Enhancer variants reveal a conserved transcription factor network governed by PU.1 during osteoclast differentiation

Abstract

Genome-wide association studies (GWASs) have been instrumental in understanding complex phenotypic traits. However, they have rarely been used to understand lineage-specific pathways and functions that contribute to the trait. In this study, by integrating lineage-specific enhancers from mesenchymal and myeloid compartments with bone mineral density loci, we were able to segregate osteoblast- and osteoclast (OC)-specific functions. Specifically, in OCs, a PU.1-dependent transcription factor (TF) network was revealed. Deletion of PU.1 in OCs in mice resulted in severe osteopetrosis. Functional genomic analysis indicated PU.1 and MITF orchestrated a TF network essential for OC differentiation. Several of these TFs were regulated by cooperative binding of PU.1 with BRD4 to form superenhancers. Further, PU.1 is essential for conformational changes in the superenhancer region of Nfatc1. In summary, our study demonstrates that combining GWASs with genome-wide binding studies and model organisms could decipher lineage-specific pathways contributing to complex disease states.

Genetics: Cellular fate dictates osteoporosis risk

Genetic variation in non-coding regions of DNA could raise osteoporosis risk by affecting osteoclast differentiation. Osteoporosis occurs when the normal process of bone remodeling by osteoblasts and osteoclasts falls out of balance. Genome-wide association studies (GWAS) have identified numerous single nucleotide polymorphisms (SNPs) associated with osteoporosis, but how these affect specific cell types was unclear. Sudarshana Sharma and Michael Ostrowski at the Medical University of South Carolina and colleagues wondered if variations in non-coding ‘enhancer’ regions of DNA, might shed light on the molecular underpinnings of osteoporosis. So, they overlaid SNPs associated with reduced bone mineral density onto enhancers in mesenchymal and myeloid cells—the precursors of osteoblasts and osteoclasts—identifying a transcription factor network in myeloid cells that drives the differentiation of osteoclasts. When this was disrupted in mice, severe defects in osteoclast differentiation and function resulted.

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