Matrix Degradative Enzymes and Their Inhibitors during Annular Inflammation: Initial Step of Symptomatic Intervertebral Disc Degeneration

Current Knowledge and Future Therapeutic Prospects in Symptomatic Intervertebral Disc Degeneration

Intervertebral disc (IVD) degeneration is the main source of intractable lower back pain, and symptomatic IVD degeneration could be due to different degeneration mechanisms. In this article, we describe the molecular basis of symptomatic IVD degenerative disc diseases (DDDs), emphasizing the role of degeneration, inflammation, angiogenesis, and extracellular matrix (ECM) regulation during this process. In symptomatic DDD, pro-inflammatory mediators modulate catabolic reactions, resulting in changes in ECM homeostasis and, finally, neural/vascular ingrowth-related chronic intractable discogenic pain. In ECM homeostasis, anabolic protein-regulating genes show reduced expression and changes in ECM production, while matrix metalloproteinase gene expression increases and results in aggressive ECM degradation. The resultant loss of normal IVD viscoelasticity and a concomitant change in ECM composition are key mechanisms in DDDs. During inflammation, a macrophage-related cascade is represented by the secretion of high levels of pro-inflammatory cytokines, which induce inflammation. Aberrant angiogenesis is considered a key initiative pathologic step in symptomatic DDD. In reflection of angiogenesis, vascular endothelial growth factor expression is regulated by hypoxia-inducible factor-1 in the hypoxic conditions of IVDs. Furthermore, IVD cells undergoing degeneration potentially enhance neovascularization by secreting large amounts of angiogenic cytokines, which penetrate the IVD from the outer annulus fibrosus, extending deep into the outer part of the nucleus pulposus. Based on current knowledge, a multi-disciplinary approach is needed in all aspects of spinal research, starting from basic research to clinical applications, as this will provide information regarding treatments for DDDs and discogenic pain.

Increased lactic acid content associated with extracellular matrix depletion in a porcine disc degeneration induced by superficial annular lesion

Background

Degenerative intervertebral disc (IVD) disease can cause lower back pain. However, the change of lactic acid content during disc degeneration process still unclear. The objective of this study was to investigate whether the change of the content of lactic acid is associated with depletion of degenerative intervertebral disc extracellular matrix.

Methods

A total of 18 miniature pigs were equally divided into annular lesion surgery (AL) and sham group. The lateral superficial annulus fibrosus (AF) of T12-L4 discs in AL group were penetrated by 3.5 mm trepan with the depth of 3 mm, the same IVD were only exposed without any injury in the sham group. At 4, 8 and 12 weeks after surgery, the degree of intervertebral disc degeneration was evaluated by magnetic resonance, histological and biochemical analysis.

Results

No obvious degeneration was found in sham group. However, disc degeneration was found and gradually worsened in AL group after surgery. Histological analysis showed that the AF was rupture and disorder, the number of cells in nucleus pulposus (NP) was decreased in AL group. Compared with the sham group, the extent of type II collagen (Col-II) and aggrecan in NP tissue was dramatically decreased in AL group, consistent with the results of Col -II immunohistochemistry staining and quantitative reverse transcription polymerase chain reaction (qRT-PCR). Besides, the gene expression of matrix metallopeptidase 3 and 13 also continuous increased in AL group. The amount of lactic acid and nerve growth factor in NP tissue was gradually increased after operation in AL group.

Conclusions

The content of lactic acid gradually increased after annular lesion, associated with the damage of AF structural and the decrease of Col -II and aggrecan in NP tissue, which leading to the disc degeneration. Depletion of extracellular matrix is consistent with lactic acid accumulation inside of IVD.

Immunobiology of periprosthetic inflammation and pain following ultra-high-molecular-weight-polyethylene wear debris in the lumbar spine

INTRODUCTION

Wear debris-induced osteolysis is a common cause of arthroplasty failure in several joints including the knee, hip and intervertebral disc. Debris from the prosthesis can trigger an inflammatory response that leads to aseptic loosening and prosthesis failure. In the spine, periprosthetic pain also occurs following accumulation of wear debris through neovascularization of the disc. The role of the immune system in the pathobiology of periprosthetic osteolysis of joint replacements is debatable. Areas covered: We discussed the stimulation of pro-inflammatory and pro-protective and pro-regenerative pathways due to debris from the prosthetics. The balance between the two pathways may determine the outcome results. Also, the role of cytokines and immune cells in periprosthetic inflammation in the etiology of osteolysis is critically reviewed. Expert commentary: Therapies targeting the inflammatory process associated with ultra-high-molecular-weight polyethylene wear debris could reduce implant failure. Additionally, therapies targeting neovascularization of discs following arthroplasty could mitigate periprosthetic pain.

IL-1β-regulating angiogenic factors expression in perforated temporomandibular disk cells via NF-κB pathway

BACKGROUND

A high density of blood vessels is observed in the perforated disks of temporomandibular joint (TMJ), but the underlying mechanism is unknown. This study aimed to explore the regulation of disk angiogenesis in the perforated disks.

METHODS

Expressions of vascular endothelial growth factor (VEGF), angiogenin-1 (Ang-1), chondromodulin-1 (ChM-1), and thrombospondins-1 (TSP-1) were compared between healthy and perforated TMJ disk cells with or without interleukin-1β (IL-1β) incubation. The tube formation, cell migration, and expressions of matrix-metalloproteinases (MMPs) in human umbilical vein endothelial cell line (HUV-EC-C) were investigated in conditional media of disk cells. Western blot was performed to determine protein level of VEGF, Ang-1, ChM-1 and TSP-1 in IL-1β-induced disk cells cultured by NF-κB- or P38-specific pathway inhibitors, respectively.

RESULTS

Conditional media from perforated disk cells induced more tube formation, cell migration, and MMPs' expression in HUV-EC-C. Expressions of VEGF and Ang-1 were significantly higher, and ChM-1 and TSP-1 were lower in perforated disks compared to healthy disks. The VEGFA concentration was 291.1 ± 36.09 pg/ml in perforated disk cell conditioned media, markedly larger than that in NDCCM (144.9 ± 33.69 pg/ml). IL-1β induced VEGF through NF-κB signaling pathway and Ang-1 through p38 MAPK pathway, while repressed expression of ChM-1 and TSP-1 was through NF-κB pathway. Blockade of each pathway markedly restrained inducing effect of cultural media on HUV-EC-C tube formation and migration.

CONCLUSIONS

Perforated disk cells secreted more angiogenic factors which might induced via NF-κB pathway.