The JMJD3 histone demethylase inhibitor GSK-J1 ameliorates lipopolysaccharide-induced inflammation in a mastitis model

Jumonji domain-containing 3 (JMJD3/KDM6B) is a histone demethylase that plays an important role in regulating development, differentiation, immunity, and tumorigenesis. However, the mechanisms responsible for the epigenetic regulation of inflammation during mastitis remain incompletely understood. Here, we aimed to investigate the role of JMJD3 in the lipopolysaccharide (LPS)-induced mastitis model. GSK-J1, a small molecule inhibitor of JMJD3, was applied to treat LPS-induced mastitis in mice and in mouse mammary epithelial cells in vivo and in vitro. Breast tissues were then collected for histopathology and protein/gene expression examination, and mouse mammary epithelial cells were used to investigate the mechanism of regulation of the inflammatory response. We found that the JMJD3 gene and protein expression were upregulated in injured mammary glands during mastitis. Unexpectedly, we also found JMJD3 inhibition by GSK-J1 significantly alleviated the severity of inflammation in LPS-induced mastitis. These results are in agreement with the finding that GSK-J1 treatment led to the recruitment of histone 3 lysine 27 trimethylation (H3K27me3), an inhibitory chromatin mark, in vitro. Furthermore, mechanistic investigation suggested that GSK-J1 treatment directly interfered with the transcription of inflammatory-related genes by H3K27me3 modification of their promoters. Meanwhile, we also demonstrated that JMJD3 depletion or inhibition by GSK-J1 decreased the expression of toll-like receptor 4 and negated downstream NF-κB proinflammatory signaling and subsequently reduced LPS-stimulated upregulation of Tnfa, Il1b, and Il6. Together, we propose that targeting JMJD3 has therapeutic potential for the treatment of inflammatory diseases.