Influence of rabbit notochordal cells on symptomatic intervertebral disc degeneration: anti-angiogenic capacity on human endothelial cell proliferation under hypoxia

The Role of Microvascular Variations in the Process of Intervertebral Disk Degeneration and Its Regulatory Mechanisms: A Literature Review

Microvascular changes are considered key factors in the process of intervertebral disk degeneration (IDD). Microvascular invasion and growth into the nucleus pulposus (NP) and cartilaginous endplates are unfavorable factors that trigger IDD. In contrast, the rich distribution of microvessels in the bony endplates and outer layers of the annulus fibrosus is an important safeguard for the nutrient supply and metabolism of the intervertebral disk (IVD). In particular, the adequate supply of microvessels in the bony endplates is the main source of the nutritional supply for the entire IVD. Microvessels can affect the progression of IDD through a variety of pathways. Many studies have explored the effects of microvessel alterations in the NP, annulus fibrosus, cartilaginous endplates, and bony endplates on the local microenvironment through inflammation, apoptosis, and senescence. Studies also elucidated the important roles of microvessel alterations in the process of IDD, as well as conducted in-depth explorations of cytokines and biologics that can inhibit or promote the ingrowth of microvessels. Therefore, the present manuscript reviews the published literature on the effects of microvascular changes on IVD to summarize the roles of microvessels in IVD and elaborate on the mechanisms of action that promote or inhibit de novo microvessel formation in IVD.

Inducing Angiogenesis in the Nucleus Pulposus

Bone morphogenetic protein (BMP) gene delivery to Lewis rat lumbar intervertebral discs (IVDs) drives bone formation anterior and external to the IVD, suggesting the IVD is inhospitable to osteogenesis. This study was designed to determine if IVD destruction with a proteoglycanase, and/or generating an IVD blood supply by gene delivery of an angiogenic growth factor, could render the IVD permissive to intra-discal BMP-driven osteogenesis and fusion. Surgical intra-discal delivery of naïve or gene-programmed cells (BMP2/BMP7 co-expressing or VEGF165 expressing) +/- purified chondroitinase-ABC (chABC) in all permutations was performed between lumbar 4/5 and L5/6 vertebrae, and radiographic, histology, and biomechanics endpoints were collected. Follow-up anti-sFlt Western blotting was performed. BMP and VEGF/BMP treatments had the highest stiffness, bone production and fusion. Bone was induced anterior to the IVD, and was not intra-discal from any treatment. chABC impaired BMP-driven osteogenesis, decreased histological staining for IVD proteoglycans, and made the IVD permissive to angiogenesis. A soluble fragment of VEGF Receptor-1 (sFlt) was liberated from the IVD matrix by incubation with chABC, suggesting dysregulation of the sFlt matrix attachment is a possible mechanism for the chABC-mediated IVD angiogenesis we observed. Based on these results, the IVD can be manipulated to foster vascular invasion, and by extension, possibly osteogenesis.

Recommendations for intervertebral disc notochordal cell investigation: From isolation to characterization

Background

Lineage-tracing experiments have established that the central region of the mature intervertebral disc, the nucleus pulposus (NP), develops from the embryonic structure called "the notochord". However, changes in the cells derived from the notochord which form the NP (i.e., notochordal cells [NCs]), in terms of their phenotype and functional identity from early developmental stages to skeletal maturation are less understood. These key issues require further investigation to better comprehend the role of NCs in homeostasis and degeneration as well as their potential for regeneration. Progress in utilizing NCs is currently hampered due to poor consistency and lack of consensus methodology for in vitro NC extraction, manipulation, and characterization.

Methods

Here, an international group has come together to provide key recommendations and methodologies for NC isolation within key species, numeration, in vitro manipulation and culture, and characterization.

Results

Recommeded protocols are provided for isolation and culture of NCs. Experimental testing provided recommended methodology for numeration of NCs. The issues of cryopreservation are demonstrated, and a pannel of immunohistochemical markers are provided to inform NC characterization.

Conclusions

Together we hope this article provides a road map for in vitro studies of NCs to support advances in research into NC physiology and their potential in regenerative therapies.

An update on animal models of intervertebral disc degeneration and low back pain: Exploring the potential of artificial intelligence to improve research analysis and development of prospective therapeutics

Animal models have been invaluable in the identification of molecular events occurring in and contributing to intervertebral disc (IVD) degeneration and important therapeutic targets have been identified. Some outstanding animal models (murine, ovine, chondrodystrophoid canine) have been identified with their own strengths and weaknesses. The llama/alpaca, horse and kangaroo have emerged as new large species for IVD studies, and only time will tell if they will surpass the utility of existing models. The complexity of IVD degeneration poses difficulties in the selection of the most appropriate molecular target of many potential candidates, to focus on in the formulation of strategies to effect disc repair and regeneration. It may well be that many therapeutic objectives should be targeted simultaneously to effect a favorable outcome in human IVD degeneration. Use of animal models in isolation will not allow resolution of this complex issue and a paradigm shift and adoption of new methodologies is required to provide the next step forward in the determination of an effective repairative strategy for the IVD. AI has improved the accuracy and assessment of spinal imaging supporting clinical diagnostics and research efforts to better understand IVD degeneration and its treatment. Implementation of AI in the evaluation of histology data has improved the usefulness of a popular murine IVD model and could also be used in an ovine histopathological grading scheme that has been used to quantify degenerative IVD changes and stem cell mediated regeneration. These models are also attractive candidates for the evaluation of novel anti-oxidant compounds that counter inflammatory conditions in degenerate IVDs and promote IVD regeneration. Some of these compounds also have pain-relieving properties. AI has facilitated development of facial recognition pain assessment in animal IVD models offering the possibility of correlating the potential pain alleviating properties of some of these compounds with IVD regeneration.

Update on the roles of macrophages in the degeneration and repair process of intervertebral discs

Intervertebral disc (IVD) degeneration is the common cause of lumbar degenerative diseases, causing severe social and economic burden. The process of IVD degeneration involves a complex of pathologic changes on both extracellular matrix degradation and resident cell apoptosis. In recent years, there is increasing evidence that macrophages play vital roles during the damage and repair process of IVD degeneration. Nevertheless, the interactions between macrophages and IVD are not well understood, even if the IVD has long been regarded as the immune privileged site. Therefore, this review mainly focuses on the progress and obstacles of studies investigating the blood supply, immune response and especially macrophages during the IVD degeneration process.

ISSLS Prize in Bioengineering Science 2022: low rate cyclic loading as a therapeutic strategy for intervertebral disc regeneration

BACKGROUND

The intervertebral disc degenerates with age and has a poor propensity for regeneration. Small molecule transport plays a key role in long-term degradation and repair. Convection (bulk flow), induced by low rate cyclic loading of the intervertebral disc, has been shown to increase transport of small molecules. However, the potential therapeutic benefit of low rate cyclic loading on degenerated discs has not been described. The purpose of this study was to determine if a sustained (daily) low rate cyclic loading regimen could slow, arrest, or reverse intervertebral disc degeneration in the rabbit lumbar spine.

METHODS

Fifty-six New Zealand white rabbits (>12 months old) were designated as either Control (no disc puncture), 8D (disc puncture followed by 8 weeks of degeneration), 16D (disc puncture followed by 16 weeks of degeneration), or Therapy (disc puncture followed by 8 weeks of degeneration and then 8 weeks of daily low rate cyclic loading). Specimens were evaluated by T2 mapping, Pfirrmann scale grading, nucleus volume, disc height index, disc morphology and structure, and proteoglycan content.

RESULTS

In every metric, mean values for the Therapy group fell between Controls and 8D animals. These results suggest that sustained low rate cyclic loading had a therapeutic effect on the already degenerated disc and the regimen promoted signs of regeneration. If these results translate clinically, this approach could fulfil a significant clinical need by providing a means of non-invasively treating intervertebral disc degeneration.

Current Knowledge and Future Therapeutic Prospects in Symptomatic Intervertebral Disc Degeneration

Intervertebral disc (IVD) degeneration is the main source of intractable lower back pain, and symptomatic IVD degeneration could be due to different degeneration mechanisms. In this article, we describe the molecular basis of symptomatic IVD degenerative disc diseases (DDDs), emphasizing the role of degeneration, inflammation, angiogenesis, and extracellular matrix (ECM) regulation during this process. In symptomatic DDD, pro-inflammatory mediators modulate catabolic reactions, resulting in changes in ECM homeostasis and, finally, neural/vascular ingrowth-related chronic intractable discogenic pain. In ECM homeostasis, anabolic protein-regulating genes show reduced expression and changes in ECM production, while matrix metalloproteinase gene expression increases and results in aggressive ECM degradation. The resultant loss of normal IVD viscoelasticity and a concomitant change in ECM composition are key mechanisms in DDDs. During inflammation, a macrophage-related cascade is represented by the secretion of high levels of pro-inflammatory cytokines, which induce inflammation. Aberrant angiogenesis is considered a key initiative pathologic step in symptomatic DDD. In reflection of angiogenesis, vascular endothelial growth factor expression is regulated by hypoxia-inducible factor-1 in the hypoxic conditions of IVDs. Furthermore, IVD cells undergoing degeneration potentially enhance neovascularization by secreting large amounts of angiogenic cytokines, which penetrate the IVD from the outer annulus fibrosus, extending deep into the outer part of the nucleus pulposus. Based on current knowledge, a multi-disciplinary approach is needed in all aspects of spinal research, starting from basic research to clinical applications, as this will provide information regarding treatments for DDDs and discogenic pain.

Exosomes Immunity Strategy: A Novel Approach for Ameliorating Intervertebral Disc Degeneration

Low back pain (LBP), which is one of the most severe medical and social problems globally, has affected nearly 80% of the population worldwide, and intervertebral disc degeneration (IDD) is a common musculoskeletal disorder that happens to be the primary trigger of LBP. The pathology of IDD is based on the impaired homeostasis of catabolism and anabolism in the extracellular matrix (ECM), uncontrolled activation of immunologic cascades, dysfunction, and loss of nucleus pulposus (NP) cells in addition to dynamic cellular and biochemical alterations in the microenvironment of intervertebral disc (IVD). Currently, the main therapeutic approach regarding IDD is surgical intervention, but it could not considerably cure IDD. Exosomes, extracellular vesicles with a diameter of 30–150 nm, are secreted by various kinds of cell types like stem cells, tumor cells, immune cells, and endothelial cells; the lipid bilayer of the exosomes protects them from ribonuclease degradation and helps improve their biological efficiency in recipient cells. Increasing lines of evidence have reported the promising applications of exosomes in immunological diseases, and regarded exosomes as a potential therapeutic source for IDD. This review focuses on clarifying novel therapies based on exosomes derived from different cell sources and the essential roles of exosomes in regulating IDD, especially the immunologic strategy.

Anti-degenerative effect of melatonin on intervertebral disc: protective contribution against inflammation, oxidative stress, apoptosis, and autophagy

Intervertebral disc (IVD) degeneration is a leading cause of lower back pain. Although the etiology of IVD degeneration (IVDD) is unclear, excessive oxidative stress, inflammation and apoptosis and disruption of autophagy play important role in the pathogenesis of IVDD. Therefore, finding a solution to mitigate these processes could stop or reduce the development of IVDD. Melatonin, a powerful antioxidant, plays an important role in regulating cartilage tissue hemostasis. Melatonin inhibits destruction of extracellular matrix (ECM) of disc. Melatonin preserves ECM contents including sox-9, aggrecan, and collagen II through inhibiting matrix degeneration enzymes such as MMP-13. These protective effects may be mediated by the inhibition of oxidative stress, inflammation and apoptosis, and regulation of autophagy in IVD cells.

Cell sources proposed for nucleus pulposus regeneration

Lower back pain (LBP) occurs in 80% of adults in their lifetime; resulting in LBP being one of the biggest causes of disability worldwide. Chronic LBP has been linked to the degeneration of the intervertebral disc (IVD). The current treatments for chronic back pain only provide alleviation of symptoms through pain relief, tissue removal, or spinal fusion; none of which target regenerating the degenerate IVD. As nucleus pulposus (NP) degeneration is thought to represent a key initiation site of IVD degeneration, cell therapy that specifically targets the restoration of the NP has been reviewed here. A literature search to quantitatively assess all cell types used in NP regeneration was undertaken. With key cell sources: NP cells; annulus fibrosus cells; notochordal cells; chondrocytes; bone marrow mesenchymal stromal cells; adipose-derived stromal cells; and induced pluripotent stem cells extensively analyzed for their regenerative potential of the NP. This review highlights: accessibility; expansion capability in vitro; cell survival in an IVD environment; regenerative potential; and safety for these key potential cell sources. In conclusion, while several potential cell sources have been proposed, iPSC may provide the most promising regenerative potential.

Suramin attenuates intervertebral disc degeneration by inhibiting NF-κB signalling pathway

Aims

Interleukin (IL)-1β is one of the major pathogenic regulators during the pathological development of intervertebral disc degeneration (IDD). However, effective treatment options for IDD are limited. Suramin is used to treat African sleeping sickness. This study aimed to investigate the pharmacological effects of suramin on mitigating IDD and to characterize the underlying mechanism.

Methods

Porcine nucleus pulposus (NP) cells were treated with vehicle, 10 ng/ml IL-1β, 10 μM suramin, or 10 μM suramin plus IL-1β. The expression levels of catabolic and anabolic proteins, proinflammatory cytokines, mitogen-activated protein kinase (MAPK), and nuclear factor (NF)-κB-related signalling molecules were assessed by Western blotting, quantitative real-time polymerase chain reaction (qRT-PCR), and immunofluorescence analysis. Flow cytometry was applied to detect apoptotic cells. The ex vivo effects of suramin were examined using IDD organ culture and differentiation was analyzed by Safranin O-Fast green and Alcian blue staining.

Results

Suramin inhibited IL-1β-induced apoptosis, downregulated matrix metalloproteinase (MMP)-3, MMP-13, a disintegrin and metalloproteinase with thrombospondin motifs (ADAMTS)-4, and ADAMTS-5, and upregulated collagen 2A (Col2a1) and aggrecan in IL-1β-treated NP cells. IL-1β-induced inflammation, assessed by IL-1β, IL-8, and tumour necrosis factor α (TNF-α) upregulation, was alleviated by suramin treatment. Suramin suppressed IL-1β-mediated proteoglycan depletion and the induction of MMP-3, ADAMTS-4, and pro-inflammatory gene expression in ex vivo experiments.

Conclusion

Suramin administration represents a novel and effectively therapeutic approach, which could potentially alleviate IDD by reducing extracellular matrix (ECM) deposition and inhibiting apoptosis and inflammatory responses in the NP cells.

Cite this article: Bone Joint Res 2021;10(8):498–513.

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.

SDF1/CXCR4 axis facilitates the angiogenesis via activating the PI3K/AKT pathway in degenerated discs

Symptomatic degenerative disc disease (DDD) is considered the leading cause of chronic lower back pain (LBP). As one of the main features of intervertebral disc degeneration (IDD), vascular ingrowth plays a crucial role in the progression of LBP. Stromal cell‑derived factor 1 (SDF1) and its receptor C‑X‑C receptor 4 (CXCR4) were reported to be overexpressed in the degenerated intervertebral discs, suggesting that they may be involved in the pathogenesis of IDD. Moreover, SDF1 has been identified to induce neovascularization in rheumatoid arthritis disease. However, the roles of the SDF1/CXCR4 axis in the neovascularization of IDD remain unclear. Therefore, the objective of the present study was to elucidate whether the SDF1/CXCR4 axis takes part in neovascularization in degenerated intervertebral discs and its underlying mechanisms. Adenovirus infection was used to upregulate SDF1 expression in primary nucleus pulposus cells (NPCs). The effects of SDF1 on the proliferation and angiogenesis of vascular endothelial cells (VECs) were assessed by Cell Counting Kit‑8 and tube formation assays after VECs were treated with the supernatants derived from SDF1 overexpressed or not treated NPCs. Transwell chambers using the supernatants from NPCs as chemokines were applied to assess VEC migration and invasion. AMD3100, MK‑2206 and SF1670 were used to antagonize CXCR4, AKT serine/threonine kinase 1 (AKT) and phosphatase and tensin homolog (PTEN) in VECs. The results revealed that SDF1 overexpression significantly increased the ratio of phosphorylated AKT to AKT and decreased PTEN expression in NPCs, as well as enhanced the proliferation, migration, invasion and angiogenesis abilities of VECs. However, these effects induced by SDF1 overexpression in NPCs were all reversed when VECs were pretreated with AMD3100 or MK‑2206, whereas enhanced by SF1670 treatment. Collectively, the present study indicated that enhancement of the SDF1/CXCR4 axis in NPCs can significantly accelerate angiogenesis by regulating the PTEN/phosphatidylinositol‑3‑kinase/AKT pathway.

Melatonin prevents the binding of vascular endothelial growth factor to its receptor and promotes the expression of extracellular matrix-associated genes in nucleus pulposus cells

The mechanisms of intervertebral disc degeneration (IDD) involve numerous factors, including loss of the extracellular matrix (ECM) and vascular ingrowth. Melatonin has been reported to protect intervertebral discs (IVDs) from degeneration and to exert a potential anti-angiogenic effect. The aim of the present study was to investigate the anti-angiogenic and anabolic effects of melatonin in IVDs. Human nucleus pulposus (NP) and degenerative nucleus pulposus (DNP) cells were isolated and treated with melatonin. The results indicated that melatonin promoted ECM synthesis and NP cell proliferation. In addition, an NP/DNP and human umbilical vein endothelial cell (HUVEC) co-culture model was used to investigate the anti-angiogenesis effect of melatonin. Melatonin was indicated to suppress tube formation and migration of HUVECs in culture with NP cell-conditioned medium, as well as in an NP cell co-culture model. Fluorescence-labeled vascular endothelial growth factor (VEGF) was used to study the binding between VEGF and its receptor. The results of the present study indicated that melatonin exerts an angiogenic effect via inhibition of the binding of VEGF to its receptor in HUVECs. Taken together, these results suggest that melatonin is a potential agent to prevent IDD.

Overcoming Hypoxia-Restrained Radiotherapy Using an Erythrocyte-Inspired and Glucose-Activatable Platform

Radiotherapy (RT) as one of the most powerful cancer treatment strategies has been greatly restricted by tumor hypoxia. A mounting effort has been devoted to develop oxygen delivery systems for boosting the RT effect. Unluckily, those systems only supplied modest oxygen, which could not afford more than once and long-time RT. Herein, we describe the development of a glucose-regulated drug release platform, allowing for a long-term tumor normoxic microenvironment and repeated RT for a long time. The repeated cycles resulted in sustained high Endostar plasma levels, which dramatically normalized the tumor vasculature and chronically reversed tumor hypoxia. Taking advantage of the inexhaustible supply of oxygen, Endo@GOx-ER enabled RT achieved an impressive cancer treatment output. To the best of our knowledge, our strategy is the initial attempt to overcome tumor-hypoxia-limited RT through the normalization of tumor vasculature by using an erythrocyte-inspired and glucose-activatable platform and it visually casts a light on the clinical development.

Stem Cell Senescence: the Obstacle of the Treatment of Degenerative Disk Disease

Intervertebral disc (IVD) has a pivotal role in the maintenance of flexible motion. IVD degeneration is one of the primary causes of low back pain and disability, which seriously influences patients' health, and increases the family and social economic burden. Recently, stem cell therapy has been proven to be more effective on IVD degeneration disease. However, stem cell senescence is the limiting factor in the IVD degeneration treatment. Senescent stem cells have a negative effect on the self-repair on IVD degeneration. In this review, we delineate that the factors such as telomerase shortening, DNA damage, oxidative stress, microenvironment and exosomes will induce stem cell aging. Recent studies tried to delay the aging of stem cells by regulating the expression of aging-related genes and proteins, changing the activity of telomerase, improving the survival microenvironment of stem cells and drug treatment. Understanding the mechanism of stem cell aging and exploring new approaches to delay or reverse stem cell aging asks for research on the repair of the degenerated disc.

Loss of TIMP3 expression induces inflammation, matrix degradation, and vascular ingrowth in nucleus pulposus: A new mechanism of intervertebral disc degeneration

Low back pain (LBP) is one of the most common complains in orthopedic outpatient department and intervertebral disc degeneration (IDD) is one of the most important reasons of LBP. The mechanisms of IDD contain a complex biochemical cascade which includes inflammation, vascular ingrowth, and results in degradation of matrix. In our study, we used both in vitro and in vivo models to investigate the relation between tissue inhibitor of metalloproteinase-3 (TIMP3) expression and IDD. Loss of TIMP3 expression was found in degenerative intervertebral disc (IVD), this change of expression was closely related with the dephosphorylation of smad2/3. Overexpression of TIMP3 significantly inhibited the release of TNF-α and matrix degradation induced by Lipopolysaccharide. Vascular ingrowth was also suppressed by TIMP3 in the in vitro and in vivo models. Further, animal experiments confirmed that the degeneration of IVD was reduced after overexpression of TIMP3 in nucleus pulposus. Taken together, our results indicated TIMP-3 might play an important role in the pathogenesis of IDD and therefore be a potential therapeutic target in the future.

The Immune Privilege of the Intervertebral Disc: Implications for Intervertebral Disc Degeneration Treatment

The intervertebral disc (IVD) is the largest avascular organ of the body. It is composed of three parts: the nucleus pulposus (NP), the annulus fibrosus (AF) and the cartilaginous endplate (CEP). The central NP is surrounded by the AF and sandwiched by the two CEPs ever since its formation. This unique structure isolates the NP from the immune system of the host. Additionally, molecular factors expressed in IVD have been shown inhibitive effect on immune cells and cytokines infiltration. Therefore, the IVD has been identified as an immune privilege organ. The steady state of immune privilege is fundamental to the homeostasis of the IVD. The AF and the CEP, along with the immunosuppressive molecular factors are defined as the blood-NP barrier (BNB), which establishes a strong barrier to isolate the NP from the host immune system. When the BNB is damaged, the auto-immune response of the NP occurs with various downstream cascade reactions. This effect plays an important role in the whole process of IVD degeneration and related complications, such as herniation, sciatica and spontaneous herniated NP regression. Taken together, an enhanced understanding of the immune privilege of the IVD could provide new targets for the treatment of symptomatic IVD disease. However, the underlying mechanism above is still not fully clarified. Accordingly, the current study will extensively review and discuss studies regarding the immune privilege of the IVD.

SDF1/CXCR4 axis plays a role in angiogenesis during the degeneration of intervertebral discs

Low back pain (LBP) is a ubiquitous disease affecting quality of life. The ingrowth of new blood vessels is an important pathological feature of LBP, but its underlying mechanisms are poorly understood. The present study aimed to investigate the influence and relative mechanism of stromal cell derived factor 1 (SDF1) on the angiogenesis of degenerated intervertebral discs. The expression of SDF1 in nucleus pulposus cells (NPCs) was upregulated and downregulated by virus transfection, and the NPCs were allocated to either the downregulation (Down), degeneration (D) or upregulation (Up) group according to the expression of SDF1. The different groups of NPCs or NPC conditioned media were co-cultured with vascular endothelial cells (VECs) under different conditions. A Cell Counting Kit-8 (CCK-8) assay, a Transwell migration assay and a tube formation assay were conducted to evaluate the influence on angiogenesis. The results showed that SDF1 was significantly up- and downregulated in the Up and Down groups, respectively. Each group of NPCs or their conditioned medium was co-cultured with VECs; the CCK-8, Transwell migration and tube formation assays showed that cell viability, chemotactic migration and the tube formation ability of VECs increased with the rise in SDF1. The aforementioned results were significantly different between each group. After adding the CXCR4 inhibitor, AMD3100, the viability, migration and tube formation of VECs were suppressed in the D and Up groups, and there was a significant difference compared with the prior to the addition of the inhibitor, while there was a declining tendency in the Down group and no significant difference following addition of the inhibitor. The results demonstrated that SDF1 is expressed in human NPCs, and the SDF1/CXCR4 axis can influence the viability, migration and tube formation of VECs and may play an important role in the angiogenesis of human degenerated discs.

SDF1/CXCR7 Signaling Axis Participates in Angiogenesis in Degenerated Discs via the PI3K/AKT Pathway

Degenerative disc disease (DDD) is the main cause of low back pain, and the ingrowth of new blood vessels is one of its pathological features. The stromal cell-derived factor 1 (SDF1)/CXCR7 signaling axis plays a role in these physiological and pathological activities. The aims of this study were to explore whether this signaling axis participates in the angiogenesis of degenerated intervertebral discs (IVDs) and to define its underlying mechanism. In this study, we cocultured human nucleus pulposus cells (NPCs) and vascular endothelial cells (VECs) and regulated the expression of SDF1/CXCR7 to investigate the effect of VEC angiogenesis by NPCs. The results revealed that angiogenesis was enhanced with increased SDF1 and that angiogenesis was weakened with the inhibition of CXCR7. We found that PI3K/AKT was involved in the downstream pathway in the coculture. VEC angiogenesis induction by NPCs was enhanced with an increase in pAKT or a decrease in PTEN. We conclude that the SDF1/CXCR7 signaling axis plays a role in the angiogenesis of degenerated IVD through the PI3K/AKT pathway.

Notochordal cell matrix: An inhibitor of neurite and blood vessel growth?

Blood vessel and neurite ingrowth into the degenerating intervertebral disc (IVD) are related to pain. In reported studies, notochordal cell (NC)-conditioned medium (NCCM) induced a regenerative response of nucleus pulposus (NP) cells, but also inhibition of neurite and vessel formation. NC matrix (NCM) derived from NC-rich NP tissue, induced even stronger anabolic effects than NCCM. Thus, the aim was to investigate whether NCM has similar anti-neurogenic and -angiogenic properties as NCCM. NCM and NCCM where produced from porcine NC-rich NP tissue. Human umbilical vein endothelial cells (HUVECs) were cultured in base medium (BM, 300 mOsm), NCCM (produced at 300 and 400 mOsm), NCM, or with chondroitin sulfate (CS, positive control) in angiogenesis-inducing medium, after which vessel length was measured. Although CS alone inhibited vessel growth, NCCM (both osmolarities) stimulated vessel formation by HUVECs. NCM did not affect vessel growth relative to BM. SH-SY5Y cells were cultured in BM, NCCM, and NCM on poly-D-lysine coated and polystyrene surfaces, and analyzed for neurite length and percentage of neurite expressing cells. On coated surfaces, neither NCCM nor NCM affected neurite growth. On a polystyrene surface, NCCM and NCM induced a higher number of neurite-expressing cells. NCCM's previously reported anti-angiogenic and -neurogenic effects were not observed in this study. Although addition of CS inhibited HUVEC vessel formation, other factors may be present in NCCM and NCM that affect neurite and vessel growth. Therefore, future studies testing an NC-based regenerative strategy should carefully assess the risk of such adverse effects in an in vivo setting. © 2018 The Authors. Journal of Orthopaedic Research® Published by Wiley Periodicals, Inc. J Orthop Res 36:3188-3195, 2018.

Osteoporosis of the vertebra and osteochondral remodeling of the endplate causes intervertebral disc degeneration in ovariectomized mice

Background

Studies on the relationship between osteoporosis and intervertebral disc degeneration (IVDD) are inconsistent. Therefore, we assessed whether IVDD is affected by vertebral osteoporosis in ovariectomized mice and investigated the underlying pathogenesis of IVDD related to osteoporosis.

Methods

Thirty healthy female C57BL/6 J mice aged 8 weeks were randomly divided into two groups: a control group (sham operation, n = 15) and an ovariectomy group (OVX; bilateral ovariectomy, n = 15). At 12 weeks after surgery, the bone quantity and microstructure in the lumbar vertebra and endplate as well as the volume of the L4/5 disc space were evaluated by microcomputed tomography (micro-CT). The occurrence and characteristic alterations of IVDD were identified via histopathological staining. The osteoclasts were detected using tartrate-resistant acid phosphatase (TRAP) staining. Type II collagen (Col II), osterix (OSX), osteopontin (OPN), and vascular endothelial growth factor (VEGF) expression in the intervertebral disc were detected by immunohistochemical analysis.

Results

OVX significantly increased the body weight and decreased the uterus weight. Micro-CT analysis showed that osteoporosis of the vertebra and osteochondral remodeling of the endplate were accompanied by an increase in the endplate porosity and a decrease in the disc volume in the OVX group. Likewise, histological evaluation revealed that IVDD occurred at 12 weeks after ovariectomy, with features of endochondral ossification of the endplate, loose and broken annulus fibrosus, and degeneration of nucleus pulposus. TRAP staining showed that numerous active osteoclasts appeared in the subchondral bone and cartilaginous endplate of OVX mice, whereas osteoclasts were rarely detected in control mice. Immunohistochemical analysis demonstrated that the expression of osterix was significantly increased, notably in the endplate of OVX mice. In addition, Col II was decreased in the ossification endplate and the degenerative annulus fibrosus, where OPN and VEGF expressions were elevated in OVX mice.

Conclusions

OVX induced vertebral osteoporosis and osteochondral remodeling of the cartilaginous endplate contributing to the angiogenesis and an increase in porosity of the bone-cartilage surface, and also affected the matrix metabolism which consequently had detrimental effects on the intervertebral disc. Our study suggests that preserving the structural integrity and the function of the adjacent structures, including the vertebrae and endplates, may protect the disc against degeneration.

Electronic supplementary material

The online version of this article (10.1186/s13075-018-1701-1) contains supplementary material, which is available to authorized users.

An optimized culture system for notochordal cell expansion with retention of phenotype

BACKGROUND

Notochordal (NC) cells display therapeutic potential in treating degeneration of the intervertebral disc. However, research on their phenotype and function is limited by low-cell yields and a lack of appropriate methodology for cell expansion. Utilizing porcine cells, this study aimed to develop an optimized culture system which allows expansion of NC cell populations with retention of phenotype.

METHODS

Post-natal porcine and foetal human nucleus pulposus tissue was compared histologically and expression of known NC cell marker genes by porcine NC cells was analyzed. Porcine NC cells were isolated from six-week post-natal discs and cultured in vitro under varied conditions: (1) DMEM vs αMEM; (2) laminin-521, fibronectin, gelatin and uncoated tissue culture-treated polystyrene (TCP); (3) 2% O2 vs normoxia; (4) αMEM (300 mOsm/L) vs αMEM (400 mOsm/L); (5) surface stiffness of 0.5 and 4 kPa and standard TCP. Adherence, proliferation, morphology and expression of NC cell markers were assessed over a 14-day culture period.

RESULTS

Native porcine nucleus pulposus tissue demonstrated similar morphology to human foetal tissue and porcine NC cells expressed known notochordal markers (CD24, KRT8, KRT18, KRT19, and T). Use of αMEM media and laminin-521-coated surfaces showed the greatest cell adherence, proliferation and retention of NC cell morphology and phenotype. Proliferation of NC cell populations was further enhanced in hypoxia (2%) and phenotypic retention was improved on 0.5 kPa culture surfaces.

DISCUSSION

Our model has demonstrated an optimized system in which NC cell populations may be expanded while retaining a notochordal phenotype. Application of this optimized culture system will enable NC cell expansion for detailed phenotypic and functional study, a major advantage over current culture methods described in the literature. Furthermore, the similarities identified between porcine and human NC cells suggest this system will be applicable in human NC cell culture for investigation of their therapeutic potential.

Critical aspects and challenges for intervertebral disc repair and regeneration-Harnessing advances in tissue engineering

Low back pain represents the highest burden of musculoskeletal diseases worldwide and intervertebral disc degeneration is frequently associated with this painful condition. Even though it remains challenging to clearly recognize generators of discogenic pain, tissue regeneration has been accepted as an effective treatment option with significant potential. Tissue engineering and regenerative medicine offer a plethora of exploratory pathways for functional repair or prevention of tissue breakdown. However, the intervertebral disc has extraordinary biological and mechanical demands that must be met to assure sustained success. This concise perspective review highlights the role of the disc microenvironment, mechanical and clinical design considerations, function vs mimicry in biomaterial‐based and cell engineering strategies, and potential constraints for clinical translation of regenerative therapies for the intervertebral disc.

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.