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Abstract

Many of the causes of low back pain are still unknown; sufficient evidence indicates that both degenerative and mechanical change within the intervertebral disk (IVD) is a relevant factor. This article reviews intracellular signaling pathways related to pain receptors in the degenerated IVD. Several reports have demonstrated the number of nerve fibers in the IVD was increased in degenerated disks. In recent years, some groups have reported that an increase in nerve fibers is associated with the presence of inflammatory mediators and/or neurotrophins in the IVD. Cell signaling events, which are regulated by inflammatory mediators and neurotrophins, must be identified to clarify the mechanism underlying low back pain. Major intracellular signaling pathways (nuclear factor kappa β, mitogen-activated protein kinases, and Wnts) potentially play vital roles in mediating the molecular events responsible for the initiation and progression of IVD degeneration. These signaling pathways may represent therapeutic targets for the treatment of IVD degeneration and its associated back pain.

Keywords

nucleus pulposus intervertebral disk degeneration Wnt signal low back pain neurotrophic markers

Low back pain represents a significant social and economic burden, including direct medical costs, lost production, and disability benefits, and lowers the quality of life of many individuals.¹,² Low back pain is strongly associated with the intervertebral disk (IVD) degeneration, and IVD degeneration is also associated with sciatica and disk herniation or prolapse. It possibly adversely affects the behavior of other spinal structures such as muscles and ligaments. In the long term it can lead to spinal stenosis, a major cause of pain and disability in the elderly. Therefore, it follows that the suppression of IVD degeneration may limit the pain and disability associated with a range of pathologies of the back. Accordingly, clarification of the pathophysiology of IVD degeneration and its associated pain currently represents a major biomedical research priority. Much research is going on to understand IVD at a molecular level in hopes of creating clinically applicable options for treating IVD degeneration. Despite extensive study of the degenerative process in the IVD, the exact mechanism of diskogenic low back pain (IVD-related pain) has not been elucidated. In this review, we describe recent studies on diskogenic low back pain that have shed new light on the molecular mechanism and intracellular signaling pathways involved.

Disk Morphology

The IVD lies between the vertebral bodies, separated from them by the end plate and consisting of two main regions: an inner, soft and highly hydrated structure, the nucleus pulposus, and an outer, annulus fibrosus. Their major role is mechanical functions, as they constantly transmit loads arising from body weight and muscle activity through the spinal column. In addition, the IVD is the largest avascular tissue in the body, and the essential nutrients are supplied to the disk virtually entirely by diffusion.³ Some groups have reported that several intrinsic and extrinsic factors influence the cellular and molecular state of the IVD, including aging, genetics, transport of nutrients, and the mechanical environment.⁴,⁵,⁶,⁷ This makes it difficult to distinguish the vital cell type to target for therapeutic measures. Despite this complexity, recent studies have shown that there are considerable interspecies variations in the phenotypical characteristics of the cells. Although phenotypical similarities and characteristics exist between nucleus pulposus cells and articular chondrocytes, distinct differences have been identified.⁸,⁹ Nucleus pulposus cells of the IVD, which had generally been referred to as “chondrocyte-like” or “notochordal” cells, have been profiled and characterized in detail. The cells of the mature human nucleus pulposus are primarily chondrocyte-like cells, but in young individuals and in adults of some species, there is a second population of large cells with cytoplasmic inclusions. These are the “notochordal cells.” The notochordal cells express type IIA collagen, the differentially spliced form of type II collagen typical of prechondrocytes, rather than the alternate type IIB collagen, which is expressed by mature chondrocytes; they also express small proteoglycans mRNAs such as versican and decorin, more characteristic of fibroblast. These characteristics are of crucial importance for the success of regenerative and repair strategies, considering the structural and mechanical distinctions between IVD and cartilage tissues.

Effect of Degenerative Changes on Intervertebral Disk Cell Signaling

Major Intracellular Signaling Pathways for IVD Degeneration

With increasing age and degeneration, the most significant biochemical change to occur in IVD degeneration is loss of proteoglycans. These proteoglycans enable the nucleus pulposus to retain water, thereby cushioning and absorbing the considerable loads placed on the tissue. With increasing age and degeneration, the nucleus pulposus eventually becomes more fibrous tissue, and the peripheral anulus fibrosus is forced to carry larger loads, leading to tears, bulging, rupture, and herniation. In addition, loss of proteoglycans in degenerate disks influences the movement of molecules into and out of the IVD. Specifically, loss of aggrecan and type II collagen would allow increased penetration of large molecules such as growth factor complexes and cytokines into the IVD, affecting cellular behavior and possibly the progression of degeneration (Fig. 1). Therapeutic strategies for the biological treatment of IVD degeneration include the use of cellular components (mesenchymal stem cells, chondrocytes, and culture-expanded nucleus pulposus cells), matrix derivatives, molecules influencing disk-cell metabolism, and tissue-engineering strategies to restore function to the IVD degeneration.¹⁰,¹¹,¹²,¹³,¹⁴

Fig. 1

Proposed scheme of the degenerative changes on intervertebral disk cell. Abbreviations: AF, annulus fibrosus; EP, end plate; NP, nucleus pulposus.

Focusing on molecular therapy, some groups have reported that the biochemistry of IVD degeneration is commonly attributed to the dual effects of increased catabolic factors, such as matrix metalloproteinases (MMPs) and interleukin (IL)-1, and decreased anabolic factors such as transforming growth factors (TGFs) and bone morphogenetic proteins (BMPs). The balance between synthesis and breakdown of matrix macromolecules by the intracellular signaling pathways determines the quality and integrity of the matrix, and thus the mechanical behavior of the IVD.¹⁵,¹⁶,¹⁷,¹⁸ Under this paradigm, it follows that various cytokines and neurotrophic factors are secreted from the cells of the nucleus pulposus and annulus fibrosus, and these factors activate the nerve termini.¹⁹ Therefore, the gene expression and function of potential molecular mediators in IVD degeneration have been a major topic of research interest (Table 1).²⁰,²¹,²²,²³,²⁴,²⁵,²⁶,²⁷,²⁸,²⁹,³⁰,³¹,³²,³³,³⁴,³⁵,³⁶,³⁷,³⁸,³⁹,⁴⁰ This review describes each major intracellular signaling that potentially plays vital roles in mediating the molecular events responsible for the initiation and progression of IVD degeneration. In a recent review, Wuertz et al suggested that major intracellular signaling factors, such as nuclear factor kappa β (NF-κβ) and mitogen-activated protein kinases (MAPKs) play vital roles in mediating the molecular events responsible for the initiation and progression of IVD degeneration.⁴¹ Indeed many genes, including several proinflammatory mediators, are regulated by NF-κβ in the IVD.⁴²,⁴³ For example, Wang et al demonstrated that the expression of ADAMTS4 (A Disintegrin And Metalloproteinase with Thrombospondin Motifs) and ADAMTS5, the two major aggrecanases, is controlled by NF-κβ-dependent mechanisms.⁴⁴ Furthermore, stimulation by exogenous and endogenous proinflammatory mediators, such as IL-1 or tumor necrosis factor-α (TNF-α), can activate NF-κβ, in the cells of the IVD.⁴⁵,⁴⁶,⁴⁷

Table 1

Reports of signaling pathways in IVD cells

Signaling pathway	Reference
Nuclear factor kappa β	Wang et al 2012⁴⁴
	Fujita et al 2012²⁵
	Oh et al 2010⁴⁷
	Yu et al 2009⁴⁶
	Ohba et al 2009⁴⁵
	Wako et al 2008⁴²
	Hoylland et al 2008⁴³
Mitogen-activated protein kinase	Kim et al 2012⁵⁵
	Pratsinis et al 2012³¹
	Hiyama et al 2011⁷⁹
	Xia et al 2011⁵⁶
	Mavrogonatou and Kletsas 2010³²
	Studer et al 2008²⁰
	Uchiyama et al 2007⁵³
	Tsai et al 2007⁴⁰
	Pratsinis and Kletsas 2007⁵¹
	Séguin et al 2006⁴⁸
	Risbud et al 2005, 2006⁴⁹,⁵⁰
Protein kinase B	Pratsinis et al 2012³¹
	Mavrogonatou and Kletsas 2010³²
	Cheng et al 2009³³
	Risbud et al 2005⁴⁹
Nerve growth factor	Gruber et al 2012³⁴
	Lee et al 2011³⁵
	Richardson et al 2009³⁶
	Yamauchi et al 2009³⁷
	Abe et al 2007⁹³
	Freemont et al 2002⁹²
Wnt	Smolder et al 2012⁸⁰
	Wang et al 2012⁸²
	Ye et al 2011²⁹
	Kondo et al 2011³⁰
	Hiyama et al 2010, 2011⁷⁸,⁷⁹
Fibroblast growth factor	Li et al 2008⁵⁹
	Tsai et al 2007⁵²
	Peng et al 2006⁶⁰
	Nagano et al 1995⁵⁸
Protein kinase C	Arai et al 2012²⁷
Protein kinase C	Ellman et al 2012²⁸
Hypoxia-inducible factor	Gogate et al 2012²²
	Fujita et al 2012²³
	Risbud et al 2006²⁴
Notch	Hiyama et al 2011²⁶
Shh	Dahia et al 2012³⁸
Shh	Choi and Harfe 2011³⁹

MAPK signaling research in the IVD has shown that the p38 and extracellular signal-regulated kinase (ERK) signaling pathways play a significant role in extracellular metabolism, because treatment with targeted kinase inhibitors significantly counteracted cytokine-induced changes in proteoglycan content, synthesis, and release.²⁰,⁴⁸ In addition, several signaling intermediates and factors of the MAPK pathway have been identified in IVD cells.⁴⁹,⁵⁰ Some groups have reported that TGF, nerve growth factor (NGF), platelet-derived growth factor, insulin-like growth factor-I, and basic fibroblast growth factor, all known to be overexpressed in degenerated disk tissue, can stimulate p38/ERK signaling in IVD of various species.⁵¹,⁵²,⁵³ Furthermore MMPs, inducible nitric oxide synthase, tissue inhibitor of metalloproteinases, aggrecan, type II collagen, Sox-9, acid-sensing ion channel, and tonicity-responsive enhancer-binding protein have all been identified as target genes of ERK in IVD cells.³⁸,⁴⁷,⁵⁴,⁵⁵,⁵⁶ In addition, fibroblast growth factor-2 (FGF-2) has been identified as an anabolic mediator of disk homeostasis, an effect that may result from FGF-2-mediated stimulation of proteoglycan synthesis, such as seen in a canine IVD tissue culture system, or upregulation of cell proliferation such as seen in rat disks.⁵⁷,⁵⁸ In contrast, the findings of Li et al and Peng et al suggest that FGF-2 primarily has a catabolic role in disk homeostasis.⁵⁹,⁶⁰ Based on these apparently conflicting findings, it seems likely that FGF-2 plays multiple roles in disk homeostasis, and also that this may change depending on the stage of degeneration and the nature of the disease process.

Against the background of these intracellular signaling pathways, cell or growth factor therapies have recently been suggested to induce IVD repair in these signals and/or factors as target. However, one problem with the use of growth factors and/or cytokines in clinical trials is their high cost and safety. For these concern, Mwale et al have reported that Link N (DHLSDNYTLDHDRAIH) can stimulate the synthesis of aggrecan and collagen in the bovine IVD cells in vitro,⁶¹,⁶² as well as in the IVDs of rabbits in vivo.⁶³ The changes in proteoglycan synthesis with Link N are similar to those reported previously with the same concentration of osteogenic protein-1 (OP-1). Link N agent can be treated with the low cost than OP-1 for the IVD degeneration. Link N therefore represents a potential economical therapeutic agent with beneficial effects. Their group has reported that Link N is also able to downregulate MMP expression in the degenerate IVDs, enhance the chondrogenic differentiation, and downregulate hypertrophic and osteogenic differentiation of human MSCs.⁶⁴

Roll of Wnt Signaling in IVD Cells

In recent years, it has been also reported that Wnt signaling may play a crucial role of the cellular responses that lead to IVD inflammation and catabolism, much as they are involved in bone and cartilage metabolism. Wnts are secretory proteins of ∼40 kDa that control multiple aspects of development, including the proliferation, fate specification, polarity, and migration of cells.⁶⁵,⁶⁶ In addition, Chou et al reported that Wnt-1 and Wnt-3a both inhibit NGF-induced neurite outgrowth from PC12 cells.⁶⁷ These results showed that sensory nerve receptors and neurotrophic markers cooperate with Wnt signals in regulating many biological processes, but the mechanisms of their interaction remain poorly defined in the IVD.

Wnt signaling can occur via the canonical Wnt/β-catenin-dependent pathway (hereafter called Wnt) or the noncanonical β-catenin-independent pathway, which itself can be divided into the planar cell polarity pathway and the Wnt/Ca²⁺ pathway.⁶⁸ Among these, the canonical pathway is the most well characterized. Wnt proteins are glycoproteins that bind to the N-terminal extracellular cysteine-rich domain of the Frizzled (Fz) receptor family, of which there are 10 variants in humans. Fz is a seven-transmembrane-span protein with topological homology to G-protein-coupled receptors. In addition to the interaction between Wnt and Fz, co-receptors are also required for mediating the Wnt signaling. For example, the low-density-lipoprotein-related protein 6 is required to mediate Wnt signaling via the canonical pathway. On activation of this pathway, the cytoplasmic β-catenin is translocated to the nucleus, where it promotes binding of the transcription factor, T-cell factor/lymphocyte-enhancing factor, thereby accelerating the expression of target genes.⁶⁹,⁷⁰,⁷¹ It is well known that Wnt signaling plays a major role in bone metabolism. It has been shown that although the Wnt signaling suppresses differentiation of mesenchymal stem cells into chondrocytes and adipocytes, it accelerates their differentiation into osteoblasts and osteocytes. Following activation of the Wnt signaling, osteoprotegerin, which is a decoy for the receptor activator of NF-κβ ligand, is generated from osteoblasts, and ossification is accelerated as a result of inhibiting the activation of osteoclasts. Moreover, cross talk between Wnt signaling and other pathways that regulate ossification, such as the BMP pathway, is also known.⁷²,⁷³ In cartilage metabolism, it has been suggested that β-catenin is involved in the modulation of both anabolic and catabolic activities, suggesting that Wnt signaling also modulates inflammatory cytokine expression.⁷⁴,⁷⁵,⁷⁶ Furthermore, it also appears that the activation of Wnt signaling may cause cellular senescence and thereby contribute to the process of IVD degeneration.⁷⁷

Hiyama et al reported that rat nucleus pulposus cells undergo aging when treated with LiCl, consistent with the fact that LiCl is an activator of Wnt signaling that suppresses cell proliferation.⁷⁸ Moreover, it has been reported that the activation of Wnt signaling in the IVD induces other pathways, including the TGF/BMP pathway, and that it is the cross talk between these pathways that ultimately controls the turnover of the extracellular matrix.⁷⁹ Moreover, Smolders et al have reported that the activation of Wnt signaling occurs primarily in the notochordal cells during the initial stage of IVD degeneration.⁸⁰ Similarly, Ukita et al have shown that Wnt signaling in the notochord progenitor cells (NPCs) is essential for posterior extension of the notochord in Not-Cre; β-catenin^flox/flox embryos. In addition, they demonstrated both the expression of notochord-specific genes and the size of the notochord decline in the absence of Wnt signaling, and this is probably because Wnt signaling is essential for stabilization of the NPC phenotype.⁸¹ Wang et al also investigated the gene expression of catabolic factors with β-catenin conditional (cAct) mice and found that the expression of both MMP13 and ADAMTS-5 was increased in the IVDs of β-catenin knockouts, consistent with the observed IVD degeneration. Moreover, they found that IVD degeneration was suppressed when an inhibitor of MMP13 was administered to β-catenin cAct mice. From these results, it was concluded that β-catenin is a key factor responsible for the maintenance of the IVD tissue structure.⁸²

To date, although there are a lot of studies of the intracellular signaling pathways in IVD, we should keep in mind that the final effect of the activation of signaling depends on their “signaling cross talk” with other activated signaling pathways. Therefore, it is necessary to investigate the importance of elucidating the cellular mechanisms of IVD degeneration and to build map of intracellular signaling pathways in IVD.

Pain and Innervations for the IVD

The normal IVD is considered to be a poorly innervated organ that is supplied only by sensory and sympathetic perivascular nerve fibers. Furthermore, there is widespread agreement that an important priority is to identify factors sensitizing the sensory nerves of the degenerated IVD. Regarding the neuropathology of IVDs studied in Japan, the analysis performed on surgical samples in 1970 by Shinohara was the first to describe a novel nerve terminal in the process of invading the annulus fibrosus.⁸³ Subsequently, Yoshizawa et al and Bogduk et al searched for nerve cells inside degenerated IVDs and reported their presence in the outer layers of the annulus fibrosus.⁸⁴,⁸⁵ Moreover, Freemont et al examined nerve growth in degenerate IVDs associated with chronic low back pain.⁸⁶ They collected 46 IVDs from 38 patients during spinal fusion and used standard immunohistochemical techniques to describe the abundance and location of a general nerve marker, a nociceptive neurotransmitter (substance-P), and a protein expressed during axonogenesis (growth-associated protein 43 [GAP43]). They reported that although nerve fibers were not present in the inner layer of the annulus fibrosus (or the nucleus pulposus) of normal human IVDs, they were present in the inner layer of the annulus fibrosus of degenerate IVDs.⁸⁶ Subsequently, Roberts et al reported the presence of mechanoreceptors in the IVD and anterior longitudinal ligament.⁸⁷ Burke et al have compared the levels of L-6, IL-8, and prostaglandin E₂ in disk tissue from patients undergoing diskectomy for sciatica (n = 63) with that from patients undergoing fusion for diskogenic low back pain (n = 20). They suggested that the presence of inflammatory mediators IL-6 and IL-8 in the IVD might be involved in axonal ingrowth.⁸⁸ Le Maitre et al demonstrated that herniated disks and degenerated disks from patients with chronic back pain showed a higher expression of IL-1β and TNF-α than nondegenerated disks derived from normal postmortem tissue.⁸⁹ Weiler et al also demonstrated that surgical disk tissue from symptomatic back pain patients contained more TNF-α-positive cells than asymptomatic autopsy samples, with a positive correlation to the degree of IVD degeneration.⁹⁰ These findings suggest that inflammation promotes the growth of afferent fibers in the disk and that this growth might be the cause of low back pain. To elucidate the cause of diskogenic low back pain, we also think that these points are very important.

Furthermore, the predominant nerve cells of the IVD have been characterized in recent years using activating transcription factor 3 (ATF3) as a marker of nerve injuries and GAP43 as a marker of axonal growth. In one study, Inoue et al characterized nerve cells in a rat model of IVD disease by creating a punch hole connecting the outside of the annulus fibrosus and the nucleus pulposus. They concluded that the procedure induced nerve injury and resulted in nerve ingrowth into the disks.⁹¹ A role for NGF in the ingrowth was indicated by subsequent studies showing enhanced levels in degenerated IVDs. Indeed, the study of neural and neurotrophic markers has been a very active area of IVD research in recent years.⁹²,⁹³,⁹⁴,⁹⁵,⁹⁶ For example, neurotrophins have been shown to enhance the survival and differentiation of discrete populations of peripheral nerve neurons. The neurotrophins NGF and brain-derived neurotrophic factor (BDNF), which are associated with stimulation of axonal outgrowth and nociception by neuronal cells, are both expressed by nucleus pulposus cells, with BDNF levels increasing with disease severity.

Meanwhile, the pain transmitters in the sensory nerves dominating the IVDs have also been characterized, and it has been shown that neuropeptides such as substance-P and calcitonin gene-related peptide are expressed in the outer layer of the annulus fibrosus.⁹⁷ In addition, sensory nerve receptors such as NGF receptors, tyrosine kinase A, p75 neurotrophin receptor, and transient receptor potential V1 are present in IVDs.⁹⁸ Moreover, degenerative conditions have been shown to induce the expression of receptor ligands and could modify the perception of pain.

Regarding modulation of the afferent pathway of IVD-related low back pain, it is generally accepted that nerve excitation is enhanced by inflammation of the nerves and by mechanical stress. In terms of the specific afferent pathways involved, in 1993 Takahashi et al reported that the L5–6 IVD in the rat is innervated bilaterally from the L1 and L2 dorsal root ganglia through the paravertebral sympathetic trunk.⁹⁹ The authors found that injection of capsaicin, a C-fiber stimulator, into the anterior portion of a lumbar IVD of rats pretreated intravenously with Evans blue caused dye extravasation of the pigment in the groin skin. Evans Blue is an azo dye which has a very high affinity for serum albumin. Vascular permeability was assessed by measuring Evans blue dye extravasation. These results suggested the presence of dichotomizing sensory C-fibers, which innervate both the IVDs and the groin skin in the L2 spinal nerve.⁹⁹ Subsequently, to elucidate the afferent pathways of diskogenic low back pain in humans, Nakamura et al hypothesized that low back pain was transmitted mainly by sympathetic afferent fibers in the L2 nerve root, and selective local anesthesia of this nerve was employed in 33 patients. Low back pain disappeared or decreased significantly in all patients after the injection.¹⁰⁰ Furthermore, to investigate the innervation of annulus fibrosus in the posterior region of the IVD, Ohtori et al used a 21-gauge needle with the tip filled with the nerve tracer, Fluoro-Gold (FG) crystals.¹⁵,¹⁰¹ The tracer was injected along the axis connecting a point 4 mm from the ventral surface of the disk to the most dorsal region, and it was found that sensory fibers from the upper dorsal root ganglions innervated the dorsal portion of the disks via the paravertebral sympathetic trunks. However, fibers from the lower dorsal root ganglions were found to be innervated via the sinuvertebral nerves, showing that the innervation of the dorsal portion of the disks was under the control of both the paravertebral sympathetic trunks and the sinuvertebral nerves.¹⁵,¹⁰¹ Moreover, Kurokawa et al employed double fluorescent labeling using two types of neurotracers, 1,1-dioctadecyl-3,3,3,3- tetramethylindocarbocyanine perchlorate and FG, in rat lumbar disks and reported that one sensory nerve was innervating lumbar disks at multiple levels.¹⁶

From these basic research results, it is believed that when IVD degeneration occurs, such as inflammation within the annulus fibrosus and/or herniation of the nucleus pulposus, nerves with mainly C-fibers germinate from the annulus fibrosus inward, thereby causing neurogenic inflammation and leading to aggravation of pain.

Accordingly, clarifying the pathophysiologic mechanism by which IVD degeneration occurs will be required for any improvement in the current treatments for diskogenic low back pain.

Summary

Low back pain is attributed to several medical disorders including lumbar herniation, scoliosis, and muscle and ligament damage, although most importantly, IVD degeneration is associated with up to 40% of individuals under 30 years of age.¹⁰²

In recent years, attention has begun to focus on the cellular and molecular mechanism and signaling of IVD in the search for an understanding of the pathophysiology of low back pain (Fig. 2). In terms of molecular alterations, the balance between matrix anabolism and catabolism that exists in the nondegenerate IVD is shifted toward catabolism in degeneration, due to the production of matrix-degrading enzymes MMPs and ADAMTSs by MAPK and/or NF-κβ pathways, among others. The most significant molecular alteration is thought to be the upregulated expression of inflammatory cytokines and/or neurotrophins. In addition, it was demonstrated recently that Wnt signaling is a key pathway to regulate and maintain the IVD homeostasis. However, degeneration of the IVD is an incredibly complex disorder; moreover, many of the results implicating molecular signaling were obtained with cells and tissues from rodent models. Therefore, much research is needed to gain a better understanding of these signals and how their “cross talk” with other pathways will be likely to influence the outcome of treatments for IVD degeneration in vivo. Recent studies have demonstrated the presence of cell niches and progenitor cells in the IVD.¹⁰³,¹⁰⁴ Kim et al have reported that end plate chondrocytes of the IVD, like articular chondrocytes, are capable of migration and that soluble factors produced by notochordal cells stimulate the migration.¹⁰⁵ The identification of progenitor cells within IVD indicates that natural repair mechanisms exist within the IVD and may be activated for regeneration, although the signal mechanisms and function of these cells need to be elucidated. Sakai et al also showed for the first time an experimental model of nucleus pulposus differentiation induced from functional progenitor cells in vivo. They suggested that Tie2 is a sensitive marker of aging and degeneration of IVDs and will be a useful marker for the diagnosis of IVD degeneration.¹⁰⁶ Future studies are needed to examine whether progenitor cells can be used to inhibit nerve ingrowth or nociceptor formation in degenerate IVDs. Novel biological strategies will be more successful to treat and prevent disk degeneration and finally contribute to treatment of the low back pain if the specific disk cell phenotypes, functions, and molecular signaling are taken into consideration.

Fig. 2

Signal pathway implicated in disk intervertebral disk degeneration. Abbreviations: ADAMTS, A Disintegrin And Metalloproteinase with Thrombospondin Motifs; AF, annulus fibrosus; BDNF, brain-derived neurotrophic factor; BMP, bone morphogenetic protein; CGRP, calcitonin gene-related peptide; DRG, dorsal root ganglion; FGF-2, fibroblast growth factor-2; HIF, hypoxia-inducible factor; IGF, MAPK, mitogen-activated protein kinase; MMP, matrix metalloproteinase; NF-κβ, nuclear factor kappa β; NGF, nerve growth factor; NP, nucleus pulposus; PDGF, platelet-derived growth factor; PKC, protein kinase C; SP, substance P; TGF, transforming growth factor; TNF α, tumor necrosis factor-α.

Disclosures

Akihiko Hiyama, None

Daisuke Sakai, None

Joji Mochida, None

References

Rizzo

J A

Abbott

T A

III

Berger

M L

The labor productivity effects of chronic backache in the United States

Med Care 1998 36 1471–1488

Guo

H R

Tanaka

Cameron

L L

, et al.

Back pain among workers in the United States: national estimates and workers at high risk

Am J Ind Med 1995 28 591–602

Urban

J P

Smith

Fairbank

J C

Nutrition of the intervertebral disc

Spine 2004 29 2700–2709

Antoniou

Steffen

Nelson

, et al.

The human lumbar intervertebral disc: evidence for changes in the biosynthesis and denaturation of the extracellular matrix with growth, maturation, ageing, and degeneration

J Clin Invest 1996 98 996–1003

Chan

Song

Sham

Cheung

K M

Genetics of disc degeneration

Eur Spine J 2006 15 03 S317–S325, 98, 996–1003

Grunhagen

Wilde

Soukane

D M

Shirazi-Adl

S A

Urban

J P

Nutrient supply and intervertebral disc metabolism

J Bone Joint Surg Am 2006 88 02 30–35

Iatridis

J C

MacLean

J J

Roughley

P J

Alini

Effects of mechanical loading on intervertebral disc metabolism in vivo

J Bone Joint Surg Am 2006 88 02 41–46

Sakai

Nakai

Mochida

Alini

Grad

Differential phenotype of intervertebral disc cells: microarray and immunohistochemical analysis of canine nucleus pulposus and anulus fibrosus

Spine 2009 34 1448–1456

Rutges

Creemers

L B

Dhert

, et al.

Variations in gene and protein expression in human nucleus pulposus in comparison with annulus fibrosus and cartilage cells: potential associations with aging and degeneration

Osteoarthritis Cartilage 2010 18 416–423

10.

Richardson

S M

Walker

R V

Parker

, et al.

Intervertebral disc cell-mediated mesenchymal stem cell differentiation

Stem Cells 2006 24 707–716

11.

Sakai

Mochida

Iwashina

, et al.

Differentiation of mesenchymal stem cells transplanted to a rabbit degenerative disc model: potential and limitations for stem cell therapy in disc regeneration

Spine 2005 30 2379–2387

12.

Yoon

S T

Patel

N M

Molecular therapy of the intervertebral disc

Eur Spine J 2006 15 03 S379–S388

13.

Richardson

S M

Curran

J M

Chen

, et al.

The differentiation of bone marrow mesenchymal stem cells into chondrocyte-like cells on poly-L-lactic acid (PLLA) scaffolds

Biomaterials 2006 27 4069–4078

14.

Roughley

Hoemann

DesRosiers

Mwale

Antoniou

Alini

The potential of chitosan-based gels containing intervertebral disc cells for nucleus pulposus supplementation

Biomaterials 2006 27 388–396

15.

Ohtori

Takahashi

Chiba

Yamagata

Sameda

Moriya

Sensory innervation of the dorsal portion of the lumbar intervertebral discs in rats

Spine 2001 26 946–950

16.

Kurokawa

DRG neurons innervating three levels of lumbar intervertebral discs in rats

Abstracts of 30th Annual Meeting of International Society for the Study of the Lumbar Spine; Vancouver, Canada; May 13–17, 2003

17.

Cui

Urban

J P

Young

D A

Differential gene expression profiling of metalloproteinases and their inhibitors: a comparison between bovine intervertebral disc nucleus pulposus cells and articular chondrocytes

Spine 2010 35 1101–1108

18.

Roberts

Caterson

Menage

Evans

E H

Jaffray

D C

Eisenstein

S M

Matrix metalloproteinases and aggrecanase: their role in disorders of the human intervertebral disc

Spine 2000 25 3005–3013

19.

Weiler

Nerlich

A G

Zipperer

Bachmeier

B E

Boos

2002 SSE Award Competition in Basic Science: expression of major matrix metalloproteinases is associated with intervertebral disc degradation and resorption

Eur Spine J 2002 11 308–320

20.

Studer

R K

Gilbertson

L G

Georgescu

Sowa

Kang

J D

p38 MAPK inhibition modulates rabbit nucleus pulposus cell response to IL-1

J Orthop Res 2008 26 991–998

21.

Koshi

Ohtori

Inoue

, et al.

Lumbar posterolateral fusion inhibits sensory nerve ingrowth into punctured lumbar intervertebral discs and upregulation of CGRP immunoreactive DRG neuron innervating punctured discs in rats

Eur Spine J 2010 19 593–600

22.

Gogate

S S

Fujita

Skubutyte

Shapiro

I M

Risbud

M V

Tonicity enhancer binding protein (TonEBP) and hypoxia-inducible factor (HIF) coordinate heat shock protein 70 (Hsp70) expression in hypoxic nucleus pulposus cells: role of Hsp70 in HIF-1α degradation

J Bone Miner Res 2012 27 1106–1117

23.

Fujita

Chiba

Shapiro

I M

Risbud

M V

HIF-1α and HIF-2α degradation is differentially regulated in nucleus pulposus cells of the intervertebral disc

J Bone Miner Res 2012 27 401–412

24.

Risbud

M V

Guttapalli

Stokes

D G

, et al.

Nucleus pulposus cells express HIF-1 alpha under normoxic culture conditions: a metabolic adaptation to the intervertebral disc microenvironment

J Cell Biochem 2006 98 152–159

25.

Fujita

Gogate

S S

Chiba

Toyama

Shapiro

I M

Risbud

M V

Prolyl hydroxylase 3 (PHD3) modulates catabolic effects of tumor necrosis factor-α (TNF-α) on cells of the nucleus pulposus through co-activation of nuclear factor κB (NF-κB)/p65 signaling

J Biol Chem 2012 287 39942–39953

26.

Hiyama

Skubutyte

Markova

, et al.

Hypoxia activates the notch signaling pathway in cells of the intervertebral disc: implications in degenerative disc disease

Arthritis Rheum 2011 63 1355–1364

27.

Arai

Hiyama

Sakai

Yokoyama

Mochida

The expression and role of non-canonical (PKC) signaling in nucleus pulposus cell metabolism

J Orthop Res 2012 30 1478–1485

28.

Ellman

M B

Kim

J S

H S

, et al.

The pathophysiologic role of the protein kinase Cδ pathway in the intervertebral discs of rabbits and mice: in vitro, ex vivo, and in vivo studies

Arthritis Rheum 2012 64 1950–1959

29.

Wang

Yang

, et al.

Specific inhibitory protein Dkk-1 blocking Wnt/β-catenin signaling pathway improve protectives effect on the extracellular matrix

J Huazhong Univ Sci Technolog Med Sci 2011 31 657–662

30.

Kondo

Yuasa

Shimono

, et al.

Intervertebral disc development is regulated by Wnt/β-catenin signaling

Spine 2011 36 E513–E518

31.

Pratsinis

Constantinou

Pavlakis

Sapkas

Kletsas

Exogenous and autocrine growth factors stimulate human intervertebral disc cell proliferation via the ERK and Akt pathways

J Orthop Res 2012 30 958–964

32.

Mavrogonatou

Kletsas

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

J Orthop Res 2010 28 1276–1282

33.

Cheng

C C

Uchiyama

Hiyama

Gajghate

Shapiro

I M

Risbud

M V

PI3K/AKT regulates aggrecan gene expression by modulating Sox9 expression and activity in nucleus pulposus cells of the intervertebral disc

J Cell Physiol 2009 221 668–676

34.

Gruber

H E

Hoelscher

G L

Bethea

Hanley

E N

Interleukin 1-beta upregulates brain-derived neurotrophic factor, neurotrophin 3 and neuropilin 2 gene expression and NGF production in annulus cells

Biotech Histochem 2012 87 506–511

35.

Lee

J M

Song

J Y

Baek

, et al.

Interleukin-1β induces angiogenesis and innervation in human intervertebral disc degeneration

J Orthop Res 2011 29 265–269

36.

Richardson

S M

Doyle

Minogue

B M

Gnanalingham

Hoyland

J A

Increased expression of matrix metalloproteinase-10, nerve growth factor and substance P in the painful degenerate intervertebral disc

Arthritis Res Ther 2009 11 R126

37.

Yamauchi

Inoue

Koshi

, et al.

Nerve growth factor of cultured medium extracted from human degenerative nucleus pulposus promotes sensory nerve growth and induces substance p in vitro

Spine 2009 34 2263–2269

38.

Dahia

C L

Mahoney

Wylie

Shh signaling from the nucleus pulposus is required for the postnatal growth and differentiation of the mouse intervertebral disc

PLoS ONE 2012 7 e35944

39.

Choi

K S

Harfe

B D

Hedgehog signaling is required for formation of the notochord sheath and patterning of nuclei pulposi within the intervertebral discs

Proc Natl Acad Sci USA 2011 108 9484–9489

40.

Tsai

T T

Guttapalli

Agrawal

Albert

T J

Shapiro

I M

Risbud

M V

MEK/ERK signaling controls osmoregulation of nucleus pulposus cells of the intervertebral disc by transactivation of TonEBP/OREBP

J Bone Miner Res 2007 22 965–974

41.

Wuertz

Kletsas

Boos

Inflammatory and catabolic signalling in intervertebral discs: the roles of NF-κB and MAP kinases

Eur Cell Mater 2012 23 103–119, discussion 119–120

42.

Wako

Ohba

Ando

, et al.

Mechanism of signal transduction in tumor necrosis factor-like weak inducer of apoptosis-induced matrix degradation by MMP-3 upregulation in disc tissues

Spine 2008 33 2489–2494

43.

Hoyland

J A

Le Maitre

Freemont

A J

Investigation of the role of IL-1 and TNF in matrix degradation in the intervertebral disc

Rheumatology (Oxford) 2008 47 809–814

44.

Wang

Markova

Anderson

D G

, et al.

TNF-α and IL-1β promote a disintegrin-like and metalloprotease with thrombospondin type I motif-5-mediated aggrecan degradation through syndecan-4 in intervertebral disc

J Biol Chem 2011 286 39738–39749

45.

Ohba

Haro

Ando

, et al.

TNF-alpha-induced NF-kappaB signaling reverses age-related declines in VEGF induction and angiogenic activity in intervertebral disc tissues

J Orthop Res 2009 27 229–235

46.

Z G

Wang

W B

Pan

S H

K S

Liu

J K

Interleukin-1 inhibits Sox9 and collagen type II expression via nuclear factor-kappaB in the cultured human intervertebral disc cells

Chin Med J (Engl) 2009 122 2483–2488

47.

I S

Park

S E

Son

J M

, et al.

Glucocorticoid mechanism of inhibition of the inflammatory cells in lumbar intervertebral disc cells stimulated by TNF-alpha production of nuclear factor-kappaB

J Korean Orthop Res Soc 2010 13 80–87

48.

Séguin

C A

Bojarski

Pilliar

R M

Roughley

P J

Kandel

R A

Differential regulation of matrix degrading enzymes in a TNFalpha-induced model of nucleus pulposus tissue degeneration

Matrix Biol 2006 25 409–418

49.

Risbud

M V

Fertala

Vresilovic

E J

Albert

T J

Shapiro

I M

Nucleus pulposus cells upregulate PI3K/Akt and MEK/ERK signaling pathways under hypoxic conditions and resist apoptosis induced by serum withdrawal

Spine 2005 30 882–889

50.

Risbud

M V

Guttapalli

Albert

T J

Shapiro

I M

Hypoxia activates MAPK activity in rat nucleus pulposus cells: regulation of integrin expression and cell survival

Spine 2005 30 2503–2509

51.

Pratsinis

Kletsas

PDGF, bFGF and IGF-I stimulate the proliferation of intervertebral disc cells in vitro via the activation of the ERK and Akt signaling pathways

Eur Spine J 2007 16 1858–1866

52.

Tsai

T T

Guttapalli

Oguz

, et al.

Fibroblast growth factor-2 maintains the differentiation potential of nucleus pulposus cells in vitro: implications for cell-based transplantation therapy

Spine 2007 32 495–502

53.

Uchiyama

Cheng

C C

Danielson

K G

, et al.

Expression of acid-sensing ion channel 3 (ASIC3) in nucleus pulposus cells of the intervertebral disc is regulated by p75NTR and ERK signaling

J Bone Miner Res 2007 22 1996–2006

54.

Risbud

M V

Di Martino

Guttapalli

, et al.

Toward an optimum system for intervertebral disc organ culture: TGF-beta 3 enhances nucleus pulposus and anulus fibrosus survival and function through modulation of TGF-beta-R expression and ERK signaling

Spine 2006 31 884–890

55.

Kim

J S

Ellman

M B

H S

, et al.

Lactoferricin mediates anabolic and anti-catabolic effects in the intervertebral disc

J Cell Physiol 2012 227 1512–1520

56.

Xia

Zhu

Fibronectin fragment activation of ERK increasing integrin α₅ and β₁ subunit expression to degenerate nucleus pulposus cells

J Orthop Res 2011 29 556–561

57.

Thompson

J P

Oegema

T R

Bradford

D S

Stimulation of mature canine intervertebral disc by growth factors

Spine 1991 16 253–260

58.

Nagano

Yonenobu

Miyamoto

Tohyama

Ono

Distribution of the basic fibroblast growth factor and its receptor gene expression in normal and degenerated rat intervertebral discs

Spine 1995 20 1972–1978

59.

H S

Ellman

, et al.

Action of fibroblast growth factor-2 on the intervertebral disc

Arthritis Res Ther 2008 10 R48

60.

Peng

Hao

Hou

, et al.

Possible pathogenesis of painful intervertebral disc degeneration

Spine 2006 31 560–566

61.

Mwale

Demers

C N

Petit

, et al.

A synthetic peptide of link protein stimulates the biosynthesis of collagens II, IX and proteoglycan by cells of the intervertebral disc

J Cell Biochem 2003 88 1202–1213

62.

Petit

Yao

Rowas

S A

, et al.

Effect of synthetic link N peptide on the expression of type I and type II collagens in human intervertebral disc cells

Tissue Eng Part A 2011 17 899–904

63.

Mwale

Masuda

Pichika

, et al.

The efficacy of Link N as a mediator of repair in a rabbit model of intervertebral disc degeneration

Arthritis Res Ther 2011 13 R120

64.

Antoniou

Wang

H T

Alaseem

A M

Haglund

Roughley

P J

Mwale

The effect of Link N on differentiation of human bone marrow-derived mesenchymal stem cells

Arthritis Res Ther 2012 14 R267

65.

Logan

C Y

Nusse

The Wnt signaling pathway in development and disease

Annu Rev Cell Dev Biol 2004 20 781–810

66.

Cadigan

K M

Nusse

Wnt signaling: a common theme in animal development

Genes Dev 1997 11 3286–3305

67.

Chou

A H

Howard

B D

Inhibition by Wnt-1 or Wnt-3a of nerve growth factor-induced differentiation of PC12 cells is reversed by bisindolylmaleimide-I but not by several other PKC inhibitors

Oncogene 2002 21 6348–6355

68.

Kikuchi

Kishida

Yamamoto

Regulation of Wnt signaling by protein-protein interaction and post-translational modifications

Exp Mol Med 2006 38 1–10

69.

Behrens

von Kries

J P

Kühl

, et al.

Functional interaction of beta-catenin with the transcription factor LEF-1

Nature 1996 382 638–642

70.

Behrens

Jerchow

B A

Würtele

, et al.

Functional interaction of an axin homolog, conductin, with beta-catenin, APC, and GSK3beta

Science 1998 280 596–599

71.

Korinek

Barker

Morin

P J

, et al.

Constitutive transcriptional activation by a beta-catenin-Tcf complex in APC-/- colon carcinoma

Science 1997 275 1784–1787

72.

Harada

Rodan

G A

Control of osteoblast function and regulation of bone mass

Nature 2003 423 349–355

73.

Bodine

P V

Zhao

Kharode

Y P

, et al.

The Wnt antagonist secreted frizzled-related protein-1 is a negative regulator of trabecular bone formation in adult mice

Mol Endocrinol 2004 18 1222–1237

74.

Loughlin

Dowling

Chapman

, et al.

Functional variants within the secreted frizzled-related protein 3 gene are associated with hip osteoarthritis in females

Proc Natl Acad Sci USA 2004 101 9757–9762

75.

Zhu

Rosier

R N

Zuscik

M J

O'Keefe

R J

Chen

Beta-catenin, cartilage, and osteoarthritis

Ann NY Acad Sci 2010 1192 344–350

76.

Zhu

Tang

, et al.

Activation of beta-catenin signaling in articular chondrocytes leads to osteoarthritis-like phenotype in adult beta-catenin conditional activation mice

J Bone Miner Res 2009 24 12–21

77.

Liu

Fergusson

M M

Castilho

R M

, et al.

Augmented Wnt signaling in a mammalian model of accelerated aging

Science 2007 317 803–806

78.

Hiyama

Sakai

Risbud

M V

, et al.

Enhancement of intervertebral disc cell senescence by WNT/β-catenin signaling-induced matrix metalloproteinase expression

Arthritis Rheum 2010 62 3036–3047

79.

Hiyama

Sakai

Tanaka

, et al.

The relationship between the Wnt/β-catenin and TGF-β/BMP signals in the intervertebral disc cell

J Cell Physiol 2011 226 1139–1148

80.

Smolders

L A

Meij

B P

Riemers

F M

, et al.

Canonical Wnt signaling in the notochordal cell is upregulated in early intervertebral disk degeneration

J Orthop Res 2012 30 950–957

81.

Ukita

Hirahara

Oshima

, et al.

Wnt signaling maintains the notochord fate for progenitor cells and supports the posterior extension of the notochord

Mech Dev 2009 126 791–803

82.

Wang

Tang

Shu

, et al.

Conditional activation of β-catenin signaling in mice leads to severe defects in intervertebral disc tissue

Arthritis Rheum 2012 64 2611–2623

83.

Shinohara

A study on lumbar disc lesion. Significance of histology of free nerve endings in lumbar discs

J Jpn Orthop Assoc 1970 44 553–570

84.

Yoshizawa

O'Brien

J P

Smith

W T

Trumper

The neuropathology of intervertebral discs removed for low-back pain

J Pathol 1980 132 95–104

85.

Bogduk

Tynan

Wilson

A S

The nerve supply to the human lumbar intervertebral discs

J Anat 1981 132 Pt 1 39–56

86.

Freemont

A J

Peacock

T E

Goupille

Hoyland

J A

O'Brien

Jayson

M I

Nerve ingrowth into diseased intervertebral disc in chronic back pain

Lancet 1997 350 178–181

87.

Roberts

Eisenstein

S M

Menage

Evans

E H

Ashton

I K

Mechanoreceptors in intervertebral discs. Morphology, distribution, and neuropeptides

Spine 1995 20 2645–2651

88.

Burke

J G

Watson

R W

McCormack

Dowling

F E

Walsh

M G

Fitzpatrick

J M

Intervertebral discs which cause low back pain secrete high levels of proinflammatory mediators

J Bone Joint Surg Br 2002 84 196–201

89.

Le Maitre

C L

Hoyland

J A

Freemont

A J

Catabolic cytokine expression in degenerate and herniated human intervertebral discs: IL-1beta and TNFalpha expression profile

Arthritis Res Ther 2007 9 R77

90.

Weiler

Nerlich

A G

Bachmeier

B E

Boos

Expression and distribution of tumor necrosis factor alpha in human lumbar intervertebral discs: a study in surgical specimen and autopsy controls

Spine 2005 30 44–53, discussion 54

91.

Inoue

Ohtori

Aoki

, et al.

Exposure of the nucleus pulposus to the outside of the anulus fibrosus induces nerve injury and regeneration of the afferent fibers innervating the lumbar intervertebral discs in rats

Spine 2006 31 1433–1438

92.

Freemont

A J

Watkins

Le Maitre

, et al.

Nerve growth factor expression and innervation of the painful intervertebral disc

J Pathol 2002 197 286–292

93.

Abe

Akeda

H S

, et al.

Proinflammatory cytokines stimulate the expression of nerve growth factor by human intervertebral disc cells

Spine 2007 32 635–642

94.

Navone

S E

Marfia

Canzi

, et al.

Expression of neural and neurotrophic markers in nucleus pulposus cells isolated from degenerated intervertebral disc

J Orthop Res 2012 30 1470–1477

95.

Gruber

H E

Ingram

J A

Hoelscher

Zinchenko

Norton

H J

Hanley

E N

Brain-derived neurotrophic factor and its receptor in the human and the sand rat intervertebral disc

Arthritis Res Ther 2008 10 R82

96.

Orita

Ohtori

Nagata

, et al.

Inhibiting nerve growth factor or its receptors downregulates calcitonin gene-related peptide expression in rat lumbar dorsal root ganglia innervating injured intervertebral discs

J Orthop Res 2010 28 1614–1620

97.

Suseki

Takahashi

Chiba

Yamagata

Moriya

Sensory nerve fibres from lumbar intervertebral discs pass through rami communicantes. A possible pathway for discogenic low back pain

J Bone Joint Surg Br 1998 80 737–742

98.

Sugiura

Ohtori

Yamashita

, et al.

Existence of nerve growth factor receptors, tyrosine kinase a and p75 neurotrophin receptors in intervertebral discs and on dorsal root ganglion neurons innervating intervertebral discs in rats

Spine 2008 33 2047–2051

99.

Takahashi

Nakajima

Sakamoto

Moriya

Takahashi

Capsaicin applied to rat lumbar intervertebral disc causes extravasation in the groin skin: a possible mechanism of referred pain of the intervertebral disc

Neurosci Lett 1993 161 1–3

100.

Nakamura

S I

Takahashi

Yamagata

Moriya

The afferent pathways of discogenic low-back pain. Evaluation of L2 spinal nerve infiltration

J Bone Joint Surg Br 1996 78 606–612

101.

Ohtori

Takahashi

, et al.

Sensory innervation of the dorsal portion of the lumbar intervertebral disc in rats

Spine 1999 24 2295–2299

102.

Cheung

K M

Karppinen

Chan

, et al.

Prevalence and pattern of lumbar magnetic resonance imaging changes in a population study of one thousand 7forty-three individuals

Spine 2009 34 934–940

103.

Risbud

M V

Guttapalli

Tsai

T T

, et al.

Evidence for skeletal progenitor cells in the degenerate human intervertebral disc

Spine 2007 32 2537–2544

104.

Henriksson

Thornemo

Karlsson

, et al.

Identification of cell proliferation zones, progenitor cells and a potential stem cell niche in the intervertebral disc region: a study in four species

Spine 2009 34 2278–2287

105.

Kim

K W

K Y

Lee

J S

, et al.

Notochordal cells stimulate migration of cartilage end plate chondrocytes of the intervertebral disc in in vitro cell migration assays

Spine J 2009 9 323–329

106.

Sakai

Nakamura

Nakai

, et al.

Exhaustion of nucleus pulposus progenitor cells with ageing and degeneration of the intervertebral disc

Nat Commun 2012 3 1264

Cell Signaling Pathways Related to Pain Receptors in the Degenerated Disk

Abstract

Keywords

Disk Morphology

Effect of Degenerative Changes on Intervertebral Disk Cell Signaling

Major Intracellular Signaling Pathways for IVD Degeneration

Roll of Wnt Signaling in IVD Cells

Pain and Innervations for the IVD

Summary

Disclosures Akihiko Hiyama, None Daisuke Sakai, None Joji Mochida, None

Disclosures

References

Disclosures

Akihiko Hiyama, None

Daisuke Sakai, None

Joji Mochida, None