Differential gene expression profiling of metalloproteinases and their inhibitors: a comparison between bovine intervertebral disc nucleus pulposus cells and articular chondrocytes

Role of IL3RA in a Family with Lumbar Spinal Stenosis

Lumbar spinal stenosis (LSS) is a degenerative spinal condition characterized by the narrowing of the spinal canal, resulting in low back pain (LBP) and limited leg mobility. Twin and family studies have suggested that genetics contributes to disease progression. However, the genetic causes of familial LSS remain unclear. We performed whole-exome and direct sequencing on seven female patients from a Han Chinese family with LBP, among whom four developed LSS. Based on our genetic findings, we performed gene knockdown studies in human chondrocytes to study possible pathological mechanisms underlying LSS. We found a novel nonsense mutation, c.417C > G (NM_002183, p.Y139X), in IL3RA, shared by all the LBP/LSS cases. Knockdown of IL3RA led to a reduction in the total collagen content of 81.6% in female chondrocytes and 21% in male chondrocytes. The expression of MMP-1, -3, and/or -10 significantly increased, with a more pronounced effect observed in females than in males. Furthermore, EsRb expression significantly decreased following IL3RA knockdown. Moreover, the knockdown of EsRb resulted in increased MMP-1 and -10 expression in chondrocytes from females. We speculate that IL3RA deficiency could lead to a reduction in collagen content and intervertebral disk (IVD) strength, particularly in females, thereby accelerating IVD degeneration and promoting LSS occurrence. Our results illustrate, for the first time, the association between IL3RA and estrogen receptor beta, highlighting their importance and impact on MMPs and collagen in degenerative spines in women.

Unraveling the mechanisms of intervertebral disc degeneration: an exploration of the p38 MAPK signaling pathway

Intervertebral disc (IVD) degeneration (IDD) is a worldwide spinal degenerative disease. Low back pain (LBP) is frequently caused by a variety of conditions brought on by IDD, including IVD herniation and spinal stenosis, etc. These conditions bring substantial physical and psychological pressure and economic burden to patients. IDD is closely tied with the structural or functional changes of the IVD tissue and can be caused by various complex factors like senescence, genetics, and trauma. The IVD dysfunction and structural changes can result from extracellular matrix (ECM) degradation, differentiation, inflammation, oxidative stress, mechanical stress, and senescence of IVD cells. At present, the treatment of IDD is basically to alleviate the symptoms, but not from the pathophysiological changes of IVD. Interestingly, the p38 mitogen-activated protein kinase (p38 MAPK) signaling pathway is involved in many processes of IDD, including inflammation, ECM degradation, apoptosis, senescence, proliferation, oxidative stress, and autophagy. These activities in degenerated IVD tissue are closely relevant to the development trend of IDD. Hence, the p38 MAPK signaling pathway may be a fitting curative target for IDD. In order to better understand the pathophysiological alterations of the intervertebral disc tissue during IDD and offer potential paths for targeted treatments for intervertebral disc degeneration, this article reviews the purpose of the p38 MAPK signaling pathway in IDD.

Expression Profile of New Gene Markers Involved in Differentiation of Canine Adipose-Derived Stem Cells into Chondrocytes

The interest in stem cell research continuously increased over the last decades, becoming one of the most important trends in the 21st century medicine. Stem cell-based therapies have a potential to become a solution for a range of currently untreatable diseases, such as spinal cord injuries, type I diabetes, Parkinson’s disease, heart disease, stroke, and osteoarthritis. Hence, this study, based on canine material, aims to investigate the molecular basis of adipose-derived stem cell (ASC) differentiation into chondrocytes, to serve as a transcriptomic reference for further research aiming to introduce ASC into treatment of bone and cartilage related diseases, such as osteoarthritis in veterinary medicine. Adipose tissue samples were harvested from a canine specimen subjected to a routine ovariohysterecromy procedure at an associated veterinary clinic. The material was treated for ASC isolation and chondrogenic differentiation. RNA samples were isolated at day 1 of culture, day 30 of culture in unsupplemented culture media, and day 30 of culture in chondrogenic differentiation media. The resulting RNA was analyzed using RNAseq assays, with the results validated by RT-qPCR. Between differentiated chondrocytes, early and late cultures, most up- and down-regulated genes in each comparison were selected for further analysis., there are several genes (e.g., MMP12, MPEG1, CHI3L1, and CD36) that could be identified as new markers of chondrogenesis and the influence of long-term culture conditions on ASCs. The results of the study prove the usefulness of the in vitro culture model, providing further molecular insight into the processes associated with ASC culture and differentiation. Furthermore, the knowledge obtained could be used as a molecular reference for future in vivo and clinical studies.

Impact of NF-κB pathway on the intervertebral disc inflammation and degeneration induced by over-mechanical stretching stress

Background

Intervertebral disk degeneration (IVDD) contributes to low back pain. Increased cell apoptosis and inflammation, decreased extracellular matrix are associated with IVDD. Nuclear factor-kappa B (NF-κB) signaling pathway and inflammatory cytokines are implicated in the pathophysiology of IVDD.

Methods

In present study, we established a mechanical stretching stress-stimulated nucleus pulposus (NP) cell model. We knocked down NF-κB p65 by siRNA transfection to inhibit NF-κB and evaluated the effects of NF-κB inhibition on intervertebral disk degeneration. We applied the mechanical stretching stress on NP cells and inhibited NF-κB by siRNA, then evaluated the expression of inflammatory cytokines, matrix metalloproteinase (MMP), aggrecan, collagen II, and monitored viability and apoptosis of NP cells.

Results

Mechanical stretching stress induced the expression of TNF-α, IL-1β, NF-κB, MMP-3 and MMP-13, while inhibited the production of aggrecan and collagen II in NP cells. Mechanical stretching stress decreased the cell viability and induced apoptosis in NP cells. Inhibition of NF-κB by siRNA suppressed the production of TNF-α, IL-1β, NF-κB, MMP-3 and MMP-13, while upregulated the expression of aggrecan and collagen II in NP cells.

Conclusions

Inhibition of NF-κB by knocking down p65 suppressed over-mechanical stretching stress-induced cell apoptosis and promoted viability in NP cell. Inhibition of NF-κB suppressed inflammation and degeneration of NP cells in IVDD.

Human mesenchymal stem cells respond differentially to platelet preparations and synthesize hyaluronic acid in nucleus pulposus extracellular matrix

BACKGROUND CONTEXT

In recent years, autologous platelet-rich plasma (PRP) and bone marrow aspirate concentrate (BMAC) have been used as treatments for disc-related pain. A better understanding of the effects of leukocyte-rich (LR) versus leukocyte poor (LP-) PRP on bone marrow derived human mesenchymal stem/progenitor cells (hMSCs) is likely to improve future research studies, clinical practice and care for patients with chronic discogenic back pain.

PURPOSE

The primary aim of this study is to determine the effects of LR-PRP and LP-PRP on the proliferation and migration of hMSCs in pig nucleus pulposus (NP) extracellular matrix (ECM). The secondary aim is to characterize hMSC-dependent expression of the matrix remodeling enzymes metalloproteinases MMP-2, MMP-3, MMP-9 and tissue inhibitor of metalloproteinases TIMP-2, and to determine whether transplanted hMSCs can synthesize hyaluronic acid (HA).

STUDY DESIGN

Controlled laboratory study.

METHODS

Bone marrow-derived culture expanded hMSCs were seeded onto pig NP and cultured with LR-PRP, LP-PRP or serum/platelet releasate (PR). The same conditions without hMSCs were used as controls. hMSC proliferation, migration and dispersion was assessed via fluorescent microscopy, while HA synthesis, MMP-2, MMP-3, MMP-9, and TIMP-2 protein levels were assessed via enzyme linked immunosorbent assay. All funding was provided by a 501c(3) research foundation and does not have any commercial or sponsorship interests.

RESULTS

LP-PRP and PR cultures resulted in higher hMSC proliferation, migration, dispersion, and MMP-2 expression. LP-PRP cultures resulted in the highest HA production. LR-PRP cultures resulted in lower hMSC proliferation, negligible migration and dispersion, increased MMP-9 expression and lower HA production.

CONCLUSIONS

Human bone marrow-derived hMSCs seeded onto pig NP ECM are capable of synthesizing HA, indicating a transition towards a NP cell phenotype. This process was most enhanced by LP-PRP and marked by increased hMSC proliferation, MMP-2 production, HA synthesis and reduced MMP-9 levels.

CLINICAL SIGNIFICANCE

LP-PRP and PR, with or without hMSCs, may provide better outcomes than LR-PRP in lab investigations and clinical trials for discogenic pain. Bone marrow-derived hMSCs may hold promise as a treatment for disc degeneration.

Hypo-Osmotic Loading Induces Expression of IL-6 in Nucleus Pulposus Cells of the Intervertebral Disc Independent of TRPV4 and TRPM7

Painful intervertebral disc (IVD) degeneration is an age-related process characterized by reduced tissue osmolarity, increased catabolism of the extracellular matrix, and elevated levels of pro-inflammatory molecules. With the aging population and constantly rising treatment costs, it is of utmost importance to identify potential therapeutic targets and new pharmacological treatment strategies for low back pain. Transient receptor potential (TRP) channels are a family of Ca²⁺ permeable cell membrane receptors, which can be activated by multitude of stimuli and have recently emerged as contributors to joint disease, but were not investigated closer in the IVD. Based on the gene array screening, TRPC1, TRPM7, and TRPV4 were overall the most highly expressed TRP channels in bovine IVD cells. We demonstrated that TRPV4 gene expression was down-regulated in hypo-osmotic condition, whereas its Ca²⁺ flux increased. No significant differences in Ca²⁺ flux and gene expression were observed for TRPM7 between hypo- and iso-osmotic groups. Upon hypo-osmotic stimulation, we overall identified via RNA sequencing over 3,000 up- or down-regulated targets, from which we selected aggrecan, ADAMTS9, and IL-6 and investigated whether their altered gene expression is mediated through either the TRPV4 or TRPM7 channel, using specific activators and inhibitors (GSK1016790A/GSK2193874 for TRPV4 and Naltriben/NS8593 for TRPM7). GSK1016790A induced the expression of IL-6 under iso-osmotic condition, alike to hypo-osmotic stimulation alone, indicating that this effect might be TRPV4-mediated. However, using the TRPV4 blocker GSK2193874 failed to prevent the increase of IL-6 under hypo-osmotic condition. A treatment with TRPM7-activator did not cause significant changes in the gene expression of tested targets. In conclusion, while TRPV4 and TRPM7 are likely involved in osmosensing in the IVD, neither of them mediates hypo-osmotically-induced gene expression changes of aggrecan, ADAMTS9, and IL-6.

Defects in intervertebral disc and spine during development, degeneration, and pain: New research directions for disc regeneration and therapy

Intervertebral discs are cartilaginous joints present between vertebrae. The centers of the intervertebral discs consist of a gelatinous nucleus pulposus derived from the embryonic notochord. With age or injury, intervertebral discs may degenerate, causing neurological symptoms including back pain, which affects millions of people worldwide. Back pain is a multifactorial disorder, and disc degeneration is one of the primary contributing factors. Recent studies in mice have identified the key molecules involved in the formation of intervertebral discs. Several of these key molecules including sonic hedgehog and Brachyury are not only expressed by notochord during development, but are also expressed by neonatal mouse nucleus pulposus cells, and are crucial for postnatal disc maintenance. These findings suggest that intrinsic signals in each disc may maintain the nucleus pulposus microenvironment. However, since expression of these developmental signals declines with age and degeneration, disc degeneration may be related to the loss of these intrinsic signals. In addition, findings from mouse and other mammalian models have identified similarities between the patterning capabilities of the embryonic notochord and young nucleus pulposus cells, suggesting that mouse is a suitable model system to understand disc development and aging. Future research aimed at understanding the upstream regulators of these developmental signals and the modes by which they regulate disc growth and maintenance will likely provide mechanistic insights into disc growth and aging. Further, such findings will likely provide insights relevant to the development of effective therapies for treatment of back pain and reversing the disc degenerative process. This article is categorized under: Birth Defects > Organ Anomalies Vertebrate Organogenesis > Musculoskeletal and Vascular Adult Stem Cells, Tissue Renewal, and Regeneration > Regeneration Adult Stem Cells, Tissue Renewal, and Regeneration > Stem Cells and Aging.

Effects of Oxygen Concentration and Culture Time on Porcine Nucleus Pulposus Cell Metabolism: An in vitro Study

Low back pain is a common ailment that affects millions of individuals each year and is linked to degeneration of the intervertebral discs in the spine. Intervertebral disc degeneration is known to result from an imbalance in anabolic and catabolic activity by disc cells. Due to the avascular nature of the intervertebral disc, oxygen deficiency may occur in the central nucleus pulposus (NP). The resulting hypoxia affects matrix regulation and energy metabolism of disc cells, although the mechanisms are not fully understood. This study investigates in vitro glucose consumption and gene expression by NP cells over time under varying oxygen tensions. Notochordal porcine NP cells were cultured in agarose discs at 21, 5, or 1% oxygen tension for 1, 5, or 10 days. The expression of 10 key matrix genes, as well as Brachyury (T), by NP cells was analyzed using RT-PCR. Glucose consumption was measured using a two-point method. Results show that culture time and oxygen tension significantly affect glucose consumption rates by porcine NP cells. There were also significant changes in T expression based on oxygen level and culture time. The 1% oxygen tension had a significantly higher T expression on day 10 than the other two groups, which may indicate a better maintenance of the notochordal phenotype. MMP 1 and 13 expression increased over time for all groups, while only the 5% group showed an increase over time for MMP 3. TIMP expression followed the direction of MMPs but to a lesser magnitude. Five percent and twenty-one percent oxygen tensions led to decreases in anabolic gene expression while 1% led to increases. Oxygen concentration and culture time significantly impacted glucose consumption rate and the gene expression of matrix regulatory genes with hypoxic conditions most accurately maintaining the proper NP phenotype. This information is valuable not only for understanding disc pathophysiology, but also for harnessing the potential of notochordal NP cells in therapeutic applications.

Upregulation of miR-107 expression following hyperbaric oxygen treatment suppresses HMGB1/RAGE signaling in degenerated human nucleus pulposus cells

Background

The expression of both high-mobility group box 1 (HMGB1) and receptor for advanced glycation end-products (RAGE) is upregulated in degenerated discs. HMGB1 is known to function as a coupling factor between hypoxia and inflammation in arthritis, and this inflammatory response is modulated by microRNAs (miRNAs), with miR-107 expression downregulated during hypoxia. In this study, we investigated the regulation of the miR-107/HMGB1/RAGE pathway in degenerated nucleus pulposus cells (NPCs) after hyperbaric oxygen (HBO) treatment.

Methods

NPCs were separated from human degenerated intervertebral disc tissues. The control cells were maintained in 5% CO₂/95% air, and the hyperoxic cells were exposed to 100% O₂ at 2.5 atmospheres absolute. MiRNA expression profiling was performed via microarray and confirmed by real-time PCR, and miRNA target genes were identified using bioinformatics and luciferase reporter assays. The cellular protein and mRNA levels of HMGB1, RAGE, and inducible nitric oxide synthase (iNOS) were assessed, and the phosphorylation of MAPK (p38MAPK, ERK, and JNK) was evaluated. Additionally, cytosolic and nuclear fractions of the IκBα and NF-κB p65 proteins were analyzed, and secreted HMGB1 and metalloprotease (MMP) levels in the conditioned media were quantified.

Results

Using microarray analyses, 96 miRNAs were identified as upregulated and 66 downregulated following HBO treatment. Based on these results, miR-107 was selected for further investigation. Bioinformatics analyses indicated that the 3′ untranslated region of the HMGB1 mRNA contained the “seed-matched-sequence” for hsa-miR-107, which was validated via dual-luciferase reporter assays. MiR-107 was markedly induced by HBO, and simultaneous suppression of HMGB1 was observed in NPCs. Knockdown of miR-107 resulted in upregulation of HMGB1 expression in HBO-treated cells, and HBO treatment downregulated the mRNA and protein levels of HMGB1, RAGE, and iNOS and the secretion of HMGB1. In addition, HBO treatment upregulated the protein levels of cytosolic IκBα and decreased the nuclear translocation of NF-κB in NPCs. Moreover, HBO treatment downregulated the phosphorylation of p38MAPK, ERK, and JNK and significantly decreased the secretion of MMP-3, MMP-9, and MMP-13.

Conclusions

HBO inhibits pathways related to HMGB1/RAGE signaling via upregulation of miR-107 expression in degenerated human NPCs.

Leptin and the intervertebral disc: a biochemical link exists between obesity, intervertebral disc degeneration and low back pain-an in vitro study in a bovine model

PURPOSE

The aim of this study was to identify the effects of leptin upon the intervertebral disc (IVD) and to determine whether these responses are potentiated within an environment of existing degeneration. Obesity is a significant risk factor for low back pain (LBP) and IVD degeneration. Adipokines, such as leptin, are novel cytokines produced primarily by adipose tissue and have been implicated in degradative and inflammatory processes. Obese individuals are known to have higher concentrations of serum leptin, and IVD cells express leptin receptors. We hypothesise that adipokines, such as leptin, mediate a biochemical link between obesity, IVD degeneration and LBP.

METHODS

The bovine intervertebral disc was used as a model system to investigate the biochemical effects of obesity, mediated by leptin, upon the intervertebral disc. Freshly isolated cells, embedded in 3D alginate beads, were subsequently cultured under varying concentrations of leptin, alone or together with the pro-inflammatory cytokines TNF-α, IL-1β or IL-6. Responses in relation to production of nitric oxide, lactate, glycosaminoglycans and expression of anabolic and catabolic genes were analysed.

RESULTS

Leptin influenced the cellular metabolism leading particularly to greater production of proteases and NO. Addition of leptin to an inflammatory environment demonstrated a marked deleterious synergistic effect with greater production of NO, MMPs and potentiation of pro-inflammatory cytokine production.

CONCLUSIONS

Leptin can initiate processes involved in IVD degeneration. This effect is potentiated in an environment of existing degeneration and inflammation. Hence, a biochemical mechanism may underlie the link between obesity, intervertebral disc degeneration and low back pain. These slides can be retrieved under Electronic Supplementary Material.

Downregulation of microRNA-193a-3p is involved in invertebral disc degeneration by targeting MMP14

Accumulating evidence suggests that microRNAs (miRNAs) play an important role in intervertebral disc degeneration (IDD), but the precise role of specific miRNAs involved in this disease remains elusive. The purpose of this study was to identify IDD-specific miRNAs, followed by functional validation of results. MiRNA expression profile was determined in nucleus pulposus (NP) tissues from patients with IDD and controls, employing Solexa sequencing and quantitative real-time PCR (qRT-PCR). Biological functions of differential expression miRNAs were further investigated in vitro and in vivo. Luciferase reporter assays and Western blotting were performed to determine miRNA targets. We identified 28 miRNAs that were differentially expressed in patients compared with controls. Following qRT-PCR confirmation, miR-193a-3p was significantly down-regulated in degenerative NP tissues. Moreover, its level was correlated with grade of disc degeneration. Through gain- and loss-of-function studies, miR-193a-3p was demonstrated to significantly promote type II collagen expression in NP cells. Knockdown of MMP14 induced effects on NP cells similar to those induced by miR-193a-3p. Bioinformatics target prediction identified MMP14 as a putative target of miR-193a-3p. Furthermore, luciferase reporter assays and Western blotting demonstrated that miR-193a-3p directly targets MMP14. MiR-193a-3p inhibited IDD in vitro and in vivo. The downregulation of miR-193a-3p induces the expression of MMP14, which promotes loss of type II collagen and thereby contributes to the development of human IDD. Our findings extend the role of miR-193a-3p in the pathogenesis of IDD and provide a potential novel therapeutic target for degenerative disc disease.

KEY MESSAGES

Intervertebral disc degeneration (ICC)-specific miRNA profile generated by next generation sequencing. Downregulation of miR-193a-3p promoted loss of type II collagen by directly targeting MMP14 in IDD. miR-193a-3p inhibited IDD in vitro and in vivo. miR-193a-3p may be a promising candidate for prevention of degenerative disc disease.

Expression of macrophage elastase (MMP12) in rat tail intervertebral disc and growth plate after asymmetric loading

OBJECTIVES

The aim of this study was to examine whether asymmetric loading influences macrophage elastase (MMP12) expression in different parts of a rat tail intervertebral disc and growth plate and if MMP12 expression is correlated with the severity of the deformity.

METHODS

A wedge deformity between the ninth and tenth tail vertebrae was produced with an Ilizarov-type mini external fixator in 45 female Wistar rats, matched for their age and weight. Three groups were created according to the degree of deformity (10°, 30° and 50°). A total of 30 discs and vertebrae were evaluated immunohistochemically for immunolocalisation of MMP12 expression, and 15 discs were analysed by western blot and zymography in order to detect pro- and active MMP12.

RESULTS

No MMP12 expression was detected in the nucleus pulposus. Expression of MMP12 in the annulus progressively increased from group I to groups II and III, mainly at the concave side. Many growth plate chondrocytes expressed MMP12 in the control group, less in group I and rare in groups II and III. Changes in cell phenotype and reduction of cell number were observed, together with disorganisation of matrix microstructure similar to disc degeneration. ProMMP12 was detected at the area of 54 kDa and active MMP12 at 22 kDa.

CONCLUSIONS

Expression of MMP12 after application of asymmetric loading in a rat tail increased in the intervertebral disc but decreased in the growth plate and correlated with the degree of the deformity and the side of the wedged disc. Cite this article: Bone Joint Res 2014;3:273-9.

Stromal cell-derived factor-1 and its receptor CXCR4 are upregulated expression in degenerated intervertebral discs

BACKGROUND

Although chemokine stromal cell-derived factor 1 (SDF-1) and its receptor CXCR4 induce degradation of articular cartilage in rheumatoid arthritis (RA) and osteoarthritis (OA), the association between the SDF-1/CXCR4 pathway and degradation of the cartilaginous endplate and nucleus pulposus has not been thoroughly clarified. We investigated the expression of SDF-1 and CXCR4 in intervertebral discs (IVDs).

METHODS

SDF-1 and CXCR4 levels in human IVDs and the rat L5/6 motion segment were quantified by enzyme-linked immunosorbent assay. SDF-1 staining was quantified using a microscope and Image-Pro Plus software. Integrated optical density (IOD) served as the measurement parameter. The number of CXCR4 immunoreactive cells was expressed as a percentage of the total number of cells.

RESULTS

SDF-1 and CXCR4 were both expressed in IVDs, and the levels of SDF-1 and CXCR4 were both significantly higher in the degeneration group than in the normal group of human (or rat) discs. Both nucleus pulposus cells and cartilaginous endplate cells expressed the CXCR4 protein. Furthermore, a positive correlation was observed between the SDF-1 IOD value and the percentage of CXCR4-positive disc cells in the nucleus pulposus and cartilaginous endplate. The SDF-1 IOD values were significantly higher in the outer annular fibrosus and bone/endplate junction region than in the nucleus pulposus and cartilaginous endplate in the rat specimens.

CONCLUSIONS

Our findings suggest upregulated expression of SDF-1 and its receptor CXCR4 in degenerated IVD.

Cell sources for nucleus pulposus regeneration

PURPOSE

There is increasing interest in the development of cell therapy as a possible approach for the treatment of degenerative disc disease. To regenerate nucleus pulposus tissue, the cells must produce an appropriate proteoglycan-rich matrix, as this is essential for the functioning of the intervertebral disc. The natural environment within the disc is very challenging to implanted cells, particularly if they have been subcultured in normal laboratory conditions. The purpose of this work is to discuss parameters relevant to translating different proposed cell therapies of IVD into clinical use.

RESULTS

Several sources of cells have been proposed, including nucleus pulposus cells, chondrocytes and mesenchymal stem cells derived from bone marrow or adipose tissue. There are some clinical trials and reports of attempts to regenerate nucleus pulposus utilising either autologous or allogenic cells. While the published results of clinical applications of these cell therapies do not indicate any safety issues, additional evidence will be needed to prove their long-term efficacy.

CONCLUSION

This article discusses parameters relevant for successful translation of research on different cell sources into clinically applicable cell therapies: the influence of the intervertebral disc microenvironment on the cell phenotype, issues associated with cell culture and technical preparation of cell products, as well as discussing current regulatory requirements. There are advantages and disadvantages of each proposed cell type, but no strong evidence to favour any one particular cell source at the moment.

Cell signaling pathways related to pain receptors in the degenerated disk

Many of the causes of low back pain are still unknown; sufficient evidence indicates that both degenerative and mechanical change within the intervertebral disk (IVD) is a relevant factor. This article reviews intracellular signaling pathways related to pain receptors in the degenerated IVD. Several reports have demonstrated the number of nerve fibers in the IVD was increased in degenerated disks. In recent years, some groups have reported that an increase in nerve fibers is associated with the presence of inflammatory mediators and/or neurotrophins in the IVD. Cell signaling events, which are regulated by inflammatory mediators and neurotrophins, must be identified to clarify the mechanism underlying low back pain. Major intracellular signaling pathways (nuclear factor kappa β, mitogen-activated protein kinases, and Wnts) potentially play vital roles in mediating the molecular events responsible for the initiation and progression of IVD degeneration. These signaling pathways may represent therapeutic targets for the treatment of IVD degeneration and its associated back pain.

Effects of nucleus pulposus cell-derived acellular matrix on the differentiation of mesenchymal stem cells

Recent attempts to treat disc degeneration with mesenchymal stem cells (MSCs) showed encouraging results. Differentiating MSCs towards nucleus pulposus cell (NPC)-like lineages represents a speculative mechanism. Niche factors including hypoxia, growth factors and cell-cell interactions have been suggested but the matrix niche factor has not been studied. Our collagen microencapsulation provides a 3D model to study matrix niche as it enables the encapsulated cells to remodel the template matrix. We previously demonstrated the chondro-inductive role of of chondrocytes-derived matrix in MSCs and showed that NPCs maintained their phenotype and remodeled the template matrix of collagen microspheres into a glycosaminoglycan (GAG)-rich one. Here we aim to study the effects of NPC-derived matrix on MSC differentiation towards NPC-like lineages by firstly producing an NPC-derived matrix in collagen microspheres, secondly optimizing a decellularization protocol to discard NPCs yet retaining the matrix, thirdly repopulating the acellular NPC-derived matrix with MSCs and fourthly evaluating their phenotype. Finally, we injected these microspheres in a pilot rabbit disc degeneration model. Results showed that NPCs survived, maintained their phenotypic markers and produced GAGs. A decellularization protocol with maximal removal of the NPCs, minimal loss in major matrix components and partial retention of NPC-specific markers was identified. The resulting acellular matrix supported MSC survival and matrix production, and up-regulated the gene expression of NPC markers including type II collagen and glypican 3. Finally, injection of MSC in these microspheres in rabbit degenerative disc better maintained hydration level with more pronounced staining of GAGs and type II collagen than controls.

Diversity of intervertebral disc cells: phenotype and function

The intervertebral disc (IVD) is a moderately moving joint that is located between the bony vertebrae and provides flexibility and load transmission throughout the spinal column. The disc is composed of different but interrelated tissues, including the central highly hydrated nucleus pulposus (NP), the surrounding elastic and fibrous annulus fibrosus (AF), and the cartilaginous endplate (CEP), which provides the connection to the vertebral bodies. Each of these tissues has a different function and consists of a specific matrix structure that is maintained by a cell population with distinct phenotype. Although the healthy IVD is able to balance the slow matrix turnover of synthesis and degradation, this balance is often disturbed, leading to degenerative disorders. Successful therapeutic management of IVD degeneration requires a profound understanding of the cellular and molecular characteristics of the functional IVD. Hence, the phenotype of IVD cells has been of significant interest from multiple perspectives, including development, growth, remodelling, degeneration and repair. One major challenge that complicates our understanding of the disc cells is that both the cellular phenotype and the extracellular matrix strongly depend on disc maturity and health and as a consequence are continuously evolving. This review delineates the diversity of the cell types found in the intervertebral disc, with emphasis on human, but with reference to other species. The cells of the NP appear rounded and express a proteoglycan-rich matrix, whereas the more elongated AF cells are embedded in a collagen fibre matrix and the CEPs represent a layer of cartilage. Even though all disc cells have often been referred to as 'intervertebral disc chondrocytes', distinct phenotypical differences in comparison with articular chondrocytes exist and have been reported recently. The availability of more specific markers has also improved our understanding of progenitor cell differentiation towards an IVD cell phenotype. Ultimately, new cell- and tissue-engineering approaches to regenerative therapies will only be successful if the specific characteristics of the individual tissues and their context in the function of the whole organ, are taken into consideration.

Three-dimensional culture of rabbit nucleus pulposus cells in collagen microspheres

BACKGROUND

Degenerative disc disease poses an increasing threat to our quality of life as we age. Existing treatments have limitations. New treatment modalities focusing on biologic rather than surgical approach would be appealing.

PURPOSE

Culturing intervertebral disc cells in a three-dimensional (3D) model that can retain cellular characteristics and phenotype is a critical step toward understanding how the disc cells respond to and interact with extrinsic signals before better therapeutics can be derived.

STUDY DESIGN

In this work, we studied the culture of rabbit nucleus pulposus (NP) cells in a collagen microsphere system and compared their cell morphology and expression of a few potential phenotypic markers with that in monolayer culture.

METHODS

Specifically, rabbit NP cells isolated from both young and old animals were encapsulated and cultured in collagen microspheres with different monomeric concentrations and with different cell encapsulation density for different period of time. Evaluation on the growth kinetics, the viability, the cell morphology, the expression of Types I and II collagen, glycosaminoglycans (GAGs), and Keratin 19, and the ultrastructure of the fiber meshwork were conducted to compare the microsphere 3D culture system and the traditional monolayer cultures.

RESULTS

Nucleus pulposus cells in two-dimensional culture lost the phenotypic expression of Type II collagen and keratin 19 and expressed Type I collagen. In contrast, the 3D collagen microsphere culture system consistently outperformed the traditional monolayer culture in maintaining a round morphology and preserving the phenotypes of NP cells with persistent expression of Type II collagen and Keratin 19. These cells also remodeled the template collagen matrix in the microspheres by depositing new matrices, including collagen Type II and GAGs in a cell seeding density and collagen concentration dependent manner.

CONCLUSIONS

This study demonstrates the appeal of the 3D collagen microsphere system for NP cell culture over traditional monolayer culture because it preserves the phenotypic characteristics of NP cells. This system also enables the NP cells to remodel the template collagen matrix by depositing new matrices, suggesting an innovative way to reconstitute cell-specific and native tissue-like environment in vitro for future studies on stem cell matrix niche and interactions of NP cell with extrinsic factors.

Rhein: a potential biological therapeutic drug for intervertebral disc degeneration

Intervertebral disc degeneration (IDD) is regarded as an important cause of low back pain, which continues to be a common disability. IDD is thought to involve sequential changes of intervertebral disc that lead to the reduction of disc cells and the extracellular matrix. In addition, inflammation is crucially involved in IDD. Currently, there is urgent need to develop biological therapies for IDD that can both relieve symptoms and directly reverse the process of degeneration. Rhein (RH) is an anthraquinone molecule with the abilities of enhancing the synthesis of matrix components and inhibiting inflammatory response. Recently, the metabolic precursor of RH called diacerein has been demonstrated to have significant effects on pain relief and function improvement in the treatment of osteoarthritis. Given the occurrence of matrix degeneration and involvement of inflammation in IDD, we propose that RH might be a promising biological therapeutic drug for IDD due to its bioactivities. In addition, we hypothesize that the underlying mechanisms might be that RH has the ability to diminish interleukin-1 (IL-1) induced apoptosis and inhibit IL-1 induced secretion of MMPs and aggrecanases.

Matrix metalloproteinase-26, a novel MMP, is constitutively expressed in the human intervertebral disc in vivo and in vitro

Matrix metalloproteinase (MMP) regulation and expression is important in the aging/degenerating human intervertebral disc. MMP-26 (also known as matrilysin-2 or endometase) is a newly discovered MMP which degrades type IV collagen, fibronectin, fibrinogen, vitronectin, denatured collagen types I-IV, insulin-like growth factor binding protein 1, and activated pro-MMP-9. Our objective here was to determine if it is present in human disc tissue and cultured disc cells. Immunohistochemistry and microarray gene expression analyses were used to evaluate the presence of MMP-26 in human disc tissue from healthy and degenerated discs. Immunohistochemistry was also applied to human annulus cells cultured in a collagen sponge. Cellular and matrix localization of MMP-26 was identified in the outer and inner annulus and in the nucleus pulposus. Fewer cells showed localization in the inner vs. outer annulus, and localization was sparse in the nucleus. During in vitro culture of annulus cells, MMP-26 was also expressed. Molecular analyses showed significant downregulation of expression of MMP-26 (p=0.03), and significant 9.8-fold upregulation of TGF-beta (p=0.01) in more degenerated discs vs. healthier discs. Findings document the first identification of MMP-26 in the disc at the molecular and protein levels. Results point to the potentially important role of MMP-26 in matrix modulation during disc health and degeneration.

Human MMP28 expression is unresponsive to inflammatory stimuli and does not correlate to the grade of intervertebral disc degeneration

Background

MMP28 (epilysin) is a recently discovered member of the MMP (matrix metalloproteinase) family that is, amongst others, expressed in osteoarthritic cartilage and intervertebral disc (IVD) tissue. In this study the hypothesis that increased expression of MMP28 correlates with higher grades of degeneration and is stimulated by the presence of proinflammatory molecules was tested. Gene expression levels of MMP28 were investigated in traumatic and degenerative human IVD tissue and correlated to the type of disease and the degree of degeneration (Thompson grade). Quantification of MMP28 gene expression in human IVD tissue or in isolated cells after stimulation with the inflammatory mediators lipopolysaccharide (LPS), interleukin (IL)-1β, tumor necrosis factor (TNF)-α or the histondeacetylase inhibitor trichostatin A was performed by real-time RT PCR.

Results

While MMP28 expression was increased in individual cases with trauma or disc degeneration, there was no significant correlation between the grade of disease and MMP28 expression. Stimulation with LPS, IL-1β, TNF-α or trichostatin A did not alter MMP28 gene expression at any investigated time point or any concentration.

Conclusions

Our results demonstrate that gene expression of MMP28 in the IVD is not regulated by inflammatory mechanisms, is donor-dependent and cannot be positively or negatively linked to the grade of degeneration and only weakly to the occurrence of trauma. New hypotheses and future studies are needed to find the role of MMP28 in the intervertebral disc.

Expression of matrix metalloproteinase-1 (MMP-1) in Wistar rat's intervertebral disc after experimentally induced scoliotic deformity

Introduction

A scoliotic deformity on intervertebral discs may accelerate degeneration at a molecular level with the production of metalloproteinases (MMPs). In the present experimental study we evaluated the presence of MMP-1 immunohistochemically after application of asymmetric forces in a rat intervertebral disc and the impact of the degree of the deformity on MMP-1 expression.

Material-Method

Thirty female Wistar rats (aged 2 months old, weighted 200 ± 10 grams) were used. All animals were age, weight and height matched. A mini Ilizarov external fixator was applied at the base of a rat tail under anaesthesia in order to create a scoliotic deformity of the intervertebral disc between the 9^th and 10^th vertebrae. Rats were divided into three groups according to the degree of the deformity. In group I, the deformity was 10°, in group II 30° and in group III 50°. The rats were killed 35 days after surgery. The discs were removed along with the neighbouring vertebral bodies, prepared histologically and stained immunohistochemically. Immunopositivity of disc's cells for MMP-1 was determined using a semi-quantitative scored system.

Results

MMP-1 immunopositivity was detected in disc cells of annulus fibrosus of all intervertebral disc specimens examined. The percentage of MMP-1 positive disc cells in annulus fibrosus in group I, II and III were 20%, 43% and 75%, respectively. MMP-1 positivity was significantly correlated with the degree of the deformity (p < 0,001). An increase of chondrocyte-like disc cells was observed in the outer annulus fibrosus and at the margin of the intervertebral disc adjacent to the vertebral end plates. The difference in the proportion of MMP-1 positive disc cells between the convex and the concave side was statistically not significant in group I (p = 0,6), in group II this difference was statistically significant (p < 0,01). In group III the concave side showed a remarkable reduction in the number of disc's cells and a severe degeneration of matrix microstructure.

Conclusion

The present study showed that an experimentally induced scoliotic deformity on a rat tail intervertebral disc results in over-expression of MMP-1, which is dependent on the degree of the deformity and follows a dissimilar distribution between the convex and the concave side.

Fibronectin fragment activation of ERK increasing integrin α₅ and β₁ subunit expression to degenerate nucleus pulposus cells

Fibronectin fragments (Fn-f), which are the breakdown products of fibronectin, accumulate in the disc during degeneration and are proved to induce the degeneration of intervertebral disc. The goal of this investigation was to determine the functional role of integrin α₅ β₁, extracellular signal-regulated kinase (ERK), and protein kinase C (PKC) in the process of Fn-f degeneration nucleus pulposus (NP) cells. We found that Fn-f (100 nM, 30 kDa) exposure led to degeneration of NP cells, up-regulation of integrin α₅ β₁ expression and phosphorylation of the ERK(½) . After the expression of integrin α₅ β₁ was silenced in NP cells, the phosphorylation of ERK(½) and the expression of MMP9, MMP13, and collagen II had no difference with control under the treatment of Fn-f. Finally, when the inhibitor of ERK(½) and the inhibitor of PKC were added into the medium of NP cells; we found these two inhibitors could eliminate the effect of Fn-f on NP cells. It is concluded that Fn-f had the potential to enhance the NP cell degeneration in a vicious circle. And the integrin α₅ β₁ subunit, ERK, and PKC were all included in this loop.

Hypertrophic differentiation and calcification during intervertebral disc degeneration

BACKGROUND

In degenerative intervertebral discs (IVDs) collagen type X expression and calcifications have been demonstrated, resembling advanced osteoarthritis (OA), which is associated with hypertrophic differentiation, characterized by the production of collagen type X, Runt-related transcription factor 2 (Runx2), osteoprotegerin (OPG), alkaline phosphatase (ALP) and calcifications.

OBJECTIVE

The aim of this study was to determine if hypertrophic differentiation occurs during IVD degeneration.

METHODS

IVDs from all Thompson degeneration grades were prepared for histology, extraction of nucleus pulposus (NP) and annulus fibrosis (AF) tissue (N=50) and micro-CT (N=27). The presence of collagen type X, OPG and Runx2 was determined by immunohistochemistry, with OPG levels also determined by Enzyme-linked immunosorbent assay (ELISA). The presence of calcification was determined by micro-CT, von Kossa and Alizarin Red staining.

RESULTS

Immunohistochemical staining for collagen type X, OPG, Runx2 appeared more intense in the NP of degenerative compared to healthy IVD samples. OPG levels correlated significantly with degeneration grade (NP: P<0.000; AF: P=0.002) and the number of microscopic calcifications (NP: P=0.002; AF: P=0.008). The extent of calcifications on micro-CT also correlated with degeneration grade (NP: P<0.001, AF: P=0.001) as did von Kossa staining (NP: P=0.015, AF: P=0.016). ALP staining was only incidentally seen in the transition zone of grades IV and V degenerated IVDs.

CONCLUSION

This study for the first time demonstrates that hypertrophic differentiation occurs during IVD degeneration, as shown by an increase in OPG levels, the presence of ALP activity, increased immunopositivity of Runx2 and collagen type X.