Anti-DOT1L monoclonal antibody, clone 7F8

Osteoarthritis (OA) is the most common musculoskeletal and joint disorder. However, no disease-modifying therapy for OA is currently available, and the etiology of OA is poorly understood. Epigenetics has emerged as a new and important area of research on OA. Differing from genetics, Epigenetic factors are known to be tissuespecific and highly dynamic, being dependent on environmental stimuli and developmental stages. Therefore, human studies into OA epigenetics are sensitive to confounding and reverse causation. Here, we will review the epigenetic mechanism in OA onset and progression by focusing on the opposing action of two families of enzymes: histone methyltransferases and histone demethylases, such as DOT1L, KDM4B, KDM6A, KDM6B, EZH2, and LSD1. Moreover, the TGF-beta 1 signaling pathway has proven to be one of the key factors in cartilage and bone formation, and in recent research, was found to initiate and develop OA disease by TGF-beta 1 overexpression. Besides the introduction of enzymes and TGF-beta 1 signaling, some special epigenetic regulation mechanisms associated with key transcription factors (e.g. RUNX2, NFAT1, and SOX9) in OA disease are also reviewed here in detail to clarify the OA epigenetic mechanism. The overall understanding of these epigenetic mechanisms underlying the issues will accelerate the development of novel therapeutic strategies for OA.

Growing evidence suggests that the lysine methyltransferase DOT1L/KMT4 has important roles in proliferation, survival, and differentiation of stem cells in development and in disease. We investigated the function of DOT1L in neural stem cells (NSCs) of the cerebral cortex. The pharmacological inhibition and shRNA-mediated knockdown of DOT1L impaired proliferation and survival of NSCs. DOT1L inhibition specifically induced genes that are activated during the unfolded protein response (UPR) in the endoplasmic reticulum (ER). Chromatin-immunoprecipitation analyses revealed that two genes encoding for central molecules involved in the ER stress response, Atf4 and Ddit3 (Chop), are marked with H3K79 methylation. Interference with DOT1L activity resulted in transcriptional activation of both genes accompanied by decreased levels of H3K79 dimethylation. Although downstream effectors of the UPR, such as Ppp1r15a/Gadd34, Atf3, and Tnfrsf10b/Dr5 were also transcriptionally activated, this most likely occurred in response to increased ATF4 expression rather than as a direct consequence of altered H3K79 methylation. While stem cells are particularly vulnerable to stress, the UPR and ER stress have not been extensively studied in these cells yet. Since activation of the ER stress program is also implicated in directing stem cells into differentiation or to maintain a proliferative status, the UPR must be tightly regulated. Our and published data suggest that histone modifications, including H3K4me3, H3K14ac, and H3K79me2, are implicated in the control of transcriptional activation of ER stress genes. In this context, the loss of H3K79me2 at the Atf4- and Ddit3-promoters appears to mark a point-of-no-return that activates the death program in NSCs.