Tenascin in the human intervertebral disc: alterations with aging and disc degeneration

Injectable Cell-Laden Nanofibrous Matrix for Treating Annulus Fibrosus Defects in Porcine Model: An Organ Culture Study

Lower back pain commonly arises from intervertebral disc (IVD) failure, often caused by deteriorating annulus fibrosus (AF) and/or nucleus pulposus (NP) tissue. High socioeconomic cost, quality of life issues, and unsatisfactory surgical options motivate the rapid development of non-invasive, regenerative repair strategies for lower back pain. This study aims to evaluate the AF regenerative capacity of injectable matrix repair strategy in ex vivo porcine organ culturing using collagen type-I and polycaprolactone nanofibers (PNCOL) with encapsulated fibroblast cells. Upon 14 days organ culturing, the porcine IVDs were assessed using gross optical imaging, magnetic resonance imaging (MRI), histological analysis, and Reverse Transcriptase quantitative PCR (RT-qPCR) to determine the regenerative capabilities of the PNCOL matrix at the AF injury. PNCOL-treated AF defects demonstrated a full recovery with increased gene expressions of AF extracellular matrix markers, including Collagen-I, Aggrecan, Scleraxis, and Tenascin, along with anti-inflammatory markers such as CD206 and IL10. The PNCOL treatment effectively regenerates the AF tissue at the injury site contributing to decreased herniation risk and improved surgical outcomes, thus providing effective non-invasive strategies for treating IVD injuries.

Tenascin-C: Friend or Foe in Lung Aging?

Lung aging is characterized by lung function impairment, ECM remodeling and airspace enlargement. Tenascin-C (TNC) is a large extracellular matrix (ECM) protein with paracrine and autocrine regulatory functions on cell migration, proliferation and differentiation. This matricellular protein is highly expressed during organogenesis and morphogenetic events like injury repair, inflammation or cancer. We previously showed that TNC deficiency affected lung development and pulmonary function, but little is known about its role during pulmonary aging. In order to answer this question, we characterized lung structure and physiology in 18 months old TNC-deficient and wild-type (WT) mice. Mice were mechanically ventilated with a basal and high tidal volume (HTV) ventilation protocol for functional analyses. Additional animals were used for histological, stereological and molecular biological analyses. We observed that old TNC-deficient mice exhibited larger lung volume, parenchymal volume, total airspace volume and septal surface area than WT, but similar mean linear intercept. This was accompanied by an increase in proliferation, but not apoptosis or autophagy markers expression throughout the lung parenchyma. Senescent cells were observed in epithelial cells of the conducting airways and in alveolar macrophages, but equally in both genotypes. Total collagen content was doubled in TNC KO lungs. However, basal and HTV ventilation revealed similar respiratory physiological parameters in both genotypes. Smooth muscle actin (α-SMA) analysis showed a faint increase in α-SMA positive cells in TNC-deficient lungs, but a marked increase in non-proliferative α-SMA + desmin + cells. Major TNC-related molecular pathways were not up- or down-regulated in TNC-deficient lungs as compared to WT; only minor changes in TLR4 and TGFβR3 mRNA expression were observed. In conclusion, TNC-deficient lungs at 18 months of age showed exaggerated features of the normal structural lung aging described to occur in mice between 12 and 18 months of age. Correlated to the increased pulmonary function parameters previously observed in young adult TNC-deficient lungs and described to occur in normal lung aging between 3 and 6 months of age, TNC might be an advantage in lung aging.

Proteomic Signatures of Healthy Intervertebral Discs From Organ Donors: A Comparison With Previous Studies on Discs From Scoliosis, Animals, and Trauma

OBJECTIVE

To catalog and characterize the proteome of normal human intervertebral disc (IVD).

METHODS

Nine magnetic resonance imaging (MRI) normal IVDs were harvested from 9 different brain dead yet alive voluntary organ donors and were subjected to electrospray ionization-liquid chromatography tandem mass spectrometry (ESI-LC-MS/MS) acquisition.

RESULTS

A total of 1,116 proteins were identified. Functional enrichment analysis tool DAVID ver. 6.8 categorized: extracellular proteins (38%), intracellular (31%), protein-containing complex (13%), organelle (9%), membrane proteins (6%), supramolecular complex (2%), and 1% in the cell junction. Molecular function revealed: binding activity (42%), catalytic activity (31%), regulatory activity (14%), and structural activity (7%). Molecular transducer, transporter, and transcription regulator activity together contributed to 6%. A comparison of the proteins obtained from this study to others in the literature showed a wide variation in content with only 3% of bovine, 5% of murine, 54% of human scoliotic discs, and 10.2% of discs adjacent to lumbar burst fractures common to our study of organ donors. Between proteins reported in scoliosis and lumbar fracture patients, only 13.51% were common, further signifying the contrast amongst the various MRI normal IVD samples.

CONCLUSION

The proteome of "healthy" human IVDs has been defined, and our results show that proteomic data on IVDs obtained from scoliosis, fracture patients, and cadavers lack normal physiological conditions and should not be used as biological controls despite normal MRI findings. This questions the validity of previous studies that have used such discs as controls for analyzing the pathomechanisms of disc degeneration.

Equiaxial Strain Modulates Adipose-derived Stem Cell Differentiation within 3D Biphasic Scaffolds towards Annulus Fibrosus

Recurrence of intervertebral disc (IVD) herniation is the most important factor leading to chronic low back pain and subsequent disability after discectomy. Efficacious annulus fibrosus (AF) repair strategy that delivers cells and biologics to IVD injury site is needed to limit the progression of disc degeneration and promote disc self-regeneration capacities after discectomy procedures. In this study, a biphasic mechanically-conditioned scaffold encapsulated with human adipose-derived stem cells (ASCs) is studied as a potential treatment strategy for AF defects. Equiaxial strains and frequencies were applied to ASCs-encapsulated scaffolds to identify the optimal loading modality to induce AF differentiation. Equiaxial loading resulted in 2–4 folds increase in secretion of extracellular matrix proteins and the reorganization of the matrix fibers and elongations of the cells along the load direction. Further, the equiaxial load induced region-specific differentiation of ASCs within the inner and outer regions of the biphasic scaffolds. Gene expression of AF markers was upregulated with 5–30 folds within the equiaxially loaded biphasic scaffolds compared to unstrained samples. The results suggest that there is a specific value of equiaxial strain favorable to differentiate ASCs towards AF lineage and that ASCs-embedded biphasic scaffold can potentially be utilized to repair the AF defects.

Targeting the annulus fibrosus of the intervertebral disc: Col1a2-Cre(ER)T mice show specific activity of Cre recombinase in the outer annulus fibrosus

Degeneration of the intervertebral disc (IVD) is a major underlying contributor to back pain-the single leading cause of disability worldwide. However, we possess a limited understanding of the etiology underlying IVD degeneration. To date, there are a limited number of mouse models that have been used to target proteins in specific compartments of the IVD to explore their functions in disc development, homeostasis and disease. Furthermore, the majority of reports exploring the composition and function of the outer encapsulating annulus fibrosus (AF) of the IVD have considered it as one tissue, without considering the numerous structural and functional differences existing between the inner and outer AF. In addition, no mouse models have yet been reported that enable specific targeting of genes within the outer AF. In the current report, we discuss these issues and demonstrate the localized activity of Cre recombinase in the IVD of Col1a2-Cre(ER)T;ROSA26mTmG mice possessing a tamoxifen-dependent Cre recombinase driven by a Cola2 promoter and distal enhancer and the mTmG fluorescent reporter. Following tamoxifen injection of 3-week-old Col1a2-Cre(ER)T;ROSA26mTmG mice, we show Cre activity specifically in the outer AF of the IVD, as indicated by expression of the GFP reporter. Thus, Col1a2-Cre(ER)T;ROSA26mTmG mice may prove to be a valuable tool in delineating the function of proteins in this unique compartment of the IVD, and in further exploring the compositional differences between the inner and outer AF in disc homeostasis, aging and disease.

Gene expression analysis in response to osmotic stimuli in the intervertebral disc with DNA microarray

Background

Intervertebral disc (IVD) cells experience a broad range of physicochemical stimuli under physiologic conditions, including alterations in their osmotic environment. At present, the molecular mechanisms underlying osmotic regulation in IVD cells are poorly understood. This study aims to screen genes affected by changes in osmotic pressure in cells of subjects aged 29 to 63 years old, with top-scoring pair (TSP) method.

Methods

Gene expression data set GSE1648 was downloaded from Gene Expression Omnibus database, including four hyper-osmotic stimuli samples, four iso-osmotic stimuli samples, and three hypo-osmotic stimuli samples. A novel, simple method, referred to as the TSP, was used in this study. Through this method, there was no need to perform data normalization and transformation before data analysis.

Results

A total of five pairs of genes ((CYP2A6, FNTB), (PRPF8, TARDBP), (RPS5, OAZ1), (SLC25A3, NPM1) and (CBX3, SRSF9)) were selected based on the TSP method. We inferred that all these genes might play important roles in response to osmotic stimuli and age in IVD cells. Additionally, hyper-osmotic and iso-osmotic stimuli conditions were adverse factors for IVD cells.

Conclusions

We anticipate that our results will provide new thoughts and methods for the study of IVD disease.

Structure and biology of the intervertebral disk in health and disease

The intervertebral disks along the spine provide motion and protection against mechanical loading. The 3 structural components, nucleus pulposus, annulus fibrosus, and cartilage endplate, function as a synergistic unit, though each has its own role. The cells within each of these components have distinct origins in development and morphology, producing specific extracellular matrix proteins that are organized into unique architectures fit for intervertebral disk function. This article focuses on various aspects of intervertebral disk biology and disruptions that could lead to diseases such as intervertebral disk degeneration.

Immunolocalization of MMP-19 in the human intervertebral disc: implications for disc aging and degeneration

Matrix metalloproteinases (MMPs) degrade components of the extracellular matrix of the disc, but the presence of MMP-19 has not been explored. In other tissues, MMP-19 is known to act in proteolysis of the insulin-like growth factor (IGF) binding protein-3, thereby exposing this protein to make it available to influence cell behavior. MMP-19 also has been shown to inhibit capillary-like formation and thus play a role in the avascular nature of the disc. Using immunohistochemistry, normal discs from six subjects aged newborn through 10 years and 20 disc specimens from control donors or surgical patients aged 15-76 (mean age 40.2 years) were examined for immunolocalization of MMP-19; six Thompson grade I discs, five Thompson grade II, eight Thompson grade III, five Thompson grade IV, and one Thompson grade V discs were analyzed. The results indicate that in discs from young subjects, MMP-19 was uniformly localized in the outer annulus. In discs from adult donors and surgical patients, outer and inner annulus cells only occasionally showed MMP-19 localization. The greatest expression of MMP-19 was observed in young discs, and little expression was seen in older or degenerating discs. Because MMP-19 has been shown to regulate IGF-mediated proliferation in other tissues, its decline in the aging/degenerating disc may contribute to the age-related decrease in disc cell numbers.

Cellular immunohistochemical localization of the matricellular protein myocilin in the intervertebral disc

Myocilin is a 55-57-kDa protein that is a member of the olfactomedin protein family. It is expressed in the cornea, sclera and trabecular network of the eye, myelinated peripheral nerves, heart, skeletal muscle, trachea and other tissues. Myocilin binds to a domain of fibronectin, type IV collagen and laminen in the trabecular meshwork of the eye, and its expression is influenced by transforming growth factor beta. Because these extracellular matrix components also are common in the intervertebral disc, the objective of our study was to determine whether the matricellular protein myocilin could be detected in the human or sand rat intervertebral disc using immunohistochemistry and to assess its localization. We investigated 16 specimens of human disc tissue and discs from six sand rats. Three human disc cell cultures grown in three-dimensional culture also were evaluated. Immunocytochemical annulus analysis showed the presence of myocilin within the disc cell cytoplasm in some, but not all, cells. Extracellular matrix in both the human and sand rat disc was negative for myocilin localization. Myocilin is believed to play a role in cell-cell adhesion and/or signaling. Myocilin may have such functions within the disc cell population in a manner similar to tenascin, SPARC and thrombospondin, which are other matricellular proteins recently shown to be present in the disc.

Immunolocalization of thrombospondin in the human and sand rat intervertebral disc

STUDY DESIGN

Human intervertebral disc tissue from the anulus was obtained in a prospective study investigating the presence of the matricellular protein thrombospondin (TSP) in human and sand rat discs. Studies were approved by the authors' Human Subjects Institutional Review Board and Institutional Animal Care and Use Committee.

OBJECTIVES

To determine whether TSP could be detected in the human or sand rat disc with immunohistochemistry, and to assess its localization.

SUMMARY OF BACKGROUND DATA

The role of the matricellular proteins in maintenance of disc health and extracellular matrix remodeling is as yet poorly understood. SPARC and tenascin have previously been shown to be present in the human disc. TSP has a well-recognized antiangiogenic activity in vivo and in vitro.

METHODS

Sixteen specimens of human disc tissue and discs from 7 sand rats were assessed for immunohistochemical localization of TSP. Three human disc cell cultures grown in three-dimensional culture were also evaluated. RESULTS.: Strong immunoreactivity was present in the outer anulus of both human and sand rat discs. Inner anulus showed lesser localization. In clusters, both immuno-positive and -negative cells were present. Similar patterns of localization were seen in the sand rat specimens. Human disc cells in three-dimensional culture produced abundant TSP.

CONCLUSIONS

The biologic basis for the avascular adult human disc does not appear to have been explored. Since TSP has recognized antiangiogenic effects both in vitro and in vivo, we suggest that the strong immunolocalization of TSP in the outer anulus indicates a role for TSP in the avascular status of the adult human and sand rat disc.

Three-dimensional culture of human disc cells within agarose or a collagen sponge: assessment of proteoglycan production

The objective of the present study was to assess proteoglycan production by human intervertebral disc cells cultured in vitro in selected cell carriers. Based on previous studies which evaluated disc cells seeded into collagen sponge, collagen gel, agarose, alginate or fibrin gel three-dimensional (3D) cell carriers, collagen sponge and agarose were found to provide superior microenvironments for formation of extracellular matrix (ECM). A standardized test design was used to evaluate ECM formed after 14 days of culture using the 1,9-dimethylmethylene blue (DMB) assay to assess sulfated glycosaminoglycan (S-GAG) production. Although agarose culture showed higher S-GAG levels compared to collagen sponge (2.94+/-2.20 (19) microg/ml S-GAG (mean+/-S.D. (n)) vs. 0.94+/-0.77 (22), respectively, p=0.0003), this is off-set by the significantly lower proliferation rate associated with culture of disc cells in agarose.

Cellular, but not matrix, immunolocalization of SPARC in the human intervertebral disc: decreasing localization with aging and disc degeneration

STUDY DESIGN

Human intervertebral disc anulus tissue was obtained in a prospective study of immunolocalization of SPARC (secreted protein, acidic and rich in cysteine) (osteonectin). Experimental studies were approved by the authors' Human Subjects Institutional Review Board. Discs were obtained from surgical specimens and from control donors.

OBJECTIVES

To determine whether SPARC could be detected in the disc with immunohistochemistry and to determine the incidence of SPARC-positive cells.

SUMMARY OF THE BACKGROUND DATA

SPARC is a glycoprotein that has an important role in modulating interactions between cells and matrix. It influences remodeling, collagen fibrillogenesis, metalloproteinase expression, and cytokine expression. Little is known about SPARC in the disc, and one previous study reported the absence of its immunolocalization in fetal and adult disc tissue.

METHODS

Eight normal human discs from subjects aged newborn to 10 years, and 11 disc specimens from control donors or surgical patients aged 15to 76 years were examined for immunolocalization of SPARC. Anulus cells were also tested for the presence of SPARC in vitro in monolayer or three-dimensional agarose culture.

RESULTS

In discs of subjects aged newborn to 0.19 years, SPARC was present in all cells in the outer anulus, in 76.4% of inner anulus cells, and 76.0% of nucleus cells. Localization was significantly lower in anulus cells of study participants aged 4.7 to 76 years (66.7%, P = 0.04). Anulus cells cultured in agarose or monolayer showed positive localization in all cells.

CONCLUSIONS

Findings show decreased presence of SPARC in disc cells of older subjects with disc degeneration and point to the importance of future studies designed to elucidate the unrecognized role of SPARC in disc remodeling, aging, and degeneration.

Percutaneous plasma decompression alters cytokine expression in injured porcine intervertebral discs

BACKGROUND CONTEXT

Discectomy is a surgical technique commonly used to treat bulging or herniated discs causing nerve root compression. Clinical data suggest discectomy may also help patients with contained discs and no clear neural compromise. However, the mechanisms of clinical efficacy are uncertain, and consequently bases for treatment optimization are limited.

PURPOSE

To determine the effect of percutaneous plasma decompression on the histologic, morphologic, biochemical and biomechanical features of degenerating intervertebral discs.

STUDY DESIGN

An adult porcine model of disc degeneration was used to establish a degenerative baseline against which to evaluate discectomy efficacy.

OUTCOME MEASURES

Cytokines interleukin (IL)-1, IL-6, IL-8, and tumor necrosis factor (TNF)-alpha were measured from tissue samples using enzyme-linked immunosorbent assay. Histology and morphology images were rated for degenerative findings (of cells and matrix) in both the nucleus and annulus. Proteoglycan content was determined, and intact specimen stiffness and flexibility were measured biomechanically. Magnetic resonance images were collected for biomechanical specimens.

METHODS

Using a retroperitoneal surgical approach, stab incisions were made in four or five lumbar discs per spine in 12 minipigs. Animals were allocated into one of three groups: 6-week recovery, 12-week recovery and percutaneous plasma decompression using an electrosurgical device at 6 weeks with recovery for 6 additional weeks. Four additional animals served as controls.

RESULTS

Discs treated with discectomy had a significant increase in IL-8 and a decrease in IL-1 as compared with the 12-week, nontreated discs. There were no significant differences in morphologic and biomechanical parameters or proteoglycan content between treated discs and time-matched, nontreated discs.

CONCLUSIONS

Our results demonstrate that percutaneous plasma discectomy alters the expression of inflammatory cytokines in degenerated discs, leading to a decrease in IL-1 and an increase in IL-8. Whereas both IL-1 and IL-8 have hyperalgesic properties, IL-1 is likely to be a more important pathophysiologic factor in painful disc disorders than IL-8. Therefore, the alteration in cytokine expression that we observed is consistent with this effect as a mechanism of pain relief after discectomy. In addition, given that IL-1 is catabolic in injured tissue and IL-8 is anabolic, our results suggest that a percutaneous plasma discectomy may be capable of initiating a repair response in the disc.