Aims. CRP is an acute-phase protein that is used as a biomarker to follow severity and progression in infectious and inflammatory diseases. Its pathophysiological mechanisms of action are still poorly defined. CRP in its pentameric form exhibits weak anti-inflammatory activity. The monomeric isoform (mCRP) exerts potent proinflammatory properties in chondrocytes, endothelial cells, and leucocytes. No data exist regarding mCRP effects in human intervertebral disc (IVD) cells. This work aimed to verify the pathophysiological relevance of mCRP in the aetiology and/or progression of IVD degeneration. Methods. We investigated the effects of mCRP and the signalling pathways that are involved in cultured human primary annulus fibrosus (AF) cells and in the human nucleus pulposus (NP) immortalized cell line HNPSV-1. We determined messenger RNA (mRNA) and protein levels of relevant factors involved in inflammatory responses, by quantitative real-time polymerase chain reaction (RT-qPCR) and western blot. We also studied the presence of mCRP in human AF and NP tissues by immunohistochemistry. Results. We demonstrated that mCRP increases nitric oxide synthase 2 (NOS2), cyclooxygenase 2 (COX2), matrix metalloproteinase 13 (MMP13), vascular cell adhesion molecule 1 (VCAM1), interleukin (IL)-6, IL-8, and Lipocalin 2 (LCN2) expression in human AF and NP cells. We also showed that nuclear factor-κβ (NF-κβ), extracellular signal-regulated kinase 1/2 (ERK1/2), and phosphoinositide 3-kinase (PI3K) are at play in the intracellular signalling of mCRP. Finally, we demonstrated the presence of mCRP in human AF and NP tissues. Conclusion. Our results indicate, for the first time, that mCRP can be localized in IVD tissues, where it triggers a proinflammatory and catabolic state in degenerative and healthy IVD cells, and that NF-κβ signalling may be implicated in the mediation of this mCRP-induced state. Cite this article: Bone Joint Res 2023;12(3):189–198

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Degenerative cervical spondylosis (DCS) is a common musculoskeletal disease that encompasses a wide range of progressive degenerative changes and affects all components of the cervical spine. DCS imposes very large social and economic burdens. However, its genetic basis remains elusive.

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This study was performed to explore the effect of melatonin on pyroptosis in nucleus pulposus cells (NPCs) and the underlying mechanism of that effect.

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Lumbar spinal stenosis (LSS) is a common skeletal system disease that has been partly attributed to genetic variation. However, the correlation between genetic variation and pathological changes in LSS is insufficient, and it is difficult to provide a reference for the early diagnosis and treatment of the disease.

Introduction. Herniated disc tissue removed at surgery is mostly nucleus pulposus, with varying proportions of annulus fibrosus, cartilage endplate, and bone. Herniated nucleus swells and loses proteoglycans, and herniated annulus is invaded by blood vessels and inflammatory cells. However, little is known about the significance of endplate cartilage and bone within a herniation. Methods. Herniated tissue was removed surgically from 21 patients (10 with sciatica, 11 without). 5-μm sections were examined using H&E, Toluidine blue, Giemsa, and Masson-trichrome stains. Each tissue type in each specimen was scored for tears/fissures, neovascularisation, proteoglycan loss, cell clustering, and inflammatory cell invasion. Proportions of each tissue type were quantified using image analysis software. Results. Herniations from patients with sciatica had greater nerve and blood vessel invasion (P<0.05), and a greater proportion contained cartilage endplate (7/10 vs 3/11, p<0.05). Cartilage fragments were generally small (5–20% of herniated mass) and showed little swelling or proteoglycan loss, or inflammatory cell invasion, although chondrocytes often formed small clusters. Most cartilage endplate fragments had a straight edge where it had been stripped from bone. Two cartilage fragments showed some bone still attached, and three showed small defects that were filled with nucleus tissue, bone, or endothelial cells. Conclusion. More than 50% of disc herniations contained cartilage endplate. The relatively stable nature of cartilage fragments may explain why they are less likely to resorb, and therefore more likely to cause persisting sciatica. Loss of cartilage will increase endplate permeability, increasing the risk of Modic changes, and disc infection

Introduction. The response of the intervertebral disc to asymmetric forces may accelerate degeneration through changes in the matrix. Macroscopically, the disc sustains structural changes that may play a part in the progression of a scoliotic curve. Molecularly, disc degeneration is the outcome of the action of matrix metalloproteases (MMPs), members of a family of enzymes that bring about the degradation of extracellular matrix components. In this study we measured in vivo the expression of MMPs in a rat scoliotic intervertebral disc and studied the effect of the degree of the deformity on their production. Methods. Asymmetric forces were applied in the intervertebral disc between the ninth and tenth vertebrae at the base of a rat tail with the use of a mini Ilizarov external fixator, under anaesthesia. Animals were categorised into three groups according to the degree of the deformity. In group I, the deformity that was applied on the intervertebral disc was 10°, in group II 30°, and in group III 50°. All the animals used were female Wistar rats before adulthood, to take into account the effect of growth for the study of intervertebral disc changes. The intact intervertebral discs outside the fixator were used as controls. After the rats' death on day 35, the tails were prepared and analysed with an immunohistochemical protocol for chromogenic detection and location of MMPs 1 and 12 in tissue sections of the intervertebral discs. Results. We recorded an increase of the concentration of the MMPs in all groups compared with controls. The quantity of the MMPs increased as the degree of the deformity progressed. MMPs were detected mainly in fibrocartilage cells of the degenerative part, which were formed as result of the compression forces. We detected a differentiation of a large number of disc cells into chondrocytes at the transitional zone of the intervertebral disc adjacent to the vertebral end plates. Conclusions. The application of asymmetric forces on the intervertebral discs of a rat tail results in an increase of MMP expression in the disc cells. The amount of MMPs produced is proportional to the degree of the deformity and has an asymmetrical pattern of distribution into the intervertebral disc

The belief that an intervertebral disc must degenerate before it can herniate has clinical and medicolegal significance, but lacks scientific validity. We hypothesised that tissue changes in herniated discs differ from those in discs that degenerate without herniation. Tissues were obtained at surgery from 21 herniated discs and 11 non-herniated discs of similar degeneration as assessed by the Pfirrmann grade. Thin sections were graded histologically, and certain features were quantified using immunofluorescence combined with confocal microscopy and image analysis. Herniated and degenerated tissues were compared separately for each tissue type: nucleus, inner annulus and outer annulus.

Herniated tissues showed significantly greater proteoglycan loss (outer annulus), neovascularisation (annulus), innervation (annulus), cellularity/inflammation (annulus) and expression of matrix-degrading enzymes (inner annulus) than degenerated discs. No significant differences were seen in the nucleus tissue from herniated and degenerated discs. Degenerative changes start in the nucleus, so it seems unlikely that advanced degeneration caused herniation in 21 of these 32 discs. On the contrary, specific changes in the annulus can be interpreted as the consequences of herniation, when disruption allows local swelling, proteoglycan loss, and the ingrowth of blood vessels, nerves and inflammatory cells.

In conclusion, it should not be assumed that degenerative changes always precede disc herniation.

Cite this article: Bone Joint J 2013;95-B:1127–33.

Discogenic low back pain is a common cause of disability, but its pathogenesis is poorly understood. We collected 19 specimens of lumbar intervertebral discs from 17 patients with discogenic low back pain during posterior lumbar interbody fusion, 12 from physiologically ageing discs and ten from normal control discs. We investigated the histological features and assessed the immunoreactive activity of neurofilament (NF200) and neuropeptides such as substance P (SP) and vasoactive-intestinal peptide (VIP) in the nerve fibres.

The distinct histological characteristic of the painful disc was the formation of a zone of vascularised granulation tissue from the nucleus pulposus to the outer part of the annulus fibrosus along the edges of the fissures. SP-, NF- and VIP-immunoreactive nerve fibres in the painful discs were more extensive than in the control discs. Growth of nerves deep into the annulus fibrosus and nucleus pulposus was observed mainly along the zone of granulation tissue in the painful discs. This suggests that the zone of granulation tissue with extensive innervation along the tears in the posterior part of the painful disc may be responsible for causing the pain of discography and of discogenic low back pain.

Mesenchymal stem-cell based therapies have been proposed as novel treatments for intervertebral disc degeneration, a prevalent and disabling condition associated with back pain. The development of these treatment strategies, however, has been hindered by the incomplete understanding of the human nucleus pulposus phenotype and by an inaccurate interpretation and translation of animal to human research. This review summarises recent work characterising the nucleus pulposus phenotype in different animal models and in humans and integrates their findings with the anatomical and physiological differences between these species. Understanding this phenotype is paramount to guarantee that implanted cells restore the native functions of the intervertebral disc.

Cite this article: Bone Joint Res 2013;2:169–78.