# OTUD1 inhibits osteoclast differentiation and osteoclastic bone loss through deubiquitinating and stabilizing PRDX1

## TL;DR

This study shows that OTUD1 prevents bone loss by stabilizing PRDX1, offering a new target for treating osteoclast-related bone diseases.

## Contribution

The novel finding is that OTUD1 inhibits osteoclast differentiation by deubiquitinating and stabilizing PRDX1.

## Key findings

- OTUD1 gene and protein levels are significantly reduced during osteoclastogenesis.
- OTUD1 deficiency in mice leads to reduced bone mass due to enhanced osteoclast differentiation.
- OTUD1 stabilizes PRDX1 by reversing K48-linked ubiquitination, preventing mitochondrial dysfunction.

## Abstract

Rationale: Bone homeostasis relies on a delicate equilibrium between bone formation by osteoblasts and bone resorption by osteoclasts. Disruption of this balance leads to various disorders, most notably osteoporosis. Deubiquitinating enzymes (DUBs), which cleave ubiquitin moieties from substrate proteins, play critical regulatory roles in bone pathophysiology. In this study, we explored the function of a DUB, ovarian tumor deubiquitinase 1 (OTUD1), in bone remodeling.

Methods: We examined the femur bone of Otud1+/+ and Otud1-/- male mice using micro-CT analyses and histomorphometry. The potential functions and mechanisms of OTUD1 were explored in bone marrow-derived macrophages, RAW264.7 cells, and bone marrow stromal cells using RT-qPCR, western blotting and immunofluorescence. Additionally, we employed liquid chromatography-tandem mass spectrometry (LC-MS/MS) coupled with co-immunoprecipitation (Co-IP) to identify OTUD1-interacting proteins and substrates.

Results: Our results demonstrated a significant downregulation of both the gene and protein level of OTUD1 during osteoclastogenesis. Furthermore, both whole-body knockout and myeloid-specific deficiency of OTUD1 resulted in reduced bone mass in male mice, driven by enhanced osteoclast differentiation. Mechanistically, OTUD1 maintained the stability of peroxiredoxin 1 (PRDX1) by reversing K48-linked ubiquitination, thereby mitigating mitochondrial dysfunction and suppressing osteoclast differentiation. Consistent with these results, mitochondria-targeted ubiquinone (MitoQ), a mitochondria-targeted antioxidant, effectively suppressed bone mass loss in OTUD1-deficient male mice.

Conclusions: Our findings provided the first evidence that OTUD1 suppressed osteoclastogenesis by deubiquitinating PRDX1 and maintaining its stability, thereby offering a promising therapeutic approach for osteoclast-dependent bone diseases.