Changes with age and the effect of recombinant human BMP-2 on proteoglycan and collagen gene expression in rabbit anulus fibrosus cells

Growing a backbone - functional biomaterials and structures for intervertebral disc (IVD) repair and regeneration: challenges, innovations, and future directions

Back pain and associated maladies can account for an immense amount of healthcare cost and loss of productivity in the workplace. In particular, spine related injuries in the US affect upwards of 5.7 million people each year. The degenerative disc disease treatment almost always arises due to a clinical presentation of pain and/or discomfort. Preferred conservative treatment modalities include the use of non-steroidal anti-inflammatory medications, physical therapy, massage, acupuncture, chiropractic work, and dietary supplements like glucosamine and chondroitin. Artificial disc replacement, also known as total disc replacement, is a treatment alternative to spinal fusion. The goal of artificial disc prostheses is to replicate the normal biomechanics of the spine segment, thereby preventing further damage to neighboring sections. Artificial functional disc replacement through permanent metal and polymer-based components continues to evolve, but is far from recapitulating native disc structure and function, and suffers from the risk of unsuccessful tissue integration and device failure. Tissue engineering and regenerative medicine strategies combine novel material structures, bioactive factors and stem cells alone or in combination to repair and regenerate the IVD. These efforts are at very early stages and a more in-depth understanding of IVD metabolism and cellular environment will also lead to a clearer understanding of the native environment which the tissue engineering scaffold should mimic. The current review focusses on the strategies for a successful regenerative scaffold for IVD regeneration and the need for defining new materials, environments, and factors that are so finely tuned in the healthy human intervertebral disc in hopes of treating such a prevalent degenerative process.

Intervertebral Disc Nucleus Repair: Hype or Hope?

Chronic back pain is a common disability, which is often accredited to intervertebral disc degeneration. Gold standard interventions such as spinal fusion, which are mainly designed to mechanically seal the defect, frequently fail to restore the native biomechanics. Moreover, artificial implants have limited success as a repair strategy, as they do not alter the underlying disease and fail to promote tissue integration and subsequent native biomechanics. The reported high rates of spinal fusion and artificial disc implant failure have pushed intervertebral disc degeneration research in recent years towards repair strategies. Intervertebral disc repair utilizing principles of tissue engineering should theoretically be successful, overcoming the inadequacies of artificial implants. For instance, advances in the development of scaffolds aided with cells and growth factors have opened up new possibilities for repair strategies. However, none has reached the stage of clinical trials in humans. In this review, we describe the hitches encountered in the musculoskeletal field and summarize recent advances in designing tissue-engineered constructs for promoting nucleus pulposus repair. Additionally, the review focuses on the effect of biomaterial aided with cells and growth factors on achieving effective functional reparative potency, highlighting the ways to enhance the efficacy of these treatments.

Regulation and Role of TGFβ Signaling Pathway in Aging and Osteoarthritis Joints

Transforming growth factor beta (TGFβ) is a major signalling pathway in joints. This superfamilly is involved in numerous cellular processes in cartilage. Usually, they are considered to favor chondrocyte differentiation and cartilage repair. However, other studies show also deleterious effects of TGFβ which may induce hypertrophy. This may be explained at least in part by alteration of TGFβ signaling pathways in aging chondrocytes. This review focuses on the functions of TGFβ in joints and the regulation of its signaling mediators (receptors, Smads) during aging and osteoarthritis.

Intradiscal injection of simvastatin results in radiologic, histologic, and genetic evidence of disc regeneration in a rat model of degenerative disc disease

BACKGROUND CONTEXT

A large percentage of back pain can be attributed to degeneration of the intervertebral disc (IVD). Bone morphogenetic protein 2 (BMP-2) is known to play an important role in chondrogenesis of the IVD. Simvastatin is known to upregulate expression of BMP-2. Thus, we hypothesized that intradiscal injection of simvastatin in a rat model of degenerative disc disease (DDD) would result in retardation of DDD.

PURPOSE

The purpose of the present study was to develop a novel conservative treatment for DDD and related discogenic back pain.

STUDY DESIGN/SETTING

The setting of this study is the laboratory investigation.

METHODS

Disc injury was induced in 272 rats via 21-ga needle puncture. After 6 weeks, injured discs were treated with simvastatin in a saline or hydrogel carrier. Rats were sacrificed at predetermined time points. Outcome measures assessed were radiologic, histologic, and genetic. Radiologically, the magnetic resonance imaging (MRI) index (number of pixels multiplied by the corresponding image densities) was determined. Histologically, disc spaces were read by three blinded scorers using a previously described histologic grading scale. Genetically, nuclei pulposi were harvested, and polymerase chain reaction was run to determine relative levels of aggrecan, collagen type II, and BMP-2 gene expression.

RESULTS

Radiologically, discs treated with 5 mg/mL of simvastatin in hydrogel or saline demonstrated MRI indices that were normal through 8 weeks after treatment, although this was more sustained when delivered in hydrogel. Histologically, discs treated with 5 mg/mL of simvastatin in hydrogel demonstrated improved grades compared with discs treated at higher doses. Genetically, discs treated with 5 mg/mL of simvastatin in hydrogel demonstrated higher gene expression of aggrecan and collagen type II than control.

CONCLUSIONS

Degenerate discs treated with 5 mg/mL of simvastatin in a hydrogel carrier demonstrated radiographic and histologic features resembling normal noninjured IVDs. In addition, the gene expression of aggrecan and collagen type II (important constituents of the IVD extracellular matrix) was upregulated in treated discs. Injection of simvastatin into degenerate IVDs may result in retardation of disc degeneration and represents a promising investigational therapy for conservative treatment of DDD.

Glutathione protects human nucleus pulposus cells from cell apoptosis and inhibition of matrix synthesis

Abstract Cell death (apoptosis and necrosis) and extracellular matrix destruction induced by oxidative stress have been suggested to be closely involved in the process of disc degeneration. Glutathione, a natural peptide as a powerful antioxidant in human cytoplasm, plays an important role in protecting living cells. This study is to investigate whether glutathione could retard degenerated phenotypes in cultured disc cells. Human nucleus pulposus cells were isolated and cultured in alginate beads and subsequently treated with a pro-oxidant H2O2 alone or a pro-inflammatory cytokine IL-1β alone or either of them together with glutathione. It was shown that H2O2 dose-dependently promoted nucleus pulposus cell apoptosis detected by terminal deoxynucleotidyl transferase-mediated dUTP nick end labeling (TUNEL) staining and decreased mRNA levels of matrix proteins aggrecan and type II collagen determined by quantitative reverse transcription-polymerase chain reaction (RT-PCR). IL-1β could induce production of nitric oxide and decrease of proteoglycan, detected by the Griess reagent and the dimethyl methylene blue, respectively. The deleterious effects of either H2O2 or IL-1β could be efficiently prevented by glutathione. These results indicated that glutathione might be considered as an option for intervention of disc degeneration.

Changes of number of cells expressing proliferation and progenitor cell markers with age in rabbit intervertebral discs

Basic knowledge about the normal regeneration process within the intervertebral disc (IVD) is important to the understanding of the underlying biology. The presence of progenitor and stem cells in IVD has been verified. However, changes of number of progenitor and stem cells with age are still unknown. In this study, changes of cell proliferation and progenitor cell markers with age in IVD cells from rabbits of two different ages were investigated using flow cytometry, immunohistochemistry, real-time polymerase chain reaction, and western blot analysis. Proliferating cell nuclear antigen (PCNA) was chosen as a marker for proliferation, and Notch1, Jagged1, C-KIT, CD166 were chosen as stem/progenitor cell markers. Cell cycle analysis showed that cell number in the G2/M phase of the young rabbits was significantly higher than that of mature rabbits. Immunohistochemical staining demonstrated the expression of PCNA, C-KIT, CD166, Notch1, and Jagged1 in both young and mature annulus fibrosus (AF). Protein expressions of these cell markers in the young rabbits were all significantly higher than those in the mature rabbits. The expression levels of PCNA, CD166, C-KIT, Jagged1 were significantly higher in the AF, and PCNA, C-KIT in the nucleus pulposus from young rabbits than those from the mature rabbits. These findings demonstrated that both proliferation and progenitor cells exist in rabbit IVDs and the number of cells expressing proliferation and progenitor cell markers decreases with age in the rabbit IVD cells. Methods that are designed to maintain the endogenous progenitor cells and stimulate their proliferation could be successful in preventing or inhibiting degenerative disc disease.

Bone morphogenetic proteins and degenerative disk disease

Bone morphogenetic proteins (BMPs) are involved not only in osteogenesis but also in chondrogenesis. They play an important role in the development and maintenance of the intervertebral disk (IVD). For this reason, an increasing amount of research has been performed to examine the relationship between BMPs and degenerative disk disease (DDD). Moreover, researchers are examining the safe use of BMPs as a potential treatment for diskogenic back pain. We performed a literature search using databases from the US National Library of Medicine and the National Institutes of Health to identify studies relating BMPs to DDD. According to in vitro and in vivo studies in different animal and human IVDs, BMP-2 and BMP-7 are upregulated with aging and with induced disk injury; this represents an anabolic response. Direct administration of BMP-2 to IVD cells results in increased production of components of the extracellular matrix. Upregulation of the BMP pathway via other agents, namely simvastatin and LIM mineralization protein-1, has resulted in similar outcomes. Adenoviruses loaded with BMPs, transfected either directly to IVD cells or via articular chondrocytic vectors, also resulted in reversal of the typical findings in DDD. We conclude that the use of BMPs to treat DDD has a promising future. Further studies are indicated to determine optimal delivery and efficacy in humans.

Towards biological anulus repair: TGF-β3, FGF-2 and human serum support matrix formation by human anulus fibrosus cells

Closure and biological repair of anulus fibrosus (AF) defects in intervertebral disc diseases is a therapeutic challenge. The aim of our study was to evaluate the anabolic properties of bioactive factors on cartilaginous matrix formation by AF cells. Human AF cells were harvested from degenerated lumbar AF tissue and expanded in monolayer culture. AF cell differentiation and matrix formation was initiated by forming pellet cultures and stimulation with hyaluronic acid (HA), human serum (HS), fibroblast growth factor-2 (FGF-2), transforming growth factor-β3 (TGF-β3) and TGF-β3/FGF-2 for up to 4 weeks. Matrix formation was assessed histologically by staining of proteoglycan, type I and type II collagens and by gene expression analysis of typical extracellular matrix molecules and of catabolic matrix metalloproteinases MMP-2 and MMP-13. AF cells, stimulated with HS, FGF-2 and most pronounced with TGF-β3 or TGF-β3/FGF-2 formed a cartilaginous matrix with significantly enhanced expression of matrix molecules and of MMP-13. Stimulation of AF cells with TGF-β3 was accompanied by induction of type X collagen, known to occur in hypertrophic cartilage cells having mineralizing potential. HA did not show any chondro-inductive characteristics. These findings suggest human serum, FGF-2 and TGF-β3 as possible candidates to support biological treatment strategies of AF defects.

Triamcinolone decreases bupivacaine toxicity to intervertebral disc cell in vitro

BACKGROUND CONTEXT

Local anesthetics combined with corticosteroids are commonly used for management of back pain in interventional spinal procedures. Several recent studies suggest cytotoxicity of bupivacaine, whereas others report protective and cytotoxic effects of corticosteroids on chondrocytes and intervertebral disc cells. Considering the frequent use of these agents in spinal interventions, it is meaningful to know how they affect intervertebral disc cells.

PURPOSE

This study was conducted to assess the effects of bupivacaine and triamcinolone, both alone and in combination, on viability of intervertebral disc cells in vitro.

STUDY DESIGN

Controlled laboratory study.

METHODS

Nucleus pulposus cells were isolated from human disc specimens from patients undergoing surgery because of disc herniation or degenerative disc disease. They were grown in three-dimensional alginate beads for 1 week to maintain their differentiated phenotypes and to allow for matrix formation before analysis. After 1 week of culture, the cells were exposed to bupivacaine (0.1%, 0.25%, 0.5%, and 1%) or bupivacaine (0.1%, 0.25%, 0.5%, and 1%) with 1 mg of triamcinolone for 1, 3, or 6 hours. Cell viability was measured using trypan blue exclusion assay and flow cytometry. Live cell/dead cell fluorescent imaging was assessed using confocal microscopy.

RESULTS

Trypan blue exclusion assays demonstrated dose- and time-dependent cytotoxic effects of bupivacaine on human nucleus pulposus cells. Similar but reduced cytotoxicity was observed after exposure to the combination of bupivacaine and 1 mg of triamcinolone. Flow cytometry showed a dose-dependent cytotoxic effect of bupivacaine on nucleus pulposus cells after 3 hours of exposure. The reduced cytotoxicity of bupivacaine combined with 1 mg of triamcinolone was also confirmed in flow cytometry. Confocal images showed that the increase in dead cells correlated with the concentration of bupivacaine. Nevertheless, fewer cells died after exposure to several different concentrations of bupivacaine combined with 1 mg of triamcinolone than did after exposure to bupivacaine alone.

CONCLUSIONS

The combination of bupivacaine and triamcinolone induced dose- and time-dependent cytotoxicity on human intervertebral disc cells in vitro, but the cytotoxicity was much weaker than that of bupivacaine alone. This study shows a potential protective influence of triamcinolone on intervertebral disc cells.

Cartilage intermediate layer protein (CILP) regulation in intervertebral discs. The effect of age, degeneration, and bone morphogenetic protein-2

STUDY DESIGN

An in vitro study using rabbit intervertebral disc tissue and disc cells.

OBJECTIVE

To evaluate the effects of disc degeneration, age, and bone morphogenetic proteins-2 (BMP-2) on cartilage intermediate layer protein (CILP) expression and elucidate the molecular mechanism by which BMP-2 regulates CILP expression.

SUMMARY OF BACKGROUND DATA

CILP is implicated in several diseases that affect cartilage. The CILP polymorphism acts as a modulator of lumbar disc disease susceptibility. However, regulation of the CILP gene in disc tissue remains poorly understood.

METHODS

Intact discs from young rabbits were punctured to induce disc degeneration. These young rabbits and other older rabbits were used to measure the expression of CILP, proteoglycan, and collagen II using Western blot and real-time PCR. Primary disc cells from the rabbits were treated with rhBMP-2, or siRNAs, and the gene expression was analyzed by Western blot and real-time PCR. The activity of the CILP promoter was measured by using the Dual Luciferase Reporter Assay System.

RESULTS

Our study demonstrates that the intervertebral disc expresses significant levels of CILP and that the expression of CILP increases substantially with increasing age and disc degeneration. In contrast, the expression of proteoglycan and collagen II decrease with increasing age and disc degeneration. BMP-2 induces the expression of CILP protein and stimulates the activity of the CILP promoter in rabbit primary disc cells. The induction of CILP by BMP-2 can be augmented with age. Knockdown of Smad1 by siRNA abolishes the stimulatory effects of BMP-2 on CILP expression in the primary disc cells.

CONCLUSION

Our data demonstrate that disc degeneration, age, and BMP-2 are regulators of the CILP gene. BMP-2 induces CILP expression by activating the Smad1 signal pathway.

Intervertebral disc repair using adipose tissue-derived stem and regenerative cells: experiments in a canine model

STUDY DESIGN

Therapeutic treatment of intervertebral disc repair using cells.

OBJECTIVE

The goal of the study was to test the hypothesis that repair of a damaged disc is possible using autologous adipose tissue derived stem and regenerative cells (ADRCs).

SUMMARY OF BACKGROUND DATA

Degradation resulting from either acute or chronic repetitive disc injury leads to disc degeneration. However, if a damaged disc could be repaired in the early stages, before the onslaught of degradation, then the disc degeneration process may be slowed down.

METHODS

Twelve dogs underwent a partial nucleotomy at 3 lumbar levels (L3-L4, L4-L5, and L5-L6); adjacent levels served as nonoperated controls. The animals (or discs) were allowed to recover from the surgery for 6 weeks. At that time subcutaneous adipose tissue was harvested and ADRCs were isolated. The 3 experimental discs that had undergone a partial nucleotomy were randomized to receive: (1) ADRCs in hyaluronic acid carrier (Cells/HA); (2) HA only; or (3) No Intervention. Assessments of the 3 experimental discs plus the 2 adjacent untouched discs were made using MRI, radiography, histology, and biochemistry. The animals were killed at 6 months and at 12 months.

RESULTS

Repair in this study was specifically demonstrated through histology and biochemical analysis. Disc levels receiving ADRCs more closely resembled the healthy controls as evidenced in matrix translucency, compartmentalization of the anulus, and in cell density within the nucleus pulposus. Matrix analysis for Type-II collagen and aggrecan demonstrated evidence of a statistically better regenerative stimulation to the disc provided by ADRCs when compared to either the HA only or no intervention treatments.

CONCLUSION

Autologous adipose tissue derived stem and regenerative cells, as used in this disc injury model, were effective in promoting disc regeneration, as evidenced by disc matrix production and overall disc morphology.

Truncated human LMP-1 triggers differentiation of C2C12 cells to an osteoblastic phenotype in vitro

LIM mineralization protein-1 (LMP-1) is a novel intracellular osteoinductive protein that has been shown to induce bone formation both in vitro and in vivo. LMP-1 contains an N-terminal PDZ domain and three C-terminal LIM domains. In this study, we investigated whether a truncated form of human LMP-1 (hLMP-1[t]), lacking the three C-terminal LIM domains, triggers the differentiation of pluripotent myoblastic C(2)C(12) cells to the osteoblast lineage. C(2)C(12) cells were transiently transduced with Ad5-hLMP-1(t)-green fluorescent protein or viral vector control. The expression of hLMP-1(t) RNA and the truncated protein were examined. The results showed that hLMP-1(t) blocked myotube formation in C(2)C(12) cultures and significantly enhanced the alkaline phosphatase (ALP) activity. In addition, the expressions of ALP, osteocalcin, and bone morphogenetic protein (BMP)-2 and BMP-7 genes were also increased. The induction of these key osteogenic markers suggests that hLMP-1(t) can trigger the pluripotent myoblastic C2C12 cells to differentiate into osteoblastic lineage, thus extending our previous observation that LMP-1 and LMP-1(t) enhances the osteoblastic phenotype in cultures of cells already committed to the osteoblastic lineage. Therefore, C(2)C(12) cells are an appropriate model system for the examination of LMP-1 induction of the osteoblastic phenotype and the study of mechanisms of LMP-1 action.