Inhibition of SOX9 Promotes Inflammatory and Immune Responses of Dental Pulp

The process of pulpitis is characterized by extracellular matrix imbalance and inflammatory cell infiltration. As an essential transcription factor, sex-determining region Y-box 9 (SOX9) is significantly inhibited by tumor necrosis factor alpha in inflammatory joint diseases. The aim of this study was to explore the role of SOX9 in extracellular matrix balance, cytokine expression, and the immune response in dental pulp.

The expression of SOX9 in normal and inflamed pulp tissue/human dental pulp cells (HDPCs) was detected by immunohistochemistry, Western blot, and quantitative polymerase chain reaction (qPCR). SOX9 small interfering RNA was used to knock down SOX9 expression of dental cells in vitro; extracellular matrix imbalance was analyzed by qPCR, Western blot, and gelatin/collagen zymography, and the secretion of cytokines was scanned by antibody arrays. The immune response of THP-1 was investigated by cell migration assay, cell attachment assay, phagocytosis assay, and enzyme-linked immunosorbent assay. The interaction of SOX9 with target genes was explored by chromatin immunoprecipitation (ChIP).

SOX9 was strongly expressed in normal dental pulp tissue and HDPCs and reduced in inflamed pulp. SOX9 knockdown could inhibit the production of type I collagen, stimulate the enzymatic activities of MMP2 and MMP13, and regulate the production of interleukin (IL) 8 of HDPCs. SOX9 knockdown also effectively suppressed the differentiation and functional activities of THP-1. ChIP showed that the binding of the SOX9 protein with matrix metalloproteinase (MMP)-1, MMP-13, and IL-8 gene promoters was reduced after being treated with recombinant human tumor necrosis factor alpha.

SOX9 was inhibited in inflamed dental pulp and may participate in the regulation of extracellular matrix balance, the inflammatory process, and the immune response.