Osteoclast programming and reprogramming during osteoclastogenesis

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Abstract Osteoclasts are large, myeloid-derived multinucleated cells primarily responsible for bone resorption. Dysregulation of osteoclast differentiation can result in net bone resorption and is key to the pathophysiology of osteoporosis, rheumatoid arthritis, and lytic bone metastasis. Despite substantial advances in the identification of osteoclast master regulators, developing therapeutic interventions for pathologic osteoclasts has been challenging due to off-target/side effects. Thus, we hypothesized that a better understanding of osteoclast- specific regulation can directly lead to the development of novel osteoclast-specific therapeutic strategies to prevent or halt the disease’s progression. Osteoclast gene transcription is highly organized and is understood to be driven by enhancers. In order to identify osteoclast-specific epigenetic programs, we focused on super- enhancers. Super-enhancers are clusters of enhancers that have been proposed to regulate key genes of cellular identity and fate. We found 348 super-enhancers in human osteoclasts through genome-wide analysis of differential transcriptional and epigenetic regulation. We also found that RANKL-regulated super-enhancers are specific to osteoclasts but do not present in other types of cells. To increase the feasibility of targeting these super-enhancers, we identified a new class of non-coding RNAs transcribed from super-enhancers (named Oslincs) in human osteoclasts and provided evidence showing the role of Oslincs in gene expression and osteoclastogenesis. In this application, we aim to characterize osteoclast-specific programs by investigating Oslincs’ action and biogenesis in health and disease. Our specific aims are to 1) determine the underlying mechanism of Oslincs’ function, 2) elucidate the mechanisms by which the expression of Oslincs is regulated, and 3) identify Oslincs that are differentially regulated between healthy controls and patients with rheumatoid arthritis (RA). We anticipate that the new information generated by this proposal will illuminate osteoclast-specific regulation and allow us to explore the implementation of novel, targeted therapeutic approaches for ameliorating the course of pathological bone loss.