The SOX9 transcription factor in the human disc: decreased immunolocalization with age and disc degeneration

STUDY DESIGN

Human intervertebral disc anulus tissue was obtained in a prospective study of immunolocalization of SOX9, a protein that plays a role in chondrogenesis and Type II collagen expression. The Human Subjects Institutional Review Board approved experimental studies. Discs were obtained from surgical specimens and from control donors.

OBJECTIVES

To determine whether SOX9 could be detected in discs of Thompson Grades I-IV using immunohistochemistry and to quantify the percentage of cells with SOX9 expression.

SUMMARY OF BACKGROUND DATA

SOX9 is involved with cell-specific activation of COL2A1 in chondrocytes. Recent studies have used adenoviral delivery vectors expressing SOX9 to infect a chondroblastic cell line and human disc cells; SOX9 and Type II collagen production increased. The AdSOX9 virus has also been injected directly into rabbit discs in which disc architecture was preserved for 5 weeks. Despite current interest in SOX9 for gene therapy, there have been few studies of SOX9 in normal or degenerated discs.

METHODS

Discs from 12 normal donors and 25 surgical subjects 15-76 years old were examined for SOX9 immunolocalization. Eight Thompson Grade I discs, 7 Grade II discs, 10 Grade III discs, and 12 Grade IV discs were studied.

RESULTS

In Thompson Grade I discs, SOX9 was uniformly localized throughout the anulus and in some cells of the nucleus. However, in discs from adult donors, anulus cells were present that showed no SOX9 localization, although neighboring cells might be positive. Mean percent localization was 74% for Grade II discs, 69% for Grade III, and 71.6% for Grade IV. Cervical sites showed significantly greater localization than lumbar sites.

CONCLUSIONS

Findings showed a uniform expression of SOX9 in the newborn healthy anulus. With aging and disc degeneration, some anulus cells no longer express this transcription product. These observations suggest that the loss of expression of SOX9 in some disc cells may play a role indisc aging and disc degeneration by resulting in decreased expression and production of Type II collagen.

Biologic strategies for the therapy of intervertebral disc degeneration

Recent advances in tissue engineering have led to promising new approaches for the biologic treatment of disc degeneration. At present, there is no effective therapy for disc degeneration, a condition which results in large healthcare and socio-economic costs. This article will examine the current approaches used in biologic therapies for disc degeneration, including cell-based tissue engineering, gene therapy and the application of mesenchymal stem cells, and discuss their therapeutic potential, as demonstrated in animal models and experimental studies to date.

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.

Colony formation and matrix production by human anulus cells: modulation in three-dimensional culture

STUDY DESIGN

Human intervertebral disc cells from the anulus were tested in a study of colony formation and extracellular matrix (ECM) production during long-term three-dimensional culture with exposure to selected cytokines. Experimental studies were approved by the authors' Human Subjects Institutional Review Board.

OBJECTIVES

To quantitatively evaluate colony formation and qualitatively assess ECM production (using immunohistochemistry and in situ hybridization) in cells derived from Thompson Grades I to V discs and tested in culture with cytokines and nutrient supplementation.

SUMMARY OF THE BACKGROUND DATA

Human intervertebral disc cells offer special in vitro challenges because of the slow-growing nature of these cells and their need for specialized three-dimensional in vitro conditions, which permit the expression and production of proteoglycans and Type II collagen, two ECM products that are important for disc cell biology.

METHODS

Discs from 9 human subjects (2 control donors and 7 surgical patients, Thompson Grades I-V), mean age 35.8 years, were used to obtain anulus cells to be tested in three-dimensional agarose culture. Tests of specialized growth conditions included treatment with ITS (insulin-transferrin-sodium selenite supplement), insulin-like growth factor I (IGF-I), and transforming growth factor-beta1 (TGF-beta1). Cultures were evaluated after 14 to 36 days of culture for % colony formation and cell numbers/colony; immunocytochemistry, in situ hybridization, and quantitative histology were used to evaluate colony formation and ECM production.

RESULTS

: Data showed that compared with the average 17.5% colony formation observed in controls, ITS, TGF-beta1 and ITS with IGF-I significantly increased colony formation (28.4%, 30.4%, and 30.4%, respectively, P < or = 0.04). Even cells derived from Thompson Grade V disc showed responsiveness to cytokines and improved production of ECM in vitro.

CONCLUSIONS

: Findings indicated that cells derived from discs with advanced degeneration were still responsive to cytokines and could be modulated to produce Type II collagen and proteoglycans in three-dimensional culture by the addition of enriched media and selected cytokines. Such findings are important since they advance our understanding of how to modulate disc cell behavior in vitro, and may have application to potential future biologic therapies for disc degeneration.

Surgical management of juvenile amputation overgrowth with a synthetic cap

Seventeen amputations (in 14 children) with established overgrowth were treated by capping of the residual limb with a polytetrafluoroethylene (PTFE) felt pad. Average age at the time of the procedure was 7 years 10 months. Mean follow-up was 4 years 9 months. Statistical comparisons were made to historical controls, treated by resection revision or biologic capping, from a prior overgrowth study from the authors' institution. Revision surgery was necessary in 86% of resection revisions, 29% of biologic caps, and 29% of PTFE caps. Kaplan-Meier analysis estimated survival times of 3 years 3 months for resection revision, 6 years 1 month for biologic caps, and 7 years 2 months for PTFE caps. PTFE and biologic caps were both statistically better than resection revision with regard to need for subsequent operation and survivorship, but were not statistically different from each other. Complications associated with PTFE capping and biologic capping were distinct.

Subchondral bone resorption in temporomandibular joint disorders

Several tissues are involved in temporomandibular joint (TMJ) health, including synovial fluid, the TMJ disc, articular cartilage, and subchondral bone. This article focuses upon bone resorption in temporomandibular joint disorders (TMD) and has the following objectives: (1) to provide a brief review of the current understanding of bone formation and bone resorption (bone remodeling); (2) to present selected case studies which illustrate the spectrum of bone resorption patterns in TMD patients of various ages; (3) to review previous reports in the literature describing loss of subchondral bone in TMD, and (4) to discuss the interaction between osteoporosis and TMD and the potential role for antiresorbing agents in TMD therapy.

Bone loss induced by dietary magnesium reduction to 10% of the nutrient requirement in rats is associated with increased release of substance P and tumor necrosis factor-alpha

Dietary Mg intake has been linked to osteoporosis. Previous studies have demonstrated that severe Mg deficiency [0.04% of nutrient requirement (NR)] results in osteoporosis in rodent models. We assessed the effects of more moderate dietary Mg restriction (10% of NR) on bone and mineral metabolism over a 6-mo experimental period in rats. At 2, 4 and 6 mo, serum Mg, Ca, parathyroid hormone (PTH), 1,25-dihydroxy-vitamin D, alkaline phosphatase, osteocalcin and urine pyridinoline were measured. Femurs and tibiae were collected for measurement of mineral content, microcomputerized tomography, histomorphometry, and immunocytochemical localization. By 2 mo, profound Mg deficiency had developed as assessed by marked hypomagnesemia and up to a 51% reduction in bone Mg content. These features continued through 6 mo of study. Serum Ca was slightly but significantly higher in Mg-deficient rats than in controls at all time points. At 2 mo, serum PTH was elevated in Mg-deficient rats but was significantly decreased at 6 mo in contrast to control rats in which PTH rose. Serum 1,25-dihydroxy-vitamin D was significantly lower than in controls at 4 and 6 mo. A significant fall in both serum alkaline phosphatase and osteocalcin suggested decreased osteoblast activity. Histomorphometry demonstrated decreased bone volume and trabecular thickness. This was confirmed by microcomputerized tomography analysis, which also showed that trabecular volume, thickness and number were significantly lower in Mg-deficient rats. Increased bone resorption was suggested by an increase in osteoclast number over time compared with controls as well as surface of bone covered by osteoclasts and eroded surface, but there was no difference in osteoblast numbers. The increased bone resorption may be due to an increase in TNF-alpha because immunocytochemical localization of TNF-alpha in osteoclasts was 199% greater than in controls at 2 mo, 75% at 4 mo and 194% at 6 mo. The difference in TNF-alpha may be due to substance P, which was 250% greater than in controls in mononuclear cells at 2 mo and 266% at 4 mo. These data demonstrated that a Mg intake of 10% of NR in rats causes bone loss that may be secondary to the increased release of substance P and TNF-alpha.

Cell-based tissue engineering for the intervertebral disc: in vitro studies of human disc cell gene expression and matrix production within selected cell carriers

BACKGROUND CONTEXT

Little is known about how disc cells attach, proliferate and form extracellular matrix (ECM) within carrier materials. Such information is needed to help formulate criteria for successful cell-carrier interactions in tissue engineering.

PURPOSE

To compare proliferation, ECM production and gene expression in annulus cells cultured in a variety of cell carrier materials with potential application in tissue engineering of the disc.

STUDY DESIGN

Human intervertebral disc cells from the annulus were used in a prospective study of proliferation, ECM production and gene expression within selected cell carriers.

METHODS

Annulus cells from discs of 29 individuals were tested in collagen sponge, collagen gel, agarose, alginate or fibrin gel formulations. In situ hybridization assessed ECM gene expression of Types I and II collagen, aggrecan and chondroitin-6 sulfotransferase. Cell proliferation, cell shape, attachment and ECM production were evaluated.

RESULTS

Collagen sponges provided the best microenvironment for disc cell ECM production and gene expression. Although collagen gels often could support good cell growth, such constructs did not result in either abundant ECM production or ECM gene expression, as shown by in situ hybridization. Growth and ECM production and gene expression in alginate, agarose and fibrin microenvironments were inferior.

CONCLUSIONS

Tissue engineering techniques open new therapeutic possibilities for use of autologous disc cells, but fundamental questions on how these cells interact with cell carriers are unexplored. Results provide novel data on disc cell gene expression within diverse microenvironments. The collagen sponge proved to be a superior microenvironment.

Preoperative leuprolide acetate combined with Interceed optimally reduces uterine adhesions and fibrosis in a rabbit model,

OBJECTIVE

To determine the optimal approach to prevent adhesions comparing leuprolide acetate (GnRH-a), Interceed (oxidized regenerated cellulose; Johnson & Johnson Medical, Inc., New Brunswick, NJ), and a combination of leuprolide with Interceed in a rabbit uterine horn adhesion model.

DESIGN

Prospective, randomized, blinded study.

SETTING

Certified animal care facility.

ANIMAL(S)

Twenty-eight sexually mature, female New Zealand White rabbits.

INTERVENTION(S)

Animals were prospectively randomized (by number generator) to receive GnRH-a or saline. After 6 weeks, standard surgical manipulations were performed at three sites in each uterine horn by [1]. suture, [2]. unipolar cautery, and [3]. superficial abrasion. Interceed was applied over one randomly assigned uterine horn only. Six weeks after surgery, uterine adhesions were assessed visually, and tissue fibrosis was assessed by histology.

MAIN OUTCOME MEASURE(S)

Presence or absence of adhesions and microscopic tissue fibrosis.

RESULT(S)

Gonadotropin-releasing hormone agonist significantly decreased adhesions, whereas Interceed alone did not reduce adhesions. However, GnRH agonist plus Interceed was the most effective measure to reduce tissue fibrosis.

CONCLUSION(S)

Preoperative GnRH-a is more effective than Interceed in preventing surgical adhesions in the rabbit uterine horn. However, preoperative GnRH-a plus Interceed may provide optimal results in this animal model, because microscopic tissue fibrosis is minimized with this combination.

Alterations in osteoclast morphology following osteoprotegerin administration in the magnesium-deficient mouse

In the present study, we used osteoprotegerin (OPG), which blocks osteoclastogenesis, to correct and thus explain the hypercalcemia that is seen during dietary Mg deficiency in the mouse. Control and Mg-deficient mice received injections for 12 days of either OPG or vehicle only. Serum Ca was similar in Mg-deficient mice treated with OPG and in control mice receiving OPG (9.2 +/- 0.3 mg/dl vs. 9.2 +/- 0.5). Both groups had significantly higher serum Ca than controls or Mg-deficient animals receiving vehicle alone. Surprisingly, Mg-depleted mice that received OPG in doses that inhibit osteoclastic bone resorption remained hypercalcemic. Because mature osteoclasts still present in the marrow might be hyperactive, we examined osteoclast morphology at the light microscopic and ultrastructural level. Light microscopic examination of trabecular bone showed few osteoclasts in OPG-treated mice. Ultrastructural examination revealed that osteoclasts in OPG-treated mice have decreased contact with the endosteal bone surface and absence of a ruffled border. Because the morphology of the existing pool of mature osteoclasts did not enhance resorption, another mechanism, such as increased intestinal absorption of Ca in Mg-deficient mice, likely contributes to the hypercalcemia observed during Mg deficiency.

Bone mineral density of lumbar vertebral end plates in the aging male sand rat spine

STUDY DESIGN

Lumbar vertebral segments from young and old male sand rats were assessed for quantitative determination of lumbar end plate bone mineral density.

OBJECTIVES

To determine whether bone mineral density increases in the lumbar end plate with age in the male sand rat and to investigate its relationship to disc degeneration.

SUMMARY OF THE BACKGROUND DATA

Few basic science studies evaluated the end plate and disc degeneration. The sand rat provides an excellent economical model in which disc degeneration is reliable and well characterized.

METHODS

Bone mineral density data on cranial and caudal lumbar end plates of young (mean age 6.8 months) and old (mean age 23.3 months) male sand rats were assessed for changes related to age, lumbar position, and radiologic features.

RESULTS

Mean bone mineral density was significantly greater in end plates in older compared to younger males (P <or= 0.0018). Mean end plate bone mineral density within young animals was not significantly different in levels L5 to L7; in old animals, bone mineral density was significantly different (greater) progressing from L5 to L7 (P < 0.0001). In older animals, mean end plate bone mineral density for each disc showed a significant increase with lower lumbar sites (P = 0.0068). Mean end plate bone mineral density was significantly greater in animals with radiographic evidence of disc wedging (P = 0.006). End plate bone mineral density correlated positively with age.

CONCLUSIONS

Results provide quantitative bone mineral density data on end plate sclerosis in male sand rats. Data reveal site specificities and show that in old animals, end plate bone mineral density is greater than in young animals. Mean end plate bone mineral density was significantly greater at sites with radiographic disc wedging (P = 0.006). Data support the hypothesis that end plate sclerosis may play a role in disc degeneration.

Magnesium deficiency: effect on bone mineral density in the mouse appendicular skeleton

BACKGROUND

Dietary magnesium (Mg) deficiency in the mouse perturbs bone and mineral homeostasis. The objective of the present study was to evaluate bone mineral density of the femur in control and Mg-deficient mice.

METHODS

BALB/c mice aged 28 days at study initiation were maintained on a normal or Mg deficient (0.0002% Mg) diet, and at time points 0, 2, 4 or 6 weeks bones were harvested for bone mineral density analysis. Peripheral quantitative computed tomography (pQCT) was used to assess the trabecular metaphyseal compartment and the cortical midshaft.

RESULTS

Although mean total bone density of the femoral midshaft in Mg deficient mice did not differ significantly from controls throughout the study, the trabecular bone compartment showed significantly decreased mineral content after 4 (p < 0.001) and 6 weeks (p < 0.001) of Mg depletion.

CONCLUSIONS

This study demonstrates the profound effect of Mg depletion on the trabecular compartment of bone, which, with its greater surface area and turnover, was more responsive to Mg depletion than cortical bone in the appendicular skeleton of the mouse.

Computer aided vertebral visualization and analysis: a methodology using the sand rat, a small animal model of disc degeneration

BACKGROUND

The purpose of this study is to present an automated system that analyzes digitized x-ray images of small animal spines identifying the effects of disc degeneration. The age-related disc and spine degeneration that occurs in the sand rat (Psammomys obesus) has previously been documented radiologically; selected representative radiographs with age-related changes were used here to develop computer-assisted vertebral visualization/analysis techniques. Techniques presented here have the potential to produce quantitative algorithms that create more accurate and informative measurements in a time efficient manner.

METHODS

Signal and image processing techniques were applied to digitized spine x-ray images the spine was segmented, and orientation and curvature determined. The image was segmented based on orientation changes of the spine; edge detection was performed to define vertebral boundaries. Once vertebrae were identified, a number of measures were introduced and calculated to retrieve information on the vertebral separation/orientation and sclerosis.

RESULTS

A method is described which produces computer-generated quantitative measurements of vertebrae and disc spaces. Six sand rat spine radiographs illustrate applications of this technique. Results showed that this method can successfully automate calculation and analysis of vertebral length, vertebral spacing, vertebral angle, and can score sclerosis. Techniques also provide quantitative means to explore the relation between age and vertebral shape.

CONCLUSIONS

This method provides a computationally efficient system to analyze spinal changes during aging. Techniques can be used to automate the quantitative processing of vertebral radiographic images and may be applicable to human and other animal radiologic models of the aging/degenerating spine.

Recent advances in disc cell biology

STUDY DESIGN

There have been many advances over the past decade in understanding and experimentally modulating biologic aspects of intervertebral disc cell function. An overview of the current state of this biologic research is presented.

OBJECTIVES

To provide clinicians with a review of important recent advances in biologic studies of the disc and their implications for potential disc therapies.

SUMMARY OF BACKGROUND DATA

Historically, anatomic, biochemical, radiologic, and biomechanical studies of the intervertebral disc formed the foundation on which our understanding of disc function was built. Magnetic resonance imaging techniques that allowed viewing of soft tissue components of the disc further advanced imaging capabilities.

METHODS

Recent publications are reviewed.

RESULTS

Experimental approaches over the past decade have enabled researchers to look more critically at disc cell function. This is important because disc cell function produces the extracellular matrix components of the disc, which, in turn, shape the disc's subsequent physiologic and biomechanical functions. New approaches to the study of disc cell function, methods to manipulate disc cells, studies of intact discs and disc nutrition, vertebral endplate structure and function, tissue engineering, gene therapy, and the potential of stem cells in disc therapy are reviewed and discussed.

CONCLUSIONS

Many believe that disc degeneration has a cellular basis. New research is helping us better understand healthy, aging, and degenerating discs. Modern methods to manipulate and modulate disc cell function open exciting and challenging new therapeutic possibilities for future biologic treatments of disc degeneration.

Magnesium deficiency: effect on bone and mineral metabolism in the mouse

Insufficient dietary magnesium (Mg) intake has been associated in humans with low bone mass. Mg deficiency in the rat has suggested bone loss is due to increased bone resorption and/or inadequate bone formation during remodeling. The purpose of this study was to assess the effect of a low Mg diet on bone and mineral metabolism in the young and mature BALB/c mouse and explore the hypothesis that inflammatory cytokines may contribute to Mg deficiency-induced osteoporosis. Using an artificial diet, we induced targeted Mg depletion (0.002% Mg) with all other nutrients maintained at the normal level. In all Mg-depleted mice, hypomagnesemia developed and skeletal Mg content fell significantly. The serum Ca in Mg-deficient mice was higher than in control mice; however, serum PTH levels were not significantly different. Osteoprotegerin (OPG) in dosages that inhibit osteoclastic bone resorption did not prevent hypercalcemia in Mg-deficient animals. No significant difference in serum Ca was observed between groups when dietary Ca was reduced by 50%, suggesting that a compensatory increase in intestinal absorption might account for the hypercalcemia. Growth plate width decreased 33% in young Mg-deficient animals and chondrocyte columns decreased in number and length, suggesting that Mg deficiency reduced bone growth. Trabecular bone volume in the metaphysis of the tibia in these animals was decreased and osteoclast number was increased by 135%. Osteoblast number was significantly reduced. Immunohistochemistry revealed that substance P increased 230% and 200% in megakaryocytes and lymphocytes, respectively, after 1 day of Mg depletion. IL-1 increased by 140% in osteoclasts by day 3 and TNF alpha increased in osteoclasts by 120% and 500% in megakaryocytes on day 12. This study demonstrates a profound effect of Mg depletion on bone characterized by impaired bone growth, decreased osteoblast number, increased osteoclast number in young animals, and loss of trabecular bone with stimulation of cytokine activity in bone.

Physeal fractures, part I: histologic features of bone, cartilage, and bar formation in a small animal model

Physeal fractures and the formation of physeal bars can pose significant problems in skeletal development for the injured, growing child. Regrettably, little experimental attention has been directed toward this clinical disturbance. The current study documents early histologic changes (days 2-6) and subsequent alterations (day 21) following a physeal fracture in the rat proximal tibia model. The fracture plane was usually contained within the physis but could involve many regions of the physis. In some instances, the fracture plane extended to the physeal epiphyseal border. When the fracture was contained within the physis, healing was uneventful. However, when the fracture extended through the physis to the epiphyseal physeal border, there was greater physeal disorganization and formation of vertical septa leading to physeal bars. Physeal bars appeared to form at sites of vertical fibrotic septa into which marrow cells, osteoclasts, and osteoblasts had migrated. Bar formation mediated by primary osteogenesis (rather than by endochondral bone formation) followed. This study examines the changes in the histologic features of the rat proximal tibial physis, epiphysis, and metaphysis after a physeal fracture and identifies key factors associated with physeal bar formation.

Physeal fractures, part II: fate of interposed periosteum in a physeal fracture

This study describes the histologic features of periosteum interposed into a physeal fracture of the rat proximal tibia. Periosteum was introduced into a physeal fracture in two groups of animals: those with an intact physis after fracture, and those with the medial half of the physis surgically ablated. Specimens of the proximal tibia underwent histologic analysis at 2, 4, 6, 10, and 21 days after fracture to determine the histologic features of interposed periosteum in a physeal fracture. In animals with an intact physis, interposed periosteum underwent one of two fates: it was degraded by giant cells in the fracture plane, which allowed cellular infiltration, or if the periosteum was closely surrounded by physeal cartilage, the physis grew around it and appeared to force it toward the metaphysis. In animals whose physis received surgical ablation, physeal bar formation was always present, with poor organization of the remaining lateral growth plate. Histologic evidence from this study also underscores the fact that physeal bar formation occurs from the migration of osteoblasts and osteoclasts along vertical septa.

Autologous intervertebral disc cell implantation: a model using Psammomys obesus, the sand rat

STUDY DESIGN

Work presented here used a small animal model to illustrate the feasibility of autologous disc cell implantation.

OBJECTIVES

To develop a small animal model for autologous disc cell implantation.

SUMMARY OF THE BACKGROUND DATA

The use of autologous disc cells in the potential treatment of disc degeneration offers attractive possibilities for novel therapies. Results are presented on the use of the sand rat (Psammomys obesus), a small rodent that spontaneously develops disc degeneration during aging, in experimental studies in which cells were harvested from a lumbar intervertebral disc, expanded in monolayer tissue culture, labeled with agents that allow subsequent immunolocalization of these cells, and implanted in a second disc site of the donor animal.

METHODS

Tissue culture, disc surgery, histology, and immunocytochemistry were used. Cells were either engrafted in a bioresorbable carrier tested for cell compatibility or injected into the recipient disc. Results were assessed with radiographic examination of the implantation site and with histology and immunocytochemistry.

CONCLUSION

Data from 15 animals were obtained with engraftment resident in the animal for up to 33 weeks. Immunocytologic identification of engrafted cells showed that they integrated into the disc and were surrounded by normal matrix at time points up to 8 months postengraftment. Engrafted cells exhibited either a spindle-shaped morphology in the annulus or a rounded chondrocyte-like morphology in the nucleus. Although technically challenging, the authors' experience showed that autologous disc cell implantation can be successful and that the sand rat is a valuable model for autologous disc cell studies.

Ultrastructure of the human intervertebral disc during aging and degeneration: comparison of surgical and control specimens

STUDY DESIGN

Human intervertebral disc tissue from the annulus was obtained in a prospective study investigating the ultrastructural features of disc cells and extracellular matrix. Experimental studies were approved by the authors' Human Subjects Institutional Review Board. Discs were obtained from surgical specimens and control donors.

OBJECTIVE

To compare the cellular and extracellular matrix characteristics of the annulus from control and surgical disc specimens using electron microscopy and specialized fixation that visualizes proteoglycans.

SUMMARY OF THE BACKGROUND DATA

The ultrastructural features of disc cells and the disc matrix have received little attention, as compared with the literature on age- and disease-related changes in bone and cartilage.

METHODS

Ultrastructural studies investigated disc tissue obtained from control and surgical disc specimens using transmission electron microscopy. Specialized fixation with ruthenium red was used to highlight matrix proteoglycans.

RESULTS

Cellular and extracellular matrix fine structure was assessed in disc specimens from 29 control donors (newborns to 79-year-olds) and surgical disc specimens from 49 patients (16- to 77-year-olds). Control and surgical tissue showed similar ultrastructural features. Unusual matrix surrounding and encircling single cells or clusters of cells was common (48% of control and 63% of surgical specimens) and often contained fibrous long-spacing collagen (41.3% of control and 36.7% of surgical specimens). Ruthenium red greatly aided visualization of proteoglycans pooled in lacunar spaces. Variable cross-sectional diameters of collagen fibrils was present in 34% of control and 59% of surgical specimens. Regions with sparse interterritorial matrix were common. Cell morphology showed both cells with apoptotic nuclei and synthetically active cells that appeared healthy.

CONCLUSIONS

Control and surgical specimens of the annulus showed similar ultrastructural features. Heterogeneity of collagen fibril diameter is an important observation because it is believed that fibril size relates to biomechanical disc function. Fibrous long-spacing collagen may reflect extracellular matrix remodeling or the presence of previous fibril depolymerization followed by repolymerization and reassociation with proteoglycans. Synthetic activity of disc cells is reflected in active rough endoplasmic reticulum, Golgi, and pools of proteoglycans in lacunar spaces and unusual extracellular matrix components that encircle cells and cell clusters. Such components may influence biomechanical quality. Departures from normal extracellular matrix organization of the aging or degenerating disc undoubtedly contribute to decreased biomechanical function of the annulus because they disrupt the normal annulus architecture. This study underscores the need for a fuller understanding of the dynamic relation between disc cells and the surrounding extracellular matrix, which they continually produce and remodel.

Observations on morphologic changes in the aging and degenerating human disc: secondary collagen alterations

BACKGROUND

In the annulus, collagen fibers that make up the lamellae have a wavy, planar crimped pattern. This crimping plays a role in disc biomechanical function by allowing collagen fibers to stretch during compression. The relationship between morphologic changes in the aging/degenerating disc and collagen crimping have not been explored.

METHODS

Ultrastructural studies were performed on annulus tissue from 29 control (normal) donors (aged newborn to 79 years) and surgical specimens from 49 patients (aged 16 to 77 years). Light microscopy and specialized image analysis to visualize crimping was performed on additional control and surgical specimens. Human intervertebral disc tissue from the annulus was obtained in a prospective morphologic study of the annulus. Studies were approved by the authors' Human Subjects Institutional Review Board.

RESULTS

Three types of morphologic changes were found to alter the crimping morphology of collagen: 1) encircling layers of unusual matrix disrupted the lamellar collagen architecture; 2) collagen fibers were reduced in amount, and 3) collagen was absent in regions with focal matrix loss.

CONCLUSIONS

Although proteoglycan loss is well recognized as playing a role in the decreased shock absorber function of the aging/degenerating disc, collagen changes have received little attention. This study suggests that important stretch responses of collagen made possible by collagen crimping may be markedly altered by morphologic changes during aging/degeneration and may contribute to the early tissue changes involved in annular tears.

An improved staining method for intervertebral disc tissue

The objective of this study was to design a new staining procedure for human disc tissue for visualizing both collagen and proteoglycan-matrix components on the same histology section. Weigert's hematoxylin, alcian blue and picrosirius red were combined to produce distinctive staining of collagen (red), proteoglycans (blue) and cellular elements of the intervertebral disc. This novel stain reveals sharp details of collagen composition in the perilacunar, territorial and intraterritorial extracellular matrix, and concomitantly demonstrates the presence of proteoglycan accumulations around cells in the lacunar spaces and in the extracellular matrix. These details reveal variations within the tissue that would not be apparent with routine stains.

The sand rat model for disc degeneration: radiologic characterization of age-related changes: cross-sectional and prospective analyses

STUDY DESIGN

This report is composed of two studies, one cross-sectional and one prospective cohort study, that analyze the radiologic features of disc degeneration in the sand rat (Psammomys obesus).

OBJECTIVES

To statistically assess progressive disc degeneration in this useful animal model in terms of a cross-sectional study and a prospective monthly evaluation of individual animals.

SUMMARY OF BACKGROUND DATA

P. obesus is an attractive small rodent model for spontaneous age-related disc degeneration. Because disc degeneration is spontaneous, the model avoids use of chemonucleolysis or surgical injury to cause disc degeneration. Little is understood, however, about specific details of the progressive disc deterioration.

METHODS

This study statistically assessed 158 animals in a cross-sectional study and 22 animals in a longitudinal study, which followed individual animals to 12 months of age. Radiologic features involving irregular disc margins, disc wedging, disc narrowing, endplate calcification, subchondral sclerosis, ligament calcification, and osteophyte formation were studied.

RESULTS

Significant age-related cross-sectional changes were present for all features (P < or = 0.005). Males showed a statistically greater incidence of wedging at 6 and 12 months, wedging at 2 and 6 months, and endplate calcification at 2 months than did females. By 6 months of age, however, endplate calcification had a higher incidence in females than in males. Prospective analysis showed that wedging, narrowing, endplate calcification, and irregular disc margins were more common at 12 months of age than at 2 months (P = 0.0001). By the age of 12 months, all lumbar sites of both males and females showed endplate calcification and the majority of animals showed narrowing and wedging.

CONCLUSIONS

Radiographic signs of degeneration were evident by age 2 months; wedging, narrowing, irregular disc margins, and endplate calcification were the most common degenerative changes in older animals. These data show that the sand rat provides a reliable, useful model of spontaneous disc degeneration.

Expression and localization of estrogen receptor-beta in annulus cells of the human intervertebral disc and the mitogenic effect of 17-beta-estradiol in vitro

BACKGROUND

Recent evidence suggests that estrogens exert effects in different tissues throughout the body, and that the estrogen receptor beta (ERbeta) may be important for the action of estrogen (17-beta-estradiol) on the skeleton. The cellular localization of ERbeta in the human intervertebral disc, however, has not yet been explored.

METHODS

Human disc tissue and cultured human disc cells were used for immunocytochemical localization of ERbeta. mRNA was isolated from cultured human disc cells, and RT-PCR amplification of ERbeta was employed to document molecular expression of this receptor. Cultured human disc cells were tested to determine if 17-beta-estradiol stimulated cell proliferation.

RESULTS

In this report data are presented which provide evidence for ERbeta gene expression in human intervertebral disc cells in vivo and in vitro. Culture of annulus cells in the presence of 10-7 M 17-beta-estradiol significantly increased cell proliferation.

CONCLUSIONS

These data provide new insight into the biology of cells in the annulus of the intervertebral disc.

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

Our objective for this study was to determine the presence and distribution of tenascin in the human intervertebral disc. The tenascins are a family of extracellular matrix proteins with repeated structural domains homologous to epidermal growth factor, fibronectin type III and the fibrinogens. Little is known about the presence of this protein in the disc. Ten normal human discs donated from subjects newborn to 15 years old, 10 control discs from adult donors aged 24-41 years, and 11 surgical disc specimens from patients aged 26-76 years were examined for immunolocalization of tenascin. In young discs, tenascin was localized throughout the annulus; in the nucleus, localization was confined to pericellular matrix. In adult control and degenerating disc specimens, tenascin in the annulus was localized primarily in pericellular matrix regions encircling either single cells or clusters of disc cells; in rare instances localization was more diffuse in the intraterritorial matrix. In young, healthy disc, tenascin was abundant throughout the annulus. In contrast, degenerating discs in adults showed a localization restricted to the pericellular, and rarely, more restricted intraterritorial matrix. These observations indicate that changes in the amount and distribution of tenascin may have a role in disc aging and degeneration, possibly by modulating fibronectin-disc-cell interactions, and causing alterations in the shape of disc cells.

Clinical and demographic prognostic indicators for human disc cell proliferation in vitro: pilot study

STUDY DESIGN

Human anulus cells were cultured under control and experimental conditions to study associations between proliferation and clinical-demographic features of subjects from which cells were obtained. Statistical multiple regression analyses were applied to develop mathematic models relating proliferation to age, gender, Thompson score (denoting stage of disc degeneration), and status (control donor [postmortem]; surgical patient).

OBJECTIVES

To identify the effect of donor characteristics on proliferative capacities of human disc cells.

SUMMARY OF BACKGROUND DATA

As therapeutic options for disc degeneration increase, novel biologic options are important future considerations. Little is known about the influence of clinical-demographic features on cell proliferation.

METHODS

Anulus cells were studied in two designs: 1) Cells from 12 individuals were grown in monolayer with 50 ng/mL interleukin growth factor-1 (IGF-I), 100 ng/mL insulin, or control conditions. 2) Cells from nine individuals were grown in three-dimensional culture with 10 ng/mL IGF-I or control conditions. Cell proliferation data and data on age, gender, Thompson score, and status were collected. Standard statistical analyses were used to develop correlation models.

RESULTS

Data from monolayer experiments produced significant models fitting proliferation in the presence of low serum, 50 ng/mL IGF-I, or insulin, with age, gender, Thompson score, and status (respective R2: 0.827, 0.680, 0.850). Three-dimensional cultures exposed to 10 ng/mL IGF-I resulted in proliferation that correlated in a significant negative manner with Thompson score (r = -0.798).

CONCLUSIONS

Clinical-demographic prognostic indicators may help predict levels of proliferation. Greater age, greater disc degeneration, female gender, and surgical derivation had deleterious effects on proliferation potential in this model.