Insights into the hallmarks of human nucleus pulposus cells with particular reference to cell viability, phagocytic potential and long process formation

Distribution and Polarization of Hematogenous Macrophages Associated with the Progression of Intervertebral Disc Degeneration

STUDY DESIGN

In vivo study using immunostaining and immunoblot analysis.

OBJECTIVE

To determine the distribution of bone marrow-derived macrophages (BMDMs), macrophage polarization and cytokine expression in the process of intervertebral disc (IVD) degeneration.

SUMMARY OF BACKGROUND DATA

Knowledge of the detailed distribution of exogeneous macrophages in the disc degeneration process is important for understanding the pathomechanisms and establishing novel therapeutic targets.

METHODS

To distinguish BMDMs, GFP-labeled bone marrow chimeric rats (n = 12) were generated. The degenerative process of the intervertebral disc was reproduced in a rat caudal disc puncture model (n = 49). Immunofluorescence staining was performed to observe the distribution of BMDMs, Iba-1 and GFP double-positive cells, and Iba-1 and iNOS (M1 macrophage) or arginase-1 (M2 macrophage) double-positive cells. Immunoblot analysis was used to evaluate differences in cytokines (TNF-α, IL-1β, IL-6, TGF-β, IL-4, and IL-10) depending on the distribution of BMDMs.

RESULTS

BMDMs infiltrated into the outer annulus fibrosus and endplate, while increasing tissue-resident macrophage was observed inside the annulus fibrosus/nucleus pulposus. The ratio of BMDMs and the polarity change differed among the regions. Especially in the endplate, BMDMs increased gradually and the macrophage phenotype was M2 dominant. Expression of IL-1β decreased gradually at endplate, and that of IL-4 increased early after disc puncture at inside of the annulus fibrosus.

CONCLUSION

During the disc degeneration process, BMDMs were observed mainly around the endplate and outside area of the annulus fibrosus, with few in the inside area of annulus fibrosus and nucleus pulposus. Compared to other IVD area, macrophage polarity and cytokine expression is concomitantly M2-dominant in endplate. Increased hematogenous M2-phenotype macrophages in endplate with progression of IVD degeneration could enhance our understanding of the underlying mechanisms of disc degeneration.Level of Evidence: N/A.

Standardisation of basal medium for reproducible culture of human annulus fibrosus and nucleus pulposus cells

Background

The lifetime prevalence of degenerative disc disease is dramatically high. Numerous investigations on disc degeneration have been performed on cells from annulus fibrosus (AF) and nucleus pulposus (NP) of the intervertebral disc (IVD) in cell culture experiments utilising a broad variety of basal culture media. Although the basal media differ in nutrient formulation, it is not known whether the choice of the basal media itself has an impact on the cell’s behaviour in vitro. In this study, we evaluated the most common media used for monolayer expansion of AF and NP cells to set standards for disc cell culture.

Methods

Human AF and NP cells were isolated from cervical discs. Cells were expanded in monolayer until passage P2 using six different common culture media containing alpha-Minimal Essential Medium (alpha-MEM), Dulbecco’s Modified Eagle’s Medium (DMEM) or Ham’s F-12 medium (Ham’s F-12) as single medium or in a mixture of two media (alpha/F-12, DMEM/alpha, DMEM/F-12). Cell morphology, cell growth, glycosaminoglycan production and quantitative gene expression of cartilage- and IVD-related markers aggrecan, collagen type II, forkhead box F1 and keratin 18 were analysed. Statistical analysis was performed with two-way ANOVA testing and Bonferroni compensation.

Results

AF and NP cells were expandable in all tested media. Both cell types showed similar cell morphology and characteristics of dedifferentiation known for cultured disc cells independently from the media. However, proceeding culture in Ham’s F-12 impeded cell growth of both AF and NP cells. Furthermore, the keratin 18 gene expression profile of NP cells was changed in alpha-MEM and Ham’s F-12.

Conclusion

The impact of the different media itself on disc cell’s behaviour in vitro was low. However, AF and NP cells were only robust, when DMEM was used as single medium or in a mixture (DMEM/alpha, DMEM/F-12). Therefore, we recommend using these media as standard medium for disc cell culture. Our findings are valuable for the harmonisation of preclinical study results and thereby push the development of cell therapies for clinical treatment of disc degeneration.

Accumulation and localization of macrophage phenotypes with human intervertebral disc degeneration

BACKGROUND CONTEXT

Chronic inflammation is an important component of intervertebral disc (IVD) degeneration, but there is limited knowledge about the identity and source of inflammatory cells involved with the degenerative processes. Macrophages can exhibit multiple phenotypes and are known inflammatory regulators in many tissues, but their phenotypes have not been characterized in IVD degeneration.

PURPOSE

We aimed to characterize accumulation and localization of macrophages in IVD degeneration.

STUDY DESIGN/SETTING

This is an exploratory study to characterize macrophage phenotypes in human cadaver IVDs and the effects of injury and degeneration using multiple immunohistochemistry methods.

OUTCOME MEASURES

Percent positivity of immunohistochemical markers specific for CCR7, CD163, and CD206, and qualitative assessments of dual immunofluorescence and immunostaining localization were the outcome measures.

METHODS

Macrophages were identified in human cadaveric IVDs with immunohistochemistry using cell surface markers CCR7, CD163, and CD206, which are associated with proinflammatory M1, remodeling M2c, and anti-inflammatory M2a phenotypes, respectively. Variations in the accumulation and localization of macrophage markers with degenerative grade across subjects and within donors are described.

RESULTS

Cells expressing all three macrophage markers were found in all degenerative IVDs, but not in the healthiest IVDs. Cells expressing CCR7 and CD163, but not CD206, significantly increased with degenerative grade. Many cells also co-expressed multiple macrophage markers. Across all degenerative grades, CCR7+ and CD163+ were significantly more present in unhealthy nucleus pulposus (NP), annulus fibrosus (AF), and end plate (EP) regions exhibiting structural irregularities and defects. Positively stained cells in the NP and AF closely resembled resident IVD cells, suggesting that IVD cells can express macrophage cell surface markers. In the EP, there were increasing trends of positively stained cells with atypical morphology and distribution, suggesting a source for exogenous macrophage infiltration into the IVD.

CONCLUSIONS

Chronic inflammatory conditions of IVD degeneration appear to involve macrophages or macrophage-like cells, as expression of multiple macrophage markers increased with degeneration, especially around unhealthy regions with defects and the EP. Knowledge of macrophage phenotypes and their localization better elucidates the complex injury and repair processes in IVDs and may eventually lead to novel treatments.

Local up-regulation of interferon-γ (IFN-γ) following disc herniation is involved in the inflammatory response underlying acute lumbar radicular pain

Lumbar radicular pain after disc herniation may be associated with release of pro-inflammatory cytokines from nucleus pulposus (NP) tissue. In the present study we examined the role of interferon-γ (IFN-γ) and cluster of differentiation 68 (CD68) in the acute phase of this process. First, in an animal model mimicking the clinical situation after disc herniation, the role of IFN-γ close to the dorsal nerve roots was studied. Next, in patients with lumbar radicular pain due to disc herniation, we examined how two single nucleotide polymorphisms (SNPs; rs2069705 and rs2069718) are important for the IFN-γ expression influenced the pain behavior. The animal data demonstrated a significant increase in the nociceptive activity at the spinal level after local application of NP and IFN-γ onto the dorsal nerve roots. A positive correlation between IFN-γ and CD68 in the NP tissue was also demonstrated. In the patients, a significant increase in Oswestry Disability Index (ODI) score was observed in carriers of the IFN-γ SNPs; rs2069705 A and rs2069718 G alleles. The present data suggest that IFN-γ close to the dorsal nerve roots may contribute to the pathogenesis, the nociceptive activity and the pain behavior following lumbar disc herniation.

UM-Chor1: establishment and characterization of the first validated clival chordoma cell line

OBJECTIVE Chordomas are rare malignant tumors thought to arise from remnants of the notochord. They can be located anywhere along the axial skeleton but are most commonly found in the clival and sacrococcygeal regions, where the notochord regresses during fetal development. Chordomas are resistant to many current therapies, leaving surgery as the primary method of treatment. Cancer cell lines have been useful for developing new cancer treatments in a laboratory setting that can then be transferred to the clinic, but there are only 4 validated chordoma cell lines available. The objective of this work was to establish chordoma cell lines from surgical tissue in order to expand the library of lines available for laboratory research. METHODS Chordoma tissue from the clivus was processed and sorted by flow cytometry to obtain an isolated population of chordoma cells. These cells were grown in culture and expanded until enough doublings to consider the line established. Identification of a chordoma cell line was made with known markers for chordoma, and the line was observed for ALDH (aldehyde dehydrogenase) subpopulations and tested in serum-free growth conditions as well as in vivo. RESULTS A fifth chordoma cell line, UM-Chor1, was successfully established. This is the first chordoma cell line originating from the clivus. Validation was confirmed by phenotype and positivity for the chordoma markers CD24 and brachyury. The authors also attempted to identify an ALDH^high cell population in UM-Chor1, UCH1, and UCH2 but did not detect a distinct population. UM-Chor1 cells were able to form spheroids in serum-free culture, were successfully transduced with luciferase, and could be injected parasacrally and grown in NOD/SCID mice. CONCLUSIONS The availability of this novel clival chordoma cell line for in vitro and in vivo research provides an opportunity for developments in treatment against the disease.

The influence of oxygen concentration on the extracellular matrix production of human nucleus pulposus cells during isolation-expansion process

Nucleus pulposus (NP) cells locate in the center of avascular intervertebral discs, and thus have presumably adapted to a hypoxic environment. The purpose of this study was to investigate the influences of hypoxic condition, during isolation-expansion of human NP cells, on the cellular proliferation and extracellular matrix (ECM) synthesis in later three-dimensional cultures. Human NP tissues were obtained from patients who underwent lumbar disc surgeries. Immediately after retrieval, NP tissues from each patient were divided into two aliquots for in vitro cultivation either under classical normoxic (21% O₂ ) or hypoxic (3.5% O₂ ) condition. After isolation-expansion processes, microtissues of NP cells were formed and the analysis was performed after one-week culture. Experiments of pretreatment with TGF-β1 or lovastatin were designed to investigate if the isolation-expansion conditions affect the responsiveness to later exogenous treatments. Hypoxic isolation-expansion stimulated NP cell proliferation during monolayer culture. Hypoxia also upregulated mRNA levels of SOX9 and HIF-1α but downregulated type X collagen as well as improved aggrecan and type II collagen synthesis. Although TGF-β1 had no substantial effect, lovastatin pretreatment showed a greater enhancement on type II collagen expression in hypoxic group. Normoxia negatively affected the biochemical composition of regenerated ECM attributable to downregulation of SOX9 and HIF-1α, while hypoxia enhanced cellular proliferation, improved matrix production, and maintained a functional phenotype of NP cells. Hypoxic isolation-expansion of human NP cells is important to achieve better regenerative cells for later cultivation or cell transplantation. © 2017 Wiley Periodicals, Inc. J Biomed Mater Res Part A: 105A: 1575-1582, 2017.

Identification of lumbar disc disease hallmarks: a large cross-sectional study

Background

Lumbar disc disease has a disabling impact on global people with heavy burden on society, mainly consisting of lumbar disc degeneration (LDD) and lumbar disc herniation (LDH). The recently released lumbar disc nomenclature version 2.0 deepens our understandings on the diseases. Consequently, there is an urgent need to clarify the occurrence and distribution features of LDD and LDH in a large-scale sample in terms of the novel version.

Question/purposes

We asked: (1) Is there a difference in the occurrence and distribution hallmarks of LDD and LDH in a population-based large-scale sample? (2) Does the novel nomenclature version bring novel vision on lumbar disc disease?

Methods

Five thousand two hundred eighty-eight consecutive cases (26,440 lumbar discs) undergoing lumbar spine MRI were retrospectively included from Jan 2008 to Dec 2010 in a territory university hospital. Five hundred nine cases were excluded. There were 2727 males (51.57%) and 2561 females (48.43%) with a mean age of 43.73 years. Both T1 and T2 weighted lumbar MRI images from L1/2 to L5/S1 were profoundly analyzed in axial and sagittal planes. We classified lumbar discs in terms of version 2.0.

Results

The occurrence of LDH and LDD was 14.18 and 44.23% in average, respectively. Notably, lumbar spine discs were more prone to LDD than LDH. L4/5 was the most frequent level in terms of LDH (26.08%) and LDD (56.09%), followed by L5/S1 (LDH: 24.09%; LDD: 55.33%), then L3/4, L2/3 and L1/2 in ranking order. The prevalence of LDH and LDD in upper lumbar discs from L1/2 to L3/4 was significant lower than the average prevalence rate (P < 0.05). The mean age was 24.70 (±14.81) years for normal lumbar discs; 49.76 (±14.95) years for LDD; 37.01 (±12.91) years for LDH; 51.31(±15.00) years for LDD and LDH (P < 0.05). Modic changes, HIZ, spondylosis deformans and decreased disc height were linked with older age; whereas Schmorl node and lumbar disc sequestration were not associated with age (P < 0.05).

Conclusions

The prevalence of LDD is 44.23%, higher than LDH as 14.18%. L4/5 and L5/S1 are the most frequent involved segments for the majority of lumbar disc diseases. Schmorl node occurs (1.6%) more frequently in upper lumbar spine, independent of age. Modic changes (0.87%) are closely related with older age.

Clinical relevance

When diagnosing and treating lumbar disc disease, it might be important to consider the updated nomenclature of LDD and LDH. Our study provides additional novel vision on the features of LDD and LDH in a large-scale sample based on the nomenclature of novel version.

Therapeutic effects of naringin on degenerative human nucleus pulposus cells for discogenic low back pain

BACKGROUND

Over half the population of the world will suffer from moderate or severe low back pain (LBP) during their life span. Studies have shown that naringin, a major flavonoid in grapefruit and an active compound extracted from a Chinese herbal medicine (Rhizoma Drynariae) possesses many pharmacological effects.

PURPOSE

The aim of this study was to evaluate the influence of naringin on the growth of degenerative human nucleus pulposus (NP) cells, and its repair effects on protein and gene expressions of the cells.

STUDY DESIGN/SETTING

This was an in vitro investigation of the human NP cells isolated from degenerated intervertebral discs that were interacted with various concentrated of naringin.

METHOD

This study was exempted by the institutional Human Subjects Committee-2, University of Kansas School of Medicine-Wichita. Degenerative human NP cells were isolated from intervertebral discs of patients with discogenic LBP and cultured at 37°C with 5% CO₂. The proliferation of NP cells was determined following treatment with various concentrations of naringin. The protein expressions of tumor necrosis factor-α (TNF-α) and Bone morphogenetic protein 2 (BMP-2) were tested using enzyme-linked immunosorbent assay. Aggrecan and type II collagen levels were measured by immunohistological staining. Further examination of the gene expression of aggrecan, Sox6, and MMP3 was performed after intervention with naringin for 3 days.

RESULTS

The human NP cells were successfully propagated in culture and stained positive with toluidine blue staining. Naringin effectively enhanced the cell proliferation at an optimal concentration of 20 µg/mL. Naringin treatment resulted in significant inhibition of TNF-α, but elevated protein expressions of BMP-2, collagen II, and aggrecan. Naringin also increased disc matrix gene activity including aggrecan and Sox6, and decreased the gene expression of MMP3.

CONCLUSION

Naringin effectively promotes the proliferation of degenerative human NP cells and improves the recuperation of the cells from degeneration by increasing expression of aggrecan, BMP-2, and Sox6 while inhibiting the expression of TNF-α and MMP3. This study suggests that naringin may represent an alternative therapeutic agent for disc degeneration.

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

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

Advances in biological therapy for nucleus pulposus regeneration

OBJECTIVE

The intervertebral disc (IVD) is composed of the external annulus fibrosus (AF) and the inner gel-like center, the nucleus pulposus (NP). The elastic NP can function to relieve stress and maintain IVD function by distributing hydraulic pressure evenly to annulus and endplate. Degeneration of the NP, which leads to increased death of NP cells, the loss of proteoglycan (PG), and aberrant gene expression, may result in an overall alteration of the biomechanics of the spinal column and cause low back pain. Recent advances in biological therapy strategies that target therapy at the regeneration of degenerated and damaged NP have been investigated in in vitro and in vivo studies and demonstrated promising outcomes. In this article, we review recent studies of biological approaches for NP regeneration.

METHOD

The articles regarding NP regeneration using biomaterials, stem cells, and gene vectors were identified in PubMed databases.

RESULTS

Stem cell-mediated cell therapy demonstrates the potential to restore the function and structure of the NP. The viral or non-viral vectors encoding functional genes may generate a therapeutic effect when they are introduced into grafted cells or native cells in the NP. Biomaterial scaffolds generate an initial permissive environment for cell growth and allow the remodeling of scaffolds in the regeneration process. Biomaterial scaffolds provide structural support for NP regeneration and serve as a carrier for stem cell and gene vector delivery.

CONCLUSION

Though recent studies advance the body of knowledge needed to treat degenerated discs, many challenges need to be overcome before the application of these approaches can be successful clinically.

Interleukin-2 is upregulated in patients with a prolapsed lumbar intervertebral disc and modulates cell proliferation, apoptosis and extracellular matrix metabolism of human nucleus pulposus cells

Previous studies have demonstrated that the expression levels of cytokines are increased in degenerated intervertebral disc tissues, and several cytokines are associated with the pathogenesis of intervertebral disc degeneration. However, the role of interleukin (IL)-2 in the cellular functions of intervertebral disc tissues remains unreported. The present study aimed to determine the expression levels of IL-2 in the nucleus pulposus (NP) tissues of patients with a prolapsed lumbar intervertebral disc; and to observe the changes in cell proliferation, apoptosis, extracellular matrix (ECM) metabolism and p38 mitogen-activated protein kinase (MAPK) signaling in human NP cells (HNPCs) following treatment with IL-2. The present study demonstrated that IL-2 expression levels were upregulated in the NP tissues of patients with a prolapsed lumbar intervertebral disc; and a subsequent MTT assay demonstrated that IL-2 inhibits the proliferation of HNPCs in a dose-dependent manner. Furthermore, as demonstrated by the increased protein expression levels of Fas cell surface death receptor and the induction of caspase-8 and caspase-3 activity, the death receptor pathway was activated by IL-2 in the HNPCs in order to promote cell apoptosis. In addition, IL-2 promoted ECM degradation in the HNPCs, as demonstrated by an increase in the expression levels of type I collagen, a disintegrin and metalloproteinase with thrombospondin motifs and matrix metalloproteinases, and decreased aggrecan and type II collagen expression levels. Furthermore, phosphorylated-p38 was significantly increased in the HNPCs following IL-2 treatment. In conclusion, the present study demonstrated that IL-2 inhibits cell proliferation, and induces cell apoptosis and ECM degradation, accompanied by the activation of p38 MAPK signaling in HNPCs. Therefore, IL-2 may be a potential therapeutic agent for the treatment of degenerative disc disease.

Injectable hydrogel provides growth-permissive environment for human nucleus pulposus cells

Degeneration of intervertebral discs (IVDs) results in an overall alteration of the biomechanics of the spinal column and becomes a major cause of low back pain. In this study, an injectable hydrogel composite is fabricated and characterized as a potential scaffold for the treatment of degenerated IVDs. Crosslinking of type II collagen-hyaluronic acid (HA) hydrogel with 1-ethyl-3(3-dimethyl aminopropyl) carbodiimide (EDC) increases the gel stability against collagenase digestion and reduces water uptake in comparison with non-crosslinked gel. Cell viability assay exhibits the proliferation of human nucleus pulposus (HNP) cells in hydrogels. The cells in non-crosslinked gel and the gel crosslinked with a low concentration of EDC (0.1 mM) show superior cell viability and morphology compared with cells in gels crosslinked with higher concentration of EDC. Quantitative PCR assay demonstrates the gene expression of extracellular matrix (ECM) by cells cultured in the gels. The expression of ECM genes by HNP cells in the gels demonstrated the phenotypic change of the cells. This study suggests that the type II collagen-HA hydrogel and crosslinked hydrogel (0.1 mM EDC) are permissive matrix for the growth of HNP cells and can be potentially applied in NP repair.

Mesenchymal stem cells: potential application in intervertebral disc regeneration

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

Clarifying the nomenclature of intervertebral disc degeneration and displacement: from bench to bedside

As a significant determinant of low back pain, intervertebral disc degeneration (IDD) has attracted more and more attention of both investigators and physicians. Disc herniation, termed as intervertebral disc displacement, is amongst the most prevalent spinal diseases closely linked with IDD. Due to the same origins and similar pathophysiology, the ambiguity regarding the similarity and difference of IDD and intervertebral disc displacement thus remains. The aim of this study was to clarify the nomenclature of IDD and disc herniation in terms of molecular etiology, pathophysiology, nature history and clinical outcomes. Collectively, IDD is a type of multifaceted, progressive spinal disease with or without clinical symptoms as back pain, characterized by extracellular matrix and the integrity of NP and AF lost, fissures formation. Disc herniation (termed as intervertebral disc displacement) is a type of spinal disease based on IDD or not, with local pain and/or sciatica due to mechanical compression and autoimmune cascades upon the corresponding nerve roots. Clarifying the nomenclature of intervertebral disc degeneration and displacement has important implications both for investigators and for physicians.