice breaker for neurological disorders

Neurological disorders affect a large population, often leading to different levels of disability and resulting in decreased quality of life. Due to the limited recovery obtained from surgical procedures and other medical approaches, a large number of patients with prolonged dysfunction receive neurorehabilitation protocols to improve their neural plasticity and regeneration. However, the poor neural regeneration ability cannot effectively rebuild the tissue integrity and neural functional networks; consequently, the prognoses of neurorehabilitation remain undetermined. To increase the chances of neural regeneration and functional recovery for patients with neurological disorders, regenerative rehabilitation was introduced with combined regenerative medicine and neurorehabilitation protocols to repair neural tissue damage and create an optimized biophysical microenvironment for neural regeneration potential. With the deepening of exosome research, an increasing number of studies have found that the systemic therapeutic effects of neurorehabilitation approaches are mediated by exosomes released by physically stimulated cells, which provides new insight into rehabilitative mechanisms. Meanwhile, exosome therapy also serves as an alternative cell-free therapy of regenerative medicine that is applied in partnership with neurorehabilitation approaches and formulates exosome-based neurological regenerative rehabilitation. In this study, we review the current state of exosome-associated neurorehabilitation. On the one hand, we focus on presenting the varied mediating effects of exosomes in neurorehabilitation protocols of specific neurological pathologies; on the other hand, we discuss the diverse combinations of exosome therapies and neurorehabilitation approaches in the field of neurological regenerative rehabilitation, aiming to increase the awareness of exosome research and applications in the rehabilitation of neurological disorders.

The Promising Role of a Zebrafish Model Employed in Neural Regeneration Following a Spinal Cord Injury

Spinal cord injury (SCI) is a devastating event that results in a wide range of physical impairments and disabilities. Despite the advances in our understanding of the biological response to injured tissue, no effective treatments are available for SCIs at present. Some studies have addressed this issue by exploring the potential of cell transplantation therapy. However, because of the abnormal microenvironment in injured tissue, the survival rate of transplanted cells is often low, thus limiting the efficacy of such treatments. Many studies have attempted to overcome these obstacles using a variety of cell types and animal models. Recent studies have shown the utility of zebrafish as a model of neural regeneration following SCIs, including the proliferation and migration of various cell types and the involvement of various progenitor cells. In this review, we discuss some of the current challenges in SCI research, including the accurate identification of cell types involved in neural regeneration, the adverse microenvironment created by SCIs, attenuated immune responses that inhibit nerve regeneration, and glial scar formation that prevents axonal regeneration. More in-depth studies are needed to fully understand the neural regeneration mechanisms, proteins, and signaling pathways involved in the complex interactions between the SCI microenvironment and transplanted cells in non-mammals, particularly in the zebrafish model, which could, in turn, lead to new therapeutic approaches to treat SCIs in humans and other mammals.

Cell transplantation therapies for spinal cord injury focusing on bone marrow mesenchymal stem cells: Advances and challenges

Spinal cord injury (SCI) is a devastating condition with complex pathological mechanisms that lead to sensory, motor, and autonomic dysfunction below the site of injury. To date, no effective therapy is available for the treatment of SCI. Recently, bone marrow-derived mesenchymal stem cells (BMMSCs) have been considered to be the most promising source for cellular therapies following SCI. The objective of the present review is to summarize the most recent insights into the cellular and molecular mechanism using BMMSC therapy to treat SCI. In this work, we review the specific mechanism of BMMSCs in SCI repair mainly from the following aspects: Neuroprotection, axon sprouting and/or regeneration, myelin regeneration, inhibitory microenvironments, glial scar formation, immunomodulation, and angiogenesis. Additionally, we summarize the latest evidence on the application of BMMSCs in clinical trials and further discuss the challenges and future directions for stem cell therapy in SCI models.

Bone marrow mesenchymal stem cells and exercise restore motor function following spinal cord injury by activating PI3K/AKT/mTOR pathway

Although many therapeutic interventions have shown promise in treating spinal cord injury, focusing on a single aspect of repair cannot achieve successful and functional regeneration in patients following spinal cord injury . In this study, we applied a combinatorial approach for treating spinal cord injury involving neuroprotection and rehabilitation, exploiting cell transplantation and functional sensorimotor training to promote nerve regeneration and functional recovery. Here, we used a mouse model of thoracic contusive spinal cord injury to investigate whether the combination of bone marrow mesenchymal stem cell transplantation and exercise training has a synergistic effect on functional restoration. Locomotor function was evaluated by the Basso Mouse Scale, horizontal ladder test, and footprint analysis. Magnetic resonance imaging, histological examination, transmission electron microscopy observation, immunofluorescence staining, and western blotting were performed 8 weeks after spinal cord injury to further explore the potential mechanism behind the synergistic repair effect. In vivo, the combination of bone marrow mesenchymal stem cell transplantation and exercise showed a better therapeutic effect on motor function than the single treatments. Further investigations revealed that the combination of bone marrow mesenchymal stem cell transplantation and exercise markedly reduced fibrotic scar tissue, protected neurons, and promoted axon and myelin protection. Additionally, the synergistic effects of bone marrow mesenchymal stem cell transplantation and exercise on spinal cord injury recovery occurred via the PI3K/AKT/mTOR pathway. In vitro, experimental evidence from the PC12 cell line and primary cortical neuron culture also demonstrated that blocking of the PI3K/AKT/mTOR pathway would aggravate neuronal damage. Thus, bone marrow mesenchymal stem cell transplantation combined with exercise training can effectively restore motor function after spinal cord injury by activating the PI3K/AKT/mTOR pathway.

Advanced Equipment Development and Clinical Application in Neurorehabilitation for Spinal Cord Injury: Historical Perspectives and Future Directions

Partial to complete paralysis following spinal cord injury (SCI) causes deterioration in health and has severe effects on the ability to perform activities of daily living. Following the discovery of neural plasticity, neurorehabilitation therapies have emerged that aim to reconstruct the motor circuit of the damaged spinal cord. Functional electrical stimulation (FES) has been incorporated into devices that reconstruct purposeful motions in the upper and lower limbs, the most recent of which do not require percutaneous electrode placement surgery and thus enable early rehabilitation after injury. FES-based devices have shown promising results for improving upper limb movement, including gripping and finger function, and for lower limb function such as the ability to stand and walk. FES has also been employed in hybrid cycling and rowing to increase total body fitness. Training using rehabilitation robots is advantageous in terms of consistency of quality and quantity of movements and is particularly applicable to walking training. Initiation of motor reconstruction at the early stage following SCI is likely to advance rapidly in the future, with the combined use of technologies such as regenerative medicine, brain machine interfaces, and rehabilitation robots with FES showing great promise.

miR-124-3p delivered by exosomes from heme oxygenase-1 modified bone marrow mesenchymal stem cells inhibits ferroptosis to attenuate ischemia-reperfusion injury in steatotic grafts

Background

Steatotic livers tolerate ischemia–reperfusion injury (IRI) poorly, increasing the risk of organ dysfunction. Ferroptosis is considered the initiating factor of organ IRI. Heme oxygenase oxygen-1 (HO-1)-modified bone marrow mesenchymal stem cells (BMMSCs) (HO-1/BMMSCs) can reduce hepatic IRI; however, the role of ferroptosis in IRI of steatotic grafts and the effect of HO-1/BMMSCs-derived exosomes (HM-exos) on ferroptosis remain unknown.

Methods

A model of rat liver transplantation (LT) with a severe steatotic donor liver and a model of hypoxia and reoxygenation (H/R) of steatotic hepatocytes were established. Exosomes were obtained by differential centrifugation, and the differentially expressed genes (DEGs) in liver after HM-exo treatment were detected using RNA sequencing. The expression of ferroptosis markers was analyzed. microRNA (miRNA) sequencing was used to analyze the miRNA profiles in HM-exos.

Results

We verified the effect of a candidate miRNA on ferroptosis of H/R treated hepatocytes, and observed the effect of exosomes knockout of the candidate miRNA on hepatocytes ferroptosis. In vitro, HM-exo treatment reduced the IRI in steatotic grafts, and enrichment analysis of DEGs suggested that HM-exos were involved in the regulation of the ferroptosis pathway. In vitro, inhibition of ferroptosis by HM-exos reduced hepatocyte injury. HM-exos contained more abundant miR-124-3p, which reduced ferroptosis of H/R-treated cells by inhibiting prostate six transmembrane epithelial antigen 3 (STEAP3), while overexpression of Steap3 reversed the effect of mir-124-3p. In addition, HM-exos from cell knocked out for miR-124-3p showed a weakened inhibitory effect on ferroptosis. Similarly, HM-exo treatment increased the content of miR-124-3p in grafts, while decreasing the level of STEAP3 and reducing the degree of hepatic ferroptosis.

Conclusion

Ferroptosis is involved in the IRI during LT with a severe steatotic donor liver. miR-124-3p in HM-exos downregulates Steap3 expression to inhibit ferroptosis, thereby attenuating graft IRI, which might be a promising strategy to treat IRI in steatotic grafts.

Graphical Abstract

Supplementary Information

The online version contains supplementary material available at 10.1186/s12951-022-01407-8.