PARG inhibition suppresses osteoclast differentiation through transcriptional activation of an NRF2-dependent pathway

Poly (ADP-ribose) glycohydrolase (PARG) is the main enzyme responsible for degrading poly (ADP-ribose) (PAR), which is synthesized by PARP family proteins during the poly ADP-ribosylation cycle. We previously reported that the PARG inhibitor PDD00017273 suppressed osteoclast differentiation through PAR accumulation in RANKL-stimulated RAW264 cells. However, the molecular mechanisms of osteoclast differentiation under PARG inhibition remain unclear, and elucidation of the regulatory mechanisms may contribute to the development of novel therapeutic strategies for metabolic bone diseases associated with excessive activation of osteoclasts. In the present study, we investigated the molecular mechanisms whereby PDD00017273 suppresses osteoclast differentiation. RNA-seq and pathway analyses revealed enrichment of oxidative stress- and redox regulation-related pathways, and an ATAC-seq analysis identified enrichment of the NRF2-binding motif in PDD00017273-treated RAW264 cells compared with DMSO-treated control cells. Pharmacological inhibition of NRF2 partially restored the osteoclast formation suppressed by PDD00017273. Under these conditions, the expression levels of NRF2-regulated genes were suppressed, while the expression levels of osteoclast marker genes were upregulated. Taken together, the present findings suggest that PAR accumulation via PARG inhibition suppresses osteoclast differentiation through NRF2 activation, indicating that PAR metabolism plays an important role in osteoclast differentiation.