Co-culture induces mesenchymal stem cell differentiation and modulation of the degenerate human nucleus pulposus cell phenotype

AIMS

While mesenchymal stem cell (MSC)-based therapies for repair of the degenerate intervertebral disc (IVD) have been proposed, the interaction of MSCs with cells of the degenerate IVD has not been fully investigated. Therefore, it is unclear whether implanted MSCs would differentiate into nucleus pulposus (NP) cells and/or stimulate endogenous NP cells. Here, we investigate the differences in interaction between human MSCs and NP cells from both nondegenerate and degenerate discs during in vitro co-culture with direct cell-cell contact.

MATERIALS & METHODS

Human bone marrow-derived MSCs (labeled with CFDA) were co-cultured with direct cell-cell contact in monolayer with NP cells obtained from nondegenerate or degenerate human NP tissue from lumbar IVDs at 50:50 ratios for 7 days. Differentiation of MSCs and changes of matrix-associated genes in NP cells were assessed by quantitative real-time PCR.

RESULTS

MSCs differentiated to an NP-like phenotype following direct co-culture with both nondegenerate and degenerate NP, as shown by a significant upregulation of SOX9, type VI collagen, aggrecan and versican gene expression together with a simultaneous upregulation of CDMP-1, TGF-β1, IGF-1 and CTGF. Direct co-culture of normal NP cells with MSCs had no effect on the phenotype of normal NP cells, while co-culture with degenerate NP cells resulted in enhanced matrix gene expression in degenerate NP cells, accompanied by increases in both TGF-β and CDMP-1 gene expression.

CONCLUSION

Importantly for MSC-based therapies for repair of the degenerate IVD, these data suggest that cellular interactions between MSCs and degenerate NP cells may both stimulate MSC differentiation to an NP-like phenotype and also stimulate the endogenous NP cell population to regain a nondegenerate phenotype and consequently enhance matrix synthesis for self-repair.

The involvement of interleukin-1 and interleukin-4 in the response of human annulus fibrosus cells to cyclic tensile strain: an altered mechanotransduction pathway with degeneration

Introduction

Recent evidence suggests that intervertebral disc (IVD) cells derived from degenerative tissue are unable to respond to physiologically relevant mechanical stimuli in the 'normal' anabolic manner, but instead respond by increasing matrix catabolism. Understanding the nature of the biological processes which allow disc cells to sense and respond to mechanical stimuli (a process termed 'mechanotransduction') is important to ascertain whether these signalling pathways differ with disease. The aim here was to investigate the involvement of interleukin (IL)-1 and IL-4 in the response of annulus fibrosus (AF) cells derived from nondegenerative and degenerative tissue to cyclic tensile strain to determine whether cytokine involvement differed with IVD degeneration.

Methods

AF cells were isolated from nondegenerative and degenerative human IVDs, expanded in monolayers and cyclically strained in the presence or absence of the cytokine inhibitors IL-1 receptor antagonist (IL-1Ra) or IL-4 receptor antibody (IL-4RAb) with 10% strain at 1.0 Hz for 20 minutes using a Flexcell strain device. Total RNA was extracted from the cells at time points of baseline control and 1 or 24 hours poststimulation. Quantitative real-time polymerase chain reaction was used to analyse the gene expression of matrix proteins (aggrecan and type I collagen) and enzymes (matrix metalloproteinase 3 (MMP3) and a disintegrin and metalloproteinase with a thrombospondin type 1 motif 4 (ADAMTS4)).

Results

Expression of catabolic genes (MMP3 and ADAMTS4) decreased in AF cells derived from nondegenerative tissue in response to 1.0-Hz stimulation, and this decrease in gene expression was inhibited or increased following pretreatment of cells with IL-1Ra or IL-4RAb respectively. Treatment of AF cells derived from degenerative tissue with an identical stimulus (1.0-Hz) resulted in reduced anabolic gene expression (aggrecan and type I collagen), with IL-1Ra or IL-4RAb pretreatment having no effect.

Conclusions

Both IL-1 and IL-4 are involved in the response of AF cells derived from nondegenerative tissue to 1.0-Hz cyclic tensile strain. Interestingly, the altered response observed at 1.0-Hz in AF cells from degenerative tissue appears to be independent of either cytokine, suggesting an alternative mechanotransduction pathway in operation.

The response of human anulus fibrosus cells to cyclic tensile strain is frequency-dependent and altered with disc degeneration

OBJECTIVE

Mechanical loads are important for homeostasis of the intervertebral disc (IVD) cell matrix, with physiologic and nonphysiologic loads leading to matrix anabolism and catabolism, respectively. Previous investigations into the effects of load on disc cells have predominantly used animal models, with the limited number of human studies focusing primarily on nucleus pulposus cells. The aim of this study was to examine the effect of cyclic tensile strain (CTS) on human anulus fibrosus (AF) cells to ascertain whether the response was frequency-dependent and to compare AF cells derived from nondegenerated and degenerated tissue samples.

METHODS

AF cells were isolated from nondegenerated and degenerated human IVDs, expanded in monolayer, and cyclically strained for 20 minutes, applying 10% strain at a frequency of 1.0 Hz or 0.33 Hz with the use of a Flexcell strain device. Total RNA was extracted from the cells at baseline (control) and at 1, 3, and 24 hours following application of CTS. Real-time quantitative polymerase chain reaction was used to analyze gene expression of matrix proteins (aggrecan, type I collagen, and type II collagen) and enzymes (matrix metalloproteinases [MMPs] 3, 9, 13, and ADAMTS-4).

RESULTS

The expression of catabolic genes (MMP-3 and ADAMTS-4) in AF cells derived from nondegenerated tissue decreased in response to 1.0 Hz of CTS, whereas changing the frequency to 0.33 Hz resulted in a shift toward matrix catabolism. Application of 1.0 Hz of CTS reduced anabolic gene expression (aggrecan and type I collagen) in AF cells derived from degenerated tissue, with 0.33 Hz of CTS resulting in increased catabolic gene expression.

CONCLUSION

The response of human AF cells to CTS is frequency-dependent and is altered by degeneration.

YY1 expression predicts favourable outcome in follicular lymphoma

AIMS

Follicular lymphoma is the second most common type of non-Hodgkin's lymphoma worldwide. The majority of patients diagnosed as having follicular lymphoma have an indolent form of the disease, but a subset of patients have aggressive disease with a shorter survival interval. Optimal treatment stratification requires a distinction between these two groups, though there are presently few prognostic biomarkers available. The transcription factor YY1 has been shown to play an important role in cancer biology. The authors have previously reported a correlation of Yin Yang 1 (YY1) mRNA levels with survival in FL. This study aimed to validate these findings at the protein level.

METHODS

Quantification of YY1 protein was carried out on 26 FL biopsy samples using quantum dot labelled immunohistochemistry. Ki-67 percentage, grade, YY1 protein levels and T cell and macrophage markers were used in a multivariable analysis for survival in 26 cases of FL.

RESULTS

Expression levels of YY1 protein were significantly increased in patients alive in comparison with those dead after follow-up (p ≤ 0.025). Kaplan-Meier analysis showed association of higher expression levels of YY1 with longer survival (p ≤ 0.01) (hazard ratio 3.33, 95% CI 1.26 to 8.85). The multivariable analysis identified YY1 protein level as the strongest predictor of outcome (p ≤ 0.018), with none of the other markers being significantly associated with outcome.

CONCLUSION

These results support the prognostic utility of YY1 in FL, indicating potential as a clinical biomarker.

Transcriptional profiling of bovine intervertebral disc cells: implications for identification of normal and degenerate human intervertebral disc cell phenotypes

INTRODUCTION

Nucleus pulposus (NP) cells have a phenotype similar to articular cartilage (AC) cells. However, the matrix of the NP is clearly different to that of AC suggesting that specific cell phenotypes exist. The aim of this study was to identify novel genes that could be used to distinguish bovine NP cells from AC and annulus fibrosus (AF) cells, and to further determine their expression in normal and degenerate human intervertebral disc (IVD) cells.

METHODS

Microarrays were conducted on bovine AC, AF and NP cells, using Affymetrix Genechip(R) Bovine Genome Arrays. Differential expression levels for a number of genes were confirmed by quantitative real time polymerase chain reaction (qRT-PCR) on bovine, AC, AF and NP cells, as well as separated bovine NP and notochordal (NC) cells. Expression of these novel markers were further tested on normal human AC, AF and NP cells, and degenerate AF and NP cells.

RESULTS

Microarray comparisons between NP/AC&AF and NP/AC identified 34 NP-specific and 49 IVD-specific genes respectively that were differentially expressed > or =100 fold. A subset of these were verified by qRT-PCR and shown to be expressed in bovine NC cells. Eleven genes (SNAP25, KRT8, KRT18, KRT19, CDH2, IBSP, VCAN, TNMD, BASP1, FOXF1 & FBLN1) were also differentially expressed in normal human NP cells, although to a lesser degree. Four genes (SNAP25, KRT8, KRT18 and CDH2) were significantly decreased in degenerate human NP cells, while three genes (VCAN, TNMD and BASP1) were significantly increased in degenerate human AF cells. The IVD negative marker FBLN1 was significantly increased in both degenerate human NP and AF cells.

CONCLUSIONS

This study has identified a number of novel genes that characterise the bovine and human NP and IVD transcriptional profiles, and allows for discrimination between AC, AF and NP cells. Furthermore, the similarity in expression profiles of the separated NP and NC cell populations suggests that these two cell types may be derived from a common lineage. Although interspecies variation, together with changes with IVD degeneration were noted, use of this gene expression signature will benefit tissue engineering studies where defining the NP phenotype is paramount.

Tissue section AFM: In situ ultrastructural imaging of native biomolecules

Conventional approaches for ultrastructural high-resolution imaging of biological specimens induce profound changes in bio-molecular structures. By combining tissue cryo-sectioning with non-destructive atomic force microscopy (AFM) imaging we have developed a methodology that may be applied by the non-specialist to both preserve and visualize bio-molecular structures (in particular extracellular matrix assemblies) in situ. This tissue section AFM technique is capable of: i) resolving nm–µm scale features of intra- and extracellular structures in tissue cryo-sections; ii) imaging the same tissue region before and after experimental interventions; iii) combining ultrastructural imaging with complimentary microscopical and micromechanical methods. Here, we employ this technique to: i) visualize the macro-molecular structures of unstained and unfixed fibrillar collagens (in skin, cartilage and intervertebral disc), elastic fibres (in aorta and lung), desmosomes (in nasal epithelium) and mitochondria (in heart); ii) quantify the ultrastructural effects of sequential collagenase digestion on a single elastic fibre; iii) correlate optical (auto fluorescent) with ultrastructural (AFM) images of aortic elastic lamellae.

Expression of semaphorin 3A and its receptors in the human intervertebral disc: potential role in regulating neural ingrowth in the degenerate intervertebral disc

Introduction

Intervertebral disc (IVD) degeneration is considered a major underlying factor in the pathogenesis of chronic low back pain. Although the healthy IVD is both avascular and aneural, during degeneration there is ingrowth of nociceptive nerve fibres and blood vessels into proximal regions of the IVD, which may contribute to the pain. The mechanisms underlying neural ingrowth are, however, not fully understood. Semaphorin 3A (sema3A) is an axonal guidance molecule with the ability to repel nerves seeking their synaptic target. This study aimed to identify whether members of the Class 3 semaphorins were expressed by chondrocyte-like cells of the IVD addressing the hypothesis that they may play a role in repelling axons surrounding the healthy disc, thus maintaining its aneural condition.

Methods

Human IVD samples were investigated using reverse transcription polymerase chain reaction (RT-PCR) to identify gene expression of sema3A, 3F and their receptors: neuropilins (1 and 2) and plexins (A1-4). Sema3A protein was also localised within sections of normal and degenerate human IVD and immunopositivity quantified. Serial sections were stained using PGP9.5 and CD31 to correlate semaphorin 3A expression with nerve and blood vessel ingrowth, respectively.

Results

Sema3A protein was expressed highly in the healthy disc, primarily localised to the outer annulus fibrosus. In degenerate samples, sema3A expression decreased significantly in this region, although cell clusters within the degenerate nucleus pulposus exhibited strong immunopositivity. mRNA for sema3A receptors was also identified in healthy and degenerate tissues. CD31 and PGP9.5 were expressed most highly in degenerate tissues correlating with low expression of sema3A.

Conclusions

This study is the first to establish the expression of semaphorins and their receptors in the human IVD with a decrease seen in the degenerate painful IVD. Sema3A may therefore, amongst other roles, act as a barrier to neuronal ingrowth within the healthy disc.

Skeletal muscle contractile properties and proinflammatory cytokine gene expression in human endotoxaemia

Background

Muscle dysfunction associated with sepsis contributes to morbidity and mortality but the underlying mechanisms are unclear. This study examined whether muscle weakness relates to an intrinsic defect in contraction, or to central mechanisms associated with acute illness, and whether systemic endotoxaemia induces changes in gene expression for proinflammatory cytokines within human muscle in vivo.

Methods

In this experimental study, 12 healthy men received intravenous Escherichia coli lipopolysaccharide (LPS, 4 ng/kg) or saline (control). Voluntary and electrically stimulated quadriceps contraction, and tumour necrosis factor (TNF) α mRNA expression in quadriceps muscle biopsies were studied before and after the infusion.

Results

Endotoxaemia induced transient weakness of voluntary quadriceps contraction, equivalent to a 7·8 (95 per cent confidence interval 2·1 to 13·5) per cent reduction in contractile force at 180 min (P = 0·027) and a 9·0 (5·2 to 12·8) per cent reduction at 300 min (P = 0·008). Electrically stimulated contraction was unaffected. LPS administration resulted in an apparent fibre-specific induction of TNF-α mRNA.

Conclusion

Endotoxaemia results in a reduction in voluntary muscle contractile force without an apparent defect in stimulated muscle contraction. Loss of volition may be a more important factor than intrinsic dysfunction in acute sepsis-associated human muscle weakness.

Development of an in vitro model to test the efficacy of novel therapies for IVD degeneration

Low back pain (LBP) is a major cause of disability worldwide that has been linked to intervertebral disc (IVD) degeneration. An improved understanding of the pathogenesis of disc degeneration is now developing, which is leading to the development of a number of possible future therapies targeted at the underlying pathology and regeneration strategies. Although results thus far are promising, the investigation of such therapies in an environment that mimics the mechanical environment of the human disc in vivo is problematic. The development of an in vitro model system that can maintain metabolically active IVD tissue within a loading environment pertaining to that of the human spine is crucial for testing the efficacy of future cell-based and tissue-engineering therapies for IVD degeneration. Here, using our novel loading rig, capable of mimicking the loading environment experienced within the human spine, we have cultured nucleus pulposus tissue explants, applied a daily hydrostatic loading regime for up to 2 weeks and investigated proteoglycan retention, metabolic activity and cellular phenotype. IVD tissue cultured under a loading environment pertaining to the in vivo loading environment maintained metabolic cell activity, proteoglycan content and cellular phenotype. Indeed, all parameters were improved in IVD tissue cultured with load compared to unloaded controls. Such a model is invaluable for investigations assessing the feasibility and efficacy of future therapeutic approaches to inhibiting degeneration or stimulating regeneration of the IVD, where the in vivo loading environment may be crucial to their success or failure.

Expression of cartilage-derived morphogenetic protein in human intervertebral discs and its effect on matrix synthesis in degenerate human nucleus pulposus cells

Introduction

Loss of intervertebral disc (IVD) matrix and ultimately disc height as a result of 'degeneration' has been implicated as a major cause of low back pain (LBP). The use of anabolic growth factors as therapies to regenerate IVD matrix, hence restoring disc height and thus reversing degenerative disc disease, has been suggested. Cartilage-derived morphogenetic protein (CDMP) is a growth factor which stimulates proteoglycan production in chondrocyte-like cells and thus could be a useful growth factor for LBP therapies. However, little is known about the expression of CDMP or its receptor in human IVD, nor its effects on human disc cells.

Methods

Using immunohistochemistry we investigated the localisation of CDMP in non-degenerate and degenerate human IVDs. Additionally, we investigated the effect of CDMP on aggrecan and type II collagen gene expression and proteoglycan synthesis in nucleus pulposus (NP) cells derived from degenerate IVDs.

Results

We demonstrated that CDMP 1 and 2 were expressed in the non-degenerate and degenerate IVD, particularly in cells of the NP. A small decrease in the number of CDMP 1 and 2 immunopositive cells was seen with degeneration. Treatment of human NP cells, (derived from degenerate IVD), with CDMP showed an increase in aggrecan and type II collagen gene expression and increased production of proteoglycan (GAGs).

Conclusions

The data suggests that CDMP may be a useful growth factor to stimulate proteoglycan production in the human degenerate IVD and hence the repair of the extracellular matrix.

Increased expression of matrix metalloproteinase-10, nerve growth factor and substance P in the painful degenerate intervertebral disc

Introduction

Matrix metalloproteinases (MMPs) are known to be involved in the degradation of the nucleus pulposus (NP) during intervertebral disc (IVD) degeneration. This study investigated MMP-10 (stromelysin-2) expression in the NP during IVD degeneration and correlated its expression with pro-inflammatory cytokines and molecules involved in innervation and nociception during degeneration which results in low back pain (LBP).

Methods

Human NP tissue was obtained at postmortem (PM) from patients without a history of back pain and graded as histologically normal or degenerate. Symptomatic degenerate NP samples were also obtained at surgery for LBP. Expression of MMP-10 mRNA and protein was analysed using real-time polymerase chain reaction and immunohistochemistry. Gene expression for pro-inflammatory cytokines interleukin-1 (IL-1) and tumour necrosis factor-alpha (TNF-α), nerve growth factor (NGF) and the pain-associated neuropeptide substance P were also analysed. Correlations between MMP-10 and IL-1, TNF-α and NGF were assessed along with NGF with substance P.

Results

MMP-10 mRNA was significantly increased in surgical degenerate NP when compared to PM normal and PM degenerate samples. MMP-10 protein was also significantly higher in degenerate surgical NP samples compared to PM normal. IL-1 and MMP-10 mRNA demonstrated a significant correlation in surgical degenerate samples, while TNF-α was not correlated with MMP-10 mRNA. NGF was significantly correlated with both MMP-10 and substance P mRNA in surgical degenerate NP samples.

Conclusions

MMP-10 expression is increased in the symptomatic degenerate IVD, where it may contribute to matrix degradation and initiation of nociception. Importantly, this study suggests differences in the pathways involved in matrix degradation between painful and pain-free IVD degeneration.

Human disc degeneration is associated with increased MMP 7 expression

During intervertebral disc (IVD) degeneration, normal matrix synthesis decreases and degradation of disc matrix increases. A number of proteases that are increased during disc degeneration are thought to be involved in its pathogenesis. Matrix metalloproteinase 7 (MMP 7) (Matrilysin, PUMP-1) is known to cleave the major matrix molecules found within the IVD, i.e., the proteoglycan aggrecan and collagen type II. To date, however, it is not known how its expression changes with degeneration or its exact location. We investigated the localization of MMP 7 in human, histologically graded, nondegenerate, degenerated and prolapsed discs to ascertain whether MMP 7 is up-regulated during disc degeneration. Samples of human IVD tissue were fixed in neutral buffered formalin, embedded in paraffin, and sections stained with hematoxylin and eosin to score the degree of morphological degeneration. Immunohistochemistry was performed to localize MMP 7 in 41 human IVDs with varying degrees of degeneration. We found that the chondrocyte-like cells of the nucleus pulposus and inner annulus fibrosus were MMP 7 immunopositive; little immunopositivity was observed in the outer annulus. Nondegenerate discs showed few immunopositive cells. A significant increase in the proportion of MMP 7 immunopositive cells was seen in the nucleus pulposus of discs classified as showing intermediate levels of degeneration and a further increase was seen in discs with severe degeneration. Prolapsed discs showed more MMP 7 immunopositive cells compared to nondegenerated discs, but fewer than those seen in cases of severe degeneration.

Altered relative expression of BMPs and BMP inhibitors in cartilaginous areas of human fractures progressing towards nonunion

The present study was conducted to evaluate the hypothesis that an imbalance in the local production of bone morphogenetic proteins (BMPs) and BMP inhibitors exists within the cartilaginous intermediate of nonhealing fractures. Biopsies were recovered intraoperatively from human fractures that, upon follow-up, were found to heal normally or become nonunions. The samples were examined by immunohistochemistry to determine the expression of BMP-2, BMP-14, and the BMP inhibitors noggin and chordin. Expression was determined semiquantitatively based on the area of positive staining per area of cartilage and by determining the number of positively staining cells and the intensity of staining. There was a significant reduction in BMP-2 and BMP-14 expression in cartilaginous areas of nonhealing fractures compared to healing fractures. However, there was no difference in the expression of the BMP inhibitors between the two groups of fractures. This imbalance in the expression of BMPs and BMP inhibitors within cartilaginous areas of developing nonunions may account for their reduced bone forming ability. These data suggest strategies for preventing the development of nonunions by altering levels of BMPs and their inhibitors within fracture sites.

Regulation of catabolic gene expression in normal and degenerate human intervertebral disc cells: implications for the pathogenesis of intervertebral disc degeneration

Introduction

The aim of this study was to compare the effects of tumour necrosis factor-alpha (TNF-α) and interleukin-1-beta (IL-1β) on protease and catabolic cytokine and receptor gene expression in normal and degenerate human nucleus pulposus cells in alginate culture.

Methods

Cells isolated from normal and degenerate nucleus pulposus regions of human intervertebral discs were cultured in alginate pellets and stimulated by the addition of 10 ng/mL TNF-α or IL-1β for 48 hours prior to RNA extraction. Quantitative real-time polymerase chain reaction was used to assess the effect of TNF-α or IL-β stimulation on the expression of matrix metalloproteinase (MMP)-3, -9 and -13, TNF-α, TNF receptor 1 (TNF-R1), TNF receptor 2 (TNF-R2), IL-1α, IL-1β, IL-1 receptor 1 (IL-1R1) and IL-1 receptor antagonist (IL-1Ra).

Results

MMP-3 and MMP-9 gene expressions were upregulated to a greater level by IL-1β than TNF-α. MMP-13 was upregulated by each cytokine to a similar extent. TNF-α and TNF-R2 expressions were upregulated by both TNF-α and IL-β, whereas TNF-R1 expression was not significantly affected by either cytokine. IL-1β and IL-1Ra expressions were significantly upregulated by TNF-α, whereas IL-1α and IL-1R1 were unchanged.

Conclusions

TNF-α does not induce MMP expression to the same degree as stimulation by IL-1β, but it does act to upregulate IL-1β expression as well as TNF-α and TNF-R2. The net result of this would be an increased inflammatory environment and accelerated degradation of the matrix. These results support the hypothesis that, while TNF-α may be an important initiating factor in matrix degeneration, IL-1β plays a greater role in established pathological degradation.

Modified expression of the ADAMTS enzymes and tissue inhibitor of metalloproteinases 3 during human intervertebral disc degeneration

OBJECTIVE

Intervertebral disc degeneration is linked to loss of extracellular matrix (ECM), particularly the early loss of aggrecan. A group of metalloproteinases called aggrecanases are important mediators of aggrecan turnover. The present study was undertaken to investigate the expression of the recognized aggrecanases and their inhibitor, tissue inhibitor of metalloproteinases 3 (TIMP-3), in human intervertebral disc tissue.

METHODS

Twenty-four nondegenerated and 30 degenerated disc samples were analyzed for absolute messenger RNA (mRNA) copy number of ADAMTS 1, 4, 5, 8, 9, and 15 and TIMP-3 by real-time reverse transcription-polymerase chain reaction. Thirty-six formalin-fixed embedded intervertebral disc samples of varying grades of degeneration were used for immunohistochemical analyses. In addition, samples from 8 subjects were analyzed for the presence of matrix metalloproteinase (MMP)- and aggrecanase-generated aggrecan products.

RESULTS

Messenger RNA for all the aggrecanases other than ADAMTS-8 was identified in intervertebral disc tissue, as was mRNA for TIMP-3. Levels of mRNA expression of ADAMTS 1, 4, 5, and 15 were significantly increased in degenerated tissue compared with nondegenerated tissue. All these aggrecanases and TIMP-3 were also detected immunohistochemically in disc tissue, and numbers of nucleus pulposus cells staining positive for ADAMTS 4, 5, 9, and 15 were significantly increased in degenerated tissue compared with nondegenerated tissue. Aggrecan breakdown products generated by MMP and aggrecanase activities were also detected in intervertebral disc tissue.

CONCLUSION

The aggrecanases ADAMTS 1, 4, 5, 9, and 15 may contribute to the changes occurring in the ECM during intervertebral disc degeneration. Targeting these enzymes may be a possible future therapeutic strategy for the prevention of intervertebral disc degeneration and its associated morbidity.

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

Introduction

The decreased disc height characteristic of intervertebral disc (IVD) degeneration has often been linked to low back pain, and thus regeneration strategies aimed at restoring the disc extracellular matrix and ultimately disc height have been proposed as potential treatments for IVD degeneration. One such therapy under investigation by a number of groups worldwide is the use of autologous mesenchymal stem cells (MSCs) to aid in the regeneration of the IVD extracellular matrix. To date, however, the optimum method of application of these cells for regeneration strategies for the IVD is unclear, and few studies have investigated the direct injection of MSCs alone into IVD tissues. In the present article, we investigated the survival and phenotype of human MSCs, sourced from aged individuals, following injection into nucleus pulposus (NP) tissue explant cultures.

Methods

Human MSCs extracted from bone marrow were expanded in monolayer culture and, after labelling with adenoviral vectors carrying the green fluorescent protein transcript, were injected into NP tissue explants (sourced from bovine caudal discs) and maintained in culture for 2, 7, 14 and 28 days post injection. Following fixation and paraffin embedding, cell viability was assessed using in situ hybridisation for polyA-mRNA and using immunohistochemistry for caspase 3. Immunohistochemistry/fluorescence for aggrecan, Sox-9 and types I, II and X collagen together with Alizarin red staining was employed to investigate the MSC phenotype and matrix formation.

Results

MSCs were identified in all injected tissue samples and cell viability was maintained for the 4 weeks investigated. MSCs displayed cellular staining for Sox-9, and displayed cellular and matrix staining for aggrecan and type II collagen that increased during culture. No type I collagen, type X collagen or Alizarin red staining was observed at any time point.

Conclusions

MSCs from older individuals differentiate spontaneously into chondrocyte-like NP cells upon insertion into NP tissue in vitro, and thus may not require additional stimulation or carrier to induce differentiation. This is a key finding, as such a strategy would minimise the level of external manipulation required prior to insertion into the patient, thus simplifying the treatment strategy and reducing costs.

Connective tissue growth factor expression in human intervertebral disc: implications for angiogenesis in intervertebral disc degeneration

Intervertebral disc (IVD) degeneration is strongly associated with chronic low back pain, one of the most common causes of morbidity in the West. While normal healthy IVD is avascular, angiogenesis is a constant feature of IVD degeneration and has been shown to be associated with in-growth of nerves. Connective tissue growth factor (CTGF) plays a pivotal role in angiogenesis. To investigate the expression of CTGF in both normal and degenerated IVD, 21 IVDs were obtained from patients at surgery or postmortem examination and grouped according to the severity of histological degeneration. The immunohistochemical expression of CTGF was correlated with the degree of degeneration. CD31 immunohistochemistry was used to correlate IVD degeneration with vasculature. Our results showed that CTGF is expressed in non-degenerated and degenerated human IVDs and increased expression of CTGF is associated with degenerated discs, particularly within areas of neovascularization. We suggest that CTGF may play a role in angiogenesis in the human degenerated IVD.

Quantum dots light up pathology

Quantum dots (QDs) are novel nanocrystal fluorophores with extremely high fluorescence efficiency and minimal photobleaching. They also possess a constant excitation wavelength together with sharp and symmetrical tunable emission spectra. These unique optical properties make them near-perfect fluorescent markers and there has recently been rapid development of their use for bioimaging. QDs can be conjugated to a wide range of biological targets, including proteins, antibodies, and nucleic acid probes, rendering them of particular interest to pathology researchers. They have been used in multiplex immunohistochemistry and in situ hybridization, which when combined with multispectral imaging, has enabled quantitative measurement of gene expression in situ. QDs have also been used for live in vivo animal imaging and are now being applied to an ever-increasing range of biological problems. These are detailed in this review, which also acts to outline the important advances that have been made in their range of applications. The relative novelty of QDs can present problems in their practical use and guidelines for their application are given.

Regional and cellular localisation of BMPs and their inhibitors' expression in human fractures

The objective of this study was to determine whether BMP-2 and -14, noggin, and chordin could be detected in human fractures and to assess their regional and cellular distribution. The expression of these proteins was detected by immunohistochemistry in an archive of human fractures. BMP-2 and BMP-14 expression was strongest in areas of cartilage formation and, to a lesser extent, in areas of bone formation. Within areas of cartilage formation, both BMP-2 and BMP-14 were expressed more strongly by the non-hypertrophic chondrocytes. The BMP inhibitors noggin and chordin were also expressed most intensely in areas of cartilage formation and there was no difference in their expression between the non-hypertrophic and hypertrophic chondrocytes. Our study demonstrates the expression of BMP-14 and the BMP inhibitors in human fractures for the first time, and our findings will contribute to an improved understanding of the physiological processes in bone repair.

Strategies for regeneration of the intervertebral disc

Low back pain resulting from degenerative disc disease is the most common cause of disability in the UK. Current low back pain treatments are aimed at either treating the symptoms of pain, or removing the source of pain itself, but do not address the biological basis of the disease. Our increasing understanding of the molecular biological basis for degenerative disc disease has enabled the development of strategies aimed at tackling the causes of degeneration. Here we review the progress that has been made in strategies using cells, biomaterials and growth factors aimed at regenerating the human intervertebral disc.

Investigation of the role of IL-1 and TNF in matrix degradation in the intervertebral disc

OBJECTIVE

To establish if IL-1 or TNF regulates matrix degradation in the non-degenerate or degenerate intervertebral disc (IVD).

METHODS

In situ zymography (ISZ) has been used to investigate the role of IL-1 and TNF in the matrix degradation characterizing symptomatic IVD degeneration. ISZ employed three substrates (gelatin, collagen II, casein) and four different challenges, IL-1beta, IL-1 receptor antagonist (IL-1Ra), TNF-alpha and anti-TNF.

RESULTS

We have shown for the first time that whilst IL-1beta will stimulate and IL-1 receptor antagonist will inhibit matrix degradation in intact human IVD tissue, neither TNF-alpha nor anti-TNF have any measurable effect on degradation of these matrices.

CONCLUSION

This study has addressed a current area of controversy in IVD biology, namely, whether either IL-1 or TNF or both are involved in driving matrix degradation. Our data indicate that IL-1 is a key cytokine mediating matrix degradation in the IVD and therefore a therapeutic target.

Interleukin-1 receptor antagonist delivered directly and by gene therapy inhibits matrix degradation in the intact degenerate human intervertebral disc: an in situ zymographic and gene therapy study

Data implicate IL-1 in the altered matrix biology that characterizes human intervertebral disc (IVD) degeneration. In the current study we investigated the enzymic mechanism by which IL-1 induces matrix degradation in degeneration of the human IVD, and whether the IL-1 inhibitor IL-1 receptor antagonist (IL-1Ra) will inhibit degradation. A combination of in situ zymography (ISZ) and immunohistochemistry was used to examine the effects of IL-1 and IL-1Ra on matrix degradation and metal-dependent protease (MDP) expression in explants of non-degenerate and degenerate human IVDs. ISZ employed three substrates (gelatin, collagen, casein) and different challenges (IL-1β, IL-1Ra and enzyme inhibitors). Immunohistochemistry was undertaken for MDPs. In addition, IL-1Ra was introduced into degenerate IVD explants using genetically engineered constructs. The novel findings from this study are: IL-1Ra delivered directly onto explants of degenerate IVDs eliminates matrix degradation as assessed by multi-substrate ISZ; there is a direct relationship between matrix degradation assessed by ISZ and MDP expression defined by immunohistochemistry; single injections of IVD cells engineered to over-express IL-1Ra significantly inhibit MDP expression for two weeks. Our findings show that IL-1 is a key cytokine driving matrix degradation in the degenerate IVD. Furthermore, IL-1Ra delivered directly or by gene therapy inhibits IVD matrix degradation. IL-1Ra could be used therapeutically to inhibit degeneration of the IVD.

Facilitative glucose transporters in articular chondrocytes. Expression, distribution and functional regulation of GLUT isoforms by hypoxia, hypoxia mimetics, growth factors and pro-inflammatory cytokines

Articular cartilage is a unique and highly specialized avascular connective tissue in which the availability of oxygen and glucose is significantly lower than synovial fluid and plasma. Glucose is an essential source of energy during embryonic growth and fetal development and is vital for mesenchymal cell differentiation, chondrogenesis, and skeletal morphogenesis. Glucose is an important metabolic fuel for differentiated chondrocytes during postnatal development and in adult articular cartilage and is a common structural precursor for the synthesis of extracellular matrix glycosaminoglycans. Glucose metabolism is critical for growth plate chondrocytes which participate in long bone growth. Glucose concentrations in articular cartilage can fluctuate depending on age, physical activity, and endocrine status. Chondrocytes are glycolytic cells and must be able to sense the concentration of oxygen and glucose in the extracellular matrix and respond appropriately by adjusting cellular metabolism. Consequently chondrocytes must have the capacity to survive in an extracellular matrix with limited nutrients and low oxygen tensions. Published data from our laboratories suggest that chondrocytes express multiple isoforms of the GLUT/SLC2A family of glucose/polyol transporters. In other tissues GLUT proteins are expressed in a cell-specific manner, exhibit distinct kinetic properties, and are developmentally regulated. Several GLUTs expressed in chondrocytes are regulated by hypoxia, hypoxia mimetics, metabolic hormones, and proinflammatory cytokines. In this multidisciplinary text we review the molecular and morphological aspects of GLUT expression and function in chondrocytes and their mesenchymal and embryonic stem cell precursors and propose key roles for these proteins in glucose sensing and metabolic regulation in cartilage.