Inhibition of the Histone Demethylase KDM4B Leads to Activation of KDM1A, Attenuates Bacterial-Induced Pro-Inflammatory Cytokine Release, and Reduces Osteoclastogenesis

Periodontal disease (PD) afflicts 46% of Americans with no effective adjunctive therapies available. While most pharmacotherapy for PD targets bacteria, the host immune response is responsible for driving tissue damage and bone loss in severe disease. Herein, we establish that the histone demethylase KDM4B is a potential drug target for the treatment of PD. Immunohistochemical staining of diseased periodontal epithelium revealed an increased abundance of KDM4B that correlates with inflammation. In murine calvarial sections exposed to <i>Aggregatibacter actinomycetemcomitans</i> lipopolysaccharide <i>(Aa</i>-LPS), immunohistochemical staining revealed a significant increase in KDM4B protein expression. The 8-hydroxyquinoline ML324 is known to inhibit the related demethylase KDM4E <i>in vitro</i>, but has not been evaluated against any other targets. Our studies indicate that ML324 also inhibits KDM4B (IC₅₀: 4.9 μM), and decreases the pro-inflammatory cytokine response to an <i>Aa</i>-LPS challenge <i>in vitro</i>. Our results suggest that KDM4B inhibition-induced immunosuppression works indirectly, requiring new protein synthesis. In addition, fluorescence-stained macrophages exhibited a significant decrease in global monomethyl histone 3 lysine 4 (H3K4me) levels following an <i>Aa</i>-LPS challenge that was prevented by KDM4B inhibition, suggesting this effect is produced through KDM1A-mediated demethylation of H3K4. Finally, ML324 inhibition of KDM4B in osteoclast progenitors produced a significant reduction in <i>Aa</i>-LPS-induced osteoclastogenesis. These data link histone methylation with host immune response to bacterial pathogens in PD, and suggest an alternative mechanism for epigenetic control of the host inflammatory environment that has not previously been reported. As such, KDM4B represents a new therapeutic target for treating hyper-inflammatory diseases that result in bone destruction.