Expression of cytokeratin and vimentin in nucleus pulposus cells

Notochordal cells: A potential therapeutic option for intervertebral disc degeneration

Intervertebral disc degeneration (IDD) is a prevalent musculoskeletal degenerative disorder worldwide, and ~40% of chronic low back pain cases are associated with IDD. Although the pathogenesis of IDD remains unclear, the reduction in nucleus pulposus cells (NPCs) and degradation of the extracellular matrix (ECM) are critical factors contributing to IDD. Notochordal cells (NCs), derived from the notochord, which rapidly degrades after birth and is eventually replaced by NPCs, play a crucial role in maintaining ECM homeostasis and preventing NPCs apoptosis. Current treatments for IDD only provide symptomatic relief, while lacking the ability to inhibit or reverse its progression. However, NCs and their secretions possess anti-inflammatory properties and promote NPCs proliferation, leading to ECM formation. Therefore, in recent years, NCs therapy targeting the underlying cause of IDD has emerged as a novel treatment strategy. This article provides a comprehensive review of the latest research progress on NCs for IDD, covering their biological characteristics, specific markers, possible mechanisms involved in IDD and therapeutic effects. It also highlights significant future directions in this field to facilitate further exploration of the pathogenesis of IDD and the development of new therapies based on NCs strategies.

Conserved enhancers control notochord expression of vertebrate Brachyury

The cell type-specific expression of key transcription factors is central to development and disease. Brachyury/T/TBXT is a major transcription factor for gastrulation, tailbud patterning, and notochord formation; however, how its expression is controlled in the mammalian notochord has remained elusive. Here, we identify the complement of notochord-specific enhancers in the mammalian Brachyury/T/TBXT gene. Using transgenic assays in zebrafish, axolotl, and mouse, we discover three conserved Brachyury-controlling notochord enhancers, T3, C, and I, in human, mouse, and marsupial genomes. Acting as Brachyury-responsive, auto-regulatory shadow enhancers, in cis deletion of all three enhancers in mouse abolishes Brachyury/T/Tbxt expression selectively in the notochord, causing specific trunk and neural tube defects without gastrulation or tailbud defects. The three Brachyury-driving notochord enhancers are conserved beyond mammals in the brachyury/tbxtb loci of fishes, dating their origin to the last common ancestor of jawed vertebrates. Our data define the vertebrate enhancers for Brachyury/T/TBXTB notochord expression through an auto-regulatory mechanism that conveys robustness and adaptability as ancient basis for axis development.

Conserved enhancer logic controls the notochord expression of vertebrate Brachyury

The cell type-specific expression of key transcription factors is central to development. Brachyury/T/TBXT is a major transcription factor for gastrulation, tailbud patterning, and notochord formation; however, how its expression is controlled in the mammalian notochord has remained elusive. Here, we identify the complement of notochord-specific enhancers in the mammalian Brachyury/T/TBXT gene. Using transgenic assays in zebrafish, axolotl, and mouse, we discover three Brachyury-controlling notochord enhancers T3, C, and I in human, mouse, and marsupial genomes. Acting as Brachyury-responsive, auto-regulatory shadow enhancers, deletion of all three enhancers in mouse abolishes Brachyury/T expression selectively in the notochord, causing specific trunk and neural tube defects without gastrulation or tailbud defects. Sequence and functional conservation of Brachyury-driving notochord enhancers with the brachyury/tbxtb loci from diverse lineages of fishes dates their origin to the last common ancestor of jawed vertebrates. Our data define the enhancers for Brachyury/T/TBXTB notochord expression as ancient mechanism in axis development.

Single-Cell RNA Sequencing of the Nucleus Pulposus Reveals Chondrocyte Differentiation and Regulation in Intervertebral Disc Degeneration

The nucleus pulposus (NP), a heterogeneous tissue, is an essential functional component of the intervertebral disc. However, NP cell development route and regulation mechanism in intervertebral disc degeneration (IVDD) remain unknown. Here, we performed single-cell RNA sequencing of six NP samples with normal control, mild degeneration, and severe degeneration. Based on unbiased clustering of gene expression patterns from 30,300 single-cell RNA sequencing, we identified three cell lineage families of macrophages, endothelial, and chondrocyte cells and characterized seven chondrocyte subtypes, and defined two developmental pathways of the chondrocyte cell lineage families in the process of IVDD. Additionally, CellPhoneDB analysis revealed potential interactions between chondrocyte cells and other cells in IVDD. Chondrocytes in one of the differentiated orientations interact with macrophages and endothelial cells and have an inflammatory amplification effect, which were key factors causing IVDD. Collectively, these results revealed the dynamic cell landscape of IVDD development and offered new insights into the influence of NP cells differentiation on extracellular matrix homeostasis during degeneration, providing potential treatment targets for IVDD.

Nucleus Pulposus Cell Conditioned Medium Promotes Mesenchymal Stem Cell Differentiation into Nucleus Pulposus-Like Cells under Hypoxic Conditions

Low back pain (LBP) is a major physical and socioeconomic challenge worldwide. Nucleus pulposus (NP) is directly associated with LBP due to intervertebral disc (IVD) degeneration. IVD degeneration is mainly caused by structural and matrix-related changes within the IVD occurring during aging and degeneration. Mesenchymal stem cells (MSCs) can differentiate into multiple mesenchymal lineages under specific stimulatory conditions. This study is aimed at evaluating the effectiveness of the nucleus pulposus cell (NPC) conditioned medium for promoting the expression of MSCs and at confirming the expression of healthy NP phenotypic markers recently recommended by the Spine Research Interest Group. Expression was investigated using quantitative polymerase chain reaction (qPCR) and western blotting under normoxic and hypoxic conditions. qPCR and western blotting demonstrated significant upregulation of NP marker expression in MSCs cultured under hypoxic conditions and treated with the 50% or 100% NPC conditioned medium, compared with those cultured under normoxic conditions. Upregulation was highest in the presence of the 100% NPC conditioned medium compared with the control group (aggrecan, p < 0.01; brachyury, p < 0.05; collagen II, p < 0.001; KRT8, p < 0.01; KRT19, p < 0.001; and Shh, p < 0.01). The expression levels of genes in MSCs treated with the 50% NPC conditioned medium also showed upregulation compared with the control group (collagen II, p < 0.05; KRT8, p < 0.05; and KRT19, p < 0.01). These findings suggested that the NPC conditioned medium stimulated MSC differentiation into an NP-like phenotype with distinct characteristics. The results could inform strategies for IVD regeneration.

Notochordal-Cell-Derived Exosomes Induced by Compressive Load Inhibit Angiogenesis via the miR-140-5p/Wnt/β-Catenin Axis

Angiogenesis is a pathological signature of intervertebral disc degeneration (IDD). Accumulating evidence has shown that notochordal cells (NCs) play an essential role in maintaining intervertebral disc development and homeostasis with inhibitive effect on blood vessel in-growth. However, the anti-angiogenesis mechanism of NCs is still unclear. In the current study, we, for the first time, isolated NC-derived exosomes (NC-exos) and showed their increased concentration following compressive load cultures. We further found that NC-exos from 0.5 MPa compressive load cultures (0.5 MPa/NC-exos) inhibit angiogenesis via transferring high expressed microRNA (miR)-140-5p to endothelial cells and regulating the downstream Wnt/β-catenin pathway. Clinical evidence showed that exosomal miR-140-5p expression of the nucleus pulposus is negatively correlated with angiogenesis in IDD. Finally, 0.5 MPa/NC-exos were demonstrated to have a therapeutical impact on the degenerated disc with an anti-angiogenesis effect in an IDD model. Consequently, our present findings provide insights into the anti-angiogenesis mechanism of NC-exos, indicating their therapeutic potential for IDD.

Differential Response of Bovine Mature Nucleus Pulposus and Notochordal Cells to Hydrostatic Pressure and Glucose Restriction

OBJECTIVE

The nucleus pulposus of the human intervertebral disc contains 2 cell types: notochordal (NC) and mature nucleus pulposus (MNP) cells. NC cell loss is associated with disc degeneration and this process may be initiated by mechanical stress and/or nutrient deprivation. This study aimed to investigate the functional responses of NC and MNP cells to hydrostatic pressures and glucose restriction.

DESIGN

Bovine MNP and NC cells were cultured in 3-dimensional alginate beads under low (0.4-0.8 MPa) and high (1.6-2.4 MPa) dynamic pressure for 24 hours. Cells were cultured in either physiological (5.5 mM) glucose media or glucose-restriction (0.55 mM) media. Finally, the combined effect of glucose restriction and high pressure was examined.

RESULTS

Cell viability and notochordal phenotypic markers were not significantly altered in response to pressure or glucose restriction. MNP cells responded to low pressure with an increase in glycosaminoglycan (GAG) production while high pressure significantly decreased ACAN gene expression compared with atmospheric controls. NC cells showed no response in matrix gene expression or GAG production with either loading regime. Glucose restriction decreased NC cell TIMP-1 expression but had no effect on MNP cells. The combination of glucose restriction and high pressure only affected MNP cell gene expression, with decreased ACAN, Col2α1, and ADAMTS-5 expression.

CONCLUSION

This study shows that NC cells are more resistant to acute mechanical stresses than MNP cells and provides a strong rationale for future studies to further our understanding the role of NC cells within the disc, and the effects of long-term exposure to physical stresses.

Disordered Mechanical Stress and Tissue Engineering Therapies in Intervertebral Disc Degeneration

Low back pain (LBP), commonly induced by intervertebral disc degeneration, is a lumbar disease with worldwide prevalence. However, the mechanism of degeneration remains unclear. The intervertebral disc is a nonvascular organ consisting of three components: Nucleus pulposus, annulus fibrosus, and endplate cartilages. The disc is structured to support our body motion and endure persistent external mechanical pressure. Thus, there is a close connection between force and intervertebral discs in LBP. It is well established that with aging, disordered mechanical stress profoundly influences the fate of nucleus pulposus and the alignment of collagen fibers in the annulus fibrosus. These support a new understanding that disordered mechanical stress plays an important role in the degeneration of the intervertebral discs. Tissue-engineered regenerative and reparative therapies are being developed for relieving disc degeneration and symptoms of lower back pain. In this paper, we will review the current literature available on the role of disordered mechanical stress in intervertebral disc degeneration, and evaluate the existing tissue engineering treatment strategies of the current therapies.

Mechanotransduction and cell biomechanics of the intervertebral disc

Mechanical loading of the intervertebral disc (IVD) initiates cell-mediated remodeling events that contribute to disc degeneration. Cells of the IVD, nucleus pulposus (NP) and anulus fibrosus (AF), will exhibit various responses to different mechanical stimuli which appear to be highly dependent on loading type, magnitude, duration, and anatomic zone of cell origin. Cells of the NP, the innermost region of the disc, exhibit an anabolic response to low-moderate magnitudes of static compression, osmotic pressure, or hydrostatic pressure, while higher magnitudes promote a catabolic response marked by increased protease expression and activity. Cells of the outer AF are responsive to physical forces in a manner that depends on frequency and magnitude, as are cells of the NP, though they experience different forces, deformations, pressure, and osmotic pressure in vivo. Much remains to be understood of the mechanotransduction pathways that regulate IVD cell responses to loading, including responses to specific stimuli and also differences among cell types. There is evidence that cytoskeletal remodeling and receptor-mediated signaling are important mechanotransduction events that can regulate downstream effects like gene expression and posttranslational biosynthesis, all of which may influence phenotype and bioactivity. These and other mechanotransduction events will be regulated by known and to-be-discovered cell-matrix and cell-cell interactions, and depend on composition of extracellular matrix ligands for cell interaction, matrix stiffness, and the phenotype of the cells themselves. Here, we present a review of the current knowledge of the role of mechanical stimuli and the impact upon the cellular response to loading and changes that occur with aging and degeneration of the IVD.

Meniscus, articular cartilage and nucleus pulposus: a comparative review of cartilage-like tissues in anatomy, development and function

The degradation of cartilage in the human body is impacted by aging, disease, genetic predisposition and continued insults resulting from daily activity. The burden of cartilage defects (osteoarthritis, rheumatoid arthritis, intervertebral disc damage, knee replacement surgeries, etc.) is daunting in light of substantial economic and social stresses. This review strives to broaden the scope of regenerative medicine and tissue engineering approaches used for cartilage repair by comparing and contrasting the anatomical and functional nature of the meniscus, articular cartilage (AC) and nucleus pulposus (NP). Many review papers have provided detailed evaluations of these cartilages and cartilage-like tissues individually but none have comprehensively examined the parallels and inconsistencies in signaling, genetic expression and extracellular matrix composition between tissues. For the first time, this review outlines the importance of understanding these three tissues as unique entities, providing a comparative analysis of anatomy, ultrastructure, biochemistry and function for each tissue. This novel approach highlights the similarities and differences between tissues, progressing research toward an understanding of what defines each tissue as distinctive. The goal of this paper is to provide researchers with the fundamental knowledge to correctly engineer the meniscus, AC and NP without inadvertently developing the wrong tissue function or biochemistry.

IMAGING DIAGNOSIS-MAGNETIC RESONANCE IMAGING AND HISTOPATHOLOGICAL FEATURES OF A SKULL BASE CHORDOMA IN A CAT

An 8-year-old domestic short-haired cat was presented with anorexia, lethargy, ataxia and one episode of consciousness loss. A midline vertically orientated, biconcave, extra-axial mass originating from the basioccipital bone was detected on magnetic resonance images of the head. The mass was T1W iso- to hypointense when compared with normal grey matter, T2W hyperintense with small areas of isointensity and heterogeneously enhanced with contrast. Multiple signal voids were observed on T2^* images. Histopathological evaluation confirmed a chordoma. To the authors' knowledge this is the first report of the imaging characteristics of a chordoma affecting the skull base in a cat.

Histochemical and immunohistochemical characterization of chordoma in ferrets

Chordomas of the tip of the tail in 6 ferrets were examined using histopathological, histochemical and immunohistochemical procedures. Histopathologically, round neoplastic cells containing numerous cytoplasmic vacuoles of varying sizes, categorized as “physaliphorous cells”, were observed in the amorphous eosinophilic or pale basophilic myxoid stroma. Physaliphorous cells were arranged in lobules and in a “chordoid” or “cobblestone” manner. The neoplasms were diagnosed as benign chordoma without local invasion and metastasis. Histochemically, the cytoplasm of small neoplastic cells was positive for periodic acid-Schiff stain and alcian blue (AB) pH 2.5 and pH 1.0 stains, but negative for hyaluronidase digestion-AB pH 2.5 stain. All neoplastic cells were strongly stained with colloidal ion, negative for high iron diamine AB pH 2.5 and toluidine blue pH 2.5 stains, and positive for Mayer’s mucicarmine stain. Immunohistochemistry using antibodies directed against low-molecular-weight cytokeratins (CK18, CK19 and CK20), vimentin and mucin core protein (MUC5AC) revealed that neoplastic cells had both epithelial and mesenchymal elements. The expression of low-molecular-weight cytokeratins suggests that neoplastic cells acquired the properties of glandular epithelial cells and produced epithelial mucus. Furthermore, the expression of cytokeratins, vimentin, S100 protein, brachyury and epithelial membrane antigen indicates that the neoplasms were equivalent to the classic type of human chordoma. Therefore, immunohistochemistry using these antibodies can be useful for the characterization of ferret chordoma.

Phenotypic stability, matrix elaboration and functional maturation of nucleus pulposus cells encapsulated in photocrosslinkable hyaluronic acid hydrogels

Degradation of the nucleus pulposus (NP) is an early hallmark of intervertebral disc degeneration. The capacity for endogenous regeneration in the NP is limited due to the low cellularity and poor nutrient and vascular supply. Towards restoring the NP, a number of biomaterials have been explored for cell delivery. These materials must support the NP cell phenotype while promoting the elaboration of an NP-like extracellular matrix in the shortest possible time. Our previous work with chondrocytes and mesenchymal stem cells demonstrated that hydrogels based on hyaluronic acid (HA) are effective at promoting matrix production and the development of functional material properties. However, this material has not been evaluated in the context of NP cells. Therefore, to test this material for NP regeneration, bovine NP cells were encapsulated in 1%w/vol HA hydrogels at either a low seeding density (20×10(6)cellsml(-1)) or a high seeding density (60×10(6)cellsml(-1)), and constructs were cultured over an 8week period. These NP cell-laden HA hydrogels showed functional matrix accumulation, with increasing matrix content and mechanical properties with time in culture at both seeding densities. Furthermore, encapsulated cells showed NP-specific gene expression profiles that were significantly higher than expanded NP cells prior to encapsulation, suggesting a restoration of phenotype. Interestingly, these levels were higher at the lower seeding density compared to the higher seeding density. These findings support the use of HA-based hydrogels for NP tissue engineering and cellular therapies directed at restoration or replacement of the endogenous NP.

The role of extracellular matrix elasticity and composition in regulating the nucleus pulposus cell phenotype in the intervertebral disc: a narrative review

Intervertebral disc (IVD) disorders are a major contributor to disability and societal health care costs. Nucleus pulposus (NP) cells of the IVD exhibit changes in both phenotype and morphology with aging-related IVD degeneration that may impact the onset and progression of IVD pathology. Studies have demonstrated that immature NP cell interactions with their extracellular matrix (ECM) may be key regulators of cellular phenotype, metabolism and morphology. The objective of this article is to review our recent experience with studies of NP cell-ECM interactions that reveal how ECM cues can be manipulated to promote an immature NP cell phenotype and morphology. Findings demonstrate the importance of a soft (&lt;700 Pa), laminin-containing ECM in regulating healthy, immature NP cells. Knowledge of NP cell-ECM interactions can be used for development of tissue engineering or cell delivery strategies to treat IVD-related disorders.

Same-species phenotypic comparison of notochordal and mature nucleus pulposus cells

PURPOSE

The ratio of notochordal (NC) cells to mature nucleus pulposus (MNP) cells in the nucleus pulposus varies with species, age and health. Studies suggest that loss of NC cells is a key component of intervertebral disc degeneration. However, few studies have examined the phenotypes of these two cell populations. Therefore, this study aimed to isolate NC and MNP cells from the same intervertebral disc and study phenotypic differences in extracellular matrix production and cell morphology in 3D culture over 7 days.

METHODS

Sequential mechanical dissociation and enzymatic digestion were used to isolate NC cell clusters and single MNP cells from bovine caudal discs. Cells were cultured in alginate beads and subsequently analysed for viability, cytokeratin-8 expression, GAG production and extracellular matrix gene expression.

RESULTS

Mechanical dissociation allowed NC cells to be extracted as intact cell clusters. NC cells represented 8% of the NP cell population and expressed both cytokeratin-8 and vimentin. MNP cells expressed vimentin, only. Both cells types were viable for 7 days. In addition to morphological differences, NC cells produced up to 30 times more total proteoglycan than MNP cells. NC cells had significantly higher aggrecan and brachyury expression.

CONCLUSIONS

NC and MNP cells can be isolated from the same bovine disc and maintain their distinct phenotypes in 3D culture.

Loss of notochordal cell phenotype in 3D-cell cultures: implications for disc physiology and disc repair

INTRODUCTION

Embryonic notochordal disc nucleus cells (NC) have been identified to protect disc tissue against disc degeneration but in human beings NC phenotype gets lost with aging and the pathophysiological mechanisms are poorly understood. NC may stimulate other cells via soluble factors, and NC-conditioned medium can be used to stimulate matrix production of other disc cells and mesenchymal stem cells and thus may be of special interest for biological disc repair. As this stimulatory effect is associated with the NC phenotype, we investigated how cell morphology and gene-expression of the NC phenotype changes with time in 3D-cell culture.

MATERIALS AND METHODS

NC and inner annulus chondrocyte-like cells (CLC) from immature pigtails (freshly isolated cells/tissue, 3D-alginate beads, 3D-clusters) were cultured for up to 16 days under normoxia and hypoxia. Protein-expression was analysed by immunohistology and gene-expression analysis was carried out on freshly isolated cells and cultured cells. Cell morphology and proliferation were analysed by two-photon-laser-microscopy.

RESULTS

Two-photon-laser-microscopy showed a homogenous and small CLC population in the inner annulus, which differed from the large vacuole-containing NC in the nucleus. Immunohistology found 93 % KRT8 positive cells in the nucleus and intracellular and pericellular Col2, IL6, and IL12 staining while CLC were KRT8 negative. Freshly isolated NC showed significantly higher KRT8 and CAIII but lower Col2 gene-expression than CLC. NC in 3D-cultures demonstrated significant size reduction and loss of vacuoles with culture time, all indicating a loss of the characteristic NC morphology. Hypoxia reduced the rate of decrease in NC size and vacuoles. Gene-expression of KRT8 and CAIII in NC fell significantly early in culture while Col2 did not decrease significantly within the culture period. In CLC, KRT8 and CAIII gene-expression was low and did not change noticeably in culture, whereas Col2 expression fell with time in culture.

CONCLUSIONS

3D-culture caused a rapid loss of NC phenotype towards a CLC phenotype with disappearance of vacuoles, reduced cell size, increased proliferation, and gene-expression changes. These findings may be related to NC nutritional demands and support the latest hypothesis of NC maturation into CLC opposing the idea that NC get lost in human discs by cell death or apoptosis to be replaced by CLC from the inner annulus.

Native nucleus pulposus tissue matrix promotes notochordal differentiation of human induced pluripotent stem cells with potential for treating intervertebral disc degeneration

Native porcine nucleus pulposus (NP) tissue harbors a number of notochordal cells (NCs). Whether the native NP matrix supports the homeostasis of notochordal cells is poorly understood. We hypothesized the NP matrix alone may contain sufficient regulatory factors and can serve as stimuli to generate notochordal cells (NCs) from human pluripotent stem cells. NCs are a promising cell sources for cell-based therapy to treat some types of intervertebral disc (IVD) degeneration. One major limitation of this emerging technique is the lack of available NCs as a potential therapeutic cell source. Human pluripotent stem cells derived from reprogramming or somatic cell nuclear transfer technique may yield stable and unlimited source for therapeutic use. We devised a new method to use porcine NP matrix to direct notochordal differentiation of human induced pluripotent stem cells (hiPSCs). The results showed that hiPSCs successfully differentiated into NC-like cells under the influence of devitalized porcine NP matrix. The NC-like cells expressed typical notochordal marker genes including brachyury (T), cytokeratin-8 (CK-8) and cytokeratin-18 (CK-18), and they displayed the ability to generate NP-like tissue in vitro, which was rich in aggrecan and collagen type II. These findings demonstrated the proof of concept for using native NP matrix to direct notochordal differentiation of hiPSCs. It provides a foundation for further understanding the biology of NCs, and eventually towards regenerative therapies for disc degeneration.

CK8 phosphorylation induced by compressive loads underlies the downregulation of CK8 in human disc degeneration by activating protein kinase C

Cytokeratin 8 (CK8) is a member of the cytokeratins family with multiple functions on the basis of its unique structural hallmark. The aberrant expression of CK8 and its phosphorylation are pertinent with various diseases. We have previously shown that CK8 exists in normal human nucleus pulposus (NP) cells and decreases as the intervertebral disc degenerates. However, the underlying molecular regulatory machinery of CK8 in intervertebral disc degeneration (IDD) has not been clarified. Here, we collected NP samples from patients with idiopathic scoliosis as control and IDD as degenerate groups. We found that CK8 expression decreased in IDD with an increased phosphorylation in degenerate NP cells. Moreover, NP cells were cultured under different compressive load schemes for diverse time duration. We found that compressive loads resulted in phosphorylation and disassembly of CK8 in a time-dependent and degree-dependent manner in vitro. The activation of protein kinase C was a significant molecular factor contributing to this phenomenon. Taken together, this study is the first to address the molecular mechanisms of CK8 downregulation in NP cells. Importantly, our findings provide clues regarding a molecular link between compressive loads and CK8 alterations, which shed a novel light on the etiology of IDD.

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

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

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.

Gene expression profiling of early intervertebral disc degeneration reveals a down-regulation of canonical Wnt signaling and caveolin-1 expression: implications for development of regenerative strategies

INTRODUCTION

Early degeneration of the intervertebral disc (IVD) involves a change in cellular differentiation from notochordal cells (NCs) in the nucleus pulposus (NP) to chondrocyte-like cells (CLCs). The purpose of this study was to investigate the gene expression profiles involved in this process using NP tissue from non-chondrodystrophic and chondrodystrophic dogs, a species with naturally occurring IVD degeneration.

METHODS

Dual channel DNA microarrays were used to compare 1) healthy NP tissue containing only NCs (NC-rich), 2) NP tissue with a mixed population of NCs and CLCs (Mixed), and 3) NP tissue containing solely CLCs (CLC-rich) in both non-chondrodystrophic and chondrodystrophic dogs. Based on previous reports and the findings of the microarray analyses, canonical Wnt signaling was further evaluated using qPCR of relevant Wnt target genes. We hypothesized that caveolin-1, a regulator of Wnt signaling that showed significant changes in gene expression in the microarray analyses, played a significant role in early IVD degeneration. Caveolin-1 expression was investigated in IVD tissue sections and in cultured NCs. To investigate the significance of Caveolin-1 in IVD health and degeneration, the NP of 3-month-old Caveolin-1 knock-out mice was histopathologically evaluated and compared with the NP of wild-type mice of the same age.

RESULTS

Early IVD degeneration involved significant changes in numerous pathways, including Wnt/β-catenin signaling. With regard to Wnt/β-catenin signaling, axin2 gene expression was significantly higher in chondrodystrophic dogs compared with non-chondrodystrophic dogs. IVD degeneration involved significant down-regulation of axin2 gene expression. IVD degeneration involved significant down-regulation in Caveolin-1 gene and protein expression. NCs showed abundant caveolin-1 expression in vivo and in vitro, whereas CLCs did not. The NP of wild-type mice was rich in viable NCs, whereas the NP of Caveolin-1 knock-out mice contained chondroid-like matrix with mainly apoptotic, small, rounded cells.

CONCLUSIONS

Early IVD degeneration involves down-regulation of canonical Wnt signaling and Caveolin-1 expression, which appears to be essential to the physiology and preservation of NCs. Therefore, Caveolin-1 may be regarded an exciting target for developing strategies for IVD regeneration.

Down-regulated CK8 expression in human intervertebral disc degeneration

As an intermediate filament protein, cytokeratin 8 (CK8) exerts multiple cellular functions. Moreover, it has been identified as a marker of notochord cells, which play essential roles in human nucleus pulposus (NP). However, the distribution of CK8 positive cells in human NP and their relationship with intervertebral disc degeneration (IDD) have not been clarified until now. Here, we found the percentage of CK8 positive cells in IDD (25.7±4.14%) was significantly lower than that in normal and scoliosis NP (51.9±9.73% and 47.8±5.51%, respectively, p<0.05). Western blotting and qRT-PCR results confirmed the down-regulation of CK8 expression in IDD on both of protein and mRNA levels. Furthermore, approximately 37.4% of cell clusters were CK8 positive in IDD. Taken together, this is the first study to show a down-regulated CK8 expression and the percentage of CK8 positive cell clusters in IDD based upon multiple lines of evidence. Consequently, CK8 positive cells might be considered as a potential option in the development of cellular treatment strategies for NP repair.

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.

Benign notochordal lesions of the axial skeleton: a review and current appraisal

At the 1996 meeting of the International Skeletal Society, an idea was put forth that there existed symptomatic lesions of the axial skeleton, morphologically different from chordoma, that were consistent with benign notochordal remnants (rests). A review of the embryological basis for this concept is made, along with an analysis of these lesions, termed giant notochordal rests or benign notochordal cell tumors, that have been reported in the intervening 15 years, with a commentary on their relationship, if any, to chordoma.

Notochordal cells in the adult intervertebral disc: new perspective on an old question

The intervertebral disc is a tissue positioned between each of the vertebrae that accommodates applied biomechanical forces to the spine. The central compartment of the disc contains the nucleus pulposus (NP) which is enclosed by the annulus fibrosus and the endplate cartilage.The NP is derived from the notochord, a rod-like structure of mesodermal origin. Development of the notochord is tightly regulated by interactive transcription factors and target genes. Since a number of these molecules are unique they have be used for cell lineage and fate mapping studies of tissues of the intervertebral disc. These studies have shown that in a number of species including human, NP tissue retains notochordal cells throughout life. In the adult NP, there are present both large and small notochordal cells, as well as a progenitor cell population which can differentiate along the mesengenic pathway. Since tissue renewal in the intervertebral disc is dependent on the ability of these cells to commit to the NP lineage and undergo terminal differentiation, studies have been performed to assess which signaling pathways may regulate these activities. The notch signaling pathway is active in the intervertebral disc and is responsive to hypoxia, probably through HIF-1a. From a disease viewpoint, it is hypothesized that an oxemic shift, possibly mediated by alterations in the vascular supply to the tissues of the disc would be expected to lead to a failure in notochordal progenitor cell activation and a decrease in the number of differentiated cells. In turn, this would lead to decrements in function and enhancement of the effect of agents that are known to promote disc degeneration.

Toward an understanding of the role of notochordal cells in the adult intervertebral disc: from discord to accord

The goal of this mini-review is to address the long standing argument that the pathogenesis of disc disease is due to the loss and/or the replacement of the notochordal cells by other cell types. We contend that, although cells of different size and morphology exist, there is no strong evidence to support the view that the nucleus pulposus contains cells of distinct lineages. Based on lineage mapping studies and studies of other notochordal markers, we hypothesize that in all animals, including human, nucleus pulposus retains notochordal cells throughout life. Moreover, all cells including chondrocyte-like cells are derived from notochordal precursors, and variations in morphology and size are representative of different stages of maturation, and or, function. Thus, the most critical choice for a suitable animal model should relate more to the anatomical and mechanical characteristics of the motion segment than concerns of cell loss and replacement by non-notochordal cells.

Transcriptional profiling of the nucleus pulposus: say yes to notochord

This editorial addresses the debate concerning the origin of adult nucleus pulposus cells in the light of profiling studies by Minogue and colleagues. In their report of several marker genes that distinguish nucleus pulposus cells from other related cell types, the authors provide novel insights into the notochordal nature of the former. Together with recently published work, their work lends support to the view that all cells present within the nucleus pulposus are derived from the notochord. Hence, the choice of an animal model for disc research should be based on considerations other than the cell loss and replacement by non-notochordal cells.

Immunohistochemical identification of notochordal markers in cells in the aging human lumbar intervertebral disc

The fate of notochord cells during disc development and aging is still a subject of debate. Cells with the typical notochordal morphology disappear from the disc within the first decade of life. However, the pure morphologic differentiation of notochordal from non-notochordal disc cells can be difficult, prompting the use of cellular markers. Previous reports on these notochordal cell markers only explored the occurrence in young age groups without considering changes during disc degeneration. The aim of this study, therefore, was to investigate presence, localization, and abundance of cells expressing notochordal cell markers in human lumbar discs during disc development and degeneration. Based on pilot studies, cytokeratins CK-8, -18 and -19 as well as Galectin-3 were chosen from a broad panel of potential notochordal cell markers and used for immunohistochemical staining of 30 human lumbar autopsy samples (0-86 years) and 38 human surgical disc samples (26-69 years). In the autopsy group, 80% of fetal to adolescent discs (0-17 years) and 100% of young adult discs (18-30 years) contained many cells with positive labeling. These cells were strongly clustered and nearly exclusively located in areas with granular changes (or other matrix defects), showing predominantly a chondrocytic morphology as well as (in a much lesser extent) a fibrocytic phenotype. In mature discs (31-60 years) and elderly discs (≥ 60 years) only 25 and 22-33%, respectively, contained few stained nuclear cells, mostly associated with matrix defects. In the surgical group, only 16% of samples from young adults (≤ 47 years) exhibited positively labeled cells whereas mature to old surgical discs (>47 years) contained no labeled cells. This is the first study describing the presence and temporo-spatial localization of cells expressing notochordal cell markers in human lumbar intervertebral discs of all ages and variable degree of disc degeneration. Our findings indicate that cells with a (immunohistochemically) notochord-like phenotype are present in a considerable fraction of adult lumbar intervertebral discs. The presence of these cells is associated with distinct features of (early) age-related disc degeneration, particularly with granular matrix changes.

Variations in gene and protein expression in human nucleus pulposus in comparison with annulus fibrosus and cartilage cells: potential associations with aging and degeneration

OBJECTIVE

Regardless of recent progress in the elucidation of intervertebral disc (IVD) degeneration, the basic molecular characteristics that define a healthy human IVD are largely unknown. Although work in different animal species revealed distinct molecules that might be used as characteristic markers for IVD or specifically nucleus pulposus (NP) cells, the validity of these markers for characterization of human IVD cells remains unknown.

DESIGN

Eleven potential marker molecules were characterized with respect to their occurrence in human IVD cells. Gene expression levels of NP were compared with annulus fibrosus (AF) and articular cartilage (AC) cells, and potential correlations with aging were assessed.

RESULTS

Higher mRNA levels of cytokeratin-19 (KRT19) and of neural cell adhesion molecule-1 were noted in NP compared to AF and AC cells. Compared to NP cytokeratin-18 expression was lower in AC, and alpha-2-macroglobulin and desmocollin-2 lower in AF. Cartilage oligomeric matrix protein (COMP) and glypican-3 expression was higher in AF, while COMP, matrix gla protein (MGP) and pleiotrophin expression was higher in AC cells. Furthermore, an age-related decrease in KRT19 and increase in MGP expression were observed in NP cells. The age-dependent expression pattern of KRT19 was confirmed by immunohistochemistry, showing the most prominent KRT19 immunoreaction in the notochordal-like cells in juvenile NP, whereas MGP immunoreactivity was not restricted to NP cells and was found in all age groups.

CONCLUSIONS

The gene expression of KRT19 has the potential to characterize human NP cells, whereas MGP cannot serve as a characteristic marker. KRT19 protein expression was only detected in NP cells of donors younger than 54 years.

Differential expression level of cytokeratin 8 in cells of the bovine nucleus pulposus complicates the search for specific intervertebral disc cell markers

INTRODUCTION

Development of cell therapies for repairing the intervertebral disc is limited by the lack of a source of healthy human disc cells. Stem cells, particularly mesenchymal stem cells, are seen as a potential source but differentiation strategies are limited by the lack of specific markers that can distinguish disc cells from articular chondrocytes.

METHODS

We searched for markers using the differential in-gel electrophoresis proteomic technology to compare proteins of bovine nucleus pulposus cells, phenotypically similar to mature human nucleus cells, with those of bovine articular chondrocytes. In the cohort of the differentially expressed proteins identified by mass spectrometry, cytokeratin 8 (CK8) was further validated by immunostaining of freshly isolated cells and frozen tissue sections using monoclonal antibodies.

RESULTS

We identified a set of 14 differentially expressed proteins. Immunohistochemistry showed that only a subset of cells (approximately 10%) was positive for one of these proteins, CK8, an intermediate filament protein present in epithelial but not mesenchymal cells. In tissue sections, CK8-positive cells were seen in all discs examined and appeared as small isolated clusters surrounded by gelatinous matrix. Notochordal nucleus pulposus cells from pig, phenotypically similar to human infant nucleus pulposus cells, were all CK8-positive. The mesenchymal intermediate filament protein vimentin was present in all bovine and porcine nucleus pulposus cells.

CONCLUSIONS

The notochordal cell population is reported to disappear from the nucleus pulposus of bovine discs before birth and from human discs in childhood. However our finding of the co-expression of vimentin and CK8 in small isolated clusters of the bovine nucleus pulposus cells indicates that a subpopulation of notochordal-like cells remains in the mature bovine disc. This finding agrees with reports in the literature on co-expression of cytokeratins and vimentin in adult human discs. As notochordal cells produce factors that promote matrix production, the CK8-positive subpopulation could have important implications for activity and survival of the nucleus pulposus, and should be considered in development of cell therapies for disc repair. In addition, the finding of differential expression of proteins in the cell population of nucleus pulposus has implications with regard to the search for specific markers.

A new porcine in vivo animal model of disc degeneration: response of anulus fibrosus cells, chondrocyte-like nucleus pulposus cells, and notochordal nucleus pulposus cells to partial nucleotomy

STUDY DESIGN

In vivo animal study.

OBJECTIVES

To describe a new porcine disc degeneration model, and to analyze disc remodeling and degeneration after nucleotomy with special view to the different nucleus pulposus (NP) cell types.

SUMMARY OF BACKGROUND DATA

Thus far, predominantly smaller animals were used for disc degeneration models; however, such small discs were inappropriate to investigate cell implementation therapies. Though notochordal cells (NCs) are important for disc formation and maintenance, differences in the amount of NCs between human and animal discs have often been neglected.

METHODS

Twenty-four Goettingen minipigs underwent partial nucleotomy with a 16G biopsy cannula, to remove approximately 10% of total NP volume. Animals were followed up for 3, or 24 weeks and analyzed by radiographs, MRIs, (immuno)histology, gene expression analysis, and biomechanical testing.

RESULTS

Three weeks after nucleotomy disc height was reduced by 26%, and magnetic resonance imaging signal intensity by 40%. At 24 weeks disc height was decreased by 32%. Increased degenerative changes were found in a histodegeneration score 3 and 24 weeks after nucleotomy, as well as considerable NP scarification after 3 weeks. In controls, cytokeratin-8 immunohistochemistry identified NCs in proximity to chondrocyte-like NP cells at approximately equal ratio. After nucleotomy, NCs were considerably reduced to <10% of total NP cells. Matrix genes were upregulated, except for aggrecan that decreased to 35% of initial values 3 weeks after nucleotomy. Matrix degrading factors (matrix metalloproteinases 13 and 3) were continuously upregulated, whereas transcripts of their inhibitors (tissue inhibitors of matrix metalloproteinase 2 and 3) were downregulated. No significant changes in segmental spinal flexibility or bone density were found after nucleotomy.

CONCLUSION

We introduced a new disc degeneration model with relatively large discs that could be used for cell therapeutic approaches. The study gives further information about disc remodeling after nucleotomy and indicates the relevance of an altered cellular composition for the development of disc degeneration.

Differential phenotype of intervertebral disc cells: microarray and immunohistochemical analysis of canine nucleus pulposus and anulus fibrosus

STUDY DESIGN

Microarray gene expression profiling, quantitative gene expression analysis, and immunohistochemistry was used to investigate molecular variations between nucleus pulposus (NP) and anulus fibrosus (AF) of the dog intervertebral disc (IVD).

OBJECTIVE

To identify specific molecules with differing expression patterns in NP and AF and compare their profile with articular cartilage (AC).

SUMMARY OF BACKGROUND DATA

Although experimental and animal studies have demonstrated the potential of cell based approaches for NP regeneration, there is still a deficiency of basic knowledge about the phenotype of IVD cells.

METHODS

Comparative microarray analysis of beagle lumbar NP and AF was performed. Molecules of interest were evaluated by quantitative reverse transcriptase-polymerase chain reaction and immunohistochemistry, comparing lumbar and coccygeal NP and AF and AC. To assess interspecies variations, genes that had been found differentially expressed in rat tissues were also investigated.

RESULTS

Forty-five genes with NP/AF signal log ratio > or = 1 were identified. Alpha-2-macroglobulin, cytokeratin-18, and neural cell adhesion molecule (CD56) mRNA were higher in NP compared to AF and AC, and desmocollin-2 mRNA was higher in NP than AF. The expression profiles were similar in lumbar and coccygeal discs, although certain variations were noticed. Interspecies differences between rat and dog were evident in the expression of several genes. Immunohistochemistry confirmed differences in gene expression at the protein level.

CONCLUSION

This study reports on the expression of molecules that have not been described previously in IVD, in non-notochordal discs comparable with human. Interspecies differences were noted between rat and dog tissues, whereas variations between caudal and lumbar discs were less prominent. The NP of the beagle as a chondrodystrophoid dog breed is potentially more similar to the human than the NP of species whose discs do not naturally degenerate. Therefore, studies on appropriate species may contribute to a better understanding of the cell types residing in the IVD.

The Potential of N-Rich Plasma-Polymerized Ethylene (PPE:N) Films for Regulating the Phenotype of the Nucleus Pulposus

We recently developed a nitrogen-rich plasma-polymerized biomaterial, designated “PPE:N” (N-doped plasma-polymerized ethylene) that is capable of suppressing cellular hypertrophy while promoting type I collagen and aggrecan expression in mesenchymal stem cells from osteoarthritis patients. We then hypothesized that these surfaces would form an ideal substrate on which the nucleus pulposus (NP) phenotype would be maintained. Recent evidence using microarrays showed that in young rats, the relative mRNA levels of glypican-3 (GPC3) and pleiotrophin binding factor (PTN) were significantly higher in nucleus pulposus (NP) compared to annulus fibrosus (AF) and articular cartilage. Furthermore, vimentin (VIM) mRNA levels were higher in NP versus articular cartilage. In contrast, the levels of expression of cartilage oligomeric matrix protein (COMP) and matrix gla protein precursor (MGP) were lower in NP compared to articular cartilage. The objective of this study was to compare the expression profiles of these genes in NP cells from fetal bovine lumbar discs when cultured on either commercial polystyrene (PS) tissue culture dishes or on PPE:N with time. We found that the expression of these genes varies with the concentration of N ([N]). More specifically, the expression of several genes of NP was sensitive to [N], with a decrease of GPC3, VIM, PTN, and MGP in function of decreasing [N]. The expression of aggrecan, collagen type I, and collagen type II was also studied: no significant differences were observed in the cells on different surfaces with different culture time. The results support the concept that PPE:N may be a suitable scaffold for the culture of NP cells. Further studies are however necessary to better understand their effects on cellular phenotypes.

The role of extracellular factors in human metastatic chordoma cell growth in vitro

STUDY DESIGN

Human metastatic chordoma cells were isolated, and initial in vitro characterization was performed. Biochemical and physiologic changes were observed in response to pH, oxygen, and glucose.

OBJECTIVE

The extracellular microenvironment directly affects metastatic chordoma cell phenotype in vitro.

SUMMARY OF BACKGROUND DATA

Chordomas are primary bone tumors that usually occur in the spine or skull. Chordomas arise from embryonic notochordal remnants along the axial skeleton, most commonly the sacrum, followed by the base of the skull and the mobile spine. Due to a high degree of resistance to radiation and chemotherapy, chordomas eventually cause death by direct growth or by metastasizing to other organs.

METHODS

Extracellular pH, oxygen, and glucose levels in the culture medium were controlled, and cell response was assessed using MTT staining, SDS-PAGE, Western blotting, tandem mass spectrometry, TUNEL, immunofluorescence, and flow cytometry.

RESULTS

In this study, we present a new chordoma cell line established from metastatic tissue and novel data characterizing some aspects of chordoma cell phenotype in different conditions in vitro. Chordoma biologic markers were expressed in the new cell line. Alkaline pH dramatically increased intracellular protein tyrosine phosphorylation, metabolic activity, and albumin accumulation in the cells, while acidic pH caused apoptosis.

CONCLUSION

The level of proliferation, apoptosis, and tyrosine phosphorylation, as well as the overall protein expression profile, strongly depended on extracellular media pH and oxygen/glucose levels. Chordoma's preferred extracellular microenvironment in vitro was rather alkaline, with an optimum at pH 8.5, and apoptotic changes were induced at acidic pH. We found that bovine serum albumin was accumulated by chordoma cells from the incubation media, and this accumulation depended on extracellular pH, with the highest accumulation at alkaline pH.

HIF-1 alpha is a regulator of galectin-3 expression in the intervertebral disc

The regulation of galectin-3 expression in skeletal tissues is not completely understood. Our studies indicate that HIF-1 alpha regulates galectin-3 expression by interacting with hypoxia regulatory elements in the promoter region. Finally, we show that galectin-3 serves a prosurvival role in the intervertebral disc.

INTRODUCTION

Earlier reports indicated that galectin-3 (gal-3) is highly expressed in the epiphyseal growth plate cartilage and the intervertebral disc. Because these skeletal tissues have a limited vascular supply and the cells reside in a low O2 environment, we determined if the oxemic status modulates gal-3 expression.

MATERIALS AND METHODS

Cells were cultured in normoxia (21% O2) or hypoxia (2% O2), and gal-3 expression and promoter activity were evaluated. Interaction of hypoxia inducible factor (HIF)-1 alpha with the gal-3 promoter was confirmed by gel shift and site-directed mutagenesis.

RESULTS

There was minimal oxygen-dependent change in HIF-1 alpha levels and no change in gal-3 expression and promoter activity in nucleus pulposus cells. In contrast, hypoxia induced gal-3 mRNA, protein, and promoter activity in HeLa cells and mouse embryonic fibroblasts (MEFs) from HIF-1 alpha wildtype but not HIF-1-null mice. To evaluate the importance of HIF-1 in regulation of gal-3 expression, we overexpressed HIF-1 alpha or constitutively active-HIF-1 alpha in null MEF. An increase in gal-3 promoter activity was observed in both normoxia and hypoxia. Similarly, suppression of HIF-1 alpha in nucleus pulposus cells, and wildtype MEF, using siRNA and pharmacological inhibitors resulted in suppression of gal-3 promoter activity and mRNA levels. Analysis of the gal-3 promoter indicated that it contained two hypoxia response elements (HREs). Gel-shift and chromatin immunoprecipitation analysis confirmed that there was binding of HIF-1 alpha to the gal-3 HRE. Furthermore, site-directed mutagenesis of HRE completely blocked hypoxic induction of gal-3 promoter activity. In nucleus pulposus cells, suppression of gal-3 expression promoted FasL-mediated apoptosis.

CONCLUSIONS

Together, these studies showed that gal-3 is a HIF-1-regulated lectin that plays an important role in nucleus pulposus cell survival.

A phenotypic comparison of intervertebral disc and articular cartilage cells in the rat

The basic molecular characteristics of intervertebral disc cells are still poorly defined. This study compared the phenotypes of nucleus pulposus (NP), annulus fibrosus (AF) and articular cartilage (AC) cells using rat coccygeal discs and AC from both young and aged animals and a combination of microarray, real-time RT-PCR and immunohistochemistry. Microarray analysis identified 63 genes with at least a fivefold difference in fluorescence intensity between the NP and AF cells and 41 genes with a fivefold or greater difference comparing NP cells and articular chondrocytes. In young rats, the relative mRNA levels, assessed by real-time RT-PCR, of annexin A3, glypican 3 (gpc3), keratin 19 (k19) and pleiotrophin (ptn) were significantly higher in NP compared to AF and AC samples. Furthermore, vimentin (vim) mRNA was higher in NP versus AC, and expression levels of cartilage oligomeric matrix protein (comp) and matrix gla protein (mgp) were lower in NP versus AC. Higher NP levels of comp and mgp mRNA and higher AF levels of gpc3, k19, mgp and ptn mRNA were found in aged compared to young tissue. However, the large differences between NP and AC expression of gpc3 and k19 were obvious even in the aged animals. Furthermore, the differences in expression levels of gpc3 and k19 were also evident at the protein level, with intense immunostaining for both proteins in NP and non-existent immunoreaction in AF and AC. Future studies using different species are required to evaluate whether the expression of these molecules can be used to characterize NP cells and distinguish them from other chondrocyte-like cells.

The functional significance of cell clusters in the notochordal nucleus pulposus: survival and signaling in the canine intervertebral disc

STUDY DESIGN

Cell viability was assessed in relation to cell clustering, and mechanisms of cell-cell signaling in the clusters were investigated.

OBJECTIVES

To explore the functional role of cell clustering in the notochordal nucleus pulposus.

SUMMARY OF BACKGROUND DATA

The intervertebral disc of some species contains residual cells from the embryonic notochord. These cells form large three-dimensional clusters in the young, healthy disc but are replaced by chondrocyte-like cells during aging and degeneration.

METHODS

Forty nucleus pulposi of adult dog lumbar intervertebral discs were isolated, and were left untreated, mechanically disrupted through a syringe, or enzymatically digested. The presence of functional gap junctions was determined by the fluorescence recovery after photobleaching method. Cell viability was also assessed over 20 days in vitro.

RESULTS

The cell clusters were interconnected via functional gap junctions. Mechanical disruption of the tissue had little effect on long-term cell viability, but enzymatic disruption of the tissue had a substantial negative impact on cell survival.

CONCLUSIONS

These results demonstrate that the notochordal cells in adult dog nucleus pulposi are able to communicate via cytoplasmic signals and that such communications may influence the functionality of these cells in the young disc.

The Notochordal Cell in the Nucleus Pulposus: A Review in the Context of Tissue Engineering

An understanding of developmental biology can provide useful insights into how different tissue-engineered repairs might be designed. During embryogenesis of the intervertebral disk, the cells of the notochord play a critical role in initiating tissue formation, and may be responsible for development of the nucleus pulposus. In some species, including humans, these notochordal cells may eventually be lost, either through apoptosis or terminal differentiation, and are replaced by chondrocyte-like cells. However, there is some evidence that the notochordal cells may persist in at least some humans. This review discusses some of the potential applications of notochordal cells in tissue engineering of the nucleus pulposus.

The three-dimensional architecture of the notochordal nucleus pulposus: novel observations on cell structures in the canine intervertebral disc

Cells from the nucleus pulposus of young (< 2 years) and old (> 5 years) non-chondrodystrophoid dogs were studied using routine histology, confocal laser scanning microscopy and transmission electron microscopy. The architecture of cell structures--from the tissue scale down to subcellular scale--was reported. Clusters of notochordal cells were observed in young nuclei pulposi, ranging from 10 to 426 cells each. These clusters resisted mechanical disruption and showed evidence of cell-cell signalling via gap junctions. Cells (30-40 microm in diameter) within the clusters had a physaliferous appearance, containing numerous large inclusions which ranged from 1 to 20 microm in diameter. The inclusions were surrounded by a dense actin cortex but were not contained by a lipid bilayer. The contents of the inclusions were determined not to be predominantly carbohydrate or neutral lipid as assessed by histochemical staining, but the exact composition of the contents remained uncertain. There were striking differences in the cell architecture of young vs. old nuclei pulposi, with a loss of both cell clusters and physaliferous cells during ageing. These observations demonstrate unique cell structures, which may influence our understanding of the differences between notochordal and chondrocytic cells in the nucleus pulposus. Such differences could have substantial impact upon how we think about development, degeneration and repair of the intervertebral disc.

Matrix gene expression analysis and cellular phenotyping in chordoma reveals focal differentiation pattern of neoplastic cells mimicking nucleus pulposus development

Chordoma is the fourth most common malignant primary neoplasm of the skeleton and almost the only one showing a real epithelial phenotype. Besides classic chordoma, so-called chondroid chordoma was described as a specific entity showing cartilage-like tissue within chordomatoid structures. However, since its first description, strongly conflicting results have been reported about the existence of chondroid chordoma and several studies suggested chondroid chordomas being in fact low-grade conventional chondrosarcomas. In the present study, we used cytoprotein expression profiling and molecular in situ localization techniques of marker gene products indicative of developmental phenotypes of chondrocytes to elucidate origin and biology of chondroid chordoma. We were able to demonstrate the chondrogenic potential of chordomas irrespectively of the appearance of overt cartilage formation by identifying the multifocal expression of type II collagen, the main marker of chondrocytic differentiation. Additionally, the cartilage-typical large aggregating proteoglycan aggrecan was present throughout all chordomas and, thus, a very characteristic gene product and marker of these neoplasms. Biochemical matrix composition and cell differentiation pattern analysis showed a high resemblance of classic chordomas and in chordoid areas of chondroid chordomas to the fetal chorda dorsalis, whereas chondroid areas of chondroid chordomas showed features similar to adult nucleus pulposus. This demonstrates on the cell function level the chondrocytic differentiation potential of neoplastic chordoid cells as a characteristic facet of chordomas, mimicking fetal vertebral development, ie, the transition of the chorda dorsalis to the nucleus pulposus. Our study firmly establishes a focal real chondrocytic phenotype of neoplastic cells in chordomas. Chondroid chordoma is neither a low-grade chondrosarcoma nor a misnomer as discussed previously.

Extradural ecchordosis physaliphora of the thoracic spine: case report

OBJECTIVE AND IMPORTANCE

We report an unusual case of ecchordosis physaliphora of the thoracic spine.

CLINICAL PRESENTATION

The clinical presentation was one of disabling thoracic radicular pain without objective neurological deficit. The imaging characteristics of the lesion were those of a cyst containing aqueous fluid. There was no bone destruction.

INTERVENTION

Gross total removal of the lesion was accomplished.

CONCLUSION

We present the only well-documented case of thoracic extradural ecchordosis physaliphora and discuss the relationship between the notochord, ecchordosis physaliphora, and chordoma. We provide a comprehensive list of lesions exhibiting physaliphorous cells.

Cytoskeleton gradients in three dimensions during neurulation in the rabbit

Morphogenetic movements leading to the formation of the neural tube and cellular differentiation leading to neuronal and glial cell lineages are both part of early development of the vertebrate nervous system. In order to analyze the degree of overlap between these processes, cellular differentiation during the shaping of the neural plate is investigated immunohistochemically by using monoclonal intermediate filament protein antibodies and the 7.5-8.0-day-old rabbit embryo as a model. Western blotting is used to confirm the specificity of the antibodies, which include a new monoclonal vimentin antibody suitable for double-labeling in combination with monoclonal cytokeratin (and fibronectin) antibodies. Starting in the early somite embryo and concomitant with neural plate folding, a gradual loss of cytokeratin 8 (and 18) expression in the neuroepithelium is mirrored by a gain in vimentin expression with partial coexpression of both proteins. At the prospective rhombencephalic and spino-caudal levels, vimentin expression, in particular, changes (i.e., increases) along gradients in three dimensions: along the longitudinal axis of each neuroepithelial cell from basal to apical, in the transverse plane of the embryo from dorsolateral to ventromedial and along the craniocaudal axis from prospective rhombencephalic toward spino-caudal levels of the neural plate. At the prospective mes- and prosencephalic levels, the expression change also proceeds from basal to apical within each neuroepithelial cell, but along the other axes described here, the progress in expression change is more complex. Although the functional meaning of these highly ordered expression changes is at present unclear, the gradients suggest a novel pattern of neuroepithelial differentiation which may be functionally related to the process of interkinetic nuclear migration (Sauer [1935] J. Comp. Neurol. 62:377-402) and which partially coincides with the morphogenetic movements involved in the shaping of the neural plate.

Changes in the expression of intermediate filaments and desmoplakins during development of human notochord

Indirect immunofluorescence was used to study the expression of desmosomal and intermediate filament (IF) proteins in the human notochord between the 4th and 12th weeks of embryonic development. Towards the end of this period, the development of the notochord is characterized by its gradual physiological atrophy and disappearance inside the vertebral bodies. In all of our embryos, the notochord cells expressed cytokeratin and vimentin but not desmin, neurofilament protein or glial fibrillary acidic protein. Throughout the stages studied, the expression of cytokeratin was strong. Vimentin expression, on the other hand, changed during the stages studied. In our youngest embryos, vimentin could be detected only in the peripheral cells of the notochord. During development, a distinct increase occurred in vimentin expression, and in the oldest embryos, all notochord cells showed bright vimentin-specific fluorescence. Simultaneously with this modification, a change occurred in the expression of desmosomal proteins: The notochord cells expressed desmoplakins abundantly during early stages, but weakly or not at all during later stages. Correspondingly, electron microscopy of the same stages showed a striking decrease in the number of desmosomes between notochord cells. Our results confirm that, during early development, the notochord displays features specific for epithelial cells. This accords with the view that notochord is of epithelial origin. The modifications observed in the expression of IF and desmosomal proteins were temporally correlated with developmentally regulated atrophy of the notochord. The programmed regression of the notochord cells is thus associated with a switch from a predominantly epithelial phenotype to a more mesenchymal one.

Intermediate filament typing of the human embryonic and fetal notochord

In order to characterize human notochordal tissue we investigated notochords from 32 human embryos and fetuses ranging between the 5th and 13th gestational week, using immunohistochemistry to detect intermediate filament proteins cytokeratin, vimentin and desmin, the cytokeratin subtypes 7, 8, 18, 19 and 20, epithelial membrane antigen (EMA), and adhesion molecules pan-cadherin and E-cadherin. Strong immunoreactions could be demonstrated for pan-cytokeratin, but not for desmin or EMA. Staining for pan-cadherin and weak staining for E-cadherin was found on cell membranes of notochordal cells. Also it was demonstrated that notochordal cells of all developmental stages contain the cytokeratins 8, 18 and 19, but not 7 or 20. Some cells in the embryonic notochord also contained some vimentin. Vimentin reactivity increased between the 8th and 13th gestational week parallel to morphological changes leading from an epithelial phenotype to the chorda reticulum which represents a mesenchymal tissue within the intervertebral disc anlagen. This coexpression reflects the epithelial-mesenchymal transformation of the notochord, which also loses E-cadherin expression during later stages. Our findings cannot elucidate a histogenetic germ layer origin of the human notochord but demonstrate its epithelial character. Thus, morphogenetic inductive processes between the human notochord and its surrounding vertebral column anlagen can be classified as epithelial-mesenchymal interactions.

Keratin and vimentin distribution patterns in the epithelial structures of the canine anal region

The intermediate filament labeling pattern of the epithelial structures of the canine anal region was studied with different polypeptide specific keratin monoclonal antibodies (MoAbs) and with a monoclonal and polyclonal vimentin antibody. The epithelial structures in this region could be discriminated and characterized by differences in their keratin staining pattern. The basal cells in the different epithelial structures showed a similar staining pattern characterized by reactivity with MoAbs staining keratins 5, 8, 14, and 17. Columnar epithelial cells showed a completely different phenotype mostly characterized by reactivity with MoAbs staining keratins 7, 5, 8, 18, and 19. A restricted number of differentiated perianal gland cells showed perinuclear vimentin staining. Myoepithelial cells did not stain for vimentin, but, as other basal cells, were positive for MoAbs staining keratins 5, 8, 14, and 17.

A histomorphologic and immunohistochemical study of chordoma in twenty ferrets (Mustela putorius furo)

The histomorphologic and immunohistochemical features of chordoma in 20 ferrets were evaluated. The mean age was 3.4 years, and, in the cases for which sex was known, females (n = 10) outnumbered males (n = 5) two to one. All 20 tumors occurred on the tip of the tail. Nineteen of 20 tumors (95%) were composed of three tissue components, often arranged concentrically with lobules of physaliferous cells at the periphery, trabecular bone in the center, and cartilage in between. The bone often contained marrow and hematopoietic cells. One tumor lacked chondromatous or osseous tissue. Immunohistochemical results were consistent with previous studies of chordoma. All 20 tumors (100%) were positive for keratin and vimentin intermediate filaments; 15 (75%) were positive for S-100 protein; and 17 (85%) were positive for neuron specific enolase. This neoplasm shares morphologic and immunohistochemical features with "classic," as well as chondroid chordoma, of human beings, making it a potential animal model.

Cell type-specific and efficient synthesis of human cytokeratin 19 in transgenic mice

In studies designed to identify cis-regulatory elements involved in the cell-type-specific expression of human cytokeratin (CK) genes we have dissected from the major type I CK gene locus on chromosome 17 a region containing the gene that encodes CK 19, with flanking segments of different lengths, and have examined the expression of related gene constructs in transgenic mice. Adult transgenic mice have been characterized by immunohistochemistry, gel-electrophoretic analyses of cytoskeletal proteins and genomic DNA (Southern blots). We have found that a construct harbouring the transcriptional unit plus approximately 0.7 kb downstream from the polyA-addition site and an immediately adjacent 5' upstream segment of approximately 3.6 kb, when combined with a further 5' upstream element of -6.4 - -8.6 kb, is sufficient to guarantee the synthesis of human CK 19 in the same cells and to a similar extent as the murine genome expresses its endogenous CK 19 gene. The findings demonstrate that all cis-elements necessary for the specific and efficient expression of a single type I CK gene, in the context of epithelial differentiation, can be located in the vicinity of the gene itself and that more-distant elements are not required.

Immunohistochemistry of ecchordosis physaliphora and chordoma

Immunohistochemical stains for cytokeratins, vimentin, epithelial membrane antigen, carcinoembryonic antigen and S-100 were performed on nine ecchordoses and 10 chordomas. 100% of the ecchordoses were positive for cytokeratin, vimentin and epithelial membrane antigen. 78% were S-100 positive. 100% of the chordomas stained positively for cytokeratin, vimentin and S-100 and 90% were positive for epithelial membrane antigen. No ecchordosis or chordoma was carcinoembryonic-antigen positive. These findings are interesting for two reasons. First, the similar staining properties of chordoma and ecchordosis physaliphora support the embryologic hypothesis of their common origin from the fetal notochord. Second, they indicate that when an ecchordosis causes symptoms prompting surgical resection, differentiation of the lesion from chordoma with routine immunohistochemistry would not be helpful.