The presence of stem cells in potential stem cell niches of the intervertebral disc region: an in vitro study on rats. Eur Spine J. 2015;24:2411-2424. [PMID: 26228187 DOI: 10.1007/s00586-015-4168-7]

Single-cell atlas unveils cellular heterogeneity and novel markers in human neonatal and adult intervertebral discs

The origin, composition, distribution, and function of cells in the human intervertebral disc (IVD) have not been fully understood. Here, cell atlases of both human neonatal and adult IVDs have been generated and further assessed by gene ontology pathway enrichment, pseudo-time trajectory, histology, and immunofluorescence. Comparison of cell atlases revealed the presence of two subpopulations of notochordal cells (NCs) and their associated markers in both the neonatal and adult IVDs. Developmental trajectories predicted 7 different cell states that describe the developmental process from neonatal to adult cells in IVD and analyzed the NC’s role in the IVD development. A high heterogeneity and gradual transition of annulus fibrosus cells (AFCs) in the neonatal IVD was detected and their potential relevance in IVD development assessed. Collectively, comparing single-cell atlases between neonatal and adult IVDs delineates the landscape of IVD cell biology and may help discover novel therapeutic targets for IVD degeneration.

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Compared scRNA-seq between human neonatal and adult IVD

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Identified two notochordal cell populations in adults and their novel markers

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Notochordal cells preserved their identity and functions into adulthood

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Unveiled heterogeneity of nucleus pulposus and annulus fibrosus cells in human IVD

Icariin regulates stem cell migration for endogenous repair of intervertebral disc degeneration by increasing the expression of chemotactic cytokines

Background

Icariin (ICA) can promote the migration and bone formation of bone marrow mesenchymal stem cells. This study explored a potential role of ICA in recruiting stem cell niches (SCNs) within the intervertebral disc region (ISN)-derived stem cells (ISN-SCs) to treat intervertebral disc degeneration (IVDD).

Materials and methods

EdU staining, transwell, and wound healing tests were used to analyze the function of ICA on ISN-SCs proliferation and migration ability. Simultaneously, the IVDD rat model was constructed by the acupuncture and divided into Sham, Sham + ICA, IVDD, and IVDD + ICA groups. H&E and PAS staining were performed to detect the pathological changes of IVDD tissues. Immunofluorescence was performed to discover relevant marker expression on the surface of stem cells in the IVDD tissues. Western blot and qPCR were executed to find the protein and mRNA expression of related cytokines in the IVDD tissues.

Results

ISN-SCs treated with 1 μM ICA obtained the better ability of proliferation and migration. H&E staining showed that the annulus fibrosus in the IVDD group was obviously hyperplasia with cavities and fissures; the nucleus pulposus was reduced. PAS staining showed that the content of polysaccharides was significantly reduced in the nucleus pulposus of IVDD group. However, the ICA treatment alleviated the pathological trends of the IVDD tissues. Simultaneously, ICA treatment increased significantly the expression of stem cells and IGF-1, TGF-β, SDF-1, CCL-5, Collagen I, Collagen II, Aggrecan, and SOX9 in IVDD tissues.

Conclusions

ICA treatment promoted the migration of stem cell in IVDD by increasing the expression of chemotactic cytokines, including IGF-1, TGF-β, SDF-1, and CCL-5.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12906-022-03544-x.

Endogenous repair theory enriches construction strategies for orthopaedic biomaterials: a narrative review

The development of tissue engineering has led to new strategies for mitigating clinical problems; however, the design of the tissue engineering materials remains a challenge. The limited sources and inadequate function, potential risk of microbial or pathogen contamination, and high cost of cell expansion impair the efficacy and limit the application of exogenous cells in tissue engineering. However, endogenous cells in native tissues have been reported to be capable of spontaneous repair of the damaged tissue. These cells exhibit remarkable plasticity, and thus can differentiate or be reprogrammed to alter their phenotype and function after stimulation. After a comprehensive review, we found that the plasticity of these cells plays a major role in establishing the cell source in the mechanism involved in tissue regeneration. Tissue engineering materials that focus on assisting and promoting the natural self-repair function of endogenous cells may break through the limitations of exogenous seed cells and further expand the applications of tissue engineering materials in tissue repair. This review discusses the effects of endogenous cells, especially stem cells, on injured tissue repairing, and highlights the potential utilisation of endogenous repair in orthopaedic biomaterial constructions for bone, cartilage, and intervertebral disc regeneration.

HIF1A Alleviates compression-induced apoptosis of nucleus pulposus derived stem cells via upregulating autophagy

Intervertebral disc degeneration (IDD) is the primary pathological mechanism that underlies low back pain. Overloading-induced cell death, especially endogenous stem cell death, is the leading factor that undermines intrinsic repair and aggravates IDD. Previous research has separately studied the effect of oxygen concentration and mechanical loading in IDD. However, how these two factors synergistically influence endogenous repair remains unclear. Therefore, we established in vitro and in vivo models to study the mechanisms by which hypoxia interacted with overloading-induced cell death of the nucleus pulposus derived stem cells (NPSCs). We found the content of HIF1A (hypoxia inducible factor 1 subunit alpha) and the number of NPSCs decreased with disc degeneration in both rats and human discs. Hence, we isolated this subpopulation from rat discs and treated them simultaneously with hypoxia and excessive mechanical stress. Our results demonstrated that hypoxia exerted protective effect on NPSCs under compression, partially through elevating macroautophagy/autophagy. Proteomics and knockdown experiments further revealed HIF1A-BNIP3-ATG7 axis mediated the increase in autophagy flux, in which HMOX1 and SLC2A1 were also involved. Moreover, HIF1A-overexpressing NPSCs exhibited stronger resistance to over-loading induced apoptosis in vitro. They also showed higher survival rates, along with elevated autophagy after being intra-disc transplanted into over-loaded discs. Jointly, both in vivo and in vitro experiments proved the anti-apoptotic effect of HIF1A on NPSCs under the excessive mechanical loading, suggesting that restoring hypoxia and manipulating autophagy is crucial to maintain the intrinsic repair and to retard disc degeneration.Abbreviations: 3-MA: 3-methyladenine; ACAN: aggrecan; ATG7: autophagy related 7; BafA1: bafilomycin A1; BAX: BCL2 associated X, apoptosis regulator; BECN1: beclin 1; BNIP3: BCL2 interacting protein 3; BNIP3L: BCL2 interacting protein 3 like; CASP3: caspase 3; CCK8: cell counting kit-8; CHT: chetomin; CMP: compression; CoCl2: cobalt chloride; COL2A1: collagen type II alpha 1 chain; Ctrl: control; DAPI: 4,6-diamidino-2-phenylindole; DEP: differentially expressed protein; DiR: 1,1-dioctadecyl-3,3,3,3-tetramethyl indotricarbocyanine; ECM: extracellular matrix; FCM: flow cytometry; GD2: disialoganglioside GD 2; GFP: green fluorescent protein; GO: gene ontology; GSEA: gene set enrichment analysis; H&E: hematoxylin-eosin; HIF1A: hypoxia inducible factor 1 subunit alpha; HK2: hexokinase 2; HMOX1: heme oxygenase 1; HX: hypoxia mimicry; IDD: intervertebral disc degeneration; IF: immunofluorescence; IHC: immunohistochemistry; IVD: intervertebral disc; KEGG: kyoto encyclopedia of genes and genomes; LBP: low back pain; Lv: lentivirus; MAP1LC3B/LC3B: microtubule associated protein 1 light chain 3 beta; MMP: mitochondrial membrane potential; NC: negative control; NIR: near-infrared; NP: nucleus pulposus; NPC: nucleus pulposus cell; NPSC: nucleus pulposus derived stem cell; NX: normoxia; PPI: protein-protein interactions; RFP: red fluorescent protein; SLC2A1/GLUT1: solute carrier family 2 member 1; SQSTM1/p62: sequestosome 1; TEK/TIE2: TEK receptor tyrosine kinase; TEM: transmission electron microscopy; TUBB: tubulin beta class I.

Intervertebral Disc Stem/Progenitor Cells: A Promising "Seed" for Intervertebral Disc Regeneration

Intervertebral disc (IVD) degeneration is considered to be the primary reason for low back pain (LBP), which has become more prevalent from 21 century, causing an enormous economic burden for society. However, in spite of remarkable improvements in the basic research of IVD degeneration (IVDD), the effects of clinical treatments of IVDD are still leaving much to be desired. Accumulating evidence has proposed the existence of endogenous stem/progenitor cells in the IVD that possess the ability of proliferation and differentiation. However, few studies have reported the biological properties and potential application of IVD progenitor cells in detail. Even so, these stem/progenitor cells have been consumed as a promising cell source for the regeneration of damaged IVD. In this review, we will first introduce IVD, describe its physiology and stem/progenitor cell niche, and characterize IVDSPCs between homeostasis and IVD degeneration. We will then summarize recent studies on endogenous IVDSPC-based IVD regeneration and exogenous cell-based therapy for IVDD. Finally, we will discuss the potential applications and future developments of IVDSPC-based repair of IVD degeneration.

[Research progress of endogenous repair strategy in intervertebral disc]

Objective

To review the research progress of endogenous repair strategy (ERS) in intervertebral disc (IVD).

Methods

The domestic and foreign literature related to ERS in IVD in recent years was reviewed, and its characteristics, status, and prospect in the future were summarized.

Results

The key of ERS in IVD is to improve the vitality of stem/progenitor cells in IVD or promote its migration from stem cell Niche to the tissue that need to repair. These stem/progenitor cells in IVD are derived from nucleus pulposus, annulus fibrosus, and cartilaginous endplate, showing similar biological characteristics to mesenchymal stem cells including the expression of the specific stem/progenitor cell surface markers and gene, and also the capacity of multiple differentiations potential. However, the development, senescence, and degeneration of IVD have consumed these stem/progenitor cells, and the harsh internal microenvironment further impair their biological characteristics, which leads to the failure of endogenous repair in IVD. At present, relevant research mainly focuses on improving the biological characteristics of endogenous stem/progenitor cells, directly supplementing endogenous stem/progenitor cells, biomaterials and small molecule compounds to stimulate the endogenous repair in IVD, so as to improve the effect of endogenous repair.

Conclusion

At present, ERS has gotten some achievements in the treatment of IVD degeneration, but its related studies are still in the pre-clinical stage. So further studies regarding ERS should be carried out in the future, especially in vivo experiments and clinical transformation.

Modulation of Local Overactive Inflammation via Injectable Hydrogel Microspheres

Although injectable hydrogel microsphere has demonstrated tremendous promise in clinical applications, local overactive inflammation in degenerative diseases could jeopardize biomaterial implantation's therapeutic efficacy. Herein, an injectable "peptide-cell-hydrogel" microsphere was constructed by covalently coupling of APETx2 and further loading of nucleus pulposus cells, which could inhibit local inflammatory cytokine storms to regulate the metabolic balance of ECM in vitro. The covalent coupling of APETx2 preserved the biocompatibility of the microspheres and achieved a controlled release of APETx2 for more than 28 days in an acidic environment. By delivering "peptide-cell-hydrogel" microspheres to a rat degenerative intervertebral disc at 4 weeks, the expression of ASIC-3 and IL-1β was significantly decreased for 3.53-fold and 7.29-fold, respectively. Also, the content of ECM was significantly recovered at 8 weeks. In summary, the proposed strategy provides an effective approach for tissue regeneration under overactive inflammatory responses.

Novel biomarkers of intervertebral disc cells and evidence of stem cells in the intervertebral disc

OBJECTIVE

Rat intervertebral disc (IVD) is one of the most commonly used and cost-effective alternative models for human IVD. Many IVD related clinical studies need to be pre-tested on rat IVDs. However, studies on the heterogeneous cell clusters of the rat IVD are inadequate, and a further understanding of the marker genes and cell phenotypes of healthy mature IVD cells is essential.

METHODS

In this study, we used the 10X Genomics technology to analyze the single-cell transcriptome of purified wild-type rat IVDs.

RESULTS

We identified potentially new gene markers of IVDs via single-cell sequencing. Based on the unsupervised cluster analysis of 13,578 single-cell transcripts, 3 known IVD cell types were identified. We provided a complete single-cell gene expression map of the IVD. Immunohistochemical and immunofluorescence images of rat disc sections confirmed the new marker genes of all cell types. One group of heterologous cell groups expressed multi-functional stem cell (MSC)-specific genes, indicating the stem cell potential of IVD cells.

CONCLUSION

We provided the phenotype and marker genes of IVD cells at the single-cell level, reconfirmed existing data, and proposed new marker genes, including MSC marker genes. By identifying more accurate target cells and genes, our results pave the way for further study of the response of individual disc cells to disease states and provide the basis for future disc regeneration therapies.

Nucleus Pulposus Cell Conditioned Medium Promotes Mesenchymal Stem Cell Differentiation into Nucleus Pulposus-Like Cells under Hypoxic Conditions

Low back pain (LBP) is a major physical and socioeconomic challenge worldwide. Nucleus pulposus (NP) is directly associated with LBP due to intervertebral disc (IVD) degeneration. IVD degeneration is mainly caused by structural and matrix-related changes within the IVD occurring during aging and degeneration. Mesenchymal stem cells (MSCs) can differentiate into multiple mesenchymal lineages under specific stimulatory conditions. This study is aimed at evaluating the effectiveness of the nucleus pulposus cell (NPC) conditioned medium for promoting the expression of MSCs and at confirming the expression of healthy NP phenotypic markers recently recommended by the Spine Research Interest Group. Expression was investigated using quantitative polymerase chain reaction (qPCR) and western blotting under normoxic and hypoxic conditions. qPCR and western blotting demonstrated significant upregulation of NP marker expression in MSCs cultured under hypoxic conditions and treated with the 50% or 100% NPC conditioned medium, compared with those cultured under normoxic conditions. Upregulation was highest in the presence of the 100% NPC conditioned medium compared with the control group (aggrecan, p < 0.01; brachyury, p < 0.05; collagen II, p < 0.001; KRT8, p < 0.01; KRT19, p < 0.001; and Shh, p < 0.01). The expression levels of genes in MSCs treated with the 50% NPC conditioned medium also showed upregulation compared with the control group (collagen II, p < 0.05; KRT8, p < 0.05; and KRT19, p < 0.01). These findings suggested that the NPC conditioned medium stimulated MSC differentiation into an NP-like phenotype with distinct characteristics. The results could inform strategies for IVD regeneration.

Insights of stem cell-based endogenous repair of intervertebral disc degeneration

Low back pain has become more prevalent in recent years, causing enormous economic burden for society and government. Common therapies used in clinics including conservative treatment and surgery can only relieve pain. Subsequent cell-based treatment such as mesenchymal stem cell transplantation poses problems such as short duration of therapeutic effect and tumorigenesis. Recently, the discovery and identification of stem cell niche and stem/progenitor cells in intervertebral disc bring increased attention to endogenous repair strategy. Therefore, we review the studies involving endogenous repair strategy and present the characteristics and current status of this treatment. Meanwhile, we also discuss the strategy and perspective of endogenous repair strategy in future.

Heme Oxygenase-1-Mediated Autophagy Protects against Oxidative Damage in Rat Nucleus Pulposus-Derived Mesenchymal Stem Cells

Although endogenous nucleus pulposus-derived mesenchymal stem cell- (NPMSC-) based regenerative medicine has provided promising repair strategy for intervertebral disc (IVD) degeneration, the hostile microenvironments in IVD, including oxidative stress, can negatively affect the survival and function of the NPMSCs and severely hinder the endogenous repair process. Therefore, it is of great importance to reveal the mechanisms of the endogenous repair failure caused by the adverse microenvironments in IVD. The aim of this study was to investigate the effect of oxidative stress on the rat NPMSCs and its underlying mechanism. Our results demonstrated that oxidative stress inhibited cell viability, induced apoptosis, and increased the production of reactive oxygen species (ROS) in NPMSCs. In addition, the results showed that the expression level of heme oxygenase-1 (HO-1) increased at an early stage but decreased at a late stage when NPMSCs were exposed to oxidative stress, and the oxidative damages of NPMSCs could be partially reversed by promoting the expression of HO-1. Further mechanistic analysis indicated that the protective effect of HO-1 against oxidative damage in NPMSCs was mediated by the activation of autophagy. Taken together, our study revealed that oxidative stress could inhibit cell viability, induce apoptosis, and increase ROS production in NPMSCs, and HO-1-mediated autophagy might act as a protective response to the oxidative damage. These findings might enhance our understanding on the mechanism of the endogenous repair failure during IVD degeneration and provide novel research direction for the endogenous repair of IVD degeneration.

IVD progenitor cells: a new horizon for understanding disc homeostasis and repair

Intervertebral disc (IVD) degeneration is associated with low back pain. In IVDs, a high mechanical load, high osmotic pressure and hypoxic conditions create a hostile microenvironment for resident cells. How IVD homeostasis and function are maintained under stress remains to be understood; however, several research groups have reported isolating native endogenous progenitor-like or otherwise proliferative cells from the IVD. The isolation of such cells implies that the IVD might contain a quiescent progenitor-like population that could be activated for IVD repair and regeneration. Increased understanding of endogenous disc progenitor cells will improve our knowledge of IVD homeostasis and, when combined with tissue engineering techniques, might hold promise for future therapeutic applications. In this Review, the characteristics of progenitor cells in different IVD compartments are discussed, as well as the potency of different cell populations within the IVD. The stem cell characteristics of these cells are also compared with those of mesenchymal stromal cells. On the basis of existing evidence, whether and how IVD degeneration and the hostile microenvironment might affect endogenous progenitor cell function are considered, and ways to channel the potential of these cells for IVD repair are suggested.

Intervertebral disc regeneration: From cell therapy to the development of novel bioinspired endogenous repair strategies

Low back pain (LBP), frequently associated with intervertebral disc (IVD) degeneration, is a major public health concern. LBP is currently managed by pharmacological treatments and, if unsuccessful, by invasive surgical procedures, which do not counteract the degenerative process. Considering that IVD cell depletion is critical in the degenerative process, the supplementation of IVD with reparative cells, associated or not with biomaterials, has been contemplated. Recently, the discovery of reparative stem/progenitor cells in the IVD has led to increased interest in the potential of endogenous repair strategies. Recruitment of these cells by specific signals might constitute an alternative strategy to cell transplantation. Here, we review the status of cell-based therapies for treating IVD degeneration and emphasize the current concept of endogenous repair as well as future perspectives. This review also highlights the challenges of the mobilization/differentiation of reparative progenitor cells through the delivery of biologics factors to stimulate IVD regeneration.

A histocytological and radiological overview of the natural history of intervertebral disk: from embryonic formation to age-related degeneration

PURPOSE

To elucidate the natural history of intervertebral disk (IVD) and characterize its embryonic beginnings and age-related degeneration.

METHODS

Coronal sections of embryonic (E13.5-neonatal) and postnatal (4-60-week-old) Sprague-Dawley rat IVD were stained by a series of histological stainings (hematoxylin and eosin, Alcian blue, Picrosirius red, Masson, Periodic acid-Schiff). Growth kinetics within embryonic IVD were evaluated by immunohistochemical staining of Ki67 and proliferating cell nuclear antigen. Postnatal maturation and degeneration of IVD were visualized on radiology by X-ray, CT, and MR imaging.

RESULTS

During the formation of rat IVD, inner annulus fibrosus (AF) and cartilaginous endplate (CEP) shared similar cell density, extracellular matrix, and potential of growth kinetics; notochord provided increased and enlarged cytoplasmic vacuoles to generate nucleus pulposus (NP), part of which was retained within CEP. Postnatally, vacuolated notochord cells were reduced by devacuolation, while chondrocytic NP cells increased; cartilaginous layers of CEP were narrowed by vertebrae growth and secondary ossification; fibrotic portion of AF decreased as cartilaginous matrix accumulated and infiltrated outward. In aged and degenerated IVD, large longitudinal fissures were detected near the boundaries between inner and outer AF, whereas both reduced cellularity and accumulated cell clusters were evident within the dehydrated NP; only part of these histocytological changes could be reported on radiology.

CONCLUSIONS

By showing that the natural history of IVD is orchestrated by a dynamic histocytological regulation, our study may facilitate better understanding of the developmental defects, cellular heterogeneity, age-related degenerative mechanisms, and biological regeneration of IVD. These slides can be retrieved under Electronic Supplementary Material.

Mechanisms of endogenous repair failure during intervertebral disc degeneration

Intervertebral disc (IVD) degeneration is frequently associated with Low back pain (LBP), which can severely reduce the quality of human life and cause enormous economic loss. However, there is a lack of long-lasting and effective therapies for IVD degeneration at present. Recently, stem cell based tissue engineering techniques have provided novel and promising treatment for the repair of degenerative IVDs. Numerous studies showed that stem/progenitor cells exist naturally in IVDs and could migrate from their niche to the IVD to maintain the quantity of nucleus pulposus (NP) cells. Unfortunately, these endogenous repair processes cannot prevent IVD degeneration as effectively as expected. Therefore, theoretical basis for regeneration of the NP in situ can be obtained from studying the mechanisms of endogenous repair failure during IVD degeneration. Although there have been few researches to study the mechanism of cell death and migration of stem/progenitor cells in IVD so far, studies demonstrated that the major inducing factors (compression and hypoxia) of IVD degeneration could decrease the number of NP cells by regulating apoptosis, autophagy, and necroptosis, and the particular chemokines and their receptors played a vital role in the migration of mesenchymal stem cells (MSCs). These studies provide a clue for revealing the mechanisms of endogenous repair failure during IVD degeneration. This article reviewed the current research situation and progress of the mechanisms through which IVD stem/progenitor cells failed to repair IVD tissues during IVD degeneration. Such studies provide an innovative research direction for endogenous repair and a new potential treatment strategy for IVD degeneration.

Intervertebral Disc-Derived Stem/Progenitor Cells as a Promising Cell Source for Intervertebral Disc Regeneration

Intervertebral disc (IVD) degeneration is considered to be the primary reason for low back pain. Despite remarkable improvements in both pharmacological and surgical management of IVD degeneration (IVDD), therapeutic effects are still unsatisfactory. It is because of the fact that these therapies are mainly focused on alleviating the symptoms rather than treating the underlying cause or restoring the structure and biomechanical function of the IVD. Accumulating evidence has revealed that the endogenous stem/progenitor cells exist in the IVD, and these cells might be a promising cell source in the regeneration of degenerated IVD. However, the biological characteristics and potential application of IVD-derived stem/progenitor cells (IVDSCs) have yet to be investigated in detail. In this review, the authors aim to perform a review to systematically discuss (1) the isolation, surface markers, classification, and biological characteristics of IVDSCs; (2) the aging- and degeneration-related changes of IVDSCs and the influences of IVD microenvironment on IVDSCs; and (3) the potential for IVDSCs to promote regeneration of degenerated IVD. The authors believe that this review exclusively address the current understanding of IVDSCs and provide a novel approach for the IVD regeneration.

Autogenic mesenchymal stem cells for intervertebral disc regeneration

PURPOSE

A systematic review of the literature was conducted to clarify the outcomes of autologous mesenchymal stem cells (MSC) injections for the regeneration of the intervertebral disc (IVD).

METHODS

The following databases were accessed: PubMed, Medline, CINAHL, Cochrane, Embase and Google Scholar bibliographic databases. Articles including previous or planned surgical interventions were excluded. Only articles reporting percutaneous autologous MSC injection to regenerate IVD in humans were included. We referred to the Coleman Methodology Score for the methodological quality assessment. The statistical analysis was performed using Review Manager Software 5.3.

RESULTS

After the databases search and cross-references of the bibliographies, seven studies were included in the present work. The funnel plot detected low risk of publication bias. The Coleman Methodology Score reported a good result, scoring 61.07 points. A total of 98 patients were enrolled, with 122 treated levels. All the patients underwent conservative therapies prior to injection. A remarkable improvement in the quality of life were reported after the treatment. The average Oswestry Disability Index (ODI) improved from "severe disability" to "minimal disability" at one year follow-up. The visual analogue scale (VAS) showed an improvement of ca. 30% at one year follow-up. Only one case of herniated nucleus pulposus was reported. No other adverse events at the aspiration or injection site were observed.

CONCLUSIONS

This systematic review of the literature proved MSC injection to be a safe and feasible option for intervertebral disc regeneration in the early-degeneration stage patients. Irrespective of the source of the MSCs, an overall clinical and radiological improvement of the patients has been evidenced, as indeed a very low complication rate during the follow-up.

Effect of Compression Loading on Human Nucleus Pulposus-Derived Mesenchymal Stem Cells

Purpose

Mechanical loading plays a vital role in the progression of intervertebral disc (IVD) degeneration, but little is known about the effect of compression loading on human nucleus pulposus-derived mesenchymal stem cells (NP-MSCs). Thus, this study is aimed at investigating the effect of compression on the biological behavior of NP-MSCs in vitro.

Methods

Human NP-MSCs were isolated from patients undergoing lumbar discectomy for IVD degeneration and were identified by immunophenotypes and multilineage differentiation. Then, cells were cultured in the compression apparatus at 1.0 MPa for different times (0 h, 24 h, 36 h, and 48 h). The viability-, differentiation-, and differentiation-related genes (Runx2, APP, and Col2) and colony formation-, migration-, and stem cell-related proteins (Sox2 and Oct4) were evaluated.

Results

The results showed that the isolated cells fulfilled the criteria of MSC stated by the International Society for Cellular Therapy (ISCT). And our results also indicated that compression loading significantly inhibited cell viability, differentiation, colony formation, and migration. Furthermore, gene expression suggested that compression loading could downregulate the expression of stem cell-related proteins and lead to NP-MSC stemness losses.

Conclusions

Our results suggested that the biological behavior of NP-MSCs could be inhibited by compression loading and therefore enhanced our understanding on the compression-induced endogenous repair failure of NP-MSCs during IVDD.

Co-culturing nucleus pulposus mesenchymal stem cells with notochordal cell-rich nucleus pulposus explants attenuates tumor necrosis factor-α-induced senescence

Background

Cell therapy for the treatment of intervertebral disc degeneration (IDD) faces serious barriers since tissue-specific adult cells such as nucleus pulposus cells (NPCs) have limited proliferative ability and poor regenerative potential; in addition, it is difficult for exogenous adult stem cells to survive the harsh environment of the degenerated intervertebral disc. Endogenous repair by nucleus pulposus mesenchymal stem cells (NPMSCs) has recently shown promising regenerative potential for the treatment of IDD. Notochordal cells (NCs) and NC-conditioned medium (NCCM) have been proven to possess regenerative ability for the treatment of IDD, but this approach is limited by the isolation and passaging of NCs. Our previous study demonstrated that modified notochordal cell-rich nucleus pulposus (NC-rich NP) has potential for the repair of IDD. However, whether this can protect NPMSCs during IDD has not been evaluated.

Methods

In the current study, tumor necrosis factor (TNF)-α was used to mimic the inflammatory environment of IDD. Human NPMSCs were cocultured with NC-rich NP explants from healthy rabbit lumbar spine with or without TNF-α. Cell proliferation and senescence were analyzed to investigate the effect of NC-rich NP explants on TNF-α-treated NPMSCs. The expression of mRNA encoding proteins related to matrix macromolecules (such as aggrecan, Sox-9, collagen Iα, and collagen IIα), markers related to the nucleus pulposus cell phenotype (including CA12, FOXF1, PAX1, and HIF-1α), and senescence markers (such as p16, p21, and p53), senescence-associated proinflammatory cytokines (IL-6), and extracellular proteases (MMP-13, ADAMTS-5) was assessed. The protein expression of CA12 and collagen II was also evaluated.

Results

After a 7-day treatment, the NC-rich NP explant was found to enhance cell proliferation, decrease cellular senescence, promote glycosaminoglycan (GAG), collagen II, and CA12 production, upregulate the expression of extracellular matrix (ECM)-related genes (collagen I, collagen II, SOX9, and ACAN), and enhance the expression of nucleus pulposus cell (NPC) markers (HIF-1α, FOXF1, PAX1, and CA12).

Conclusion

Modified NC-rich NP explants can attenuate TNF-α-induced degeneration and senescence of NPMSCs in vitro. Our findings provide new insights into the therapeutic potential of NC-rich NP for the treatment of IDD.

Characteristics and potentials of stem cells derived from human degenerated nucleus pulposus: potential for regeneration of the intervertebral disc

BACKGROUND

Eliminating the symptoms during treatment of intervertebral disc degeneration (IVDD) is only a temporary solution that does not cure the underlying cause. A biological method to treat this disorder may be possible by the newly discovered nucleus pulposus derived stem cells (NPDCs). However, the uncertain characteristics and potential of NPDCs calls for a comprehensive study.

METHODS

In the present study, nucleus pulposus samples were obtained from 5 patients with IVDD undergoing discectomy procedure and NPDCs were harvested using fluorescence activated cell sorting (FACS) by the co-expression of GD2+ and Tie2+. After in vitro expansion, the properties of NPDCs were compared with those of bone marrow mesenchyme stem cells (BMSCs) from the same subjects.

RESULTS

NPDCs performed similar properties in cell colony-forming ability, cell proliferation rate, cell cycle and stem cell gene expression similar to those of BMSCs. In addition, NPDCs could be differentiated into osteoblasts, adipocytes, and chondrocytes, and are found to be superior in chondrogenesis but inferior in adipocyte differentiation.

CONCLUSIONS

NPDCs derived from the degenerated intervertebral disc still keep the regeneration ability similar to BMSCs. Besides, the superior capacity in chondrogenesis may provide a promising cell candidate for cell-based regenerative medicine and tissue engineering in IVDD.

Implications for a Stem Cell Regenerative Medicine Based Approach to Human Intervertebral Disk Degeneration

The human body develops from a single cell, the zygote, the product of the maternal oocyte and the paternal spermatozoon. That 1-cell zygote embryo will divide and eventually grow into an adult human which is comprised of ~3.7 × 10¹³ cells. The tens of trillions of cells in the adult human can be classified into approximately 200 different highly specialized cell types that make up all of the different tissues and organs of the human body. Regenerative medicine aims to replace or restore dysfunctional cells, tissues and organs with fully functional ones. One area receiving attention is regeneration of the intervertebral discs (IVDs), which are located between the vertebrae and function to give flexibility and support load to the spine. Degenerated discs are a major cause of lower back pain. Different stem cell based regenerative medicine approaches to cure disc degeneration are now available, including using autologous mesenchymal stem cells (MSCs), induced pluripotent stem cells (iPSCs) and even attempts at direct transdifferentiation of somatic cells. Here we discuss some of the recent advances, successes, drawbacks, and the failures of the above-mentioned approaches.

Stem cells sources for intervertebral disc regeneration

Intervertebral disc regeneration field is rapidly growing since disc disorders represent a major health problem in industrialized countries with very few possible treatments. Indeed, current available therapies are symptomatic, and surgical procedures consist in disc removal and spinal fusion, which is not immune to regardable concerns about possible comorbidities, cost-effectiveness, secondary risks and long-lasting outcomes. This review paper aims to share recent advances in stem cell therapy for the treatment of intervertebral disc degeneration. In literature the potential use of different adult stem cells for intervertebral disc regeneration has already been reported. Bone marrow mesenchymal stromal/stem cells, adipose tissue derived stem cells, synovial stem cells, muscle-derived stem cells, olfactory neural stem cells, induced pluripotent stem cells, hematopoietic stem cells, disc stem cells, and embryonic stem cells have been studied for this purpose either in vitro or in vivo. Moreover, several engineered carriers (e.g., hydrogels), characterized by full biocompatibility and prompt biodegradation, have been designed and combined with different stem cell types in order to optimize the local and controlled delivery of cellular substrates in situ. The paper overviews the literature discussing the current status of our knowledge of the different stem cells types used as a cell-based therapy for disc regeneration.

Angiopoietin-1 receptor Tie2 distinguishes multipotent differentiation capability in bovine coccygeal nucleus pulposus cells

BACKGROUND

The intervertebral disc (IVD) has limited self-healing potential and disc repair strategies require an appropriate cell source such as progenitor cells that could regenerate the damaged cells and tissues. The objective of this study was to identify nucleus pulposus-derived progenitor cells (NPPC) and examine their potential in regenerative medicine in vitro.

METHODS

Nucleus pulposus cells (NPC) were obtained from 1-year-old bovine coccygeal discs by enzymatic digestion and were sorted for the angiopoietin-1 receptor Tie2. The obtained Tie2- and Tie2+ fractions of cells were differentiated into osteogenic, adipogenic, and chondrogenic lineages in vitro. Colony-forming units were prepared from both cell populations and the colonies formed were analyzed and quantified after 8 days of culture. In order to improve the preservation of the Tie2+ phenotype of NPPC in monolayer cultures, we tested a selection of growth factors known to have stimulating effects, cocultured NPPC with IVD tissue, and exposed them to hypoxic conditions (2 % O2).

RESULTS

After 3 weeks of differentiation culture, only the NPC that were positive for Tie2 were able to differentiate into osteocytes, adipocytes, and chondrocytes as characterized by calcium deposition (p < 0.0001), fat droplet formation (p < 0.0001), and glycosaminoglycan content (p = 0.0095 vs. Tie2- NPC), respectively. Sorted Tie2- and Tie2+ subpopulations of cells both formed colonies; however, the colonies formed from Tie2+ cells were spheroid in shape, whereas those from Tie2- cells were spread and fibroblastic. In addition, Tie2+ cells formed more colonies in 3D culture (p = 0.011) than Tie2- cells. During expansion, a fast decline in the fraction of Tie2+ cells was observed (p < 0.0001), which was partially reversed by low oxygen concentration (p = 0.0068) and supplementation of the culture with fibroblast growth factor 2 (FGF2) (p < 0.0001).

CONCLUSIONS

Our results showed that the bovine nucleus pulposus contains NPPC that are Tie2+. These cells fulfilled formally progenitor criteria that were maintained in subsequent monolayer culture for up to 7 days by addition of FGF2 or hypoxic conditions. We propose that the nucleus pulposus represents a niche of precursor cells for regeneration of the IVD.