Abstract
High mobility group 1 protein (HMGB1), a highly conserved nuclear DNA‐binding protein and inflammatory mediator, has been recently found to be involved in angiogenesis. Our previous study has demonstrated the elevation of HMGB1 in the tissue of perforated disc of temporomandibular joint (TMJ). Here, we investigated a novel mediator of HMGB1 in regulating hypoxia‐inducible factor‐1α (HIF‐1α) and vascular endothelial growth factor (VEGF) to mediate angiogenesis in perforated disc cells of TMJ. HMGB1 increased the expression of HIF‐1α and VEGF in a dose‐ and time‐dependent manner in these cells. Moreover, immunofluorescence assay exhibits that the HIF‐1α were activated by HMGB1. In addition, HMGB1 activated extracellular signal‐related kinase 1/2 (Erk1/2), Jun N‐terminal kinase (JNK), but not P38 in these cells. Furthermore, both U0126 (ErK inhibitor) and SP600125 (JNK inhibitor) significantly suppressed the enhanced production of HIF‐1α and VEGF induced by HMGB1. Tube formation of human umbilical vein endothelial cells (HUVECs) was significantly increased by exposure to conditioned medium derived from HMGB1‐stimulated perforated disc cells, while attenuated with pre‐treatment of inhibitors for VEGF, HIF‐1α, Erk and JNK, individually. Therefore, abundance of HMGB1 mediates activation of HIF‐1α in disc cells via Erk and JNK pathway and then, initiates VEGF secretion, thereby leading to disc angiogenesis and accelerating degenerative change of the perforated disc.
Highlights
Disc perforation, widely accepted as the most seriously pathologic subtype in osteoarthritis of temporomandibular joint (TMJOA), is one of the main causes of joint pain, limited mouth opening and cartilage degeneration [1]
We investigated whether the expression of vascular endothelial growth factor (VEGF) in perforated disc cells was raised after incubation of High mobility group box 1 (HMGB1)
Pre-treatment with VEGF antibodies inhibited HMGB1-induced tube formation and migration of human umbilical vein endothelial cells (HUVECs) (Fig. 1F). These results indicated that VEGF is involved in HMGB1-induced angiogenesis in perforated disc cells of TMJ
Summary
Widely accepted as the most seriously pathologic subtype in osteoarthritis of temporomandibular joint (TMJOA), is one of the main causes of joint pain, limited mouth opening and cartilage degeneration [1]. The underlying mechanism of disc perforation has been attributed to diverse factors including aberrant occlusal forces, sexual difference and accelerated chondrocyte-like apoptosis [2, 3]. Kiga et al reported that neovascularization, accompanied with the accumulation of VEGF, correlates with the severity of deformed discs. They suggested that VEGF initiates proliferation and chemotaxis of endothelial cells, augments vascular permeability and induces the secretion of matrix metalloproteases (MMPs), which attribute to the degradation of extracellular matrix of discs [7]. Agrawal et al indicated that enhanced vascular invasion boosted by VEGF and HIF-1a contributes to degenerative changes in the intervertebral disc [8]
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