Hdac9-Mediated Pyroptosis Promotes Orthodontic Inflammatory Root Resorption

Orthodontic inflammatory root resorption (OIIRR) is a common iatrogenic outcome of orthodontic treatment. Both epigenetic modifications and pyroptosis have demonstrated a certain role in OIIRR. This study aims to investigate whether epigenetic modifications regulate pyroptosis to be involved in OIIRR. Rat model of OIIRR was established, and the periodontal tissues were utilized for H&E staining, TRAP staining, immunofluorescence, transcriptome sequencing, and RT-qPCR analysis. Human periodontal ligament fibroblasts (hPDLFs) were overexpressed with HDAC9, treated with pyroptosis inhibitor, incubated with osteoclast, and then subjected to CUT&Tag sequencing Orthodontic force increased the distance of orthodontic tooth movement and the abundance of osteoclast. Transcriptome sequencing identified that Hdac9 was upregulated in the periodontal tissues of OIIRR compared to the control. Immunofluorescence revealed that HDAC9 was present in periodontal ligament fibroblasts, with reduced fluorescence of HDAC9 in OIIRR compared to the control. HDAC9 overexpression in hPDLFs induced pyroptosis and promoted osteoclast differentiation. These effects were reversed by pyroptosis inhibitors. CUT&Tag analysis showed that HDAC9 overexpression resulted in an enrichment of deacetylated genes on mitochondrial dysfunction-associated pathways. CUT&Tag-PCR analysis confirmed reduced H3K9ac enrichment on the mitochondrial dysfunction-associated genes VPS13D, AQP1, PEX2, CDK1, and PLEKHA1 after HDAC9 overexpression, and RT-qPCR analysis revealed a corresponding decrease in their respective expression levels. Accordingly, the ROS level was also increased by HDAC9 overexpression. HDAC9-mediated histone deacetylation induces mitochondrial dysfunction and pyroptosis in hPDLFs, thereby promoting osteoclast differentiation and OIIRR progression.