Growth factor expression in degenerated intervertebral disc tissue. An immunohistochemical analysis of transforming growth factor beta, fibroblast growth factor and platelet-derived growth factor

Intervertebral disc degeneration is rescued by TGFβ/BMP signaling modulation in an ex vivo filamin B mouse model

Spondylocarpotarsal syndrome (SCT) is a rare musculoskeletal disorder characterized by short stature and vertebral, carpal, and tarsal fusions resulting from biallelic nonsense mutations in the gene encoding filamin B (FLNB). Utilizing a FLNB knockout mouse, we showed that the vertebral fusions in SCT evolved from intervertebral disc (IVD) degeneration and ossification of the annulus fibrosus (AF), eventually leading to full trabecular bone formation. This resulted from alterations in the TGFβ/BMP signaling pathway that included increased canonical TGFβ and noncanonical BMP signaling. In this study, the role of FLNB in the TGFβ/BMP pathway was elucidated using in vitro, in vivo, and ex vivo treatment methodologies. The data demonstrated that FLNB interacts with inhibitory Smads 6 and 7 (i-Smads) to regulate TGFβ/BMP signaling and that loss of FLNB produces increased TGFβ receptor activity and decreased Smad 1 ubiquitination. Through the use of small molecule inhibitors in an ex vivo spine model, TGFβ/BMP signaling was modulated to design a targeted treatment for SCT and disc degeneration. Inhibition of canonical and noncanonical TGFβ/BMP pathway activity restored Flnb-/- IVD morphology. These most effective improvements resulted from specific inhibition of TGFβ and p38 signaling activation. FLNB acts as a bridge for TGFβ/BMP signaling crosstalk through i-Smads and is key for the critical balance in TGFβ/BMP signaling that maintains the IVD. These findings further our understanding of IVD biology and reveal new molecular targets for disc degeneration as well as congenital vertebral fusion disorders.

Reparative effects of chronic intermittent hypobaric hypoxia pre‑treatment on intervertebral disc degeneration in rats

Previous studies have indicated that chronic intermittent hypobaric hypoxia (CIHH) preconditioning can inhibit TNF-α and other related inflammatory cytokines and exerts protective effect on intervertebral disc degeneration disease (IDD) in rats; however, the mechanism is still unclear. The present study aimed to explore the repair mechanisms of CIHH on IDD in rats. In the experiment, 48 adult Sprague-Dawley rats were selected and randomly divided into an experimental group (CIHH-IDD), a degenerative group (IDD) and a control group (CON). The CIHH-IDD group of rats (n=16) were treated with CIHH (simulated 3000 m altitude, 5 h per day, 28 days; P_O2=108.8 mmHg) before disc degeneration surgery. The IDD group of rats (n=16) underwent tail-vertebral intervertebral disc surgery to establish a model of intervertebral disc degeneration. The CON group of rats (n=16) did not receive any treatments. After surgery, the disc height index was calculated using X-ray analysis of rat tail vertebrae, the degeneration process was observed and repair was evaluated by chemically staining degenerative intervertebral disc tissue slices. The expression levels of basic fibroblast growth factor (bFGF), TGFβ1, Collagen I and Collagen II were measured in the intervertebral disc tissue using western blotting; while the expression levels of bFGF, TGFβ1 and hypoxia-inducible factor 1-α (HIF-1α) were measured in rat serum using ELISA. The results demonstrated that: i) The degree of intervertebral disc height degeneration in CIHH-IDD rats was significantly lower compared with that in IDD rats (P<0.05); ii) the expression levels of bFGF, TGFβ1 and HIF-1α were higher in CIHH-IDD rat serum compared with those in IDD rat serum (P<0.05); iii) optical microscopy revealed that the degree of disc degeneration was relatively mild in CIHH-IDD rats; and iv) the protein expression levels of bFGF, TGFβ1 and collagen II were increased in CIHH-IDD rat intervertebral disc tissues compared with those of IDD rats, while the overexpression of collagen I protein was inhibited. Overall, after CIHH pre-treatment, the expression levels of bFGF and TGFβ1 were up-regulated, which play notable roles in repairing degenerative intervertebral discs in rats.

Origin of M2 Mϕ and its macrophage polarization by TGF-β in a mice intervertebral injury model

Introduction

Studies have identified the presence of M1 and M2 macrophages (Mϕ) in injured intervertebral discs (IVDs). However, the origin and polarization-regulatory factor of M2 Mϕ are not fully understood. TGF-β is a regulatory factor for M2 polarization in several tissues. Here, we investigated the source of M2 Mϕ and the role of TGF-β on M2 polarization using a mice disc-puncture injury model.

Methods

To investigate the origin of M2 macrophages, 30 GFP chimeric mice were created by bone marrow transplantation. IVDs were obtained from both groups on pre-puncture (control) and post-puncture days 1, 3, 7, and 14 and CD86 (M1 marker)- and CD206 (M2 marker)-positive cells evaluated by flow cytometry (n = 5 at each time point). To investigate the role of TGF-β on M2 polarization, TGF-β inhibitor (SB431542) was also injected on post-puncture days (PPD) 5 and 6 and CD206 expression was evaluated on day 7 by flow cytometry (n = 5) and real time PCR (n = 10).

Results

The proportion of CD86⁺ Mϕ within the GFP+ population was significantly increased at PPD 1, 3, 7, and 14 compared to control. CD206-positive cells in GFP-populations were significantly increased on PPD 7 and 14. In addition, the percentage of CD206-positive cells was significantly higher in GFP-populations than in GFP+ populations. TGF-β inhibitor reduced CD206-positive cells and Cd206 expression at 7 days after puncture.

Conclusion

Our findings suggest that M2 Mϕ following IVD injury may originate from resident Mϕ. TGF-β is a key factor for M2 polarization of macrophages following IVD injury.

Hypothetical Role of Growth Factors to Reduce Intervertebral Disc Degeneration Significantly through Trained Biological Transformations

BACKGROUND

Given the evidence of little or no therapeutic benefit of injection-based growth factor therapies, it has been proposed that a naturally triggered uninterrupted blood circulation of the growth factors would be superior.

OBJECTIVE

We seek to stimulate discussions and more research about the possibility of using the already available growth factors found in the prostate gland and endometrium by starting novel educable physiology, known as biological transformations controlled by the mind.

METHODS

We summarized the stretch-gated ion channel mechanism of the cell membrane and offer several practical methods that can be applied by anyone, in order to stimulate and enhance the blood circulation of the growth factors from the seminal fluid to sites throughout the body. This study describes, in detail, the practical application of our earlier published studies about biological transformations.

RESULTS

A previously reported single-patient case study has been extended, adding more from his personal experiences to continually improve this novel physiological training and extending the ideas from our earlier findings in detail.

CONCLUSION

The biological transformation findings demonstrate the need for additional research to establish the benefits of these natural therapies to repair and rejuvenate tissues affected by various chronic diseases or aging processes.

TGF-β regulates nerve growth factor expression in a mouse intervertebral disc injury model

Background

Intervertebral disc (IVD) degeneration is a major cause of low back pain (LBP). Following disc injury, nerve growth factor (NGF) concentrations rise in IVDs, and anti-NGF therapy has been shown to attenuate LBP in humans. Increased levels of tumor necrosis factor-α (TNF-α) and transforming growth factor-β (TGF-β) in degenerative IVDs and in in vitro studies suggest that these factors promote NGF production. However, whether these factors regulate NGF in vivo remains unclear. Thus, we studied NGF regulation in a mouse model of IVD injury.

Methods

After inducing IVD injury, we examined mRNA levels of Tnfa, Tgfb, and Ngf in IVDs from control and IVD-injured mice across 7 days. To do this, we used magnetic cell separation to isolate CD11b ( +) (macrophage-rich) and CD11b (-) (IVD cell-rich) cell fractions from injured IVDs. To study the effect of TNF-α on Ngf expression, we examined Ngf expression in injured IVDs from C57BL/6 J and Tnfa-knockout (KO) mice (C57BL/6 J background). To study the effect of TGF-β on Ngf expression, C57/BL6J mice were given an intraperitoneal injection of either the TGF-β inhibitor SB431542 or DMSO solution (vehicle) one and two days before harvesting IVDs.

Results

mRNA expression of Tnfa, Tgfb, and Ngf was significantly increased in injured IVDs. Tnfa was predominantly expressed in the CD11b ( +) fraction, and Tgfb in the CD11b (-) fraction. Ngf expression was comparable between CD11b ( +) and CD11b (-) fractions, and between wild-type and Tnfa-KO mice at post-injury day (PID) 1, 3, and 7. SB431542 suppressed TGF-β-mediated Ngf expression and NGF production in vitro. Further, administration of SB431542 significantly reduced Ngf expression in IVDs such that levels were below those observed in vehicle-treated animals at PID3 and PID7.

Conclusion

A TGF-β inhibitor reduced Ngf expression in a mouse model of IVD injury, suggesting that TGF-β may regulate NGF expression in vivo.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12891-021-04509-w.

The Role of Panx3 in Age-Associated and Injury-Induced Intervertebral Disc Degeneration

Pannexin 3 (Panx3) is a mechanosensitive, channel-forming glycoprotein implicated in the progression of post-traumatic osteoarthritis. Despite evidence for Panx3 expression in the intervertebral disc (IVD), its function in this cartilaginous joint structure remained unknown. Using Panx3 knockout mice, this study investigated the role of Panx3 in age-associated IVD degeneration and degeneration induced by annulus fibrosus (AF) needle puncture. Loss of Panx3 did not significantly impact the progression of age-associated histopathological IVD degeneration; however, loss of Panx3 was associated with decreased gene expression of Acan, Col1a1, Mmp13 and Runx2 and altered localization of COLX in the IVD at 19 months-of-age. Following IVD injury in the caudal spine, histological analysis of wild-type mice revealed clusters of hypertrophic cells in the AF associated with increased pericellular proteoglycan accumulation, disruptions in lamellar organization and increased lamellar thickness. In Panx3 knockout mice, hypertrophic AF cells were rarely detected and AF structure was largely preserved post-injury. Interestingly, uninjured IVDs adjacent to the site of injury more frequently showed evidence of early nucleus pulposus degeneration in Panx3 knockout mice but remained healthy in wild-type mice. These findings suggest a role for Panx3 in mediating the adaptive cellular responses to altered mechanical stress in the IVD, which may buffer aberrant loads transferred to adjacent motion segments.

A small-molecule inhibitor of the Wnt pathway, lorecivivint (SM04690), as a potential disease-modifying agent for the treatment of degenerative disc disease

BACKGROUND CONTEXT

Abnormal Wnt signaling in intervertebral discs (IVDs) progresses degenerative disc disease (DDD) pathogenesis by impairing nucleus pulposus cell function, decreasing matrix deposition, and accelerating fibrosis.

PURPOSE

This study was conducted to evaluate the effects of lorecivivint (LOR; SM04690), a small-molecule Wnt pathway inhibitor, on IVD cells and in an animal model of DDD.

STUDY DESIGN

We used in vitro assays and a rat model of DDD to test the effects of LOR on nucleus pulposus cell senescence and viability, annulus fibrosus (AF) cell fibrosis, and cartilage regeneration and protection.

METHODS

Wnt pathway gene expression was measured in human NP and AF cell cultures treated with LOR or DMSO (vehicle). Chondrocyte-like differentiation of rat and human NP cells, NP cell senescence and protection, and AF cell fibrosis were assessed using gene expression and immunocytochemistry. Disc and plasma pharmacokinetics were analyzed following intradiscal LOR injection in rats. In vivo effects of LOR and vehicle on AF integrity, AF/NP junction, NP cellularity and matrix, and disc height were compared using histopathology and radiography in a rat coccygeal IVD needle-puncture model of DDD.

RESULTS

In NP and AF cell cultures, LOR-inhibited Wnt pathway gene expression compared with vehicle. In NP cells, LOR inhibited senescence, decreased catabolism, and induced differentiation into chondrocyte-like cells; in AF cells, LOR decreased catabolism and inhibited fibrosis. A single intradiscal LOR injection in rats resulted in therapeutic disc concentrations (~30 nM) for >180 days and minimal systemic exposure. DDD-model rats receiving LOR qualitatively demonstrated increased cartilage matrix and reduced AF lamellar disorganization and fragmentation with significantly (p<.05) improved histology scores and increased disc height compared with vehicle.

CONCLUSIONS

LOR showed beneficial effects on IVD cells in vitro and reduced disease progression in a rat model of DDD compared with vehicle, suggesting that LOR may have disease-modifying therapeutic potential.

CLINICAL SIGNIFICANCE

The current therapeutic options for DDD are pain management and surgical intervention; there are no approved therapies that alter the progression of DDD. Our data support advancing LOR into clinical development as an injectable, small-molecule, potential disease-modifying treatment for DDD in humans.

High-dose TGF-β1 degrades human nucleus pulposus cells via ALK1-Smad1/5/8 activation

Transforming growth factor β1 (TGF-β1) can promote the proliferation and differentiation of intervertebral disc cells and participates in its repair process. However, whether TGF-β1 engages in the process of disc degeneration has not yet been fully elucidated. The present study aimed to investigate the function of high-dose TGF-β1 on the metabolism of nucleus pulposus cells (NPCs). TGF-β1 levels in human degenerative intervertebral disc tissues and tumor necrosis factor (TNF)-α-induced degenerative NPCs were analyzed. Furthermore, NPCs were treated with TGF-β1 and inhibitors of TGF-β1 receptors [ALK tyrosine kinase receptor (ALK) 1 and ALK5] to determine the effect of the receptors in the mediation of NPC degeneration. The NPC state was determined by the components of secretory collagen I/II, tissue inhibitor of metalloproteinase-3 (TIMP-3) and matrix metalloproteinase (MMP)-13. The mRNA expression of Smad1/2/3/5/8, the downstream gene of TGF-β1 mediated by ALK, was also measured. Results showed that TGF-β1 and ALK1 were positively associated with the degree of degeneration of NP or NPCs in vitro, but negatively associated with ALK5. Furthermore, high-doses of TGF-β1 suppressed collagen II, but enhanced collagen I, TIMP-3, MMP-13, ALK1/5 and Smad1/2/3/5/8 expression. ALK5 inhibition induced the suppression of Smad2/3 and aggravated high-dose TGF-β1-induced NPC degeneration, as shown by the reduction in collagen II and increase in collagen I, TIMP-3 and MMP-13. By contrast, ALK1 inhibition resulted in Smad1/5/8 suppression and alleviated high-dose TGF-β1-induced NPC degeneration. Taken together, it was concluded that high-doses of TGF-β1 contributed to the degeneration of NPCs via the upregulation of ALK1 and Smad1/5/8.

Efficacy of matrilin-3-primed adipose-derived mesenchymal stem cell spheroids in a rabbit model of disc degeneration

BACKGROUND

Chronic low back pain is a prevalent disability, often caused by intervertebral disc (IVD) degeneration. Mesenchymal stem cell (MSC) therapy could be a safe and feasible option for repairing the degenerated disc. However, for successful translation to the clinic, various challenges need to be overcome including unwanted adverse effects due to acidic pH, hypoxia, and limited nutrition. Matrilin-3 is an essential extracellular matrix (ECM) component during cartilage development and ossification and exerts chondrocyte protective effects.

METHODS

This study evaluated the effects of matrilin-3-primed adipose-derived MSCs (Ad-MSCs) on the repair of the degenerated disc in vitro and in vivo. We determined the optimal priming concentration and duration and developed an optimal protocol for Ad-MSC spheroid generation.

RESULTS

Priming with 10 ng/ml matrilin-3 for 5 days resulted in the highest mRNA expression of type 2 collagen and aggrecan in vitro. Furthermore, Ad-MSC spheroids with a density of 250 cells/microwell showed the increased secretion of favorable growth factors such as transforming growth factor beta (TGF-β1), TGF-β2, interleukin-10 (IL-10), granulocyte colony-stimulating factor (G-CSF), and matrix metalloproteinase 1 (MMP1) and decreased secretion of hypertrophic ECM components. In addition, matrilin-3-primed Ad-MSC spheroid implantation was associated with optimal repair in a rabbit model.

CONCLUSION

Our results suggest that priming MSCs with matrilin-3 and spheroid formation could be an effective strategy to overcome the challenges associated with the use of MSCs for the treatment of IVD degeneration.

Absence of VEGFR-1/Flt-1 signaling pathway in mice results in insensitivity to discogenic low back pain in an established disc injury mouse model

Although degenerative disc disease (DDD) and related low back pain (LBP) are growing public health problems, the underlying disease mechanisms remain unclear. An increase in the vascular endothelial growth factor (VEGF) levels in DDD has been reported. This study aimed to examine the role of VEGF receptors (VEGFRs) in DDD, using a mouse model of DDD. Progressive DDD was induced by anterior stabbing of lumbar intervertebral discs in wild type (WT) and VEGFR-1 tyrosine-kinase deficient mice (vegfr-1TK-/- ). Pain assessments were performed weekly for 12 weeks. Histological and immunohistochemical assessments were made for discs, dorsal root ganglions, and spinal cord. Both vegfr-1TK-/- and WT mice presented with similar pathological changes in discs with an increased expression of inflammatory cytokines and matrix-degrading enzymes. Despite the similar pathological patterns, vegfr-1TK-/- mice showed insensitivity to pain compared with WT mice. This insensitivity to discogenic pain was related to lower levels of pain factors in the discs and peripheral sensory neurons and lower spinal glial activation in the vegfr-1TK- /- mice than in the WT mice. Exogenous stimulation of bovine disc cells with VEGF increased inflammatory and cartilage degrading enzyme. Silencing vegfr-1 by small-interfering-RNA decreased VEGF-induced expression of pain markers, while silencing vegfr-2 decreased VEGF-induced expression of inflammatory and metabolic markers without changing pain markers. This suggests the involvement of VEGFR-1 signaling specifically in pain transmission. Collectively, our results indicate that the VEGF signaling is involved in DDD. Particularly, VEGFR-1 is critical for discogenic LBP transmission independent of the degree of disc pathology.

Intervertebral disc ageing and degeneration: The antiapoptotic effect of oestrogen

As an important part of the spinal column, the intervertebral disc (IVD) plays an important role in the intervertebral juncture and spinal movement in general. IVD degeneration (IVDD), which mimics disc ageing but at an accelerated rate, is a common and chronic process that results in severe spinal symptoms, such as lower back pain. It is generally assumed that lower back pain caused by IVDD can also develop secondary conditions, including spinal canal stenosis, spinal segmental instability, osteophyte formation, disc herniation and spinal cord and nerve root compression. Over the past few years, many researchers around the world have widely studied the relevance between oestrogen and IVDD, indicating that oestrogen can effectively alleviate IVDD development by inhibiting the apoptosis of IVD cells. Oestrogen can decrease IVD cell apoptosis in multiple ways, including the inhibition of the inflammatory cytokines IL-1β and TNF-α, reducing catabolism because of inhibition of matrix metalloproteinases, upregulating integrin α₂β₁ and IVD anabolism, activating the PI3K/Akt pathway, decreasing oxidative damage and promoting autophagy. In this article, we perform an overview of the literature regarding the antiapoptotic effect of oestrogen in IVDD.

Overexpression of miR-150 Inhibits the NF-κB Signal Pathway in Intervertebral Disc Degeneration through Targeting P2X7

Objective: To elaborate the mechanism of miR-150 in the regulation of the NF-κB signal pathway in intervertebral disc degeneration (IDD) by targeting P2X7. Methods: The degenerative and normal intervertebral disc tissues were collected to detect the expressions of miR-150 and P2X7. Nucleus pulposus cells were transfected and divided into different groups. Cell apoptosis was determined by flow cytometry and TUNEL staining. The expressions of IL-6, TNF-α, MMP-3, MMP-13, Cox-2, iNOS, collagen II and aggrecan, as well as NF-κB-associated proteins were measured by qRT-PCR and Western blotting. Furthermore, IDD rat models were established to validate the role of miR-150 in vivo.Results: miR-150 was down-regulated but P2X7 was up-regulated in the degenerative intravertebral disc tissues. The apoptosis of nucleus pulposus cells in the IL-1β-induced group with the transfection of miR-150 mimic and siP2X7 was significantly decreased, with reduced levels of IL-6, TNF-α, MMP-3, MMP-13, Cox-2 and iNOS, increased levels of collagen II and aggrecan, as well as decreased P2X7, p-p65/p65 and cleaved caspase-3. However, the above factors showed an opposite tendency after treatment with miR-150 inhibitor. Furthermore, the P2X7 siRNA transfection could reverse the effects caused by miR-150 inhibitor. Simultaneously, pcDNA P2X7 transfection also inhibited the function of miR-150 mimic in IL-1β-induced nucleus pulposus cells. In vivoexperiments further verified the protective role of miR-150 in IDD rats. Conclusion: miR-150 may alleviate the degeneration of the intervertebral disc partially since it could restrict the NF-κB pathway by targeting P2X7, and thereby inhibiting IL-1β-induced matrix catabolism, inflammatory responses and apoptosis of the nucleus pulposus cells.

Strategies for Annulus Fibrosus Regeneration: From Biological Therapies to Tissue Engineering

Intervertebral disc (IVD) is an avascular tissue which contributes to the weight bearing, motion, and flexibility of spine. However, IVD is susceptible to damage and even failure due to injury, pathology, and aging. Annulus fibrosus (AF), the structural and functional integrity of which is critically essential to confine nucleus pulpous (NP) and maintain physiological intradiscal pressure under mechanical loading, plays a critical role in the biomechanical properties of IVD. AF degeneration commonly results in substantial deterioration of IVD. During this process, the biomechanical properties of AF and the balance between anabolism and catabolism in IVD are progressively disrupted, leading to chronic back pain, and even disability of individuals. Therefore, repairing and regenerating AF are effective treatments to degeneration-associated pains. However, they remain highly challenging due to the complexity of natural AF tissue in the aspects of cell phenotype, biochemical composition, microstructure, and mechanical properties. Tissue engineering (TE), by combining biological science and materials engineering, shed lights on AF regeneration. In this article, we review recent advances in the pro-anabolic approaches in the form of cell delivery, bioactive factors delivery, gene therapy, and TE strategies for achieving AF regeneration.

Novel therapeutic strategies for degenerative disc disease: Review of cell biology and intervertebral disc cell therapy

Intervertebral disc degeneration is a disease of the discs connecting adjoining vertebrae in which structural damage leads to loss of disc integrity. Degeneration of the disc can be a normal process of ageing, but can also be precipitated by other factors. Literature has made substantial progress in understanding the biological basis of intervertebral disc, which is reviewed here. Current medical and surgical management strategies have shortcomings that do not lend promise to be effective solutions in the coming years. With advances in understanding the cell biology and characteristics of the intervertebral disc at the molecular and cellular level that have been made, alternative strategies for addressing disc pathology can be discovered. A brief overview of the anatomic, cellular, and molecular structure of the intervertebral disc is provided as well as cellular and molecular pathophysiology surrounding intervertebral disc degeneration. Potential therapeutic strategies involving stem cell, protein, and genetic therapy for intervertebral disc degeneration are further discussed.

TGF-β1 suppresses CCL3/4 expression through the ERK signaling pathway and inhibits intervertebral disc degeneration and inflammation-related pain in a rat model

The objective of this study was to investigate the regulatory effects of TGF-β1 on CCL3/4 expression and inflammation-related pain during intervertebral disc degeneration (IVDD). TGF-β1 and CCL3/4 expression patterns in different degenerative human nucleus pulposus (NP) tissues were measured by qPCR and immunohistochemistry (IHC), and the effects of TGF-β1 on CCL3/4 expression were measured by qPCR, ELISA and immunofluorescence. The roles of NF-κB and MAPK in TGF-β1-mediated CCL3/4 promoter activity were studied using siRNAs, western blotting and qPCR. After establishing an IVDD rat model in vivo, we administered intradiscal injections of TGF-β1. The effects of TGF-β1 on IVDD were determined by MRI and histological analyses, and the effects of TGF-β1 on dorsal root ganglion (DRG) inflammation and pain development were determined by IHC staining and pain-behavior testing, respectively. TGF-β1 and CCL3/4 expression was elevated in degenerative NP tissue. CCL4 expression was significantly inhibited by TGF-β1 treatment. Pharmacological inhibition or siRNA knockdown of the ERK1/2 signaling attenuated TGF-β1-mediated suppression of CCL4 expression. In vivo, TGF-β1 injection inhibited the development of degenerative features in the IVDD model. Moreover, TGF-β1 prevented the inflammatory response and pain development. The results of this study show that TGF-β1 downregulates CCL4 expression through ERK1/2 signaling activation in NP cells. Furthermore, TGF-β1 can prevent degenerative processes, inhibit inflammatory responses in the DRG and prevent pain development in the IVDD rat model. The results of this study indicate that TGF-β1 may represent a therapeutic target for the control of inflammation-related pain associated with IVDD.

Bone morphogenetic protein-2 provokes interleukin-18-induced human intervertebral disc degeneration

OBJECTIVES

Interleukin 18 (IL-18) is a regulatory cytokine that degrades the disc matrix. Bone morphogenetic protein-2 (BMP-2) stimulates synthesis of the disc extracellular matrix. However, the combined effects of BMP-2 and IL-18 on human intervertebral disc degeneration have not previously been reported. The aim of this study was to investigate the effects of the anabolic cytokine BMP-2 and the catabolic cytokine IL-18 on human nucleus pulposus (NP) and annulus fibrosus (AF) cells and, therefore, to identify potential therapeutic and clinical benefits of recombinant human (rh)BMP-2 in intervertebral disc degeneration.

METHODS

Levels of IL-18 were measured in the blood of patients with intervertebral disc degenerative disease and in control patients. Human NP and AF cells were cultured in a NP cell medium and treated with IL-18 or IL-18 plus BMP-2. mRNA levels of target genes were measured by real-time polymerase chain reaction, and protein levels of aggrecan, type II collagen, SOX6, and matrix metalloproteinase 13 (MMP13) were assessed by western blot analysis.

RESULTS

The serum level of patients (IL-18) increased significantly with the grade of IVD degeneration. There was a dramatic alteration in IL-18 level between the advanced degeneration (Grade III to V) group and the normal group (p = 0.008) Furthermore, IL-18 induced upregulation of the catabolic regulator MMP13 and downregulation of the anabolic regulators aggrecan, type II collagen, and SOX6 at 24 hours, contributing to degradation of disc matrix enzymes. However, BMP-2 antagonised the IL-18 induced upregulation of aggrecan, type II collagen, and SOX6, resulting in reversal of IL-18 mediated disc degeneration.

CONCLUSIONS

BMP-2 is anti-catabolic in human NP and AF cells, and its effects are partially mediated through provocation of the catabolic effect of IL-18. These findings indicate that BMP-2 may be a unique therapeutic option for prevention and reversal of disc degeneration.Cite this article: S. Ye, B. Ju, H. Wang, K-B. Lee. Bone morphogenetic protein-2 provokes interleukin-18-induced human intervertebral disc degeneration. Bone Joint Res 2016;5:412-418. DOI: 10.1302/2046-3758.59.BJR-2016-0032.R1.

Development of a two-step protocol for culture expansion of human annulus fibrosus cells with TGF-β1 and FGF-2

BACKGROUND

Different biologic approaches to treat disc regeneration, including growth factors (GFs) application, are currently under investigation. Human annulus fibrosus (hAF) repair or regeneration is one of the key elements for maintenance and restoration of nucleus pulposus function. However, so far there is no effective treatment for this purpose. The aim of the present study was to investigate the response of hAF cells to different combinations of GFs, and develop a protocol for efficient culture expansion.

METHODS

hAF cells were harvested from degenerated disc tissues during surgical intervertebral disc removal, and hAF cells were expanded in a monolayer. The experiments were categorized based on different protocols with transforming growth factor (TGF-β1) and fibroblast growth factor (FGF-2) culture for 14 days: group 1 had no GFs (control group); group 2 received TGF-β1; group 3 received FGF-2; group 4 received both GFs; and group 5 (two-step) received both GFs for the first 10 days and TGF-β1 only for the next 4 days. Cell proliferation, collagen, and noncollagen extracellular matrix (ECM) production and genes expression were compared among these groups.

RESULTS

At days 3, 7 and 10 of cultivation, groups 4 and 5 had significantly more cell numbers and faster cell proliferation rates than groups 1, 2, and 3. At 14 days of cultivation, significantly more cell numbers were observed in groups 3 and 4 than in group 5. The group 4 had the most cell numbers and the fastest proliferation rate at 14 days of cultivation. After normalization for cell numbers, group 5 (two-step) produced the most collagen and noncollagen ECM at 10 and 14 days of cultivation among the five groups. In group 5, ECM gene expression was significantly upregulated. High expression of matrix metalloproteinase-1 was upregulated with FGF-2 on the different days as compared to the other groups. Annulus fibrosus cell phenotypes were only marginally retained under the different protocols based on quantitative polymerase chain reaction results.

CONCLUSION

Taken together, the two-step protocol was the most efficient among these different protocols with the most abundant ECM production after normalization for cell numbers for culture expansion of hAF cells. The protocol may be useful in further cell therapy and tissue engineering approaches for disc regeneration.

Association Between Lumbar Disc Degeneration and Propionibacterium acnes Infection: Clinical Research and Preliminary Exploration of Animal Experiment

STUDY DESIGN

Clinical research and animal experiment.

OBJECTIVE

To investigate whether lumbar disc degeneration is associated with Propionibacterium acnes (P acnes) infection.

SUMMARY OF BACKGROUND DATA

The hypothesis that herniated discs may be infected with P acnes by way of bacteremia is remarkable. This may bring a tremendous change in treatment of lumbar disc herniation (LDH). However, this hypothesis is still controversial. Since P acnes isolated may be related to contamination.

METHODS

Nucleus pulposus from 22 patients (30 discs) with lumbar disc herniation was collected during discectomy, following aerobic and anaerobic cultures for 10 days.Twenty-four rabbits were divided into four groups. After L3-L6 being exposed, an incision was made into the three discs in groups A and B. While in groups C and D, two random segments were operated. Six weeks later, 0.05 mL of 5 × 10 CFU/mL P acnes was inoculated into operated discs in group A and sterile physiological saline in group B. In group C, 0.2 mL of 5 × 10 CFU/mL P acnes was injected through ear vein. Sterile saline was used in group D. Six weeks later, MRI was performed. Then, nucleus pulposus and paraspinal muscles were harvested for aerobic and anaerobic cultures.

RESULTS

Clinical research: Anaerobic cultures were positive in three cases: two coagulase-negative staphylococci, one particles chain bacterium. No P acnes was found. Staphylococcus epidermidis was isolated in one aerobic culture.Animal experiment: P acnes was found in 11 out of 18 (61%) discs in group A. There was no P acnes found in the other three groups.

CONCLUSION

Degenerated discs were suitable for P acnes growth. This research did not find the evidence of the symptomatic degenerated lumbar discs infected with P acnes or that P acnes could infect the degenerated lumbar discs by way of bacteremia.

LEVEL OF EVIDENCE

N/A.

TGFβ and BMP Dependent Cell Fate Changes Due to Loss of Filamin B Produces Disc Degeneration and Progressive Vertebral Fusions

Spondylocarpotarsal synostosis (SCT) is an autosomal recessive disorder characterized by progressive vertebral fusions and caused by loss of function mutations in Filamin B (FLNB). FLNB acts as a signaling scaffold by linking the actin cytoskleteon to signal transduction systems, yet the disease mechanisms for SCT remain unclear. Employing a Flnb knockout mouse, we found morphologic and molecular evidence that the intervertebral discs (IVDs) of Flnb^–/–mice undergo rapid and progressive degeneration during postnatal development as a result of abnormal cell fate changes in the IVD, particularly the annulus fibrosus (AF). In Flnb^–/–mice, the AF cells lose their typical fibroblast-like characteristics and acquire the molecular and phenotypic signature of hypertrophic chondrocytes. This change is characterized by hallmarks of endochondral-like ossification including alterations in collagen matrix, expression of Collagen X, increased apoptosis, and inappropriate ossification of the disc tissue. We show that conversion of the AF cells into chondrocytes is coincident with upregulated TGFβ signaling via Smad2/3 and BMP induced p38 signaling as well as sustained activation of canonical and noncanonical target genes p21 and Ctgf. These findings indicate that FLNB is involved in attenuation of TGFβ/BMP signaling and influences AF cell fate. Furthermore, we demonstrate that the IVD disruptions in Flnb^–/–mice resemble aging degenerative discs and reveal new insights into the molecular causes of vertebral fusions and disc degeneration.

Whereas there is a large foundation of knowledge concerning skeletal formation and development, identifying the molecular changes behind Intervertebral Disc (IVD) aging and degeneration has been a challenge. The loss of Filamin B, a protein component of the cell’s cytoskeletal structure, gives rise to Spondylocarpotarsal Synostosis, a rare genetic disorder characterized by fusions of the vertebral bodies. Similarly, mice lacking the Filamin B protein show fusions of the vertebral bodies. We found that these fusions are caused by the early degeneration and eventual ossification of the IVDs. Our study demonstrates that this degeneration is caused by the increase in TGFβ and BMP activity, developmental pathways essential in bone and cartilage formation. These findings represent a significant step forward in our understanding of the molecular basis of IVD degeneration. as well as revealing filamin B’s role in TGFβ/BMP signaling regulation. Moreover, we demonstrate that the study of the rare disease spondylocarpotarsal synostosis in a model organism can uncover mechanisms underlying more common diseases. Finally, our findings provide a model system that will facilitate further discoveries regarding disc degeneration, which affects a significant proportion of the population.

Stem Cell Approaches to Intervertebral Disc Regeneration: Obstacles from the Disc Microenvironment

Intervertebral disc (IVD) degeneration results in segmental instability and irritates neural compressive symptoms, such as low back pain and motor deficiency. The transplanting of stem cell into degenerative discs has attracted increasing clinical attention, as a new and proven approach to alleviating disc degeneration and to relieving discogenic pains. Aside from supplementation with stem cells, the IVD itself already contains a pool of stem and progenitor cells. Since the resident disc stem cells are incapable of reversing the pathologic changes that occur during aging and disc degeneration, it has been debated as to whether transplanted stem cells are capable of providing an efficient and durable therapeutic effect, even though there have been positive outcomes in both animal models and in clinical trials. This review aims to decipher the interactions between the stem cell and the disc microenvironment. Within their new niches in the IVD, the exogenous stem cell shows metabolic adaptation to the low-glucose supply, hypoxia, and compressive loadings, but demonstrates little tolerance to the disc-like acidity and hypertonicity. Similarly, the survival of endogenous stem cells is threatened as well by the harsh disc microenvironment, which may exhaust the stem cell resources and restrict the self-repair capacity of a degenerating IVD. To eliminate the intrinsic obstacles within the stressful disc niches, stem cells should be delivered with an injectable scaffold that provides both survival and mechanical support. Quick healing or concretion of the injection injuries, which minimizes stem cell leakage and disturbance to disc homeostasis, is of equal importance toward achieving efficient stem cell-based disc regeneration.

What is the preclinical evidence on platelet rich plasma and intervertebral disc degeneration?

PURPOSE

Intervertebral disc degeneration is a common disease that usually starts from the third decade of life and it represents a significant cause of socio-economic problems. The accepted surgical treatment for disc degeneration is disc removal and vertebral fusion or, in selected cases, intervertebral disc arthroplasty. Several studies have demonstrated the ability of platelet rich plasma (PRP) to stimulate cell proliferation and extracellular matrix regeneration. However, literature results are still limited and more studies are required to clarify the role of PRP in the prevention or in the treatment of degenerative disc disease. The aim of this review is to summarize and critically analyze the current preclinical evidence about the use of PRP in intervertebral disc degeneration.

METHODS

Literature search was performed through various combinations of the following keywords: Intervertebral Disc Degeneration, Platelet Rich Plasma, PRP, Intervertebral disc regeneration. Papers included in our review cover the period between 2006 and 2014. The PRISMA 2009 checklist was followed.

RESULTS

At the end of the review process, 12 articles were included in our final manuscript, including 6 "in vitro" and 6 "in vivo" studies. All the included studies lead to positive preclinical results. No standardization of methodological analysis was observed.

CONCLUSION

It is not possible to draw definitive evidence about the use of PRP in IVD regeneration. We advise a proper standardization of the methodological analysis in order to compare the available data and achieve definitive results. This should be the cornerstone for future clinical applications.

Role of interleukin-17 in chondrocytes of herniated intervertebral lumbar discs

Lumbar disc herniation (LDH) is a common cause of lumbosacral radiculopathy. An autoimmune response to a herniated nucleus pulposus (NP) has been suggested to play an important role in the initiation of radiculopathy. Interleukin-17 (IL-17) is a cytokine associated with inflammation and autoimmunity. The presence of IL-17 has been studied in patients with LDH; however, extensive investigation into the expression of IL-17 in different disc pathologies of LDH has not yet been conducted. The aim of the present study was to investigate the role of neovascularization and hypertrophic chondrocytes in herniated intervertebral lumbar discs. Fifty-two intervertebral lumbar disc specimens were extracted from 46 patients with LDH and were subsequently classified as either contained or non-contained disc herniation (CDH and NCDH, respectively). The specimens were stained with hematoxylin and eosin or toluidine blue, or were immunostained with polyclonal antibodies to IL-17 using the streptavidin-peroxidase method. The neovascular tissue and staining results were graded to establish the histological differences between the two herniation types. The intervertebral discs (IVDs) obtained from patients with NCDH showed significantly more neovascularization and granulation tissue than the discs obtained from patients with CDH (P<0.05). Furthermore, hypertrophic chondrocytes were more abundant in the NCDH specimens than in the CDH specimens (P<0.05). Similarly, the number of IL-17-immunoreactive cells was significantly higher in the NCDH specimens than that in the CDH specimens (P<0.01). In conclusion, local inflammation and autoreactive immune activation may play an important role in the pathogenesis of LDH. These results also suggest a role of chondrocytes in the repair of herniated IVDs.

Evidence for an Important Role of Smad-7 in Intervertebral Disc Degeneration

Smad-7 inhibited the transforming growth factor beta (TGF-β)-induced proteoglycan synthesis in chondrocytes and completely antagonized the effect of TGF-β on the proliferation of the cells. The aim of this study was to evaluate the contribution of Smad-7 to the pathophysiology of disc degeneration by determining the expression of Smad-7 in the degenerative intervertebral discs and its effect on the extracellular matrix metabolism of disc cells. Instability of the lumbar spine produced by imbalanced dynamic and static forces was used to induce intervertebral disc degeneration in rats. The expression of Smad-7 was assessed by the immunohistochemical method. Disc cell apoptosis was detected by in situ TUNEL staining. The effect of Smad-7 overexpression on the matrix metabolism of disc cells was analyzed in vitro by real-time polymerase chain reaction (PCR) and Western blotting. Finally, intradiscal injection of the Smad-7 overexpression lentivirus was performed to evaluate the in vivo effect of Smad-7 on disc degeneration. Radiographic and histomorphological examinations showed that lumbar disc degeneration became more and more severe in the rats with induced instability. Immunohistochemical observation demonstrated increasing protein expression of Smad-7 in the degenerative discs. A significantly positive correlation was found between Smad-7 expression and the degree of disc degeneration and between Smad-7 expression and disc cell apoptosis. Overexpression of Smad-7 in disc cells inhibited the expression of TGF-β1, collagen type-I, collagen type-II, and aggrecan and promoted the expression of MMP-13, but did not change the expression of ADAMTS-5. The in vivo findings illustrated that intradiscal injection of lentivirus vector with Smad-7 overexpression accelerated the progress of disc degeneration. In conclusion, Smad-7 was highly expressed in the degenerative discs. Overexpression of Smad-7 weakened the protective role of TGF-β and accelerated the progress of disc degeneration. Interference on Smad-7 might be a potential therapeutic method for the prevention and treatment of degenerative disc diseases.

Growth factors and platelet-rich plasma: promising biological strategies for early intervertebral disc degeneration

Intervertebral disc degeneration (IDD) is a complex process with the mechanism not fully elucidated. The current clinical treatments for IDD are mainly focused on providing symptomatic relief without addressing the underlying cause of the IDD. Biological therapeutic strategies to repair and regenerate the degenerated discs are drawing more attention. Growth factor therapy is one of the biological strategies and holds promising prospects. As a promising bioactive substance, platelet-rich plasma (PRP) is considered to be an ideal growth factor "cocktail" for intervertebral disc (IVD) restoration. Results from many in vitro and in vivo studies have confirmed the efficacy of growth factors and PRP in IVD repair and regeneration. It is essential to advance the research on growth factor therapy and associated mechanism for IDD. This article reviews the background of IDD, current concepts in growth factor and PRP-related therapy for IDD. Future research perspectives and clinical directions are also discussed.

Cell and molecular biology of intervertebral disc degeneration: current understanding and implications for potential therapeutic strategies

Intervertebral disc degeneration (IDD) is a chronic, complex process associated with low back pain; mechanisms of its occurrence have not yet been fully elucidated. Its process is not only accompanied by morphological changes, but also by systematic changes in its histological and biochemical properties. Many cellular and molecular mechanisms have been reported to be related with IDD and to reverse degenerative trends, abnormal conditions of the living cells and altered cell phenotypes would need to be restored. Promising biological therapeutic strategies still rely on injection of active substances, gene therapy and cell transplantation. With advanced study of tissue engineering protocols based on cell therapy, combined use of seeding cells, bio-active substances and bio-compatible materials, are promising for IDD regeneration. Recently reported progenitor cells within discs themselves also hold prospects for future IDD studies. This article describes the background of IDD, current understanding and implications of potential therapeutic strategies.

Imbalanced protein expression patterns of anabolic, catabolic, anti-catabolic and inflammatory cytokines in degenerative cervical disc cells: new indications for gene therapeutic treatments of cervical disc diseases

Degenerative disc disease (DDD) of the cervical spine is common after middle age and can cause loss of disc height with painful nerve impingement, bone and joint inflammation. Despite the clinical importance of these problems, in current publications the pathology of cervical disc degeneration has been studied merely from a morphologic view point using magnetic resonance imaging (MRI), without addressing the issue of biological treatment approaches. So far a wide range of endogenously expressed bioactive factors in degenerative cervical disc cells has not yet been investigated, despite its importance for gene therapeutic approaches. Although degenerative lumbar disc cells have been targeted by different biological treatment approaches, the quantities of disc cells and the concentrations of gene therapeutic factors used in animal models differ extremely. These indicate lack of experimentally acquired data regarding disc cell proliferation and levels of target proteins. Therefore, we analysed proliferation and endogenous expression levels of anabolic, catabolic, ant-catabolic, inflammatory cytokines and matrix proteins of degenerative cervical disc cells in three-dimensional cultures. Preoperative MRI grading of cervical discs was used, then grade III and IV nucleus pulposus (NP) tissues were isolated from 15 patients, operated due to cervical disc herniation. NP cells were cultured for four weeks with low-glucose in collagen I scaffold. Their proliferation rates were analysed using 3-(4, 5-dimethylthiazolyl-2)-2,5-diphenyltetrazolium bromide. Their protein expression levels of 28 therapeutic targets were analysed using enzyme-linked immunosorbent assay. During progressive grades of degeneration NP cell proliferation rates were similar. Significantly decreased aggrecan and collagen II expressions (P<0.0001) were accompanied by accumulations of selective catabolic and inflammatory cytokines (disintegrin and metalloproteinase with thrombospondin motifs 4 and 5, matrix metalloproteinase 3, interleukin-1β, interleukin-1 receptor) combined with low expression of anti-catabolic factor (metalloproteinase inhibitor 3) (P<0.0001). This study might contribute to inhibit inflammatory catabolism of cervical discs.

VEGF and BFGF Expression and Histological Characteristics of the Bone-Tendon Junction during Acute Injury Healing

Bone-tendon junction (BTJ) injuries are common and may be caused by acute trauma and delayed healing during exercise or work. To understand the nature of the healing process of BTJ injuries would help to prevent injuries and improve treatment. Thirty-three mature female rabbit hindlimbs were assigned to normal control (CON, n = 7) and injury groups (n = 26). The acute injury was established by administering one 7 plum-blossom needle puncture. Specimens were harvested post injury at 1, 2, 4, and 8 weeks (ND1W, n = 6; ND2W, n = 6; ND4W, n = 7; and ND8W, n = 7). The injury existed in all of the injury groups. Compared with the CON group, all of the animals in the injury group showed poor cell profiles, an unclear or undetectable tide mark, a proteoglycan area and profile changes; the BTJ cell density diminished significantly in the ND1W (p < 0.01), ND2W (p < 0.05), ND4W (p < 0.01), and ND8W groups (p < 0.01); the fibrocartilage zone thickness in all injury groups was significantly thicker than in the CON group (p < 0.05), but no significant difference was found among the injury groups (p>0.05). The basic fibroblast growth factor (bFGF) expression in the CON group was significantly less than in the ND1W group (p<0.01), but no significant difference was found when compared with the ND2W, ND4W, and ND8W groups. The bFGF expression in the ND1W group was higher than that of the ND4W (p < 0.05) and ND8W groups (p < 0.01). The vascular endothelial growth factor (VEGF) levels were not significantly different among the groups (p > 0.05). The bFGF and VEGF expression levels indicated that the healing process stopped at 8 weeks post injury or was not activated, although the injury had not healed by histological examination. A repeatable animal model of BTJ acute injury was established in this study, and the results described the BTJ acute injury healing difficult concerned with the repairing stop. Key PointsThis study described the bone-tendon junction acute injury nature healing process.The bone-tendon junction acute injury could not be repaired naturally in 8 weeks.The bFGF and VEGF expression revealed that the bone-tendon junction acute injury delayed healing concern with the repairing stop.

Effects of TGF-β1 and IL-1β on expression of ADAMTS enzymes and TIMP-3 in human intervertebral disc degeneration

The aim of this study was to investigate the effects of transforming growth factor-β1 (TGF-β1) and interleukin-1β (IL-1β) on the expression of a disintegrin and metalloproteinase with thrombospondin motifs (ADAMTS) enzymes and their inhibitor, tissue inhibitor of metalloproteinase 3 (TIMP-3), in human intervertebral disc (IVD) degeneration. Cells from patients with IVD degeneration were cultured with Dulbecco's modified Eagle's medium with Ham's F12 nutrient mixture (DMEM/F12) medium at 37°C in a 5% CO2 incubator. Cell proliferation was measured by cell counting kit-8 assays with varying concentrations of TGF-β1 and IL-1β in a time-response experiment. The mRNA and protein expression levels of ADAMTS-4, ADAMTS-5 and TIMP-3 were detected with qPCR and western blot analysis, respectively. The present study demonstrated that TGF-β1 promoted nucleus pulposus (NP) cell proliferation, decreased the expression of ADAMTS-4 and -5 and increased the expression of TIMP-3. By contrast, the IL-1β treatment inhibited NP cell proliferation and significantly increased the expression of ADAMTS-4 and -5. However, IL-1β appeared to have no marked effect on the expression of TIMP-3. This study suggests that TGF-β1 and IL-1β are involved in the synthesis and degradation of the extracellular matrix and may act as potential therapeutic targets for the prevention or reversal of IVD degeneration.

A combinatorial relative mass value evaluation of endogenous bioactive proteins in three-dimensional cultured nucleus pulposus cells of herniated intervertebral discs: identification of potential target proteins for gene therapeutic approaches

Painful degenerative disc diseases have been targeted by different biological treatment approaches. Nucleus pulposus (NP) cells play a central role in intervertebral disc (IVD) maintenance by orchestrating catabolic, anabolic and inflammatory factors that affect the extracellular matrix. IVD degeneration is associated with imbalances of these factors, resulting in a catabolic inflammatory metabolism. Therefore, accurate knowledge about their quantity and quality with regard to matrix synthesis is vital for a rational gene therapeutic approach. NP cells were isolated from 63 patients operated due to lumbar disc herniation (mean age 56 / range 29 - 84 years). Then, three-dimensional culture with low-glucose was completed in a collagen type I scaffold for four weeks. Subsequently cell proliferation evaluation was performed using 3-(4, 5-dimethylthiazolyl-2)-2,5-diphenyltetrazolium bromide and intracellular concentration of 28 endogenously expressed anabolic, catabolic, inflammatory factors and relevant matrix proteins was determined by enzyme-linked immunosorbent assay. Specimen-related grades of degeneration were confirmed by preoperative magnetic resonance imaging. Independent from gender, age and grade of degeneration proliferation rates remained similar in all groups of NP cells. Progressive grades of degeneration, however, showed a significant influence on accumulation of selective groups of factors such as disintegrin and metalloproteinase with thrombospondin motifs 4 and 5, matrix metalloproteinase 3, metalloproteinase inhibitor 1 and 2, interleukin-1β and interleukin-1 receptor. Along with these changes, the key NP matrix proteins aggrecan and collagen II decreased significantly. The concentration of anabolic factors bone morphogenetic proteins 2, 4, 6 and 7, insulin-like growth factor 1, transforming growth factor beta 1 and 3, however, remained below the minimal detectable quantities. These findings indicate that progressive degenerative changes in NP may be problematic with regard to biologic treatment strategies. Hence, gene therapeutic interventions regulating relevant bioactive factors identified in this work might contribute to the development of regenerative treatment approaches for degenerative disc diseases.

Fibroblast growth factor control of cartilage homeostasis

Osteoarthritis (OA) and degenerative disc disease (DDD) are similar diseases involving the breakdown of cartilage tissue, and a better understanding of the underlying biochemical processes involved in cartilage degeneration may allow for the development of novel biologic therapies aimed at slowing the disease process. Three members of the fibroblast growth factor (FGF) family, FGF-2, FGF-18, and FGF-8, have been implicated as contributing factors in cartilage homeostasis. The role of FGF-2 is controversial in both articular and intervertebral disc (IVD) cartilage as it has been associated with species- and age-dependent anabolic or catabolic events. Recent evidence suggests that FGF-2 selectively activates FGF receptor 1 (FGFR1) to exert catabolic effects in human articular chondrocytes and IVD tissue via upregulation of matrix-degrading enzyme production, inhibition of extracellular matrix (ECM) accumulation and proteoglycan synthesis, and clustering of cells characteristic of arthritic states. FGF-18, on the other hand, most likely exerts anabolic effects in human articular chondrocytes by activating the FGFR3 pathway, inducing ECM formation and chondrogenic cell differentiation, and inhibiting cell proliferation. These changes result in dispersed chondrocytes or disc cells surrounded by abundant matrix. The role of FGF-8 has recently been identified as a catabolic mediator in rat and rabbit articular cartilage, but its precise biological impact on human adult articular cartilage or IVD tissue remains unknown. The available evidence reveals the promise of FGF-2/FGFR1 antagonists, FGF-18/FGFR3 agonists, and FGF-8 antagonists (i.e., anti-FGF-8 antibody) as potential therapies to prevent cartilage degeneration and/or promote cartilage regeneration and repair in the future.

The molecular basis of intervertebral disc degeneration

BACKGROUND

Intervertebral disc (IVD) degeneration remains a clinically important condition for which treatment is costly and relatively ineffective. The molecular basis of degenerative disc disease has been an intense focus of research recently, which has greatly increased our understanding of the biology underlying this process.

PURPOSE

To review the current understanding of the molecular basis of disc degeneration.

STUDY DESIGN

Review article.

METHODS

A literature review was performed to identify recent investigations and current knowledge regarding the molecular basis of IVD degeneration.

RESULTS

The unique structural requirements and biochemical properties of the disc contribute to its propensity toward degeneration. Mounting evidence suggests that genetic factors account for up to 75% of individual susceptibility to IVD degeneration, far more than the environmental factors such as occupational exposure or smoking that were previously suspected to figure prominently in this process. Decreased extracellular matrix production, increased production of degradative enzymes, and increased expression of inflammatory cytokines contribute to the loss of structural integrity and accelerate IVD degeneration. Neurovascular ingrowth occurs, in part, because of the changing degenerative phenotype.

CONCLUSIONS

A detailed understanding of the biology of IVD degeneration is essential to the design of therapeutic solutions to treat degenerative discs. Although significant advances have been made in explaining the biologic mediators of disc degeneration, the inhospitable biochemical environment of the IVD remains a challenging environment for biological therapies.

The challenge and advancement of annulus fibrosus tissue engineering

BACKGROUND

Intervertebral disc degeneration, a main cause of back pain, is an endemic problem and a big economic burden for the health care system. Current treatments are symptom relieving but do not address underlying problems-biological and structural deterioration of the disc. Tissue engineering is an emerging approach for the treatment of intervertebral disc degeneration since it restores the functionality of native tissues. Although numerous studies have focused on the nucleus pulposus tissue engineering and achieved successes in laboratory settings, disc tissue engineering without annulus fibrosus for the end stage of disc degeneration is deemed to fail. The purpose of this article is to review the advancement of annulus fibrosus tissue engineering.

MATERIAL AND METHODS

Relevant articles regarding annulus fibrosus tissue engineering were identified in PubMed and Medline databases.

RESULTS

The ideal strategy for disc regeneration is to restore the function and integrity of the disc by using biomaterials, native matrices, growth factors, and cells that producing matrices. In the past decades there are tremendous advancement in annulus fibrosus tissue engineering including cell biology, biomaterials, and whole disc replacement. The recent promising results on whole disc tissue engineering-a composite of annulus fibrosus and nucleus pulposus-make the tissue engineering approach more appealing.

CONCLUSION

Despite the promising results in disc tissue engineering, there is still much work to be done regarding the clinical application.

Anabolic effects of Peniel 2000, a peptide that regulates TGF-β1 signaling on intervertebral disc degeneration

STUDY DESIGN

An in vitro study with bovine intervertebral disc (IVD) cells and an in vivo study with a rabbit disc degeneration model on the extracellular matrix metabolism by a biglycan-derived peptide (Peniel 2000; P2K).

OBJECTIVE

To investigate the mechanism for P2K-induced increases in extracellular matrix and in vitro and in vivo effects of the peptide on IVD.

SUMMARY OF BACKGROUND DATA

Transforming growth factor-β (TGF-β) has a functional versatility on the metabolism of IVD cells, suggesting that the regulation of TGF-β signaling is important in IVD degeneration. P2K was explored by an in silico drug discovery strategy to regulate TGF-β signaling.

METHODS

The putative target of P2K was verified by Biacore 3000 analysis and affinity purification using biotin-P2K. A monolayer culture system of bovine IVD cells was used to demonstrate the mechanism underlying the anabolic effects of P2K. Smad signaling and extracellular matrix metabolism of the IVD cells were investigated by Western blot and reverse transcription-polymerase chain reaction, respectively. The in vivo effect of P2K on degenerated disc was investigated using a rabbit model of disc degeneration. In 14 New Zealand white rabbits, disc degeneration was induced by percutaneous annular punctures. After 4 weeks, 3 consecutive discs in the same animal were treated with 5% lactose or P2K per disc. Twelve weeks after the treatment, the regenerative activity in the disc was examined by radiography, magnetic resonance imaging, and biochemical and histological analyses.

RESULTS

Direct binding of P2K to an active form of TGF-β1 was shown. Type II collagen and aggrecan were increased in TGF-β1/P2K-treated bovine IVD cells, compared with nontreated and TGF-β1-treated cells.In in vivo analysis, a single injection of P2K increased the disc height (P < 0.001) on the radiographs and improved the magnetic resonance imaging grade (P < 0.05) compared with controls. Biochemical analysis, showed a significant increase in PG content because of P2K treatment (P < 0.05). Histological analysis using disc degeneration grades demonstrated improvement in P2K-treated discs (P <0.01).

CONCLUSION

A novel peptide, P2K, regulating TGF-β1 signaling had an anabolic effect on bovine IVD cells and rabbit degenerated discs. The results suggest that P2K has considerable potential as a treatment of degenerative disc disease.

Increased expression of netrin-1 and its deleted in colorectal cancer receptor in human diseased lumbar intervertebral disc compared with autopsy control

STUDY DESIGN

The expression of netrin-1 and its deleted in colorectal cancer (DCC) receptor was investigated in human lumbar discs using immunohistochemistry.

OBJECTIVE

To investigate the expression of netrin-1 and DCC receptor in human diseased and healthy lumbar intervertebral discs (IVDs) and to clarify the correlation between netrin-1 expression and the degree of neurovascular ingrowth.

SUMMARY OF BACKGROUND DATA

Previous studies have shown neurovascular ingrowth into the inner regions of degenerated IVD and suggested that the ingrowth may contribute to discogenic low back pain. Netrin-1 is an axon guidance molecule that regulates axons seeking their final targets and has been identified as involved in various pathological conditions, so is its DCC receptor. However, the role of netrin-1 in diseased IVDs remains unknown.

METHODS

Thirty-five diseased IVD specimens were collected from 34 patients with different lumbar diseases during posterior lumbar interbody fusion. Eight normal discs were obtained at autopsy as control. Using polyclonal or monoclonal antibody, the disc slides were immmunostained to detect the expression and distribution of netrin-1, the DCC, the neuronal marker (neurofilament), and the vascular endothelial cell marker (CD34).

RESULTS

Netrin-1 and DCC immunopositive cells distributed substantially from the annulus fibrosus to the nucleus pulposus (NP), and the immunopositivity was detected in the disc cells, endothelial cells and granulation tissue cells in the diseased discs. The percentage of netrin-1 positive disc cells of the NP was more than that of the annulus fibrosus. The expression of netrin-1 and DCC was weak in the normal discs. A significant positive correlation between the percentage of netrin-1 immunopositive disc cells and neurovascular scores was found.

CONCLUSION

The increased expression of netrin-1 and DCC in diseased IVDs compared with controls suggested that they might play an important role in the process of neurovascular ingrowth.

Molecular basis of intervertebral disc degeneration

Intervertebral disc (IVD) degeneration is a disease of the discs connecting adjoining vertebrae in which structural damage leads to degeneration of the disc and surrounding area. Degeneration of the disc is considered to be a normal process of aging, but can accelerate faster than expected or be precipitated by other factors. The scientific community has come a long way in understanding the biological basis and interpreting the lifestyle implications of IVD degeneration. Of all the diseases of the intervertebral disc, degeneration is the most common and has earned much attention due to its diversity in presentation and potential multiorgan involvement. We will provide a brief overview of the anatomic, cellular, and molecular structure of the IVD, and delve into the cellular and molecular pathophysiology surrounding IVD degeneration. We will then highlight some of the newest developments in stem cell, protein, and genetic therapy for IVD degeneration.

Growth factors and anticatabolic substances for prevention and management of intervertebral disc degeneration

Intervertebral disc (IVD) degeneration is frequent, appearing from the second decade of life and progressing with age. Conservative management often fails, and patients with IVD degeneration may need surgical intervention. Several treatment strategies have been proposed, although only surgical discectomy and arthrodesis have been proved to be predictably effective. Biological strategies aim to prevent and manage IVD degeneration, improving the function and anabolic and reparative capabilities of the nucleus pulposus and annulus fibrosus cells and inhibiting matrix degradation. At present, clinical applications are still in their infancy. Further studies are required to clarify the role of growth factors and anticatabolic substances for prevention and management of intervertebral disc degeneration.

Intervertebral disk degeneration and emerging biologic treatments

Although understanding of the biologic basis of intervertebral disk (IVD) degeneration is rapidly advancing, the unique IVD environment presents challenges to the development and delivery of biologic treatments. Acceleration of cellular senescence and apoptosis in degenerative IVDs and the depletion of matrix proteins have prompted the development of treatments based on replacing IVD cells using various cell sources. However, this strategy has not been tested in animal models. IVD degeneration and associated pain have led to interest in pathologic innervation of the IVD and ultimately to the development of percutaneous devices to ablate afferent nerve endings in the posterior annulus. Degeneration leads to changes in the expression of matrix protein, cytokines, and proteinases. Injection of growth factors and mitogens may help overcome these degenerative changes in IVD phenotype, and these potential treatments are being explored in animal studies. Gene therapy is an elegant method to address changes in protein expression, but efforts to apply this technology to IVD degeneration are still at early stages.

Ex vivo observation of human nucleus pulposus chondrocytes isolated from degenerated intervertebral discs

Study Design

We performed an ex vivo study to observe cell morphology and viability of human nucleus pulposus (NP) chondrocytes isolated from degenerated intervertebral discs (IVD).

Purpose

To better understand the biological behavior of NP chondrocytes in monolayer cultures.

Overview of Literature

Biological repair of IVDs by cell-based therapy has been shown to be feasible in clinical trials. As one of the most promising transplanting seeds, how the isolated NP chondrocytes behavior ex vivo has not been fully understood.

Methods

Human NP chondrocytes were harvested from 20 degenerated IVDs and cultured in monolayers. Histological and immunochemistry staining was used to detect cell morphology change. Cell viability was studied by analyzing cell cycle distribution and apoptotic rate in the primary and subculuted cells.

Results

The round or polygonal primary NP chondrocytes had an average adherence time of 7 days and took nearly 31 days to reach 95% confluence. The spindle-shaped P1 NP chondrocytes increased growth kinetics and took about 12 hours to adhere and 6.6 days to get 95% confluent. Immunochemistry staining of collagen II was positive in the cell cytoplasm. Nearly 90% of the confluent NP chondrocytes stayed in G1 phase while 16% underwent apoptosis. No significant difference of the collagen II expression, cell cycle distribution or the apoptosis indices were detected between the primary and subcultured NP chondrocytes.

Conclusions

Human NP chondrocytes undergo significant morphological change in monolayer cultures. Cell cycle distribution pattern and apoptosis index of the cutured NP chondrocytes potentially influence their clinical transplantation or laboratory use.

Piriformis syndrome after percutaneous endoscopic lumbar discectomy via the posterolateral approach

Percutaneous endoscopic lumbar discectomy (PELD) can be performed under local anesthesia with intravenous analgesics. To define the incidence of piriformis syndrome (PS) after PELD via the posterolateral approach under local anesthesia compared to that of general patients presenting with low back pain with/without lower leg pain. The incidence and time of occurrence of positive FAIR test after PELD within a 3-month follow-up period were evaluated retrospectively, and compared with the prevalence of general patients who visited the pain clinic for LBP with/without lower leg pain. Factors that may increase the incidence of PS after PELD were also evaluated. There was no patient with positive FAIR test immediately after PELD in the operation room and before walking. The prevalence of PS in general patients was 317/2,320 (13.7%); however, the incidence of PS after PELD within a 3-month follow-up period was 61/151 (40.4%), peaking at 32 days. High anxiety scale scores during operation led to increased incidence of PS after PELD. PELD under local anesthesia with high level of anxiety may increase the incidence of PS after walking, peaking around the first month, compared with the results for general patients with low back pain with/without lower leg pain.

Effect of varying osmotic conditions on the response of bovine nucleus pulposus cells to growth factors and the activation of the ERK and Akt pathways

Intervertebral disc and especially nucleus pulposus is characterized by low cellularity. Additionally, extreme variations in osmolality are observed in this tissue, as a result of its specific physicochemical environment, daily activities, or degeneration. In this study, we investigated the role of osmotic fluctuations in the proliferative response of nucleus pulposus cells to exogenous growth factors. In particular, we examined the effect of platelet-derived growth factor (PDGF) and insulin-like growth factor-I (IGF-I) on the proliferation of bovine nucleus pulposus cells and on the activation of the MEK/ERK and PI-3-K/Akt pathways under varying osmotic conditions, in an effort to understand the mechanisms regulating cell proliferation in the intact and the degenerated intervertebral disc. Exposure of cells to high osmolality restrained novel DNA synthesis induced by PDGF or IGF-I in a dose-dependent manner and reduced ERK and Akt activation stimulated by serum or isolated growth factors. Our findings indicate that hyperosmolality imposes a strict control in intervertebral disc cells' proliferation, while hypo-osmotic conditions prevailing in degenerated discs may offer a more permissive environment for cellular proliferation.

Comparison of growth factor and cytokine expression in patients with degenerated disc disease and herniated nucleus pulposus

OBJECTIVES

This study was conducted to investigate the expression of cytokines and growth factors in disc specimens obtained from patients with herniated nucleus pulposus (HNP) and degenerated disc disease (DDD).

DESIGN AND METHODS

MRI and Western blot analyses were performed to evaluate the levels of disc degeneration and the expression levels of cytokines and growth factors.

RESULTS

The levels of TNF-alpha and IL-8 were significantly greater in the DDD group than in the HNP group, but no statistical differences were observed in the expression of IL-1beta, IL-6 and IL-12 between the HNP and DDD groups. In addition, the expression of TGF beta, VEGF and NGF was significantly higher in the DDD group than in the HNP group.

CONCLUSION

The greater levels of cytokine and growth factor expression in the DDD group than in the HNP explain why discogenic patients usually have more severe back pain than patients with herniated discs.

A continuous observation of the degenerative process in the intervertebral disc of Smad3 gene knock-out mice

STUDY DESIGN

Pathologic changes were observed in the spine of small mother against decapentaplegic (Smad) 3 mice at different time points.

OBJECTIVE

To observe the degeneration of the intervertebral disc (IVD) in Smad3 gene knock-out mice with growth.

SUMMARY OF BACKGROUND DATA

Smad3 gene knock-out (Smad3) mice displays phenotypes similar to human osteoarthritis. Despite the similarities between IVD cartilage endplate and the articular cartilage, there has been relatively little interest in exploring the possibility that IVD degeneration might be driven by the deficiency of Smad3.

METHODS

The Smad3 mice were killed at the 10th, 30th, and 60th day after their birth and the IVD samples of spine were harvested for histologic and immunohistochemical studies. Total RNA isolated from these samples were used for real-time PCR analysis of type II collagen (Col2alpha1), type X collagen (Col10alpha1), aggrecan, and transforming growth factor-beta1 (TGF-beta1).

RESULTS

Compared with the wild-type mice, Smad3 mice appeared significantly smaller in size. Radiograph showed that the spine of Smad3 mice is malformation and kyphosis. Histologic analysis revealed the declined height of cartilage endplate, decreased proteoglycan and collagen content in disc of Smad3 mice. With growth, especially of the 30- and 60-day old Smad3 mice, the protein positive staining of type II collagen, aggrecan, and TGF-beta1 in the disc decreased, while that of type X collagen increased. And the analysis of real-time PCR showed that the mRNA expression of Col2alpha1, aggrecan, and TGF-beta1 decreased, while that of Col10alpha1 increased.

CONCLUSION

Smad3 gene knock-out mice develop IVD degeneration with growth.

Biological impact of the fibroblast growth factor family on articular cartilage and intervertebral disc homeostasis

Two members of the fibroblast growth factor (FGF) family, basic FGF (bFGF) and FGF-18, have been implicated in the regulation of articular and intervertebral disc (IVD) cartilage homeostasis. Studies on bFGF from a variety of species have yielded contradictory results with regards to its precise role in cartilage matrix synthesis and degradation. In contrast, FGF-18 is a well-known anabolic growth factor involved in chondrogenesis and articular cartilage repair. In this review, we examined the biological actions of bFGF and FGF-18 in articular and IVD cartilage, the specific cell surface receptors bound by each factor, and the unique signaling cascades and molecular pathways utilized to exert their biological effects. Evidence suggests that bFGF selectively activates FGF receptor 1 (FGFR1) to exert degradative effects in both human articular chondrocytes and IVD tissue via upregulation of matrix-degrading enzyme activity, inhibition of matrix production, and increased cell proliferation resulting in clustering of cells seen in arthritic states. FGF-18, on the other hand, most likely exerts anabolic effects in human articular chondrocytes by activating FGFR3, increasing matrix formation and cell differentiation while inhibiting cell proliferation, leading to dispersed cells surrounded by abundant matrix. The results from in vitro and in vivo studies suggest the potential usefulness of bFGF and FGFR1 antagonists, as well as FGF-18 and FGFR3 agonists, as potential therapies to prevent cartilage degeneration and/or promote cartilage regeneration and repair in the future.

Action of fibroblast growth factor-2 on the intervertebral disc

Introduction

Fibroblast growth factor 2 (FGF2) is a growth factor that is immediately released after cartilage injury and plays a pivotal role in cartilage homeostasis. In human adult articular cartilage, FGF2 mediates anti-anabolic and potentially catabolic effects via the suppression of proteoglycan (PG) production along with the upregulation of matrix-degrading enzyme activity. The aim of the present study was to determine the biological effects of FGF2 in spine disc cells and to elucidate the complex biochemical pathways utilized by FGF2 in bovine intervertebral disc (IVD) cells in an attempt to further understand the pathophysiologic processes involved in disc degeneration.

Methods

We studied the effect of FGF2 on IVD tissue homeostasis by assessing MMP-13 expression (potent matrix-degrading enzyme), PG accumulation, and PG synthesis in the bovine spine IVD, as well as evaluating whether FGF2 counteracts known anabolic factors such as BMP7. To understand the molecular mechanisms by which FGF2 antagonizes BMP7 activity, we also investigated the signaling pathways utilized by FGF2 in bovine disc tissue.

Results

The primary receptor expressed in bovine nucleus pulposus cartilage is FGFR1, and this receptor is upregulated in degenerative human IVD tissue compared with normal IVD tissue. Stimulation of bovine nucleus pulposus cells cultured in monolayer with FGF2 augmented the production of MMP-13 at the transcriptional and translational level in a dose-dependent manner. Stimulation of bovine nucleus pulposus cells cultured in alginate beads for 21 days with FGF2 resulted in a dose-dependent decrease in PG accumulation, due at least in part to the inhibition of PG synthesis. Further studies demonstrate that FGF2 (10 ng/ml) antagonizes BMP7-mediated acceleration of PG production in bovine nucleus pulposus cells via the upregulation of noggin, an inhibitor of the transforming growth factor beta/bone morphogenetic protein signaling pathway. Chemical inhibitor studies showed that FGF2 utilizes the mitogen-activated protein kinase and NF-κB pathways to upregulate noggin, serving as one potential mechanism for its anti-anabolic effects.

Conclusion

FGF2 is anti-anabolic in bovine spine disc cells, revealing the potential of FGF2 antagonists as unique biologic treatments for both prevention and reversal of IVD degeneration.

Growth factors in intervertebral disc homeostasis

Intervertebral disc degeneration is a complex age-related pathology associated with back pain. Research on the growth factors that regulate disc homeostasis is of critical importance for understanding the basis of the disease. Here we summarize the data on the expression and function of various growth factors in the disc from in vivo and in vitro studies, as well as on their alterations during degeneration and ageing. Such studies are becoming more crucial in the prospect of clinical application of growth factors for the treatment of disc degeneration.

The cell biology of intervertebral disc aging and degeneration

Intervertebral disc degeneration, which mimics disc aging but occurs at an accelerated rate, is considered to be related to neck or low back pain and disc herniation. Degenerated discs show breakdown of the extracellular matrix and thus fail to bear the daily loadings exerted on the spine. Rather than a passive process of wear and tear, disc degeneration is an aberrant, cell-mediated response to progressive structural failure due to aging and other environmental factors such as abnormal mechanical stress. With aging and degeneration, disc cells undergo substantially biologic changes, including alternation of cell type in the nucleus pulposus, increased cell density but decreased number of viable cells as a result of increased cell death and increased cell proliferation, increased cell senescence, and altered cell phenotype which is characterized by compromised capability of synthesizing correct matrix components and by enhanced catabolic metabolism. These changes are involved in the process of disc degeneration through the complicated interactions among them. To retard or reverse disc degeneration, the abnormal conditions of the decreased viable cell population and the altered cell phenotype should be corrected. As potential therapies for disc degeneration, intradiscal protein injection, gene transfer and cell implantation are being understudied in vivo. Suppression of excessive apoptosis and accelerated senescence of disc cells may be other choices for treating disc degeneration. When performing a biologic therapy in order to repair or regenerate the degenerated disc, nutrient and biomechanical factors should also be incorporated, because they are the major causes of the biologic changes experienced by disc cells. Moreover, a very early intervention is indicated by the finding that the onset of human disc degeneration occurs as early as by adolescence.