Bap1 promotes osteoclast function by metabolic reprogramming

Treatment of osteoporosis most commonly diminishes osteoclast number which suppresses bone formation thus compromising fracture prevention. Bone formation is not suppressed, however, when bone degradation is reduced by retarding osteoclast functional resorptive capacity, rather than differentiation. We find deletion of deubiquitinase, BRCA1-associated protein 1 (Bap1), in myeloid cells (Bap1∆LysM), arrests osteoclast function but not formation. Bap1∆LysM osteoclasts fail to organize their cytoskeleton which is essential for bone degradation. Consequently, bone mass increases in the mutant mice. The deubiquitinase activity of Bap1 modifies osteoclast function by metabolic reprogramming. Bap1 deficient osteoclast lineage cells upregulate the cystine transporter, Slc7a11, by enhanced H2Aub occupancy of its promoter. SLC7A11 controls cellular ROS levels and redirects the mitochondrial metabolites away from the TCA cycle, both of which are necessary for osteoclast function. Thus in osteoclasts, Bap1 appears to regulate the epigenetic-metabolic axis and is a potential target to reduce bone degradation while maintaining osteogenesis in osteoporotic patients.