An in vitro study investigating the survival and phenotype of mesenchymal stem cells following injection into nucleus pulposus tissue

Current Therapeutic Strategies of Intervertebral Disc Regenerative Medicine

Intervertebral disc degeneration (IDD) is one of the most frequent causes of low back pain. No treatment is currently available to delay the progression of IDD. Conservative treatment or surgical interventions is only used to target the symptoms of IDD rather than treat the underlying cause. Currently, numerous potential therapeutic strategies are available, including molecular therapy, gene therapy, and cell therapy. However, the hostile environment of degenerated discs is a major problem that has hindered the clinical applicability of such approaches. In this regard, the design of drugs using alternative delivery systems (macro-, micro-, and nano-sized particles) may resolve this problem. These can protect and deliver biomolecules along with helping to improve the therapeutic effect of drugs via concentrating, protecting, and prolonging their presence in the degenerated disc. This review summarizes the research progress of diagnosis and the current options for treating IDD.

Injectable biomaterial induces regeneration of the intervertebral disc in a caprine loaded disc culture model

Back pain is the leading cause of disability with half of cases attributed to intervertebral disc (IVD) degeneration, yet currently no therapies target this cause. We previously reported an ex vivo caprine loaded disc culture system (LDCS) that accurately represents the cellular phenotype and biomechanical environment of human IVD degeneration. Here, the efficacy of an injectable hydrogel system (LAPONITE® crosslinked pNIPAM-co-DMAc, (NPgel)) to halt or reverse the catabolic processes of IVD degeneration was investigated within the LDCS. Following enzymatic induction of degeneration using 1 mg mL-1 collagenase and 2 U mL-1 chondroitinase ABC within the LDCS for 7 days, IVDs were injected with NPgel alone or with encapsulated human bone marrow progenitor cells (BMPCs). Un-injected caprine discs served as degenerate controls. IVDs were cultured for a further 21 days within the LDCS. Tissues were then processed for histology and immunohistochemistry. No extrusion of NPgel was observed during culture. A significant decrease in histological grade of degeneration was seen in both IVDs injected with NPgel alone and NPgel seeded with BMPCs, compared to un-injected controls. Fissures within degenerate tissue were filled by NPgel and there was evidence of native cell migration into injected NPgel. The expression of healthy NP matrix markers (collagen type II and aggrecan) was increased, whereas the expression of catabolic proteins (MMP3, ADAMTS4, IL-1β and IL-8) was decreased in NPgel (±BMPCs) injected discs, compared to degenerate controls. This demonstrates that NPgel promotes new matrix production at the same time as halting the degenerative cascade within a physiologically relevant testing platform. This highlights the potential of NPgel as a future therapy for IVD degeneration.

Human 3D nucleus pulposus microtissue model to evaluate the potential of pre-conditioned nasal chondrocytes for the repair of degenerated intervertebral disc

Introduction: An in vitro model that appropriately recapitulates the degenerative disc disease (DDD) microenvironment is needed to explore clinically relevant cell-based therapeutic strategies for early-stage degenerative disc disease. We developed an advanced 3D nucleus pulposus (NP) microtissues (µT) model generated with cells isolated from human degenerating NP tissue (Pfirrmann grade: 2-3), which were exposed to hypoxia, low glucose, acidity and low-grade inflammation. This model was then used to test the performance of nasal chondrocytes (NC) suspension or spheroids (NCS) after pre-conditioning with drugs known to exert anti-inflammatory or anabolic activities. Methods: NPµTs were formed by i) spheroids generated with NP cells (NPS) alone or in combination with ii) NCS or iii) NC suspension and cultured in healthy or degenerative disc disease condition. Anti-inflammatory and anabolic drugs (amiloride, celecoxib, metformin, IL-1Ra, GDF-5) were used for pre-conditioning of NC/NCS. The effects of pre-conditioning were tested in 2D, 3D, and degenerative NPµT model. Histological, biochemical, and gene expression analysis were performed to assess matrix content (glycosaminoglycans, type I and II collagen), production and release of inflammatory/catabolic factors (IL-6, IL-8, MMP-3, MMP-13) and cell viability (cleaved caspase 3). Results: The degenerative NPµT contained less glycosaminoglycans, collagens, and released higher levels of IL-8 compared to the healthy NPµT. In the degenerative NPµT, NCS performed superior compared to NC cell suspension but still showed lower viability. Among the different compounds tested, only IL-1Ra pre-conditioning inhibited the expression of inflammatory/catabolic mediators and promoted glycosaminoglycan accumulation in NC/NCS in DDD microenvironment. In degenerative NPµT model, preconditioning of NCS with IL-1Ra also provided superior anti-inflammatory/catabolic activity compared to non-preconditioned NCS. Conclusion: The degenerative NPµT model is suitable to study the responses of therapeutic cells to microenvironment mimicking early-stage degenerative disc disease. In particular, we showed that NC in spheroidal organization as compared to NC cell suspension exhibited superior regenerative performance and that IL-1Ra pre-conditioning of NCS could further improve their ability to counteract inflammation/catabolism and support new matrix production within harsh degenerative disc disease microenvironment. Studies in an orthotopic in vivo model are necessary to assess the clinical relevance of our findings in the context of IVD repair.

Low Back Pain, Disability, and Quality of Life One Year following Intradiscal Injection of Autologous Bone Marrow Aspirate Concentrate

Introduction

Degenerative disc disease is a common cause of chronic low back pain. Surgical intervention is an invasive treatment associated with high costs. There is growing interest in regenerative medicine as a less invasive but direct disc treatment for chronic discogenic low back pain.

Objective

To evaluate clinical improvement of primary discogenic low back pain with intradiscal injection of autologous bone marrow aspirate concentrate (BMAC). Study Design. Prospective cohort study. Setting. Single, multiphysician center. Patients. 32 adult patients undergoing intradiscal injection of autologous BMAC for the treatment of primary discogenic low back pain. Interventions. Intradiscal injection of autologous BMAC. Main Outcome Measures. Primary outcome measure is visual analog back pain scale (VAS back pain). Secondary outcome measures include ODI, VAS leg pain, and EQ-5D-5L scores. Outcomes were compared from baseline to 1 year.

Results

Thirty-two patients (56.3% male) with a mean age of 45.9 years were enrolled, giving 92 treated levels. Mean VAS back and leg pain scores improved from 5.4 to 3.0 (p < 0.001) and 2.8 to 1.3 (p = 0.005), respectively. Mean ODI scores decreased from 33.5 to 21.1 (p < 0.001), and EQ-5D-5L scores improved from 0.69 to 0.78 (p = 0.001). Using established MCID values, 59.4% had clinically significant improvement in VAS back pain, 43.8% in VAS leg pain, and 56.3% in ODI scores.

Conclusion

Intradiscal injection of autologous BMAC significantly improved low back pain, disability, and quality of life at one year. This study suggests that intradiscal BMAC has the potential to be an effective nonsurgical treatment for chronic discogenic low back pain.

Gene expression profiling in nucleus pulposus of human ruptured lumbar disc herniation

Purpose: To examine the differences in gene expression between ruptured and non-ruptured nucleus pulposus tissues of the intervertebral discs using gene chip technology. Methods: A total of 8 patients with nucleus pulposus from a lumbar disc herniation (LDH) undergoing discectomy in our hospital were selected, including 4 ruptured and 4 non-ruptured herniated nucleus pulposus cases. Total RNA was extracted from cells by using TRIzol reagent. Nucleus pulposus cDNA probes of the two groups were obtained by the single marker method and hybridized with a human gene expression profiling chip (Agilent). The fluorescence signal images were scanned by a laser, and the obtained genes were analyzed by bioinformatics. Results: There were 75 differentially expressed genes with more than 2-fold-changes, of which 56 were up-regulated and 19 were down-regulated. The differential expression of THSD7A, which was up-regulated 18 times, was the most significant, followed by CCL5, AQP3 and SDC4. Conclusion: THSD7A can be used as a characteristic differentially expressed gene in human ruptured nucleus pulposus. Moreover, CCL5, AQP3 and SDC4 may improve the chemotaxis of stem cell migration for self-healing of damaged disc tissue, increase water uptake by nucleus accumbens cells, and inhibit the inflammatory response, thus delaying the process of intervertebral disc degeneration.

The Influence of Intervertebral Disc Microenvironment on the Biological Behavior of Engrafted Mesenchymal Stem Cells

Intervertebral disc degeneration is the main cause of low back pain. Traditional treatment methods cannot repair degenerated intervertebral disc tissue. The emergence of stem cell therapy makes it possible to regenerate and repair degenerated intervertebral disc tissue. At present, mesenchymal stem cells are the most studied, and different types of mesenchymal stem cells have their own characteristics. However, due to the harsh and complex internal microenvironment of the intervertebral disc, it will affect the biological behaviors of the implanted mesenchymal stem cells, such as viability, proliferation, migration, and chondrogenic differentiation, thereby affecting the therapeutic effect. This review is aimed at summarizing the influence of each intervertebral disc microenvironmental factor on the biological behavior of mesenchymal stem cells, so as to provide new ideas for using tissue engineering technology to assist stem cells to overcome the influence of the microenvironment in the future.

Should Degenerated Intervertebral Discs of Patients with Modic Type 1 Changes Be Treated with Mesenchymal Stem Cells?

Low back pain (LBP) has been among the leading causes of disability for the past 30 years. This highlights the need for improvement in LBP management. Many clinical trials focus on developing treatments against degenerative disc disease (DDD). The multifactorial etiology of DDD and associated risk factors lead to a heterogeneous patient population. It comes as no surprise that the outcomes of clinical trials on intradiscal mesenchymal stem cell (MSC) injections for patients with DDD are inconsistent. Intradiscal MSC injections have demonstrated substantial pain relief and significant disability-related improvements, yet they have failed to regenerate the intervertebral disc (IVD). Increasing evidence suggests that the positive outcomes in clinical trials might be attributed to the immunomodulatory potential of MSCs rather than to their regenerative properties. Therefore, patient stratification for inflammatory DDD phenotypes may (i) better serve the mechanisms of action of MSCs and (ii) increase the treatment effect. Modic type 1 changes—pathologic inflammatory, fibrotic changes in the vertebral bone marrow—are frequently observed adjacent to degenerated IVDs in chronic LBP patients and represent a clinically distinct subpopulation of patients with DDD. This review discusses whether degenerated IVDs of patients with Modic type 1 changes should be treated with an intradiscal MSC injection.

MiR-1260b protects against LPS-induced degenerative changes in nucleus pulposus cells through targeting TCF7L2

Nucleus pulposus (NP) cells play a critical role in maintaining intervertebral disc integrity through producing the components of extracellular matrix (ECM). NP cell dysfunction, including senescence and hyper-apoptosis, has been regarded as critical events during intervertebral disc degeneration development. In the present study, we found that Transcription Factor 7-Like 2 (TCF7L2) was overexpressed within degenerative intervertebral disc tissue samples, and TCF7L2 silencing improved lipopolysaccharide (LPS)-induced repression on NP cell proliferation, ECM synthesis, and LPS-induced NP cell senescence. miR-1260b directly targeted TCF7L2 and inhibited TCF7L2 expression. miR-1260b overexpression improved LPS-induced degenerative changes in NP cells; more importantly, TCF7L2 overexpression significantly reversed the effects of miR-1260b overexpression on LPS-stimulated degenerative changes within NP cells. For the first time, we demonstrated the function of the miR-1260b/TCF7L2 axis on the phenotypic maintenance of chondrocyte-like NP cells and ECM synthesis by NP cells under LPS stimulation.

Application of stem cells in the repair of intervertebral disc degeneration

Intervertebral disc degeneration (IDD) is a common disease that increases with age, and its occurrence is stressful both psychologically and financially. Stem cell therapy for IDD is emerging. For this therapy, stem cells from different sources have been proven in vitro, in vivo, and in clinical trials to relieve pain and symptoms, reverse the degeneration cascade, delay the aging process, maintain the spine shape, and retain mechanical function. However, further research is needed to explain how stem cells play these roles and what effects they produce in IDD treatment. This review aims to summarize and objectively analyse the current evidence on stem cell therapy for IDD.

ADSC-Based Cell Therapies for Musculoskeletal Disorders: A Review of Recent Clinical Trials

Recently published clinical trials involving the use of adipose-derived stem cells (ADSCs) indicated that approximately one-third of the studies were conducted on musculoskeletal disorders (MSD). MSD refers to a wide range of degenerative conditions of joints, bones, and muscles, and these conditions are the most common causes of chronic disability worldwide, being a major burden to the society. Conventional treatment modalities for MSD are not sufficient to correct the underlying structural abnormalities. Hence, ADSC-based cell therapies are being tested as a form of alternative, yet more effective, therapies in the management of MSDs. Therefore, in this review, MSDs subjected to the ADSC-based therapy were further categorized as arthritis, craniomaxillofacial defects, tendon/ligament related disorders, and spine disorders, and their brief characterization as well as the corresponding conventional therapeutic approaches with possible mechanisms with which ADSCs produce regenerative effects in disease-specific microenvironments were discussed to provide an overview of under which circumstances and on what bases the ADSC-based cell therapy was implemented. Providing an overview of the current status of ADSC-based cell therapy on MSDs can help to develop better and optimized strategies of ADSC-based therapeutics for MSDs as well as help to find novel clinical applications of ADSCs in the near future.

Stem Cells and Intervertebral Disc Regeneration Overview-What They Can and Can't Do

BACKGROUND

Low back pain (LPB) is the main cause of disability worldwide with enormous socioeconomic burdens. A major cause of LBP is intervertebral disc degeneration (IDD): a chronic, progressive process associated with exhaustion of the resident cell population, tissue inflammation, degradation of the extracellular matrix and dehydration of the nucleus pulposus. Eventually, IDD may lead to serious sequelae including chronic LBP, disc herniation, segmental instability, and spinal stenosis, which may require invasive surgical interventions. However, no treatment is actually able to directly tackle IDD and hamper the degenerative process. In the last decade, the intradiscal injection of stem cells is raising as a promising approach to regenerate the intervertebral disc. This review aims to describe the rationale behind a regenerative stem cell therapy for IDD as well as the effect of stem cells following their implantation in the disc environment according to preclinical studies. Furthermore, actual clinical evidence and ongoing trials will be discussed, taking into account the future perspective and current limitations of this cutting-edge therapy.

METHODS

A literature analysis was performed for this narrative review. A database search of PubMed, Scopus and ClinicalTrials.gov was conducted using "stem cells" combined with "intervertebral disc", "degeneration" and "regeneration" without exclusion based on publication date. Articles were firstly screened on a title-abstract basis and, subsequently, full-text were reviewed. Both preclinical and clinical studies have been included.

RESULTS

The database search yielded recent publications from which the narrative review was completed.

CONCLUSIONS

Based on available evidence, intradiscal stem cell therapy has provided encouraging results in terms of regenerative effects and reduction of LBP. However, multicenter, prospective randomized trials are needed in order confirm the safety, efficacy and applicability of such a promising treatment.

Bone mesenchymal stem cell-derived extracellular vesicles promote the repair of intervertebral disc degeneration by transferring microRNA-199a

Extracellular vesicles (EVs) secreted by bone marrow mesenchymal stem cells (BMSCs) protect intervertebral disc degeneration (IDD) by regulating nucleus pulposus cell (NPC) apoptosis. But the mechanism of BMSCs-EVs-microRNA (miR)-199a in IDD remains unclear. In this study, after the acquisition and identification of BMSCs and BMSCs-EVs, IDD mouse model was established and treated with BMSCs-EVs. The pathological changes of NPCs, positive expression of MMP-2, MMP-6 and TIMP1, and the senescence and apoptosis of NPCs were evaluated. Microarray analysis was employed to analyze the differentially expressed miRs and genes after EV treatment. NPCs were treated with EVs/miR-199a/TGF-β agonist SRI-011381. The positive expression of col II and Aggrecan was assessed. The target gene and downstream pathway of miR-199a were analyzed. In vivo experiment, after BMSCs-EV treatment, MMP-2, MMP-6, TIMP1 and TUNEL-positive cells in IDD mice were decreased, and miR-199a was increased. In vitro experiments, the expression of col Ⅱ and Aggrecan, SA-β gal positive cells and apoptosis rate of NPCs were decreased after EV intervention. The protective effect of BMSCs-EVs on NPCs was impaired by reducing miR-199a carried by EVs. miR-199a could target GREM1 to inactivate the TGF-β pathway. miR-199a carried by BMSCs-EVs promotes IDD repair by targeting GREM1 and downregulating the TGF-β pathway. Our work confers a promising therapeutic strategy for IDD.

Uncovering the secretome of mesenchymal stromal cells exposed to healthy, traumatic, and degenerative intervertebral discs: a proteomic analysis

BACKGROUND

Mesenchymal stromal cells (MSCs) have been introduced as promising cell source for regenerative medicine. Besides their multilineage differentiation capacity, MSCs release a wide spectrum of bioactive factors. This secretome holds immunomodulatory and regenerative capacities. In intervertebral disc (IVD) cells, application of MSC secretome has been shown to decrease the apoptosis rate, induce proliferation, and promote production of extracellular matrix (ECM). For clinical translation of secretome-based treatment, characterization of the secretome composition is needed to better understand the induced biological processes and identify potentially effective secretomes.

METHODS

This study aimed to investigate the proteome released by bone marrow-derived MSCs following exposure to a healthy, traumatic, or degenerative human IVD environment by mass spectroscopy and quantitative immunoassay analyses. Exposure of MSCs to the proinflammatory stimulus interleukin 1β (IL-1β) was used as control.

RESULTS

Compared to MSC baseline secretome, there were 224 significantly up- or downregulated proteins following healthy, 179 following traumatic, 223 following degenerative IVD, and 160 proteins following IL-1β stimulus. Stimulation of MSCs with IVD conditioned media induced a more complex MSC secretome, involving more biological processes, compared to stimulation with IL-1β. The MSC response to stimulation with IVD conditioned medium was dependent on their pathological status.

CONCLUSIONS

The MSC secretome seemed to match the primary need of the IVD: homeostasis maintenance in the case of healthy IVDs, versus immunomodulation, adjustment of ECM synthesis and degradation disbalance, and ECM (re) organization in the case of traumatic and degenerative IVDs. These findings highlight the importance of cell preconditioning in the development of tailored secretome therapies. The secretome of human bone marrow-derived mesenchymal stromal cells (MSCs) stimulated with intervertebral disc (IVD) conditioned medium was analyzed by proteomic profiling. Depending on the pathological state of the IVD, the MSC secretome protein composition indicated immunomodulatory or anabolic activity of the secretome. These findings may have implications for tailored secretome therapy for the IVD and other tissues.

Animal models of regenerative medicine for biological treatment approaches of degenerative disc diseases

Degenerative disc disease (DDD) is a painful, chronic and progressive disease, which is characterized by inflammation, structural and biological deterioration of the intervertebral disc (IVD) tissues. DDD is specified as cell-, age-, and genetic-dependent degenerative process that can be accelerated by environmental factors. It is one of the major causes of chronic back pain and disability affecting millions of people globally. Current treatment options, such as physical rehabilitation, pain management, and surgical intervention, can provide only temporary pain relief. Different animal models have been used to study the process of IVD degeneration and develop therapeutic options that may restore the structure and function of degenerative discs. Several research works have depicted considerable progress in understanding the biological basis of disc degeneration and the therapeutic potentials of cell transplantation, gene therapy, applications of supporting biomaterials and bioactive factors, or a combination thereof. Since animal models play increasingly significant roles in treatment approaches of DDD, we conducted an electronic database search on Medline through June 2020 to identify, compare, and discuss publications regarding biological therapeutic approaches of DDD that based on intradiscal treatment strategies. We provide an up-to-date overview of biological treatment strategies in animal models including mouse, rat, rabbit, porcine, bovine, ovine, caprine, canine, and primate models. Although no animal model could profoundly reproduce the clinical conditions in humans; animal models have played important roles in specifying our knowledge about the pathophysiology of DDD. They are crucial for developing new therapy approaches for clinical applications.

Growing a backbone - functional biomaterials and structures for intervertebral disc (IVD) repair and regeneration: challenges, innovations, and future directions

Back pain and associated maladies can account for an immense amount of healthcare cost and loss of productivity in the workplace. In particular, spine related injuries in the US affect upwards of 5.7 million people each year. The degenerative disc disease treatment almost always arises due to a clinical presentation of pain and/or discomfort. Preferred conservative treatment modalities include the use of non-steroidal anti-inflammatory medications, physical therapy, massage, acupuncture, chiropractic work, and dietary supplements like glucosamine and chondroitin. Artificial disc replacement, also known as total disc replacement, is a treatment alternative to spinal fusion. The goal of artificial disc prostheses is to replicate the normal biomechanics of the spine segment, thereby preventing further damage to neighboring sections. Artificial functional disc replacement through permanent metal and polymer-based components continues to evolve, but is far from recapitulating native disc structure and function, and suffers from the risk of unsuccessful tissue integration and device failure. Tissue engineering and regenerative medicine strategies combine novel material structures, bioactive factors and stem cells alone or in combination to repair and regenerate the IVD. These efforts are at very early stages and a more in-depth understanding of IVD metabolism and cellular environment will also lead to a clearer understanding of the native environment which the tissue engineering scaffold should mimic. The current review focusses on the strategies for a successful regenerative scaffold for IVD regeneration and the need for defining new materials, environments, and factors that are so finely tuned in the healthy human intervertebral disc in hopes of treating such a prevalent degenerative process.

Effect of Conditioned Medium from Human Umbilical Cord-Derived Mesenchymal Stromal Cells on Rejuvenation of Nucleus Pulposus Derived Stem/Progenitor Cells from Degenerated Intervertebral Disc

Background and Objectives

Mesenchymal stromal cells (MSCs)-based treatment for degeneration of intervertebral disc (IVD) has been proposed recently. We here addressed whether MSC secreted factors can rejuvenate nucleus pulposus-derived stem/progenitor cells from degenerated disc (D-NPSCs) in vitro.

Methods and Results

We analyzed the expression of MSCs and NP cell specific surface markers, pluripotency related genes, multilineage potential and cell proliferative capacity of D-NPSCs upon incubation with the conditioned medium which was collected from the umbilical cord derived MSCs (UCMSCs). Our results indicated that the conditioned medium restore the stemness of D-NPSCs by up-regulating the expression level of CD29 and CD105, pluripotency related genes OCT4 and Nanog, and NP progenitor marker Tie2. The increased stemness was accompanied by promoted cell proliferative capacity and improved osteogenic and chondrogenic differentiation potential.

Conclusions

Our findings suggested that the UCMSCs derived conditioned medium might be used to rejuvenate the degenerated NP stem/progenitor cells.

Systematic Review: Is Intradiscal Injection of Bone Marrow Concentrate for Lumbar Disc Degeneration Effective?

Current studies evaluating the outcomes of an intradiscal injection of bone marrow concentrate (BMC) for lumbar disc degeneration are limited. The purpose of this review was to determine if an intradiscal injection of BMC for lumbar disc degeneration results in a statistically significant improvement in clinical outcomes. A systematic review was performed using Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) guidelines. Levels I-IV investigations of intradiscal BMC injections in symptomatic lumbar disc degeneration were included in the analysis. Modified Coleman Methodology Scores (MCMS) were used to analyze study methodological quality. Only outcome measurements used by more than 50% of included studies, with a minimum follow-up of 12 months, were eligible for final data analysis. Pre-injection and post-injection visual analog scale (VAS) and Oswestry disability index (ODI) were compared using two-sample Z-tests. Seven articles (97 subjects (47 males, 38 females, 12 unspecified), mean age 33.9 ± 14.3 years, mean follow-up 44.4 ± 25.4 months) were analyzed. Six articles were level IV evidence and one article was level II. Mean MCMS was 56.6 ± 9.1. All subjects received single injections into the nucleus pulposus of one or more affected discs. VAS (66.0 mm to 20.9 mm; p<0.001) and ODI (44.4 to 19.1; p<0.001) significantly improved following the intradiscal BMC injection. One patient (1.0%) experienced herniated nucleus pulposus (HNP) following treatment. No other complications or re-injections were reported. In conclusion, despite our skepticism regarding the efficacy of the procedure, intradiscal injection of BMC for lumbar disc degeneration resulted in statistically significant improvement in VAS and ODI with low re-injection and complication rates in the studies assessed. Given that this study is limited to level IV evidence, the findings suggest that further randomized controlled studies may be worthwhile to evaluate the true efficacy of this treatment.

The effect of high glucose on the biological characteristics of nucleus pulposus-derived mesenchymal stem cells

Diabetes mellitus (DM) is a dependent risk factor in the progression of intervertebral disc degeneration (IVDD). High glucose supply has negative effects on nucleus pulpous (NP) cell and mesenchymal stem cell (MSC) biology. However, the effect of hyperglycaemia on the biological characterization of nucleus pulpous-derived mesenchymal stem cell (NPMSC) has not been investigated previously. Therefore, further exploration of the effects of DM-associated hyperglycaemia on NPMSC biology is important to better understand and develop endogenous repair strategies of DM patient-associated IVDD. Therefore, the cell biological characteristics were compared between NPMSC cultured in media with low glucose concentration (LG-NPMSC) and high glucose concentration (HG-NPMSC). The results demonstrated that HG-NPMSC showed significantly decreased cell proliferation, colony formation ability, migration and wound-healing capability compared with those of LG-NPMSC. HG-NPMSC also showed significantly decreased expressions of stemness genes and mRNA and protein expressions of silent information regulator protein 1 (SIRT1), SIRT6, hypoxia inducible factor-1α (HIF-1α) and glucose transporter 1 (GLUT-1), whereas increased cell apoptosis, cell senescence and caspase-3 expression. These results suggest that high glucose may decrease proliferation and stemness maintenance ability and increase apoptosis and senescence of NPMSC. SIGNIFICANCE OF THE STUDY: We found that high glucose concentration significantly decreased cell proliferation, colony formation ability, migration and wound-healing capability of nucleus pulposus-derived mesenchymal stem cells. Moreover, high glucose cultured nucleus pulposus-derived mesenchymal stem cells showed significantly decreased expression of stemness genes, related mRNA and protein, whereas increased cell apoptosis, cell senescence and expression of caspase-3. The present study indicated that better control of high concentration glucose in the early stage of diabetes mellitus should be recommended to prevent or limit intervertebral disc degeneration.

Human iPSCs can be differentiated into notochordal cells that reduce intervertebral disc degeneration in a porcine model

Introduction: As many as 80% of the adult population experience back pain at some point in their lifetimes. Previous studies have indicated a link between back pain and intervertebral disc (IVD) degeneration. Despite decades of research, there is an urgent need for robust stem cell therapy targeting underlying causes rather than symptoms. It has been proposed that notochordal cells (NCs) appear to be the ideal cell type to regenerate the IVD: these cells disappear in humans as they mature, are replaced by nucleus pulposus (NP) cells, and their disappearance correlates with the initiation of degeneration of the disc. Human NCs are in short supply, thus here aimed for generation of notochordal-like cells from induced pluripotent cells (iPSCs). Methods: Human iPSCs were generated from normal dermal fibroblasts by transfecting plasmids encoding for six factors: OCT4, SOX2, KLF4, L-MYC, LIN28, and p53 shRNA. Then the iPSCs were treated with GSK3i to induce differentiation towards Primitive Streak Mesoderm (PSM). The differentiation was confirmed by qRT-PCR and immunofluorescence. PSM cells were transfected with Brachyury (Br)-encoding plasmid and the cells were encapsulated in Tetronic-tetraacrylate-fibrinogen (TF) hydrogel that mimics the NP environment (G'=1kPa), cultured in hypoxic conditions (2% O2) and with specifically defined growth media. The cells were also tested in vivo in a large animal model. IVD degeneration was induced after an annular puncture in pigs, 4 weeks later the cells were injected and IVDs were analyzed at 12 weeks after the injury using MRI, gene expression analysis and histology. Results: After short-term exposure of iPSCs to GSK3i there was a significant change in cell morphology, Primitive Streak Mesoderm (PSM) markers (Brachyury, MIXL1, FOXF1) were upregulated and markers of pluripotency (Nanog, Oct4, Sox2) were downregulated, both compared to the control group. PSM cells nucleofected with Br (PSM-Br) cultured in TF hydrogels retained the NC phenotype consistently for up to 8 weeks, as seen in the gene expression analysis. PSM-Br cells were co-cultured with bone marrow (BM)-derived mesenchymal stem cells (MSCs) which, with time, expressed the NC markers in higher levels, however the levels of expression in BM-MSCs alone did not change. Higher expression of NC and NP marker genes in human BM-MSCs was found to be induced by iNC-condition media (iNC-CM) than porcine NC-CM. The annular puncture induced IVD degeneration as early as 2 weeks after the procedure. The injected iNCs were detected in the degenerated discs after 8 weeks in vivo. The iNC-treated discs were found protected from degeneration. This was evident in histological analysis and changes in the pH levels, indicative of degeneration state of the discs, observed using qCEST MRI. Immunofluorescence stains show that their phenotype was consistent with the in vitro study, namely they still expressed the notochordal markers Keratin 18, Keratin 19, Noto and Brachyury. Conclusion: In the present study, we report a stepwise differentiation method to generate notochordal cells from human iPSCs. These cells not only demonstrate a sustainable notochordal cell phenotype in vitro and in vivo, but also show the functionality of notochordal cells and have protective effect in case of induced disc degeneration and prevent the change in the pH level of the injected IVDs. The mechanism of this effect could be suggested via the paracrine effect on resident cells, as it was shown in the in vitro studies with MSCs.

Lessons learned from intervertebral disc pathophysiology to guide rational design of sequential delivery systems for therapeutic biological factors

Intervertebral disc (IVD) degeneration has been associated with low back pain, which is a major musculoskeletal disorder and socio-economic problem that affects as many as 600 million patients worldwide. Here, we first review the current knowledge of IVD physiology and physiopathological processes in terms of homeostasis regulation and consecutive events that lead to tissue degeneration. Recent progress with IVD restoration by anti-catabolic or pro-anabolic approaches are then analyzed, as are the design of macro-, micro-, and nano-platforms to control the delivery of such therapeutic agents. Finally, we hypothesize that a sequential delivery strategy that i) firstly targets the inflammatory, pro-catabolic microenvironment with release of anti-inflammatory or anti-catabolic cytokines; ii) secondly increases cell density in the less hostile microenvironment by endogenous cell recruitment or exogenous cell injection, and finally iii) enhances cellular synthesis of extracellular matrix with release of pro-anabolic factors, would constitute an innovative yet challenging approach to IVD regeneration.

CD146/MCAM distinguishes stem cell subpopulations with distinct migration and regenerative potential in degenerative intervertebral discs

OBJECTIVE

This study aimed to characterize the mesenchymal stem cell (MSC) subpopulation migrating towards a degenerated intervertebral disc (IVD) and to assess its regenerative potential.

DESIGN

Based on initial screening for migration towards C-C motif chemokine ligand 5 (CCL5), the migration potential of CD146+ and CD146- mesenchymal stem cells (MSCs) was evaluated in vitro and in a degenerated organ culture model (degeneration by high-frequency loading in a bioreactor). Discogenic differentiation potential of CD146+ and CD146- MSCs was investigated by in vitro pellet culture assay with supplementation of growth and differentiation factor-6 (GDF6). Furthermore, trypsin degenerated IVDs were treated by either homing or injection of CD146+ or CD146- MSCs and glycosaminoglycan synthesis was evaluated by Sulphur 35 incorporation after 35 days of culture.

RESULTS

Surface expression of CD146 led to a higher number of migrated MSCs both in vitro and in organ culture. CD146+ and CD146- pellets responded with a similar up-regulation of anabolic markers. A higher production of sulfated glycosaminoglycans (sGAG)/DNA was observed for CD146+ pellets, while in organ cultures, sGAG synthesis rate was higher for IVDs treated with CD146- MSCs by either homing or injection.

CONCLUSIONS

The CD146+ MSC subpopulation held greater migration potential towards degenerative IVDs, while the CD146- cells induced a stronger regenerative response in the resident IVD cells. These findings were independent of the application route (injection vs migration). From a translational point of view, our data suggests that CD146+ MSCs may be suitable for re-population, while CD146- MSCs may represent the primary choice for stimulation of endogenous IVD cells.

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.

Intervertebral disc tissue engineering: A brief review

Intervertebral disc (IVD) degeneration (IDD) is associated with low back pain and significantly affects the patient's quality of life. Degeneration of the IVD alters disk height and the mechanics of the spine, leading to chronic segmental spinal instability. The pathophysiology of IVD disease is still not well understood. Current therapies for IDD include conservative and invasive approaches, but none of those treatments are able to restore the disc structure and function. Recently, tissue engineering techniques emerged as a possible approach to treat IDD, by replacing a damaged IVD with scaffolds and appropriate cells. Advances in manufacturing techniques, material processing and development, surface functionalization, drug delivery systems and cell incorporation furthered the development of tissue engineering therapies. In this review, biomaterial scaffolds and cell-based therapies for IVD regeneration are briefly discussed.

Treatment of Naturally Degenerated Canine Lumbosacral Intervertebral Discs with Autologous Mesenchymal Stromal Cells and Collagen Microcarriers: A Prospective Clinical Study

Intervertebral disc (IVD) degeneration is a frequent disease in modern societies and at its later stages is likely to cause chronic low back pain. Although many studies have been published, the available treatments for IVD degeneration fail to promote regeneration or even marginal repair of the IVD structure. In this study, we aimed to establish veterinary canine patients as a translational large animal model that recapitulates IVD degeneration that occurs in humans, and to investigate the suitability of intradiscal application of mesenchymal stromal cells (MSC). Twenty client-owned dogs diagnosed with spontaneous degenerative lumbosacral IVD and low back pain were included in the study. Autologous MSC were isolated from bone marrow and cultured for 2 weeks. Prior to injection, MSC were attached on collagen microcarriers for delivery, with or without TGF-β1 crosslinking. After decompressive spinal surgery, dogs received an intradiscal injection of MSC-microcarriers (n = 11), MSC-TGF-β1-microcarriers (n = 6) or microcarriers only (control, n = 3). MSC-microcarriers were initially evaluated in vitro and ex vivo, to test cell chondrogenic potential and biomechanical properties of the microcarriers, respectively. Clinical performance and Pfirrmann grading were evaluated at 10 months after the injection by magnetic resonance imaging. MSC differentiated successfully in vitro towards chondrogenic phenotype and biomechanical tests showed no significant differences of IVD stiffness after microcarrier injection. In vivo injection was successful in all dogs, without any visible leakage, and clinical functioning was restored back to normality. However, postoperative Pfirrmann grade remained identical in all dogs, and formation of Schmorl’s nodes was detected in 45% of dogs. This side effect was reduced by halving the injection volume, which was then observed only in 11% of dogs. In conclusion, we observed marked clinical improvement in all groups, despite the formation of Schmorl’s nodes, but microcarriers and MSC failed to regenerate the structure of degenerated IVD.

Leaping the hurdles in developing regenerative treatments for the intervertebral disc from preclinical to clinical

Chronic back and neck pain is a prevalent disability, often caused by degeneration of the intervertebral disc. Because current treatments for this condition are less than satisfactory, a great deal of effort is being applied to develop new solutions, including regenerative strategies. However, the path from initial promising idea to clinical use is fraught with many hurdles to overcome. Many of the keys to success are not necessarily linked to science or innovation. Successful translation to clinic will also rely on planning and awareness of the hurdles. It will be essential to plan your entire path to clinic from the outset and to do this with a multidisciplinary team. Take advice early on regulatory aspects and focus on generating the proof required to satisfy regulatory approval. Scientific demonstration and societal benefits are important, but translation cannot occur without involving commercial parties, which are instrumental to support expensive clinical trials. This will only be possible when intellectual property can be protected sufficiently to support a business model. In this manner, commercial, societal, medical, and scientific partners can work together to ultimately improve patient health. Based on literature surveys and experiences of the co-authors, this opinion paper presents this pathway, highlights the most prominent issues and hopefully will aid in your own translational endeavors.

Stromal Cell Derived Factor-1-Mediated Migration of Mesenchymal Stem Cells Enhances Collagen Type II Expression in Intervertebral Disc

Intervertebral disc (IVD) degeneration is characterized by an unbalanced cell catabolic/anabolic activity and cell death, resulting in the degradation of extracellular matrix components and water loss. Repopulating the IVD with new cells may help in recovering tissue homeostasis and reverting the degenerative process. In this study the regenerative potential of a hyaluronan (HA)-based chemoattractant delivery system able to recruit mesenchymal stem cells (MSCs) seeded on the cartilaginous endplate (CEP) of IVD was explored. A HA delivery system containing stromal cell derived factor-1 (SDF-1) (5 ng/μL) (HAPSDF5) was injected in the cavity of nucleotomized bovine discs. Human MSCs (1 × 106) were seeded on the opposite CEP and allowed to migrate for up to 21 days. Migration of fluorescently labelled MSCs from CEP toward the IVD was enhanced by HAPSDF5. Likewise, an increase in collagen type II was detected at earlier time points, whereas no effect on proteoglycan content within the nucleotomized IVDs was found. MSCs produced an increased concentration of pro-catabolic factors, such as interleukin (IL)-6, IL-8, and monocyte chemoattractant protein-1 (MCP-1). Overall, this study demonstrates that HAPSDF5 increased MSC recruitment, while the higher number of recruited cells partially contributed to accelerate matrix remodeling in nucleotomized IVDs.

In vivo safety and efficacy testing of a thermally triggered injectable hydrogel scaffold for bone regeneration and augmentation in a rat model

Bone loss resulting from degenerative diseases and trauma is a significant clinical burden which is likely to grow exponentially with the aging population. In a number of conditions where pre-formed materials are clinically inappropriate an injectable bone forming hydrogel could be beneficial. The development of an injectable hydrogel to stimulate bone repair and regeneration would have broad clinical impact and economic benefit in a variety of orthopedic clinical applications.

We have previously reported the development of a Laponite^® crosslinked pNIPAM-co-DMAc (L-pNIPAM-co-DMAc) hydrogel delivery system, loaded with hydroxyapatite nanoparticles (HAPna), which was capable of inducing osteogenic differentiation of mesenchymal stem cells (MSCs) without the need for additional growth factors in vitro. However to enable progression towards clinical acceptability, biocompatibility and efficacy of the L-pNIPAM-co-DMAc hydrogel to induce bone repair in vivo must be determined.

Biocompatibility was evaluated by subcutaneous implantation for 6 weeks in rats, and efficacy to augment bone repair was evaluated within a rat femur defect model for 4 weeks. No inflammatory reactions, organ toxicity or systemic toxicity were observed. In young male rats where hydrogel was injected, defect healing was less effective than sham operated controls when rat MSCs were incorporated. Enhanced bone healing was observed however, in aged exbreeder female rats where acellular hydrogel was injected, with increased deposition of collagen type I and Runx2. Integration of the hydrogel with surrounding bone was observed without the need for delivered MSCs; native cell infiltration was also seen and bone formation was observed within all hydrogel systems investigated.

This hydrogel can be delivered directly into the target site, is biocompatible, promotes increased bone formation and facilitates migration of cells to promote integration with surrounding bone, for safe and efficacious bone repair.

Thermally triggered hydrogel injection into bovine intervertebral disc tissue explants induces differentiation of mesenchymal stem cells and restores mechanical function

We previously reported a synthetic Laponite® crosslinked pNIPAM-co-DMAc (L-pNIPAM-co-DMAc) hydrogel which promotes differentiation of mesenchymal stem cells (MSCs) to nucleus pulposus (NP) cells without additional growth factors. The clinical success of this hydrogel is dependent on: integration with surrounding tissue; the capacity to restore mechanical function; as well as supporting the viability and differentiation of delivered MSCs. Bovine NP tissue explants were injected with media (control), human MSCs (hMSCs) alone, acellular L-pNIPAM-co-DMAc hydrogel or hMSCs incorporated within the L-pNIPAM-co-DMAc hydrogel and maintained at 5% O₂ for 6weeks. Viability of native NP cells and delivered MSCs was maintained. Furthermore hMSCs delivered via the L-pNIPAM-co-DMAc hydrogel differentiated and produced NP matrix components: aggrecan, collagen type II and chondroitin sulphate, with integration of the hydrogel with native NP tissue. In addition L-pNIPAM-co-DMAc hydrogel injected into collagenase digested bovine discs filled micro and macro fissures, were maintained within the disc during loading and restored IVD stiffness. The mechanical support of the L-pNIPAM-co-DMAc hydrogel, to restore disc height, could provide immediate symptomatic pain relief, whilst the delivery of MSCs over time regenerates the NP extracellular matrix; thus the L-pNIPAM-co-DMAc hydrogel could provide a combined cellular and mechanical repair approach.

STATEMENT OF SIGNIFICANCE

Low back pain (LBP) is associated with degeneration of the intervertebral disc (IVD). We have previously described development of a jelly delivery system (hydrogel). This has the potential to deliver adult stem cells to the centre of the IVD, known as the nucleus pulposus (NP). Here, we have demonstrated that adult stem cells can be safely injected into the NP using small bore needles, reducing damage to the disc. Following injection the hydrogel integrates with surrounding NP tissue, promotes differentiation of stem cells towards disc cells and restores IVD mechanical function. The hydrogel could be used to restore mechanical function to the IVD and deliver cells to promote regeneration of the disc as a minimally invasive treatment for LBP.

Intervertebral disc response to stem cell treatment is conditioned by disc state and cell carrier: An ex vivo study

In vitro and in vivo studies evidenced that mesenchymal stem cells (MSCs) contribute to intervertebral disc (IVD) regeneration by differentiation towards the disc phenotype and matrix synthesis and/or by paracrine signalling to endogenous cells, thereby promoting a healthier disc phenotype in degenerative discs. The aim of this study was to investigate IVD response to human MSC (hMSC) treatment based on the disc degenerative state and hMSC carrier. Bovine caudal IVDs with endplates were cultured in a bioreactor under simulated physiological (0.1 Hz load and sufficient glucose) or degenerative (10 Hz load and limited glucose) conditions for 7 days. Discs were partially nucleotomised, restored with hMSCs in either fibrin gel or saline solution and cultured under physiological conditions for 7 days. Controls included fibrin and saline without hMSCs. Cell viability, histology, disc height, and gene expression analyses were performed to evaluate regeneration. hMSCs in fibrin were viable and homogenously distributed following 7 days of culture under dynamic loading in partially nucleotomised discs. IVD response to hMSCs was conditioned by both disc degenerative state and hMSC carrier. The effect of the regenerative treatment was stronger on simulated-degenerative discs than on simulated-physiological discs. hMSCs in fibrin induced a superior anabolic response in degenerative IVDs compared with fibrin alone, thus suggesting an added value of the cellular therapy compared with an acellular solution. When comparing fibrin and saline as a hMSC carrier, a significantly higher anabolic response was observed in IVDs treated with hMSCs in fibrin. Moreover, it was found that the degenerative state of the disc influenced hMSC differentiation. Indeed, a significantly higher expression of specific discogenic markers (ACAN and CA12) was observed in hMSCs implanted into physiological discs than in those implanted into degenerative discs. In conclusion, host disc cells and donor hMSC response depend on the degenerative state of the host disc and carrier used for hMSC delivery, and these two aspects need to be considered for a successful translation of hMSC therapies for the treatment of IVD degeneration.

Biomimetic nucleus pulposus scaffold created from bovine caudal intervertebral disc tissue utilizing an optimal decellularization procedure

Intervertebral disc (IVD) degeneration (IDD) and herniation (IDH) can result in low back pain and impart significant socioeconomic burden. These pathologies involve detrimental alteration to the nucleus pulposus (NP) either via biochemical degradation or extrusion from the IVD, respectively. Thus, engineering living NP tissue utilizing biomaterial scaffolds that recapitulate native NP microarchitecture, biochemistry, mechanical properties, and which support cell viability represents an approach to aiding patients with IDD and IDH. To date, an ideal biomaterial to support NP regeneration has yet to be developed; however, one promising approach to generating biomimetic materials is to employ the decellularization (decell) of xenogeneic NP tissue to remove host DNA while maintaining critical native extracellular matrix (ECM) components. Herein, 13 different procedures were evaluated in an attempt to decell bovine caudal IVD NP tissue. An optimal method was identified which was confirmed to effectively remove bovine DNA, while maintaining physiologically relevant amounts of glycosaminoglycan (GAG) and type II collagen. Unconfined static and dynamic compressive mechanical properties of scaffolds approached values reported for human NP and viability of human amniotic stem cells (hAMSCs) was maintained on noncrosslinked and EDC/NHS treated scaffolds for up to 14 days in culture. Taken together, NP tissue obtained from bovine caudal IVDs can be successfully decelled in order to generate a biomimetic scaffold for NP tissue regeneration. © 2016 Wiley Periodicals, Inc. J Biomed Mater Res Part A: 104A: 3093-3106, 2016.

Mesenchymal Stem/Stromal Cells seeded on cartilaginous endplates promote Intervertebral Disc Regeneration through Extracellular Matrix Remodeling

Intervertebral disc (IVD) degeneration is characterized by significant biochemical and histomorphological alterations, such as loss of extracellular matrix (ECM) integrity, by abnormal synthesis of ECM main components, resultant from altered anabolic/catabolic cell activities and cell death. Mesenchymal Stem/Stromal Cell (MSC) migration towards degenerated IVD may represent a viable strategy to promote tissue repair/regeneration. Here, human MSCs (hMSCs) were seeded on top of cartilaginous endplates (CEP) of nucleotomized IVDs of bovine origin and cultured ex vivo up to 3 weeks. hMSCs migrated from CEP towards the lesion area and significantly increased expression of collagen type II and aggrecan in IVD, namely in the nucleus pulposus. Concomitantly, hMSCs stimulated the production of growth factors, promoters of ECM synthesis, such as fibroblast growth factor 6 (FGF-6) and 7 (FGF-7), platelet-derived growth factor receptor (PDGF-R), granulocyte-macrophage colony-stimulating factor (GM-CSF) and insulin-like growth factor 1 receptor (IGF-1sR). Overall, our results demonstrate that CEP can be an alternative route to MSC-based therapies for IVD regeneration through ECM remodeling, thus opening new perspectives on endogenous repair capacity through MSC recruitment.

The potential of chondrogenic pre-differentiation of adipose-derived mesenchymal stem cells for regeneration in harsh nucleus pulposus microenvironment

Recent studies indicated that cell-based therapy could be a promising approach to treat intervertebral disc degeneration. Though the harsh microenvironment in disc is still challenging to implanted cells, it could be overcome by pre-conditioning graft cells before transplantation, suggested by previous literatures. Therefore, we designed this study to identify the potential effect of chondrogenic pre-differentiation on adipose-derived mesenchymal stem cells in intervertebral disc-like microenvironment, characterized by limited nutrition, acidic, and high osmosis in vitro. Adipose-derived mesenchymal stem cells of rat were divided into five groups, embedded in type II collagen scaffold, and cultured in chondrogenic differentiation medium for 0, 3, 7, 10, and 14 days. Then, the adipose-derived mesenchymal stem cells were implanted and cultured in intervertebral disc-like condition. The proliferation and differentiation of adipose-derived mesenchymal stem cells were evaluated by cell counting kit-8 test, real-time quantitative polymerase chain reaction, and Western blotting and immunofluorescence analysis. Analyzed by the first week in intervertebral disc-like condition, the results showed relatively greater proliferative capability and extracellular matrix synthesis ability of the adipose-derived mesenchymal stem cells pre-differentiated for 7 and 10 days than the control. We concluded that pre-differentiation of rat adipose-derived mesenchymal stem cells in chondrogenic culture medium for 7 to 10 days could promote the regeneration effect of adipose-derived mesenchymal stem cells in intervertebral disc-like condition, and the pre-differentiated cells could be a promising cell source for disc regeneration medicine.

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.

Establishment of a Cytocompatible Cell-Free Intervertebral Disc Matrix for Chondrogenesis with Human Bone Marrow-Derived Mesenchymal Stromal Cells

Tissue-engineered intervertebral discs (IVDs) utilizing decellularized extracellular matrix (ECM) could be an option for the reconstruction of impaired IVDs due to degeneration or injury. The objective of this study was to prepare a cell-free decellularized human IVD scaffold and to compare neotissue formation in response to recellularization with human IVD cells (hIVDCs) or human bone marrow-derived (hBM) mesenchymal stromal cells (MSCs). IVDs were decellularized via freeze-thaw cycles, detergents and trypsin. Histological staining was performed to monitor cell removal and glycosaminoglycan (GAG) removal. The decellularized IVD was preconditioned using bovine serum albumin and fetal bovine serum before its cytocompatibility for dynamically cultured hBM-MSCs (chondrogenically induced or not) and hIVDCs was compared after 14 days. In addition, DNA, total collagen and GAG contents were assessed. The decellularization protocol achieved maximal cell removal, with only few remaining cell nuclei compared with native tissue, and low toxicity. The DNA content was significantly higher in scaffolds seeded with hIVDCs compared with native IVDs, cell-free and hBM-MSC-seeded scaffolds (p < 0.01). The GAG content in the native tissue was significantly higher compared to the others groups except for the scaffolds reseeded with chondrogenically induced hBM-MSCs (p < 0.05). In addition, there was a significantly increased total collagen content in the chondrogenically induced hBM-MSCs group (p < 0.01) compared with the native IVDs, cell-free and hIVDC-seeded scaffolds (p < 0.01); both recolonizing cell types were more evenly distributed on the scaffold surface, but only few cells penetrated the scaffold. The resulting decellularized ECM was cytocompatible and allowed hBM-MSCs/hIVDCs survival and ECM production.

Collagen-low molecular weight hyaluronic acid semi-interpenetrating network loaded with gelatin microspheres for cell and growth factor delivery for nucleus pulposus regeneration

Intervertebral disc (IVD) degeneration is one of the main causes of low back pain. Current surgical treatments are complex and generally do not fully restore spine mobility. Development of injectable extracellular matrix-based hydrogels offers an opportunity for minimally invasive treatment of IVD degeneration. Here we analyze a specific formulation of collagen-low molecular weight hyaluronic acid (LMW HA) semi-interpenetrating network (semi-IPN) loaded with gelatin microspheres as a potential material for tissue engineering of the inner part of the IVD, the nucleus pulposus (NP). The material displayed a gel-like behavior, it was easily injectable as demonstrated by suitable tests and did not induce cytotoxicity or inflammation. Importantly, it supported the growth and chondrogenic differentiation potential of mesenchymal stem cells (MSC) and nasal chondrocytes (NC) in vitro and in vivo. These properties of the hydrogel were successfully combined with TGF-β3 delivery by gelatin microspheres, which promoted the chondrogenic phenotype. Altogether, collagen-LMW HA loaded with gelatin microspheres represents a good candidate material for NP tissue engineering as it combines important rheological, functional and biological features.

Molecular basis of intervertebral disc degeneration and herniations: what are the important translational questions?

BACKGROUND

Intervertebral disc degeneration is a common condition with few inexpensive and effective modes of treatment, but current investigations seek to clarify the underlying process and offer new treatment options. It will be important for physicians to understand the molecular basis for the pathology and how it translates to developing clinical treatments for disc degeneration. In this review, we sought to summarize for clinicians what is known about the molecular processes that causes disc degeneration.

RESULTS

A healthy disc requires maintenance of a homeostatic environment, and when disrupted, a catabolic cascade of events occurs on a molecular level resulting in upregulation of proinflammatory cytokines, increased degradative enzymes, and a loss of matrix proteins. This promotes degenerative changes and occasional neurovascular ingrowth potentially contributing to the development of pain. Research demonstrates the molecular changes underlying the harmful effects of aging, smoking, and obesity seen clinically while demonstrating the variable influence of exercise. Finally, oral medications, supplements, biologic treatments, gene therapy, and stem cells hold great promise but require cautious application until their safety profiles are better outlined.

CONCLUSIONS

Intervertebral disc degeneration occurs where there is a loss of homeostatic balance with a predominantly catabolic metabolic profile. A basic understanding of the molecular changes occurring in the degenerating disc is important for practicing clinicians because it may help them to inform patients to alter lifestyle choices, identify beneficial or harmful supplements, or offer new biologic, genetic, or stem cell therapies.

Three-dimensional hypoxic culture of human mesenchymal stem cells encapsulated in a photocurable, biodegradable polymer hydrogel: a potential injectable cellular product for nucleus pulposus regeneration

Nucleus pulposus (NP) tissue damage can induce detrimental mechanical stresses and strains on the intervertebral disc, leading to disc degeneration. This study demonstrates the potential of a novel, photo-curable, injectable, synthetic polymer hydrogel (pHEMA-co-APMA grafted with polyamidoamine (PAA)) to encapsulate and differentiate human mesenchymal stem cells (hMSC) towards a NP phenotype under hypoxic conditions which could be used to restore NP tissue function and mechanical properties. Encapsulated hMSC cultured in media (hMSC and chondrogenic) displayed good cell viability up to day 14. The genotoxicity effects of ultraviolet (UV) on hMSC activity confirmed the acceptability of 2.5min of UV light exposure to cells. Cytotoxicity investigations revealed that hMSC cultured in media containing p(HEMA-co-APMA) grafted with PAA degradation product (10% and 20%v/v concentration) for 14days significantly decreased the initial hMSC adhesion ability and proliferation rate from 24hrs to day 14. Successful differentiation of encapsulated hMSC within hydrogels towards chondrogenesis was observed with elevated expression levels of aggrecan and collagen II when cultured in chondrogenic media under hypoxic conditions, in comparison with culture in hMSC media for 14days. Characterization of the mechanical properties revealed a significant decrease in stiffness and modulus values of cellular hydrogels in comparison with acellular hydrogels at both day 7 and day 14. These results demonstrate the potential use of an in vivo photo-curable injectable, synthetic hydrogel with encapsulated hMSC for application in the repair and regeneration of NP tissue.

Influence of hypoxia in the intervertebral disc on the biological behaviors of rat adipose- and nucleus pulposus-derived mesenchymal stem cells

Adipose-derived mesenchymal stem cells (ADMSCs) and nucleus pulposus-derived mesenchymal stem cells (NPMSCs) are two cell candidates for cell-based therapies for intervertebral disc (IVD) regeneration. However, little work has been done to determine the influence of hypoxia in the IVD on the biological behaviors of ADMSCs and NPMSCs. This study aimed to investigate the viability, proliferation and differentiation of rat ADMSCs and NPMSCs in the hypoxic environment of IVD in vitro. ADMSCs and NPMSCs isolated from 6 SD rats were cultured under normoxia (20% O2) and hypoxia (2% O2) mimicking the standard condition and hypoxic environment of the IVD for 14 days. Cell viability was determined by the annexin-V-FITC/propidium iodide double-staining assay and cell proliferation was measured by MTT assay. The expression of hypoxia-inducible factor-1α, glucose transporter (GLUT)-1, GLUT-3 and vascular endothelial growth factor-A at the mRNA level was examined by RT-PCR. In cells cultured in three-dimensional micromass and differentiation medium, aggrecan, collagen-II and Sox-9 expression at mRNA and protein levels were examined by RT-PCR and Western blot. Hypoxia inhibited the viability and proliferation of both ADMSCs and NPMSCs, but promoted the chondrocytic differentiation of ADMSCs and NPMSCs. Compared to ADMSCs, NPMSCs showed greater viability, proliferation and chondrocytic differentiation under hypoxia. In conclusion, hypoxia in the IVD had a significant impact on the viability, proliferation and chondrocytic differentiation of ADMSCs and NPMSCs. NPMSCs exhibited more potent biological activity than ADMSCs in the hypoxic environment of the IVD and may represent another candidate for cell-based therapy for IVD regeneration.

Identification of novel nucleus pulposus markers: Interspecies variations and implications for cell-based therapiesfor intervertebral disc degeneration

Mesenchymal stem-cell based therapies have been proposed as novel treatments for intervertebral disc degeneration, a prevalent and disabling condition associated with back pain. The development of these treatment strategies, however, has been hindered by the incomplete understanding of the human nucleus pulposus phenotype and by an inaccurate interpretation and translation of animal to human research. This review summarises recent work characterising the nucleus pulposus phenotype in different animal models and in humans and integrates their findings with the anatomical and physiological differences between these species. Understanding this phenotype is paramount to guarantee that implanted cells restore the native functions of the intervertebral disc. Cite this article: Bone Joint Res 2013;2:169-78.

Long-term culture of bovine nucleus pulposus explants in a native environment

BACKGROUND CONTEXT

Chronic low back pain is a disease with tremendous financial and social implications, and it is often caused by intervertebral disc degeneration. Regenerative therapies for disc repair are promising treatments, but they need to be tested in physiological models.

PURPOSE

To develop a physiological in vitro explant model that incorporates the native environment of the intervertebral disc, for example, hypoxia, low glucose, and high tissue osmolarity.

STUDY DESIGN

Bovine nucleus pulposus (NP) explants were cultured for 42 days in conditions mimicking the native physiological environment. Two different approaches were used to balance the swelling pressure of the NP: raised medium osmolarity or an artificial annulus.

METHODS

Bovine NP explants were either cultured in media with osmolarity balanced at isotonic and hypertonic levels compared with the native tissue or cultured inside a fiber jacket used as an artificial annulus. Oxygen and glucose levels were set at either standard (21% O2 and 4.5 g/L glucose) or physiological (5% O2 and 1 g/L glucose) levels. Samples were analyzed at Day 0, 3, and 42 for tissue composition (water, sulfated glycosaminoglycans, DNA, and hydroxyproline contents and fixed charge density), tissue histology, cell viability, and cellular behavior with messenger RNA (mRNA) expression.

RESULTS

Both the hypertonic culture and the artificial annulus approach maintained the tissue matrix composition for 42 days. At Day 3, mRNA expressions of aggrecan, collagen Type I, and collagen Type II in both hypertonic and artificial annulus cultures were not different from Day 0; however, at Day 42, the artificial annulus preserved the mRNA expression closer to Day 0. Gene expressions of matrix metalloprotease 13, tissue inhibitor of matrix metalloprotease 1, and tissue inhibitor of matrix metalloprotease 2 were downregulated under physiological O2 and glucose levels, whereas the other parameters analyzed were not affected.

CONCLUSIONS

Although the hypertonic culture and the artificial annulus approach are both promising models to test regenerative therapies, the artificial annulus was better able to maintain a cellular behavior closer to the native tissue in longer term cultures.

Molecular and genetic advances in the regeneration of the intervertebral disc

Background:

Owing to the debilitating nature of degenerative disc disease (DDD) and other spine pathologies, significant research has been performed with the goal of healing or regenerating the intervertebral disc (IVD). Structural complexity, coupled with low vascularity and cellularity, make IVD regeneration an extremely challenging task.

Methods:

Tissue engineering-based strategies utilize three components to enhance tissue regeneration; scaffold materials to guide cell growth, biomolecules to enhance cell migration and differentiation, and cells (autologous, or allogeneic) to initiate the process of tissue formation. Significant advances in IVD regeneration have been made utilizing these tissue engineering strategies.

Results:

The current literature demonstrates that members of the transforming growth factor beta (TGF-β) superfamily are efficacious in the regeneration of an anabolic response in the IVD and to facilitate chondrogenic differentiation. Gene therapy, though thwarted by safety concerns and the risk of ectopic transfection, has significant potential for a targeted and sustained regenerative response. Stem cells in combination with injectable, biocompatible, and biodegradable scaffolds in the form of hydrogels can differentiate into de novo IVD tissue and facilitate regeneration of the existing matrix. Therapies that address both anabolism and the inherent catabolic state of the IVD using either direct inhibitors or broad-spectrum inhibitors show extensive promise.

Conclusion:

This review article summarizes the genetic and molecular advances that promise to play an integral role in the development of new strategies to combat DDD and promote healing of injured discs.

The effects of microenvironment in mesenchymal stem cell-based regeneration of intervertebral disc

BACKGROUND CONTEXT

Recent studies have demonstrated new therapeutic strategy using transplantation of mesenchymal stem cells (MSCs), especially bone marrow-derived MSCs (BM-MSCs), to preserve intervertebral disc (IVD) structure and functions. It is important to understand whether and how the MSCs survive and thrive in the hostile microenvironment of the degenerated IVD. Therefore, this review majorly examines how resident disc cells, hypoxia, low nutrition, acidic pH, mechanical loading, endogenous proteinases, and cytokines regulate the behavior of the exogenous MSCs.

PURPOSE

To review and summarize the effect of the microenvironment in biological characteristics of BM-MSCs for IVD regeneration; the presence of endogenous stem cells and the state of the art in the use of BM-MSCs to regenerate the IVD in vivo were also discussed.

STUDY DESIGN

Literature review.

METHODS

MEDLINE electronic database was used to search for articles concerning stem/progenitor cell isolation from the IVD, regulation of the components of microenvironment for MSCs, and MSC-based therapy for IVD degeneration. The search was limited to English language.

RESULTS

Stem cells are probably resident in the disc, but exogenous stem cells, especially BM-MSCs, are currently the most popular graft cells for IVD regeneration. The endogenous disc cells and the biochemical and biophysical components in the degenerating disc present a complicated microenvironment to regulate the transplanted BM-MSCs. Although MSCs regenerate the mildly degenerative disc effectively in the experimental and clinical trials, many underlying questions are in need of further investigation.

CONCLUSIONS

There has been a dramatic improvement in the understanding of potential MSC-based therapy for IVD regeneration. The use of MSCs for IVD degeneration is still at the stage of preclinical and Phase 1 studies. The effects of the disc microenvironment in MSCs survival and function should be closely studied for transferring MSC transplantation from bench to bedside successfully.

Stemming the Degeneration: IVD Stem Cells and Stem Cell Regenerative Therapy for Degenerative Disc Disease

The intervertebral disc (IVD) is immensely important for the integrity of vertebral column function. The highly specialized IVD functions to confer flexibility and tensile strength to the spine and endures various types of biomechanical force. Degenerative disc disease (DDD) is a prevalent musculoskeletal disorder and is the major cause of low back pain and includes the more severe degenerative lumbar scoliosis, disc herniation and spinal stenosis. DDD is a multifactorial disorder whereby an imbalance of anabolic and catabolic factors, or alterations to cellular composition, or biophysical stimuli and genetic background can all play a role in its genesis. However, our comprehension of IVD formation and theetiology of disc degeneration (DD) are far from being complete, hampering efforts to formulate appropriate therapies to tackle DD. Knowledge of the stem cells and various techniques to manipulate and direct them to particular fates have been promising in adopting a stem-cell based regenerative approach to DD. Moreover, new evidence on the residence of stem/progenitor cells within particular IVD niches has emerged holding promise for future therapeutic applications. Existing issues pertaining to current therapeutic approaches are also covered in this review.

The cytokine and chemokine expression profile of nucleus pulposus cells: implications for degeneration and regeneration of the intervertebral disc

INTRODUCTION

The aims of these studies were to identify the cytokine and chemokine expression profile of nucleus pulposus (NP) cells and to determine the relationships between NP cell cytokine and chemokine production and the characteristic tissue changes seen during intervertebral disc (IVD) degeneration.

METHODS

Real-time q-PCR cDNA Low Density Array (LDA) was used to investigate the expression of 91 cytokine and chemokine associated genes in NP cells from degenerate human IVDs. Further real-time q-PCR was used to investigate 30 selected cytokine and chemokine associated genes in NP cells from non-degenerate and degenerate IVDs and those from IVDs with immune cell infiltrates (‘infiltrated’). Immunohistochemistry (IHC) was performed for four selected cytokines and chemokines to confirm and localize protein expression in human NP tissue samples.

RESULTS

LDA identified the expression of numerous cytokine and chemokine associated genes including 15 novel cytokines and chemokines. Further q-PCR gene expression studies identified differential expression patterns in NP cells derived from non-degenerate, degenerate and infiltrated IVDs. IHC confirmed NP cells as a source of IL-16, CCL2, CCL7 and CXCL8 and that protein expression of CCL2, CCL7 and CXCL8 increases concordant with histological degenerative tissue changes.

CONCLUSIONS

Our data indicates that NP cells are a source of cytokines and chemokines within the IVD and that these expression patterns are altered in IVD pathology. These findings may be important for the correct assessment of the ‘degenerate niche’ prior to autologous or allogeneic cell transplantation for biological therapy of the degenerate IVD.

Epidural abscess and cauda equina syndrome after percutaneous intradiscal therapy in degenerative lumbar disc disease

BACKGROUND CONTEXT

Percutaneous intradiscal therapies are gaining popularity as a regenerative treatment option for spinal disc degeneration. The risks, benefits, and possible complications associated with such procedures have been poorly defined. As these procedures are performed with increasing frequency, the likelihood that clinicians will be faced with significant complications also increases.

PURPOSE

The purpose of this study is to describe a significant complication of a percutaneous intradiscal bone marrow and adipose tissue transplantation for symptomatic lumbar disc degeneration.

STUDY DESIGN

The study design is a case report.

METHODS

Two weeks after an injection of adipose cells, bone marrow aspirate and plasma into his L3-L4 and L5-S1 lumbar discs, a 64-year-old patient presented to the emergency room with cauda equina syndrome, fever, and back pain. Magnetic resonance imaging diagnosed L3-L4 disc extrusion, discitis with osteomyelitis, and epidural abscess, resulting in emergency decompressive surgery. An epidural abscess was drained, extruded disc material was removed, and cultures obtained. Five days later, once afebrile on antibiotics, he underwent a definitive interbody arthrodesis and stabilization.

RESULTS

Cauda equina syndrome resolved, osteomyelitis (methicillin-resistant Staphylococcus epidermidis) was treated, and instrumented arthrodesis stabilized the involved segment.

CONCLUSIONS

Complications associated with the intradiscal injection of agents, such as stem cells, fibrin glue, adipose tissue, or bone marrow, have been poorly defined. Given the nature of the degenerating disc, serious adverse events, including discitis, osteomyelitis, and extrusion of disc contents, may occur.

Homing of mesenchymal stem cells in induced degenerative intervertebral discs in a whole organ culture system

STUDY DESIGN

Homing of human bone marrow-derived mesenchymal stem cells (BMSCs) was studied using ex vivo cultured bovine caudal intervertebral discs (IVDs).

OBJECTIVE

To investigate in a whole organ culture whether metabolic and mechanical challenges can induce BMSC recruitment into the IVD.

SUMMARY OF BACKGROUND DATA

Cells from injured tissues release cytokines and mediators that enable the recruitment of progenitor cells. BMSCs have the ability to survive within the IVD.

METHODS

Bovine IVDs with or without endplates were cultured for 1 week under simulated physiological or degenerative conditions; disc cells were analyzed for cell viability and gene expression, whereas media was analyzed for nitric oxide production and chemotaxis. Homing of BMSCs was investigated by supplying PKH-labeled human BMSCs onto cultured IVDs (1 × 10(6) cells/disc on d 8, 10, and 12 of culture); on day 14, the number of homed BMSCs was microscopically assessed. Moreover, a comparative study was performed between transduced BMSCs (transduced with an adenovirus encoding for insulin-like growth factor 1 [IGF-1]) and nontransduced BMSCs. Disc proteoglycan synthesis rate was quantified via (35)S incorporation. The secretion of IGF-1 was evaluated by enzyme-linked immunosorbent assay on both simulated physiological and degenerative discs.

RESULTS

Discs cultured under degenerative conditions showed reduced cell viability, upregulation of matrix degrading enzymes, and increased nitric oxide production compared with simulated physiological discs. Greater homing occurred under degenerative compared with physiological conditions with or without endplate. Media of degenerative discs demonstrated a chemoattractive activity toward BMSCs. Finally, discs homed with IGF-1-transduced BMSCs showed increased IGF-1 secretion and significantly higher proteoglycan synthesis rate than discs supplied with nontransduced BMSCs.

CONCLUSION

We have demonstrated for the first time that degenerative conditions induce the release of factors promoting BMSC recruitment in an ex vivo organ culture. Moreover, IGF-1 transduction of BMSCs strongly increases the rate of proteoglycan synthesis within degenerative discs. This finding offers a new delivery system for BMSCs and treatment strategy for IVD regeneration.