The role of microenvironment in stem cell-based regeneration of intervertebral disc

Esterase-responsive kartogenin composite hydrogel microspheres boost nucleus pulposus regeneration in intervertebral disc degeneration

Cell transplantation for nucleus pulposus (NP) regeneration represents a promising strategy for intervertebral disc degeneration (IVDD). Nonetheless, the hostile microenvironment within the degenerated intervertebral discs, characterized by redox imbalance and elevated mechanical pressure, poses risks of low cell survival and inadequate cell colonization for efficient NP regeneration. To address these challenges, we developed a biomimetic, esterase-responsive composite hydrogel microsphere (GHKM) for cell delivery, consisting of gelatin methacrylate (GelMA) mixed with HAMA-KGN, a conjugate of hyaluronic acid methacrylate (HAMA) and the small heterocyclic molecule kartogenin (KGN) via ester bonds. GHKM mimic the NP extracellular matrix (ECM), providing essential adhesion and mechanical support for cell proliferation, while facilitating cellular adaptation to the adverse microenvironment through the esterase-responsive release of KGN. Furthermore, GHKM exhibit favorable biocompatibility and promote or protect ECM synthesis by nucleus pulposus cells (NPCs) under both normal and inflammatory conditions. Transcriptomic sequencing analysis indicates a correlation between enhanced ECM synthesis and enrichment of antioxidant-related pathways. Subsequent cellular biological studies reveal that GHKM can also reduce reactive oxygen species production within the inflammatory milieu. The underlying mechanism of its protective effect on matrix metabolism may involve the activation of nuclear factor erythroid 2-related factor 2 (NRF2) and the upregulation of downstream antioxidant enzymes. In vivo implantation of NPCs-laden GHKM into rat tail nuclectomy models for 4 and 8 weeks preserved disc height, structure, and biological function, with histological analysis confirming NP regeneration. These findings present GHKM as a promising, synergistic transplantation strategy for NP regeneration in IVDD. STATEMENT OF SIGNIFICANCE: This study introduces an esterase-responsive gelatin methacrylate/hyaluronic acid methacrylate-kartogenin composite hydrogel microsphere (GHKM) system, aimed at mimicing the extracellular matrix (ECM) of the nucleus pulposus (NP) to address the pressing challenge of intervertebral disc degeneration (IVDD). These microspheres offer an innovative solution for cell transplantation therapy by simultaneously addressing two critical barriers: the harsh microenvironment of the degenerated disc and the need for sustained therapeutic effects. GHKM provide mechanical support, enhance cell survival, and adapt dynamically to adverse conditions through esterase-responsive release of kartogenin (KGN), a multifunctional molecule with chondrogenic, anti-inflammatory, and antioxidative properties. This study will not only interest researchers focused on regenerative medicine and biomaterials but also inspire new directions for tackling complex degenerative diseases.

Inflammatory Modulation of Toll-like Receptors in Periodontal Ligament Stem Cells: Implications for Periodontal Therapy

Toll-like receptors (TLRs) play a crucial role in the innate immune response, mediating cellular interactions with the microenvironment and influencing periodontal disease progression. This in vitro study aimed to comprehensively characterize the TLR expression profile of periodontal ligament mesenchymal stem/progenitor cells (PDLSCs) and investigate its modulation by inflammatory stimuli associated with periodontal disease. PDLSCs (n = 6) were isolated, selected using anti-STRO-1 antibodies, and cultured to evaluate their colony-forming abilities and stem/progenitor characteristics. Baseline and inflammation-induced TLR expressions were evaluated using RT-PCR and protein analyses following cytokine-mediated stimulation. PDLSCs exhibited the expected stem cell characteristics and expressed multiple TLRs under both conditions. Notably, inflammatory stimulation significantly upregulated TLR1 and TLR2 while downregulating TLR10 (p < 0.05). These findings provide a comprehensive characterization of TLR expression in PDLSCs and demonstrate how inflammation modulates their innate immune profile. The observed shifts in TLR expression may influence PDLSC responses to microbial pathogens and impact their immunomodulatory and regenerative properties in periodontal tissues. Understanding these interactions could contribute to developing targeted strategies for improving PDLSC-based therapies in periodontal disease.

Exploring the potential of stem cell therapy: Applications, types, and future directions

One of the most significant treatment approaches now accessible is stem cell therapy. Over the last few decades, a lot of study has been done in this field, and this fascinating feature of plasticity could have therapeutic uses. The potential of stem cells to restore function lost as a result of disease, trauma, congenital defects, and age has made stem cell research a key priority for scientific and medical organizations across the world. Stem cells are a crucial topic of study in regenerative medicine because of their capacity to replace, repair, or regenerate damaged cells, tissues, or organs. As a result, stem cell therapy is being used as a treatment strategy for a number of illnesses. Because stem cells may proliferate indefinitely and generate vast quantities of differentiated cells needed for transplantation, they hold enormous promise for regenerative medicine. Stem cells can be reprogrammed from adult cell types or originate from embryonic or fetal origins. Depending on their availability and place of origin, stem cells can be totipotent, pluripotent, multipotent, oligopotent, or unipotent. With stem cell treatment, many ailments, including diabetes, liver disease, infertility, wounds and traumas, neurological disorders, cardiovascular disease, and cancer, might be cured. Various types of stem cell treatment are described in this review along with their applications in different therapeutic fields, ethical considerations, and advantages and disadvantages.

Low-intensity ultrasound stimulation promotes differentiation of bone marrow mononuclear cells to nucleus pulposus cells for matrix synthesis

OBJECTIVE

To investigate the role of low-intensity ultrasound stimulation (LIUS) in facilitating the differentiation of bone marrow mononuclear cells (BMMNCs) into nucleus pulposus cells (NPCs) for matrix synthesis, offering a possible new therapeutic approach for intervertebral disc degeneration.

METHODS

Human BMMNCs and NPCs were cultured, and exosomes were extracted from NPCs using differential ultracentrifugation, followed by characterization. LIUS was utilized to evaluate exosome uptake, induce cell differentiation, measure apoptosis, and track DNA synthesis by EdU assays. Various experimental conditions were tested, including different LIUS intensities and differentiation durations. A range of detection techniques, such as RT-qPCR, western blotting, and cellular staining, were employed to monitor relevant indicators.

RESULTS

Exosomes were successfully isolated from NPCs, and their purity was confirmed using nanoparticle tracking analysis (NTA), transmission electron microscopy, and western blot. PKH67-labeled exosomes were internalized by BMMNCs during co-incubation. LIUS treatment at different intensities revealed that the LIUS-100 group exhibited the most significant cell proliferation, as shown by EdU assays. Flow cytometry revealed that the LIUS-100 and LIUS-150 groups demonstrated the most pronounced inhibition of apoptosis. In NPC exosome-induced differentiation experiments, the expression of relevant marker mRNA and protein levels increased over time under standard conditions, with even greater upregulation observed under LIUS-100 stimulation. Moreover, LIUS-100 enhanced the intracellular accumulation of glycosaminoglycans and proteoglycans, suggesting its role in promoting BMMNC differentiation into NPCs and matrix component synthesis.

CONCLUSION

NPC exosomes and LIUS are essential for guiding the differentiation of BMMNCs into NPCs, representing a promising therapeutic strategy for intervertebral disc degeneration. However, further in vivo studies are needed to refine LIUS technique, ensure safety, and evaluate long-term efficacy.

A Novel Superparamagnetic-Responsive Hydrogel Facilitates Disc Regeneration by Orchestrating Cell Recruitment, Proliferation, and Differentiation within Hostile Inflammatory Niche

In situ disc regeneration is a meticulously orchestrated process, which involves cell recruitment, proliferation and differentiation within a local inflammatory niche. Thus far, it remains a challenge to establish a multi-staged regulatory framework for coordinating these cellular events, therefore leading to unsatisfactory outcome. This study constructs a super paramagnetically-responsive cellular gel, incorporating superparamagnetic iron oxide nanoparticles (SPIONs) and aptamer-modified palladium-hydrogen nanozymes (PdH-Apt) into a double-network polyacrylamide/hyaluronic acid (PAAm/HA) hydrogel. The Aptamer DB67 within magnetic hydrogel (Mag-gel) showed a high affinity for disialoganglioside (GD2), a specific membrane ligand of nucleus pulposus stem cells (NPSCs), to precisely recruit them to the injury site. The Mag-gel exhibits remarkable sensitivity to a magnetic field (MF), which exerts tunable micro/nano-scale forces on recruited NPSCs and triggers cytoskeletal remodeling, consequently boosting cell expansion in the early stage. By altering the parameters of MF, the mechanical cues within the hydrogel facilitates differentiation of NPSCs into nucleus pulposus cells to restore disc structure in the later stage. Furthermore, the PdH nanozymes within the Mag-gel mitigate the harsh inflammatory microenvironment, favoring cell survival and disc regeneration. This study presents a remote and multi-staged strategy for chronologically regulating endogenous stem cell fate, supporting disc regeneration without invasive procedures.

Hotspot Analysis and Frontier Exploration of Stem Cell Research in Intervertebral Disc Regeneration and Repair: A Bibliometric and Visualization Study

BACKGROUND

Stem cells have shown tremendous potential and vast prospects in the research of intervertebral disc (IVD) regeneration and repair, attracting considerable attention in recent years. In this study, a bibliometric analysis and visualization techniques were employed to probe and analyze the hotspots and frontiers of stem cell research in IVD regeneration and repair, aiming to provide valuable references and insights for further investigations.

METHODS

This study utilized the Science Citation Index Expanded from the Web of Science Core Collection database to retrieve and extract relevant literature records as research samples. Visual analysis tools such as VOSviewer 1.6.19, CiteSpace 6.2.R4, and bibliometric online analysis platforms were employed to construct scientific knowledge maps, providing a comprehensive and systematic exposition from various perspectives including collaboration networks, cocitation networks, and co-occurrence networks.

RESULTS

A total of 1075 relevant studies have been published in 303 journals by 4181 authors from 1198 institutions across 54 countries/regions. Over the past 20 years, the field of research has witnessed a significant growth in annual publications and citations. China and the United States have emerged as the primary participants and contributors, with the AO Research Institute Davos, Zhejiang University, and Tokai University being the top 3 leading research institutions. The most productive and highly cited author is Sakai D, who is regarded as a key leader in this research field. The journals with the highest number of publications and citations are Spine and Biomaterials, which are considered to be high-quality and authoritative core journals in this field. The current research focuses primarily on the sources and selection of stem cells, optimization of transplantation strategies, mechanisms of IVD regeneration, and the combined application of stem cells and biomaterials. However, there are still some challenges that need to be addressed, including posttransplantation stability, assessment of regenerative effects, and translation into clinical applications. Future research will concentrate on the diversity of stem cell sources, the application of novel biomaterials, personalized treatments, and the development of gene editing technologies, among other cutting-edge directions.

CONCLUSIONS

This study utilized bibliometric analysis and visualization techniques to unveil the hotspots and frontiers in the research on stem cells for IVD regeneration and repair. These research findings provide essential guidance and references for further experimental design and clinical applications. However, additional experiments and clinical studies are still needed to address the challenges and difficulties faced in the field of IVD regeneration and repair, thus offering novel strategies and approaches for the treatment of IVD diseases.

Future of low back pain: unravelling IVD components and MSCs' potential

Low back pain (LBP) mainly emerges from intervertebral disc (IVD) degeneration. However, the failing mechanism of IVD ́s components, like the annulus fibrosus (AF) and nucleus pulposus (NP), leading to IVD degeneration/herniation is still poorly understood. Moreover, the specific role of cellular populations and molecular pathways involved in the inflammatory process associated with IVD herniation remains to be highlighted. The limited knowledge of inflammation associated with the initial steps of herniation and the lack of suitable models to mimic human IVD ́s complexity are some of the reasons for that. It has become essential to enhance the knowledge of cellular and molecular key players for AF and NP cells during inflammatory-driven degeneration. Due to unique properties of immunomodulation and pluripotency, mesenchymal stem cells (MSCs) have attained diverse recognition in this field of bone and cartilage regeneration. MSCs therapy has been particularly valuable in facilitating repair of damaged tissues and may benefit in mitigating inflammation' degenerative events. Therefore, this review article conducts comprehensive research to further understand the intertwine between the mechanisms of action of IVD components and therapeutic potential of MSCs, exploring their characteristics, how to optimize their use and establish them safely in distinct settings for LPB treatment.

Regulating pyroptosis by mesenchymal stem cells and extracellular vesicles: A promising strategy to alleviate intervertebral disc degeneration

Intervertebral disc degeneration (IVDD) is a main cause of low back pain (LBP), which can lead to disability and thus generate a heavy burden on society. IVDD is characterized by a decrease in nucleus pulposus cells (NPCs) and endogenous mesenchymal stem cells (MSCs), degradation of the extracellular matrix, macrophage infiltration, and blood vessel and nerve ingrowth. To date, the therapeutic approaches regarding IVDD mainly include conservative treatment and surgical intervention. However, both can only relieve symptoms rather than stop or revert the progression of IVDD, since the pathogenesis of IVDD is not yet clear. Pyroptosis, which is characterized by Caspase family dependence and conducted by the Gasdermin family, is a newly discovered mode of programmed cell death. Pyroptosis has been observed in NPCs, annulus fibrosus cells (AFCs), chondrocytes, MSCs, macrophages, vascular endothelial cells and neurons and may contribute to IVDD. MSCs are a kind of pluripotent stem cell that can be found in almost all tissues. MSCs have a strong ability to secrete extracellular vesicles (EVs), which contain exosomes, microvesicles and apoptotic bodies. EVs derived from MSCs play an important role in pyroptosis regulation and could be beneficial for alleviating IVDD. This review focuses on clarifying the regulation of pyroptosis to improve IVDD by MSCs and EVs derived from MSCs.

How to enhance the ability of mesenchymal stem cells to alleviate intervertebral disc degeneration

Intervertebral disc (ID) degeneration (IDD) is one of the main causes of chronic low back pain, and degenerative lesions are usually caused by an imbalance between catabolic and anabolic processes in the ID. The environment in which the ID is located is harsh, with almost no vascular distribution within the disc, and the nutrient supply relies mainly on the diffusion of oxygen and nutrients from the blood vessels located under the endplate. The stability of its internal environment also plays an important role in preventing IDD. The main feature of disc degeneration is a decrease in the number of cells. Mesenchymal stem cells have been used in the treatment of disc lesions due to their ability to differentiate into nucleus pulposus cells in a nonspecific anti-inflammatory manner. The main purpose is to promote their regeneration. The current aim of stem cell therapy is to replace the aged and metamorphosed cells in the ID and to increase the content of the extracellular matrix. The treatment of disc degeneration with stem cells has achieved good efficacy, and the current challenge is how to improve this efficacy. Here, we reviewed current treatments for disc degeneration and summarize studies on stem cell vesicles, enhancement of therapeutic effects when stem cells are mixed with related substances, and improvements in the efficacy of stem cell therapy by adjuvants under adverse conditions. We reviewed the new approaches and ideas for stem cell treatment of disc degeneration in order to contribute to the development of new therapeutic approaches to meet current challenges.

Alginate hydrogels: A potential tissue engineering intervention for intervertebral disc degeneration

Intervertebral disc (IVD) degeneration is a major cause of low back pain and disability, affecting millions of people worldwide. Current treatments for IVD degeneration are limited to invasive surgery or pain management. Recently, there has been increasing interest in the use of biomaterials, such as alginate hydrogels, for the treatment of IVD degeneration. Alginate hydrogels are an example of such a biomaterial that is biocompatible and can be tailored to mimic the native extracellular matrix of the IVD. Derived from alginate, a naturally derived polysaccharide from brown seaweed that can be transformed into a gelatinous solution, alginate hydrogels are emerging in the field of tissue engineering. They can be used to deliver therapeutic agents, such as growth factors or cells, to the site of injury, providing a localized and sustained release that may enhance treatment outcomes. This paper provides an overview on the use of alginate hydrogels for the treatment of IVD degeneration. We discuss the properties of alginate hydrogels and their potential applications for IVD regeneration, including the mechanism against IVD degeneration. We also highlight the research outcomes to date along with the challenges and limitations of using alginate hydrogels for IVD regeneration, including their mechanical properties, biocompatibility, and surgical compatibility. Overall, this review paper aims to provide a comprehensive overview of the current research on alginate hydrogels for IVD degeneration and to identify future directions for research in this area.

Nucleus pulposus cell-derived efficient microcarrier for intervertebral disc tissue engineering

Adipose-derived stem cells (ADSCs) show great potential for the treatment of intervertebral disc (IVD) degeneration. An ideal carrier is necessary to transplant ADSCs into degenerated IVDs without influencing cell function. Nucleus pulposus cells (NPCs) can synthesize and deposit chondroitin sulfate and type II collagen which are NP-specific extracellular matrix (ECM) and can also regulate the NP-specific differentiation of stem cells. Bioscaffolds fabricated based on the ECM synthesis functions of NPCs have possible roles in cell transplantation and differentiation induction, but it has not been studied. In this study, we first aggregated NPCs into pellets, and then, NPC-derived efficient microcarriers (NPCMs) were fabricated by pellet cultivation under specific conditions and optimized decellularization. Thirdly, we evaluated the microstructure, biochemical composition, biostability and cytotoxicity of the NPCMs. Finally, we investigated the NP-specific differentiation of ADSCs induced by the NPCMsin vitroand NP regeneration induced by the ADSC-loaded NPCMs in a rabbit model. The results indicated that the injectable NPCMs retained maximal ECM and minimal cell nucleic acid after optimized decellularization and had good biostability and no cytotoxicity. The NPCMs also promoted the NP-specific differentiation of ADSCsin vitro. In addition, the results of MRI, x-ray, and the structure and ECM content of NP showed that the ADSCs-loaded NPCMs can partly restored the degenerated NPin vivo. Our injectable NPCMs regenerated the degenerated NP and provide a simplified and efficient strategy for treating IVD degeneration.

Core-shell oxygen-releasing fibers for annulus fibrosus repair in the intervertebral disc of rats

The repair of annulus fibrosus (AF) defect after discectomy in the intervertebral disc (IVD) has presented a challenge over the past decade. Hostile microenvironments in the IVD, including, compression and hypoxia, are critical issues that require special attention. Till date, little information is available on potential strategies to cope with the hypoxia dilemma in AF defect sites. In this study, perfluorotributylamine (PFTBA) core-shell fibers were fabricated by coaxial electrospinning to construct oxygen-releasing scaffold for promoting endogenous repair in the AF after discectomy. We demonstrated that PFTBA fibers (10% chitosan, chitosan: PCL, 1:6) could release oxygen for up to 144 ​h. The oxygen released from PFTBA fibers was found to protect annulus fibrosus stem cells (AFSCs) from hypoxia-induced apoptosis. In addition, the PFTBA fibers were able to promote proliferation, migration and extracellular matrix (ECM) production in AFSCs under hypoxia, highlighting their therapeutic potential in AF defect repair. Subsequent in vivo studies demonstrated that oxygen-supplying fibers were capable of ameliorating disc degeneration after discectomy, which was evidenced by improved disc height and morphological integrity in rats with the oxygen-releasing scaffolds. Further transcriptome analysis indicated that differential expression genes (DEGs) were enriched in "oxygen transport" and "angiogenesis", which likely contributed to their beneficial effect on endogenous AF regeneration. In summary, the oxygen-releasing scaffold provides novel insights into the oxygen regulation by bioactive materials and raises the therapeutic possibility of oxygen supply strategies for defect repair in AF, as well as other aerobic tissues.

Stem cell homing in periodontal tissue regeneration

The destruction of periodontal tissue is a crucial problem faced by oral diseases, such as periodontitis and tooth avulsion. However, regenerating periodontal tissue is a huge clinical challenge because of the structural complexity and the poor self-healing capability of periodontal tissue. Tissue engineering has led to advances in periodontal regeneration, however, the source of exogenous seed cells is still a major obstacle. With the improvement of in situ tissue engineering and the exploration of stem cell niches, the homing of endogenous stem cells may bring promising treatment strategies in the future. In recent years, the applications of endogenous cell homing have been widely reported in clinical tissue repair, periodontal regeneration, and cell therapy prospects. Stimulating strategies have also been widely studied, such as the combination of cytokines and chemokines, and the implantation of tissue-engineered scaffolds. In the future, more research needs to be done to improve the efficiency of endogenous cell homing and expand the range of clinical applications.