Structured coculture of mesenchymal stem cells and disc cells enhances differentiation and proliferation

A Review: Methodologies to Promote the Differentiation of Mesenchymal Stem Cells for the Regeneration of Intervertebral Disc Cells Following Intervertebral Disc Degeneration

Intervertebral disc (IVD) degeneration (IDD), a highly prevalent pathological condition worldwide, is widely associated with back pain. Treatments available compensate for the impaired function of the degenerated IVD but typically have incomplete resolutions because of their adverse complications. Therefore, fundamental regenerative treatments need exploration. Mesenchymal stem cell (MSC) therapy has been recognized as a mainstream research objective by the World Health Organization and was consequently studied by various research groups. Implanted MSCs exert anti-inflammatory, anti-apoptotic, and anti-pyroptotic effects and promote extracellular component production, as well as differentiation into IVD cells themselves. Hence, the ultimate goal of MSC therapy is to recover IVD cells and consequently regenerate the extracellular matrix of degenerated IVDs. Notably, in addition to MSC implantation, healthy nucleus pulposus (NP) cells (NPCs) have been implanted to regenerate NP, which is currently undergoing clinical trials. NPC-derived exosomes have been investigated for their ability to differentiate MSCs from NPC-like phenotypes. A stable and economical source of IVD cells may include allogeneic MSCs from the cell bank for differentiation into IVD cells. Therefore, multiple alternative therapeutic options should be considered if a refined protocol for the differentiation of MSCs into IVD cells is established. In this study, we comprehensively reviewed the molecules, scaffolds, and environmental factors that facilitate the differentiation of MSCs into IVD cells for regenerative therapies for IDD.

Elucidating the role of cell-mediated inflammatory cytokines on allogeneic mouse-derived nucleus pulposus mesenchymal stem cells

In this present study, our aim was to evaluate the cell-mediated specific anti-donor antibody and its associated inflammatory cytokine secretion along with its succeeding effects on Nucleus pulposus-derived mesenchymal stem cells (NPMSCs). Tissue from the NP compartment of 12 normal mice was isolated, expanded in cell culture, and the cell phenotypes were confirmed by flow cytometry. Multipotent differentiation and its specific gene expression analysis were confirmed by reverse transcriptase PCR. T and B cells were monitored for both donor and recipient mouse and further analysis of anti-donor antibody secretion was confirmed by lymphocyte crossmatch. In conjunction with anti-donor-specific antibody analysis, the associated inflammatory cytokine expression was analyzed by ELISA. In co-culture, cell-mediated antibody secretion was elevated in T and B cells positive mouse group, when compared to control mouse group. Allogeneic-derived donor NPMSCs were found to be stimulated the secretion of pro-inflammatory cytokines and the level of pro-inflammatory cytokines showed reduced expression in control mouse serum. In co-culture group the concentration of the cell-mediated pro- and anti-inflammatory cytokines found to be increased. PRACTICAL APPLICATIONS: Mesenchymal stem cell exhibit good regeneration capacity for many types of disease, and the mechanism belongs to regeneration is not clear. In intervertebral disc, the nucleus pulposus-derived mesenchymal stem cells showed a better regeneration capacity. On the contrary, the NP cells-based therapy, the Mesenchymal stem cells showed expanded anabolic and reduced catabolic activity together with induced anti-inflammatory effect. In this study, the T & B cells were used to evaluate the anti-donor antibody secretion and also to study how it stimulates the production of anti-donor antibodies against the donor cells. Finally, it was found that T & B cells lead the synthesis of inflammatory cytokines are IL-1, IL-6, and TNF-α. From this study, the results proved that the cell-mediated pro- and anti-inflammatory cytokines to be monitored in allogeneic stem cells-based therapy of intervertebral disc degeneration.

Fabrication, maturation, and implantation of composite tissue-engineered total discs formed from native and mesenchymal stem cell combinations

Low back pain arising from disc degeneration is one of the most common causes of limited function in adults. A number of tissue engineering strategies have been used to develop composite tissue engineered total disc replacements to restore native tissue structure and function. In this study we fabricated a composite engineered disc based on the combination of a porous polycaprolactone (PCL) foam annulus fibrosus (AF) and a hyaluronic acid (HA) hydrogel nucleus pulposus (NP). To evaluate whether native tissue cells or mesenchymal stem cells (MSCs) would perform better, constructs were seeded with native AF/NP cells or with MSCs in the foam and/or gel region. Maturation of these composite engineered discs was evaluated for 9 weeks in vitro culture by biochemical content, histological analysis and mechanical properties. To evaluate the performance of these constructs in the in vivo space, engineered discs were implanted into the caudal spines of athymic rats for 5 weeks. Our findings show that engineered discs comprised of AF/NP cells and MSCs performed similarly and maintained their structure after 5 weeks in vivo. However, for both cell types, loss of proteoglycan was evident in the NP region. These data support the continued development of the more clinically relevant MSCs population for disc replacement applications. STATEMENT OF SIGNIFICANCE: A number of tissue engineering strategies have emerged that are focused on the creation of a composite disc replacement. We fabricated a composite engineered disc based on the combination of a porous foam AF and a HA gel NP. We used these constructs to determine whether the combination of AF/NP cells or MSCs would mature to a greater extent in vitro and which cell type would best retain their phenotype after implantation. Engineered discs comprised of AF/NP cells and MSCs performed similarly, maintaining their structure after 5 weeks in vivo. These data support the successful fabrication and in vivo function of an engineered disc composed of a PCL foam AF and a hydrogel NP using either disc cells or MSCs.

Bone Morphogenetic Proteins for Nucleus Pulposus Regeneration

Matrix production by nucleus pulposus (NP) cells, the cells residing in the center of the intervertebral disc, can be stimulated by growth factors. Bone morphogenetic proteins (BMPs) hold great promise. Although BMP2 and BMP7 have been used most frequently, other BMPs have also shown potential for NP regeneration. Heterodimers may be more potent than single homodimers, but it is not known whether combinations of homodimers would perform equally well. In this study, we compared BMP2, BMP4, BMP6, and BMP7, their combinations and heterodimers, for regeneration by human NP cells. The BMPs investigated induced variable matrix deposition by NP cells. BMP4 was the most potent, both in the final neotissue glysosaminoglycan content and incorporation efficiency. Heterodimers BMP2/6H and BMP2/7H were more potent than their respective homodimer combinations, but not the BMP4/7H heterodimer. The current results indicate that BMP4 might have a high potential for regeneration of the intervertebral disc. Moreover, the added value of BMP heterodimers over their respective homodimer BMP combinations depends on the BMP combination applied.

Micro Fragmented Adipose Tissue Promotes the Matrix Synthesis Function of Nucleus Pulposus Cells and Regenerates Degenerated Intervertebral Disc in a Pig Model

Intervertebral disc (IVD) degeneration and consequent lower back pain is a common disease. Micro fragmented adipose tissue (MFAT) is promising for a wide range of applications in regenerative medicine. In this study, MFAT was isolated by a nonenzymatic method and co-cultured with nucleus pulposus cells (NPCs) using an indirect co-culture system in vitro. A pig disc degeneration model was used to investigate the regenerative effect of MFAT on degenerated IVDs in vivo. The mRNA expression of Sox9, Acan, and Col2 in NPCs was significantly increased, while no significant increase was observed in the mRNA expression of proinflammatory cytokine genes after the NPCs were co-cultured with MFAT. Nucleus pulposus (NP)-specific markers were increased in MFAT cells after co-culture with NPCs. After injection of MFAT, the disc height, water content, extracellular matrix, and structure of the degenerated NP were significantly improved. MFAT promoted the matrix synthesis function of NPCs, and NPCs stimulated the NP-like differentiation of MFAT cells. In addition, MFAT also partly regenerated degenerated IVDs in the pig model.

Incorporation of Collagen and Hyaluronic Acid to Enhance the Bioactivity of Fibrin-Based Hydrogels for Nucleus Pulposus Regeneration

Hydrogels, such as fibrin, offer a promising delivery vehicle to introduce cells into the intervertebral disc (IVD) to regenerate damaged disc tissue as a potential treatment for low back pain. However, fibrin lacks key extracellular matrix (ECM) components, such as collagen (Col) and hyaluronan (HA), normally found in native nucleus pulposus (NP) tissue. The overall aim of this work was to create a fibrin-based hydrogel, by incorporating Col and HA into the matrix to enhance NP-like matrix accumulation using articular chondrocytes (CC). Firstly, we assessed the effect of fibrin concentrations on hydrogel stability, and the viability and proliferation kinetics of articular chondrocytes. Secondly, we investigated the effect of incorporating Col and HA to enhance NP-like matrix accumulation, and finally, examined the influence of various HA concentrations. Results showed that increasing fibrin concentration enhanced cell viability and proliferation. Interestingly, incorporation of HA promoted sGAG accumulation and tended to suppress collagen formation at higher concentrations. Taken together, these results suggest that incorporation of ECM components can enhance the bioactivity of fibrin-based hydrogels, which may help advance the clinical potential of commercial cell and biomaterial ventures in the treatment of IVD regeneration.

Mesenchymal Stem Cells Protect Nucleus Pulposus Cells from Compression-Induced Apoptosis by Inhibiting the Mitochondrial Pathway

Objective

Excessive apoptosis of nucleus pulposus cells (NPCs) induced by various stresses, including compression, contributes to the development of intervertebral disc degeneration (IVDD). Mesenchymal stem cells (MSCs) can benefit the regeneration of NPCs and delay IVDD, but the underlying molecular mechanism is poorly understood. This study aimed to evaluate the antiapoptosis effects of bone marrow-derived MSC (BMSC) on rat NPCs exposed to compression and investigate whether the mitochondrial pathway was involved.

Methods

BMSCs and NPCs were cocultured in the compression apparatus at 1.0 MPa for 36 h. Cell viability, apoptosis, mitochondrial function, and the expression of apoptosis-related proteins were evaluated.

Results

The results showed that coculturing with BMSCs increased the cell viability and reduced apoptosis of NPCs exposed to compression. Meanwhile, BMSCs could relieve the compression-induced mitochondrial damage of NPCs by decreasing reactive oxygen species level and maintaining mitochondrial membrane potential as well as mitochondrial integrity. Furthermore, coculturing with BMSCs suppressed the activated caspase-3 and activated caspase-9, decreased the expressions of cytosolic cytochrome c and Bax, and increased the expression of Bcl-2.

Conclusions

Our results suggest that BMSCs can protect against compression-induced apoptosis of NPCs by inhibiting the mitochondrial pathway and thus enhance our understanding on the MSC-based therapy for IVDD.

Effects of cell type and configuration on anabolic and catabolic activity in 3D co-culture of mesenchymal stem cells and nucleus pulposus cells

Tissue engineering constructs to treat intervertebral disc degeneration must adapt to the hypoxic and inflammatory degenerative disc microenvironment. The objective of this study was to determine the effects of two key design factors, cell type and cell configuration, on the regenerative potential of nucleus pulposus cell (NPC) and mesenchymal stem cell (MSC) constructs. Anabolic and catabolic activity was quantified in constructs of varying cell type (NPCs, MSCs, and a 50:50 co-culture) and varying configuration (individual cells and micropellets). Anabolic and catabolic outcomes were both dependent on cell type. Gene expression of Agg and Col2A1, glycosaminoglycan (GAG) content, and aggrecan immunohistochemistry (IHC), were significantly higher in NPC-only and co-culture groups than in MSC-only groups, with NPC-only groups exhibiting the highest anabolic gene expression levels. However, NPC-only constructs also responded to inflammation and hypoxia with significant upregulation of catabolic genes (MMP-1, MMP-9, MMP-13, and ADAMTS-5). MSC-only groups were unaffected by degenerative media conditions, and co-culture with MSCs modulated catabolic induction of the NPCs. Culturing cells in a micropellet configuration dramatically reduced catabolic induction in co-culture and NPC-only groups. Co-culture micropellets, which take advantage of both cell type and configuration effects, had the most immunomodulatory response, with a significant decrease in MMP-13 and ADAMTS-5 expression in hypoxic and inflammatory media conditions. Co-culture micropellets were also found to self-organize into bilaminar formations with an MSC core and NPC outer layer. Further understanding of these cell type and configuration effects can improve tissue engineering designs. © 2016 The Authors. Journal of Orthopaedic Research published by Wiley Periodicals, Inc. on behalf of the Orthopaedic Research Society. J Orthop Res 35:61-73, 2017.

Developments in intervertebral disc disease research: pathophysiology, mechanobiology, and therapeutics

Low back pain is a leading cause of disability worldwide and the second most common cause of physician visits. There are many causes of back pain, and among them, disc herniation and intervertebral disc degeneration are the most common diagnoses and targets for intervention. Currently, clinical treatment outcomes are not strongly correlated with diagnoses, emphasizing the importance for characterizing more completely the mechanisms of degeneration and their relationships with symptoms. This review covers recent studies elucidating cellular and molecular changes associated with disc mechanobiology, as it relates to degeneration and regeneration. Specifically, we review findings on the biochemical changes in disc diseases, including cytokines, chemokines, and proteases; advancements in disc disease diagnostics using imaging modalities; updates on studies examining the response of the intervertebral disc to injury; and recent developments in repair strategies, including cell-based repair, biomaterials, and tissue engineering. Findings on the effects of the omega-6 fatty acid, linoleic acid, on nucleus pulposus tissue engineering are presented. Studies described in this review provide greater insights into the pathogenesis of disc degeneration and may define new paradigms for early or differential diagnostics of degeneration using new techniques such as systemic biomarkers. In addition, research on the mechanobiology of disease enriches the development of therapeutics for disc repair, with potential to diminish pain and disability associated with disc degeneration.

Defining the phenotype of young healthy nucleus pulposus cells: recommendations of the Spine Research Interest Group at the 2014 annual ORS meeting

Low back pain is a major physical and socioeconomic problem. Degeneration of the intervertebral disc and especially that of nucleus pulposus (NP) has been linked to low back pain. In spite of much research focusing on the NP, consensus among the research community is lacking in defining the NP cell phenotype. A consensus agreement will allow easier distinguishing of NP cells from annulus fibrosus (AF) cells and endplate chondrocytes, a better gauge of therapeutic success, and a better guidance of tissue-engineering-based regenerative strategies that attempt to replace lost NP tissue. Most importantly, a clear definition will further the understanding of physiology and function of NP cells, ultimately driving development of novel cell-based therapeutic modalities. The Spine Research Interest Group at the 2014 Annual ORS Meeting in New Orleans convened with the task of compiling a working definition of the NP cell phenotype with hope that a consensus statement will propel disc research forward into the future. Based on evaluation of recent studies describing characteristic NP markers and their physiologic relevance, we make the recommendation of the following healthy NP phenotypic markers: stabilized expression of HIF-1α, GLUT-1, aggrecan/collagen II ratio >20, Shh, Brachyury, KRT18/19, CA12, and CD24.

Mesenchymal stem cells: potential application in intervertebral disc regeneration

Chronic low back pain is one of the leading public health problems in developed countries. Degeneration of the intervertebral disc (IVD) is a major pathological process implicated in low back pain, which is characterized by cellular apoptosis and senescence with reduced synthesis of extracellular matrix (ECM). Currently, there is no clinical therapy targeting the reversal of disc degeneration. Recent advances in cellular and molecular biology have provided an exciting approach to disc regeneration that focuses on the delivery of viable cells to the degenerative disc. Adult mesenchymal stem cells (MSCs) are multipotent stem cells with self-renewal capacities and are able to differentiate into diverse specialized cell types, including chondrocyte lineages. The potential of stem cell therapy in disc degeneration is to repopulate the disc with viable cells capable of producing the ECM and restoring damaged tissue. The present literature review summarizes recent advances in basic research and clinical trials of MSCs to provide an outline of the key roles of MSCs therapies in disc repair. The review also discusses the controversies, challenges and therapeutic concepts for the future.

Potential regenerative treatment strategies for intervertebral disc degeneration in dogs

Pain due to spontaneous intervertebral disc (IVD) disease is common in dogs. In chondrodystrophic (CD) dogs, IVD disease typically develops in the cervical or thoracolumbar spine at about 3–7 years of age, whereas in non-chondrodystrophic (NCD) dogs, it usually develops in the caudal cervical or lumbosacral spine at about 6–8 years of age. IVD degeneration is characterized by changes in the biochemical composition and mechanical integrity of the IVD. In the degenerated IVD, the content of glycosaminoglycan (GAG, a proteoglycan side chain) decreases and that of denatured collagen increases. Dehydration leads to tearing of the annulus fibrosus (AF) and/or disc herniation, which is clinically characterized by pain and/or neurological signs. Current treatments (physiotherapy, anti-inflammatory/analgesic medication, surgery) for IVD disease may resolve neurological deficits and reduce pain (although in many cases insufficient), but do not lead to repair of the degenerated disc. For this reason, there is interest in new regenerative therapies that can repair the degenerated disc matrix, resulting in restoration of the biomechanical function of the IVD. CD dogs are considered a suitable animal model for human IVD degeneration because of their spontaneous IVD degeneration, and therefore studies investigating cell-, growth factor-, and/or gene therapy-based regenerative therapies with this model provide information relevant to both human and canine patients. The aim of this article is to review potential regenerative treatment strategies for canine IVD degeneration, with specific emphasis on cell-based strategies.

Dynamic three-dimensional micropatterned cell co-cultures within photocurable and chemically degradable hydrogels

In this paper we report on the development of dynamically controlled three-dimensional (3D) micropatterned cellular co-cultures within photocurable and chemically degradable hydrogels. Specifically, we generated dynamic co-cultures of micropatterned murine embryonic stem (mES) cells with human hepatocellular carcinoma (HepG2) cells within 3D hydrogels. HepG2 cells were used due to their ability to direct the differentiation of mES cells through secreted paracrine factors. To generate dynamic co-cultures, mES cells were first encapsulated within micropatterned photocurable poly(ethylene glycol) (PEG) hydrogels. These micropatterned cell-laden PEG hydrogels were subsequently surrounded by calcium alginate (Ca-Alg) hydrogels containing HepG2 cells. After 4 days, the co-culture step was halted by exposing the system to sodium citrate solution, which removed the alginate gels and the encapsulated HepG2 cells. The encapsulated mES cells were then maintained in the resulting cultures for 16 days and cardiac differentiation was analysed. We observed that the mES cells that were exposed to HepG2 cells in the co-cultures generated cells with higher expression of cardiac genes and proteins, as well as increased spontaneous beating. Due to its ability to control the 3D microenvironment of cells in a spatially and temporally regulated manner, the method presented in this study is useful for a range of cell-culture applications related to tissue engineering and regenerative medicine. Copyright © 2013 John Wiley & Sons, Ltd.

A simple PCR-based strategy for estimating species-specific contributions in chimeras and xenografts

Many tissue-engineering approaches for repair and regeneration involve transplants between species. Yet a challenge is distinguishing donor versus host effects on gene expression. This study provides a simple molecular strategy to quantify species-specific contributions in chimeras and xenografts. Species-specific primers for reverse transcription quantitative real-time PCR (RT-qPCR) were designed by identifying silent mutations in quail, duck, chicken, mouse and human ribosomal protein L19 (RPL19). cDNA from different pairs of species was mixed in a dilution series and species-specific RPL19 primers were used to generate standard curves. Then quail cells were transplanted into transgenic-GFP chick and resulting chimeras were analyzed with species-specific primers. Fluorescence-activated cell sorting (FACS) confirmed that donor- and host-specific levels of RPL19 expression represent actual proportions of cells. To apply the RPL19 strategy, we measured Runx2 expression in quail-duck chimeras. Elevated Runx2 levels correlated with higher percentages of donor cells. Finally, RPL19 primers also discriminated mouse from human and chick. Thus, this strategy enables chimeras and/or xenografts to be screened rapidly at the molecular level.

Structured three-dimensional co-culture of mesenchymal stem cells with chondrocytes promotes chondrogenic differentiation without hypertrophy

OBJECTIVE

This study investigated a novel approach to induce chondrogenic differentiation of human mesenchymal stem cells (hMSC). We hypothesized that a structured three-dimensional co-culture using hMSC and chondrocytes would provide chondroinductive cues to hMSC without inducing hypertrophy.

METHOD

In an effort to promote optimal chondrogenic differentiation of hMSC, we created bilaminar cell pellets (BCPs), which consist of a spherical population of hMSC encased within a layer of juvenile chondrocytes (JC). In addition to histologic analyses, we examined proteoglycan content and expression of chondrogenic and hypertrophic genes in BCPs, JC pellets, and hMSC pellets grown in the presence or absence of transforming growth factor-β (TGFβ) following 21 days of culture in either growth or chondrogenic media.

RESULTS

In either growth or chondrogenic media, we observed that BCPs and JC pellets produced more proteoglycan than hMSC pellets treated with TGFβ. BCPs and JC pellets also exhibited higher expression of the chondrogenic genes Sox9, aggrecan, and collagen 2A1, and lower expression of the hypertrophic genes matrix metalloproteinase-13, Runx2, collagen 1A1, and collagen 10A1 than hMSC pellets. Histologic analyses suggest that JC promote chondrogenic differentiation of cells in BCPs without hypertrophy. Furthermore, when cultured in hypoxic and inflammatory conditions intended to mimic the injured joint microenvironment, BCPs produced significantly more proteoglycan than either JC pellets or hMSC pellets.

CONCLUSION

The BCP co-culture promotes a chondrogenic phenotype without hypertrophy and, relative to pellet cultures of hMSCs or JCs alone, is more resistant to the adverse conditions anticipated at the site of articular cartilage repair.